JP5334747B2 - Optical code division multiplexing transmission system and optical code division multiplexing transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical CDM transmission system and an optical CDM transmission method, which require no adjustment of intervals between voltage levels corresponding to symbol values of multiple-value electric signals generated even if a multiplexing number N of a binary data signal changes, and which can extend N to more than 3 and flexibly. <P>SOLUTION: In an optical CDM transmission system and an optical CDM transmission method, a binary dummy signal is added to a binary data signal inputted to a binary/multiple-value conversion means, and multiple values are made fixed regardless of a multiplexing number of the binary data signal, whereby multiple-value ASK signal light is generated whose light strength levels corresponding to symbol values become an equal interval without adjusting voltage levels corresponding to the symbol values of multiple-value electric signals generated by the binary/multiple-value conversion means even when the multiplexing number increases/decreases. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an optical code division multiplexing system used for optical code division multiplexing communication and a transmission method thereof.

  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).

Multilevel amplitude modulation is performed using a Mach-Zehnder interferometer-type optical intensity modulator such as an LN (LiNbO ₃ ) intensity modulator, and the generated multilevel ASK signal light has an optical intensity level corresponding to each symbol value. Evenly 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 decoder according to 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 a method of performing time spreading (see, for example, Non-Patent Document 5). It is unnecessary and 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

When the number of multiplexed binary data signals is N = 3 in the method of Non-Patent Document 4, Hadamard codes {1, 1, 0, 0}, {1, 0, 1, 0}, {0, , 1, 0} are assigned to the spreading encoders 1 to 3 in the binary / multi-level conversion means in order, the symbol values D ₁ (t) to D ₃ (t ) And the symbol values D ^# ₁ (t) to D ^# ₄ (t) of each generated multilevel electric signal are shown in FIG. In this case, D ^# ₁ (t) to D ^# ₃ (t) take three values, "0", "1", and "2". When the LN intensity modulator is used, as shown in FIG. 2, the voltage level corresponding to the symbol value “1” that is intermediate between the maximum voltage value and the minimum voltage value that the ternary electric signal can take is a quadrature of the transmission curve of the modulator. By adjusting the bias voltage so as to be Point (V _Q ), a desired ternary ASK signal light whose light intensity levels corresponding to each symbol value are equally spaced can be obtained. When the ternary ASK signal light is directly detected, a ternary electric signal having voltage intervals corresponding to each symbol value at equal intervals is generated. Therefore, MAI can be removed by addition / subtraction in the electric decoder in the receiving circuit.

By extending the code length of the unique code, it is possible to increase the multiplexing number N of binary data signals. At this time, the multi-value number of the multi-value ASK also increases. When a Hadamard code is used as the unique code, when N> 3, the multilevel number M of the signal having the maximum multilevel value among the multilevel electric signals generated by the binary / multilevel conversion means is M> 3. It becomes. When M-value ASK (M> 3) is performed using an LN intensity modulator, as in the above-described three-value ASK, the intermediate voltage level of the M-value electric signal applied to the modulator is a quadrature of the transmission curve of the modulator. When the bias voltage is adjusted to be Point (V _Q ), the output M-value ASK signal light does not have equal light intensity level intervals corresponding to the respective symbol values (FIG. 3). Therefore, the M-value electric signal generated by directly detecting the M-value ASK signal light has voltage levels corresponding to each symbol value that are not equally spaced, and the MAI is removed by addition / subtraction in the electric decoder in the receiving circuit. become unable.

Here, as shown in FIG. 4, by applying an M-value electric signal pre-biased with voltage level intervals X _{1 to} X _M−1 corresponding to each symbol value to the modulator, N> 3 light M-value ASK (M> 3), which is required in the CDM transmission system, is equal in the interval of the light intensity level corresponding to each symbol value.

However, in the optical CDM transmission system, X _{1 to} X _M-1 must be adjusted each time according to the change in the number N of multiplexed binary data signals. That is, there is a problem that it is difficult to flexibly extend the number N of binary data signals multiplexed.

For example, consider the case of a Hadamard code with N = 6 and code length 8.
Inherent code 1 {1, 1, 0, 0, 1, 1, 0, 0},
Inherent code 2 {1, 0, 1, 0, 1, 0, 1, 0},
Inherent code 3 {0, 1, 1, 0, 0, 1, 1, 0},
Inherent code 4 {1, 1, 1, 1, 0, 0, 0, 0},
Inherent code 5 {0, 0, 1, 1, 1, 1, 0, 0},
Inherent code 6 {0, 1, 0, 1, 1, 0, 1, 0},
Inherent code 7 {1, 0, 0, 1, 0, 1, 1, 0}
Suppose that the unique codes 1 to 6 are assigned in order to the spreading coders 1 to 6 in the binary / multilevel conversion means. In this case, as shown in FIG. 25, the binary / multilevel conversion means adds the same code elements of the respective unique codes, and adds four quaternary electric signals having a maximum symbol value of “3” and a maximum of Three quinary electrical signals having a symbol value of “4” are generated.

Each quaternary electric signal is applied to the modulators 1, 4, 6 and 7. On the other hand, each quinary electric signal is applied to the modulators 2, 3 and 5. In order for the MAI to be removed by the receiving circuit, the output signal light of each modulator has an equal light intensity level corresponding to each symbol value, and the light intensity level intervals are different between the output signal lights of different modulators. It is required to match. Therefore, for example, when a single-drive LN intensity modulator is used, X ₁ = Vp / 3 X ₂ = Vp / 6 X ₃ = Vp / 6 X ₄ in the optical modulators 2, 3, and 5 as shown in FIG. = Vp / 3, X _{1 to} X ₄ need to be set to values different from those of the optical modulators 2, 3, 5 in the modulators _{1, 4} , 6, 7. V _π is a voltage required to change the optical phase shift amount of the transmitted light in each arm of the Mach-Zehnder interferometer type light intensity modulator by π.

When N changes from 6 to 7, it is assumed that the unique codes 1 to 7 are sequentially assigned to the spreading encoders 1 to 7 in the binary / multilevel conversion means. In this case, as shown in FIG. 26, the binary / multilevel converter generates seven quinary electrical signals having a maximum symbol value of “4”. Since the quinary electric signal is applied to the modulators 1 to 7, the modulators 1 to 7 output the quinary ASK signal light. At this time, by setting X ₁ = Vp / 3 X ₂ = Vp / 6 X ₃ = Vp / 6 X ₄ = Vp / 3 in all the modulators, a desired quinary ASK signal light can be obtained.

As described above, when the multiplexing number N of the binary data signal is changed from 6 to 7, the modulators _{1, 4} , 6 and 7 readjust the voltage level intervals X _{1 to} X ₄ corresponding to the respective symbol values. It becomes difficult to expand N flexibly.

  Therefore, the present invention does not require adjustment of the voltage level interval corresponding to each symbol value of the generated multilevel electrical signal even if the number N of binary data signals multiplexed changes, and N is more flexible than 3. It is an object of the present invention to provide an optical CDM transmission system and an optical CDM transmission method that can be extended to the above.

  In order to achieve the above object, an optical CDM transmission system and an optical CDM transmission method according to the present invention add a binary dummy signal to a binary data signal input to a binary / multi-level conversion means. Even if the multiplex number increases or decreases by keeping the multiple value constant regardless of the multiplex number, it corresponds to each symbol value without readjusting the voltage level interval corresponding to each symbol value of the multi-level electric signal. The multi-level ASK signal light having the same light intensity level is generated.

  Specifically, in the optical CDM transmission system according to the present invention, an optical code division multiplexing transmission circuit is connected to a plurality of optical code division multiplexing reception circuits via an optical fiber transmission line.

  The optical code division multiplexing transmission circuit includes N ′ (N ′ is equal to or greater than N) including N (N is an integer equal to or greater than 2) binary data signals and (N′−N) binary dummy signals that are input. N 'unique signals that are composed of two kinds of code elements and have a code length k (k = 1, 2,..., K, where K is an integer of 2 or more). Binary / multilevel conversion means for generating K multilevel electrical signals based on the sign and adjusting the voltage level corresponding to each symbol value of the multilevel electrical signal to a desired interval; and optical frequency A plurality of optical modulation means for modulating K optical carriers having different values using the multi-value electric signal from the binary / multi-value conversion means and outputting multi-value signal light, and each of the light modulation means comprises: Optical multiplexing means for outputting multi-wavelength signal light obtained by multiplexing the output multi-level signal light to the optical fiber transmission line; Obtain.

  The optical code division multiplexing receiving circuit includes: an optical frequency demultiplexer for demultiplexing the multi-wavelength signal light from the optical fiber transmission line for each optical frequency component; and the optical frequency demultiplexed by the optical frequency demultiplexer. One of the K optical detection means for detecting each of the components and one of the binary data signals assigned to one of the first to Nth unique codes and input to the binary / multilevel conversion means And an electric decoder for selectively extracting.

  The optical CDM transmission method according to the present invention provides an optical code division multiplexing transmission system in which an optical code division multiplexing transmission circuit is connected to a plurality of optical code division multiplexing reception circuits via an optical fiber transmission line. Multiplex transmission method.

  The optical code division multiplex transmission circuit is composed of two code elements from N ′ binary electric signals composed of N binary data signals and (N′−N) binary dummy signals, K multi-valued electrical signals are generated based on N ′ unique codes having a code length k (k = 1, 2,..., K, K being an integer of 2 or more), and the multi-valued electrical signals are generated. The binary / multilevel conversion procedure for adjusting the voltage level corresponding to each symbol value to a desired interval, and K optical carriers having different optical frequencies were generated by the binary / multilevel conversion procedure. An optical modulation procedure for generating a multilevel signal light by modulating with the multilevel electrical signal, and a multiwavelength signal light obtained by multiplexing the multilevel signal light generated in the optical modulation procedure to the optical fiber transmission line And an optical multiplexing procedure to output.

  In the optical code division multiplex receiving circuit, an optical frequency demultiplexing procedure for demultiplexing the multi-wavelength signal light from the optical fiber transmission path for each optical frequency component, and the light demultiplexed by the optical frequency demultiplexing procedure An optical detection procedure for detecting each frequency component, and an electrical decoding procedure for selectively extracting one of the binary data signals based on one of the first to Nth unique codes .

  In the optical CDM transmission system and the optical CDM transmission method according to the present invention, the number of binary electric signals input to the binary / multilevel conversion means is fixed by adding a binary dummy signal to the binary data signal. . For this reason, the multi-value number of the multi-value electric signal output from the binary / multi-value conversion means is constant regardless of the number of multiplexed binary data signals. For this reason, the optical CDM transmission system and the optical CDM transmission method according to the present invention can fix the voltage level interval corresponding to each symbol value of the multilevel electrical signal to a predetermined value. Therefore, the present invention does not require adjustment of the voltage level interval corresponding to each symbol value even if the number of multiplexed binary data signals N changes, and the light that can flexibly expand N to be larger than 3. A CDM transmission system and an optical CDM transmission method can be provided.

