JP2020036149A - Light receiving element protection device, light receiving element protection program, and light receiving device - Google Patents

Abstract

To prevent a light receiving element (avalanche photodiode) from being destroyed by inputting light with high light intensity to the light receiving element having high light receiving sensitivity.SOLUTION: A light receiving element protection device that protects a light receiving element includes a monitoring light receiving element, an optical path switching unit that switches to one of an optical path of an input signal light into a first optical path where the signal light travels to the light receiving element or a second optical path where the signal light travels to the monitoring light receiving element, a monitoring unit that amplifies and outputs an output signal from the monitoring light receiving element, a switching control unit that performs switching control of the optical path to the optical path switching unit by outputting a signal from the monitoring unit, and a voltage control unit that controls a voltage value applied to the light receiving element according to an output value of the output signal from the monitoring unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light receiving element protection device, a light receiving element protection program, and an optical receiving device, and can be applied to, for example, an optical receiving device mounted on an optical line terminal in an optical communication network.

  For example, in a PON (Passive Optical Network) system, an optical component called a BOSA (Bi-directional Optical Sub Assembly) is generally used.

  BOSA is a device in which a transmitting-side element using a laser diode (LD) is joined to a receiving-side element using a photodiode (see FIG. 4).

  For example, the GE-PON system is a system in which an OLT (Optical Line Terminal) is deployed on the base station side of a communication carrier, and an ONU (Optical Network Unit) is mainly deployed to general subscribers.

  It is stipulated that a signal light in the 1490 nm band is output for the light wavelength in the downstream direction from the OLT side, and a signal light in the 1310 nm band is output for the light wavelength in the upstream direction from the ONU side.

  On the ONU side, a photodiode capable of receiving an optical signal of 1490 nm from the OLT or an avalanche photodiode which is a high-sensitivity element is used. A photodiode is used as an element on the receiving side, but an avalanche photodiode (APD) having higher light receiving sensitivity is also used.

  The avalanche photodiode generates a photocurrent with a high doubling rate when a reverse voltage is applied. Since the avalanche photodiode has a higher current amplification factor than the photodiode, the amplitude of a minute signal value can be increased. By using such an avalanche photodiode having high light-receiving sensitivity, the distance of the optical fiber can be increased.

  However, it is generally known that when high-intensity light is input to an avalanche photodiode having high light-receiving sensitivity, an excessive current is generated and an expensive avalanche photodiode is destroyed.

  For example, in Patent Document 1, in order to protect the avalanche photodiode from destruction, the protection circuit detects the application of a high voltage to the avalanche photodiode, and the bias control circuit does not apply an excessive high voltage to the avalanche photodiode. Is described.

JP-A-11-275755

  However, the conventional technology controls so that a high voltage value is not excessively applied to the avalanche photodiode, and protects the avalanche photodiode from destruction when high-intensity light enters the avalanche photodiode. It does not do.

  Therefore, a light-receiving element protection device, a light-receiving element protection program, and a light-receiving element that can prevent the light-receiving element from being destroyed by inputting high-intensity light to a light-receiving element (avalanche photodiode) with high light-receiving sensitivity. There is a need for a receiving device.

  In order to solve this problem, a light-receiving element protection device according to a first aspect of the present invention is a light-receiving element protection device for protecting a light-receiving element, comprising: (1) a monitoring light-receiving element; An optical path switching unit that switches between a first optical path in which the signal light travels to the light receiving element and a second optical path in which the signal light travels to the monitoring light receiving element; and (3) an output signal from the monitoring light receiving element. A monitoring unit that amplifies and outputs the signal, (4) a switching control unit that controls the optical path switching unit based on the output of the signal from the monitoring unit, and (5) an output value of an output signal from the monitoring unit. And a voltage control unit that controls a voltage value applied to the light receiving element according to

  A light-receiving element protection program according to a second aspect of the present invention includes a monitoring light-receiving element, a first light path through which the signal light travels to the light-receiving element, and a second light path through which the signal light travels to the monitoring light-receiving element. A light path switching unit for switching to one of an optical path and a light receiving element protection program for protecting the light receiving element, the computer comprising: (1) a monitoring unit that amplifies and outputs an output signal from the monitoring light receiving element; 2) a switching control unit that controls the optical path switching unit based on the output of a signal from the monitoring unit; and (3) a voltage value applied to the light receiving element according to the output value of the output signal from the monitoring unit. Characterized by functioning as a voltage control unit for controlling the voltage.

