JP2008219211A - Ocdma system of fsk data format - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OCDMA (optical code division multiple access) system which operates based on a pulse light, is hardly influenced by MAI and beat noise and is excellent in security. <P>SOLUTION: The problem is solved by a coding device (1) for the OCDMA system having an FSK (phase shift keying) modulator (2) for superimposing a frequency FSK modulation signal on a pulse signal from a pulse light source; a data control section (3) for controlling the data to be superimposed on the FSK modulator; and an OCDMA coding device (4) for multiplexing an output signal from the FSK modulator. The OCDMA system includes the coding device. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an OCDMA system of FSK data format. More specifically, the present invention relates to an OCDMA system in which the influence of noise and the like can be reduced and security can be improved by using payload data in the FSK data format.

  Conventionally, the OOK data format is used exclusively for the payload in OCDMA. This is because the PSK data format is often used for the optical code and it is easy to separate them 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.

Furthermore, since OOK is a data format that uses whether or not there is an optical signal as information, a third party who intercepted the signal can easily decode the OOK information, which has a problem in terms of security.
Japanese Patent No. 3038378

  An object of the present invention is to provide an OCDMA system that operates with pulsed light.

  An object of the present invention is to provide an OCDMA system that is not easily affected by MAI or beat noise.

  An object of the present invention is to provide an OCDMA system excellent in security.

  The present invention basically employs pulsed light in a conventional OCDMA system, and an FSK data generation unit is provided in the payload data generation unit in the encoding unit, so that the decoding unit can decode the FSK data. Things (especially those for balance detection).

  That is, the encoding device for the OCDMA system of the present invention controls the FSK modulator (2) for placing the frequency shift keying (FSK) modulation signal on the pulse signal from the pulse light source, and the data to be placed on the FSK modulator. An OCDMA system encoding apparatus (1), comprising: a data control unit (3) for controlling the output signal; and an optical code division multiple access (OCDMA) encoder (4) for multiplexing the output signal from the FSK modulator. About. This apparatus achieves OCDMA encoding using a pulse signal and an FSK modulation signal.

According to a preferred aspect of the encoding device for an OCDMA system of the present invention, the FSK modulator (2) includes a first sub Mach-Zehnder waveguide (MZ _A ) (12); and a second sub-Mach-Zehnder waveguide (MZ). _B ) (13); an optical signal input section (14), and the optical signal is sent to the first sub Mach-Zehnder waveguide (MZ _A ) and the second sub-Mach-Zehnder waveguide (MZ _B ). A branching section (15), the first sub Mach-Zehnder waveguide (MZ _A ), the second sub-Mach-Zehnder waveguide (MZ _B ), and the first sub-Mach-Zehnder waveguide (MZ); _A ) and an optical signal output from the second sub Mach-Zehnder waveguide (MZ _B ) are combined, and an optical signal combined at the multiplexer is output. Main Mach-Zehnder waveguide including optical signal output section (17) Road (MZ _C) (18) and; said first sub Mach-Zehnder waveguide (MZ _A) a first electrode (RF _A electrode) for inputting a radio frequency (RF) signal to the two arms composing the (19); and a second electrode (RF _B electrode) (20) for inputting a radio frequency (RF) signal to the two arms constituting the second sub Mach-Zehnder waveguide (MZ _B ); By applying a voltage to the main Mach-Zehnder waveguide (MZ _C ), an output signal from the first sub-Mach-Zehnder waveguide (MZ _A ) and the second sub-Mach-Zehnder waveguide (MZ _B ) An encoding device for an OCDMA system as described above, which is an optical modulator comprising a main Mach-Zehnder electrode (electrode C) (21) for controlling a phase difference with an output signal from the above. In an OCDMA system, pulse light is not normally used, and OOK modulation is common. The optical pulse period of the OCDMA system is high-speed, and it is difficult to perform FSK modulation with a normal apparatus. Therefore, in the present invention, the OCDMA encoding in which the FSK modulation signal is carried on the pulsed light is achieved by combining with the above FSK modulator and synchronizing with the pulsed light.

  According to a preferred aspect of the encoding apparatus for the OCDMA system of the present invention, the OCDMA encoder (4) includes a circulator (31) to which an output signal from the FSK modulator is input, and a fiber to which an optical signal from the circulator is input. An encoding apparatus for an OCDMA system according to any one of the above, comprising: a grating (FBG) (32); and an output path (33) for outputting an optical signal from the FBG input to the circulator. It is preferable that the OCDMA encoder (4) is also synchronized with the data control unit (3) described above. Then, information such as an optical payload is carried by the OCDMA encoder.

  According to a preferred aspect of the encoding device for the OCDMA system of the present invention, the OCDMA encoder (4) includes a first total reflection mirror (101a) on which pulsed light is incident and a first total reflection mirror (101a). The first diffraction grating (102a) to which the reflected light is incident and the diffracted light from the first diffraction grating (102a) is transmitted and the transmitted light is subjected to Fourier transform processing. The output light from the Fourier lens (103a) and the first Fourier lens (103a) enters, the mask (104) having a specific code pattern, and the output light from the mask (104) enters and enters. A second Fourier lens (103b) that performs inverse Fourier transform on the light, a second diffraction grating (102b) on which the output light of the second Fourier lens (103b) is incident, and the second diffraction A second total reflection mirror (101b) on which diffracted light from the grating (102b) is incident; To Bei is the coding device for OCDMA system described in any one. It is preferable that the OCDMA encoder (4) is also synchronized with the data control unit (3) described above. Then, information such as an optical payload is carried by the OCDMA encoder.

  According to a preferred aspect of the encoding device for the OCDMA system of the present invention, the OCDMA encoder (4) is decomposed into frequency spectrum components by the first AWG (111) on which pulsed light is incident and the first AWG. A phase modulator (112) corresponding to each channel for giving a phase change to each pulsed light, and a second AWG (113) to which output light from each phase modulator is input, It is the encoding apparatus for OCDMA systems described in any one. It is preferable that the OCDMA encoder (4) is also synchronized with the data control unit (3) described above. Then, information such as an optical payload is carried by the OCDMA encoder.

  According to a preferred aspect of the encoding device for the OCDMA system of the present invention, the OCDMA encoder (4) is configured to give a phase change to the AWG (121) and each pulse light decomposed into frequency spectrum components by the AWG. The encoding for an OCDMA system according to any one of the above, comprising: a phase modulator (122) corresponding to each channel; and a total reflection mirror 123 to which output light from each phase modulator (122) is input. Device. It is preferable that the OCDMA encoder (4) is also synchronized with the data control unit (3) described above. Then, information such as an optical payload is carried by the OCDMA encoder.

  According to a preferred aspect of the encoding device for the OCDMA system of the present invention, the OCDMA encoder (4) includes a plurality of variable optical taps (141) to which an optical pulse is input, and an optical connecting the variable optical taps (141). A delay line (142), an optical phase modulator (143) for adjusting the phase of each light demultiplexed from each variable optical tap (141), and output light from each optical phase modulator (143) The OCDMA system encoding apparatus according to any one of the above, comprising a multiplexer (144) for multiplexing the two. It is preferable that the OCDMA encoder (4) is also synchronized with the data control unit (3) described above. Then, information such as an optical payload is carried by the OCDMA encoder.

  The OCDMA system of the present invention receives an OCDMA system encoding device, a transmission line (41) through which an output signal from the OCDMA system encoding device is transmitted, and an optical signal that has passed through the transmission line (41). An OCDMA system including an OCDMA system decoding device, wherein the OCDMA system encoding device is the OCDMA system encoding device (1) described above, and the OCDMA system decoding device. (42) is a circulator (43) to which an optical signal passed through the transmission line (41) is input; a fiber grating (FBG) (44) to which an optical signal from the circulator is input; and the FBG input to the circulator An output path (45) for outputting an optical signal from: a demultiplexing section (46) for demultiplexing an optical signal passing through the output path (45); and demultiplexed by the demultiplexing section (46) An optical filter (48) provided in a waveguide (47) through which one of the lights propagates and transmits an upper sideband (USB) signal in the output signal; and the remaining wave separated by the demultiplexing unit (46) An optical filter (50) provided in a waveguide (49) through which light propagates, and transmits a lower sideband (LSB) signal among output signals; and an optical signal transmitted through the two optical filters (48, 50) This is an OCDMA system which is a decoding device (42) for an OCDMA system including a balance detector (51) to which.

  In a preferred aspect of the encoding device for the OCDMA system according to the present invention, the OCDMA encoder (4) converts the output signal from the FSK modulator into an upper sideband (USB) signal and a lower sideband (LSB) signal. A demultiplexing unit (61) for demultiplexing; a first circulator (62) to which a USB signal demultiplexed by the demultiplexer is input; and a first circulator for inputting an optical signal from the first circulator A first output path (64) for outputting an optical signal from the first FBG input to the circulator; and a first input path (64) for inputting the LSB signal demultiplexed by the demultiplexer. A second circulator (65); a second FBG (66) to which an optical signal from the second circulator is input; and a second FBG to which an optical signal from the second FBG input to the circulator is output. An output path (67): an output signal from the first output path and Serial output signal from the second output path; and a multiplexing unit which is combined (68), which is the coding device for OCDMA system described in any one. It is preferable that the OCDMA encoder (4) is also synchronized with the data control unit (3) described above. Then, information such as an optical payload is carried by the OCDMA encoder.

  A preferred embodiment of the OCDMA system according to the present invention includes an OCDMA system encoding device, a transmission line (41) through which an output signal from the OCDMA system encoding device is transmitted, and an optical signal transmitted through the transmission line (41). An OCDMA system including an input OCDMA system decoding device, wherein the OCDMA system encoding device is any one of the OCDMA system encoding devices (1) described above, and the OCDMA system encoding device The decoding device (71) receives the optical signal that has passed through the transmission line (41), and is demultiplexed by the demultiplexing unit (72); and one of the lights demultiplexed by the demultiplexing unit (72) An optical filter (74) provided in a propagating waveguide (73) and transmitting an upper sideband (USB) signal among output signals; a circulator (75) to which an output signal from the optical filter (74) is input; From the circulator A fiber grating (FBG) (76) to which an optical signal is input; an output path (77) from which the optical signal from the FBG input to the circulator is output; and demultiplexed by the demultiplexing unit (72) An optical filter (79) provided in a waveguide (78) through which the remaining light propagates and transmits a lower sideband (LSB) signal among output signals; and an output signal from the optical filter (79) is input A circulator (80); a fiber grating (FBG) (81) for inputting an optical signal from the circulator; and an output path (82) for outputting an optical signal from the FBG input to the circulator: the two This is an OCDMA system which is a decoding device (71) for an OCDMA system including a balance detector (83) to which an optical signal transmitted through an output path (77, 72) is input.

  According to the present invention, since the payload generation unit of the encoding unit is an FSK data generation unit, it is possible to provide an OCDMA system that operates with pulsed light. In particular, since an FSK data generation unit is formed using an optical FSK modulator including a main Mach-Zehnder waveguide including two sub-Mach-Zehnder waveguides and an electrode, an FSK signal having an extremely fast period is used. Thus, an OCDMA system that operates effectively with pulsed light can be provided. Furthermore, in the case of OOK modulation, a signal is generated depending on whether the light intensity is present or not, so that if the signal is intercepted, it is easily decoded. On the other hand, since FSK uses a frequency difference as a signal, the light intensity itself can be kept constant. That is, in general, a modulated signal can be obtained more easily with OOK, but by adopting FSK, payload data is less likely to be decoded even when an optical signal is intercepted. Therefore, an OCDMA system excellent in security can be provided.

  In the case of encoding by FSK modulation, decoding can be performed by balance detection. Decoding by balance detection increases resistance to MAI, beat noise, and the like, so that it is possible to provide an OCDMA system that is less susceptible to MAI and beat noise.

1. A first aspect of the present invention An encoding apparatus for an OCDMA system according to the first aspect of the present invention basically includes an FSK modulator for placing an FSK modulation signal on a pulse signal from a pulse light source, and an FSK modulation. A data control unit for controlling data to be placed on the unit, and an OCDMA encoder for multiplexing the output signal from the FSK modulator. Then, FSK information is superimposed on the pulse signal from the pulse light source by the phase modulator and multiplexed by the OCDMA encoder to obtain an OCDMA signal whose payload portion is in the FSK data format. The system of the present invention is a system for performing information communication by decoding a signal encoded by such an OCDMA system encoding apparatus.

