JP4753135B2 - Optical code division multiple access system - Google Patents

Description

  The present invention relates to an optical code division multiplexing system and a coding apparatus used therefor.

  The optical code division multiple access (OCDMA) system is a system that occupies the same frequency band at the same time and is distinguished by a code that is a series of signal waveforms. The unit in which the bit interval is divided by the code length is called a chip. For example, if the data is “1”, the code assigned to that channel is sent, and if the data is “0”, a signal is sent in that bit interval. Do not put. In the conventional OCDMA system, multiplexing is performed depending on whether each code is present (OOK: on-off keying). In the OCDMA system, the optical signal encoded in this way is received by a receiver and decoded by an optical correlator. That is, when it coincides with the transmitted code, a signal is output and information “1” is obtained. This is because when the codes coincide with each other, they are integrated by the optical correlation operation, whereas when the codes are different, random values are obtained. By using this principle and designing the codes to be independent of each other, signals of many channels are multiplexed even in the same wavelength band.

Conventionally, an OOK data format has been used as a payload in an optical code division multiple access (OCDMA) system. This is because the PSK modulation format is often used for the optical code, so that they can be easily separated from the payload data. For example, in Japanese Patent No. 3038378 (Patent Document 1 below), payload information is encoded using different optical codes, a plurality of encoded information signals are multiplexed, and transmitted simultaneously using one transmission path, In addition, an optical code division multiplex communication system is disclosed in which a channel is separated by decoding an optical code assigned to the channel on the receiving side. However, multiple users can use multiple access interference (MAI) caused by using the same optical path and beat noise (noise) caused by two signals combined at the detector. It was done. Also, since the threshold value changes depending on factors such as the number of users and the optical path length, it is not easy to optimize the changing threshold value. Furthermore, since OOK is a data format that uses whether there is an optical signal or not, there is a problem in terms of security because a third party who intercepts the signal can easily decode the OOK information.
Japanese Patent No. 3038378

  An object of the present invention is to provide an OCDMA system that can reduce multiple access interference (MAI) and beat noise.

  An object of the present invention is to provide an OCDMA system in which a third party cannot easily intercept and analyze information.

  The optical code division multiplexing system of the present invention basically has a phase shift keying (PSK) data generation unit such as a phase modulator provided in the code unit of a conventional OCDMA system. The OCDMA system of the present invention, as confirmed by the theoretical calculation and examples described later, encodes by the encoder after modulating the phase of the pulse signal, so that it can provide an OCDMA system that can reduce MAI and beat noise. Based on knowledge.

  That is, the optical code division multiplexing system of the present invention has a phase shift keying (PSK) modulator (3) to which a pulse signal from a pulse light source (2) is input, and an output signal from the PSK modulator (3). An optical code division multiple access (OCDMA) encoder (4), a signal source (5) for supplying an electrical signal to the PSK modulator and the OCDMA system encoder, and the signal source comprising the PSK modulation And an optical code division multiplexing system of the present invention comprising an OCDMA system encoder comprising a controller and a controller (6) for controlling an electrical signal supplied to the OCDMA system encoder. As described above, the PSK modulator (3) performs phase modulation on the pulse signal, and the phase-modulated optical signal is multiplexed by the encoder, so that an OCDMA system that can reduce MAI and beat noise can be provided. In the figure, reference numeral 7 denotes an arbitrary matching unit for adjusting a modulation signal to the phase modulator. For example, the matching unit may convert information into a data format such as DPSK described later in accordance with a control command from the control unit.

  According to the present invention, by providing a phase modulator or the like in front of the encoder, it is possible to provide an OCDMA system that can reduce MAI and beat noise as confirmed by theoretical calculation and examples described later.

  An object of the present invention is to provide an OCDMA system in which information cannot be easily intercepted and analyzed by a third party because encoding is performed using PSK data instead of OOK data as in the prior art.

1. Encoder
1.1. Basic Configuration of Encoding Device The encoding device of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a coding apparatus according to the present invention. As shown in FIG. 1, the OCDMA system encoder (1) of the present invention basically includes a phase shift keying (PSK) modulator (3) to which a pulse signal from a pulse light source (2) is input. , An optical code division multiplexing (OCDMA) encoder (4) to which an output signal from the PSK modulator (3) is input, and a signal for supplying an electrical signal to the PSK modulator and the OCDMA system encoder And a control unit for controlling an electric signal supplied from the signal source to the PSK modulator and the OCDMA system encoder.

  As the light source, the PSK modulator (phase modulator), the OCDMA encoder, the signal source, the control unit, etc., known ones used for optical information communication may be appropriately used. An example of the phase modulator is a phase modulator provided on a lithium niobium substrate. In that case, the light phase may be modulated by a bias voltage applied to the phase modulator. The OCDMA encoder is a 511 chip fiber grating to which an optical signal from the circulator and the circulator is input.

  What has a DPSK conversion part according to DPSK modulation is preferable. That is, the control unit may function so as to convert information into a DPSK modulated signal. In such a DPSK modulation conversion unit, unlike the normal PSK modulation, the difference from the previous signal is used as information, so that it is necessary to convert normal data into DPSK modulation. However, even if a third party intercepts this DPSK-modulated signal, it becomes more difficult to decrypt the intercepted optical signal, so that the security of information is increased and decryption is performed by a relatively simple decryption device. It will be possible.

  Such a control unit can be realized by a computer, for example. That is, such a computer includes an input device, an output device, a calculation unit, a control unit, and a storage unit. When data is input from the input device, the input data is stored in the storage unit. A memory such as an included buffer temporarily stores the data, and a control unit such as a CPU reads a control program stored in a main memory included in the storage unit, receives an instruction from the control program, and stores it. The read data is read out and converted into DPSK data by applying a predetermined calculation process.

  For example, if the DPSK modulation is “0” when there is no difference from the previous data and “1” when there is a difference, if the input data is 0000111100 and the initial data is π, Data after π may be converted to be πππ00π0πππ. Then, such a converted signal is transmitted to the signal source. The signal source is a phase modulator or an OCDMA encoder (preferably a phase modulator), and a bias voltage or a modulation signal is applied. The phase of the optical signal is ππππ00π0πππ. Adjust so that it is applied to the phase modulator. As a result, DPSK modulation is loaded.

  In the OCDMA encoder of the present invention, the modulation signal by the phase shift keying (PSK) modulator (3) may be a DQPSK modulation signal, and the control unit may convert data into a DQPSK modulation signal. In this case as well, information can be converted in the same manner as in the case of DPSK modulation. Note that DQPSK modulation uses a 90 ° phase difference (for example, a phase difference of 0, π / 2, π, 3π / 2 with respect to the previous signal) as quaternary information. The DPSK modulation method and the DQPSK modulation method are also one mode of the PSK modulation method.

1.2. Operation of Encoding Device Next, the encoding operation by the encoding device will be described. A pulse signal from the pulse light source (2) is input to a phase shift keying (PSK) modulator (3) such as a phase modulator. A modulation signal is applied to the phase modulator, whereby PSK data is placed on the pulse signal. Since the modulation signal applied to the phase modulator is preferably synchronized with the pulse light source, it is controlled so that the phase of a predetermined pulse signal can be modulated. What is necessary is just to adjust suitably the phase modulation amount of the optical signal by a phase modulator by the voltage amount etc. which are applied to a phase modulator.

  The pulse signal carrying the PSK modulation signal is input to an optical code division multiple access (OCDMA) encoder (4). The OCDMA encoder (4) encodes this pulse signal. Each code carries a PSK modulation signal, but the encoding by the encoder may be a normal encoding performed by an OCDMA encoder. That is, for each channel, a chip which is a unit obtained by dividing the bit interval by the code length is assigned, and when the signal is “1”, the signal is put on the assigned chip according to the channel. In this way, each OCDMA encoded signal is further loaded with a PSK modulated signal. Further, information indicating whether or not there is a sign may be expressed by phase modulation. In this case, for example, encoding is performed using an optical orthogonal code such as 0 and π. In this way, it is possible to obtain an OCDMA signal whose payload part is in the PSK data format.