  According to a third aspect of the present invention, there is provided an optical receiving apparatus having a light receiving element for receiving input signal light, the light receiving apparatus including the light receiving element protecting device according to the first present invention.

  ADVANTAGE OF THE INVENTION According to this invention, it can avoid that a light receiving element is destroyed by inputting the light with high light intensity to the light receiving element (avalanche photodiode) with a high light receiving sensitivity.

FIG. 2 is an internal configuration diagram illustrating an internal configuration of an optical transceiver mounted on the ONU according to the embodiment. FIG. 1 is an overall configuration diagram illustrating an overall configuration of an optical communication system according to an embodiment. 6 is a flowchart illustrating an operation of a light receiving element protection process according to the embodiment. FIG. 8 is an internal configuration diagram showing an internal configuration of an optical transmission / reception device mounted on a conventional ONU.

(A) Main Embodiment Hereinafter, embodiments of a light-receiving element protection device, a light-receiving element protection program, and an optical receiving device according to the present invention will be described in detail with reference to the drawings.

  This embodiment exemplifies a case in which the present invention is applied to an optical transmission / reception device mounted on an optical line terminal constituting an optical communication system.

(A-1) Configuration of Embodiment [Optical Communication System (Optical Access System)]
FIG. 2 is an overall configuration diagram illustrating the overall configuration of the optical communication system according to this embodiment.

  In FIG. 2, an optical communication system 5 according to this embodiment includes an optical line terminal (hereinafter, referred to as “OLT”) 1 and a plurality of optical line terminals (hereinafter, referred to as “ONUs”). .) 2 (2-1 to 2-n; n is a positive integer) and an optical splitter 3.

  For example, a case where the optical communication system 5 is a Gigabit Ethernet (registered trademark) PON (GE-PON) is illustrated.

  The optical communication system 5 is not particularly limited as long as it is a PON system. The optical communication system 5 is based on a technology conforming to ITU-T recommendations such as a TWDM-PON system conforming to ITU-T recommendations or an IEEE standard such as IEEE802.3ah. Technology can also be applied.

  The optical splitter 3 distributes and aggregates the signal light between each of the ONUs 2-1 to 2-n and the OLT 1. That is, the optical splitter 3 distributes downstream signal light (hereinafter, also referred to as “downstream signal light”) transmitted from the OLT 1 to each of the ONUs 2-1 to 2-n and each of the ONUs 2-1 to 2-n. And transmits the upstream signal light (hereinafter, also referred to as “uplink signal light”) to the OLT 1.

  The OLT 1 is an optical line terminal on the office side. The OLT 1 converts the upstream signal light received from each of the ONUs 2-1 to 2-n into an electric signal and relays the signal to an upper network (not shown). Further, the OLT 1 converts a downstream electric signal received from the upper network into a signal light, and relays the signal to each of the ONUs 2-1 to 2-n as a downstream signal light.

  Each of the ONUs 2-1 to 2-n is a subscriber-side optical line terminal. Each of the OLTs 2-1 to 2-n converts a downstream signal light received from the OLT 1 into an electric signal, and relays the electric signal to a lower network (not shown). Further, each of the ONUs 2-1 to 2-n converts an upstream electric signal received from the lower network into a signal light, and relays the converted signal to the OLT 1 as an upstream signal light.

  In the optical communication system 5, the OLT 1 and each of the ONUs 2-1 to 2-n share the single optical fiber 4 between the OLT 1 and the optical splitter 3 between the plurality of ONUs 2-1 to 2-n. This is economically advantageous as compared with the case where the optical fiber 4 is laid between them. The optical communication system 5 enables a maximum of 32 branches, and one OLT 1 can accommodate 32 ONUs 2. Note that the number of branches is not limited to this.

  In the optical communication system 5, time-division communication (TDM communication) is performed between the OLT 1 and each of the ONUs 2-1 to 2-n, but generally, between the optical splitter 3 and each of the ONUs 2-1 to 2-n. Are different, the distance between the OLT 1 and each of the ONUs 2-1 to 2-n is different.

  For example, each of the ONUs 2-1 to 2-n transmits a signal light using a wavelength of 1310 nm, but the light intensity (power level) of the upstream signal light from each of the ONUs 2-1 to 2-n is different. For this reason, since the upstream signal light without collision is received, the receiving side of the optical transmission and reception device of the OLT 1 instantaneously follows each power level and performs communication in order.

