JP2011250079A - Optical-code-division-multiplex transmitting circuit and optical-code-division-multiplex receiving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical-code-division-multiplex transmitting circuit and an optical-code-division-multiplex receiving circuit that are capable of increasing the degree of encoding multiplexing without requiring an increase in the number of optical modulating means and optical detecting means and causing deterioration in wavelength dispersion.SOLUTION: The optical-code-division-multiplex transmitting circuit performs, for plural optical carriers having different optical frequencies, multi-valued modulation on each of two branched optical carriers with two of plural multi-valued electric signals to generate a multi-valued signal beam obtained such that phases of both are made orthogonal to each other for combination, and performs optical frequency multiplexing on the multi-valued signal beam before output.

Description

  The present invention relates to an optical code division multiplexing transmission circuit and an optical code division multiplexing reception circuit used for optical code division multiplexing communication.

  An optical code division multiplexing (CDM) system is a system that multiplex-transmits an optical CDM signal that has been code-spread according to a specific code. A unique code is assigned to each optical CDM transmission / reception circuit. Each transmission circuit outputs an optical CDM signal spread by encoding corresponding to the assigned unique code. On the receiving side, only the optical CDM signal output from the transmission circuit assigned the same unique code as that of the reception circuit can be decoded from the multiplexed optical CDM signal, and a desired optical CDM signal is selectively received.

  So far, there has been proposed a method of spreading the pulse signal light on the time axis by modulating the optical phase of each optical frequency component of the pulse signal light in accordance with the unique code assigned to the transmission circuit ( For example, see Non-Patent Documents 1 and 2.) In addition, a method of directly diffusing pulse signal light on the time axis using SSFBG (Superstructured Fiber Bragg Grating) or the like has been proposed (for example, see Non-Patent Document 3).

  However, these systems require an optical codec device that performs strict control of the optical phase and time control of the chip time (= bit time / code length) order. In addition, the number of code multiplexing is limited by multiple access interference (MAI) and beat noise generated at the time of detection when a plurality of optical CDM signals are simultaneously input to the receiving circuit. Therefore, the influence of MAI and beat noise is reduced by applying a time gate based on time synchronization between signal lights, an optical threshold device using nonlinear characteristics of an optical medium, and forward error correction (FEC). This requires a complicated transmission / reception circuit configuration.

  On the other hand, as shown in FIG. 1, each optical frequency component is multi-valued amplitude modulated (ASK: ASK) with a multi-valued electrical signal generated based on electrical stage code diffusion in the binary / multi-value converting means in the transmission circuit. There has been proposed a method for transmitting / receiving multi-wavelength signal light obtained by optical frequency multiplexing of multi-level ASK signal light (Amplitude Shift Keying) (see, for example, Non-Patent Document 4).

  The light intensity level of the multilevel ASK signal light varies according to the symbol value of the multilevel electrical signal applied to the modulator, and the possible light intensity levels are equally spaced. On the receiving side, the multi-value electric signal generated by directly detecting each optical frequency component demultiplexed for each optical frequency is added / subtracted in the electric decoding means in accordance with the unique code assigned to the receiving circuit. Here, in the generated multilevel electric signal, the voltage levels corresponding to the respective symbol values are equally spaced, and the voltage level intervals coincide with each other between the multilevel electric signals generated by the different optical detectors. Therefore, when an orthogonal code such as a Hadamard code or a bit-shifted M-sequence code is used as a unique code, MAI can be removed by addition / subtraction. In addition, since signal light is not multiplexed in the optical region, no beat noise occurs during detection. That is, in this system, an optical codec device is not required for performing code decoding at the electric stage, and a time gate and an optical threshold device required in References 1 to 3 for MAI and beat noise reduction are provided. Is unnecessary. Therefore, the optical device configuration in the transmission / reception circuit can be greatly simplified.

  Furthermore, since code spreading at the electrical stage is performed spatially, an operation at a chip rate (= bit rate ′ code length) required in time spreading (see, for example, Non-Patent Document 5) is unnecessary. It can be configured by an electric circuit having an operation speed equivalent to the bit rate.

V. J. et al. Hernandez, et al. , “A 320-Gb / s capacity (32-user′10 Gb / s) SPECTS O-CDMA network testbed with enhanced spectral efficiency through error correction,”. Lightwave Technol. , Pp. 79-86, Jan. 2007 P. Toliver, et al. , “Demonstration of high spectral efficiency coherent OCDM using DQPSK, FEC, and integrated ring resonator-based spectral phase encoder / decoders 7 T.A. Hamanaka, et al. , “Compound data rate and data-rate-flexible 622 Mb / s-10 Gb / s OCDMA experiments using 511-chip Selected Topics in Quantum Electron. , Pp. 1516-1521, Sep. / Oct. 2007) S. Kaneko, et al. , “Beat-noise-free OCDM technical encoding spectral M-ary ASK based on electrical-domain spatial code spreading,” OFC2009, OThI5, 2009 G. C. Gupta, et al. "A simple one-system solution COF-PON for metro / access networks," J. et al. Lightwave Technol. , Pp. 193-200, Jan. 2007

  The number of code multiplexes that can be taken from a predetermined code length is finite, and in order to expand the code multiplex number beyond that, it is necessary to extend the code length. In the method of Reference 4, the number of optical frequency components constituting the transmitted / received multi-wavelength signal light is equal to the code length of the unique code having the longest code length among the unique codes. Therefore, when the number of code multiplexes is increased, there is a problem that it is necessary to increase the number of required optical intensity modulators and optical detectors due to an increase in the number of optical frequency components accompanying the extension of the code length. Furthermore, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light is widened by increasing the number of code multiplexes, and there is another problem that the influence of chromatic dispersion becomes large.

  Therefore, the present invention does not require an increase in the number of optical intensity modulators or optical detectors, and does not deteriorate the chromatic dispersion tolerance, and can increase the number of code multiplexes compared with the conventional method. It is another object of the present invention to provide a receiving circuit for optical code division multiplexing.

  In order to achieve the above object, an optical code division multiplexing transmission circuit according to the present invention splits two optical carriers into two of a plurality of multilevel electric signals for each of a plurality of optical carriers having different optical frequencies. Then, multi-level modulation is performed, and multi-level signal light is generated by combining the phases so that the phases are orthogonal to each other. The multi-level signal light is further optical frequency multiplexed and output. In the following description, the optical code division multiplexing transmission circuit and the optical code division multiplexing reception circuit are referred to as an optical CDM transmission circuit and an optical CDM reception circuit, respectively.

