JP2007124375A - Light receiving circuit and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily perform fine adjustment in gain to be required in system adjustment without affecting a correction amount corresponding to optical transmission loss though there is the problem that it is difficult to perform the fine adjustment by an arrangement condition at every slave station, etc., in the conventional light receiving circuit for correcting the optical propagation loss. <P>SOLUTION: In the light receiving circuit, the MPU 14c of an integrated automatic correcting part 14 calculates an optical propagation loss correcting voltage value by interpolation processing referring to a correction data table on the basis of a detection voltage value corresponding to average light reception power from an A/D converting part 14b, performs an additional correcting operation on the basis of an additional correcting value which is manually input from a setting unit 17 to the optical propagation loss correcting voltage value, calculates a final correcting value so as to output it to a D/A converter 14d, and applies the obtained control voltage Vc to a voltage control variable RF attenuator 16. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light receiving circuit provided in a slave station of a high-frequency analog optical transmission system such as an analog optical transmission system for mobile communication, and in particular, a correction for controlling a gain of an output level of a demodulated signal based on an optical propagation loss. The present invention relates to a light receiving circuit and an optical transmission system in which values can be easily fine-tuned according to installation conditions for each slave station.

In a mobile communication system typified by a mobile phone system, an analog optical transmission system for mobile communication is used as an auxiliary system for the purpose of dead zone relief in underground spaces or tunnels.
Analog optical transmission systems for mobile communications use high-frequency electrical signals used for mobile communications to modulate optical signals as modulation signals and transmit them over optical fibers, etc., and receive radio waves such as shadows in underground spaces, tunnels, mountains, and high-rise buildings. It re-converts to a high-frequency electrical signal in a difficult dead zone to ensure communication with a mobile wireless terminal in the dead zone.

An analog optical transmission system for mobile communication will be described with reference to FIG. FIG. 7 is a schematic configuration diagram of an analog optical transmission system for mobile communication.
As shown in FIG. 7, the analog optical transmission system for mobile communication includes an optical transmission master station device 21, optical fibers 27 and 28, and an optical transmission slave station device 29 connected to a radio modulation / demodulation device 26 that is a base station. And an antenna 35, which secures communication between the radio modulation / demodulation device 26 of the base station and the mobile radio terminal 36 that normally exists in a disturbed area where radio waves are difficult to reach.

Each component will be specifically described.
The optical transmission master station device (master station device) 21 includes a downlink amplifier 24 that amplifies the downlink signal from the radio modulation / demodulation device 26 at a constant amplification factor, and an electrical / optical converter (converter that converts the amplified signal into an optical signal). E / O) 22, an optical / electrical converter (O / E) 23 that converts an optical signal received from the optical fiber 28 into an electrical signal, and an amplifier 25 that amplifies the converted electrical signal at a constant amplification factor. It has.
The optical fiber 27 transmits a downstream optical signal from the master station device 21 to the slave station device 29, and the optical fiber 28 transmits an upstream optical signal from the slave station device 29 to the master station device 21. .

The optical transmission slave station device (slave station device) 29 is an optical / electrical converter (O / E) 30 that converts the downstream optical signal received from the optical fiber 27 into an electrical signal, and amplifies the downstream signal at a constant amplification factor. An amplifier 32, an antenna duplexer 34, an amplifier 33 that amplifies the upstream signal from the mobile radio terminal 36, and an electrical / optical converter (E / O) 31 that converts the amplified upstream electrical signal into an optical signal. It has.
The antenna 35 is provided in an insensitive area such as an underground space or a tunnel, and transmits and receives a radio signal.

The operation in the analog optical transmission system for mobile communication will be described with reference to FIG.
Here, the information transmission from the radio modulation / demodulation device 26 of the base station to the mobile radio terminal 36 present in the dead area will be described as an example.
The signal modulated and output as a high-frequency signal by the radio modem device 26 is normally added to the antenna through the feeder and radiated as a radio wave to the space. However, in the analog optical transmission system for mobile communication, the radio modem device 26 It is input to the master station device 21 placed in the vicinity.

