WO2013178847A1 - Sampled delay line - Google Patents
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- WO2013178847A1 WO2013178847A1 PCT/ES2013/070292 ES2013070292W WO2013178847A1 WO 2013178847 A1 WO2013178847 A1 WO 2013178847A1 ES 2013070292 W ES2013070292 W ES 2013070292W WO 2013178847 A1 WO2013178847 A1 WO 2013178847A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29371—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion
- G02B6/29374—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating principle based on material dispersion in an optical light guide
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2581—Multimode transmission
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/03—WDM arrangements
- H04J14/0307—Multiplexers; Demultiplexers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04J14/00—Optical multiplex systems
- H04J14/05—Spatial multiplexing systems
- H04J14/052—Spatial multiplexing systems using multicore fibre
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02042—Multicore optical fibres
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
- G02B6/2861—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using fibre optic delay lines and optical elements associated with them, e.g. for use in signal processing, e.g. filtering
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29301—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means based on a phased array of light guides
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- H—ELECTRICITY
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- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0298—Wavelength-division multiplex systems with sub-carrier multiplexing [SCM]
Definitions
- the present invention relates to a sampled delay line that aims to allow the use of multicore optical fibers (MCF) as sampled and reconfigurable delay lines for the implementation of various functionalities employed in Microwave Photonics, which involve the processing of radio frequency spectrum signals carried by one or more carriers located in the optical region of the spectrum.
- MCF multicore optical fibers
- the use of heterogeneous multicore fibers, in which each core has a different composition and chromatic dispersion properties allows the implementation of different incremental delays on the same signal fed to each of the nuclei.
- Homogeneous multicore fibers can also be used to implement sampled delay lines, including at the exit of each core of the multicore fiber an additional fiber segment that provides the differential delay.
- WDM Wavelength Multiplexing Division
- Another object of the invention is the use of new connectors between multicore fibers and mononuclear fibers, both at their input and at their output, either for the injection of a single modulated optical signal at the input of the MCF, or for the joint detection of the N signal samples in the MCF output plane.
- the present invention is within the framework of Microwave Photonics. Specifically, within the general scope of photonic processing of radiofrequency signals, microwaves and millimeter waves. It is also part of the field of multicore optical fiber applications, a carrier for recently developed broadband telecommunication systems to support spatial division multiplexing techniques. This new carrier, originally designed for high-speed digital baseband transmission applications, can also offer advantages in the transmission of analog optical signals, typical of radio-fiber systems and microwave photonics. Specifically and given its unique properties, it provides a unique platform for the development of new devices and photonic systems specific to this field of application, with distinctive and novel properties.
- MCF multicore fiber optic fiber
- SMF single-mode transmission guide
- SCF single-mode fibers
- the N cores are arranged in the same diameter cover (b) and the density of cores is determined by the distance ( ⁇ ) between cores that guarantees a certain level of interference or crosstalk along a given propagation length (L).
- the N nuclei have the same diameter and the same propagation characteristics, that is to say the same refractive index (/ 3 ⁇ 4), the same propagation constant ⁇ , and therefore the same group delay r, and the same chromatic dispersion (D).
- Multicore optical fibers were initially conceived in response to the exponential growth in the demand for transmission capacity that is taking place in optical telecommunications networks.
- Fiber optic telecommunication systems have been using various multiplexing schemes to date, such as time division multiplexing (TDM, Time Division Multiplexing), optical wavelength division (WDM, Wavelength Division Multiplexing) and by polarization division (PDM, Polarized Division Multiplexing), thanks to which it is possible to transport transmission rates of up to several tens of Tb / s through standard single-mode fiber optic links.
- TDM Time Division Multiplexing
- WDM Wavelength Division Multiplexing
- PDM Polarization division
- the increase in transmission capacity is achieved by transmitting a different signal for each of the N cores that make up the MCF and acting as independent channels, requiring therefore the use of N transmitters at its input and N receivers at its output , that is, a transmitter connected to the input of each core and a receiver connected to the output of each core.
- the second proposal would also allow up to 19 cores, reducing the cover diameter to 125 ⁇ , thanks to the use of heterogeneous MCF, in whose structure the nuclei are distributed spatially in triangular (with the same un) or rectangular patterns (in a network with two values of ⁇ different).
- multicore fibers have been designed and manufactured to date, always seeking the lowest possible levels of propagation loss and interference between cores to obtain the highest possible density.
- the level of interference that is, the maximum power transferred between cores, as well as the losses caused by micro and macrocurvatures, depend on the design of the refractive index profile of the cores (n co ) of the cover refractive index ⁇ n c ⁇ ) and the geometry of the core network (distance between cores ⁇ ).
- OFS Labs USA
- NTT Nippon Telegraph and Telephone Corporation, Japan
- Sumitono Electric Industries Japan
- Fujikura Fujikura
- the homogeneous 7-core MCFs manufactured by OFS Labs offer losses around 0.37dB / km and 0.23 dB / km respectively in the second and third transmission window for the central core, while passing values of 0.40 and 0.26 dB / km for the outer cores. Similar attenuation values, between 0.22 and 0.24 dB / km, were obtained for homogeneous MCFs with different separation between cores manufactured by Fujikura.
- Multicore fibers have never been used as sampled delay lines, or with any other functionality, in the field of application of microwave photonics or radio-fiber systems.
- a variety of patents have been found that refer to the design and construction of various types of multicore fibers with controlled coupling or free of coupling between cores.
- patent documents can be cited: US201 10243517 (Uncoupled Multi-Core Fiber), US201 10182557 (Multi-Core Fiber), US201 10206330 (Multicore Optical Fiber) and US7418178 (Multicore Fiber.)
- US201 1274435 Multicore Fiber Transmission Systems and Methods in which the application of optical fibers to systems is discussed. This patent relates to the transmission of data in digital CWDM / DWDM systems through the cores of multicore fibers using vertical cavity lasers and photodetector arrays.
- multicore optical fibers have been used as a transmission medium for N independent channels, and never as a delay line or in the fields of microwave photonics.
- the invention provides a new delay line characterized in that it comprises at least one optical source for generating an optical signal, at least one RF (Radio Frequency) modulator of the optical signal. , to modulate the optical carrier with the RF signal, and a multi-core optical fiber (MCF).
- Said MCF can be both a heterogeneous MCF and a homogeneous MCF.
- the N nuclei have the same length L and a different color dispersion D.
- the modulated signal is applied to each of the cores, to provide at the output of each core N that forms the delay line, the same signal but delayed according to different incremental delays depending on the chromatic dispersion of each core, providing then N samples spaced in time.
- each core N of the homogeneous MCF is connected to a single mode optical fiber, which can be single mode fibers of different lengths with the same chromatic dispersion D, or they can also be fibers with the same length and different chromatic dispersion D; to, in any of the cases, provide at the output of the delay line, corresponding to the output of each single mode fiber, a same signal but delayed according to different incremental delays, acting as a delay line sampled over time.
- the incremental time delays of each nucleus of the heterogeneous MCF and of each single-mode fiber can be constant between each pair of adjacent or non-constant nuclei.
- Each nucleus of the heterogeneous MCF has a linear group delay with a different slope wavelength.
- the incremental delay value can be varied, acting as the sampled delay line in the reconfigurable time.
- a multichannel M-channel optical source generated well by the modeling technique, which provides a pulse train with different wavelengths that are modulated with the same RF signal and applied to the N nuclei of the fiber, or generated by a plurality of optical sources M of different emission wavelengths, which are multiplexed in wavelength (WDM) and modulated with the same RF signal.
- Said pulse train equivalent to the optical multiplex is responsible for feeding each of the MCF cores, so that at the output of each core a delay line of the M modulated signals is obtained, each line experiencing a given incremental delay given by the particular dispersion characteristics of each core.
- a second variant of the invention comprises an M-channel multichannel optical source, well generated by the modeling technique, which provides a pulse train with different wavelengths that are modulated with the same RF signal and applied to the N cores of the fiber or generated by a plurality of optical sources M of different emission wavelengths, which are multiplexed in wavelength (WDM) and modulated with the same RF signal.
- Said pulse train or optical multiplex is responsible for feeding each of the MCF cores, but in this case the set of outputs of the N cores is connected to a WDM demultiplexer. Through this configuration, at the output of the demultiplexer M delay lines are obtained, each corresponding to one of the M optical wavelengths, each consisting of N samples.
- a third variant of the invention comprises various multichannel optical channels of M channels generated by the modeling technique or by pluralities of optical sources of different emission wavelengths, which are multiplexed in wavelength (WDM) by N different multiplexers, modulating each of the N multiplexed groupings with a different RF signal.
- WDM wavelength
- N multiplexed in wavelength
- each core k that makes up the MCF is fed with a different WDM multiplex, consisting of M k optical carriers.
- This configuration provides the output of each of the N cores, a different and independent delay line, where the number of samples is given by the number of wavelengths that make up a certain multiplex (Mk), while the incremental delay is defined according to the dispersion characteristics of each of the N cores
- the separation between the wavelengths corresponding to adjacent optical sources may be constant or not constant, according to the required needs.
- the RF modulation can be an amplitude modulation or a phase modulation.
- the above embodiments have the advantage that they can be adapted for use in various Microwave Photonics applications.
- the sampled delay line is applied as a fixed and tunable transverse filter, where the outputs of the cores that make up the MCF are grouped and connected to a photodetector in order to detect the RF signal.
- Samples of the modulating signal can be independently weighed by variable optical attenuators.
- the simplest implementation of microwave transverse filtering considers a single modulated optical source, so that the MCF acts as a delay line Composed of N samples. Through this scheme, tuning the emission wavelength of the optical source allows the free spectral range (FSR) of the radio frequency response of the implemented filter to be varied.
- FSR free spectral range
- a variant of the above scheme consists in using either a multichannel M channel optical source generated by the modeling technique or a plurality of M optical sources, of different emission wavelengths, which are multiplexed in wavelength (WDM) and They are modulated with the same RF signal.
- WDM wavelength
- an independent transverse filter is established, characterized by a different FSR, tunable by varying the separation between emission wavelengths of the optical sources.
- the output of each MCF core is connected to a different RF photodetector.
- Another variant is also provided in which the output of the delay line is connected to a WDM demultiplexer, so that in each of the M outputs of the demultiplexer, a different filter is established consisting of N samples, with different FSR. For this, each output of the demultiplexer is connected to a different photodetector.
- the sampled delay line is applied to arrays of phase microwave antenna arrays (Phased array antennas, PAA).
- PAA phase microwave antenna arrays
- the output of each core of the MCF is photodetected independently and connected to a different antenna element, where each antenna element belongs to a set or array of antennas in phase.
- the pointing direction The resulting array factor is governing by varying the incremental group delay between cores through the tuning of the wavelength.
- a variant of the above scheme includes the inclusion of a different optical source and electro-optic modulator at the input of each core.
- the outputs from the N Cores that make up the MCF are connected to a single photodetector for the reception of the radiated signals.
- variable optical attenuators can be included at the exit of each core to implement various poisoning schemes.
- the sampled delay line is applied to the arbitrary optical generation of RF signals.
- the device comprises an RF pulse generator connected to a first and a second electro-optic modulator, fed in regions with opposite slopes, by different voltages, so that the same electric pulse is injected into both modulators.
- Both electro-optical modulators are connected to a single optical emission source at their input.
- the first modulator is connected at its output to a 1 xN optical coupler followed by 2x1 optical switches that connect to each of the N cores of the MCF.
- the selection state of the 2x1 switch allows to provide a selection of ⁇ ⁇ positive samples to be transmitted through a subset of ⁇ ⁇ cores.
- the second electro-optical modulator is connected to a second 1xN optical coupler also followed by a series of 2x1 optical switches, in order to provide a selection of N 2 negative samples to be transmitted by a second subset of N 2 cores.
- the output of the N cores is connected to a single RF photodetector, obtaining the desired RF pulse pattern.
- variable optical attenuators at the output of the first and second 1 xN optical coupler, to control the amplitude of the samples individually.
- the RF pulse generator is connected to a single electro-optical modulator, whose output is connected to the input of the N cores of the MCF.
- Each output of said cores is connected to a 1 x 2 optical switch, each of which is connected to a first and a second optical coupler.
- Nx1 which, in turn, are connected to a balanced photodetector, which allows the separation of a subset Ni of positive pulses and a subset N 2 of negative pulses.
- Pulse selection is made by controlling the 1 x 2 switches at the output of each core that directs the signal to one of the balanced photodetectors. For example to the upper balanced photodetector, for positive coefficients, or to the lower balanced photodetector, for negative coefficients.
- variable optical attenuators is provided in each of the inputs of the first and second optical coupler Nx1, to control the amplitude of the samples individually.
- the invention has developed a device responsible for connecting a single mononuclear fiber with the N cores of the MCF.
- Said element is arranged at the entrance of the MCF fiber in cases where it is required to perform the injection of a single modulated optical signal to the MCF input, while it is placed reciprocally at the MCF output in those cases. in which it is necessary to detect the N samples of the signal in the output plane of the MCF.
- the invention can be used for use as a fixed and tunable transverse filter, as optical feed of arrays of phase antennas or to implement arbitrary generators of radiofrequency signals
- Figure 1. Shows a schematic view of the representation of a multicore fiber.
- Figure 2. Shows an embodiment of the invention in which a heterogeneous multicore fiber is used as a discrete optical delay line.
- a single optical carrier is applied at the input of the different N cores to obtain spatial diversity at its output.
- Figures 3a and 3b.- Shows a graph of the group delay of each of the nuclei that make up a heterogeneous multicore fiber as a function of the optical wavelength. Each core has a different linear slope of a different slope, or what is the same, a different value of the chromatic dispersion parameter D. In figure 3a for a wavelength ⁇ an incremental delay Ti is obtained, and in the figure 3b for a ⁇ 2 an incremental delay T 2 is obtained.
- Figure 4.- Shows an embodiment of the invention in which a sampled delay line based on a homogeneous multicore fiber and optical delay lines is obtained.
- Figure 5. Shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber with multichannel optical input or WDM and with spatial diversity output of the WDM signal is obtained.
- Figure 6. Shows a graph of the group delay versus the wavelength to indicate the principle of operation of the delay line with multichannel or WDM optical input signals of Figure 5.
- Figure 7.- Shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber similar to that of Figure 5 is obtained, with multichannel optical input or WDM, but with the difference that the output is obtained in the wavelength domain through demultiplexing in WDM.
- Figure 8 shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber with input from several different multichannel or multiplex WDM optical sources for each core and with output in spatial diversity is obtained.
- Figure 9. Shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber is obtained whose nuclei have different group delay slopes D ⁇ . Single optical carrier input with output in spatial diversity.
- Figure 10. Shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber is obtained, with input from a multichannel optical source or WDM with non-constant wavelength separation ⁇ , with output in spatial diversity .
- Figure 11.- Shows an implementation of a microwave transverse photonic filter using a heterogeneous multicore fiber.
- Figures 12a - 12d.- They show a series of graphs of the characteristic electrical transfer function of the microwave transverse photonic filter, highlighting the tunability and reconfigurability functionalities, according to the embodiment of the previous figure.
- Figure 13 Shows an implementation of a feed network in arrays of antennas in phase using a heterogeneous multicore fiber.
- Figure 14.- Shows a scheme for the generation of arbitrary RF signals by phase inversion in a Mach-Zehnder modulator, using a heterogeneous multicore fiber.
- Figure 15. Shows a scheme for the generation of arbitrary RF signals by balanced detection, using a heterogeneous multicore fiber.
- Figure 16. It shows the structure of the connectors that the invention provides to allow the connection of a mononuclear fiber with the N cores at the input of the MCF fiber and the connection of the N cores at the MCF output with a mononuclear fiber .
- the multicore fibers comprise N cores that are arranged in the same cover of diameter b and the density of cores is determined by the distance ⁇ between cores that guarantees a certain level of interference or crosstalk at along a given propagation length L, as shown in Figure 1.
- the N nuclei have the same diameter and the same propagation characteristics, that is to say the same refractive index n c ⁇ , the same propagation constant ⁇ , and therefore the same delay of group T, and the same dispersion chromatic D, unlike heterogeneous multicore fibers that have different propagation characteristics.
- each core therefore acts as a waveguide that transmits a different propagation mode that has a propagation constant / 3 ⁇ 4 ⁇ , which can be expressed according to its second-order Taylor series development along the angular central frequency of emission of the optical source ⁇ 0 as: ⁇ ] ( ⁇ ) ( ⁇ - ⁇ 0 )
- FIG. 2 An example of the invention of an implementation of a sampled delay line using a heterogeneous multicore fiber optic 2 formed by heterogeneous dispersive cores 3 of different composition fed by the same input signal from an optical source is shown in Figure 2.
- RF radio frequency
- the modulated signal 8 is divided between the N cores 3 that make up the heterogeneous multicore fiber 2.
- a connector 31 is provided, which is described later with the help of Figure 16.
- all the cores 3 have the same length L , each of them presents a linear group delay with the different slope wavelength, or what is the same, a different value of the chromatic dispersion parameter D, as shown by way of example in Figures 3a and 3b.
- the characteristic of the group delay of each of them can be approximated by
- FIG. 3a shows the distribution of delays when the working wavelength is .
- the delay line produces N replicas of the modulated signal at its input delayed respectively by values 0, Ti, 27 ⁇ , ... ( ⁇ / -1) 7 ⁇ .
- the change of said basic delay of 7 ⁇ ⁇ T 2 is shown in Figure 3b, when the laser wavelength 4 feeder changes from ⁇ ⁇ ⁇ 2 .
- the proposed delay line provides N samples 10 time-equalized at the output 9 of the N cores 3, where the basic delay between samples 10 is tunable by modifying the wavelength. Therefore, samples 10 are obtained at spatially different outputs 9 and therefore this configuration is referred to as spatial diversity.
