KR101355011B1 - Receiver for optical transverse-mode-multiplexed signals - Google Patents

Abstract

Exemplary optical receivers of the present invention receive a wide transverse mode multiplexed (TMM) signal over a multimode fiber supporting a plurality of transverse modes. The optical receiver has a plurality of photo detectors operatively coupled to the digital signal processor configured to process the TMM signal to determine its mode composition. Based on the determined mode composition, the optical receiver demodulates each of the independently modulated components of the TMM signal to recover the encoded data on the TMM signal at the remote transmitter.

Description

Wide Transverse-Mode-Receiver for Multiplexed Signals {RECEIVER FOR OPTICAL TRANSVERSE-MODE-MULTIPLEXED SIGNALS}

Cross-Reference to Related Applications

The claims of this application are filed on the same day as this application, and is entitled "Transverse-Mode Multiplexing for Optical Communication Systems." To a claim in US Patent Application No. 12 / 492,399 (agent case number Essiambre 22-36) by Essiambre, R. Ryf and P. Winzer.

TECHNICAL FIELD The present invention relates to optical communication equipment, and more particularly, to equipment that enables lateral mode multiplexing (TMM) in an optical communication system.

This section introduces aspects that may help promote a good understanding of the present invention (s). Thus, the discussion in this section should be read in this respect and should not be understood as an admission as to what is prior art or what is not prior art.

Wireless communication systems with multiple-input multiple-output (MIMO) capabilities increase the overall transmission capacity by utilizing multi-path spreading (instead of trying to relax) in the wireless channel. In particular, wireless MIMO improves efficiency and reliability through the use of multiple antennas at the transmitter and receiver. The resulting increase in average throughput is realized at the expense of greater complexity in signal processing and hardware implementation, without sacrificing additional spectral bandwidth or higher signal power.

In optical communication systems, for example, since the mode dispersion in multimode fibers is similar to multipath delay in wireless transmission media, a MIMO approach to increasing transmission capacity is feasible. As a result, optical MIMO can be leveraged to take advantage of the inherently high transmission capacity of multimode fibers. However, hardware that implements optical MIMO has not been fully developed yet.

Various embodiments of an optical receiver for optical transverse-mode-multiplexed (TMM) signals are disclosed herein. An exemplary optical receiver of the present invention receives a TMM signal over a multimode fiber that supports multiple transverse modes. The optical receiver has a plurality of optical detectors operatively coupled to the digital signal processor configured to process the TMM signal to determine the mode composition. Based on the determined mode composition, the optical receiver demodulates each of the independently modulated components of the TMM signal to recover the encoded data on the TMM signal at the remote transmitter.

According to one embodiment, (A) a tap module configured to sample an optical TMM signal having N independently modulated components to generate K samples per signaling interval, where N and K are greater than one. An integer and K≥N, said tap module; (B) a local oscillator (LO) source configured to generate an optical local oscillator (LO) signal; And (C) K coherent detectors optically coupled to the tap module and the LO source, respectively. Each of the K coherent detectors comprises (i) mixing each optical sample and the LO signal to produce one or more optical interference signals; (Ii) configured to convert the one or more optical interference signals into one or more electrical signals representing in-phase and quadrature components of the light sample. The optical receiver is operably coupled to the K coherent detectors and processes the electrical signals generated by the coherent detectors to recover data carried by each of the N independently modulated components of the TMM signal. It further has a digital signal processor (DSP) configured to. The optical receiver receives the TMM signal over a multimode fiber that supports multiple transverse modes. At the remote end of the multimode fiber, each independently modulated component of the TMM signal corresponds to each single transverse mode of the multimode fiber.

According to another embodiment, an optical receiver having a tap module configured to sample a TMM signal having N independently modulated components to generate K optical samples per signaling interval, wherein N and K is greater than 1 It is a large positive integer and K≥N. The tap module receives the TMM signal over a multimode fiber that supports multiple transverse modes. The optical receiver further has (i) a local oscillator (LO) source configured to generate an optical local oscillator (LO) signal and (ii) K coherent detectors optically coupled to the tap module and the LO source, respectively. Each of the K coherent detectors are: (a) each phase filtered beam having a PFS pattern corresponding to the phase / field intensity (PFS) pattern of each selected transverse mode of the multimode fiber by phase filtering the LO signal. Generates; (b) mix each optical sample and phase filtered beam to generate one or more optical interference signals; (iii) configured to convert the one or more optical interference signals into one or more electrical signals representing in-phase and quadrature components of the light sample. The optical receiver is operably coupled to the K coherent detectors and processes electrical signals generated by the coherent detectors to retrieve data carried by each of the N independently modulated components of the TMM signal. It further has a digital signal processor (DSP) configured to recover.

According to another embodiment, (i) split a light beam corresponding to an optical TMM signal received over a multimode fiber having a plurality of independently modulated components and supporting a plurality of transverse modes into a plurality of sub-beams and ; (Ii) split the light beam corresponding to the local oscillator (LO) source into a second plurality of sub-beams; (Iii) An optical receiver having a plurality of beam splitters configured to mix the first and second plurality of sub-beams to produce two or more mixed light beams. The optical receiver comprises: (a) a first arrayed detector configured to detect a first interference pattern corresponding to a first light beam of the two or more mixed light beams; (b) a second arrayed detector configured to detect a second interference pattern corresponding to a second one of the two mixed light beams; And (c) operatively coupled to the first and second arrayed detectors, processing the first and second interference pattern to determine a mode composition of the TMM signal, and based on the mode composition, independently of the TMM signal. It further has a digital signal processor (DSP) configured to recover data carried by the modulated components.

According to yet another embodiment, there is provided an optical receiver having a tap module configured to sample an optical transverse-mode-multiplexed (TMM) signal having N independently modulated components to generate K optical samples per signaling interval. Where N and K are positive integers greater than 1 and K ≧ N. The optical receiver further has (i) a local oscillator (LO) source configured to generate an optical local oscillator (LO) signal and (ii) K coherent detectors optically coupled to the tap module and the LO source, respectively. Each of the K coherent detectors (a) mixes each optical sample and the LO signal to produce one or more optical interference signals, and (b) converts the one or more optical interference signals into in-phase component and quadrature of the optical sample. And convert one or more electrical signals representing the phase component. The optical receiver is operably coupled to the K coherent detectors and processes electrical signals generated by the coherent detectors to retrieve data carried by each of the N independently modulated components of the TMM signal. It further has a digital signal processor (DSP) configured to recover. The optical receiver receives the TMM signal over a multimode fiber that supports multiple transverse modes. The tap module comprises: (A) K multimode fiber (MMF) combiners each tapping off optical power from the multimode fiber to a single mode fiber to generate a corresponding optical sample of the TMM signal; And (B) K-1 mode scramblers each disposed between two adjacent MMF couplers.

The patent or application file includes at least one drawing made in color. Copies of this patent or patent application publication with color drawing (s) will be provided by the Agency upon request and payment of the necessary fee.

Other aspects, features and advantages of various embodiments of the invention will become more fully apparent from the following detailed description and the accompanying drawings, for example.

1 is a block diagram of an optical communication system in which various embodiments of the present invention may be practiced.
2A-2H are cross-sectional views of optical fibers that may be used in the system of FIG. 1 in accordance with various embodiments of the present invention.
3A and 3B illustrate an optical transmitter that may be used at a node of the system shown in FIG. 1 in accordance with an embodiment of the present invention.
4A and 4B illustrate an optical mode combining (OMC) module that may be used in the transmission of FIG. 3 in accordance with an embodiment of the present invention.
5 is a block diagram of an OMC module that may be used in the transmitter of FIG. 3 in accordance with another embodiment of the present invention.
6 is a block diagram of an OMC module that may be used in the transmitter of FIG. 3 in accordance with another embodiment of the present invention.
7 is a block diagram of an optical transmitter that may be used at a node of the system shown in FIG. 1 in accordance with another embodiment of the present invention.
8 is a block diagram of an optical transmitter that may be used at a node of the system shown in FIG. 1 in accordance with another embodiment of the present invention.
9 is a block diagram of an optical receiver that may be used at a node of the system shown in FIG. 1 in accordance with an embodiment of the present invention.
10A and 10B illustrate tap modules and coherent detectors that may be used in the optical receiver shown in FIG. 9 in accordance with one embodiment of the present invention.
FIG. 11 illustrates a tap module that may be used in the optical receiver shown in FIG. 9 in accordance with another embodiment of the present invention.
12 is a block diagram of an optical receiver that may be used at a node of the system shown in FIG. 1 in accordance with another embodiment of the present invention.

Optical communication systems

1 shows a block diagram of an optical communication system 100 in which various embodiments of the invention may be practiced. System 100 has a plurality of communication nodes 110 interconnected through a network of optical communication links 120. The system 100 further has an optical branch / coupling multiplexer (ADM) 130, an optical amplifier 140, and an optical line splitter 150, all of which are variously arranged between the nodes 110.

Each node 110 has optical multiple-input multiple-output (MIMO) capabilities achieved through the use of lateral-mode multiplexing (TMM). Node 110 generally includes an optical transmitter and an optical receiver (neither explicitly shown in FIG. 1) to enable bidirectional communication between the various nodes of system 100. In addition to TMM multiplexing, individual nodes 110 may also use wavelength division multiplexing (WDM) and / or polarization multiplexing (PM), or both. Representative embodiments of an optical transmitter and receiver that can be used at individual nodes 110 are described in more detail below in the corresponding subsections herein.

Each optical communication link 120 includes: (i) a single mode fiber; (Ii) multimode fibers; (Iii) multicore fibers; And (iii) a bundle of single mode fibers. In one embodiment, the multimode fiber used in the link 120 supports between two hundred transverse modes and about one hundred transverse modes. In an alternative embodiment, the multimode fiber supports more than one hundred transverse modes. In one embodiment, each core of the multicore fiber used in the link 120 supports a single transverse mode. In an alternative embodiment, some or all cores of the multi core fiber support multiple transverse modes as well as the super-modes of the multi core fiber as a whole.

As used herein, the term "transverse mode" has an electric field or magnetic field distribution (hereinafter referred to as an optical field distribution) in a plane perpendicular to (i.e., transverse to) a propagation direction that is substantially independent of the propagation distance. It refers to induced electromagnetic waves. In particular, if the loss or gain of optical power in the fiber is excluded, the optical field distributions of the modes measured at two different locations along the fiber reflect the overall phase change caused by the mode between these two locations. It will only differ by a factor. Each transverse mode is the eigenmode of the fiber and different transverse modes are orthogonal to each other. In general, an optical fiber can support a fixed number of transverse modes whose optical field distributions and propagation constants are clearly determined by waveguide structure, material properties, and optical frequency (wavelength). Note that the concept of transverse modes is applicable to various types of fibers including multicore fibers. For example, the transverse mode of an individual core in a multicore fiber is also the transverse mode of that multicore fiber as a whole.

In one embodiment, optical branch / combination multiplexer 130 is a reconfigurable branch / combination multiplexer. Since link 120 typically features a relatively high degree of inter-mode mixing, node 110 generally uses the same optical frequency to properly process the TMM signal and recover the data carried by that signal. It is necessary to receive all transverse modes with (wavelength). As a result, the multiplexer 130 (i) diverges from the incoming link 120 all transverse modes with the same optical frequency and / or (ii) all populated transverse modes with the same optical frequency. To the outgoing link 120. In other words, the multiplexer 130 implements conventional WDM branching / coupling functionality, but acts entirely on the TMM multiplex of each particular wavelength.

To support the intended functions, multiplexer 130 uses narrowband interleaver type optical filters having substantially the same transmission characteristics for all transverse modes. In addition, the multiplexer 130 has a relatively low level WDM crosstalk (ie, crosstalk between different optical frequencies of the WDM multiplexer). The latter feature may be used, for example, to (i) perform the necessary filtering in a single mode domain (see, eg, FIG. 8) before all combining modules, (ii) use sink-type waveform shaping, and / or (Iii) by using Orthogonal Frequency Division Multiplexing (OFDM).

If system 100 uses multi-core fibers in links 120, multiplexer 130 unifies a selected set of cores (which can be all cores of the multi-core fiber or any subset thereof). It can be designed to treat as an entity, combining and / or diverting wavelength channels from the whole set at the same time. If the link 120 has a relatively low level of crosstalk between different cores, the multiplexer 130 combines communication signals to each individual core while treating the inter-core crosstalk as noise / fault. It can be designed to branch communication signals from each individual core.

In various embodiments, optical amplifier 140 may be a concentrated amplifier or a distributed amplifier. In general, system 100 may be designed to preserve a single characteristic of the mode mixing matrix across the entire link between two communication nodes 110. As a result, optical amplifier 140 is designed to exhibit substantially the same gain for all transverse modes of link 120.

In one embodiment, optical amplifier 140 has a relatively long fiber amplifier (i.e., longer than about 100 m) having (i) a plurality of active sections and (ii) a plurality of mode scramblers interposed between the active sections. to be. Each active section provides a medium gain (eg, between about 1 dB and about 5 dB). Mode scramblers (also known as mode mixers) are optical devices that induce relatively large mode coupling between different transverse modes. Ideally, the mode scrambler produces a statistically uniform mode mix at the output that is substantially independent of the mode variance received by the mode scrambler at the input. Those skilled in the art will understand that the combination of medium gain and relatively frequent mode scrambling in each active section ensures that all transverse modes applied to amplifier 140 receive substantially the same amount of amplification.

In one embodiment, optical line splitter 150 is reconfigurable to enable desired routing of optical signals between different nodes 110. As already mentioned above, in order to properly decode individual independently modulated components of a TMM multiplex, node 110 generally needs to receive the entire TMM multiplex. Thus, optical line splitter 150 is designed to operate on the TMM multiplex corresponding to each wavelength as a whole while performing WDM routing functions. Those skilled in the art will appreciate that optical line splitter 150 may generally be implemented as a number of identical components as multiplexer 130.

Illustratively, the system 100 has four nodes 110, one optical branch / combination multiplexer 130, one optical amplifier 140, and one optical line splitter 150. Is shown. Those skilled in the art will appreciate that in other embodiments, the system 100 may employ different numbers of nodes 110, optical branch / combination multiplexers 130, optical amplifiers 140, and / or optical line splitters 150. It will be appreciated that you may have. Those skilled in the art will also appreciate that these elements may be arranged and interconnected in a different manner than shown in FIG. 1.

Optical fiber

2A-2H show cross-sectional views (not scaled) of optical fibers that may be used in system 100 in accordance with various embodiments of the present invention. In particular, the various optical fibers shown in FIGS. 2A-2H may include nodes 110, optical communication links 120, optical branch / coupling multiplexers 130, optical amplifiers 140, and / or optical lines. May be used in the dispensers 150.

2A shows a cross-sectional view of single mode fiber 210. The fiber 210 has a cladding 212 and a core 216. Core 216 has a relatively small diameter that allows fiber 210 to support a single transverse mode for each wavelength from the range of wavelengths used in system 100.

2B shows a cross-sectional view of the multimode fiber 220. Fiber 220 has a cladding 222 and a core 226. The fiber 220 is different from the fiber 210 in that the core 226 has a larger diameter than the core 216. In various embodiments, the diameter of the core 226 is selected such that the fiber 220 can support the desired number of transverse modes selected from a range between two hundred and about one hundred.

