JP5347858B2 - Optical signal channel division multiplexing communication method and optical signal channel division multiplexing communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate transmission signals of a plurality of multiplexed channels, while using one light source outputting an optical pulse of a single wavelength and a single optical modulator, and even if the center wavelength of wavelength spectrum of the optical pulse fluctuates, to prevent communication functions from being affected by the fluctuations. <P>SOLUTION: A series electrical transmission signal generator 12 sequentially outputs, on a time base, first to eighth channel electrical transmission signals 13. An optical pulse train generator 18 outputs an optical pulse train 19. An optical pulse wavelength diffuser 20 generates and outputs a diffused optical pulse train 21. An optical modulator 22 inputs thereto the diffused optical pulse train and the first to eighth channel electrical transmission signals 17 and sequentially generates first to eighth channel modulated optical transmission signals 23. A timing controller 16 controls the input timings of the first to eighth channel electrical transmission signals. A first receiver 32 receives the first channel modulated optical transmission signal and outputs a first channel optical demodulation receiving signal. A first receiving signal reproducing section 36 outputs a first channel electrical regenerative receiving signal 37. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention divides an optical pulse having a unique maximum in the wavelength spectrum into different wavelength components and distributes them to a plurality of channels, and uses the difference in wavelength components as a channel identification mark for optical transmission. The present invention relates to a channel division multiplexing communication method and system.

  In recent years, the demand for communication is rapidly increasing due to the spread of the Internet and the like, and the capacity of communication is increased correspondingly. Various forms of communication systems have been built, and flexible bus or ring communication networks with optical ADM (Add-Drop-Multiplexer) capable of high-capacity transmission are actively proposed and studied. Has been.

  As a technique for increasing the communication capacity, attention is focused on an optical multiplexing technique that transmits optical pulse signals for a plurality of channels collectively on a single optical fiber transmission line. As an optical multiplexing technique, an optical time division multiplexing (OTDM) system, a wavelength division multiplexing (WDM) system, and an optical code division multiplexing (OCDM) system have been actively studied. ing.

  According to the OTDM system, a single light source and an optical modulator can generate signals for multiple channels. This is a system often used in communication networks such as PON (Passive Optical Network) configured with a star coupler. is there. In addition, according to the WDM system or OCDM system, the channel can be identified in the state of the optical signal by the wavelength filter or encoder, so these communication systems are used for flexible communication networks such as buses and rings. This is the preferred method.

  However, in the OTDM system, channel identification is performed in the form of electrical signals by reproducing all data, so in a bus or ring network that uses the OTDM system, a receiver is provided at each branch point. Need to be placed. In other words, this bus or ring network requires a light source and an optical modulator that generate signals for sending data signals of other channels to the next branch point.

  Further, the WDM system requires a light source that generates a multi-wavelength optical carrier wave. A light source that generates a multi-wavelength optical carrier is expensive, and the wavelength resources that can be used in a multiplex transmission system are limited. In addition, ensuring long-term stability of the wavelength of output light from a multi-wavelength light source requires advanced technology and is expensive.

  On the other hand, even in the OCDM system, it is possible to share a light source in a transmission apparatus, but an optical modulator for the number of multiplexed channels is required.

  Therefore, in the WDM system, a system for generating data signals of a plurality of channels from one or two variable wavelength light sources and one optical modulator has been proposed (see, for example, Patent Document 1). However, according to this method, it is possible to generate a data signal of a plurality of channels from one optical modulator, but the wavelength grid interval should be set narrow in response to increasing the number of multiplexed channels. Is required.

  When the wavelength grid interval is set, it is required that the amount of wavelength drift of the light source that generates the optical carrier wave be within the range of the set wavelength grid interval. Here, the wavelength drift of the light source refers to a phenomenon in which the wavelength output from the light source changes with time. If there is a wavelength variation exceeding the range of the wavelength grid spacing, the channel identification capability is lost in the method disclosed in Patent Document 1 described above. Incidentally, according to the ITU (International Telecommunication Union) international standard, WDM wavelength grids are defined at intervals of 100 GHz (approximately 0.8 nm intervals), 50 GHz intervals (approximately 0.4 nm intervals), and the like.

  On the other hand, in the WDM system, one short pulse light (for example, an optical pulse with a center wavelength of 1550 nm, a half width of 70 nm, and a half width of a time wavelength of 50 fs) is time-diffused by a wavelength dispersion medium A method of generating data signals for a plurality of channels from one optical modulator is disclosed (for example, see Non-Patent Document 1). According to this method, it is possible to generate a multi-channel signal.

  However, since this method assigns one wavelength to one channel, it is necessary to widen the wavelength band used for communication in response to increasing the number of multiplexed channels, and between channels. In order to secure a uniform signal intensity with a stable wavelength, the half width of the time waveform of the optical pulse output from the light source to be used is required to be extremely narrow. For this reason, the data transfer rate is lowered in communication using this method.

JP 2008-281869 A

Jason B. Stark, et al., "Cascaded WDM Passive Optical Network with a Highly Shared Source", IEEE PHOTONICS TECHNOLOGY LETTERS, Vol. 9, No. 8, (1997)

  As described above, the OTDM system requires a light source that generates a multi-wavelength optical carrier wave. Even in the OCDM system, it is possible to share a light source in a transmission apparatus, but an optical modulator for the number of multiplexed channels is required.

  Further, as methods for solving these problems, new methods are disclosed in the above-mentioned Patent Document 1 and Non-Patent Document 1, respectively, but in the former method disclosed in Patent Document 1, the wavelength drift amount is reduced. A sufficiently small and expensive light source is required, and the latter method disclosed in Non-Patent Document 1 requires a light source that outputs a light pulse with an extremely narrow half-width of the time waveform. There is a problem that the rate becomes low.

  The inventor of the present invention divides the wavelength spectrum component into a plurality of groups, even if the wavelength spectrum has a single maximum, so long as the wavelength spectrum has a finite width. It came to mind that it is possible to assign a channel to each group of different wavelength spectral components.

  That is, the wavelength spectrum component of the optical pulse having the only maximum is divided into a plurality of parts on the time axis by the optical modulator, and a channel is assigned to each group of the divided wavelength spectrum components, and a superlattice structure fiber black grating ( Establishing a method for identifying the wavelength spectrum components of optical pulses in a group assigned to each channel by SSFBG (Superstructured Fiber Bragg Grating), and this fluctuation can be communicated even if the center wavelength of the optical pulse wavelength spectrum fluctuates. We were convinced that it was possible to realize optical signal channel division multiplexing communication that would not affect the system.

  Therefore, an object of the present invention is to generate a transmission signal of a plurality of channels to be multiplexed by one light source that outputs an optical pulse of a single wavelength and one optical modulator, and the wavelength of the optical pulse An object of the present invention is to provide an optical channel division multiplexing communication method and an optical channel division multiplexing communication system in which even if the center wavelength of the spectrum varies, this variation does not affect the communication function.

  In this optical channel division multiplex communication, dividing the wavelength spectrum component of an optical pulse having the only maximum into multiple groups is equivalent to pseudo optical coding, and the group of optical pulses assigned to each channel by SSFBG To identify the wavelength spectral components of the two corresponds to pseudo optical decoding. Therefore, hereinafter, this optical channel division multiplex communication method is sometimes referred to as a pseudo OCDM method.

  Here, the terms “single wavelength optical pulse” and “pseudo OCDM” are defined as follows. That is, a single-wavelength optical pulse refers to an optical pulse whose wavelength spectrum has a single maximum. In addition, the pseudo OCDM means a method of dividing a wavelength spectrum of a single-wavelength optical pulse and assigning it to each channel, and identifying channel identification based on a difference in wavelength spectrum components and a difference in code described later. Shall.

  In ordinary WDM, an optical pulse having a plurality of maximums in the wavelength spectrum is distributed to each channel in correspondence with the maximum wavelength, and identification of these channels is realized by identifying these wavelengths. In other words, the wavelength spectrum of the optical carrier of the wavelength multiplexed signal in the normal WDM system takes a plurality of maximums, whereas the wavelength spectrum of the optical carrier of the signal in the pseudo OCDM system of the present invention takes a single maximum. There are differences.

  In the following description, the terms “encoding” and “decoding” are used in a broad sense by extending from the conventional practice. In other words, the rule for diffusing the optical pulse constituting the optical pulse signal on the time axis is not limited to the code in the normal sense (code in the narrow sense), but is an arbitrary rule (broad sense code) that is uniquely determined. Even so, the terms encoding and decoding described above are used. Accordingly, even in the case of codes in a broad sense, terms such as encoded optical pulse signals and chip pulses are used.

  In addition, the sequence of chip pulses output from the SSFBG that constitutes the optical pulse time spreading device of the present invention described below is strict like the sequence of chip pulses output from the SSFBG to which a normal code is set. The optical pulse is not generated by time spreading based on the meaning sign. However, in the following description, for convenience, conversion of an optical pulse into a sequence of chip pulses is referred to as encoding, and generation of a sequence of chip pulses as an autocorrelation wave or cross-correlation wave is also referred to as decoding. is there.

  Therefore, according to the gist of the present invention, there is provided an optical signal channel division multiplexing communication method and apparatus having the following configuration.

  The first optical signal channel division multiplexing communication method of the present invention includes a transmission step and a reception step, and the transmission step and the reception step include the following steps.

  The transmission step includes a serial electrical transmission signal generation step, an optical pulse train generation step, an optical pulse chromatic dispersion step, an optical modulation step, and a timing adjustment step. The reception step includes first to Nth reception steps (N is an integer equal to or greater than 2), and the jth reception step (j is an integer from 1 to N) includes the jth channel light. A pulse demodulation step and a j-th channel received signal reproduction step.

  The serial electrical transmission signal generation step is a step of sequentially outputting the first to Nth channel electrical transmission signals on the time axis.

  The optical pulse train generation step is a step of outputting an optical pulse train in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis.

  In the optical pulse chromatic dispersion step, the continuous wavelength spectrum component of the optical pulse is linearly diffused on the time axis so that adjacent optical pulses constituting this optical pulse train overlap on the time axis, and then diffused. This is a step of generating and outputting an optical pulse train.

  The optical modulation step is a step in which the diffused optical pulse train is modulated with the first to Nth channel electrical transmission signals, and the first to Nth channel modulated optical transmission signals are sequentially generated and output.

  The timing adjustment step is a step of adjusting the transmission timing of the first to Nth channel electrical transmission signals so that the wavelength spectrum components of the optical pulses constituting the first to Nth channel modulated optical transmission signals are different from each other.

  The 1st to Nth reception steps respectively receive the 1st to Nth channel modulated optical transmission signals, demodulate the 1st to Nth channel modulated optical transmission signals, and 1st to Nth electrical regeneration reception signals, respectively. Is a step of outputting.

  The jth channel optical pulse demodulation step is a step of generating and outputting a jth channel optical demodulation reception signal from the received first to Nth channel modulation optical transmission signals.

  The j-th channel reception signal regeneration step is a step in which the j-th channel optical demodulation reception signal is input, and a j-th channel electrical regeneration reception signal is generated and output.

  The second optical signal channel division multiplex communication method of the present invention includes a transmission step and a reception step, and the transmission step and the reception step include the following steps.

  The transmission step includes a parallel-serial conversion step, an optical pulse train generation step, an optical pulse chromatic dispersion step, and an optical modulation step. The reception step includes first to Nth reception steps, and the jth reception step includes a jth channel optical pulse demodulation step and a jth channel reception signal regeneration step.

  The parallel-serial conversion step is a step of converting the first to N-th channel parallel electric transmission signals arranged in parallel on the same time axis into serial electric transmission signals arranged serially on the time axis. The transmission signal components of the first to Nth channels constituting the serial electrical transmission signal under the condition that the wavelength spectrum components of the optical pulses constituting the first to Nth channel modulated optical transmission signals are modulated differently. Adjust the transmission timing and output.

  The optical pulse train generation step is a step of outputting an optical pulse train in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis.

  In the optical pulse chromatic dispersion step, the continuous wavelength spectrum component of the optical pulse is linearly diffused on the time axis so that adjacent optical pulses constituting this optical pulse train overlap on the time axis, and then diffused. This is a step of generating and outputting an optical pulse train.

  The optical modulation step is a step in which the diffused optical pulse train is modulated with a serial electrical transmission signal, and first to N-th channel modulated optical transmission signals are sequentially generated and output.

  The 1st to Nth reception steps respectively receive the 1st to Nth channel modulated optical transmission signals, demodulate the 1st to Nth channel modulated optical transmission signals, and 1st to Nth electrical regeneration reception signals, respectively. Is a step of outputting.

  The jth channel optical pulse demodulation step is a step of generating and outputting a jth channel optical demodulation reception signal from the received first to Nth channel modulation optical transmission signals.

  The j-th channel reception signal regeneration step is a step in which the j-th channel optical demodulation reception signal is input, and a j-th channel electrical regeneration reception signal is generated and output.

  The first optical signal channel division multiplexing communication method of the present invention is realized by the first optical signal channel division multiplexing communication system of the present invention. The first optical signal channel division multiplexing communication system according to the present invention includes a transmission device and a reception device, and each of the transmission device and the reception device includes the following components.

  The transmission device includes a serial electrical transmission signal generator, an optical pulse train generator, an optical pulse wavelength disperser, an optical modulator, and a timing adjuster. The receiving device includes first to Nth receiving units, and the jth receiving unit includes a jth channel optical pulse demodulator and a jth channel received signal reproducing unit.

  The serial electrical transmission signal generator sequentially outputs the first to Nth channel electrical transmission signals on the time axis.

  The optical pulse train generator outputs an optical pulse train in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis.

  The optical pulse wavelength disperser linearly spreads the continuous wavelength spectrum components of the optical pulse on the time axis so that adjacent optical pulses that make up this optical pulse train overlap on the time axis. An optical pulse train is generated and output.

  The optical modulator receives the diffused optical pulse train and the first to Nth channel electrical transmission signals, modulates the diffused optical pulse train with the first to Nth channel electrical transmission signals, and transmits the first to Nth channel modulated optical transmissions. Generate and output signals sequentially.

  The timing adjuster adjusts the transmission timing of the first to N-th channel electrical transmission signals input to the optical modulator so that the wavelength spectrum components of the optical pulses constituting the first to N-th channel modulated optical transmission signals are different from each other. adjust.

  The 1st to Nth receivers respectively receive the 1st to Nth channel modulated optical transmission signals, demodulate the 1st to Nth channel modulated optical transmission signals, and 1st to Nth electrical regeneration reception signals, respectively. Is output.

  The jth channel optical pulse demodulator generates and outputs a jth channel optical demodulated reception signal from the received first to Nth channel modulated optical transmission signals.

  The j-th channel reception signal regeneration unit receives the j-th channel optical demodulation reception signal, and generates and outputs a j-th channel electrical regeneration reception signal.

  The second optical signal channel division multiplexing communication method of the present invention is realized by the second optical signal channel division multiplexing communication system of the present invention. The second optical signal channel division multiplexing communication system of the present invention comprises a transmission device and a reception device, and each of the transmission device and the reception device comprises the following components.

  The transmission device includes an electrical transmission signal generator, an optical pulse train generator, an optical pulse wavelength disperser, and an optical modulator. The receiving device includes first to Nth receiving units, and the jth receiving unit includes a jth channel optical pulse demodulator and a jth channel received signal reproducing unit.

  The electrical transmission signal generators 1st to Nth channels arranged in parallel on the same time axis (N is an integer of 2 or more) parallel electrical transmission signals arranged serially in sequence on the time axis It has a parallel-serial converter that converts signals. The parallel-serial converter has the first to Nth components constituting the serial electrical transmission signal under the condition that the wavelength spectrum components of the optical pulses constituting the first to Nth channel modulated optical transmission signals are modulated differently. The transmission timing of the serial electric transmission signal is adjusted and output so that the transmission signal component of the channel is input to the optical modulator.

  The optical pulse train generator outputs an optical pulse train in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis.

  The optical pulse wavelength disperser linearly spreads the continuous wavelength spectrum components of the optical pulse on the time axis so that adjacent optical pulses that make up this optical pulse train overlap on the time axis. An optical pulse train is generated and output.

  The optical modulator receives the spread optical pulse train and the serial electrical transmission signal, modulates the diffuse optical pulse train with the serial electrical transmission signal, and sequentially generates and outputs first to N-th channel modulated optical transmission signals.

  The 1st to Nth receivers respectively receive the 1st to Nth channel modulated optical transmission signals, demodulate the 1st to Nth channel modulated optical transmission signals, and 1st to Nth electrical regeneration reception signals, respectively. Is output.

  The jth channel optical pulse demodulator generates and outputs a jth channel optical demodulated reception signal from the received first to Nth channel modulated optical transmission signals.

  The j-th channel reception signal regeneration unit receives the j-th channel optical demodulation reception signal, and generates and outputs a j-th channel electrical regeneration reception signal.

  The above-mentioned j-th channel optical pulse demodulator comprises SSFBGs comprising M (M is an integer satisfying N ≦ M) unit fiber black gratings (FBG: Fiber Bragg Grating). It is preferable to configure.

The Bragg reflection wavelength λ _b of the unit fiber black grating is expressed by the following equations (1a) and (1b)
λ _b = λ _s + {k + (1/2)} Δλ _s / N (1a)
(Where N is an even number and k is an integer in the range of -N / 2 to (N / 2) -1)
λ _b = λ _s + {k + (1/2)} Δλ _s / N (1a)
(Where N is an odd number and k is an integer in the range of-(N-1) / 2 to (N-1) / 2)
Set to the value given by.

The full width at half maximum Δλ _b of the Bragg reflection wavelength band of the unit fiber black grating is _expressed by the following equation (2)
Δλ _b = Δλ _s = T _d / D _p (2)
Set to the value given by.

The arrangement period L of adjacent unit fiber black gratings is expressed by the following equation (3)
L = {(λ _b −Δλ _b / 2) × (λ _b + Δλ _b / 2)} ÷ (2 · n _eff Δλ _b ) (3)
Set to the value given by.

The phase difference Θ of Bragg reflected light from adjacent unit fiber Bragg gratings is expressed by the following equation (4)
Θ = (1/2) × (λ _s + j · Δλ _s / N) (4)
Set to the value given by.

Where T _d is the repetition period of the optical pulse of the optical pulse train, D _p is the chromatic dispersion amount of the optical pulse wavelength disperser, λ _s is the peak wavelength of the wavelength spectrum of the optical pulse train output from the optical pulse generator, Δλ _s Is the full width at half maximum of the wavelength spectrum of the optical pulse train, and n _eff is the effective refractive index of the optical fiber constituting the superlattice structure fiber black grating.