  The optical signal encoded by the OCDMA system encoder in this way propagates through the propagation path (11). Although only one OCDMA system encoder is shown in FIG. 1, actually, a plurality of OCDMA system encoders are connected to one network, and a chip corresponding to each channel is assigned. Therefore, an OCDMA encoded signal encoded by each OCDMA system encoding device is input to the network.

2.Decryption device
2.1. Basic Configuration of Decoding Device FIG. 2 is a schematic diagram showing the basic configuration of the decoding device of the present invention. As shown in FIG. 2, the decoding apparatus of the present invention basically includes an OCDMA decoder (22) to which an optical signal propagated through the propagation path is input, and an optical signal output from the OCDMA decoder. An input branch path (23), a delay section (24) provided in one of the waveguides demultiplexed by the branch path, and a multiplexing section in which both waveguides branched by the branch path are combined ( 25), a photodetector (26a, 26b) provided in each of the two waveguides branched from the multiplexing unit, and a differencer (27) to which an output signal of the photodetector is input. The decoding device (21) for the OCDMA system.

  Note that the branch path, the multiplexing section, and the delay section may be configured by a Mach-Zehnder type waveguide having a delay means such as a 1-bit delay device on one arm. In this case, the multiplexing portion is an X branch, and the photodetector provided in the waveguide extending from each branch portion may be configured as a so-called dual pin photodiode.

2.2. Basic operation of decoding device The basic operation of the decoding device is described below. First, the optical signal propagated through the propagation path is input to the OCDMA decoder. Then, the OCDMA decoder performs decoding according to the format encoded by the encoder. The dual pin photodiode measures an input signal and a time delay applied to the input signal, and obtains a difference by a differentiator. In this way, DPSK decoding is achieved. By using DPSK modulation, the structure of the decoder can be facilitated.

  Specifically, an optical signal propagated through one arm of a Mach-Zehnder interferometer and an optical signal propagated through an arm having a 1-bit delay device are detected, and the difference between them is detected, thereby obtaining the previous information ( For example, since the difference from one chip before) can be easily analyzed, DPSK decoding can be easily performed. For example, if the phase of the signal input to the OCDMA demodulator is ππππ00π0πππ, the information analyzed by the Mach-Zehnder interferometer having a 1-bit delay device, the dual pin photodiode, and the differentiator is 0000111100. Since this decoding process is implemented by hardware, it can be performed very quickly. Furthermore, since the OCDMA signal itself is encoded by DPSK modulation or the like, it is difficult to analyze even if the signal is intercepted.

3.OCDMA system
3.1. Basic Configuration of OCDMA System FIG. 3 is a schematic diagram showing the basic configuration of the OCDMA system of the present invention. As shown in FIG. 3, the OCDMA system of the present invention includes a phase shift keying (PSK) modulator (3) to which a pulse signal from a pulse light source (2) is input, and an output from the PSK modulator (3). An optical code division multiple access (OCDMA) encoder (4) for inputting a signal; a signal source for supplying an electrical signal to the PSK modulator and the OCDMA system encoder; and the signal source includes the PSK modulation. And a control unit for controlling an electrical signal supplied to the OCDMA system encoder and a control unit for converting data into a DPSK modulation signal; and an OCDMA system encoding device (1); A propagation path (11) for propagating an optical signal encoded by the OCDMA system encoder; an OCDMA decoder (22) for receiving the optical signal propagated through the propagation path; and the OCDMA recovery A branch path (23) to which an optical signal output from the optical device is input, a delay section (24) provided in one of the waveguides demultiplexed by the branch path, and both of the branches branched by the branch path An optical detector (26a, 26b) provided in each of a multiplexing unit (25) where the waveguides are combined, two waveguides branched from the multiplexing unit, and an output signal of the photodetector are input An OCDMA system (31) comprising: an OCDMA system decoding device (21) comprising a differentiator (27).

  Since this OCDMA system includes the above-described encoding device and the above-described decoding device, the payload data is encoded as an OCDMA signal in the DPSK data format and decoded as described above.