2C shows a cross-sectional view of multimode fiber 230. The fiber 230 has a cladding 232 and a core 236. Core 236 has a larger diameter than core 226, which enables fiber 230 to support more than about one hundred transverse modes.

2D shows a cross-sectional view of multi-core fiber 240. Fiber 240 has a first (outer) cladding 242 and a second (inner) cladding 244. The fiber 240 further has a plurality of cores 246 enclosed within the inner cladding 244. The diameter of each core 246 may be selected to allow the core to support a single transverse mode or multiple transverse modes.

In one embodiment, the fiber 240 is designed for use in the optical amplifier 140. In particular, inner cladding 244 and / or cores 246 are doped (eg, with erbium ions) to provide a photoactive medium. The light pumps (not explicitly shown in FIG. 1) of the amplifier 140 inject the light pump waves into the inner cladding 244, which are due to the refractive index opposite to the outer cladding 242. It may be guided along the longitudinal axis of the fiber 240. Guided light pump waves couple from inner cladding 244 to individual cores 246, thereby providing a source of energy for amplification of the optical signals guided by the cores. The inner cladding 244 has a diameter that allows this cladding to function as a multimode core for the light pump waves, which ensures that the pump energy is distributed substantially uniformly among the cores 246.

2E shows a cross-sectional view of the multi-core fiber 250. Fiber 250 has a cladding 252 and a plurality of cores 256. Cores 256 are distributed in cladding 252 such that there is a relatively large separation between the cores. Due to the relatively large distribution, the amount of inter-core crosstalk in the fiber 250 is small, which allows the individual cores 256 to function as separate and independent conduits for optical communication signals. In various embodiments, each individual core 256 may be designed to support a single transverse mode or multiple transverse modes.

2F shows a cross-sectional view of multi-core fiber 260. Fiber 260 has a cladding 262 and a plurality of cores 266. The cores 266 are small enough that the separation between the cores (i) produces a moderate amount of linear coupling between the cores, and (ii) to produce a relatively small amount of non-linear coupling between the cores. Distributed within the cladding 262 to be sufficiently large. If each of the cores 266 supports each single transverse mode, these properties of the fiber 260 may be used to generate a relatively small number of well defined and spatially separated transverse modes relative to the fiber as a whole. have.

2G shows a cross-sectional view of multi-core fiber 270. Fiber 270 has a cladding 272, a first plurality of cores 276, and a second plurality of cores 278. Cores 276 have a smaller diameter than cores 278. The separation between the various cores in the fiber 270 is similar to the separation used in the fiber 260 (FIG. 2F).

One reason for having two different core types in the fiber 270 is to create two types of transverse modes characterized by different propagation constants. Mismatch of propagation constants results in group-rate differences, which are generally useful for reducing the deleterious effects of fiber nonlinearity. For example, the deleterious effects of cross phase modulation can be significantly reduced for signals from different WDM channels when different WDM channels have a relatively large group-rate difference. In one embodiment, cores 276 and 278 are distributed throughout cladding 272 to achieve maximum spatial separation between cores of the same type.

2H shows a cross-sectional view of the multi-core fiber 280. Fiber 280 has a cladding 282, a first plurality of cores 286, and a second plurality of cores 288. Although the cores 286 and 288 have the same diameter, they are made of materials with different refractive indices. The refractive index difference causes the cores 286 and 288 to have different propagation constants, which will reduce the deleterious effects of fiber nonlinearity through a mechanism qualitatively similar to the mechanism in which fiber 280 is effective in fiber 270 (FIG. 2G). To be able.

Those skilled in the art will appreciate that in addition to the fibers shown in FIGS. 2A-2H, other types of fibers are also possible. For example, a multi-core fiber having two or more different sized cores of two or more different materials may be manufactured to implement the features shown in both FIGS. 2G and 2H.

As used herein, “multi-path fiber” includes multimode fibers (eg, fibers 220 and 230 (FIGS. 2B and 2C)) and multi-core fibers (eg, fibers Fields 240 to 280 (FIGS. 2D to 2H).

Optical transmitter

3A and 3B illustrate an optical transmitter 300 that may be used at node 110 (FIG. 1) in accordance with one embodiment of the present invention. In particular, FIG. 3A shows a block diagram of the transmitter 300. 3B graphically illustrates the operation of the optical mode-combining (OMC) module 340 used in the transmitter 300.

3A illustratively illustrates transmitter 300 as coupled to communication link 120 via output fiber 350. Fiber 350 is generally the same type as the fiber used in the immediately adjacent section of communication link 120. As already described above, communication link 120 may be implemented using any suitable type of fiber as shown in FIG. 2. The following description is illustrative and corresponds to an embodiment where the output fiber 350 is similar to the fiber 220 (FIG. 2B). Based on this description, those skilled in the art will understand how to design other embodiments of a transmitter 300 suitable for coupling optical communication signals to other types of fibers.

The transmitter 300 has a laser 310 configured to produce an output light beam of a designated wavelength. Beam splitter 320 splits the beam generated by laser 310 in N manners, and combines the resulting N beams into N single mode fibers 322, where N is an integer greater than one. to be. Each fiber 322 directs its respective beam to a corresponding light modulator 330, where the beam is modulated with data supplied to the modulator via a control signal 328. Note that different modulators 330 or suitable modulator devices may modulate respective light beams using different independent or correlated data streams derived from control signal 328. In an exemplary configuration, each modulator 330 modulates its light beam based on the corresponding independent data stream intended for transmission from the transmitter 300 to the remote receiver. The modulated light signals generated by the modulator 330 ultimately act as independently modulated components of the TMM signal applied to the fiber 350 by the OMC module 340.

In an alternative embodiment, the laser 310 may be directly coupled to the modulators 330 or may be coupled to the modulators through free space rather than through fibers.

One function of the OMC module 340 is to properly couple the N modulated optical signals received over the N single mode fibers 332 to the fiber 350. In particular, each modulated light signal received by the OMC module 340 is substantially coupled to a single selected transverse mode of the fiber 350 and different modulated optical signals are coupled to different transverse modes. As used herein, the phrase “to substantially combine a signal into a single transverse mode” may have two possible but not mutually exclusive meanings. According to a first meaning, this phrase means that at least about 50% (and possibly at least about 80% or 90% or more) of the total energy of the signal binds to one selected transverse mode. According to a second meaning, such phrases refer to, for a portion of the total energy of the signal coupled to the multimode fiber, at least about 50% (and perhaps at least about 80% or 90% or more) of that portion in one selected transverse mode. It means to go ahead and the rest of that part to go to other transverse modes. Individual optical signals are substantially coupled to a single transverse mode of the multimode fiber (eg, fiber 350) at the proximal end of the fiber (eg, by OMC module 340) to launch into the multimode fiber. When converted into the light component of the TMM signal, the light component of the TMM signal can be said to "correspond to a single transverse mode of the multimode fiber at the proximal end of the multimode fiber".

In one embodiment of the transmitter 300, the number N is selected to be equal to the total number of transverse modes supported by the fiber 350. In other words, this embodiment of the transmitter 300 utilizes an OMC module 340 that can populate each and all of the multimode fibers 350 with each independently modulated optical signal.

3B graphically illustrates the light beam shaping performed by the OMC module 340. In particular, the different panels of FIG. 3B show various phase / field intensity (PFS) patterns that may be produced by the OMC module 340 at the end 348 of the fiber 350, and the different panels show different light of the OMC module. Corresponds to channels. Each PFS panel is represented in FIG. 3B using a color scheme in which (i) the degree of color saturation represents the optical field intensity, and (ii) the color itself represents the phase of the optical field. For example, a pale red color corresponds to a lower field intensity than the dark red color. A rainbow-like change in color from blue to red represents a continuous change in phase from -π to + π.

For each optical channel of the OMC module 340, the PFS pattern generated by that channel at the end 348 of the fiber 350 substantially matches the PFS pattern of the transverse mode assigned to that channel. Those skilled in the art will appreciate that the mode coupling loss indicated above may be caused by a mismatch between these PFS patterns. Light energy corresponding to mode coupling loss may be coupled dependently to other transverse modes of fiber 350 and / or may be rejected together by the fiber.

As used herein, “substantially matches” means that the difference between the PFS pattern generated by the optical channel and the corresponding transverse mode PFS pattern is relatively small, of two possible but not mutually exclusive criteria. Means that at least one is met. According to the first criterion, this difference is small such that at least about 50% (and possibly at least about 80% or 90% or more) of the total energy of the PFS pattern generated by the light channel couples to the corresponding transverse mode. According to the second criterion, this difference is that, with respect to the portion of the total energy of the PFS pattern generated by the optical channel coupled to the multimode fiber, at least about 50% (and about 80% or 90% or more) of this portion Proceed to the corresponding transverse mode, and the rest of the portion proceeds to other transverse modes.

Different transverse modes corresponding to different PFS patterns in FIG. 3B are labeled using the following notation. The letter "LP" stands for "linearly polarized". The numbers according to "LP" in the label provide the values of the two quantized parameters in the specified order. For the transverse mode, the first quantized parameter provides the number of phase increments of 2π magnitude per one azimuth rotation about the fiber axis, and the second quantized parameter provides the number of phase increments of π magnitude on the fiber radius. . For example, the transverse mode designated as LP01 has (i) no azimuthal phase increment, and (ii) one radial phase increment. Similarly, the transverse mode designated as LP32 has (i) three azimuthal phase increments and (ii) two radial phase increments.

If the OMC module 340 has eight optical channels, the following representative mode assignments can be used: (Ch.l) -LP0l; (Ch.2) -LPl1; (Ch. 3) -LP21; (Ch.4) -LP02; (Ch. 5) -LP31; (Ch.6) -LP12; (Ch.7) -LP41; And (Ch. 8) -LP22. Those skilled in the art will appreciate that different mode assignments are dependent on the spirit and principles of the present invention, depending on which optical channel of the OMC module 340 is configured to produce a PFS pattern that substantially matches the PFS pattern of the assigned transverse mode of the fiber 350. It will be appreciated that it can be used similarly without departing from.

Those skilled in the art will understand that FIG. 3B corresponds to one possible transverse-mode foundation set, and that other foundation sets each including a plurality of mutually orthogonal transverse modes may be similarly used to implement the OMC module 340. .

4A and 4B illustrate an OMC module 400 that can be used as the OMC module 340 (FIG. 3) in accordance with one embodiment of the present invention. In particular, FIG. 4A shows a block diagram of the OMC module 400. 4B shows phase masks 420 that can be used in OMC module 400.

OMC module 400 has two optical channels and, as such, is shown as coupled to two input fibers 332 (see also FIG. 3A). Those skilled in the art will appreciate that the OMC module 400 can be modified in a simple manner to have three or more optical channels. In particular, a new optical channel can be created by adding a set of optical elements similar to those used to form channel 2 in the OMC module 400.

The OMC module 400 has two lenses 410 each collimating each diverging light beam applied to the OMC module by each one of the fibers 332. As a result, each of the collimated beams passes through each one of the phase masks 420 to produce a corresponding phase filtered beam 422. A plurality of mirrors 430 then spatially overlap the two phase filtered beams 422 and guide the resulting " nested " beam 432 towards the fiber 350. And transparent mirror with a mirror (430 ₄₎ in part, should be noted that the mirror (430 ₁ to 430 ₃₎ are conventional non-transparent mirror. Two lenses 442 and 446 and aperture 444 compress (ie, reduce size) and spatially filter the beam 432 to reach the output beam 452 on the end 348 of the fiber 350. And generate the intended overlap of the PFS patterns shown in FIG. 3B.

Depending on the transverse modes assigned to the two optical channels of the OMC module 400, the phase masks 420 ₁ and 420 ₂ are appropriately selected from the classification of the phase masks shown in FIG. 4B, for example. . For example, if the LP11 mode of fiber 350 is assigned to a particular optical channel of OMC module 400, then a phase mask labeled LP11 in FIG. 4B is used as phase mask 420 in that optical channel. Similarly, if the LP21 mode of fiber 350 is assigned to a particular optical channel of OMC module 400, then a phase mask labeled LP21 in FIG. 4B is used as phase mask 420 in that optical channel. The combined effect of phase filtering imposed by phase mask 420 and spatial filtering imposed by aperture 444 is that the PFS patterns shown in FIG. 3B in which the optical channel is at the end 348 of the fiber 350. By generating one of the intended ones, the optical signal from the optical channel is efficiently coupled to the corresponding transverse mode of the fiber.

Note that the phase masks shown in FIG. 4B are binary phase masks (ie, phase masks that can locally impose only one of two possible phase shifts, eg, 0 or π). In particular, the phase masks corresponding to the LP01, LP02, and LP03 modes are binary phase masks. The remaining phase masks shown in FIG. 4B are "analog" phase masks because different portions of the phase mask may impose phase shifts selected from a continuous phase shift range. Analog phase masks are shown in FIG. 4B in a color scheme, where (i) different colors represent different phase shifts in consecutive 2 [pi] intervals, and (ii) different bands of the same color differ from each other by an integer multiple of 2 [pi]. Indicates.

In one embodiment, the OMC module 400 may use a single relatively large continuous phase mask instead of two separate phase masks 420 ₁ and 420 ₂ . This relatively large continuous phase mask, hereinafter referred to as a "multi-section phase mask", may include two or more phase masks from FIG. 4B, in its different sections (portions). The sections of the multi-section phase mask are arranged such that one section acts as phase mask 420 ₁ and the other section acts as phase mask 420 ₂ .

5 shows a block diagram of an OMC module 500 that may be used as the OMC module 340 (FIG. 3) in accordance with another embodiment of the present invention. OMC module 500 is generally similar to OMC module 400 (FIG. 4), and includes many of the same elements, such as lenses 410, 442, and 446, mirrors 430, and aperture 444. Use them. The description of these elements is not repeated here. Instead, the following description of the OMC module 500 focuses on the differences between the OMC modules 400 and 500.

One difference between the OMC modules 400 and 500 is that the latter uses a spatial light modulator (SLM) 520 instead of the phase masks 420. In one embodiment, the SLM 520 is a liquid-crystal-on-silicon (LCOS) SLM. Representative LCOS SLMs that can be used as SLM 520 are, for example, "Polarization Engineering" by MG Robinson, J. Chen, GD Sharp, Wiley, Chichester (England), the teachings of which are hereby incorporated by reference in their entirety. for LCD Projection, 2005, Chapter 11, pages 257-275. LCOS SLMs that can be configured for use as the SLM 520 are also disclosed, for example, in US Pat. Nos. 7,268,852, 6,940,577, and 6,797,983, all of which are incorporated herein by reference in their entirety. Suitable LCOS SLMs that can be used as the SLM 520 are manufactured by JVC and are commercially available as part of the JVC projector model DLA-HD2K.

SLM 520 has two regions 524 ₁ and 524 ₂ configured to perform the required phase filtering for each of channel 1 and channel 2 of OMC module 500. In particular, area 524 ₁ is configured to display a spatial modulation pattern that results in phase filtering similar to phase mask 420 ₁ (see FIG. 4A). Similarly, region 524 ₂ is configured to display a spatial modulation pattern that results in phase filtering similar to phase mask 420 ₂ (see FIG. 4A).