  The binary / multi-level conversion means of the optical CDM transmission system according to the present invention includes N ′ spread encoders, K adders, and K inputs to which N ′ binary electric signals are respectively input. Each of the spreading encoders is assigned with the unique code, and has a number of output terminals equal to or greater than the code length of the assigned unique code, and constitutes the unique code. When each code element is sequentially assigned to the output end, the symbol value matches the binary electric signal input to the spreading encoder from the output end to which one of the code elements is assigned. Output a signal to output 0 from the output end to which the other code element of the code elements is assigned, and the k-th adder has a symbol value of the k-th multi-value electrical signal, Kth of each said spreading encoder The symbol values of the output signals from the k-th output terminal of each of the spread encoders are added so that the sum of the symbol values of the output signals from the power terminals is obtained, and each of the pre-bias circuits The voltage level of the output of the adder is adjusted so that the voltage level corresponding to each symbol value of the electrical signal has a desired interval, and the electrical decoder includes the code elements constituting the assigned intrinsic code. When the light detection means is assigned in order, the output of the light detection means to which one of the code elements constituting the unique code is assigned is positive, and the light detection means to which the other code element is assigned. Addition / subtraction is performed by adding the output of.

  The binary / multi-level conversion procedure of the optical CDM transmission method according to the present invention includes a code spreading process, an adding process, and a pre-bias process, and the code spreading process includes N ′ binary electric signals. In a spreading coder having a number of output ends equal to or greater than the code length of the assigned unique code, each code element constituting the unique code is sent to the output end When sequentially assigned, the binary electrical signal input to the spreading encoder is output from the output end to which one of the code elements is assigned, and a signal whose symbol value matches, and the code 0 is output from the output end to which the other code element of the elements is assigned, and the addition process is performed so that the symbol value of the kth multi-level electrical signal is the kth output of each spreading encoder. The symbol values of the output signals from the k-th output terminal of each spreading encoder are added so that the sum of the symbol values of the output signals from the terminals is added, and the pre-bias process is performed by The voltage level is adjusted so that the voltage level corresponding to each symbol value has a desired interval, and the electrical decoding procedure configures the unique code for the output signal detected and output in the optical detection procedure. Addition / subtraction is performed by adding the output signal to which one of the code elements is assigned as positive and adding the output signal to which the other code element is assigned as negative.

  The optical modulation means of the optical CDM transmission system according to the present invention modulates the amplitude of the optical carrier and outputs multilevel amplitude modulated signal light, and the pre-bias circuit captures the multilevel amplitude modulated signal light. The voltage level corresponding to each symbol value of the multi-valued electrical signal is adjusted so that the light intensity levels that can be obtained are equally spaced.

  In the optical modulation procedure of the optical CDM transmission method according to the present invention, the amplitude of the optical carrier wave is modulated to output a multi-level amplitude modulated signal light, and the pre-bias process is performed by taking the multi-level amplitude modulated signal light. The voltage level corresponding to each symbol value of the multi-valued electrical signal is adjusted so that the light intensity levels that can be obtained are equally spaced.

  The MAI is removed by the electric decoder of the optical CDM receiving circuit by adjusting the voltage level corresponding to each symbol value of the multilevel electric signal so that the light intensity level that the multilevel amplitude modulation signal light can take is equal. Is possible.

  The optical modulation means of the optical CDM transmission system according to the present invention includes a Mach-Zehnder interferometer type light intensity modulator.

  The optical detection means of the optical CDM transmission system according to the present invention is characterized in that the output light of the optical frequency demultiplexer is square-detected.

  The optical detection means of the optical CDM transmission system according to the present invention includes a local light source, an optical detector, a bandpass filter, and an envelope detector, and the optical frequency of the output light of the local light source is the optical frequency. The optical detector is adjusted to have a predetermined frequency difference from the output light of the demultiplexer, and the optical detector squares the mixed light of the output light from the local light source and the output light of the optical frequency demultiplexer. The band-pass filter transmits a signal component carried by a carrier whose frequency matches the predetermined frequency difference from the output of the optical detector, and the envelope detector transmits the band-pass filter from the band-pass filter. The output is square-detected and output.

  The optical detection means of the optical CDM transmission system according to the present invention comprises a local light source, an optical hybrid, a plurality of optical detectors, a plurality of squarers, and an adder, and the optical frequency of the output light of the local light source Is adjusted so that the optical frequency difference from the output light of the optical frequency demultiplexer is sufficiently smaller than the symbol speed of the multilevel signal light, and the optical hybrid has a plurality of output ends. The output light of the local light source and the output light of the local light source at each output terminal and the output light of the optical frequency demultiplexer are set to have a predetermined difference between the output terminals. The output light of the optical frequency demultiplexer is mixed, the optical detectors are connected to the output ends of the different optical hybrids, respectively, the input light is square detected, and the square detectors are different from each other. Connected to a detector, squared and output the output of the optical detector, Calculation device is characterized by adding and outputting the output of each of said squarer.

  The optical modulation means of the optical CDM transmission system according to the present invention modulates the amplitude and optical phase of the optical carrier to output multilevel amplitude phase modulated signal light, and the pre-bias circuit includes the multilevel amplitude modulation. The voltage level corresponding to each symbol value of the multi-value electric signal is adjusted so that the amplitude level of the optical electric field that can be taken by the signal light is equidistant, and the light of the optical carrier in the optical modulation means The phase shift amount is any one of binary values having a difference of π according to the symbol value of the multi-level electric signal.

  In the optical CDM transmission method according to the present invention, the optical modulation procedure modulates the amplitude and optical phase of input light and outputs a multilevel amplitude phase modulated signal light, and the pre-bias process includes the multilevel amplitude modulated signal. The voltage level corresponding to each symbol value of the multilevel electrical signal is adjusted so that the amplitude level of the optical electric field that light can take is equally spaced, and the optical phase shift amount of the optical carrier after the optical modulation procedure is Depending on the symbol value of the multi-valued electrical signal, the difference is one of binary values of π.

  The optical modulation means of the optical CDM transmission system according to the present invention comprises: a differential signal generating means for outputting two electric signals whose polarity is inverted from one input electric signal; and two applied electric signals A Mach-Zehnder interferometer-type light intensity modulator that modulates input light with a signal, wherein the light intensity modulator indicates the amplitude and optical phase of the optical carrier, and the differential signal generation means includes the multi-value electric signal. It modulates with the two electric signals produced | generated from 1. It is characterized by the above-mentioned.

  In the optical modulation means of the optical CDM transmission system according to the present invention, an optical amplitude modulation means and an optical phase modulation means are connected in series, and the optical amplitude modulation means is connected to the binary / multilevel conversion means. The signal conversion circuit that outputs the absolute value of the potential difference between the voltage value of the input signal and the maximum voltage value that the input signal can take and the intermediate voltage value of the minimum voltage value, and the polarity is inverted from one input electric signal A differential signal generating means for outputting two electric signals in relation to each other, and a Mach-Zehnder interferometer type light intensity modulator for modulating input light by the two applied electric signals, and in the light intensity modulator, The amplitude of the input light is modulated by two electrical signals generated from the output signal of the signal conversion circuit by the differential signal generation unit, and the optical phase modulation unit has a voltage value of the input signal equal to or greater than a threshold voltage value. And the threshold voltage value A discriminator that outputs a different voltage in the above case, and an optical phase modulator that modulates the optical phase of the input light by the output of the discriminator, and the discriminator is connected to the binary / multi-level conversion means, The threshold voltage value is set equal to an intermediate voltage value between a maximum voltage value and a minimum voltage value that can be taken by an input signal to the discriminator.

  In the optical modulation means of the optical CDM transmission system according to the present invention, an optical amplitude modulation means and an optical phase modulation means are connected in series, and the optical amplitude modulation means is connected to the binary / multilevel conversion means. The signal conversion circuit that outputs the absolute value of the potential difference between the voltage value of the input signal and the maximum voltage value that the input signal can take and the intermediate voltage value of the minimum voltage value, and the polarity is inverted from one input electric signal A differential signal generating means for outputting two electric signals in relation to each other, and a Mach-Zehnder interferometer type light intensity modulator for modulating input light by the two applied electric signals, and in the light intensity modulator, The amplitude of the input light is modulated by two electrical signals generated from the output signal of the signal conversion circuit by the differential signal generation unit, and the optical phase modulation unit has a voltage value of the input signal equal to or greater than a threshold voltage value. And the threshold voltage value In the above case, a discriminator for outputting different voltages, the differential signal generating means, and the light intensity modulator are connected to the binary / multi-value converting means, and the threshold voltage value is An input signal to the discriminator is set equal to an intermediate voltage value between a maximum voltage value and a minimum voltage value that can be taken, and the optical phase of the input light is set in the optical intensity modulator, and the differential signal generator is connected to the discriminator. It is characterized by being modulated by two signals generated from the output of.

  The optical detection means of the optical CDM transmission system according to the present invention comprises a local light source, an optical detector, a band pass filter, an electric phase locked loop circuit, and a low pass filter, and the optical frequency of the output light of the local light source is The output light of the optical frequency demultiplexer is adjusted to have a predetermined frequency difference, and the optical detector is a mixed light of the output light from the local light source and the output light of the optical frequency demultiplexer The band-pass filter transmits a signal component carried by a carrier whose frequency matches the predetermined frequency difference from the output of the optical detector, and the electric phase-locked loop circuit The band is sufficiently narrower than the symbol rate of the multilevel signal light, the output of the bandpass filter is synchronously detected, and the lowpass filter is a baseband signal output from the electrical phase locked loop circuit Characterized by transmission.

  The optical detection means of the optical CDM transmission system according to the present invention comprises an optical phase-locked loop including a local light source, an optical detector, and a loop filter, and an electric band is the multi-level signal in the optical phase-locked loop. The optical frequency and optical phase of the output light of the local light source are adjusted to be synchronized with the output light of the optical frequency demultiplexer by the loop filter that is sufficiently narrower than the symbol speed of light, and the optical detection The detector squarely detects mixed light of the output light from the local light source and the output light of the optical frequency demultiplexer.

  The optical code division multiplexing transmission circuit of the optical CDM transmission system according to the present invention outputs, in addition to the multi-wavelength signal light, multi-wavelength continuous light including an optical frequency component whose optical frequency matches the multi-wavelength signal light, At the output end of the optical code division multiplexing transmission circuit, the multi-wavelength signal light and the multi-wavelength continuous light have an optical phase difference of 0 or π between optical frequency components having the same optical frequency, and the optical code division The optical detection means in the multiplex receiving circuit is characterized in that the optical frequency component is square-detected.