  Specifically, the optical CDM transmission circuit according to the present invention has a code length composed of two types of code elements from N (N is an integer of 2 or more) binary signals, where K is 2 or less (K is 2 or more). Binary / multilevel conversion means for generating K multilevel signals based on N unique codes, and an optical carrier wave that is continuous light of different optical frequencies, and the optical carrier wave is The two optical signals are branched into two to modulate each of the optical carriers using two of the multilevel signals from the binary / multilevel conversion means, and to make the optical phases of the optical carriers orthogonal to each other. A plurality of optical modulation means for outputting multi-level signal light combined with a carrier wave; and an optical multiplexing means for outputting multi-wavelength signal light obtained by multiplexing the multi-level signal light output from each of the optical modulation means. . Here, “the optical carrier is branched into two and each of the optical carriers is modulated using two of the multilevel signals from the binary / multilevel converter” means “optical carrier” 1 is modulated by the multilevel signal 1 and the optical carrier wave 2 is modulated by the multilevel signal 2.

  The optical CDM receiving circuit according to the present invention receives the multi-wavelength signal light output from the optical CDM transmission circuit via an optical fiber transmission line, and demultiplexes the multi-wavelength signal light into optical frequency components. Output optical frequency demultiplexing means, and the optical frequency components input from the optical frequency demultiplexing means are detected, and respective multilevel signals carried by two optical carriers whose optical phases are orthogonal to each other are output 2 An optical detection means having a number of output ends and one of the 1st to Nth unique codes are assigned, and each output end of the optical detection means is connected to form the assigned unique code When the code elements corresponding to the output terminal of the optical detection means are sequentially associated, the input from the output terminal corresponding to one of the two kinds of code elements constituting the unique code is positive, the other To the sign element of Electro-decoding means for selectively extracting one of the binary signals input to the binary / multi-value conversion means by performing addition / subtraction to add the input from the corresponding output terminal as negative; Is provided. Here, “outputting each multilevel signal carried by two optical carriers whose optical phases are orthogonal to each other” means “outputting the multilevel signal 1 from the output end 1 and the multilevel signal 2 from the output end 2”. It means “output”.

  The optical CDM transmission circuit and the optical CDM reception circuit according to the present invention modulate and demodulate optical carriers whose optical phases are orthogonal to each other, thereby providing the same number of optical modulation means and optical detection means as the optical CDM transmission system of Non-Patent Document 4. The code length can be doubled. By improving the frequency utilization efficiency, the optical CDM transmission circuit and the optical CDM reception circuit according to the present invention do not change the optical frequency band of the multi-wavelength signal light even when the code length is increased, and the chromatic dispersion tolerance does not deteriorate.

  Accordingly, the present invention provides an optical CDM transmission circuit and an optical CDM reception circuit that can increase the number of code multiplexes without requiring an increase in the number of optical modulation means and optical detection means, and without causing deterioration of chromatic dispersion tolerance. can do.

  The binary / multilevel conversion means of the optical CDM transmission circuit according to the present invention has N spreading codes and K adders corresponding to the N binary signals on a one-to-one basis. Each of the spreading encoders is assigned with the unique code, has a number of output ends equal to or greater than the code length of the assigned unique code, and sequentially transmits each code element constituting the unique code to the output end. When it is made to correspond, a signal whose symbol value matches the binary signal input to the spreading encoder is output from the output end corresponding to one of the two types of code elements, 0 is output from the output terminal, and the k-th (k = 1, 2,..., K) adder indicates that the symbol value of the k-th multilevel signal is equal to each spread encoder. Each of the spreads to be the sum of the symbol values of the output signals from the kth output terminal Characterized by adding the symbol value of the output signal from the k th said output end of issue unit.

  The multilevel signal light output from the optical modulation means of the optical CDM transmission circuit according to the present invention has optical field amplitude levels that can be taken by each of the two optical carriers whose optical phases are orthogonal to each other, and It fluctuates according to the symbol value of one of the two multi-level signals input to the light modulation means.

  The multi-level signal light output from the optical modulation means of the optical CDM transmission circuit according to the present invention has optical field amplitude levels that can be taken by each of two optical carriers whose optical phases are orthogonal to each other, and It fluctuates in accordance with one symbol value of the two multi-level signals input to the optical modulation means, and the optical phase shift amount of each of the optical carriers in the optical modulation means is input to the optical modulation means. According to the symbol value of one of the two multi-level signals, the difference is one of the binary values of π.

  The optical detection means of the optical CDM receiving circuit according to the present invention includes a local light source adjusted so that the optical frequency of the output light is a predetermined frequency difference from the input light from the optical frequency demultiplexing means, An optical detector that squarely detects mixed light of the output light from the local light source and the input light from the optical frequency demultiplexing means; and the frequency from the output of the optical detector is the predetermined frequency difference Including a band-pass filter that transmits a signal component carried by each of two carriers whose phases are orthogonal to each other, a VCO, a mixer, and a loop filter. A phase-locked loop having a phase-locked loop and demodulating a multilevel signal carried by each of the two carriers and outputting them separately, and the frequency and phase of the output of the VCO are the two carriers of The mixer is adjusted by the loop filter so as to be synchronized with one of the two, and the mixer detects the input from the bandpass filter by the output of the VCO, and outputs a multilevel signal carried by one of the two carriers. It is characterized by demodulating.

  The optical detection means of the optical CDM receiving circuit according to the present invention includes a local light source, an optical detector, and a loop filter, and includes an optical phase-locked loop having an electrical band sufficiently narrower than the signal band of the binary signal. The multi-level signal carried by each of the two optical carriers whose optical phases are orthogonal to each other is demodulated and output separately, and the optical frequency and optical phase of the output light of the local light source are the two of the two optical carriers. Adjusted by the loop filter so as to synchronize with one of the light, and the optical detector squarely detects mixed light of the output light from the local light source and the input light from the optical frequency demultiplexing means. It is characterized by.

  The present invention does not require an increase in the number of optical intensity modulators or optical detectors, and does not deteriorate the chromatic dispersion tolerance, and can increase the number of code multiplexes as compared with the conventional system, and an optical CDM transmission circuit and an optical CDM reception circuit Can be provided.

It is a figure explaining the example of a structure of the conventional optical CDM transmission system using electrical stage code | symbol spreading | diffusion and multi-value amplitude modulation. It is a figure explaining the optical CDM transmission circuit and optical CDM receiving circuit which concern on this invention. It is a figure explaining the binary / multi-value conversion means of the optical CDM transmission circuit according to the present invention. It is a figure explaining the pre-bias circuit which the binary / multi-value conversion means of the optical CDM transmission circuit concerning this invention has. It is a figure explaining the pre-bias circuit which the binary / multi-value conversion means of the optical CDM transmission circuit concerning this invention has. It is a figure explaining the optical electric field of the multilevel signal light which the optical CDM transmission circuit which concerns on this invention outputs. It is a figure explaining the optical modulation means of the optical CDM transmission circuit based on this invention. It is a figure explaining the optical detection means of the optical CDM receiving circuit which concerns on this invention. It is a figure explaining the optical CDM receiving circuit based on this invention. It is a figure explaining the optical detection means of the optical CDM receiving circuit which concerns on this invention. It is a figure explaining the optical electric field of the multilevel signal light which the optical CDM transmission circuit which concerns on this invention outputs.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components. Moreover, when it demonstrates without attaching a branch number, it is description common to all the components.

