JP2002530906A - Code, method and apparatus for optical encoding and decoding - Google Patents

Abstract

(57) [Summary] An encoder (211 and 231) and a decoder (243 and 261) that apply both a subcode and a supercode are encoders and decoders that apply a composite code to an optical data signal. include. The subcode has a duration selected to be less than or equal to the duration of the supercode or the duration between chips. The encoder (211 231) and decoder (243 261) ("coder") comprise a fiber Bragg grating configured to encode or decode a subcode, supercode, or composite code. . By encoding and decoding with a subcode coder, the coder can be reconfigured by selecting a different subcode or supercode. It also describes a communication system and method using composite code.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to an optical communication system.

BACKGROUND OF THE INVENTION Code division multiple access is used in satellite communications and radiotelephones. CDM
Method A is a broadband method for multiplexing and distributing multiple data-carrying electromagnetic signals on a signal transmission medium. These data signals are distinguished by encoding with different composite spectral codes or time codes. The spectrum of the resulting coded data signal is much wider than the spectrum of the uncoded data signal. The number of data signals that can be well multiplexed and distributed in a CDMA system depends on the complexity of the coding. Traditionally, CDMA codes are divided into "chips", which are defined as the shortest duration of a temporal feature that encodes into a data signal. The greater the number of chips, the greater the number of users, or the less the user-to-user interface for a fixed number of multiplexed data signals.

Radio frequency (RF) CDMA utilizes a binary phase code, in which each chip has one of two values for the phase of the electromagnetic field that carries the data signal. Such a binary code can be generated in real time by a fast shift register array. Code generation algorithms for generating a binary CDMA code set include algorithms for generating a Gold code, a Kasami code, a maximum column length code, a JPL code, and a Walsh code.

[0004] One alternative to using these code sets is to generate a new code set with Monte Carlo or other code search algorithms. However, as the number of code chips increases, the operation time of these algorithms becomes unrealistically long. If a non-binary CDMA code set is required, that is, if a chip that assumes three or more levels is used, the operation time further increases.

[0005] Optical CDMA systems use passive optical coding and decoding, for example with a diffraction grating. Since encoding and decoding are performed passively, high-speed digital logic circuits for encoding and decoding optical signals are unnecessary. Thus, optical CDMA systems are not limited to the binary phase or amplitude codes used in RF CDMA.

Finding new code sets, especially for use in optical communication systems, can be difficult and time consuming. Therefore, there is a need for a method and apparatus for generating code sets, especially code sets with a large number of chips, having predictable crosstalk characteristics. Also, encoders and decoders for encoding and decoding optical fields or other electromagnetic signals using such encoding are required.

FIG. 1 is a diagram of a data transmission system 101 that generates a data signal 103 from a data source 105. As shown in FIG. 1, the data signal 103 is represented by binary, ie, on-off modulation of an electromagnetic carrier such as an optical carrier. The on-off modulation has been chosen for illustrative purposes only, and there may be other modulations including phase, amplitude, luminance, and frequency modulation. In addition, non-binary modulation with more than two modulation levels can be used.

[0008] Super code encoder 107 receives the data signal 103, applies a predetermined code R _i selected from the code group R to a data signal 103. For illustrative purposes, the code R _i = {1, −1,1} is selected to represent the representative bit 109 of the data signal 103
Apply to As indicated by code R, encoder 107 receives bits 109 and converts them into “super-coded” bit packets 111. Super coded bit packet 111 includes a delay time T _RC only relatively delayed super coded bits ( "Super Bit") 113-115, where T _RC is the duration of the super-code chips. In addition to this, the super bit 113
, 115 are inverted, but the phase of the super bit 114 is inverted. The encoder 107 applies the code R _i to the entire digital signal 103 to generate a super-coded data signal, which is the sum of the super bits corresponding to all of the bits of the data signal 103.

The sub-code encoder 117 receives the super-coded data signal, and
Code S selected from code set S_iApply Code S for illustrative purposes_i= ｛-1,
1, -1}. Code S_iFor super-coded bit packets.
Combined sub-coding and super-coding ("composite-coded"
) Generate a bit packet 121, which contains super bits 113, 1,
14 and 115, the sub-coded bits 123, 125, 1
27. The encoder 117 provides a delay time T, which is the duration of the subcode chip. _SC Only by relatively delaying some, and super-coded bits
By changing the phase of the
Each of the sub-bits 123 to 115
, 125, 127 are generated. The encoder 117 outputs the code S_iSuper coded
A composite coded data signal is generated by applying to the converted data signal.