  In the master station device 21, the signal level is adjusted by the amplifier 24 as necessary, and then the optical / optical conversion unit 22 performs analog optical modulation to convert it into an optical signal. This optical signal reaches the optical / electrical conversion unit 30 of the slave station device 29 installed in the vicinity of the dead area via the optical fiber 27.

  In the optical / electrical converter 30, the original high frequency signal is demodulated from the received optical signal and input to the amplifier 32. The amplifier 32 amplifies the power of the high frequency signal to a level necessary and sufficient for servicing the dead area, and feeds power to the antenna 35 installed in the dead area connected by the feeder line via the antenna duplexer 34. . The radio waves radiated to the dead area by the antenna 35 are received by the mobile radio terminal 36 and information is transmitted. In this way, the downlink signal is transmitted from the wireless modem device 26 to the mobile wireless terminal 36.

Information transmission from the mobile radio terminal 36 to the radio modulation / demodulation device 26 is performed in the same manner as described above in the transmission system via the optical fiber 28, and thus description thereof is omitted here.
Recently, this system is sometimes used not only as a closed space such as an underground space but also as a simple area expansion means in an open space.
Normally, these mobile communication systems perform two-way (simultaneous) communication, but in the following description, only one-way transmission will be described in order to avoid complicated description.

In such an analog optical transmission system, for example, when it is necessary to simultaneously receive an optical signal transmitted from one place at a plurality of places and convert it into a high-frequency electric signal, an optical branching device such as an optical star coupler is used. In many cases, the optical signal is distributed and transmitted to a required place by an optical fiber or the like.
In this one-to-many topology system configuration, differences in optical propagation loss due to optical star coupler distribution errors, transmission distance differences in optical fibers, etc., and connection loss differences in optical connectors, etc. Since they are different, the average optical power Pr incident on each light receiving circuit (optical receiver) is different.

ここで、Ｐｒは平均光電力、ＲＩＮは光源の相対雑音強度、ＯＭＩは光変調度、ηは受光素子の光電変換効率、Ｉｔｈは初段増幅器の入力換算雑音電流密度、ＢＷは信号の等価雑音帯域幅であり、ｑは電気素量である。また分母のブラケット＜＞で括られた項は、初段増幅器の入力換算雑音電流密度の２乗平均を表す。 In the analog optical transmission system, the reception CNR (Carrier to Noise Ratio) of a high-frequency electrical signal after restoration from an optical signal is generally expressed by [Equation 1].

Here, Pr is the average optical power, RIN is the relative noise intensity of the light source, OMI is the optical modulation factor, η is the photoelectric conversion efficiency of the light receiving element, Ith is the input equivalent noise current density of the first stage amplifier, and BW is the equivalent noise band of the signal It is a width and q is an elementary electric quantity. The term enclosed in the denominator bracket <> represents the root mean square of the input equivalent noise current density of the first stage amplifier.

  In [Equation 1], the relative noise intensity (RIN) of the light source, the degree of optical modulation (OMI), the photoelectric conversion efficiency (η) of the light receiving element, the input equivalent noise current density (Ith) of the first stage amplifier, the equivalent noise bandwidth, etc. If the parameter is constant, the received CNR varies depending on the average received light level Pr. [Equation 1] is an approximate expression that holds when a Pin photodiode is used as the light receiving element.

  Accordingly, as described above, when an optical signal transmitted from one place is distributed by an optical star coupler or the like and transmitted to an optical fiber to each place, the distribution deviation of the optical star coupler, the difference in optical transmission loss in the process of optical transmission, If the average optical power Pr incident on the light receiving circuit at each location is different due to a difference in connection loss at the connection section, the reception CNR of the high-frequency electrical signal obtained by optical demodulation is different. Further, the output power level of the high-frequency electrical signal, which is the product of the numerator of [Equation 1] and the RF load impedance, also differs.

