JP5487052B2 - Optical CDM transmission circuit, optical CDM reception circuit, and optical CDM transmission system - Google Patents

Description

  The present invention relates to an optical CDM transmission circuit, an optical CDM reception circuit, and an optical CDM transmission system including these, which are 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 binary / multi-value conversion means is configured to select K (K is 2 or more) from N (N is an integer of 2 or more) binary signals based on N unique codes corresponding to the binary signal on a one-to-one basis. A multi-value signal. The symbol value of the k-th (k = 1, 2,..., K) multilevel signal is a value obtained by adding the symbol values of the binary signal whose k-th code element of the corresponding inherent code is {1}. It is. FIG. 2 shows an example of the configuration of the binary / multilevel conversion means.

  On the reception side, the multi-value baseband signal generated by directly detecting each optical frequency component demultiplexed for each optical frequency is added / subtracted in the electric decoding unit according to the corresponding inherent code. Here, in the multilevel signal to be generated, the voltage levels corresponding to the respective symbol values are equally spaced, and the multilevel signals generated by the different photodetection means are coincident with each other. Therefore, when a code having orthogonality between codes is used as a unique code, undesired signal components 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 required in Non-Patent Documents 1 to 3 for reducing MAI and beat noise are required. A device is not required.

  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 SSFBG and cascaded SHG-DFG based EPP. 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

  In the method of Non-Patent Document 4, in order to remove an undesired signal component by addition / subtraction in the electric decoding means, it is necessary that the unique code used has orthogonality between the codes. If Hadamard code is used as the unique code and the code length is K, K orthogonal codes can be obtained. Here, in one of the K codes, all code elements are {1}, but when this code is assigned to the electric decoding means, multilevel baseband signals from all the optical detection means Therefore, the undesired signal component cannot be removed. Therefore, the number of codes that can be actually allocated to the electric decoding means is K−1 excluding codes whose all code elements are {1}.

  Here, the number of optical frequency components of the transmitted / received multi-wavelength signal light is K equal to the code length of the code assigned to the electrical decoding means. For this reason, the method of Non-Patent Document 4 has a problem that the maximum number of multiplexed codes / the number of optical frequency components is limited to less than 1 and the frequency utilization efficiency is limited.

  Therefore, the present invention increases the amount of information that can be sent within the same wavelength band by setting the maximum code multiplexing number / the number of optical frequency components = 1, and an optical CDM transmission circuit and optical CDM that solve the limitation of frequency utilization efficiency. An object is to provide a receiving circuit and an optical CDM transmission system.

  In order to achieve the above object, the optical CDM transmission circuit, the optical CDM reception circuit, and the optical CDM transmission system according to the present invention cannot be used as a unique code among the allocation codes in the conventional electric codec process. By making it possible to use the code, it is possible to improve the frequency utilization efficiency as compared with the conventional method.

  Specifically, the optical CDM transmission circuit according to the present invention is composed of two types of code elements, has N unique codes whose code length is K or less (K is an integer of 2 or more), and N (N Is an integer greater than or equal to 2), when generating K multilevel signals from the binary signal by associating the inherent code with each binary signal, k of the inherent code corresponding to the binary signal If the code element of the th (k = 1, 2,..., K) is one of the two kinds of code elements, the symbol value of the binary signal corresponds to the k-th code element of the inherent code as it is. If the other of the two types of code elements is the spread value, the inverted symbol value of the binary signal is the spread value corresponding to the kth code element of the unique code, and the spread values are added together. A binary / multi-level conversion means for the symbol value of the k-th multi-level signal, and the optical frequency A plurality of optical modulation means for outputting a multi-level signal light obtained by modulating the optical carrier with the multi-level signal generated by the binary / multi-level conversion means. Optical multiplexing means for outputting multi-wavelength signal light obtained by multiplexing the multi-level signal light output from the optical modulation means.

If a unique code #h (h = 1, 2,..., K) whose code elements are all {1} is assigned to the electric decoding means of the optical CDM receiving circuit, all the electric decoding means Multilevel baseband signals from the optical detection means are added. When attention is paid to an undesired binary signal component (symbol value: D _k (t)) that is spread based on the unique code #k (k ≠ h) in the binary / multilevel conversion means in the optical CDM transmission circuit, Half of the K multi-level baseband signals input to the electrical encoding means include a component of D _k (t), and the other half includes a component of 1-D _k (t) in which a symbol value is inverted. Therefore, the undesired signal component is canceled by adding all the multi-value baseband signals.

  Therefore, the present invention provides an optical CDM transmission circuit that increases the amount of information that can be transmitted within the same wavelength band by setting the maximum number of code multiplexes / the number of optical frequency components = 1, and solves the limitation of frequency utilization efficiency. be able to.

  The binary / multi-level conversion means of the optical CDM transmission circuit according to the present invention has a number of output ends equal to or greater than the code length of the corresponding unique code, and each code element of the unique code is sent to the output end. The spreading value that matches the symbol value of the input binary signal is output from the output end to which one of the two kinds of code elements is assigned, and the other of the two kinds of code elements is assigned. N spread encoders that output the spread value obtained by inverting the symbol value of the input binary signal from the output end, and the spread values from the kth output end of each of the spread encoders And K adders that are added to obtain the k-th multilevel signal.

  In a first form of the optical CDM transmission circuit according to the present invention, the multilevel signal light output from the optical modulation means has a light intensity level that is unique and equally spaced according to the symbol value of the input multilevel signal. The average light intensity is constant regardless of N.

  The second form of the optical CDM transmission circuit according to the present invention is such that the multilevel signal light output from the optical modulation means is an optical field amplitude level that is unique and equally spaced according to the symbol value of the input multilevel signal. The optical phase shift amount of the optical carrier in the optical modulation means is any one of binary values having a difference of π according to the symbol value of the multilevel signal.

  According to a third aspect of the optical CDM transmission circuit of the present invention, continuous light of K optical frequency components matching the optical frequency of the multilevel signal light included in the multiwavelength signal light is used as the multiwavelength signal light. At the output end to output, the polarization state of the multilevel signal light with which the optical frequency components match is such that the optical phase difference with the multilevel signal light with which the optical frequency components match is 0 or π. It further comprises an optical mixer that mixes and outputs the multi-wavelength signal light or the multi-level signal light whose optical frequency components match so as to match.

  The optical CDM receiving circuit according to the present invention includes an optical frequency demultiplexing unit that demultiplexes the multi-wavelength signal light from the optical CDM transmission circuit for each optical frequency component, and a signal light from the optical frequency demultiplexing unit. And a plurality of optical detection means for demodulating the multilevel signal and one of the 1st to Nth unique codes are allocated, and each output terminal of the optical detection means is connected, The code elements constituting the assigned unique code are sequentially associated with the output end of the optical detection means, and the input from the output end corresponding to one of the two types of code elements is positive, the 2 Of the binary signals input to the binary / multilevel conversion means, the inherent code is added to the inherent code by performing addition / subtraction by adding the input from the output terminal corresponding to the other of the code elements of the seed as negative. Selectively select the corresponding binary signal Comprising an electrical decoding means issuing Ri, a.

If a unique code #h (h = 1, 2,..., K) whose code elements are all {1} is assigned to the electric decoding means of the optical CDM receiving circuit, all the electric decoding means Multilevel baseband signals from the optical detection means are added. When attention is paid to an undesired binary signal component (symbol value: D _k (t)) that is spread based on the unique code #k (k ≠ h) in the binary / multilevel conversion means in the optical CDM transmission circuit, Half of the K multi-level baseband signals input to the electrical encoding means include a component of D _k (t), and the other half includes a component of 1-D _k (t) in which a symbol value is inverted. Therefore, the undesired signal component is canceled by adding all the multi-value baseband signals.

  Accordingly, the present invention provides an optical CDM receiving circuit that increases the amount of information that can be sent within the same wavelength band by setting the maximum number of code multiplexes / the number of optical frequency components = 1 and solves the limitation of frequency utilization efficiency. be able to.

  The optical detection means of the optical CDM reception circuit corresponding to the first form of the optical CDM transmission circuit performs square detection of the signal light from the optical frequency demultiplexing means.

