CN111327976A

CN111327976A - Optical fiber communication network protection circuit

Info

Publication number: CN111327976A
Application number: CN202010230078.8A
Authority: CN
Inventors: 舒新建; 张勇; 王春迎; 安致嫄; 秦晓阳; 董凯丽; 王雷; 盛磊
Original assignee: State Grid Corp of China SGCC; Information and Telecommunication Branch of State Grid Henan Electric Power Co Ltd
Current assignee: State Grid Corp of China SGCC; Information and Telecommunication Branch of State Grid Henan Electric Power Co Ltd
Priority date: 2020-03-27
Filing date: 2020-03-27
Publication date: 2020-06-23
Anticipated expiration: 2040-03-27
Also published as: CN111327976B

Abstract

The invention relates to an optical fiber communication network protection circuit, which is characterized in that an optical signal average power calculation circuit calculates the average value of optical power, and is beneficial to avoiding the misoperation of an optical switch caused by instantaneous and accidental abnormality, an optical signal frequency-voltage conversion circuit converts an optical frequency signal into linear direct-current voltage, an optical switch starting circuit calculates the difference value between the lower limit value of preset optical power and the average value of the optical power, the difference signal enters an inverse time limit comparison circuit for judgment, outputs high and low levels to an AND gate chip U3, calculates the difference value between the lower limit value of the preset optical signal frequency and the direct-current voltage, the difference signal enters the inverse time limit comparison circuit for judgment, outputs high and low levels to an AND gate chip U3, the setting of inverse time limit can provide a basis for the judgment of abnormality of a main channel rapidly, the AND gate chip U3 outputs logic level to trigger the light to switch the main channel to a standby channel when the light-off light is lower than the, the accuracy of judging whether the working state of the main channel is normal or not is improved.

Description

Optical fiber communication network protection circuit

Technical Field

The invention relates to the technical field of communication networks, in particular to an optical fiber communication network protection circuit.

Background

The existing method mainly comprises monitoring according to optical power change and automatic analysis of alarm information, when the optical fiber is broken or loss is increased to cause communication quality reduction or communication interruption, when the optical power reaches an abnormal value, a working main channel is switched to a standby channel through an optical switch, whether the working state of the channel is normal or not can not be accurately judged only according to the optical power parameter, and the optical switch switching also needs a process, so that the problem that the optical switch cannot be accurately and timely switched is caused.

Disclosure of Invention

In view of the above situation, an object of the present invention is to provide a protection circuit for an optical fiber communication network, which effectively solves the problems that the working state of the channel in the prior art cannot be accurately determined and the switching cannot be performed in time when the channel is abnormal.

The technical scheme for solving the problem is that the optical switch is automatically switched to the standby channel when the main channel is abnormal, so that the optical fiber communication quality is ensured;

the optical signal average power calculating circuit adopts PD probe to detect the optical power transmitted by the optical fiber, the optical power signal is amplified by a gain amplifier taking an operational amplifier AR1 as a core, the average value of the optical power is calculated by an average value circuit taking operational amplifiers AR2 and AR3 as cores, and then sent to an optical switch starting circuit, the optical signal frequency-voltage converting circuit adopts a photoelectric detector to convert the optical signal transmitted by the optical fiber into an electric signal, the electric signal is converted into an electric pulse signal by a photoelectric coupler U1, and then converted into a direct current voltage linear with the electric pulse signal by a frequency-voltage converter taking a chip U2 and an operational amplifier AR5 as cores, and sent to the optical switch starting circuit, the optical switch starting circuit adopts a triode Q2 and a triode Q3 to calculate the difference value between the preset lower limit value of the optical power and the average value of the optical power output by the optical signal average power calculating circuit, and the difference signal enters an operational amplifier AR4 as an inverse, and outputting high and low levels to a pin 1 of an AND gate chip U3, calculating a difference value between a preset optical signal frequency lower limit value and a direct current voltage output by an optical signal frequency voltage conversion circuit by adopting a triode Q4 and a triode Q5, judging the difference value signal by an inverse time limit comparison circuit taking an operational amplifier AR6 as a core, outputting the high and low levels to a pin 2 of the AND gate chip U3, and triggering and emitting light to switch a main channel to a standby channel by the AND gate chip U3 outputting logic levels.

The invention has the beneficial effects that: by calculating the average value of the optical power, then performing inverse time limit comparison and judgment with a lower power limit value (96% of the lower limit value allowed by normal optical power) through an inverse time limit comparison circuit according to the severity of optical power attenuation, converting an optical frequency signal into direct current voltage, and performing inverse time limit comparison and judgment with the lower limit value (98% of the lower limit value allowed by normal optical frequency) through the inverse time limit comparison circuit according to the severity of optical frequency slow, wherein the setting of the inverse time limit can provide a basis for the main channel to judge abnormity quickly;

when the outputs of the two inverse time limit comparison circuits are both high levels, the AND gate chip U3 outputs a logic level 1, and then triggers the optical switch to switch the main channel to the standby channel, so that the accuracy of judging whether the working state of the main channel is normal or not is improved, and the optical switch can be switched to the standby channel in time when the working state of the main channel is lower than the lower limit value allowed by normal optical power and the lower limit value allowed by normal optical frequency.

Drawings

Fig. 1 is a schematic diagram of an average power calculation circuit according to the present invention.

Fig. 2 is a schematic diagram of an optical signal frequency-to-voltage conversion circuit according to the present invention.

Fig. 3 is a schematic diagram of the starting circuit of the optical switch of the present invention.

Detailed Description

The foregoing and other aspects, features and advantages of the invention will be apparent from the following more particular description of embodiments of the invention, as illustrated in the accompanying drawings in which reference is made to figures 1 to 3. The structural contents mentioned in the following embodiments are all referred to the attached drawings of the specification.

Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

A kind of optical fiber communication network protective circuit, main channel, spare channel, photoswitch, the said photoswitch switches to the spare channel automatically when the main channel is unusual, guarantee the optical fiber communication quality, the working condition of the said photoswitch is triggered and controlled by mean power calculation circuit of the optical signal, optical signal frequency voltage conversion circuit, photoswitch starting circuit;

the optical signal average power calculating circuit adopts a PD probe to detect optical power transmitted by an optical fiber, optical power signals are sequentially amplified by a gain amplifier taking an operational amplifier AR1 as a core, the average value of the optical power is calculated by an average value circuit taking operational amplifiers AR2 and AR3 as the core, then the optical power signals are sent to an optical switch starting circuit, the average value of the waveform of the optical power signals for a period of time is calculated, the optical switch starting circuit is beneficial to avoiding the false operation of an optical switch caused by instantaneous and accidental abnormity, the optical signal frequency-voltage converting circuit adopts a photoelectric detector to convert optical signals transmitted by the optical fiber into electric signals, the electric signals are converted into electric pulse signals through a photoelectric coupler U1, then are converted into direct current voltage linear with the electric pulse signals through a frequency-voltage converter taking a chip U2 and an operational amplifier AR5 as the core, and then the direct current voltage is sent to the optical switch starting, The triode Q3 calculates the difference between the preset lower limit value of the optical power and the average value of the optical power output by the optical signal average power calculating circuit, the difference signal enters an inverse time limit comparing circuit, the inverse time limit is compared and judged with the lower limit value of the optical power according to the severity of the optical power attenuation, otherwise, a low level is output when the difference signal is normal, namely, when the difference signal is higher than the allowable lower limit value of the optical power, a high level is output to the pin 1 of the AND gate chip U3, the triode Q4 and the triode Q5 are adopted to calculate the difference between the preset lower limit value of the optical signal frequency and the DC voltage output by the optical signal frequency voltage converting circuit, the difference signal enters the inverse time limit comparing circuit, the inverse time limit is compared and judged with the lower limit value of the optical frequency signal according to the severity of the slow optical frequency, the setting of the inverse time limit can quickly provide basis for the main channel to judge the abnormity, when, and if the output level is low, otherwise, the output level is high, the output level is sent to a pin 2 of the AND gate chip U3, the AND gate chip U3 outputs a logic level 1 when the output level is high, and then the optical switch is triggered to switch the main channel to the standby channel, so that the accuracy of judging whether the working state of the main channel is normal or not is improved.

On the basis of the scheme, the optical signal average power calculating circuit detects the optical power transmitted by the optical fiber by adopting a PD probe, the waveform of an optical power signal is firstly amplified by a gain amplifier consisting of an operational amplifier AR1, a triode Q1, a capacitor C5 and a grounded capacitor C5, wherein the base electrode and the collector electrode of the triode Q1 are connected together to be used as a diode which is connected with a feedback loop of an operational amplifier AR1 in parallel with a capacitor C5 to play a role of amplitude limiting, the amplified signal enters the operational amplifier AR2 and AR3, a resistor R10-resistor R16, a diode D3 and D4 and an average value circuit consisting of electrolytic capacitors E2 and E3 to calculate the average value of the optical power and send the average value to an optical switch starting circuit to calculate the average value of the optical power signal waveform for a period of time, so as to avoid the false operation of the optical switch caused by instantaneous and accidental abnormality, wherein the operational amplifier 2, the resistor R10-resistor R14, The full-wave rectifier is composed of diodes D3 and D4, the mean value filter is composed of an operational amplifier AR3, a resistor R14-resistor R16 and an electrolytic capacitor E3, and comprises a PD probe, the cathode of the PD probe is respectively connected with the inverting input end of the operational amplifier AR1, the collector and the base of a triode Q1 and one end of a capacitor C5, the anode of the PD probe and the non-inverting input end of the operational amplifier AR1 are connected to the ground, the output end of the operational amplifier AR1 is respectively connected with the emitter of the triode Q1, the other end of the capacitor C5, one end of a grounded capacitor C6 and the anode of an electrolytic capacitor E2, the cathode of the electrolytic capacitor E2 is respectively connected with one end of a resistor R10 and one end of a resistor R11, the other end of the resistor R11 is respectively connected with the inverting input end of the operational amplifier AR2, one end of a resistor R13 and the cathode of a diode D3, the non-inverting input end of the operational amplifier AR3 is connected, The negative electrode of the diode D4, the positive electrode of the diode D4 are connected to the other end of the resistor R13 and one end of the resistor R14, the other end of the resistor R14 is connected to the inverting input terminal of the operational amplifier AR3, the other end of the resistor R10, one end of the resistor R16 and the positive electrode of the electrolytic capacitor E3, the non-inverting input terminal of the operational amplifier AR3 is connected to the ground through the resistor R15, the output terminal of the operational amplifier AR3 is connected to the other end of the resistor R16 and the negative electrode of the electrolytic capacitor E3, and the output terminal of the operational amplifier AR3 is an output signal of the optical signal average power calculation circuit.

On the basis of the scheme, the optical signal frequency-voltage conversion circuit converts an optical signal transmitted by an optical fiber into an electric signal by using a photoelectric detector GD1, the electric signal is converted into an electric pulse signal by a photoelectric coupler U1, the electric pulse signal is amplified by a triode Q1 and then converted into a direct current voltage linear to the electric pulse signal by a chip U2, an operational amplifier AR5, a resistor R6, a resistor R7, a capacitor C2-a capacitor C4, a capacitor C7 and a voltage regulator tube Z1 of the type LTC1013, and the direct current voltage is sent to an optical switch starting circuit, specifically, the electric pulse signal is input to a pin 16 of the chip U2, if the electric pulse signal is high level, the pin 12 and the pin 13 of the chip U2 are short-circuited, the capacitor C3 is charged, if the electric pulse signal is low level, the pin 12 and the pin 14 of the chip U2 are short-circuited, the capacitor C3 is discharged, the discharge current passes through a feedback capacitor C4 of the operational amplifier AR5, and, the operational amplifier AR5 outputs a direct current voltage which is linear with an electric pulse signal because negative feedback is performed and the output is positive and repeated before the inverting input end of the operational amplifier AR5 is zero, the photoelectric detector GD1 comprises a photoelectric detector GD1, the collector of the photoelectric detector GD1 and one end of a resistor R1 are connected with a power supply +5V, the emitter of the photoelectric detector GD1 is respectively connected with one end of a grounding resistor R2 and the cathode of an electrolytic capacitor E1, the anode of the electrolytic capacitor E1 is respectively connected with the anode of the electrolytic capacitor E1, the other end of a resistor R1 and one end of a resistor R3, the other end of the resistor R3 is respectively connected with the anode of a diode D1, the cathode of a diode D2, the pin 1 of a photoelectric coupler U1 and one end of a grounding capacitor C1, the cathode of a diode D1 is connected with the power supply +5V, the anode of the diode D2 is connected with the ground, the pin 2 and the pin 3 of the photoelectric coupler U5 are connected with the one end of the, The base of a triode Q1, the emitter of a triode Q1 are connected to the ground, the collector of a triode Q1 is respectively connected to one end of a resistor R5 and one end of a capacitor C2, the other end of a resistor R5 is connected to +5V, the other end of a capacitor C2 is connected to a pin 16 of a chip U2, a pin 12 of a chip U2 is connected to the ground through a capacitor C3, a pin 13 of a chip U2 is respectively connected to one end of a capacitor C7, the anode of a voltage regulator Z1 and one end of a resistor R6, the other end of a resistor R6 is connected to +5V, the other end of a capacitor C7 and the cathode of a voltage regulator Z1 are connected to the ground, a pin 14 of a chip U2 is respectively connected to one end of a resistor R7, one end of a capacitor C4 and the inverting input end of an operational amplifier AR5, the other end of an AR 7 is respectively connected to the other end of a capacitor C4 and the output end of an operational amplifier, the non-inverting input terminal of the operational amplifier AR5 is connected to ground.