  The present invention does not require adjustment of the voltage level interval corresponding to each symbol value of the generated multilevel electrical signal even if the number of multiplexed binary data signals N changes, and N can be flexibly expanded larger than 3. An optical CDM transmission system and an optical CDM transmission method that can be performed 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 ternary ASK using a LN intensity modulator. It is a figure explaining M value ASK (M> 3) using a LN intensity modulator. It is a figure explaining the pre-bias M value ASK (M> 3) using a LN intensity modulator. It is a figure explaining the multi-value amplitude modulation in an LN intensity modulator. It is a figure explaining the example of an optical CDM transmission system structure using electrical stage code | symbol spreading | diffusion and multi-value amplitude modulation. It is a figure explaining the optical CDM transmission circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the binary / multi-value conversion means of the optical CDM transmission system according to the present invention. It is a figure explaining the pre-bias circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the pre-bias circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the optical CDM transmission circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the optical CDM receiving circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the heterodyne envelope detection circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the phase diversity homodyne detection circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the example of an optical CDM transmission system structure using electrical stage code | symbol spreading | diffusion and multi-value amplitude phase modulation. It is a figure explaining the optical electric field of the quinary APSK signal light produced | generated using the Dual-Drive LN intensity modulator. It is a figure explaining the heterodyne synchronous detection circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the optical phase synchronous homodyne detection circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the optical CDM transmission circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the optical CDM transmission circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the optical CDM transmission circuit of the optical CDM transmission system which concerns on this invention. It is a figure explaining the optical amplitude phase modulation means of the optical CDM transmission system according to the present invention. It is a figure explaining the optical amplitude phase modulation means of the optical CDM transmission system according to the present invention. It is a figure explaining the response | compatibility of the input binary data signal and output multi-value electric signal to a binary / multi-value conversion means. It is a figure explaining operation | movement of the binary / multi-value conversion means of the optical CDM transmission system which concerns on this invention. It is a figure explaining operation | movement of the binary / multi-value conversion means of the optical CDM transmission system which concerns 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)
FIG. 6 is a diagram for explaining the optical CDM transmission system 301 of 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,...).

[Optical CDM transmission circuit]
The optical CDM transmission circuit 201 includes a binary / multilevel conversion unit 11, a plurality of light intensity modulation units 17, and an optical multiplexing unit 13. Optical light carriers (f _{1 to} f _K ) having different optical frequencies are input from the light source 14 to each light intensity modulation unit 17, and the input optical carrier is generated by the binary / multilevel conversion unit 11. Modulated with a multi-value electrical signal and output. The output light of each light intensity modulation means 17 is generated by an optical frequency multiplexer such as an arrayed waveguide grating (AWG) or a multilayer filter, an optical fiber or a light produced by a PLC (Planar Lightwave Circuit). The multi-wavelength signal light combined by the optical combining means 13 such as a coupler is transmitted to each optical CDM receiving circuit 202 via the optical fiber transmission path 203. Here, the 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 intensity modulation means 17 having different optical frequencies of output light are connected one-to-one like the optical CDM transmission circuit 201 in FIG. 6, the multi-wavelength light source 14T of FIG. A configuration in which the output is separated for each optical frequency component by the optical frequency demultiplexer 15 and input to each light intensity modulation means 17 is also possible. The multi-wavelength light source 14T can be configured to be a multi-wavelength configuration or mode-locked laser by modulating the output of single mode light with a high frequency sine wave.

The binary / multilevel conversion means 11 includes N ′ spreading encoders to which unique codes are assigned, and N ′ binary electric signals that are always input are used to transmit the unique codes assigned to the respective spreading encoders. Among them, the multi-value electric signal having the number of the code length K of the code having the longest code length is generated. Here, the multilevel electric signal generated by the binary / multilevel conversion means in the conventional optical CDM transmission system has a voltage level corresponding to each symbol value (D ^# ₁ (t) to D ^# _K (t)). The multi-value electric signal generated by the binary / multi-value conversion means 11 in the present embodiment corresponds to each symbol value (D ^# ₁ (t) to D ^# _K (t)) while being equally spaced. The voltage level is adjusted to have a desired interval.

  A binary data signal which is a desired signal of at least one optical CDM receiving circuit 202 is input to each of the first to Nth (N ≦ N ′) spreading coders, and is input to the (N + 1) th to N′th spreading coders. Is inputted with a binary dummy signal. The binary dummy signal may be an electrical signal having two possible symbol values, “0” and “1”. For example, a pattern in which “0” and “1” are alternately arranged, or a binary random signal is used. This is the case with patterns. That is, the binary electric signal input to the binary / multilevel conversion means is composed of N binary data signals and (N′−N) binary dummy signals.

As the inherent code, a Hadamard code used in the optical CDM system that performs encoding in the optical frequency domain is used. The spreading encoder has a number of output ends equal to or greater than the code length of the assigned unique code, and the code elements {1} and {0} constituting the unique code are sequentially assigned to the output ends. Each output end to which the code element {1} is assigned outputs a signal whose symbol value matches the symbol value of the binary electric signal input to the spreading encoder. The other output terminals output 0. That is, the spread encoder n to which the k-th (k = 1, 2,..., K) code element c _{n, k of} the unique code n (n = 1, 2,..., N ′) is assigned. The symbol value of the output signal of the k-th output terminal is the product c _{n, k} × value of the code element c _{n, k} and the symbol value D _n (t) of the binary electric signal input to the spread encoder n. D _n (t).

と表せる。多値電気信号の多値数Ｍは、２値データ信号の多重数Ｎによらず、常に一定となる。 The symbol value D ^# _k (t) of the k-th (k = 1, 2,..., K) multi-level electric signal is the symbol value of the output signal from the k-th output end of each spreading encoder. Matches the sum of

It can be expressed. The multi-value number M of the multi-value electric signal is always constant regardless of the multiplex number N of the binary data signal.

  FIG. 8 is a configuration example of the binary / multi-value conversion means 11. The binary / multilevel conversion unit 11 includes N ′ spread encoders 21, K adders 22, and a pre-bias circuit 24.

The spread encoder 21 includes K switches (SW). The input binary electric signal is branched and output from the output terminal 23 via each SW. Here, by turning on only the SW connected to the output terminal 23 to which the code element {1} is assigned, the product of the value of each code element and the value of the electric signal input to the spread encoder is obtained from the output terminal. It becomes possible to output. 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. 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 111, where M is the number of multi-level electric signals. The input multi-value electric signal is branched and input to each weighting circuit 111. The weighting circuit 111 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 ,...) Are multiplied and output. The outputs of the weighting circuits 111 are added by the adder 114 and applied to the light intensity modulation means 17.

The threshold voltage V _th — m of the discriminator 112 in the m-th (m = 1, 2,..., M−1) weighting circuit 111-m corresponds to the symbol value “m−1” of the input multilevel electric signal. It is set between the voltage level and the voltage level corresponding to the symbol value “m”. When an input signal at a certain time corresponds to the symbol value “i”, the discriminators 112 in the weighting circuits 111-1 to 111-i output 1 and the other discriminators 112 output 0. The output of the pre-bias circuit 24 obtained by adding the outputs of the circuit 111 is X ₁ + X ₂ +... + X _i . Similarly, when the input 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 multi-valued electrical signal after the pre-bias are sequentially X ₁ , X ₂ ,..., X _M−1 . That is, by changing the weighting coefficients X _{1 to} X _M−1 , it is possible to flexibly generate a multi-value electric signal whose voltage level corresponding to each symbol value is a desired interval.

Here, the N ′ binary electric 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, a memory and a D / A converter in which the computations in the spread encoder 21, adder 22, and pre-bias circuit 24 are stored in advance can be used. Furthermore, a circuit as shown in FIG. 10 in which any _{one of the} switches (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.

The light intensity modulator 17 modulates the optical carrier wave (f _{1 to} f _K ) with the multi-value electric signal generated by the binary / multi-value converter 11, and the light intensity level interval corresponding to each symbol value is changed. Equal multi-level ASK signal light is output. The light intensity modulation means 17 includes a Mach-Zehnder interferometer type light intensity modulator such as an LN intensity modulator, an electro-absorption (EA) optical modulator, a semiconductor optical amplifier (SOA) modulator, and the like. can do.

  As shown in FIG. 11, two electrical signals having a polarity inversion relationship generated by the differential signal generating unit 25 from the multi-value electrical signal are applied to each electrode of the dual-drive Mach-Zehnder interferometer type light intensity modulator 26. An application configuration is also possible. In this configuration, the peak-to-peak voltage of the multilevel electric signal applied to the light intensity modulator may be half that when a single-drive Mach-Zehnder interferometer type light intensity modulator is used. The differential signal generation means 25 is, for example, a differential amplifier.

  In the optical CDM transmission circuit 201, the multi-value number M of the multi-value electric signal input to the light intensity modulation means 17 is always constant regardless of the multiplex number N of the binary data signal due to the effect of the binary dummy signal. . Therefore, in each case where N is different, the optical CDM transmission circuit 201 can generate a desired multi-level ASK signal light whose light intensity levels corresponding to each symbol value are equally spaced without changing the weighting coefficient. is there.

[Optical CDM receiver circuit]
The optical CDM receiving circuit 202 includes an optical frequency demultiplexer 42, K optical detectors 47, and an electric decoder 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 demultiplexer 42. Each optical frequency component is directly detected by an optical detector 47 connected one-to-one with each output terminal of the optical frequency demultiplexer 42, and voltage levels corresponding to each symbol value are equally spaced. A value electrical signal is generated.

  When the electric decoder 45 sequentially assigns each element {1}, {0} constituting the assigned unique code to each optical detector 47, the output of the optical detector 47 corresponding to {1} is positive, Addition / subtraction is performed by adding the output of the optical detector 47 corresponding to {0} as negative. Since the multilevel electric signals output from the optical detector 47 have equal voltage levels, and the voltage level intervals match between the multilevel electric signals generated by the different optical detectors 47, Hadamard codes or bit shifts are performed. When an M-sequence code or the like is used as a unique code, MAI can be removed due to code orthogonality. Therefore, the optical CDM receiving circuit 202 can selectively receive the binary data signal input to the spreading encoder 21 in the optical CDM transmitting circuit 201 to which the same unique code as that of the electric decoder 45 is assigned. is there.

  Each optical CDM receiving circuit 202 shown in FIG. 6 has a configuration including one electrical decoder 45. However, like the optical CDM receiving circuit 202 ′ shown in FIG. 12, a plurality of electrical decoders 45 to which different unique codes are assigned. It is also possible to have '. The output of the optical detector 47 is branched and input to each electric decoder 45 '. Each electric decoder 45 ′ assigned with a unique code outputs a binary data signal input to the spreading encoder 21 assigned with the same code as the assigned unique code.

  If the electric decoder 45 ′ to which no code is assigned outputs 0, the assignment of the unique code to the electric decoder 45 ′ is dynamically changed according to the amount of information desired by the optical CDM receiving circuit 202 ′. As a result, transmission efficiency can be improved. In other words, by assigning unique codes to the plurality of electric decoders 45 ′ of the optical CDM receiving circuit 202 ′ that desires a large amount of information, a plurality of signals can be received simultaneously and the amount of information that can be received in a certain time can be increased. It becomes possible.

[Optical CDM transmission system]
In this embodiment, in addition to N (N ≦ N ′) binary data signals, (N′−N) binary dummy signals are input to the binary / multi-value conversion means 11 to obtain binary data. / The number of binary electrical signals input to the multi-value conversion means 11 is always N ′ regardless of the number N of binary data signal multiplexing. Therefore, even in each case where N is different, the multilevel number M of the multilevel electrical signal input to the light intensity modulation means is constant, and without changing the voltage level corresponding to each symbol value of the multilevel electrical signal, It is possible to generate multilevel ASK signal light with equal intervals of light intensity levels corresponding to the respective symbol values. Since the voltage levels of the multi-level electric signal obtained by directly detecting the multi-level ASK signal light by the optical CDM receiving circuit 202 are equal, the MAI is removed and a desired binary data signal can be selectively demodulated. That is, according to the present embodiment, an optical CDM transmission system 301 that can flexibly expand the number of multiplexed binary data signals larger than 3 can be realized.

(Embodiment 2)
The second embodiment is an optical CDM transmission system in which the optical detector 47 in the optical CDM reception circuit 202 in the first embodiment is the heterodyne envelope detection circuit of FIG. The heterodyne envelope detector circuit shown in FIG. 13 includes a local light source 51, an optical detector 53, a BPF (Bandpass Filter) 54, and an envelope detector 57.

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ＡＳＫ信号光の光電界Ｅ_Ｓ（ｔ）は、

と表せる。Ｐ_Ｓ（ｔ），φ_Ｓ（ｔ）は、それぞれ、多値ＡＳＫ信号光の光強度および位相雑音であり、θ（ｔ）は、光ＣＤＭ送信回路内での多値ＡＳＫに伴う位相チャープ量である。光強度変調器として、Ｄｕａｌ−Ｄｒｉｖｅのマッハツェンダ干渉計型の光強度変調器を用いる場合、θ（ｔ）＝０である。 The optical frequency of the local light of the local light source 51 is adjusted so as to be different from the multilevel ASK signal light input to the heterodyne envelope detection circuit by f _IF . That is, the optical frequency of the local light is adjusted to be f _k −f _IF in the k-th heterodyne envelope detection circuit to which the multilevel ASK signal light having the optical frequency f _k is input, and the optical electric field is 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 ASK signal light is

It can be expressed. P _S (t) and φ _S (t) are the light intensity and phase noise of the multilevel ASK signal light, respectively, and θ (t) is the amount of phase chirp associated with the multilevel ASK in the optical CDM transmission circuit. It is. When a dual-drive Mach-Zehnder interferometer type light intensity modulator is used as the light intensity modulator, θ (t) = 0.

と表せる。ここで、

とした。 The optical detector 53 squarely detects the mixed light of the local light and the multi-level ASK signal light, and its output Q (t) 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 ASK signal light, the local light and the multilevel ASK signal light are adjusted so as to coincide with each other. In the heterodyne envelope detection circuit of FIG. 13, the polarization adjusting means 52 adjusts the polarization of the local light. In the optical CDM transmission circuit 201, in the configuration of polarization scramble that changes the polarization state of the signal light with time, the configuration of transmitting signal light in which the orthogonal polarization states are added, or in the heterodyne envelope detection circuit By adopting a configuration of polarization diversity, the polarization adjusting means 52 can be omitted.

The BPF 54 has a transmission band in the vicinity of f _IF , removes direct detection components corresponding to the first and second terms in Expression (4), and an intermediate frequency signal having f _IF represented by Expression (6) as a center frequency. R (t) is output.

を出力する。ここで、多値ＡＳＫ信号光の光強度Ｐ_Ｓ（ｔ）は、対応する各シンボル値に対して線形である。よって、ヘテロダイン包絡線検波回路の出力する多値電気信号Ｓ（ｔ）の電圧レベルも、対応する各シンボル値に対して線形となり、電圧レベルの間隔は等しくなる。 The envelope detector 57 square-detects the intermediate frequency signal R (t) from the BPF 54 and multi-level electric signal S (t) that is a baseband signal.

Is output. Here, the light intensity P _S (t) of the multilevel ASK signal light is linear with respect to each corresponding symbol value. Therefore, the voltage level of the multilevel electric signal S (t) output from the heterodyne envelope detection circuit is also linear with respect to each corresponding symbol value, and the voltage level intervals are equal.

  The multi-value electric signal output from each heterodyne envelope detection circuit 48 is input to the electric decoder 45 and added or subtracted according to the unique code assigned to the electric decoder 45. Here, as described above, the multilevel electric signal output from the heterodyne envelope detection circuit 48 has voltage levels corresponding to each symbol value at equal intervals. In addition, since the light intensities of the multilevel ASK signal lights input to the heterodyne envelope detection circuits match, the voltage level intervals of the multilevel electrical signals output from different heterodyne envelope detection circuits 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 the orthogonality of the code, and a desired binary data signal can be selectively received.

  In the second embodiment, in addition to N (N ≦ N ′) binary data signals, (N′−N) binary dummy signals are input to the binary / multilevel converter 11. The number of binary electrical signals input to the binary / multilevel converter 11 is always N ′ regardless of the number N of binary data signals multiplexed. Therefore, even in cases where the number N of multiplexed binary data signals is different, the multilevel number M of the multilevel electrical signal input to the light intensity modulation means is constant, and the voltage corresponding to each symbol value of the multilevel electrical signal. Without changing the level, it is possible to generate multilevel ASK signals in which the intervals of the light intensity levels corresponding to the respective symbol values are equal. Each voltage level of the multilevel electric signal obtained by heterodyne envelope detection of the multilevel ASK signal by the optical CDM receiving circuit 202 is equally spaced, so that MAI can be removed and a desired binary data signal can be selectively demodulated. . That is, according to the present embodiment, an optical CDM transmission system 301 that can flexibly expand the number of multiplexed binary data signals to be larger than 3 can be realized.

(Embodiment 3)
In the third embodiment, the optical detector 47 in the optical CDM receiving circuit 202 in the first embodiment is used.
Is an optical CDM transmission system which is a phase diversity homodyne detection circuit. FIG. 14 shows a configuration example of the phase diversity homodyne detection circuit. The phase diversity homodyne detection circuit of FIG. 14 includes a local light source 51, an optical hybrid 133, a differential detector 134, a square 135, and an adder 136.

  The optical frequency of local light from the local light source 51 is such that the optical frequency difference from the multilevel ASK signal light input to the phase diversity / homodyne detection circuit is sufficiently smaller than the symbol speed of the multilevel ASK signal light. Adjusted to

  The optical hybrid 133 has a plurality of output ends, and the local light and the multi-level ASK signal light are combined so that the optical phase difference between the local light and the multi-level ASK signal light becomes a predetermined difference between the output ends. Mix and output. FIG. 14 shows a case where a 90 ° optical hybrid is used as the optical hybrid 133. The 90 ° optical hybrid has four output ends. If the optical phase difference between the local light and the multilevel ASK signal light in one of them is Δθ (t), the optical phase difference in the other three output ends. Are Δθ (t) + π / 2, Δθ (t) + π, and Δθ (t) + 3π / 2. Optical phase adjustment for optical couplers created with optical fiber or PLC, etc., with local light and multi-level ASK signal light adjusted in polarization state input to a spatial circuit incorporating a λ / 2 plate or λ / 4 plate A 90 ° optical hybrid can be realized by a configuration incorporating a part.

と表せる。同様にして、差動検波器１３４−２の出力Ｑ_２ ^＊（ｔ）は、式（９）で表せる。

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, if the optical phase difference between the local light at the output terminal # 1 and the multilevel ASK signal light is Δθ (t), the optical phase differences at the output terminals # 2 to # 4 are Δθ (t) + π, Δθ (t) + π / 2, Δθ (t) + 3π / 2. At this time, the output Q ₁ ^* (t) of the differential detector 134-1 is

It can be expressed. Similarly, the output Q ₂ ^* (t) of the differential detector 134-2 can be expressed by Expression (9).

となり、Δθ（ｔ）によらず、多値ＡＳＫ信号光の光強度Ｐ_Ｓ（ｔ）に比例する。ここで、Ｐ_Ｓ（ｔ）は、対応する各シンボル値に対して線形である。よって、位相ダイバーシティ・ホモダイン検波回路の出力する多値電気信号Ｓ^＊（ｔ）の電圧レベルも、対応する各シンボル値に対して線形となり、電圧レベルの間隔は等しくなる。 The outputs of the differential detector 134 are squared by the squarer 135 and then added by the adder 136. The output S ^* (t) of the phase diversity homodyne detection circuit of FIG.

Therefore, it is proportional to the light intensity P _S (t) of the multilevel ASK signal light regardless of Δθ (t). Here, P _S (t) is linear for each corresponding symbol value. Therefore, the voltage level of the multilevel electric signal S ^* (t) output from the phase diversity homodyne detection circuit is also linear with respect to each corresponding symbol value, and the voltage level intervals are equal.

  The multi-value electric signal output from each phase diversity / homodyne detection circuit 49 is input to the electric decoder 45 and is added / subtracted according to the unique code assigned to the electric decoder 45. Here, as described above, in the multilevel electric signal output from the phase diversity homodyne detection circuit 49, the voltage levels corresponding to the respective symbol values are equally spaced. Further, since the light intensity of the multilevel ASK signal light input to each phase diversity / homodyne detection circuit is the same, the voltage level interval between the multilevel electric signals output from different phase diversity / homodyne detection circuits is the same. . 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 the orthogonality of the code, and a desired binary data signal can be selectively received.

  In the third embodiment, in addition to N (N ≦ N ′) binary data signals, (N′−N) binary dummy signals are input to the binary / multilevel converter 11. The number of binary electrical signals input to the binary / multilevel converter 11 is always N ′ regardless of the number N of binary data signals multiplexed. Therefore, even in cases where the number N of multiplexed binary data signals is different, the multilevel number M of the multilevel electrical signal input to the light intensity modulation means is constant, and the voltage corresponding to each symbol value of the multilevel electrical signal. Without changing the level, it is possible to generate multilevel ASK signals in which the intervals of the light intensity levels corresponding to the respective symbol values are equal. The voltage levels of the multilevel electrical signal obtained by phase diversity and homodyne detection of the multilevel ASK signal by the optical CDM receiving circuit 202 are equally spaced. Therefore, the MAI is removed and the desired binary data signal is selectively demodulated. it can. That is, according to the present embodiment, it is possible to realize an optical CDM transmission system in which the number of multiplexed binary data signals can be flexibly expanded larger than three.