  In the system of the present invention, the payload data is in the FSK data format, so that the influence of MAI, beat noise, etc. can be reduced as compared with the conventional OCDMA in the OOK data format. If it is in the OOK data format, it can be easily decrypted by a third party, but if it is in the FSK format, not only can the decoder be manufactured relatively easily, but also because the third party cannot easily decrypt it, the security of information is also improved. Will be.

1.1. FIG. 1 is a block diagram for explaining an OCDMA system encoding apparatus according to the present invention. As shown in FIG. 1, the OCDMA system encoding apparatus (1) includes an FSK modulator (2) for placing a frequency shift keying (FSK) modulation signal on a pulse signal from a pulse light source, and the FSK modulator. A data control unit (3) for controlling data to be placed on the optical signal, and an optical code division multiple access (OCDMA) encoder (4) for multiplexing the output signal from the FSK modulator.

  In the above encoding apparatus, an optical signal from a continuous (CW) light source can also be used, but since an FSK modulator for converting payload data into an FSK data format is used, a pulsed light source is used as the light source. OCDMA communication can be performed using such light. That is, according to the present invention, the pulse signal is subjected to FSK modulation and the FSK modulated signal is used as payload data. The FSK modulator itself is publicly known, and a data control unit for controlling the FSK modulated data may be appropriately used one used for the known FSK modulator. The data control unit switches between the USB signal and the LSB signal, which corresponds to 0 or 1. The data control unit and the pulse light source are connected, and the modulation signal (a signal for switching between the USB signal and the LSB signal) applied to the FSK modulator by the data control unit and the pulsed light are synchronized. It is preferable to switch between the USB signal and the LSB signal for each pulse signal. That is, it is preferable that the data control unit functions as a unit that adjusts information carried on the basic signal as the FKS signal.

FIG. 2 is a conceptual diagram illustrating an example of an FSK modulator. As shown in FIG. 2, as the FSK modulator (2), a first sub Mach-Zehnder waveguide (MZ _A ) (12); a second sub-Mach-Zehnder waveguide (MZ _B ) (13); An optical signal input unit (14) and a branching unit (15) for branching the optical signal to the first sub Mach-Zehnder waveguide (MZ _A ) and the second sub-Mach-Zehnder waveguide (MZ _B ) The first sub-Mach-Zehnder waveguide (MZ _A ), the second sub-Mach-Zehnder waveguide (MZ _B ), the first sub-Mach-Zehnder waveguide (MZ _A ), and the second sub-Mach-Zehnder waveguide (MZ _A ). A multiplexing unit (16) for multiplexing the optical signals output from the sub Mach-Zehnder waveguide (MZ _B ), and an optical signal output unit (17 for outputting the optical signals combined by the multiplexing unit) ) and the main Mach-Zehnder waveguide (MZ C) ₍₁₈₎ comprising; said first sub Mach-Zehnder waveguide (MZ _A) a first electrode (RF _A electrode) for inputting a radio frequency (RF) signal to the two arms composing the (19) and; the second sub Mach-Zehnder waveguide ( A second electrode (RF _B electrode) (20) for inputting a radio frequency (RF) signal to the two arms constituting MZ _B ); and applying a voltage to the main Mach-Zehnder waveguide (MZ _C ) _A main Mach for controlling a phase difference between an output signal from the first sub Mach-Zehnder waveguide (MZ _A ) and an output signal from the second sub-Mach-Zehnder waveguide (MZ _B ). An optical modulator comprising a Zender electrode (electrode C) (21) is mentioned.

The first electrode (RF _A electrode) (19) and the second electrode (RF _B electrode) (20) are output from, for example, the same power source, and delay one electrical signal by π / 2. The modulated signal is applied. This modulation frequency is the amount of shift of the optical signal. In the FSK modulator, information “0” or “1” is obtained by switching between the USB signal and the LSB signal. The switching of “0” or “1” is performed by the main Mach-Zehnder electrode (electrode C). This is achieved by controlling the voltage applied to (21).

  Therefore, the data control unit converts the information to be loaded as payload data for FSK modulation, temporarily stores it, issues a command to apply a voltage for realizing the converted conversion signal, and receives the command. Such a voltage value is output. The voltage signal thus controlled is applied to the main Mach-Zehnder electrode (electrode C) (21), so that predetermined information is put on the payload data as an FSK modulation signal.

  As the optical code division multiple access (OCDMA) encoder (4), a known one used as an OCDMA encoder can be used as appropriate, and an optical label or the like is generated. The optical label functions like a so-called address or address.

  Specifically, the OCDMA encoder (4) includes a circulator (31) to which an output signal from an FSK modulator is input; a fiber grating (FBG) (32) to which an optical signal from the circulator is input; And an output path (33) through which an optical signal from the FBG input to the circulator is output.

  The optical signal that has been FSK modulated by the FSK modulator is input to the circulator (31). Then, the optical signal from the circulator is input to the fiber grating (FBG) (32). Then, since the turning point differs depending on the wavelength of the FSK modulation signal, etc., it is multiplexed and OCDMA encoded. The optical signal from the FBG input to the circulator is output from the output path (33) and transmitted to the OCDMA decoding apparatus through the transmission path. Any known FBG can be used as appropriate.

1.2. OCDMA System of the Present Invention An OCDMA system of the present invention includes an OCDMA system encoding device, a transmission line (41) for transmitting an output signal from the OCDMA system encoding device, and an optical signal transmitted through the transmission line (41). An OCDMA system including an OCDMA system decoding apparatus to which a signal is input. The OCDMA system encoding device is the above-described OCDMA system encoding device (1). The decoding device (42) for the OCDMA system includes a circulator (43) to which an optical signal passed through the transmission line (41) is input; a fiber grating (FBG) (44) to which an optical signal from the circulator is input; An output path (45) for outputting an optical signal from the FBG input to the circulator; and a demultiplexing section (46) for demultiplexing an optical signal passing through the output path (45); An optical filter (48) provided in a waveguide (47) through which one of the lights demultiplexed by (46) propagates, and transmits an upper sideband (USB) signal among output signals; ) And an optical filter (50) that transmits the lower sideband (LSB) signal among the output signals, and is provided in the waveguide (49) through which the remaining light demultiplexed by (2) is propagated; and the two optical filters (48 , 50) and a balanced detector (51) to which an optical signal transmitted is transmitted. System decoding device (42).

  The configuration and operation of the encoding device for the OCDMA system are as described above.

  The OCDMA system decoding apparatus is an apparatus for decoding the signal encoded by the OCDMA system encoding apparatus. The multiplexing by the OCDMA encoding unit can be decoded by using the same one as a known OCDMA decoding unit. As a specific OCDMA decoding unit, as described above, a circulator (43) to which an optical signal passed through the transmission line (41) is input; and a fiber grating (FBG) (44) to which an optical signal from the circulator is input And an output path (45) through which an optical signal from the FBG input to the circulator is output.

When the optical signal that has passed through the transmission line (41) is input to the circulator (43), the optical signal from the circulator is converted into a fiber grating (FBG) (44).
To enter. Since the point where the input signal is turned back by the FBG differs depending on the wavelength or the like, decoding is achieved.

  The optical signal from the FBG input to the circulator is output to the output path (45). The optical signal that has passed through the output path (45) is demultiplexed by the demultiplexing section (46). An optical filter (48) such as a band-pass filter that transmits the upper sideband (USB) signal of the output signal is provided in the waveguide (47) through which one of the lights demultiplexed by the demultiplexing unit (46) propagates. Since it is provided, it is output from the optical filter (48) as an optical signal mainly having a USB signal. The optical filter (48) is not particularly limited as long as it can weaken the strength of the LSB signal compared to the USB signal (that is, the transmittance of the USB signal is higher than the transmittance of the LSB signal).

  On the other hand, in the waveguide (49) through which the remaining light demultiplexed by the demultiplexing unit (46) propagates, an optical filter such as a bandpass filter that transmits the lower sideband (LSB) signal of the output signal ( 50) is provided, so that it is output from the optical filter (50) mainly as an optical signal having an LSB signal. The optical filter (50) is not particularly limited as long as it can weaken the strength of the USB signal as compared with the LSB signal (that is, the transmittance of the LSB signal is higher than the transmittance of the USB signal).

  The optical signals that have passed through the two optical filters (48, 50) are input to a balance detector (51) for balance detection. Such a balance detector includes a dual pin photodiode. By performing the balance detection, the FSK modulation signal can be easily demodulated, whereby the information converted into the FSK modulation signal can be decoded.

2. Second aspect of the present invention An OCDMA system encoding apparatus according to the second aspect of the present invention basically also includes an FSK modulator for placing an FSK modulation signal on a pulse signal from a pulse light source, and an FSK modulation. A data control unit for controlling data to be placed on the unit, and an OCDMA encoder for multiplexing the output signal from the FSK modulator. Then, FSK information is superimposed on the pulse signal from the pulse light source by the phase modulator and multiplexed by the OCDMA encoder to obtain an OCDMA signal whose payload portion is in the FSK data format. The system of the present invention is a system for performing information communication by decoding a signal encoded by such an OCDMA system encoding apparatus.

2.1. FIG. 3 is a block diagram showing the basic configuration of the OCDMA system of the present invention according to the second aspect. As shown in FIG. 3, the OCDMA system encoding apparatus (4) of the present invention according to the second aspect is basically substantially the same as the OCDMA system encoding apparatus of the present invention according to the first aspect. Although based on the same idea, a USB signal and an LSB signal are multiplexed separately, and they are combined and transmitted. More specifically, a demultiplexing unit (61) for demultiplexing an output signal from the FSK modulator into an upper sideband (USB) signal and a lower sideband (LSB) signal; A first circulator (62) to which a USB signal demultiplexed by is input; a first FBG (63) to which an optical signal from the first circulator is input; and the first FBG input to the circulator A first output path (64) for outputting an optical signal from: a second circulator (65) for receiving an LSB signal demultiplexed by the demultiplexer; and an optical signal from the second circulator A second FBG (66) input to the circulator; a second output path (67) from which the optical signal from the second FBG input to the circulator is output; and an output signal from the first output path And a combining unit (68) for combining the output signals from the second output path. DMA system for encoding device and the like.

  The demultiplexing unit (61) includes, for example, a coupler and the optical filter described above, and the output signal from the FSK modulator is demultiplexed and demultiplexed by a coupler (directional coupler) or the like. Each optical signal is demultiplexed into an upper sideband (USB) signal and a lower sideband (LSB) signal by passing through the optical filter described above.

  The USB signal demultiplexed by the demultiplexer is multiplexed by the first OCDMA encoder. The USB signal demultiplexed by the demultiplexer is input to the first circulator (62). When the optical signal from the first circulator is input to the first FBG (63), the turn-back point differs depending on the wavelength of the optical signal, so that a time delay occurs, thereby causing multiplexing. The optical signal from the first FBG is output from the first output path (64) via the first circulator.

  On the other hand, the LSB signal demultiplexed by the demultiplexer is multiplexed by the second OCDMA encoder. The LSB signal demultiplexed by the demultiplexer is input to the second circulator (65). The optical signal from the second circulator is input to the second FBG (66). The optical signal from the second FBG is output from the second output path (67) via the second circulator.

  The output signal from the first output path and the output signal from the second output path are combined by the multiplexing unit (68), and transmitted to the decoding device for the OCDMA system via the transmission path.

2.2. OCDMA system according to the second aspect of the present invention OCDMA system encoding apparatus, transmission path (41) through which an output signal from the OCDMA system encoding apparatus is transmitted, and an optical signal transmitted through the transmission path (41) Is an OCDMA system including a decoding device for an OCDMA system. The OCDMA system encoding apparatus is basically the OCDMA system encoding apparatus (1) according to the second aspect described above. The OCDMA system decoding device (71) receives the optical signal that has passed through the transmission line (41), and is demultiplexed by the demultiplexing unit (72) and demultiplexed by the demultiplexing unit (72). An optical filter (74) provided in a waveguide (73) through which one of the lights propagates, and transmits an upper sideband (USB) signal among output signals; and an output signal from the optical filter (74) is input A circulator (75); a fiber grating (FBG) (76) for inputting an optical signal from the circulator; an output path (77) for outputting an optical signal from the FBG input to the circulator; An optical filter (79) provided in a waveguide (78) through which the remaining light demultiplexed by the unit (72) propagates, and transmits a lower sideband (LSB) signal among output signals; 79) a circulator (80) to which an output signal is input; and A fiber grating (FBG) (81) to which the optical signal is input; an output path (82) for outputting the optical signal from the FBG input to the circulator; and the two output paths (77, 72). It is a decoding device (71) for an OCDMA system comprising a balance detector (83) to which a transmitted optical signal is input.