  In high-frequency signal analog optical transmission systems for mobile communications such as mobile phones and commercial radios, demodulated high-frequency signals are finally transmitted in the form of radio waves by antennas or LCX (leaky coaxial cable) after optical transmission. It is necessary to radiate to. In order to radiate into the space as a radio wave, there is a regulation by laws and regulations such as the Radio Law regarding transmission power, spurious radiation, etc., and these must normally satisfy the same value in each of the slave station devices distributed.

  However, as derived from [Equation 1], the variation of the received light power of ± 1 dB is a variation of ± 2 dB (in the same order) with the power of the high-frequency electric signal. When it is necessary to make the power levels of the same, some correction means is necessary.

  In addition, it is often not known at the device manufacturing stage which optical fiber transmission line with how much optical loss is connected to which port of the optical distributor. The system gain adjustment performed to keep the (transmission power) within the specified value range needs to be adjusted on site after the installation of the apparatus.

  On the other hand, if such a value is known in advance, it is possible to adjust it individually, but in that case, the degree of freedom of installation of a device (hereinafter referred to as a slave station device) including each light receiving unit Is significantly reduced. That is, there is a restriction that only a specific slave station device can be connected to a specific distribution (branch) output.

  Also, after the distribution output of the optical distributor, in order to make the average optical power of each light receiving unit constant, an optical variable attenuator is inserted in the middle of each optical fiber transmission line to adjust the average optical power. Means are also conceivable. However, such components for optical fiber transmission are generally more expensive than general high-frequency components, and there is a problem that the introduction cost of the entire system is increased.

As a prior art for solving these problems, Japanese Patent Laid-Open No. 2000-216733 “Optoelectric Conversion Method, Light Receiving Circuit, and Optical Communication System” published on August 4, 2000 (Applicant: Kokusai Electric Co., Ltd., Invention) Party: Yoshihiro Imazo).
In this prior art, after receiving an optical signal that has been subjected to analog optical modulation and restoring it to an electric signal, the high-frequency component of the electric signal (wireless high-frequency signal to be transmitted) is passed to an amplifying circuit system with variable gain. Since the direct current component of the electrical signal is proportional to the received average optical power, the amplification level required based on this value is determined so that the output level of the high frequency signal becomes a desired value, This is a light receiving circuit provided with a means for controlling a gain variable amplifier circuit that amplifies a high frequency component, thereby correcting a variation in the high frequency signal level caused by the difference in average optical power caused by the installation location of the slave station device. Is.

JP 2000-216733 A

  However, the conventional light receiving circuit has an excellent function of automatically determining the gain correction amount according to the optical transmission loss. However, in actual installation and operation of the apparatus, the output level is further increased for various reasons. There is a case where a request for fine adjustment is generated.

  For example, in addition to the correction of optical transmission loss, when a fixed gain power amplifier or the like is installed in the subsequent stage of the slave station device, the level must be adjusted by the slave station device in order to adjust the antenna terminal output. This is the case when it is not possible. This is used when it is necessary to adjust the wireless area (radio wave reachable range) in a small zone wireless system or the like.

  In such a case, it is possible to change the control amount by changing the parameter of the automatic gain correction amount determination circuit corresponding to the optical transmission loss. This parameter change is, for example, changing the reference voltage or changing the amplification factor of the operational amplifier when the control amount is determined by analog calculation. Further, when the average optical power detection value is digitized and the correction amount is determined by the CPU and the program, the program itself is changed or the calculation weighting coefficient is changed.

  However, in the above conventional example, the main purpose is mainly to absorb the change in the optical transmission loss, and it is optimal after considering the control characteristics of the voltage (or current) control type high frequency attenuator for variable gain. Since it is configured so that the amount can be obtained, if the parameter change for fine adjustment is made in addition to that, it is not possible to handle the dispersion correction of optical transmission loss and the fine adjustment related to each slave station device independently. There has been a problem that the subsequent maintenance may be hindered. It was particularly inconvenient when the level adjustment of each slave station was performed during operation by the end user, not on-site adjustment accompanying installation work.