  The optical detection means of the optical CDM reception circuit corresponding to the first form of the optical CDM transmission circuit is configured such that the optical frequency of the continuous light to be output is a predetermined frequency difference from the signal light from the optical frequency demultiplexing means. From the adjusted local light source, an optical detector that squarely detects the mixed light of the continuous light from the local light source and the signal light from the optical frequency demultiplexing means, and from the output of the optical detector, Includes a bandpass filter that transmits a signal component carried by a carrier wave that matches the predetermined frequency difference, and an envelope detector that square-detects the output of the bandpass filter.

  The optical detection means of the optical CDM reception circuit corresponding to the first form of the optical CDM transmission circuit has the binary signal in which the optical frequency of the continuous light to be output is different from the signal light from the optical frequency demultiplexing means. A local light source that is adjusted to be sufficiently smaller than the signal band, and a plurality of output ends, and an optical phase difference between continuous light from the local light source and signal light from the optical frequency demultiplexing means Is a one-to-one relationship between the optical hybrid that mixes the continuous light from the local light source and the signal light from the optical frequency demultiplexing means, and the output end of the optical hybrid so that there is a predetermined difference between the output ends. A plurality of photodetectors that squarely detect the input light, a plurality of squarers that square the output of the photodetector, and an adder that adds the outputs of the squarers, It is characterized by providing.

  The optical detection means of the optical CDM reception circuit corresponding to the second form of the optical CDM transmission circuit is configured such that the optical frequency of the continuous light to be output is a predetermined frequency difference from the signal light from the optical frequency demultiplexing means. From the adjusted local light source, the continuous light from the local light source, and the optical detector that squarely detects the mixed light of the signal light from the optical frequency demultiplexing means, and the output of the optical detector, An electric phase synchronization including a bandpass filter that transmits a signal component carried by a carrier wave whose frequency matches the predetermined frequency difference, a VCO, a mixer, and a loop filter, whose electric band is sufficiently narrower than the signal band of the binary signal A phase-locked detection circuit having a loop, and the frequency and phase of the output of the VCO are adjusted so as to be synchronized with the carrier wave by the loop filter, and the mixer includes the bandpass filter Characterized by integrating the output of the input signal and the VCO from.

  The optical detection means of the optical CDM reception circuit corresponding to the second form of the optical CDM transmission circuit includes a local light source, an optical detector, and a loop filter, and the electrical band is sufficiently narrower than the signal band of the binary signal. A phase-locked loop, and the optical frequency and optical phase of the continuous light output from the local light source are adjusted by the loop filter so as to be synchronized with the optical carrier wave of the signal light from the optical frequency demultiplexing means, The optical detector performs square detection of mixed light of continuous light from the local light source and signal light from the optical frequency demultiplexing means.

  The optical detection means of the optical CDM reception circuit corresponding to the third form of the optical CDM transmission circuit performs square detection of the signal light from the optical frequency demultiplexing means.

  An optical CDM transmission system according to the present invention includes the optical CDM transmission circuit, the optical CDM reception circuit, an optical fiber transmission line that propagates the multi-wavelength signal light from the optical CDM transmission circuit to the optical CDM reception circuit, Is provided.

  An optical CDM transmission system according to the present invention propagates the multi-wavelength signal light from the optical CDM transmission circuit to the optical CDM reception circuit from the optical CDM transmission circuit corresponding to the optical CDM transmission circuit of the first form. An optical fiber transmission line.

  An optical CDM transmission system according to the present invention propagates the multi-wavelength signal light from the optical CDM transmission circuit to the optical CDM reception circuit from the optical CDM transmission circuit corresponding to the optical CDM transmission circuit of the second form. An optical fiber transmission line.

  An optical CDM transmission system according to the present invention propagates the multi-wavelength signal light from the optical CDM transmission circuit to the optical CDM reception circuit, and an optical CDM reception circuit corresponding to the optical CDM transmission circuit of the third form. An optical fiber transmission line.

  Since the optical CDM transmission system according to the present invention includes the optical CDM transmission circuit and the optical CDM reception circuit described above, the amount of information that can be transmitted within the same wavelength band by setting the maximum code multiplexing number / the number of optical frequency components = 1. And the limitation of the frequency utilization efficiency can be solved.

  The present invention increases the amount of information that can be transmitted within the same wavelength band by setting the maximum code multiplexing number / the number of optical frequency components = 1, and an optical CDM transmission circuit and an optical CDM reception circuit that solve the limitation of frequency utilization efficiency In addition, an optical CDM transmission system can be provided.

It is a figure explaining the structural example of an optical CDM transmission system. It is a figure explaining the structural example of the binary / multi-value conversion means of an optical CDM transmission circuit. 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 which concerns on 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 which concerns on this invention has. 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 detection means of the optical CDM receiving circuit which concerns on this invention. It is a figure explaining the optical electric field state of the multilevel signal light which the binary / multilevel conversion means of 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 detection means of the optical CDM receiving circuit which concerns on this invention. It is a figure explaining the optical CDM transmission circuit based on this invention. It is a figure explaining the optical CDM transmission circuit based on this invention.

  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)
The optical CDM transmission system of Embodiment 1 has a configuration in which an optical CDM transmission circuit 201 and a plurality of optical CDM reception circuits 202 are connected by an optical fiber transmission line 203, as in the optical CDM transmission system of FIG.

[Optical CDM transmission circuit]
The optical CDM transmission circuit 201 is composed of two types of code elements, has N unique codes whose code length is K or less (K is an integer of 2 or more), and N (N is an integer of 2 or more) 2 When generating K multilevel signals from the binary signal by associating the unique code with each of the value signals, the k-th (k = 1, 2, k) of the unique code corresponding to the binary signal. .., K) if the code element is one of the two kinds of code elements, the symbol value of the binary signal is directly used as the spread value corresponding to the k-th code element of the inherent code, and the 2 If it is the other of the code elements of the seed, the symbol value of the inverted binary signal is set as a spread value corresponding to the k-th code element of the inherent code, and the spread values are added together to obtain the k-th multi-value. The binary / multi-value conversion means 111 that is a symbol value of the signal and the optical frequency are different from each other. A plurality of optical modulation means 12 for outputting a multilevel signal light obtained by modulating an optical carrier wave with the multilevel signal generated by the binary / multilevel conversion means 111; And optical multiplexing means 13 for outputting multi-wavelength signal light obtained by multiplexing the multilevel signal light output by the optical modulation means.

  Each light modulator 12 receives continuous light having different optical frequencies from the light source 14, and converts the light intensity of the input continuous light from among the multilevel signals generated by the binary / multilevel converter 111. The multilevel signal light modulated using any one of them is output. The multilevel signal light output from each optical modulation means 12 is transmitted by an optical waveguide combining means 13 such as an arrayed waveguide grating (AWG) or a multilayer filter, an optical fiber or a PLC (Planar Lightwave Circuit). The multi-wavelength signal light combined by the created optical coupler is transmitted to each optical CDM receiving circuit 202 via the optical fiber transmission path 203. Here, the average 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. 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。固有符号としては、各符号間で直交性を有するアダマール符号などを用いる。ここで、多値信号は、各シンボル値に対応する電圧レベルが光多値変調における所望の間隔となるように、２値／多値変換手段１１１内にて調整されている。 The binary / multi-level conversion unit 111 receives N binary signals having symbol values D ₁ (t) to D _N (t), and N unique signals corresponding to the binary signal in a one-to-one relationship. Based on the code, K multilevel signals having symbol values of D ^# ₁ (t) to D ^# _K (t) are generated. The unique code is composed of two types of code elements, and the code length is K or less. The symbol value of the k-th multilevel signal is the same as the symbol value of the binary signal which is one of the two possible code elements of the k-th code element of the unique code corresponding to one-to-one. The symbol value of the binary signal is a value obtained by inverting and adding the symbol values of N binary signals. Assuming that the kth code element of the unique code n (n = 1, 2,..., N) is cn _{, k} , the symbol value D ^# _k (t) of the _kth multilevel signal is

It can be expressed. As the unique code, a Hadamard code having orthogonality between codes is used. Here, the multilevel signal is adjusted in the binary / multilevel conversion means 111 so that the voltage level corresponding to each symbol value becomes a desired interval in the optical multilevel modulation.

