WO2000027055A1

WO2000027055A1 - System suitable for monitoring control in optical transmission

Info

Publication number: WO2000027055A1
Application number: PCT/JP1998/004920
Authority: WO
Inventors: Noriaki Mizuguchi
Original assignee: Fujitsu Limited
Priority date: 1998-10-30
Filing date: 1998-10-30
Publication date: 2000-05-11

Abstract

A system has first and second terminal station devices and first and second optical fiber transmission lines installed between the terminal station devices. The first terminal station device includes a first unit which sends out a first light signal through the first optical fiber transmission line. The second terminal station device includes a second unit which receives the first light signal transmitted through the first optical fiber transmission line, a third unit which detects a parameter concerning the waveform of the received first light signal, and a fourth unit which sends out a second light signal representing the detected parameter through a second optical fiber transmission line. The first terminal station device includes a fifth unit which receives the second light signal transmitted through the second optical fiber transmission line, a sixth unit which compares the parameters before and after the transmission of the first light signal with each other with reference to the received second light signal, and a seventh unit which controls the first light signal in accordance with the comparison results so as to optimize the parameter after the transmission of the first light signal.

Description

System technology suitable for monitoring and control in optical transmission

The present invention relates to a system suitable for monitoring and control in optical transmission. Art

In recent years, the manufacturing technology and use technology of low-loss (for example, 0. 2 dB / km) quartz optical fiber have been established, and optical communication systems using optical fiber as a transmission path have been established. Stems have been put into practical use. Optical amplifiers for amplifying optical signals or signal light have been put to practical use in order to compensate for the loss in the optical fiber and enable long-distance transmission. It has been.

Conventionally known are an optical amplifying medium to which the signal light to be amplified is supplied, and an optical amplifying medium such that the optical amplifying medium provides a gain band including the wavelength of the signal light. An optical amplifier consisting of a means for pumping is used.

For example, an enormous beam fiber-optic amplifier (EDFA) was developed to amplify signal light in the 1.5-m wavelength band with low loss in a quartz fiber. ing . EDFA is an optical amplification medium (EDF), and a pump light source for supplying a pump light having a predetermined wavelength to the EDF. . The 0.998 9111 band has a gain band including the wavelength of 1.55 / m by using pump light having a wavelength of 1.48 zm band. can get .

Wavelength division multiplexing (WDM) is a technique for increasing the transmission capacity of an optical fiber. In a system to which WDM is applied, a plurality of optical carriers having different wavelengths are used. Multiple optical signals obtained by independently modulating each optical carrier were wavelength-division multiplexed by an optical multiplexer, and the results were obtained. The WDM signal light is sent out to the optical fiber transmission line. On the receiving side, the received WDM signal light is separated into individual optical signals by an optical demultiplexer, and transmission data is reproduced based on each optical signal. Therefore, by applying WDM, it is possible to increase the transmission capacity in one optical fiber according to the multiplexing number.

In this type of system, it is important to measure the chromatic dispersion of the optical fiber transmission line and control the spectrum of the signal light. Chromatic dispersion, often referred to simply as dispersion, is a function of the group velocity of an optical signal in an optical fiber as a function of the wavelength (frequency) of the optical signal. This is a phenomenon that changes as a result. For example, in a standard single mode optic, for a wavelength shorter than 1.3 μm, an optical signal with a longer wavelength is often better. Propagation faster than an optical signal having a shorter wavelength and the resulting dispersion is usually referred to as normal dispersion. For wavelengths longer than 1.3 / m, an optical signal with a shorter wavelength propagates faster than an optical signal with a longer wavelength, and The resulting variance is called the anomalous variance.

The spectrum of the signal light is controlled by automatic temperature control of the laser diode used as the light source or by band control of the optical bandpass filter. These can be provided by a control loop in the optical transmitter.

The dispersion measurement of the optical fiber can be performed by comparing the detection results of the pulse width when transmitting and receiving the optical signal. For example, based on the result of dispersion measurement, control is performed by using the spread spectrum of the transmission signal light and the feedforward so that the optimum reception state is obtained. It is done. That is, the specifications of the spectrum are determined from the dispersion measurement results, and an optical signal having the optimum amplitude, center wavelength, and pulse width is generated.