(Embodiment 1)
FIG. 2 is a diagram illustrating the optical CDM transmission system 301 according to the present embodiment. The optical CDM transmission system 301 has a structure in which an optical fiber transmission line 203 connects an optical CDM transmission circuit 201 and a plurality of optical CDM reception circuits (202-1, 202-2,... 202-N). .

[Optical CDM transmission circuit]
The optical CDM transmission circuit 201 includes a binary / multilevel conversion unit 11, a plurality of optical modulation units 12, and an optical multiplexing unit 13. Each optical modulation means 12 receives an optical carrier wave, which is continuous light having a different optical frequency f, from the light source 14, and converts the input optical carrier wave into a multilevel signal generated by the binary / multilevel conversion means 11. Multi-level signal light modulated using two of them is output. The optical frequency multiplexing unit 13 combines the multi-level signal light output from each optical modulation unit 12 and outputs multi-wavelength signal light. The optical frequency multiplexing means 13 is, for example, an arrayed waveguide grating (AWG) or a multilayer filter. Instead of the optical frequency multiplexing means 13, it is also possible to use an optical coupler made of an optical fiber or PLC (Planar Lightwave Circuit). The multiwavelength signal light is transmitted to each optical CDM receiving circuit 202 via the optical fiber transmission line 203.

  Here, the light intensity of each optical frequency component of the multi-wavelength signal light is equal. In addition to the configuration in which each light source 14 and each light modulation means 12 having different optical frequencies of output light are connected one-to-one like the optical CDM transmission circuit 201 in FIG. 2, the output of the multi-wavelength light source is output for each optical frequency component. A configuration in which the signals are separated and input to each light modulation means 12 is also possible. A configuration in which the output of single-mode light is modulated with a high-frequency sine wave to obtain multiple wavelengths, a mode-locked laser, or the like can be used as the multi-wavelength light source.

と表せる。ｃ_ｎ，ｋは固有符号ｎ（ｎ＝１，２，・・・，Ｎ）のｋ番目（ｋ＝１，２，・・・，Ｋ）の符号要素である。固有符号としては、光周波数領域において符号化を行う光ＣＤＭ方式において用いられるアダマール符号やビットシフトしたＭ系列符号などを用いる。ここで、各シンボル値Ｄ^＃ _１（ｔ）〜Ｄ^＃ _Ｋ（ｔ）に対応する電圧レベルは、２値／多値変換手段１１内にて、所望の間隔となるように調整されている。 The binary / multi-level conversion means 11 is based on N unique codes, and has a longest code length from N binary signals having symbol values D ₁ (t) to D _N (t), respectively. The number of multilevel signals corresponding to the code length K of the code is generated. The symbol value D ^# _k (t) of the k-th (k = 1, 2,..., K) multilevel signal is

It can be expressed. cn _{, k} are k-th (k = 1, 2,..., K) code elements of the unique code n (n = 1, 2,..., N). As the inherent code, Hadamard code used in the optical CDM system that performs encoding in the optical frequency domain, bit-shifted M-sequence code, or the like is used. Here, the voltage levels corresponding to the symbol values D ^# ₁ (t) to D ^# _K (t) are adjusted in the binary / multilevel conversion means 11 so as to have a desired interval.

  FIG. 3 is a configuration example of the binary / multi-value conversion means 11. The binary / multilevel conversion means 11 includes N spreading coders 21, K adders 22, and a pre-bias circuit 24.

The spread encoder 21 has a number of output ends 23 equal to or greater than the code length of the assigned unique code, and sequentially associates each code element {1}, {0} constituting the unique code with each output end 23. At this time, a signal whose symbol value matches the symbol value of the binary signal input to the spread encoder 21 is output from each output terminal 23 corresponding to the code element {1}. The other output terminals 21 output 0. That is, the spread encoder n to which the k-th (k = 1, 2,..., K) code element cn _{, k of} the unique code n (n = 1, 2,..., N) is assigned. The symbol value of the output signal at the k-th output terminal is the product c _{n, k} × D _{n of the} value of the code element c _{n, k} and the symbol value D _n (t) of the binary signal input to the spread encoder _n. It can be expressed by (t).

The spread encoder 21 includes K switches (SW). The input binary signal is branched and output from the output terminal 23 via each SW. By turning on only the SW connected to the output terminal 23 corresponding to the code element {1}, the product of the value of each code element and the symbol value of the input signal to the spread encoder 21 is output from the output terminal 23. It becomes possible. For example, the symbol value of the output signal of each output terminal 23 of the spreading encoder 21-1 to which the unique code 1 {1, 1, 0,..., 0} is assigned is D ₁ (t) = 1. In this order, “1”, “1”, “0”,..., “0”, and when D ₁ (t) = 0, all become “0”.

The pre-bias circuit 24 adjusts the voltage level interval corresponding to each symbol value of the output signal of the adder 22. FIG. 4 is a configuration example of the pre-bias circuit 24. The pre-bias circuit 24 includes M−1 or more weighting circuits 31 where M is the number of multi-level signals. The input multilevel signal is branched and input to each weighting circuit 31. The weighting circuit 31 outputs a 1 when the voltage level of the input signal is equal to or higher than the threshold voltage, a 0 when the voltage level is lower than the threshold voltage, and a predetermined weighting coefficient (X ₁ , X ₂ ,...) And a multiplier 33 that outputs the result. The outputs of the weighting circuits 31 are added and input to the light modulation means 12.

The threshold voltage V _{Th_m} of the discriminator 32 in the m-th (m = 1, 2,..., M−1) weighting circuit 31 is a voltage level corresponding to the symbol value “m−1” of the input multilevel signal. , And a voltage level corresponding to the symbol value “m”. When the input multilevel signal at a certain time corresponds to the symbol value “i”, the identification circuit 32 in the weighting circuit (31-1 to 31-i) outputs 1 and the other identification circuit 32 outputs 0. Therefore, the output of the pre-bias circuit 24 obtained by adding the outputs of the weighting circuits 31 is X ₁ + X ₂ +... + X _i . Similarly, when the input multilevel signal corresponds to the symbol value “i + 1”, the output of the pre-bias circuit 24 is X ₁ + X ₂ +... + X _i + X _{i + 1} . Therefore, the voltage level intervals corresponding to the respective symbol values of the multilevel signal output from the pre-bias circuit 24 are X ₁ , X ₂ ,..., X _M−1 in order. That is, by changing the weighting coefficients X _{1 to} X _M−1 , it is possible to flexibly generate a multilevel signal in which the voltage level interval corresponding to each symbol value is a desired ratio.

The N binary signals input to the binary / multilevel conversion means 11 do not necessarily have to be bit-synchronized between the signals, and may have different signal speeds. Further, the binary / multilevel conversion means 11 may be configured by combining a memory in which the computations of the spread encoder 21, adder 22, and pre-bias circuit 24 are stored in advance and a D / A converter. Furthermore, a circuit as shown in FIG. 5 in which any _one of SW ₀ to SW _M−1 is turned on according to the symbol value D ^# _k (t) can be used as the pre-bias circuit 24.

と表せる。Ｄ^＃ _ｈ（ｔ），Ｄ^＃ _ｈ＋１（ｔ） （ｈ＝１，３，・・・，Ｋ−１）は光変調手段１２へ入力された２個の多値信号のシンボル値、ｆ_ｋ，φ_Ｓ（ｔ）は、それぞれ多値信号光の光周波数、位相雑音である。多値信号光の光電界状態をプロットすると、Ｄ^＃ _ｈ（ｔ），Ｄ^＃ _ｈ＋１（ｔ）の組み合わせに応じて、図６のように格子点を遷移する。図６中のＭ_ｈ，Ｍ_ｈ＋１は、光変調手段１２へ入力される各多値信号の多値度である。 The optical modulation means 12 outputs multilevel signal light in which the optical electric field amplitude levels that can be taken by two optical carriers whose optical phases are orthogonal to each other are equally spaced. The optical electric field amplitude level varies according to the symbol value of one of the two multilevel signals input from the binary / multilevel converter 11. The optical electric field state E _S (t) of the multilevel signal light has an amplitude level interval of ΔE.

It can be expressed. D ^# _h (t), D ^# _{h + 1} (t) (h = 1, 3,..., K−1) are symbol values of two multilevel signals input to the optical modulation means 12, f _k , φ _S (t) is the optical frequency and phase noise of the multilevel signal light, respectively. When the optical electric field state of the multi-level signal light is plotted, the lattice point transitions as shown in FIG. 6 according to the combination of D ^# _h (t) and D ^# _{h + 1} (t). M _h and M _{h + 1 in} FIG. 6 are the multilevel values of the multilevel signals input to the optical modulation means 12.

  FIG. 7 is a configuration example of the light modulation means 12. A zero-chirp type light intensity modulation means 81 having no phase chirp due to intensity modulation is incorporated in each arm of a Mach-Zehnder interferometer having the same arm length, and multi-level ASK signal light obtained by intensity-modulating each branched input light is multiplexed. It is the structure to do. An optical phase shifter 82 is disposed in at least one arm. The optical phase shifter 82 adjusts the optical phase of the optical carrier so that the optical phases of the optical carriers are orthogonal to each other when the multi-level ASK signal light is multiplexed. The optical modulation unit 12 in FIG. 7 shifts the optical phase of the optical carrier wave that passes through one arm by p / 2 compared with the optical phase of the optical carrier wave that passes through the other arm.

  The multilevel signal input to the light intensity modulation means 81 is adjusted in voltage level corresponding to each symbol value in the binary / multilevel conversion means 11. By adjusting the voltage level interval so as to compensate for the non-linearity of the light intensity modulation, multilevel ASK signal light having optical field amplitude levels corresponding to each symbol value at equal intervals is generated.

  For example, as shown in FIG. 7, the zero chirp type light intensity modulation unit 81 generates two signals whose polarity is inverted from the multilevel signal from the binary / multilevel conversion unit 11 by the differential signal generation unit 83. It can be realized by a configuration in which each electrode of a dual-drive Mach-Zehnder interferometer type light intensity modulator 84 such as an LN intensity modulator is applied. As the differential signal generation means 83, a differential amplifier can be used in addition to a configuration in which a divider and an inverter are combined.

[Optical CDM receiver circuit]
The optical CDM receiving circuit 202 includes an optical frequency demultiplexing unit 16, a plurality of optical detection units 43, and an electrical decoding unit 45. The multi-wavelength signal light input to the optical CDM receiving circuit 202 is separated for each optical frequency component by the optical frequency demultiplexing means 16. Each optical frequency component is input to the optical detection means 43 connected one-to-one with each output terminal of the optical frequency demultiplexing means 16. The optical frequency component input to the k-th optical detection means 43-k is multilevel signal light whose optical frequency is represented by equation (2) as _fk . Here, the light intensity is equal between the optical frequency components. The optical detection means 43 performs heterodyne synchronous detection on the input multilevel signal light, demodulates the multilevel signal carried by each of the two optical carriers whose optical phases are orthogonal to each other, and outputs them from separate output ends. .

と表せる。ここで、Ｅ_Ｌ，φ_Ｌ（ｔ）は、それぞれ、局発光の光電界振幅および位相雑音である。 FIG. 8 is a configuration example of the optical detection means 43 using heterodyne synchronous detection. The optical detection unit 43 includes a local light source 51, an optical detector 53, a band pass filter (BPF) 54, and a phase-locked detection circuit 55. Bureau optical frequency of the emitted light is adjusted by different multilevel signal light and f _IF input to the optical detecting means 43. That is, the optical frequency of the local light is adjusted to be f _k −f _IF in the k-th optical detection means 43 to which the multilevel signal light having the optical frequency f _k is input, and the optical electric field E _L (T)

It can be expressed. Here, E _L and φ _L (t) are the local electric field amplitude and phase noise, respectively.

と表せる。但し、［ ］^ｍｓは時間に関する二乗平均を表す。ここで、

であり、φ_Ｓ（ｔ），φ_Ｌ（ｔ）の時間変動は、送信回路にて２値／多値変換手段１１へ入力される２値信号の信号速度と比べて、十分に緩やかである。 The optical detector 53 square-detects the mixed light of the multilevel signal light and the local light, and its output Q (t) is

It can be expressed. However, [] ^ms represents the root mean square regarding time. here,

The time fluctuations of φ _S (t) and φ _L (t) are sufficiently gradual as compared with the signal speed of the binary signal input to the binary / multilevel conversion means 11 in the transmission circuit. .

  The optical detection means 43 adjusts the polarization state of the local light and the multilevel signal light so that the polarization states of the local light and the multilevel signal light coincide with each other by adjusting the polarization state of at least one of the local light and the multilevel signal light. . In the optical CDM transmission circuit 201, a configuration of polarization scrambling for changing the polarization state of the signal light with time, a configuration of transmitting signal light in which the orthogonal polarization states are added, and polarization diversity in the optical detection means 43 The polarization adjustment in the optical CDM receiving circuit 202 can be omitted by the above configuration.

The BPF 54 has a transmission band in the vicinity of f _IF , removes direct detection components corresponding to the first to third terms on the right side in the equation (4), and outputs an intermediate frequency signal R (t) having f _IF as the center frequency. . The intermediate frequency signal R (t) is the sum of two signals whose carrier phases are orthogonal to each other, as represented by Expression (6).