  The present invention has been made in view of the above circumstances, and can appropriately correct an optical transmission loss and fine adjustment according to circumstances of each slave station device to obtain an appropriate gain. Therefore, fine adjustment of the gain required for system adjustment can be performed easily and economically without affecting the correction amount that is automatically determined according to the level, and the output level of the demodulated signal is kept constant and maintenance is performed. It is an object of the present invention to provide a light receiving circuit and an optical transmission system that can facilitate the above.

  The present invention for solving the problems of the above conventional example is applied with an optical / electrical converter that converts a received optical signal into an electrical signal and a high-frequency component of the electrical signal converted by the optical / electrical converter. An amplification unit that amplifies and outputs with a gain based on the control voltage, and detects an average light reception level based on a direct current component of the electrical signal converted by the optical / electrical conversion unit, and in the amplification unit according to the average light reception level A light receiving circuit including a correction unit that obtains an optical propagation loss correction voltage for adjusting the gain and outputs it as a control voltage, and the correction unit additionally corrects the optical propagation loss correction voltage based on an external setting. Thus, the correction unit outputs the control voltage.

  An optical transmission system comprising a master station device having an optical transmitter for transmitting an optical signal and a slave station device having the light receiving circuit according to claim 1, wherein the optical transmitter of the master station device is externally set. Is an optical transmission unit configured to multiplex a signal including an additional correction value that specifies a correction amount for additional correction and is transmitted with the original transmission signal through the same optical fiber. Receives the optical signal transmitted from the master station device, demodulates the original transmission signal and the signal including the additional correction value, and corrects the optical propagation loss based on the demodulated additional correction value. It is a light receiving circuit that additionally corrects the voltage and outputs it as a control voltage.

  According to the present invention, the optical / electrical converter that converts the received optical signal into an electrical signal, and the high-frequency component of the electrical signal converted by the optical / electrical converter are amplified with a gain based on the applied control voltage. And a light propagation loss correction voltage for detecting an average received light level based on a direct current component of an electric signal converted by the optical / electrical converter and adjusting a gain in the amplifier according to the average received light level And a correction unit that outputs a control voltage as a control voltage. The correction unit additionally corrects the light propagation loss correction voltage based on an external setting and outputs the correction voltage as a control voltage. In this light receiving circuit, the optical transmission loss and the fine adjustment according to the installation conditions of each slave station device can be corrected independently to obtain an appropriate gain. Shadow on the automatic correction amount by automatic determination The without giving the fine adjustment of the gain required on the system adjust easily and economically can be performed, along with keeping the output level of the demodulated signal constant, there is an effect that can facilitate maintenance.

  According to the present invention, there is provided an optical transmission system comprising a master station device having an optical transmitter for transmitting an optical signal and a slave station device having the light receiving circuit according to claim 1, wherein the optical transmission of the master station device is performed. Is an optical transmission unit configured to multiplex a signal including an additional correction value that is set from an external setting device and designates a correction amount of additional correction with an original transmission signal and transmits the signal through the same optical fiber. The light receiving circuit of the device receives the optical signal transmitted from the master station device, demodulates the original transmission signal and the signal including the additional correction value, and demodulates the signal to the demodulated additional correction value. Based on this, in addition to the above effects, the optical transmission loss correction voltage is additionally corrected and the optical transmission system is a light receiving circuit that outputs it as a control voltage. Set the additional correction value to be performed on the master station side. Batch and can be performed remotely by an effect capable of improving the convenience.

Embodiments of the present invention will be described with reference to the drawings.
The light receiving circuit of the present invention includes analog means or digital arithmetic means for further fine adjustment to the correction amount according to the conventional optical transmission loss, and according to the individual slave stations with the correction value according to the optical transmission loss. The final device gain control value is determined by adding the correction value, and fine adjustment can be performed without affecting the correction amount of the optical transmission loss, and the output level of the demodulated signal is kept constant. It is possible to facilitate maintenance.

  The optical transmission system according to the present invention further adds a fine adjustment to the correction value according to the optical transmission loss of the slave station device by remote control from the master station device on the optical transmission side. The final device gain control value is determined by adding the correction value according to the individual slave station to the correction value according to, and fine adjustment can be performed without affecting the correction amount of the optical transmission loss. The output level of the demodulated signal can be kept constant and maintenance can be facilitated.