With this conventional technology, it is not possible to monitor the characteristics of an optical signal after transmission, and if an error occurs in the line, In this case, it is only possible to switch to a backup line after the occurrence of an error, for example, and it is not possible to optimize the characteristics.

A feedback control technique between terminal devices, including matters related to the dispersion of optical fibers, is disclosed in, for example, Japanese Patent Application Laid-Open No. H08-321805. . However, the specific configuration of the control circuit is not disclosed in the official gazette.

Accordingly, it is an object of the present invention to provide a specific configuration of a system for monitoring and controlling suitable for feedback control between terminal devices. .

Opening of the light

According to the present invention, the first and second terminal stations and the first and second terminal devices laid between the first and second terminal devices are provided.

A system having first and second optical fiber transmission lines is provided. First end station device, it leaves send a first Mitsunobu ^"1 7 to the first optical full § I bus transmission path first

Includes 1 means. The second terminal device comprises: a second means for receiving the first optical signal transmitted by the first optical fiber transmission line; and a waveform of the received first optical signal. A third means for detecting a parameter relating to the second parameter, and transmitting a second optical signal representing the detected parameter to a second optical fiber transmission line. And the fourth means. Then, the first terminal device is connected to the second terminal device. Fifth means for receiving the second optical signal transmitted by the optical fiber transmission path of the first optical signal, and before and after the transmission of the first optical signal based on the received second optical signal. A sixth means for comparing the parameters of the first optical signal, and a first optical signal such that the parameters after the transmission of the first optical signal are optimized based on the comparison result. And a seventh means for controlling

According to this system, since the first and second optical fiber transmission lines are laid between the first and second terminal devices, the first optical fiber is provided. Information including parameters relating to the waveform of the first optical signal transmitted by the fiber transmission path is transmitted to the second optical fiber via the second optical fiber transmission path. Since the signal can be transmitted from the second terminal device to the first terminal device by the signal, feedback control between the terminal devices with respect to the first optical signal can be performed. O It is possible to provide a specific configuration of the system for monitoring and control.o Brief description of drawings

FIG. 1 is a block diagram showing an embodiment of the system according to the present invention;

Figure 2 is a block diagram of each optical transceiver shown in Figure 1;

FIG. 3 shows the unit control circuit 5 2 shown in FIG. Peripheral block diagram;

FIG. 4 is a flow chart showing a first embodiment of the control flow according to the present invention;

Figures 5A and 5B show the results of chromatic dispersion. Diagram to explain the change of the loose waveform;

FIG. 6 is a flowchart showing a second embodiment of the control flow according to the present invention;

Figure 7 illustrates the pulse width;

FIG. 8 is a circuit diagram around the photodetector 78 shown in FIG. 2;

Fig. 9A is a graph showing the relationship between the multiplication factor and the bias in an anodized photo diode; Fig. 9B is an avalanche photo diode. A graph showing the relationship between the frequency band and the magnification in the photodiode; and

FIG. 10 is a diagram for explaining a change in the pulse width due to a change in the noise voltage. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, there is shown an outline of an overall configuration of an embodiment of a system according to the present invention. This system includes terminal equipments 2 and 4, and optical fiber transmission lines 6 and 6 laid between terminal equipments 2 and 4. And 8 are provided. Each of the terminal devices 2 and 4 has an output port 10 and an input port 12 for signal light. The optical fiber transmission line 6 optically connects the output port 10 of the terminal device 2 and the input port 12 of the terminal device 4 to form an optical fiber transmission line 8. Is optically connected to the output port 10 of the terminal device 4 and the input port 12 of the terminal device 2. Since the contents of the terminal devices 2 and 4 are substantially the same, the configuration of the terminal device 2 will be described.

5] The device 2 includes a plurality of optical transceivers for transmitting and receiving optical signals having different wavelengths; I 1,..., Λ η n are integers greater than 1). 14

(# 1,..., #N) and a spare optical transceiver 16 for transmitting and receiving an optical signal having a wavelength; Ix. Wavelength; lx is equal to or not equal to any one of the following wavelengths: 11,..., Λη.

The optical signals output from the optical transceivers 14 (# 1,…, # η) and 16 are converted to an optical multiplexer.

(MUX) 18, and the resulting WD signal light is output through a dispersion compensation fiber (DCF) 20 through an output port 10. The light is transmitted to the optical fiber transmission line 6.

Similarly, the optical fiber transmission line from the terminal equipment 4 The WDM signal light transmitted by (8) is transmitted to the optical network unit (2) through the input port (12) through the DCF (22) to the optical demultiplexer (DMUX) (24). Supplied. The optical demultiplexer 24 divides the supplied WDM signal light into individual optical signals, and each optical signal is divided into optical transceivers 14 (# 1,..., #N) and 16 Received by each.

Each of the optical transceivers 14 (# 1,..., # N) and 16 is a device control circuit 26 and a line setting circuit

28 The device control circuit 26 is connected to the line control circuit 30 by a bidirectional data node, and the device control circuit 26 is connected to the line control circuit 30 by a bidirectional data bus.

30 controls each of the optical transceivers 14 (# 1, ..., # n) and 16

FIG. 2 is a block diagram of an optical transceiver applicable to the present invention. This optical transceiver can be used as each of the optical transceivers 14 (# 1,..., #N) and 16 shown in FIG. This optical transmission / reception includes an optical transmission unit 32, an optical reception unit 34, and peripheral circuits.

The light transmission unit 32 is a peltier for controlling the temperature of the laser diode (LD) 36 as a light source and the laser diode 36. It has an LD module 38 including an element (or an electronically cooled element). Laser Diode 3 6 Power The energized light beam is split by the optical circuit 40 into first and second beams for wavelength monitoring and a main beam. The optical circuit 40 can be provided by one or more optical power blurs. Optical circuit

The main beam output from the camera 40 passes through the optical band-pass filter 42 and the optical power coupler 44 in this order, and the optical multiplexer 18 (see FIG. 1).

In the optical power puller 44, a branch beam is mainly used to detect the power and pulse width of the “is is” signal output from the optical transmission unit 32. The beam branches off. The branch beam is supplied to a photodetector (PD) 46 composed of a photo diode or the like, and an output signal of the photodetector 46 is provided. The pulse width monitor 48 detects the output optical signal based on the pulse width. Detects the width of the noise. The detection result is converted to a digital signal by an analog-to-digital converter (AZD) 50, and the converted digital signal is converted to a unit control circuit.

5 2 supplied to o

The first branch beam branched by the optical circuit 40 passes through the optical band-pass filter 54, and the passing beam is converted by the photo detector 56. The electric signal is converted to an electric signal, and the electric signal is supplied to the power monitor 62. The second branch beam branched by the optical circuit 40 passes through the optical bandpass filter 58. Then, the passing beam is converted to electricity 15 by the photodetector 60, and the electric signal is supplied to the power module 62. The fins 54 and 58 pass the shorter and longer wavelengths than the wavelength harmed to the optical transmission unit 32, respectively, in the passband. It has as the center wavelength of. And follow one, ⁰ Wa one mode is two-six other 2 off O door de I Te-click data 5 of 6及beauty 6 0 of the output signal ratio or in One by the and the child you calculate the difference, this optical transmission The center wavelength of the optical signal output from the unit 32 is detected.

A signal about the center wavelength detected by the monitor 62 is supplied to the control circuit 64. The signals from the unit control circuit 52 are also supplied to the control circuit 64 via a digital / analog converter (D / A) 66. The control circuit 64 controls the drive current of the penetrating element of the LD module 38 based on the signals from the unit control circuit 52 and the power monitor 62. Thus, the laser diode 36 controls the central wavelength of the light output from the laser diode. The output signal of the photodetector 46 is also supplied to the primary monitor 62, and the power monitor 62 outputs the optical transmission unit 32 from the optical monitor unit 62. The first monitoring of the input optical signal is also performed.

The unit control circuit 52 is connected to the device control circuit 26 and the line control circuit 30 (see FIG. 1). The detailed configuration around the JX unit control circuit 52 will be described later. The signal from the line setting circuit 28 (see Fig. 1) is supplied to the transmission S0H (section-over-head) input circuit 68 and output from the circuit 68. The signal is supplied to the LD module 38 via the scrambler 70 and the manifold multiplexer (MUX) 72 in this order, and thereby the LD module 38. The laser diode 36 is directly modulated. The output signal of the unit control circuit 52 is transmitted via a transmission S0H (section head, head) and an external INF (interface) circuit 74. SOH is supplied to insertion circuit 68

The control circuit 6 4 also controls Interview one Tsu preparative control circuit 5 2 and Nono ⁰ Wa one motor two motor 6 2 of the output signal based-out optical band communication over full Note1 4 2, the Re their The center wavelength and / or spectrum width of the optical signal output from the optical transmission unit 32 is controlled.

The optical receiving unit 34 has an optical band-pass filter 76 to which an optical signal from the optical demultiplexer 24 (see FIG. 1) is supplied. . The optical signal that has passed through the finol- ter 76 is converted to an electric signal (n) by a photodetector 78. In this embodiment, in particular, the photodetector is used. As a result, the output signal of the 780 is equalized. vessel The signal is equalized by the (EQL) 80, and the output signal of the equalizer 80 is supplied to the discriminator (DEC) 84. The evening circuit (TIM) 82 regenerates a clock based on the output signal of the equalizer 80, and the clock is supplied to the discriminator 84. . The output signal of the discriminator 84 is output from a demodulator (DM

U X) 8 6 ヽ Synchronous circuit 8 8 and descrambler

90 is passed in this order, and is supplied to the S SH (section head, —head) Xbyte extraction circuit 92. Circuit 92 is connected to line setting circuit 28 (see Figure 1). The output signal of the circuit 92 is supplied to a reception S0H (section overhead) external INF (interface) circuit 94, and is supplied to the circuit 94. The output signal is supplied to the unit control circuit 52.

The output signals of the photo detector 78 and the equalizer 80 are supplied to a pulse width monitor 96, and the pulse width monitor 96 is connected to the light receiving unit 3 4 detects the panel width of the received optical signal. The detection result of the pulse width is supplied to the unit control circuit 52 via the analog-to-digital converter 98, and is also supplied directly to the control circuit 100. It is done. The control circuit 100 is supplied with a signal from the knit control circuit 52 via a digital / analog converter 102. The control circuit 100 is a unit control circuit. 5 2 and pulse width monitor 96 based on these signals, control and equalize the bias circuit 104 of the photo amplifier 78 Controls the heater 80. The threshold value of the another 84 may be controlled by the control circuit 100. The details of the control by the control circuit 100 will be described later.

FIG. 3 is a detailed block diagram of the periphery of the unit control circuit 52. The signal from the line control circuit 30 is supplied to the line selector 106 for transmission characteristic calculation, and the selector 106 stores the line initial value memory circuit 108. The operations of the line characteristic storage circuit 110 and the unit control circuit 52 are controlled. The signal from the initial value input interface (INF) 112 is supplied to the line initial value storage circuit 108. The line characteristic storage circuit 110 receives the received Xbyte (characteristic detection result before transmission) and the characteristic detection result after transmission (pulse width, etc.). The receiver 1S X b y t e is supplied, for example, from the extraction circuit 92 shown in FIG.

Unit control circuit 52 includes a comparison operation circuit 114 that performs a comparison operation based on the output signals of circuits 108 and 110. The comparison operation circuit 114 is connected to the transmission characteristic function operation circuit 116 via a bidirectional bus. Parameter calculation based on output signal of transmission characteristic function calculation circuit 1 16 Start Z End The processing circuit 118 operates, and the line characteristic storage circuit 110 is controlled based on the result. The output signal of the transmission characteristic function operation circuit 1 16 is supplied to the transmission side control circuit 120 and the reception side control circuit 122. The transmission-side control circuit 120 operates according to the transmission-side synchronization circuit 124 to control the optical transmission unit 32. The receiving side control circuit 122 operates in accordance with the receiving side synchronizing circuit 126 to control the optical receiving unit 34. The control of the unit control circuit 52 by the selector 106 is, for example, a set and a reset.

FIG. 4 is a flowchart showing a first embodiment of the monitoring control in the system shown in FIG. Prior to describing this flow, the effect of chromatic dispersion on the optical fiber transmission line will be described with reference to FIGS. 5A and 5B.

In general, an optical signal has a pulse waveform, and the wavelength of light changes at the rising and falling portions. In addition, when light having different wavelengths is transmitted through an optical fiber transmission line, the time required to reach the end of the optical fiber transmission line is different. Specifically, when light of wavelength I is transmitted by an optical fiber having a length L and having no dispersion and having a wavelength of 0, the light having a wavelength of I is transmitted with respect to the light having a wavelength of 0. The time difference Δt to reach the optical fiber end is given by the following equation, where m is a constant. Given by

Δ t = m L (λ-λ 0)

Fig. 5 (1) shows the wavelength shift at the rising edge and the falling edge of the optical transmission pulse whose center wavelength is λ0. In the rising part, the wavelength shifts to the short wavelength side (bull shift), and in the falling part, the wavelength shifts to the long wavelength side (red shift). ). When the optical signal shown in Fig. 5 (1) is transmitted by an optical fiber, the time difference between the rising and falling portions is enlarged, and the optical signal is transmitted. The pulse width of the received pulse is expanded as shown in FIG. 5B. It is well known that the optical spectrum, which represents the relationship between optical power and wavelength, hardly changes before and after transmission.

If the dispersion characteristics of the optical fiber change, the pulse width after transmission changes even if the optical spectrum does not change. Also, even if the dispersion characteristics of the optical fibers are the same, the waveform after transmission changes when the optical spectrum changes.

Specifically, when the center wavelength of the optical spectrum changes on the transmission side, the time width of the reception pulse is disturbed. Specifically, in the optical transceiver shown in FIG. 2, the time width of the reception noise and the temperature of the laser are determined by the temperature of the laser diode 36 and the optical band-pass Determined by the characteristics of the filter 42 and the dispersion characteristics of the optical fiber transmission line. Is defined.

Also, when the power of the optical signal changes on the transmitting side, the amplitude of the receiving pulse is disturbed. Specifically, in the optical transceiver shown in FIG. 2, the amplitude of the received pulse is determined by the drive current of the laser diode 36, the optical band-pass filter, and the like. It is determined by the characteristic of 42, the multiplication factor of the photodetector 78 (the bias given by the bias circuit 104).

In each of the terminal devices 2 and 4 shown in FIG. 1, the optical transceiver 14 (# 1,..., #N) is used for the active line and is used for the optical line. Transceiver 16 is used for the protection line. In this embodiment, each of the optical transceivers 14 (# 1) and each of the optical transceivers 16 are switched to each other so that the frame synchronization is obtained. Each optical transmitter / receiver 16 is provided for the working line, and in this state, monitoring control using each optical transmitter / receiver 14 (# 1) is performed. This will be described in more detail with reference to a flowchart shown in FIG.

First, in step 201, the characteristics before and after transmission are input to the line characteristic storage circuit 110. This will be exemplified by the case where the terminal device 2 is on the transmitting side and the terminal device 4 is on the receiving side. The optical transceiver of the optical transceiver 14 (# 1) of the terminal equipment 2 In the unit 32, the center wavelength λ, the spectrum width, and the pulse width of the transmitted optical signal are closely monitored, and the monitoring is performed. The ring result is written to an unused byte (X byte) in the transmission S0Ηinsertion circuit 68. An optical signal having information related to the monitoring result is sent from the terminal device 2 to the terminal device 4 via the optical fiber transmission line 6. In the optical transmitter / receiver 14 (# 1) of the terminal device 4, an extraction circuit 9 2 is extracted based on the received optical signal, and an X byte is extracted.The result is a unit. It is supplied to the control circuit 52. Therefore, the line characteristic storage circuit 110 included in the optical transceiver 14 (# 1) of the terminal device 4 stores the optical transmitter / receiver 14 (# 1) of the terminal device 2. ) Will be the result of monitoring the optical signal output from. On the other hand, in the optical receiving unit 34 of the optical transceiver 14 (# 1) of the terminal device 4, the optical signal was transmitted by the optical fiber transmission line 6. The center wavelength λ spectrum width and pulse width of the optical signal are monitored, and the results are also input to the line characteristic storage circuit 110.

Next, in step 202, the comparison operation circuit 114 is turned on based on the result of step 201 and immediately based on the storage contents of the line characteristic storage circuit 110. The dispersion characteristic of the fiber transmission line 6 is calculated. Then, in step 203, the result in step 202 and the line initial value storage circuit 1

08 is compared with the initial value of the dispersion characteristic of the optical fiber transmission line 6 which is thought to be self-considered. Specifically, in step 204, the dispersion characteristic of the optical fiber transmission line 6 is not changed from the initial value, and it is determined that the dispersion characteristic is strong, and the dispersion characteristic is not changed. Step 2

Proceed to 06 and if so, step 2

Go to 0 5. In step 205, the pulse width is adjusted by adjusting the center wavelength and the spectral width of the optical signal output from the optical transceiver 14 (# 1) of the terminal device 2. The force that can be compensated, δ, is determined, and if it is possible, proceed to step 206.If it is impossible, ¾7 V is the second implementation described later. Proceed to form.

In step 206, the transmission characteristic function arithmetic circuit 1 16 is powerful, and the optical reception pulse width at the optical transceiver 14 (# 1) of the terminal device 4 is optimized. Calculate the center wavelength λ and the spectrum width of the optical signal output from the optical transceiver 14 (# 1) of the terminal device 2.

In step 207, the calculation result in step 206 is input to the transmission characteristic function operation circuit 116 and the transmission side control circuit 120. . Next, in step 208, The result of the calculation of the optimum conditions in step 206 is determined by the insertion circuit 68 included in the optical transmitter / receiver 14 (# 1) of the terminal equipment 4, and the unused bytes ( X byte), and the obtained optical signal is transmitted from the terminal device 4 to the terminal device 2 via the optical fiber transmission line 8. . In the optical transmitter / receiver 14 (# 1) of the first terminal device 2, information that gives the optimum conditions by extracting the extraction circuit 92 and the X byte is powerful. The optical transmission unit is supplied to the optical transmission unit 52, and the control circuit 64 operates according to the instruction of the unit control circuit 52. 3 2 Feedback control is performed vigorously. The object of control is the temperature of the laser diode 36 or the characteristics of the optical band-pass fin- olator 42 by the pel- gy device.

Next, in step 209, it is determined whether or not the pulse width of the optical signal received by the receiving side, that is, the terminal device 4, has been corrected. If the correction has not been made, the process returns to step 201. If the correction has been made, the process proceeds to step 210.

In step 210, the series of operations described above are sequentially performed for the optical transceivers 14 (# 2, ..., #n).

The above description is for monitoring and controlling the transmission conditions from the terminal equipment 2 to the terminal equipment 4. The same applies to the monitoring and control of the transmission conditions from the device 4 to the terminal device 2.

FIG. 6 is a flowchart illustrating the operation of the second embodiment performed when it is determined in step 205 of FIG. 4 that the pulse width cannot be compensated. It is.

First, in step 221, the first terminal device 2 confirms that the center wavelength λ and the spectrum width on the transmitting side have been optimized by the second terminal device. Notify device 4. The unused bytes (Xbyte) described above are used as the communication medium.

Next, in step 222, the reception pulse width monitored by the pulse width monitor 96 in the terminal equipment 4 is used to store the line characteristic storage circuit. It is input to 110.

Then, in step 2 23, in the second terminal device 4, the bias set value of the photo detector 78 is used to store the line characteristic storage circuit 110. Entered in o

Figure 7 is a diagram for explaining the definition of the pulse width. The pulse width of the '5' is defined as its half-width, as indicated by the symbol PW in the figure.

Next, in step 224, the initial value storage circuit

The output of the photodetector 780 is read out as a function of the input power versus the magnification ratio. 8 is a circuit diagram around the photodetector 78. The Photo 7 "Detector 78 is provided by the balunshadow, which has a negative voltage bias. Circuit 104

They are connected. The anode current of the heat sink connector 78 is converted to a voltage signal by the pre-pump 128 and the negative feedback resistor 130, and this voltage signal is converted to a voltage signal. Supplied to equalizer 80

9 (A) shows the relationship between the magnification and the bias voltage in the avalanche photodiode.

, '—

FIG. 9B shows the relationship between the frequency band and the multiplication factor in the fan-shaped photo diode. As the bias increases, the multiplication factor increases, and accordingly, in FIG. 8, the output amplitude of the pre-amplifier 128 increases. Also, as the bias becomes longer, the frequency band is expanded, so that the rise time and fall time of the reception pulse are shortened, and intersymbol interference is reduced. It gets smaller. Therefore, the range in which data can be identified is expanded in principle

,-This, yo. However, as the bias increases, the frequency band is expanded, the amount of amplified noise increases, and the signal-to-noise ratio (SNR) deteriorates. Range that can be identified may be reduced

In this embodiment, steps 2 25 The comparison operation circuit 114 performs a comparison operation based on steps 222 to 224, and the bias voltage of the photodetector 78 is optimized. Is controlled. It should be noted that, depending on the individual characteristics of the antenna photodiode used as the photodetector 78, the frequency band versus the multiplication factor may be different. The characteristics are different.