- the heterogeneous multicore fiber 2 used in the scheme of Figure 2 can be replaced by a homogeneous multicore fiber 2a, followed by a set of optical delay lines 1 1 implemented by single-mode fiber segments (SMF, single-mode fibers) 1 1 mononuclear (SCF) , singlecore fiber) standard of various lengths, as illustrated in Figure 4.
- each core 3a of the homogeneous multicore fiber has the same group delay
- the SMF does not present chromatic dispersion
- L S MF represents the basic difference between the lengths of contiguous sections and the group speed V 9 SMF is the same for each fiber section 1 1. If, on the contrary, the SMF introduced has chromatic dispersion, the difference between contiguous delays would be
- the tuning of the emission wavelength of the laser 4 makes it possible to dynamically control the incremental basic delay.
- FIG. 5 Another embodiment of the invention is shown in Figure 5 in which the sampled delay line is fed by a multiplex of optical sources.
- the fed signal comes from a WDM wavelength multiplex of modulated lasers 4a-4c, instead of a single optical source.
- An equivalent configuration consists in using a single emitting laser of different channels or wavelength optical modes as a power source using the phase phase modeling or modeling technique, which provides a pulse train with different wavelengths that are modulated with the same RF signal and apply to the N fiber cores.
- the optical power signal is composed of M lasers 4A-4M whose wavelengths of the signals 5A
- each output 9 of the cores 3 corresponds to a delay line of M samples 15A-15N, each delayed by a different incremental delay value.
- the heterogeneous optical fiber 2 is fed, with a different WDM 17A-17N multiplex for each of the cores, (or by an equivalent configuration that would use a single emitting laser of different channels as a power source or wavelength-balanced optical modes using the phase-mode or modeling technique) each in turn modulated by a different 7A - 7N radio frequency signal, with RF modulators 6A - 6N, whose modulated signal 8A -8N is applied to each of the nuclei 3 of the heterogeneous multicore fiber 2 taking its outputs 9 separately, in which case the structure functions as a set of N different and independent delay lines.
- samples 15A-15N are obtained, each delayed by a different incremental delay value.
- a single optical carrier signal 5 (P1) and a heterogeneous fiber 2 of cores 3 are used, as in the description made for Figure 2, with the difference that the cores 3 have slopes of different group delay D / (Di, ..., D k ..., D N ), unrelated through a constant increase, obtaining 10 'samples at its output.
- WDM multiplex signals are used at the input of the heterogeneous fiber 2, in the same way as described for Figure 5, but with the difference that non-constant wavelength separation ⁇ is expected, obtaining the samples 15 ⁇ - 15'N.
- microwave photonic filters of the prior art can be classified according to: a.1) Filters with lines of delay based on parallel fiber optic sections.
- this type of filters uses a single optical source 4, this type of filters generates N samples of the modulated optical signal that are independently weighed by variable optical attenuators (not shown) and delayed by delay lines determined according to the optical path along which They spread. Through this scheme, constant delays are obtained with the laser emission wavelength. a.2) Filters with dispersive delay lines.
- the use of multiple optical sources allows N optical carriers to be modulated with the same RF signal.
- the dispersive element will generate a different delay for each of the propagated optical wavelengths, that is, for each of the samples.
- the implementation of delay lines sampled by heterogeneous multicore fibers 2, where each core 3 has different dispersive characteristics allows the implementation of filters with dispersive delay lines using a single optical source. 4, as illustrated in Figure 1 1.
- the optical signal is applied to an intensity modulator 21 Mach-Zehnder MZM and to a phase modulator 22, which modulate the optical carrier by means of an RF signal 7 and are applied to the different cores 3, whose outputs are connected to a photodetector 19
- the joint photodetection of each of the N delayed samples of the modulating RF signal results in a microwave FIR (finite impulse response) filtering phenomenon, characterized by the frequency response:
- H (Q) ⁇ a n e- j ⁇ nnT + you where T is the basic delay unit of the filter, while a n and ⁇ ⁇ represent, respectively, the amplitude and phase of the ⁇ -th coefficient.
- T is the basic delay unit of the filter
- a n and ⁇ ⁇ represent, respectively, the amplitude and phase of the ⁇ -th coefficient.
- the above expression identifies an electrical transfer function with a periodic spectral characteristic, as can be seen in Figure 12a - 12d, whose frequency period or free spectral range (FSR) is inversely proportional to the basic delay between T samples.
- FSR free spectral range
- Q FSR / AQFWHM
- AQFWHM denotes the width of the resonance when the response falls 3 dB with respect to its maximum
- the tunability of the filter that is the change in the position of its center frequency, can be controlled by varying the phase ⁇ ⁇ of the samples, Fig. 12d.
- the variation of the module of the frequency response normalized to the unit is represented and in the horizontal axis the frequency.
- the second extension is based on the grouping of the outputs of the N cores and their subsequent wavelength demultiplexing, as illustrated in Figure 7, so that it is possible to obtain M different filters composed of N samples each one.
- each output of the demultiplexer 14 is connected to a photodetector 19.
- the implementation of poisoning techniques in this case would require the inclusion of N variable optical attenuators at the input or output of each of the cores.
- microwave transverse filters can also be obtained using as a base element the delay line composed of a homogeneous multicore fiber 2a and various sections of 1 1 single-mode fiber. b) Secondly, an adaptation is described for its application as optical feed of arrays of antennas 23 in phase.
- the microwave array antenna feed systems 23 in phase are composed of a group of multiple antennas, arranged in one or two dimensions, which are fed individually and coherently by a phase control system or a time delay (true time delay), so that it is possible to produce a radiation pattern determined at a given angular direction.
- phase control system or a time delay (true time delay)
- a time delay true time delay
- the direct application of this technology is found in radar systems that can be found both in the civil field (radio astronomy, climatology, space communications, terrestrial broadcasting) and in the military.
- One of the facets of the use of optical power networks in PAA in addition to the advantages inherent in the use of microwave photonics technology, lies in the possibility of distributing the microwave signals generated from / to a central unit to / from a remote location.
- the key element of a PAA is found in the beam forming network composed of several independent physical paths and responsible for connecting the radiating elements with an RF source (uplink: the RF signal is processed through the forming network and radiated to free space) or with an RF detector (downlink: the incident radiation is received by the antennas and transferred to the same RF receiver).
- the transmission characteristics of each path and, therefore, the aiming direction of the shaped beam can be modified if amplitude and phase / delay control elements are included.
- optical forming networks we find in the literature various techniques that can be classified into two categories: fiber-based networks and / or in integrated waveguides and networks based on free space optics.
- the solution proposed by the invention relates to fiber optic based networks and is based on the use of a heterogeneous multicore fiber 2 as a parallel feed network.
- the implementation scheme is very similar to that described in Figure 1 1 for microwave photonic filters, with the proviso that at the final end of MCF 2, the optical signal is detected from independently of the output of each of the N cores by means of a photodetector 19.
- Figure 1 1 corresponds to the case of RF signal emission
- the N battery Photodetectors are replaced by N transmitters (not shown) each composed of a laser 4 emitting in continuous wave and an electro-optic modulator 6. In that case, at the output of the MCF 2 the optical signal is detected together by a single photodetector 19.
- the Array Factor (AF) is used, by which the radiation pattern of the cluster is obtained, as the product of the array factor and the radiation pattern of the antenna element.
- the variation in the direction of aiming of the beam ⁇ is achieved by varying the complex weights or coefficients at r that make up the array factor:
- AF (e) ⁇ a r e
- u sin (6)
- d x the separation distance between the radiating elements on the x-axis.
- said control is implemented by varying the incremental basic group delay T between adjacent cores 3 of the MCF 2, that is, thanks to the tuning of the emission wavelength of the laser A, as it has been previously described:
- variable optical attenuators at the exit of each core would allow the implementation of various poisoning schemes.
- optical shaping networks for antenna arrays 23 can also be obtained using as a base element the delay line composed of a homogeneous multicore fiber 2a and various sections of single mode fiber 1 1. c) Arbitrary optical generation of radio frequency signals
- the proposed optical delay line can also be applied to the arbitrary optical generation of radiofrequency signals and, as a particular case, to one of the formats that has been most interesting in recent years: the ultrawideband standard (UWB).
- UWB ultrawideband standard
- An optical RF pulse generator is based on a discrete microwave photonic filtering scheme where the possibility of synthesis of a specific impulse response is sought. In said filtering scheme the possibility of obtaining positive and negative coefficients together is required.
- the use of MCF allows two different schemes to be obtained to obtain negative coefficients.
- the first scheme, illustrated in Figure 14, is based on the use of two electro-optic modulators 6A, 6B that are fed in regions with opposite slopes through two supply voltages. and V dC 2, respectively. Both modulators 6A, 6B are modulated by the same electrical pulse from an RF 24 pulse generator. The modulated optical signal from modulator 6A will be released to a subset of Ni cores and will be responsible for providing the Ni positive samples to the line. delay set by the N-core MCF 3.
- the optical signal from 6B will be injected into a subset of N 2 cores, thus providing the N 2 negative samples that are required for the synthesis of the final pulse.
- the selection of the polarity of the pulses to be transmitted by the MCF 2 is carried out at the input of each core 3 by means of an optical coupler 26 of type 1 xN followed by a switch 27 or optical switch 2x1 that allows to select the signal from one or Another modulator dynamically.
- a photodetector 19 is arranged to perform the joint detection of all samples, duly delayed according to the dispersion characteristics of each of the cores, allowing to obtain the desired RF pulse 30.
- the control over the amplitude of the samples individually for positive and negative polarities can be implemented by introducing variable optical attenuators (not shown) to each of the outputs of the optical couplers 26 of type 1 xN.
- each of the N total samples comes from the same electro-optic modulator, as shown in Figure 15.
- the separation between positive and negative coefficients is carried out by means of an architecture of balanced photodetection 19, whereby the desired subset of Ni positive samples and the subset of N 2 negative samples are selected at the output of each core 3 by means of an optical switch 28 of type 1 x2 followed by an optical coupler 29 of type Nx1.
- Pulse selection is done by controlling switches 28 of type 1 x2 at the output of each core 3, which directs the signal to one of the balanced photodetectors 19. For example, to the upper balanced photodetector, for coefficients positive, or to the lower balanced photodetector, for negative coefficients.
- the amplitude of the pulses can be controlled individually by the introduction of variable optical attenuators in each of the inputs of the optical couplers 29 of type Nx1.
- Both schemes proposed for the generation of arbitrary RF pulses can also be implemented using as an optical delay line the one composed of a homogeneous multicore fiber 2a and various sections of 1 1 single-mode fiber.
- the RF 24 generated optical pulses can also be used to perform pulse coding techniques by employing various modulation formats, such as, for example, pulse position modulation (PMM), modulation by pulse polarization or bi-phase modulation (BPM), amplitude modulation Pulse Rate (PAM), On-Off Keying Modulation (OOK) and Orthogonal Pulse Modulation (OPM).
- PMM pulse position modulation
- BPM bi-phase modulation
- PAM amplitude modulation Pulse Rate
- OSK On-Off Keying Modulation
- OFM Orthogonal Pulse Modulation
- Figure 16 shows the structure of a connector 12 for the connection between a mononuclear fiber 18 and the N cores of the MCF, SMC connector (Single to Multicore Connector), which allows the injection of a single optical signal modulated to the io MCF entry. It also shows the structure of a connector 20, for the connection between the MCF cores and a single-core fiber 18, MSC connector (Multi to Singlecore Connector), for the joint detection of the N signal samples in the output plane of the MCF.
- SMC connector Single to Multicore Connector
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Abstract
The invention relates to a sampled delay line comprising a homogeneous or heterogeneous multi-core optical fibre (2, 2a) used as a sampled delay line that can be reconfigured for implementation of microwave photonics functionalities, involving the processing of radio-frequency signals carried by one or more optical carriers. In particular, the invention relates to the use of heterogeneous multi-core fibres (2), the cores (3) of which have different chromatic dispersion properties, for implementing different incremental delays on a single signal supplied to each of the cores. The invention also involves supplying a single signal to all of the cores, which signal is wavelength multiplexed (WDM) or obtained from a single emitter laser having multiple channels or optical modes equally spaced in wavelength, using the modelocking technique, and supplying different independent WDM signals to each of the cores (3). The invention can be used as a tunable, fixed transverse filter, as an optical power supply for phased array antennas, and as an arbitrary generator of radio-frequency signals.
Description
LÍNEA DE RETARDO MUESTREADA DESCRIPCIÓN SAMPLE DELAY LINE DESCRIPTION
OBJETO DE LA INVENCIÓN OBJECT OF THE INVENTION
La presente invención se refiere a una línea de retardo muestreada que tiene por objeto permitir el uso de fibras ópticas multinúcleo (MCF, Multicore Fiber) como líneas de retardo muestreadas y reconfigurables para la implementación de diversas funcionalidades empleadas en Fotónica de Microondas, que involucran el procesamiento de señales del espectro de radiofrecuencia transportadas por una o varias portadoras situadas en la región óptica del espectro. En particular, el uso de fibras multinúcleo heterogéneas, en las que cada núcleo posee una composición y propiedades de dispersión cromática diferentes, permite la implementación de diferentes retardos increméntales sobre una misma señal alimentada a cada uno de los núcleos. The present invention relates to a sampled delay line that aims to allow the use of multicore optical fibers (MCF) as sampled and reconfigurable delay lines for the implementation of various functionalities employed in Microwave Photonics, which involve the processing of radio frequency spectrum signals carried by one or more carriers located in the optical region of the spectrum. In particular, the use of heterogeneous multicore fibers, in which each core has a different composition and chromatic dispersion properties, allows the implementation of different incremental delays on the same signal fed to each of the nuclei.
Las fibras multinúcleo homogéneas pueden también emplearse para implementar líneas de retardo muestreadas, incluyendo a la salida de cada núcleo de la fibra multinúcleo un tramo de fibra adicional que proporcione el retardo diferencial. Homogeneous multicore fibers can also be used to implement sampled delay lines, including at the exit of each core of the multicore fiber an additional fiber segment that provides the differential delay.
También es objeto de la invención proporcionar una gran versatilidad de la línea de retardo muestreada propuesta según la estructura de alimentación óptica de la fibra multinúcleo: alimentando una única señal óptica multicanal a todos los núcleos, bien generada por enganche de modos (modelocking) o bien multiplexada en longitud de onda (WDM, Wavelength División Multiplexing), mediante el empleo de múltiples fuentes ópticas (de diferentes longitudes de onda de emisión), de modo que la señal óptica multicanal alimenta a cada núcleo por separado y, finalmente, mediante alimentación de señales ópticas multicanal o WDM independientes a cada uno de los núcleos. It is also the object of the invention to provide a great versatility of the proposed sampled delay line according to the multicore fiber optical feeding structure: feeding a single multichannel optical signal to all the cores, either generated by mode coupling or modeling. wavelength multiplexing (WDM, Wavelength Multiplexing Division), by using multiple optical sources (of different emission wavelengths), so that the multichannel optical signal feeds each core separately and, finally, by feeding Multichannel or WDM optical signals independent of each of the cores.
En cualquiera de los casos el retardo incremental puede ser constante o variable.
Es otro objeto de la invención el empleo de nuevos conectores entre las fibras multinúcleos y las fibras mononúcleo, tanto a su entrada como a su salida, bien para la inyección de una única señal óptica modulada a la entrada de la MCF, o bien para la detección conjunta de las N muestras de la señal en el plano de salida de la MCF. In either case the incremental delay can be constant or variable. Another object of the invention is the use of new connectors between multicore fibers and mononuclear fibers, both at their input and at their output, either for the injection of a single modulated optical signal at the input of the MCF, or for the joint detection of the N signal samples in the MCF output plane.
La presente invención se sitúa dentro del marco de la Fotónica de Microondas. En concreto, dentro del ámbito general del procesado de fotónico de señales de radiofrecuencia, microondas y ondas milimétricas. También se enmarca dentro del campo de las aplicaciones de las fibras ópticas multinúcleo, un portador para sistemas de telecomunicación de banda ancha recientemente desarrollado para poder soportar técnicas de multiplexación por división espacial. Este nuevo portador, originalmente concebido para aplicaciones de transmisión banda base digital de alta velocidad, puede ofrecer ventajas también en la transmisión de señales ópticas analógicas, propias de los sistemas radio-fibra y la fotónica de microondas. En concreto y dada sus singulares propiedades, proporciona una plataforma única para el desarrollo de nuevos dispositivos y sistemas fotónicos específicos para este campo de aplicación, con propiedades distintivas y novedosas. The present invention is within the framework of Microwave Photonics. Specifically, within the general scope of photonic processing of radiofrequency signals, microwaves and millimeter waves. It is also part of the field of multicore optical fiber applications, a carrier for recently developed broadband telecommunication systems to support spatial division multiplexing techniques. This new carrier, originally designed for high-speed digital baseband transmission applications, can also offer advantages in the transmission of analog optical signals, typical of radio-fiber systems and microwave photonics. Specifically and given its unique properties, it provides a unique platform for the development of new devices and photonic systems specific to this field of application, with distinctive and novel properties.
ANTECEDENTES DE LA INVENCIÓN BACKGROUND OF THE INVENTION
En el estado de la técnica es conocido el empleo de la fibra óptica multinúcleo (MCF, multicore fiber) que posee diversos núcleos en una misma cubierta debidamente situados en el plano seccional de modo que cada núcleo actúa como una guía de transmisión monomodo (SMF, singlemode fibers) compuesta por un único núcleo independiente. Por ello, su incorporación a las redes de comunicaciones ópticas puede ofrecer capacidades de transmisión muy superiores a las obtenidas con las fibras mononúcleo (SCF, singlecore fibers) estándares. Las primeras fibras multinúcleo en diseñarse y fabricarse fueron las fibras multinúcleo homogéneas, compuestas por N núcleos idénticos en cuanto a su tamaño y a sus características de propagación. En este tipo de MCF, los N núcleos están dispuestos en una misma cubierta de diámetro (b) y la densidad de núcleos está determinada por la distancia (Λ) entre núcleos que
garantiza un determinado nivel de interferencia o crosstalk a lo largo de una longitud (L) de propagación dada. En las fibras homogéneas los N núcleos tienen el mismo diámetro y las mismas características de propagación, es decir el mismo índice de refracción (/¾), la misma constante de propagación β, y por tanto el mismo retardo de grupo r, y la misma dispersión cromática (D). In the state of the art, the use of multicore fiber optic fiber (MCF) is known, which has several cores in the same cover duly located in the sectional plane so that each core acts as a single-mode transmission guide (SMF, singlemode fibers) composed of a single independent core. Therefore, its incorporation into optical communications networks can offer transmission capacities far superior to those obtained with standard single core fibers (SCF). The first multicore fibers to be designed and manufactured were homogeneous multicore fibers, composed of N identical cores in terms of size and propagation characteristics. In this type of MCF, the N cores are arranged in the same diameter cover (b) and the density of cores is determined by the distance (Λ) between cores that guarantees a certain level of interference or crosstalk along a given propagation length (L). In the homogeneous fibers the N nuclei have the same diameter and the same propagation characteristics, that is to say the same refractive index (/ ¾), the same propagation constant β, and therefore the same group delay r, and the same chromatic dispersion (D).
Recientemente se ha propuesto el diseño de fibras multinúcleo heterogéneas, donde todos o parte de los núcleos que la conforman presentan propiedades de propagación distintas. Este tipo de MCF puede diseñarse para aportar menores niveles de interferencia entre pares de núcleos que la MCF homogénea y, además, permite obtener una mayor densidad de núcleos para un mismo diámetro de cubierta, tal y como más adelante se detalla. Recently the design of heterogeneous multicore fibers has been proposed, where all or part of the nuclei that make it up have different propagation properties. This type of MCF can be designed to provide lower levels of interference between pairs of cores than the homogeneous MCF and, in addition, allows to obtain a higher density of cores for the same cover diameter, as detailed below.
Las fibras ópticas multinúcleo fueron concebidas en sus inicios como respuesta al crecimiento exponencial de la demanda en capacidad de transmisión que está teniendo lugar en las redes de telecomunicaciones ópticas. Los sistemas de telecomunicación por fibra óptica han venido empleando hasta la actualidad diversos esquemas de multiplexación, como son la multiplexación por división en el tiempo (TDM, Time División Multiplexing), por división en longitud de onda óptica (WDM, Wavelength División Multiplexing) y por división en polarización (PDM, Polarizaron División Multiplexing), gracias a los cuales es posible transportar tasas de transmisión de hasta varias decenas de Tb/s a través de enlaces de fibras ópticas estándares monomodo. Sin embargo, el aumento de las tasas de transmisión a valores en torno los 100 Tb/s a través de una fibra monomodo convencional se percibe como difícil debido, entre otros, a la limitación en ancho de banda de los amplificadores de fibra, a los requerimientos en la relación señal a ruido, a los límites en la potencia óptica inyectada y a las nolinealidades inherentes a la fibra óptica. En consecuencia, y una vez sobrecargadas las posibles dimensiones de multiplexación, diversos grupos de investigación empezaron a considerar nuevas soluciones, como es el caso de la técnica de multiplexación por división espacial (SDM, space- division multiplexing) empleando fibras ópticas multinúcleo. Así pues, como una particularización de los sistemas de transmisión de múltiple entrada múltiple
salida, el aumento en capacidad de transmisión se logra al transmitir una señal diferente por cada uno de los N núcleos que conforman la MCF y que actúan como canales independientes, requiriéndose en consecuencia el empleo de N transmisores a su entrada y N receptores a su salida, es decir un transmisor conectado a la entrada de cada núcleo y un receptor conectado a la salida de cada núcleo. Multicore optical fibers were initially conceived in response to the exponential growth in the demand for transmission capacity that is taking place in optical telecommunications networks. Fiber optic telecommunication systems have been using various multiplexing schemes to date, such as time division multiplexing (TDM, Time Division Multiplexing), optical wavelength division (WDM, Wavelength Division Multiplexing) and by polarization division (PDM, Polarized Division Multiplexing), thanks to which it is possible to transport transmission rates of up to several tens of Tb / s through standard single-mode fiber optic links. However, the increase in transmission rates to values around 100 Tb / s through a conventional single-mode fiber is perceived as difficult due, among others, to the bandwidth limitation of fiber amplifiers, to the requirements in the signal-to-noise ratio, to the limits in the injected optical power and to the inherent lines of the optical fiber. Consequently, and once the possible multiplexing dimensions were overloaded, various research groups began to consider new solutions, such as the spatial division multiplexing technique (SDM) using multicore optical fibers. Thus, as a particularization of multiple input multiple transmission systems output, the increase in transmission capacity is achieved by transmitting a different signal for each of the N cores that make up the MCF and acting as independent channels, requiring therefore the use of N transmitters at its input and N receivers at its output , that is, a transmitter connected to the input of each core and a receiver connected to the output of each core.
Mediante la multiplexación espacial se han demostrado enlaces implementados mediante MCF homogénea compuesta por 7 núcleos, con separación entre núcleos Λ constante, que han alcanzado capacidades de transmisión de hasta 109 Tb/s en las bandas ópticas C y L a lo largo de 16.8 km y valores de hasta 56 Tb/s en la banda C para una distancia de 76.8 km. Mejoras en el diseño de los enlaces de MCF se han logrado recientemente empleando separaciones entre núcleos no constantes o bien recurriendo a esquemas heterogéneos. Mediante el primer diseño y gracias a una estructura circular, ha sido posible proponer un aumento sustancial en el número de núcleos hasta 19, lográndose fabricar fibras compuestas por 10 núcleos en un diámetro de cubierta de 204.4 μΐΎΐ . La segunda propuesta permitiría disponer también de hasta 19 núcleos, reduciendo el diámetro de cubierta a 125 μιη, gracias al empleo de MCF heterogéneas, en cuya estructura los núcleos se distribuyen espacialmente en patrones triangulares (con un mismo Λ) o rectangulares (en una red con dos valores de Λ diferentes). Through spatial multiplexing, links implemented by homogeneous MCF composed of 7 cores have been demonstrated, with constant separation between cores Λ, which have reached transmission capacities of up to 109 Tb / s in the optical bands C and L along 16.8 km and values of up to 56 Tb / s in the C band for a distance of 76.8 km. Improvements in the design of the MCF links have been achieved recently using separations between non-constant cores or using heterogeneous schemes. Through the first design and thanks to a circular structure, it has been possible to propose a substantial increase in the number of cores up to 19, being able to manufacture fibers composed of 10 cores in a cover diameter of 204.4 μΐΎΐ. The second proposal would also allow up to 19 cores, reducing the cover diameter to 125 μιη, thanks to the use of heterogeneous MCF, in whose structure the nuclei are distributed spatially in triangular (with the same un) or rectangular patterns (in a network with two values of Λ different).
Diversos tipos de fibras multinúcleo han sido diseñados y fabricados hasta la actualidad buscando siempre los menores niveles posibles de pérdidas de propagación y de interferencia entre núcleos para así obtener la mayor densidad posible. El nivel de interferencia, es decir, la máxima potencia transferida entre núcleos, así como las pérdidas causadas por micro y macrocurvaturas, dependen del diseño del perfil de índice de refracción de los núcleos (nco) del índice de refracción de la cubierta {nc¡) y de la geometría de la red de núcleos (distancia entre núcleos Λ). De entre las compañías que fabrican actualmente fibras multinúcleo podemos destacar OFS Labs (USA), NTT (Nippon Telegraph and Telephone Corporation, Japón), Sumitono Electric
Industries (Japón) y Fujikura (Japón). Las MCF homogéneas de 7 núcleos fabricadas por OFS Labs ofrecen pérdidas en torno a los 0,37dB/km y 0,23 dB/km respectivamente en la segunda y tercera ventana de transmisión para el núcleo central, mientras que pasan a valores de 0.40 y 0.26 dB/km para los núcleos exteriores. Valores similares de atenuación, entre los 0.22 y los 0.24 dB/km, se obtuvieron para las MCF homogéneas con distintas separación entre núcleos fabricadas por Fujikura. Various types of multicore fibers have been designed and manufactured to date, always seeking the lowest possible levels of propagation loss and interference between cores to obtain the highest possible density. The level of interference, that is, the maximum power transferred between cores, as well as the losses caused by micro and macrocurvatures, depend on the design of the refractive index profile of the cores (n co ) of the cover refractive index {n c ¡) and the geometry of the core network (distance between cores Λ). Among the companies that currently manufacture multicore fibers we can highlight OFS Labs (USA), NTT (Nippon Telegraph and Telephone Corporation, Japan), Sumitono Electric Industries (Japan) and Fujikura (Japan). The homogeneous 7-core MCFs manufactured by OFS Labs offer losses around 0.37dB / km and 0.23 dB / km respectively in the second and third transmission window for the central core, while passing values of 0.40 and 0.26 dB / km for the outer cores. Similar attenuation values, between 0.22 and 0.24 dB / km, were obtained for homogeneous MCFs with different separation between cores manufactured by Fujikura.
Otra de las cuestiones importantes a tratar en cuanto a enlaces implementados con MCF es la conectividad entre las MCF y las fibras mononúcleo estándares. El empleo comercial de las MCF como medio de transmisión en paralelo en las redes de comunicaciones ópticas requiere contar con dispositivos de bajo coste fiables para implementar el acoplo de señales a la entrada y a la salida de cada uno de los núcleos de manera individual. Hasta la fecha, se han diseñado varios dispositivos orientados a sistemas de multiplexado espacial, como es el caso del conector de fibra multinúcleo TMC (Tapered Multicore fiber Connector) de OFS labs diseñado para MCF de 7 núcleos, mediante el cual 7 fibras mononúcleo independientes son fusionadas conjuntamente de forma que coincidan con la disposición espacial transversal de los núcleos en la MCF. De este modo se han logrado pérdidas de inserción en entre 0.38 y 1 .8 dB, con niveles de interferencia entre núcleos inferiores a los -38 dB. No se conocen conectores que permitan la conexión de una única fibra SCF a una fibra MCF. Another important issue to address regarding links implemented with MCF is the connectivity between MCFs and standard mononuclear fibers. The commercial use of MCFs as a means of parallel transmission in optical communications networks requires reliable low-cost devices to implement the coupling of signals at the input and output of each of the cores individually. To date, several devices have been designed for spatial multiplexing systems, such as the OFC labs TMC (Tapered Multicore fiber Connector) multicore fiber connector designed for 7-core MCF, through which 7 independent mononuclear fibers are fused together to match the transverse spatial arrangement of the nuclei in the MCF. In this way, insertion losses have been achieved between 0.38 and 1 .8 dB, with interference levels between cores below -38 dB. There are no known connectors that allow the connection of a single SCF fiber to an MCF fiber.
Las fibras multinúcleo nunca se han empleado como líneas de retardo muestreadas, ni con ninguna otra funcionalidad, en el campo de aplicación de la fotónica de microondas o sistemas radio-fibra. Se han encontrado una variedad de patentes que hacen referencia al diseño y construcción de diversos tipos de fibras multinúcleo con acoplo controlado o libres de acoplo entre núcleos. A modo de ejemplo pueden citarse los documentos de patentes: US201 10243517 (Uncoupled Multi-Core Fiber), US201 10182557 (Multi-Core Fiber), US201 10206330 (Multicore Optical Fiber) y US7418178 (Multicore Fiber.)
También puede citarse el documento de patente US201 1274435 (Multicore Fiber Transmission Systems and Methods) en el que se trata la aplicación de fibras ópticas a sistemas. En esta patente se hace relación a la transmisión de datos en sistemas CWDM/DWDM digitales a través de los núcleos de las fibras multinúcleo empleando láseres de cavidad vertical y arrays de fotodetectores. Multicore fibers have never been used as sampled delay lines, or with any other functionality, in the field of application of microwave photonics or radio-fiber systems. A variety of patents have been found that refer to the design and construction of various types of multicore fibers with controlled coupling or free of coupling between cores. As an example, patent documents can be cited: US201 10243517 (Uncoupled Multi-Core Fiber), US201 10182557 (Multi-Core Fiber), US201 10206330 (Multicore Optical Fiber) and US7418178 (Multicore Fiber.) It can also be cited patent document US201 1274435 (Multicore Fiber Transmission Systems and Methods) in which the application of optical fibers to systems is discussed. This patent relates to the transmission of data in digital CWDM / DWDM systems through the cores of multicore fibers using vertical cavity lasers and photodetector arrays.
En el estado de la técnica, las fibras ópticas multinúcleo se han empleado como medio de transmisión para N canales independientes, y nunca como línea de retardo o en los campos de la fotónica de microondas. In the state of the art, multicore optical fibers have been used as a transmission medium for N independent channels, and never as a delay line or in the fields of microwave photonics.
DESCRIPCIÓN DE LA INVENCIÓN DESCRIPTION OF THE INVENTION
Para conseguir los objetivos y resolver los inconvenientes anteriormente señalados, la invención proporciona una nueva línea de retardo que se caracteriza por que comprende al menos una fuente óptica de generación de una señal óptica, al menos un modulador de RF (Radiofrecuencia) de la señal óptica, para modular la portadora óptica con la señal de RF, y una fibra óptica multinúcleo (MCF). Dicha MCF puede ser tanto una MCF heterogénea como una MCF homogénea. To achieve the objectives and solve the aforementioned drawbacks, the invention provides a new delay line characterized in that it comprises at least one optical source for generating an optical signal, at least one RF (Radio Frequency) modulator of the optical signal. , to modulate the optical carrier with the RF signal, and a multi-core optical fiber (MCF). Said MCF can be both a heterogeneous MCF and a homogeneous MCF.
En el caso de que se emplee una MCF heterogénea, sus N núcleos poseen la misma longitud L y una dispersión cromática D diferente. A cada uno de los núcleos se les aplica la señal modulada, para proporcionar a la salida de cada núcleo N que conforma la línea de retardo, ,una misma señal pero retardada según diferentes retardos increméntales en función de la dispersión cromática de cada núcleo, proporcionando pues N muestras espaciadas en el tiempo. In the case that a heterogeneous MCF is used, its N nuclei have the same length L and a different color dispersion D. The modulated signal is applied to each of the cores, to provide at the output of each core N that forms the delay line, the same signal but delayed according to different incremental delays depending on the chromatic dispersion of each core, providing then N samples spaced in time.
En el caso de emplear una MCF homogénea, sus N núcleos poseen la misma longitud L y una misma dispersión cromática D, y a cada uno de los núcleos se les aplica la señal modulada. La salida de cada núcleo N de la MCF homogénea está conectada a una fibra óptica monomodo, que pueden ser fibras monomodo de diferente longitud con la misma dispersión cromática D, o también pueden ser fibras con la misma longitud y diferente dispersión cromática D; para, en cualquiera de los casos, proporcionar en la salida de la línea de retardo, correspondiente a la salida de cada fibra monomodo, una
misma señal pero retardada según diferentes retardos increméntales, actuando como línea de retardo muestreada en el tiempo. In the case of using a homogeneous MCF, its N nuclei have the same length L and the same chromatic dispersion D, and the modulated signal is applied to each of the nuclei. The output of each core N of the homogeneous MCF is connected to a single mode optical fiber, which can be single mode fibers of different lengths with the same chromatic dispersion D, or they can also be fibers with the same length and different chromatic dispersion D; to, in any of the cases, provide at the output of the delay line, corresponding to the output of each single mode fiber, a same signal but delayed according to different incremental delays, acting as a delay line sampled over time.
Los retardos de tiempo incremental de cada núcleo de la MCF heterogénea y de cada fibra monomodo, pueden ser constantes entre cada par de núcleos adyacentes o no constantes. The incremental time delays of each nucleus of the heterogeneous MCF and of each single-mode fiber can be constant between each pair of adjacent or non-constant nuclei.
Cada núcleo de la MCF heterogénea presenta un retardo de grupo lineal con la longitud de onda de pendiente diferente. Mediante el cambio de la longitud de onda de la señal óptica, se logra variar el valor del retardo incremental, actuando como línea de retardo muestreada en el tiempo reconfigurable. Each nucleus of the heterogeneous MCF has a linear group delay with a different slope wavelength. By changing the wavelength of the optical signal, the incremental delay value can be varied, acting as the sampled delay line in the reconfigurable time.
En una primera realización de la invención se prevé que comprenda una fuente óptica multicanal de M canales generada bien por la técnica de modelocking, que proporciona un tren de impulsos con diferente longitud de onda que se modulan con una misma señal de RF y se aplican a los N núcleos de la fibra, o bien generada por una pluralidad de fuentes ópticas M de diferentes longitudes de onda de emisión, que se multiplexan en longitud de onda (WDM) y se modulan con una misma señal de RF. Dicho tren de impulsos equivalente al múltiplex óptico se encarga de alimentar a cada uno de los núcleos de la MCF, de modo que a la salida de cada núcleo se obtiene una línea de retardo de las M señales moduladas experimentando cada línea un retardo incremental diferente dado por las características de dispersión particulares de cada núcleo. In a first embodiment of the invention it is envisioned that it comprises a multichannel M-channel optical source generated well by the modeling technique, which provides a pulse train with different wavelengths that are modulated with the same RF signal and applied to the N nuclei of the fiber, or generated by a plurality of optical sources M of different emission wavelengths, which are multiplexed in wavelength (WDM) and modulated with the same RF signal. Said pulse train equivalent to the optical multiplex is responsible for feeding each of the MCF cores, so that at the output of each core a delay line of the M modulated signals is obtained, each line experiencing a given incremental delay given by the particular dispersion characteristics of each core.
