JP2008003008A - Optical pulse tester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pulse tester capable of measuring optical fiber to be measured, even when receiving light for optical communication and pulsing light, in a superimposed state. <P>SOLUTION: This tester is acquired, by improving an optical pulse tester wherein the pulsing light is emitted into the optical fiber to be measured for transmitting the light for optical communication, and the optical fiber to be measured is measured by a signal processing part, based on return light of the emitted pulsing light. This device is characterized by having a light-receiving part for receiving the light for optical communication and the return light, and an offset adjusting part for canceling the influencing portion of the light for optical communication received by the light-receiving part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention provides an optical pulse test in which pulse light is emitted to an optical fiber to be measured through which light for optical communication is transmitted, and a signal processing unit measures the optical fiber to be measured based on the return light of the emitted pulsed light More particularly, the present invention relates to an optical pulse tester capable of measuring an optical fiber to be measured even if light for optical communication and pulsed light are superimposed and received.

  In an optical communication system that performs data communication using an optical signal, it is important to monitor an optical fiber that transmits the optical signal. An optical pulse tester (hereinafter abbreviated as OTDR (Optical Time Domain Reflectometer)) is used for laying and maintaining optical fibers. The OTDR repeatedly inputs pulsed light from the measurement connector to the optical fiber to be measured, and measures the level of the reflected light and backscattered light from the optical fiber to be measured and the light reception time, thereby disconnecting the optical fiber to be measured. Measure loss and other conditions.

  FIG. 3 is a diagram showing a configuration of a conventional OTDR (see, for example, Patent Document 1). In FIG. 3, a measured optical fiber F1 is an optical fiber to be measured. The OTDR 100 has an input / output end measurement connector CN connected to the optical fiber F1 to be measured. The OTDR 100 emits pulsed light from the measurement connector CN to the optical fiber F1 to be measured, and the return light (reflected light or Backscattered light) is incident via the measurement connector CN.

  The OTDR 100 includes a light emitting unit 10, an optical coupler 20, a band pass filter (hereinafter abbreviated as BPF (Band Pass Filter)) 30, a light receiving unit 40, a signal processing unit 50, and a display unit 60. The light emitting unit 10 outputs pulsed light. The optical coupler 20 outputs the pulsed light from the light emitting unit 10 to the bandpass filter 30 and outputs the return light from the measured optical fiber F1 to the light receiving unit 40. The BPF 30 is provided between the optical coupler 20 and the measurement connector CN, and transmits only light in a predetermined wavelength band (including the wavelength of the pulsed light output from the light emitting unit 10). The light receiving unit 40 receives light from the optical coupler 20. The signal processing unit 50 controls the output timing of the pulsed light from the light emitting unit 10, and an electric signal is input from the light receiving unit 40. The display unit 60 displays the processing result of the signal processing unit 50.

The operation of such an apparatus will be described.
The light emitting unit 10 outputs pulsed light at a predetermined timing in accordance with an instruction from the signal processing unit 50. Then, the pulsed light output from the light emitting unit 10 enters the measured optical fiber F1 through the optical coupler 20, the BPF 30, and the measurement connector CN. Rayleigh scattering occurs inside the optical fiber F1 to be measured, and a part thereof travels in the direction opposite to the traveling direction of the pulsed light and returns to the OTDR 100 as backscattered light. Further, the Fresnel reflected light generated at the connection point of the measured optical fiber F1 also returns to the OTDR 100.

  Then, the return light from the measured optical fiber F1 enters the light receiving unit 40 through the measurement connectors CN, BPF 30, and the optical coupler 20. Further, the light receiving unit 40 converts the incident light into an electrical signal corresponding to the optical power of the incident light, and outputs it to the signal processing unit 50.

  Then, the signal processing unit 50 measures the distance of the optical fiber F1 to be measured and the optical signal level of the return light from the time from when the pulse light is emitted until it enters the light receiving unit 40, and the measurement result is plotted on the horizontal axis. The distance and the vertical axis are displayed on the display unit 60 as the optical signal level of the return light.

  Further, since the signal level of the return light is very weak, the pulse light is repeatedly output to the optical fiber F1 to be measured, and the noise is reduced by averaging a plurality of measurement values.