  FIG. 3 is a configuration example of the binary / multi-value conversion unit 111. The binary / multi-value conversion means 111 has a number of output ends 23 equal to or greater than the code length of the corresponding unique code, and assigns each code element of the unique code to the output end 23 in order. The spread value that matches the symbol value of the input binary signal is output from the output end 23 to which one of the elements is assigned, and is input from the output end 23 to which the other of the two types of code elements is assigned. N spread encoders 121 that output the spread values obtained by inverting the symbol values of the binary signal, and the spread values from the kth output terminal 23 of each spread encoder 121 are added to obtain the kth And K adders 22 serving as the multilevel signal. In the present embodiment, the binary / multi-value conversion unit 111 has a pre-bias circuit 24 connected to the subsequent stage of the adder 22.

The spreading encoder 121 has a number of output ends 23 equal to or greater than the code length of the corresponding unique code, and assigns each code element {1}, {0} constituting the unique code to each output end 23 in order. , A signal (spread value) matching the binary signal to which the symbol value is input is output from each output end 23 to which the code element {1} is assigned. On the other hand, from each output end 23 to which the code element {0} is assigned, a binary signal to which the symbol value is input and an inverted signal (spread value) are output. FIG. 3 shows a case where the code lengths of all the unique codes and the number of output terminals 23 are K. For example, the symbol value of the output signal of each output terminal 23 of the spread encoder 121-1 assigned the unique code 1 {1, 1, 0,..., 0} is D ₁ (t) = 1. Are sequentially “1”, “1”, “0”,..., “0”, and when D ₁ (t) = 0, “0”, “0”, “1”,. “1”.

The output signals of each spreading encoder 121 are added to generate K multilevel signals. The k-th adder 22 adds the output signals from the k-th output terminal 23-k of each spreading encoder 121, and the multi-value in which the symbol value D ^# _k (t) is expressed by Expression (1). Generate a signal.

The pre-bias circuit 24 adjusts the voltage level interval corresponding to each symbol value of the output signal of the adder 22. A configuration example of the pre-bias circuit 24 is shown in FIG. 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 in the m-th (m = 1, 2,..., M−1) weighting circuit 31-m 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 an input multilevel signal at a certain time corresponds to the symbol value “i”, the discriminating circuit 32 in the weighting circuits 31-1 to 31-i outputs 1 and the other discriminating circuits 32 output 0. The output of the pre-bias circuit 24 obtained by adding the outputs of the circuit 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, the pre-bias circuit 24 can flexibly generate a multi-value signal in which the voltage level interval corresponding to each symbol value has a desired ratio by changing the weighting coefficients X _{1 to} X _M−1. It is.

The N binary signals input to the binary / multilevel conversion unit 111 may not necessarily be bit-synchronized between the signals and may have different signal speeds. In addition, a binary / multi-level conversion means can be configured by combining a memory storing the operations of the spread encoder 121, the adder 22, and the pre-bias circuit 24 with a D / A converter. Furthermore, a memory having stored an operation by the adder 22 and the spreading code 121, as shown in Figure 5 either _SW 0 _{~SW M-1} is turned ON in response to the symbol values ^D _# k (t) By combining with a pre-bias circuit, the D / A converter is not required, and the sampling speed of the D / A converter can be increased.

  The multilevel signal light output from the optical modulation means 12 has a light intensity level that is unique and equally spaced according to the symbol value of the input multilevel signal, and the average light intensity is constant regardless of N. The light modulation means 12 takes a specific light intensity according to the symbol value of the multi-value signal input from the binary / multi-value conversion means 111, and outputs multi-value signal light whose possible light intensity levels are equally spaced. To do. The multilevel signal input to the optical modulation means 12 is adjusted in voltage level corresponding to each symbol value in the binary / multilevel conversion means 111. By adjusting the voltage level interval so as to compensate for the non-linearity of the optical multi-level modulation, multi-level signal light in which each light intensity level is equally spaced is generated.

と表せる。ｍＤ^＃ _ｋは多値信号のシンボル値Ｄ^＃ _ｋ（ｔ）がとりうる最大値と最小値の中間値、θ_Ｓ（ｔ）は光強度変調に伴う位相チャープ量、φ_Ｓ（ｔ）は多値信号光の位相雑音である。 The optical electric field state E _S (t) of the multilevel signal light output from the k-th optical modulation means 12-k to which continuous light having an optical frequency of f _k is input depends on the average light intensity and the symbol value. Given the possible light intensity level intervals as P _S and ΔP _S , respectively,

It can be expressed. mD ^# _k intermediate values of the maximum value and the minimum value symbol value ^D _# k of the multi-level signal (t) can assume, theta _S (t) is the phase chirp amount due to the light intensity modulation, phi _S (t) is multi This is the phase noise of the value signal light.

As the optical modulation means 12, a Mach-Zehnder interferometer type optical intensity modulator such as an LN intensity modulator, an electroabsorption (EA) modulator, a semiconductor optical amplifier (SOA) modulator, or the like Can be used. When a Dual-Drive Mach-Zehnder interferometer type light intensity modulator is operated in a Push-Pull operation, θ _S (t) = 0.

[Optical CDM receiver circuit]
The optical CDM receiving circuit 202 detects the signal light from the optical frequency demultiplexing means 42 and the optical frequency demultiplexing means 42 for demultiplexing the multi-wavelength signal light from the optical CDM transmission circuit 201 for each optical frequency component. A plurality of optical detection means 43 for demodulating the multilevel signal and one of the first to Nth unique codes are assigned, and each output terminal of the optical detection means 43 is connected and assigned. The code elements constituting the unique code are sequentially corresponded to the output end of the optical detection means 43, the input from the output end corresponding to one of the two types of code elements is positive, and the two types of code elements Among the binary signals input to the binary / multilevel converter 111 by performing addition / subtraction by adding the input from the output terminal corresponding to the other of the two as negative. Selectively take out electricity Comprises a Goka means 45.

となり、電圧レベルがシンボル値Ｄ^＃ _ｋ（ｔ）に対して線形であることが分かる。 The optical frequency demultiplexing unit 42 separates the multi-wavelength signal light input to the optical CDM receiving circuit 202 for each optical frequency component, and outputs the multilevel signal light to the optical detection unit 43. In the present embodiment, a light detector (PD: Photo-Detector) is used as the light detection means 43. Each optical detection unit 43 square-detects the multilevel signal light from the optical frequency demultiplexing unit 42 to generate a multilevel baseband signal whose voltage levels corresponding to each symbol value are equally spaced. Here, the voltage level intervals coincide among the multilevel baseband signals generated by the respective optical detection means 43. Assuming that the optical field state of the multilevel signal light input to the kth optical detection means 43-k is the multilevel signal light whose optical frequency expressed by the equation (2) is f _k , the multilevel baseband signal R _k (t) ⁽¹⁾ is

Thus, it can be seen that the voltage level is linear with respect to the symbol value D ^# _k (t).

  The electric decoding unit 45 includes a plurality of input terminals and one output terminal. Each input end is connected to the output end of each optical detection means 43 in a one-to-one relationship, and each code element {1}, {0} constituting the corresponding unique code is sequentially assigned to the output end of each optical detection means 43. Then, addition / subtraction is performed by adding the input from the output end assigned {1} as positive and the input from the output end assigned {0} as negative. In the addition / subtraction, undesired signal components are removed by the orthogonality of the codes, and a desired binary signal is selectively extracted.

In the present embodiment, unlike the conventional method, all code elements correspond to the unique code #h (h = 1, 2,..., K) with {1}, and from all the optical detection means 43. The electrical decoding means 45 for adding the multi-value baseband signal can remove undesired signal components and selectively extract a desired binary signal. Pay attention to an undesired binary signal component (symbol value: D _k (t)) that is spread based on the unique code #k (k ≠ h) in the binary / multi-level conversion means 111 in the optical CDM transmission circuit 201. Then, the K multi-value baseband signals input to the electrical encoding means 45 include a component of D _k (t) in half and a component of 1-D _k (t) in which the other half is inverted in symbol value. including. Therefore, the undesired signal component is canceled by adding all the multi-value baseband signals.

  In the conventional optical CDM transmission system, codes whose code elements are {1} among codes whose code lengths are orthogonal to each other cannot be used as unique codes. On the other hand, in this embodiment, it is possible to use all codes whose code lengths are orthogonal to each other, and the code multiplexing number N at the same code length is increased. Here, the number of optical frequency components of the transmitted / received multi-wavelength signal light is a code length K, and the optical frequency band of the multi-wavelength signal light is the same as that of the conventional optical CDM transmission system. Therefore, frequency utilization efficiency is improved as compared with the conventional method.

