KR20010074726A - Photonic integrated circuit for optical cdma - Google Patents

Abstract

The optical CDMA system of the present invention is implemented at least partially in a photon integrated circuit, where the broadband light source is modulated using data to be transmitted, the light source being spatially diffused using, for example, a diffraction grating and contained within the photon integrated circuit. Passed through a spectrum-coding mask, the spreading frequency of the encoded modulated light beam is then recombined to provide an encoded spread spectrum optical signal that has been modulated for scanning into an optical fiber or optical communication system, and the received light is two Divided into components and provided to a pair of complementary decoders, inside each of the complementary encoders the received portion of the light beam is spatially spread and transmitted through a spatial decoding mask, both the diffusing element and the mask being contained within the photon integrated circuit, One of the decoders is the original transmission mask and the spatial decoding function of the other, complementary decoder. A spatial decoding mask comprising U and comprising a complementary function U ^m , wherein within each complementary decoder, the spatially spread optical signal is passed through the decoding mask and then recombined, and the signal passing through the complementary decoding mask It is then provided to the other input of the differential detector and is characterized in that the original modulated signal is recovered in the light.

Description

Photonic integrated circuit for optical CDA {PHOTONIC INTEGRATED CIRCUIT FOR OPTICAL CDMA}

preference

This application claims the priority of provisional patent application 60 / 100,223, filed September 14, 1998.

In recent years, the demand for communication bandwidth is expanding with the increased use of spread-spectrum telephony, including technologies such as satellite communications, image programming assignment networks such as cable TV, and code-division multiple access telephony. . This technology integrates well with everyday communication. Increasing demand for wide area communications requires significant investment in new communications technologies and new communications infrastructure. For example, the presence of the cable TV industry, telephone companies, Internet providers, and various organizations is investing in long-distance fiber optic networks and equipment for fiber networks. The addition of this infrastructure, which has an active demand for bandwidth to use, still requires additional investment in new technologies and infrastructure.

Installing fiber over long distances is expensive. In addition, conventional fiber optics or other optical communication networks are only useful in a small fraction of the available bandwidth of a communication system. Thus, consideration is given to gaining higher utility of the fiber network and increasing the bandwidth of the fiber optic system. Techniques have been developed to vaporize the bandwidth of a fiber optic communication system and transfer information from multiple sources of fiber systems. In general, these techniques seek to use the readily available optical bandwidth of optical fibers by complementing the relatively simple coding organization conventionally used by such systems. In some improvement of the bandwidth of a fiber system, optical fibers carry optical channels on optical carrier signals of a single narrow wavelength configuration, and multiple users use time-division multiplexing (TDM) or time-division multiple access (TDMA). Access the fiber. Time division techniques transmit frames of data by allocating consecutive time slots within a frame to a particular communication channel. Optical TDM requires a short-pulse diode laser and provides only a moderate improvement in bandwidth availability. In addition, improving the transmission rate on the TDM network requires that all transceivers be attached to the upgraded network at high transmission rates. Partial network upgrades are preferred for less flexible TDM systems. TDM systems, on the other hand, provide a highly desirable uniform data flow, expressed as "bursty" in predictive and multi-user systems. Thus, TDM technology continues to be important in optical communication systems, but other technologies must be used to obtain the desired communication bandwidth for the entire system. Accordingly, it would be desirable to provide increased bandwidth in optical systems that are compatible with TDM communication technology.

One way to improve the usability of optical communication networks is to employ wavelength-division multiplexing (WDM) or wavelength-division multiple access (WDMA) to increase system bandwidth and support independent forms of multi-user access over TDM. The WDM system provides a plurality of optical channels each using one set of non-overlapping wavelength bands to provide extended bandwidth. Information is transmitted independently of each optical channel using light beams within the assigned wavelength band typically generated by narrow wavelength band optical sources such as lasers or light emitting diodes. Each light source is modulated with data, and the resulting modulated light output for all of the different wavelength bands is multiplexed, combined into an optical fiber and transmitted to the fiber. Each channel's corresponding modulation of narrow wavelength band light can encode a plurality of communication channels formed by simple digital data or TDM. Small interference will occur between channels formed in different wavelength bands. At the receiving end, each WDM channel is terminated at the receiver, assigned to the wavelength band used to transmit data on the WDM channel. This can be achieved in the system by separating the entire received optical signal into different wavelengths using a demultiplexer, such as a tuning filter, and irradiating a narrow wavelength band optical signal to a receiver assigned to a particular channel wavelength. .

In particular, the cost of a WDM system limits the application of this technique. One embodiment of a WDM fiber optical communication system is disclosed in US Pat. No. 5,579,143 with an image segmentation network having 128 different channels. The 128 different channels are formed using 128 different lasers operating at 128 closely spaced but distinct wavelengths. These lasers have a correctly selected wavelength, and also have a finite doped structure and obtain the required characteristics from the communication system. Lasers suitable for WDM image distribution systems are expensive and the demand for 128 lasers, each with the desired optical properties, can result in excessive costs for all systems. The cost of the system is undesirable for use in applications such as local computer networks and limits the application of this technique. As described below, embodiments of the present invention may provide an image distribution network as described in US Pat. No. 5,579,143, and an embodiment of the present invention is a system with flexibility and economy, and may be applied to medium and wide area networks. Other forms of can be provided. Unlike the WDM of many laser systems of US Pat. No. 5,579,143, one embodiment of the present invention can provide sufficient flexibility and sufficient cost effectiveness for use in at least some form of local network.

As described below, one embodiment of the present invention uses spread spectrum communication techniques to obtain an improved loading of the bandwidth of an optical fiber communication system at a lower cost than known WDM systems. Spread-spectrum communication technology has been known to have significant advantages and excellent utility, particularly for military security and mobile phones. Accordingly, spread spectrum techniques that can be applied to optical communication techniques have been proposed in code-division multiple access (CDMA). Spread-spectrum technology is preferred for optical communication systems because the bandwidth of optical fiber based optical communication systems is large enough, and multi-dimensional coding techniques can be used without affecting the data rate of the electrically generated signal that can be immediately input into the optical communication system. Different channels of data can be formed in the frequency domain and independent data streams can be supplied to different channels without limiting the data rate within any one of the channels. From a simple point of view, the above-described WDM system needs to consider the problem of the limitation of spread spectrum systems in which a plurality of data channels are defined for different wavelengths. Different wavelength channels are limited to the optical frequency domain and time domain signals that can be transmitted on each wavelength channel. From CDMA, the separate wavelength channels of the aforementioned WDM communication system provide a single location code where each code vector is orthogonal because there is no overlap between the code vectors.

Suggestions for optical CDMA systems are described, for example, in Kavrrad, "Optical Code-Division-Multiplexed Systems Based on Spectral Encoding of Noncoherent Sources," J. Lightwave Tech., Vol. 13, No. 3, pp. It is similar to the traditional form of radio frequency CDMA of 534-545 (1995). For the WDM system described above, the proposed optical CDMA system uses a wide-spectrum source and combines frequency (even wavelength) coding in addition to time-domain coding. A schematic description of the theoretical optical CDMA proposed in Kavrad's paper is shown in FIG. 1. The proposed optical CDMA system uses a wide spectrum, edge-emitting and heterogeneous source super light emitting diode or erbium-doped fiber amplifier. In the illustrated CDMA system, the wideband source is modulated into a time-domain data stream 10, and the time-domain modulated wide-spectrum light 14 is spatial spatial modulator 16 by a mirror 18 or other steering light. Is investigated.

Light beam 20 in spatial light modulator 16 is incident on diffraction grating 22 which spatially diffuses the spectrum of light to produce light beam 24 having wavelengths of various components that diffuse through space. Thereafter, a spatially spread spectrum beam 24 is incident on the spherical lens 26 and irradiates the beam onto a spatially patterned mask 28 that filters the incident light. Spatially filtered light by the mask 28 is passed through the second spherical lens 30 on the second diffraction grating 34 to recombine the light. The mask 28 is located midway between the pair of coordination lenses 26, 30, and the diffraction gratings 22, 34 are located at the respective focus of the confocal lenses 26, 30. The broad optical spectrum of the heterogeneous source is spatially enlarged in the spatially patterned mask 28, which spatially modulates the spread spectral light. Since the spectrum of light is spatially enlarged, spatial modulation has the effect of modulating the wavelength of the light, or equally modulating the frequency of the light. Thus, the modulated light has the frequency pattern characteristics of the particular mask used to modulate the light. This frequency pattern can then be used to indicate a particular user in the optical network or to indicate a particular channel in a multi-channel propagation system.

After passing through the mask 28, the spatially modulated light passes through the lens 30, and the wavelength modulated light beam 32 is spatially collected by the second diffraction grating 34. The wavelength modulated and spatially concentrated light beam 36 passes out of the spatial light modulator 16 and is irradiated by a mirror 38 or other beam that directs light into the fiber network or transmission system. Part of the CDMA system represents the transmitter portion of the system and another portion of the CDMA system shown below the optical path from the fiber network 42 represents the receiver for the system shown. The receiver represents a specific transmitter in the network that includes many users. This is accomplished by providing a characteristic space mask 28 in the transmitter to detect the spatial encoding characteristics of the transmission mask at the receiver along many transmitted signals in the optical network. As described in the Kavrad paper, it is important for the mask 28 to be variable so that the transmitter can select various separate receivers on the network. In other words, frequency coding of the transmitted beam 40 when a particular user with the illustrated transmitter selects a particular receiver or when the user receives the transmitted data stream by changing the spatial pattern of the mask 28. 마스크 corresponds to the spatial coding characteristics of the receiver for which the transmitter mask 28 is intended.

The receiver shown in FIG. 1 detects data transmitted from a particular transmitter by detecting a rejected signal having a characteristic spatial modulation pattern that is different from the spatial (frequency or wavelength) modulation characteristic of the transmitter mask 28. Light received from the fiber optic network 42 is coupled into two different receiving channels by the coupler 44. The first receiver channel comprises a spatial light demodulator 46 with one mask used for the spatial light modulator 16, and the second receiver channel has a modulator mask (similar to the spatial light modulator 16 of the transmitter). A spatial light demodulator 48 having an "opposing" mask of 28). Each spatial light demodulator 46, 48 performs a filtering function of the received optical signal and sends the filtered light out of the combined photodetectors 50, 52. Photodetectors 50 and 52 detect the filtered optical signal and provide an output signal to another amplifier 54. The output of the other amplifier 54 is provided to the low path filter 56, and the original transmission data 58 is recovered.

2 is a detailed view of a receiver circuit diagram. In this figure, spatial light demodulators 46 and 48 are similar to the spatial light modulator 16 shown in FIG. 1, and individual components of the system are not shown separately. The received light 60 is input to the receiver and split using a coupler 62, some of the light is directed into the spatial light demodulator 46, and other parts of the light are mirrored 64 to another spatial light demodulator. It is indicated in 48. The spatial light demodulator 46 filters the received light 60 as used in the spatial light modulator 16 of the transmitter using the same spatial (frequency, wavelength) modulation function, and filters the filtered light into a photodetector ( To 50). Spatial light demodulator 48 filters the received light using an auxiliary spatial filtering function and provides its output to detector 52. Amplifier 54 subtracts the output signals from the two photodetectors. For the same filtering function effect as the spatial light modulator 16 of the transmitter, the spatial light demodulator 46 includes the same mask 66 as the transmitter mask 28. Spatial light demodulator 48 includes a mask 68 that performs filtration functions secondary to masks 28 and 66, such that spatial light demodulator 48 is assisted in filtration functions of spatial light modulators 16 and 46. Enable the filtration function. In Kabhirrad's paper, each mask 16, 66, 68 is a liquid crystal element, and these masks are fully programmable.

The specific code embedded in the mask should be suitable for the intended optical application. Although CDMA is widely used in radio frequency (RF) domain communication systems, its application in frequency (wavelength) domain encoding in optical systems is limited. This is because the success of the RF CDMA system is critically dependent on the use of well-designed bipolar code sequences (i.e., sequences of +1 and -1 values) with good correction characteristics. Such codes include M-sequences, gold sequences, casami sequences, and orthogonal Walsh codes. These bipolar codes can be used in the RF domain because electromagnetic signals containing phase information can be detected. RF CDMA technology is not widely applicable to optical systems employing heterogeneous light sources and direct detection (i.e. density squared detection using photodetectors) because such optical systems cannot detect phase information. Code sequences that define negative symbol values cannot be used in such optical systems. As a result, only bipolar codes, i.e., code sequences of zero and zero values, can be used for CDMA in direct detection optical systems.

The Kabhihad paper proposes the application of various bipolar codes to masks in the system shown in FIGS. 1 and 2, including masks provided with monopolar (0's and 1's only) M-sequences or monopolar forms of Hadamag codes. . For these kinds of bipolar cords, the Khabhard Hard paper indicates that bipolar codes of length N must be converted to a monopolar code sequence of length 2N, and the system containing such codes must be able to support the entire N-1 user. . The Kabhihad paper mainly describes the theory of CDMA systems with little discussion of the specific facilities of such systems.

Another particular example of an optical CDMA system that includes a converted bipolar code sequence has been proposed for the transmission and detection of bipolar codes in unipolar systems. The system is described in L. Nguyen, B. Aazhang and JFYoung, including "Optical CDMA with Spectral Encoding and Bipolar Codes," Proc. 29th Annual Conf. Information Sciences and System (Johns Hopkins University, March 22024, 1995), and "All-Optical CDMA with Bipolar Codes," Elec, Lett., 16th March 1995, Vol 3, No 6, pp. 468-470. This is also summarized in US Pat. No. 5,760,941 to Young et al. The Young's US patent system is schematically illustrated in FIG. 3, wherein the transmitter 80 employs a wide spectrum light source 82, the output of which is spaced by two beam splitters 84, two spatial light modulators 90, 92. Are split into two beams 86, 88 which are processed by < RTI ID = 0.0 > The first spatial light modulator 90 selectively passes through or blocks the spectral components of the light beam and the spectral diffraction grating 94 for spectral spectroscopy of the light beam 86. And a lens 96 for collimating and irradiating the light. Lens 100 collects spatial components of a spatially modulated light beam, and recombinant diffraction grating 102 recombines the diffuse beam with encoded beam 104. The "pass" and "block" states of the encoding mask represent sequences of 0's and 1's, ie binary, monopolar codes. The code 106 for the first mask 98 is code To have, here, U is the length of the N-pole cord, U ^★ his maintenance, Denotes the connection of two codes. The second encoder 92 (not shown in detail) has its encoding mask coded It is similar to the first encoder 90 except for having. The symbol source 108 outputs a sequence of phases representing 0's and 1's to the first ON / OFF modulator 110 and to the second ON / OFF modulator 114 via the converter 112. Two modulators 110, 114 modulate two spatially modulated light beams, the two beams being combined using beam splitter 116 to combine the two encoded light beams 118, 120. . The modulated light beam is selectively coupled to the output port depending on the bit from which the source is zero or one.

This system may use a receiver with different detection of two auxiliary channels as shown in the receiver of FIG. Receiving channel code And code Masks are respectively employed, and sequences of 0's and 1's are detected according to a channel receiving a signal associated with a mask of the channel. The system proposed in Young's US patent allows the use of bipolar codes developed for the RF CDMA technology used in optical CDMA systems. However, for a mask of length 2N, only N codes can be formed since code U and its complement U ^★ must appear connected on the mask.

It is therefore an object of the present invention to provide a frequency-range CDMA encoding / decoding structure and an optical communication system that embodies the structure when the number of users is maximized without excessively increasing interference. Another object of the present invention is to provide a system that uses a relatively simple system for encoding and decoding but uses a valid spectrum.

The optical CDMA system and the optical CDMA system listed below and incorporated by reference in the relevant application are all designed from discrete optical elements such as gratings, lenses, and detectors. Discrete optical devices are used in many of the preferred examples because discrete optical devices readily provide precision and flexibility. Discrete optical systems, on the other hand, tend to be large and expensive. In some aspects of the invention that will be most widely used, it is desirable to provide a smaller optical system formed from integrated optical devices. Optical CDMA communication systems implemented with optical or photonic integrated circuits have the advantages of smaller size and must be more stringent than discrete optical systems. Preferably, an optical CDMA system implemented using photonic integrated circuits can be sufficiently inexpensive and strict enough to be used in local networks and homes.