  Next, FIG. 4 is a diagram illustrating a configuration of the light receiving unit 40. In FIG. 4, the light receiving unit 40 includes an avalanche photodiode (hereinafter abbreviated as APD (Avalanche Photo Diode)) 41, a bias circuit 42, a DA converter circuit 43, a resistor 44, an IV converter circuit 45, an amplifier circuit 46, and an AD converter circuit 47. Have

  The APD 41 receives light from the optical coupler 20. The bias circuit 42 applies a bias voltage to the APD 41. The DA conversion circuit 43 and the resistor 44 are offset circuits, and apply a predetermined offset voltage to the output of the APD 41. The IV conversion circuit 45 receives the photocurrent of the APD 41 and the voltage of the offset circuit. The amplifier circuit 46 includes a plurality of amplifiers, and amplifies the voltage from the IV conversion circuit 45. The AD conversion circuit 47 converts the analog signal (voltage electrical signal) from the amplification circuit 46 into a digital signal and outputs the digital signal to the signal processing unit 50. Note that the magnitude of the applied voltage output from the bias circuit 42 is variable, and the multiplication factor M of the APD 41 also varies depending on the applied voltage. The multiplication degree M can be changed within a predetermined step width within a range of M = 1 to 20 (M = 1 is the smallest multiplication degree), for example. Each of the IV conversion circuit 45 and the amplification circuit 46 has a variable gain, and a plurality of ranges can be set.

Next, an operation in which the light receiving unit 40 outputs digital data obtained by converting the return light to the signal processing unit 50 will be described.
The signal processing unit 50 outputs pulsed light with a predetermined pulse intensity and pulse width based on a range in the vertical axis (optical signal level) direction to be measured, a distance range in the horizontal axis direction, and the like. In addition, the signal processing unit 50 sets the IV conversion circuit 45 and the amplification circuit 46 so as to obtain a predetermined gain for each range, and outputs a predetermined bias voltage for each range to the bias circuit 42. Let That is, the gains of the circuits 45 and 46 are fixed depending on the range, and the bias voltage of the bias circuit 42 is also fixed.

  The APD 41 converts the received return light into a photocurrent. However, the APD 41 converts the return light into a photocurrent at a multiplication factor M determined by the bias voltage from the bias circuit 42 and outputs the photocurrent to the IV conversion circuit 45. The IV conversion circuit 45 converts the photocurrent of the APD 41 into a voltage, adds the voltage from the offset circuit to the converted voltage, and outputs the voltage to the amplification circuit 46. Further, the amplifier circuit 46 amplifies the voltage with a predetermined gain and outputs it to the AD conversion circuit 47. Then, the AD conversion circuit 47 converts the analog signal into a digital signal and outputs it to the signal processing unit 50.

  An operation for canceling the offset generated in the light receiving unit 41 shown in FIG. 4 will be described. Here, FIG. 5 is a flowchart showing an operation of removing the offset. The offset is due to the dark current of the APD 41. In addition, the measurement error due to the offset may be due to noise in the IV conversion circuit 45 and the amplification circuit 46, but is usually mainly influenced by the dark current of the APD 41.

  The signal processing unit 50 stops the emission of the pulsed light from the light emitting unit 10 (S10). When the signal processing unit 50 confirms the value of the digital data from the AD conversion circuit 47 of the light receiving unit 40 and is within the specified range, the offset due to the dark current of the APD 41 has an influence on the measurement. Assuming that there is little, pulse light is output to the light emitting section 10, and measurement of the optical fiber F1 to be measured is started (S11, S12).

  On the other hand, if the value of the digital data of the light receiving unit 40 is not within the specified range, the signal processing unit 50 performs offset adjustment by changing the output voltage of the DA conversion circuit 43 (S11, S13). If the set value for the DA converter circuit 43 has reached full scale, an offset error is displayed on the display unit 60 (S14, S15). If the full scale is not reached, the signal processing unit 50 again determines the digital data of the AD conversion circuit 47 (S14, S11 to S13).

JP 2001-099750 A

  In the measurement by the OTDR 100 shown in FIG. 3, the light for optical communication used in the optical communication system is stopped, and external light other than the pulse light of the light emitting unit 10 from the OTDR 100 (for example, optical communication) is placed in the measured optical fiber F1. Measurement was performed in the absence of optical communication light used in the system. Note that external light other than the pulsed light from the light emitting unit 10 in the optical fiber F1 to be measured is referred to as communication light.