  According to the first and second optical signal channel division multiplex communication methods and systems of the present invention, in the optical pulse train generation step, the optical pulse train in which the optical pulses having the only maximum in the wavelength spectrum are arranged at equal intervals on the time axis is provided. In this optical pulse train, in the optical pulse chromatic dispersion step, the continuous wavelength spectrum component of the optical pulse is converted to the time axis so that adjacent optical pulses constituting the optical pulse train overlap on the time axis. Linearly diffused upward. In the optical modulation step, the diffused optical pulse train generated by linear diffusion is modulated with the first to N-th channel electric transmission signals, and the first to N-th channel modulated optical transmission signals are sequentially generated.

  The optical modulation step of dividing the wavelength spectrum component of the optical pulse having the only maximum into a plurality of groups and assigning it to each channel can be realized by one optical modulator. In order to realize the optical pulse train generation step, it is only necessary to prepare one light source that outputs an optical pulse having a single maximum, and no light source that generates a multi-wavelength optical carrier wave is required.

  In addition, even if the wavelength fluctuation of the single wavelength optical carrier generation light source occurs when the wavelength spectrum component of the optical pulse having the only maximum is divided into a plurality of groups, it is determined by the modulation timing in the optical modulation step. The wavelength spectral components of each group are not changed, and the wavelength components identified by the SSFBG and the wavelength spectral components of each group identified are not changed because they are determined by the configuration of the SSFBG. Therefore, in the pseudo OCDM system adopted by the first and second optical signal channel division multiplex communication methods of the present invention, channel identification is possible without being affected by the fluctuation of the wavelength of the single wavelength optical carrier generation light source. Become.

  By configuring the j-th channel optical pulse demodulator using the SSFGB including the unit FBG set so as to satisfy the above-described equations (1a) and (1b) to (4), the first to It is possible to generate and output a jth channel optical demodulated reception signal from the Nth channel modulated optical transmission signal.

1 is a schematic block diagram of a first optical signal channel division multiplexing communication system according to an embodiment of the present invention. It is a schematic block block diagram of a timing adjuster. FIG. 3 is a schematic block configuration diagram of a second optical signal channel division multiplexing communication system according to an embodiment of the present invention. FIG. 2 is a schematic block diagram showing a parallel-serial converter and a transmission control signal generator and first to eighth channel electrical transmission signal generators necessary for explaining the structure and operation thereof. FIG. 3 is a schematic block configuration diagram of a first received signal reproduction unit. FIG. 7 is a diagram for explaining a method of generating a diffused optical pulse train used when generating first to eighth channel modulated optical transmission signals and a property of the diffused optical pulse train, and (A) shows a time waveform of the optical pulse train. (B) is a diagram showing a wavelength spectrum of an optical pulse constituting a diffused optical pulse train, and (C) is used to explain the overlapping state of the optical pulses constituting the diffused optical pulse train on the time axis. (D) is a diagram for explaining the wavelength distribution on the time axis of the optical pulses constituting the diffused optical pulse train. FIG. 7 is a diagram for explaining the encoding process of the first optical signal channel division multiplexing communication system according to the embodiment of the present invention, and (A) is a timing adjuster that is given to each channel and a time delay amount is adjusted and output. (B-1) and (B-2) are the first channel and the eighth channel electrical transmission signal from the spread optical pulse train by the first channel and the eighth channel electrical transmission signal It is a figure which shows a mode that the wavelength spectrum component of a 2nd channel is cut out, (C) is the wavelength cut out from the wavelength spectrum component of the optical pulse which comprises a diffused optical pulse train, and is distributed to a 1st channel and a 2nd channel It is a figure where it uses for description about a component. FIG. 7 is a diagram for explaining the encoding process of the second optical signal channel division multiplexing communication system according to the embodiment of the present invention, and (A) shows the first output from the first to eighth channel electric transmission signal generators, respectively. It is a diagram showing a time waveform of the first to eighth channel electrical transmission signal, (B) is a diagram showing the time waveform of the serial electrical transmission signal, (C) is a wavelength spectrum component of the optical pulse constituting the diffused optical pulse train It is a figure where it uses for description about the wavelength component cut out from and distributed to the 1st-8th channel. It is a diagram for explaining the optical pulse demodulator of each channel of the first and second optical signal channel division multiplexing communication system of the embodiment of the present invention, (A) of SSFBG schematically showing a unit FBG in a rectangle FIG. 2B is a schematic diagram showing a refractive index modulation structure of SSFBG, and FIG. 3C is a graph showing a refractive index modulation amount Δn of an optical fiber core. It is a figure which shows the time waveform of the 1st-8th channel modulation | alteration optical transmission signal used as the premise of operation | movement description of a 1st-8th optical pulse demodulator, (A) is three optical pulses which comprise a diffused optical pulse train. FIG. 6 is a diagram schematically showing a wavelength spectrum component of a first channel cut out from each of the optical pulses, and (B) is a diagram schematically showing a time waveform of a modulated optical transmission signal for one bit of the first channel. is there. FIG. 2 is a diagram for explaining the configuration and operation of the first optical pulse demodulator, (A) is a diagram showing a schematic configuration of the first optical pulse demodulator, and (B) is a first optical pulse demodulator. Each of the M chip pulses constituting the chip pulse train input to the SSFBG is converted into M chip pulses by the SSFBG, and the autocorrelation wave is generated by interference of these total (M × M) chip pulses. FIG. 4 is a diagram illustrating a process in which a cross-correlation wave is generated.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Each drawing is for one configuration example according to this embodiment, and only schematically shows the arrangement relationship of each component to the extent that the embodiment of the present invention can be understood. It is not limited to the illustrated example. Also, well-known components that are not characteristic features of the present invention are usually omitted as long as they are communication devices of the same type as the first and second optical signal channel division multiplex communication systems of the embodiments of the present invention, and illustration thereof is omitted. There are also things. In the following description, specific equipment and conditions may be used, but these materials and conditions are only one of preferred examples, and thus are not limited to these. Moreover, in each figure, the same component is shown with the same number, and the overlapping description may be omitted. In the block configuration diagram shown below, the path of an optical signal such as an optical fiber is indicated by a thick line, and the path of an electrical signal is indicated by a thin line.

<First Optical Signal Channel Division Multiplexing Communication System According to Embodiment of the Present Invention>
With reference to FIG. 1, the structure and operation of a first optical signal channel division multiplexing communication system according to an embodiment of the present invention will be described. FIG. 1 is a schematic block diagram of a first optical signal channel division multiplexing communication system according to an embodiment of the present invention.

  A first optical signal channel division multiplexing communication system according to an embodiment of the present invention includes a transmission device 10 and a reception device 30, and each of the transmission device 10 and the reception device 30 includes the following components. Yes. Here, as an example, the description will be made assuming that the number of multiplexed channels is eight. That is, description will be made assuming that N = 8. However, the gist of the following description is not limited to the case where N = 8.

  The transmission device 10 includes a serial electrical transmission signal generator 12, an optical pulse train generator 18, an optical pulse wavelength disperser 20, an optical modulator 22, and a timing adjuster 16. The receiving device 30 includes first to eighth receiving units. The first receiving unit 32 includes a first channel optical pulse demodulator 34 and a first channel received signal reproducing unit 36. The second receiving unit 40 to the eighth receiving unit 44 also include the same optical pulse demodulator and received signal reproducing unit. In FIG. 1, the first to eighth channel received signal regeneration units are simply abbreviated as first to eighth received signal regeneration units, and the first to eighth channel optical pulse demodulators are simply referred to as first to eighth optical pulses. Abbreviated as demodulator.

  The serial electrical transmission signal generator 12 sequentially outputs the first to eighth channel electrical transmission signals 13 on the time axis.

  The optical pulse train generator 18 outputs an optical pulse train 19 in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis.

  The optical pulse wavelength disperser 20 linearly diffuses the wavelength spectrum component of each optical pulse on the time axis so that adjacent optical pulses constituting the optical pulse train 19 overlap each other on the time axis. Then, the diffused light pulse train 21 is generated and output. Here, the optical pulses constituting the optical pulse train 19 need only realize a state in which at least adjacent optical pulses overlap on the time axis, and there may be overlap of three or more consecutive optical pulses. Also good.

  The optical modulator 22 receives the diffused optical pulse train 21 and the first to eighth channel electrical transmission signals 17 and modulates the diffused optical pulse train 21 with the first to eighth channel electrical transmission signals 17 to obtain the first to eighth channels. The 8-channel modulated optical transmission signal 23 is sequentially generated and output.

  The timing adjuster 16 receives the first to eighth channel electrical transmission signals 13 input to the optical modulator 22 so that the wavelength spectrum components of the optical pulses constituting the first to eighth channel modulated optical transmission signals 23 are different from each other. The first to eighth channel electrical transmission signals 17 whose timings are adjusted are output.

  Since each of the first receiving unit 32, the second receiving unit 40,..., The eighth receiving unit 44 has the same structure including an optical pulse demodulator and a received signal reproducing unit, the first receiving is mainly performed here. The section 32 will be described as a representative. In FIG. 1, the optical pulse demodulator and the reception signal regeneration unit provided in the first reception unit 32 are shown as a first optical pulse demodulator 34 and a first reception signal regeneration unit 36, respectively. The second receiving unit 40 to the eighth receiving unit 44 have the same structure.

  Each of the first receiving unit 32, the second receiving unit 40,..., The eighth receiving unit 44 sequentially receives the first to eighth channel modulated optical transmission signals 23, and each of the first receiving unit 32, the second receiving unit 40,. The first to eighth channel modulated optical transmission signals are demodulated, and the first channel electric reproduction reception signal 37 to the eighth channel electric reproduction reception signal are output, respectively.

  The first to eighth channel modulated optical transmission signals 23 are first input to the first receiver 32, and are assigned to the first channel by the first optical pulse demodulator 34 provided in the first receiver 32. Only the spectral components are separated to generate the first channel optical demodulated reception signal 35-1.