  The configuration and operation of the encoding device for the OCDMA system are as described above.

  The OCDMA system decoding device 71 is a device for decoding the signal encoded by the OCDMA system encoding device. The multiplexing by the OCDMA encoding unit can be decoded by using the same one as a known OCDMA decoding unit.

  When the optical signal that has passed through the transmission line (41) is input to a demultiplexing unit (72) such as a coupler, the intensity ratio is demultiplexed to 1: 1, for example. In the waveguide (73) through which one of the lights demultiplexed by the demultiplexing unit (72) propagates, an optical filter (74) that transmits the upper sideband (USB) signal of the output signal is provided. The output signal from the filter (74) is input to the circulator (75). The optical signal from the circulator is input to a fiber grating (FBG) (76) and decoded in the same manner as in a known OCDMA decoder. The optical signal from the FBG is output to the output path (77) via the circulator.

  On the other hand, in the waveguide (78) through which the remaining light demultiplexed by the demultiplexing unit (72) such as a coupler propagates, an optical filter (79) that transmits the lower sideband (LSB) signal of the output signal. The output signal from the optical filter (79) is input to the circulator (80). When the optical signal from the circulator is input to the fiber grating (FBG) (81), it is decoded in the same manner as in a known OCDMA decoder. The optical signal from the FBG is output to the output path (82) via the circulator. The optical signal transmitted through the two output paths (77, 72) is balance-detected by a balance detector (83) such as a dual pin photodetector, and the optical FSK modulation signal is decoded.

3. Manufacturing Method The OCDMA system of the present invention can be manufactured by appropriately combining known components. As a method for forming the optical waveguide, a known forming method such as an internal diffusion method such as a titanium diffusion method or a proton exchange method can be used. That is, the optical FSK modulator of the present invention can be manufactured as follows, for example. First, titanium is patterned on a lithium niobate wafer by photolithography, and titanium is diffused by thermal diffusion to form an optical waveguide. The conditions at this time may be that the thickness of titanium is 100 to 2000 angstroms, the diffusion temperature is 500 to 2000 ° C., and the diffusion time is 10 to 40 hours. An insulating buffer layer (thickness 0.5-2 μm) of silicon dioxide is formed on the main surface of the substrate. Next, an electrode made of metal plating having a thickness of 15 to 30 μm is formed thereon. The wafer is then cut. In this way, an optical modulator having a titanium diffusion waveguide is formed.

  The FSK modulator can be manufactured, for example, as follows. First, a waveguide is formed on a substrate. The waveguide can be provided by performing a proton exchange method or a titanium thermal diffusion method on the surface of the lithium niobate substrate. For example, Ti metal stripes of about several micrometers are formed on the LN substrate in a row on the LN substrate by photolithography. Thereafter, the LN substrate is exposed to a high temperature around 1000 ° C. to diffuse Ti metal into the substrate. In this way, a waveguide can be formed on the LN substrate.

The electrode can be manufactured in the same manner as described above. For example, in order to form an electrode, the gap between the electrodes is set to about 1 to 50 micrometers with respect to both sides of a large number of waveguides formed with the same width by the photolithography technique as in the formation of the optical waveguide. Can be formed.

In addition, when using a silicon substrate, it can manufacture as follows, for example. A lower cladding layer mainly composed of silicon dioxide (SiO ₂ ) is deposited on a silicon (Si) substrate by flame deposition, and then silicon dioxide (SiO ₂ ) doped with germanium dioxide (GeO ₂ ) as a dopant is deposited. A core layer as a main component is deposited. After that, it is made into transparent glass in an electric furnace. Next, an optical waveguide portion is fabricated by etching, and an upper clad layer mainly composed of silicon dioxide (SiO ₂ ) is deposited again. Then, a thin film heater type thermo-optic intensity modulator and a thin film heater type thermo-optic phase modulator are formed on the upper cladding layer.

4). OCDMA Encoding Device In the above description, the example in which the frequency spectrum is encoded using FBG has been described. However, for example, encoding can also be performed by an apparatus as described below. That is, the encoder described below can be used in appropriate combination with the above-described system. FIG. 6 is a schematic diagram of an apparatus for encoding a frequency spectrum by giving a phase shift to the frequency spectrum of an optical pulse. That is, in order to encode a frequency spectrum, a first total reflection mirror 101a into which pulsed light is incident, a first diffraction grating 102a in which reflected light from the first total reflection mirror 101a is incident and subjected to space-time conversion processing, A first Fourier lens 103a that transmits the diffracted light from the first diffraction grating 102a and applies a Fourier transform to the transmitted light, and an output light from the first Fourier lens 103a is incident, and a mask 104 having a specific code pattern , The output light from the mask 104 is incident, the second Fourier lens 103b for performing the inverse Fourier transform process on the incident light, the second diffraction grating 102b to which the output light of the second Fourier lens 103b is incident, and the second diffraction And a second total reflection mirror 101b on which diffracted light from the grating 102b is incident. The input light pulse is space-time converted by the first total reflection mirror 101a and the first diffraction grating 102a, and then Fourier-transformed by the first Fourier lens 103a. Optical phase masking (giving a phase shift of “0” or “π”) is performed on the frequency spectrum field formed by Fourier transform using a mask 104 having a specific code pattern. The masked field is subjected to inverse Fourier transform by the second Fourier lens 103b, and then subjected to inverse space-time transform by the second diffraction grating 102b and the second total reflection mirror 101b, thereby encoding the frequency spectrum. This device functions not only as an OCDMA encoder but also as an OCDMA decoder because it can recover the phase shift given to the frequency spectrum.

  FIG. 7 is a schematic diagram of an apparatus for encoding a frequency spectrum by giving a phase shift to the frequency spectrum of an optical pulse. As shown in FIG. 7, this apparatus has a first AWG (arrayed-waveguide grating) (111) on which pulsed light is incident and a phase change for each light decomposed into frequency spectrum components by the first AWG. And a second AWG (113) to which output light from each phase modulator is input. The input optical pulse is decomposed into frequency spectrum components by the first AWG (111). Each frequency spectrum component is given a phase change (“0” or “π”) according to a specific code pattern by each optical phase shifter (112), and then converted into a time waveform by the second AWG (113). By converting again, frequency spectrum coding is performed. This device functions not only as an OCDMA encoder but also as an OCDMA decoder because it can recover the phase shift given to the frequency spectrum.

