EP1141756A1 - Codes, procedes et dispositif de codage et de decodage optique - Google Patents

Codes, procedes et dispositif de codage et de decodage optique

Info

Publication number
EP1141756A1
EP1141756A1 EP99960431A EP99960431A EP1141756A1 EP 1141756 A1 EP1141756 A1 EP 1141756A1 EP 99960431 A EP99960431 A EP 99960431A EP 99960431 A EP99960431 A EP 99960431A EP 1141756 A1 EP1141756 A1 EP 1141756A1
Authority
EP
European Patent Office
Prior art keywords
subcode
supercode
signal
optical
code
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99960431A
Other languages
German (de)
English (en)
Other versions
EP1141756A4 (fr
Inventor
Anders Grunnet-Jepsen
Alan E. Johnson
Eric S. Maniloff
Thomas W. Mossberg
Michael J. Munroe
John N. Sweetser
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Templex Technology Inc
Original Assignee
Templex Technology Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Templex Technology Inc filed Critical Templex Technology Inc
Publication of EP1141756A1 publication Critical patent/EP1141756A1/fr
Publication of EP1141756A4 publication Critical patent/EP1141756A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29317—Light guides of the optical fibre type
    • G02B6/29319—With a cascade of diffractive elements or of diffraction operations
    • G02B6/2932—With a cascade of diffractive elements or of diffraction operations comprising a directional router, e.g. directional coupler, circulator
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/29395—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device configurable, e.g. tunable or reconfigurable
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/10—Code generation
    • H04J13/102—Combining codes
    • H04J13/107—Combining codes by concatenation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/005—Optical Code Multiplex
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0005—Switch and router aspects
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0005—Switch and router aspects
    • H04Q2011/0007—Construction
    • H04Q2011/0015—Construction using splitting combining
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0005—Switch and router aspects
    • H04Q2011/0007—Construction
    • H04Q2011/0035—Construction using miscellaneous components, e.g. circulator, polarisation, acousto/thermo optical

Definitions

  • the invention pertains to optical communication systems.
  • CDMA Code-division-multiple-access
  • CDMA methods are spread-spectrum methods for multiplexing and demultiplexing a plurality of data-carrying electromagnetic signals onto a single transmission medium. These data signals are distinguished by encoding with different complex spectral or temporal codes. The resultant spectra of the encoded data signals are much broader than the spectra of the uncoded data signals.
  • the number of data signals that can be successfully multiplexed and demultiplexed in a CDMA system is dependent on the complexity of the coding.
  • CDMA codes are traditionally divided into "chips," defined as a temporal duration of the shortest temporal feature encoded onto the data signal. Larger numbers of chips permit larger numbers of users, or, alternatively, the less inter- user interference for a fixed number of multiplexed data signals.
  • Radio-frequency (RF) CDMA makes use of binary phase codes in which each chip assumes one of two values for the phase of the electromagnetic field that carries data signals. Such binary codes can be generated in real time with fast sequences of shift registers. Code- generation algorithms for the production of binary CDMA code sets include algorithms that generate Gold codes, Kasami codes, maximal sequence length codes, JPL codes, and Walsh codes.
  • Optical CDMA systems use passive optical encoding and decoding with, for example, diffraction gratings. Since the coding and encoding are performed passively, no fast digital logic is needed to encode or decode the optical signal. Therefore, optical CDMA systems are not limited to the binary phase or amplitude codes used in RF CDMA. Finding new code sets, particularly for use in optical communication systems can be difficult and time-consuming. Therefore, methods and apparatus for generating code sets and especially large-chip-number code sets having predictable cross-talk characteristics are needed. Also needed are encoders and decoders for encoding and decoding, respectively, an optical field or other electromagnetic signal using such codes.
  • FIG. 1 is a schematic diagram of a data-transmission system using 3-chip supercodes and 3-chip subcodes.
  • FIG. 2A is a schematic diagram of a subcode of an encoded data pulse.
  • FIG. 2B is a schematic diagram of a supercode of an encoded data pulse.