  On the other hand, the optical wavelength spectrum component 35-2 of the first to eighth channel modulated optical transmission signals 23 transmitted through the first optical pulse demodulator 34 is generated by the second optical pulse demodulator provided in the second receiver 40. Only the optical wavelength spectrum component allocated to the two channels is separated to generate the second channel optical demodulated reception signal.

  Thereafter, in the third receiving unit (not shown) to the eighth receiving unit 44, similarly, only the optical wavelength spectrum component assigned to each channel is separated to generate a channel optical demodulated reception signal for each channel. Is done.

  The first reception signal reproduction unit 36 receives the first channel optical demodulation reception signal 35-1 and generates and outputs a first channel electric reproduction reception signal 37.

  The structure and operation of the timing adjuster 16 will be described with reference to FIG. FIG. 2 is a schematic block diagram of the timing adjuster 16. As shown in FIG.

  The timing adjuster 16 includes a transmission side switch control signal generator 28, a changeover switch 24, and a coupler 26. A first channel electrical transmission signal is first input to the changeover switch 24, followed by a second channel electrical transmission signal. Thereafter, the third to eighth channel electrical transmission signals are sequentially input to the changeover switch 24. The electrical transmission signals input to the sequential changeover switch 24 in this order in the channel order are shown as first to eighth channel electrical transmission signals 13 in FIG.

  In addition to the first to eighth channel electrical transmission signals 13, a transmission-side switch control signal 29 output from the transmission-side switch control signal generator 28 is input to the changeover switch 24. The first to eighth channel electrical transmission signals 13 are switched for each channel in synchronization with the transmission side switch control signal 29 by the changeover switch 24 and are sequentially input to the delay lines 25-1 to 25-8. Done. That is, the first channel electric transmission signal is input to the delay line 25-1, the second channel electric transmission signal is input to the delay line 25-2, and the third channel electric transmission signal to the eighth channel electric transmission signal are similarly input. Input to delay lines 25-3 to 25-8, respectively.

  In the delay lines 25-1 to 25-8, a delay is given to the electrical transmission signals of the respective channels so that the electrical transmission signals of the adjacently input channels do not overlap on the time axis. That is, a delay is given to the electrical transmission signal of each channel so that the time slots distributed to each channel do not overlap. The lengths of the delay lines 25-1 to 25-8 are adjusted so that the delay amount sequentially increases. The electrical transmission signals of the respective channels output from the delay lines 25-1 to 25-8 are combined by the coupler 26 and output as the first to eighth channel electrical transmission signals 17.

<Second Optical Signal Channel Division Multiplexing Communication System According to Embodiment of the Present Invention>
With reference to FIG. 3, the structure and operation of the second optical signal channel division multiplexing communication system according to the embodiment of the present invention will be described. FIG. 3 is a schematic block diagram of a second optical signal channel division multiplexing communication system according to the embodiment of the present invention.

  The second optical signal channel division multiplexing communication system according to the embodiment of the present invention includes a transmission device 50 and a reception device 30. Since the receiving device 30 is the same as the receiving device provided in the first optical signal channel division multiplexing communication system of the embodiment of the present invention described above, the second optical signal channel division multiplexing communication of the embodiment of the present invention is used. Also in the system, the receiving device is shown as the receiving device 30. That is, the difference between the first optical signal channel division multiplexing communication system and the second optical signal channel division multiplexing communication system of the embodiment of the present invention is in the configuration of the transmission apparatus.

  Therefore, in the following description of the configuration and operation of the second optical signal channel division multiplexing communication system of the embodiment of the present invention, the transmission device 50 will be described. Here, as in the description of the first optical signal channel division multiplexing communication system of the embodiment of the present invention described above, the number of channels to be multiplexed is described as eight as an example.

  The transmission device 50 includes an electrical transmission signal generator 46, an optical pulse train generator 18, an optical pulse wavelength disperser 20, and an optical modulator 22. The difference from the transmission device 10 of the first optical signal channel division multiplexing communication system of the above-described embodiment of the present invention resides in the electric signal generator 46, the optical pulse train generator 18, the optical pulse wavelength disperser 20, and The optical modulator 22 is a common component in both systems.

  The electric transmission signal generator 46 converts the first to eighth channel parallel electric transmission signals 53-1 to 53-8 arranged in parallel on the same time axis into serial electric transmission signals 55 arranged serially on the time axis. A parallel-serial converter 54 for conversion is provided.

  The parallel-serial converter 54 is configured to configure the first electrical transmission signal 55 on the condition that the wavelength spectrum components of the optical pulses constituting the first to eighth channel modulated optical transmission signals 43 are modulated differently. The transmission timing of the serial electrical transmission signal 55 is adjusted and output so that the transmission signal component of the eighth channel is input to the optical modulator 22.

  The optical modulator 22 receives the diffuse optical pulse train 21 and the serial electrical transmission signal 55, modulates the diffuse optical pulse train with the serial electrical transmission signal 55, and sequentially generates the first to N-th channel modulated optical transmission signals 43. Output.

  The first to eighth channel modulated optical transmission signals 23 output from the transmission apparatus 10 of the first optical signal channel division multiplexing communication system according to the embodiment of the present invention described above are a group of transmission signals for each channel. It is a signal that is arranged on the axis in order from the first channel electrical transmission signal to the eighth channel electrical transmission signal. That is, the first to eighth channel modulated optical transmission signals 23 are configured to be time-multiplexed with the transmission signal for each channel as a unit.

  On the other hand, the first to eighth channel modulated optical transmission signals 43 output from the transmission device 50 of the second optical signal channel division multiplexing communication system are the first channel electric transmission signals converted into serial electric transmission signals. The 1st to 8th channel first bits constituting the 53-1 to 8th channel electric transmission signals 53-8 are arranged in the order of the 1st to 8th channels, and then the second bit is the 1st to 8th bits. They differ in that they are arranged on the time axis in the order of channels, and the third and subsequent bits are arranged in the same order. That is, the first to eighth channel modulated optical transmission signals 43 are configured to be time-multiplexed in bit units.

  The structure and operation of the parallel-serial converter 54 will be described with reference to FIG. FIG. 4 shows the parallel-serial converter 54 and the transmission control signal generator 58 and the first to eighth channel electric transmission signal generators 52-1 to 52-8 necessary for explaining the structure and the operation thereof. FIG.

  The parallel-serial converter 54 includes delay lines 55-1 to 55-8 and a coupler 56.

  A transmission control signal 59 is supplied from the transmission control signal generator 58 to each of the first to eighth channel electric transmission signal generators 52-1 to 52-8. With this transmission control signal 59, the transmission timings of the first to eighth channel parallel electric transmission signals 53-1 to 53-8 output from the first to eighth channel electric transmission signal generators 52-1 to 52-8 are set. Adjusted.

  In the delay lines 55-1 to 55-8, the first bit of the second channel electric transmission signal follows the first bit of the first channel electric transmission signal, and the first bit of the eighth channel electric signal sequentially on the time axis. Followed by the second bit of the first channel electric transmission signal, followed by the second bit of the second channel electric transmission signal, and then the second bit of the eighth channel electric signal, and so on. On the time axis, the last bit of the second channel electrical transmission signal follows the last bit of the first channel electrical transmission signal, and the last bit of the eighth channel electrical transmission signal in sequence on the time axis. A time delay is given to the first channel electric transmission signal 53-1 to the eighth channel electric transmission signal 53-8 so that the signal bits are arranged at the same time.

  The electrical transmission signals of the respective channels output from the delay lines 55-3 to 55-8 are combined by the coupler 56 and output as the serial electrical transmission signal 55.

<Received signal reproduction unit>
With reference to FIG. 5, the configuration and operation of the first received signal regeneration unit 36 included in the receiving device 30 of the first and second optical signal channel division multiplexing communication systems according to the embodiment of the present invention will be described. FIG. 5 is a schematic block configuration diagram of the first received signal reproducing unit 36. Since the second to eighth received signal reproducing units included in the second receiving unit 40 to the eighth receiving unit 44 have the same configuration and operation, the first received signal reproducing unit 36 is used here as an example. This will be taken up as a representative.

  The first received signal reproduction unit 36 converts a first channel optical demodulated received signal 35-1 output from the first optical pulse demodulator 34 into a first channel electric demodulated signal 61 in the form of an electric signal (Photodiode : PD) 60, an amplifier 62 that amplifies the first channel electrical demodulated signal 61 and outputs it as a first channel electrical demodulated signal 63, and a clock data recovery (CDR) circuit 64. Yes.

  The CDR circuit 64 includes a distributor 68, a band pass filter 72, and a D-FF (D-flip flop) circuit 70. The distributor 68 branches the first channel electrical demodulated signal 63 into a branched first channel electrical demodulated signal 68-1 and a branched first channel electrical demodulated received signal 68-2.

  The branched first channel electrical demodulated signal 68-2 is input to a band pass filter 72 that regenerates the clock signal 73 by filtering a frequency component equal to the bit rate frequency of the first channel optical demodulated reception signal 35-1. That is, from the band pass filter 72, the clock signal 73 regenerated from the first channel optical demodulated reception signal 35-1 is output.

  The branched first channel electrical demodulated signal 68-1 and the clock signal 73 are input to the D-FF circuit 70, and the first channel electrical reproduction reception signal 37 is generated from the D-FF circuit 70 and output.

  The configuration of the CDR circuit 64 included in the first reception signal reproducing unit 36 shown in FIG. 5 is a well-known configuration that is generally used to shape the time waveform of an electrical reception signal received with a distorted time waveform. It is an electric circuit.