FIG. 1 is a block diagram showing a configuration of a light receiving circuit (first light receiving circuit) according to the first embodiment of the present invention.
The first light receiving circuit according to the present embodiment corresponds to the light receiving circuit portion (optical / electrical conversion unit 30 and amplifier 32) of the optical transmission slave station device 29 in the optical transmission system shown in FIG. As shown in FIG. 1, the light receiving element 1 using a Pin diode that converts an optical signal into an electric signal and a high-frequency load connected in series to the cathode side of the light receiving element 1 are the same components as the above-described prior art. A resistor 3 and a bias resistor 7, a capacitor 6 connected in parallel between the RF (high frequency) load resistor 3 and the bias resistor 7 and grounded at one end, a capacitor 2 for cutting a DC component, a first-stage amplifier 10, A voltage-controlled variable gain amplifier 11, an inductor 4, a detection resistor 8 and a bias resistor 9 connected in series on the anode side of the light receiving element 1, and a parallel connection between the inductor 4 and the detection resistor 8. A capacitor 5 having one end grounded and a light propagation loss correction unit 12 connected to both ends of the detection resistor 8 are provided. As a characteristic part of the first light receiving circuit, an output side of the light propagation loss correction unit 12 is provided. The control voltage correction unit 13 is provided.

  That is, the first light receiving circuit is provided with an optical propagation loss correcting unit 12 that corrects the amplification gain of the demodulated signal in accordance with the optical propagation loss, as in the conventional light receiving circuit, and further, the output of the optical propagation loss correcting unit 12 A correction voltage Vb for correcting the voltage Va is added to obtain a final correction voltage, and this final correction voltage is applied as a control voltage for the voltage-controlled variable gain amplifier 11.

  The inductance 4 is inserted for the purpose of blocking the RF component of the photocurrent. The capacitor 5 is provided for the purpose of grounding a frequency component that could not be blocked by the inductance 4. The bias resistors 7 and 9 are provided for the purpose of limiting the photocurrent when the optical input is excessive, and are not essential elements for the configuration of the present invention.

The operation of the light receiving circuit having the above configuration will be described.
The optical signal incident on the light receiving element 1 is converted into an electric signal by the light receiving element 1. When the light receiving element is a Pin photodiode to which a necessary and sufficient reverse bias voltage (+ Vr in this example) is applied, the optical signal is converted into a photocurrent having a light receiving sensitivity (conversion efficiency) as a proportional coefficient. In this case, the light receiving element can be regarded as a high-impedance current source, and a photocurrent flows through an external circuit including the bias resistors 7 and 9, the RF load resistor 3, the inductor 4, and the detection resistor 8.

  The RF component of this photocurrent is input to the first stage amplifier 10 by the RF load resistor 3 grounded in a high frequency by the capacitor 6 and the capacitor 2 that cuts (couples) the DC component, and further, the voltage controlled gain variable amplifier 11. Is amplified and output as an RF signal. Here, the amplification degree in the voltage controlled variable gain amplifier 11 is determined by a control voltage (final correction voltage) Vc from a control voltage correction unit 13 described later.

  On the other hand, the direct current component of the photocurrent proportional to the average optical power causes a potential difference across the detection resistor 8 via the inductance 4. The potential difference between both ends of the detection resistor 8 is output by the light propagation loss correction unit 12 as Va, which is a control voltage before correction of the voltage controlled variable gain amplifier 11. Hereinafter, Va is referred to as a light propagation loss correction voltage.

  The optical propagation loss correction unit 12 can use the above-described configuration of the prior art. Here, the differential input DC amplification circuit 12a, the low-pass filter 12b, and the reference voltage Vref are applied to the negative input side. And a control voltage generating circuit 12c.

In the light propagation loss correction unit 12, the potential difference between both ends of the detection resistor 8 is amplified by the DC amplifier circuit 12a, the AC component is removed by the low-pass filter 12b, and only the DC component is the anode input side of the control voltage generation circuit 12c. Is output. This DC component corresponds to the average received light power (average received light level).
Then, the control voltage generation circuit 12c amplifies the difference between the DC component and the reference voltage Vref to obtain the light propagation loss correction voltage Va.