  • FIG. 2C is a schematic diagram of a composite-coded data pulse, obtained by combining the subcode of FIG. 2A with the supercode of FIG. 2B.
  • FIG. 2D is a schematic diagram of a subcode encoder that produces a subcode-encoded data pulse.
  • FIG. 2E is a schematic diagram of a supercode encoder that receives the subcode-encoded data pulse of FIG. 2D and produces a composite-coded data pulse.
  • FIG. 2F is a schematic diagram of a supercode decoder that receives a composite-coded data signal and produces a subcoded data signal.
  • FIG. 2G is a schematic diagram of a subcode decoder that receives a supercoded data signal and produces a decoded data signal.
  • FIG. 3A is a schematic diagram of a fiber Bragg grating for encoding or decoding a subcode.
  • FIG. 3B is a schematic diagram of a fiber Bragg grating for encoding or decoding a supercode.
  • FIG. 4 is a schematic diagram of a reconfigurable encoder for applying a selected composite code.
  • FIG. 5A is a schematic diagram of a transmitter that transmits optical signals coded with a composite code.
  • FIG. 5B is a schematic diagram of the reconfigurable encoder shown in FIG. 5A.
  • FIG. 6A is a schematic diagram of a fiber Bragg grating that encodes a subcode.
  • FIG. 6B is a graph of refractive-index variations as a function of position in the fiber Bragg grating of FIG. 6A.
  • FIG. 6C is a schematic diagram of a fiber Bragg grating that encodes a supercode.
  • FIG. 6D is a graph of refractive-index variations as a function of position in the fiber Bragg grating of FIG. 6C.
  • FIG. 7 is a schematic diagram of a receiver that decodes an optical signal coded with a composite code.
  • FIG. 8A is a graph of power as a function of time for an optical signal encoded and decoded with a matched composite code.
  • FIG. 8B is a graph of power as a function of time for an optical signal encoded and decoded with unmatched composite codes.
  • FIGS. 9A-9C are graphs of power as a function of time for encoding and decoding an optical signal with a matched code and with unmatched codes.
  • FIGS. 1 0A-1 0B are graphs of power as a function of time for encoding and decoding an optical signal with a matched composite code and with unmatched composite codes.
  • FIG. 1 is a schematic of a data transmission system 1 01 that produces a data signal 1 03 from a data source 1 05.
  • the data signal 1 03 is represented as a binary, on-off modulation of an electromagnetic carrier such as an optical carrier.
  • the on-off modulation is selected for convenience only, and other modulations can include phase, amplitude, intensity, and frequency modulation.
  • non-binary modulation having more than two modulation levels can be used.
  • a supercode encoder 1 07 receives the data signal 1 03 and applies a predetermined code Ri selected from a code set R to the data signal 1 03.
  • a code R ⁇ ⁇ 1 , -1 , 1 ⁇ is selected and applied to a representative bit 1 09 of the data signal 1 03.
  • the encoder 1 07 receives the bit 1 09 and transforms the bit into a "supercoded" bit packet 1 1 1 .
  • the supercoded bit packet 1 1 1 includes super-coded bits ("superbits") 1 1 3-1 1 5 that are relatively delayed by a delay time 7RC, wherein 7RC is a supercode chip duration.
  • 7RC is a supercode chip duration.
  • the phase of the superbit 1 4 is inverted, while the phases of the superbits 1 1 3, 1 1 5 are unchanged.
  • the encoder 107 applies the code R ⁇ to the entire data signal 1 03 to produce a supercoded data signal that is a sum of superbits corresponding to all respective bits of the data signal 1 03.
  • the encoder 1 1 7 encodes each of the supercoded bits 1 1 3-1 1 5 by relatively delaying portions by a delay time Tsc wherein Tsc is a subcode chip duration, and changing the phase of the supercoded bits 1 1 3, 1 1 5, to produce the corresponding subcoded bits 1 23, 1 25, 1 27.
  • the encoder 1 1 7 applies the code Si to the supercoded data signal, producing a composite-coded data signal.