  FIG. 8 is a schematic diagram of an apparatus for encoding a frequency spectrum by giving a phase shift to the frequency spectrum of an optical pulse. As shown in FIG. 8, the apparatus includes an AWG (121), a phase modulator (122) corresponding to each channel for giving a phase change to each light decomposed into frequency spectrum components by the AWG, And a total reflection mirror (123) to which output light from each phase modulator is input. The input optical pulse is decomposed into frequency spectrum components by the AWG (121). Each frequency spectrum component is given a phase change (“0” or “π / 2” corresponding to half of the required change amount) according to a specific code pattern by each optical phase modulator (122). After being reflected by the total reflection mirror (123) and again given a phase change by each optical phase modulator (122) ..., it is converted again into a time waveform by the AWG (121), thereby performing frequency spectrum coding. . Also in this configuration example, since the phase shift given to the frequency spectrum can be recovered by the same method as the above operation, the frequency spectrum can be decoded by the same configuration. This device functions not only as an OCDMA encoder but also as an OCDMA decoder because it can recover the phase shift given to the frequency spectrum.

  FIG. 9 is a schematic configuration diagram of an optical encoder constituted by a PLC type chip optical bipolar encoder. As shown in FIG. 9, the encoder includes a plurality of variable optical taps (141) to which optical pulses are input, an optical delay line (142) connected to each variable optical tap (141), and each variable optical tap ( 141) an optical phase modulator (143) for adjusting the phase of each light demultiplexed from the optical phase modulator (143), a coupler (144) such as a coupler for multiplexing the output light from each optical phase modulator (143), It comprises. This optical encoder can be used not only for encoding optical signals but also for decoding. The optical pulse incident on the optical encoder has, for example, equal intensity having a delay time difference of every 5 ps by the action of the optical delay line (142) connecting the variable optical tap (141) and each variable optical tap (141). Are divided into a plurality of (for example, eight) chip pulses. Each of the demultiplexed chip pulses is given a phase shift of “0” or “π” to the optical carrier phase by the optical phase modulator (143), and is multiplexed by the multiplexer (144). A code is generated. The combination of phase shifts given here corresponds to one code, and a desired optical bipolar code can be generated by controlling each optical phase modulator (143) in accordance with the sub-regional address code. This device functions not only as an OCDMA encoder but also as an OCDMA decoder because it can recover the phase shift given to the frequency spectrum.

Demonstration of OCDMA System of the Present Invention According to the First Aspect FIG. 4 is a schematic configuration diagram showing an experimental system for demonstrating the OCDMA system of the present invention according to the first aspect. As shown in FIG. 4, the OCDMA system controls an FSK modulator (2) for placing a frequency shift keying (FSK) modulation signal on a pulse signal from a pulse light source, and data to be placed on the FSK modulator. An OCDMA system encoding apparatus (1), comprising: a data control unit (3) for controlling the output signal; and an optical code division multiple access (OCDMA) encoder (4) for multiplexing the output signal from the FSK modulator. It is.

The FSK modulator (2) includes a first sub Mach-Zehnder waveguide (MZ _A ) (12); a second sub-Mach-Zehnder waveguide (MZ _B ) (13); and an optical signal input section ( 14), a branching section (15) for branching the optical signal into the first sub Mach-Zehnder waveguide (MZ _A ) and the second sub-Mach-Zehnder waveguide (MZ _B ), Sub-Mach-Zehnder waveguide (MZ _A ), the second sub-Mach-Zehnder waveguide (MZ _B ), the first sub-Mach-Zehnder waveguide (MZ _A ), and the second sub-Mach-Zehnder waveguide ( A main Mach including a multiplexing unit (16) for multiplexing the optical signal output from MZ _B ) and an optical signal output unit (17) for outputting the optical signal combined by the multiplexing unit. Zender waveguide (MZ _C ) (18); and the first sub Mach-Zehnder guide _A first electrode (RF _A electrode) (19) for inputting a radio frequency (RF) signal to the two arms constituting the waveguide (MZ _A ); and the second sub Mach-Zehnder waveguide (MZ _B ) A second electrode (RF _B electrode) (20) for inputting a radio frequency (RF) signal to the two arms constituting the above; and applying a voltage to the main Mach-Zehnder waveguide (MZ _C ), _A main Mach-Zehnder electrode (for controlling a phase difference between an output signal from the first sub-Mach-Zehnder waveguide (MZ _A ) and an output signal from the second sub-Mach-Zehnder waveguide (MZ _B )) An optical modulator comprising electrodes C) and (21).

  The OCDMA encoder (4) includes a circulator (31) to which an output signal from the FSK modulator is input; a fiber grating (FBG) (32) to which an optical signal from the circulator is input; and an input to the circulator. And an output path (33) for outputting an optical signal from the FBG.

  On the other hand, the decoding device (42) for the OCDMA system includes a circulator (43) to which an optical signal passed through the transmission line (41) is input; a fiber grating (FBG) (44) to which an optical signal from the circulator is input; An output path (45) for outputting an optical signal from the FBG input to the circulator; and a demultiplexing section (46) for demultiplexing an optical signal passing through the output path (45); An optical filter (48) provided in a waveguide (47) through which one of the lights demultiplexed by (46) propagates, and transmits an upper sideband (USB) signal among output signals; ) And an optical filter (50) that transmits the lower sideband (LSB) signal among the output signals, and is provided in the waveguide (49) through which the remaining light demultiplexed by (2) is propagated; and the two optical filters (48 , 50) and a balanced detector (51) to which an optical signal transmitted is transmitted. A beam decryption device (42).

The 10 GHz electrical signal synthesized by the power source is separated into two by a splitter, and one is input to a mode-locked laser diode (MLLD). The other one is input to the pattern generator. Since this embodiment is an experimental example, a pattern generator was used. The mode-locked laser diode outputs a 1.8 ps pulse signal, and after the plane of polarization is adjusted by the polarization adjuster (PC), components other than the frequency f ₀ are suppressed by the band-pass filter and sent to the FSK modulator. Enter.

FSK modulator electrical signal from the power supply frequency f _m is applied to the two sub Mach-Zehnder electrodes. One electric signal is given a delay of π / 2 by a delay device. Then, an electric signal whose voltage pattern is controlled by the pattern generator is applied to the main Mach-Zehnder electrode, whereby an FSK modulation signal is obtained.