(Embodiment 4)
FIG. 15 is a block diagram illustrating an optical CDM transmission system 302 according to the fourth embodiment. The optical CDM transmission system 302 has a structure in which an optical fiber transmission line 203 connects an optical CDM transmission circuit 211 and a plurality of optical CDM reception circuits (212-1, 212-2,...).

[Optical CDM transmission circuit]
The optical CDM transmission circuit 211 includes a binary / multilevel conversion unit 11, a plurality of optical amplitude / phase modulation units 12, and an optical multiplexing unit 13. Similarly to the first to third embodiments, the binary / multi-level conversion means 11 adds (N′−N) to N binary data signals that are desired signals of at least one optical CDM receiving circuit 212. Pieces of binary dummy signals are inputted. Therefore, N ′ binary electric signals are always input regardless of the multiplexing number N of the binary data signals, and the multi-value number M of the generated K multi-value electric signals is constant. Voltage level corresponding to each symbol value of the multi-level electric signal ^{_{(D # 1 (t) ~D}} # K (t)) is adjusted to a desired spacing.

The optical amplitude phase modulation means 12 modulates an optical carrier wave (f _{1 to} f _K ) with the multi-value electric signal generated by the binary / multi-value conversion means 11, and multi-value amplitude phase modulation (APSK: Amplitude Phase Shift). Keying) Outputs signal light. Here, the amplitude levels of the optical electric field that the signal light can take are equally spaced. Further, the optical phase shift amount of the input light in the optical amplitude phase modulator 12 can be any of binary values having a difference of π depending on the symbol value of the multilevel electric signal input to the optical amplitude phase modulator 12. It becomes. The optical amplitude phase modulator 12 includes a differential signal generation means 25 and a dual-drive Mach-Zehnder interferometer type optical intensity modulator 26. The differential signal generation means 25 outputs two signals whose polarities are in an inverted relationship based on the multi-value electric signal. The differential signal generation means 25 is, for example, a differential amplifier.

  The two outputs of the differential signal generating means 25 are applied to an optical phase modulator (not shown) in each arm of the Mach-Zehnder interferometer type optical intensity modulator 26. The bias voltage to the light intensity modulator 26 is set so that the transmittance of the modulator is minimized when the intermediate voltage value of the output signal of the differential signal generating means 25 is applied. The light intensity modulator 26 is, for example, a Dual-Drive LN intensity modulator.

For example, when N ′ = 7, the Hadamard codes 1 to 7 having a code length of 8 are assigned as unique codes to the spreading encoders (21-1 to 21-7) in the binary / multilevel conversion unit 11. Regardless of the number N of binary data signals multiplexed, seven quinary electric signals are generated and input to the optical amplitude phase modulation means (12-1 to 12-7), respectively. Here, according to the change of the symbol value of the quinary electric signal, the optical field of the output light from one arm of the light intensity modulator 26 is B ₀ (−a, 0) → on the optical field plane of FIG. B ₁ (-a / 2, √ (3a) / 2)-> B ₂ (0, a)
-> B ₃ (a / 2, √ (3a) / 2)-> B ₄ (a, 0)
In the order of
The optical field of the output light of the other arm is B ₀ (−a, 0) → B ₇ (−a / 2, −√ (3a) / 2) → B ₆ (0, −a)
_{-> B 5 (a / 2} , -√ (3a) / 2) -> B 4 (a, 0)
When the respective voltage levels corresponding to the respective symbol values are adjusted so as to transition in the order of ## EQU3 ## the 5-value APSK signal light output from the light intensity modulator, which is a vector combination of the optical electric fields of the output light of both arms, The optical electric fields corresponding to “0” to “4” are sequentially A ₀ (−2a, 0).
A ₁ (−a, 0)
A ₂ (0,0)
A ₃ (a, 0)
A ₄ (2a, 0)
It corresponds to. Therefore, the optical amplitude phase modulation means 12 has a binary value in which the amplitude level of the optical field that can be taken is equal, and the optical phase shift amount of the input light in the optical intensity modulator is π depending on the symbol value. A desired quinary APSK signal light that is any one of the above is generated.

[Optical CDM receiver circuit]
The optical CDM receiving circuit 212 includes an optical frequency demultiplexer 42, K heterodyne synchronous detection circuits 58, and an electric decoder 45. The multi-wavelength signal light input to the optical CDM receiving circuit 212 is separated for each optical frequency component by the optical frequency demultiplexer 42. Each optical frequency component is detected by a heterodyne synchronous detection circuit 58 connected one-to-one with each output terminal of the optical frequency demultiplexer 42, and a multi-value electric signal is generated. In the generated multilevel electric signal, the voltage levels corresponding to the respective symbol values are equally spaced.

  FIG. 17 is a configuration example of the heterodyne synchronous detection circuit 58. The heterodyne synchronous detection circuit 58 includes a local light source 51, an optical detector 53, a BPF 54, an electric phase-locked loop (PLL) circuit 55, and an LPF (Lowpass Filter) 56.

The optical frequency of the local light of the local light source 51 is adjusted so as to differ from the multilevel APSK signal light input to the heterodyne synchronous detection circuit 58 by f _IF . That is, in the k-th heterodyne synchronous detection circuit to which multi-level APSK signal light having an optical frequency of f _k is input, the optical frequency of local light is adjusted to be f _k −f _IF, and the optical electric field E _L (t) can be expressed by equation (2).

と表せる。Ｐ’_Ｓ（ｔ），φ’_Ｓ（ｔ）は、それぞれ、多値ＡＰＳＫ信号光の光強度および位相雑音であり、θ’（ｔ）は、シンボル値に応じて、０またはπをとる。局発光および信号光の位相雑音の時間変動は、多値ＡＰＳＫ信号のシンボル速度と比べて、十分に緩やかである。 On the other hand, the optical electric field E ′ _S (t) of the multilevel APSK signal light input to the heterodyne synchronous detection circuit 58 is

It can be expressed. P ′ _S (t) and φ ′ _S (t) are the light intensity and phase noise of the multilevel APSK signal light, respectively, and θ ′ (t) takes 0 or π depending on the symbol value. The temporal fluctuations of the local noise and the phase noise of the signal light are sufficiently gradual compared with the symbol rate of the multilevel APSK signal.

と表せる。ここで、

とした。 The optical detector 53 squarely detects the mixed light of the local light and the multilevel APSK signal light, and its output Q ^** (t) is

It can be expressed. here,

It was.

  In the heterodyne synchronous detection circuit 58, the polarization state of the local light and the multi-level APSK signal light is adjusted by adjusting the polarization state of at least one of the local light and the multi-level APSK signal light. In the heterodyne synchronous detection circuit 58 of FIG. 17, the polarization adjusting means 52 adjusts the polarization of the local light. The optical CDM transmission circuit 211 has a polarization scramble configuration that changes the polarization state of the signal light with time, a configuration that transmits signal light in which the orthogonal polarization states are added, and a heterodyne synchronous detection circuit. By adopting a wave diversity configuration, it is possible to omit polarization adjustment in the receiving circuit.

The BPF 54 has a transmission band in the vicinity of f _IF , removes direct detection components corresponding to the first and second terms in Expression (12), and an intermediate frequency signal having f _IF represented by Expression (14) as a center frequency. R ^** (t) is output.

と表せる。 The electric PLL circuit 55 includes a VCO 61, a mixer 62, and a loop filter 63, and synchronously detects the intermediate frequency signal R ^** (t). The loop filter 63 adjusts so that the oscillation frequency and phase of the VCO are synchronized with the intermediate frequency signal R ^** (t). Here, if the electrical band of the electrical PLL circuit 55 is sufficiently narrower than the symbol speed of the multilevel APSK signal light, the loop filter 63 cannot capture the voltage fluctuation of the symbol speed due to the fluctuation of θ ′ (t). The phase of the VCO 61 is synchronized with Δφ ′ (t), and the output S ^** (t) from the electric PLL circuit 55 is

It can be expressed.

The output of the electric PLL circuit 55 is low-pass filtered by the LPF 56, and the second term on the right side of the equation (15) is output. Here, the amplitude level √ (P ′ _S (t)) of the optical electric field that can be taken by the multilevel APSK signal light is equally spaced. Since θ ′ (t) takes 0 or π depending on the symbol value, each voltage level of the multilevel electric signal generated by the heterodyne synchronous detection circuit 58 is symmetric with respect to the intermediate voltage value. The potential difference from the voltage value is proportional to the amplitude level √ (P ′ _S (t)) of the optical electric field of the multilevel APSK signal light. Therefore, the multilevel electric signal output from the heterodyne synchronous detection circuit 58 has equal voltage levels corresponding to each symbol value.

  The multilevel electric signal output from each heterodyne synchronous detection circuit 58 is input to the electric decoder 45, and is added or subtracted according to the unique code assigned to the electric decoder 45. Here, as described above, in the multilevel electric signal output from the heterodyne synchronous detection circuit 58, the voltage levels corresponding to the symbol values are equally spaced. Further, since the light intensities of the multilevel APSK signal lights input to the heterodyne synchronous detection circuits 58 match, the voltage level intervals of the multilevel electrical signals output from the different heterodyne synchronous detection circuits 58 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 the orthogonality of the code, and a desired binary data signal can be selectively received.

  In the fourth embodiment, in addition to N (N ≦ N ′) binary data signals, (N′−N) binary dummy signals are input to the binary / multilevel converter 11. The number of binary electrical signals input to the binary / multilevel converter 11 is always N ′ regardless of the number N of binary data signals multiplexed. Therefore, even in each case where the number of multiplexed binary data signals N is different, the multilevel number M of the multilevel electrical signal input to the optical amplitude phase modulation means 12 is constant and corresponds to each symbol value of the multilevel electrical signal. Without changing the voltage level, the amplitude level of the optical field that can be taken is equally spaced, and the optical phase shift amount of the input light in the optical amplitude phase modulation means 12 is π depending on the symbol value A multi-valued APSK signal that is either binary can be generated. Each voltage level of the multilevel electric signal obtained by heterodyne synchronous detection of the multilevel APSK signal by the optical CDM receiving circuit 212 is equidistant, so that MAI can be removed and a desired binary data signal can be selectively demodulated. That is, according to the present embodiment, an optical CDM transmission system 302 that can flexibly expand the number of multiplexed binary data signals larger than 3 can be realized.

(Embodiment 5)
The fifth embodiment is an optical CDM transmission system that uses the optical phase-locked homodyne detection circuit 59 of FIG. 18 as an alternative to the heterodyne synchronous detection circuit 58 in the optical CDM reception circuit 212 in the fourth embodiment. The optical phase-locked homodyne detection circuit 59 in FIG. 18 includes the local light source 51, the loop filter 63, and the optical detector 53 to constitute an optical PLL.

  The optical detector 53 square-detects the mixed light of the local light and the multilevel APSK signal light. In the optical phase-locked homodyne detection circuit 59, the polarization state of the local light and the multilevel APSK signal light is adjusted by adjusting the polarization state of at least one of the local light and the multilevel APSK signal light. . In the optical phase-locked homodyne detection circuit 59 of FIG. 18, the polarization adjusting unit 52 adjusts the polarization of the local light. In addition, in the optical CDM transmission circuit 211, 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 an optical phase-locked homodyne detection circuit It is possible to omit the polarization adjusting means 52 by adopting a polarization diversity configuration in FIG.

となる。 The loop filter 63 performs adjustment so that the optical frequency and optical phase of the local light are synchronized with the multilevel APSK signal light. Here, it is assumed that the electrical band of the loop filter 63 is sufficiently narrower than the symbol rate of the multilevel APSK signal light. Assuming that the optical electric field E ′ _S (t) of the multilevel APSK signal can be expressed by Expression (11) in the fourth embodiment, the loop filter does not feel the voltage fluctuation of the symbol speed due to the fluctuation of θ ′ (t). Therefore, the optical phase of the local light is synchronized with φ ′ _S (t), and the output Q ^*** (t) of the optical detector is

It becomes.

The light intensity P _L of the local light, when the light intensity of the multi-level APSK signal input to the optical phase-locked homodyne detection circuit 59 P 'than _{S (t)} is set to be sufficiently large, multilevel APSK signal light The second term on the right side of Equation (16), which is a direct detection component, can be ignored compared to the third term on the right side, which is a beat component with local light. Here, the amplitude level √ (P ′ _S (t)) of the optical electric field that can be taken by the multilevel APSK signal light is equally spaced. Since θ ′ (t) takes 0 or π depending on the symbol value, each voltage level of the multilevel electric signal generated by the optical phase-locked homodyne synchronous detection circuit 59 is symmetric with respect to the intermediate voltage value. Thus, the potential difference from the intermediate voltage value is proportional to the amplitude level √ (P ′ _S (t)) of the optical electric field of the multilevel APSK signal light. Therefore, the multilevel electric signal output from the optical phase-locked homodyne synchronous detection circuit 59 has equal voltage levels corresponding to the symbol values.

  The multi-value electric signal output from each optical phase-locked homodyne detection circuit 59 is input to the electric decoder 45 and added / subtracted according to the unique code assigned to the electric decoder 45. Here, as described above, in the multilevel electric signal output from the optical phase-locked homodyne detection circuit 59, the voltage levels corresponding to the symbol values are equally spaced. In addition, since the light intensity of the multilevel APSK signal light input to each optical phase-locked homodyne detection circuit 59 matches, the voltage level interval between the multilevel electrical signals output from different optical phase-locked homodyne detection circuits 59 is different. 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 the orthogonality of the code, and a desired binary data signal can be selectively received.

  In the fifth embodiment, in addition to N (N ≦ N ′) binary data signals, (N′−N) binary dummy signals are input to the binary / multilevel converter 11. The number of binary electrical signals input to the binary / multilevel converter 11 is always N ′ regardless of the number N of binary data signals multiplexed. Therefore, even in each case where the number of multiplexed binary data signals N is different, the multilevel number M of the multilevel electrical signal input to the optical amplitude phase modulation means 12 is constant and corresponds to each symbol value of the multilevel electrical signal. Without changing the voltage level, the amplitude level of the optical field that can be taken is equally spaced, and the optical phase shift amount of the input light in the optical amplitude phase modulation means 12 is π depending on the symbol value A multi-valued APSK signal that is either binary can be generated. Since each voltage level of the multilevel electric signal obtained by optical phase-locked homodyne detection of the multilevel APSK signal by the optical CDM receiving circuit 212 is equal, MAI is removed and a desired binary data signal is selectively demodulated. it can. That is, according to the present embodiment, an optical CDM transmission system 302 that can flexibly expand the number of multiplexed binary data signals larger than 3 can be realized.

(Embodiment 6)
In the sixth embodiment, an optical CDM transmission circuit includes a multi-wavelength signal light in which each optical frequency component is subjected to multi-level amplitude phase modulation, and includes a multi-wavelength signal light whose optical frequency matches that of the multi-wavelength signal light. Output light. In the multiwavelength signal light and the multiwavelength continuous light, the optical phase difference between optical frequency components having the same optical frequency is 0 or π at the output end of the optical CDM transmission circuit.

  FIG. 19 is a block diagram illustrating the optical CDM transmission circuit 221. The continuous light output from each light source 14 is branched in front of the light amplitude phase modulation means 12. The continuous light that has passed through one path is not modulated, but is combined with the multilevel APSK signal light generated by the optical amplitude phase modulation means 12 in the other path. Here, the optical phase adjuster 92 arranged in at least one of the paths adjusts the optical phase of the multilevel APSK signal light and the continuous light so that the optical phase difference becomes 0 or π when they are combined. The The light intensity of the multilevel APSK signal light and the continuous light is adjusted by a light intensity adjuster 93 arranged in at least one of the paths so that the light intensity of the continuous light is sufficiently larger than the multilevel APSK signal light. The The polarization states of the multilevel APSK signal light and the continuous light are adjusted by the polarization adjuster 94 disposed in at least one of the paths so as to coincide with each other when they are combined. If the polarization state is maintained in both paths, the polarization adjuster 94 can be omitted.

For example, in the case of N ′ = 7, the five values output when the Hadamard codes 1 to 7 having a code length of 8 are assigned to the spreading encoders 1 to 7 in the binary / multilevel conversion means as the unique codes The optical electric fields of the APSK signal light and continuous light are shown in FIG. The optical phase difference between the points A ₀ and A ₁ corresponding to the symbol values “0” and “1” of the quinary APSK signal light and the point B corresponding to continuous light is π. On the other hand, the optical phase difference between the points A ₃ and A ₄ corresponding to the symbol values “3” and “4” and the point B is zero.

Multi-level APSK signal light and continuous light whose optical frequency is f ₁ , multi-level APSK signal light and continuous light whose optical frequencies are f ₂ ,..., F _K , and optical frequencies such as AWG and multilayer filter Multiplexed by an optical multiplexer 13 such as an optical coupler or an optical coupler created by an optical fiber or PLC, multi-wavelength signal light and multi-wavelength continuous light are output. WDM signal light and the multi-wavelength continuous light is, as described above, f ₁ component together, f ₂ components together, ..., optical retardation 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 of the f ₁ components, the f ₂ components,..., The f _K components, but f ₁ , f ₂ ,. .., F The polarization state between the _K components does not necessarily match. In FIG. 19, the output of the optical phase adjuster 92 is input to the polarization adjuster 94, but the polarization adjuster 94 may be disposed in front of the optical phase adjuster 92. Similarly, the light intensity adjuster 93 can be disposed in front of the light amplitude phase modulation means 12.

  In FIG. 19, each light source 14 that outputs optical carriers having different optical frequencies and each optical amplitude and phase modulation means 12 are connected in a one-to-one relationship. However, as shown in FIG. A configuration in which each optical frequency component is separated by the optical frequency demultiplexer 15 and input to each optical amplitude phase modulation means 12 is also possible. Further, as shown in FIG. 21, the output of the multi-wavelength light source 14T is branched in front of the optical frequency demultiplexer 15, and the multi-wavelength continuous light that has passed through one path is converted into multi-value amplitude phase modulation. It is also possible to combine with the multi-wavelength signal light.

  The optical CDM receiving circuit corresponding to the optical CDM transmitting circuit (221, 231, 241) has the same configuration as that of the optical CDM receiving circuit 202 in the first embodiment, and continuous light and multilevel APSK having the same optical frequency. The mixed light of the signal light is square-detected. Here, the optical phase of the continuous light and the multilevel APSK signal light having the same optical frequency is set such that the optical phase difference becomes 0 or π in the optical CDM transmission circuit 202 according to the symbol value of the multilevel APSK signal. Has been adjusted. Further, since the phase shift amounts of these lights in the optical fiber transmission line 203 are equal, the optical phase difference in the optical CDM receiving circuit 202 is also 0 or π.

Ｐ_ＣＷ（ｔ）は、連続光の光強度である。光検波器の出力Ｑ^＊＊＊＊ （ｔ）は、

となる。 Therefore, the input optical field E _Total (t) to the optical detector 47 is the continuous light optical field E _CW (t) and the multilevel APSK signal light represented by the expression (11) in the fourth embodiment. As the sum of the optical electric field E ′ _S (t), it can be expressed by Expression (17).

P _CW (t) is the light intensity of continuous light. The output Q ^*** (t) of the optical detector is

It becomes.

In the optical CDM transmission circuit (221, 231, 241), the light intensity P _{CW of} continuous light is adjusted to be sufficiently larger than the light intensity P ′ _S (t) of the multilevel APSK signal. The second term on the right side, which is the direct detection component of the multilevel APSK signal light in Expression (18), can be ignored as compared with the third term on the right side, which is a beat component with continuous light. Here, the amplitude level √ (P ′ _S (t)) of the optical electric field that can be taken by the multilevel APSK signal light is equally spaced. Also, θ ′ (t) takes 0 or π according to the symbol value of the multi-value electric signal input to the optical amplitude phase modulation means 12, so that each of the multi-value electric signals generated by the optical detector 47 is The voltage level is symmetrical about the intermediate voltage value, and the potential difference from the intermediate voltage value is proportional to the amplitude level √ (P ′ _S (t)) of the optical electric field of the multilevel APSK signal light. Therefore, in the multi-value electric signal output from the optical detector 47, the voltage levels corresponding to the respective symbol values are equally spaced.

  Multi-level APSK signal light and continuous light having the same optical frequency are adjusted so that their polarization states coincide in the optical CDM transmission circuit (221, 231, 241). In addition, since the polarization shift during the optical fiber transmission is uniform, the polarization state is even at the input end of the optical detector 47. Therefore, in the optical CDM receiving circuit 202 in the sixth embodiment, it is not necessary to adjust the polarization state that is required in a normal coherent detector.

  Since the multilevel electric signal output from each optical detector 47 is the same as the output from each optical phase-locked homodyne detection circuit 49 in the fifth embodiment, the number of multiplexed binary data signals is set to 3 according to this embodiment. An optical CDM transmission system that can be expanded more flexibly and flexibly can be realized.

