JP4000372B2 - Optical CDMA communication system using optical CSK modulation - Google Patents

Description

  The present invention relates to. More particularly, it relates to a novel 10 Gbit / s optical code division multiple access (CDMA) system based on binary phase shift keying (BPSK) coding, code shift keying (CSK) data modulation.

  Currently, in order to realize an ultra high-speed optical network, research on optical code division multiplexing (OCDM) has been actively conducted. Optical CDMA uses a temporary waveform as a communication channel [P. Prucnal and M.M. Santoro, J, Lightwave Technology No. 4, pages 307-314 (1986). Sampson, G.M. Pendock and R.W. Griffin, Fiber and integrated optics 16, pp. 129-157 (1997)]. Thus, an optical CDMA system can share the same time slot with the same wavelength division multiplexing (WDM) channel of the time division multiplexing (TDM) method. Therefore, the optical CDMA method can be overlaid on the WDM network, thereby increasing the versatility and expandability of the network [Kenichi Kitayama, selected area No. in IEEE communication. 16, pp. 1309-1319 (1998)]. Optical CDMA is believed to further increase the security of data communication networks [K. Umeno, Y. et al. Awaji and Kenichi Kitayama, Proceedings of the 5th Experimental Chaos Conference (World Science 2000)]. Optical CDMA can be applied to self-routing photonic transport networks [Kenichi Kitayama and Naoya Wada, IEEE Photon Technical Document, Vol. 11, No. 12, pp. 1689-1691 (1999)].

  FIG. 8 is a conceptual diagram showing a basic configuration of an optical CDMA system using conventional OOK (On-Off Keying) data modulation. As shown in FIG. 8, the conventional optical CDMA system 17 includes a transmitter 2, a receiver 3, and a fiber 4 connecting them. The transmitter 2 includes a light source 5, an external modulator 18 such as an external electro-optic modulator (EOM), and an optical encoder 19, and the receiver 3 includes an optical decoder 20, an optical detector 21, and data determination. (Threshold processing device) 16 is provided. In OOK data modulation, an optical pulse is modulated “on” and “off” by data “1” and “0”, respectively. A pulse of data “1” is encoded into an optical BPSK code.

  The operation of the conventional optical CDMA system 17 based on the OOK modulation will be described below with reference to FIG. An optical pulse train generated from the light source 5 in a bit cycle is associated with a mark (corresponding to “1” of digital data) and a space (corresponding to “0” of digital data) by the external modulator 18 depending on the presence or absence of a pulse. Is done. Thereafter, the optical pulse is encoded by an optical encoder 19 prepared for the mark. The encoding in the optical encoder 19 demultiplexes an optical pulse to a desired code length by a delay element, and then gives a phase shift of “0” or “π” to the phase of each pulse. In this way, encoding is performed in the transmitter 2.

  The code sequence of the optical decoder 20 in the receiver 3 is obtained by time-inverting the code sequence of the optical encoder 19. The received signal is subjected to correlation calculation by the optical decoder 20. When the mark signal is subjected to correlation calculation, an autocorrelation waveform having a high vertex at the center of the bit is obtained. This optical signal is converted into an electric signal having a peak value P by a photo detector 21 such as a photodiode. FIG. 9 shows an example of an electrical signal converted by the optical detector 21 in the conventional optical CDMA system. In the data determiner 16, for example, data is determined at a determination level P / 2 [V].

  Therefore, the conventional optical CDMA system using OOK data modulation has a problem that the determination range that can be determined by the data determination unit 10 is limited to P [V] as shown in FIG. In particular, when multiple users use an optical CDMA system, interference noise from other users, shot noise at the time of detection, thermal noise, and the like cause a problem in that the input voltage of the data determiner fluctuates greatly, causing a data determination error. . For this reason, in order to raise the tolerance with respect to the various noise of a data determination device, expanding the determination range was desired.

  Further, as shown in FIG. 9, the envelope of the autocorrelation waveform in the optical CDMA system using the conventional OOK data modulation has a side lobe around the apex. This side lobe has a problem that its performance is greatly degraded as noise during detection.

  In a conventional optical CDMA system using OOK data modulation, the threshold level (threshold value) is set to a value (P / 2) that is half the normal peak value P. Since the width of P / 2 at the peak voltage is relatively narrow, it is necessary to appropriately correct the optimum threshold during communication. For this reason, the conventional optical CDMA system using OOK data modulation has a system for changing the threshold value during communication, and there is a problem that the circuit configuration of the receiver becomes complicated.