Una segunda variante de la invención comprende una fuente óptica multicanal de M canales, bien generada por la técnica de modelocking, que proporciona un tren de impulsos con diferente longitud de onda que se modulan con una misma señal de RF y se aplican a los N núcleos de la fibra o bien generada mediante una pluralidad de fuentes ópticas M de diferentes longitudes de onda de emisión, que se multiplexan en longitud de onda (WDM) y se modulan con una misma señal de RF. Dicho tren de impulsos o el múltiplex óptico se encargan de alimentar a cada uno de los núcleos de la MCF, pero en este caso el conjunto de las salidas de los N núcleos está conectada a un demultiplexor WDM. Mediante esta configuración, a la salida del demultiplexor
se obtienen M líneas de retardo, correspondientes cada una a una de las M longitudes de onda ópticas, compuestas cada una por N muestras. A second variant of the invention comprises an M-channel multichannel optical source, well generated by the modeling technique, which provides a pulse train with different wavelengths that are modulated with the same RF signal and applied to the N cores of the fiber or generated by a plurality of optical sources M of different emission wavelengths, which are multiplexed in wavelength (WDM) and modulated with the same RF signal. Said pulse train or optical multiplex is responsible for feeding each of the MCF cores, but in this case the set of outputs of the N cores is connected to a WDM demultiplexer. Through this configuration, at the output of the demultiplexer M delay lines are obtained, each corresponding to one of the M optical wavelengths, each consisting of N samples.
Una tercera variante de la invención comprende diversas fuentes ópticas multicanal de M canales generadas por la técnica de modelocking o bien por pluralidades de fuentes ópticas de diferentes longitudes de onda de emisión, que se multiplexan en longitud de onda (WDM) mediante N multiplexores diferentes, modulándose cada una de las N agrupaciones multiplexadas con una señal de RF diferente. Mediante este esquema, cada núcleo k que conforma la MCF queda alimentado con un múltiplex WDM distinto, compuesto por Mk portadoras ópticas. Esta configuración proporciona a la salida de cada uno de los N núcleos, una línea de retardo diferente e independiente, donde el número de muestras viene dado por el número de longitudes de onda que componen un determinado múltiplex (Mk), mientras que el retardo incremental queda definido según las características de dispersión de cada uno de los N núcleos A third variant of the invention comprises various multichannel optical channels of M channels generated by the modeling technique or by pluralities of optical sources of different emission wavelengths, which are multiplexed in wavelength (WDM) by N different multiplexers, modulating each of the N multiplexed groupings with a different RF signal. Through this scheme, each core k that makes up the MCF is fed with a different WDM multiplex, consisting of M k optical carriers. This configuration provides the output of each of the N cores, a different and independent delay line, where the number of samples is given by the number of wavelengths that make up a certain multiplex (Mk), while the incremental delay is defined according to the dispersion characteristics of each of the N cores
En cualquiera de los casos anteriores, la separación entre las longitudes de onda correspondientes a fuentes ópticas adyacentes puede ser constante o no constante, de acuerdo a las necesidades requeridas. In any of the above cases, the separation between the wavelengths corresponding to adjacent optical sources may be constant or not constant, according to the required needs.
También, en cualquiera de los casos anteriores, la modulación de RF puede ser una modulación en amplitud o una modulación en fase. Also, in any of the above cases, the RF modulation can be an amplitude modulation or a phase modulation.
Las anteriores realizaciones presentan la ventaja de que se pueden adaptar para su uso en diversas aplicaciones de la Fotónica de Microondas. The above embodiments have the advantage that they can be adapted for use in various Microwave Photonics applications.
En un primer tipo de adaptación, la línea de retardo muestreada se aplica como filtro transversal fijo y sintonizable, donde las salidas de los núcleos que conforman la MCF se agrupan y se conectan a un fotodetector a fin de detectar la señal de RF. Las muestras de la señal moduladora pueden ser sopesadas independientemente por atenuadores ópticos variables. La implementación más sencilla de filtrado transversal de microondas considera una única fuente óptica modulada, de forma que la MCF actúa como una línea de retardo
compuesta por N muestras. Mediante este esquema, la sintonización de la longitud de onda de emisión de la fuente óptica permite variar el rango espectral libre (FSR, Free Spectral Range) de la respuesta de radiofrecuencia del filtro implementado. In a first type of adaptation, the sampled delay line is applied as a fixed and tunable transverse filter, where the outputs of the cores that make up the MCF are grouped and connected to a photodetector in order to detect the RF signal. Samples of the modulating signal can be independently weighed by variable optical attenuators. The simplest implementation of microwave transverse filtering considers a single modulated optical source, so that the MCF acts as a delay line Composed of N samples. Through this scheme, tuning the emission wavelength of the optical source allows the free spectral range (FSR) of the radio frequency response of the implemented filter to be varied.
Una variante del anterior esquema consiste en utilizar bien una fuente óptica multicanal de M canales generada por la técnica de modelocking o bien una pluralidad de fuentes ópticas M, de diferentes longitudes de onda de emisión, que se multiplexan en longitud de onda (WDM) y se modulan con una misma señal de RF. De este modo, a la salida de cada núcleo de la MCF, se establece un filtro transversal independiente, caracterizado por un FSR distinto, sintonizable variando la separación entre longitudes de onda de emisión de las fuentes ópticas. Para ello, la salida de cada núcleo de la MCF se conecta a un fotodetector de RF distinto. A variant of the above scheme consists in using either a multichannel M channel optical source generated by the modeling technique or a plurality of M optical sources, of different emission wavelengths, which are multiplexed in wavelength (WDM) and They are modulated with the same RF signal. Thus, at the output of each core of the MCF, an independent transverse filter is established, characterized by a different FSR, tunable by varying the separation between emission wavelengths of the optical sources. To do this, the output of each MCF core is connected to a different RF photodetector.
También se prevé otra variante en la que la salida de la línea de retardo está conectada a un demultiplexor WDM, de modo que en cada una de las M salidas del demultiplexor, se establece un filtro distinto compuesto por N muestras, con distinto FSR. Para ello cada salida del demultiplexor se conecta a un fotodetector diferente. Another variant is also provided in which the output of the delay line is connected to a WDM demultiplexer, so that in each of the M outputs of the demultiplexer, a different filter is established consisting of N samples, with different FSR. For this, each output of the demultiplexer is connected to a different photodetector.
En un segundo tipo de adaptación, la línea de retardo muestreada se aplica a sistemas de alimentación de arrays de antenas de microondas en fase (Phased array antennas, PAA). Para ello, la salida de cada núcleo de la MCF es fotodetectada de manera independiente y conectada a un elemento de antena diferente, donde cada elemento de antena pertenece a un conjunto o array de antenas en fase.. En este caso, la dirección de apuntamiento del factor de array resultante es gobernando mediante la variación del retardo de grupo incremental entre núcleos a través de la sintonización de la longitud de onda. In a second type of adaptation, the sampled delay line is applied to arrays of phase microwave antenna arrays (Phased array antennas, PAA). To do this, the output of each core of the MCF is photodetected independently and connected to a different antenna element, where each antenna element belongs to a set or array of antennas in phase. In this case, the pointing direction The resulting array factor is governing by varying the incremental group delay between cores through the tuning of the wavelength.
El caso anterior corresponde a un sistema transmisor de RF. Para sistemas de recepción de señales de RF radiadas, una variante del esquema anterior comprende la inclusión de una fuente óptica y modulador electroóptico diferentes a la entrada de cada núcleo. Las salidas provenientes de los N
núcleos que componen la MCF se conectan a un único fotodetector para la recepción de las señales radiadas. The previous case corresponds to an RF transmitter system. For reception systems of radiated RF signals, a variant of the above scheme includes the inclusion of a different optical source and electro-optic modulator at the input of each core. The outputs from the N Cores that make up the MCF are connected to a single photodetector for the reception of the radiated signals.
En los casos anteriores de aplicación en sistemas de alimentación de arrays, se pueden incluir atenuadores ópticos variables a la salida de cada núcleo para implementar diversos esquemas de enventanado. In the previous cases of application in array feeding systems, variable optical attenuators can be included at the exit of each core to implement various poisoning schemes.
En un tercer tipo de adaptación, la línea de retardo muestreada se aplica a la generación óptica arbitraria de señales de RF. En una primera variante, el dispositivo comprende un generador de pulsos de RF conectado a un primer y a un segundo modulador electroóptico, alimentados en regiones con pendientes opuestas, mediante voltajes diferentes, de modo que un mismo pulso eléctrico es inyectado a ambos moduladores. Ambos moduladores electroópticos están conectados a una única fuente de emisión óptica a su entrada. El primer modulador está conectado en su salida a un acoplador óptico 1 xN seguido de unos conmutadores ópticos 2x1 que se conectan a cada uno de los N núcleos de la MCF. El estado de selección del conmutador 2x1 permite proporcionar una selección de Ν Ϊ muestras positivas a ser transmitidas a través de un subconjunto de ΝΪ núcleos. Por otro lado, el segundo modulador electroóptico está conectado a un segundo acoplador óptico 1xN seguido también de una serie de conmutadores ópticos 2x1 , con el fin de proporcionar una selección de N2 muestras negativas para ser transmitidas por un segundo subconjunto de N2 núcleos. La salida de los N núcleos está conectada a un único fotodetector de RF, obteniendo el patrón de pulso de RF deseado. In a third type of adaptation, the sampled delay line is applied to the arbitrary optical generation of RF signals. In a first variant, the device comprises an RF pulse generator connected to a first and a second electro-optic modulator, fed in regions with opposite slopes, by different voltages, so that the same electric pulse is injected into both modulators. Both electro-optical modulators are connected to a single optical emission source at their input. The first modulator is connected at its output to a 1 xN optical coupler followed by 2x1 optical switches that connect to each of the N cores of the MCF. The selection state of the 2x1 switch allows to provide a selection of Ν Ϊ positive samples to be transmitted through a subset of Ν Ϊ cores. On the other hand, the second electro-optical modulator is connected to a second 1xN optical coupler also followed by a series of 2x1 optical switches, in order to provide a selection of N 2 negative samples to be transmitted by a second subset of N 2 cores. The output of the N cores is connected to a single RF photodetector, obtaining the desired RF pulse pattern.
Se prevé que comprenda atenuadores ópticos variables a la salida del primer y segundo acoplador óptico 1 xN, para controlar la amplitud de las muestras de manera individual. It is expected that it comprises variable optical attenuators at the output of the first and second 1 xN optical coupler, to control the amplitude of the samples individually.
En una segunda variante de generación de señales de RF arbitraria, el generador de pulsos de RF está conectado a un único modulador electroóptico, cuya salida está conectada a la entrada de los N núcleos de la MCF. Cada salida de dichos núcleos está conectada a un conmutador óptico 1 x2, cada uno de los cuales están conectados a un primer y a un segundo acoplador óptico
Nx1 , que, a su vez, están conectados a un fotodetector balanceado, que permite la separación de un subconjunto Ni de pulsos positivos y de un subconjunto N2 de pulsos negativos. La selección de los pulsos se realiza mediante el control de los conmutadores 1 x2 que hay a la salida de cada núcleo que dirige la señal a uno de los fotodetectores balanceados. Por ejemplo al fotodetector balanceado superior, para coeficientes positivos, o al fotodetector balanceado inferior, para coeficientes negativos. In a second variant of arbitrary RF signal generation, the RF pulse generator is connected to a single electro-optical modulator, whose output is connected to the input of the N cores of the MCF. Each output of said cores is connected to a 1 x 2 optical switch, each of which is connected to a first and a second optical coupler. Nx1, which, in turn, are connected to a balanced photodetector, which allows the separation of a subset Ni of positive pulses and a subset N 2 of negative pulses. Pulse selection is made by controlling the 1 x 2 switches at the output of each core that directs the signal to one of the balanced photodetectors. For example to the upper balanced photodetector, for positive coefficients, or to the lower balanced photodetector, for negative coefficients.
Se prevé la inclusión de atenuadores ópticos variables en cada una de las entradas del primer y segundo acoplador óptico Nx1 , para controlar la amplitud de las muestras de manera individual. The inclusion of variable optical attenuators is provided in each of the inputs of the first and second optical coupler Nx1, to control the amplitude of the samples individually.
Para realizar las conexiones de la entrada y/o salida de la línea de retardo, anteriormente indicadas, la invención ha desarrollado un dispositivo encargado de conectar una única fibra mononúcleo con los N núcleos de la MCF. Dicho elemento se dispone a la entrada de la fibra MCF en los casos en los que se requiera efectuar la inyección de una única señal óptica modulada a la entrada de MCF, mientras que se coloca de manera recíproca a la salida de la MCF en aquellos casos en los que requiera realizar la detección de las N muestras de la señal en el plano de salida de la MCF. In order to make the connections of the input and / or output of the delay line, indicated above, the invention has developed a device responsible for connecting a single mononuclear fiber with the N cores of the MCF. Said element is arranged at the entrance of the MCF fiber in cases where it is required to perform the injection of a single modulated optical signal to the MCF input, while it is placed reciprocally at the MCF output in those cases. in which it is necessary to detect the N samples of the signal in the output plane of the MCF.
De acuerdo con todo lo anteriormente expuesto, la invención puede ser empleada para su uso como filtro transversal fijo y sintonizable, como alimentación óptica de arrays de antenas en fase o para implementar generadores arbitrarios de señales de radiofrecuencia In accordance with all of the foregoing, the invention can be used for use as a fixed and tunable transverse filter, as optical feed of arrays of phase antennas or to implement arbitrary generators of radiofrequency signals
Las ventajas que aporta la presente realización frente a otras correspondientes al estado de la técnica residen principalmente en el aprovechamiento del paralelismo que las MCF ofrecen en un tamaño de portador reducido y capaz de distribuir las señales a larga distancia y con bajas pérdidas. El proporcionar dicho paralelismo dentro de una única estructura física aporta además ventajas en cuanto a uniformidad en la longitud de los portadores y comportamiento uniforme frente a variaciones mecánicas y medioambientales.
BREVE ENUNCIADO DE LAS FIGURAS The advantages provided by the present embodiment over others corresponding to the state of the art reside mainly in the use of the parallelism that the MCFs offer in a reduced carrier size and capable of distributing the signals over long distances and with low losses. Providing such parallelism within a single physical structure also provides advantages in terms of uniformity in the length of the carriers and uniform behavior against mechanical and environmental variations. BRIEF STATEMENT OF THE FIGURES
Figura 1.- Muestra una vista esquemática de la representación de una fibra multinúcleo. Figure 1.- Shows a schematic view of the representation of a multicore fiber.
Figura 2.- Muestra una realización de la invención en la que una fibra multinúcleo heterogénea se utiliza como línea de retardo óptica discreta. En este ejemplo se aplica en la entrada de los diferentes núcleos N una sola portadora óptica para obtener en su salida una diversidad espacial. Figure 2.- Shows an embodiment of the invention in which a heterogeneous multicore fiber is used as a discrete optical delay line. In this example, a single optical carrier is applied at the input of the different N cores to obtain spatial diversity at its output.
Figuras 3a y 3b.- Muestra una gráfica del retardo de grupo de cada uno de los núcleos que componen una fibra multinúcleo heterogénea en función de la longitud de onda óptica. Cada núcleo presenta un retardo de grupo lineal de pendiente diferente, o lo que es lo mismo, un valor diferente del parámetro de dispersión cromática D. En la figura 3a para una longitud de onda Λι se obtiene un retardo incremental Ti , y en la figura 3b para una Λ2 se obtiene un retardo incremental T2. Figures 3a and 3b.- Shows a graph of the group delay of each of the nuclei that make up a heterogeneous multicore fiber as a function of the optical wavelength. Each core has a different linear slope of a different slope, or what is the same, a different value of the chromatic dispersion parameter D. In figure 3a for a wavelength Λι an incremental delay Ti is obtained, and in the figure 3b for a Λ 2 an incremental delay T 2 is obtained.
Figura 4.- Muestra una realización de la invención en la que se obtiene una línea de retardo muestreada basada en una fibra multinúcleo homogénea y en líneas de retardo ópticas. Figure 4.- Shows an embodiment of the invention in which a sampled delay line based on a homogeneous multicore fiber and optical delay lines is obtained.
Figura 5.- Muestra una realización de la invención en la que se obtiene una línea de retardo basada en una fibra multinúcleo heterogénea con entrada óptica multicanal o WDM y con salida en diversidad espacial de la señal WDM. Figure 5.- Shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber with multichannel optical input or WDM and with spatial diversity output of the WDM signal is obtained.
Figura 6.- Muestra una gráfica del retardo de grupo frente a la longitud de onda para indicar el principio de funcionamiento de la línea de retardo con señales de entrada óptica multicanal o WDM de la figura 5. Figure 6.- Shows a graph of the group delay versus the wavelength to indicate the principle of operation of the delay line with multichannel or WDM optical input signals of Figure 5.
Figura 7.- Muestra una realización de la invención en la que se obtiene una línea de retardo basada en una fibra multinúcleo heterogénea similar al de la figura 5, con entrada óptica multicanal o WDM, pero con la diferencia que la salida se obtiene en el dominio de la longitud de onda mediante demultiplexación en WDM.
Figura 8.- Muestra una realización de la invención en la que se obtiene una línea de retardo basada en una fibra multinúcleo heterogénea con entrada de varias fuentes ópticas multicanal o múltiplex WDM distintos para cada núcleo y con salida en diversidad espacial. Figure 7.- Shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber similar to that of Figure 5 is obtained, with multichannel optical input or WDM, but with the difference that the output is obtained in the wavelength domain through demultiplexing in WDM. Figure 8 shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber with input from several different multichannel or multiplex WDM optical sources for each core and with output in spatial diversity is obtained.
Figura 9.- Muestra una realización de la invención en la que se obtiene una línea de retardo basada en una fibra multinúcleo heterogénea cuyos núcleos presentan pendientes de retardo de grupo diferentes D¡. Entrada de una sola portadora óptica con salida en diversidad espacial. Figure 9.- Shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber is obtained whose nuclei have different group delay slopes D¡. Single optical carrier input with output in spatial diversity.
Figura 10.- Muestra una realización de la invención en la que se obtiene una línea de retardo basada en una fibra multinúcleo heterogénea, con entrada de una fuente óptica multicanal o WDM con separación en longitud de onda no constante ΔΛ, con salida en diversidad espacial. Figure 10.- Shows an embodiment of the invention in which a delay line based on a heterogeneous multicore fiber is obtained, with input from a multichannel optical source or WDM with non-constant wavelength separation ΔΛ, with output in spatial diversity .
Figura 11.- Muestra una implementación de un filtro fotónico transversal de microondas mediante una fibra multinúcleo heterogénea. Figure 11.- Shows an implementation of a microwave transverse photonic filter using a heterogeneous multicore fiber.
Figuras 12a - 12d.- Muestran una serie de gráficas de la función de transferencia eléctrica característica del filtro fotónico transversal de microondas, destacando las funcionalidades de sintonizabilidad y reconfigurabilidad, de acuerdo con la realización de la figura anterior. Figures 12a - 12d.- They show a series of graphs of the characteristic electrical transfer function of the microwave transverse photonic filter, highlighting the tunability and reconfigurability functionalities, according to the embodiment of the previous figure.
Figura 13.- Muestra una implementación de una red de alimentación en arrays de antenas en fase mediante una fibra multinúcleo heterogénea. Figure 13.- Shows an implementation of a feed network in arrays of antennas in phase using a heterogeneous multicore fiber.
Figura 14.- Muestra un esquema para la generación de señales de RF arbitrarias mediante inversión de fase en un modulador Mach-Zehnder, empleando una fibra multinúcleo heterogénea. Figure 14.- Shows a scheme for the generation of arbitrary RF signals by phase inversion in a Mach-Zehnder modulator, using a heterogeneous multicore fiber.
Figura 15.- Muestra un esquema para la generación de señales de RF arbitrarias mediante detección balanceada, empleando una fibra multinúcleo heterogénea.
Figura 16.- Muestra la estructura de los conectores que la invención aporta para permitir realizar la conexión de una fibra mononúcleo con los N núcleos en la entrada de la fibra MCF y la conexión de los N núcleos a la salida de MCF con una fibra mononúcleo. Figure 15.- Shows a scheme for the generation of arbitrary RF signals by balanced detection, using a heterogeneous multicore fiber. Figure 16.- It shows the structure of the connectors that the invention provides to allow the connection of a mononuclear fiber with the N cores at the input of the MCF fiber and the connection of the N cores at the MCF output with a mononuclear fiber .
DESCRIPCIÓN DE LA FORMA DE REALIZACIÓN PREFERIDA DESCRIPTION OF THE PREFERRED EMBODIMENT
Tal y como se indicó en el apartado de antecedentes, la fibras multinúcleo comprenden N núcleos que están dispuestos en una misma cubierta de diámetro b y la densidad de núcleos está determinada por la distancia Λ entre núcleos que garantiza un determinado nivel de interferencia o crosstalk a lo largo de una longitud L de propagación dada, tal y como se muestra en la figura 1 . En las fibras homogéneas los N núcleos tienen el mismo diámetro y las mismas características de propagación, es decir el mismo índice de refracción nc¡, la misma constante de propagación β, y por tanto el mismo retardo de grupo T, y la misma dispersión cromática D, a diferencia de las fibras multinúcleo heterogéneas que tienen diferentes características de propagación. As indicated in the background section, the multicore fibers comprise N cores that are arranged in the same cover of diameter b and the density of cores is determined by the distance Λ between cores that guarantees a certain level of interference or crosstalk at along a given propagation length L, as shown in Figure 1. In the homogeneous fibers the N nuclei have the same diameter and the same propagation characteristics, that is to say the same refractive index n c ¡, the same propagation constant β, and therefore the same delay of group T, and the same dispersion chromatic D, unlike heterogeneous multicore fibers that have different propagation characteristics.
Seguidamente, se describen las características de propagación de una fibra multinúcleo, para ello se considera el caso más genérico de MCF heterogénea, donde cada uno de los diversos núcleos j de los N núcleos que la conforman posee el mismo diámetro a y distinto índice de refracción ncoj. Cada núcleo actúa, por tanto, como una guía onda que transmite un modo de propagación distinto que tiene una constante de propagación /¾■ , que puede expresarse según su desarrollo en serie de Taylor de segundo orden a lo largo de la frecuencia central angular de emisión de la fuente óptica ω0 como: β] (ω) (ω - ω0 )
Next, the propagation characteristics of a multicore fiber are described, for this the most generic case of heterogeneous MCF is considered, where each of the different nuclei j of the N nuclei that make it up has the same diameter a and different index of refraction n bearing Each core therefore acts as a waveguide that transmits a different propagation mode that has a propagation constant / ¾ ■ , which can be expressed according to its second-order Taylor series development along the angular central frequency of emission of the optical source ω 0 as: β ] (ω) (ω - ω 0 )
1 one
= β° + β\ {ω - ω0 ) + -β^ω - ω0Υ. = β ° + β \ {ω - ω 0 ) + -β ^ ω - ω 0 Υ.
El retardo de grupo η a una longitud de onda óptica dada λ puede derivarse de la ecuación anterior como
donde L es la longitud del enlace de la MCF, c es la velocidad de la luz en el vacío, v¡¡ ¡ = \ i β representa la velocidad de grupo de propagación del núcleo j- ésimo y D¡ es el parámetro de dispersión asociado al núcleo '-ésimo definido como The group delay η at a given optical wavelength λ can be derived from the above equation as where L is the length of the MCF bond, c is the speed of light in a vacuum, v¡¡ = \ i β represents the propagation group velocity of the jth core and D¡ is the scatter parameter associated to the nucleus ' -th defined as
La particularización de las expresiones anteriores al caso de una MCF homogénea se obtiene considerando la misma constante de propagación β, y por tanto el mismo retardo de grupo r, para cada uno de los núcleos. The particularization of the previous expressions to the case of a homogeneous MCF is obtained considering the same propagation constant β, and therefore the same group delay r, for each of the nuclei.
En la figura 2 se muestra un ejemplo de realización de la invención de una implementación de una línea de retardo muestreada empleando una fibra óptica multinúcleo heterogénea 2 formada por núcleos heterogéneos 3 dispersivos de diferente composición alimentados por una misma señal de entrada proveniente de una fuente óptica 4, constituida por un láser, que proporciona una señal óptica portadora continua 5 (P1 ) que se aplica a un modulador electroóptico 6 para modular la señal 5 mediante una señal de radiofrecuencia (RF) 7. La modulación en radiofrecuencia, bien puede realizarse en amplitud o en fase. An example of the invention of an implementation of a sampled delay line using a heterogeneous multicore fiber optic 2 formed by heterogeneous dispersive cores 3 of different composition fed by the same input signal from an optical source is shown in Figure 2. 4, constituted by a laser, which provides a continuous carrier optical signal 5 (P1) that is applied to an electro-optic modulator 6 to modulate the signal 5 by a radio frequency (RF) signal 7. Radiofrequency modulation can well be performed in amplitude or phase.
La señal modulada 8 se divide entre los N núcleos 3 que componen la fibra multinúcleo heterogénea 2. Para lo que se prevé un conector 31 , que se describe más adelante con ayuda de la figura 16. Aunque todos los núcleos 3 poseen la misma longitud L, cada uno de ellos presenta un retardo de grupo lineal con la longitud de onda de pendiente diferente, o lo que es lo mismo, un valor diferente del parámetro de dispersión cromática D, tal y como se muestra a modo de ejemplo en las figuras 3a y 3b. Bajo aproximación lineal, y mediante el adecuado diseño material de cada núcleo, la característica del retardo de grupo de cada uno de ellos puede aproximarse mediante The modulated signal 8 is divided between the N cores 3 that make up the heterogeneous multicore fiber 2. For which a connector 31 is provided, which is described later with the help of Figure 16. Although all the cores 3 have the same length L , each of them presents a linear group delay with the different slope wavelength, or what is the same, a different value of the chromatic dispersion parameter D, as shown by way of example in Figures 3a and 3b. Under linear approximation, and by the appropriate material design of each core, the characteristic of the group delay of each of them can be approximated by
T0 + jDL (A - Á0 )
donde λ representa la longitud de onda de la portadora óptica, j el número de núcleo, D el parámetro básico de dispersión del núcleo menos dispersivo y r0 un retardo de grupo básico e igual para todas los núcleos 3 que se produce a una longitud de onda de referencia λ0, τ0 = Uvg. El retardo básico incremental entre las señales de salida de dos núcleos 3 que posean retardo de grupos adyacentes viene entonces dado por: T 0 + jDL (A - Á 0 ) where λ represents the wavelength of the optical carrier, j the core number, D the basic dispersion parameter of the least dispersive core and r 0 a basic and equal group delay for all cores 3 that occurs at a wavelength reference λ 0 , τ 0 = Uv g . The basic incremental delay between the output signals of two cores 3 that possess delay of adjacent groups is then given by:
Este retardo de grupo incremental es fijo para un valor dado de la longitud de onda de trabajo. Por ejemplo, en la figura 3a se observa la distribución de retardos cuando la longitud de onda de trabajo es
. En este caso, la línea de retardo produce N réplicas de la señal modulada a su entrada retardadas respectivamente por valores 0, Ti, 27Ί , ... (Λ/-1 )7Ί . Para cambiar el valor del retardo básico solamente hay que cambiar la longitud de onda de operación del láser 4. Por ejemplo, en la figura 3b se muestra el cambio de dicho retardo básico de 7Ί→ T2, cuando la longitud de onda del láser 4 alimentador cambia de Λι→ λ2. Así pues, la línea de retardo propuesta proporciona N muestras 10 equiespaciadas en el tiempo en la salida 9 de los N núcleos 3, donde el retardo básico entre muestras 10 es sintonizable mediante la modificación de la longitud de onda. Por tanto las muestras 10 se obtienen en salidas 9 espacialmente diferentes y por tanto se denomina a esta configuración como de diversidad espacial. This incremental group delay is fixed for a given value of the working wavelength. For example, Figure 3a shows the distribution of delays when the working wavelength is . In this case, the delay line produces N replicas of the modulated signal at its input delayed respectively by values 0, Ti, 27Ί, ... (Λ / -1) 7Ί. To change the value of the basic delay, only the operating wavelength of the laser 4 must be changed. For example, the change of said basic delay of 7Ί → T 2 is shown in Figure 3b, when the laser wavelength 4 feeder changes from Λι → λ 2 . Thus, the proposed delay line provides N samples 10 time-equalized at the output 9 of the N cores 3, where the basic delay between samples 10 is tunable by modifying the wavelength. Therefore, samples 10 are obtained at spatially different outputs 9 and therefore this configuration is referred to as spatial diversity.
La fibra multinúcleo heterogénea 2 empleada en el esquema de la figura 2 puede sustituirse por una fibra multinúcleo homogénea 2a, seguida de un conjunto de líneas de retardo ópticas 1 1 implementadas mediante tramos de fibra monomodo (SMF, singlemode fibers) 1 1 mononúcleo (SCF, singlecore fiber) estándar de diversas longitudes, tal y como se ilustra en la figura 4. En este caso cada núcleo 3a de la fibra multinúcleo homogénea presenta el mismo retardo de grupo
De acuerdo con lo anterior se puede disponer de un filtro transversal con un retardo básico incremental entre muestras T, para lo que cada núcleo k debe acoplarse a un tramo k de SMF 1 1 de longitud LSMF,k, tal y que la diferencia entre retardos asociados a tramos contiguos sea precisamente TSMF = T. En el supuesto de que la SMF no presente dispersión cromática, éste vendría dado por The heterogeneous multicore fiber 2 used in the scheme of Figure 2 can be replaced by a homogeneous multicore fiber 2a, followed by a set of optical delay lines 1 1 implemented by single-mode fiber segments (SMF, single-mode fibers) 1 1 mononuclear (SCF) , singlecore fiber) standard of various lengths, as illustrated in Figure 4. In this case each core 3a of the homogeneous multicore fiber has the same group delay According to the above, a transverse filter with an incremental basic delay between samples T can be available, for which each core k must be coupled to a section k of SMF 1 1 of length L S MF, k, such that the difference between delays associated with contiguous sections, it is precisely T S MF = T. In the event that the SMF does not present chromatic dispersion, this would be given by
LsMF Lsmf
^SMF ~ (LsMF,k+l ~ LsMF,k ) ^ SMF ~ (LsMF, k + l ~ LsMF, k)
vgSMF vgSMF donde LSMF representa la diferencia básica entre las longitudes de tramos contiguos y la velocidad de grupo V9SMF es la misma para cada tramo de fibra 1 1 . Si, por el contrario, la SMF introducida presenta dispersión cromática, la diferencia entre retardos contiguos sería vgSMF v gSMF where L S MF represents the basic difference between the lengths of contiguous sections and the group speed V 9 SMF is the same for each fiber section 1 1. If, on the contrary, the SMF introduced has chromatic dispersion, the difference between contiguous delays would be
' SMF (λ) - (LSMF k+1 - LSMF k ) 1 - + D (A - A0 ) ~ LsMF 1 - + D (A - A0 ) 'SMF (λ) - (L SMF k + 1 - L SMF k ) 1 - + D (A - A 0 ) ~ LsMF 1 - + D (A - A 0 )
vgSMF vgSMF vgSMF v gSMF
En este caso, la sintonización de la longitud de onda de emisión del láser 4 permite controlar dinámicamente el retardo básico incremental. In this case, the tuning of the emission wavelength of the laser 4 makes it possible to dynamically control the incremental basic delay.
En la figura 5 se muestra otra realización de la invención en la que la línea de retardo muestreada es alimentada por un múltiplex de fuentes ópticas. En este caso la señal alimentada proviene de un múltiplex en longitud de onda WDM de láseres 4a - 4c modulados, en vez de una única fuente óptica. Una configuración equivalente consiste en emplear como fuente alimentadora un único láser emisor de diferentes canales o modos ópticos equiespaciados en longitud de onda mediante la técnica de enganche en fase de modos o modelocking, que proporciona un tren de impulsos con diferente longitud de onda que se modulan con una misma señal de RF y se aplican a los N núcleos de la fibra. Refiriéndonos a dicha figura 5, la señal de alimentación óptica está compuesta por M láseres 4A - 4M cuyas longitudes de onda de las señales 5AAnother embodiment of the invention is shown in Figure 5 in which the sampled delay line is fed by a multiplex of optical sources. In this case the fed signal comes from a WDM wavelength multiplex of modulated lasers 4a-4c, instead of a single optical source. An equivalent configuration consists in using a single emitting laser of different channels or wavelength optical modes as a power source using the phase phase modeling or modeling technique, which provides a pulse train with different wavelengths that are modulated with the same RF signal and apply to the N fiber cores. Referring to said figure 5, the optical power signal is composed of M lasers 4A-4M whose wavelengths of the signals 5A
- 5M que producen siguen la ley Á¡ = λ0 + i , i = 1 , 2, ... M. Dichas señales 5A- 5M they produce follow the law Á¡ = λ 0 + i, i = 1, 2, ... M. Such signals 5A
- 5M se aplican a un multiplexor 13 cuya salida se aplica al modulador de radiofrecuencia 6. En caso de emplear una fuente modelocking el multiplexor
WDM no es necesario. De esta forma el múltiplex se modula 8A - 8M por una señal de radiofrecuencia 7 que alimenta a cada uno de los núcleos N de una MCF heterogénea 2. En consecuencia, tal y como se muestra en la figura 6, que ilustra la generación de los retardos increméntales, cada múltiplex sufre en cada núcleo j un retardo básico diferente que puede expresarse como: j = Tj (Ák ) - τ ¡ (Ák_i ) = jDLAÁ - 5M are applied to a multiplexer 13 whose output is applied to the radiofrequency modulator 6. In case of using a modeling source the multiplexer WDM is not necessary. In this way the multiplex is modulated 8A-8M by a radiofrequency signal 7 that feeds each of the nuclei N of a heterogeneous MCF 2. Accordingly, as shown in Figure 6, which illustrates the generation of the incremental delays, each multiplex suffers in each core j a different basic delay that can be expressed as: j = Tj (Á k ) - τ ¡(Á k _i) = jDLAÁ
Es decir, cada salida 9 de los núcleos 3, corresponde a una línea de retardo de M muestras 15A - 15N, cada una de ellas retardadas por un valor de retardo incremental diferente. That is, each output 9 of the cores 3 corresponds to a delay line of M samples 15A-15N, each delayed by a different incremental delay value.
La línea de retardo proporciona una configuración bidimensional de retardos donde el retardo experimentado por una muestra transportada por la longitud de onda Á¡ = λ0 + /ΔΛ y saliendo por el núcleo j experimenta un retardo dado por: The delay line provides a two-dimensional delay configuration where the delay experienced by a sample carried by the wavelength Á¡ = λ 0 + / ΔΛ and leaving through the core j experiences a delay given by:
T¡,j = To + ijDLÁÁ T ¡, j = T or + ijDLÁÁ
Esta funcionalidad puede explotarse de dos formas según se contemple el dominio espacial o el dominio de la longitud de onda. En la figura 5 se describió el primer caso, donde la salida 9 de cada núcleo 3 proporciona una línea de retardo muestreada cuyo retardo incremental se obtiene al fijar el valor de j en la expresión anterior y calcular la diferencia entre los retardos experimentados por la longitud de onda i+ y la /, es decir 7} = jDL . Así pues se habilitan N líneas de retardo, cada una proporcionando M muestras. El segundo caso, se muestra en la figura 7, donde se agrupan las N salidas 9 de la fibra 2 aplicándose a un demultiplexor 14, que las demultiplexá en longitud de onda para obtener M líneas de retardo de N muestras 16A - 16M cada una. En este caso el retardo básico para cada línea de retardo de cada longitud de onda se obtiene al fijar / y calcular la diferencia entre los retardos experimentados por núcleos contiguos j+ y j, T¡ = iDL . Para permitir realizar la conexión agrupada de la salida de los N núcleos, la invención ha desarrollado un conector 20 que se describirá con ayuda de la figura 16.
Los esquemas anteriores pueden ampliarse y/o modificarse, según se muestra en las figuras 8, 9 y 10. This functionality can be exploited in two ways depending on whether the spatial domain or the wavelength domain is contemplated. In Figure 5 the first case was described, where the output 9 of each core 3 provides a sampled delay line whose incremental delay is obtained by setting the value of j in the previous expression and calculating the difference between the delays experienced by the length of wave i + and /, that is 7} = jDL. Thus N delay lines are enabled, each providing M samples. The second case is shown in Figure 7, where the N outputs 9 of the fiber 2 are grouped by applying to a demultiplexer 14, which demultiplexes them in wavelength to obtain M delay lines of N samples 16A-16M each. In this case the basic delay for each delay line of each wavelength is obtained by setting / and calculating the difference between the delays experienced by contiguous cores j + and j, T¡ = iDL. In order to allow the grouped connection of the output of the N cores, the invention has developed a connector 20 which will be described with the aid of Figure 16. The above schemes can be extended and / or modified, as shown in Figures 8, 9 and 10.
En la realización de la figura 8 se alimenta la fibra óptica hetereogenea 2, con un multiplex WDM 17A - 17N distinto para cada uno de los núcleos , (o bien mediante una configuración equivalente que emplearía como fuente alimentadora un único láser emisor de diferentes canales o modos ópticos equiespaciados en longitud de onda mediante la técnica de enganche en fase de modos o modelocking) modulado a su vez cada uno de ellos por una señal de radiofrecuencia 7A - 7N diferente, con los moduladores de RF 6A - 6N, cuya señal modulada 8A -8N se aplica a cada una de los núcleos 3 de la fibra multinúcleo hetereogenea 2 tomando sus salidas 9 de forma separada, en cuyo caso la estructura funciona como un conjunto de N líneas de retardo diferentes e independientes. Cada una de las líneas de retardo posee un retardo básico diferente 7} = DLAÁj donde j expresa la separación en longitud de onda de dos portadoras contiguas del múltiplex WDM que se inyecta al núcleo j. En cada salida 9 se obtienen muestras 15A - 15N, cada una de ellas retardadas por un valor de retardo incremental diferente. In the embodiment of Figure 8, the heterogeneous optical fiber 2 is fed, with a different WDM 17A-17N multiplex for each of the cores, (or by an equivalent configuration that would use a single emitting laser of different channels as a power source or wavelength-balanced optical modes using the phase-mode or modeling technique) each in turn modulated by a different 7A - 7N radio frequency signal, with RF modulators 6A - 6N, whose modulated signal 8A -8N is applied to each of the nuclei 3 of the heterogeneous multicore fiber 2 taking its outputs 9 separately, in which case the structure functions as a set of N different and independent delay lines. Each of the delay lines has a different basic delay 7} = DLAÁ j where j expresses the wavelength separation of two contiguous carriers of the WDM multiplex that is injected into the core j. In each output 9 samples 15A-15N are obtained, each delayed by a different incremental delay value.
En la realización de la figura 9, se emplea una única señal portadora óptica 5 (P1 ) y una fibra heterogénea 2 de núcleos 3, al igual que en la descripción realizada para la figura 2, con la diferencia que los núcleos 3 tienen pendientes de retardo de grupo diferentes D/ (Di , ... , Dk... ,DN), no relacionadas a través de un incremento constante, obteniéndose en su salida las muestras 10'. In the embodiment of Figure 9, a single optical carrier signal 5 (P1) and a heterogeneous fiber 2 of cores 3 are used, as in the description made for Figure 2, with the difference that the cores 3 have slopes of different group delay D / (Di, ..., D k ..., D N ), unrelated through a constant increase, obtaining 10 'samples at its output.
Respecto a la figura 10, se emplean señales multiplex WDM a la entrada de la fibra heterogénea 2, de forma igual a lo descrito para la figura 5, pero con la diferencia que se prevé separación en longitud de onda no constante ΔΛ, obteniéndose las muestras 15Ά - 15'N. With respect to Figure 10, WDM multiplex signals are used at the input of the heterogeneous fiber 2, in the same way as described for Figure 5, but with the difference that non-constant wavelength separation ΔΛ is expected, obtaining the samples 15Ά - 15'N.
A continuación se describen unas adaptaciones de las realizaciones anteriores, para su uso en diversas aplicaciones de la Fotónica de Microondas: a) En primer lugar se describe una adaptación para su aplicación como filtro transversal fijo y sintonizable.
Una de las aplicaciones de mayor interés en el campo de la fotónica de microondas constituye el uso de dispositivos fotónicos con el fin de implementar filtros sintonizables y reconfigurables para realizar tareas de procesado de señal en sistemas de RF. En el esquema más genérico de un filtro fotónico de microondas del estado de la técnica, la portadora óptica modulada en intensidad (o en fase) por la señal de RF atraviesa una etapa de procesado óptico que se encarga de muestrear la señal en el dominio del tiempo. La señal óptica resultante es detectada mediante un fotodetector 19. Según la naturaleza de las líneas ópticas de retardo que conforman la etapa de procesado óptico, los filtros fotónicos de microondas del estado de la técnica pueden clasificarse según: a.1 ) Filtros con líneas de retardo basadas en tramos de fibra óptica paralelos. Some adaptations of the previous embodiments are described below, for use in various Microwave Photonics applications: a) Firstly, an adaptation for its application as a fixed and tunable transverse filter is described. One of the most interesting applications in the field of microwave photonics is the use of photonic devices in order to implement tunable and reconfigurable filters to perform signal processing tasks in RF systems. In the most generic scheme of a microwave photonic filter of the state of the art, the optical carrier modulated in intensity (or in phase) by the RF signal crosses an optical processing stage that is responsible for sampling the signal in the domain of the weather. The resulting optical signal is detected by a photodetector 19. Depending on the nature of the optical delay lines that make up the optical processing stage, the microwave photonic filters of the prior art can be classified according to: a.1) Filters with lines of delay based on parallel fiber optic sections.
Recurriendo al empleo de una única fuente óptica 4, este tipo de filtros genera N muestras de la señal óptica modulada que son sopesadas independientemente por unos atenuadores ópticos variables, (no representados) y retardadas por líneas de retardo determinadas según el camino óptico por el que se propagan. Mediante este esquema se obtienen retardos constantes con la longitud de onda de emisión del láser. a.2) Filtros con líneas de retardo dispersivas. Using a single optical source 4, this type of filters generates N samples of the modulated optical signal that are independently weighed by variable optical attenuators (not shown) and delayed by delay lines determined according to the optical path along which They spread. Through this scheme, constant delays are obtained with the laser emission wavelength. a.2) Filters with dispersive delay lines.
En este caso el empleo de múltiples fuentes ópticas permite que N portadoras ópticas sean moduladas con la misma señal de RF. El elemento dispersivo generará un retardo diferente para cada una de las longitudes de onda ópticas propagadas, es decir, para cada una de las muestras. In this case the use of multiple optical sources allows N optical carriers to be modulated with the same RF signal. The dispersive element will generate a different delay for each of the propagated optical wavelengths, that is, for each of the samples.
En el caso particular de la invención, la implementación de líneas de retardo muestreadas mediante fibras multinúcleo heterogéneas 2, donde cada núcleo 3 presenta unas características dispersivas diferentes, permite la implementación de filtros con líneas de retardo dispersivas empleando una única fuente óptica
4, tal y como se ilustra en la figura 1 1 . La señal óptica se aplica a un modulador de intensidad 21 Mach-Zehnder MZM y a un modulador de fase 22, que modulan la portadora óptica mediante una señal de RF 7 y se aplican a los diferentes núcleos 3, cuyas salidas están conectadas a un fotodetector 19. Mediante dicho esquema, la fotodeteccion conjunta de cada una de las N muestras retardadas de la señal de RF moduladora resulta en un fenómeno de filtrado FIR (finite impulse response) de microondas, caracterizado por la respuesta en frecuencia: In the particular case of the invention, the implementation of delay lines sampled by heterogeneous multicore fibers 2, where each core 3 has different dispersive characteristics, allows the implementation of filters with dispersive delay lines using a single optical source. 4, as illustrated in Figure 1 1. The optical signal is applied to an intensity modulator 21 Mach-Zehnder MZM and to a phase modulator 22, which modulate the optical carrier by means of an RF signal 7 and are applied to the different cores 3, whose outputs are connected to a photodetector 19 By said scheme, the joint photodetection of each of the N delayed samples of the modulating RF signal results in a microwave FIR (finite impulse response) filtering phenomenon, characterized by the frequency response:
N-l N-l
H(Q) =∑ane-j{nnT+tí donde T es la unidad de retardo básica del filtro, mientras que an y φη representan, respectivamente, la amplitud y la fase del coeficiente π-ésimo. La expresión anterior identifica una función de transferencia eléctrica con una característica espectral periódica, tal y como se aprecia en la figura 12a - 12d, cuyo periodo frecuencial o rango espectral libre (FSR, Free Spectral Range) es inversamente proporcional al retardo básico entre muestras T. Así pues, el control de T, que se logra al sintonizar la longitud de onda de emisión de la fuente óptica, permite reconfigurar la respuesta del filtro, cambiando el FSR, Fig. 12a. La selectividad del filtro, dada por el factor de calidad Q: Q = FSR/AQFWHM, donde AQFWHM denota el ancho de la resonancia cuando la respuesta cae 3 dB respecto a su máximo, está relacionada con el número de muestras N, tal y como se aprecia en la Fig. 12b. Por lo tanto, el número de núcleos que compondrá la MCF permite diseñar el filtro con unas características de selectividad concretas. Mediante la inclusión de atenuadores ópticos variables a la entrada o salida de la MCF (no representados) se pueden implementar técnicas de enventanado o apodización en los valores de amplitud de los coeficientes an, lo que permite controlar el nivel de rechazo de las bandas eliminadas, nivel de lóbulo principal a secundario (MSLR, mam to secondary lobe ratio) o nivel de lóbulo secundario (SLL, secondary lobe level), Fig. 12c. Finalmente, la sintonizabilidad del filtro, es decir el cambio en la posición de su frecuencia central, puede ser controlada variando la fase φη de
las muestras, Fig. 12d. En el eje vertical de dichas figuras 12a - 12d se representa la variación del modulo de la respuesta en frecuencia normalizado a la unidad y en el eje horizontal la frecuencia. H (Q) = ∑a n e- j {nnT + you where T is the basic delay unit of the filter, while a n and φ η represent, respectively, the amplitude and phase of the π-th coefficient. The above expression identifies an electrical transfer function with a periodic spectral characteristic, as can be seen in Figure 12a - 12d, whose frequency period or free spectral range (FSR) is inversely proportional to the basic delay between T samples. Thus, the control of T, which is achieved by tuning the emission wavelength of the optical source, allows reconfiguring the filter response, changing the FSR, Fig. 12a. The selectivity of the filter, given by the quality factor Q: Q = FSR / AQFWHM, where AQFWHM denotes the width of the resonance when the response falls 3 dB with respect to its maximum, is related to the number of samples N, as It can be seen in Fig. 12b. Therefore, the number of cores that will make up the MCF allows the filter to be designed with specific selectivity characteristics. By including variable optical attenuators at the input or output of the MCF (not shown), poisoning or apodization techniques can be implemented in the amplitude values of the coefficients at n , which allows controlling the rejection level of the eliminated bands , primary to secondary lobe level (MSLR, mam to secondary lobe ratio) or secondary lobe level (SLL), Fig. 12c. Finally, the tunability of the filter, that is the change in the position of its center frequency, can be controlled by varying the phase φ η of the samples, Fig. 12d. In the vertical axis of said figures 12a-12d the variation of the module of the frequency response normalized to the unit is represented and in the horizontal axis the frequency.
La extensión del esquema de filtrado propuesto en la figura 1 1 al supuesto en que la señal óptica está compuesta por M portadoras ópticas multiplexadas en longitud de onda (o bien generadas por un único láser emisor de diferentes canales o modos ópticos equiespaciados en longitud de onda mediante la técnica de enganche en fase de modos o modelocking), permite dos ampliaciones de la funcionalidad de filtrado de especial interés en el campo de la fotónica de microondas. The extension of the filtering scheme proposed in Figure 1 to the assumption that the optical signal is composed of M optical carriers multiplexed in wavelength (or generated by a single emitting laser of different channels or optical modes equiespaced in wavelength by means of the technique of hitching in mode phase or modeling), it allows two extensions of the filtering functionality of special interest in the field of microwave photonics.
En primer lugar, tal y como se describía anteriormente en la figura 5, al disponer a la salida de cada núcleo j que compone la MCF de una línea de retardo óptico de M muestras con retardo básico 7), (dado por la diferencia entre los retardos experimentados por longitudes de onda contiguas, 7} = jDL ), se puede implementar un filtro con distinto FSRj a la salida de cada núcleo 3, cada una de las cuales está conectada a un fotodetector 19, de detección de la señal en el dominio de la frecuencia. Esta estructura permite disponer de manera compacta de N filtros con FSR diferente, sintonizable variando la separación en longitud de onda de emisión de las fuentes ópticas 4A - 4M. El control del nivel de potencia de emisión de cada uno de los láseres 4A -4M, permite aplicar técnicas de apodización por igual a cada uno de los N núcleos. First, as described previously in Figure 5, by having at the output of each core j that composes the MCF an optical delay line of M samples with basic delay 7), (given by the difference between the delays experienced by adjacent wavelengths, 7} = jDL), a filter with different FSRj can be implemented at the output of each core 3, each of which is connected to a photodetector 19, for detecting the signal in the domain of the frequency This structure allows N filters to be compactly arranged with different FSR, tunable by varying the emission wavelength separation of the optical sources 4A-4M. The control of the emission power level of each of the 4A -4M lasers makes it possible to apply apodization techniques equally to each of the N cores.
La segunda ampliación se basa en la agrupación de las salidas de los N núcleos y en su posterior demultiplexación en longitud de onda, tal y como se ilustraba en la figura 7, de modo que se es posible obtener M filtros distintos compuestos por N muestras cada uno. Para ello cada salida del demultiplexor 14 está conectada a un fotodetector 19. En este caso, cada filtro está caracterizado por un FSR¡ inversamente proporcional al retardo básico dado por la diferencia entre los retardos experimentados entre núcleos contiguos, T¡ = iDL . La implementación de técnicas de enventanado en este caso requeriría la inclusión de N atenuadores ópticos variables a la entrada o salida
de cada uno de los núcleos. The second extension is based on the grouping of the outputs of the N cores and their subsequent wavelength demultiplexing, as illustrated in Figure 7, so that it is possible to obtain M different filters composed of N samples each one. For this, each output of the demultiplexer 14 is connected to a photodetector 19. In this case, each filter is characterized by an FSR¡ inversely proportional to the basic delay given by the difference between the delays experienced between adjacent cores, T¡ = iDL. The implementation of poisoning techniques in this case would require the inclusion of N variable optical attenuators at the input or output of each of the cores.
La implementación de filtros transversales de microondas puede obtenerse también empleando como elemento base la línea de retardo compuesta por una fibra multinúcleo homogénea 2a y diversos tramos de fibra monomodo 1 1 . b) En segundo lugar se describe una adaptación para su aplicación como alimentación óptica de arrays de antenas 23 en fase. The implementation of microwave transverse filters can also be obtained using as a base element the delay line composed of a homogeneous multicore fiber 2a and various sections of 1 1 single-mode fiber. b) Secondly, an adaptation is described for its application as optical feed of arrays of antennas 23 in phase.
Así la segunda aplicación la encontramos en los sistemas de alimentación de arrays de antenas 23 de microondas en fase (Phased array antennas, PAA). Estas estructuras radiantes están compuestas por una agrupación de múltiples antenas, dispuestas en una o dos dimensiones, que son alimentadas de manera individual y coherente por un sistema de control de fase o de retardo temporal (true time delay), de modo que es posible producir un diagrama de radiación determinado a una dirección angular dada. La aplicación directa de esta tecnología se halla en los sistemas radar que podemos encontrar tanto en el ámbito civil (radioastronomía, climatología, comunicaciones espaciales, radiodifusión terrestre) como en el militar. Una de las facetas a destacar del empleo de redes de alimentación ópticas en PAA, además de las ventajas inherentes al empleo de la tecnología de fotónica de microondas, reside en la posibilidad de distribuir las señales de microondas generadas desde/hacia una unidad central hacia/desde una localización remota. Thus the second application is found in the microwave array antenna feed systems 23 in phase (Phased array antennas, PAA). These radiating structures are composed of a group of multiple antennas, arranged in one or two dimensions, which are fed individually and coherently by a phase control system or a time delay (true time delay), so that it is possible to produce a radiation pattern determined at a given angular direction. The direct application of this technology is found in radar systems that can be found both in the civil field (radio astronomy, climatology, space communications, terrestrial broadcasting) and in the military. One of the facets of the use of optical power networks in PAA, in addition to the advantages inherent in the use of microwave photonics technology, lies in the possibility of distributing the microwave signals generated from / to a central unit to / from a remote location.