  The time waveform of the first channel optical demodulated reception signal 35-1 obtained by being demodulated by the first optical pulse demodulator 34 is distorted in shape and includes noise components. The time waveforms of the first channel electrical demodulated signal 61, the first channel electrical demodulated signal 63, and the branched first channel electrical demodulated signal 68-1 have the same distortion and also include noise components.

  Therefore, the CDR circuit 64 generates the first channel electric reproduction reception signal 37 in which the time waveform is shaped and the noise component is removed.

<Encoding>
The encoding will be described with reference to FIGS. 6 (A) to 8 (C).

  First, in describing the encoding, with reference to FIGS. 6 (A) to 6 (D), the signal is output from the optical pulse train generator 18 included in the transmission device 10 described with reference to FIG. The optical pulse train 19 and the diffused optical pulse train 21 output from the optical pulse wavelength disperser 20 will be described.

  6 (A) to 6 (D) are diagrams for explaining the generation method of the diffused optical pulse train 21 used when generating the first to eighth channel modulated optical transmission signals 23 and the properties of the diffused optical pulse train 21. FIG. 6 (A) is a diagram showing a time waveform of the optical pulse train 19, and FIG. 6 (B) is a diagram showing a wavelength spectrum of the optical pulses constituting the diffused optical pulse train 21, and FIG. FIG. 6C is a diagram for explaining the overlapping state of the optical pulses constituting the diffused optical pulse train 21 on the time axis. FIG. 6D is a diagram illustrating the optical pulses constituting the diffused optical pulse train 21 on the time axis. It is a figure where it uses for description of wavelength distribution.

  In FIGS. 6 (A), 6 (C), and 6 (D), the horizontal axis represents the time axis, and in FIG. 6 (B), the horizontal axis represents the wavelength axis, and the scale is arbitrarily scaled. In each figure, the vertical axis is omitted, but the intensity is shown in an arbitrary scale.

As shown in FIG. 6A, the optical pulse train 19 is an optical pulse train in which a plurality of optical pulses are arranged at a time interval _Td . In FIG. 6 (A), three optical pulses are shown as representatives, and in order to make these three optical pulses distinguishable, the envelopes of the optical pulses are each made up of fine wavy lines (optical pulse 19-1). , A solid line (light pulse 19-2) and a rough wavy line (light pulse 19-3). Such an optical pulse train can be generated using a known technique such as a mode-locked laser. The full width at half maximum of the time waveform of the optical pulse constituting the optical pulse train 19 need only be as wide as ps (picoseconds), and does not need to have a very narrow full width at half maximum in the fs (femtosecond) region. . This is because the optical pulse wavelength disperser 20 employs a technique of extending the time width of the optical pulse that constitutes the optical pulse train 19.

  The optical pulse train 19 is converted by the optical pulse wavelength disperser 20 into a diffused optical pulse train 21 with the full width at half maximum of the time waveform of the constituent optical pulses expanded. The optical pulse wavelength disperser 20 can be formed by using a known element such as a chirped grating type FBG formed so that the period of the periodic effective refractive index distribution gradually changes in the propagation direction. . The optical pulse wavelength disperser 20 can also be formed by a dispersion compensating optical fiber or the like.

As shown in FIG. 6 (B), the wavelength spectrum of the optical pulse constituting the diffused optical pulse train 21 has a center wavelength of λ _s and a full width at half maximum of Δλ _s . Further, the wavelength spectrum of the optical pulse constituting the diffused optical pulse train 21 has a shape that can be approximated by a curve representing a Gaussian function having a single maximum. In other words, the light pulse that forms the diffused light pulse train 21 is a single-wavelength light pulse.

The values of the center wavelength λ _s and the full width at half maximum Δλ _s are indispensable parameters when designing the SSFBG that constitutes the demodulator used when performing demodulation in the receiving apparatus 30 described later.

  In the time waveform of the diffused light pulse train 21 output from the optical pulse wavelength disperser 20, adjacent optical pulses partially overlap on the time axis as shown in FIG. 6 (C).

  Each optical pulse constituting the diffused optical pulse train 21 is an optical pulse formed by wavelength-dispersing each optical pulse constituting the optical pulse train 19 by the optical pulse wavelength disperser 20, so this optical pulse on the time axis Wavelength spectral components are separated and arranged in order. For example, when the wavelength dispersion characteristic of the optical pulse wavelength disperser 20 is such that the delay amount given to the short wavelength component is smaller than the delay amount given to the long wavelength component, the optical pulse train 19 is configured as shown in FIG. Each optical pulse is transformed into a shape arranged in the order of long wavelength to short wavelength along the direction of the time axis. Conversely, when the wavelength dispersion characteristic of the optical pulse wavelength disperser 20 has a smaller amount of delay given to the long wavelength component than the amount of delay given to the short wavelength component, in contrast to the shape shown in FIG. The shape is arranged in the order of short wavelength to long wavelength along the axial direction. In other words, the wavelength dispersion characteristic of the optical pulse wavelength disperser 20 may be any of the above-described relationships between the delay amount given to the long wavelength component and the delay amount given to the short wavelength component.

  With reference to FIG. 7 (A) to FIG. 7 (C), the encoding process of the first optical signal channel division multiplexing communication system according to the embodiment of the present invention will be described.

  FIGS. 7 (A) to 7 (C) are diagrams for explaining the encoding process of the first optical signal channel division multiplexing communication system according to the embodiment of the present invention. FIG. 7 (A) is a timing adjustment. FIG. 7 is a diagram showing time waveforms of the first to eighth channel electrical transmission signals 17 which are given to each channel by the device 16 and output after adjusting the time delay amount, and are shown in FIG. 7 (B-1) and FIG. 2) is a diagram showing how the wavelength spectrum components of the first channel and the second channel are cut out from the diffused light pulse train 21 by the first to eighth channel electrical transmission signals 17, and FIG. 7C is a diffused light pulse train. 21 is a diagram for explaining wavelength components that are cut out from the wavelength spectrum components of the optical pulses that form 21 and distributed to the first channel and the second channel. FIG.

  In Fig. 7 (A), Fig. 7 (B-1), and Fig. 7 (B-2), the horizontal axis is the time axis, and in Fig. 7 (C), the horizontal axis is the wavelength axis, and the scale is an arbitrary scale. It is shown. In each figure, the vertical axis is omitted, but the intensity is shown in an arbitrary scale.

  The first to eighth channel electric transmission signals 13 output from the serial electric transmission signal generator 12 are adjusted in time delay amount given to each channel by the timing adjuster 16, and the first to eighth channel electric transmission signals 17 are adjusted. Is output as As shown in FIG. 7 (A), the first to eighth channel electrical transmission signals 17 are signals in which the electrical transmission signals of the first channel to the eighth channel are grouped for each channel and sequentially arranged on the time axis. It is.

In FIG. 7A, the first channel electrical transmission signal is indicated as CH-1, the second channel electrical transmission signal as CH-2, and the eighth channel electrical transmission signal as CH-8. The time interval between the first channel electrical transmission signal CH-1 and the second channel electrical transmission signal CH-2 is set to σ ₁ , and the seventh channel electrical transmission signal (not shown) is omitted. )) And the eighth channel electric transmission signal CH-8 is set to σ ₇ . Further, the signal bits (time slot occupied by one electrical pulse) constituting each channel are indicated by a vertically long rectangle, and each channel can be identified by different hatching applied to the vertically long rectangle.

  In FIG. 7 (B-1), the envelopes of the three optical pulses constituting the diffused optical pulse train 21 are divided into fine wavy lines (optical pulse 19-1), solid lines (optical pulse 19-2), The time of the electric pulse constituting the first channel electric transmission signal CH-1 indicated by the rough wavy line (optical pulse 19-3) and serving to cut out each optical pulse constituting this diffused optical pulse train 21 on the time axis The position on the axis is indicated by a vertically long rectangle. FIG. 7 (B-2) is the same diagram as FIG. 7 (B-1), and the second channel electric transmission signal CH-2 is superimposed on the diagram showing the envelope of three optical pulses. The positions of the electric pulses that are configured on the time axis are indicated by vertically long rectangles.

  When comparing FIG. 7 (B-1) and FIG. 7 (B-2), the time axis of the electric pulse constituting the electric transmission signal CH-1 of the first channel and the electric transmission signal CH-2 of the second channel is shown. It can be seen that the existence positions at are different, and accordingly, the wavelength spectrum components extracted from the optical pulses constituting the diffused light pulse train 21 are different. Thus, by extracting different wavelength spectral components from the respective optical pulses constituting the diffused optical pulse train 21, it becomes possible to identify the channel, and the generation of the modulated optical transmission signal 23 by this extraction is encoded. Equivalent to.

The position on the time axis of the electric pulse of each channel constituting the first to eighth channel electric transmission signals 17 is determined by the timing adjuster 16, and as shown in FIG. The existence position is quantitatively given by a value such as σ ₁ indicating the time interval between the electric transmission signal CH-1 and the electric transmission signal CH-2 of the second channel. That is, the encoding process of each channel in the transmission apparatus 10 is determined by the parameter given by this σ ₁ or the like.

With reference to FIG. 7C, the optical pulse 19-2 constituting the diffused optical pulse train 21 is taken up, and the wavelength spectrum component distributed to the first channel and the second channel from the wavelength spectrum of the diffused optical pulse train 21 explain. As described with reference to FIG. 7 (B-1) and FIG. 7 (B-1), the existence position on the time axis of the electric pulse of each channel gives the time interval between adjacent channels σ Since it is determined by a value of ₁ or the like, the wavelength spectrum component of the diffused light pulse train 21 cut out by the first to eighth channel electrical transmission signals 17 is determined.