A 10 Gbit / s optical CDMA system using a BPSK code by temporally matched filtering and sidelobe suppression by time-gating detection is proposed, and multiple channel transmission of the optical CDMA system is experimentally demonstrated. Reference 1 (see Naoya Wada, Hideyuki Tonobayashi and Kenichi Kitayama, IEEE Electronic Engineering Document, No. 35, pages 83-383 (1999))]. Also, large-capacity optical code division multiplexing transmission was shown [Hideyuki Tonobayashi, Wataru Nakajo and Kenichi Kitayama, IEEE Photonics Technical Document, Vol. 14, No. 4, pp. 555-557, 2002]. The performance of an optical CMDA system is degraded by optical interference noise. Sidelobe suppression is necessary in some high bit rate optical CDMA systems to reduce interference noise [D. Sampson, Naoya Wada, Kenichi Kitayama and Wataru Nakajo, IEEE Electronics Document, No. 36, pages 445-447 (2000), Naoya Wada and Kenichi Kitayama, J. Am. Lightwave Technology, No. 17, pages 1758 to 1765 (1999)]. However, the sidelobe suppression technique using the time gating system introduced in the previous paper basically requires active operations such as chip synchronization and clock recovery, similar to the system used for TDM demodulation. There's a problem.
Naoya Wada, Hideyuki Tonobayashi and Kenichi Kitayama, IEEE Electronic Engineering Documents, NO. 35, 833-834 (1999)

  An object of the present invention is to provide an optical CDMA system having a wide determination range, and a transmitter and a receiver used in such an optical CDMA system.

  It is another object of the present invention to provide an optical CDMA system that provides a data decision input voltage spectrum with less side lobes, and a transmitter and receiver used in such an optical CDMA system.

  Another object of the present invention is to provide an optical CDMA system that does not need to modify the threshold value of the data determiner during communication, and a transmitter and a receiver used in such an optical CDMA system.

  Another object of the present invention is to provide a novel high speed (10 Gbit / s) optical code division multiple access (CDMA) system based on binary phase shift keying (BPSK) coding, code shift keying (CSK) data modulation. And

(1) In order to solve at least one or more of the above problems, an optical CDMA communication transmitter for use in such using optical code shift keying modulation of the present invention, marks an optical pulse train generated by the bit period from the light source A modulator for allocating the signal (corresponding to “1” of digital data) and a space (corresponding to “0” of digital data) ”, and an optical pulse train for marks distributed by the modulator. An optical encoder for a mark that is encoded as an optical pulse train in which the phase of each pulse is controlled, and an optical pulse train that is encoded by the optical encoder for a space that is distributed by the modulator is for each pulse. Encoding by using optical pulse trains with different phase combinations, and encoding by the mark optical encoder A pulse train, comprising a multiplexer for multiplexing the coded pulse train by the space optical encoder. More specifically, a modulator (6) that distributes an optical pulse train generated at a bit period from the light source (5) into a mark and a space based on input data representing a mark or a space ; The mark optical encoder (7) for encoding the mark optical pulse distributed by the modulator as an optical pulse train having a fixed phase combination in which the phase of each pulse is controlled, and the mark optical pulse distributed by the modulator An optical encoder for a space which encodes an optical pulse for space by using an optical pulse train having a combination of fixed phases different from the optical pulse train encoded by the optical encoder for marks. (8) and the optical pulse train encoded by the mark optical encoder and the optical pulse train encoded by the space optical encoder are combined. Multiplexer for (9), comprises a.

  That is, the transmitter of the present invention requires more optical encoders than the conventional optical CDMA communication using OOK modulation, and the apparatus becomes complicated. However, in the transmitter of the present invention, a “0” signal that has not been encoded in the conventional optical CDMA system is also encoded by the newly added space optical encoder (optical encoder B). By combining this with a later-described decoder, side lobes can be suppressed and the data measurement decision range can be increased.