よって、

となり、光ＣＤＭ送信回路２０１内の２値／多値変換手段に入力されたｈ番目の２値信号のシンボル値Ｄ_ｈ（ｔ）に応じて、シンボル値が変化する所望の２値信号が取り出せることが分かる。 Hereinafter, in the case of using a Hadamard code having a code length of K as a unique code, the electric decoding unit 45 corresponding to the h-th unique code having all code elements {1} Indicates that it can be selectively extracted. The output S _h (t) ⁽¹⁾ of the electrical decoding means is the sum of the multi-value baseband signal R _k (t) ⁽¹⁾ from the optical detection means. Here, equations (4)-(6) hold.

Therefore,

Thus, a desired binary signal whose symbol value changes can be extracted in accordance with the symbol value D _h (t) of the h-th binary signal input to the binary / multilevel conversion means in the optical CDM transmission circuit 201. I understand that.

(Embodiment 2)
In the optical CDM transmission system of the second embodiment, a heterodyne envelope detection circuit is disposed as the optical detection means 43 in the optical CDM reception circuit 202 of the optical CDM transmission system of the first embodiment. The heterodyne envelope detection circuit includes a local light source, an optical detector, a BPF (Bandpass Filter), and an envelope detector, and detects multilevel signal light from the optical frequency demultiplexing means to correspond to each symbol value. A multi-value baseband signal having an equal voltage level is generated.

  FIG. 6 is an example of a heterodyne envelope detection circuit. That is, the optical detection means 43 includes a local light source 51 adjusted so that the optical frequency of the continuous light to be output becomes a predetermined frequency difference from the signal light from the optical frequency demultiplexing means 42, and the local light source 51. The optical detector 53 that squarely detects the mixed light of the continuous light and the signal light from the optical frequency demultiplexing means 43, and the carrier wave whose frequency matches the predetermined frequency difference is conveyed from the output of the optical detector 53. A BPF 54 that transmits a signal component to be transmitted, and an envelope detector 59 that square-detects the output of the BPF 54.

と表せる。ここで、Ｐ_Ｌ，φ_Ｌ（ｔ）は、それぞれ、局発光の光強度および位相雑音である。一方、多値信号光の光電界Ｅ_Ｓ（ｔ）は、実施形態１中の式（２）で表せる。 The optical frequency of the local light source 51 is adjusted to be different from the optical frequency of the multilevel signal light by f _IF . That is, in the k-th heterodyne envelope detection circuit to which multilevel signal light whose optical frequency is represented by the equation (2) in the first embodiment and whose optical frequency is f _k is input, the optical frequency of local light is emitted. Is adjusted to be f _k −f _IF . The optical electric field state E _L (t) is

It can be expressed. Here, P _L and φ _L (t) are the local light intensity and phase noise, respectively. On the other hand, the optical electric field E _S (t) of the multilevel signal light can be expressed by Expression (2) in the first embodiment.

と表せる。ここで、

とした。 The optical detection means 43 square-detects the mixed light of local light and multilevel signal light. Its output Q _k (t) ⁽²⁾ is

It can be expressed. here,

It was.

  In the heterodyne envelope detection circuit, by adjusting the polarization state of at least one of the local light and the multilevel signal light, adjustment is made so that the polarization state of the local light and the multilevel signal light is matched. In FIG. 6, the polarization adjusting means 52 adjusts the polarization of the local light. In the optical CDM transmission circuit 201, a configuration of polarization scramble that changes the polarization state of the signal light with time, a configuration of transmitting signal light in which the orthogonal polarization states are added, and a polarization in the optical CDM reception circuit 202 Due to the diversity configuration, it is possible to omit polarization adjustment in the heterodyne envelope detection circuit.

The BPF 54 has a transmission band in the vicinity of f _IF , removes a direct detection component, and outputs an intermediate frequency signal (the third term on the right side of Expression (9)) having f _IF as a center frequency.

となり、電圧レベルがシンボル値Ｄ^＃ _ｋ（ｔ）に対して線形であることが分かる。 The intermediate frequency signal from the BPF 54 is subjected to square detection in the envelope detector 59 and then low-pass filtered in an LPF (Lowpass Filter), and a multilevel baseband signal in which voltage levels corresponding to each symbol value are equally spaced is obtained. Generated. Here, the voltage level intervals coincide among the multi-value baseband signals generated by the respective heterodyne envelope detection circuits. The multi-value baseband signal R _k (t) ⁽²⁾ generated by the k th heterodyne envelope detection circuit is

Thus, it can be seen that the voltage level is linear with respect to the symbol value D ^# _k (t).

The electric decoding unit 45 has the same configuration as that of the first embodiment, and adds / subtracts the input multi-level baseband signal according to the corresponding inherent code to selectively extract a desired binary signal. In the present embodiment, unlike the conventional method, all code elements correspond to the unique code #h (h = 1, 2,..., K) with {1}, and from all the optical detection means 43. The electrical decoding means 45 for adding the multi-value baseband signal can remove undesired signal components and selectively extract a desired binary signal. Pay attention to an undesired binary signal component (symbol value: D _k (t)) that is spread based on the unique code #k (k ≠ h) in the binary / multi-level conversion means 111 in the optical CDM transmission circuit 201. Then, the K multi-value baseband signals input to the electrical encoding means 45 include a component of D _k (t) in half and a component of 1-D _k (t) in which the other half is inverted in symbol value. including. Therefore, the undesired signal component is canceled by adding all the multi-value baseband signals.

  In the conventional optical CDM transmission system, codes whose code elements are {1} among codes whose code lengths are orthogonal to each other cannot be used as unique codes. On the other hand, in this embodiment, it is possible to use all codes whose code lengths are orthogonal to each other, and the code multiplexing number N at the same code length is increased. Here, the number of optical frequency components of the transmitted / received multi-wavelength signal light is a code length K, and the optical frequency band of the multi-wavelength signal light is the same as that of the conventional optical CDM transmission system. Therefore, frequency utilization efficiency is improved as compared with the conventional method.

(Embodiment 3)
In the optical CDM transmission system of the third embodiment, a phase diversity homodyne detection circuit is arranged as the optical detection means 43 in the optical CDM reception circuit 202 of the optical CDM transmission system of the first embodiment. The phase diversity homodyne detection circuit includes a local light source, an optical hybrid, a plurality of optical detectors, a squarer, and an adder. The multi-level signal light from the optical frequency demultiplexing means is detected and converted to each symbol value. A multi-value baseband signal having corresponding voltage levels at equal intervals is generated.

  FIG. 7 is an example of a phase diversity homodyne detection circuit. That is, the optical detection means 43 is a station in which the optical frequency of the continuous light to be output is adjusted so that the frequency difference from the signal light from the optical frequency demultiplexing means is sufficiently smaller than the signal band of the binary signal. The light source 51 has a plurality of output ends, and the optical phase difference between the continuous light from the local light source 51 and the signal light from the optical frequency demultiplexing means 42 is a predetermined difference between the output ends. The optical hybrid 133 that mixes the continuous light from the local light source 51 and the signal light from the optical frequency demultiplexing means 42 is connected to the output end of the optical hybrid 133 on a one-to-one basis, and a plurality of squares are detected for the input light. Optical detector 134, a plurality of squarers 135 that square the output of optical detector 134, and an adder 136 that adds the outputs of each squarer 135.

と表せる。 As for the optical frequency of local light, the optical frequency difference ε with respect to the multilevel signal light is sufficiently smaller than the signal band of the binary signal input to the binary / multilevel conversion means 111 in the optical CDM transmission circuit 201. To be adjusted. In the k-th phase diversity homodyne detection circuit to which multi-level signal light whose optical frequency is f _k represented by the formula (2) in the first embodiment is input, the optical electric field state of local light emission E _L ^' (t) is

It can be expressed.

  The optical hybrid 133 has a plurality of output ends, and the local light and the multi-level signal light are mixed so that the optical phase difference between the local light and the multi-level signal light becomes a predetermined difference between the output ends. Output. If four optical terminals are provided and the optical phase difference between the local light and the multilevel signal light at the first output terminal is ψ (t), the optical phase difference at the other three output terminals is ψ (t) + This includes 90 ° optical hybrids such as π / 2, ψ (t) + π, and ψ (t) + 3π / 2. By incorporating an optical phase adjuster into a spatial system circuit incorporating a λ / 2 plate or λ / 4 plate that realizes the desired optical phase relationship using polarization, or an optical coupler made of optical fiber or PLC, etc. , 90 ° optical hybrid can be configured.

