JPH104386A - Optical homodyne detection communication system and equipment, and system and equipment for optical code division multiplex transmission using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a frequency of a conventional homodyne communication system stable in which an optical frequency converter is used to recover a reception signal as a local oscillating light with a different frequency and to detect the signal. SOLUTION: An optical coder 10 generates an optical pulse of an orthogonal code from a beam of a laser 1 on the transmitter side and an optical amplitude modulator 2 applies optical amplitude modulation to the generated light by information bits. Then an output of an optical local oscillator 5 having a frequency different from the frequency of the laser 1 is branched into two to conduct optical homodyne detection on the receiver side, a frequency converter 6 is used to recover information of the received signal with one local oscillation light, the recovered information is synthesized with the other local oscillation light at a 3dB coupler 8, a balanced photoelectric converter 9 conducts inverse spread and photoelectric conversion and an optical current is integrated by an integration device 13 and discriminated by a peak discrimination device 14 to detect the transmission information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical homodyne detection system and apparatus using an optical frequency converter, and an optical code division multiplex transmission system and apparatus using the optical homodyne detection technique.

[0002]

2. Description of the Related Art The greatest advantage of the homodyne system is that the receiving sensitivity is improved. The conventional homodyne receiver is characterized in that the frequency and phase of the local oscillation light are adjusted on the receiving side so that they always match those of the received signal carrier.

On the other hand, in the optical code division multiplex communication, the same optical transmission line is shared by using different spreading codes for a plurality of communication channels, the transmission band of the transmission line is effectively used, and the communication capacity is expanded. Multiplex transmission technology for A conventional optical code division multiplex transmission type receiver is characterized in that, for example, the output of a ladder network type optical matched filter is directly detected.

[0004]

As shown in FIG. 3, in the conventional homodyne receiver, the frequency and phase of the local oscillation light must be adjusted to always match that of the carrier of the received signal. . Therefore, what is important is how to stabilize the frequency of the optical local oscillator 5. If the oscillation light is unstable, the frequency fluctuation or phase fluctuation degrades the bit error rate, and consequently the receiving sensitivity. That is, since the problems of frequency stability and frequency and phase adjustment techniques remain, the homodyne reception technique has not been put to practical use at present.

In the conventional optical pulse time-division division multiplexing transmission system shown in FIG. 5, an optical pulse modulated by information bits is spread in a time domain by a ladder network type optical encoder 22 and sent to a receiving side. On the receiving side, after despreading by the ladder network type matched filter decoder 23, the photocurrent directly detected by the photodetector 24 is integrated, and
Further, transmission information is detected by discriminating the wave height.

However, a problem with this optical pulse time spreading division multiplexing transmission method is that despreading is performed by the ladder network type matched filter decoder 23.
Even if the orthogonal code is used, other channel interference remains, and the reception sensitivity is degraded. In addition, since sidelobes occur in despreading, the wave height discriminator 14 must be operated at the chip rate. Therefore, the chip rate is limited to the threshold processing ability, and if the transmission band of the transmission path is used effectively, it will not be a hindrance to the expansion of the communication capacity.

[0007]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above, and has a transmitting side which outputs an optical pulse signal obtained by modulating an output light of a transmission laser with an information bit by an optical amplitude modulator. In order to transmit through an optical transmission line and perform optical homodyne detection on the receiving side, the output of an optical local oscillator that outputs a frequency different from that of the transmitting laser is split into two,
The output of one of the optical local oscillators is multiplexed with the received signal,
Further, by inputting to the optical frequency converter, the information bits of the received signal are reproduced as an optical signal equal to the frequency of the optical local oscillator, and multiplexed with the output of the other optical local oscillator for photoelectric conversion. To provide an optical homodyne detection communication system for detecting transmission information.

According to the present invention, the transmitter comprises a transmission laser and an optical amplitude modulator, and the receiver comprises an optical frequency converter.
Provided is an optical homodyne detection communication device including an optical local oscillator, first and second optical multiplexers, and an optical detector.