  The FSK modulated signal is arbitrarily amplified and then encoded by the OCDMA encoding unit. The encoded signal is transmitted to the OCDMA decoding apparatus via the transmission path (41) and decoded.

Demonstration of OCDMA System of the Present Invention According to Second Aspect FIG. 5 is a schematic configuration diagram showing an experimental system for demonstrating the OCDMA system of the present invention according to the second aspect. As shown in FIG. 5, this OCDMA system controls an FSK modulator (2) for placing a frequency shift keying (FSK) modulation signal on a pulse signal from a pulse light source, and data to be placed on the FSK modulator. An OCDMA system encoding apparatus (1), comprising: a data control unit (3) for controlling the output signal; and an optical code division multiple access (OCDMA) encoder (4) for multiplexing the output signal from the FSK modulator. It is.

The FSK modulator (2) includes a first sub Mach-Zehnder waveguide (MZ _A ) (12); a second sub-Mach-Zehnder waveguide (MZ _B ) (13); and an optical signal input section ( 14), a branching section (15) for branching the optical signal into the first sub Mach-Zehnder waveguide (MZ _A ) and the second sub-Mach-Zehnder waveguide (MZ _B ), Sub-Mach-Zehnder waveguide (MZ _A ), the second sub-Mach-Zehnder waveguide (MZ _B ), the first sub-Mach-Zehnder waveguide (MZ _A ), and the second sub-Mach-Zehnder waveguide ( A main Mach including a multiplexing unit (16) for multiplexing the optical signal output from MZ _B ) and an optical signal output unit (17) for outputting the optical signal combined by the multiplexing unit. Zender waveguide (MZ _C ) (18); and the first sub Mach-Zehnder guide _A first electrode (RF _A electrode) (19) for inputting a radio frequency (RF) signal to the two arms constituting the waveguide (MZ _A ); and the second sub Mach-Zehnder waveguide (MZ _B ) A second electrode (RF _B electrode) (20) for inputting a radio frequency (RF) signal to the two arms constituting the above; and applying a voltage to the main Mach-Zehnder waveguide (MZ _C ), _A main Mach-Zehnder electrode (for controlling a phase difference between an output signal from the first sub-Mach-Zehnder waveguide (MZ _A ) and an output signal from the second sub-Mach-Zehnder waveguide (MZ _B )) An optical modulator comprising an electrode C) (21).

  The OCDMA encoder (4) includes a demultiplexing unit (61) for demultiplexing the output signal from the FSK modulator into an upper sideband (USB) signal and a lower sideband (LSB) signal; A first circulator (62) to which a USB signal demultiplexed by the demultiplexer is input; a first FBG (63) to which an optical signal from the first circulator is input; and the circulator input to the circulator A first output path (64) for outputting an optical signal from the first FBG; a second circulator (65) for receiving an LSB signal demultiplexed by the demultiplexer; and the second circulator A second FBG (66) to which an optical signal from the second FBG is input; a second output path (67) from which the optical signal from the second FBG input to the circulator is output; and the first output path A multiplexing unit (68) for combining the output signal from the second output path and the output signal from the second output path; Comprising.

  The OCDMA system decoding device (71) receives the optical signal that has passed through the transmission path (41) and is demultiplexed by the demultiplexing unit (72); and demultiplexed by the demultiplexing unit (72) An optical filter (74) that is provided in a waveguide (73) through which one of the transmitted light propagates and transmits an upper sideband (USB) signal among output signals; and an output signal from the optical filter (74) is input A circulator (75) that receives the optical signal from the circulator (FBG) (76); an output path (77) that outputs the optical signal from the FBG input to the circulator; An optical filter (79) provided in a waveguide (78) through which the remaining light demultiplexed by the wave part (72) propagates, and transmits a lower sideband (LSB) signal among output signals; A circulator (80) to which an output signal from (79) is input; and A fiber grating (FBG) (81) to which an optical signal from the data is input; an output path (82) from which the optical signal from the FBG input to the circulator is output; and the two output paths (77, 72) And a balance detector (83) to which an optical signal transmitted through is input, and a decoding device (71) for an OCDMA system.

  The operation is basically the same as that of the first embodiment.

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

FIG. 1 is a block diagram for explaining an encoding apparatus for an OCDMA system according to the present invention. FIG. 2 is a conceptual diagram illustrating an example of an FSK modulator. FIG. 3 is a block diagram showing a basic configuration of the OCDMA system according to the second aspect of the present invention. FIG. 4 is a schematic configuration diagram showing an experimental system for demonstrating the OCDMA system of the present invention according to the first aspect. FIG. 5 is a schematic configuration diagram showing an experimental system for demonstrating the OCDMA system of the present invention according to the second aspect. FIG. 6 is a schematic diagram of an apparatus for encoding a frequency spectrum by giving a phase shift to the frequency spectrum of an optical pulse. FIG. 7 is a schematic diagram of an apparatus for encoding a frequency spectrum by giving a phase shift to the frequency spectrum of an optical pulse. FIG. 8 is a schematic diagram of an apparatus for encoding a frequency spectrum by giving a phase shift to the frequency spectrum of an optical pulse. FIG. 9 is a schematic configuration diagram of an optical encoder constituted by a PLC type chip optical bipolar encoder.

Explanation of symbols

1 Coding device for OCDMA system 2 FSK modulator 3 Data control unit 4 OCDMA encoder

Claims (10)