The phase-locked detection circuit 55 includes an electric phase-locked loop 57 including a VCO 61, a mixer 62, and a loop filter 63. The phase-locked detection circuit 55 detects the intermediate frequency signal R (t) synchronously, and the symbol value is D ^# _h (t), D ^A multi-value baseband signal of ^# _{h + 1} (t) is output separately. In FIG. 8, the phase shifter 64 shifts the phase of the output of the VCO 61 that is phase-synchronized with one carrier wave by π / 2, and is input to the mixer 58 outside the electric phase-locked loop 57 so that it is conveyed to the other carrier wave. The signal component is demodulated. In the electric phase locked loop 57, the oscillation frequency and phase of the VCO 61 are adjusted by the loop filter 63 so as to synchronize with one of the two carriers constituting the intermediate frequency signal R (t).

と表せる。ミキサー６２の出力は、ＬＰＦ５６Ａにて低域濾波され、式（７）の右辺第３項で表される多値ベースバンド信号が出力される。多値ベースバンド信号は、シンボル値Ｄ^＃ _ｈ（ｔ）に対応する各電圧レベルが等間隔である。 When the phase of the VCO 61 is synchronized with the carrier phase Δφ (t) of the first term on the right side of Equation (6) in the electrical phase locked loop 57, the detection output S ₁ (t) from the mixer 62 is

It can be expressed. The output of the mixer 62 is low-pass filtered by the LPF 56A, and a multi-value baseband signal expressed by the third term on the right side of Expression (7) is output. In the multi-level baseband signal, each voltage level corresponding to the symbol value D ^# _h (t) is equally spaced.

と表せる。ミキサー５８の出力は、ＬＰＦ５６Ｂにて低域濾波され、シンボル値Ｄ^＃ _ｈ＋１（ｔ）に対応する各電圧レベルが等間隔である多値ベースバンド信号が生成される。 The mixer 58 receives the output of the VCO 61 whose phase is synchronized with Δφ (t) with the phase shifted by π / 2. The detection output S ₂ (t) from the mixer 58 is

It can be expressed. The output of the mixer 58 is low-pass filtered by the LPF 56B, and a multi-value baseband signal in which each voltage level corresponding to the symbol value D ^# _{h + 1} (t) is equally spaced is generated.

  A multi-value baseband signal from each output terminal of the optical detection means 43 is input to the electrical decoding means 45, and each code element {1}, {0} constituting the assigned inherent code is assigned to each optical detection means. When the output terminals 71 of 43 are sequentially associated, addition / subtraction is performed by adding the input from the output terminal corresponding to {1} as positive and the input from the output terminal corresponding to {0} as negative. Here, as described above, in the multi-level baseband signal output from the optical detection means, the voltage levels corresponding to the respective symbol values are equally spaced. In addition, since the light intensities of the multilevel signal lights input to the respective optical detection means 43 match, the voltage level intervals of the multilevel baseband signals output from the different optical detection means 43 match. Therefore, when a Hadamard code, a bit-shifted M-sequence code, or the like is used as a unique code, MAI can be removed due to code orthogonality. Therefore, it is possible to selectively receive a desired signal among the N binary signals input to the binary / multilevel converter 11 in the optical CDM transmission circuit 201.

  Each optical CDM receiving circuit 202 in FIG. 2 is configured to include one electrical decoding unit 45, but includes a plurality of electrical decoding units 45 ′ to which different unique codes are assigned as shown in FIG. It is also possible. The output of the optical detection means 43 is branched and input to each electric decoding means 45 '. Each electric decoding unit 45 ′ assigned with a unique code outputs a binary signal that is code-spread based on the same code by the binary / multilevel conversion unit 11 in the optical CDM transmission circuit 201. On the other hand, if the electrical encoding means 45 ′ to which no code is assigned outputs 0, the electrical decoding in each optical CDM reception circuit 202 ′ is performed according to the amount of information desired by each optical CDM reception circuit 202 ′. Transmission efficiency can be improved by dynamically changing the assignment of the unique code to the means 45 ′. That is, by assigning a unique code to a plurality of electro-decoding means 45 ′ in the optical CDM receiving circuit 202 ′ for which a large amount of information is desired, a plurality of signals are received at the same time, and the amount of information that can be received in a fixed time is increased. It becomes possible.

  In the first embodiment, two multi-level signals generated by the binary / multi-level conversion unit 11 are input to each optical modulation unit 12 in the optical CDM transmission circuit 201, so that a conventional optical CDM transmission system is used. By using the same number of optical modulation means 12 and optical detection means 43 as in FIG. 1, the code length can be doubled to increase the maximum possible code multiplexing number. At this time, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light does not change, so that the chromatic dispersion tolerance does not deteriorate.

(Embodiment 2)
Embodiment 2 is an optical CDM transmission system in which optical detection means 43 ′ for performing homodyne detection is arranged in the optical CDM receiving circuit 202 in Embodiment 1 instead of the optical detection means 43 for heterodyne synchronous detection.

  A configuration example of the optical detection means 43 'is shown in FIG. The optical detection means 43 ′ includes an optical phase locked loop 91 including a local light source 51, an optical detector 53, and a loop filter 63, and receives a multilevel signal carried by each of two optical carriers whose optical phases are orthogonal to each other. Demodulated by optical phase-locked homodyne detection and output separately. The optical detector 53 squarely detects mixed light of local light and multilevel signal light. The optical detection means 43 ′ adjusts the polarization state of at least one of the local light and the multilevel signal light by the polarization adjustment means 52 so that the local light and the multilevel signal light have the same polarization state. To do. In the optical CDM transmission circuit 201, a configuration of polarization scrambling for changing the polarization state of the signal light with time, a configuration of transmitting signal light in which the orthogonal polarization states are added, and polarization in the optical detection means 43 ′ The polarization adjustment in the optical CDM receiving circuit 202 can be omitted depending on the diversity configuration or the like.

  The loop filter 63 adjusts the optical frequency and optical phase of the local light so as to synchronize with one of the two optical carriers whose optical phases of the multilevel signal light are orthogonal to each other. Here, the optical electric field state of the multilevel signal light can be expressed by Expression (2) in the first embodiment.

と表せる。局発光の光電界振幅Ｅ_Ｌを、光位相同期ホモダイン検波回路へ入力される多値信号の光電界振幅Ｄ^＃ _ｈ（ｔ）・ΔＥ，Ｄ^＃ _ｈ＋１（ｔ）・ΔＥよりも十分に大きくすると、多値信号光の直接検波成分である式（９）の右辺第１、２項は、局発光とのビート成分である右辺第４項と比べて無視できる。よって、位相同期ループ１の出力は、シンボル値Ｄ^＃ _ｈ（ｔ）に対応する各電圧レベルが等間隔である多値ベースバンド信号と見なせる。 When the optical phase of the local light is synchronized with the optical phase φ _S (t) of the optical carrier of the first term on the right side of Expression (2) in the optical phase locked loop 91, the output Q ₁ ^* (t) of the optical detector. Is

It can be expressed. The optical field amplitude E _L of the local light, optical field amplitude of the multilevel signal to be input to the optical phase synchronous homodyne detection circuit _{^{D # h (t) · ΔE}} , when sufficiently larger than _{^{D # h + 1 (t)}} · ΔE The first and second terms on the right side of Equation (9), which are direct detection components of multilevel signal light, can be ignored compared to the fourth term on the right side, which is a beat component with local light. Therefore, the output of the phase locked loop 1 can be regarded as a multi-value baseband signal in which each voltage level corresponding to the symbol value D ^# _h (t) is equally spaced.