  FIG. 7 shows a configuration in which the polarization adjusting unit 52 adjusts the polarization state of the local light and the multilevel signal light at the input end of the 90 ° optical hybrid 133. In the optical CDM transmission circuit 201, a configuration of polarization scramble that changes the polarization state of the signal light with time, a configuration of transmitting signal light in which the orthogonal polarization states are added, and a polarization in the optical CDM reception circuit 202 Depending on the configuration of diversity, it is possible to omit polarization adjustment in the phase diversity homodyne detection circuit.

と表せる。同様にして、差動検波器２の出力Ｑ_２（ｔ）^（３）は、次式で表せる。

差動検波器の出力は、それぞれ２乗された後に加算され、各シンボル値に対応する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。ここで、各位相ダイバーシティ・ホモダイン検波回路で生成される多値ベースバンド信号間で、電圧レベル間隔は一致する。ｋ番目の位相ダイバーシティ・ホモダイン検波回路で生成される多値ベースバンド信号Ｒ_ｋ（ｔ）^（３）は、

となり、電圧レベルがシンボル値Ｄ^＃ _ｋ（ｔ）に対して線形であることが分かる。 The output terminals # 1 and # 2 of the 90 ° optical hybrid are connected to the differential detector 134-1 and the output terminals # 3 and # 4 are connected to the differential detector 134-2. Here, when the optical phase difference between the local light and the multilevel signal light at the output terminal # 1 is ψ (t), the optical phase differences at the output terminals 2 to 4 are ψ (t) + π, ψ (t ) + Π / 2, ψ (t) + 3π / 2. At this time, the output Q ₁ (t) ⁽³⁾ of the differential detector 1 is

It can be expressed. Similarly, the output Q ₂ (t) ⁽³⁾ of the differential detector 2 can be expressed by the following equation.

The outputs of the differential detectors are respectively squared and then added to generate a multi-value baseband signal whose voltage levels corresponding to each symbol value are equally spaced. Here, the voltage level intervals coincide among the multi-value baseband signals generated by the phase diversity and homodyne detection circuits. The multilevel baseband signal R _k (t) ⁽³⁾ generated by the k-th phase diversity homodyne detection circuit is

Thus, it can be seen that the voltage level is linear with respect to the symbol value D ^# _k (t).

The electric decoding unit 45 has the same configuration as that of the first embodiment, and adds / subtracts the input multi-level baseband signal according to the corresponding inherent code to selectively extract a desired binary signal. In the present embodiment, unlike the conventional method, all code elements correspond to the unique code #h (h = 1, 2,..., K) with {1}, and from all the optical detection means 43. The electrical decoding means 45 for adding the multi-value baseband signal can remove undesired signal components and selectively extract a desired binary signal. Pay attention to an undesired binary signal component (symbol value: D _k (t)) that is spread based on the unique code #k (k ≠ h) in the binary / multi-level conversion means 111 in the optical CDM transmission circuit 201. Then, the K multi-value baseband signals input to the electrical encoding means 45 include a component of D _k (t) in half and a component of 1-D _k (t) in which the other half is inverted in symbol value. including. Therefore, the undesired signal component is canceled by adding all the multi-value baseband signals.

  In the conventional optical CDM transmission system, codes whose code elements are {1} among codes whose code lengths are orthogonal to each other cannot be used as unique codes. On the other hand, in this embodiment, it is possible to use all codes whose code lengths are orthogonal to each other, and the code multiplexing number N at the same code length is increased. Here, the number of optical frequency components of the transmitted / received multi-wavelength signal light is a code length K, and the optical frequency band of the multi-wavelength signal light is the same as that of the conventional optical CDM transmission system. Therefore, frequency utilization efficiency is improved as compared with the conventional method.

(Embodiment 4)
Similar to the optical CDM transmission system of the first embodiment, the optical CDM transmission system of the fourth embodiment has a configuration in which an optical CDM transmission circuit 201 and a plurality of optical CDM reception circuits 202 are connected by an optical fiber transmission path 203. In the first embodiment, the optical modulation means 12 in the optical CDM transmission circuit 201 modulates the optical intensity of the optical carrier, whereas in the fourth embodiment, the optical electric field amplitude and optical phase of the optical carrier are modulated. Further, in the optical CDM receiving circuit 202 of the fourth embodiment, a heterodyne synchronous detection circuit is arranged as the optical detection means 43.

  The multilevel signal light output from the optical modulation means 12 has optical field amplitude levels that are unique and equally spaced according to the symbol value of the input multilevel signal, and the optical carrier wave in the optical modulation means 12 The optical phase shift amount is one of binary values having a difference of π according to the symbol value of the multilevel signal.

  The multilevel signal light output from the optical modulation means 12 takes a specific optical electric field amplitude level in accordance with the symbol value of the multilevel signal input from the binary / multilevel conversion means 111, and can take an optical electric field amplitude level. Are equally spaced. Further, the optical phase shift amount of the optical carrier wave in the optical modulation means 12 is one of binary values having a difference of π depending on the symbol value. The multilevel signal input to the optical modulation means 12 is adjusted in voltage level corresponding to each symbol value in the binary / multilevel conversion means 111. By adjusting the voltage level interval so as to compensate for the non-linearity of the optical multilevel modulation, multilevel signal light in which the optical electric field amplitude levels are equally spaced is generated.

と表せる。ω_ｋ（ｔ）は、Ｄ^＃ _ｋ（ｔ）に応じて、差がπである２値のいずれかをとる。ω_ｋ（ｔ）が、０またはπのいずれかとすると、多値信号光の光電界状態は、Ｄ^＃ _ｋ（ｔ）に応じて、図８のように遷移する。図８中のＭ_ｋは、光変調手段へ入力される多値信号の多値数である。 The optical electric field state E _S (t) ^* of the multilevel signal light output from the k-th optical modulation means 12-k to which continuous light having an optical frequency of f _k is input is an optical electric field that can be taken according to the symbol value. Given the distance between the amplitude level in Delta] E _S,

It can be expressed. ω _k (t) takes one of two values having a difference of π according to D ^# _k (t). When ω _k (t) is either 0 or π, the optical electric field state of the multilevel signal light transitions as shown in FIG. 8 according to D ^# _k (t). M _{k in} FIG. 8 is the multi-value number of the multi-value signal input to the light modulation means.

  FIG. 9 is an example of the light modulation means 12. The light modulation means 12 includes a differential signal generation means 25 and a zero chirp type light intensity modulator 26 having no phase chirp due to the light intensity modulation. The zero chirp type light intensity modulator 26 is, for example, a Dual-Drive Mach-Zehnder interferometer type light intensity modulator. The light intensity modulator 26 outputs two signals that are generated by the differential signal generation means 25 from the multi-value signal from the binary / multi-value conversion means 111 and that have opposite polarities as output signals of the differential signal generation means 25. When the intermediate voltage between the maximum voltage and the minimum voltage that can be taken is applied, the transmission is biased so that the transmittance is minimized, and desired multilevel signal light is generated. The differential signal generating means 25 can use a differential amplifier in addition to a configuration in which a divider and an inverter are combined.

  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 42 and input to each optical detection means 43 (heterodyne synchronous detection circuit). The heterodyne synchronous detection circuit includes a local light source, an optical detector, a BPF, and a phase synchronous detection circuit, detects multilevel signal light from the optical frequency demultiplexing means, and voltage levels corresponding to each symbol value are equally spaced. A multi-value baseband signal is generated.

  FIG. 10 is an example of a heterodyne synchronous detection circuit. That is, the optical detection means 43 includes a local light source 51 adjusted so that the optical frequency of the continuous light to be output becomes a predetermined frequency difference from the signal light from the optical frequency demultiplexing means 42, and the local light source 51. , The optical detector 53 that squarely detects the mixed light of the continuous light and the signal light from the optical frequency demultiplexing means 42, and the carrier wave whose frequency matches the predetermined frequency difference from the output of the optical detector 53. A BPF 54 that transmits a signal component to be conveyed; and a phase-locked detection circuit 55 that includes a VCO 61, a mixer 62, and a loop filter 63, and has an electric phase-locked loop whose electric band is sufficiently narrower than the signal band of the binary signal. The frequency and phase of the output of the VCO 61 are adjusted so as to be synchronized with the carrier wave by the loop filter 63, and the mixer 62 integrates the input signal from the BPF 54 and the output of the VCO 61. And wherein the Rukoto.