Attempts have been made to implement partial segmentation techniques in communication systems at least partially implemented in optical integrated circuits. For example, Rzeszewski, U.S. Patent No. 4,989,199, "Photonic Switch Architecture Ytilizing Code and Wavelength Multiplexing," describes a communication system that implements both wavelength division multiplexing (WDM) and phase-type code division. The Rzeszewski system utilizes a plurality of sets of coherent sources, where each set of coherent sources has the same wavelength, and performs phase modulation on the source for phase encoding to distinguish the sources in a set. Each set of coherent sources is input to a corresponding one of the phase encoders. Different phase encoders modulate sets of sources with different wavelengths so that outputs from other phase encoders can be combined into a WDM structure. Since the system uses phase encoding to distinguish some of its channels, any optical system through which these signals are transmitted must maintain phase and consistency. Thus, when a signal encoded by the method of the Rzeszewski patent is transmitted on an optical fiber, a special fiber must be used, after which the system will not be able to transmit the signal on the fiber by a length of distance as desired in a fiber communication system. Accordingly, it is desirable to provide an integrated optical communication system that does not rely on the use of consistent signals.

The present invention relates to an optical communication system, in particular an optical code-division multiple access communication system implemented using one or more transcription integrated circuits.

1 illustrates a conventional optical fiber mediated CDMA communication system;

2 is a detailed view of one receiver configuration that may be used in the system of FIG.

3 is a schematic illustration of an entire optical CDMA system using the FIG.

4 is a diagram illustrating one configuration of a PIC configuration of an encoder;

5 is a diagram illustrating one configuration of a PIC configuration of a decoder;

6 illustrates another configuration of the system of FIG. 3;

7 is a diagram illustrating another configuration of a PIC configuration of an encoder or a decoder;

8 is a diagram illustrating another configuration of a PIC configuration of an encoder or a decoder;

9 is a diagram illustrating another configuration of a PIC configuration of an encoder or a decoder;

10 shows a particularly compact configuration of an array waveguide grating;

FIG. 11 is a schematic illustration of an apparatus for generating N wide spectrum light source arrays having sufficient intensity to produce an optical beam for communication of N channels over a fiber using the method according to the present invention; FIG.

12 is a schematic illustration of a polarization insensitive beam splitter in accordance with a preferred embodiment of the present invention;

FIG. 13 shows a photodetector circuit device schematically illustrated in FIG. 3 in more detail;

14 is a view showing a modification of the light source generating mechanism of FIG. 13;

15 shows a set of data streams (a)-(c) that can be used to modulate a light source in accordance with aspects of the present invention, and

FIG. 16 illustrates a circuit that can be used to generate a pulse stream such as that shown in FIG. 15B or FIG. 15C from a data stream as shown in FIG. 15A. .

Cross-Referenced Patents and Applications

The following patents and applications are related to the present application, each of which is incorporated herein by reference in its entirety.

1. U.S. Patent 5,867,290, entitled "High Capacity Distributed Spectrum Optical Communication System", issued February 2, 1999

2. Serial application number 09 / 126,310, entitled “Optical CDMA System”, filed July 30, 1998

3. Serial application number 09 / 126,217, entitled “Optical CDMA System Using Sub-Band Coding”, filed July 30, 1998

4. Serial application number 09 / 127,343, entitled “Methods and Apparatuses for Reduced Interference in Optical CDMA,” filed July 30, 1998

This and other objects are achieved using an optical CDMA system in which a spatial encoder is implemented at least partially within a photon integrated circuit. The broadband light beam is spatially diffused using, for example, a diffraction grating and transmitted through a spatial spectral-coding mask contained within the photon integrated circuit. Spatial coding masks usually include one monopole code belonging to a set of monopole codes appropriately derived from a set of balanced bi-orthogonal codes. The spreading frequency of the encoded modulated light beam is then recombined to provide a modulated, encoded spread spectrum optical signal for scanning into an optical fiber or other optical communication system.

Alternatively, aspects of the present invention may provide an optical CDMA system in which a receiver is at least partially implemented within an optical integrated circuit. A wide spectrum light source modulated with the spatial encoding function U is received at the receiver. The received light is divided into two components and provided to a pair of complementary decoders. The receiving portion of the light beam in each complementary encoder is distributed into space, for example using a diffraction grating, and passed through a spatial decoding mask implemented in an optical integrated circuit. One of the decoders includes a spatial decoding mask that implements the spatial encoding function U of the original transmission mask, and the other complementary decoder includes a complementary function U ^* . The spatial encoding functions U, U ^{* implement} preferably monopolar codes belonging to a set of monopole codes derived from a set of balanced bipolar orthogonal codes. The spatially dispersed optical signal within each complementary decoder is recombined after passing through the decoding mask. The signal passing through the complementary decoding mask is then provided to different inputs of the differential detector, and the data initially modulated in the light is recovered. Suitable differential detectors may include, for example, back to back diodes.

Another aspect of the invention relates to an optical communication system providing an encoder and a data source providing a data stream. The encoder provides an optical output that is modulated into a data stream and implements a first code, wherein the first code is selected from a set of unipolar codes, wherein each code in the set is combined with other codes in the set. Orthogonal to the difference between the complements of the different codes, the codes in the set are defined as a sequence of N digits, each digit having one of at least two values, and each of the N digits of the code to be output from the encoder. Corresponds to one of the N potential spectral ranges. The light output from the encoder includes M components corresponding to M different spectral ranges within the spectral range of the N potentials, each of the M components characterized by an Mth component light level corresponding to the value of the corresponding code digit. do. As a result, the light output of the encoder is wide spectrum light modulated by a code function defined by the data stream and spectrum. The encoder includes an optical integrated circuit.

Another aspect of the invention provides an optical communication system having a decoder coupled to receive an optical signal from an optical communication system and recover the transmitted data. The decoder includes an optical power splitter for splitting the received optical signal into first and second optical components of approximately equal power.

The first and second spectral filters are coupled to receive the first and second light components, wherein the first spectral filter implements a first code and the second spectral filter implements complement of the first code. The first and second spectral filters output first and second filtered components of the received light. The photo detector receives the first and second filtered components of the received light and provides an electrical signal output. The first code is selected from a set of unipolar codes, in which each code in the set is orthogonal to the difference between any other code in the set and the complement of the other code, with N codes in the set Defined as a sequence of digits, each digit has one of at least two values, and each of the N digits of the code has N potential spectral ranges that can be output from the encoder (the Is defined). The received optical signal is wide spectral light modulated with a code function defined as a spectrum having a M component corresponding to M different spectral ranges within the data stream and the N potential spectral ranges, and the encoder comprises an optical integrated circuit.

A particularly preferred embodiment of the present invention provides an optical CDMA system employing spread spectrum technology for communication over optical fibers or over other communication links to take advantage of better bandwidth. The components of the optical fiber communication system are preferably implemented in an optical integrated circuit. For example, the implementation of an encoder or decoder of an optical CDMA system may make the system cheaper, more robust, and easier to align than an implementation of an optical CDMA system using completely separate components. Certain particularly preferred systems of the present invention provide an integrated encoder and decoder in which optical components are implemented in an optical integrated circuit and electrical components are implemented in an integrated circuit. This implementation implements at least some optical integrated circuit components on the same semiconductor substrate as used to implement the electrical integrated circuit.

The optical CDMA system according to the present invention preferably transmits signals using a spatial encoder with a single channel of binary or analog encoding and receives signals using a two channel spatial decoder. The spatial encoder includes two channels, one of which implements the same transport code as the encoder and the other of the decoder channels implements the complement of the transport code. Preferably, the encoder modulates the spatial spectral light source in space by a code identifying the channel transmitting the data. Most typically the broad spectral light source is at least partially contradictory. Spatial modulation of the light source is achieved by dispersing the input light into space using, for example, array waveguide gratings or diffraction gratings. The spatially dispersed spectrum is then provided to a spectral coding mask. In some embodiments this is accomplished by providing scattered light to an optical switch array that can be selected to represent a spatial modulation function. If the switch does not need to be selectable, the encoding mask is simpler to implement, such as providing or not providing an optical link between points on each side of each of the discrete wavelengths or frequency bins defined within the mask. Can be.

More preferably, the spectrum of the optical signal is distributed such that the spectrum of the optical signal is divided into a plurality of bins of the same bandwidth or into a plurality of bins of the same intensity. The spatial coding mask used to modulate the optical signal provides a corresponding number of bins that independently attenuate the signal provided to the bins. Each bin can be switched, for example, to pass or block an optical signal input into the bin, thus performing binary form encoding. Since each successive bin in the mask provides light within a sequential range of wavelengths, the spatial modulation of the mask gives the light a frequency distribution that can be used as a code in a CDMA communication system. The spatial coding mask described above preferably implements a unipolar code belonging to a set of unipolar codes derived from a set of balanced bipolar orthogonal codes. After spatial modulation, the dispersion frequency of the encoded light beam is recombined to provide a modulated and encoded distributed spectral optical signal for input into an optical fiber or other optical communication system.