The control voltage correction unit 13, which is a characteristic part of the light receiving circuit, includes load resistors 13a and 13b, a variable resistor 13c, an amplifier 13d, and a load resistor 13e.
Here, the variable resistor 13c determines the correction voltage Vb, and allows Vb to be adjusted in a range of −Vadj ≦ Vb ≦ + Vadj.
Then, the light propagation loss correction voltage Va and the correction voltage Vb are added by an adder circuit having a voltage amplification factor of 1 by an operational amplifier to be a final correction voltage, which is given as the control voltage Vc of the voltage controlled variable gain amplifier 11.
That is, Vc = Va + Vb (where −Vadj ≦ Vb ≦ + Vadj). Usually, the absolute value of Vb is smaller than Va.

Therefore, the value of Vb may be adjusted to an appropriate value by the variable resistor 13c so as to perform a specific fine adjustment depending on the installation location of each slave station device 29, and is corrected separately from the light propagation loss correction voltage Va. By determining the voltage Vb, the output level of the demodulated signals of the plurality of slave station devices can be kept constant by performing fine adjustment for each slave station device without affecting the correction process of the optical propagation loss. is there.
In the first light receiving circuit, the combination of the functions of the light propagation loss correction unit 12 and the control voltage correction unit 13 corresponds to the “correction unit” recited in the claims.

  According to the light receiving circuit according to the first embodiment of the present invention, the control voltage correction unit 13 for fine adjustment is provided in the subsequent stage of the light propagation loss correction unit 12, and the light propagation loss correction unit 12 is based on the average received light power. The control voltage Vc of the voltage controlled gain variable amplifier 11 is obtained by adding the correction voltage Vb adjusted by the variable resistor 13c according to the installation location of each light receiving circuit to the light propagation loss correction voltage Va determined in Therefore, in addition to the correction of the optical propagation loss, the gain of the voltage controlled gain variable amplifier 11 is finely adjusted according to the individual circumstances depending on the installation location of each light receiving circuit, etc. Variations in the output level of the demodulated signal for each device can be eliminated, and the correction voltage Vb is adjusted separately from the control of the optical propagation loss correction voltage Va. Without affecting the settings Can be fine-tuned in motion, there is an effect that can facilitate the maintenance during operation.

  Although only the downstream signal has been described here, the control voltage Vc determined by the light receiving circuit can also be applied to the upstream signal amplifier 33 of the slave station device 29, so that the upstream signal can also be transmitted to the slave station. It is possible to prevent variations in the transmitted optical signal level due to circumstances such as installation conditions for each apparatus.

Next, a light receiving circuit according to a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing the configuration of a light receiving circuit (second light receiving circuit) according to the second embodiment of the present invention.
As shown in FIG. 2, the basic configuration of the second light receiving circuit is substantially the same as that of the first light receiving circuit, but the configuration of the light propagation loss correction unit 12 'is partially different from that of the first light receiving circuit. Is different.
The light propagation loss correction unit 12 'of the second light receiving circuit includes a DC amplification circuit 12d, an A / D conversion unit (ADC) 12e, an MPU (Micro Processing Unit) 12f, D / A converter (DAC: Digital Analog Converter) 12g.
The MPU 12f requires a memory for storing programs and calculation data, an input / output interface with peripheral devices, etc., but in order to simplify the drawing, the illustration is omitted in FIG. It shall be written as

  Furthermore, the MPU 12f stores in advance a processing program or a correspondence table for calculating a control amount in accordance with the detected voltage value from the A / D converter 12e. Specifically, the optimum control amount corresponding to a plurality of detected voltage values is stored in a nonvolatile memory as a table in advance, and numerical interpolation is performed by referring to the table according to the detected voltage value. A method of determining a control value, a method of calculating a control amount based on an arithmetic expression that incorporates a control voltage-gain variable characteristic of the voltage controlled variable gain amplifier 11 and the like are conceivable.