と表せる。 The optical frequency of the local light source 51 is adjusted so as to differ from the optical frequency of the multilevel signal light input to the optical detection means by f _IF . In other words, in the k-th heterodyne synchronous detection circuit to which multilevel signal light whose optical electric field state is represented by the equation (16) is f _k is input, the optical frequency of local light is f _k −f _IF . The optical field state E _L (t) ^* is adjusted so that the optical field amplitude is E _L.

It can be expressed.

と表せる。Δφ（ｔ）の時間変動は、光ＣＤＭ送信回路２０１にて２値／多値変換手段１１１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 squarely detects the mixed light of the local light and the multilevel signal light, and its output Q _k (t) ⁽⁴⁾ is

It can be expressed. The time variation of Δφ (t) is sufficiently gradual as compared with the signal speed of the binary signal input to the binary / multilevel converter 111 in the optical CDM transmission circuit 201.

  In the heterodyne synchronous detection circuit, the polarization adjustment means 52 adjusts the polarization state of at least one of the local light and the multilevel signal light 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 scramble that changes the polarization state of the signal light with time, a configuration of transmitting signal light in which the orthogonal polarization states are added, and a polarization in the optical CDM reception circuit 202 Depending on the diversity configuration, etc., it is possible to omit polarization adjustment in the heterodyne synchronous detection circuit.

The BPF 54 has a transmission band in the vicinity of f _IF , removes the direct detection component, and outputs an intermediate frequency signal (the third term on the right side of Expression (18)) having f _IF as the center frequency.

と表せる。ミキサー６２の出力Ｔ_ｋ（ｔ）^（４）をＬＰＦ５６にて低域濾波した多値ベースバンド信号

が電気復号化手段へ入力される。ω_ｋ（ｔ）は、Ｄ^＃ _ｋ（ｔ）に応じて、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^＃ _ｋ（ｔ）に応じてとりうる電圧レベルがｍＤ^＃ _ｋに対応する０Ｖを中心として対称かつ等間隔となることが分かる。 The phase synchronous detection circuit 55 synchronously detects the intermediate frequency signal from the BPF 54, and generates a multi-value baseband signal whose voltage levels corresponding to each symbol value are equally spaced. Here, the voltage level intervals coincide among the multilevel baseband signals generated by the respective optical detection means 43 (heterodyne synchronous detection circuits). The output T _k (t) ⁽⁴⁾ of the mixer 62 in the phase synchronous detection circuit 55 is

It can be expressed. Multilevel baseband signal obtained by low-pass filtering the output T _k (t) ⁽⁴⁾ of the mixer 62 by the LPF 56

Is input to the electric decoding means. Since ω _k (t) takes one of two values whose difference is π according to D ^# _k (t), the multi-value baseband signal is taken according to the symbol value D ^# _k (t). It can be seen that the voltage levels that can be obtained are symmetrical and equally spaced around 0V corresponding to mD ^# _k .

The electric decoding unit 45 has the same configuration as that of the first embodiment, and adds / subtracts the input multi-level baseband signal according to the corresponding inherent code to selectively extract a desired binary signal. In the present embodiment, unlike the conventional method, all code elements correspond to the unique code #h (h = 1, 2,..., K) with {1}, and from all the optical detection means 43. The electrical decoding means 45 for adding the multi-value baseband signal can remove undesired signal components and selectively extract a desired binary signal. Pay attention to an undesired binary signal component (symbol value: D _k (t)) that is spread based on the unique code #k (k ≠ h) in the binary / multi-level conversion means 111 in the optical CDM transmission circuit 201. Then, the K multi-value baseband signals input to the electrical encoding means 45 include a component of D _k (t) in half and a component of 1-D _k (t) in which the other half is inverted in symbol value. including. Therefore, the undesired signal component is canceled by adding all the multi-value baseband signals.

  In the conventional optical CDM transmission system, codes whose code elements are {1} among codes whose code lengths are orthogonal to each other cannot be used as unique codes. On the other hand, in this embodiment, it is possible to use all codes whose code lengths are orthogonal to each other, and the code multiplexing number N at the same code length is increased. Here, the number of optical frequency components of the transmitted / received multi-wavelength signal light is a code length K, and the optical frequency band of the multi-wavelength signal light is the same as that of the conventional optical CDM transmission system. Therefore, frequency utilization efficiency is improved as compared with the conventional method.

(Embodiment 5)
The optical CDM transmission system according to the fifth embodiment includes an optical phase-locked homodyne detection circuit as the optical detection means 43 in the optical CDM reception circuit 202 in the optical CDM transmission system according to the fourth embodiment. The optical phase-locked homodyne detection circuit has an optical phase-locked loop composed of a local light source, a light detector, and a loop filter, and detects multilevel signal light from the optical frequency demultiplexing means and supports each symbol value A multi-valued baseband signal having equal voltage levels is generated.

  FIG. 11 is an example of an optical phase-locked homodyne detection circuit. That is, the light detection means 43 includes a local light source 51, a light detector 53, and a loop filter 63, and includes an optical phase-locked loop whose electric band is sufficiently narrower than the signal band of the binary signal. The optical frequency and optical phase of the continuous light to be output are adjusted by the loop filter 63 so as to be synchronized with the optical carrier wave of the signal light from the optical frequency demultiplexing means 42, and the optical detector 53 is supplied from the local light source 51. The mixed light of the continuous light and the signal light from the optical frequency demultiplexing means 42 is square-detected.

と表せる。 The loop filter 63 adjusts the optical frequency and optical phase of the local light so as to be synchronized with the optical carrier wave of the multilevel signal light. In the k-th optical phase-locked homodyne detection circuit to which multi-level signal light whose optical frequency is represented by the equation (16) in Embodiment 4 and whose optical frequency is f _k is input, the electrical band of the optical phase-locked loop Is sufficiently narrower than the signal band of the binary signal input to the binary / multilevel converter 111 in the optical CDM transmission circuit 201. Therefore, the loop filter 63 does not feel voltage fluctuation at the signal speed of the binary signal due to θ _S (t), and the optical phase of the local light is synchronized with φ _S (t), and the optical field state of the local light is obtained. E _L ^' (t) ^* is

It can be expressed.

と表せる。局発光の光電界振幅を、多値信号光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（式（２２） 右辺第２項）は、局発光と多値信号光のビート成分（式（２２） 右辺第３項）と比べて無視できるため、Ｒ_ｋ（ｔ）^（５）は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 optical detector 53 squarely detects mixed light of local light and multilevel signal light. Its output R _k (t) ⁽⁵⁾ is

It can be expressed. When the optical electric field amplitude of local light is sufficiently larger than the optical electric field amplitude of multilevel signal light, the direct detection component of the multilevel signal light (the second term on the right side of equation (22)) is the local light and multilevel signal light. Therefore, R _k (t) ⁽⁵⁾ can be regarded as a multi-value baseband signal in which each voltage level is equidistant from the beat component (equation (22), third term on the right side).

  In the optical phase-locked homodyne detection circuit, the polarization adjustment means 52 adjusts the polarization state of at least one of the local light and the multilevel signal light so that the local light and the multilevel signal light have the same polarization state. Adjust to. In the optical CDM transmission circuit 201, a configuration of polarization scramble that changes the polarization state of the signal light with time, a configuration of transmitting signal light in which the orthogonal polarization states are added, and a polarization in the optical CDM reception circuit 202 Depending on the diversity configuration, it is possible to omit polarization adjustment in the optical phase-locked homodyne detection circuit.

  As the optical detection means 43, a digital coherent receiver including a local light source, a 90 ° optical hybrid, a differential optical detector, and a digital signal processing (DSP) circuit is used instead of the optical phase-locked homodyne detection circuit. Is possible. 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 light intensity modulation means is differentially encoded (Differential Encoding).

The electric decoding unit 45 has the same configuration as that of the first embodiment, and adds / subtracts the input multi-level baseband signal according to the corresponding inherent code to selectively extract a desired binary signal. In the present embodiment, unlike the conventional method, all code elements correspond to the unique code #h (h = 1, 2,..., K) with {1}, and from all the optical detection means 43. The electric decoding means 45 for adding the multi-level baseband signal can remove undesired signal components and selectively extract a desired binary signal. Pay attention to an undesired binary signal component (symbol value: D _k (t)) that is spread based on the unique code #k (k ≠ h) in the binary / multi-level conversion means 111 in the optical CDM transmission circuit 201. Then, the K multi-value baseband signals input to the electrical encoding means 45 include a component of D _k (t) in half and a component of 1-D _k (t) in which the other half is inverted in symbol value. including. Therefore, the undesired signal component is canceled by adding all the multi-value baseband signals.