  On the other hand, in recent years, in order to improve work efficiency, measurement in the presence of communication light is required. Therefore, as a measurement method in the presence of communication light, the wavelength of the pulsed light of the light emitting unit 10 is shifted from the wavelength of the light for optical communication so that the light for optical communication does not enter the OTDR 100. A BPF 30 is provided. The wavelengths of light for optical communication are typically 1.31 [μm] band and 1.55 [μm] band, and the wavelength of pulse light for measurement of OTDR 100 is, for example, 1. 65 [μm].

  However, when the wavelength of the optical communication light and the pulse light of the OTDR 100 are shifted, if the optical communication system is provided with a wavelength filter or the like that allows only the wavelength of the optical communication light to pass, There is a problem that the optical fiber F1 to be measured cannot be measured. In addition, there is a problem that the BPF 30 also increases the cost of the measurement system including the OTDR 100.

  In addition, when measurement is performed using pulsed light having the same wavelength as the light for optical communication in the optical communication system, there is a problem that the measurement waveform measured by the OTDR 100 is disturbed by the light for optical communication. That is, although the light for optical communication is modulated and the optical power fluctuates, the modulation speed is significantly higher than the response speed of the APD 41 of the light receiving unit 40. Accordingly, the light for optical communication is received as CW light by the light receiving unit 40, and the offset light is added to the return light. Further, the offset due to light for optical communication is larger by one digit or more than the offset due to the dark current of the APD 41, and offset adjustment is difficult. And many users of OTDR100 have construction workers and the like, and they do not always have the skill to judge the disturbance of the measurement waveform due to the influence of light for optical communication, and accurately measure / monitor the measured optical fiber F1. There was a problem that it was difficult to do.

  Therefore, an object of the present invention is to measure an optical fiber to be measured even if light for optical communication and pulsed light are superimposed and received, and particularly for pulsed light having the same wavelength as light for optical communication. Thus, an object of the present invention is to realize an optical pulse tester capable of measuring an optical fiber to be measured even when measuring the optical fiber to be measured.

The invention described in claim 1
In an optical pulse tester that emits pulsed light to a measured optical fiber to which light for optical communication is transmitted, and the signal processing unit measures the measured optical fiber based on the return light of the emitted pulsed light,
A light receiving unit for receiving the light for optical communication and the return light;
An offset adjustment unit for canceling the influence of the light for optical communication received by the light receiving unit is provided.
The invention according to claim 2 is the invention according to claim 1,
The optical communication light and the pulsed light have the same wavelength.
The invention according to claim 3 is the invention according to claim 1 or 2,
Among the light from the optical fiber to be measured, there is provided a band-pass filter for outputting the light for optical communication transmitted through the optical fiber to be measured and the return light to the light receiving unit. is there.
The invention according to claim 4 is the invention according to any one of claims 1 to 3,
The light receiver
An avalanche photodiode for receiving the return light;
A bias circuit for adjusting a multiplication factor by applying a bias voltage to the avalanche photodiode;
A DA converter that can output a variable voltage;
An IV conversion circuit having a variable gain, performing IV conversion on the output of the avalanche photodiode, and adding the voltage of the DA conversion circuit to the output of the avalanche photodiode;
An amplifying circuit having a variable gain and amplifying a voltage from the IV conversion circuit;
An AD conversion circuit that AD-converts the output of the amplifier circuit and outputs the converted signal to the signal processing unit and the offset adjustment unit is provided.
The invention according to claim 5 is the invention according to claim 4,
The offset adjuster
Bias control means for controlling the bias voltage of the bias circuit;
DA control means for controlling the output voltage of the DA converter circuit;
IV control means for controlling the gain of the IV conversion circuit;
The bias control means, the DA control means, and the IV control means determine reference means for canceling the influence by referring to the digital data from the AD conversion circuit.
The invention according to claim 6 is the invention according to claim 5,
The determining means is characterized by determining the presence or absence of light for optical communication based on a multiplication factor by the bias control means, an output voltage by the DA control means, and a gain by the IV control means.