  Hereinafter, the OCDMA system of the present invention will be described using embodiments. In this embodiment, theoretical calculation related to the OCDMA system of the present invention was performed. FIG. 4 is a diagram showing a model of the OCDMA system employed for performing the theoretical calculation.

  As shown in FIG. 4, in this model, an optical pulse generator, a phase modulator on which data is loaded, an OCDMA encoder, a star coupler to which an encoded signal is input, and an output signal from the star coupler Is provided with an OCDMA encoder, a Mach-Zehnder interferometer having a 1-bit delay unit on one arm, a dual pin photodiode, a difference unit, and a signal detector. Then, the data is converted into data in the DPSK data format by the DPSK encoder and applied as a modulation signal of the phase modulator. Thereby, data of the DPSK modulation method is generated.

Some users' clients are connected to the star coupler. Since encoded optical signals from a plurality of users are input to one star coupler, MAI is generated. In the following, we will theoretically calculate the noise included in the output. First, the light field in the Mach-Zehnder interferometer is E ₁ (t) in the arm without the 1-bit delay and E ₂ (t) in the arm with the 1-bit delay. It becomes as follows.

In the above formula, the subscript d indicates a target user (Target User), and the subscript i indicates other users. The first term in each equation indicates the target signal, and the second term indicates interference from other users. Where P represents the intensity of the optical signal (Power), ω represents the angular frequency of the optical signal, φ (t) represents the phase of the optical signal, D (t) represents the data phase, τ ₀ represents a 1-bit delay time, τ _i represents the delay time of user i, and m represents the number of other users.

  Beat noise occurs when performing OE conversion in a photodiode. In addition, thermal noise is generated in the electrical signal system. Considering these, the output current is as follows.

In the above equation, Tc represents a period, R represents a constant, n ₀ (t) represents a noise component (a term in which various noise components are combined), and Δω _{i, d} represents ω _i and ω _d Δ (ωτ) _{i, d} represents the difference between ωτ _i and ωτ _d , and Δφ (t, τ, τ ₀ ) _{i, d} represents φ (t, τ, τ ₀ ) _i and φ ( t, τ, τ ₀ ) _d difference. Note that the integrated value of n ₀ (t), which is the final term among the above, indicates receiver noise. In other words, the output current is proportional to the following values:

  In the above equation, the first term indicates a signal, the second term indicates a term according to MAI, the third term indicates first-order beat noise, the fourth term indicates second-order beat noise, and the final term is received. Indicates the noise of the vessel.

  Next, an experiment on the OCDMA system of the present invention was performed. FIG. 5 is a block diagram illustrating the setup of an OCDMA experiment in the example. As the phase modulator in the present embodiment, a phase modulator provided on a lithium niobium substrate was used. The phase was modulated by a bias voltage applied to the phase modulator. As the OCDMA encoder, a 511 chip fiber grating to which an optical signal from the circulator and the circulator is input was used. In the figure, EDFA is an erbium-doped optical fiber amplifier. Originally, an OCDMA encoder corresponding to the number of other users should be prepared, and these should be propagated together and analyzed for interference, but in this embodiment, for the sake of simplicity, modulation other than the target user is performed. An OOK signal using an intensity modulator was used, and an MAI was generated using an MAI generator and combined with an OCDMA signal in order to adjust kesai and K. As a control experiment, the phase modulator of the OCDMA encoder was replaced with an intensity modulator, and OOK modulation was performed. In the figure, VOA indicates a delay device.

  FIG. 6 is a block diagram for explaining the MAI generation unit in FIG. That is, this example assumes 8 users as other users, performs OCDMA encoding with a circulator and a fiber grating, and gives a delay of, for example, 0, 15 milliseconds,. .

  The high-frequency signal source generates a 10-GHz high-frequency electrical signal, divides the signal, and applies it to a mode-locked laser diode, a pulse pattern generator for application to the target user's phase modulator, and other user's intensity modulators Applied to the pulse pattern generator for. The mode-locked laser diode is a 1.8 ps pulse, demultiplexed after passing through an EDFA or bandpass filter, given a predetermined adjustable delay, adjusted the polarization with a polarization adjuster, and then phase modulated with a phase modulator I put a signal. In this phase modulation, an electric field is generated in the waveguide by a bias signal based on a voltage signal from the pulse pattern generator, and thus phase modulation is performed. The signal carrying the modulation signal was enhanced by EDFA. After that, the optical signal which was guided to the fiber grating of 511 chip through the circulator and encoded was again introduced into the circulator and propagated to the multiplexing part.