[0010] Encoders 107 and 117 convert codes from respective sets R and S into data signal 1
Apply to 03. If the sets R, S include N _R and N _S codes respectively,
N _R × N _S different encodings are possible. For example, if each of the sets R and S includes 5 codes, 25 encodings are possible. Thus, as the product of N _R and N _S increases, the number of possible encodings increases, allowing a large number of encodings even with a small number of code sets. In addition, the sets R, S can be subsets of a large code set, and these sets can include different codes as well as identical codes. In this way, N ² different encodings can be performed using N code sets.

Although FIG. 1 shows encoding with two sets of codes (sets R, S), additional sets of codes can be used to further increase the number of possible encodings. If the sub-code bits 113 to 115 are further encoded with a code set Q having N _Q codes, the number of possible encodings is N _R × N _S × N _Q. A code obtained by combining two or more code sets such as the code sets R and S is referred to herein as a “composite code”.

[0012] The encoders 107 and 117 are adapted to perform encoding or decoding according to the type of signal to be encoded or decoded.
It can be an electronic, acoustic, or optical encoder. Optical encoders are described, for example, in US patent application Ser. No. 09 / 354,851 entitled "TIME-WAVELENGTH MULTIPLE ACCESS O."
PTICAL COMMUNICATION SYSTEM AND METHOD ", No. 09 / 120,959," SEGMENTED COMP
LEX FIBER GRATING ", 09 / 115,331" SEGMENTED TASM GRATINGS ", and U.S. Patent No. 5,812,318, which are incorporated herein by reference.

The codes R _i and S _i used above are selected as typical examples. More generally, a code includes more than one "chip" that specifies the modulation to be applied to the signal. At times that are relatively different by the chip duration T _C , chip modulation is applied to the signal. Thus, the coding of the data signal is specified by the code and the chip duration. Further, the supercode is specified by the duration between chips. Code R with total duration T _R , number of chips N _R , and chip duration or inter-chip delay T _RC , and total duration T _S , number of chips N _S , and chip duration or inter-chip delay T _SC Are actually orthogonal so that they can be decoded if T _R ≦ T _SC . A composite code can be generated from the code R (subcode) and the code S (supercode). The composite code has a predetermined 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 number of chips of the supercode. The chip duration of the composite code is equal to the chip duration of the subcode. In the composite code, the subcode is repeated a number of times equal to the number of chips in the subcode.

A code group, a super code and a sub code (and a sub-sub code) so that a data signal encoded with a specific composite code is decoded only with a decoding composite code that matches the code signal. It is preferable to select the chip duration. Decoding with mismatched decoding codes only produces a noisy background signal or low amplitude "side lobes" or "crosstalk".

If there is temporal orthogonality between the supercode and the subcode (ie, low-amplitude cross-correlation and a noise-like background signal), if the codes of the code set are sufficiently orthogonal, a small number of chips Can be generated from the code set having By using the selected code of the composite code set as a supercode and using the other selected code of the composite code set as a subcode, a code in the composite code set can be generated. The composite code set is composed of all combinations of supercode and subcode. For example, if the code set has M codes each including N _m chips, the composite code set includes M × M codes each having N _m × N _m chips.

FIG. 2A shows a single data bit after being encoded with a 5-chip subcode that can be represented by {1,1,0,1,1}. This data bit can be divided into five parts that are relatively delayed by a delay time _TRC . In this code, one part corresponding to "0" has no data pulse amplitude.

FIG. 2B shows data bits encoded with a 5-chip supercode, which can be represented by {1,1,1,0,1}. The sub-coded data bits are repeated once for each non-zero chip of the super code, and the bits of each sub code are multiplied by the code value associated with the corresponding super code chip. Although both the supercode and the subcode have a time characteristic of approximately the same duration, the characteristics of the chip spacing (for the supercode) are larger than the duration of the entire subcode, so that T _R ≦ T _SC Where T _R is the duration of the subcode and T _SC is the chip spacing of the supercode. The total duration of the subcode of FIG. 2A is:
It is less than the interval between chips of the super code.