  According to the present invention, the offset adjustment unit cancels the influence of the light for optical communication in the optical fiber to be measured, so that the light to be measured can be received even if the light for optical communication and the pulse light are superimposed and received. Fiber measurements can be made. Thereby, working efficiency can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. Here, the same components as those in FIGS. 3 and 4 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 1, an offset adjustment unit 70 is provided in the OTDR 100. The offset adjustment unit 70 includes a bias control unit 71, a DA control unit 72, an IV control unit 73, an amplifier circuit control unit 74, and a determination unit 75, and is connected to the signal processing unit 50 to perform AD conversion of the light receiving unit 40. An electric signal of a digital signal is input from the circuit 47.

  Further, the light emitting unit 10 outputs light having the same wavelength as the light for optical communication transmitted through the optical fiber F1 to be measured as pulsed light. In reality, the wavelength of light for optical communication varies slightly. Therefore, it is rare that the wavelength of the light for optical communication and the wavelength of the pulsed light of the light emitting unit 10 completely match. In addition, since the wavelength of light for optical communication should actually exist within the wavelength range defined by the communication standard, the same wavelength as the light for optical communication means within that range. It is.

  A BPF 31 is provided instead of the BPF 30. The BPF 31 selects only light in a predetermined wavelength band and outputs it to the light receiving unit 40. Specifically, light for optical communication and pulsed light (return light) are transmitted.

  The bias control means 71 controls the magnitude of the bias voltage output from the bias circuit 42 and controls the multiplication factor M of the APD 41. The DA control unit 72 controls the voltage level output from the DA conversion circuit 43. The IV control unit 73 controls the gain of the IV conversion circuit 45. The amplifier circuit control means 74 controls the gain of the amplifier circuit 46. The determination unit 75 receives the digital data from the AD conversion circuit 47. The determination unit 75 controls the control units 71 to 74 in the offset adjustment unit 70 as a whole.

The operation of such an apparatus will be described.
A vertical axis and a horizontal axis range are set in the signal processing unit 50 from a setting unit (not shown). In accordance with the range setting from this setting section (not shown), the signal processing section 50 controls the bias control means 71 of the offset adjustment section 70 for the multiplication factor M, the DA control means 72 for the DA value, the IV control means 73, and the amplifier circuit control. The gain factor is output to the means 74. Then, the bias control means 71 causes the bias circuit 42 to output the applied voltage having the designated multiplication factor M, and the DA control means 72 causes the DA conversion circuit 43 to output the voltage having the designated DA value. The IV control means 73 adjusts the IV conversion circuit 43 so that the instructed gain is obtained, and the amplifier circuit control means 74 adjusts each amplifier of the amplifier circuit 46 so that the instructed gain is obtained.

  Then, the signal processing unit 50 causes the offset adjustment unit 70 to cancel the offset amount superimposed on the output of the AD conversion circuit 47 (what is generated in the light receiving unit 40 or communication light).

  Here, FIG. 2 is a flowchart for explaining the operation for canceling the offset included in the output of the AD conversion circuit 47.

  The signal processing unit 50 stops the output of the pulsed light from the light emitting unit 10. As a result, the electrical signal input to the AD conversion circuit 47 of the light receiving unit 40 is offset by the dark current of the APD 41 and the communication light. Further, the offset is smaller than the dark current of the APD 41, but includes the offset by the amplifier of the IV conversion circuit 45 and the amplifier circuit 46 (S20).

  Then, the signal processing unit 50 instructs the determination unit 75 of the offset adjustment unit 70 to cancel the offset. In response to this instruction, the determination unit 75 sets the gain of the amplifier circuit 46 to the minimum via the amplifier circuit control unit 74 (S21).

  Then, the determination unit 75 refers to the digital data from the AD conversion circuit 47 and determines whether the offset is within a predetermined range within a specified range, that is, in a state where no pulsed light exists. If it is within the specified range, the determination unit 75 returns the gain of the amplifier circuit 46 to the original value via the amplifier circuit control unit 74 and notifies the signal processing unit 50 that the offset adjustment is completed (S22, S22). S23). And the signal processing part 50 starts the measurement of the to-be-measured optical fiber F1 similarly to the apparatus shown in FIG. 3 (S24).

  On the other hand, if the digital data is not within the specified range, the determination means 75 changes the DA value of the DA conversion circuit 43 via the DA control means 72 and performs offset adjustment (S22, S25).

  If the DA value set to the DA conversion circuit 43 is not full scale, the determination means 75 again determines the value of the digital data from the AD conversion circuit 47 (S26, S22).