Since SLM 520 is a reconfigurable device, it can be used to dynamically change or adjust the patterns displayed in its various regions, eg, regions 524 ₁ and 524 ₂ . This feature enables, for example, a relatively easy change in lateral mode assignment for different optical channels of OMC module 500 and / or in related features of multimode fiber 350. It may be useful to maintain optimal optical coupling for different optical channels of the OMC module under changing operating conditions that may result in corresponding changes.

The OMC module 500 is adapted to properly guide the collimated beams generated by the lenses 410 to the SLM 520 and to properly guide the filtered beams generated by the SLM to the mirrors 430. Polarizing beam splitters 528. In one embodiment, a quarter-wave plate (not explicitly shown in FIG. 5) properly rotates the polarization of the beam transmitted through the plate such that the polarization beam splitter mirrors the phase filtered beam 430. Can be inserted between the polarizing beam splitter 528 and the SLM 500 to enable guiding the collimated beam to the SLM. In an alternative embodiment, SLM 500 may be designed to rotate the polarization of the reflected light to enable polarizing beam splitters 528 to perform the same beam routing.

In one embodiment, the OMC module 500 may also be used to generate a TMM signal that is polarized multiplexed. In particular, where the SLM 520 itself is substantially polarization insensitive, the same SLM can be used to process both polarizations used for polarization multiplexing.

6 shows a block diagram of an OMC module 600 that may be used as the OMC module 340 (FIG. 3) in accordance with another embodiment of the present invention. OMC module 600 is generally functionally similar to OMC modules 400 and 500 (FIGS. 4 and 5). However, the OMC module 600 differs from the OMC modules 400 and 500 in that it uses a volume hologram 620 that can generally be seen as a three-dimensional phase mask. Note that, in contrast to volume hologram 620, phase mask 420 and SLM 520 can generally be seen as thin film or two-dimensional phase masks.

In the OMC module 600, the volume hologram 620 performs at least two different functions. The first of these functions is a phase filtering function similar to the phase masks 420 in the OMC module 400 and the SLM 520 in the OMC module 500. The second of these functions is a beam combining function similar to the mirrors 430. The volume hologram 620 can apply the necessary different phase filtering to the different light signals received from the fibers 332 as the corresponding light beams traverse different sub-volumes of the volume hologram. Also for this reason, the volume hologram 620 can change the propagation direction for different optical signals by different amounts. Volume holograms are known in the art and are described, for example, in more detail in US Pat. Nos. 7,416,818, 7,323,275, and 6,909,528, all of which are incorporated herein by reference in their entirety.

OMC module 600 is illustratively shown as having three optical channels. Those skilled in the art will appreciate that the OMC module 600 can be modified in a simple manner to have a different number of optical channels.

7 shows a block diagram of an optical transmitter 700 that may be used at node 110 (FIG. 1) in accordance with another embodiment of the present invention. Similar to transmitter 300 (FIG. 3), transmitter 700 has the ability to selectively couple independently modulated optical signals to respective transverse modes of output fiber (ie, fiber 750). However, in addition, the transmitter 700 is polarized multiplexing (PM) enabled by the use of the polarization beam splitter 714 and polarization combiners 734 in the transmitter's modulation and polarization multiplexing (MPM) module 712. Have abilities. Transmitter 700 is illustratively shown as having three optical channels per polarization. Those skilled in the art will appreciate that the transmitter 700 can be modified in a simple manner to have a different number of channels (eg, two or four or more) per polarization.

The transmitter 700 has a laser 710 configured to generate an output light beam of a designated wavelength. The laser 710 is supplied to the MPM module 712, where the polarization beam splitter 714 splits the beam generated by the laser into beams 716 ₁ and 716 ₂ having mutually orthogonal polarization. The MPM module 712 splits each polarization beam received from the polarization beam splitter 714 in three ways, and combines the two resulting power beams into three single mode fibers 722. It further has splitters 720. Each fiber 722 directs its respective beam to a corresponding light modulator 730, where the beam is modulated with data supplied to the modulator via a control signal 728. Modulated optical signals generated by the modulators 730 are coupled to the single mode fibers 732 and directed to the corresponding polarization combiner 734. Each polarization combiner 734 combines the two received orthogonal polarized signals into a corresponding PM signal, which then directs the PM signal through each single mode fiber 736 to the OMC module 740.

In alternative embodiments, the transmitter 700 may use direct light coupling or through-free-space light coupling instead of or in addition to at least a portion of the fiber coupling shown in FIG. 7. .

The OMC module 740 of the transmitter 700 is generally similar to the OMC module 340 of the transmitter 300 (FIG. 3) and acts to properly couple the three received PM signals to the fiber 750. In particular, each PM signal received by the OMC module 740 is coupled to a selected transverse mode of the fiber 750, and different PM signals are coupled to different transverse modes. For an individual PM signal (with two orthogonally polarized components), each of its polarization components is subjected to substantially the same phase filtering at the OMC module 740. In various embodiments, OMC module 740 can be implemented similar to OMC modules 400, 500, and 600 (see FIGS. 4-6). However, in designing the OMC module 740, particular attention is given to its polarization processing features to enable the OMC module to be substantially polarized insensitive.

8 shows a block diagram of an optical transmitter 800 that may be used at node 110 (FIG. 1) in accordance with another embodiment of the present invention. Similar to each of transmitters 300 and 700 (see FIGS. 3 and 7), transmitter 800 has the ability to selectively couple optical communication signals to various transverse modes of an output fiber (ie, fiber 850). Has Similar to the transmitter 700, the transmitter 800 has polarization multiplexing capabilities each enabled by the use of three MPM modules 812 similar to the MPM module 712 (FIG. 7). However, in addition, the transmitter 800 has WDM capabilities. Thus, the transmitter uses three different types of multiplexing: transverse mode multiplexing (TMM), polarization multiplexing (PM), and wavelength division multiplexing (WDM).

Transmitter 800 includes three TMM channels, three enabling the transmitter to generate a TMM signal having up to 18 independently modulated optical communication signals (up to six here per transverse mode). WDM channels, and two PM channels. Those skilled in the art can change in a relatively simple manner such that the transmitter 800 can produce different numbers of independently modulated components, and couple them to the selected transverse modes of the fiber 850 in any desired manner.

Each WDM channel of the transmitter 800 has a respective laser 810 that generates a designated wavelength and applies it to each MPM module 812. The three outputs of the MPM module 812 are applied to an optical filter (OF) 818 that performs relatively tight bandpass filtering intended to reduce crosstalk between optical signals corresponding to different WDM channels. . The filtered signal is WDM multiplexed at multiplexers 826 and the resulting signals are directed to OMC module 840 via single mode or integrated fibers 836.

The OMC module 840 of the transmitter 800 is generally similar to the OMC module 340 of the transmitter 300 (FIG. 3) and serves to properly couple the three received WDM signals to the fiber 850. . In particular, each WDM signal received by the OMC module 840 is coupled to a selected transverse mode of the fiber 850, and different WDM signals are coupled to different transverse modes. Although the PFS pattern corresponding to the transverse mode of the multimode fiber is wavelength dependent, the typical spectral bands used in WDM systems are relatively narrow, which in tense allows the use of the same phase mask for all WDM channels. do. For example, a spectral band concentrated at about 1550 nm and having a total width of about 100 nm has only about 6% variation in carrier frequency over the entire spectral band. Due to this relatively small deviation, the specified phase mask for a wavelength located near the middle of the spectral band will work well enough for all wavelengths in the band. As a result, in various embodiments, the OMC module 840 may be implemented similar to the OMC modules 400, 500, and 600 (see FIGS. 4-6).