(2) In order to solve at least one of the above problems, a receiver used for optical code division multiple access communication using optical code shift keying modulation according to the present invention demultiplexes optical data transmitted by a transmitter. And the optical data encoded by the mark optical encoder among the optical data demultiplexed by the demultiplexer (10) is output as an optical signal having an autocorrelation waveform. A first optical decoder (11), a first optical detector (13) for detecting an optical signal output from the first optical decoder (11), and a demultiplexer by the demultiplexer (10). A second optical decoder (12) for outputting the optical data encoded by the space optical encoder as an optical signal having an autocorrelation waveform, and the second optical decoder (12). The second optical detector (14) for detecting the optical signal output from the first optical detector (1) 3) and a calculation circuit (15) for obtaining a difference between detection data of the second optical detector (14), and a reference of 0 [V] based on the difference between the detection data obtained by the calculation circuit (15) And a data judgment unit (16) for judging whether the mark or the space depends on whether the voltage value is higher or lower. That is, the number of optical decoders is larger than that of a conventional receiver and the apparatus is complicated. However, when used together with the transmitter, the side lobe of determination data can be suppressed, and the determination range for data measurement is increased. it can.

  As described above, even for a decoded signal from a space that has not been used conventionally, an envelope of the autocorrelation waveform is output, and a difference from the envelope of the autocorrelation waveform from the decoded signal from the mark signal is obtained. The side lobe of the determination data can be suppressed, and the data measurement determination range can be increased.

In order to solve at least one of the above problems, an optical code division multiple access communication system of the present invention includes an optical code division multiple access including a plurality of optical communication transmitters and a plurality of optical communication receivers. In the communication system, each of the plurality of transmitters for optical communication includes an optical pulse train generated at a bit period from the light source (5), based on input data representing marks or spaces , A modulator (6) that distributes to a space, and a mark optical encoder that encodes a mark optical pulse distributed by the modulator as an optical pulse train having a fixed phase combination in which the phase of each pulse is controlled (7) and an optical pulse train obtained by encoding the optical pulse for space distributed by the modulator by the optical encoder for mark are different in phase for each pulse. Space optical encoder for encoding by looking combined to an optical pulse train having a combination of different constant phase (8), an optical pulse train encoded by the mark optical encoder, the space for optical code A multiplexer (9) for multiplexing the optical pulse train encoded by the transmitter, wherein the plurality of optical communication receivers each demultiplex the optical data transmitted by the transmitter. And the optical data encoded by the mark optical encoder among the optical data demultiplexed by the demultiplexer (10) is output as an optical signal having an autocorrelation waveform. A first optical decoder (11), a first optical detector (13) for detecting an optical signal output from the first optical decoder (11), and a demultiplexer by the demultiplexer (10). Of the optical data, the optical data encoded by the space optical encoder A second optical decoder (12) that outputs an optical signal having a correlation waveform; a second optical detector (14) that detects the optical signal output by the second optical decoder (12); A calculation circuit (15) for obtaining a difference between detection data of the first optical detector (13) and the second optical detector (14), and a difference between the detection data obtained by the calculation circuit (15); A data determination unit (16) for determining whether the mark or space is based on a voltage value higher or lower than 0 [V].

In order to solve at least one of the above problems, an optical code division multiple access communication method of the present invention is an optical code division multiple access communication method using the optical code division multiple access communication system described above, wherein the modulation A step of allocating an optical pulse train generated from a light source in a bit period to a mark and a space based on a data signal representing the input mark or space, and the mark optical encoder includes the modulation A step of encoding the optical pulse train for marks distributed by the detector into an optical pulse train having a certain phase combination, and the optical encoder for space distributes the optical pulse train for spaces distributed by the modulator to the mark a step of encoding the optical pulse train having a combination of different constant phase and use optical encoders, the multiplexer is, the mer A step of multiplexing the pulse train encoded by the optical encoder for the space and the pulse train encoded by the optical encoder for the space, a step of transmitting the optical data combined in the step, and the duplexer (10) demultiplexing the optical data transmitted by the transmitter, and the first optical decoder (11) receives the optical data demultiplexed by the demultiplexer (10), A step of outputting optical data encoded by the mark optical encoder as an optical signal having an autocorrelation waveform; and the first optical detector (13) detects the output signal of the first optical decoder (11). And the second optical decoder (12) receives the optical data demultiplexed by the demultiplexer (10) and converts the optical data encoded by the space optical encoder into an autocorrelation waveform. The step of outputting as an optical signal and the second optical detector (14) are connected to a second optical decoder (12 ) Detecting the output signal of the first optical detector (13) and the second optical detector (14), and the calculation circuit (15) calculating the difference between the detected data of the first optical detector (13) and the second optical detector (14); A determination unit (16) determining whether the mark or space is based on a voltage value higher or lower than 0 [V] based on a difference between detection data obtained by the calculation circuit (15); ,including.