  On the other hand, the transmitting side of the optical transmitting and receiving apparatus of the OLT 1 outputs a signal light using a predetermined working wavelength to a high output (high transmission) so that the downstream signal light can reach each of the ONUs 2-1 to 2-n stably. Output value). Specifically, for example, the transmission side of the optical transmission and reception device of the OLT 1 has an LD (Laser Diode) as a light emitting element, and the LD continuously transmits signal light at a high output using a wavelength of 1490 nm. I have to.

  When viewed from each of the ONUs 2-1 to 2-n, when the distance to the OLT 1 is relatively short, the power level (light intensity) of the downstream signal light becomes a relatively large value, and the distance to the OLT 1 is relatively long ( In the case where the distance is far, the power level of the downstream signal light becomes a relatively small value.

  Then, the ONU 2 existing at a position relatively short from the OLT 1 will receive a signal light having a relatively high power level, and conversely, if the distance from the OLT 1 is long, the ONU 2 will have a relatively low power level. The signal light will be received.

  Therefore, for example, the ONU 2 located at a position close to the OLT 1 may receive a signal light with a high power level. Further, for example, even when the power of the ONU 2 is turned on, a signal light having a high power level may be received by the ONU 2.

  As will be described later, when an avalanche photodiode (APD) 11 is used as a light receiving element of the optical transmission / reception device 10 (see FIG. 1) of the ONU 2, an excessive current flows in the APD 11 that has received the signal light of the high power level. This may cause the APD 11 to be destroyed.

  Therefore, in this embodiment, the optical transmission / reception device 10 of the ONU 2 is provided with a light receiving element protection circuit for protecting the APD 11 from being destroyed due to an overcurrent, thereby preventing the APD 11 from being destroyed.

[Internal Configuration of Optical Transmission / Reception Device of ONU 2]
FIG. 1 is an internal configuration diagram showing an internal configuration of an optical transceiver 10 mounted on the ONU 2 according to this embodiment.

  In FIG. 1, an optical transmission / reception device 10 of the ONU 2 includes an avalanche photodiode (APD) 11, a laser diode (LD) 12, an optical fiber 13, a wavelength filter unit 14, and a light receiving element protection circuit unit 100.

  Further, the light receiving element protection circuit unit 100 includes a movable mirror unit 101, a photodiode (PD) 102, a current monitoring unit 103, a switching control unit 110, and an applied voltage control unit 106. Further, the switching control unit 110 includes a timing detection unit 104 and a delay circuit unit 105.

  The hardware configuration of the light receiving element protection circuit unit 100 includes an optical member, an electronic component, a control device that executes a processing program (for example, a light receiving element protection program), and the like. Further, a light receiving element protection program may be installed.

  The optical transmission / reception device 10 is a communication module that transmits signal light or receives signal light mounted on the ONU 2 in the subscriber's house. As the optical transmitting / receiving device 10, for example, a device in which an optical component on the transmitting side called BOSA and an optical component on the receiving side are joined can be applied.

  Note that the optical transmission / reception device 10 of FIG. 1 illustrates a case having a single-fiber bidirectional function of transmitting and receiving signal light using one optical fiber 13. However, the optical transceiver 10 is not limited to the single-fiber bidirectional function, and may be a module that performs transmission and reception of signal light using separate optical fibers.

  The APD 11 is a light receiving element of the optical component on the receiving side of the optical transmitting and receiving device 10. When a voltage in the opposite direction (reverse voltage) is applied to the APD 11 from the applied voltage control unit 106 and light (signal light) is incident, a photocurrent is generated. A detailed description of the configuration for inputting the signal light to the APD 11 will be given in the description of each component of the light receiving element protection circuit section 100.

  The laser diode 12 is a light emitting element of a transmitting optical member of the optical transmitting and receiving device 10. The upstream signal light emitted by the laser diode 12 passes through the wavelength filter section 14, and an optical signal having a wavelength of 1310 nm enters the optical fiber 13.

  The optical fiber 13 is an end of the optical fiber 4 that is a component of the optical communication system 5. For example, the optical transceiver 10 of the ONU 2 attaches an optical fiber pigtail to the optical fiber 4 in order to connect to the optical fiber 4. In such a case, the optical fiber 4 exposed from the other end of the optical fiber pigtail is shown as an optical fiber 13.

  The wavelength filter unit 14 separates the wavelengths of the upstream optical signal and the downstream optical signal, and may use, for example, a WDM (wavelength division multiplex) filter. For example, the wavelength filter section 14 can be formed by forming a filter film on a glass substrate or the like. The wavelength filter unit 14 is mounted with the reflection surface of the wavelength filter unit 14 inclined at 45 degrees with respect to the optical axis of light emitted from the optical fiber 13.