と表せる。ここで、局発光の光電界振幅Ｅ_Ｌは、光位相同期ホモダイン検波回路へ入力される多値信号の光電界振幅Ｄ^＃ _ｈ（ｔ）・ΔＥ， Ｄ^＃ _ｈ＋１（ｔ）・ΔＥよりも十分に大きいため、光位相同期ループ内の光検波手段と同様に多値信号光の直接検波成分が無視でき、光検波器の出力は、シンボル値Ｄ^＃ _ｈ＋１（ｔ）に対応する各電圧レベルが等間隔である多値ベースバンド信号と見なせる。 The local light whose optical phase is synchronized with φ _S (t) is input to the optical detector 53 ′ outside the optical phase locked loop with the phase shifted by p / 2 by the optical phase shifter 65. The output Q ₂ ^* (t) of the optical detector 53 ′ is

It can be expressed. Here, the optical field amplitude _{E L} of the local light, optical field of the multi-level signal input to the optical phase-locked homodyne detection circuit amplitude _{^{D # h (t) · ΔE}} , than _{^{D # h + 1 (t)}} · ΔE sufficient Therefore, the direct detection component of the multilevel signal light can be ignored similarly to the optical detection means in the optical phase locked loop, and the output of the optical detector has each voltage level corresponding to the symbol value D ^# _{h + 1} (t). It can be regarded as a multi-value baseband signal that is equally spaced.

  When each binary signal input to the binary / multilevel conversion means 11 in the optical CDM transmission circuit 201 is bit-synchronized, a local light source, a 90 ° optical hybrid, a differential optical detector, a digital signal A digital coherent receiver provided with a processing (DSP: Digital Signal Processing) circuit can be used as the optical detection means 43 ′. Since the DSP circuit can estimate the optical phase difference between the multilevel signal light and the local light, the optical phase synchronization between the multilevel signal light and the local light, which is necessary in the optical phase-locked homodyne detection, is unnecessary. When this optical detection means is used, the multilevel signal input to the optical modulation means 12 is differentially encoded (Differential Encoding).

  As described in the first embodiment, the multi-value baseband signal from each output terminal of the optical detection unit 43 ′ is input to the electric decoding unit 45. Therefore, it is possible to selectively receive a desired signal among the N binary signals input to the binary / multilevel converter 11 in the optical CDM transmission circuit 202.

  As described above, even in the second embodiment, the code length is doubled by using the same number of optical modulation means 12 and optical detection means 43 ′ as the conventional optical CDM transmission system (FIG. 1), and the maximum possible The number of code multiplexes can be expanded. At this time, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light does not change, so that the chromatic dispersion tolerance does not deteriorate.

と表せる。また、θ_ｈ（ｔ），θ_ｈ＋１（ｔ） （ｈ＝１，３，・・・，Ｋ−１）は、それぞれＤ^＃ _ｈ（ｔ），Ｄ^＃ _ｈ＋１（ｔ）に応じて、差がπである２値のいずれかをとる。θ_ｈ（ｔ），θ_ｈ＋１（ｔ）が、０またはπのいずれかをとるとすると、多値信号光の光電界状態は、Ｄ^＃ _ｈ（ｔ），Ｄ^＃ _ｈ＋１（ｔ）の組み合わせに応じて、図１１のように格子点を遷移する。図１１中のＭ_ｈ，Ｍ_ｈ＋１は、光変調手段１２へ入力される各多値信号の多値度である。 (Embodiment 3)
In the optical CDM transmission system according to the third embodiment, the optical modulation means 12 in the optical CDM transmission circuit 201 according to the first embodiment modulates the optical electric field amplitude and optical phase of two optical carriers whose optical phases are orthogonal to each other. Outputs value signal light. The optical amplitude levels that can be taken by each optical carrier are equally spaced, and the optical phase shift amount in the optical modulation means 12 is one of binary values having a difference of π. The optical electric field amplitude and the optical phase shift amount vary according to the symbol value of the corresponding one of the two multilevel signals input from the binary / multilevel converter 11. The optical electric field state E ′ _S (t) of the multilevel signal light has an amplitude level interval of ΔE.

It can be expressed. Further, θ _h (t), θ _{h + 1} (t) (h = 1, 3,..., K−1) have a difference according to D ^# _h (t) and D ^# _{h + 1} (t), respectively. It takes one of two values that are π. Assuming that θ _h (t) and θ _{h + 1} (t) are either 0 or π, the optical electric field state of the multi-level signal light is a combination of D ^# _h (t) and D ^# _{h + 1} (t). In response, the grid points are changed as shown in FIG. M _h and M _{h + 1 in} FIG. 11 are the multilevel values of the multilevel signals input to the light modulation means 12.

  For example, the optical modulation unit 12 of FIG. 7 is used as the optical modulation unit 12, and a dual-drive Mach-Zehnder interferometer type optical intensity modulator 84 incorporated in each arm is used. A desired multilevel signal light is generated by biasing so that the transmittance is minimized when an intermediate voltage between the maximum voltage and the minimum voltage that can be taken is applied.

The optical CDM receiving circuit 202 has the same configuration as that of the first embodiment, and each optical frequency component of the multi-wavelength signal light input to the optical CDM receiving circuit 202 is connected to each output terminal of the optical frequency demultiplexing means 16 and 1. The optical detection means 43 connected to the pair 1 performs heterodyne synchronous detection. The optical frequency component input to the k-th optical detection means 43 is multilevel signal light whose optical frequency is represented by the equation (11) and whose optical frequency is f _k .

電気位相同期ループ５７は、ＶＣＯ６１の発振周波数および位相が、中間周波信号Ｒ^＊＊（ｔ）を構成する２信号のどちらか一方の搬送波と同期するように、ループフィルタ６３により調整される。ここで、電気位相同期ループ５７の電気帯域は、光ＣＤＭ送信回路２０１にて２値／多値変換手段１１へ入力される２値信号の信号帯域よりも十分に狭い。 When the optical detection means 43 of FIG. 8 is used, the intermediate frequency signal R ^** (t) output from the BPF 54 is represented by the sum of two signals as shown in Expression (12).

The electric phase locked loop 57 is adjusted by the loop filter 63 so that the oscillation frequency and phase of the VCO 61 are synchronized with either one of the two carriers constituting the intermediate frequency signal R ^** (t). Here, the electric band of the electric phase-locked loop 57 is sufficiently narrower than the signal band of the binary signal input to the binary / multilevel converter 11 in the optical CDM transmission circuit 201.