Optical receiver

Since the transverse modes of the multipath fiber propagate along the length of the fiber, it is known in the art that the transverse modes of the multipath fiber are subjected to inter-mode mixing. In general, the effect of inter-mode mixing is stronger in multimode fibers. However, multi-core fibers with relatively closely spaced cores may also exhibit relatively strong inter-mode mixing (eg, inter-core crosstalk). As a result, even if a communication signal is coupled to a particular signal transverse mode at the front end of the multipath fiber, other transverse modes will have contributions from that communication signal at the far end of the fiber. Thus, a significant amount of signal processing needs to be performed at the receiver to fully recover data carried by different independently modulated components of the TMM signal. In general, to decode N independently modulated components of a TMM signal, the receiver needs to obtain at least N independent samples of the signal. Signal processing applied to these samples is generally based on matrix-diagonalization algorithms aimed at reversing the effects of inter-mode mixing on multipath fibers.

9 shows a block diagram of an optical receiver 900 that may be used at node 110 (FIG. 1) in accordance with one embodiment of the present invention. Receiver 900 may be configured to receive input TMM signal 902, for example, from link 120. The TMM signal 902 is applied to the tap module 910 which generates K samples 912 of the TMM signal, where K is a positive integer greater than one. Each sample 912 is detected coherently by a corresponding coherent detector 930 using a local oscillator (LO) signal 922 supplied by a local oscillator (LO) source 920. Detection results generated by the coherent detector 930 from the sample 912, such as the in-phase component (I) and quadrature phase component (Q) of the sample, are transmitted to the digital signal processor (DSP) 940. Apply. For each signaling interval (eg, bit period), DSP 940 properly processes the full set of detection results generated by coherent detectors 930 ₁ through 930 _K to output data stream 942. ). Once the tap module 910 generates enough samples of the TMM signal 902, the DSP 940 returns all the data that was originally encoded by the remote transmitter on the TMM signal received by the receiver 900 as the TMM signal 902. The data may be recovered and output through the stream 942.

Those skilled in the art will understand that one function of the DSP 940 is to invert the mode-mixing matrix corresponding to the link 120. In general, the link state changes over time, causing the mode-mixing matrix to also generally change over millisecond periods or slower. In one embodiment, the DSP 940 is configured to adaptively follow link state variations. For example, the DSP 940 may use a blind adaptive algorithm to learn and adapt the link states, as known in the art. Alternatively or in addition, sometimes a controller 950 coupled to the DSP 940 may request that the remote transmitter send a training sequence for the DSP to the receiver 900 to obtain the current mode-mixing matrix. have. An exemplary training sequence applied to link 120 by a remote transmitter may have a TMM signal in which different transverse modes are sequentially excited in a known order so that only one transverse mode is excited at any given time. Signal processing implemented in the DSP 940 may also compensate for certain nonlinear disturbances such as phase shifts caused by self-mode and cross-mode fiber nonlinearity.

10A and 10B illustrate exemplary modules that may be used in receiver 900 (FIG. 9) in accordance with one embodiment of the present invention. In particular, FIG. 10A shows a block diagram of a tap module 1010 that can be used as the tap module 910. 10B shows a block diagram of a coherent decoder 1030 that can be used as the coherent decoder 930.

Referring to FIG. 10A, the tap module 1010 receives a TMM signal 902 over the multimode fiber 1002. The collimation lens 1004 collimates the divergent light beam generated by the fiber 1002, and the resulting collimated beam is subjected to K-1 partially transparent mirrors 1006 ₁ to 1006 _K-1 and terminal opaque mirror 1006. _K ). In one embodiment, different mirror 1006 has a reflection means for causing the beams ₍₁ to 10 12 10 12 _K) reflected from the mirror have substantially the same intensity.

Referring to FIG. 10B, the detector 1030 receives the LO signal 922 from the LO source 920 over the single mode fiber 1016. The collimating lens 1018 collimates the divergent light beam generated by the fiber 1016 and directs the resulting collimated beam to the phase mask 1020. Phase mask 1020 is generally similar to phase mask 420 (see FIGS. 4A and 4B). In particular, phase mask 1020 generates a phase filtered beam 1022 having a PFS pattern that is an enlarged (enlarged) version of the PFS pattern corresponding to the selected transverse mode of multimode fiber 1002 (FIG. 10A). As already shown above, FIG. 4B shows a classification of phase masks, each suitable for use as phase mask 1020. When each detector 930 at the receiver 900 is implemented using the decoder 1030, different instances of the decoder 1030 at the receiver generally have different phase masks 1020 (eg, FIG. 4B). Different phase masks) selected from the classification shown in FIG. In various embodiments, these different phase masks 1020 can be implemented as different sections of the multi-section phase mask or use different portions of the SLM similar to the SLM 520 (FIG. 5).

A phase filtered beam 1022 and a beam 1012 (which carries a TMM sample 912 (see FIGS. 9 and 10A)) are applied to the 2x4 optical hybrid 1026, where they bump into each other Generate interference signals 1032 ₁ through 1032 ₄ . The interference signal (1032 ₁ to 1032 ₄₎ each of which is applied to an optical detector (e.g., photodiode) 1034 corresponding to convert into an electric signal corresponding to it. Electrical signals generated by the photo detectors 1034 are digitized and guided for further processing in the DSP 940. 2 × 4 optical hybrids that can be used as the hybrid 1026 in the detector 1030 are known in the art, and representative examples are disclosed, for example, as filed Dec. 18, 2008, all of which are incorporated herein by reference in their entirety. US Patent Application Publication No. 2007/0297806 and (ii) US Patent Application No. 12 / 338,492.

The electric fields E ₁ to E _{4 of} each of the interference signals 1032 ₁ to 1032 ₄ are provided by equation (1),

Here, E _S and E _LO are the electric fields of each of the optical signals 1012 and 1022. Equation (1) holds for all points of the transverse cross section of the beam 1032. This means that the detector 1030 measures not only how the beams 1012 and 1022 hit each other in time, but how much they hit each other in space. Also, due to the mutual orthogonality of the different transverse modes of the fiber 1016, different instances of the detector 1030 with different phase masks 1020 effectively validate the electric fields corresponding to different transverse modes of the TMM signal 902. Measure Those skilled in the art will appreciate that if K≥N, the coherent detectors 930 (or 1030) will properly invert the mode-mixing matrix where the DSP 940 corresponds to the communication link 120 and the remote transmitter (eg, It will be appreciated that sufficient sampling data is generated to be able to recover data carried by independently modulated components of the TMM signal transmitted from the transmitter 300 to the receiver 900.

11 shows a block diagram of a tap module 1110 that can be used as the tap module 910 according to another embodiment of the present invention. The tap module 1110 has a multimode fiber 1102 on which it receives the TMM signal 902. Depending on the length of the fiber 1102, tap module 1110 has a K of a multi-mode fiber (MMF) coupler s (1106 ₁ to 1106 _K) and K-1 in one mode scrambler (1108 ₂ to 1108 _K). Each MMF combiner 1106 is a fiber tap that branches a portion of the TMM signal 902 and couples that portion to the corresponding single mode fiber 1110. The signals carried by the fiber (1110 ₁ to 1110 _K) (1112 ₁ to 1112 _K) acts as the samples in the receiver 900 (912 ₁ to 912 _K), respectively.

Each signal 1112 represents a linear combination of transverse modes present in the multimode fiber 1102 at the location of the corresponding MMF coupler 1106. Modes scrambler (1108 ₂ to 1108 _K) because the mixing-up (mix up) the transverse mode among the MMF combiner (1106 ₁ to 1106 _K), the signal (1112 ₁ to 1112 _K), each multi-mode fiber ( A different linear combination of the transverse modes in 1102. Those skilled in the art will appreciate that if K≥N, the coherent detectors 930 will properly invert the mode-mixing matrix where the DSP 940 corresponds to the communication link 120 and the remote transmitter (eg, transmitter 300). It will be appreciated that it generates sufficient sampling data to be able to recover the data carried by the independently modulated components of the TMM signal transmitted from the receiver to the receiver 900.

In one embodiment, receiver 900 with tap module 1110 may use coherent detectors designed for detection of PM signals as coherent detector 930. Coherent detectors for the detection of PM signals are known in the art and are described, for example, in US Patent Application Publication No. 2007/029806 and US Patent Application No. 12 / 338,492, cited above. Those skilled in the art will appreciate that the receiver 900 using the tap module 1110 and a plurality of coherent detectors for detection of PM signals can properly detect optical signals generated using both TMM and PM multiplexing. . Those skilled in the art will also appreciate that a WDM receiver capable of properly detecting optical signals generated using all three aforementioned types of multiplexing (i.e., TMM, PM and WDM) has a TMM and PM for each WDM channel of the WDM receiver. It will be appreciated that it may be configured by deploying one receiver 900 having both capabilities.

12 shows a block diagram of an optical receiver 1200 that may be used at node 110 (FIG. 1) in accordance with another embodiment of the present invention. Receiver 1200 receives TMM signal 1201 (eg, from link 120) over multimode fiber 1202. A collimator lens (1204 ₁₎ collimating a diverging light beam generated by the fiber (1202), and guides the resultant collimated beam 1205 to the beam splitter (1206 ₁ to 1206 _4). In one embodiment, each beam splitter 1206 is a translucent mirror.

Receiver 1200 also has an LO source 1220 that passes its output through collimating lens 1204 ₂ to form collimated LO beam 1221. In analogy to the beam (1205), LO beam 1221 is also directed to the beam splitter (1206 ₁ to 1206 _4). A 90 degree phase shifter 1208 located between the beam splitters 1206 ₁ and 1206 ₂ introduces a 90 degree phase shift to the beam transmitted therethrough.

The beam splitter (1206 ₁ to 1206 ₄₎ beams (1205 and 1221) a plurality of sub-properly split into beams, and then, the sub-recombine some of the beams 4 in the array of detectors (e. For example, it produces four mixed light beams that touch on the light receiving surfaces of the pixels of CCDs 1230 ₁ to 1230 ₄ . Each arrayed detector 1230 operates at a sufficiently high rate that makes it possible to capture and output data corresponding to at least one interference pattern per signaling interval (eg, symbol period) of the TMM signal 1201. Each interference pattern is generated at the light receiving surface of the pixels of the arrayed detector 1230 by striking each other the reference field generated by the LO source 1220 and the optical field of the TMM signal 1201. The arrayed detector 1230 captures the interference pattern by measuring the light intensity of the pattern at the various pixels of the arrayed detector, producing a two-dimensional cross-sectional intensity profile of the mixed beam.

Data corresponding to the four interference patterns detected by the arrayed detectors 1230 ₁ through 1230 ₄ is supplied to the DSP 1240 for processing. Of the array detector (1230 ₁ to 1230 ₄₎ is sufficiently high resolution from has the (e. G., Sufficiently large number of relatively small pixels in), DSP (1240) is of the four interference patterns, TMM signal ( Sufficient data is received to determine the mode composition of 1201). Here, the term "mode composition" refers to the representation of the TMM signal 1201 regarding the transverse modes of the multimode fiber 1202. Typically, this representation is a linear composition of appropriately weighted transverse modes. The knowledge of the mode composition then allows the DSP to properly invert the mode mixing matrix corresponding to the communication link 120, and to determine the TMM signal transmitted from the remote transmitter (e.g., transmitter 300) to the receiver 1200. It is possible to recover data carried by independently modulated components. The DSP 1240 outputs the recovered data via the data stream 1242.

Those skilled in the art will appreciate that the arrayed detectors 1230 ₁ and 1230 ₄ are optional and are used at the receiver 1200 to implement a balanced detection scheme similar to that implemented in the detector 1030. In particular, the four interference pattern detected by the detector array (1230 ₁ to 1230 ₄₎ are processed by a DSP (1240) generates two map section of TMM signal 1201. The first cross-sectional map is an in-phase map of the TMM signal 1201, and the second cross-sectional map is an orthogonal phase map of the TMM signal. It would be desirable to have in-phase and quadrature phase maps of the TMM signal 1201 because the DSP 1240 may use these maps to determine the mode composition of the TMM signal faster, more accurately and / or more efficiently. It may be.

In various embodiments, receiver 1200 may include additional optical components to enable the use of less than four individual arrayed detectors. For example, in one embodiment, the receiver 1200 may have two relatively large arrayed detectors, where (i) the first detector is a detector 1230 _{1 in} which a portion of the first detector is arrayed. And the other portion of the first detector is partitioned to act as an arrayed detector 1230 ₂ , (ii) the second detector acts as a detector 1230 ₃ with a portion of the second detector arrayed, and Another portion of the two detectors is similarly partitioned to act as an arrayed detector 1230 ₄ . In an alternative embodiment, the receiver 1200 may have one very large arrayed detector, each partitioned into four portions acting as a corresponding one of the detectors 1230 ₁ through 1230 ₄ .

Although the present invention has been described with reference to exemplary embodiments, this description is not intended to be interpreted in a limiting sense. Various modifications of the described embodiments as well as other embodiments of the present invention that are apparent to those skilled in the art to which this invention pertains are considered to be within the spirit and scope of the invention as expressed in the claims below.

Unless expressly stated otherwise, each numerical value and range should be construed as an approximation, such that the word "about" or "approximately" precedes that value or range.

It is also to be understood that various changes in details, material, and arrangement of components described and illustrated to illustrate the nature of the invention may be made by those skilled in the art without departing from the scope of the invention as described in the claims below. Will be.

If present, the elements in the method claims below are described in a particular sequence having a corresponding labeling, but unless the claim descriptions otherwise imply a particular sequence implementing some or all of these elements, these elements are It is not necessarily intended to be limited to being implemented as.

Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present invention. . The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily referring to the same embodiment and not to individual or alternative embodiments, except for the other embodiments. The same applies to the term "implementation".

Also, for purposes of this description, the terms “couples”, “couples”, “coupled”, “connects”, “connects” or “connected” means energy between two or more elements. Refers to any manner known in the art or later developed that is acceptable for delivery, and the insertion of one or more additional elements is not required but contemplated. On the contrary, the terms "directly coupled", "directly connected" and the like refer to the absence of such additional elements.

The invention may be implemented in other specific apparatus and / or methods. The described embodiments are to be considered in all respects only as illustrative and not restrictive. In particular, the scope of the invention is indicated by the appended claims rather than by the description and figures herein. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

The description and drawings merely illustrate the principles of the present invention. Thus, although not explicitly described or shown herein, it will be understood that those skilled in the art may invent various devices that implement the principles of the invention and are included within its spirit and scope. In addition, all examples described herein are in principle intended only to be clearly intended for educational purposes to aid the reader in understanding the principles contributed by the present invention and concepts contributed by the inventor (s) in order to facilitate technology, and these specifics It should be construed as not limited to the examples and conditions described. Moreover, all sentences herein describing the principles, aspects, and embodiments of the present invention, as well as specific examples thereof, are intended to include their equivalents.

Those skilled in the art should understand that any block diagrams herein represent a conceptual diagram of an exemplary circuit implementing the principles of the present invention. Similarly, any flow charts, flow diagrams, state transition diagrams, pseudo code, etc. may be substantially represented on a computer readable medium such that the computer or processor is explicitly shown or not. It will be appreciated that it represents various processes that may be executed by a processor.

110: node 140: amplifier
150: optical line splitter 730: modulator
740: OMC module 910: tab
920: local oscillator 930: coherent detector
950: controller

Claims (10)

For an optical receiver:
A tap module configured to sample a transverse-mode multiplexed (TMM) signal with N independently modulated components to generate K optical samples per signaling interval, wherein N and K are greater than 1 The tap module, positive integers, where K ≧ N;
A local oscillator (LO) source configured to generate an optical local oscillator (LO) signal;
K coherent detectors, each optically coupled to the tap module and the LO source,
Mix each optical sample and the LO signal to generate one or more optical interference signals,
The K coherent detectors configured to convert the one or more optical interference signals into one or more electrical signals representing in-phase and quadrature phase components of the optical sample; And
Data operably coupled to the K coherent detectors, the data carried by each of the N independently modulated components of the TMM signal by processing the electrical signals generated by the coherent detectors A digital signal processor (DSP) configured to recover the
The optical receiver is configured to receive the TMM signal over a multimode fiber supporting a plurality of transverse modes,
Coherent detectors are:
A phase mask configured to phase filter the LO signal to generate a phase filtered beam, the phase mask configured to cause the phase filtered beam to correspond to a phase / field-strength (PFS) of a selected lateral mode; The phase mask, having a field intensity (PFS) pattern;
an optical hybrid configured to (i) mix the light beam corresponding to each of the optical samples with (ii) the phase filtered beam to generate the one or more optical interference signals; And
And a plurality of photo detectors for converting the one or more optical interference signals into the one or more electrical signals. The method of claim 1,
The TMM signal is inter-mode mixed in the multimode fiber before being received by the optical receiver,
And the DSP is configured to recover the data by inverting the effects of the inter-mode mixing. The method of claim 1,
And a controller operatively coupled to the DSP, the controller configured to send a request to a remote transmitter to transmit an optical training signal to the optical receiver, the DSP corresponding to the multimode fiber based on the optical training signal. And configured to derive the mode-mixing matrix. For an optical receiver:
A tap module configured to sample a wide transverse mode multiplexed (TMM) signal having N independently modulated components to generate K optical samples per signaling interval, wherein N and K are positive integers greater than 1 ≧ N, and the tap module is configured to receive the TMM signal over a multimode fiber supporting a plurality of transverse modes;
A local oscillator (LO) source configured to generate an optical local oscillator (LO) signal;
K coherent detectors, each optically coupled to the tap module and the LO source, respectively
Phase filtering the LO signal to generate respective phase filtered beams having a phase / field intensity (PFS) pattern corresponding to the phase / field intensity pattern (PFS) of each selected transverse mode of the multimode fiber,
Mixing each optical sample with the phase filtered beam to generate one or more optical interference signals,
The K coherent detectors configured to convert the one or more optical interference signals into one or more electrical signals representing in-phase and quadrature phase components of the optical sample; And
Data operably coupled to the K coherent detectors, the data carried by each of the N independently modulated components of the TMM signal by processing the electrical signals generated by the coherent detectors And a digital signal processor (DSP) configured to recover the data. 5. The method of claim 4,
At least one of the K coherent detectors is:
A phase mask configured to phase filter the LO signal to generate the respective phase filtered beams;
An optical hybrid configured to mix the phase filtered beam and a light beam corresponding to each optical sample to generate one or more optical interference signals; And
And a plurality of photo detectors for converting the one or more optical interference signals into the one or more electrical signals. For an optical receiver:
As a plurality of beam splitters,
(Iii) converting a light beam corresponding to a wide transverse mode multiplexed (TMM) signal into a first plurality of sub-beams, received over a multimode fiber having a plurality of independently modulated components and supporting a plurality of transverse modes; Split,
(Ii) split the light beam corresponding to the local oscillator (LO) signal into a second plurality of sub-beams,
(Iii) the plurality of beam splitters configured to mix the first and second plurality of sub-beams to produce two or more mixed light beams;
A first arrayed detector configured to detect a first two-dimensional interference pattern corresponding to a first mixed light beam of the two or more mixed light beams and having a receiving surface of each pixel;
A second arrayed detector configured to detect a second two-dimensional interference pattern corresponding to a second mixed light beam of the two or more mixed light beams and having a light receiving surface of each pixel; And
Operably coupled to the first and second arrayed detectors, processing the first and second two-dimensional interference patterns to determine a mode composition of the TMM signal and based on the mode composition, the And a digital signal processor (DSP) configured to recover data carried by independently modulated components. The method according to claim 6,
Each of the first and second arrayed detectors is configured to capture a corresponding one of the first and second two-dimensional interference patterns at least once per signaling interval of the TMM signal,
The optical receiver further includes a phase shifter for causing a first sub-beam from the second plurality of sub-beams to have a specified phase shift with respect to a second sub-beam from the second plurality of sub-beams. and,
The plurality of beam splitters are:
(Iii) mix a first sub-beam from the first plurality of sub-beams and a first sub-beam from the second plurality of sub-beams to produce the first mixed light beam;
(Ii) mixing the second sub-beam from the first plurality of sub-beams with the second sub-beam from the second plurality of sub-beams to produce the second mixed light beam,
And the specified phase shift is 90 degrees. The method of claim 7, wherein
A third arrayed detector configured to detect a third two-dimensional interference pattern corresponding to the third mixed light beam and having a light receiving surface in each pixel; And
Further comprising a fourth arrayed detector configured to detect a fourth two-dimensional interference pattern corresponding to the fourth mixed light beam and having a light receiving surface in each pixel,
The phase shifter is configured to cause a third sub-beam from the second plurality of sub-beams to specify a phase shift designated with respect to each of the second and fourth sub-beams from the second plurality of sub-beams. To have
The plurality of beam splitters are:
(Iii) mixing the third sub-beam from the first plurality of sub-beams with the third sub-beam from the second plurality of sub-beams to produce the third mixed light beam;
(Iii) mixing the fourth sub-beam from the first plurality of sub-beams with the fourth sub-beam from the second plurality of sub-beams to produce the fourth mixed light beam,
The DSP is operably coupled to the third and fourth arrayed detectors and configured to process the third and fourth two-dimensional interference patterns to determine the mode composition of the TMM signal. The method of claim 8,
The arrayed detectors and the DSP implement a balanced detection scheme,
The first and third two-dimensional interference patterns are processed to generate an in-phase map of the TMM signal,
The second and fourth two-dimensional interference patterns are processed to generate an orthogonal phase map of the TMM signal,
And the in-phase and quadrature phase maps are processed to determine a mode composition of the TMM signal. For an optical receiver:
A tap module configured to sample a wide transverse mode multiplexed (TMM) signal having N independently modulated components, to generate K optical samples per signaling interval, wherein N and K are positive integers greater than one, The tap module, K≥N;
A local oscillator (LO) source configured to generate an optical local oscillator (LO) signal;
K coherent detectors, each optically coupled to the tap module and the LO source,
Mixing each optical sample with the LO signal to generate one or more optical interference signals,
The K coherent detectors configured to convert the one or more optical interference signals into one or more electrical signals representing in-phase and quadrature phase components of the optical sample; And
Data operably coupled to the K coherent detectors, the data carried by each of the N independently modulated components of the TMM signal by processing the electrical signals generated by the coherent detectors A digital signal processor (DSP) configured to recover
The optical receiver receives the TMM signal over a multimode fiber supporting a plurality of transverse modes,
The tap module is:
K multimode fiber (MMF) combiners, each tapping off the optical power from the multimode fiber into a single mode fiber to generate a corresponding optical sample of the TMM signal. field; And
K-1 mode scramblers, each comprising the K-1 mode scramblers, disposed between two adjacent MMF combiners.

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