An FSK modulator (2) for placing a frequency shift keying (FSK) modulation signal on the pulse signal from the pulse light source;
A data control unit (3) for controlling data to be placed on the FSK modulator;
An optical code division multiple access (OCDMA) encoder (4) for multiplexing the output signal from the FSK modulator,
Encoder for OCDMA system (1). The FSK modulator (2)
A first sub-Mach-Zehnder waveguide (MZ _A ) (12);
A second sub Mach-Zehnder waveguide (MZ _B ) (13);
An optical signal input unit (14) and a branching unit (15) for branching the optical signal to the first sub Mach-Zehnder waveguide (MZ _A ) and the second sub-Mach-Zehnder waveguide (MZ _B ) The first sub-Mach-Zehnder waveguide (MZ _A ), the second sub-Mach-Zehnder waveguide (MZ _B ), the first sub-Mach-Zehnder waveguide (MZ _A ), and the second sub-Mach-Zehnder waveguide (MZ _A ). A multiplexing unit (16) for multiplexing the optical signals output from the sub Mach-Zehnder waveguide (MZ _B ), and an optical signal output unit (17 for outputting the optical signals combined by the multiplexing unit) And a main Mach-Zehnder waveguide (MZ _C ) (18) including:
_A first electrode (RF _A electrode) (19) for inputting a radio frequency (RF) signal to the two arms constituting the first sub Mach-Zehnder waveguide (MZ _A );
A second electrode (RF _B electrode) (20) for inputting a radio frequency (RF) signal to two arms constituting the second sub Mach-Zehnder waveguide (MZ _B );
By applying a voltage to the main Mach-Zehnder waveguide (MZ _C ), an output signal from the first sub-Mach-Zehnder waveguide (MZ _A ) and the second sub-Mach-Zehnder waveguide (MZ _B ) An optical modulator comprising a main Mach-Zehnder electrode (electrode C) (21) for controlling a phase difference from an output signal from
The encoding device for an OCDMA system according to claim 1. The OCDMA encoder (4)
A circulator (31) to which an output signal from the FSK modulator is input;
A fiber grating (FBG) (32) to which an optical signal from the circulator is input;
An output path (33) for outputting an optical signal from the FBG input to the circulator;
Comprising
The encoding device for an OCDMA system according to claim 1. The OCDMA encoder (4)
A first total reflection mirror (101a) on which pulsed light is incident;
A first diffraction grating (102a) that receives the reflected light from the first total reflection mirror (101a) and applies a space-time conversion process;
A first Fourier lens (103a) that transmits the diffracted light from the first diffraction grating (102a) and applies a Fourier transform to the transmitted light;
A mask (104) having a specific code pattern, upon which output light from the first Fourier lens (103a) is incident;
A second Fourier lens (103b) that receives the output light from the mask (104) and performs an inverse Fourier transform process on the incident light;
A second diffraction grating (102b) on which the output light of the second lens (103b) is incident;
The encoding device for an OCDMA system according to claim 1, further comprising: a second total reflection mirror (101b) on which diffracted light from the second diffraction grating (102b) is incident. The OCDMA encoder (4)
A first AWG (111) on which pulsed light is incident;
A phase modulator (112) corresponding to each channel for giving a phase change to each pulse light decomposed into frequency spectrum components by the first AWG;
The encoding device for an OCDMA system according to claim 1, further comprising: a second AWG (113) to which output light from each phase modulator is input. The OCDMA encoder (4)
AWG (121),
A phase modulator (122) corresponding to each channel for giving a phase change to each pulse light decomposed into frequency spectrum components by the AWG;
A total reflection mirror (123) to which output light from each of the phase modulators (122) is input,
The encoding device for an OCDMA system according to claim 1. The OCDMA encoder (4)
A plurality of variable optical taps (141) for inputting optical pulses;
An optical delay line (142) connecting the variable optical taps (141);
An optical phase modulator (143) for adjusting the phase of each light demultiplexed from each variable optical tap (141);
A multiplexer (144) for multiplexing the output light from each of the optical phase modulators (143),
The encoding device for an OCDMA system according to claim 1. An OCDMA system encoding device, a transmission line (41) through which an output signal from the OCDMA system encoding device is transmitted, and an OCDMA system decoding device through which an optical signal passed through the transmission line (41) is input An OCDMA system including:
The OCDMA system encoding device is an OCDMA system encoding device (1) according to any one of claims 1 to 7,
The decoding device (42) for the OCDMA system includes:
A circulator (43) to which an optical signal passed through the transmission path (41) is input;
A fiber grating (FBG) (44) to which an optical signal from the circulator is input;
An output path (45) through which an optical signal from the FBG input to the circulator is output:
A demultiplexing unit (46) for demultiplexing the optical signal that has passed through the output path (45);
An optical filter (48) provided in a waveguide (47) through which one of the lights demultiplexed by the demultiplexing unit (46) propagates, and transmits an upper sideband (USB) signal among output signals;
An optical filter (50) provided in a waveguide (49) through which the remaining light demultiplexed by the demultiplexing unit (46) propagates, and transmits a lower sideband (LSB) signal among output signals;
A decoder (42) for an OCDMA system, comprising: a balance detector (51) to which an optical signal transmitted through the two optical filters (48, 50) is input;
OCDMA system. The OCDMA encoder (4)
A demultiplexing unit (61) for demultiplexing the output signal from the FSK modulator into an upper sideband (USB) signal and a lower sideband (LSB) signal;
A first circulator (62) to which the USB signal demultiplexed by the demultiplexer is input;
A first FBG (63) to which an optical signal from the first circulator is input;
A first output path (64) through which an optical signal from the first FBG input to the circulator is output;
A second circulator (65) to which the LSB signal demultiplexed by the demultiplexer is input;
A second FBG (66) to which an optical signal from the second circulator is input;
A second output path (67) for outputting an optical signal from the second FBG input to the circulator;
A multiplexing unit (68) for combining the output signal from the first output path and the output signal from the second output path,
The encoding device for an OCDMA system according to claim 1 or 2. An OCDMA system encoding device, a transmission line (41) through which an output signal from the OCDMA system encoding device is transmitted, and an OCDMA system decoding device through which an optical signal passed through the transmission line (41) is input An OCDMA system including:
The OCDMA system encoding device is an OCDMA system encoding device (1) according to claim 9,
The decoding device (71) for the OCDMA system includes:
A demultiplexing unit (72) for inputting and demultiplexing an optical signal that has passed through the transmission path (41);
An optical filter (74) provided in a waveguide (73) through which one of the lights demultiplexed by the demultiplexing unit (72) propagates, and transmits an upper sideband (USB) signal among output signals;
A circulator (75) to which an output signal from the optical filter (74) is input;
A fiber grating (FBG) (76) to which an optical signal from the circulator is input;
An output path (77) through which an optical signal from the FBG input to the circulator is output;
An optical filter (79) provided in a waveguide (78) through which the remaining light demultiplexed by the demultiplexing unit (72) propagates, and transmits a lower sideband (LSB) signal among output signals;
A circulator (80) to which an output signal from the optical filter (79) is input;
A fiber grating (FBG) (81) to which an optical signal from the circulator is input;
An output path (82) through which an optical signal from the FBG input to the circulator is output:
A decoder (71) for an OCDMA system comprising a balance detector (83) to which an optical signal transmitted through the two output paths (77, 72) is input;
OCDMA system.

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