FIG. 2C shows data bits after being encoded by the subcode and the supercode for performing the encoding shown in FIGS. 2A and 2B, respectively. The encoding in FIG. 2C is equivalent to the encoding with the composite code defined by the subcode and the supercode.

Extending the procedure for generating composite code beyond two consecutive levels shown in FIGS. 1 and 2A-2C to include three or more levels that provide longer composite code it can. Further, a composite code set can be generated with a code set having a different number of chips for each code used to define a supercode and a subcode.

Optical encoders and decoders for generating the composite code can include those disclosed in the references cited above. Using the linear spectral filtering techniques described in these references, the composite code can be optically encoded and decoded onto the optical data stream. A preferred encoder / decoder using an optical circulator and a reflective fiber Bragg grating is described below. Other encoders / decoders use a beam splitter or diffraction grating to simultaneously encode or decode both subcodes and supercodes. In addition, sub-codes and super-codes can be encoded or decoded in any order or at the same time, and the sub-coding or super-coding operations may be performed at a single point or at different points. Can be.

FIGS. 2D and 2E show two-stage optical encoding using the codes of FIGS. 2A to 2C. FIG. 2D shows a single shot input data pulse 201 received by a subcode encoder 211 with an optical circulator 213 and a fiber Bragg grating 215 selected to encode the selected subcode. The sub-coded data pulse 217 is output from the sub-code encoder 211 through the output port 219 of the optical circulator. As shown in FIG. 2E, the super code encoder 2
31 receives the sub-coded data pulse 217. The supercode encoder 231 includes an optical circulator 233 and a fiber Bragg grating 235 for encoding the selected supercode. The data pulse 241 generated by the super code encoder 231 is encoded according to the composite code.

FIGS. 2F and 2G show two-stage optical decoding. FIG. 2F shows a supercode decoder 243 that receives the data pulse 241 encoded in the composite code. The super code decoder 243 includes 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 super code from the data pulse 241, and the resulting super code decoded data pulse 254 is output via the output port 255. Data pulse 254 corresponds to the data pulse encoded in the subcode. When the fiber Bragg grating 253 decodes a super code that does not match the super code of the data pulse 241, the output of the super code decoder 243 becomes a noise-like signal, that is, a low-power signal.

FIG. 2G shows a sub-code decoder 261 that receives the sub-coded data pulses 254. The subcode decoder 261 comprises an optical circulator 263 and a fiber Bragg grating 265 for decoding the selected subcode. The decoded data pulse 271 is output from the output port 26 of the optical circulator 263.
0 and output from the subcode decoder. If the data pulse 254 is encoded with a sub-code that matches the fiber Bragg grating 265, the sub-code is stripped (released) and the output of the sub-code decoder 261 becomes an uncoded optical data pulse. The subcode of the data pulse 254 is
If the subcode does not match the subcode 1, the output of the subcode decoder 261 becomes a noise-like signal, that is, a low-power signal.

FIG. 3A is a diagram of a segmented fiber Bragg grating (“fBg”) 301 for encoding or decoding a subcode. fBg 301 comprises a grating segment 305 and a fiber length 355. The grating segments 305 have a periodic change in the refractive index of the fiber core or cladding, as described in US patent application Ser. No. 09 / 120,959. Grating segment 305 and fiber length 407 are in direction 3
Along the 07, extending a length corresponding to the subcode chip time T _RC. fBg3
01 has five chip segments 311 to 315, and the code R = {1,1,0
, 1,1}.

FIG. 3B is a diagram of fBg 351 for encoding or decoding a supercode. fBg 351 comprises a grating segment 353 and has a fiber length 355. Each grid segment 353 has a length corresponding to T _RC of FBg351, by a length corresponding to the number of chips × T _RC, i.e. for example 5T _RC are separated from each other. The fBg 351 encodes a 5-chip subcode, and has five chip segments 361 to 365.

For efficient subcode and supercode encoding / decoding, the lattice segment lengths for the matching subcode and supercode fBg are approximately equal. In addition to this, the chip segment 361 of the supercode grid 351
The spatial period of ~ 365 is made larger than the total length of the subcode grating 301. This guideline is the result of matching the bandwidth of the subcode and supercode fBg. Further, the total duration of the subcode is preferably equal to or less than the duration of the subcode chip (that is, the chip segments 361 to 365). Similar guidelines apply to other linear spectral filtering devices for encoding and decoding subcodes and supercodes.

FIG. 4 is a diagram of a switched encoder 400 that can apply any of a number of separate composite codes to an input data pulse. (The corresponding switched decoder also has a similar structure.) 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 converts this data pulse to 1 × 1
The switch 405 transmits the data pulse to the 10-segment fiber Bragg grating 40 under the control of the address selector 406.
7-416. Fiber Bragg grating (fBg
) Select 407-416 to encode the selected supercode.

After the encoding of the super code, the circulator 403
The supercoded data pulse 422 provided by 16 is directed to an optical circulator 421. The circulator 421 directs the pulse 422 to 1 × 10 switches 430, and the switch 430 divides the data pulse into a 10-segment fiber Bragg grating 4 as indicated by the address selector 406.
Selectively direct one of 31-440. Then, a composite coded pulse is generated and directed to the output 443 by the circulator 421. From each of the 10 supercodes and 10 subcodes (ie, fBg 407-4
16 and fBg 431-440, respectively, by selecting one
100 composite codes can be applied.

The code C of N chips is a complex or real chip modulation C to be applied to the optical signal. _i The set {C1,. . . , CN}. These
In addition to the top modulation, the kth chip contains the modulation exp (-jωkT). Next in time
T = T for subcodes with adjacent chips_chipAnd into the super code
For T = T_DchipAnd where T_DchipIs the temporal chip interval.

FIG. 5A is a diagram of a preferred transmitter 501 with a distributed feedback (DFB) laser.
Which receives an electrical data signal 505 and generates an optical data signal 507.
It is. As shown in FIG. 5A, the electrical data signal 505 and the optical data signal 507
Is an amplitude-modulated binary signal. Optical data signal generated by DFB laser 503
507 is almost BW_pulse= 35 GHz duration, with an optical bandwidth of approximately T _pulse = 25 ps consisting of a series of laser pulses 509 or "bits". D
The FB laser 503 emits a laser pulse 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
However, no laser pulse is emitted for the “0” bit. DFB laser 503
Used with an optical modulator, the DFB laser 503 selected a series of laser pulses.
Emit at the bit rate and the modulator selectively absorbs these pulses or
If so, these pulses are modulated according to the electrical data signal 505. Mark
The encoder 511 receives the optical data signal 507 and transmits it on the optical fiber 515.
A composite coded optical signal 513 is generated. This encoder has a code select input 517
Through which the ith subcode and the jth supercode are selected.
You.

As shown in FIG. 5B, the encoder 511 includes optical circulators 521 and 523, optical switches 525 and 527, and fiber Bragg gratings 531 to 536. Optical circulator 521 directs optical data signal 507 to optical switch 525. Optical switch 525 responds to input 541 by sending optical data pulse 507 to several output ports 543-545 (corresponding to j = 1, 2, or 3, respectively).
Orient to. As shown in FIG. 5B, the optical switch 525 has three outputs 543-545 connected to fiber Bragg gratings 531-533, respectively. The fiber Bragg gratings 531 to 533 encode each subcode into an input optical signal 507. When the fiber Bragg grating 531 is selected (j = 1), the fiber Bragg grating 531 reflects the optical signal 507 back to the circulator 521 to generate a sub-coded optical signal. The circulator 521 directs the sub-coded optical signal to the circulator 523, and the circulator 523 directs the sub-coded optical signal to the optical switch 527. The optical switch 527 is i
A corresponding fiber Bragg grating is selected from the fiber Bragg gratings 534-536 in response to an input 551 enabling selection of the (i = 1,2,3) th supercode. In FIG. 5B, corresponding to i = 1, ie, fiber Bragg grating 534
The super code corresponding to is selected. Fiber Bragg grating 534 reflects the sub-coded optical signal to generate a super-coded and sub-coded (ie, composite coded) optical signal that is converted to optical switch 527, optical circulator 523, and It is directed back to fiber 515.

In a preferred embodiment, three 3-chip code sets {1, -1, 1}, {1, -1, -1}, and ｛, respectively, corresponding to i = j = 1, 2, 3 respectively. 1,1,1} is used for the subcode and the supercode. From these codes, nine composite codes are formed, each corresponding to nine chips. The complete set of these nine 9-chip codes is as follows: Table 1 Three-chip code # 1,-used together as subcode and supercode
1, 1}, {1, -1, -1}, and a composite code i j code 1 1 {1, -1, 1, -1, 1, -1, -1, 1 generated by {1, 1, 1} , −1,1} 12 {1, −1, −1, −1,1,1,1, −1, −1,1} 13 {1,1,1, −1, −1, −− 1,1,1,1} 2 1 {1, -1,1, -1,1, -1, -1, -1, -1, -1,} 2 2 {1, -1, -1, -1, -1,1, 1, -1,1,1} 23 {1,1,1, -1, -1, -1, -1, -1, -1, -1, -1} 31 {1, -1,1,1, -1 , 1,1, -1,1} 32 {1, -1, -1, -1, -1, -1, -1,1, -1, -1} 33 {1,1,1,1,1,1 For the 1,1,1,1} sub-code, a chip time delay T _sub less than the bit duration of the optical data signal is selected, that is, T _sub is less than 25 ps. Here for convenience selected T _sub to 25 ps.

FIG. 6A is a diagram of a fiber Bragg grating 601, such as any of the fiber Bragg gratings 531-533, for encoding a subcode selected from the three-chip code described above. The fiber Bragg grating 601 comprises grating segments 603-605, wherein the refractive index in each core 607 varies periodically.
In an alternative configuration, a change in the refractive index can occur in the cladding region 609. The optical signal propagates along the z-axis of the fiber Bragg grating 601.

FIG. 6B is a graph of the change in reflectance of the grating segments 603-605. In the fiber Bragg grating 601, an optical data signal propagates a distance L at a time t given by t = 100 Lps / cm. (This relationship is normal for silica based optical fibers.) For a three-chip subcode of T = 25 ps, each of the grating segments 603-605 of the fiber Bragg grating 601 is 2.5 mm long ( 25ps /
(100ps / cm)), the total length is 7.5mm. Bragg gratings are segments 603-60
5, each index of refraction is the wavelength λ of the optical data signal and the fiber core 607.
Periodically changes with a period corresponding to the refractive index n _core of N _{co re} in telecommunication fiber is usually n _core = 1.5. For a DFB wavelength of 1550 nm, the grating period is about 516
nm.

The fiber Bragg grating 601 encodes an optical signal with a code selected based on the relative phase shift of the spatial variation of the refractive index within the segments 603-605. As shown in FIG. 6B, the fiber segment 604 has a 180 degree phase shift with respect to the fiber segments 603 and 605, and these segments correspond to the subcodes {1, -1, 1}. (If an absolute phase reference is specified, this code and other codes can be specified by absolute phase and phase difference.)

FIG. 6C is a diagram of a fiber Bragg grating 651 (supercode fiber) for supercode encoding, such as fiber Bragg gratings 534-536. The supercode fiber 651 comprises grating segments 653-655 having a change in refractive index selected based on the pulse width and bandwidth of the laser. As shown in FIG. 6C, these lattice segment lengths are the subcode lattice segment lengths.
Choose to be equal to 2.5mm. The spacing of the subcode grating segments is chosen such that the time delay between adjacent chips is well over the subcoded laser pulse. Since the total duration of the subcodes corresponds to a fiber Bragg grating length of 7.5 mm, the supercode grating segments have a spacing of 7.5 mm corresponding to T _SC . The grating segments of supercode grating 651 are similar to subcode grating segments 603-605 and have the same spatial period Λ and the same relative phase, ie, segment 654 is 180 degrees out of phase with segments 653,655. ,
This phase difference is not shown in FIG. 6D.

FIG. 7 illustrates decoding of the composite coded optical signal generated by the encoder of FIG. 5B,
It is a figure of the receiver 701 which converts into an electric signal. Receiver 701 includes a decoder 703 that includes fiber Bragg gratings 705-710 and selects these fiber Bragg gratings to decode the composite code encoded by the encoder of FIG. 5B. In addition, receiver 701 includes photodetector 711, amplifier 713, and threshold electronics 715. The photodetector 711 converts the optical signal into an electrical signal, and the threshold electronic circuit 715 supplies an electrical signal corresponding to the decoded optical signal with the side lobe and / or noise-like background signal attenuated. .