  In the conventional optical CDM transmission system, codes whose code elements are {1} among codes whose code lengths are orthogonal to each other cannot be used as unique codes. On the other hand, in this embodiment, it is possible to use all codes whose code lengths are orthogonal to each other, and the code multiplexing number N at the same code length is increased. Here, the number of optical frequency components of the transmitted / received multi-wavelength signal light is a code length K, and the optical frequency band of the multi-wavelength signal light is the same as that of the conventional optical CDM transmission system. Therefore, frequency utilization efficiency is improved as compared with the conventional method.

(Embodiment 6)
The optical CDM transmission system according to the sixth embodiment is the same as the optical CDM transmission system according to the fourth embodiment, except that the optical CDM transmission circuit 201 has an optical frequency component whose optical frequency matches the multi-wavelength signal light in addition to the multi-wavelength signal light. Multi-wavelength continuous light including At the output end of the optical CDM transmission circuit 201, the multi-wavelength signal light and the multi-wavelength continuous light are optical frequency components having the same optical frequency, the optical phase difference is 0 or π, and the polarization states match. Further, in the optical CDM receiving circuit 202 of the sixth embodiment, an optical detector is disposed as the optical detection means 43.

  FIG. 12 is a configuration example of the optical CDM transmission circuit 201. The optical CDM transmission circuit 201 outputs continuous light of K optical frequency components that match the optical frequency of the multilevel signal light included in the multiwavelength signal light at an output end that outputs the multiwavelength signal light. The multi-level signal light matches the multi-level signal light having the same optical frequency component, and the polarization state of the multi-level signal light matches the optical frequency component so that the optical phase difference is 0 or π. It further includes an optical mixer 91 that mixes and outputs the wavelength signal light or the multilevel signal light having the same optical frequency component.

  The output light of each light source 14 is branched in front of the light intensity modulation means 12. In one path, the optical modulation unit 12 in the path modulates the optical electric field amplitude and optical phase of the input light with the multilevel signal from the binary / multilevel conversion unit 111 to generate multilevel signal light. In contrast, the input light to the other path is not modulated and is output as continuous light. Thereafter, the optical mixer 91 combines the multilevel signal light and the continuous light.

  Here, the optical phase of the multilevel signal light and the continuous light is adjusted by the optical phase adjusting means 92 arranged in at least one of the paths so that the optical phase difference becomes 0 or π when they are combined. . The light intensity of the multilevel signal light and the continuous light is adjusted by the light intensity adjusting means 93 disposed in at least one of the paths so that the light intensity of the continuous light is sufficiently larger than that of the multilevel signal light. The polarization states of the multilevel signal light and the continuous light are adjusted by the polarization adjusting means 94 disposed in at least one of the paths so as to coincide with each other when they are combined. When the polarization state is maintained in both paths, the polarization adjusting means 94 can be omitted.

The optical frequency multiplexing means 13 combines the multilevel signal light and continuous light whose optical frequency is f ₁ and the multilevel signal light and continuous light whose optical frequencies are f ₂ ,..., F _K. Thus, multi-wavelength signal light and multi-wavelength continuous light are output. WDM signal light and the multi-wavelength continuous light, as described above, f ₁ component together, f ₂ components together, ..., the optical phase difference between f _K component may be a 0 or [pi, f _1, The optical phase relationship between the f ₂ ,..., f _K components is arbitrary. Further, the multi-wavelength signal light and the multi-wavelength continuous light have the same polarization state between the f ₁ components, the f ₂ components,..., The f _K components, but f ₁ , f ₂ , .., F The polarization states between the _K components do not necessarily match. In FIG. 12, the output of the optical phase adjustment unit 92 is input to the polarization adjustment unit 94, but the polarization adjustment unit 94 may be disposed in front of the optical phase adjustment unit 92. Similarly, the light intensity adjusting means 93 can be disposed in front of the light modulating means 12.

  In FIG. 12, each light source having a different optical frequency of output light and each light modulation unit are connected one-to-one. However, the output of the multi-wavelength light source is separated for each light frequency component and sent to each light modulation unit 12. An input configuration is also possible. Further, as shown in FIG. 13, the output of the multi-wavelength light source is branched in front of the optical frequency demultiplexing means 16, and the multi-wavelength continuous light that has passed through one path is converted into A configuration for combining with signal light is also possible.

  The multi-wavelength signal light and the multi-wavelength continuous light input to the optical CDM receiving circuit 202 are separated for each optical frequency component by the optical frequency demultiplexing means 42 and input to each optical detection means 43. The optical detection unit 43 square-detects the input light from the optical frequency demultiplexing unit, and generates a multilevel baseband signal whose voltage levels corresponding to each symbol value are equally spaced.

と表せる。ここで、Ｅ_ＣＷは、連続光の光電界振幅である。よって、光検波手段４３−ｋの出力Ｑ_ｋ（ｔ）^（６）は、

と表せる。光ＣＤＭ送信回路２０１内において、連続光の光電界振幅が、多値信号光の光電界振幅よりも十分に大きくなるように調整されているため、多値信号光の直接検波成分（式（２４） 右辺第２項）は、連続光と多値信号光のビート成分（式（２４） 右辺第３項）と比べて無視できるため、Ｑ_ｋ（ｔ）^（６）は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。 Here, the optical phase of the multilevel signal light and the continuous light having the same optical frequency is set so that the optical phase difference becomes 0 or π in the optical CDM transmission circuit 201 according to the symbol value of the multilevel signal light. It has been adjusted. Further, since the phase shift amounts during the optical fiber transmission of these lights are equal, the optical phase difference in the optical CDM receiving circuit 202 is also 0 or π. The optical electric field state E _Total (t) of the input light to the k-th optical detection means 43-k is the sum of the optical electric field E _CW (t) of continuous light and the optical electric field E _S (t) ^* of multilevel signal light. And

It can be expressed. Here, E _CW is the optical electric field amplitude of continuous light. Therefore, the output Q _k (t) ⁽⁶⁾ of the optical detection means 43-k is

It can be expressed. Since the optical electric field amplitude of continuous light is adjusted to be sufficiently larger than the optical electric field amplitude of multilevel signal light in the optical CDM transmission circuit 201, the direct detection component (formula (24) ) Since the second term on the right side is negligible compared to the beat component of continuous light and multilevel signal light (equation (24), the third term on the right side), Q _k (t) ⁽⁶⁾ Can be regarded as a multi-value baseband signal.

  Multilevel signal light and continuous light having the same optical frequency are adjusted in the optical CDM transmission circuit 201 so that their polarization states coincide. Further, since the polarization shift during the optical fiber transmission is uniform, the polarization state is even at the input end of the optical detection means 43. Therefore, in the optical CDM receiving circuit 202 in the present embodiment, it is not necessary to adjust the polarization state that is required in the normal coherent detection means.

The electric decoding unit 45 has the same configuration as that of the first embodiment, and adds / subtracts the input multi-level baseband signal according to the corresponding inherent code to selectively extract a desired binary signal. In the present embodiment, unlike the conventional method, all code elements correspond to the unique code #h (h = 1, 2,..., K) with {1}, and from all the optical detection means 43. The electrical decoding means 45 for adding the multi-value baseband signal can remove undesired signal components and selectively extract a desired binary signal. Pay attention to an undesired binary signal component (symbol value: D _k (t)) that is spread based on the unique code #k (k ≠ h) in the binary / multi-level conversion means 111 in the optical CDM transmission circuit 201. Then, the K multi-value baseband signals input to the electrical encoding means 45 include a component of D _k (t) in half and a component of 1-D _k (t) in which the other half is inverted in symbol value. including. Therefore, the undesired signal component is canceled by adding all the multi-value baseband signals.

  In the conventional optical CDM transmission system, codes whose code elements are {1} among codes whose code lengths are orthogonal to each other cannot be used as unique codes. On the other hand, in this embodiment, it is possible to use all codes whose code lengths are orthogonal to each other, and the code multiplexing number N at the same code length is increased. Here, the number of optical frequency components of the transmitted / received multi-wavelength signal light is a code length K, and the optical frequency band of the multi-wavelength signal light is the same as that of the conventional optical CDM transmission system. Therefore, frequency utilization efficiency is improved as compared with the conventional method.