In this case, based on the gain and the characteristic power of the bias shown in FIG. 9A, the frequency band for the bias is obtained with reference to FIG. 9B, and the frequency band is obtained. As a result, the optimum pulse width is converted. In other words, it is possible to calculate a bias to expand the range of the threshold for which data can be identified.

Figure 10 shows how the pulse width changes according to the bias voltage. The pulse width PW2 with respect to the pulse width PW1 is obtained when the bias is reduced. The pulse width PW3 with respect to the pulse width PW1 is obtained when the bias is increased. If the rise time and fall time of the pulse on the receiving side increase due to dispersion, it is identified as increasing the magnification of the photodetector 78. There is a tendency to expand the threshold value range.

In step 222, it is determined whether or not the pulse width has been corrected by the noise control of the photodetector 78, and the pulse width has been corrected. Step if necessary Proceed to 2 2 8. If no correction is made, go to step 2 27. In step 2 27, it is determined whether or not an identification error occurs by correcting the data identification threshold, and if it does not occur, step 2 Proceed to step 28, and if it is determined that this will occur, proceed to step 230.

At step 228, the data discriminating threshold value of the discriminator 84 is controlled, and at step 229, the control of other lines is sequentially performed. .

In step 230, it is determined whether the transmission quality cannot be satisfied based on the amount of dispersion of the optical fins. Then, the process proceeds to step 231, and the alarm (ALM) notifies that the amount of dispersion of the optical fiber needs to be changed. If Step 23 is satisfactory, proceed to Step 23 to check that the transmission quality is abnormal due to other factors such as deterioration of the optical transceiver characteristics with time. A notification of the presumption is sent before the error occurs.9 o Industrial availability

As described above, according to the present invention, it is possible to provide a system suitable for monitoring and control in optical transmission. In addition, according to this system, a specific configuration suitable for feedback control between terminal devices is provided. CO

o o

Claims

The scope of the claims

1. The first and second terminal devices and the first and second terminal devices laid between the first and second terminal devices.

And a second optical fiber transmission line, wherein the first terminal equipment transmits the first optical signal to the first optical signal.

Including the first means for transmitting to the first optical fiber transmission line,

The second terminal device is

Second means for receiving the first optical signal transmitted by the first optical fiber transmission line, and parameters relating to the waveform of the received first optical signal A third means of detecting data,

And fourth means for transmitting a second optical signal representing the detected parameter to the second optical fiber transmission line.

The first terminal device is

Fifth means for receiving the second optical signal transmitted by the second optical fiber transmission line, and the first optical signal based on the received second optical signal A sixth means of comparing the parameters before and after the signal transmission, and

And a seventh means for controlling the first optical signal so that the parameter after transmission of the first optical signal is optimized based on the comparison result. Shi Stem.

2. The system according to claim 1, wherein

The first means includes a laser diode for outputting the first optical signal, and means for changing a temperature of the laser diode,

The seventh means is a system for controlling the temperature of the laser diode.

3. The system according to claim 1, wherein

The first means comprises: a laser diode for outputting the first optical signal; and an optical band-pass filter through which the first optical signal output from the laser diode passes. Filter and

The optical band-pass filter has a pass band including the wavelength of the first optical signal,

The seventh means is a system for controlling the pass band.

4. The system according to claim 1, wherein

The parameter is a system that is a pulse width of the first optical signal.

5. The system according to claim 1, wherein

The first terminal equipment controls the first optical signal. A system further including means for notifying the second terminal device by the first optical signal that the control has been optimized.

6. The system according to claim 5, wherein

The second means includes an avalanche photodiode, the gain of which varies according to the applied bias voltage;

The second terminal device includes a means for correcting the pulse width of the output signal of the avalanche photodiode by the bias voltage based on the notification. System to further include.

7. The system according to claim 6, wherein:

The second means further includes a discriminator for receiving an output signal of the avalanche photodiode.

A system wherein the second terminal device further includes means for correcting a threshold value of the discriminator based on the notification.

8. The system according to claim 1, wherein

Each of the first and second optical signals is provided by one channel of WDM signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths. 92

02

ST

0ΐ

. W $

8 Z

Z6tO / 86df / XDd SSO / Z / 00 OW