  According to the present invention, the determination range in the data determination unit can be set to 2P [V] which is twice the conventional P [V], so that an optical CDMA system with a wide determination range can be provided. Therefore, according to the present invention, there is an effect that the SN ratio of the system is increased and the resistance to the noise of the system is enhanced.

That is, in the OOK data modulation system (FIG. 8) which is a conventional optical CDMA system, the signal body noise power density (SN) ratio γ is defined as γ = (P / σ) ² . On the other hand, in the optical CDMA system of the present invention, the signal determination range is 2P [V]. Then, as the photodetector, Dual - when using a balance detector comprising a pin PD, its dispersion becomes 2 [sigma] ^2. Therefore, the standard deviation is 2 ^1/2 σ. Therefore, when the SN ratio of the present invention is γ ′, γ ′ = 2γ. Therefore, in the CSK data modulation system of the present invention, a 3 dB performance improvement can be expected compared to the conventional OOK modulation system.

  According to the present invention, the cross-correlation waveform output from the optical detector when receiving the space signal suppresses the side lobe of the data determiner input voltage. As a result, it is possible to provide an optical CDMA system that provides a voltage spectrum with less side lobes for data determination. Furthermore, according to the present invention, since the side lobe of the voltage spectrum input to the data decision device is small, it is possible to reduce inter-channel interference during multiplexing.

  According to the present invention, since the determination range in the data determiner can be set to 2P [V] (−P to + P), it is sufficient even if the determination level in the data determiner of the system is always fixed at, for example, 0 [V]. Can determine the data. As a result, according to the present invention, it is possible to provide an optical CDMA system that does not require the threshold level to be corrected during communication.

  According to the present invention, a novel CDMA system based on BPSK coding and CSK data modulation can be provided.

  As shown in FIG. 1, an optical CDMA system 1 according to the present invention includes a transmitter 2, a receiver 3, and a fiber 4 connecting them as in the conventional optical CDMA system. As shown in FIG. 1, the transmitter 2 in the optical CDMA system of the present invention uses an optical pulse train generated from a light source at a bit period for marks (for data “1”) and for spaces (for data “0”). A modulator 6 such as an LN modulator, a mark optical encoder (also referred to as “optical encoder A”) 7 for encoding the mark optical pulse train distributed by the modulator, and the modulation. A space optical encoder (also referred to as “optical encoder B”) 8 for encoding the space optical pulse train distributed by the detector, the pulse train encoded by the mark optical encoder, A multiplexer 9 such as an optical coupler for multiplexing the pulse train encoded by the space optical encoder is provided.

  As shown in FIG. 1, the receiver in the optical CDMA system of the present invention includes a duplexer 10 such as an optical coupler that demultiplexes a pulse train transmitted from the transmitter, and a mark optical encoder. When the transmitter receives the converted optical data, the mark optical decoder 11 (optical decoder A) for outputting the envelope of the autocorrelation waveform from the optical detector and the space optical encoder are encoded. When the optical data is received by the transmitter, the optical decoder for the space (optical decoder B) for outputting the envelope of the autocorrelation waveform from the optical detector and the signal decoded by the optical decoder for the mark are output. An optical detector (balance detector) comprising: a photodiode 13 (optical detector A) that outputs, and a photodiode 14 (optical detector B) that outputs a signal decoded by the space optical decoder; The output from the instrument That the calculating circuit 15 comprises a data decider (thresholding unit) 16.

  In the optical CDMA system of the present invention, preferably two compatible optical N-chip BPSK codes are used for one user. In the transmitter 2, the optical encoder A7 and the optical encoder B8 correspond to data “1” and data “0”, respectively. That is, if the transmission data of the transmitter is “1”, the optical pulse train is transmitted to the optical encoder A7 by the modulator 6, and the optical encoder A7 encodes the optical pulse train. On the other hand, if the transmission data of the transmitter is “0”, the optical pulse train is transmitted to the optical encoder B8 by the modulator 6, and the optical encoder B8 encodes the optical pulse train. The optical pulse train encoded by the optical encoder A7 and the optical pulse train encoded by the optical encoder B8 are combined by the multiplexer 9 and transmitted to the receiver through the optical fiber 4.

  When the data “1” signal is received by the optical decoder A11, the envelope of the autocorrelation waveform is output from the optical detector A13, and the data “0” signal is received by the optical decoder B12. Then, the envelope of the autocorrelation waveform is output from the optical detector B14. The calculation circuit 15 subtracts the output of the optical detector B14 from the output of the optical detector A (upper arrow).

  FIG. 2 is a conceptual diagram for explaining an electric signal waveform in the receiver. FIG. 2A is a diagram illustrating an example of an output waveform of the optical detector A. FIG. FIG. 2B is a diagram illustrating an example of an output waveform of the optical detector B. FIG. 2C shows an input waveform of the data determiner. As shown in FIG. 2, the peak value of the output voltage from each optical decoder is P [V]. That is, a balance detector (13, 14) such as a dual-pin PD outputs a positive voltage P when a data “1” signal is received, and a negative voltage − when a data “0” signal is received. P is output. Since the calculation circuit subtracts these outputs, the peak value of the data input to the data decision unit is 2P [V] as shown in FIG.

  The data determiner determines the data by comparing the output of a balance detector (13, 14) such as a dual-pin PD with a threshold level. As this threshold level, for example, a voltage of 0 [V] is used.

(2. Relationship between OOK data modulation and CSK data modulation)
The relationship between OOK data modulation and CSK data modulation will be described below. As described above, in the OOK data modulation, the optical pulse is modulated to “on” and “off” by data “1” and “0”, respectively. A pulse of data “1” is encoded into an optical BPSK code. On the other hand, in CSK data modulation, an optical pulse is modulated to “on” and “on” by data “1” and “0”, respectively. A pulse of data “0” is also encoded into another optical BPSK code B. Therefore, in CSK data modulation, the encoded signal consists of code A and code B for data “1” and “0”, respectively.

(2.1. BER of OOK Data Modulated Optical CDMA System)
As shown in FIG. 8, the conventional optical CDMA system 17 includes a transmitter 2, a receiver 3, and a fiber 4 connecting them. The transmitter 2 includes a light source 5, an external modulator 18 such as an external electro-optic modulator (EOM), and an optical encoder 19, and the receiver 3 includes an optical decoder 20, an optical detector 21, and data determination. (Threshold processing device) 16 is provided.

  Assuming K is the number of active users, in the transmitter 2 an optical N-chip BPSK code is generated only for data “1”. In the receiver 3, K different N-chip optical BPSK codes are matched and filtered by passing through the optical decoder 20. If this input code matches the decoding code, the optical decoder 20 outputs an autocorrelation waveform having large peaks at all centers of the designated mark bits. On the other hand, if the codes do not match, the optical decoder 20 outputs a cross-correlation waveform that does not have a large peak in any bit. In an asynchronous optical CDMA system using OOK data modulation, interference noise is generated in the photodetector 21 such as a PD (photodiode) due to this cross-correlation from an undesired user, and the system performance deteriorates.

  Theoretically, assuming that the number of users is 1, the photodetector 21 outputs a positive voltage P when a data “1” signal is received, and a voltage 0 when a data “0” signal is received. Output. This voltage P is detected from a large peak of the autocorrelation waveform. The data determiner 16 determines the data by comparing the output of the PD with a threshold level. The voltage P / 2 is used as the threshold level. On the other hand, if the number of users is K, we assume user 1 is the desired user and send all active user signals by asynchronous operation, and the chip is assumed to be synchronous between users. did.

τ _k ε (T _c , 2T _c ,..., 2T _b ) is defined as the relative time shift between user k and user 1. Tc and Tb are chip time and bit time, respectively. The photodetector 21 outputs a voltage S _1m (τ ₂ , τ ₃ ,..., Τ _k ) when a data “1” signal is received, and a voltage S _1S when a data “0” signal is received. (Τ ₂ , τ ₃ ,..., Τ _k ) are output. These voltages are modified by the relative time shift τ _k

When obtaining the BER, the thermal noise of the PD circuit is considered as zero average Gaussian noise having a deviation of σ ² . This noise is added to the output of the PD. Signal of the data "1" and "0" if they have equal probability for active users K's, the use of Gaussian approximation formula to thermal noise, BER P _e is as follows:

  FIG. 3 is a graph showing the calculation result of the bit error rate (BER). FIG. 3A shows the result of simulating the BER of the optical CDMA system based on the OOK modulation calculated as a function of γ from the equation (1). In this calculation, a Monte Carlo simulation was performed on the assumption that the maximum number of active users was 4 based on an 8-chip BPSK code and OOK data modulation in an optical CDMA system of 10 Gbit / s. Also, the relative time shift was changed randomly. In the figure, ch is an error floor when the number of channels, that is, the number of simultaneous users representing the number of users exceeds two. This indicates that asynchronous operation is not possible.