El elemento clave de un PAA lo encontramos en la red de conformado de haz compuesta por varios caminos físicos independientes y encargada de conectar los elementos radiantes con una fuente de RF (enlace ascendente: la señal de RF es procesada a través de la red de conformado y radiada al espacio libre) o bien con un detector de RF (enlace descendente: la radiación incidente es recibida por las antenas y trasladada a un mismo receptor de RF). Las características de transmisión de cada camino y, por tanto, la dirección de apuntamiento del haz conformado, pueden modificarse si se incluyen elementos de control de amplitud y de fase/retardo. En lo que a redes de conformado ópticas se refiere, encontramos en la literatura diversas técnicas que pueden clasificarse en dos categorías: redes basadas en fibra óptica y/o en
guías de onda integradas y redes basadas en óptica de espacio libre. La solución que la invención propone se refiere a redes basadas en fibra óptica y se basa en el empleo de una fibra multinúcleo heterogénea 2 como red de alimentación en paralelo. Tal y como se muestra en la figura 13, el esquema de implementación es muy similar al descrito en la figura 1 1 para filtros fotónicos de microondas, con la salvedad de que en el extremo final de la MCF 2, la señal óptica es detectada de manera independiente a la salida de cada uno de los N núcleos mediante un fotodetector 19. Cabe tener en cuenta que la figura 1 1 corresponde al caso de emisión de señales de RF, mientras que para sistemas de recepción de señales radiadas, la batería de N fotodetectores se sustituye por N transmisores (no representados) compuestos cada uno de un láser 4 emitiendo en onda continua y un modulador electroóptico 6. En ese caso, a la salida de la MCF 2 la señal óptica es detectada conjuntamente por un único fotodetector 19. The key element of a PAA is found in the beam forming network composed of several independent physical paths and responsible for connecting the radiating elements with an RF source (uplink: the RF signal is processed through the forming network and radiated to free space) or with an RF detector (downlink: the incident radiation is received by the antennas and transferred to the same RF receiver). The transmission characteristics of each path and, therefore, the aiming direction of the shaped beam can be modified if amplitude and phase / delay control elements are included. As far as optical forming networks are concerned, we find in the literature various techniques that can be classified into two categories: fiber-based networks and / or in integrated waveguides and networks based on free space optics. The solution proposed by the invention relates to fiber optic based networks and is based on the use of a heterogeneous multicore fiber 2 as a parallel feed network. As shown in Figure 13, the implementation scheme is very similar to that described in Figure 1 1 for microwave photonic filters, with the proviso that at the final end of MCF 2, the optical signal is detected from independently of the output of each of the N cores by means of a photodetector 19. It should be noted that Figure 1 1 corresponds to the case of RF signal emission, while for systems receiving radiated signals, the N battery Photodetectors are replaced by N transmitters (not shown) each composed of a laser 4 emitting in continuous wave and an electro-optic modulator 6. In that case, at the output of the MCF 2 the optical signal is detected together by a single photodetector 19.
Para la descripción del diagrama de radiación de una agrupación de antenas lineal en una dimensión, se emplea el Factor de array (AF, Array Factor), mediante el cual se obtiene el diagrama de radiación de la agrupación, como el producto del factor de array y el diagrama de radiación del elemento antena. La variación en la dirección de apuntamiento del haz Θ se logra variando los pesos o coeficientes complejos ar que conforman el factor de array:For the description of the radiation pattern of a linear antenna group in one dimension, the Array Factor (AF) is used, by which the radiation pattern of the cluster is obtained, as the product of the array factor and the radiation pattern of the antenna element. The variation in the direction of aiming of the beam Θ is achieved by varying the complex weights or coefficients at r that make up the array factor:
AF(e) =∑are siendo u = sin(6) y dx la distancia de separación entre los elementos radiantes en el eje x. En la invención, dicho control se implementa mediante la variación del retardo de grupo básico incremental T entre núcleos 3 adyacentes de la MCF 2, es decir, gracias a la sintonización de la longitud de onda de emisión del láser A, tal y como ha sido descrito anteriormente: AF (e) = ∑a r e where u = sin (6) and d x the separation distance between the radiating elements on the x-axis. In the invention, said control is implemented by varying the incremental basic group delay T between adjacent cores 3 of the MCF 2, that is, thanks to the tuning of the emission wavelength of the laser A, as it has been previously described:
T = Tj+l (A) - Tj (A ) = DL (A - A0 ) T = T j + l (A) - Tj (A) = DL (A - A 0 )
Mediante este sistema de control retardo o true time delay, los coeficientes ar se pueden expresar como
.rVídxu0 con lo que el AF resultaría
cumpliéndose T = dxUo/c para u0 = sin(e0), siendo θ0 el ángulo de apuntamiento mediante el cual el factor de array es máximo. Through this delay or true time delay control system, the coefficients at r can be expressed as .rVíd x u 0 with what the AF would result where T = d x Uo / c is fulfilled for u 0 = sin (e 0 ), where θ 0 is the aiming angle by which the array factor is maximum.
Cabe destacar que la inclusión de atenuadores ópticos variables a la salida de cada núcleo permitiría implementar diversos esquemas de enventanado. It should be noted that the inclusion of variable optical attenuators at the exit of each core would allow the implementation of various poisoning schemes.
Finalmente, la implementación de redes ópticas conformadoras para arrays de antenas 23 puede obtenerse también empleando como elemento base la línea de retardo compuesta por una fibra multinúcleo homogénea 2a y diversos tramos de fibra monomodo 1 1 . c) Generación óptica arbitraria de señales de radiofrecuencia Finally, the implementation of optical shaping networks for antenna arrays 23 can also be obtained using as a base element the delay line composed of a homogeneous multicore fiber 2a and various sections of single mode fiber 1 1. c) Arbitrary optical generation of radio frequency signals
La línea de retardo óptica propuesta puede aplicarse también a la generación óptica arbitraria de señales de radiofrecuencia y, como caso particular, a uno de los formatos que mayor interés ha venido suscitando durante los últimos años: el estándar ultrawideband (UWB). Esta funcionalidad es aplicable principalmente a sistemas radar y a redes de comunicaciones inalámbricas, donde se pueden obtener beneficios, como se ha comentado anteriormente para PAA, referente a las ventajas que ofrece la propagación óptica en la distribución de señales de RF desde una unidad central hacia un emplazamiento remoto. The proposed optical delay line can also be applied to the arbitrary optical generation of radiofrequency signals and, as a particular case, to one of the formats that has been most interesting in recent years: the ultrawideband standard (UWB). This functionality is mainly applicable to radar systems and wireless communications networks, where benefits can be obtained, as discussed above for PAA, referring to the advantages offered by optical propagation in the distribution of RF signals from a central unit to a remote location
Un generador óptico de pulsos de RF se basa en un esquema de filtrado fotónico de microondas discreto donde se busca la posibilidad de síntesis de una respuesta impulsiva concreta. En dicho esquema de filtrado se requiere la posibilidad de obtener conjuntamente coeficientes positivos y negativos. La utilización de MCF permite disponer de dos esquemas diferentes para la obtención de coeficientes negativos.
El primer esquema, ilustrado en la figura 14, se basa en el empleo de dos moduladores electroópticos 6A, 6B que son alimentados en regiones con pendientes opuestas a través de sendos voltajes de alimentación
y VdC2, respectivamente. Ambos moduladores 6A, 6B son modulados por el mismo pulso eléctrico proveniente de un generador de pulsos de RF 24. La señal óptica modulada proveniente del modulador 6A será lanzada a un subconjunto de Ni núcleos y se encargará de proporcionar las Ni muestras positivas a la línea de retardo configurada mediante la MCF de N núcleos 3. Por otro lado, la señal óptica proveniente del 6B será inyectada a un subconjunto de N2 núcleos, proporcionando así las N2 muestras negativas que se requieran para la síntesis del pulso final. La selección de la polaridad de los pulsos a transmitir por la MCF 2 se realiza a la entrada de cada núcleo 3 mediante un acoplador óptico 26 de tipo 1 xN seguido de un conmutador 27 o switch óptico 2x1 que permite seleccionar la señal proveniente de uno u otro modulador de manera dinámica. A la salida 9 de la MCF 2, se dispone un fotodetector 19 para realizar la detección conjunta de todas las muestras, debidamente retardadas según las características de dispersión de cada uno de los núcleos, permitiendo obtener el pulso 30 de RF deseado. El control sobre la amplitud de las muestras de manera individual para polaridades positivas y negativas puede implementarse mediante la introducción de atenuadores ópticos variables (no representados) a cada una de las salidas de los acopladores ópticos 26 de tipo 1 xN. An optical RF pulse generator is based on a discrete microwave photonic filtering scheme where the possibility of synthesis of a specific impulse response is sought. In said filtering scheme the possibility of obtaining positive and negative coefficients together is required. The use of MCF allows two different schemes to be obtained to obtain negative coefficients. The first scheme, illustrated in Figure 14, is based on the use of two electro-optic modulators 6A, 6B that are fed in regions with opposite slopes through two supply voltages. and V dC 2, respectively. Both modulators 6A, 6B are modulated by the same electrical pulse from an RF 24 pulse generator. The modulated optical signal from modulator 6A will be released to a subset of Ni cores and will be responsible for providing the Ni positive samples to the line. delay set by the N-core MCF 3. On the other hand, the optical signal from 6B will be injected into a subset of N 2 cores, thus providing the N 2 negative samples that are required for the synthesis of the final pulse. The selection of the polarity of the pulses to be transmitted by the MCF 2 is carried out at the input of each core 3 by means of an optical coupler 26 of type 1 xN followed by a switch 27 or optical switch 2x1 that allows to select the signal from one or Another modulator dynamically. At the output 9 of the MCF 2, a photodetector 19 is arranged to perform the joint detection of all samples, duly delayed according to the dispersion characteristics of each of the cores, allowing to obtain the desired RF pulse 30. The control over the amplitude of the samples individually for positive and negative polarities can be implemented by introducing variable optical attenuators (not shown) to each of the outputs of the optical couplers 26 of type 1 xN.
A modo de ejemplo, la figura 14 (y la posterior figura 15) ilustra a la salida del fotodetector 19 un pulso 30 del tipo doblete, correspondiente al caso en que N = 3 (Ni = 2 y Λ/2 = 1 ) para una selección de amplitudes de muestras de [0.5,- 1 ,0.5]. By way of example, figure 14 (and subsequent figure 15) illustrates at the output of photodetector 19 a pulse 30 of the doublet type, corresponding to the case where N = 3 (Ni = 2 and Λ / 2 = 1) for a sample amplitude selection of [0.5, - 1, 0.5].
En el segundo esquema para la generación de pulsos eléctricos, cada una de las N muestras totales proviene de un mismo modulador electroóptico, tal y como se muestra en la figura 15. La separación entre coeficientes positivos y negativos se lleva a cabo mediante una arquitectura de fotodetección 19 balanceada, mediante la cual el subconjunto deseado de Ni muestras positivas y el subconjunto de N2 muestras negativas son seleccionados a la salida de
cada núcleo 3 mediante un conmutador óptico 28 de tipo 1 x2 seguido de un acoplador óptico 29 de tipo Nx1 . La selección de los pulsos se realiza mediante el control de los conmutadores 28 de tipo 1 x2 que hay a la salida de cada núcleo 3, que dirige la señal a uno de los fotodetectores balanceados 19. Por ejemplo, al fotodetector balanceado superior, para coeficientes positivos, o al fotodetector balanceado inferior, para coeficientes negativos. La amplitud de los pulsos puede controlarse de manera individual mediante la introducción de atenuadores ópticos variables en cada una de las entradas de los acopladores ópticos 29 de tipo Nx1 . In the second scheme for generating electrical pulses, each of the N total samples comes from the same electro-optic modulator, as shown in Figure 15. The separation between positive and negative coefficients is carried out by means of an architecture of balanced photodetection 19, whereby the desired subset of Ni positive samples and the subset of N 2 negative samples are selected at the output of each core 3 by means of an optical switch 28 of type 1 x2 followed by an optical coupler 29 of type Nx1. Pulse selection is done by controlling switches 28 of type 1 x2 at the output of each core 3, which directs the signal to one of the balanced photodetectors 19. For example, to the upper balanced photodetector, for coefficients positive, or to the lower balanced photodetector, for negative coefficients. The amplitude of the pulses can be controlled individually by the introduction of variable optical attenuators in each of the inputs of the optical couplers 29 of type Nx1.
Es importante destacar que ambos esquemas dotan a la generación de pulsos de RF de gran flexibilidad puesto que, además de la generación de los pulsos más comunes del tipo monociclo (N = 2) o doblete (N = 3), permite el diseño de pulsos de orden superior. It is important to note that both schemes provide the generation of RF pulses with great flexibility since, in addition to the generation of the most common pulses of the unicycle type (N = 2) or doublet (N = 3), it allows the design of pulses of higher order.
La sintonización de la longitud de onda óptica de emisión del láser 4 permite variar el retardo básico incremental entre pulsos T, el cual, al emplear MCF heterogéneas 2, en las que la diferencia entre pendientes de dispersión de núcleos adyacentes es constante (D/c+i - Dk = D), se mantiene idéntico entre pares de pulsos adyacentes. Si, por el contrario, la síntesis final del pulso de RF requiriese de muestras con un retardo básico incremental no constante Tk, emplearíamos MCF heterogéneas cuyos núcleos tuvieran pendientes de dispersión no sujetas a dicha relación constante. The tuning of the optical emission wavelength of the laser 4 makes it possible to vary the incremental basic delay between T pulses, which, when using heterogeneous MCF 2, in which the difference between dispersion slopes of adjacent nuclei is constant (D / c + i - Dk = D), remains identical between pairs of adjacent pulses. If, on the contrary, the final synthesis of the RF pulse required samples with a non-constant incremental basic delay Tk, we would use heterogeneous MCFs whose nuclei had dispersion slopes not subject to said constant relationship.
Ambos esquemas propuestos para la generación de pulsos de RF arbitrarios pueden implementarse también empleando como línea de retardo óptica la compuesta por una fibra multinúcleo homogénea 2a y diversos tramos de fibra monomodo 1 1 . Both schemes proposed for the generation of arbitrary RF pulses can also be implemented using as an optical delay line the one composed of a homogeneous multicore fiber 2a and various sections of 1 1 single-mode fiber.
Se debe tener en cuenta que los generados ópticos de pulsos de RF 24 descritos pueden emplearse también para realizar técnicas de codificación de pulsos mediante el empleo de diversos formatos de modulación, como por ejemplo, la modulación por posición de pulso (PMM), la modulación por polarización de pulso o modulación bi-fase (BPM), la modulación por amplitud
de pulso (PAM), la modulación On-Off Keying (OOK) y la modulación ortogonal de pulsos (OPM). It should be noted that the RF 24 generated optical pulses can also be used to perform pulse coding techniques by employing various modulation formats, such as, for example, pulse position modulation (PMM), modulation by pulse polarization or bi-phase modulation (BPM), amplitude modulation Pulse Rate (PAM), On-Off Keying Modulation (OOK) and Orthogonal Pulse Modulation (OPM).
Por último, cabe señalar que para realizar las conexiones de la entrada y/o salida, indicadas en los ejemplos anteriores, de la fibra óptica multinúcleo 2, 2a,Finally, it should be noted that to make the connections of the input and / or output, indicated in the previous examples, of the multicore fiber optic 2, 2a,
5 con una fibra mononúcleo 18, la invención ha desarrollado los conectores correspondientes que permiten realizar dichas conexiones. En la figura 16 se ilustra la estructura de un conector 12 para la conexión entre una fibra mononúcleo 18 y los N núcleos de la MCF, conector SMC (Single to Multicore Connector), que permite la inyección de una única señal óptica modulada a la i o entrada de la MCF. También muestra la estructura de un conector 20, para la conexión entre los núcleos de la MCF y una fibra mononúcleo 18, conector MSC (Multi to Singlecore Connector), para la detección conjunta de las N muestras de la señal en el plano de salida de la MCF.
5 with a mononuclear fiber 18, the invention has developed the corresponding connectors that allow such connections to be made. Figure 16 shows the structure of a connector 12 for the connection between a mononuclear fiber 18 and the N cores of the MCF, SMC connector (Single to Multicore Connector), which allows the injection of a single optical signal modulated to the io MCF entry. It also shows the structure of a connector 20, for the connection between the MCF cores and a single-core fiber 18, MSC connector (Multi to Singlecore Connector), for the joint detection of the N signal samples in the output plane of the MCF.
Claims
REIVINDICACIONES
1 . LÍNEA DE RETARDO MUESTREADA, caracterizada por que comprende: one . SAMPLE DELAY LINE, characterized by comprising:
- Al menos una fuente óptica de generación de una señal óptica, - At least one optical source for generating an optical signal,
- Al menos un modulador de RF de la señal óptica, para modular la portadora óptica con la señal de RF, - At least one RF modulator of the optical signal, to modulate the optical carrier with the RF signal,
- Una fibra óptica multinúcleo (MCF), seleccionada entre una MCF heterogénea y una MCF homogénea, - A multicore optical fiber (MCF), selected between a heterogeneous MCF and a homogeneous MCF,
- donde en el caso de una MCF heterogénea, sus núcleos N posen la misma longitud L y una dispersión cromática D diferente, y a cada uno de los cuales se les aplica la señal modulada, para proporcionar en la salida de la línea de retardo, correspondiente a la salida de cada núcleo N, una misma señal pero retardada según diferentes retardos increméntales en función de la dispersión cromática de cada núcleo, proporcionando N muestras espaciadas en el tiempo, - where in the case of a heterogeneous MCF, their nuclei N have the same length L and a different color dispersion D, and to each of which the modulated signal is applied to them, to provide the corresponding delay line output at the exit of each core N, the same signal but delayed according to different incremental delays depending on the chromatic dispersion of each core, providing N samples spaced in time,
- donde en el caso de una MCF homogénea, sus núcleos N posen la misma longitud L y una misma dispersión cromática D, y a cada uno de los cuales se les aplica la señal modulada; estando la salida de cada núcleo N de la MCF homogénea conectada a una fibra óptica monomodo, seleccionadas entre fibras monomodo de diferente longitud con la misma dispersión cromática D, y fibras con la misma longitud y diferente dispersión cromática D; para proporcionar en la salida de la línea de retardo, correspondiente a la salida de cada una de las N fibras monomodo, una misma señal pero retardada según diferentes retardos increméntales, actuando como línea de retardo muestreada en el tiempo. - where in the case of a homogeneous MCF, their nuclei N have the same length L and the same chromatic dispersion D, and to each of which the modulated signal is applied; the output of each core N of the homogeneous MCF being connected to a single mode optical fiber, selected from single mode fibers of different length with the same chromatic dispersion D, and fibers with the same length and different chromatic dispersion D; to provide at the output of the delay line, corresponding to the output of each of the N single-mode fibers, the same signal but delayed according to different incremental delays, acting as the time-sampled delay line.
2. LÍNEA DE RETARDO MUESTREADA, según reivindicación 1 , caracterizada por que el retardo de tiempo incremental de cada uno de los N núcleos de la MCF heterogénea, y de la estructura formada por la
MCF homogénea seguida por tramos de fibra monomodo, se selecciona entre un valor constante y un valor no constante. 2. SAMPLED DELAY LINE, according to claim 1, characterized in that the incremental time delay of each of the N nuclei of the heterogeneous MCF, and of the structure formed by the Homogeneous MCF followed by stretches of single-mode fiber, is selected between a constant value and a non-constant value.
3. LÍNEA DE RETARDO MUESTREADA, según reivindicación 2, caracterizado por que cada uno de los N núcleos de la MCF heterogénea, y de la estructura formada por la MCF homogénea seguida por tramos de fibra monomodo, presentan un retardo de grupo lineal con la longitud de onda de pendiente diferente, para mediante el cambio de la longitud de onda de la señal óptica, cambiar el valor del retardo incremental, actuando como línea de retardo muestreada en el tiempo reconfigurable. 3. SAMPLED DELAY LINE, according to claim 2, characterized in that each of the N nuclei of the heterogeneous MCF, and of the structure formed by the homogeneous MCF followed by stretches of single-mode fiber, have a linear group delay with the length of a different slope wave, for changing the wavelength of the optical signal, changing the incremental delay value, acting as the sampled delay line in the reconfigurable time.
4. LÍNEA DE RETARDO MUESTREADA, según reivindicación 1 , caracterizada por que comprende medios de generación de un tren de pulsos de diferentes longitudes de onda que están seleccionados entre: 4. SAMPLE DELAY LINE, according to claim 1, characterized in that it comprises means for generating a pulse train of different wavelengths that are selected from:
- una pluralidad de M fuentes ópticas de diferentes longitudes de onda de emisión, que se multiplexan en longitud de onda (WDM) y se modulan con una señal de RF, de modo que el mismo múltiplex alimenta a cada uno de los núcleos de la MCF, - a plurality of M optical sources of different emission wavelengths, which are multiplexed in wavelength (WDM) and modulated with an RF signal, so that the same multiplex feeds each of the MCF cores ,
- un único láser emisor de diferentes canales ópticos mediante la técnica de enganche en fase de modos (modelocking), que proporciona un tren de impulsos con diferente longitud de onda que se modulan con una misma señal de RF y se aplican a los N núcleos de la fibra para obtener a la salida de cada núcleo una línea de retardo en ambos casos compuesta por M muestras retardadas por valores de retardo incremental diferente. - a single laser emitter of different optical channels by means of the technique of phase-mode hitching (modeling), which provides a pulse train with different wavelengths that are modulated with the same RF signal and applied to the N cores of the fiber to obtain at the exit of each core a delay line in both cases composed of M samples delayed by different incremental delay values.
5. LÍNEA DE RETARDO MUESTREADA, según reivindicación 1 , caracterizada por que comprende medios de generación de un tren de pulsos de diferentes longitudes de onda que están seleccionados entre:
- una pluralidad de M fuentes ópticas de diferentes longitudes de onda de emisión, que se multiplexan en longitud de onda (WDM) y se modulan con una señal de RF, de modo que el mismo múltiplex alimenta a cada uno de los núcleos de la MCF, 5. SAMPLE DELAY LINE, according to claim 1, characterized in that it comprises means for generating a pulse train of different wavelengths that are selected from: - a plurality of M optical sources of different emission wavelengths, which are multiplexed in wavelength (WDM) and modulated with an RF signal, so that the same multiplex feeds each of the MCF cores ,
- un único láser emisor de diferentes canales ópticos mediante la técnica de enganche en fase de modos (modelocking), que proporciona un tren de impulsos con diferente longitud de onda que se modulan con una misma señal de RF y se aplican a los N núcleos de la fibra; estando la salida de la línea de retardo en ambos casos conectada a un demultiplexor WDM, para obtener M líneas de retardo de N muestras cada una. - a single laser emitter of different optical channels by means of the technique of phase-mode hitching (modeling), which provides a pulse train with different wavelengths that are modulated with the same RF signal and applied to the N cores of the fiber; the output of the delay line being in both cases connected to a WDM demultiplexer, to obtain M delay lines of N samples each.
LÍNEA DE RETARDO MUESTREADA, según reivindicación 1 , caracterizada por que comprende M agrupaciones de medios de generación de un tren de pulsos de diferentes longitudes de onda que están seleccionados entre: SAMPLED DELAY LINE, according to claim 1, characterized in that it comprises M groups of means for generating a pulse train of different wavelengths that are selected from:
- diversas pluralidades de fuentes ópticas de diferentes longitudes de onda de emisión, que se multiplexan en longitud de onda (WDM) y se modulan con una señal de RF diferente, alimentado así cada uno de los N núcleos con un múltiplex WDM distinto - various pluralities of optical sources of different emission wavelengths, which are multiplexed in wavelength (WDM) and modulated with a different RF signal, thus feeding each of the N cores with a different WDM multiplex
- diversos láseres emisores de diferentes canales ópticos mediante la técnica de enganche en fase de modos (modelocking), que se modulan con una señal de RF diferente y se aplican a los N núcleos de la fibra; - various emitting lasers of different optical channels by means of the phase-mode modeling technique, which are modulated with a different RF signal and applied to the N fiber cores;
Obteniendo en ambos casos en el plano de salida, N líneas de retardo diferentes e independientes. Obtaining in both cases in the output plane, N different and independent delay lines.
LÍNEA DE RETARDO MUESTREADA, según reivindicaciones 4, 5 o 6, caracterizada por que la separación en longitud de onda entre fuentes ópticas adyacentes presenta un valor seleccionado entre un valor constante y un valor no constante.
SAMPLED DELAY LINE, according to claims 4, 5 or 6, characterized in that the wavelength separation between adjacent optical sources has a value selected between a constant value and a non-constant value.
8. LÍNEA DE RETARDO MUESTREADA, según reivindicaciones 1 , 4, 5 o 6, caracterizada por que la modulación de RF está seleccionada entre una modulación en amplitud de RF y una modulación en fase de RF. 8. SAMPLED DELAY LINE, according to claims 1, 4, 5 or 6, characterized in that the RF modulation is selected between an RF amplitude modulation and an RF phase modulation.
9. FILTRO FOTÓNICO TRANSVERSAL DE MICROONDAS, según reivindicación 1 , caracterizado por una línea de retardo óptica donde la salida de cada uno de los N núcleos que la componen están agrupadas y conectadas a un fotodetector, para realizar funciones de filtrado transversal fotónico de microondas; donde la sintonización de la longitud de onda permite reconfigurar la respuesta del filtro. 9. MICROWAVE TRANSVERSAL PHOTONIC FILTER, according to claim 1, characterized by an optical delay line where the output of each of the N cores that compose it are grouped and connected to a photodetector, to perform microwave photonic transverse filtering functions; where the tuning of the wavelength allows reconfiguring the filter response.
10. FILTRO FOTÓNICO TRANSVERSAL DE MICROONDAS, según reivindicación 4, caracterizado por una línea de retardo óptica donde la salida de cada uno de los N núcleos de la MCF está conectada a un fotodetector diferente para establecer N filtros con distinto FSR (Free Spectral Range) en la salida de cada núcleo de la MCF, sintonizables variando la separación entre longitudes de onda de emisión de las fuentes ópticas; . 10. MICROWAVE TRANSVERSAL PHOTONIC FILTER, according to claim 4, characterized by an optical delay line where the output of each of the N cores of the MCF is connected to a different photodetector to establish N filters with different FSR (Free Spectral Range) at the output of each MCF core, tunable by varying the separation between emission wavelengths of the optical sources; .
1 1 . FILTRO FOTÓNICO TRANSVERSAL DE MICROONDAS, según reivindicación 5, caracterizado por una línea de retardo óptica, donde la salida de cada uno de los N núcleos de la MCF está conectada a un demultiplexor de agrupación por longitud de onda de las N salidas, y donde cada salida del demultiplexor comprende un fotodetector diferente, para establecer M filtros distintos compuestos por N muestras cada uno, con distinto FSR,. eleven . MICROWAVE TRANSVERSAL PHOTONIC FILTER, according to claim 5, characterized by an optical delay line, where the output of each of the N cores of the MCF is connected to a wavelength grouping demultiplexer of the N outputs, and where each The demultiplexer output comprises a different photodetector, to establish M different filters composed of N samples each, with different FSR.
12. FILTRO FOTÓNICO TRANSVERSAL DE MICROONDAS, según reivindicación 1 1 , caracterizado por que cada entrada o salida de los N núcleos de la MCF se conecta a un atenuador variable para enventanar la amplitud de las muestras. 12. MICROWAVE TRANSVERSAL PHOTONIC FILTER, according to claim 1, characterized in that each input or output of the MCF N cores is connected to a variable attenuator to poison the amplitude of the samples.
13. ALIMENTACIÓN ÓPTICA DE ARRAYS DE ANTENAS EN FASE, según reivindicación 3, caracterizada por una línea de retardo óptica donde la
salida de cada uno de los N núcleos de la MCF se conecta a una antena a través de un fotodetector de radiofrecuencia; donde cada una de las N antenas se corresponde con un elemento del array de antenas en fase, para obtener una red de alimentación en paralelo, y donde la dirección de apuntamiento del factor de array es gobernando mediante la variación del retardo de grupo incremental entre núcleos a través de la sintonización de la longitud de onda. 13. OPTICAL FEEDING OF PHASE ANTENNA ARRAYS, according to claim 3, characterized by an optical delay line where the The output of each of the N cores of the MCF is connected to an antenna through a radiofrequency photodetector; where each of the N antennas corresponds to an element of the array of antennas in phase, to obtain a parallel feed network, and where the pointing direction of the array factor is governing by varying the incremental group delay between cores through the tuning of the wavelength.
14. ALIMENTACIÓN ÓPTICA DE ARRAYS DE ANTENAS EN FASE, según reivindicación 13, caracterizada por una línea de retardo óptica donde la entrada de cada uno de los N núcleos de la MCF se conecta a una fuente óptica a través de un modulador electroóptico; estando todas las salidas de los N núcleos agrupadas y conectando dicha agrupación a un único fotodetector para sistemas de recepción de señales radiadas. 14. OPTICAL FEEDING OF PHASE ANTENNA ARRAYS, according to claim 13, characterized by an optical delay line where the input of each of the N nuclei of the MCF is connected to an optical source through an electro-optic modulator; all the outputs of the N cores being grouped and connecting said grouping to a single photodetector for reception systems of radiated signals.
15. ALIMENTACIÓN ÓPTICA DE ARRAYS DE ANTENAS EN FASE, según reivindicaciones 13 o 14, caracterizada por una línea de retardo óptica que incorpora atenuadores ópticos variables a la salida de cada núcleo para implementar diversos esquemas de enventanado. 15. OPTICAL FEEDING OF PHASE ANTENNA ARRAYS, according to claims 13 or 14, characterized by an optical delay line incorporating variable optical attenuators at the exit of each core to implement various poisoning schemes.
16. GENERACIÓN ÓPTICA ARBITRARIA DE SEÑALES DE RADIOFRECUENCIA , caracterizada por una línea de retardo óptica, según reivindicación 1 , que comprende un generador de pulsos de RF conectado a un primer y a un segundo modulador electroóptico alimentados en regiones con pendientes opuestas, mediante voltajes diferentes, para modular con el mismo pulso eléctrico; estando la entrada de ambos moduladores electroópticos conectada a una única fuente de emisión óptica: donde la salida del primer modulador conectada a un primer acoplador óptico 1 xN seguido de unos conmutadores ópticos 2x1 que se conectan a cada uno de los N núcleos, para proporcionar una selección de muestras positivas a un primer subconjunto de Ni núcleos y donde la salida del segundo modulador electroóptico está conectada a un segundo acoplador óptico
1xN seguido de unos conmutadores ópticos 2x1 para proporcionar una selección de muestras negativas a un segundo subconjunto de N2 núcleos, comprendiendo medios de selección de la señal proveniente del primer o segundo modulador electroóptico dinámicamente; y comprendiendo a la salida de los N núcleos un fotodetector, para generar una señal de RF deseada. 16. ARBITRARY OPTICAL GENERATION OF RADIO FREQUENCY SIGNS, characterized by an optical delay line, according to claim 1, comprising an RF pulse generator connected to a first and a second electro-optic modulator fed in regions with opposite slopes, by different voltages, to modulate with the same electric pulse; the input of both electro-optical modulators being connected to a single optical emission source: where the output of the first modulator connected to a first 1 xN optical coupler followed by 2x1 optical switches that connect to each of the N cores, to provide a selection of positive samples to a first subset of Ni cores and where the output of the second electro-optic modulator is connected to a second optical coupler 1xN followed by 2x1 optical switches to provide a selection of negative samples to a second subset of N 2 cores, comprising means for selecting the signal from the first or second dynamically electro-optic modulator; and comprising at the output of the N cores a photodetector, to generate a desired RF signal.
17. GENERACIÓN ÓPTICA ARBITRARIA DE SEÑALES DE RADIOFRECUENCIA, caracterizada por una línea de retardo óptica, según reivindicación 16, comprendiendo atenuadores ópticos variables a la salida del primer y segundo acoplador óptico 1xN, para controlar la amplitud de las muestras de manera individual para polaridades positivas y negativas. 17. ARBITRARY OPTICAL GENERATION OF RADIO FREQUENCY SIGNS, characterized by an optical delay line, according to claim 16, comprising variable optical attenuators at the output of the first and second 1xN optical coupler, to control the amplitude of the samples individually for positive polarities and negative
18. GENERACIÓN ÓPTICA ARBITRARIA DE SEÑALES DE RADIOFRECUENCIA, caracterizada por una línea de retardo óptica, según reivindicación 1 , que comprende un generador de pulsos de RF conectado a un único modulador electroóptico, que está conectado a una única fuente de emisión óptica y a la entrada de los N núcleos de la MCF, donde la salida de cada uno de dichos N núcleos está conectada a un conmutador óptico 1 x2, cada uno de los cuales están conectados a un primer y a un segundo acoplador óptico Nx1 , que, a su vez, están conectados a un fotodetector balanceado, permitiendo la detección diferenciada entre un subconjunto de Ni pulsos positivos y un subconjunto de N2 pulsos negativos mediante un control de los conmutadores 1x2 que hay a la salida de cada núcleo que dirigen la señal a uno de dichos fotodetectores balanceados. 18. ARBITRARY OPTICAL GENERATION OF RADIO FREQUENCY SIGNS, characterized by an optical delay line, according to claim 1, comprising an RF pulse generator connected to a single electro-optical modulator, which is connected to a single optical emission source and to the input of the N cores of the MCF, where the output of each of said N cores is connected to a 1 x 2 optical switch, each of which is connected to a first and a second Nx1 optical coupler, which, in turn, They are connected to a balanced photodetector, allowing differential detection between a subset of Ni positive pulses and a subset of N 2 negative pulses by controlling the 1x2 switches at the output of each core that direct the signal to one of said photodetectors balanced.
19. GENERACIÓN ÓPTICA ARBITRARIA DE SEÑALES DE RADIOFRECUENCIA, caracterizada por una línea de retardo óptica, según reivindicación 18, que comprende atenuadores ópticos variables en cada una de las entradas del primer y segundo acoplador óptico 1xN,
para controlar la amplitud de las muestras de manera individual para polaridades positivas y negativas. 19. ARBITRARY OPTICAL GENERATION OF RADIO FREQUENCY SIGNS, characterized by an optical delay line, according to claim 18, comprising variable optical attenuators at each of the inputs of the first and second 1xN optical coupler, to control the amplitude of the samples individually for positive and negative polarities.
20. CONECTOR PARA LÍNEA DE RETARDO MUESTREADA BASADA EN FIBRA ÓPTICA MULTINUCLEO, según reivindicación 1 , caracterizado por que comprende un conector de una fibra mononúcleo con los N núcleos en la entrada de la fibra MCF para inyección de una única señal óptica modulada a la entrada de MCF; y un conector de conexión de los N núcleos a la salida de la MCF con una fibra mononúcleo, para la detección de las N muestras de la señal en el plano de salida.
20. CONNECTOR FOR SAMPLED DELAY LINE BASED ON MULTI-OPTIC FIBER, according to claim 1, characterized in that it comprises a single-core fiber connector with the N cores at the input of the MCF fiber for injection of a single optical signal modulated at the input of MCF; and a connection connector of the N cores at the output of the MCF with a mononuclear fiber, for the detection of the N samples of the signal in the output plane.
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