  • the encoders 1 07, 1 1 7 apply codes from respective sets R, S to the data signal 1 03. If the sets R, S contain NR and Ns codes, respectively, then NR X NS different encodings are available. For example, if sets R, S each include 5 codes, then 25 encodings are possible. Thus, the number of available encodings increases as the product of NR and Ns increases so that large numbers of encodings are possible even with small code sets.
  • the sets R, S can be subsets of a large code set and can include different or identical codes. In this way, a set of N codes can be used to produce N 2 different encodings.
  • FIG. 1 illustrates encoding, with two sets of codes (sets R, S), but additional code sets can be used to further increase the number of available encodings.
  • Subcode bits 1 1 3-1 1 5 can be further encoded with a code set Q having No codes, so that the number of available encodings is NR x Ns x N ⁇ .
  • Codes obtained by combining two or more code sets such as the code sets R, S are referred to herein as "composite codes.
  • the encoders 107, 1 1 7 can be electronic, acoustic, or optical encoders, depending on the type of signal to be encoded or decoded. Optical encoders are described in, for example, U.S. Patent Applications Nos.
  • codes R ⁇ , Si used above are selected as representative examples. More generally, codes include two or more "chips" that specify modulations to be applied to a signal. The chip modulations are applied to a signal at relative times differing by a chip duration 7c. Thus, a code and a chip duration specify an encoding of a data signal. A supercode is further specified by an interchip duration.
  • a code R, having a total duration 7R, a number of chips NR, and a chip duration 7RC, and a code S, having a total duration 7s, a number of chips Ns, and chip duration or interchip delay 7sc, are effectively orthogonal as decoded if 7R ⁇ 7sc.
  • a composite code can be produced from the code R (a subcode), and from the code S (a supercode) .
  • the composite code has a given duration equal to the duration of the supercode and has a number of chips equal to the product of the number of chips of the subcode and the supercode.
  • the chip duration is equal to the subcode chip duration.
  • the subcode is repeated a number of times equal to the number of chips in the supercode.
  • Code sets and chip durations of supercodes and subcodes (and sub-subcodes) are preferably selected so that a data signal encoded with a particular composite code is decoded only with a matching decoding composite code. Decoding with an unmatched composite code produces only a noise-like background or low amplitude "sidelobes" or "crosstalk. "
  • composite code sets of sufficient orthogonality can be generated from a code set with a small number of chips if the codes of the code set are sufficiently orthogonal.
  • a code in a composite code set can be generated by using a selected code of the code set as a supercode and another selected code of the code set as a subcode.
  • a composite code set comprises all combinations of supercodes and subcodes. For example, if a code set has M codes each containing Nm chips, then the composite code set contains M x M codes each having NmxNm chips.
  • FIG. 2A illustrates a single data bit after encoding with a 5-chip subcode that can be represented as ⁇ 1 , 1 , 0, 1 , 1 ⁇ .
  • the data bit is divided into five portions that are relatively delayed by a delay time 7RC In this code, one portion, corresponding to "0", has no data-pulse amplitude.
  • FIG. 2B illustrates a data bit encoded with a 5-chip supercode that can be represented as ⁇ 1 , 1 , 1 , 0, 1 ⁇ .
  • the subcoded data bit is replicated once for each of the non-zero chips of the supercode and each subcoded bit is multiplied by a code value associated with a corresponding supercode chip.
  • Both the supercode and subcode have temporal features of approximately the same duration, but the chip- spacing features are greater (for the supercode) than the duration of the entire subcode, so that 7R ⁇ 7sc, wherein 7R is a duration of the subcode and 7sc is a supercode chip spacing.
  • the total duration of the subcode of FIG. 2A is less than or equal to the interchip spacing of the supercode.
  • FIG. 2C illustrates a data bit after encoding with the subcode and supercode that produce the codings of FIGS. 2A-2B, respectively.
  • the encoding of FIG. 2C is equivalent to encoding with a composite code defined by this subcode and supercode.
  • the procedure for generation of composite codes can be extended beyond the two sequential levels shown in FIG . 1 and FIGS. 2A-2C to include three or more levels to provide longer composite codes.