と表せる。ミキサー６２の出力は、ＬＰＦ５６Ａにて低域濾波され、式（１３）の右辺第３項で表される多値ベースバンド信号が出力される。θ_ｈ（ｔ）は差がπである２値のいずれかをとるため、多値ベースバンド信号は、シンボル値Ｄ^＃ _ｈ（ｔ）に対応してとりうる各電圧レベルが、

に対応する電圧レベルを中心として対称で、等間隔となる。 If the phase of the VCO 61 is synchronized with the phase of the carrier wave of the first term on the right side of the equation (12) in the electrical phase locked loop 57, the electrical band is input to the binary / multilevel converter 11 by the optical CDM transmission circuit 201. Since the loop filter 63 that is sufficiently narrower than the signal band of the binary signal does not feel voltage fluctuation due to θ _h (t), the phase of the VCO 61 is synchronized with Δφ (t) and the detection output S ₁ ^* from the mixer 62 is detected ^{. *} (T) is

It can be expressed. The output of the mixer 62 is low-pass filtered by the LPF 56A, and a multi-value baseband signal expressed by the third term on the right side of Expression (13) is output. Since θ _h (t) takes one of two values with a difference of π, the multilevel baseband signal has each voltage level that can be taken corresponding to the symbol value D ^# _h (t),

Symmetrically and equally spaced around the voltage level corresponding to.

と表せる。ミキサー５８の出力は、ＬＰＦ５６Ｂにて低域濾波され、シンボル値Ｄ^＃ _ｈ＋１（ｔ）に対応してとりうる各電圧レベルが、

に対応する電圧レベルを中心として対称で、等間隔である多値ベースバンド信号が生成される。 The output of the VCO 61 whose phase is synchronized with Δφ (t) is input to the mixer 58 outside the electrical phase locked loop with the phase shifted by π / 2. The detection output S ₂ ^** (t) from the mixer 58 is

It can be expressed. The output of the mixer 58 is low-pass filtered by the LPF 56B, and each voltage level that can be taken corresponding to the symbol value D ^# _{h + 1} (t)

A multi-value baseband signal that is symmetric with respect to the voltage level corresponding to is equally spaced.

  The multi-value baseband signal from each output terminal of the optical detection means 43 is input to the electric decoding means 45 as described in the first embodiment. Therefore, it is possible to selectively receive a desired signal among the N binary signals input to the binary / multilevel converter 11 in the optical CDM transmission circuit 202.

  As described above, also in the third embodiment, the code length is doubled by using the same number of optical modulation means 12 and optical detection means 43 as the conventional optical CDM transmission system (FIG. 1), and the maximum code that can be taken Multiplex number can be expanded. At this time, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light does not change, so that the chromatic dispersion tolerance does not deteriorate.

(Embodiment 4)
Embodiment 4 is an optical CDM transmission system in which optical detection means 43 ′ for performing homodyne detection is arranged in the optical CDM reception circuit 202 in Embodiment 3 instead of the optical detection means 43 for heterodyne synchronous detection.

The optical CDM receiving circuit 202 has the same configuration as that of the second embodiment, and each optical frequency component of the multi-wavelength signal light input to the optical CDM receiving circuit 202 is connected to each output terminal of the optical frequency demultiplexing means 16 and 1. The optical detection means 43 'connected to the pair 1 performs homodyne detection. The optical frequency component input to the k-th optical detection means 43′-k is multilevel signal light whose optical frequency is represented by the equation (11) as _fk .

と表せる。局発光の光電界振幅Ｅ_Ｌを、光位相同期ホモダイン検波回路へ入力される多値信号の光電界振幅

よりも十分に大きくすると、多値信号光の直接検波成分である式（１５）の右辺第１，２項は、局発光とのビート成分である右辺第４項と比べて無視できる。よって、光位相同期ループの出力は、シンボル値Ｄ^＃ _ｈ（ｔ）に対応する各電圧レベルが、

に対応する電圧レベルを中心として対称で、等間隔である多値ベースバンド信号と見なせる。 In the optical phase-locked loop 91, the electrical band is sufficiently narrower than the signal band of the binary signal input to the binary / multilevel converter 11 in the optical CDM receiving circuit 201. In the optical phase locked loop 91, when the optical phase of the local light is synchronized with the optical phase of the optical carrier of the first term on the right side of the equation (11), the loop filter 63 does not feel voltage fluctuation due to θ _h (t). The optical phase of local light is synchronized with φ _S (t), and the output Q ₁ ^*** (t) of the optical detector is

It can be expressed. The optical field amplitude E _L of the local light, optical field amplitude of the multilevel signal to be input to the optical phase synchronous homodyne detection circuit

If it is made sufficiently larger, the first and second terms on the right side of Equation (15), which are direct detection components of multilevel signal light, can be ignored compared to the fourth term on the right side, which is a beat component with local light. Therefore, the output of the optical phase-locked loop has each voltage level corresponding to the symbol value D ^# _h (t) as

It can be regarded as a multi-value baseband signal that is symmetric with respect to the voltage level corresponding to 1 and is equally spaced.

と表せる。ここで、局発光の光電界振幅Ｅ_Ｌは、光位相同期ホモダイン検波回路へ入力される多値信号の光電界振幅

よりも十分に大きいため、光検波器の出力は、シンボル値Ｄ^＃ _ｈ＋１（ｔ）に対応する各電圧レベルが、

に対応する電圧レベルを中心として対称で、等間隔である多値ベースバンド信号と見なせる。 The optical detector 53 ′ outside the optical phase locked loop 91 receives the local light whose phase is synchronized with φ _S (t) with the optical phase shifted by π / 2 by the optical phase shifter 65. The output Q ₂ ^*** (t) of the optical detector is

It can be expressed. Here, local light optical field amplitude E _L is the optical field amplitude of the multilevel signal to be input to the optical phase synchronous homodyne detection circuit

Is sufficiently larger than the output of the optical detector so that each voltage level corresponding to the symbol value D ^# _{h + 1} (t)

It can be regarded as a multi-value baseband signal that is symmetric with respect to the voltage level corresponding to 1 and is equally spaced.

  When each binary signal input to the binary / multilevel conversion means in the transmission circuit is bit-synchronized, a digital coherent receiver can be used as the optical detection means as described in the second embodiment. It is. Since the DSP circuit can estimate the optical phase difference between the multilevel signal light and the local light, the optical phase synchronization between the multilevel signal light and the local light, which is necessary in the optical phase-locked homodyne detection, is unnecessary. When this optical detection means is used, the multilevel signal input to the optical modulation means is differentially encoded (Differential Encoding).

  As described in the first embodiment, the multi-value baseband signal from each output terminal of the optical detection unit 43 ′ is input to the electric decoding unit 45. Therefore, it is possible to selectively receive a desired signal among the N binary signals input to the binary / multilevel converter 11 in the optical CDM transmission circuit 202.

  As described above, even in the second embodiment, the code length is doubled by using the same number of optical modulation means 12 and optical detection means 43 ′ as the conventional optical CDM transmission system (FIG. 1), and the maximum possible The number of code multiplexes can be expanded. At this time, if the interval between adjacent optical frequency components is constant, the optical frequency band of the multi-wavelength signal light does not change, so that the chromatic dispersion tolerance does not deteriorate.

11: Binary / multilevel conversion means 12, 12-1, 12-2,..., 12-K ′: Optical modulation means 13: Optical frequency multiplexing means 14, 14-1, 14-2,. 14-K ′: light source 16: optical frequency demultiplexing means 21, 21-1, 21-2,..., 21-N: spreading encoders 22, 22-1, 22-2,. 22-K: adders 23, 23-11, 23-12,...: Output terminals 24, 24-1, 24-2,..., 24-K: pre-bias circuits 31, 31-1, 31 -2, ..., 31-M-1: Weighting circuit 32: Discriminator 33: Multiplier 42: Optical frequency demultiplexing means 43, 43-1, 43-2, ..., 43-K ': Light Detection means 43 ', 43'-1, 43'-2, ..., 43'-K': Optical detection means 45, 45-1, 45-2, ..., 45-N: Electric decoding means 45 ', 45' -1, 45′-2,..., 45′-N: Electrical decoding means 51: Local light source 52, 52 ′: Polarization adjusting means 53, 53 ′: Optical detector 54: BPF
55: Electric phase-locked loop circuit 56A, 56B: LPF
57: Electric phase locked loop 58: Mixer 61: VCO
62: Mixer 63: Loop filter 64: Phase shifter 65: Optical phase shifter 71: Input end 81: Light intensity modulation means 82: Optical phase shifter 83: Differential signal generation means 84: Light intensity modulator 91: Optical phase locked loop 201: Optical CDM transmission circuit 202, 202-1, 202-2, ..., 202-N: Optical CDM reception circuit 202 ': Optical CDM reception circuit 203: Optical fiber transmission line 301: Optical CDM transmission system

Claims (7)

Based on N (N is an integer greater than or equal to 2) binary signals and K unique codes whose code length is composed of two types of code elements and whose code length is less than or equal to K (K is an integer greater than or equal to 2). Binary / multi-value conversion means for generating a multi-value signal of
An optical carrier wave that is continuous light having different optical frequencies is input, the optical carrier wave is branched into two, and each of the optical carrier waves is obtained by using two of the multilevel signals from the binary / multilevel converter. And a plurality of optical modulation means for outputting multi-level signal light obtained by joining the two optical carriers, with the optical phases of the optical carriers orthogonal to each other, and
Optical multiplexing means for outputting multi-wavelength signal light obtained by multiplexing the multi-level signal light output by each of the light modulation means;
An optical CDM transmission circuit. The binary / multivalue conversion means includes:
N number of the binary signals and N number of spreading coders and K number of adders corresponding to each other,
Each of the spreading encoders is assigned with the unique code, has a number of output ends equal to or greater than the code length of the assigned unique code, and sequentially corresponds each code element constituting the unique code to the output end. A signal whose symbol value matches the binary signal input to the spreading encoder is output from the output end corresponding to one of the two types of code elements. 0 is output from the output end,
The k-th (k = 1, 2,..., K) adder is such that the symbol value of the k-th multilevel signal is an output signal from the k-th output terminal of each spreading encoder. 2. The optical CDM transmission circuit according to claim 1, wherein the symbol values of the output signals from the k-th output terminal of each of the spreading encoders are added so as to be a sum of the symbol values. The multi-level signal light output from the light modulation means is
The optical electric field amplitude levels that can be taken by each of the two optical carriers whose optical phases are orthogonal to each other are equally spaced, and according to one symbol value of the two multilevel signals input to the optical modulation means The optical CDM transmission circuit according to claim 1, wherein the optical CDM transmission circuit varies. The multi-level signal light output from the light modulation means is
The optical field amplitude levels that can be taken by each of the two optical carriers whose optical phases are orthogonal to each other are equally spaced, and according to one symbol value of the two multilevel signals input to the optical modulation means Fluctuate,
A binary value in which the optical phase shift amount of each of the optical carrier waves in the optical modulation means is a difference of π according to one symbol value of the two multilevel signals input to the optical modulation means The optical CDM transmission circuit according to claim 1, wherein the optical CDM transmission circuit is any one of the following. 5. The multi-wavelength signal light output from the optical CDM transmission circuit according to claim 1 is input via an optical fiber transmission line, and the multi-wavelength signal light is demultiplexed and output for each optical frequency component. Optical frequency demultiplexing means to perform,
Optical detection means having two output terminals for detecting the optical frequency components input from the optical frequency demultiplexing means and outputting respective multilevel signals carried by two optical carriers whose optical phases are orthogonal to each other; ,
One of the first to Nth unique codes is assigned, and each output terminal of the optical detection means is connected, and the code elements constituting the assigned unique code are assigned to the optical detection means When corresponding to the output terminal in order, the input from the output terminal corresponding to one of the two types of code elements constituting the unique code is positive, and the output terminal corresponding to the other code element is Electrodecoding means for selectively extracting one of the binary signals input to the binary / multilevel conversion means by performing addition / subtraction to add the input of
An optical CDM receiving circuit. The optical detection means includes
A local light source adjusted so that an optical frequency of output light has a predetermined frequency difference from input light from the optical frequency demultiplexing means;
An optical detector that squarely detects mixed light of output light from the local light source and input light from the optical frequency demultiplexing means;
A band pass filter that transmits a signal component carried by each of two carrier waves having a frequency that matches the predetermined frequency difference and whose phases are orthogonal to each other, from the output of the optical detector;
A phase lock circuit that includes a VCO, a mixer, and a loop filter, has an electrical phase locked loop having an electrical band narrower than the signal band of the binary signal, and demodulates and outputs separately the multilevel signal carried by each of the two carrier waves A detection circuit;
With
The frequency and phase of the output of the VCO are adjusted by the loop filter so as to be synchronized with one of the two carriers.
6. The light according to claim 5, wherein the mixer detects an input from the band-pass filter based on an output of the VCO, and demodulates a multilevel signal carried by one of the two carrier waves. CDM receiving circuit. The optical detection means includes
Including a local light source, an optical detector and a loop filter, comprising an optical phase-locked loop having an electrical band narrower than the signal band of the binary signal, and carrying a multilevel signal carried by each of two optical carriers whose optical phases are orthogonal to each other Demodulate and output separately,
The optical frequency and optical phase of the output light of the local light source are adjusted by the loop filter so as to be synchronized with one of the two optical carriers,
6. The optical CDM receiving circuit according to claim 5, wherein the optical detector square-detects a mixed light of the output light from the local light source and the input light from the optical frequency demultiplexing means. .

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