On the basis of the scheme, the optical switch starting circuit adopts a triode Q2 and a triode Q3 to calculate the difference value between the lower limit value of the preset optical power and the average value of the optical power output by the optical signal average power calculating circuit, the difference signal enters an inverse time limit comparison circuit consisting of an operational amplifier AR4, a resistor R17, a resistor R18, an electrolytic capacitor E4 and a voltage regulator tube Z2, according to the severity of optical power attenuation, inverse time limit is compared and judged with the lower limit value of the optical power (96 percent of the lower limit value allowed by the normal optical power), when the difference value is higher than the lower limit value of the optical power, a low level is output, otherwise, a high level is output to a pin 1 of an AND gate chip U3, the difference value between the lower limit value of the preset optical signal frequency and the direct current voltage output by the optical signal frequency voltage converting circuit is calculated by adopting a triode Q4 and a triode Q5, and the difference signal Q6, an inverse time limit comparison circuit consisting of a resistor R8, a resistor R9, an electrolytic capacitor E5 and a voltage regulator tube Z3 compares and judges the inverse time limit with the lower limit value of an optical frequency signal (98 percent of the lower limit value allowed by the normal optical frequency) according to the severity degree of slow optical frequency, the setting of the inverse time limit can quickly provide basis for judging the abnormity of a main channel, when the abnormal state is normal, namely higher than the lower limit value of the optical frequency signal, a low level is output, otherwise, a high level is output, the low level is output to a pin 2 of an AND gate chip U3, the AND gate chip U3 outputs a logic level 1 when the high level is both output, then the optical open light is triggered to switch the main channel to a standby channel, the accuracy of judging whether the working state of the main channel is normal or not is improved, the inverse time limit comparison circuit comprises a triode Q2 and a triode Q4, the base of the triode Q2 is connected with the output end of an operational amplifier AR3, the collector of the triode Q2 is, the emitter of the triode Q3 is respectively connected with one end of a resistor R17 and the cathode of a voltage regulator tube Z2, the other end of the resistor R17 is respectively connected with the anode of a voltage regulator tube Z2 and one end of a resistor R18, the other end of the resistor R18 is respectively connected with the anode of an electrolytic capacitor E4 and the inverting input end of an operational amplifier AR4, the cathode of the electrolytic capacitor E4 is connected with the ground, the non-inverting input end of the operational amplifier AR4 is connected with a preset lower limit value of optical power, the output end of the operational amplifier AR4 is connected with a pin 1 of an AND gate chip U3, the base of the triode Q4 is connected with the output end of the operational amplifier AR5, the collector of the triode Q4 is connected with the base of the triode Q5, the emitter of the triode Q4 and the collector of the triode Q5 are connected with a power supply of +10V, the emitter of the triode Q5 is respectively connected with one end of a resistor R8 and the cathode of a voltage regulator, the other end of the resistor R9 is connected with the anode of the electrolytic capacitor E5 and the inverting input end of the operational amplifier AR6 respectively, the cathode of the electrolytic capacitor E5 is connected with the ground, the non-inverting input end of the operational amplifier AR6 is connected with the lower limit value of the preset optical signal frequency, the output end of the operational amplifier AR6 is connected with the pin 1 of the AND gate chip U3, and the pin 3 of the AND gate chip U3 outputs a signal to the optical switch.

When the optical switch is used specifically, the optical switch is automatically switched to a standby channel when a main channel is abnormal, so that the communication quality of an optical fiber is ensured, the working state of the optical switch is triggered and controlled by an optical signal average power calculation circuit, an optical signal frequency-voltage conversion circuit and an optical switch starting circuit, the optical signal average power calculation circuit adopts a PD probe to detect the optical power transmitted by the optical fiber, the waveform of an optical power signal is firstly amplified by a gain amplifier, the amplified signal enters an average value circuit to calculate the average value of the optical power, then the average value of the waveform of the optical power signal for a period of time is calculated, the optical switch starting circuit is favorable for avoiding the false operation of the optical switch caused by instantaneous and accidental abnormality, the difference value between the preset lower limit value of the optical power and the average value of the optical power output by the optical signal average power calculation circuit is calculated by adopting a triode Q2 and a triode Q3, An inverse time limit comparison circuit composed of a resistor R17, a resistor R18, an electrolytic capacitor E4 and a voltage regulator tube Z2 compares and judges inverse time limit with a lower limit value of optical power according to the severity of optical power attenuation, outputs low level when the optical power is normal, otherwise outputs high level to a pin 1 of an AND gate chip U3, an optical signal frequency and voltage conversion circuit converts an optical signal transmitted by an optical fiber into an electric signal by using a photoelectric detector GD1, the electric signal is converted into an electric pulse signal by using a photoelectric coupler U1, the electric pulse signal is amplified by a triode Q1 and then converted into a direct current voltage linear with the electric pulse signal by using a chip U2 of an LTC1013, an operational amplifier AR5, a resistor R6, a resistor R7, a capacitor C2-capacitor C4, a capacitor C7 and a voltage regulator tube Z1, the direct current voltage is sent to an optical switch starting circuit, and a direct current voltage calculation circuit for calculating the preset lower limit value of the optical signal frequency and the optical signal voltage by using a triode Q4 and a triode Q5 The difference of the voltage and the difference signal enter an inverse time limit comparison circuit consisting of an operational amplifier AR6, a resistor R8, a resistor R9, an electrolytic capacitor E5 and a voltage stabilizing tube Z3, inverse time limit is compared and judged with the lower limit value of the optical frequency signal according to the severity of slow optical frequency, the setting of the inverse time limit can quickly provide a basis for judging abnormity of the main channel, when the abnormity is normal, namely higher than the lower limit value of the optical frequency signal, low level is output, otherwise, high level is output, the high level is output to a pin 2 of an AND gate chip U3, the AND gate chip U3 outputs logic level 1 when the high level is both, then light is triggered to turn on to switch the main channel to a standby channel, and the accuracy of judging whether the working state of the main channel is normal or.

Claims

1. A kind of optical fiber communication network protective circuit, main channel, spare channel, photoswitch, the said photoswitch switches to the spare channel automatically when the main channel is unusual, guarantee the optical fiber communication quality, characterized by that, the working condition of the said photoswitch is triggered and controlled by mean power calculation circuit of the optical signal, optical signal frequency voltage conversion circuit, photoswitch starting circuit;

2. The optical fiber communication network protection circuit of claim 1, wherein the optical signal average power calculation circuit comprises a PD probe, a cathode of the PD probe is connected to an inverting input terminal of an operational amplifier AR1, a collector and a base of a transistor Q1, and one end of a capacitor C5, an anode of the PD probe and a non-inverting input terminal of an operational amplifier AR1 are connected to ground, an output terminal of an operational amplifier AR1 is connected to an emitter of a transistor Q1, the other terminal of a capacitor C5, one terminal of a grounding capacitor C6, and an anode of an electrolytic capacitor E2, a cathode of an electrolytic capacitor E2 is connected to one terminal of a resistor R10 and one terminal of a resistor R11, the other terminal of the resistor R11 is connected to an inverting input terminal of an operational amplifier AR2, one terminal of a resistor R13, and a cathode of a diode D3, a non-inverting input terminal of an operational amplifier AR2 is connected to ground through a resistor R12, an output terminal of an operational amplifier AR2 is connected, The negative electrode of the diode D4, the positive electrode of the diode D4 are connected to the other end of the resistor R13 and one end of the resistor R14, the other end of the resistor R14 is connected to the inverting input terminal of the operational amplifier AR3, the other end of the resistor R10, one end of the resistor R16 and the positive electrode of the electrolytic capacitor E3, the non-inverting input terminal of the operational amplifier AR3 is connected to the ground through the resistor R15, the output terminal of the operational amplifier AR3 is connected to the other end of the resistor R16 and the negative electrode of the electrolytic capacitor E3, and the output terminal of the operational amplifier AR3 is an output signal of the optical signal average power calculation circuit.

3. The protection circuit of claim 1, wherein the optical signal frequency-to-voltage conversion circuit comprises a photo-detector GD1, a collector of the photo-detector GD1 and one end of a resistor R1 are connected to +5V, an emitter of the photo-detector GD1 is connected to one end of a ground resistor R2 and a cathode of an electrolytic capacitor E1, respectively, an anode of the electrolytic capacitor E1 is connected to an anode of the electrolytic capacitor E1, the other end of the resistor R1 and one end of a resistor R3, the other end of the resistor R3 is connected to an anode of a diode D1, a cathode of a diode D2, a pin 1 of a photocoupler U1 and one end of a ground capacitor C1, a cathode of a diode D1 is connected to +5V, an anode of a diode D2 is connected to ground, a pin 2 and a pin 3 of the photocoupler U1 are connected to ground, a pin 4 of the photocoupler U1 is connected to one end of a resistor R4 and a base of a triode Q1, the emitter of the triode Q1 is connected with the ground, the collector of the triode Q1 is respectively connected with one end of a resistor R5 and one end of a capacitor C2, the other end of the resistor R5 is connected with +5V of a power supply, the other end of the capacitor C2 is connected with a pin 16 of a chip U2, a pin 12 of the chip U2 is connected with the ground through a capacitor C3, a pin 13 of the chip U2 is respectively connected with one end of a capacitor C7, the anode of a voltage regulator tube Z1 and one end of a resistor R6, the other end of the resistor R6 is connected with +5V of the power supply and the other end of the capacitor, the negative electrode of the voltage regulator tube Z1 is connected to the ground, the pin 14 of the chip U2 is respectively connected with one end of a resistor R7, one end of a capacitor C4 and the inverting input end of an operational amplifier AR5, the other end of a resistor R7 is respectively connected with the other end of a capacitor C4 and the output end of an operational amplifier AR5, the output end of the operational amplifier AR5 is an output signal of the optical signal frequency-voltage conversion circuit, and the non-inverting input end of the operational amplifier AR5 is connected to the ground.

4. The optical fiber communication network protection circuit as claimed in claim 1, wherein the optical switch start circuit comprises a transistor Q2, a transistor Q4, a base of the transistor Q2 is connected with the output terminal of the operational amplifier AR3, a collector of the transistor Q2 is connected with the base of the transistor Q3, an emitter of the transistor Q2 and a collector of the transistor Q3 are connected with +10V, an emitter of the transistor Q3 is respectively connected with one end of a resistor R17 and a cathode of a regulator Z2, the other end of the resistor R17 is respectively connected with an anode of a regulator Z2 and one end of a resistor R18, the other end of the resistor R18 is respectively connected with an anode of an electrolytic capacitor E4 and an inverting input terminal of an operational amplifier AR4, a cathode of the electrolytic capacitor E4 is connected with ground, a non-inverting input terminal of the operational amplifier AR4 is connected with a preset optical power lower limit value, an output terminal of the operational amplifier AR4 is connected with a pin 1 of an AND gate chip U3, a base of the transistor Q, the collector of the triode Q4 is connected with the base of the triode Q5, the emitter of the triode Q4 and the collector of the triode Q5 are connected with +10V, the emitter of the triode Q5 is respectively connected with one end of the resistor R8 and the cathode of the voltage regulator tube Z3, the other end of the resistor R8 is respectively connected with the anode of the voltage regulator tube Z3 and one end of the resistor R9, the other end of the resistor R9 is respectively connected with the anode of the electrolytic capacitor E5 and the inverting input end of the operational amplifier AR6, the cathode of the electrolytic capacitor E5 is connected with the ground, the non-inverting input end of the operational amplifier AR6 is connected with the lower limit value of the preset optical signal frequency, the output end of the operational amplifier AR6 is connected with the pin 1 of the AND gate chip U3, and the pin 3.