In addition to spatial encoding modulation, the input light is also modulated into the data stream, preferably within the time domain. In a preferred embodiment of the present invention that implements an optical integrated circuit ("PIC") encoder, modulation of the input light signal may be accomplished within the PIC. For example, where the encoder is formed from a suitable combination of III-IV semiconductors (eg, a suitable combination of InGaAsP, AlGaAs or other similar system), the modulation can be accomplished by one component of the optical integrated circuit. Likewise, PIC encoders can achieve modulation if the encoder is implemented in optoelectronic materials such as LiNO ₃ . In any of these embodiments, the switch used to define the space mask function can be configured to perform time domain modulation of the optical signal.

Recovery of the transmitted signal is achieved by using a decoder corresponding to the spectral modulation function implemented in the encoding mask or code. In some particularly preferred embodiments of any receiver, the beam splitter, which is a polarization insensitive splitter, splits the beam into two equal intensity portions. Each of the optical signal portions is dispersed into space using an array waveguide grating or diffraction grating to spatially separate the spectrum of the portion of the optical signal. The spatially separated received signal is provided to one of two different masks. The light passing through the two decoding masks is then recombined using an array waveguide grating or a diffraction grating, and the two light signals are converted into electrical signals by differential detection. For example, two decoded light signals may be provided to each of the two back to back diodes. The resulting electrical signal is preferably low pass filtered in a particularly advantageous embodiment, which is then provided to a limiting element for removing negative components of the electrical signal.

In a particularly preferred embodiment, the masks in the encoder and decoder comprise unipolar binary codes consisting of zeros and ones, such as Walsh codes. The advantages, usefulness, and derivatives of these codes are described in the referenced applications and are incorporated by reference in the cross-reference applications section above. While reference portions of the above application have not been repeated herein for the sake of brevity, the portions form part of the disclosure of the present invention. In addition, other encoding schemes have been described in the related application, including the use of discrete analog basis functions. Within the exemplary embodiments described herein it is particularly emphasized to use a binary mask for the mask with the bins on or off, or transmitted or non-transmitted. In such an embodiment, it is possible to provide an L location mask to define an L-1 communication channel for all L-1 users. Those skilled in the art will appreciate that the optical integrated circuits described below can be used to generate analog transfer functions for each of the bins of the mask, and are therefore well suited to implementing a set of orthogonal basis functions. A system for implementing aspects of the present invention will now be described, with particular emphasis on implementing optical CDMA systems within one or more optical integrated circuits.

FIG. 3 schematically illustrates one embodiment of a CDMA communication system including both a PIC encoder and a PIC decoder. A wide light source 90, such as a super light emitting diode (SLD) or erbium doped fiber source (EDPS), is coupled to the CDMA PIC encoder 92. Encoder 92 may provide a function somewhat similar to spatial wide modulator 16 shown in FIG. 1 which spatially encodes a modulated wide spectrum spectral light beam. More preferably, however, encoder 92 includes both spatial and time domain modulation functions, whereby the time domain of encoder 92 may be modified using a data or data source (e.g., using key or pulse code modulation). Modulates the input light based on other information from 94). As shown schematically in FIG. 4, optical integrated circuit encoder 92 includes a substrate 120 having an arrayed waveguide grating or diffraction grating 122 that disperses the spectrum of a light beam modulated along an axis into space. . Array waveguide gratings are known in the art and are described, for example, in US Pat. No. 5,002,350, incorporated herein by reference in its entirety and issued to Dragone. Suitable embodiments of waveguides may be formed in III-IV or silicon semiconductor systems, where light propagates through the synthesized waveguide or is plated through semiconductor channels formed over the semiconductor substrate by etching into the semiconductor substrate. Array waveguide gratings may also be implemented in optoelectronic materials such as LiNbO ₃ , which doped with titanium or etched channels to form waveguides, for example. Another PIC embodiment of a spatial dispersion element is a curved grating implemented with a semiconductor, optoelectronic optical circuit or other suitable waveguide material. One example of such a system provided in the PIC of AlGaAs is shown in US Pat. No. 5,355,237, which is incorporated herein by reference in its entirety and is issued to Lang et al. The embodiment of FIG. 4 uses a curved grating to achieve a significant level of spatial separation of light components in a smaller space than can be achieved using conventional planar gratings. Another possible embodiment uses silica on a silicon assembly, which will be described below. Advantageously, preferred PIC embodiments of the spatial dispersion device use both beam shaping elements (eg, collimation or focusing) or dispersion elements (lattice or array waveguides) within the PIC. The number of different bins in which the spatial dispersion element will scatter the beam will depend on the respective application. Although a system with only 16 bins is readily available and available in many current applications, it is assumed in this description to have a total of 128 bins.

Next, the spatially dispersed light beam is passed through the encoding mask and modulator array 124. Encoding mask and modulator 124 includes a number of independently switchable optical elements that define the attenuation provided by the different bins of the mask / modulator, the total number of bins being defined by spatial dispersion element 122. It is equal to the number of bins (for example 128). The mask confinement function and the time domain modulation function are input to a switch array constituting the mask / modulator 122. The signal 94 input to the mask / modulator selectively turns on or off various switch elements of the mask / modulator, and applies a time domain modulation function to at least the switch in the on or transmitting state. Typically the same time domain modulation function is applied to all switch elements regardless of the switching state. The mask / modulator provides a spatially encoded and modulated light beam collected and recombined into an optical spectral beam by a second array waveguide grating, curved diffraction grating, or other similar element 126. The signal recombined into the spectrum and modulated in the space and time domains is then output for input into fiber 96, which may be a single mode optical fiber. Optical couplers 98, such as star couplers, Y couplers, and the like can be used to couple the encoded code from the fiber onto a large network for long distance transmission. Alternatively, the network of FIG. 3 may simply have a star configuration, not shown other than the two users illustrated.

Referring also to FIG. 3, the modulated optical signal is transmitted over an optical piper or other optical communication link 100, and then two channels 104, 106 are coupled to two decoding PICs 108, 110. Provided to the decoder. An optical signal comprising a multi-potential spread spectrum signal is deflected from the fiber 100 using an optical coupler (not shown) and split into two parts by the divider 102. The divider is most preferably a polarization insensitive element as illustrated in FIG. 12 and described below with reference to this figure. One portion of the received light is provided to the CDMA PIC decoder via fiber or other link 104 and the other portion of the received light is provided to the second CDMA PIC decoder 110 via another fiber or other link 104. Each of the CDMA PIC decoders 108 and 110 may have a fixed mask or a selectable mask implemented in a switch array. Such a preferred embodiment of the present invention is particularly suitable in a network environment where any one user wishes to send and receive data with any other user connected to the network. In such a switchable mask decoder, each of the masks in the decoders 108 and 110 receives respective mask signals 112 and 114 that select a mask distribution. In general, a good mask will implement an encoding mask that is mutually complementary. As a result, the mask signals 112 and 114 may be bitwise complementary to each other.

FIG. 5 illustrates an embodiment of PIC decoders 108, 110 provided on a semiconductor, silica / silicon or optoelectronic substrate 130 that may be used in the system of FIG. 3. Referring to FIG. 5C, incident light is dispersed into space along an axis by an array waveguide grating or curved diffraction grating 132 and then passed through a detection or decoding mask 134. One of the decoders 108 preferably implements the same coding function U as the decoding mask 134 is used to encode the desired transmission optical channel, while the other decoder 108 is a complement of the transmission coding function. It is desirable to implement (U ^* ). The light passed through the decoding mask 134 is then provided to a second array waveguide grating 136 or other diffraction grating 136 that recombines the spatially dispersed light into a broad spectral beam, which is the output of the encoder. . Most preferably, the encoder and decoder of FIG. 3 includes a mask that is fixed or switchably configured to implement the converted binary Hadamard code.

The output from decoders 108 and 110 is then provided to differential detector 116, which may be a pair of back to back detector diodes that naturally perform a subtraction operation. Other detection configurations may be used, some of which will be described below. In addition, two gain control circuits can separately process two signals output from the decoder, such as using multi-channel detection within the decoder itself. Next, the differential electrical signal is detected for data recovery. Data recovery for the digital data stream may include, for example, integrating or square-detecting the signal difference at processor 118.