  In the case of full scale, the offset adjustment by the output voltage of the DA conversion circuit 43 cannot be performed any more, so the determination unit 75 confirms the multiplication factor M of the APD 41 by the bias control unit 71. When the multiplication factor M is not the minimum multiplication factor M = 1, the determination unit 75 causes the bias control unit 71 to lower the multiplication factor M of the APD 41 by one range. In accordance with this instruction, the bias control means 71 decreases the applied voltage output from the bias circuit 42 and decreases the multiplication degree M of the APD 41 by one range. Further, the determination means 75 determines again the value of the digital data from the AD conversion circuit 47 (S27, S28, S22).

  Further, when the multiplication factor M = 1, the offset adjustment by reducing the dark current of the APD 41 cannot be performed any more, so the determination unit 75 confirms the gain of the IV conversion circuit 45 by the IV control unit 73. If the gain of the IV conversion circuit 45 is not the minimum, the determination unit 75 causes the IV control unit 73 to decrease the gain of the IV conversion circuit 45 by one range. In accordance with this instruction, the IV control means 73 reduces the gain of the IV conversion circuit 45. Further, the determination means 75 determines the value of the digital data from the AD conversion circuit 47 again (S29, S30, S22).

  Further, when the gain of the IV conversion circuit 45 is minimum, the offset adjustment cannot be performed any more by the gain of the IV conversion 45, so the determination unit 75 notifies the signal processing unit 50 that the offset adjustment has failed. Then, the signal processing unit 50 displays an offset error on the display unit 60 (S29, S31).

  The operation of measuring the measured optical fiber F1 after adjusting the offset (S22, S23) (the signal processing unit 50 causes the light emitting unit 10 to output pulsed light to the measured optical fiber F1. And the measured light The light receiving unit 40 receives the return light and the communication light from the fiber F1 and outputs the digital data to the signal processing unit 50. Further, the signal processing unit 50 emits pulse light and then enters the light receiving unit 40. 3), the distance of the optical fiber F1 to be measured and the optical signal level of the return light are measured, and the measurement result is displayed on the display unit 60 with the horizontal axis as the distance and the vertical axis as the optical signal level of the return light. Since this is the same as the apparatus shown in FIG.

  As described above, the offset adjustment unit 70 cancels the offset due to the communication light. Therefore, even if the light for optical communication and the pulse light are superimposed and received, that is, the light for optical communication included in the communication light. Even when the optical fiber under measurement is measured with pulsed light having the same wavelength as that of the optical fiber under measurement, the optical fiber under measurement can be measured. Thereby, working efficiency can be improved.

  That is, in the apparatus shown in FIG. 3, the applied voltage of the bias circuit 42, the gain of the IV conversion circuit 45, and the gain of the amplifier circuit 46 are fixed values based on the pulse width and light intensity of the pulsed light. Only the DA conversion circuit 43 that cancels the offset due to the dark current of the APD 41 is variable. For this reason, if pulse light having the same wavelength as the light for optical communication is used, it is difficult to cancel the offset amount of communication light, and it is difficult to measure the optical fiber F1 to be measured. However, since the determination unit 75 refers to the digital data from the AD conversion circuit 47 and causes the bias control unit 71, the DA control unit 72, and the IV control unit 73 to cancel the influence, the offset due to the communication light is canceled. Can do. Thereby, even when the measurement optical fiber is measured with pulsed light having the same wavelength as the light for optical communication, the measurement optical fiber can be measured. Therefore, the user of OTDR 100 can perform measurement without being aware of the presence or absence of communication light, and does not affect the skill of the user.

  In addition, since the wavelength of the LD of the light emitting unit 10 is set to the same wavelength as the light for optical communication (1.55 [μm] band or 1.31 [μm] band), a general LD for optical communication is sufficient. The cost of the light emitting unit 10 can be reduced. And BPF31 can also be made into the general thing for optical communications, and can suppress cost.

The present invention is not limited to this, and may be as shown below.
In the apparatus shown in FIG. 1, in step S21, after the gain of the amplifier circuit 46 is changed to the minimum, the DA value of the DA converter circuit 43, the multiplication factor M of the APD 41, and the gain of the IV converter circuit 45 are adjusted. Although shown, the offset amount may be adjusted without changing the gain range of the amplifier circuit 46. That is, steps S21 and S23 may be omitted.