11, 111: 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 15: Multi-wavelength light source 16: Optical frequency demultiplexing means 21, 21-1, 21-2,..., 21-N, 121, 121-1, 121-2,. 121-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 circuit 25: differential signal generating means 26: light intensity modulators 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: Optical detection means 45, 45- , 45-2, ···, 45-N: Electrical decoding means 51: local light source 52 ,: polarization adjusting means 53 ,: light detector 54: BPF
55: Phase synchronous detection circuit 56: LPF
57: Electrical phase locked loop 59: Envelope detector 61: VCO
62: mixer 63: loop filter 87: optical phase locked loop 91: optical mixer 92: optical phase adjusting means 93: light intensity adjusting means 94: polarization adjusting means 133: 90 ° optical hybrids 134, 134-1, 134- 2: Differential detectors 135, 135-1, 135-2: Squarer 136: Adder 201: Optical CDM transmission circuit 202, 202-1, 202-2,..., 202-N: Optical CDM reception Circuit 203: Optical fiber transmission line 301: Optical CDM transmission system

Claims (16)

It consists of two types of code elements, has N (N = K) unique codes with a code length of K (K is an integer of 2 or more), and each unique code has the same number of binary signals as the unique code. To generate K multilevel signals from the binary signal,
The k-th (k = 1, 2,..., K) code element of the inherent code corresponding to the binary signal is
If it is one of the two types of code elements, the symbol value of the binary signal is used as it is.
A spreading value corresponding to the kth code element of the unique code,
If it is the other of the two types of code elements, the symbol value of the binary signal inverted is used.
A spreading value corresponding to the kth code element of the unique code,
Binary / multilevel conversion means for adding the spread values to obtain a symbol value of the kth multilevel signal;
A plurality of optical modulators that input K optical carriers having optical frequencies different from each other and output multilevel signal light obtained by modulating the optical carrier with the multilevel signal generated by the binary / multilevel converter;
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:
Each of the output ends having a number equal to or greater than the code length of the corresponding unique code, sequentially assigning each code element of the unique code to the output end, from the output end assigned one of the two types of code elements, The spread value that matches the symbol value of the input binary signal is output, and the symbol value of the input binary signal is inverted from the output end to which the other of the two types of code elements is assigned. N spreading coders that output spreading values;
K adders that add the spread values from the k-th output terminal of each of the spread encoders to form the k-th multi-level signal;
The optical CDM transmission circuit according to claim 1, comprising: The multi-level signal light output from the light modulation means is
3. The optical CDM according to claim 1, wherein the optical CDM has a light intensity level that is unique and equally spaced according to a symbol value of the input multilevel signal, and the average light intensity is constant regardless of N. 4. Transmitter circuit. The multi-level signal light output from the light modulation means is
Depending on the symbol value of the input multilevel signal, the optical field amplitude level is unique and equally spaced, and the optical phase shift amount of the optical carrier in the optical modulation means becomes the symbol value of the multilevel signal. 3. The optical CDM transmission circuit according to claim 1, wherein the optical CDM transmission circuit is any one of binary values having a difference of π. Continuous light of K optical frequency components matching the optical frequency of the multilevel signal light included in the multiwavelength signal light,
At the output end for outputting the multi-wavelength signal light,
The optical phase difference with the multilevel signal light with which the optical frequency components match is 0 or π,
And so that the polarization state of the multi-level signal light having the same optical frequency component matches,
5. The optical CDM transmission circuit according to claim 4, further comprising an optical mixer that mixes and outputs the multi-wavelength signal light or the multi-level signal light having the same optical frequency component. Optical frequency demultiplexing means for demultiplexing the multi-wavelength signal light from the optical CDM transmission circuit according to any one of claims 1 to 5 for each optical frequency component;
A plurality of optical detection means for detecting signal light from the optical frequency demultiplexing means and demodulating the multilevel signal;
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 Corresponding to the output terminal in order, the input from the output terminal corresponding to one of the two types of code elements is positive, and the input from the output terminal corresponding to the other of the two types of code elements is negative. Adding / subtracting as described above, among the binary signals input to the binary / multi-value conversion means, electrical decoding means for selectively extracting the binary signal corresponding to the unique code;
An optical CDM receiving circuit comprising:   7. The optical CDM receiving circuit according to claim 6, wherein the optical detection means squarely detects the signal light from the optical frequency demultiplexing means. The optical detection means includes
A local light source adjusted so that the optical frequency of the continuous light to be output is a predetermined frequency difference from the signal light from the optical frequency demultiplexing means;
An optical detector that squarely detects mixed light of continuous light from the local light source and signal light from the optical frequency demultiplexing means;
A bandpass filter that transmits a signal component carried by a carrier wave whose frequency matches the predetermined frequency difference from the output of the optical detector;
An envelope detector that square-detects the output of the bandpass filter;
The optical CDM receiving circuit according to claim 6, wherein the optical CDM receiving circuit is cited. The optical detection means includes
A local light source in which the optical frequency of the continuous light to be output is adjusted so that the frequency difference from the signal light from the optical frequency demultiplexing means is sufficiently smaller than the signal band of the binary signal;
The local light source has a plurality of output ends, and the optical phase difference between the continuous light from the local light source and the signal light from the optical frequency demultiplexing means is a predetermined difference between the output ends. An optical hybrid that mixes continuous light from and signal light from the optical frequency demultiplexing means;
A plurality of optical detectors connected to the output ends of the optical hybrid in a one-to-one relationship and detecting squared input light;
A plurality of squarers for squaring the output of the optical detector;
An adder for adding the outputs of each of the squarers;
The optical CDM receiving circuit according to claim 6, wherein the optical CDM receiving circuit is cited. The optical detection means includes
A local light source adjusted so that the optical frequency of the continuous light to be output is a predetermined frequency difference from the signal light from the optical frequency demultiplexing means;
An optical detector that squarely detects mixed light of continuous light from the local light source and signal light from the optical frequency demultiplexing means;
A bandpass filter that transmits a signal component carried by a carrier wave whose frequency matches the predetermined frequency difference from the output of the optical detector;
A phase-locked detector circuit including a VCO, a mixer, and a loop filter, and having an electrical phase-locked loop whose electrical band is sufficiently narrower than the signal band of the binary signal;
With
The frequency and phase of the output of the VCO are adjusted to synchronize with the carrier by the loop filter,
7. The optical CDM receiving circuit according to claim 6, wherein the mixer integrates an input signal from the bandpass filter and an output of the VCO. The optical detection means includes
An optical phase-locked loop including a local light source, an optical detector, and a loop filter, the electrical band being sufficiently narrower than the signal band of the binary signal;
The optical frequency and optical phase of continuous light output from the local light source are adjusted by the loop filter so as to be synchronized with the optical carrier wave of the signal light from the optical frequency demultiplexing means,
The said optical detector carries out square detection of the mixed light of the continuous light from the said local light source, and the signal light from the said optical frequency demultiplexing means, Claim 6 characterized by the above-mentioned. Optical CDM receiver circuit.   7. The optical CDM receiving circuit according to claim 6, wherein the optical detection means squarely detects the signal light from the optical frequency demultiplexing means. An optical CDM transmission circuit according to claim 1 or 2,
An optical CDM receiving circuit according to claim 6,
An optical fiber transmission line for propagating the multi-wavelength signal light from the optical CDM transmission circuit to the optical CDM reception circuit;
An optical CDM transmission system. An optical CDM transmission circuit according to claim 3,
An optical CDM receiving circuit according to any one of claims 7 to 9,
An optical fiber transmission line for propagating the multi-wavelength signal light from the optical CDM transmission circuit to the optical CDM reception circuit;
An optical CDM transmission system. An optical CDM transmission circuit according to claim 4,
An optical CDM receiving circuit according to claim 10 or 11,
An optical fiber transmission line for propagating the multi-wavelength signal light from the optical CDM transmission circuit to the optical CDM reception circuit;
An optical CDM transmission system. An optical CDM transmission circuit according to claim 5;
An optical CDM receiving circuit according to claim 12,
An optical fiber transmission line for propagating the multi-wavelength signal light from the optical CDM transmission circuit to the optical CDM reception circuit;
An optical CDM transmission system.

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