The fiber gratings 705 to 710 of the decoder are selected to decode the composite code (combination of subcode and supercode) used by the encoder. Fiber gratings 705 to 710 of the decoder corresponds to the code C used in coding, and corresponding to _{D i} = C nc- _i ^* becomes code D. For fiber Bragg gratings with medium or low grating segment reflectivity, the decoder grating is identical to the encoder grating, but the optical signal to be encoded and decoded is input to the fiber Bragg grating from different directions. To be done. For example, the end 721 of the fiber Bragg grating 705 is used as an input for decoding, and the end 723 is used as an input for encoding. Alternatively,
Ends 721 and 723 can be used as inputs for encoding and decoding, respectively.

The decoder 703 includes optical circulators 727 and 729 and an optical switch 731,
733. These optical switches provide j for decoding the composite code.
Respond to the ith subcode and the ith supercode. As a result, the decoder 703 can be reconfigured (rearranged). If reconfigurable encoding and decoding is not required, a single fiber Bragg grating that encodes the optical signal with a composite code can be provided, and a single matching fiber Bragg grating It can serve to decrypt the composite code. Providing separate fiber Bragg gratings for subcodes and supercodes is useful for reconfigurable coding.

A code C having N chips (whether a subcode or a supercode), ie, C = {C ₁ , C ₂ ,. . . , C _N } are decoded by the code D = {D ₁ , D ₂ ,
. . . , D _N }, where D _i = C _Ni ^* . “*” Represents a complex conjugate number. Then, the decoded optical signal E _decode becomes the total (or integrated value) over all the chips, that is, E _decode = ΣC _i D _ji . This sum is
Similar to cross-correlation.

FIGS. 8A and 8B show decoded optical signals generated by a matching decoder and a mismatching decoder, respectively. The matched decoded output signal of FIG. 8A has a correlation peak 803 corresponding to the input laser pulse. There is also some power in the matched decoding output, one or more sidelobes 805 and the noisy background signal. In contrast, the mismatched decoded output of FIG. 8B has a side lobe peak 809 inserted into the noisy background signal 811.

For purposes of illustration, configurable encoding and decoding has been described above for three and five chips. More chips and different encoding methods (eg, phase codes or multi-level phase and / or amplitude codes) can be used. Codes with more chips generally produce less crosstalk (reduced side lobe amplitude and noise-like background signal amplitude) and encode more optical signals onto a single optical fiber. It can be so. A larger number of channels requires fiber grating codes with a larger number of gratings, which can be more expensive and more difficult to achieve. For many applications, the number of channels is chosen in consideration of these factors.

FIGS. 9A to 9C show decoded optical signals 901, 903, and 905, each of which is a composite coded optical signal (encoded by {1, −1, −1}). It is generated by decoding with codes {1, -1, 1}, {1, -1, -1}, and {1, 1, 1}. The maximum power associated with decoding with mismatched codes is referred to as "crosstalk" or "side lobes". 9A and 9
As shown in C, the crosstalk for these codes is four. The power generated by decoding with matching codes is called the decoded signal level. As shown in FIG. 9B, the decoded signal level for these codes is nine.

FIGS. 10A to 10C show decoded optical signals 1001, 1003, and 1005, which are composite encoded optical signals (encoded by {1, -1, -1}), respectively. The codes {1, -1,1}, {1, -1, -1} and {1,1,
This is caused by decoding at 1｝. The maximum power associated with decoding with mismatched codes is referred to as "crosstalk" or "side lobes". FIG.
As shown at 0C, the crosstalk for these codes is 36. The power generated by decoding with matching codes is called the decoded signal level. As shown in FIG. 10A, the decoded signal level for these codes is 81. A longer code does not always result in an improved worst-case decoded signal-to-crosstalk ratio, i.e., the worst-case ratio is 9: 4; The talk ratio is as high as 81: 4. Worst case ratios are generally obtained for encoding and decoding with the same supercode but different subcodes, and for the same subcode but different supercodes. 3
For composite codes formed of one or more codes, the greater the number of code mismatches in encoding and decoding, the lower the signal-to-crosstalk ratio.