(Embodiment 7)
The seventh embodiment is an optical CDM transmission system in which the optical amplitude phase modulation means in the optical CDM transmission circuit in the fourth to sixth embodiments is configured such that the optical amplitude modulation means and the optical phase modulation means are connected in series. It is. The optical amplitude modulation means modulates the amplitude of the input light having a constant amplitude, and outputs the multilevel ASK signal light in which the amplitude level of the possible optical electric field is equally spaced. The optical phase modulation means modulates the optical phase of the input light and outputs it. Here, the optical phase shift amount of the input light in the optical phase modulation means becomes one of binary values having a difference of π according to the symbol value, and outputs from the optical amplitude phase modulation means are the fourth to sixth outputs. The multilevel APSK signal light is the same as that of the embodiment. Either the optical amplitude modulation means or the optical phase modulation means may be disposed in front.

  FIG. 22 is a block diagram illustrating the light amplitude phase modulation means 12. The optical amplitude phase modulation unit 12 includes an optical amplitude modulation unit 75 and an optical phase modulation unit 76. The voltage level corresponding to each symbol value of the multilevel electric signal input to the optical amplitude phase modulation means 12 is symmetric about the intermediate voltage value.

The optical amplitude modulation means 75 includes a signal conversion circuit 81, a differential signal generation means 82, and a dual-drive Mach-Zehnder interferometer type light intensity modulator 83. Signal conversion circuit 81 is connected to the binary / multi-level conversion means 11, and outputs the absolute value of the potential difference from the voltage value of the input signal minus the intermediate voltage value V _m of the multi-level electrical signals. Signal conversion circuit 81, as shown in FIG. 22, a subtracter 101 for outputting a difference signal obtained by subtracting the V _m from the input signal, a V _m and the threshold voltage, when the voltage value of the input signal is equal to or higher than the threshold voltage 1 Can be configured by a discriminator 102 that outputs −1 when it is equal to or lower than a threshold voltage, and a multiplier 103 that outputs a product of the outputs of the subtractor 101 and the discriminator 102. Multilevel electrical signal, the voltage level corresponding to each symbol value for a symmetric about the intermediate voltage value V _m, it is also possible to arrange the DC block instead of the subtractor 101. When the output terminal of the binary / multi-value conversion means 11 is AC coupled, the DC block can be omitted.

  The difference signal output from the multiplier 103 is input to the differential signal generation means 82, and two signals having opposite polarities are output. The differential signal generation means 82 is, for example, a differential amplifier.

  A dual-drive Mach-Zehnder interferometer-type optical intensity modulator 83 modulates input light with two outputs of differential signal generation means 82 applied to a phase modulation section in each arm, and can take an amplitude of an optical electric field that can be obtained. A multi-level ASK signal light whose levels are equally spaced is generated.

For example, when N ′ = 7, Hadamard codes 1 to 7 having a code length of 8 are assigned as unique codes to spreading encoders (21-1 to 21-7) in the binary / multilevel conversion means 11 The multi-value number M = 5 of the multi-value electric signal input to the optical amplitude phase modulation means 12 is obtained. Here, when the voltage level intervals corresponding to the respective symbol values of the quinary electric signal are X ₁ , X ₂ , X ₃ (= X ₂ ), and X ₄ (= X ₁ ) in order, the output signal of the signal conversion circuit The multi-value number is 3, and the interval between the voltage levels is X ₂ and X ₁ .

Here, according to the change of the symbol value of the output signal of the signal conversion circuit 81, the optical field of the output light of one arm of the light intensity modulator 83 is B ₀ (0, a)-> B on the optical field plane. ₁ (a / 2, √ (3a) / 2)-> B ₂ (a, 0)
And the optical field of the output light of the other arm is B ₄ (0, −a) → B ₃ (a / 2, −√ (3a) / 2) → B ₂ (a, 0)
Assuming that X ₁ = V _π / 3 and X ₂ = V _π / 6, the output of the light intensity modulator, which is a vector combination of the optical electric fields of the output light of both arms, is a quinary electric signal. The optical electric fields corresponding to the symbol values “0” to “4” are sequentially A ₀ (2a, 0).
A ₁ (a, 0)
A ₂ (0,0)
A ₃ (a, 0)
A ₄ (2a, 0)
The ternary ASK signal light corresponding to V _π is a voltage required to change the optical phase shift amount of the transmitted light in each arm of the Mach-Zehnder interferometer type light intensity modulator by π.

The optical phase modulation means 76 includes an identifier 84 and an optical phase modulator 85. The discriminator 84 is connected to the binary / multilevel converter 11 and outputs a positive voltage when the voltage value of the input signal is equal to or higher than the threshold voltage value, and outputs a negative voltage when the voltage value is equal to or lower than the threshold voltage value. To do. The threshold voltage value is set to be equal to the intermediate voltage value V _m of the multi-value electric signal.

  The output of the discriminator 84 is applied to the optical phase modulator 85. Here, the peak-to-peak voltage of the output signal of the discriminator 84 is adjusted so that the optical phase shift amount in the optical phase modulator 85 in each arm is different by π at the maximum voltage and the minimum voltage. The multilevel ASK signal light output from the light intensity modulator 83 is subjected to binary phase modulation to generate a desired multilevel APSK signal.

  FIG. 23 is a block diagram for explaining another optical amplitude phase modulation means 12 '. The difference between the optical amplitude phase modulation means 12 in FIG. 22 and the optical amplitude phase modulation means 12 ′ in FIG. 23 is that the optical amplitude phase modulation means 12 ′ has an optical phase modulation means 76 ′ instead of the optical phase modulation means 76. is there. The optical phase modulation means 76 ′ realizes optical phase modulation by means of a differential signal generation means 87 and a dual-drive Mach-Zehnder interferometer type optical intensity modulator 88. The two outputs of the differential signal generation means 87 are applied to the phase modulators in the respective arms constituting the dual-drive Mach-Zehnder interferometer type light intensity modulator 88. Here, a binary voltage is set by setting the bias voltage to the light intensity modulator 88 so that the transmittance of the modulator is minimized when the intermediate voltage value of the output signal of the differential signal generating means 87 is applied. Phase modulation can be realized. Therefore, a desired multilevel APSK signal obtained by binary phase modulation of the multilevel ASK signal light output from the light intensity modulator 83 is generated.

11: Binary / multilevel conversion means 12, 12′12-1, 12-2,..., 12-K: optical amplitude phase modulation means 13: optical multiplexing means 14, 14-1, 14-2,. .., 14-K: light source 14T: multi-wavelength light source 15: optical frequency demultiplexers 17, 17-1, 17-2,..., 17-N ′: light intensity modulation means 21, 21-1, 21 -2, ..., 21-N ': spreading coders 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: Optical intensity modulator 42: Optical frequency demultiplexers 45, 45 ′, 45′− 1, 45′-2,..., 45′-N: electric decoders 47, 47-1, 47-2,..., 47-K: optical detectors 48, 48-1, 48-2, ... , 48-K: heterodyne envelope detection circuits 49, 49-1, 49-2,..., 49-K: phase diversity homodyne detection circuit 51: local light source 52: polarization adjusting means 53: optical detector 54: BPF
55: Electric phase-locked loop circuit 56: LPF
57: Envelope detectors 58, 58-1, 58-2,..., 58-K: Heterodyne synchronous detection circuits 59, 59-1, 59-2,..., 59-K: Optical phase synchronous homodyne Detection circuit 61: VCO
62: mixer 63: loop filter 75: optical amplitude modulation means 76, 76 ′: optical phase modulation means 81: signal conversion circuit 82, 87: differential signal generation means 83, 88: light intensity modulators 84, 86: discriminator 85: Optical phase modulators 92, 92-1, 92-2, ..., 92-K: Optical phase adjusters 93, 93-1, 93-2, ..., 93-K: Light intensity adjusters 94, 94-1, 94-2, ..., 94-K: Polarization adjuster 101: Subtractor 102: Discriminator 103: Multipliers 111, 111-1, 111-2, ..., 111- (M-1),...: Weighting circuit 112: Discriminator 113: Multiplier 114: Adder 133: Optical hybrids 134, 134-1 and 134-2: Differential detectors 135, 135-1 and 135-2 : Squarer 136: Adders 201, 211, 221, 231, 24 1: Optical CDM transmission circuit 202, 202-1, 202-2, ..., 202-N: Optical CDM reception circuit 212, 212-1, 212-2, ..., 212-N: Optical CDM reception circuit 203: Optical fiber transmission line 301, 302: Optical CDM transmission system

Claims (18)

The optical code division multiplexing transmission circuit is an optical code division multiplexing transmission system connected to a plurality of optical code division multiplexing reception circuits via an optical fiber transmission line,
The optical code division multiplexing transmission circuit includes:
A fixed integer value N ′ of 3 or more is set,
It is composed of two kinds of code elements from N ′ binary electric signals composed of N (N is an integer of 2 to N ′ ) binary data signals and (N′−N) binary dummy signals. And K multi-value electrical signals are generated based on N ′ unique codes having a code length k (k = 1, 2,..., K, K being an integer of 2 or more), and the multi-value Binary / multi-value conversion means for adjusting the voltage level corresponding to each symbol value of the electrical signal to be a constant interval regardless of N ;
A plurality of optical modulation means for modulating K optical carriers having different optical frequencies using the multi-value electric signal from the binary / multi-value conversion means and outputting multi-value signal light;
Optical multiplexing means for outputting, to the optical fiber transmission line, multi-wavelength signal light obtained by multiplexing the multilevel signal light output by each of the optical modulation means;
With
The optical code division multiplex receiving circuit includes:
An optical frequency demultiplexer for demultiplexing the multi-wavelength signal light from the optical fiber transmission line for each optical frequency component;
K optical detection means for detecting each of the optical frequency components demultiplexed by the optical frequency demultiplexer;
One of the first to Nth unique codes, and an electrical decoder that selectively retrieves one of the binary data signals input to the binary / multilevel conversion means;
An optical code division multiplex transmission system comprising: The binary / multivalue conversion means includes:
N ′ spread encoders to which N ′ binary electric signals are input, K adders, and K pre-bias circuits,
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 assigns each code element constituting the unique code to the output end. A signal whose symbol value coincides with the binary electrical signal input to the spreading encoder from the output end to which one of the code elements is assigned. 0 is output from the output end to which the other code element is assigned,
The k-th adder is configured so that the symbol value of the k-th multilevel electrical signal is the sum of the symbol values of the output signals from the k-th output terminals of the respective spread encoders. Add the symbol value of the output signal from the kth output terminal of the spreading encoder,
Each of the pre-bias circuits adjusts the voltage level of the output of the adder so that the voltage level corresponding to each symbol value of the multi-valued electrical signal has a desired interval,
The electric decoder is
When the code elements constituting the assigned intrinsic code are assigned to the optical detection means in order, the output of the optical detection means to which one of the code elements constituting the intrinsic code is assigned is positive, 2. The optical code division multiplexing transmission system according to claim 1, wherein addition / subtraction is performed by adding the output of the optical detection means to which the other code element is assigned as negative. The light modulation means modulates the amplitude of the optical carrier wave and outputs a multi-value amplitude modulated signal light,
The pre-bias circuit adjusts a voltage level corresponding to each symbol value of the multi-value electric signal so that light intensity levels that can be taken by the multi-value amplitude-modulated signal light are equally spaced. Item 3. The optical code division multiplexing transmission system according to Item 2.   4. The optical code division multiplexing transmission system according to claim 3, wherein the optical modulation means includes a Mach-Zehnder interferometer type optical intensity modulator.   5. The optical code division multiplex transmission system according to claim 3, wherein the optical detection means square-detects the output light of the optical frequency demultiplexer. The light detection means includes a local light source, a light detector, a bandpass filter, and an envelope detector,
The optical frequency of the output light of the local light source is adjusted to be a predetermined frequency difference from the output light of the optical frequency demultiplexer,
The optical detector squarely detects mixed light of the output light from the local light source and the output light of the optical frequency demultiplexer,
The band-pass filter transmits a signal component carried by a carrier whose frequency matches the predetermined frequency difference from the output of the optical detector,
5. The optical code division multiplexing transmission system according to claim 3, wherein the envelope detector outputs the output from the bandpass filter by squaring detection. 6. The optical detection means includes a local light source, an optical hybrid, a plurality of optical detectors, a plurality of squarers, and an adder,
The optical frequency of the output light of the local light source is adjusted so that the optical frequency difference with the output light of the optical frequency demultiplexer is sufficiently smaller than the symbol speed of the multilevel signal light,
The optical hybrid has a plurality of output ends, and an optical phase difference between the output light of the local light source and the output light of the optical frequency demultiplexer at each output end is a predetermined difference between the output ends. So that the output light of the local light source and the output light of the optical frequency demultiplexer are mixed,
The optical detectors are connected to the output ends of the different optical hybrids, respectively, and square-detect the input light,
The squarer is connected to each of the different optical detectors, squares and outputs the output of the optical detector,
The optical code division multiplex transmission system according to claim 3 or 4, wherein the adder adds and outputs the outputs of the squarers. The optical modulation means modulates the amplitude and optical phase of the optical carrier, and outputs multilevel amplitude phase modulated signal light,
The pre-bias circuit adjusts the voltage level corresponding to each symbol value of the multi-value electric signal so that the amplitude level of the optical electric field that the multi-value amplitude modulation signal light can take is equally spaced;
3. The optical phase shift amount of the optical carrier wave in the optical modulation unit is one of binary values having a difference of π according to a symbol value of the multilevel electrical signal. Optical code division multiplexing transmission system. The light modulating means includes
Differential signal generating means for outputting two electrical signals having polarity inversion from one input electrical signal;
A Mach-Zehnder interferometer-type light intensity modulator that modulates input light with two applied electrical signals,
The optical intensity modulator modulates the amplitude and optical phase of the optical carrier wave with two electrical signals generated from the multilevel electrical signal by the differential signal generation means. Optical code division multiplexing transmission system. The light modulation means, an optical amplitude modulation means and an optical phase modulation means are connected in series,
The light amplitude modulation means includes
A signal conversion circuit connected to the binary / multi-value conversion means and outputting an absolute value of a potential difference between a voltage value of an input signal and an intermediate voltage value of a maximum voltage value and a minimum voltage value that can be taken by the input signal;
Differential signal generating means for outputting two electrical signals having polarity inversion from one input electrical signal;
A Mach-Zehnder interferometer type light intensity modulator that modulates input light by two applied electrical signals;
Within the light intensity modulator, the amplitude of the input light is modulated by two electrical signals generated from the output signal of the signal conversion circuit by the differential signal generation means,
The optical phase modulation means includes
A discriminator that outputs different voltages depending on whether the voltage value of the input signal is equal to or higher than the threshold voltage value, or lower than the threshold voltage value;
An optical phase modulator that modulates the optical phase of the input light according to the output of the discriminator,
The discriminator is connected to the binary / multi-level conversion means, and the threshold voltage value is set equal to an intermediate voltage value between a maximum voltage value and a minimum voltage value that can be taken by an input signal to the discriminator. The optical code division multiplex transmission system according to claim 8. The light modulation means, an optical amplitude modulation means and an optical phase modulation means are connected in series,
The light amplitude modulation means includes
A signal conversion circuit connected to the binary / multi-value conversion means and outputting an absolute value of a potential difference between a voltage value of an input signal and an intermediate voltage value of a maximum voltage value and a minimum voltage value that can be taken by the input signal;
Differential signal generating means for outputting two electrical signals having polarity inversion from one input electrical signal;
A Mach-Zehnder interferometer type light intensity modulator that modulates input light by two applied electrical signals;
Within the light intensity modulator, the amplitude of the input light is modulated by two electrical signals generated from the output signal of the signal conversion circuit by the differential signal generation means,
The optical phase modulation means includes
A discriminator that outputs different voltages depending on whether the voltage value of the input signal is greater than or equal to a threshold voltage value and less than or equal to the threshold voltage value; the differential signal generating means; and the light intensity modulator,
The discriminator is connected to the binary / multi-level conversion means, and the threshold voltage value is set equal to an intermediate voltage value between a maximum voltage value and a minimum voltage value that can be taken by an input signal to the discriminator.
9. The optical code division according to claim 8, wherein the optical phase of the input light is modulated by two signals generated by the differential signal generator from the output of the discriminator in the optical intensity modulator. Multiplex transmission system. The optical detection means includes a local light source, an optical detector, a band pass filter, an electric phase locked loop circuit, and a low pass filter,
The optical frequency of the output light of the local light source is adjusted to be a predetermined frequency difference from the output light of the optical frequency demultiplexer,
The optical detector squarely detects mixed light of the output light from the local light source and the output light of the optical frequency demultiplexer,
The band-pass filter transmits a signal component carried by a carrier whose frequency matches the predetermined frequency difference from the output of the optical detector,
The electrical phase-locked loop circuit has a sufficiently narrow electrical band compared to the symbol rate of the multilevel signal light, and synchronously detects the output of the bandpass filter,
The optical code division multiplexing transmission system according to any one of claims 8 to 11, wherein the low-pass filter transmits a baseband signal output from the electrical phase-locked loop circuit. The optical detection means constitutes an optical phase-locked loop with a local light source, an optical detector, and a loop filter,
In the optical phase-locked loop, the optical frequency and optical phase of the output light of the local light source are reduced by the loop filter whose electrical band is sufficiently narrow compared with the symbol rate of the multilevel signal light. Adjusted to synchronize with the output light of the instrument,
The said optical detector carries out square detection of the mixed light of the output light from the said local light source, and the output light of the said optical frequency demultiplexer, The Claim 8 characterized by the above-mentioned. Optical code division multiplexing transmission system. The optical code division multiplexing transmission circuit outputs a multi-wavelength continuous light including an optical frequency component having an optical frequency that matches the multi-wavelength signal light in addition to the multi-wavelength signal light,
At the output end of the optical code division multiplexing transmission circuit, the multi-wavelength signal light and the multi-wavelength continuous light have an optical phase difference of 0 or π between optical frequency components having the same optical frequency,
The optical code division multiplex transmission system according to any one of claims 8 to 11, wherein the optical detection means in the optical code division multiplex receiving circuit square-detects the optical frequency component. The optical code division multiplexing transmission circuit is an optical code division multiplexing transmission method for an optical code division multiplexing transmission system connected to a plurality of optical code division multiplexing reception circuits via an optical fiber transmission line,
In the optical code division multiplexing transmission circuit,
Set a fixed integer value N ′ of 3 or more,
N ( binary data signal) consisting of N (N is an integer from 2 to N ′) binary data signals and (N′−N) binary dummy signals are composed of two kinds of code elements. And K multi-value electrical signals are generated based on N ′ unique codes having a code length k (k = 1, 2,..., K, K being an integer of 2 or more), and the multi-value A binary / multi-level conversion procedure for adjusting the voltage level corresponding to each symbol value of the electrical signal to be a constant interval regardless of N ;
An optical modulation procedure for generating multilevel signal light by modulating K optical carriers having different optical frequencies using the multilevel electrical signal generated by the binary / multilevel conversion procedure;
An optical multiplexing procedure for outputting, to the optical fiber transmission line, multi-wavelength signal light obtained by multiplexing the multilevel signal light generated in the optical modulation procedure;
And
In the optical code division multiplexing receiver circuit,
An optical frequency demultiplexing procedure for demultiplexing the multi-wavelength signal light from the optical fiber transmission line for each optical frequency component;
An optical detection procedure for detecting each of the optical frequency components demultiplexed in the optical frequency demultiplexing procedure;
An electro-decoding procedure that selectively retrieves one of the binary data signals based on one of the first to Nth unique codes;
An optical code division multiplex transmission method. The binary / multi-value conversion procedure is:
A code spreading process, an adding process, and a pre-bias process;
In the code spreading process, N ′ binary electric signals are respectively input, the unique codes are respectively assigned, and a spread encoder having a number of output ends equal to or greater than the code length of the assigned unique code, The binary electricity inputted to the spreading encoder from the output end to which one of the code elements is assigned when the code elements constituting the unique code are sequentially assigned to the output end. A signal having a symbol value that matches the signal, and outputting 0 from the output end to which the other code element of the code elements is assigned,
In the addition process, each spreading encoder is configured such that the symbol value of the kth multi-level electrical signal is the sum of the symbol values of the output signals from the kth output terminal of each spreading encoder. The symbol value of the output signal from the kth output terminal of
The pre-bias process adjusts the voltage level so that the voltage level corresponding to each symbol value of the multi-value electrical signal has a desired interval,
The electrical decoding procedure includes:
For the output signal detected and output in the optical detection procedure, the output signal to which one of the code elements constituting the inherent code is assigned is positive, and the output signal to which the other code element is assigned. 16. The optical code division multiplexing transmission method according to claim 15, wherein addition / subtraction is performed as a negative addition. The optical modulation procedure modulates the amplitude of the optical carrier and outputs a multilevel amplitude modulated signal light,
The pre-bias process is characterized in that a voltage level corresponding to each symbol value of the multi-value electric signal is adjusted so that light intensity levels that can be taken by the multi-value amplitude-modulated signal light are equally spaced. Item 17. The optical code division multiplexing transmission method according to Item 16. The optical modulation procedure modulates the amplitude and optical phase of the input light and outputs a multi-value amplitude phase modulated signal light,
In the pre-bias process, the voltage level corresponding to each symbol value of the multi-value electric signal is adjusted so that the amplitude level of the optical electric field that can be taken by the multi-value amplitude-modulated signal light is equal.
The optical phase shift amount of the optical carrier wave after the optical modulation procedure is one of binary values having a difference of π according to a symbol value of the multi-level electric signal. Optical code division multiplexing transmission method.

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