JPH0340541A - Optical signal input disconnection detector - Google Patents

Abstract

PURPOSE:To correctly detect the disconnection of a non-return-to-zero(NRZ) optical signal input by comparing an output signal from a differential circuit for forming an RZ waveform from the output signal of a photoelectric conversion circuit and for outputting the shaped signal with a previously determined threshold to decide the 'disconnection' of the optical signal input. CONSTITUTION:An NRZ optical signal is converted into an NRZ electric signal by the photoelectric conversion circuit 1 and its RZ waveform is shaped by the differential circuit 2. A clock whose phase is different from the output signal of the circuit 2 only by a half wavelength is extracted from a clock extraction circuit 3 and an optical input disconnection deciding circuit 7 compares the output signal of the circuit 2 with the threshold by the timing of the clock to decide the 'disconnection' of the optical signal input. Thus, the disconnection of the NRZ optical signal input can correctly be detected.

Description

[Detailed Description of the Invention] [Summary] An optical signal input disconnection detection device that can correctly detect an NRZ optical signal input disconnection, regarding an NRZ modulated digital optical signal input disconnection detection device in an optical receiver for optical communication. A photoelectric conversion circuit that inputs an NRZ-modulated digital optical signal, converts it into an electrical signal, and outputs it, and a differentiation circuit that performs RZ filtering and outputting the output signal of the photoelectric conversion circuit. and a clock extraction circuit that extracts a clock whose phase differs by half a wavelength from the output signal of the differentiation circuit, and the output signal from the differentiation circuit is determined in advance based on the timing of the clock output from the clock extraction circuit. and an optical input disconnection determination circuit that determines whether the optical signal input is disconnected by comparing it with a threshold value.

[Industrial application field]

The present invention relates to an input disconnection detection device for an NRZ (non-return-to-zero) modulated digital optical signal in an optical receiver for optical communications.

Optical communication systems require various failure detection functions in order to discover whether the system is operating normally or not and to discover failure points in the event of an abnormality. Among them,
The function of detecting whether an optical signal is being received or not, that is, whether the input of an optical signal is disconnected, is an indispensable function of an optical receiver, and must operate normally in order to discover failure points.

[Conventional technology]

Conventionally, an NRZ optical signal input disconnection detection device first converts an NRZ optical signal into an NRZ electrical signal, then forms an RZ filter from the NRZ signal using a differentiating circuit, and extracts a timing component from the RZ filtered waveform. By amplifying the signal, detecting the peak value of the timing component, and comparing the peak value with a predetermined threshold value, a "cut" in the optical signal input was detected.

[Problem to be solved by the invention]

However, the timing component naturally disappears when the mark rate of the predecessor force signal becomes low. Then, the peak value also decreases, causing the problem of erroneously determining that the optical signal is "off."

In addition, if the gain of the timing component amplification is increased to prevent the peak value from decreasing, the amplifier circuit will oscillate in the event of an optical signal input disconnection, and the peak value will not decrease, resulting in the erroneous determination that the optical signal input is not disconnected. There was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical signal input disconnection detection device that can eliminate such conventional drawbacks and correctly detect an optical signal input disconnection of NRZ.

[Means to solve the problem]

In order to achieve the above object, the optical signal input disconnection detection device of the present invention, as shown in FIG. 1, a differentiating circuit 2 that performs RZ filtering on the output signal of the photoelectric conversion circuit 1 and outputs the same, and a clock extraction circuit 3 that extracts a clock whose phase differs by half a wavelength from the output signal of the differentiating circuit 2. , depending on the timing of the clock output from the clock extraction circuit 3,
The present invention is characterized in that it includes an optical input disconnection determination circuit 7 that determines whether the optical signal input is "OFF" by comparing the output signal from the differentiating circuit 2 with a predetermined threshold value.

[Effect]

The NRZ optical signal is converted into an NRZ electrical signal by a photoelectric conversion circuit 1, and further subjected to RZ filtering formation by a differentiating circuit 2.

Then, a clock whose phase differs by half a wavelength from the output signal of the differentiating circuit 2 is extracted by the clock extracting circuit 3, and the optical input disconnection determining circuit 7 detects the output signal from the differentiating circuit 2 depending on the timing of the clock. It is compared with a threshold value to determine whether the optical signal is "broken".

〔Example〕

Examples will be described with reference to the drawings.

FIG. 2 is a circuit block diagram of the embodiment. In the figure, 11 is an avalanche photodiode (APD) that inputs an NRZ-modulated digital optical signal and converts it into an electrical signal.
This NRZ electric signal output is input to the equalization amplification circuit 12 and is equalized and amplified.

The equalization amplifier circuit 12 detects the peak of the equalized waveform to control the gain, and also feeds back a control signal for controlling the multiplication factor of the APD to the APD bias control circuit 13. This provides automatic gain control.

The output signal of the equalization amplifier circuit 12 is output to the identification circuit 5 and the differentiation circuit 2.

In the differentiating circuit 2, the input NRZ electrical signal is subjected to RZ filtering. FIGS. 3 and 5 show examples of such differentiating circuits.

The differential circuit shown in FIG. 3 inputs an input NRZ signal to a slice amplifier 21, amplifies and extracts only the waveform in a narrow band, obtains a reflected wave that is inverted from the ground through a coaxial line 22 of a predetermined length, The reflected wave is superimposed on the output signal from the slice amplifier 21 and rectified by the rectifier circuit 23. The two capacitors 24 cut off DC components entering from the ground or the like.

As a result, as shown in FIG.
The reflected wave from the coaxial line 22 is superimposed on the output signal from the rectifier circuit 2 to form a superimposed wave.
3, and the RZ waveform ■ is output.

The differentiating circuit shown in FIG. 5 branches the output signal of the slice amplifier 21 and inputs it to the delay circuit 25, and exclusively divides the signal ■ delayed by a predetermined time and the original signal ■ output from the slice amplifier 21. OR (EX-OR) circuit 26
input, and it becomes "1" only when both human power signals are "1".
I am trying to output .

As a result, as shown in FIG. 6, an RZ waveform (2) with a width corresponding to the delay time is output.

In this way, R output from the differentiating circuit 2 in FIG.
The Z-filtered waveform signal is branched and sent to the clock extraction circuit 3 and the optical input disconnection determination circuit 7.

32 and 33 are a bandpass filter and a limiter amplifier circuit forming the clock extraction circuit 3.

The clock pulse output from the limiter amplifier circuit 33 is sent to the identification circuit 5', and the inverted clock pulse is sent to the optical input disconnection determination circuit 7. Therefore, a clock pulse whose phase is shifted by a half wavelength with respect to the output signal of the differentiating circuit 2 is inputted to the optical input disconnection determination circuit 7.

The discrimination circuit 5 discriminates between "rl" and "0" with respect to the manual data from the equalization amplifier circuit 12 at the timing of the clock from the limiter amplifier circuit 33, and outputs the result together with the clock.

The optical input disconnection determination circuit 7 is formed by an identification circuit 71, a peak detection circuit 72, and a comparison circuit 73. Here, the RZ waveform signal from the differentiating circuit 2 and the clock pulse from the limiter amplifier circuit 33 whose phase is shifted by a half-wavelength needle from the RZ waveform signal are input to the discrimination circuit 71.

When the optical signal is input, the identification circuit 71
In this case, as shown in FIG. 7, due to the falling edge of the clock pulse that is half a wavelength out of phase with the RZ waveform signal,
The ``l'L'' level of the RZ waveform signal is identified, and the ``L'' level of the RZ waveform signal is identified.
” level value is output to the peak detection circuit 72. As a result, the output of the identification circuit 71 is always at the "L" level of the emitter coupled logic (ECL), regardless of the mark rate of the optical signal. Therefore, the output of the peak detection circuit 72 naturally also goes to the "L" level of ECL.

On the other hand, when the input of the optical signal is "off", as shown in FIG. The output from the circuit 72 becomes the "H" level of ECL.

By inputting the output signal of such a peak detection circuit 72 to the comparison circuit 73 shown in FIG. , the presence or absence of optical signal input is determined, that is, the detection of the optical signal being "off" by human input is performed. When the optical signal input is "off", the output signal from the comparator circuit 73 allows
An alarm circuit 9 issues an alarm by sound or light.

〔Effect of the invention〕

According to the optical signal human power failure detection device of the present invention, even if the mark rate of the NR2 optical signal changes, the level of the identification point does not change, and it is possible to stably determine the presence or absence of optical signal human power. , it is possible to always accurately detect "disconnection" of the NRZ optical signal input without being affected by the mark rate at all.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is a circuit block diagram of an embodiment, Fig. 3 is a circuit diagram of a differential circuit, Fig. 4 is a time chart showing the operation of the differential circuit, and Fig. 5 is a differential circuit diagram. The circuit diagram of the circuit, Figure 6 is a time chart showing the operation of the differential circuit, Figure 7 is a diagram explaining the operation when the optical signal input is disconnected, and Figure 8 is the diagram explaining the operation when the optical signal input is disconnected. . In the figure, L: Photoelectric conversion circuit, 2: Differential circuit, 3: Clock extraction circuit, 7: Optical input disconnection determination circuit. Ia circuit/) Circuit diagram Figure 3 shows the operation of the ``M operation'' Figure 4 Figure 5 shows the operation of the micro-return circuit Dime call~-G field Ruiba Flash Figure 7 □ The sound of the pigeonhole in which the metering light is believed is entered 4th movement B Figure 8

Claims (1)

[Claims] A photoelectric conversion circuit (1) that inputs an NRZ-modulated digital optical signal, converts it into an electrical signal, and outputs it; and a photoelectric conversion circuit (1) that forms an RZ waveform from the output signal of the photoelectric conversion circuit (1). A differentiating circuit (2) that outputs, a clock extraction circuit (3) that extracts a clock whose phase differs by half a wavelength from the output signal of the differentiating circuit (2), and a clock that is output from the clock extraction circuit (3). An optical input disconnection determination circuit (7) is provided, which determines whether the optical signal input is disconnected by comparing the output signal from the differentiating circuit (2) with a predetermined threshold value depending on the clock timing. An optical signal input disconnection detection device characterized by: