JP2009253830A - Reception light power monitoring device, and reception light power monitoring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reception light power monitoring device that attain reduction of an error contained in a reception light power monitor output obtained from a photodetector. <P>SOLUTION: The invention relates to a reception light power monitoring device for monitoring reception light power in a light receiving section in an optical communication system, including: a voltage detecting means for detecting an inverse bias voltage to be applied to a photodetector, constituting a photodetecting section, with respect to light power input to the light receiving section; a photo current detecting means for detecting a photo current flowing to the photodetector with respect to the light power input to the light receiving section; an arithmetic means for predetermining a parameter specifying a linear expression of the inverse bias voltage so that a ratio of the light input power and the photo current becomes the linear expression of the inverse bias voltage in adjustment; and a storage means for storing the parameter determined by the arithmetic means, wherein, in reception light power monitoring, the arithmetic means fetches detection outputs of the voltage detecting means and the photo current detecting means and calculates reception light power by using the parameter stored in the storage means on the basis of the detection outputs. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present embodiment relates to a received optical power monitoring function in an optical receiving apparatus of each station such as an optical communication system, and more particularly to a received optical power monitoring apparatus and a received optical power monitoring method suitable for use in a WDM optical communication system.

In an optical communication system such as a WDM (Wavelength Division Multiplexing) system, a receiving device is required to have a monitoring function such as an optical reception power monitor for device monitoring.
FIG. 9 shows the configuration of a WDM optical communication system. In the figure, a WDM optical communication system includes a multiplexer 500, a transmitter 501, an optical multiplexer 510, an optical fiber transmission line 520, an optical demultiplexer 530, a receiver 540, and a demultiplexer. And a conversion device 550.

The transmission apparatus 501 includes a transmission code processing unit 502, a drive circuit 503 that drives a laser diode (LD), a laser diode (LD) 504, and an output level control unit that controls the output of the laser diode (LD) 504 to be constant. 505.
The receiving device 540 includes a light receiving element 541, an equalizing amplifier 542, an AGC circuit 543, an identification reproducing unit 544, a received code processing unit 545, a received power monitor circuit 546, and a timing extracting circuit 547. is doing.
Multiplexers 500, transmitters 501, receivers 540, and demultiplexers 550 are provided as many as the number of wavelengths of optical signals used in the WDM system.

In the above configuration, the signal from the signal source is converted into a multiplexed digital signal by the multiplexer 500, and the synchronization information and control information are added to the input data from the transmission code processing unit 502, and the encoding process is performed. .
The output of the transmission signal processing unit 502 is photoelectrically converted by the drive circuit 503, the laser diode (LD) 504, and the output level control unit 505, and is output to the optical multiplexer 510.

In the optical multiplexer 510, optical signals having different wavelengths λ 1, λ 2,..., Λn output from the plurality of transmission devices 501 are multiplexed and input to the optical demultiplexer 530 via the optical fiber transmission line 520. The
The optical demultiplexer 530 demultiplexes the plurality of optical signals multiplexed by the optical multiplexer 510 for each wavelength and outputs the demultiplexed signals to each receiving device 540.
In the receiving device 540, an optical signal is received by the light receiving element 541 and an output signal obtained by photoelectric conversion is output to the equalizing amplifier 542, the AGC circuit 543, and the reception power monitor circuit 546.

The output signal of the light receiving element 541 is equalized and amplified by the equalizing amplifier 542 whose gain is controlled by the AGC circuit 543, and is output to the identification reproduction unit 544 and the timing extraction circuit 547.
In the timing extraction circuit 547, a clock indicating the timing for identifying the logic “1” (mark) and the logic “0” (space) is extracted, and the timing extraction circuit 547 outputs the clock to the identification reproduction unit 544.

  The discriminating / reproducing unit 544 discriminates the logic “1” (mark) and the logic “0” (space) and outputs the discriminating logic to the reception code processing unit 545. In the reception code processing unit 545, the reverse process of the transmission code processing unit 502 is performed, and the original signal is acquired by the demultiplexing device 550.

In the communication system configured as described above, the receiving device 540 monitors the input optical power received by the received power monitor circuit 546, and outputs a voltage signal corresponding to the received light power as a monitor signal to the receiving device body.
As described above, the optical communication system generally has a function of monitoring the input power of the optical signal received on the receiving device side (see, for example, Patent Document 1).

In general, a photodiode such as a PIN diode or an avalanche photodiode (APD) is used as a light receiving element that receives an optical signal in a receiving device of an optical communication system.
The PIN diode has a PIN structure in which an intrinsic semiconductor region (i layer) is provided between an n-type semiconductor region and a p-type semiconductor region in order to increase the width of the depletion layer and increase quantum efficiency and response speed. Yes.

In the PIN diode, a photocurrent Ipd proportional to the optical input Pin flows. Therefore, the monitor output Vmon for the optical input Pin is
The monitor output Vmon can be obtained by adjusting the value of the proportional coefficient K as Vmon = K · Ipd (K is a proportional coefficient).

On the other hand, there is an avalanche photodiode (APD) as a photodiode for high sensitivity. This photodiode is used in an optical communication system that performs long-distance transmission.
The avalanche photodiode (APD) has a function of obtaining a large photocurrent when a traveling carrier collides with another electron and is excited from a valence band to a conduction band to increase the number of carriers. That is, a photocurrent Iapd obtained by multiplying a photocurrent proportional to the optical input Pin M times by the reverse bias voltage Vr of the avalanche photodiode flows through the avalanche photodiode (APD).

Therefore, the monitor output Vmon for the optical input Pin is obtained by monitoring the photocurrent Iapd and the reverse bias voltage Vr applied to the avalanche photodiode (APD) and calculating in consideration of the multiplication factor.
Therefore, the monitor output Vmon for the optical input Pin is
Vmon = F (Iapd, Vr) (1)
Can be written.

Thus, the monitor output Vmon of the received light power of the avalanche photodiode (APD) is a function of the photocurrent Iapd of the avalanche photodiode and the reverse bias voltage Vr applied to the avalanche photodiode.
JP 2004-120669 A

  FIG. 10 schematically shows a schematic configuration of the reception power monitor circuit 546 in FIG. In the figure, a reception power monitor circuit 546 detects a high voltage circuit 600 that applies a reverse bias voltage Vr to an avalanche photodiode (APD) 541 as a light receiving element, a current limiting resistor R10, and a reverse bias voltage Vr. It has voltage dividing resistors R12 and R13, a photocurrent detector 601 that detects a photocurrent, and a reverse bias voltage detector 602.

In the above configuration, an optical signal having a wavelength λ and a power Pin is converted into a valanche as a light receiving element in a state where a reverse bias voltage Vr is applied to the avalanche photodiode (APD) 541 from the high voltage circuit 600 via the resistors R10 and R11. When input to the photodiode (APD) 541, a photocurrent Iapd corresponding to the power Pin and the reverse bias voltage Vr flows through the avalanche photodiode (APD) 541. This photocurrent Iapd is detected as a voltage signal by the photocurrent detector 601.
The reverse bias voltage Vr is detected by the reverse bias voltage detector 602 as a voltage signal divided by the voltage dividing resistors R12 and R13.

  FIG. 11 shows the light receiving sensitivity characteristic with respect to the reverse bias voltage Vr of the avalanche photodiode (APD) 541 in the reception power monitor circuit 546 configured as described above. As shown in the figure, in the avalanche photodiode (APD) 541, the carrier image magnification increases in proportion to the applied reverse bias voltage Vr (V), and the value of the photocurrent Iapd increases.

For this reason, it can be seen that the light receiving sensitivity (mA / mW) changes nonlinearly according to the reverse bias voltage Vr (V). In FIG. 11, at the point P1 where the light receiving sensitivity on the light receiving sensitivity characteristic curve S is 1 (= 10 ⁰ ), the photocurrent Iapd of 1 mA flows when the input light power Pin is 1 mW, and at the point P2 where the light receiving sensitivity is 3. A 3 mA photocurrent Iapd flows with an input optical power Pin of 1 mW, and a photocurrent Iapd of 10 mA flows with an input optical power Pin of 1 mW at a point P3 where the light receiving sensitivity becomes 10 (= 10 ¹ ).

FIG. 12 shows the characteristics of the photocurrent Iapd, the reverse bias voltage Vr, and the received optical power monitor output Vmon with respect to the input optical power Pin of the avalanche photodiode (APD) 541.
As shown in FIG. 12 (a), if the photocurrent Iapd is linearly related to the input optical power Pin as shown by the straight line Q0, the received optical power monitor output Vmon is input as shown in FIG. 12 (d). It is proportional to the optical power Pin.

  However, actually, since the photocurrent Iapd changes with respect to the input optical power Pin as indicated by the curve Q1, the received optical power monitor output Vmon has a non-linear relationship with respect to the input optical power Pin. There is a problem that an error occurs in the received light power monitor output Vmon from the avalanche photodiode (APD) as an element.

  The present invention has been made in view of such circumstances, and provides a received light power monitor device and a received light power monitor method that reduce errors included in a received light power monitor output obtained from a light receiving element. For the purpose.

  In order to achieve the above object, a received optical power monitor apparatus according to the present invention is a received optical power monitor apparatus that monitors received light power in an optical receiving section in an optical communication system, and is an optical power input to the optical receiving section. Voltage detecting means for detecting a reverse bias voltage applied to a light receiving element constituting the light receiving section with respect to the light, and a photocurrent detecting means for detecting a photocurrent flowing in the light receiving element with respect to the optical power input to the optical receiving section; Calculating means for predetermining a parameter defining the primary expression so that a ratio of the optical input power and the photocurrent becomes a primary expression of the reverse bias voltage at the time of adjustment; and Storage means for storing parameters, and the calculation means obtains the detection outputs of the voltage detection means and the photocurrent detection means when monitoring the received optical power. Inclusive, and calculates the received optical power by using the parameters stored in the storage means based on the detected output.

In the received optical power monitoring apparatus of the present invention having the above-described configuration, a reverse bias voltage applied to the optical power input to the optical receiving unit is detected by the voltage detecting unit, and the photocurrent detecting unit detects the reverse bias voltage applied to the optical receiving unit. A photocurrent flowing in the light receiving element with respect to the input optical power is detected.
Further, at the time of adjustment, the computing means predetermines a parameter that defines the primary expression so that the ratio of the optical input power to the photocurrent becomes a primary expression of the reverse bias voltage, and the storage means determines the parameter. The parameters are stored.

At the time of monitoring the received light power, the calculation means takes in the detection outputs of the voltage detection means and the photocurrent detection means, and receives the received light using the parameters stored in the storage means based on these detection outputs. Calculate power.
As a result, the optical power input to the optical receiver and the monitor output of the received optical power with respect to the optical power input to the optical receiver have a linear relationship, and the error in the monitor output of the detected received optical power is reduced. Is done.

In the received light power monitoring apparatus of the present invention, the calculating means applies the optical power input to the receiving unit to Pin, the photocurrent flowing through the light receiving element to Iapd ′, and the light receiving element during adjustment. A linear expression in which the reverse bias voltage is Vr, the offset considering the error of the obtained photocurrent Iapd 'is C (T), and the ratio between the optical input power Pin and the photocurrent Iapd' is the reverse bias voltage Vr as a variable. Where the coefficient of the reverse bias voltage Vr is A (T), the constant term is B (T) (where T indicates temperature, and A (T), B (T), and C (T) indicate temperature As a function)
The following formula (2)
Pin / (Iapd′−C (T)) = A (T) · Vr + B (T) (2)
Parameters A (T), B (T), C (T) are calculated from the parameters, and the obtained parameters A (T), B (T), C (T) are stored in the storage means.

In the received light power monitoring apparatus of the present invention having the above-described configuration, the calculation means includes a photocurrent Iapd ′ flowing through the light receiving element with respect to the optical power Pin input to the receiving unit, and a reverse bias voltage applied to the light receiving element. Vr is acquired, offset C (T) is added to the acquired photocurrent Iapd ′, and in the above equation (2), the offset C (T) is determined so that the right side is closest to the primary equation.
Next, the coefficient A (T) and the constant term B (T) are calculated and obtained by a linear regression method.
The parameters A (T), B (T), and C (T) obtained in this way are stored in the storage means and provided for arithmetic processing during reception monitoring.

  By determining the parameter parameters A (T), B (T), and C (T) in this way, the ratio of the optical input power input to the light receiving element and the photocurrent of the light receiving element is the reverse bias voltage. This is a linear expression, and the optical power input to the optical receiver and the monitor output of the received optical power with respect to the optical power input to the optical receiver have a linear relationship, reducing the error in the monitor output of the detected received optical power. Is done.

Further, in the received light power monitoring apparatus of the present invention, the calculating means is a signal indicating a photocurrent Iapd ′ flowing through the light receiving element and a signal indicating a reverse bias voltage Vr applied to the light receiving element when the received light power is monitored. And using the parameters A (T), B (T), C (T) stored in the storage means, the following equation (3)
Vmon = (A (T) .Vr + B (T)). (Iapd'-C (T)) (3)
The reception power monitor output Vmon is obtained from the above.

In the received light power monitoring apparatus of the present invention having the above-described configuration, the calculation means indicates a signal indicating the photocurrent Iapd flowing through the light receiving element and a reverse bias voltage Vr applied to the light receiving element when the received light power is monitored. Using the parameters A (T), B (T), and C (T) stored in the storage means, the received power monitor output Vmon is calculated from the above equation (3) and output. .
As a result, a ratio between the optical input power input to the light receiving element and the photocurrent of the light receiving element is calculated as a primary expression of the reverse bias voltage. As a result, the optical power input to the optical receiving unit and the optical receiving unit are calculated. The monitor output of the received optical power has a linear relationship with the optical power input to, and the error in the monitor output of the detected received optical power is reduced.

Further, in the received light power monitoring device of the present invention, the calculation means includes:
At the time of adjustment, an optical signal having the shortest wavelength and an optical signal having the longest wavelength used for communication are input to the light receiving element, and averages of the parameters A (T), B (T), and C (T) respectively obtained Parameters A (T), B (T), B (T), which are used when calculating the received power monitor output Vmon using the average values of the calculated parameters A (T), B (T), C (T) C (T) is stored in the storage means.

  In the received light power monitoring apparatus of the present invention having the above-described configuration, the calculation means inputs the shortest wavelength optical signal and the longest wavelength optical signal used for communication to the optical receiving unit during adjustment, and adjusts each wavelength. For the optical signal, the parameters A (T), B (T), and C (T) are calculated, and the average values of the parameters A (T), B (T), and C (T) that are output are received power monitor output The parameters A (T), B (T), and C (T) used when calculating Vmon are stored in the storage means.

  A light receiving element such as an avalanche photodiode (APD) or a PIN photodiode has a wavelength dependency with respect to the received optical signal, and therefore an error occurs in the received optical power monitor output Vmon depending on the wavelength of the received optical signal. By using the parameters A (T)), B (T), and C (T) stored in the storage means when calculating the received power monitor output Pin ′, a plurality of all different wavelengths used for communication are used. With respect to the optical signal, the error can be reduced within a range determined by the target specification.

  Further, the received optical power monitoring method of the present invention is a received optical power monitor method for monitoring received optical power in an optical receiving unit in an optical communication system, wherein the light receiving unit for optical power input to the optical receiving unit is provided. A first step of detecting a reverse bias voltage applied to the light receiving element constituting by the voltage detecting means, and a current detecting means for detecting a photocurrent flowing in the light receiving element with respect to the optical power input to the optical receiver. And a third step of pre-determining a parameter defining the primary expression by a calculation means so that a ratio of the optical input power to the photocurrent becomes a primary expression of the reverse bias voltage at the time of adjustment. A fourth step of storing the parameter determined by the calculating means in the storage means, and the calculating means at the time of monitoring the received light power. A fifth step of fetching detection outputs of the recording voltage detection means and the photocurrent detection means and calculating received optical power using the parameters stored in the storage means based on the detection outputs; It is characterized by that.

In the received light power monitoring method configured as described above, in the first step, the reverse bias voltage applied to the light receiving element constituting the light receiving unit with respect to the optical power input to the optical receiving unit is detected by the voltage detecting means. Then, in a second step, the photocurrent flowing in the light receiving element with respect to the optical power input to the optical receiving unit is detected by a current detecting means.
At the time of adjustment, in a third step, a parameter that defines the primary expression is determined in advance by a calculation means so that the ratio of the optical input power to the photocurrent becomes a linear expression of the reverse bias voltage, In this step, the parameter determined by the calculation means is stored in the storage means.

At the time of monitoring the received light power, in the fifth step, the calculation means fetches the detection outputs of the voltage detection means and the photocurrent detection means, and stores them in the storage means based on these detection outputs. The received optical power is calculated using the parameters.
As a result, the optical power input to the optical receiver and the monitor output of the received optical power with respect to the optical power input to the optical receiver have a linear relationship, and the error in the monitor output of the detected received optical power is reduced. Is done.

In the third step, the received light power monitoring method of the present invention includes:
At the time of adjustment, the optical power input to the receiving unit is Pin, the photocurrent flowing through the light receiving element is Iapd ′, the reverse bias voltage applied to the light receiving element is Vr, and the error of the acquired photocurrent Iapd ′ is considered. The coefficient of the reverse bias voltage Vr when the offset is C (T) and the ratio between the optical input power Pin and the photocurrent Iapd ′ is expressed by a linear expression using the reverse bias voltage Vr as a variable is A (T), The constant term is B (T) (where T represents temperature, and A (T), B (T), and C (T) are functions of temperature).
Pin / (Iapd′−C (T)) = A (T) · Vr + B (T) (4)
Parameter A (T), B (T), C (T) from
In the fourth step, the obtained parameters A (T), B (T), and C (T) are stored in the storage means.

In the received light power monitoring method having the above-described configuration, in the third step, the calculating means includes a photocurrent Iapd ′ that flows through the light receiving element with respect to the optical power Pin input to the receiving unit during adjustment, and the light receiving element. The applied reverse bias voltage Vr is acquired, the offset C (T) is added to the acquired photocurrent Iapd ′, and the offset C (T) is set so that the right side is closest to the primary expression in the above equation (4). To decide.
Next, the coefficient A (T) and the constant term B (T) are calculated and obtained by a linear regression method.
The parameters A (T), B (T), and C (T) obtained in this way are stored in the storage means and provided for arithmetic processing during reception monitoring.

  By determining the parameter parameters A (T), B (T), and C (T) in this way, the ratio of the optical input power input to the light receiving element and the photocurrent of the light receiving element is the reverse bias voltage. This is a linear expression, and the optical power input to the optical receiver and the monitor output of the received optical power with respect to the optical power input to the optical receiver have a linear relationship, reducing the error in the monitor output of the detected received optical power. Is done.

In the received light power monitoring method of the present invention, in the fifth step, at the time of received light power monitoring, a signal indicating a photocurrent Iapd flowing through the light receiving element by the calculating means and a reverse bias applied to the light receiving element. A signal indicating the voltage Vr is taken in, and using the parameters A (T), B (T), C (T) stored in the storage means, the following equation (5)
Vmon = (A (T) .Vr + B (T)). (Iapd'-C (T)) (5)
The reception power monitor output Vmon is obtained from the above.

  In the received light power monitoring method having the above-described configuration, in the fifth step, a signal indicating the photocurrent Iapd flowing through the light receiving element and a reverse bias applied to the light receiving element are calculated by the calculation means during the received light power monitoring. A signal indicating the voltage Vr is taken in, and the received power monitor output Vmon is calculated from the above equation (5) using the parameters A (T), B (T) and C (T) stored in the storage means. And output.

  As a result, a ratio between the optical input power input to the light receiving element and the photocurrent of the light receiving element is calculated as a primary expression of the reverse bias voltage. As a result, the optical power input to the optical receiving unit and the optical receiving unit are calculated. The monitor output of the received optical power has a linear relationship with the optical power input to, and the error in the monitor output of the detected received optical power is reduced.

  In the received light power monitoring method of the present invention, in the third step, at the time of adjustment, an optical signal having the shortest wavelength and an optical signal having the longest wavelength that are used for communication are input to the light receiving element by the calculating means. Then, average values of the parameters A (T), B (T), and C (T) obtained are calculated, and in the fourth step, the calculated parameters A (T), B (T), and C are calculated. The average value of (T) is stored in the storage means as parameters A (T), B (T), and C (T) used when calculating the received power monitor output Vmon.

  In the received light power monitoring method configured as described above, in the third step, at the time of adjustment, an optical signal having the shortest wavelength and an optical signal having the longest wavelength used for communication are input to the optical receiving unit by the calculating means. For the optical signals of each wavelength, the parameters A (T), B (T), and C (T) are calculated, and the average values of the calculated parameters A (T), B (T), and C (T) are calculated. The received power monitor output Vmon is stored in the storage means as parameters A (T), B (T), and C (T) used when calculating the received power monitor output Vmon.

  A light receiving element such as an avalanche photodiode (APD) or a PIN photodiode has a wavelength dependency with respect to the received optical signal, and therefore an error occurs in the received optical power monitor output Vmon depending on the wavelength of the received optical signal. By using the parameters A (T), B (T), and C (T) stored in the storage means when calculating the received power monitor output Vmon, a plurality of light of all different wavelengths used for communication. The error of the signal can be reduced within a range determined by the target specification.

    As described above, according to the present invention, at the time of adjustment, the primary expression is defined so that the ratio between the optical input power and the photocurrent flowing through the light receiving element is the primary expression of the reverse bias voltage of the light receiving element. Parameters to be determined are stored in advance, and the determined parameters are stored by a storage unit, and at the time of received light power monitoring, detection outputs of the voltage detection unit and the photocurrent detection unit are captured, and based on these detection outputs Since the received optical power is calculated using the parameter stored in the storage means, the optical power input to the optical receiver and the received light with respect to the optical power input to the optical receiver The power monitor output has a linear relationship, and the error in the monitor output of the detected received light power is reduced.

  Further, according to the present invention, the optical signal having the shortest wavelength and the optical signal having the longest wavelength used for communication are input to the optical receiver, and the parameter A (T), B (T) and C (T) are calculated, and the average value of the output parameters A (T), B (T) and C (T) is used to calculate the parameter A ( Since T), B (T), and C (T) are stored in the storage unit, the parameters A (T) and B (T) stored in the storage unit when calculating the reception power monitor output Vmon are calculated. ), By using C (T), the error can be reduced within the range determined by the target specification for the shortest wavelength optical signal and the longest wavelength optical signal used for communication.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a received light power monitoring apparatus according to an embodiment of the present invention. In the figure, a received light power monitoring apparatus 1 according to an embodiment of the present invention includes a high voltage generation circuit 10, a light receiving element 12, a photocurrent detection unit 14, a reverse bias voltage detection unit 16, and an arithmetic processing circuit 20. And have.

The high voltage circuit 10 applies a reverse bias voltage Vr to the light receiving element 12 via the current limiting resistor R1 and the photocurrent detector 14.
In the present embodiment, the light receiving element 12 is an avalanche photodiode (APD).
The reverse bias voltage detector 16 detects the bias voltage Vr applied to the light receiving element 12 as a voltage signal divided by the voltage dividing resistors R2 and R3.

The photocurrent detector 14 outputs the photocurrent Iapd flowing through the light receiving element 12 as a voltage signal.
The arithmetic processing circuit 20 includes a photocurrent / reverse bias voltage acquisition unit 200, a parameter calculation unit 202, a storage unit 204, and a reception power calculation unit 206.

The photocurrent / reverse bias voltage acquisition unit 200 takes in detection outputs of the reverse bias voltage detection unit 16 and the photocurrent detection unit 14, A / D converts these detection outputs, converts them into digital signals, and has a predetermined format. The data is stored in the storage unit 204.
The parameter calculation unit 202 has a function of calculating parameters A (T), B (T), and C (T) necessary for calculation processing described later.

In addition to the parameters A (T), B (T), and C (T) calculated at the time of adjustment, the storage unit 204 stores various types of data necessary for arithmetic processing.
The reception power calculation unit 206 calculates the reception optical power using the parameters A (T), B (T), and C (T) based on a predetermined arithmetic expression, and receives the reception optical power monitor output Vmon. As an output function.

Prior to describing the operation of the received light power monitoring device having the above-described configuration, the optical power input to the light receiving element 12 is Pin, the photocurrent flowing through the light receiving element 12 (photocurrent when the offset current is ignored) is Iapd, Consider a relational expression among the optical power Pin, the photocurrent Iapd, and the reverse bias voltage Vr when the reverse bias voltage applied to the light receiving element 12 is Vr. Here, α (A / W) is the conversion efficiency (ratio of the number of electrons generated by absorption of received light) at the multiplication factor 1 in the avalanche photodiode (APD) as the light receiving element 12, and the breakdown of the avalanche photodiode If the voltage is Vb,
In general, the following equation holds.

Iapd / αPin = 1 / (1- (Vr / Vb) ⁿ ) (6)
In the above equation (6), when n = 1,
Pin / Iapd = (1 / α) · (1− (Vr / Vb)) (7)
It becomes.
Also, the above equation (7) is
Pin / Iapd = (− 1 / αVb) · Vr + 1 / α (8)
And can be transformed.

In the above equation (8), if (−1 / αVb) is A and 1 / α is B,
Pin / Iapd = AVr + B (9)
It becomes.
Here, A and B are parameters obtained by actual measurement during module adjustment of the received light power monitoring device. Since the conversion efficiency α of the avalanche photodiode and the breakdown voltage Vb are temperature dependent, they are functions of the temperature T. There are A (T) and B (T).

Further, since the photocurrent Iapd ′ of the avalanche photodiode acquired at the time of module adjustment includes an offset current (error) flowing into the avalanche photodiode on the circuit, this is expressed as C (T) and the expression (9) When Iapd in is Iapd′-C (T), the formula (9) is
Pin / (Iapd′−C (T)) = A (T) · Vr + B (T) (10)
It becomes.

Next, the operation at the time of adjustment of the received light power monitoring apparatus according to the embodiment of the present invention shown in FIG. 1 will be described with reference to FIGS. FIG. 2 is a flowchart showing a processing procedure at the time of adjustment, and FIG. 3 shows calculation processing contents at the time of adjustment of the parameter calculation unit 202.
In these figures, first, the reverse bias voltage Vr applied to the light receiving element 12 by the high voltage generation circuit 10 for the optical input power Pin of the light receiving element 12 is detected by the reverse bias voltage detecting unit 14 via the voltage dividing resistors R4 and R5. It is detected (step 301).

The photocurrent Iapd ′ (including the offset current) flowing in the light receiving element 12 with respect to the optical input power Pin of the light receiving element 12 is detected by the photocurrent detection unit 16 via the shunt resistor R3 (step 302).
The photocurrent / reverse bias voltage acquisition unit 200 takes in the reverse bias voltage Vr and the photocurrent Iapd ′, which are detection outputs of the bias voltage detection unit 14 and the photocurrent detection unit 16, and performs A / D conversion on these detection outputs. Then, it is converted into a digital signal, converted into data of a predetermined format, and stored in the storage unit 204 as a table having the contents shown in FIG. 4 (step 303).

Next, the parameter calculation unit 202 calculates the photocurrent (Iapd′−C (T)) taking into account the offset current that actually flows through the light receiving element 12 by the adder 310 (304).
Further, the parameter calculation unit 202 calculates the reciprocal of the photocurrent (Iapd′−C (T)) by the inverse calculator 311 (step 305).
Further, the parameter calculation unit 202 multiplies the inverse of the photocurrent (Iapd′−C (T)) obtained in step 305 by the multiplier 312 by the optical input power Pin, and the ratio Pin between the optical input power Pin and the photocurrent. / (Iapd'-C (T)) is calculated (step 306).

  Next, the parameter calculation unit 202 takes the reverse bias voltage Vr on the horizontal axis and the ratio Pin / (Iapd′−C (T)) between the optical input power Pin and the photocurrent on the vertical axis, and uses the optical input power Pin. The parameter C (T) is determined so that the ratio Pin / (Iapd'-C (T)) between the current and the photocurrent is in a linear relationship with the reverse bias voltage Vr, and the determined parameter C (T) is The data is stored in the storage unit 204 (step 307).

Furthermore, the parameter calculation unit 202 uses a linear regression method,
Pin / (Iapd′−C (T)) = A (T) · Vr + B (T) (10)
The parameters A (T) and B (T) are calculated, and the calculated parameters A (T) and B (T) are stored in the storage unit 204 (step 308).
In this way, the parameters A (T), B (T), and C (T) are acquired at the time of adjustment, and are prepared for arithmetic processing at the time of reception monitoring. The

  By determining the parameter parameters A (T), B (T), and C (T) in this way, the ratio Pin / (Iapd′− between the optical input power input to the light receiving element and the photocurrent of the light receiving element. C (T)) is a linear expression of the reverse bias voltage Vr, and the optical power input to the optical receiver and the monitor output of the received optical power with respect to the optical power input to the optical receiver have a linear relationship and are detected. It is possible to reduce the error in the monitor output of the received optical power.

Next, the operation at the time of received light power monitoring of the received light power monitoring apparatus according to the embodiment of the present invention shown in FIG. 1 will be described with reference to FIGS. FIG. 5 is a flowchart showing a processing procedure when monitoring the received light power, and FIG. 6 shows the contents of the calculation processing of the parameter calculation unit 202 when monitoring the received light power.
In these drawings, first, the reverse bias voltage Vr applied to the light receiving element 12 by the high voltage generation circuit 10 for the optical input power Pin of the light receiving element 12 is detected by the reverse bias voltage detecting unit 16 via the voltage dividing resistors R2 and R3. It is detected (step 401).

Further, the photocurrent detection unit 14 detects the photocurrent Iapd ′ (including the offset current) flowing in the light receiving element 12 with respect to the optical input power Pin of the light receiving element 12 (step 402).
The photocurrent / reverse bias voltage acquisition unit 200 takes in the reverse bias voltage Vr and the photocurrent Iapd ′, which are detection outputs of the reverse bias voltage detection unit 16 and the photocurrent detection unit 14, and A / D converts these detection outputs. Then, it is converted into a digital signal and stored in the storage unit 204 as data in a predetermined format (step 403).

Next, the parameter calculation unit 202 calculates the photocurrent (Iapd′−C (T)) that takes into account the offset current that actually flows through the light receiving element 12 by the adder 410 (404).
Also, the parameter calculation unit 202 calculates A (T) · Vr by multiplying the reverse bias voltage Vr acquired by the coefficient multiplier 411 by the parameter A (T), and the adder 412 adds the parameter to the multiplication result. B (T) is added to calculate A (T) · Vr + B (T) (step 405).

Further, the parameter calculation unit 202 multiplies the photocurrent (Iapd′−C (T)) calculated in step 404 by A (T) · Vr + B (T) calculated in step 405 by the multiplier 413, and receives it. The optical power monitor output Vmon (= (Iapd′−C (T)) · (A (T) · Vr + B (T))) is calculated (step 407).
As a result, a ratio between the optical input power input to the light receiving element and the photocurrent of the light receiving element is calculated as a primary expression of the reverse bias voltage. As a result, the optical power input to the optical receiving unit and the optical receiving unit are calculated. The monitor output of the received optical power has a linear relationship with the optical power input to, and the error in the monitor output of the detected received optical power is reduced.

  Incidentally, in a WDM optical communication system, an optical signal having a wavelength in a wide wavelength range is used. Since the light receiving sensitivity of the light receiving element (avalanche photodiode (APD)) of the receiving unit has a wavelength characteristic, an error occurs in the received light power monitor output Vmon depending on the wavelength of the received signal light. FIG. 7 shows the characteristics of the received light power monitor output with respect to the received light power. FIG. 7A shows the characteristics of an optical signal having a single wavelength, and FIG. 7B shows the optical signals of a plurality of wavelengths. The characteristics of each are shown.

Further, since the wavelength characteristic of the light receiving sensitivity of the light receiving element also changes depending on the temperature as shown in FIG. 8, the parameter is a function of temperature.
In the received light power monitoring apparatus according to the embodiment of the present invention, the parameter calculation unit 202 inputs the shortest wavelength optical signal and the longest wavelength optical signal used for communication to the light receiving element 12 during adjustment, respectively. An average value of the obtained parameters A (T), B (T), and C (T) is calculated, and the calculated average values of the parameters A (T), B (T), and C (T) are calculated as received power. Parameters A (T), B (T), and C (T) used when calculating the monitor output Vmon are stored in the storage unit 204.

  A light receiving element such as an avalanche photodiode (APD) or a PIN photodiode has a wavelength dependency with respect to the received optical signal, and therefore an error occurs in the received optical power monitor output Vmon depending on the wavelength of the received optical signal. By using the parameters A (T), B (T), and C (T) stored in the storage means when calculating the received power monitor output Vmon, a plurality of light of all different wavelengths used for communication. The error of the signal can be reduced within a range determined by the target specification.

  As described above, according to the embodiment of the present invention, in the received light power monitoring device that monitors the received light power in the optical receiving unit in the optical communication system, the ratio between the optical input power and the photocurrent that flows through the light receiving element by the calculating means during adjustment. Is determined in advance so as to be a linear expression of the reverse bias voltage of the light receiving element, the determined parameter is stored by a storage means, and the received voltage is monitored when the received light power is monitored. And the detection output of the photocurrent detection means is taken in, and based on these detection outputs, the received optical power is calculated using the parameters stored in the storage means. And the received optical power monitor output with respect to the optical power input to the optical receiver has a linear relationship, and the detected received light Error of word monitor output is reduced.

  Further, according to the present embodiment, in the received light power monitoring device that monitors the received light power in the optical receiving unit in the optical communication system, the optical signal having the shortest wavelength and the optical signal having the longest wavelength used for communication are optically received. The parameters A (T), B (T), C (T) are calculated for the optical signals of the respective wavelengths by the calculation means, and the calculated parameters A (T), B (T), C Since the average value of (T) is stored in the storage means as parameters A (T), B (T), and C (T) used when calculating the received power monitor output Vmon, the received power monitor output By using the parameters A (T), B (T), and C (T) stored in the storage means when calculating Vmon, the target for all of the optical signals having a plurality of different wavelengths used for communication is obtained. Determined by the specifications Thereby reduce the error in the range

The block diagram which shows the structure of the received light power monitor apparatus which concerns on embodiment of this invention. The flowchart which shows the process sequence at the time of adjustment of the arithmetic processing circuit in the received light power monitor apparatus which concerns on embodiment of this invention shown in FIG. Explanatory drawing which shows the calculation processing content at the time of adjustment of the parameter calculating part in the received light power monitor apparatus which concerns on embodiment of this invention shown in FIG. Explanatory drawing which shows the content of the data memorize | stored in the memory | storage part in the received light power monitor apparatus which concerns on embodiment of this invention shown in FIG. The flowchart which shows the process sequence at the time of the received light power monitoring of the arithmetic processing circuit in the received light power monitor apparatus which concerns on embodiment of this invention shown in FIG. Explanatory drawing which shows the calculation processing content at the time of the received light power monitoring of the parameter calculating part 202 in the received light power monitor apparatus which concerns on embodiment of this invention shown in FIG. The characteristic view which shows the characteristic of the reception light power monitor output with respect to the light reception power in the reception light power monitor apparatus which concerns on embodiment of this invention. The characteristic view which shows the wavelength characteristic which uses the temperature of the light reception sensitivity of the light receiving element in the received light power monitor apparatus which concerns on embodiment of this invention as a parameter. 1 is a block diagram showing a configuration of a WDM optical communication system. FIG. 10 is a diagram schematically illustrating a schematic configuration of a reception power monitor circuit in the WDM optical communication system illustrated in FIG. 9. FIG. 10 is a characteristic diagram illustrating a light receiving sensitivity characteristic with respect to a reverse bias voltage Vr of a light receiving element in a reception power monitor circuit in the WDM optical communication system illustrated in FIG. 9. FIG. 10 is a diagram illustrating characteristics of a photocurrent Iapd, a reverse bias voltage Vr, and a received optical power monitor output Vmon with respect to an input optical power Pin of a light receiving element in the received power monitor circuit in the WDM optical communication system illustrated in FIG. 9.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... High voltage generation circuit, 12 ... Light receiving element, 14 ... Photocurrent detection part, 16 ... Reverse bias voltage detection part, 20 ... Arithmetic processing circuit, 200 ... Photocurrent / reverse bias voltage acquisition part, 202 ... Parameter acquisition part, 204: Storage unit, 206: Received power calculation unit

Claims (8)

A received light power monitoring device for monitoring a received light power in an optical receiver in an optical communication system,
Voltage detecting means for detecting a reverse bias voltage applied to a light receiving element constituting the light receiving unit with respect to optical power input to the light receiving unit;
A photocurrent detection means for detecting a photocurrent flowing in the light receiving element with respect to the optical power input to the optical receiver;
Arithmetic means for pre-determining a parameter defining the primary expression so that a ratio of the optical input power and the photocurrent becomes a primary expression of the reverse bias voltage at the time of adjustment;
Storage means for storing the parameters determined by the calculation means;
Have
The calculation means captures the detection outputs of the voltage detection means and the photocurrent detection means during reception light power monitoring, and uses the parameters stored in the storage means based on these detection outputs to receive light. A received light power monitoring apparatus characterized by calculating power. The computing means is
At the time of adjustment, the optical power input to the receiving unit is Pin, the photocurrent flowing through the light receiving element is Iapd ', the reverse bias voltage applied to the light receiving element is Vr, and an offset considering the error of the acquired photocurrent Iapd C (T), the ratio of the optical input power Pin and the photocurrent Iapd is expressed by a linear expression with the reverse bias voltage Vr as a variable, the coefficient of the reverse bias voltage Vr is A (T), a constant term As B (T) (where T represents temperature, and A (T), B (T), and C (T) are functions of temperature), the following equation (1)
Pin / (Iapd′−C (T)) = A (T) · Vr + B (T) (1)
Parameter A (T), B (T), C (T) from
The received optical power monitoring apparatus according to claim 1, wherein the obtained parameters A (T), B (T), and C (T) are stored in the storage means. The computing means is
At the time of reception light power monitoring, a signal indicating a photocurrent Iapd ′ flowing through the light receiving element and a signal indicating a reverse bias voltage Vr applied to the light receiving element are captured,
Using the parameters A (T), B (T), C (T) stored in the storage means, the following equation (2)
Vmon = (A (T) .Vr + B (T)). (Iapd'-C (T)) (2)
3. The received light power monitor apparatus according to claim 2, wherein a received power monitor output Vmon is obtained from the received light power. The computing means is
At the time of adjustment, an optical signal having the shortest wavelength and an optical signal having the longest wavelength used for communication are input to the light receiving element, and the averages of the parameters A (T), B (T), and C (T) obtained respectively. Parameters A (T), B (T), B (T), which are used when calculating the received power monitor output Vmon using the average values of the calculated parameters A (T), B (T), C (T) The received light power monitoring apparatus according to claim 2, wherein C (T) is stored in the storage unit. A received optical power monitoring method for monitoring received optical power in an optical receiver in an optical communication system,
A first step of detecting, by a voltage detection means, a reverse bias voltage applied to a light receiving element constituting the light receiving unit with respect to an optical power input to the light receiving unit;
A second step of detecting a photocurrent flowing in the light receiving element with respect to the optical power input to the light receiving unit by a current detecting unit;
A third step of pre-determining by a calculation means a parameter that defines the linear expression so that a ratio of the optical input power to the photocurrent becomes a linear expression of the reverse bias voltage at the time of adjustment;
A fourth step of storing in the storage means the parameter determined by the calculation means;
At the time of received light power monitoring, the calculation means fetches the detection outputs of the voltage detection means and the photocurrent detection means, and based on these detection outputs, the received light power is stored using the parameters stored in the storage means. A fifth step of calculating
A received light power monitoring method comprising: In the third step,
At the time of adjustment, the optical power input to the receiving unit is Pin, the photocurrent flowing through the light receiving element is Iapd ′, the reverse bias voltage applied to the light receiving element is Vr, and the error of the acquired photocurrent Iapd ′ is considered. The coefficient of the reverse bias voltage Vr when the offset is C (T) and the ratio between the optical input power Pin and the photocurrent Iapd is expressed by a linear expression with the reverse bias voltage Vr as a variable is A (T), a constant The term is B (T) (where T represents temperature, and A (T), B (T), and C (T) are functions of temperature).
Pin / (Iapd′−C (T)) = A (T) · Vr + B (T) (1)
Parameter A (T), B (T), C (T) from
6. The received optical power monitoring method according to claim 5, wherein in the fourth step, the obtained parameters A (T), B (T), and C (T) are stored in the storage unit. In the fifth step,
During reception light power monitoring, a signal indicating a photocurrent Iapd ′ flowing through the light receiving element and a signal indicating a reverse bias voltage Vr applied to the light receiving element are fetched by the calculating means,
Using the parameters A (T), B (T), C (T) stored in the storage means, the following equation (2)
Vmon = (A (T) .Vr + B (T)). (Iapd'-C (T)) (2)
7. The received light power monitoring method according to claim 6, wherein the received power monitor output Vmon is obtained from the received light power. In the third step,
At the time of adjustment, an optical signal having the shortest wavelength and an optical signal having the longest wavelength used for communication are input to the light receiving element by the calculation means, and the parameters A (T), B (T), C ( T) is averaged,
In the fourth step,
The average values of the calculated parameters A (T), B (T), and C (T) are used as parameters A (T), B (T), and C (T) used when calculating the received power monitor output Vmon. The received light power monitoring method according to claim 6, wherein the received light power is stored in the storage means.

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