  As shown in FIG. 7 (C), the wavelength spectrum component distributed to the first channel is a wavelength spectrum component that fits in a vertically long rectangular area indicated as CH-1. The wavelength spectrum component distributed to the second channel is a wavelength spectrum component that fits in a vertically long rectangular area indicated as CH-2.

In FIG. 7 (C), only the wavelength spectrum components distributed to the first and second channels are shown so that the drawing is not complicated and difficult to see, but in reality, the first and second channels are shown in the first and second channels. Wavelength spectral components other than the wavelength spectral components distributed to the second channel are distributed. The wavelength spectral components distributed to the third to eighth channels are not shown, but are determined by the values of σ _{2 to} σ ₇ , and the values of σ _{1 to} σ ₇ are set to different values from each other. Yes.

  With reference to FIG. 8 (A) to FIG. 8 (C), the encoding process of the second optical signal channel division multiplexing communication system according to the embodiment of the present invention will be described.

  FIGS. 8 (A) to 8 (C) are diagrams for explaining the encoding process of the second optical signal channel division multiplexing communication system according to the embodiment of the present invention, and FIG. FIG. 8 is a diagram showing time waveforms of first to eighth channel electrical transmission signals 53-1 to 53-8 output from the eighth channel electrical transmission signal generators 52-1 to 52-8, respectively. ) Is a diagram showing a time waveform of the serial electrical transmission signal 55, and FIG. 8 (C) is a wavelength extracted from the wavelength spectrum component of the optical pulse constituting the diffused optical pulse train 21 and distributed to the first to eighth channels. It is a figure where it uses for description about a component.

  In FIG. 8 (A) to FIG. 8 (C), signal bits (time slots occupied by one electrical pulse) constituting each channel are indicated by a vertically long rectangle, and each channel is indicated by different hatching applied to this vertically long rectangle. Can be identified. In FIGS. 8 (A) to 8 (C), the horizontal axis shows the time axis on an arbitrary scale, and the vertical axis is omitted, but the intensity is shown on an arbitrary scale.

  FIG. 8 (A) shows the first to eighth channel electrical transmission signals 53-1 to 53-8 respectively output from the first to eighth channel electrical transmission signal generators 52-1 to 52-8 in order from the top. A time waveform is shown. In FIG. 8 (A), the electrical pulse of the signal constituting each channel is indicated by a vertically long rectangle, and each channel can be identified by different hatching applied to this vertically long rectangle.

  The phases of the first to eighth channel electrical transmission signals 53-1 to 53-8 output from the first to eighth channel electrical transmission signal generators 52-1 to 52-8, respectively, are transmitted from the transmission control signal generator 58. Although it is defined by the transmission control signal 59 to be output, as shown in FIG. 8 (B), the first bit of the first to eighth channel electrical transmission signals is finally set to the first by the parallel-serial converter 54. To the 8th channel, then the second bit is arranged on the time axis in the order of the 1st to 8th channels, and the phase is adjusted so that the 3rd and subsequent bits are arranged in the same order. Is done.

  FIG. 8 (C) is similar to the above-described FIG. 7 (B-1) and FIG. 7 (B-2), and each of the envelopes of the three optical pulses constituting the diffused optical pulse train 21 is finely divided. Indicated by a simple wavy line (light pulse 19-1), solid line (light pulse 19-2), and rough wave line (light pulse 19-3), and the role of cutting out each light pulse constituting this diffused light pulse train 21 on the time axis The positions on the time axis of the electric pulses constituting the first to eighth channel electric transmission signals CH-1 to CH-8 that fulfill the above are indicated by vertically long rectangles.

  As shown in FIG. 8 (C), the wavelength spectrum components distributed to the first to eighth channels are wavelength spectrum components that exist at positions that fall within a vertically long rectangular area indicated as CH-1 to CH-8. . As shown in FIG. 6 (D), the light pulses that make up the diffused light pulse train 21 are arranged in the order of long wavelength to short wavelength along the direction of the time axis. Depending on the position, the wavelength spectral components cut out differ. That is, unique wavelength spectrum components are cut out from the vertically long rectangular regions indicated by CH-1 to CH-8, and each channel is identified by the difference in the unique wavelength spectrum components.

  As described above, the optical modulator 22 makes it possible to identify channels by extracting different wavelength spectrum components from the respective optical pulses constituting the diffused optical pulse train 21, and generating the modulated optical transmission signal 43 by this extraction. Corresponds to encoding.

<Decryption>
Referring to FIGS. 9 (A) to 9 (C), details of SSFBG used in the optical pulse demodulator of each channel of the first and second optical signal channel division multiplexing communication systems of the embodiment of the present invention A simple structure will be described. FIGS. 9A to 9C are diagrams for explaining the optical pulse demodulator of each channel of the first and second optical signal channel division multiplexing communication systems according to the embodiment of the present invention.

  FIG. 9A is a schematic diagram of the SSFBG schematically showing the unit FBG as a rectangle, and FIG. 9B is a diagram schematically showing the refractive index modulation structure of the SSFBG. The horizontal axis is the position coordinate along the longitudinal direction of the optical fiber on which the SSFBG is formed. The vertical axis represents the refractive index modulation amount Δn of the optical fiber in a graph, and the refractive index modulation amount Δn means the difference between the maximum and minimum refractive indexes of the cores constituting the optical fiber. FIG. 9C is a partially enlarged graph showing the refractive index modulation amount Δn of the core of the optical fiber. In FIGS. 9 (A), (B), and (C), the value of M indicating the number of unit FBGs is 32, that is, SSFBG including 32 unit FBGs is shown as an example.

The period Λ of the refractive index periodic structure of the unit FBG determines the Bragg wavelength λ _b of the unit FBG described later. That is, when the average effective refractive index of the optical fiber constituting the SSFBG is n _eff , λ _b is given by 2 · n _eff Λ.

  In the description of the decoding, the following conditions are set for convenience of description, but the technical features of the contents described below are not affected even if the setting conditions are changed. Further, since the decoding process is common to the first and second optical signal channel division multiplexing communication systems of the embodiment of the present invention, in the following description, the description related to the first optical signal channel division multiplexing communication system Or a description regarding the second optical signal channel division multiplexing communication system.

The repetition period _Td of the optical pulse train 19 is set to 800 ps (= 1 / 1.25 GHz), the center wavelength of the wavelength spectrum of the optical pulse train 19 is 1549.3 nm, and the full width at half maximum Δλ _s of the wavelength spectrum of the optical pulse constituting the optical pulse train 19 is 0.64 nm (corresponding to 6 ps in terms of the full width at half maximum of the time waveform).

The chromatic dispersion amount D _p of the optical pulse wavelength disperser 20 was set to D _p = 800 ps × (1 / 0.64 nm) = 1250 ps / nm.

Further, the modulation speed in the optical modulator 22 was set to 1.25 Gb / s, and the modulation width was set to 100 ps or less. Since the repetition period _Td is 800 ps (= 1 / 1.25 GHz), the time slot corresponding to this repetition period is divided into 8 time slots, and each bit of the 1st to 8th channels is within this repetition period. It was set to fit one bit at a time.

  In the embodiment of the present invention, the full width at half maximum of the time waveform of the optical pulse constituting the optical pulse train 19 is 6 ps. For this reason, the wavelength band of the wavelength spectrum allocated to each channel of the first to eighth channels is a wavelength band that is cut out with two to three cutout positions per one optical pulse that constitutes the diffused optical pulse train 21. Become.

  That is, as shown in FIG. 7 (C), the vertically long rectangular region indicated by CH-1 has three locations per optical pulse constituting the diffused optical pulse train 21, and is indicated by CH-2. There are two vertically elongated rectangular regions per light pulse constituting the diffused light pulse train 21. Similarly, although not shown in FIG. 7C, the wavelength spectrum region allocated to CH-3 to CH-8 is also a wavelength band cut out with two to three cutout portions.

  By forming the SSFBG used for the optical pulse demodulator for each channel under the conditions described below, the first to eighth optical pulse demodulators in the receiving device 30 can generate optical demodulated signals for each channel. It becomes possible.

  Referring to FIGS. 10A and 10B, the first to eighth preconditions for the operation of the first to eighth optical pulse demodulators included in the first to eighth channel receiving units, respectively. The time waveform of the channel modulated optical transmission signal will be described. 10 (A) and 10 (B) are diagrams showing time waveforms of the first to eighth channel modulated optical transmission signals that are the premise for explaining the operation of the first to eighth optical pulse demodulators. (A) is a diagram schematically showing the wavelength spectrum component of the first channel cut out from each of the three optical pulses constituting the diffused optical pulse train 21, FIG. 10 (B) is the first channel FIG. 6 is a diagram schematically showing a time waveform of a modulated optical transmission signal 23 or 43 for 1 bit of FIG. In the embodiment of the present invention, modulation is performed by interference between wavelength components of an optical pulse, and a chip pulse train is generated.

  In the modulated optical transmission signal 35-2 input to the second optical pulse demodulator, the wavelength spectrum component assigned to the first channel is removed from the first to eighth channel modulated optical transmission signals 23 or 43. Similarly, the modulated optical transmission signals input to the third to eighth optical pulse demodulators lack the wavelength spectrum component removed by the optical pulse demodulator disposed at a position earlier than that, respectively. However, in the following explanation, even if there is this missing wavelength spectrum component, the wavelength spectrum component assigned to each channel is extracted from the remaining wavelength spectrum components, and the channel optical demodulation reception signal is obtained. Since it is generated, the missing wavelength spectral component has no effect on this decoding.

  The configuration and operation of the first optical pulse demodulator 34 will be described with reference to FIGS. 11 (A) and 11 (B). 11 (A) and 11 (B) are diagrams for explaining the configuration and operation of the first optical pulse demodulator 34. FIG. 11 (A) is a schematic diagram of the first optical pulse demodulator 34. FIG. 11 (B) is a diagram showing a configuration, and each of M (M ≧ 8) chip pulses constituting the chip pulse train input to the SSFBG included in the first optical pulse demodulator 34 is generated by the SSFBG. It is a figure explaining the process in which an autocorrelation wave or a cross-correlation wave is produced | generated by the interference of these total (MxM) chip pulses by converting into M chip pulses.

  In order to describe the decoding operation of the embodiment of the present invention more generally, the number of unit FBGs included in the SSFBG is not limited to eight and is expressed as M. In FIG. 11A, the SSFBG is configured with M unit FBGs, and the arrangement interval period of the unit FBGs is L.

  As shown in FIG. 11 (A), M optical pulse trains constituting the first to eighth channel modulated optical transmission signals are input from the first port of the optical circulator 74 and output to the second port to the SSFBG 76. The Bragg-reflected wavelength spectrum component is input to the second port again, and the modulated optical transmission signal including the wavelength spectrum component assigned to each channel is output from the third port.

  In FIG. 11B, the horizontal axis indicates the time axis T. In the vertical direction, M chip pulse trains obtained by converting each of the M chip pulses constituting the modulated optical transmission signal input to the SSFBG into M optical pulses by the SSFBG, These are shown in M stages, reflecting the relationship of the time delay output from SSFBG. The chip pulse train indicated as i = 1 is obtained by generating the first chip pulse of the chip pulses constituting the chip pulse train output from the encoder as a chip pulse train by the decoder. Similarly, the chip pulse train indicated as i = 2 to M is a chip pulse train generated as a chip pulse train by the decoder from the 2nd to Mth chip pulses constituting the chip pulse train output from the encoder. is there. As shown in Fig. 11 (B), chip pulse trains indicated as i = 1 to M overlap on the time axis and interfere with each other. As a result, the SSFBG that is a decoder outputs an autocorrelation wave or a cross-correlation wave. The

  In the following description, the number of channels is generally set to N without setting the number of channels to 8 so that the formula is easy to see because of the use of the formula.

The Bragg reflection wavelength λ _b of the unit FBG is expressed by the following equations (1a) and (1b)
λ _b = λ _s + {k + (1/2)} Δλ _s / N (1a)
(Where N is an even number and k is an integer in the range of -N / 2 to (N / 2) -1)
λ _b = λ _s + k · Δλ _s / N (1b)
(Where N is an odd number and k is an integer in the range of-(N-1) / 2 to (N-1) / 2)
Set to the value given by.

The full width at half maximum of the Bragg reflection wavelength band of the unit FBG, Δλ _b, is given by the following equation (2)
Δλ _b = Δλ _s = T _d / D _p (2)
Set to the value given by.

The arrangement period L of the adjacent unit FBG is expressed by the following equation (3)
L = {(λ _b −Δλ _b / 2) × (λ _b + Δλ _b / 2)} ÷ (2 · n _eff Δλ _b ) (3)
Set to the value given by.

The phase difference Θ of the Bragg reflected light from the adjacent unit FBG is expressed by the following equation (4)
Θ = (1/2) × λ _b = (1/2) × (λ _s + j · Δλ _s / N) (4)
Set to the value given by.

Where T _d is the repetition period of the optical pulse of the optical pulse train, D _p is the chromatic dispersion amount of the optical pulse wavelength disperser, λ _s is the peak wavelength of the wavelength spectrum of the optical pulse train output from the optical pulse train generator, Δλ _s Is the full width at half maximum of the wavelength spectrum of the optical pulse train, and n _eff is the effective refractive index of the optical fiber constituting the SSFBG.

  As described above, by setting the phase difference Θ of the Bragg reflected light, each channel described with reference to FIGS. 7 (A) to 7 (C) and FIGS. 8 (A) to 8 (C). The wavelength spectral component assigned to is determined. That is, for example, when the multiplexing number is 8 channels, the optical pulses constituting the diffused optical pulse train 21 set to the 1st to 8th channels by giving 1 to 8 respectively to the factor j in the formula (4) The cut-out position on the time axis is determined, and accordingly, the wavelength spectrum allocated to the first to eighth channels is determined.

  As already described with reference to FIG. 1 or FIG. 3, the first to eighth channel electrical transmission signals 17 or the serial electrical transmission signal 55 constitute the diffused light pulse train 21 set to the first to eighth channels. The cut-out position of the optical pulse on the time axis, that is, the phase for cutting out the optical pulse constituting the diffused optical pulse train 21 and determining the wavelength assigned to each channel is set to match the phase difference Θ of the Bragg reflected light described above. In addition, the phase is adjusted. In order to adjust the timing on the time axis of the optical pulses constituting the diffused optical pulse train 21 in this way, for example, the light of each channel output from the first to eighth optical pulse demodulators included in the receiving device. The delay amount of the transmission signal of each channel may be set by the timing adjuster 16 or the parallel-serial converter 54 so that the intensity of the demodulated reception signal is maximized.

As shown in FIG. 7 (C), the full width at half maximum of the optical pulse constituting the diffused light pulse train 21 is Δλ _s , and the wavelength on the short wavelength side giving this full width at half maximum Δλ _s is λ ₁ and the wavelength on the long wavelength side Is λ ₂ . The pulse period t _b of the chip pulse train in FIG. 10 (B) is given by the following equation (5).
t _b = {1 / c} × {(λ ₁・ λ ₂ ) / Δλ _s } (5)
Here, c is the speed of light. Further, Δλ _s = λ ₂ −λ ₁ (λ ₂ > λ ₁ ).

Central wavelength lambda _s of the wavelength spectrum of the chip pulse train a 1.55 .mu.m, if [Delta] [lambda] _s is 0.64 nm, t _b is approximately 12.5 ps.

Also, set the wavelength λ _b of the Bragg reflected light of the unit FBG to a value given by the following equation (6),
λ _b = (λ ₁ + λ ₂ ) / 2 = λ ₁ + Δλ _s / 2 = λ ₂ −Δλ _s / 2 (6)
And the arrangement period L of the adjacent unit FBG is expressed by the following equation (7)
L = (c × t _b ) / (2n _eff ) (7)
Set to the value represented by.

The phase difference of the Bragg reflected light that is reflected from the adjacent units FBG constituting the SSFBG 76, as given by the following equation (8), the arrangement period L of the Bragg reflection wavelength lambda _b and unit FBG of each unit FBG is set ing.
2π × 2 × L × n _eff / λ _b = 2π × (m + (1/2)) (8)
Here, m is an integer of 0 or more.

The phase difference φ between the chip pulses that are Bragg-reflected from the adjacent unit FBG is given by the following equation (9).
φ = 2π × 2 × L × n _eff / λ _x = 2π × (m + (1/2)) × λ _b / λ _x (9)
Here, x = 1 or 2.
That is,
φ = 2π × (m + (1/2)) × (1+ (Δλ _s / 2λ ₁ ))
Or
= 2π × (m + (1/2)) × (1− (Δλ _s / 2λ ₂ ))
Or
φ = π + {2π × (m + (1/2)) × (Δλ _s / λ ₁ )
Or
= Π− {2π × (m + (1/2)) × (Δλ _s / λ ₂ )
It becomes. That is, the value of φ is determined by the magnitude of Δλ _s .

Chip pulse generated by the transmitter 10 or 50 and output with the phase Δφ _e , i.e., the i-th chip constituting the chip pulse train input to the first port of the optical circulator 74 in FIG. Assuming that the pulse is decoded by the j-th unit FBG of SSFBG 76 and added with a phase Δφ _d , this chip pulse is based on the first chip pulse of the chip pulse train output from SSFBG 76. Is the following formula (10)
Δφ _ij = j × Δφ _e + j × Δφ _d (10)
Has a phase Δφ _ij given by

  As shown in FIG. 11B, each of the M chip pulses constituting the chip pulse train input to the SSFBG 76 is converted into M chip pulses by the SSFBG 76. As a result, a total of (M × M) chip pulses are generated. Each chip pulse of the M chip pulses generated by the transmitter 10 or 50 becomes a chip pulse train consisting of M chip pulses again by the SSFBG 76, and self-interference occurs due to the overlap of these chip pulse trains on the time axis. Correlation waves or cross-correlation waves are generated.

The phase Δφ _jj (T) of chip pulses overlapping on the time axis at time T = j + j is expressed by the following equation (11)
Δφ _jj (T) = T × Δφ _d + (Δφ _e −Δφ _d ) × j (11)
Given in.

When Δφ _e = Δφ _d = Δφ, Δφ _jj (T) = T × Δφ, and all chip pulses interfere with each other in the same phase at time T regardless of the value of j. That is, a very large peak is formed at time T, and an autocorrelation wave is formed.

On the other hand, when Δφ _e and Δφ _d are different, the phase Δφ _ij (T) of the chip pulses that overlap on the time axis at time T = i + j has different values of Δφ _ij (T) depending on the value of j. As a result, the chip pulses cancel each other out due to interference, and a peak is not formed but a cross-correlation wave is formed.