  • composite code sets can be generated with code sets having different numbers of chips for the codes used to define the supercodes and subcodes.
  • Optical encoders and decoders for generating composite codes can include those disclosed in the references cited above. Using the linear spectral filtering techniques described in these references, composite codes can be optically encoded and decoded onto optical data streams. Representative encoders/decoders using optical circulators and reflective fiber Bragg gratings are discussed below. Other encoders/decoders use beam splitters, or diffraction gratings, to simultaneously encode or decode both a subcode and a supercode. In addition, a subcode and supercode can be encoded or decoded in any order, or simultaneously, and the subcoding and supercoding operations can be performed at a single location or at different locations. FIGS.
  • FIG. 2D-2E illustrate two-stage optical encoding using the codes of FIGS. 2A-2C.
  • FIG. 2D shows a single incoming data pulse 201 that is received by a subcode encoder 21 1 comprising an optical circulator 21 3 and a fiber Bragg grating 21 5, selected to encode a selected subcode.
  • a subcoded data pulse 21 7 exits the subcode encoder 21 1 through an exit port 21 9 of the optical circulator 21 3.
  • a supercode encoder 231 receives the subcoded data pulse 21 7.
  • the supercode encoder 231 comprises an optical circulator 233 and a fiber Bragg grating 235 that encodes a selected supercode.
  • a data pulse 241 produced by the supercode encoder 231 is coded according to a composite code.
  • FIGS. 2F-2G illustrate two-stage optical decoding.
  • FIG. 2F shows a supercode decoder 243 that receives the composite-code-encoded data pulse 241 .
  • the supercode decoder 243 comprises an optical circulator 251 and a fiber Bragg grating 253.
  • the fiber Bragg grating 253 is selected to correspond to the supercode to be decoded.
  • the fiber Bragg grating 253 removes the supercode from the data pulse 241 and a resulting supercode-decoded data pulse 254 exits via an exit port 255.
  • the data pulse 254 corresponds to a subcode-encoded data pulse. If the fiber Bragg grating 253 decodes a supercode that does not match the supercode of the data pulse 241 , then the output of the supercode decoder 243 is a noise-like, low-power signal.
  • FIG. 2G shows a subcode decoder 261 that receives the subcode- encoded data pulse 254.
  • the subcode decoder 261 comprises an optical circulator 263 and a fiber Bragg grating 265 for decoding a selected subcode.
  • a decoded data pulse 271 exits the subcode decoder through an exit port 260 of the optical circulator 263. If the data pulse
  • FIG. 3A is a schematic diagram of a segmented fiber Bragg grating ("fBg") 301 for encoding or decoding a subcode.
  • the fBg 301 comprises grating segments 305 and fiber lengths 355.
  • the grating segments 305 have periodic variations in an index of refraction of a fiber core or cladding, as discussed in U .S. Patent Application No. 09/1 20,959.
  • the grating segments 305 and the fiber length 407 extend a length corresponding to a subcode chip time 7RC along the direction 307.
  • FIG. 3B is a schematic diagram of an fBg 351 for encoding or decoding a supercode.
  • the fBg 351 comprises grating segments 353 and fiber lengths 355.
  • the grating segments 353 have lengths corresponding to 7RC of the fBg 351 but are separated by a length corresponding to a chip number times 7RC, i.e., 57RC for the example.
  • the fBg 351 encodes a 5-chip supercode and has 5 chip segments 361 - 365. For efficient subcode and supercode encoding/decoding, grating segment lengths are approximately equal for a matched subcode and supercode fBg.
  • the spatial period of the chip segments 361 - 365 of the supercode grating 351 is larger than the total length of the subcode grating 301 .
  • This guideline is a result of matching the bandwidths of the subcode and supercode fBgs.
  • the total duration of a subcode is preferably less than or equal to the duration of a supercode chip (i.e., the chip segments 361 -365) . Similar guidelines apply to other linear spectral filtering devices used for encoding and decoding of subcodes and supercodes.