(2.2. BER of Optical CDMA System of the Present Invention)
Assuming asynchronous operation when the number of users is K, a balanced detector (optical detector A) such as a dual-pin PD receives a voltage S ₁ ^m (τ ₂ , τ) when data “1” is received. ₃ ,..., Τ _k ) and the data “0” signal is received, the balance detector (photodetector B) detects the voltage S ₁ ^s (τ ₂ , τ ₃ ,. _k ) is output. Dual - thermal noise of the pin PD is considered to be zero mean Gaussian noise with a deviation of 2 [sigma] ^2. If the signals of data “1” and “0” have equal probability for K active users, the BER (bit error rate) of an optical CDMA system using CSK data modulation can be obtained using a Gaussian approximation for thermal noise. ) Is expressed as the following equation (2).

FIG. 3B shows the result of simulating the BER value of the optical CDMA system of the present invention calculated from the equation (2) as a function of γ. Assuming 2 concurrent users, the BER is less than 10 ⁻⁹ in a 10 Gb / s optical CDMA system based on 8-chip BPSK code, CSK data modulation.

  That is, FIG. 3A and FIG. 3B show that the performance of the asynchronous optical CDMA system is improved by the CSK modulation of the present invention as compared with the conventional OOK modulation.

  Examples of the optical code shift keying system according to the present invention will be described below. FIG. 4 is a diagram showing a basic configuration of the 10 Gb / s optical CDMA system based on the 8-chip BPSK code and CSK data modulation used in the first embodiment. FIG. 5 shows waveforms at each point and experimental results. As shown in FIG. 4, the transmitter includes a light source 5, a 1 × 2 LN modulator (switch) as a modulator 6, two optical encoders A, and an optical encoder B.

  In this system, MLLD with a repetition frequency (10 GHz) was used as a light source. The 10 GHz 2.0-ps pulse train output from the MLLD is divided into two by the 1 × 2 LN modulator 6. A pulse for data “1” and a pulse for data “0” are supplied to optical encoders A and B, respectively. The monolithically integrated all-optical 8-chip BPSK code encoder / decoder consists of a tunable tap delay line shifter and an optical phase shifter. These are manufactured by planar lightwave circuit (PLC) technology. The tap was tuned to generate 8 pulses of equal amplitude. The optical carrier phase of each chip pulse is shifted by 0 or π by a phase shifter to generate an 8-chip optical BPSK code. The optical coupler (combiner) 9 is composed of a PLC 3 dB coupler.

  FIG. 5A shows the encoded signal A encoded by the optical encoder A. In FIG. 5A, there is data “1” (left side), and the phase of the optical pulse train giving “1” is “00000000” (8-chip BPSK code). FIG. 5B shows the encoded signal B encoded by the optical encoder B. In FIG. 5B, there is data of “0” (right side), and the phase of the optical pulse train giving “0” is “0π0π0π0π” (8-chip BPSK code).

  As shown in FIG. 4, the receiver includes two optical decoders A <b> 11, an optical decoder B <b> 12, dual pin PDs (balance detectors) 13 and 14, and a data determiner (threshold processing device) 15. FIG. 5C shows a signal received by the receiver. The reception signal is a decoded signal when data “10” is transmitted. That is, the signal received by the receiver is a combination of the signal in FIG. 5A and the signal in FIG. Therefore, in FIG. 5C, there are data of “1” (left side) and “0” (right side), and the phase of the optical pulse train giving “1” is “00000000”, giving “0”. The phase of the optical pulse train is “0π0π0π0π”.

  When the optical decoder A11 receives the data “1” signal, it outputs an autocorrelation waveform of code A. FIG. 5D shows the decoded signal A decoded by the optical decoder A. In FIG. 5D, there is data “1” (left side), and the optical pulse train giving “1” is an autocorrelation waveform.

  When the optical decoder B12 receives the data “0” signal, it outputs the autocorrelation of the code B. FIG. 5E shows the decoded signal B decoded by the optical decoder B. In FIG. 5E, there is data “0” (right side), and the optical pulse train giving “0” is an autocorrelation signal.

  The output signals of the optical decoder B12 and optical decoder A11 are balance detected by the dual-pin PD by subtracting the lower arm from the upper arm. FIG. 5F shows the data sent to the data determiner.