  Further, when the offset value cannot be canceled only by the DA value of the DA conversion circuit 43 and the multiplication degree M of the APD 41 and the gain of the IV conversion circuit 45 are adjusted, the determination means 75 determines that communication light is included in the offset amount. Then, the signal processing unit 50 may be notified that communication light exists. Then, the signal processing unit 50 may display the measurement result on the display unit 60 and display a message in which communication light is superimposed on the return light.

  Also, the configuration in which the BPF 31 selects the light for optical communication and the return light of the pulsed light transmitted through the optical fiber to be measured from the light from the optical fiber to be measured F1 is output to the light receiving unit. The BPF 31 may not be provided. Thereby, the cost of the measurement system including the OTDR 100 can be suppressed, and the OTDR 100 can be downsized.

  Moreover, although the structure which makes the wavelength of pulsed light the same wavelength as the light for optical communication was shown, as long as it is in the transmission wavelength of BPF31 (of course, the light for optical communication is permeate | transmitted), what kind of wavelength may be sufficient . Further, when the BPF 31 is not provided, the wavelength of the pulsed light only needs to be within the wavelength range that the APD 41 can receive.

  A directional coupler or the like may be used instead of the optical coupler 20. In short, the pulse light from the light emitting unit 10 is output only to the measured optical fiber F1, and the return light from the measured optical fiber F1. May be output only to the light receiving unit 40.

It is the block diagram which showed one Example of this invention. It is the flowchart explaining the operation | movement which cancels the part for offset in the apparatus shown in FIG. It is the figure which showed the structure of the conventional OTDR which measures the to-be-measured optical fiber F1. FIG. 4 is a diagram showing a configuration of a light receiving unit 40. 6 is a flowchart illustrating an operation for canceling an offset amount in the apparatus illustrated in FIG. 5.

Explanation of symbols

40 Light Receiving Unit 41 Avalanche Photodiode 42 Bias Circuit 43 DA Conversion Circuit 45 IV Conversion Circuit 46 Amplification Circuit 47 AD Conversion Circuit 50 Signal Processing Unit 70 Offset Adjustment Unit 71 Bias Control Unit 72 DA Control Unit 73 IV Control Unit 75 Determination Unit 100 OTDR
F1 Optical fiber to be measured

Claims (6)

In an optical pulse tester that emits pulsed light to a measured optical fiber to which light for optical communication is transmitted, and the signal processing unit measures the measured optical fiber based on the return light of the emitted pulsed light,
A light receiving unit for receiving the light for optical communication and the return light;
An optical pulse tester comprising: an offset adjustment unit that cancels an influence of the light for optical communication received by the light receiving unit.   2. The optical pulse tester according to claim 1, wherein the wavelengths of the light for optical communication and the pulsed light are the same.   A band-pass filter is provided for outputting light for optical communication transmitted through the optical fiber under measurement and return light to the light receiving unit among the light from the optical fiber under measurement. 3. The optical pulse tester according to 1 or 2. The light receiver
An avalanche photodiode that receives light;
A bias circuit for adjusting a multiplication factor by applying a bias voltage to the avalanche photodiode;
A DA converter that can output a variable voltage;
An IV conversion circuit having a variable gain, performing IV conversion on the output of the avalanche photodiode, and adding the voltage of the DA conversion circuit to the output of the avalanche photodiode;
An amplifying circuit having a variable gain and amplifying a voltage from the IV conversion circuit;
The optical pulse tester according to any one of claims 1 to 3, further comprising: an AD conversion circuit that AD-converts an output of the amplifier circuit and outputs the converted signal to the signal processing unit and the offset adjustment unit. The offset adjuster
Bias control means for controlling the bias voltage of the bias circuit;
DA control means for controlling the output voltage of the DA converter circuit;
IV control means for controlling the gain of the IV conversion circuit;
5. The optical pulse according to claim 4, further comprising: a determination unit that refers to digital data from the AD conversion circuit and causes the bias control unit, the DA control unit, and the IV control unit to cancel the influence. Tester. 6. The light according to claim 5, wherein the determination means determines the presence or absence of light for optical communication based on a multiplication factor by the bias control means, an output voltage by the DA control means, and a gain by the IV control means. Pulse tester.

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