  • FIG. 4 is a schematic diagram of a switched encoder 400 that can apply any of a hundred distinct composite codes onto an input data pulse.
  • the switched encoder 400 of FIG. 4 receives a single data pulse 402 or multiple data pulses from a modulated data source 401 at an optical circulator 403.
  • the optical circulator 403 delivers the data pulse to a 1 x1 0 switch 405 that selectively directs the data pulse to one of ten segmented fiber Bragg gratings 407-41 6 as controlled by an address selector 406.
  • Each of the fiber Bragg gratings (fBgs) 407-41 6 is selected to encode a selected supercode.
  • the circulator 403 directs a supercoded data pulse 422 produced by the fBgs 407-41 6 to an optical circulator 421 .
  • the circulator 421 directs the pulse 422 to a 1 x1 0 switch 431 that selects one of the subcoded fBgs 431 -440 as directed by the address selector 406.
  • a composite-code-encoded pulse is then produced and direct to an output 443 by the circulator 421 .
  • 1 00 composite codes can be applied.
  • An N-chip code C is conveniently represented as a set ⁇ C1 , . . . ,
  • a rth chip includes a modulation exp(-j ⁇ kT) .
  • FIG. 5A is a schematic diagram of a representative transmitter 501 that comprises a distributed feedback (DFB) laser 503 that receives an electrical data signal 505 and produces an optical data signal 507.
  • the electrical data signal 505 and the optical data signal 507 are binary amplitude-modulated signals.
  • the DFB laser 503 emits the laser pulses 509 at a repetition rate of about 2.5 Gbit/s.
  • Each of the laser pulses typically corresponds to a "1 " bit in the electrical data signal 505 and no laser pulses are emitted for the "0" bits.
  • the DFB laser 503 can be used with an optical modulator so that the DFB laser 503 emits a series of laser pulses at a selected bit rate, and the modulator selectively absorbs or otherwise modulates the pulses according to the electrical data signal 505.
  • An encoder 51 1 receives the optical data signal 507 and produces a composite-coded optical signal 51 3 that is transmitted on an optical fiber 51 5.
  • the encoder includes a code-selection input 51 7 through which an /th subcode and a / ' th supercode are selected. Referring to FIG.
  • the encoder 51 1 comprises optical circulators 521 , 523, optical switches 525, 527, and fiber Bragg gratings 531 -536.
  • the optical circulator 521 directs the optical data signal 505 to the optical switch 525.
  • the optical switch 525 has three outputs 543-545 that connect to the fiber Bragg gratings 531 -533, respectively.
  • the fiber Bragg gratings 531 -533 encode respective subcodes onto the input optical signal 505.
  • the circulator 521 directs the subcoded optical signal to the circulator 523 that directs the subcoded optical signal to the optical switch 527.
  • the fiber Bragg grating 534 reflects the subcoded optical signal, producing a supercoded and subcoded (i.e., composite-coded) optical signal that is directed back to the optical switch 527, the optical circulator 523, and to a fiber 515.
  • Nine composite codes are formed from these codes, each of the nine codes comprising nine chips.
  • the complete set of these nine nine-chip codes is:
  • FIG.6A is a schematic of a fiber Bragg grating 601, such as any of the fiber Bragg gratings 531-533, for encoding a subcode selected from the above 3-chip codes.
  • the fiber Bragg grating 601 includes grating segments 603-605 that have respective periodic variations in refractive index in a core 607. In an alternative configuration, refractive-index variations can be provided in a cladding region 609.
  • FIG. 6B is a graph of refractive-index variations of the grating segments 603-605.
  • each of the grating segments 603-605 of the fiber Bragg grating 601 are 2.5 mm long (25 ps/( 1 00 ps/cm)), for a total length of 7.5 mm.
  • Bragg gratings are defined in the segments
  • ⁇ the wavelength of the optical data signal
  • rico the refractive index rico of the fiber core 607.
  • the grating period about 51 6 nm.