In the above, for convenience, “encoder” and “encoding” are used in connection with applying the code to the optical signal, and “decoding” is performed in conjunction with removing or removing the code from the optical signal. ”And“ decoding ”. The terms "coder" and "coding" may be used both to apply and to remove the code. In addition, decoding, as used herein, refers to "removing" or "decoding" a code from an optical data signal, but nevertheless, decoding does not necessarily involve encoding. The purpose is not to return the optical data signal to the form before encoding, but to remove the code so that data recovery from the optical data signal is sufficiently performed.

Although the preferred embodiment has been described in connection with coding optical signals, electrical and acoustic signals (such as radio frequency signals) can be coded as well. Optical signals are typically described as electromagnetic radiation at a wavelength between about 100 nm and about 0.1 mm, but can include longer or shorter wavelengths. In addition, the subcode is represented as having no time gap between chips. In general, the time chips need not be adjacent.

In the above embodiments, the principle of the present invention has been shown and described. However, it is possible to change the details of these embodiments and to modify the apparatus without departing from the scope of the present invention. That will be apparent to those skilled in the art. We claim all matters falling within the scope of the claims as right inventions.

[Brief description of the drawings]

FIG. 1 is a diagram of a data transmission system using a 3-chip supercode and a 3-chip subcode.

FIG. 2A is a diagram of a subcode of an encoded data pulse. FIG. 2B is a diagram of the supercode of the encoded data pulse. FIG. 2C is a composite coded data pulse obtained by combining the subcode of FIG. 2A with the supercode of FIG. 2B. FIG. 2D is a diagram of a sub-code encoder that generates data pulses encoded into sub-codes. FIG. 2E is a diagram of a supercode encoder that receives data pulses encoded in the subcode of FIG. 2D and generates a composite encoded data pulse. FIG. 2F is a diagram of a supercode decoder that receives a composite coded signal and generates a subcoded data signal. FIG. 2G is a diagram of a sub-code decoder that receives a super-coded data signal and generates a sub-coded data signal.

FIG. 3A is a diagram of a fiber Bragg grating for encoding or decoding a subcode. FIG. 3B is a diagram of a fiber Bragg grating that encodes or decodes a supercode.

FIG. 4 is a diagram of a reconfigurable encoder that applies a selected composite code.

FIG. 5A is a diagram of a transmitter for transmitting an optical signal encoded with a composite code. FIG. 5B is a configuration diagram of the reconfigurable encoder shown in FIG. 5A.

FIG. 6A is a diagram of a fiber Bragg grating that encodes a subcode. FIG. 6B is a graph showing the change in refractive index as a function of position in the fiber Bragg grating of FIG. 6A. FIG. 6C is a diagram of a fiber Bragg grating that encodes a supercode. FIG. 6D is a graph showing the change in refractive index as a function of position in the fiber Bragg grating of FIG. 6C.

FIG. 7 is a diagram of a receiver that decodes an optical signal encoded with a composite code.

FIG. 8A is a graph showing the power of an optical signal encoded and decoded with a matching composite code as a function of time. FIG. 8B is a graph showing the power of an optical signal encoded and decoded with a mismatched composite code as a function of time.

9A to 9C are graphs showing power as a function of time for encoding and decoding an optical signal with a mismatched code.

10A and 10B are graphs showing power as a function of time for encoding and decoding an optical signal with a composite code for matching and a composite code for mismatch.

[Procedure amendment]

[Submission date] June 15, 2001 (2001.6.15)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 25

[Correction method] Change

[Correction contents]

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI theme coat ゛ (Reference) H04B 10/152 H04J 13/00 (72) Inventor Eric Es Manilov 97404 Eugene Alindale Drive, Oregon United States 3160 (72 Inventor Tomers W. Mossburg 97404 Oregon, United States of America 97404 Eugene Limbrook Drive 548 (72) Inventor Michael John Munroe United States of America Oregon 97403 Eugene Walnut Street 1639 (72) Inventor John N. Sweeter United States of America 97405 Oregon Street Oregon 3230 F-term (reference) 2H050 AB05X AC84 AD00 5K002 AA02 AA04 BA02 BA05 BA13 BA21 CA12 DA06 FA01 5K022 EE0 1 EE11 EE21 EE31 [Continued summary]

Claims (27)

[Claims] A sub-code encoder configured to receive a signal and apply a sub-code to the signal; and a sub-code encoder configured to receive the signal and apply the sub-code to the signal. A coder provided, wherein the total duration of the subcodes is less than or equal to the interval between chips of the supercode. 2. The coder according to claim 1, wherein said signal is an optical signal. 3. The sub-code encoder according to claim 2, wherein the sub-code encoder is configured to direct the optical signal to the super code encoder after applying the sub-code. Coder described. 4. The super code encoder according to claim 2, wherein the super code encoder is configured to direct the optical signal to the sub code encoder after applying the super code. Coder described. 5. The coder according to claim 2, wherein said supercode is a number of chips Nc _super , said subcode is a number of chips N _sub , and N _sub is not equal to Nc _super . 6. The coder according to claim 2, wherein said supercode encoder comprises a fiber Bragg grating. 7. The coder according to claim 2, wherein said sub-code encoder comprises a fiber Bragg grating. 8. A plurality of coders corresponding to respective subcodes; a plurality of coders corresponding to respective supercodes; an optical switch; a composite code selected by setting the optical switch; A composite code, comprising: an optical addresser that causes an optical data signal to be coded by at least one selected of the sub-codes of at least one of the sub-codes and at least one selected of the plurality of super-codes. A reconfigurable coder for applying to a signal, wherein the optical addresser specifies the selected sub-code and the selected super-code. 9. The reconfigurable coder of claim 8, wherein the plurality of coders corresponding to subcodes are respective fiber Bragg gratings. 10. The reconfigurable coder of claim 8, wherein the plurality of coders corresponding to a supercode are respective fiber Bragg gratings. 11. The reconfigurable coder of claim 8, wherein the subcode has a duration that is less than or equal to the duration between chips of the supercode. 12. Applying to the data signal a sub-code comprising N _sub code chips of duration Tc _sub ; either before or after applying said sub-code, to a chip of duration Tc _super Applying a super code comprising N _super to said signal. 13. The method according to claim 12, wherein said signal is an optical signal. 14. The method according to claim 13, wherein said N _sub × Tc _sub is less than or equal to said Tc _super . 15. The method of claim 14, further comprising: selecting a code; and defining a supercode and a subcode based on the code. 16. Selecting a set of codes for a supercode; selecting a set of codes for a subcode; based on the set of subcodes and the set of supercodes, Forming a set of composite codes; and applying at least one of the composite codes to an optical data signal. 17. The method of claim 16, further comprising the step of defining a duration between chips for supercode to be greater than or equal to a duration for subcodes. 18. The set of codes selected for a supercode and the set of codes selected for a subcode are the same.
The method described in. 19. The method of claim 16, further comprising the step of providing a fiber Bragg grating for applying a subcode portion of the composite code.
The method described in. 20. The method of claim 16, further comprising providing a fiber Bragg grating for applying a supercode portion of the composite code. 21. A method for coding an optical signal with a composite code, comprising: applying a subcode R having a total duration T _sub , a number of chips N _sub , and a chip duration Tc _sub to the optical signal; Applying a supercode S having a time T _super , a number of chips N _super , and a chip duration Tc _super , wherein T _sub ≦ T _super and applying the subcode R and the supercode S. Encoding the optical signal with the composite code. 22. The method of claim 21, further comprising selecting the sub-code R and the super-code S to remove a composite code from the optical signal. 23. The method of claim 21, wherein said composite code has a number of chips equal to N _sub × N _super . 24. The method of claim 21, further comprising selecting a set of sub-subcodes having a duration less than or equal to the duration of the subcode. 25. An encoder configured and applied to apply the composite code to the optical data signal; a transmission medium configured to receive the optical signal to which the composite code is applied; and And a decoder for removing the composite code from the signal. 26. The system of claim 25, wherein the encoder is reconfigurable to encode a set of composite codes. 27. The system of claim 26, wherein said encoder comprises a set of fiber Bragg gratings for encoding said set of composite codes.