Embodiments of the invention may be implemented in a variety of different communication environments, including intra-backbone communication links, wide area networks, video distribution networks, and the like. Some of these applications are described and illustrated in more detail in the applications identified in the relevant application section above and incorporated herein by reference. Aspects of the present invention may also be applied to hybrid systems where discrete optical coding systems are used in centralized transmission and retransmission facilities and optical integrated circuit (PIC) CDMA receivers are provided at remote reception sites. For example, such a system can be applied in particular to a video distribution system. In such applications, a discrete optical CDMA system may be provided at a central distribution point, such as a head-end in a cable distribution system, and a PIC-CDMA receiver capable of selecting different codes selectively selects the receiver to receive data on different channels. Can be provided at the local receiving base station to tune. Ideally, the local receiving base station may be implemented in a local area or other computer network using only PIC-CDMA components.

In a CDMA system, the basic requirement for spectral encoding / decoding configuration is that the decoding device at the receiving user can recover data signals from the corresponding transmitting user while reducing or eliminating signal interference from all other users. . In some systems the reception mask is fixed such that a particular receiver always receives data on the same channel. In this way a centralized and switchable broadcast base can direct the data flow to the selected receiver. In other systems, different signal sources may be programmed to select many sources to be delivered on a common transport network or system. In a spread-spectrum CDMA system using scattered light sources, phase information is not available because only the scattered light system is delivered to the positive signal, and only unipolar codes can be used to encode. The single binary code can be represented by a sequence of binary digits such as u _i = 110011110101011, where i represents the i ^lh user channel. The number of digits in the sequence, N, is related to the length of the code. Practically, in a preferred binary monopolar code mask, each code value is assigned to an interval slot, transparent or opaque body where each code value is fixed on a patterned mask that corresponds to a fixed frequency or wavelength interval in the spread spectrum beam of modulated light. Corresponding.

If a mask is used for encoding and decoding, the code is chosen to be square, or:

u _i u _j = (One)

Where "·" represents the bit-vice dot product of the two codes. If a vertical code is used, each transport channel uses the same decoding mask as the encoding mask to recover the signal in the corresponding transport channel while interfering the signal in all other codes. This is consequently desirable, but only occurs when the code is chosen as a binary basis vector.

u ₁ = 000 ..... 001

u ₂ = 000 ..... 010

u _N = 100 ..... 000

This set of codes is undesirable because only one digit of the entire code is 1, most bins are blocked while only one mask frequency bin passes. Such a system is seen in a wave division multiple access (WDMA) system. This code is undesirable because only 1 / N of the source power is delivered and power is wasted.

In the encoding and decoding system shown in FIG. 3, one mask is used for encoding and two masks are used for decoding, and the monopolar code of the set differs according to the definition of vertical in which the code u _i in the set is set above. Not perpendicular to code u _j . The code u _i is also chosen vertically by the difference between any other code u _j and the composite component u _j ^* .

u _i (uu _j ^* ) =

Where M ^' is a constant. The derivation of a suitable code set, such as the Hadamard code that is converted to a monopole code set, is described in the application referenced above.

In addition, various combinations are possible for multiple purposes, and various network algorithms are also feasible. For example, in the present invention, a plurality of users s ₁ , s ₂ , ... s _N are connected to the optical fiber medium 130 and each user s _j connects to a certain user s _i through the optical fiber. It can be applied to various fiber communication system structures such as a network environment that can communicate. Each user or node s _j is assigned code u _j to receive data from another user, and the other user is sorted by a different code. When the user s _i transmits data to the user s _j , the transmitting user s _i encodes an optical signal using a code assigned to the receiving user s _j and receives the user ( s _i ) decodes the signal using the assigned code. This requires that the code can be dynamically changed so that the sending user can send data according to the receiving user's code. The code for any one node can be assigned to one or more master nodes that break down through the network. Then, when the node is in use in the network, it needs a code for encoding to select one spread spectrum channel for communication. When a node leaves the network, the code used by a particular code is recycled to other nodes in the network. Various designs can be designed to use techniques such as CSMA / CD technology or token passing on a permanently assigned channel. Alternatively, the Token Passing technique can be used to gain code to lock one code division channel.

Although only the CDMA technique has been described above, those skilled in the art can easily understand the system parameters, and the system can be used in combination with wavelength (frequency) division multiplexing and time division multiplexing. For example, a code may be designed for other parts of the light spectrum such that wavelength division multiplexing is used. In addition, the code may be partitioned based on time division to provide time division multiplexing. In addition, frequency domain CDMA may be coupled with optical CDMA over time to reduce the number of codes and users in the network. Spread Spectrum in Time Range In an embodiment, several users are provided with spread spectrum in a different temporal range to encode the data before the data is provided to the optical encoder. However, these users can be divided into the same wavelength encoding design discussed above. Of course, at the decoder, once the received light information is converted to the electrical digital domain, the digital signal is processed according to a spread spectrum code in the temporal range to recover the desired transmitted information.

The modification of the embodiment of FIG. 3 is described in FIG. 6. This does not provide an external broadband light source. PIC CDMA encoders also include an array of N lasers that emit light in different N wavelength ranges. The N wavelength output of the N laser is combined to use an array waveguide grating or a curved diffraction grating to provide an output at encoder 140. The mask and modulation functions can be performed by turning the laser entirely in the spectral pattern assigned to the channel corresponding to the monopole code. All lasers are modulated with the same temporal range of modulation, which distinguishes CDMA embodiments in wavelength division modulation systems. By selecting the appropriate sparse spreading element at the decoder, the remaining elements described in FIG. 6 are also identical to the embodiment of FIG. 3.

FIG. 7 shows a change on the encoder of FIG. 4, which can be used with the encoder of FIG. 5. In the CDMA PIC of FIG. 7, optical input is provided through a coupler or circulator 150 in a waveguide grating or diffraction grating 152. The grating 152 spreads the spectrum of input light in the manner described above, and modulates the spectral light diffused in the mask / modulator 154 in the manner described above to modulate the input signal and the defined code in the optical frequency domain. to provide. The code is a binary code defined by choosing between two attenuated levels, for example between high and low attenuation levels within each bin of the mask. In the mask / modulator, the signal outputs are waveguides that are each coupled in the bin of the mask as described above. Instead of recombining the spread spectral signal as in the above embodiment, the signal is reflected through the mask / modulator 154 by a highly reflective coating on the end of the fiber light or waveguide. The light modulated by the mask / modulator 154 is initially recombined by an arranged waveguide grating or diffraction grating 152 used to disperse broadband light. This embodiment has the advantage that no second array waveguide grating or diffraction grating is required in the PIC. The output of the modulated signal is provided through a coupler or circulator 150.

Another variation of the FIG. 7 embodiment that may replace the encoders and decoders of FIGS. 4 and 5 is shown in FIG. 8. The encoder / decoder of FIG. 8 provides a fixed mask embodiment of a decoder and encoder that can be used in the system of FIG. No array of switches is provided. In addition, the output of the array waveguide grating or diffraction grating 152 is optionally provided with a high reflective or anti-reflective coating in the pattern exhibited by the cord pulled into the communication channel. By selectively providing a high reflective and anti reflective coating, the bin corresponding to one binary state reflects light output at grating 152 as the code appears in the selected channel. The bin corresponding to another binary state does not reflect light. The light reflected through the array waveguide grating is recombined to provide a modulated broadband optical signal in an appropriate manner for use within the communication system of FIG. 3. Another aspect of the embodiment of FIG. 8 is similar to the embodiment of FIG. 7. The embodiment of Figure 8 provides a low cost fixed encoder and decoder so that the communication system can be implemented in a range where cost and simplicity apply.

Another embodiment of an encoder / decoder is shown in FIG. The embodiment of FIG. 9 is silica on silicon, which is an embodiment of an encoder / decoder according to the invention, similar to that described in FIGS. 4 and 5. The CDMA PIC of FIG. 9 is formed of array waveguide gratings 160 and 164 provided by silica on a silicon structure. In this embodiment the mask 162 provided between the two array waveguide gratings comprises silica on a silicon structure. In particular, the mask consists of an array of thermal switches configured in a known manner to change the attenuation through a portion of the silica waveguide. In this embodiment, the broad spectrum light source is preferably modulated in the CDMA PIC circuit, since the column switch array generally cannot modulate the optical signal at the desired rate. For this reason, the mask control signal provided by the mask controller 166 generally controls the on / off state of the mask element and does not include a temporal range modulation function.