  On the other hand, the demultiplexed optical signal was intensity-modulated by an intensity modulator. Originally, it is desirable to multiplex using a circulator and a fiber grating in the same manner as described above, but this embodiment is for analyzing the influence of MAI and the like due to interference from other users. Then, OCDMA modulation by ordinary OOK was performed without performing phase modulation.

  The combined optical signal is amplified by an EDFA, decoded by a decoder composed of a circulator and a 511-chip fiber grating, and introduced into a Mach-Zehnder interferometer and a dual pin photodiode via an EDFA filter. did. The delay device provided on one arm of the Mach-Zehnder waveguide gave a delay of 100 ps. When analyzing the OCDMA signal in the OOK format, the Mach-Zehnder interferometer was removed, and the signal was detected using one photodiode (in the experiment, one diode of a dual pin photodiode). In this example, a signal was transmitted to a BER tester through a 7.5 GHz low-pass filter (LPF), and the BER (bit error rate) was measured.

  FIG. 7 is a graph (oscilloscope diagram) instead of a drawing showing an OSDMA signal after encoding when there is another user. FIG. 7A shows the state of interference when there is one other user in addition to the target user, and FIG. 7B shows the interference when there are eight other users in addition to the target user. The state of is shown. On the other hand, FIG. 8 is a graph (oscilloscope diagram) instead of a drawing showing an OSDMA signal after encoding when there is no other user. From FIG. 7A, FIG. 7B, and FIG. 8, it can be seen that as the number of other users increases, the interference increases.

  FIG. 9 is a graph instead of a drawing showing a pulse signal (modulated signal) when OCDMA encoding is performed by DPSK modulation. FIG. 9A shows an observation waveform of sampling light by an oscilloscope, and FIG. 9B shows a spectrum of an optical signal. The vertical axis | shaft of FIG.9 (b) is intensity | strength.

  FIG. 10 is a graph (an oscilloscope diagram) instead of a drawing showing a signal after encoding when OCDMA encoding is performed by DPSK modulation. FIG. 10A shows the target user only, and FIG. 10B shows the case where there are eight other users in addition to the target user.

FIG. 11 is a graph (oscilloscope diagram) instead of a drawing showing a signal after decoding when OCDMA encoding is performed by DPSK modulation. FIG. 11A shows only the target user, and FIG. 11B shows the case where there are eight other users in addition to the target user. In FIG. 11B, ξ ₁ indicating interference was −10.5 dB.

  FIG. 12 is a graph (oscilloscope diagram) instead of a drawing showing an eye pattern when OCDMA encoding is performed by DPSK modulation. FIG. 12A shows only the target user, and FIG. 12B shows the case where there are eight other users in addition to the target user. In any figure, the signal is thick due to MAI, beat noise, and the like. In FIG. 12B, the eye opening is smaller than that in FIG. 12A because of MAI caused by other users.

  However, also in the graph of FIG. 12B, the eye opening is large, the signals 1 and 0 are in opposite phases, and have a symmetrical shape. Since the eye is wide open, it can measure well even if noise appears and the eye narrows. Further, since the signals 1 and 0 are in opposite phases and have a symmetrical shape, the threshold value (Th) can be fixed to 0.

  FIG. 13 is a graph instead of a drawing showing a pulse signal (modulated signal) when OCDMA encoding is performed by OOK modulation. FIG. 13A shows an observation waveform of sampling light by an oscilloscope, and FIG. 13B shows a spectrum of an optical signal. The vertical axis | shaft of FIG.13 (b) is intensity | strength.

  FIG. 14 is a graph (an oscilloscope diagram) instead of a drawing showing a signal after encoding when OCDMA encoding is performed by OOK modulation. FIG. 14A shows the target user only, and FIG. 14B shows the case where there are eight other users in addition to the target user.