Also, the present invention provides a method for multiplexing a plurality of channels using different optical codes using the above-described optical homodyne detection communication system, transmitting the multiplexed signals simultaneously using one optical transmission line, and optically decoding each of the channels. In an optical code division multiplexing communication network that performs channel identification by converting the output, the output of the transmission laser is converted into an optical pulse code by an optical encoder, and the generated optical code is optically amplitude-modulated with information bits, and On the receiving side, despreading and photoelectric conversion are performed by an optical frequency converter, an optical local oscillator that outputs a frequency different from that of the transmission laser, an optical encoder, first and second multiplexers, and an optical detector. An optical pulse time-division division multiplexing transmission method for detecting transmission information by integrating the output and discriminating the wave height is provided.

According to the present invention, a plurality of channels are multiplexed using different optical codes using the above-mentioned optical homodyne detection communication system, and are simultaneously transmitted through one optical transmission line, and each of the channels is optically decoded. In an optical code division multiplex communication network that performs channel identification by
On the transmitter side, the output of the transmission laser is converted into an optical pulse code by an optical encoder, and the generated optical code is optically amplitude-modulated with an information bit by an optical amplitude modulator, and on the receiver side, an optical frequency converter, An optical local oscillator that outputs a frequency different from that of the transmission laser, an optical encoder similar to the optical encoder, first and second multiplexers, and despreading and photoelectric conversion by an optical detector, and a photoelectric output is performed. Provided is an optical pulse time-division-division multiplexing transmission device that detects transmission information by integrating with an integrator and discriminating a peak with a peak discriminator.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows an optical homodyne detection system using an optical frequency converter according to a first embodiment of the present invention. On the transmitting side, amplitude modulation is performed on a laser 1 by a modulator 2 using information bits, and this modulation is performed. The output of the optical local oscillator 5 that outputs a frequency different from that of the laser 1 is split into two in order to transmit the resulting signal through the optical transmission line 3 and perform optical homodyne detection. The signal is multiplexed with the received signal by the coupler 4 and input to the optical frequency converter 6, where the information bits of the received signal are reproduced as an optical signal having the frequency of the optical local oscillator 5.

When the information signal is "1", the optical frequency converter 6 does not amplify the local oscillation light by the received signal,
When the information signal is "0", the local oscillation light is amplified, so that the output of the optical amplifier reproduces the transmission signal as an optical signal having the frequency of the local oscillation light.

The output of the optical amplifier is filtered using a filter 7 to remove the frequency component of the transmission signal, multiplexed with a local oscillation light, which is the other output, by a 3 dB coupler 8, and output by a balanced optical detector 9. This is an optical homodyne detection method for detection.

FIG. 4 shows a conventional optical frequency converter as an example. The output light of the laser 1 is amplitude-modulated by the modulator 2, multiplexed with the output light of the optical local oscillator 5 having a different frequency by the 10/1 coupler 4, and input to the optical frequency converter 6.

The optical frequency converter 6 does not amplify the local oscillation light according to the received signal when the information signal is "1" and amplifies the local oscillation light when the information signal is "0". At the output, the transmission signal is reproduced as an optical signal having the frequency of the local oscillation light. Further, since the frequency components of the laser 1 and the frequency component of the optical local oscillator 5 pass through the filters 20 and 7, respectively, it is possible to detect the respective signals.

FIG. 2 is a block diagram showing the concept of the optical code division multiplex transmission system of the present invention. An optical pulse generated by an optical encoder 10 which is opposite to the orthogonal code of the laser 1 as a light source is modulated by an amplitude modulator 2 by a signal which is opposite to an information bit, and a star coupler 12 is formed like other channels.
Are transmitted on the same optical transmission line. On the receiving side, the light of the optical local oscillator 5 is split into two waves, and the transmission signal is reproduced by the optical frequency converter 6 with an optical signal having the frequency of one of the local oscillation lights.

The other local oscillation light is converted into an orthogonal code optical signal by the encoder 10, further multiplexed with the output light of the optical frequency converter 6 by the 3 dB coupler 8, and despread by the balanced optical detector 9. This is a transmission method in which photoelectric conversion is performed, and a photocurrent is detected by using an integrator 13 and a wave height discriminator 14 to detect transmission information. Since the despreading process is different from the conventional method,
When a synchronous orthogonal code transmission system is used, there is no interference component. In addition, since the wave height discriminator operates at the bit rate, the chip rate is not limited to the threshold processing capacity.

As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and may be implemented in any manner unless the configuration described in the claims is changed. it can.

[0019]

As described above, in the optical homodyne communication system and apparatus according to the present invention, unlike the conventional optical homodyne communication system, the received signal is reproduced by the optical frequency converter as locally oscillated light having a different frequency, and detected. Therefore, the problem of frequency stability in the conventional homodyne communication method can be overcome.

Further, in the optical code division multiplex transmission system of the present invention, since despreading and detection without any other channel interference can be realized, the threshold value processing capability and the other channel interference in the conventional optical code division multiplex transmission system are realized. It has tremendous effects, such as overcoming the problem described above.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an optical homodyne detection system according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an optical code division multiplex transmission system using optical homodyne detection according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional optical homodyne detection system.

FIG. 4 is a block diagram showing a configuration of a conventional optical frequency converter.

FIG. 5 is a block diagram showing a configuration of a conventional all-optical time-band spreading / encoding multiplex transmission system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmission laser 2 optical amplitude modulator 3 optical transmission line 4 10/1 coupler 5 optical local oscillator having wavelength different from transmission laser 6 optical frequency converter 7 optical local oscillator wavelength pass filter 8 3 dB coupler 9 optical balance detector 10 (0 1) Optical encoder of code 12 Star coupler 13 Integrator 14 Wave height discriminator 15 Preamplifier 16 Mixer 17 Baseband amplifier 18 Equalizer 19 Optical local oscillator having the same wavelength as transmitting laser 20 Transmitting laser wavelength pass filter 21 Reception 22 Ladder network type optical encoder 23 Ladder network type matched filter decoder 24 Photoelectric converter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location H04J 14/00 14/04 14/06 H04B 1/707

Claims (4)

[Claims] 1. A transmitting side outputs an optical pulse signal obtained by modulating an output light of a transmitting laser with an information bit by an optical amplitude modulator and transmits the signal through an optical transmission path, and performs optical homodyne detection on a receiving side. Therefore, by splitting the output of the optical local oscillator that outputs a frequency different from that of the transmission laser into two, multiplexing the output of one of the optical local oscillators with the received signal, and further inputting it to the optical frequency converter, The information bits of the received signal are reproduced as an optical signal equal to the frequency of the optical local oscillator, and the transmission information is detected by multiplexing with the output of the other optical local oscillator and performing photoelectric conversion. Optical homodyne detection communication system. 2. The transmitter comprises a transmission laser and an optical amplitude modulator, and the receiver comprises an optical frequency converter, an optical local oscillator, first and second optical multiplexers, and an optical detector. An optical homodyne detection and communication device, comprising: 3. An optical homodyne detection communication system according to claim 1, wherein a plurality of channels are multiplexed using different optical codes and transmitted simultaneously using one optical transmission line.
In an optical code division multiplexing communication network that performs channel identification by optically decoding each of the above channels, on the transmitting side, the output of the transmission laser is converted into an optical pulse code by an optical encoder, and the generated optical code is converted into information bits. At the same time as the optical amplitude modulation at the receiving side, an optical frequency converter on the receiving side, an optical local oscillator that outputs a frequency different from the transmission laser, an optical encoder,
Despreading by the first and second multiplexers and the photodetector,
An optical code division multiplexing transmission system for detecting transmission information by performing photoelectric conversion, integrating photoelectric output, and discriminating wave height. 4. Using the optical homodyne detection communication system according to claim 1, a plurality of channels are multiplexed using different optical codes and transmitted simultaneously using one optical transmission line.
In an optical code division multiplexing communication network that performs channel identification by optically decoding each of the above channels, on the transmitter side, the output of the transmission laser is converted into an optical pulse code by an optical encoder, and the generated optical code is converted into information. At the receiver side, the optical amplitude modulator modulates the optical amplitude with the bit, and at the receiver side, an optical frequency converter, an optical local oscillator that outputs a frequency different from the transmission laser, an optical encoder similar to the optical encoder, first and The second multiplexer and the photodetector perform despreading and photoelectric conversion, integrate the photoelectric output with an integrator, and then discriminate the wave height with a wave height discriminator to detect transmission information. Optical code division multiplex transmission equipment.