Partial integration of the array waveguide gratings used in accordance with the present invention is described in FIG. 10. Array waveguide gratings are implemented by any of the semiconductor, electro-optical or passive (eg, silica on silicon) materials described herein. The waveguide has the advantage that it can be effectively miniaturized by using the reflection passage of the waveguide. Such miniaturization devices can be integrated in PICs having two gratings and an array of switches constituting a mask. Alternatively, the output of the waveguide can be selectively blocked by the effect of a miniaturized mask encoder / decoder.

As will be described in detail below, various embodiments of the present invention provide many similar light sources. For example, some embodiments provide 128 light sources that are substantially the same in width and intensity. Current systems generally require many sources. Economical implementation of multiple sources with spectral similarity is desirable to provide one light source to be combined with the fiber. Each segmented component is magnified to an appropriate level and then each segmented and magnified component is provided in a separate start splitter. The hierarchical structure of the original source is divided and enlarged, and each successive source channel is used to develop a number of sources that essentially have the same spectral characteristics in that segmented and enlarged.

The difficulty observed in the present invention when implementing such a source is an undesirable correlation between other sources. This level of correlation creates undesirable correlations between different communication channels that cooperate with other sources. As a result, different sources are not related to each other in the preferred embodiment. This is done by inserting a different light delay along the output path of the other source channel. This optical delay may be composed of optical delay lines. Proper delay is provided by passing each source through a different length of fiber delay line. Alternatively, the delay can be generated using free space transfer through other optical paths. Fiber delay is desirable because it can be implemented using minimal space, and as a result the entire optical system can be effectively provided in a small space while allowing the implementation of the diffusion range in accordance with the present invention.

FIG. 11 shows a number of low cost multiple layers using one erbium-doped fiber source and a layer of erbium-doped fiber amplifiers to provide a sufficient source of channels while having sufficient strength to drive the channels of the optical communication system. An apparatus for generating a spread spectrum source is described. As shown, one erbium-doped fiber source 300 outputs light with an acceptable spread spectrum and provides a bandwidth of about 28 nanometers at wavelengths where the source's intensity varies less than about 5 dB. . The 28-nanometer bandwidth corresponds to a system bandwidth of about 3.5 THz. The output of an erbium-doped fiber source, also known as a light emitting fiber source, is provided to the fiber in a splitter such as a star coupler 302 that splits the output source signal and provides four fiber outputs in the array of four fiber amplifiers 304. Lose.

As the output of the fiber source 300 is divided into four different sources, the intensity drops in a predetermined way. Each four divided source is amplified by four fiber amplifiers to provide four spread spectral light beams whose intensity is approximately equal to that of the original source 300. In the 128 channel system described, this process is repeated through another hierarchical stage. In this way, the output at the four fiber amplifier 304 is provided over the fiber at the corresponding set of four splitters 306, which become star couplers. Splitter 306 splits the output into a number of outputs whose strength is reduced in the fiber amplifier. The split output at the splitter 306 is provided to another array of fiber amplifiers 308, which provides the intensity of multiple channels of diffuse-spectrum light to provide another set of source light beams 310 with appropriate intensity. Amplify This process is repeated until the number of spread-spectrum sources with the appropriate intensity generates 128 independent sources, for example for a 128 channel fiber communication system. Such a hierarchical arrangement preferably uses one original source and multiple fiber amplifiers to obtain the desired set of spread spectrum light sources, which has the advantage of being low cost when compared to the cost of the fiber amplifier and the fiber source.

After sufficient channels of source light have been generated, the channels of source light provide an array of spatial light modulated or encoders each having the shape shown in FIGS. 3 and 4. 128 different encoders use 128-empty masks to encode the input optical signal, and each 128 masks will have a unipolar Hadamard code vector generated by the method described above. Each mask is a fixed mask and has a total of 128 identical size bins, which span the usable width of the liner mask. This results in 128 bins spanning approximately 3.5 THz (28 nanometers) in bandwidth, with each adjacent bin forming a dependent frequency spacing provided with a bandwidth of about 25 GHz. Equally sized bins of the fixed mask, which may be the encoder / decoder of FIG. 8, are allocated according to a code vector having one or two binary values. Each 128 channel of the communication system is formed by a separate spatial encoding function and each channel is modulated with a signal in the temporal range using, for example, a modulator. After the various channels have been spatially and temporarily modulated, 128 channels can be combined or injected into the fiber.

Long distance transmission for a fiber communication system is coordinated similarly to other conventional fiber communication system methods. As conventional, this generally uses one mode fiber. In addition, the signals are distributed and lost on the fiber. The signal on the fiber is therefore preferably amplified at regular intervals, for example at 40 to 80 kilometers using a conventional fiber doped amplifier.

At the other end of the transmission fiber, the combined optical signal is divided, amplified, and provides an array of 128 receivers, each corresponding to one, in a fixed mask channel formed by 128 transmitters coupled into the fiber. The main purpose of this embodiment is to extend the use or loading of the fiber so that the receiver includes a fixed mask to represent a signal of 128 channels. The receivers having the structures shown in FIGS. 3 and 8 each represent a particular channel formed by a particular transmitter by including in one mask of the same receiver as the transmitter mask and the second mask is the bit-wise component of the transmission mask. In an embodiment, the use of a fixed mask on the transmitter and receiver ends of the communication system provides a reduced cost system provided that the bandwidth for high volume fiber links is significantly improved.

As described above, the recovery of the optical signal in the fiber communication link is performed by a receiver that splits the light beam received in the optical system into two components having substantially similar power levels. 12 shows a beam separator that is preferably used for input at the decoder. The separator according to the invention can split the received light into two parts of the same power level so that other detection of the optical CDMA receiver effectively detects the user channel.

An embodiment of the nonpolar beam splitter consists of a first polar element that splits the received light beam into first and second channels of light having two different polarities. For example, one channel of light may comprise a vertically polarized component of the received light and another channel may comprise a horizontally polarized component of the received light beam. Then the polarity of one channel is switched to the polarity of another light beam. Linearly polarized light consists of the polarity of the rotating light. The two channels of light are then recombined and provided in the beam splitter. Such beam splitters are generally well-formed and predictable in the polarity of the combined beams, thus splitting the polarity element into two beams of substantially equal power in the exactly combined beam.

Referring to FIG. 12, an embodiment is described in which light is received from one mode fiber 350. Since fiber 350 generally has no polarity observed and light in fiber 35 has linear polarity in any direction, it is useful to use conventional linear polarizers such as beam splitter 352 or polarity analyzers. Polar photosensitive element 352 splits the input light beam into two vertical polar components and provides these two components in two different optical paths 354 and 356. Typically different power levels exist along each path. This optical path travels through free space or through fiber where polarity is observed. In this case, the polarity of the light in each arm has a constant polarity until the polarity is changed.

One component of the light is provided along the light path 354 and maintains a vertical linear polarity 358 through the light path 354. Along another optical path 356, the polarity is initially in the horizontal position 360 and then the polarity is rotated 362 such that the light in the second optical path is linearly vertical as indicated by " 364 " Rotate 90 ° by When the second optical path 356 is passed through the free space, the rotating element becomes a half waveplate or an appropriate Faraday rotor. When the second optical path 356 is transmitted through the fiber where the polarity is observed, the rotating element 362 preferably makes the mechanical rotation of the fiber 90 degrees. In general, most of the rotation of the fiber proceeds continuously over the length of the fiber. Of course, it is possible to carry out the rotation via another means, such as inserting the rotating element at the fiber end of the second optical path.

Once the two beams on the two optical paths are polarized in the proper direction, the two beams are recombined and then split a pair of substantially equal power beams for delivery along two additional beam paths. After the beams from the paths 354 and 356 are combined, it is possible to use a general polar beam splitter 366 to split the beam into two substantially equal power beams. Two output beams are provided along light paths 368 and 370 through one mode optical fiber having linear polarity in the described embodiment. The splitter from which the beam was received is then provided to decoders 108 and 110 in FIG. Those skilled in the art will appreciate that the polar beam splitter is implemented in conjunction with another waveguide, such as a rotating element, as described above with respect to the fiber.

In the described optical CDMA system, it is highly desirable to reduce the interference between different channels of the user or other diversified signals so that many channels can be provided on a single fiber. Various mechanisms have been identified to accomplish this task and have been described in this and other applications made by the disorder. The basic method of reducing the disturbance of the system is to indicate only one binary state by injecting light into the optical communication system. A source is a time-domain formed in order to generate a production intensity in which the source is indicative of one logical binary state, for example logical one. Light is not provided to indicate Logical 0. This has the effect of reducing the overall failure in the system. Of course, particularly preferred coding schemes, including those receiving and receiving other channels with complementary filtration, provide a very important and fundamental mechanism for reducing disturbances.

It is also possible to reduce the disturbance in the signal sensitive circuit of translation or reception. The signals in the two channels of reception are preferably sensitive in different ways, for example in the form of combining light from each channel to another photodiode pair in the back-to-back form. The electricity production at the photodiode will then be a different measurement of the signal received on both channels. In particular in embodiments of the invention, the electrical production signal has low pass filtration and is provided to electrically squared circuit elements such as diodes. The square element or limiter may also be used to amplify the increasing portion of the received electrical signal, preferably eliminating the decreasing portion of the received electrical signal. The decreasing portion of the electrical signal is immediately identified as noise and can be removed to improve the signal to the noise ratio of the overall system.

The preferred electrical system illustrated diagrammatically in FIG. 13 also provides a mechanism to reduce disturbances. The subsystem described in FIG. 13 is provided with further details in addition to the back-to-back diode arrangement indicated at 116 in FIG. Two complementary filtered optical signals are provided to the back-to-back diodes that affect both the squared optical response as well as the distinct amplification action. Other combinations of optical sensitizers, distinct sensitizers and electrical amplifications are known and can be well substituted for this action. In a particularly preferred embodiment of the invention, the electricity produces a signal in the diode pair and is filtered in low pass by filter 380. For the translator instrumented in a semiconductor device, the sensitive circuit is also provided in the same chip or in a single PIC circuit. Low pass filtration is implemented to remove high frequency noise signals. In the described system, which can receive one of a plurality of channel image data from an optical communication system at a data rate of approximately 622 MHz, the filtration can pass frequencies below about 630-650 MHz. The filtered electrical signal is then provided to an electrical squared circuit element 382 such as a diode. The square element or limiter may preferably also be used to eliminate the decreasing portion of the received electrical signal and to amplify the increasing portion of the received electrical signal. The decreasing portion of the electrical signal is identified as noise and can therefore be removed to improve the signal to the noise ratio of the overall system. The electrical signal produced from the limiter 382 is analyzed to respond to signals above the starting value that are considered to be delivered.

Another way to reduce the disturbance is to reduce the correlation between the others of the noise signal. The difficulty observed by the inventors is an unwanted level of instantaneous correlation between different sources when instrumenting the source plan shown in FIG. The level of correlation may cause unwanted levels of correlation between the noise source's correlation or other communication channels associated with other sources. Thus, preferred embodiments do not correlate with other sources. This can be done by inserting different optical delays for each production process of the different source channel. One simple mechanism for doing this is described in FIG. 14. Many distinct sources 400-403 are defined using, for example, the technique described in FIG. 11 so that the sources provide similar optical production with band widths and force distributions of similar spectra. While four sources are shown, the system will typically include all sources that match 128 or 128 or more users.

The production of each source 400-403 is passed through a delay which reduces the one-time agreement between the other sources. The optical delay includes an optical delay line or an extended optical propagation path. Allowing each source to pass through a different length of fiber delay line is the most desirable mechanism to provide a moderate delay. The delay is optionally generated using free space propagation through another optical path. Fiber retardation is desirable because it can be instrumented using only minimal space, so that the entire optical system can be provided in a sufficiently small space to allow a wider range of instrumentation for the system representing this aspect of the present invention. Referring back to FIG. 14, an appropriate delay is effected as it passes through the production of each source 400-403 through the different lengths of single mode fibers 404-407. Different length fibers are chosen to impose a delay between about one and two or more data rates in successive sources. Considering a data rate of approximately 622 Mbt / sec, a suitable delay can be made by adding about 1.5 feet of optical fiber (equivalent ˜1.5 GHz) for each required delay. The added length of the fiber for the first source 400 was added as it represents the baseline. 1.5 feet of added fiber 405 for the second source 401 includes a production path and for the third source 402, 3 feet of fiber 406 below the baseline length of fiber 404 is provided. Similarly, production from source 403 combines through fiber 407, which is about 4.5 feet (˜4.5 GHz) longer than fiber 404. Each user in the system having a total of 128 users or more or the same number of various 128 channels of various data is provided to a source originating from a central source and delayed in different amounts from all of the other sources. Of course, it will be appreciated that other mechanisms for performing optical delay are known and may be implemented to obtain similar results.

Another way to reduce the disturbance and what has been observed to be particularly effective is the use of data conditioning schemes that limit the amount of time the source remains intact. A time domain for controlling data is provided to the optical communication system by adjusting the source. The source can be adjusted directly or by passing the source light through a source adjustable element. In a preferred embodiment of the invention, the adjustment is obtained and a predetermined amount of light pulse is provided to the optical system when one binary value is delivered and no light is provided to the optical system when the other binary value is delivered. A schematic example of adjusting the source of data flow is shown in FIG. 3.

In a regulated data flow, there is typically a clock that determines the data rate for the regulated binary data and the binary data flow is typically characterized by a duty cycle. This is illustrated schematically in FIG. 15, where the various data flows (a)-(c) are seen in the background of the clock cycle at the beginning identified by the vertical dashed lines. Conventionally, each clock cycle defines a data period and the data may consume some or all clock cycles. If all clock cycles are consumed by the data, the duty cycle is described as 100%. If the data is consumed only half of the clock cycle, the duty cycle is described as 50%. This includes the signal shown in FIG. It is desirable to reduce the time of light injected into the system to reduce the amount of disturbances present between the various users or in channels within the system. As above, data conditioning is performed in a particularly preferred embodiment of the present invention using a data flow having a duty cycle of 25% as shown in FIG. 15 (b) or having a duty cycle of 12.5%. shorter as shown in c).

In a particularly preferred embodiment of the invention, it is preferred that the duty cycle is reduced to a low but still acceptable level using a duty cycle of generally 50% or less. This has the effect of reducing the overall optical signal present in the optical fiber system at some point. On the other hand, the use of shortened duty cycles reduces the amount of light in the system, thereby reducing the amount of disturbances tested by noise and desirable signals. Schematics exist to significantly reduce the duty cycle. However, like real materials, the reduction in duty cycle must be limited to expansion in order to keep the optical signal sensitive. Amplification of the input source or amplification of the response scheme must increase the rate of decrease in the data duty cycle. The noise floor associated with the amplifier sets a limit on how small the duty cycle is reduced. The duty cycle cannot reduce the amplifier noise below the level at which the signal is dominant.

The data source can be selected to provide a data flow of the required duty cycle characteristic. On the other hand, it is typically desirable to provide more flexibility if any input data flow, for example the 50% duty cycle flow described in FIG. 15 (a), can be converted into a relatively short duty cycle pulse. FIG. 16 schematically illustrates an apparatus for switching input data flows such as that of FIG. 15 (a) into the data flow as shown in FIG. 15 (b) or 15 (c). The circuit of Figure 16 is installed between the data source and the regulator. The electrical signal travels along two paths for the signal rate to pass through the delay element 422. Delay element 422 delays with respect to the undelayed signal of the other path. Both signals are recombined by recombiner 424 in a way that produces a positive pulse, as long as both the undelayed signal and the delayed signal are "1". Delay circuit 422 is a planned delay or includes a series of inverters. The recombination group is, for example, an excluded OR gate. By using the circuit of FIG. 16, a pulse of any selected duty cycle can be provided.

The present invention is not limited to the specific embodiments described below, as long as the present invention is particularly emphasized in certain preferred embodiments of the present invention. Ordinarily, those skilled in the art will recognize that certain modifications and variations are made in the specific embodiments of the present invention within the guidelines of the present invention. For example, as long as the above embodiments are described in the terminology of communication systems to convey fibers, the appearance of the present invention is used immediately above the air optical system. As above, the scope of the present invention will be determined by the claims that follow.

Claims (46)

Light source; A data source providing a data stream; And An encoder for receiving light output from the light source, The encoder includes a first spectral filtration assembly comprising a first code, the first code being a sequence of N digits each having one of at least two values, the assembly each outputting a light source. By separating into N spectral components corresponding to one digit of the first code, the output of the light source is spectrally encoded using the first code, and each spectral component is attenuated according to the value of the corresponding code digit. Recombine the spectral components to produce an encoded optical signal, Wherein the encoder is coupled to a data source to modulate the output of the light source to generate a data-modulated-encoded light signal. The method of claim 1, The first code is selected from a set of unipolar codes, and each code in the set is orthogonal to the difference between any other code in the set and the complement of the other code. An optical communication system characterized by the above. The method of claim 1, A decoder coupled to receive the optical signal from the optical fiber and recover data transmitted from the optical fiber, Wherein the decoder comprises a phase insensitive optical power separator for dividing the received optical signal into first and second optical components of approximately equal power. The method of claim 3, wherein The decoder includes second and third spectral filtration assemblies coupled to receive the first and second light components; And A photodetector provided to receive the first and second filtration components of the received light, Wherein the second spectral filtration assembly comprises a first cord, the third spectral filtration assembly comprises repair of the first cord, and wherein the second and third spectral filtration assemblies comprise a first and a second of the received light. 2 output the filtration components, And the photodetector provides an electrical signal output. The method of claim 1, And the encoder is a photonic integrated circuit. The method of claim 1, And said first spectral filtration assembly comprises an array waveguide grating. The method of claim 4, wherein And the spectral filtration assembly comprises an array waveguide grating. The method of claim 4, wherein And the spectral filtration assembly comprises a plurality of array waveguide gratings. The method of claim 4, wherein Wherein said decoder is formed at least in part as a photonic integrated circuit. The method of claim 9, And wherein the encoder is formed at least in part as a photon integrated circuit. The method of claim 4, wherein The electrical signal output is indicative of a differential measurement between the first and second filtration components of the received light. The method of claim 4, wherein The electrical signal output is provided to a limiting circuit for removing an electrical noise signal having an opposite sign of the recovered data. The method of claim 4, wherein And said electrical signal output is provided to a limiting circuit comprising an electric square law detector. The method of claim 3, wherein The phase unreacted optical power separator is: A first polarization reaction element arranged to receive an optical signal and to separate the optical signal into first and second optical components; A first beam path along which the first light component moves and a second beam path along which the second light component moves accordingly; A polarization modifier disposed along the second beam path; And A beam splitter that receives the first and second light components and splits the first and second light components into third and fourth light components, As the output from the first polarization reaction element, the first light component has a first polarization, the second light component has a second polarization, and the polarization modifier is a polarization of the second light component mainly being a first polarization. Optical communication system, characterized in that for changing to be. A data source providing a data stream; And An encoder that provides an optical output that is modulated using the data stream and includes a first code, The first code is selected from a set of unipolar codes, each code in the set orthogonal to the difference between any other code in the set and the complement of the other code, wherein the code in the set is Defined as a sequence of N digits having one of at least two values, each of the N digits of the code corresponding to one of the N potential spectral ranges that can be output from the encoder, The light output from the encoder includes M components corresponding to M different spectral ranges within the N potential spectral ranges, Each of the M components is characterized by an Mth component light level corresponding to a value of a corresponding code digit, The optical power of the encoder to be wide spectrum light modulated using a code function defined by the data stream and spectrum, And the encoder comprises a photonic integrated circuit. The method of claim 15, Wherein the first code is a discrete analog function, and M is equal to N. The method of claim 15, Wherein the first code is binary and M is less than N. 3. The method of claim 15, And said first code is defined within a set of N waveguides. The method of claim 18, M of said waveguides are terminated by a reflective coating. The method of claim 15, And the encoder comprises an array of N sources. The method of claim 15, And said encoder comprises a spectral spreading element which is a photon integrated circuit. The method of claim 21, And said spectrum spreader comprises an array of waveguides. The method of claim 22, The spectrum scattering device is an optical communication system, characterized in that the curved grating. The method of claim 15, And wherein the first code is defined within a set of N waveguides by a switch for changing the optical characteristics of the waveguide. The method of claim 24, And said switch generates heat to alter optical characteristics of said waveguide. The method of claim 24, And the data source comprises a broadband light source modulated using the data stream. The method of claim 15, A decoder coupled to receive the optical signal from the optical fiber and recover data transmitted from the optical fiber, Wherein said decoder comprises a phase unreacted optical power separator for separating received optical signals into first and second optical components of approximately equal power. The method of claim 27, The decoder is: Second and third spectral filtering assemblies coupled to receive the first and second optical components; And A photodetector provided to receive the first and second filtration components of the received light, Wherein the second spectral filtration assembly comprises a first cord, the third spectral filtration assembly comprises repair of the first cord, and wherein the second and third spectral filtration assemblies comprise first and first of the received light. And 2 outputting the filtering component, wherein the photodetector provides an electrical signal output. The method of claim 28, The electrical signal output is indicative of a difference amount between the first and second filtration components of the received light. The method of claim 31, wherein The electrical signal output is provided to a limiting circuit for removing an electrical noise signal having an opposite sign of the recovered data. The method of claim 28, And said electrical signal output is provided to a limiting circuit comprising an electric square law detector. The method of claim 27, The phase unreacted optical power separator is: A first polarization reaction element arranged to receive an optical signal and to separate the optical signal into first and second optical components; A first beam path along which the first light component moves and a second beam path along which the second light component moves accordingly; A polarization modifier disposed along the second beam path; A beam splitter that receives the first and second light components and splits the first and second light components into third and fourth light components, As the output from the first polarization reaction element, the first light component has a first polarization, the second light component has a second polarization, and the polarization modifier is a polarization of the second light component mainly being a first polarization. Optical communication system, characterized in that for changing to be. An optical communication system comprising a decoder coupled to receive an optical signal from an optical communication system and recover the transmitted data, The decoder is: An optical power separator for dividing the received optical signal into first and second optical components of approximately the same power; First and second spectral filters coupled to receive the first and second light components; A photodetector provided to receive the first and second filtration components of the received light, The first spectral filter includes a first code and the second spectral filter includes the complement of the first code, wherein the first and second spectral filters filter the first and second filtration components of the received light. Output, The photodetector provides an electrical signal output, The first code is selected from a set of monopole codes, each code in the set orthogonal to the difference in complement of the other code and any other code in the set, wherein the code in the set is at least one digit in each digit. Defined as a sequence of N digits having one of two values, each N digits of the code corresponding to one of the N potential spectral ranges in which the code set is defined, The received optical signal is a broad spectral light modulated using a code function defined by a spectrum with M components corresponding to different M spectral ranges within the data stream and the N potential spectral range, And the decoder comprises a photon integrated circuit. The method of claim 33, wherein Wherein the first code is a discrete analog function, and M is equal to N. The method of claim 33, wherein Wherein the first code is binary and M is less than N. 3. The method of claim 33, wherein And said first code is defined within a set of N waveguides. The method of claim 36, M of said waveguides are terminated by a reflective coating. The method of claim 33, wherein And said first filter comprises a spectral spreading element which is a photon integrated circuit. The method of claim 38, And said spectral spreader comprises an array of waveguides. The method of claim 38, The spectrum scattering device is an optical communication system, characterized in that the curved grating. The method of claim 33, wherein And wherein the first code is defined within a set of N waveguides by a switch for changing the optical characteristics of the waveguide. 42. The method of claim 41 wherein And said switch generates heat to alter optical characteristics of said waveguide. The method of claim 33, wherein The electrical signal output is indicative of a difference amount between the first and second filtration components of the received light. The method of claim 43, And the electrical signal output is provided to a limiting circuit for removing an electrical noise signal having an opposite sign of the recovered data. The method of claim 33, wherein And the electrical signal output is supplied to a limiting circuit including an electric square detector. The method of claim 33, wherein The optical power separator is: A first polarization reaction element arranged to receive an optical signal and to separate the optical signal into first and second optical components; A first beam path along which the first light component moves and a second beam path along which the second light component moves accordingly; A polarization modifier disposed along the second beam path; And A beam splitter for receiving the first and second optical components and separating the first and second optical components into third and fourth optical components, As the output from the first polarization reaction element, the first light component has a first polarization, the second light component has a second polarization, and the polarization modifier is a polarization of the second light component mainly being a first polarization. Optical communication system, characterized in that for changing to be.