  • the fiber Bragg grating 601 encodes an optical signal with a selected code based upon the relative phase shifts of the spatial variations in refractive index in the segments 603-605. As illustrated in FIG. 6B, the fiber segment 604 has a 1 80-degree phase shift with respect to fiber segments 603, 605 so that these segments correspond to the subcode ⁇ 1 , -1 , 1 ⁇ . (If an absolute phase reference is specified, this and other codes can be specified in terms of absolute phases as well as phase differences.)
  • FIG. 6C is a schematic view of a fiber Bragg grating 651 for encoding a supercode (a supercode fiber), such as the fiber Bragg gratings 534-536.
  • the supercode fiber 651 includes grating segments 653-655 having refractive-index variations selected based upon the laser pulse width and bandwidth. As shown in FIG. 6C, the grating segment lengths are selected to equal the subcode grating-segment lengths of 2.5 mm. The separation of the supercode grating segments is selected so that the time delay between adjacent chips is sufficient to span a subcoded laser pulse.
  • the supercode grating segments have a 7.5-mm separation, corresponding to 7sc
  • the grating segments of the supercode grating 651 are similar to those of the subcode grating segments 603-605, having the same spatial period ⁇ and the same relative phases, i.e., segment 654 is 1 80 degrees out of phase from segments 653, 655, but this phase difference is not shown in FIG. 6D.
  • FIG. 7 is a schematic view of a receiver 701 that decodes and transduces a composite-coded optical signal produced by the encoder of FIG. 5B into an electrical signal.
  • the receiver 701 comprises a decoder 703 that includes fiber Bragg gratings 705-71 0 that are selected to decode the composite codes encoded by the encoder of FIG . 5B.
  • the receiver 701 comprises a photodetector 71 1 , amplifier 71 3, and thresholding electronics 71 5.
  • the photodetector 71 1 converts an optical signal into an electrical signal and the thresholding electronics 71 5 provide an electrical signal corresponding to the decoded optical signal with sidelobes and/or noise-like backgrounds attenuated.
  • the decoder fiber gratings 705-71 0 are selected to decode the composite codes (combined subcodes and supercodes) used by the encoder.
  • the decoder gratings are identical to the encoder gratings but with the optical signals to be coded and decoded input to the fiber Bragg gratings from different directions.
  • an end 721 of the fiber grating 705 is used as an input for decoding, and an end 723 is used as an input for decoding.
  • the ends 721 , 723 can be used as inputs for encoding and decoding, respectively.
  • the decoder 703 includes optical circulators 727, 729 and optical switches 731 , 733.
  • the optical switches are responsive to inputs that select a jth subcode and an ith supercode for decoding a composite code.
  • the decoder 703 is reconfigurable. If reconfigurable coding is unnecessary, then a single fiber Bragg grating can be provided that encodes an optical signal with a composite code, and a single matched fiber Bragg grating can serve to decode this composite code. Providing separate fiber Bragg gratings for subcodes and supercodes is beneficial for reconfigurable coding.
  • FIGS. 8A-8B illustrate decoded optical signals produced with a matched decoder and an unmatched decoder, respectively.
  • the matched decoded output signal of FIG. 8A includes a correlation peak 803 corresponding to the input laser pulse.
  • the matched decoded output also includes some power in one or more sidelobes 805 and a noise-like background 807.
  • the unmatched decoded output of FIG. 8B includes sidelobe peaks 809 superimposed on a noise-like background 81 1 .
  • configurable encoding and decoding is described above with reference to 3-chip and 5-chip codes.
  • Larger numbers of chips and various coding methods for example, phase codes or multilevel phase and/or amplitude codes
  • Codes having larger numbers of chips generally produce lower crosstalk (reduced sidelobe amplitude and noise-like background amplitude) and permit larger numbers of optical signals to be coded onto a single optical fiber.
  • the higher numbers of channels requires fiber grating codes having larger numbers of grating segments, and can be more expensive and difficult to implement. For many applications, the number of channels is selected in consideration of these factors.