  According to the first and second optical signal channel division multiplexing communication systems of the present invention, it is possible to narrow the wavelength grid in response to increasing the number of channels to be multiplexed. For example, the wavelength grid can be set to 0.1 nm or less. Moreover, the wavelength spectrum assigned to each channel does not vary.

The SFBBG unit FBG Bragg reflection wavelength λ _{b of} the optical pulse demodulator installed in each channel of the receiving device 30 or the arrangement period L of the unit FBG of the optical pulse constituting the diffused optical pulse train 21 The pseudo OCDM is realized by setting the center wavelength λ _s and the full width at half maximum Δλ _s of the wavelength spectrum and the factor j in the equation (4) for determining the wavelength spectrum component assigned to each channel for each channel.

10, 50: Transmitter
12: Serial electrical transmission signal generator
16: Timing adjuster
18: Optical pulse train generator
20: Optical pulse wavelength disperser
22: Optical modulator
24: Changeover switch
25-1 to 25-8, 55-1 to 55-8: Delay line
26, 56: Coupler
28: Transmitter side switch control signal generator
30: Receiver
32: First receiver
34: First optical pulse demodulator
36: First received signal regeneration unit
40: Second receiver
44: 8th receiver
46: Electric transmission signal generator
52-1 to 52-8: 1st to 8th channel electric transmission signal generator
54: Parallel-serial converter
58: Transmission control signal generator
60: Photodiode (PD)
62: Amplifier
64: CDR circuit
68: Distributor
70: D-FF (D-FF) circuit
72: Bandpass filter
74: Optical circulator
76: SSFBG

Claims (5)

1st to Nth channels (N is an integer of 2 or more) Serial electrical transmission signal generating step for sequentially outputting electrical transmission signals on a time axis;
An optical pulse train generation step for outputting an optical pulse train in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis;
A diffused optical pulse train is generated by linearly diffusing successive wavelength spectrum components of the optical pulse on the time axis so that adjacent optical pulses constituting the optical pulse train overlap on the time axis. Output optical pulse chromatic dispersion step;
An optical modulation step of modulating the diffused optical pulse train with the first to N-th channel electrical transmission signals to sequentially generate and output first to N-channel modulated optical transmission signals;
A timing adjustment step of adjusting a transmission timing of the first to N-th channel electrical transmission signals so that wavelength spectrum components of optical pulses constituting the first to N-th channel modulated optical transmission signals are different from each other. Receiving the first to N-th channel modulated optical transmission signals, demodulating the first to N-th channel modulated optical transmission signals, and outputting the first to N-th electrical regeneration reception signals, respectively. Including 1st to Nth receiving steps,
The j-th receiving step (j is an integer from 1 to N) generates the j-th channel optical demodulated received signal from the received first to N-th channel modulated optical transmission signals and outputs the j-th channel demodulated received signal. A channel light pulse demodulation step;
An optical signal channel division comprising a reception step including a j-th channel reception signal regeneration step of receiving the j-th channel optical demodulation reception signal and generating and outputting a j-th channel electrical regeneration reception signal Multiple communication method. 1st to Nth channels arranged in parallel on the same time axis (N is an integer of 2 or more) Parallel-serial that converts parallel electrical transmission signals into serial electrical transmission signals that are serially arranged in sequence on the time axis A conversion step;
An optical pulse train generation step for outputting an optical pulse train in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis;
A diffused optical pulse train is generated by linearly diffusing successive wavelength spectrum components of the optical pulse on the time axis so that adjacent optical pulses constituting the optical pulse train overlap on the time axis. Output optical pulse chromatic dispersion step;
An optical modulation step of modulating the spread optical pulse train with the serial electrical transmission signal to sequentially generate and output first to N-th channel modulated optical transmission signals; and the first to N-th channel modulation Receiving first optical transmission signals, demodulating the first to N-th channel modulated optical transmission signals, and respectively including first to N-th reception steps for outputting first to N-th electric regeneration reception signals,
The j-th receiving step (j is an integer from 1 to N) generates the j-th channel optical demodulated received signal from the received first to N-th channel modulated optical transmission signals and outputs the j-th channel demodulated received signal. A channel light pulse demodulation step;
A reception step including a j-th channel reception signal regeneration step of receiving the j-th channel optical demodulation reception signal and generating and outputting a j-th channel electrical regeneration reception signal;
In the parallel-serial conversion step, the first electrical signal constituting the serial electrical transmission signal is modulated under a condition that the wavelength spectrum components of the optical pulses constituting the first to N-th channel modulated optical transmission signals are modulated differently. An optical signal channel division multiplex communication method comprising adjusting and outputting the transmission timing of the transmission signal component of the Nth channel. 1st to Nth channels (N is an integer of 2 or more), a serial electrical transmission signal generator that sequentially outputs electrical transmission signals on a time axis,
An optical pulse train generator for outputting an optical pulse train in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis;
The wavelength spectrum component of the optical pulse is linearly diffused on the time axis so that a portion where adjacent optical pulses constituting the optical pulse train overlap on the time axis is generated and output. An optical pulse wavelength disperser;
The diffused optical pulse train and the first to Nth channel electrical transmission signals are input, and the diffused optical pulse train is modulated with the first to Nth channel electrical transmission signals to obtain first to Nth channel modulated optical transmission signals. An optical modulator that sequentially generates and outputs
The transmission timing of the first to N-th channel electrical transmission signals input to the optical modulator is adjusted so that the wavelength spectrum components of the optical pulses constituting the first to N-th channel modulated optical transmission signals are different from each other. A transmitter comprising a timing adjuster; and receiving the first to Nth channel modulated optical transmission signals, respectively, demodulating the first to Nth channel modulated optical transmission signals, and Comprising first to Nth receivers for outputting electrical regeneration reception signals;
A j-th receiving unit (j is an integer from 1 to N) generates a j-th channel optical demodulated reception signal from the received first to N-th channel modulated optical transmission signals and outputs it. A channel optical pulse demodulator;
An optical signal channel comprising: a receiving device including a j-th channel reception signal regeneration unit that receives the j-th channel optical demodulation reception signal and generates and outputs a j-th channel electrical regeneration reception signal. Division multiplexing communication system. 1st to Nth channels arranged in parallel on the same time axis (N is an integer of 2 or more) Parallel-serial that converts parallel electrical transmission signals into serial electrical transmission signals that are serially arranged in sequence on the time axis An electrical transmission signal generator comprising a converter;
An optical pulse train generator for outputting an optical pulse train in which optical pulses having a single maximum in the wavelength spectrum are arranged at equal intervals on the time axis;
A diffused optical pulse train is generated by linearly diffusing successive wavelength spectrum components of the optical pulse on the time axis so that adjacent optical pulses constituting the optical pulse train overlap on the time axis. An output optical pulse wavelength disperser;
An optical modulator that receives the spread optical pulse train and the serial electrical transmission signal, modulates the diffuse optical pulse train with the serial electrical transmission signal, and sequentially generates and outputs first to N-th channel modulated optical transmission signals When,
And a first to Nth electric regeneration reception signal by receiving the first to Nth channel modulated optical transmission signals and demodulating the first to Nth channel modulated optical transmission signals, respectively. Comprising 1st to Nth receivers,
A j-th receiving unit (j is an integer from 1 to N) generates a j-th channel optical demodulated reception signal from the received first to N-th channel modulated optical transmission signals and outputs it. A channel optical pulse demodulator;
A receiving device comprising a j-th channel reception signal regeneration unit that receives the j-th channel optical demodulated reception signal and generates and outputs a j-th channel electrical regeneration reception signal;
The parallel-serial converter is configured to configure the first serial electrical transmission signal under a condition that wavelength spectrum components of optical pulses constituting the first to N-th channel modulated optical transmission signals are modulated differently. An optical signal channel division multiplexing communication system that adjusts the transmission timing of the serial electrical transmission signal so that the transmission signal component of the Nth channel is input to the optical modulator. The j-th channel optical pulse demodulator
M (M is an integer satisfying N ≦ M.) Comprising a superlattice structure fiber black grating comprising unit fiber black gratings,
The Bragg reflection wavelength λ _b of the unit fiber black grating is set to a value given by the following equations (1a) and (1b):
λ _b = λ _s + {k + (1/2)} Δλ _s / N (1a)
(Where N is an even number and k is an integer in the range of -N / 2 to (N / 2) -1)
λ _b = λ _s + {k + (1/2)} Δλ _s / N (1b)
(Where N is an odd number and k is an integer in the range of-(N-1) / 2 to (N-1) / 2)
The full width at half maximum Δλ _b of the Bragg reflection wavelength band of the unit fiber black grating is set to a value given by the following equation (2):
Δλ _b = Δλ _s = T _d / D _p (2)
The arrangement period L of the adjacent unit fiber black gratings is set to a value given by the following equation (3):
L = {(λ _b −Δλ _b / 2) × (λ _b + Δλ _b / 2)} ÷ (2 · n _eff Δλ _b ) (3)
The phase difference Θ of Bragg reflected light from the adjacent unit fiber Bragg gratings is set to a value given by the following equation (4) Θ = (1/2) × λ _b = (1/2) × ( λ _s + j · Δλ _s / N) (4)
5. The optical signal channel division multiplexing communication system according to claim 3 or 4,
Here, T _d is the repetition period of the optical pulse of the optical pulse train, D _p is the chromatic dispersion amount of the optical pulse chromatic dispersion device, λ _s is the peak wavelength of the wavelength spectrum of the optical pulse train output from the optical pulse train generator , Δλ _s is the full width at half maximum of the wavelength spectrum of the optical pulse train, and n _eff is the effective refractive index of the optical fiber constituting the superlattice structure fiber black grating.

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