FIG. 6 shows the result of measuring the BER of an optical CDMA system based on CSK modulation and OOK modulation with PRBS of (2 ²³ -1) at 10 Gb / s when there is one user (Sinle ch .; single channel). To express. The measured BER is less than 10 ⁻⁹ . From FIG. 6, it can be seen that when the BER is 10 ⁻⁹ , according to the CSK modulation of the present invention, the optical input intensity is increased by 3 dB compared to the conventional OOK modulation.

  FIG. 7 shows an electrical signal input to the data determiner. FIG. 7A shows the CSK modulation of the present invention, and FIG. 7B shows the OOK modulation. In FIG. 7, the horizontal axis represents time, and the vertical axis represents voltage. The position on the horizontal axis corresponds to the threshold value in the data determiner. FIG. 7A shows that the threshold value can be set to 0 [V], for example, in the optical CDMA system of the present invention. At 0 [V], the range in which data can be discriminated is wide. On the other hand, the conventional OOK modulation optical CDMA system employs P / 2 [V] (a voltage position that is approximately half of the peak value) as a threshold value, and therefore the range in which data can be discriminated is narrow.

  The optical CDMA system of the present invention can be effectively used as a new optical CDMA system.

It is the schematic which shows the basic composition of the optical CDMA system of this invention. FIG. 2 is a conceptual diagram for explaining an electric signal waveform in the receiver. FIG. 2A is a diagram illustrating an example of an output waveform of the optical detector A. FIG. FIG. 2B is a diagram illustrating an example of an output waveform of the optical detector B. FIG. 2C shows an input waveform of the data determiner. FIG. 3 is a graph showing the calculation result of the bit error rate (BER). FIG. 3A shows the result of simulating the BER of the optical CDMA system based on the OOK modulation calculated as a function of γ from the equation (1). FIG. 3B shows the result of simulating the BER value of the optical CDMA system of the present invention calculated from the equation (2) as a function of γ. FIG. 4 is a diagram showing a basic configuration of the 10 Gb / s optical CDMA system based on the 8-chip BPSK code and CSK data modulation used in the first embodiment. FIG. 5 shows measurement data changed to a drawing showing examples of optical pulse trains and electrical signals at each point of the optical CDMA system of the present invention. FIG. 5A shows the encoded signal A encoded by the optical encoder A. FIG. 5B shows the encoded signal B encoded by the optical encoder B. FIG. 5C shows a signal received by the receiver. FIG. 5D shows the decoded signal A decoded by the optical decoder A. FIG. 5E shows the decoded signal B decoded by the optical decoder B. FIG. 5F shows the data sent to the data determiner. FIG. 6 shows the result of measuring the BER of an optical CDMA system based on CSK modulation and OOK modulation with PRBS of (2 ²³ -1) at 10 Gb / s when there is one user (Sinle ch .; single channel). It is a graph to represent. FIG. 7 shows an electrical signal input to the data determiner. FIG. 7A shows the CSK modulation of the present invention, and FIG. 7B shows the OOK modulation. FIG. 8 is a conceptual diagram showing a basic configuration of an optical CDMA system using conventional OOK data modulation. FIG. 9 shows an example of an electrical signal converted by the optical detector 21 in the conventional optical CDMA system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical CDMA system 2 of this invention Transmitter 3 Receiver 4 Fiber 5 Light source 6 Modulator 7 Mark optical encoder (optical encoder A)
8 Optical encoder for space (optical encoder B)
9 multiplexer 10 splitter 11 mark optical decoder (optical decoder A)
12 space optical decoder (optical decoder B)
13 Photodiode (Optical detector A)
14 Photodiode (Optical detector B)
15 Calculation circuit 16 Data judgment unit (threshold processing unit)
17 Optical CDMA system based on OOK modulation 18 External modulator 19 Optical encoder 20 Optical decoder 21 Optical detector

Claims (5)