FIG. 15 is a graph (oscilloscope diagram) instead of a drawing showing a signal after decoding when OCDMA encoding is performed by OOK modulation. FIG. 15A shows the target user only, and FIG. 15B shows the case where there are eight other users in addition to the target user. In FIG. 15B, ξ ₁ indicating interference was −13.5 dB.

  Comparing FIG. 11 (b) and FIG. 15 (b), it can be seen that the effect of interference is smaller when the coding is performed by the DPSK modulation of the present invention.

  FIG. 16 is a graph (oscilloscope diagram) instead of a drawing showing an eye pattern when OCDMA encoding is performed by OOK modulation. FIG. 16A shows only the target user, and FIG. 16B shows the case where there are eight other users in addition to the target user. In either figure, the signal is thick due to MAI, beat noise, and the like. In FIG. 16 (b), the eye opening is smaller than that in FIG. 16 (a) because of MAI caused by other users.

  In the graph of FIG. 16B, since the signal corresponding to “0” is OFF (no intensity), the signal is asymmetric as a whole. Compared to the embodiment of FIG. 12B, the eye opening is small, so that measurement becomes difficult when noise is placed and the eye is narrowed. In this case, since the shape of the spectrum changes according to the number of users and the like, it is desirable to determine the threshold value after grasping the number of users in advance. That is, the threshold value changes depending on the number of other users, and it is difficult to determine an appropriate threshold value.

  FIG. 17 is a diagram for explaining a threshold value when OCDMA encoding is performed by PSK modulation (DPSK) modulation (example). FIG. 17A shows measured data, and FIG. 17B shows signal distribution. FIG. 18 is a diagram for explaining a threshold value when OCDMA encoding is performed by OOK modulation (comparative example). 18A shows actual measurement data, and FIG. 18B shows signal distribution.

  From FIG. 17, it can be seen that the signal, noise due to MAI, and beat noise are on the signal in the embodiment as described above. It can also be seen that the threshold value (Th) can be fixed to 0 since the eye is the target. It can be said that the BER corresponding to the overlapping portion of the signal corresponding to “0” and the signal corresponding to “1” is relatively small. On the other hand, it can be seen from FIG. 18 that the signal corresponding to “0” in the comparative example carries a square component of beat noise in addition to MAI, and the threshold value increases as the signal shape changes. You can see that it changes. Further, the BER is larger than that in the embodiment.

FIG. 19 is a graph instead of a drawing showing the interference level when the BER is 10 ⁻⁹ . The horizontal axis is the interference level and the unit is dB. On the other hand, the vertical axis represents the number of other users. As shown in FIG. 19, for example, when encoding is performed using a 511 chip FBG and the BER is 1 × 10 ⁻⁹ , the conventional OOK can use only up to 7 users, but the DPSK can use up to 13 users. It becomes. In any case, the number of users that can be used by the OSDMA system of the present invention increases.

FIG. 20 is a graph instead of a drawing showing the interference level when the BER is 6 × 10 ⁻⁵ . The horizontal axis is the interference level and the unit is dB. On the other hand, the vertical axis represents the number of other users. As shown in FIG. 20, for example, when encoding is performed using a 511 chip FBG and the BER is set to 1 × 10 ⁻⁹ , the conventional OOK can use only up to 7 users when the threshold value is fixed. Even if the threshold is optimized (optTh), only 8 users can use it. On the other hand, DPSK can use up to 17 users. The number of users that can be used by the OSDMA system of the present invention increases.

  FIG. 21 is a graph instead of a drawing showing the relationship between quasi (ξ) and Q penalty (dB) when the number of other users in the example (DPSK) and the comparative example (OOK) is changed. In the figure, K indicates the number of other users.

  FIG. 22 is a graph instead of a drawing showing the relationship of xi (ξ) when the number of other users K is changed in the example (DPSK) and the comparative example (OOK). In the figure, K indicates the number of other users. From FIG. 22, it can be seen that the embodiment improves about 3.5 dB to 4 dB.

  FIG. 23 is a graph instead of a drawing showing the relationship between BER and output in the example (DPSK) and the comparative example (OOK).

  As confirmed through the first and second embodiments, it can be seen that the OCDMA system of the present invention has an improved beat noise resistance of about 3 to 6 dB compared to the conventional system. This can increase the number of active users in the OCDMA network. Furthermore, in the OCDMA system of the present invention, it is only necessary to fix the threshold value to 0, so that it is not necessary to optimize the threshold value. In particular, in the conventional OCDMA system, it is necessary to optimize the threshold according to the number of users, but in the OCDMA system of the present invention, this is not necessary. Furthermore, if encoding is performed by PSK modulation such as DPSK modulation, it is possible to improve information security that a signal is not easily decoded when intercepted, compared to an OOK modulated signal.

  The OCDMA encoding apparatus and OCDMA system of the present invention can be suitably used in the field of optical information communication.

FIG. 1 is a schematic configuration diagram of a coding apparatus according to the present invention. FIG. 2 is a schematic diagram showing the basic configuration of the decoding apparatus of the present invention. FIG. 3 is a schematic diagram showing the basic configuration of the OCDMA system of the present invention. FIG. 4 is a diagram showing a model of the OCDMA system employed for performing the theoretical calculation. FIG. 5 is a block diagram illustrating the setup of an OCDMA experiment in the example. FIG. 6 is a block diagram for explaining the MAI generation unit in FIG. FIG. 7 is a graph (oscilloscope diagram) instead of a drawing showing an OSDMA signal after encoding when there is another user. FIG. 7A shows the state of interference when there is one other user in addition to the target user, and FIG. 7B shows the interference when there are eight other users in addition to the target user. The state of is shown. FIG. 8 is a graph (oscilloscope diagram) instead of a drawing showing the OSDMA signal after encoding when there is no other user. FIG. 9 is a graph instead of a drawing showing a pulse signal (modulated signal) when OCDMA encoding is performed by DPSK modulation. FIG. 9A shows an observation waveform of sampling light by an oscilloscope, and FIG. 9B shows a spectrum of an optical signal. The vertical axis | shaft of FIG.9 (b) is intensity | strength. FIG. 10 is a graph (an oscilloscope diagram) instead of a drawing showing a signal after encoding when OCDMA encoding is performed by DPSK modulation. FIG. 10A shows the target user only, and FIG. 10B shows the case where there are eight other users in addition to the target user. FIG. 11 is a graph (oscilloscope diagram) instead of a drawing showing a signal after decoding when OCDMA encoding is performed by DPSK modulation. FIG. 11A shows only the target user, and FIG. 11B shows the case where there are eight other users in addition to the target user. FIG. 12 is a graph (oscilloscope diagram) instead of a drawing showing an eye pattern when OCDMA encoding is performed by DPSK modulation. FIG. 12A shows only the target user, and FIG. 12B shows the case where there are eight other users in addition to the target user. FIG. 13 is a graph instead of a drawing showing a pulse signal (modulated signal) when OCDMA encoding is performed by OOK modulation. FIG. 13A shows an observation waveform of sampling light by an oscilloscope, and FIG. 13B shows a spectrum of an optical signal. The vertical axis in FIG. FIG. 14 is a graph (an oscilloscope diagram) instead of a drawing showing a signal after encoding when OCDMA encoding is performed by OOK modulation. FIG. 14A shows the target user only, and FIG. 14B shows the case where there are eight other users in addition to the target user. FIG. 15 is a graph (oscilloscope diagram) instead of a drawing showing a signal after decoding when OCDMA encoding is performed by OOK modulation. FIG. 15A shows the target user only, and FIG. 15B shows the case where there are eight other users in addition to the target user. FIG. 16 is a graph (oscilloscope diagram) instead of a drawing showing an eye pattern when OCDMA encoding is performed by OOK modulation. FIG. 16A shows only the target user, and FIG. 16B shows the case where there are eight other users in addition to the target user. FIG. 17 is a diagram for explaining a threshold value when OCDMA encoding is performed by PSK modulation (DPSK) modulation (example). FIG. 17A shows measured data, and FIG. 17B shows signal distribution. FIG. 18 is a diagram for explaining a threshold value when OCDMA encoding is performed by OOK modulation (comparative example). 18A shows actual measurement data, and FIG. 18B shows signal distribution. FIG. 19 is a graph instead of a drawing showing the interference level when the BER is 10 ⁻⁹ . The horizontal axis is the interference level and the unit is dB. On the other hand, the vertical axis represents the number of other users. FIG. 20 is a graph instead of a drawing showing the interference level when the BER is 6 × 10 ⁻⁵ . The horizontal axis is the interference level and the unit is dB. On the other hand, the vertical axis represents the number of other users. FIG. 21 is a graph instead of a drawing showing the relationship between quasi (ξ) and Q penalty (dB) when the number of other users in the example (DPSK) and the comparative example (OOK) is changed. In the figure, K indicates the number of other users. FIG. 22 is a graph instead of a drawing showing the relationship of xi (ξ) when the number of other users K is changed in the example (DPSK) and the comparative example (OOK). FIG. 23 is a graph instead of a drawing showing the relationship between BER and output in the example (DPSK) and the comparative example (OOK).

