JP2688352B2 - Optical communication system and system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention mainly relates to a specific transmitter and receiver in a local optical fiber transmission system (so-called optical LAN system) having a loop / ring configuration or a bus configuration. The present invention relates to an optical communication system and system for performing communication by selecting a fixed frequency channel on the receiving side from which a communication is to be performed and transmitting a signal on that channel when setting communication between them. [Prior Art] Conventionally, in the case of a loop / ring configuration in which a transmission line is not terminated at a tip and is connected in a ring as an access method of a private optical transmission method, a token without a destination address is mainly used in the loop / ring. A token system in which a code called circulates in a fixed direction in sequence between terminal stations (Reference: Shigeo Tsujii,
Others "Optical Fiber Information Network", Shokodo pp.84-1
06) is used. On the other hand, in the case of a bus configuration in which the transmission path is terminated at the tip and the terminal station is connected to the T-branched tip, CSMA / CD (Carrier Sensing) that detects the usage status of the transmission path and accesses the other party
se Multiple Access with Collision Detection) method is mainly adopted. [Problems to be Solved by the Invention] In the token method, when a station having a transmission request receives a token, a transmission right is obtained, the token is taken into the own station, and data including a destination code and a transmission station code is transmitted. Therefore, the transmitting side and the receiving side are not in a state where they can directly transmit signals, and it is necessary to acces each terminal station one by one, and jump directly over the other terminal stations to access the other receiving station directly. There was a drawback that it was impossible to do. Moreover, when the token is lost from the loop / ring network, a plurality of tokens are generated, or the code format of the token is incorrect, there is a drawback that recovery is difficult. In addition, in the loop / ring configuration, optical (O) / electrical (E) conversion, electrical (E) / optical (O) conversion (hereinafter abbreviated to O / E conversion, E / O conversion) are used. Through,
Since tokens are exchanged, there is also a drawback that failures in O / E conversion and E / O conversion parts other than the optical transmission line make the operation of the entire system impossible. On the other hand, even in the CSMA / CD method used in the bus configuration, it is necessary to judge whether or not a call can be made based on the result of detecting the usage status of the transmission path due to the collision of signals. There was a problem that the utilization efficiency was relatively low. Therefore, an object of the present invention is to provide a local optical transmission system,
Access from the sending side to the receiving side can be done only indirectly, regardless of the loop / ring configuration, bus configuration, star configuration, etc., and in the O / E, E / O conversion part It is an object of the present invention to provide an optical communication system that solves the drawback that a failure stops the operation of the entire system. [Means for Solving the Problems] In order to achieve such an object, the present invention inserts optical branching / coupling means at a plurality of positions of an optical fiber transmission line, Transmitting / receiving devices are connected to each other via a branch optical fiber transmission line, each of the transmitting / receiving devices has a local oscillation light source for reception, and the optical frequency of the local oscillation light source is set differently for each transmitting / receiving device in advance. Fixed to a frequency, the optical frequency of the transmitting light source installed via the optical branching / coupling means is a predetermined optical frequency difference between the optical frequency of the receiving local oscillation light source of the transmitting / receiving device to be accessed among the transmitting / receiving devices. The optical communication system in which the light wave of the light source for transmission is incident on the optical fiber transmission line and propagated, and the transmitter / receiver to be accessed is selected and a signal is transmitted. The optical frequencies of the four-wave mixed light and the Brillouin scattered light generated by the light from the transmission light source and the reception local oscillation light source due to the third-order nonlinear optical effect in the optical fiber transmission line are the transmission frequencies. The optical frequencies of the transmitting light source and the receiving local oscillation light source are arranged so as not to overlap with the optical frequencies of the light source and the receiving light source. [Operation] According to the present invention, the optical transmission line network and the transmitter / receiver are connected via the optical fiber coupler which is a passive optical element regardless of the loop / ring configuration, the bus configuration, or the star configuration. The oscillation light frequency of the local oscillation light source for reception installed in the transmitter / receiver is set to a different value for each transmitter / receiver and fixed, and the oscillation light of the light source for transmission also installed in the transmitter / receiver is fixed. Optical heterodyne detection is performed by sweeping the frequency and fixing it so that the difference between it and the oscillation frequency of the receiving local oscillation light source of the transmitter / receiver of the other party you want to access becomes a predetermined intermediate frequency (for example, 1 to 2 GHz). . On the accessed side, the transmitting side can be grasped by the identification code sent from the transmitting / receiving device of the other party who has accessed, so that the difference between the transmitting side and the oscillation frequency of the local light source for reception on the transmitting side has a predetermined intermediate value. Access by frequency. As described above, both sides can transmit and receive. At that time, the optical frequencies of the four-wave mixed light and the Brillouin scattered light generated due to the third-order nonlinear optical effect in the optical fiber transmission line by the light from the transmission light source and the reception local oscillation light source are the same as those for the transmission. The optical frequencies of the transmission light source and the reception local oscillation light source are arranged so as not to overlap with the optical frequencies of the light source and the reception local oscillation light source, and further, if necessary, the optical frequencies of the transmission light source and the reception light source. By variably adjusting the frequency difference with the optical frequency in each transmitting / receiving device, crosstalk between channels occurring in the optical fiber transmission line can be suppressed.
According to the present invention, it is possible to directly access the partner receiving terminal station,
Also, the optical fiber transmission line and the transmission / reception terminal station are connected without passing through the O / E and E / O conversion elements. Example An example of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a system diagram showing the configuration of the first embodiment of the present invention, in which 1 is a single-mode optical fiber transmission line having a loop / ring configuration, 2-1, 2-2, ... 2-N is a transmission / reception device, that is, a terminal device. 3-1,3-2, ..., 3-N, 3-
J is the optical fiber transmission line 1 and each terminal station device 2-1, 2-2, ..., 2
-N, an optical branching / coupling unit, 4-1 and 4-2, ...,
4-N and 4-J are terminal devices 2-1 and 2-2, ..., 2-N and optical branching / coupling units 3-1, 3-2, ..., 3-N and 3-J. It is a single mode optical fiber for wiring that connects the two. The N-th terminal station device 2-N and the optical branching / coupling unit 3-N will be described in detail below as an example. In the optical branching / coupling unit 3-N, 5 is an optical branching / coupling device arranged between the optical fiber transmission line 1 and the wiring optical fiber 4-N, and 6 is the optical fiber transmission line 1 and the wiring optical fiber 4. It is an optical coupler disposed between the -N and the -N. In the terminal device 2-N, 7 is an optical coupler, 8 and 9 are optical isolators, 10 is a transmitting DFB laser or CSP laser,
11, 12 is an optical frequency adjusting device, 13 is a modulator, 14 is a local laser for reception by DFB laser or CSP laser, and 15 is InGaA
avalanche photo diode (APD) or Ge
An APD photodetector, 16 a bandpass filter, 17 a demodulator, and 18 a signal processor. Here, the oscillation frequency f _LN of the receiving local laser 14 is fixed by the optical frequency adjusting device 12 configured by a feedback system using the Fabry-Perot etalon and PID control (e.g., EJBachus, et al., Electron. Lett., Vol.21,
p.1203,1985). The light of this frequency f _LN is _supplied to the optical isolator 9
And is led to the optical coupler 7. The optical signal propagating through the optical fiber transmission line 1 is passed from the optical branching / coupling device 5 to the wiring optical fiber 4-N and further to the optical coupler 7 and the light of the frequency f _LN from the optical isolator 9 and the photodetector 15 The optical heterodyne beat spectrum is detected here. Since optical signals from various terminal equipments are propagating in the optical fiber transmission line 1, various beat outputs with the local oscillation frequency f _LN extracted from the optical coupler 7 are generated. Here, in the present embodiment, an optical signal having a frequency whose frequency difference from the frequency f _LN is smaller than a predetermined intermediate frequency f _im is transmitted from the partner terminal station apparatus which wants to communicate with the terminal apparatus 2-N. The frequency band of the bandpass filter 16 is determined so that the signal in the frequency domain of the intermediate frequency f _im passes through the bandpass filter 16. Therefore, of the beat signals detected by the photodetector 15, only the signal from the partner terminal device that wants to communicate with the terminal device 2-N passes through the bandpass filter 16. By demodulating the filter output by the demodulation device 17, data from the other party, for example, a message text is extracted. This data is supplied to the signal processing device 18, for example, a microprocessor to decode the other party's identification code, and data such as message text is output from the output unit 19 such as a display, a printer or a speaker. With respect to the other party identified here, the terminal station device 2-
In order to send the signal from N, the frequency f _TN of the optical signal from the transmitting laser 10 is _beaten at the identified other party with a constant frequency difference with respect to the local oscillation frequency, that is, the intermediate frequency f _im. It is necessary to adjust to a frequency that can be taken. Therefore, the identification code of the other party obtained by the signal processing device 18 is supplied to the optical frequency adjusting device 11,
The transmission light frequency f _TN of the transmission laser 10 is adjusted. The optical frequency adjusting device 11 can be configured on the same principle as the optical frequency adjusting device 12. In the signal processing device 18, the data input from the input unit 20 such as a keyboard and a microphone is organized into an appropriate format, the data is sent to the transmitting laser 10 via the modulator 13, and the optical frequency f _TN is sent. To the optical fiber transmission line 1 via the optical isolator 8 and the wiring optical fiber 4-N through the optical branching / coupling device 5. Reference numeral 21 is an optical frequency monitor device, which is a terminal device 2-1 or 2
This is for monitoring the local oscillation frequency of each of the receiving local oscillation lasers 14 installed at -2, ..., 2-N. Here, the local oscillation frequency signal of the local oscillation laser 14 in each terminal equipment is sent from the optical isolator 9 to the optical fiber transmission line 1 by the optical coupler 6 via the optical coupler 7 and the wiring optical fiber 4-N. To be done. In the optical frequency monitoring device 21, from the optical signals branched from the optical fiber transmission line 1 by the optical branching / coupling unit 3-J and further guided through the wiring optical fiber 4-J, the above-mentioned local oscillation frequencies The signal of is taken out and monitored. Next, the operation principle of this embodiment will be described. Here, as an example, consider a case where the terminal station 2-J accesses the terminal station device 2-N. As shown in FIG. 2, the oscillation frequencies f _L1 , f _L2 , ..., f _LN of the local laser for reception 14 installed in each terminal device are Δf _k (k = 1,
2, ..., N-1) are arranged at the peripheral fractional intervals and are fixed by the optical frequency adjusting device 12. The band pass filter 16 of the terminal device 2-N has an intermediate frequency.
Since it is configured to pass a signal in the frequency domain of f _im (f _im <Δf _k / 2), the terminal station device 2-J (J ≠) on the transmission side.
In N), the optical frequency f _TJ of the transmission laser 10 is swept by the optical frequency adjusting device 11, and the terminal device 2 to which the communication is desired.
The optical heterodyne beat spectrum as shown in FIG. 3 can be detected only when f _TJ = f _LN ± f _im (1) is fixed to the local oscillation frequency f _{LN of} N. Third
In the illustrated example, f _im = 1.35 GHz. In addition, each terminal device, RO in the signal processing device 18 the data on the local oscillation frequency pre-allocated to all the terminal equipment, that is, the data of the local oscillation frequency for each terminal equipment.
It should be stored in M beforehand. As described above, the call from the terminal device 2-J to the terminal device 2-N becomes possible. It should be noted that, even in the terminal devices other than the terminal device 2-N, the transmission signal from the terminal device 2-J is incident as the light intensity via the optical branching / combining device corresponding to the optical branching / combining device 5. However, since the optical frequency arrangement shown in FIG. 2 is set in advance so as not to satisfy the condition of the expression (1), information cannot be transmitted to other terminal stations. In this way, it becomes possible to directly access the receiving end terminal device 2-N from the transmitting end terminal device 2-J, and moreover, from which end terminal device the message text from the transmitting end terminal device 2-J is transmitted. By inserting an identification code that clearly indicates whether or not the optical frequency adjusting device 11 receives the terminal device 2-N on the receiving side.
The optical frequency f _TN of the transmitting laser 10 is swept to a value different from the oscillation frequency f _LJ of the receiving local oscillator 14 of the terminal device 2-J by an intermediate frequency f _im , and is fixed, so that the two ends are fixed. It is possible to transmit and receive a complete data signal or the like between the station device 2-J and the terminal device 2-N. Moreover, it is possible to perform signal transmission / reception without adversely affecting any terminal equipment other than these two terminal equipments. At that time, four-wave mixing light (for example, N.Shibat
a.et al., Electron.Lett., vol.22, p.675,1986) and Brillouin scattered light (for example, N.Shibata, et al., Opt.Lett., v
ol.12, p269, 1987) so that the frequency interval must be set so that it does not overlap with the oscillation optical frequency of the transmitting and receiving light source. For four-wave mixed light, Δf _i ≠ Δf _j (i ≠ j; i, j = 1,2, ..., N-1) in the frequency arrangement shown in FIG.
Should be arranged so as to satisfy. Regarding the Brillouin scattered light, it is necessary to adjust the operating wavelength so that the optical frequency difference between the transmitting and receiving lasers does not match the Brillouin shift amount. Further, it is also necessary to make the intermediate frequency f _im variable in each transmitting / receiving device. FIG. 4 is a system diagram showing the configuration of the second embodiment of the present invention. Here, the same parts as those in FIG. 1 are designated by the same reference numerals. In FIG. 4, reference numeral 30 denotes an optical fiber transmission line having a bus structure,
Reference numerals 31 and 32 are terminations for terminating both ends of the transmission line 30 by impedance matching. In this embodiment, in the optical branching / combining device 3-N, the optical branching / combining device 5 is for receiving a signal from the optical fiber transmission line 30, and receives the optical signal from the transmitting laser 10 by the optical fiber transmission line. A separate optocoupler 33 is provided for delivery to 30. The configuration itself of the terminal equipment 2-N is the same as that of the embodiment shown in FIG. 1, and therefore the transmission / reception between the terminal equipments is also the first.
This is exactly the same as the case of the loop / ring configuration shown in the figure. It should be noted that it is clear from the aforementioned reference: Shigeo Tsujii et al., The optical fiber information network that the star configuration of the optical fiber transmission line is included in a part of the bus configuration.
Since the configuration shown in FIG. 4 can be used, its details are omitted. [Effects of the Invention] As described above, according to the present invention, a terminal station connected to an optical fiber transmission line of various forms such as a loop / ring configuration, a bus configuration or a star configuration via a passive optical element. When communicating between devices, set the oscillation optical frequency of the local oscillator for reception installed in the transmitter and receiver to a different value for each transmitter and receiver, and fix it. Optical heterodyne detection is performed by sweeping the oscillation light frequency of the credit light source and fixing it so that the difference between it and the oscillation frequency of the receiving local oscillation light source of the transmitter / receiver of the other party to access is a predetermined intermediate frequency. , It is possible to directly access the receiving terminal equipment of the other party, and it is not necessary to connect the optical fiber transmission line and the terminal equipment via the O / E and E / O conversion parts. Compared to down method or CSMA / CD method has an advantage of high utilization efficiency of the optical fiber transmission line. Furthermore, the optical frequencies of the four-wave mixed light and Brillouin scattered light generated due to the third-order nonlinear optical effect in the optical fiber transmission line by the light from the transmission light source and the reception local oscillation light source are the transmission light source and The optical frequencies of the transmitting light source and the receiving local oscillation light source are arranged so as not to overlap with the optical frequency of the receiving local oscillation light source, and further, if necessary, the optical frequencies of the transmitting light source and the receiving light source. By variably adjusting the frequency difference between the transmission and reception devices, it is possible to suppress crosstalk between channels that occurs in the optical fiber transmission line.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram showing a configuration of an embodiment in which the present invention is applied to a loop / ring optical fiber transmission line, and FIG. 2 is an optical frequency of oscillation light of a local laser for reception. FIG. 4 is a layout diagram, FIG. 3 is a waveform diagram showing an example of the measurement result of the optical heterodyne beat spectrum between the transmitting laser light and the receiving local laser light, and FIG. It is a systematic diagram which shows the structure of the applied example. 1 ... Loop / ring single-mode optical fiber transmission line, 2-1-2-2, ..., 2-N ... Terminal device, 3-1, 3-2, ..., 3-N, 3 -J ... Optical branching / coupling unit composed of optical fiber coupler, etc., 4-1,4-2, ..., 4-N, 4-J ... Single-mode optical fiber transmission line for wiring, 5 , 6,7 …… Single-mode optical fiber coupler, 8,9 …… Optical isolator, 10 …… Transmit DFB laser or CSP laser, 11,12 …… For example optical frequency adjustment using Fabry etalon and PCD control mechanism Device, 13 ... Modulator, 14 ... Receiving DFB laser or CSP laser, 15 ... Photodetector such as InGaAs-APD, Ge-APD, 16 ... Bandpass filter, 17 ... Demodulator, 18 ... … Signal processing device, 19 …… output part, 20 …… input part, 21 …… optical frequency monitor device, 30 …… bus configuration single mode optical fiber transmission line, 31,32 …… terminating part, 33 …… optical Combiner .

Claims (1)

(57) [Claims] Optical branching at multiple positions in the optical fiber transmission line
A coupling means is inserted, and a transmission / reception device is connected to the optical branching / coupling means via a branch optical fiber transmission line, and each of the transmission / reception devices has a local oscillation light source for reception, and light of the local oscillation light source. The frequency is fixed to a predetermined frequency different from each other for each transmitting / receiving device, and the optical frequency of the transmitting light source installed via the optical branching / coupling means is for receiving the transmitting / receiving device of the transmitting / receiving device to be accessed. The optical frequency of the local oscillation light source is adjusted so as to have a predetermined optical frequency difference, the light wave of the light source for transmission is incident and propagated in the optical fiber transmission line, and the transmission / reception device to be accessed is selected to output a signal. An optical communication system for transmitting, which is generated by light from the transmitting light source and the receiving local oscillation light source due to a third-order nonlinear optical effect in the optical fiber transmission line. Arranging the optical frequencies of the transmitting light source and the receiving local oscillation light source so that the optical frequencies of the generated four-wave mixed light and the Brillouin scattered light do not overlap with the optical frequencies of the transmitting light source and the receiving light source. A characteristic optical communication system. 2. Optical branching at multiple positions in the optical fiber transmission line
A coupling means is inserted, and a transmission / reception device is connected to the optical branching / coupling means via a branch optical fiber transmission line, and each of the transmission / reception devices has a local oscillation light source for reception, and light of the local oscillation light source. The frequency is fixed to a predetermined frequency different from each other for each transmitting / receiving device, and the optical frequency of the transmitting light source installed via the optical branching / coupling means is for receiving the transmitting / receiving device of the transmitting / receiving device to be accessed. The optical frequency of the local oscillation light source is adjusted so as to have a predetermined optical frequency difference, the light wave of the light source for transmission is incident and propagated in the optical fiber transmission line, and the transmission / reception device to be accessed is selected to output a signal. In the transmitting / receiving device which is desired to be transmitted and accessed, the optical frequency of the optical signal received from the optical branching / coupling means for the transmitting / receiving device and the receiving station oscillation light Output of the difference frequency from the local oscillation frequency, and extracts the frequency component within the predetermined frequency from the difference frequency output, and reproduces the signal from the transmission / reception device requesting access from the frequency component. In the optical communication system, the optical frequencies of the four-wave mixed light and Brillouin scattered light generated due to the third-order nonlinear optical effect in the optical fiber transmission line by the light from the transmitting light source and the receiving light source are An optical communication system, wherein the optical frequencies of the transmitting light source and the receiving local oscillation light source are arranged so as not to overlap with the optical frequencies of the transmitting light source and the receiving light source. 3. When the optical frequency of the transmitting light source and the optical frequency of the receiving local oscillation light source are adjusted to have a predetermined optical frequency difference, the predetermined optical frequency difference can be variably adjusted by each transmitting / receiving device. The optical communication system according to claim 1 or 2, characterized in that it is made. 4. An optical fiber transmission line, an optical branching / coupling unit inserted at each of a plurality of positions of the optical fiber transmission line, and a transmitting / receiving device connected to the optical branching / coupling unit via a branching optical fiber transmission line, respectively. Each of the transmitting / receiving devices has a receiving local oscillation light source, a transmitting light source, and a frequency adjusting means, and the optical frequency of the receiving local oscillation light source is a predetermined frequency different from each other for each transmitting / receiving device. The frequency adjusting means adjusts the optical frequency of the transmitting light source so as to have a predetermined optical frequency difference from the optical frequency of the receiving local oscillation light source of the transmitting / receiving device to be accessed among the transmitting / receiving devices, and transmits the signal. The optical frequencies of the credit light source and the receiving local oscillation light source are determined by the light from the transmitting light source and the receiving local oscillation light source, and the third-order nonlinear optical in the optical fiber transmission line. An optical communication system, wherein the optical frequency of the four-wave mixing light generated due to the fruit and the Brillouin scattered light is arranged so as not to overlap with the optical frequency of the transmission source and the reception source.