  • FIGS.9A-9C illustrate decoded optical signals 901, 903, 905, respectively, produced by decoding a composite-coded optical signal (coded with ⁇ 1, -1, -1 ⁇ ) with codes ⁇ 1, -1, 1 ⁇ , ⁇ 1, -1, -1 ⁇ , and ⁇ 1, 1, 1 ⁇ , respectively.
  • a maximum power associated with decoding with an unmatched code is referred to as "crosstalk” or a "sidelobe.”
  • the crosstalk for these codes is 4.
  • a maximum power produced in decoding with a matched code is referred to as a decoded signal level.
  • the decoded signal level for these codes is 9.
  • FIGS. 10A-10C illustrate decoded optical signals 1001, 1003, 1005, respectively, produced by decoding a composite-coded optical signal (coded with ⁇ 1, -1, -1 ⁇ ) with codes ⁇ 1 , -1 , 1 ⁇ , ⁇ 1 , -1 , -1 ⁇ , and ⁇ 1, 1, 1 ⁇ , respectively.
  • a maximum power associated with decoding with an unmatched code is referred to as "crosstalk” or a "sidelobe.”
  • the crosstalk for these codes is 36.
  • a maximum power produced in decoding with a matched coded is referred to as a decoded signal level.
  • the decoded signal level for these codes is 81.
  • the worst-case ratio generally obtains for encoding and decoding with the same supercode but with a different subcode, or with the same subcode but a different supercode. For composite codes formed of three or more codes, the greater the number of code mismatches in encoding and decoding, the lower better the signal-to- crosstalk ratio.
  • encoder and decoding were used with reference to applying a code to an optical signal
  • decoder and decoding were used with reference to removing or stripping a code from an optical signal.
  • coder and coding can be used to describe both applying and removing a code.
  • decoding does not necessarily return an encoded optical data signal to its form prior to encoding, but removes the code sufficiently to permit data recovery from the optical data signal Nevertheless, as used herein, decoding is referred to as "removing” or “stripping" a code from an optical data signal. Representative embodiments were discussed with respect to coding optical signals, but electric signals (such as radio-frequency signals) and acoustic signals can be similarly coded.
  • Optical signals are typically described as electromagnetic radiation of wavelengths between about 1 00 nm and 0.1 mm, but longer and shorter wavelengths can be included.
  • subcodes are illustrated in which there are no temporal gaps between chips. In general, time chips need not be adjacent.

Abstract

L'invention concerne des codeurs et des décodeurs permettant un codage composites de signaux de données optiques. Ces codeurs (211, 231) et décodeurs (243, 261) appliquent des sous-codes et des supercodes. Les sous-codes sont choisis de manière à présenter une durée inférieure à la durée inter-circuits ou intra circuit des supercodes. Les codeurs (211, 231) et les décodeurs (243, 261) ('codeurs') comprennent des réseaux de Bragg à fibre configurés de manière à pouvoir coder et décoder un sous-code, un supercode ou un code composite. En utilisant un codeur de sous-code et un codeur de supercode on peut reconfigurer un codeur en sélectionnant différents sous-codes et supercodes. L'invention concerne également des systèmes et des procédés de communication utilisant des codes composites.
EP99960431A 1998-11-17 1999-11-17 Codes, procedes et dispositif de codage et de decodage optique Withdrawn EP1141756A4 (fr)

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US10870098P 1998-11-17 1998-11-17
PCT/US1999/027257 WO2000029887A1 (fr) 1998-11-17 1999-11-17 Codes, procedes et dispositif de codage et de decodage optique
US108700P 2008-10-27

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EP1141756A4 EP1141756A4 (fr) 2006-02-08

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WO2002084905A2 (fr) * 2001-04-18 2002-10-24 Accessphotonic Networks Inc. Sources optiques et emetteurs pour telecommunications optiques
US7773882B2 (en) * 2005-05-26 2010-08-10 Telcordia Technologies, Inc. Optical code-routed networks

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CA2351713A1 (fr) 2000-05-25
WO2000029887A1 (fr) 2000-05-25
JP2002530906A (ja) 2002-09-17
EP1141756A4 (fr) 2006-02-08
CA2351713C (fr) 2006-02-21

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