Explanation of symbols

1 Encoder for OCDMA system
2 Pulse light source
3 Phase shift keying (PSK) modulator
4 Optical Code Division Multiple Access (OCDMA) Encoder
5 signal source,
6 Control unit
11 Propagation path
21 Decoder for OCDMA system
22 OCDMA decoder
23 fork
24 Delay part
25 multiplexer
26 Photodetector (26a, 26b)
27 Differentiator
31 OCDMA system

Claims (4)

A phase shift keying modulator (3) for inputting a pulse signal from the pulse light source (2) and outputting a modulation signal obtained by modulating the phase of the pulse signal;
An optical code division multiple access encoder (4) that receives the modulation signal from the phase shift keying modulator and encodes the modulation signal ;
A first electric signal for modulating the phase of the pulse signal to the phase shift keying modulator, and a second electric signal for encoding the modulation signal to the optical code division multiple access encoder; a signal source for supplying (5),
A control unit (6) for controlling the first electric signal and the previous second electric signal supplied by the signal source,
The modulation signal by the phase shift keying modulator (3) is a differential four-phase phase shift keying signal ,
The optical code division multiple access encoder (4) is an encoding device for an OCDMA system that encodes the modulated signal from the phase shift keying modulator (3) by phase modulation .
The optical code division multiple access encoder (4)
A circulator to which an output signal from the phase shift keying modulator (3) is input;
The encoding apparatus for an OCDMA system according to claim 1, further comprising a 511-chip fiber grating to which an optical signal of the circulator is input.
The phase shift keying modulator (3)
The encoding device for an OCDMA system according to claim 1, wherein the encoding device is provided on a lithium niobium substrate.
A phase shift keying modulator (3) for inputting a pulse signal from the pulse light source (2) and outputting a modulation signal obtained by modulating the phase of the pulse signal;
An optical code division multiple access encoder (4) that receives the modulation signal from the phase shift keying modulator and encodes the modulation signal ;
A first electric signal for modulating the phase of the pulse signal to the phase shift keying modulator, and a second electric signal for encoding the modulation signal to the optical code division multiple access encoder; a signal source for supplying (5),
A control unit (6) for controlling the first electric signal and the previous second electric signal supplied by the signal source,
The modulated signal by the phase shift keying modulator (3) is a DQPSK modulated signal,
The optical code division multiple access encoder (4) is an OCDMA system encoder that encodes the modulated signal from the phase shift keying modulator (3) by phase modulation ;
A propagation path (11) for propagating the optical signal encoded by the encoding device for the OCDMA system;
An OCDMA decoder (22) to which an optical signal propagated through the propagation path is input;
A branch path (23) to which an optical signal output from the OCDMA decoder is input;
A delay unit (24) provided in one of the waveguides demultiplexed by the branch path;
A multiplexing section (25) where both waveguides branched by the branch path are combined;
A photodetector (26a, 26b) provided in each of the two waveguides branched from the multiplexing section;
A decoding device (21) for an OCDMA system comprising a differentiator (27) to which an output signal of the photodetector is input;
An OCDMA system (31) comprising: