JPH0946303A - Method for identifying input signal to optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recognize a fault or the like on an optical transmission line by discriminating whether control voltage inputted to a voltage controlled oscillator(VCO) indicates a fixed value or an irregular value. SOLUTION: A flip flop(FF) 6 compares the phase of an input signal from a photodiode(PD) 5 with that of an output signal from a VCO 8 and outputs an error signal. The error signal is inputted to a phase control circuit 7, a variation part is removed and control voltage is outputted. The VCO 8 outputs a timing signal (CLK) with frequency corresponding to the control voltage value inputted from the circuit 7. A discrimination circuit 9 discriminates whether the input waveform from the PD 5 is '0' or '1' based upon the CLK and outputs a pulse waveform. Since the method for discriminating whether an input signal is a normal optical signal including a main signal component or a signal including only a naturally radiated optical component, or the OFF of light input is provided, the reliability of an optical transmission system can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting an optical signal input state of an optical receiver in an optical amplification transmission system.

[0002]

2. Description of the Related Art In recent years, optical communication systems for international communication have been required to have an extremely high communication speed and a large communication capacity.

In response to the above-mentioned demands, optical amplification relay systems have been adopted in optical communication systems in place of the regenerative relay systems conventionally used. The optical amplification repeater system is a regenerative repeater system in which an optical signal is once converted into an electric signal at the repeater point, and then this electric signal is amplified and then converted to an optical signal again before being sent out. It is the method of sending out. According to this optical amplification repeater method, a circuit for converting an optical signal into an electric signal, a circuit for amplifying an electric signal, and a circuit for converting an electric signal into an optical signal are not required at the repeater point, and the structure of the repeater point is simplified. There is an advantage that it can be realized.

In the optical amplification repeater system, an optical amplifier equipped with a pump LD for amplifying light is provided at the repeater point, but an optical signal is generated before the repeater point due to a failure of the optical transmission line. In case of disconnection, the disconnection of the optical signal cannot be discriminated at the relay point, and the pump LD
Remains driven. Therefore, after the relay point, the excitation light of the excitation LD is the spontaneous emission light (AS
E) is transmitted on the optical transmission line. Then, an optical signal that does not include the main signal component, that is, an optical signal that includes only the spontaneous emission light component is input to the terminal device after the relay point. Further, when a failure of the optical transmission line occurs near the terminal device, no optical signal is input to the optical receiving device. In such a case, if the terminal device performs the reproduction process without recognizing the situation, a meaningless signal will be output. For this reason, conventionally, the terminal device monitors the frame synchronization of the reproduced electric signal and detects out-of-synchronization to identify the input signal or the interruption of the optical input. However, some terminal devices do not have a mechanism for monitoring the frame synchronization of the electric signal, and it becomes impossible to detect the input break of the optical signal, and the spontaneous emission light is reproduced and output as the electric signal. There is a problem.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention has been made in view of the above problems, and even in a terminal device that does not have a mechanism for monitoring the frame synchronization of electrical signals, the input signal is the main signal component. To improve the reliability of the optical transmission system by providing a method for identifying whether the optical signal is a normal optical signal containing light, an optical signal containing only spontaneous emission light components, or an optical input interruption. This is an issue.

[0006]

The present invention is a method applied to a communication system of an optical amplification transmission system in which an optical amplifier is arranged on an optical transmission line connecting terminal equipments, and in particular, It is effective for an optical receiving device using a phase locked loop circuit (PLL; PHASE LOCKED LOOP) as self-timing extraction means.

Here, the phase locked loop circuit (PLL) is a circuit for synchronizing the phase of the output signal with the phase of the input signal. Specifically, the phase locked loop circuit includes a phase detection circuit, a phase control circuit, a voltage controlled oscillator (VCO; VOLTAG).
E CONTROL OSCILLATOR) is a closed loop circuit. That is, the phase detection circuit, the phase control circuit, and the voltage controlled oscillator (VCO) are connected in series, and the output of the voltage controlled oscillator (VCO) is fed back and input to the phase detection circuit. And the phase detection circuit
At the same time as inputting the input signal, the voltage controlled oscillator (VC
The output signal of 0) is input, the phases of these two signals are compared, and an error signal is output. This error signal is input to the phase control circuit, the fluctuation portion is removed, and the error signal is input to the voltage controlled oscillator. The voltage controlled oscillator (VCO) outputs a signal at an oscillation frequency according to the control voltage value input from the phase control circuit. The optical receiver operates by using the output signal of the phase locked loop circuit (PLL) as a timing signal. That is, the optical receiving device identifies whether the input signal is “0” or “1” according to the timing signal, and converts the input signal into a pulse waveform.

The method of the present invention will be described below. (1) The first invention is a method of monitoring a control voltage of a voltage controlled oscillator (VCO) of a phase locked loop circuit and discriminating between an input signal containing a signal component and an input signal containing only a spontaneous emission light component. is there. For example, in the case of an input signal including a signal component, the input signal and the output signal match (PLL is established),
The control voltage of the voltage controlled oscillator (VCO) has a constant value.
On the other hand, in the case of an input signal containing only the spontaneous emission light component,
The input signal and the output signal do not match (PLL does not hold), and the control voltage of the voltage controlled oscillator (VCO) has an irregular value.

Therefore, the first aspect of the present invention is to control the control voltage value for monitoring the control voltage value input to the voltage controlled oscillator, and to determine whether the control voltage value is a constant value or an irregular value. A control voltage determining step of determining, a first determining step of determining that the input signal of the optical receiving device is an optical signal including a main signal component when the control voltage value shows a constant value, and the control voltage A second determination step of determining that the input signal of the optical receiving device is an optical signal that does not include the main signal component when the value indicates an irregular value.

(2) A second aspect of the invention is to monitor the output signal of the phase detection circuit of the phase locked loop circuit, that is, the waveform of the error signal between the input signal and the output signal, and to monitor the input signal including the signal component and the spontaneous emission. This is a method of distinguishing from an input signal containing only a light component. For example, in the case of an input signal containing signal components,
The output signal from the phase detection circuit will show a waveform having a constant period. On the other hand, in the case of the input signal containing only the spontaneous emission light component, the frequency of the input signal does not match the frequency of the output signal, and the error signal shows a waveform having an irregular cycle.

Therefore, a second aspect of the invention is a waveform monitoring step for monitoring the waveform of the error signal output from the phase detection circuit, and the waveform of the error signal is a waveform with a constant cycle or an irregular cycle. Waveform determining step of determining whether the waveform of the error signal is an amplitude waveform, and when the waveform of the error signal is a waveform having an amplitude with a constant period, the input signal of the optical receiving device is an optical signal including a main signal component And a third determination step of determining that the input signal of the optical receiving device is an optical signal that does not include a main signal component when the waveform of the error signal has a waveform that has an irregular cycle. The method includes a fourth determination step.

(3) The third invention provides a normal input signal (input light containing a signal component), an input signal containing only a spontaneous emission light component, and an optical input disconnection in which no optical signal is input. It is a method aimed at identifying. in this way,
First, the input light input to the optical receiver is converted into an electric signal by using a photoelectric element such as a photodiode (PD),
This electric signal is input to the peak detection circuit. here,
The output value of the peak detection circuit shows a small value in the presence of the input light, but a much larger value in the absence of the input light than in the case of the input light.

Therefore, a third aspect of the present invention is a photoelectric conversion step of converting an input signal of the optical receiver from an optical signal to an electric signal, and a peak for detecting a peak value of the electric signal converted in the photoelectric conversion step. A detection step, a peak value determination step of determining whether or not the peak value detected in the peak detection step is a preset value outside a specific range, and the peak value is a value outside the specific range. In some cases, an optical input disconnection determination step of determining that the input signal of the optical receiving device is disconnected, and, when the peak value is a value within the specific range, a voltage forming the phase-locked loop circuit. A control voltage monitoring step of monitoring a control voltage value input to the controlled oscillator, and a control voltage determination step of determining whether the control voltage shows a constant value or an irregular value. And-up, when the control voltage value indicates a constant value, a first determination step of determining that the input signal of the optical receiver is an optical signal comprising a main signal component,
And a second determination step of determining that the input signal of the optical receiving device is an optical signal that does not include a main signal component when the control voltage value shows an irregular value.

(4) A fourth aspect of the present invention is to provide a normal input signal (input light including a signal component), an input signal including only a spontaneous emission light component, and an interruption of optical input as in the third aspect. It is intended to identify.

A fourth aspect of the invention is a photoelectric conversion step for converting an input signal of the optical receiving device from an optical signal to an electrical signal, and a peak for detecting a peak value of the electrical signal converted in the photoelectric conversion step. A detection step, a peak value determination step of determining whether or not the peak value detected in the peak detection step is a preset value outside a specific range, and the peak value is a value outside the specific range. In some cases, an optical input disconnection determination step of determining that the input signal of the optical receiving device is disconnected, and, if the peak value is a value within the specific range, a phase forming the phase locked loop circuit. A waveform monitoring step of monitoring the waveform of the error signal output from the detection circuit; And a third determination step of determining that the input signal of the optical receiving device is an optical signal including a main signal component, when the waveform of the error signal is a waveform that amplifies in a constant cycle. And a fourth determination step of determining that the input signal of the optical receiving device is an optical signal that does not include a main signal component when the waveform of the error signal has a waveform with an irregular cycle. I have a method.

(5) A fifth aspect of the present invention is a method of identifying a light input break. In the phase locked loop circuit, the output signal of the phase control circuit, that is, the control voltage of the voltage controlled oscillator (VCO) shows a constant value within a certain range in the case of an input signal containing an optical component. On the other hand, voltage controlled oscillator (VC
The control voltage of O) is fixed to the maximum value or the minimum value in the case of an input signal containing no optical component (when the optical input is cut off).

Therefore, a fifth aspect of the present invention is a control voltage monitoring step for monitoring a control voltage input to a voltage controlled oscillator, and when the value of the control voltage is outside a preset specific range, An optical input disconnection determining step of determining that the input signal of the optical receiving device is disconnected.

(6) A sixth invention is a combination of the first invention and the fifth invention, wherein a normal input signal containing a signal component, an input signal containing only a spontaneous emission light component, and an optical input disconnection. And the method of identifying.

That is, a sixth aspect of the present invention is a control voltage monitoring step of monitoring a control voltage input to a voltage controlled oscillator, and when the value of the control voltage is outside a preset specific range, An optical input disconnection determination step of determining that the input signal of the optical receiving device is disconnected, and when the value of the control voltage is a value within a preset specific range, the control voltage has a constant value. A control voltage determining step of determining whether the control voltage value is a constant value or an irregular value; and when the control voltage value is a constant value, the input signal of the optical receiving device is an optical signal including a main signal component. And a second determination step of determining that the input signal of the optical receiving device is an optical signal that does not include a main signal component when the control voltage value indicates an irregular value. Method involving and It is.