A modulator (6) that distributes an optical pulse train generated at a bit period from a light source (5) into a mark and a space based on input data representing the mark or space ;
A mark optical encoder (7) for encoding the mark optical pulses distributed by the modulator as an optical pulse train having a fixed phase combination in which the phase of each pulse is controlled;
The optical pulses for space distributed by the modulator are encoded by forming an optical pulse train having a constant phase combination different from the optical pulse train encoded by the optical encoder for marks. An optical encoder for space (8),
A multiplexer (9) for multiplexing the optical pulse train encoded by the mark optical encoder and the optical pulse train encoded by the space optical encoder;
An optical communication transmitter using optical code shift keying modulation.   The transmitter according to claim 1, which is used for optical code division multiple access communication. A receiver for receiving optical data transmitted by the transmitter according to claim 1 or 2,
A demultiplexer (10) for demultiplexing the optical data transmitted by the transmitter;
A first optical decoder (11) for outputting optical data encoded by the mark optical encoder as an optical signal having an autocorrelation waveform among the optical data demultiplexed by the demultiplexer (10);
A first optical detector (13) for detecting the optical signal output from the first optical decoder (11);
A second optical decoder (12) for outputting the optical data encoded by the space optical encoder as an optical signal having an autocorrelation waveform among the optical data demultiplexed by the demultiplexer (10);
A second optical detector (14) for detecting the optical signal output from the second optical decoder (12);
A calculation circuit (15) for obtaining a difference between detection data of the first optical detector (13) and the second optical detector (14);
A data determination unit (16) for determining whether a mark or a space is based on a voltage value higher or lower than 0 [V] based on a difference between detection data obtained by the calculation circuit (15);
A receiver (3) comprising: An optical code division multiple access communication system comprising a plurality of optical communication transmitters and a plurality of optical communication receivers,
Each of the plurality of transmitters for optical communication is
A modulator (6) that distributes an optical pulse train generated at a bit period from a light source (5) into a mark and a space based on input data representing the mark or space ;
A mark optical encoder (7) for encoding the mark optical pulses distributed by the modulator as an optical pulse train having a fixed phase combination in which the phase of each pulse is controlled;
The optical pulses for space distributed by the modulator are encoded by forming an optical pulse train having a constant phase combination different from the optical pulse train encoded by the optical encoder for marks. An optical encoder for space (8),
A multiplexer (9) for multiplexing the optical pulse train encoded by the mark optical encoder and the optical pulse train encoded by the space optical encoder;
Comprising
Each of the plurality of optical communication receivers,
A demultiplexer (10) for demultiplexing the optical data transmitted by the transmitter;
A first optical decoder (11) for outputting optical data encoded by the mark optical encoder as an optical signal having an autocorrelation waveform among the optical data demultiplexed by the demultiplexer (10);
A first optical detector (13) for detecting the optical signal output from the first optical decoder (11);
A second optical decoder (12) for outputting the optical data encoded by the space optical encoder as an optical signal having an autocorrelation waveform among the optical data demultiplexed by the demultiplexer (10);
A second optical detector (14) for detecting the optical signal output from the second optical decoder (12);
A calculation circuit (15) for obtaining a difference between detection data of the first optical detector (13) and the second optical detector (14);
A data discriminator (16) for determining whether a mark or a space is based on a voltage value higher or lower than 0 [V] based on a difference between detection data obtained by the calculation circuit (15);
An optical code division multiple access communication system comprising: An optical code division multiple access communication method using the optical code division multiple access communication system according to claim 4,
The modulator distributes an optical pulse train generated from a light source at a bit period based on a data signal representing an input mark or space to a mark and a space, and
The mark optical encoder encodes the mark optical pulse train distributed by the modulator into an optical pulse train having a certain combination of phases ;
The space optical encoder encodes the space optical pulse train distributed by the modulator into an optical pulse train having a constant phase combination different from that of the mark optical encoder ;
The multiplexer multiplexes the pulse train encoded by the mark optical encoder and the pulse train encoded by the space optical encoder;
Transmitting the optical data combined in the step;
The demultiplexer (10) demultiplexes the optical data transmitted by the transmitter;
The first optical decoder (11) receives the optical data demultiplexed by the demultiplexer (10), and outputs the optical data encoded by the mark optical encoder as an optical signal having an autocorrelation waveform. And a process of
The first optical detector (13) detecting the output signal of the first optical decoder (11);
The second optical decoder (12) receives the optical data demultiplexed by the demultiplexer (10), and outputs the optical data encoded by the space optical encoder as an optical signal having an autocorrelation waveform. And a process of
The second optical detector (14) detecting the output signal of the second optical decoder (12);
The calculation circuit (15) obtaining a difference between detection data of the first optical detector (13) and the second optical detector (14);
Based on the difference of the detection data obtained by the calculation circuit (15), the data judgment unit (16) judges whether the mark or space is based on 0 [V] as a reference to a higher or lower voltage value. Process,
An optical code division multiple access communication method.