  When the upstream signal light from the laser diode 12 enters the wavelength filter section 14, the upstream signal light passes through the wavelength filter section 14, and the transmitted upstream signal light (wavelength) enters the optical fiber 13.

  When the downstream signal light from the optical fiber 13 is incident on the wavelength filter unit 14, the reception wavelength of the downstream signal light is incident on the reflection surface of the wavelength filter unit 14 at an incident angle of 45 degrees. Then, light (signal light) is reflected. That is, the light (signal light) reflected on the reflection surface of the wavelength filter unit 14 bends in a direction of 90 degrees downward and perpendicular to the optical axis of the light emitted from the optical fiber 13 and proceeds. Thus, the signal light (reflected light) enters the movable mirror unit 101.

  The movable mirror section 101 optically changes an optical path for reflecting the signal light from the wavelength filter section 14. The movable mirror unit 101 is provided on the optical axis of the downstream signal light reflected by the wavelength filter unit 14.

  A drive signal for changing the optical swing angle of the mirror is supplied to the movable mirror unit 101 from the timing detection unit 104 and the delay circuit unit 105. When a drive signal is given, the optical swing angle of the movable mirror unit 101 changes.

  Specifically, the movable mirror unit 101 includes a first optical path for transmitting the signal light from the wavelength filter unit 14 to the photodiode (PD) 102 and a second optical path for transmitting the signal light from the wavelength filter unit 14 to the APD 11. The movable mirror unit 101 changes the tilt angle so as to switch to the optical path. The reflection angle when the signal light is reflected by the movable mirror unit 101 and proceeds to the first optical path is called a first angle, and the reflection angle when the signal light is reflected by the movable mirror unit 101 and proceeds to the second optical path. Is referred to as a second angle.

  As described above, when the drive signal is given, the optical swing angle of the movable mirror unit 101 changes, and the optical path of the signal light changes, so that the movable mirror unit 101 changes the optical path of the light reflected by the mirror. It can also be said to function as an optical switch (optical path switching unit) for switching.

  As the movable mirror unit 101, for example, a MEMS (Micro Electro Mechanical System) optical mirror can be applied. Although the configuration of the movable mirror unit 101 is not particularly limited, for example, the following configuration can be applied.

  For example, the movable mirror unit 101 supports a mirror on a movable plate at the center, provides a rotation axis (torsion bar) on each of two opposing sides of the four sides of the movable plate, and connects to two rotation axes. It is possible to use a mirror chip provided around the movable plate and having a coil formed thereon and a magnet provided on the periphery of the mirror chip. In the movable mirror unit 101 having such a configuration, when a current flows through the coil of the mirror chip, a Lorentz force is generated by the strength of the current and the magnetic field (according to Fleming's left-hand rule). This Lorentz force acts as a torque for rotating the movable plate supported on the rotating shaft, and the mirror carried on the movable plate tilts. Since the Lorentz force is proportional to the current value, the optical deflection angle of the mirror can be adjusted by adjusting the current value.

  The photodiode (PD) 102 receives the signal light reflected on the movable mirror unit 101 and converts the signal light into an electric signal. The photodiode (PD) 102 is connected to the current monitoring unit 103, and the current output from the photodiode (PD) 102 flows to the current monitoring unit 103.

  The current monitoring unit 103 monitors the current value of the current output from the photodiode (PD) 102, and converts the current (current value) output from the photodiode (PD) 102 into a voltage (voltage value). Then, it outputs to the timing detection unit 104 and the applied voltage control unit 106. For example, the current monitoring unit 103 includes an amplifier circuit such as a resistor and an operational amplifier, and converts a current from the photodiode (PD) 102 into a voltage by flowing the current to the resistor, and applies a voltage to the amplifier circuit. May be used to obtain an output value.

  The switching control unit 110 controls switching of the optical path of the movable mirror unit 101 based on the output of a signal from the current monitoring unit 103. That is, the switching control unit 110 outputs a drive signal to the movable mirror unit 101 to control the tilt angle of the movable mirror unit 101. The switching control unit 110 has a timing detection unit 104 and a delay circuit unit 105.

  The timing detection unit 104 outputs a drive signal for the movable mirror unit 101 to the delay circuit unit 105 based on the voltage value output from the current monitoring unit 103. That is, the timing detection unit 104 outputs a drive signal using the input voltage value as a trigger. The timing detection unit 104 intermittently (including periodically) outputs a drive signal, so that the angle of the movable mirror unit 101 also intermittently changes.

  The delay circuit section 105 delays the drive signal input from the timing detection section 104 by a predetermined time and outputs the drive signal to the movable mirror section 101.

  Therefore, the optical swing angle of the movable mirror unit 101 changes after a lapse of a predetermined time (after a delay time) after the timing detection unit 104 outputs the drive signal.

  Here, the delay time in the delay circuit unit 105 can be set to a time in consideration of a time in which an applied voltage control unit 106 described later controls a voltage value applied to the APD 11. That is, the delay time can be set to the same time as the control time of the applied voltage control unit 106, and for example, the delay time can be set to about 1 msec. Therefore, the applied voltage control unit 106 sets the voltage value within the time (that is, within the delay time) until the reflection angle of the signal light reflected by the movable mirror unit 101 changes from the first angle to the second angle. To apply a voltage value to the APD 11.

  The applied voltage control unit 106 sets a voltage value to be applied to the APD 11 according to the voltage value output from the current monitoring unit 103, and applies the voltage of the voltage value to the APD 11.

  The applied voltage control unit 106 adjusts the voltage value applied to the APD 1 by using the doubling rate-reverse voltage characteristic of the APD 11. Thereby, the doubling rate (amplification rate) of the APD 11 is controlled according to the output value based on the light intensity of the signal light received by the photodiode (PD) 102, and the light receiving sensitivity of the APD 11 is increased or decreased. be able to.

  Further, after the doubling rate (amplification rate) of the APD 11 is controlled, the optical swing angle of the movable mirror unit 101 changes, the reflection angle becomes the second angle, and the signal light enters the APD 11, so that the APD 1 becomes excessively large. Destruction by electric current can be prevented.

(A-2) Operation of the Embodiment FIG. 3 is a flowchart showing the operation of the light receiving element protection processing according to this embodiment.

  The OLT 1 transmits a downstream signal light using a wavelength of 1490 nm to each ONU 2. The downstream signal light from the OLT 1 passes through the optical fiber 4, and the downstream signal light reaches the optical transmitting / receiving device 10 composed of BOSA.

  In the optical transmitting and receiving apparatus 10, when the downstream signal light from the optical fiber enters the reflection surface of the wavelength filter section 14, the signal light is reflected at a reflection angle of 45 degrees, and the signal light enters the movable mirror section 101 (S101).

  At this time, in the light receiving element protection circuit section 100, the reflection angle of the signal light reflected on the movable mirror section 101 is set to the first angle (S102).

  Therefore, the signal light reflected by the movable mirror unit 101 travels along the first optical path, and the signal light enters the photodiode (PD) 102. When the signal light is incident on the photodiode (PD) 102, the signal light is photoelectrically converted to generate a current (photocurrent) (S103). Then, the current from the photodiode (PD) 102 is input to the current monitoring unit 103. Here, the signal light incident on the photodiode (PD) 102 is not branched. In other words, the signal light that has not been attenuated directly enters the photodiode (PD) 102, and the current flowing from the photodiode (PD) 102 corresponds to the light intensity of the signal light.

  In the current monitoring unit 103, the input current is converted into a voltage, and the voltage value of the voltage (ie, an analog value) is output to the timing detection unit 104 and the applied voltage control unit 106 (S104).

  In the timing detection unit 104, a drive signal is output to the delay circuit unit 105 using the output value (voltage value) from the current monitoring unit 103 as a trigger (S105). After delaying the drive signal from the timing detection unit 104 by a predetermined time, the delay circuit unit 105 outputs the drive signal to the movable mirror unit 101 (S106).

  When a drive signal is input to the movable mirror unit 101, the optical swing angle of the movable mirror unit 11 changes, and the reflection angle of the signal light reflected on the movable mirror unit 101 changes from the first angle to the second angle ( S107). That is, after the delay time, the reflection angle of the movable mirror unit 101 changes to the second angle.

  On the other hand, in S104, when the output value (voltage value) from the current monitoring unit 103 is output to the applied voltage control unit 106, the applied voltage control unit 106 sets the input voltage value within the delay time of the delay circuit unit 105. The application voltage is set according to, and the voltage of the set voltage value is applied to the APD 11 (S108).

  The applied voltage control unit 106 changes and sets the applied voltage value according to the analog voltage value from the current monitoring unit 103.

  That is, when the current monitor value of the photodiode (PD) 102 is large, the applied voltage control unit 106 sets the applied voltage value low, and controls so that an excessive voltage is not applied to the APD 11.

  Conversely, when the current monitor value of the photodiode (PD) 102 is small, the applied voltage control unit 106 sets the applied voltage value high, increases the doubling rate of the APD 11, and increases the generated current.

  In the APD 11, after the doubling rate is controlled by the voltage value (reverse voltage value) applied from the applied voltage control unit 106 (that is, after the delay time), the reflection angle of the movable mirror unit 101 changes to the second angle. The signal light that has traveled along the second optical path enters the APD 11.

  In the APD 11 in which the doubling rate is controlled, signal light is input. However, since the doubling rate is controlled, destruction due to an excessive current can be prevented.

(A-3) Effects of the Embodiment As described above, according to the embodiment, the movable mirror unit and the photodiode (PD) are provided, and the current value from the photodiode (PD) is used as a monitor value to control the applied voltage control unit. And changing the optical path of the reflected light from the movable mirror section, it is possible to protect the expensive APD from being destroyed due to the incidence of signal light having an excessive power level (light intensity).

(B) Other Embodiments Although various modified embodiments have been described in the above-described embodiments, the present invention can be applied to the following modified embodiments.

  (B-1) In the above-described embodiment, the light receiving element protection circuit for protecting the light receiving element in the optical transmitting and receiving apparatus has been described. However, the light receiving element protection circuit for protecting the light receiving element in the optical receiving apparatus having no optical transmission function. Also applicable to

  (B-2) Since the doubling rate of the light receiving element changes according to the environment such as temperature, the applied voltage control unit 106 may use the doubling rate-reverse voltage characteristic according to the environment such as temperature. That is, the voltage value applied to the APD may be controlled according to the environment in which the ONU is placed.

  (B-3) The configuration of the movable mirror unit described above is an example, and is not limited to the configuration of the movable mirror unit described above. At least, the movable mirror section can be widely applied as long as the entire light of the signal light is incident on the photodiode (PD) 102 and the APD 11 instead of the signal light whose light intensity is attenuated.

  DESCRIPTION OF SYMBOLS 10 ... Optical transmission / reception apparatus, 11 ... Avalanche photodiode (APD), 12 ... Laser diode (LD), 13 ... Optical fiber, 14 ... Wavelength filter part, 100 ... Light receiving element protection circuit part, 101 ... Movable mirror part, 102 ... Photodiode (PD), 103: current monitoring unit, 104: timing detection unit, 105: delay circuit unit, 106: applied voltage control unit, 110: switching control unit

Claims (6)

In the light receiving element protection device for protecting the light receiving element,
A monitoring light-receiving element,
An optical path switching unit that switches the optical path of the input signal light to one of a first optical path in which the signal light advances to the light receiving element and a second optical path in which the signal light advances to the monitoring light receiving element;
A monitoring unit that amplifies and outputs an output signal from the monitoring light receiving element,
A switching control unit that controls switching of an optical path to the optical path switching unit by outputting a signal from the monitoring unit;
A voltage control unit that controls a voltage value applied to the light receiving element according to an output value of an output signal from the monitoring unit. The switching control unit, using a signal output from the monitoring unit as a trigger, outputs a signal related to optical path switching to the optical path switching unit after a predetermined delay time,
The light-receiving element protection device according to claim 1, wherein the voltage control unit sets a voltage value to be applied to the light-receiving element within the delay time in the switching control unit.   The light-receiving element protection device according to claim 1, wherein the optical path switching unit includes a movable mirror member that changes a reflection angle of the input signal light.   The switching control section periodically varies an optical swing angle of the movable mirror member of the optical path switching section to change the reflection angle between a first angle and a second angle. The light-receiving element protection device according to claim 3. A monitoring light-receiving element,
An optical path switching unit that switches an optical path of the input signal light to one of a first optical path in which the signal light travels to the light receiving element and a second optical path in which the signal light travels to the monitoring light receiving element. In the light receiving element protection program for protecting the light receiving element,
Computer
A monitoring unit that amplifies and outputs an output signal from the monitoring light receiving element,
A switching control unit that controls switching of an optical path to the optical path switching unit by outputting a signal from the monitoring unit;
A light-receiving element protection program that functions as a voltage control section that controls a voltage value applied to the light-receiving element according to an output value of an output signal from the monitoring section. In an optical receiver having a light receiving element for receiving input signal light,
An optical receiver comprising the light-receiving element protection device according to claim 1.

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