(7) A seventh invention is a combination of the second invention and the fifth invention, wherein a normal input signal containing a signal component, an input signal containing only a spontaneous emission light component, and an optical input disconnection. This is a method aimed at identifying and.

That is, a seventh aspect of the invention is a control voltage monitoring step of monitoring the control voltage input to the voltage controlled oscillator,
When the value of the control voltage is a value outside a preset specific range, an optical input disconnection determination step of determining that the input signal of the optical receiver is disconnected, and the control voltage value is within a specific range. If the value is within the range, a waveform monitoring step of monitoring the waveform of the error signal output from the phase detection circuit that constitutes the phase locked loop circuit, and a waveform in which the waveform of the error signal has a constant amplitude or A waveform determining step of determining whether the waveform has an amplitude with a regular cycle, and when the waveform of the error signal has a waveform having an amplitude with a constant cycle, the input signal of the optical receiving device is an optical signal including a main signal component. And a third determination step for determining that the input signal of the optical receiving device is an optical signal that does not include a main signal component when the waveform of the error signal has a waveform with an irregular cycle. Judge And a method comprising a fourth judging step of.

The operation of the present invention will be described below. According to the first aspect of the present invention, the optical receiving device of the terminal device monitors the control voltage value input to the voltage controlled oscillator forming the phase locked loop circuit. Then, it is determined whether the control voltage has a constant value or an irregular value.

Here, if the control voltage shows a constant value, the input signal is judged to be a normal optical signal containing the main signal component, and the reproduction processing is performed. On the other hand, if the control voltage shows an irregular value, the input signal is an optical signal that does not contain the main signal component, that is, the transmission of the optical signal is interrupted due to a failure of the optical transmission line, and the optical amplifier in the middle It can be determined that the generated spontaneous emission light has been transmitted as an input signal.

According to the second aspect of the invention, the optical receiving device of the terminal device monitors the waveform of the error signal output from the phase detection circuit forming the phase locked loop circuit. Then, it is determined whether the waveform of the error signal is a waveform oscillating at a constant cycle or a waveform oscillating at an irregular cycle.

Here, if the waveform of the error signal is a waveform with a constant cycle, the optical receiving device determines that the input signal is an optical signal containing the main signal component, and performs the subsequent reproduction processing. On the other hand, if the waveform of the error signal has a waveform with an irregular cycle, the optical receiver determines that the input signal is an optical signal that does not include the main signal component, that is, an optical signal that includes only spontaneous emission light. To do.

Further, according to the third method, the optical receiving device converts the received input signal from an optical signal into an electric signal,
The peak value of this electric signal is detected. Further, the optical receiving device determines whether or not the detected peak value is outside the preset specific range.

Here, if the peak value is out of the specific range, the optical receiver determines that the input of the optical signal is cut off (light input cutoff). On the other hand, if the peak value is within the specific range, the input signal is identified by the same procedure as the first method.

According to the fourth method, the optical receiver converts the received input signal from an optical signal into an electric signal,
The peak value of this electric signal is detected. Further, the optical receiving device determines whether or not the detected peak value is outside the preset specific range.

Here, if the peak value is out of the specific range, the optical receiver determines that the input of the optical signal is cut off (light input cutoff). On the other hand, if the peak value is within the specific range, the input signal is identified by the same procedure as the second method.

Further, according to the fifth method, the optical receiver monitors the control voltage input to the voltage controlled oscillator constituting the phase locked loop circuit, and the value of this control voltage is specified in advance. If the value is out of the range, it is determined that the input signal is cut off.

According to the sixth method, the optical receiver monitors the control voltage input to the voltage controlled oscillator forming the phase locked loop circuit, and the value of the control voltage is specified in advance. If the value is out of the range, it is determined that the input signal is cut off.

On the other hand, if the value of the control voltage is within the preset specific range, the optical receiving device identifies the input signal by the same procedure as the first method. Further, according to the seventh method, the optical receiving device monitors the control voltage input to the voltage controlled oscillator forming the phase locked loop circuit, and the value of the control voltage is preset. If the value is outside the specified range, it is determined that the input signal is cut off.

On the other hand, if the value of the control voltage is within the preset specific range, the optical receiving device identifies the input signal by the same procedure as the second method.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[0035]

[First Embodiment] FIG. 1 shows a schematic configuration of an optical transmission system to which a first embodiment of the present invention is applied. As shown in the figure, in the optical transmission system, the terminal equipment 1 and the terminal equipment 2 are connected by an optical transmission line 11, and a plurality of optical amplification repeater stations 12 are arranged on the optical transmission line 11. Is configured. The method of the present invention is applied to the terminal device 1 and the terminal device 2, and the terminal device 2 will be described as an example here.

The terminal device 2 is composed of an optical receiving device 3 and an optical transmitting device 4, and these devices can send and receive signals to and from the terminal device 1 of the other party.
Here, the optical receiving device 3 is a device that employs a self-timing method using a PLL circuit, and based on a timing signal (clock signal; CLK) output from the PLL circuit, a value (“0” or "1") is identified and converted into a pulse waveform. The light receiving device 3 includes a photodiode (PD) 5, an identification circuit 9, and a PLL circuit.

The photodiode (PD) 5 converts the received optical signal into an electric signal, and the output of the photodiode (PD) 5 is connected to the identification circuit 9 and the PLL circuit.

The PLL circuit includes a flip-flop (FF) 6 as a phase detection circuit, a phase control circuit 7, and a voltage controlled oscillator (VCO) 8. The output of the photodiode (PD) 5 is a flip-flop (FF). ) 6 and the output (Q) of the flip-flop (FF) 6 is connected to the phase control circuit 7. The output of the phase control circuit 7 is the voltage controlled oscillator (VC
O) 8 is connected. Furthermore, a voltage controlled oscillator (V
The output (CLK) of the CO) 8 is connected to the identification circuit 9 and, at the same time, is fed back to the data input section of the flip-flop (FF) 6. In such a configuration, the flip-flop (FF) 6 has a phase of an input signal from the photodiode (PD) 5 and a voltage-controlled oscillator (V
The phase of the output signal of (CO) 8 is compared and an error signal is output. This error signal is input to the phase control circuit 7, the varying portion is removed, and the error signal is output as a control voltage. The voltage controlled oscillator (VCO) 8 is a timing signal (C) having a frequency corresponding to the control voltage value input from the phase control circuit 7.
LK) is output.

Then, the discrimination circuit 9 discriminates whether the input waveform from the photodiode (PD) 5 is "0" or "1" by the timing signal (CLK) and outputs a pulse waveform. .

Further, the optical receiving device is provided with a signal identifying circuit 10 as a circuit for realizing the first method of the present invention, and the output of the phase control circuit 7 is connected to the voltage control circuit (VCO) 8 and at the same time the signal identification is performed. It is connected to the circuit 10.

The signal discrimination circuit 10 will be described below with reference to FIG. The signal identification circuit 10 includes two comparators 101 and 102, an OR circuit 103, and a mono-multi circuit 104, and the output of the phase control circuit 7 is connected to the comparators 101 and 102. Further, the outputs of the comparator 101 and the comparator 102 are connected to the NOR circuit 103. Also, NOR
The output of the circuit 103 is connected to the mono multivibrator 104.

The minimum value "VLo" of the control voltage is set in the comparator 101, and the input voltage V and the minimum value VLo are set.
And V> VLo, a signal LOW is output, and V
If <VLo, the signal HIGH is output.

Further, the maximum value "VHi" of the control voltage is set in the comparator 102, the input voltage V is compared with the maximum value VHi, and if V <VHi, a signal LOW is output and V> If it is VHi, the signal HIGH is output.

The mono multivibrator 104 is NOR
The output signal of the circuit 103 is used as a trigger for HIG
This is a circuit that outputs a pulse signal indicating H or LOW. It should be noted that this mono multivibrator 104 has 5
A power supply circuit consisting of a volt power supply (5V), a resistor (R) and a capacitor (C) is connected, and the output time of the pulse signal can be set by the capacitance of the resistor (R) and the capacitor (C). Has become.

The operation of the signal identifying circuit 10 will be described below. (1) When the optical receiver receives a normal optical signal including the main signal component In the PLL circuit, when a normal signal is input, the phase of the input signal and the phase of the output signal of the voltage controlled oscillator (VCO) 8 And the control voltage V from the phase control circuit 7 shows a constant value equal to or higher than the minimum voltage VLo and equal to or lower than the maximum voltage VHi. This state is shown in FIG. At this time, (VLo-
V) <0, and the comparator 10 of the signal identification circuit 10
1 outputs the signal LOW. Also, (V-VHi) <0
Therefore, the comparator 102 outputs the signal LOW.

The NOR circuit 103 includes a comparator 101.
When the signal LOW is input from the
The signal LOW is output. At this time, the mono multivibrator 104 outputs a pulse signal indicating LOW for a certain period of time, triggered by the output signal LOW of the NOR circuit 103. Thereby, the optical receiving device determines that the received optical signal is a normal optical signal including the main signal component based on the pulse value “LOW” of the signal identifying circuit 10.

(2) Light receiving device emits spontaneously emitted light (ASE)
When an optical signal containing only the main signal component is cut off due to a fault in the optical transmission line 11, a spontaneous emission light (ASE) generated in the optical amplification repeater station 12 after the fault occurrence point is received. An optical signal containing only the component is transmitted to the terminal device 2. In such a case, in the PLL circuit, the phase of the input signal and the phase of the output signal of the voltage controlled oscillator (VCO) 8 do not match, and the control voltage V from the phase control circuit 7 shows an irregular value. Like This is shown in FIG. At this time, the value of the control voltage V becomes a value less than the minimum voltage VLo or a value exceeding the maximum voltage VHi. That is, at some point (VLo-V)>
0, and (V−VHi)> 0 at other times.

When (VLo-V)> 0, the comparator 101 of the signal identifying circuit 10 outputs the signal HIGH. When (VLo-V)> 0, obviously (VLo-V)
-VHi) <0, and the comparator 102 outputs the signal LO
Outputs W.

At this time, the NOR circuit 103 inputs the signal HIGH from the comparator 101, and the comparator 1
The signal LOW is input from 02. Then, the NOR circuit outputs the signal HIGH.

The mono multivibrator 104 is NOR
When the signal HIGH is input from the circuit 103, this signal is used as a trigger to output a pulse signal indicating HIGH for a certain period of time. As a result, the optical receiving device determines that the received optical signal is an optical signal including only the spontaneous emission (ASE) component due to the pulse value “HIGH” of the signal identifying circuit 10 and a failure has occurred on the optical transmission line. Can be recognized.

When (V-VHi)> 0, the comparator 102 of the signal identifying circuit 10 outputs the signal HIGH. When (V−VHi)> 0, obviously (VLo−V) <0, and the comparator 101 outputs the signal LOW.

At this time, the NOR circuit 103 inputs LOW from the comparator 101 and inputs the signal HIGH from the comparator 102. Then, the NOR circuit outputs the signal HIGH.

The mono multivibrator 104 is NOR
When the signal HIGH is input from the circuit 103, this signal is used as a trigger to output a pulse signal indicating HIGH for a certain period of time. As a result, the optical receiving device determines that the received optical signal is an optical signal including only the spontaneous emission (ASE) component due to the pulse value “HIGH” of the signal identifying circuit 10 and a failure has occurred on the optical transmission line. Can be recognized.

[0054]

Second Embodiment FIG. 5 shows the configuration of a terminal device to which the second method of the present invention is applied. The optical receiving device 3 includes a signal identifying circuit 14 as a circuit for implementing the second method of the present invention, and connects the output of the flip-flop circuit (FF) 6 to the phase control circuit 7 and at the same time to the signal identifying circuit 14. are doing. Other configurations are the same as those in the first embodiment described above, and the description thereof will be omitted.

Next, the configuration of the signal identifying circuit 14 will be described with reference to FIG. The signal identification circuit 14 has a low-pass filter (LPF) 14A and a signal identification unit 14B, connects the output of the flip-flop circuit (FF) 6 to the low-pass filter (LPF) 14A, and
F) The output of 14A is connected to the signal identifying section 14B.

The low-pass filter 14A has a resistor (R1).
And a capacitor (C1), and removes the varying portion of the error signal output from the flip-flop circuit (FF) 6.

The signal discriminating section 14B has the same structure as the signal discriminating circuit 10 of the first embodiment, and is composed of two comparators 101 and 102, an OR circuit 103, and a mono-multi circuit 104. There is.

The operation of the signal identifying circuit 14 will be described below. (1) When the optical receiver receives a normal optical signal including the main signal component In the PLL circuit, when a normal signal is input, the phase of the input signal and the phase of the output signal of the voltage controlled oscillator (VCO) 8 And the error signal output from the flip-flop circuit (FF) 6 has a waveform oscillating at a constant cycle. This is shown in FIG. At this time, the signal identification circuit 1
The low pass filter 14A of No. 4 removes the fluctuation part of the error signal and outputs it. This low pass filter (LPF) 1
The behavior of the signal output from 4A is shown in FIG. As shown in the figure, the signal that has passed through the low-pass filter (LPF) 14A exhibits the same behavior as the control voltage output from the phase control circuit 7. Then, the signal identifying section 14B
Performs the same processing as the signal identifying circuit 10 in the first embodiment, and outputs a pulse signal indicating LOW for a certain period of time. Thereby, the optical receiving device determines that the received optical signal is a normal optical signal including the main signal component based on the pulse value “LOW” of the signal identifying circuit 14.

(2) Light receiving device emits spontaneously emitted light (ASE)
When an optical signal containing only the main signal component is cut off due to a failure of the optical transmission line 11, a spontaneous emission light (ASE) generated in the optical amplification repeater station 12 after the failure occurrence point is received. An optical signal containing only the component is transmitted to the terminal device 2. In such a case, in the PLL circuit, the phase of the input signal does not match the phase of the output signal of the voltage controlled oscillator (VCO) 8, and the flip-flop circuit (FF) 6
The error signal output from outputs a waveform oscillating in an irregular cycle. This state is shown in FIG. At this time, the low-pass filter (LPF) 14A of the signal identification circuit 14 removes the fluctuation part of the error signal and outputs it. The behavior of the signal output from the low pass filter (LPF) 14A is shown in FIG. As shown in the figure, the signal that has passed through the low-pass filter (LPF) 14A exhibits the same behavior as the control voltage output from the phase control circuit 7. Then, the signal identifying unit 14B performs the same process as the signal identifying circuit 10 in the first embodiment, and outputs a pulse signal indicating HIGH for a certain period of time. As a result, in the optical receiver, the optical signal received based on the pulse value “HIGH” of the signal identifying circuit 14 is an optical signal containing only spontaneous emission light (ASE) component, and a failure occurs on the optical transmission line 11. You can recognize what you have done.

[0060]

[Third Embodiment] FIG. 11 shows the arrangement of a terminal device to which the third method of the present invention is applied. The optical receiving device 3 of the terminal device 2 according to the present embodiment includes a photodiode (PD) 13 and a peak detection circuit 15 in addition to the configuration of the first embodiment described above. Photodiode (PD) 13
Are arranged in parallel with the photodiode (PD) 5, and the received signal is input to these photodiodes (PD) 5/11. Then, the photodiode (P
The output of D) 13 is connected to the peak detection circuit 15.

A minimum value and a maximum value are set in the peak detection circuit 15, and the peak value of the electric signal input from the photodiode (PD) 13 is detected, and this peak value is the minimum value or more and the maximum value. It is determined whether it is less than or equal to the value. Then, when the peak value is smaller than the minimum value or the peak value is larger than the maximum value, the optical receiving device 3 determines that the optical signal is not input at all due to a failure of the optical transmission line 11. That is, when a failure occurs in the optical transmission line 11 and the optical amplification repeater station 12 does not exist between the failure occurrence point and the terminal station apparatus 2, no optical signal is input to the terminal station apparatus 2. Will end up. In such a case, the value of the signal output from the photodiode (PD) 13 is much larger than that when an optical signal is input. As a result, in the optical receiver 3, when the peak detection circuit 13 detects a peak value larger than the maximum value or a peak value smaller than the minimum value, the input of the optical signal is interrupted due to an obstacle such as an optical transmission line. It can be determined.

When an optical signal is input, the optical receiving device 3 performs the same processing as that of the first embodiment, and the input optical signal is an optical signal containing a main signal component or a natural signal. It is possible to determine whether the optical signal includes only the emitted light (ASE) component.

[0063]

[Fourth Embodiment] FIG. 12 shows the arrangement of a terminal device to which the fourth method of the present invention is applied. The optical receiving device 3 of the terminal device 2 in this embodiment includes a photodiode (PD) 13 and a peak detection circuit 15 in addition to the configuration of the above-described second embodiment. Photodiode (PD) 13
Are arranged in parallel with the photodiode (PD) 5, and the received signal is input to these photodiodes (PD) 5/11. Then, the photodiode (P
The output of D) 13 is connected to the peak detection circuit 15.

A minimum value and a maximum value are set in the peak detection circuit 15, and the peak value of the electric signal input from the photodiode (PD) 13 is detected, and this peak value is the minimum value or more and the maximum value. It is determined whether it is less than or equal to the value. Then, when the peak value is smaller than the minimum value or the peak value is larger than the maximum value, the optical receiving device 3 determines that the optical signal is not input at all due to a failure of the optical transmission line 11. That is, when a failure occurs in the optical transmission line 11 and the optical amplification repeater station 12 does not exist between the failure occurrence point and the terminal station apparatus 2, no optical signal is input to the terminal station apparatus 2. Will end up. In such a case, the value of the signal output from the photodiode (PD) 13 becomes a much larger value (or a smaller value) than that when an optical signal is input. This allows
When the peak detection circuit 13 detects a peak value larger than the maximum value or a peak value smaller than the minimum value, the optical receiving device 3 indicates that the input of the optical signal is cut off due to a failure of the optical transmission line or the like. Can be determined.

When an optical signal is input, the optical receiving device 3 performs the same processing as in the second embodiment described above,
It is possible to determine whether the input optical signal is an optical signal containing the main signal component or an optical signal containing only the spontaneous emission (ASE) component.

[0066]

[Fifth Embodiment] FIG. 13 shows the arrangement of a terminal device to which the fifth and sixth methods of the present invention are applied. The optical receiving device 3 of the terminal device 2 according to the present embodiment branches the output of the phase control circuit 7 into three and connects them to the voltage controlled oscillator (VCO) 8 and the signal identification circuit 10, and at the same time, the input disconnection detection circuit 1
Connected to 6. The input break detection circuit 16 is a circuit that detects a state where no optical signal is input to the terminal device 2, that is, a so-called optical input break state. Other configurations are the same as those in the first embodiment described above, and the description thereof will be omitted.

Next, the configuration of the input break detection circuit 16 will be described with reference to FIG. The input disconnection detection circuit 16 has two comparators 1601 and 1602 and an OR circuit 1603.

The control voltage input from the phase control circuit 7 is branched into two and connected to the comparator 1601 and the comparator 1602. The minimum value VLo is set in the comparator 1601 and the maximum value VHi is set in the comparator 1602. Further, the outputs of the comparators 1601 and 1602 are connected to the OR circuit 1603.

When a normal optical signal containing the main signal component is input to the optical receiving device 3, the control voltage output from the phase control circuit 7 is the minimum value VLo or more and the maximum value as shown in FIG. It shows a constant value below the value VHi. In addition, the optical receiver 3
When the optical input interruption occurs, the control voltage output from the phase control circuit 7 has a much larger value (or a smaller value) than that when the optical signal is input, as shown in FIG.

For example, when the control voltage smaller than the minimum value VLo as shown in FIG. 16 is input to the input break detection circuit 16, (minimum value VLo-control voltage V)> 0, and the comparator 1601 The signal HIGH is output. At this time, (control voltage V−maximum value VHi) <0 is apparent, and the comparator 1602 outputs the signal LOW.
At this time, the OR circuit 1603 outputs the signal LOW.

Further, the input disconnection detection circuit 16 has the maximum value VHi.
If a control voltage greater than
Lo-control voltage V) <0, and the comparator 1601
Outputs the signal LOW. At this time, control voltage V-maximum value VHi)> 0, and comparator 1602 outputs signal HIGH. At this time, the OR circuit 1603
The signal LOW is output.

Further, when the control voltage of the minimum value VLo or more and the maximum value VHi or less as shown in FIG. 15 is input, the input disconnection detection circuit becomes (minimum value VLo-control voltage) <0, and the comparator 1601 Outputs the signal LOW.
On the other hand, (control voltage V−maximum value VHi) <0, and the comparator 1602 outputs the signal LOW. At this time,
The OR circuit 1603 outputs the signal HIGH.

According to this embodiment, the optical receiver 3 can recognize that the optical input disconnection has occurred when the output signal of the input disconnection detection circuit 16 is at the LOW level.
Further, when the output signal of the input disconnection detection circuit 16 is at the HIGH level, the optical receiving device 3 performs the same processing as that of the first embodiment described above, and the input signal is a normal optical signal including the main signal component. Or it is an optical signal containing only the spontaneous emission (ASE) component.

[0074]

[Sixth Embodiment] FIG. 17 shows the arrangement of a terminal device to which the fifth and seventh methods of the present invention are applied. The optical receiving device 3 of the terminal device 2 according to the present embodiment branches the output of the flip-flop circuit (FF) 6 into three and connects them to the voltage controlled oscillator (VCO) 8 and the signal identification circuit 14 and at the same time disconnects the input. It is connected to the detection circuit 16. The input break detection circuit 16 is a circuit that detects a state where no optical signal is input to the terminal device 2, that is, a so-called optical input break state. The internal configuration of the input disconnection detection circuit 16 is the same as the fifth configuration described above.
This is the same as the embodiment described above, and the description thereof is omitted. In addition, other configurations are the same as those in the above-described second embodiment.

According to this embodiment, the optical receiver 3 can recognize that the optical input disconnection has occurred when the output signal of the input disconnection detection circuit 16 is at the LOW level.
Further, in the optical receiving device 3, when the output signal of the input disconnection detection circuit 16 is at the HIGH level, the input signal is a normal optical signal including the main signal component also based on the output signal of the signal identification circuit 14. It is possible to determine whether or not it is an optical signal including only the spontaneous emission light (ASE) component.

[0076]

According to the first method and the second method of the present invention, in the optical receiving device of the terminal device, the input signal is a normal optical signal containing the main signal component, or the optical signal is on the optical transmission line. It is possible to determine whether or not the optical signal includes only the spontaneous emission light component generated by the optical amplifier, and it is possible to recognize a failure or the like of the optical transmission line.

Further, according to the third to seventh methods of the present invention, the optical receiving device of the terminal device can determine the state in which the input of the optical signal is cut off. Therefore, according to the present invention, it is possible to suppress the reproduction processing of the optical signal that does not include the main signal component, and it is possible to improve the reliability of the optical transmission system.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical transmission system according to a first embodiment.

FIG. 2 is a diagram showing an internal configuration of a signal identification circuit 10.

FIG. 3 is a diagram showing the behavior of the control voltage when a normal optical signal is input.

FIG. 4 is a diagram showing the behavior of a control voltage when an optical signal of only spontaneous emission light is input.

FIG. 5 is a diagram showing a configuration of a terminal station device according to a second embodiment.

FIG. 6 is a diagram showing an internal configuration of a signal identification circuit 14.

FIG. 7 is a diagram showing the behavior of the error signal voltage when a normal optical signal is input.

FIG. 8 is a diagram showing the behavior of the error signal voltage when an optical signal containing only spontaneous emission light is input.

FIG. 9 is a diagram (1) showing the behavior of the voltage after passing through the LPF.

FIG. 10 is a diagram (2) showing the behavior of the voltage after passing through the LPF.

FIG. 11 is a diagram showing a configuration of a terminal station device according to a third embodiment.

FIG. 12 is a diagram showing a configuration of a terminal station device according to a fourth embodiment.

FIG. 13 is a diagram showing a configuration of a terminal station device according to a fifth embodiment.

FIG. 14 is a diagram showing an internal configuration of an input break detection circuit 16.

FIG. 15 is a diagram showing the behavior of the control voltage when a normal optical signal is input.

FIG. 16 is a diagram showing the behavior of the control voltage when the light input is cut off.

FIG. 17 is a diagram showing a configuration of a terminal station device according to a sixth embodiment.

[Explanation of symbols]

 1 ... Terminal device 2 ... Terminal device 3 ... Optical receiver 4 ... Optical transmitter 5 ... Photodiode (PD) 6 ... Flip-flop circuit (FF) 7 ... Phase control circuit 8 ... Voltage controlled oscillator (VCO) 9-Identification circuit 10-Signal identification circuit 11-Optical transmission line 12-Optical amplification relay station 13-Photodiode 14-Signal identification circuit 14A-Low-pass filter (LPF) 14B ..Signal discriminating unit 15 ... Peak detection circuit 16 ... Input disconnection detection circuit 101 ... Comparator 102 ... Comparator 103 ... NOR circuit 104 ... Mono multivibrator 1601 Comparator 1602

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H03L 7/095 H04L 7/033 25/02 301 25/40

Claims (7)

[Claims] 1. A phase-locked loop circuit (PLL; PHASE LO)
CKED LOOP) is an input signal identification method of an optical receiving device for generating a self-timing signal, and a control voltage monitoring step of monitoring a control voltage value input to a voltage controlled oscillator constituting the phase locked loop circuit, A control voltage determining step of determining whether the control voltage shows a constant value or an irregular value; and when the control voltage value shows a constant value, the input signal of the optical receiving device is a main signal. A first determination step of determining that the optical signal includes a component, and when the control voltage value shows an irregular value, the input signal of the optical receiving device is an optical signal that does not include a main signal component And a second determination step for determining the input signal identification method of the optical receiving device. 2. A phase-locked loop circuit (PLL; PHASE LO)
CKED LOOP) is an input signal identification method of an optical receiving device for generating a self-timing signal, and a waveform monitoring step of monitoring a waveform of an error signal output from a phase detection circuit constituting the phase locked loop circuit, A waveform determining step of determining whether the waveform of the error signal is a waveform that oscillates in a constant cycle or a waveform that oscillates in an irregular cycle; and when the waveform of the error signal is a waveform that oscillates in a constant cycle In the third determination step for determining that the input signal of the optical receiving device is an optical signal containing a main signal component, and if the waveform of the error signal is a waveform oscillating at an irregular cycle, the optical signal A fourth determination step of determining that an input signal of the receiving device is an optical signal that does not include a main signal component, and an input signal identifying method of the optical receiving device. 3. A phase-locked loop circuit (PLL; PHASE LO)
CKED LOOP) is used to generate a self-timing signal, which is an input signal identifying method for an optical receiving device, the photoelectric converting step of converting an input signal of the optical receiving device from an optical signal to an electrical signal, and the photoelectric conversion step. A peak detection step of detecting the peak value of the electric signal converted by, and a peak value determination step of determining whether or not the peak value detected in the peak detection step is a value outside a preset specific range When the peak value is a value outside the specific range, an optical input disconnection determination step of determining that the input signal of the optical receiving device is disconnected, and the peak value is a value within the specific range. In some cases, a control voltage monitoring step of monitoring a control voltage value input to a voltage controlled oscillator forming the phase locked loop circuit, and whether the control voltage shows a constant value. Or a control voltage determining step of determining whether it shows an irregular value, and when the control voltage value shows a constant value, the input signal of the optical receiving device is an optical signal containing a main signal component. A first determination step of determining, and a second determination step of determining that the input signal of the optical receiving device is an optical signal containing no main signal component when the control voltage value indicates an irregular value. A method for identifying an input signal of an optical receiving device including. 4. A phase-locked loop circuit (PLL; PHASE LO)
CKED LOOP) is used to generate a self-timing signal, which is an input signal identifying method for an optical receiving device, the photoelectric converting step of converting an input signal of the optical receiving device from an optical signal to an electrical signal, and the photoelectric conversion step. A peak detection step of detecting the peak value of the electric signal converted by, and a peak value determination step of determining whether or not the peak value detected in the peak detection step is a value outside a preset specific range When the peak value is a value outside the specific range, an optical input disconnection determination step of determining that the input signal of the optical receiving device is disconnected, and the peak value is a value within the specific range. In some cases, a waveform monitoring step of monitoring the waveform of the error signal output from the phase detection circuit that constitutes the phase-locked loop circuit; A waveform determining step of determining whether the waveform is a waveform having an irregular period or a waveform having an irregular period; and when the waveform of the error signal is a waveform having an amplitude with a constant period, the input signal of the optical receiving device is A third determination step of determining that the optical signal includes a main signal component, when the waveform of the error signal is a waveform oscillating in an irregular cycle, the input signal of the optical receiving device is the main signal component A fourth determination step of determining that the optical signal does not include an input signal of the optical receiving device. 5. A phase-locked loop circuit (PLL; PHASE LO)
CKED LOOP) is an input signal identification method of an optical receiving device for generating a self-timing signal, and a control voltage monitoring step of monitoring a control voltage input to a voltage controlled oscillator constituting the phase locked loop circuit, An input signal identification of an optical receiving device including an optical input disconnection determining step of determining that the input signal of the optical receiving device is disconnected when the value of the control voltage is a value outside a preset specific range. Method. 6. A phase-locked loop circuit (PLL; PHASE LO)
CKED LOOP) is an input signal identification method of an optical receiving device for generating a self-timing signal, and a control voltage monitoring step of monitoring a control voltage input to a voltage controlled oscillator constituting the phase locked loop circuit, When the value of the control voltage is a value outside a preset specific range, an optical input disconnection determination step of determining that the input signal of the optical receiver is disconnected, and the value of the control voltage is preset. When the value is within the specified range, the control voltage determining step of determining whether the control voltage shows a constant value or an irregular value, and the control voltage value shows a constant value. In the case, a first determination step of determining that the input signal of the optical receiving device is an optical signal containing a main signal component, and if the control voltage value shows an irregular value, the input of the optical receiving device Input signal identification method No. optical receiver comprising a second determination step of determining it is an optical signal which does not include the main signal component. 7. A phase-locked loop circuit (PLL; PHASE LO)
CKED LOOP) is an input signal identification method of an optical receiving device for generating a self-timing signal, and a control voltage monitoring step of monitoring a control voltage input to a voltage controlled oscillator constituting the phase locked loop circuit, When the value of the control voltage is a value outside a preset specific range, an optical input disconnection determination step of determining that the input signal of the optical receiving device is disconnected, and the control voltage value is within a specific range. If the value is, the waveform monitoring step of monitoring the waveform of the error signal output from the phase detection circuit that constitutes the phase-locked loop circuit, and the waveform of the error signal is a waveform that oscillates at a constant cycle or is irregular. A waveform determining step for determining whether the waveform of the error signal is a waveform that oscillates in a constant cycle; A third determination step of determining that the optical signal includes a component, when the waveform of the error signal is a waveform oscillating in an irregular cycle, the input signal of the optical receiving device does not include a main signal component An input signal identifying method for an optical receiving device, comprising: a fourth determining step of determining that the signal is an optical signal.