The operation of the light propagation loss correction unit 12 'of the second circuit is such that the potential difference generated at both ends of the detection resistor 8 is amplified by the DC amplification circuit 12d, and converted to a digital detection voltage value by the A / D conversion unit 12e. After the conversion, a control value (light propagation loss correction voltage value) corresponding to the detected voltage value is determined by the MPU 12f, converted to an optical propagation loss correction voltage Va, which is an analog amount, and output by the D / A converter 12g. Is.
Other operations are the same as those of the first light receiving circuit described above.
In the second light receiving circuit, the combination of the functions of the light propagation loss correction unit 12 ′ and the control voltage correction unit 13 corresponds to the “correction unit” in the claims.

  That is, in the second light receiving circuit, the control voltage correction unit 13 adds the correction voltage Vb corresponding to each slave station device to the light propagation loss correction voltage Va output from the light propagation loss correction unit 12 ′. The control voltage Vc (Va + Vb) is applied to the voltage controlled variable gain amplifier 11 to finely adjust not only the correction of the optical propagation loss but also the variation depending on the installation location of the slave station device. The output level of the demodulated signal can be kept constant, and the control voltage correction unit 13 can make fine adjustments without affecting the setting of the optical propagation loss correction unit 12 ', etc., and facilitates maintenance during operation. There is an effect that can be done.

  According to the light receiving circuit of the second embodiment of the present invention, the control voltage correction unit 13 for fine adjustment is provided in the subsequent stage of the light propagation loss correction unit 12 ′, and the light propagation loss correction unit is based on the average received power. The voltage control type gain variable amplifier 11 is obtained by adding the correction voltage Vb adjusted by the variable resistor 13c according to the installation location of each light receiving circuit to the light propagation loss correction voltage Va determined by digital processing at 12 '. Since the control voltage Vc is obtained, the gain of the voltage controlled gain variable amplifier 11 is finely adjusted in response to individual circumstances depending on the installation location of each light receiving circuit in addition to the correction of the light propagation loss. Thus, variations in the output level of the demodulated signal for each slave station device can be eliminated, and the adjustment of the correction voltage Vb is performed independently of the control of the optical propagation loss correction voltage Va. Light propagation loss correction You can manually fine adjusted without affecting the 12 setting of an effect that can facilitate maintenance during operation.

Next, a light receiving circuit according to a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration of a light receiving circuit (third light receiving circuit) according to the third embodiment of the present invention.
In the first and second light receiving circuits, the correction voltage is applied by the voltage adding circuit of the operational amplifier of the control voltage correction unit 13, but the third light receiving circuit is integrated with the processing by the MPU.

As shown in FIG. 3, in the third light receiving circuit, an integrated automatic correction unit 14 is provided. In the integrated automatic control unit 14, correction of light propagation loss and fine adjustment depending on the installation location of each slave station device, etc. That is what both are trying to do.
The integrated automatic correction unit 14 has substantially the same configuration as the light propagation loss correction unit 12 ′ in the second light receiving circuit, and includes a DC amplification circuit 14a, an A / D conversion unit 14b, an MPU (processing unit) 14c, The MPU 14c is connected to the setting device 17 via an input / output interface (I / O) 14e. The processing in the MPU 14c is partially different from the MPU 12f in the second light receiving circuit.

  In the memory (not shown) of the MPU 14c, similarly to the MPU 12f in the second light receiving circuit, a correction amount for correcting the light propagation loss according to the detection voltage value at a specific interval input from the A / D conversion unit 14b. A stored table (light correction data table) is stored, and a light propagation loss correction voltage value corresponding to the detected voltage value is determined.

  The setting device 17 is a device for setting fine adjustment required for each individual slave station with respect to a control value (optical propagation loss correction voltage value) of optical propagation loss correction, and an additional correction value input manually. (Correction amount) is stored, and an additional correction value is output to the MPU 14c in accordance with an instruction from the MPU 14c. The setting device 17 may be dedicated hardware incorporating software for operation as necessary, or may be realized by software operating on a commonly used personal computer. Further, the MPU 14c may store the additional correction value once input from the setting unit 17 and use the value until it is updated.

  It should be noted that when inputting an additional correction value from the setting device 17, it is easier for the human interface to input such as “**% increase from current output”, so that erroneous operation can be prevented. . In this case, the MPU 14c refers to the light correction data table and calculates a correction voltage value based on the light propagation loss correction voltage value and the requested additional correction value.

In the third light receiving circuit, instead of the voltage controlled variable gain amplifier 11 provided in the first and second light receiving circuits, a combination of the fixed gain amplifier 15 and the voltage controlled variable RF attenuator 16 is used to generate a demodulated signal. The output RF level is adjusted, and the control voltage Vc is applied to the voltage controlled variable RF attenuator 16. That is, in the third light receiving circuit, the combination of the functions of the fixed gain amplifier 15 and the voltage controlled variable RF attenuator 16 corresponds to the “amplifying unit” recited in the claims.
In the third light receiving circuit, the integrated automatic correction unit 14 corresponds to a “correction unit” recited in the claims.

  In the third light receiving circuit, an appropriate additional correction value corresponding to each individual slave station is manually set from the setting device 17 and stored in the MPU 14c in advance, and the optical propagation loss of the second light receiving circuit is stored. Similarly to the correction unit 12 ', when the MPU 14c obtains the light propagation loss correction voltage value for correcting the light propagation loss based on the detection voltage value corresponding to the average received light level from the D / A conversion unit 14b, the value is obtained. In addition, the stored additional correction value is added, A / D converted, and output to the voltage controlled variable RF attenuator 16 as the control voltage Vc.

Next, control voltage value calculation processing in the third light receiving circuit will be described with reference to FIG. FIG. 4 is a flowchart showing processing in the MPU 14c of the integrated automatic correction unit 14 of the third light receiving circuit.
As shown in FIG. 4, the MPU 14c inputs the detection voltage value ("light reception voltage value" in the figure) output from the A / D conversion unit 14b (100), and converts the AC component remaining in the input voltage value. In order to eliminate it, an averaging process is performed at a specific time (102), and an interpolation value is determined by interpolation based on the correction data table, and set as a temporary correction value (104). The “interpolated value” calculated here is a temporary correction value for performing only correction for the optical propagation loss, and corresponds to the optical propagation loss correction voltage value.

  Next, the MPU 14c determines whether additional correction is necessary for the calculated interpolation value (106). The determination condition in the process 106 is, for example, that it is detected that the setting device 17 is connected, and if it is connected, it is determined that additional correction is necessary, or a specific pattern at a specific position in the memory of the MPU 14c. It can be considered that additional corrections are necessary if the data is written, and further, it is possible to determine by the setting switch, etc., but the circuit scale, software resources, work environment at the installation location, etc. The optimum configuration and method may be taken into consideration.

If no additional correction is required, the MPU 14c outputs the temporary correction value obtained in the process 104 to the D / A conversion unit 14d as the final correction value (112).
On the other hand, if it is determined in process 106 that additional correction is necessary, the MPU 14c acquires an additional manual correction value from the setting device 17 (108), and performs arithmetic processing on the temporary correction value based on this (110). ) And output as a final correction value (control voltage value) to the D / A converter 14d (112).

  If it is determined in process 106 that additional correction is necessary, the MPU 14c reads the additional correction value from the setting device 17 (if stored in advance, the MPU 14c reads the additional correction value from a specific storage area. Read), additional correction calculation is performed on the temporary correction value obtained in the process 104 (110), and the final correction value (control voltage value) is output to the D / A converter 14d (112). In this way, processing in the MPU 14c of the integrated automatic correction unit 14 is performed.

  According to the light receiving circuit according to the third embodiment of the present invention, in the integrated automatic correction unit 14, the MPU 14c is based on the detected voltage value according to the average received light power input from the A / D conversion unit 14b. An optical propagation loss correction voltage value is calculated by interpolation processing with reference to the correction data table, and an additional correction operation is performed based on the additional correction value manually input from the setting device 17 with respect to the optical propagation loss correction voltage value. The final correction value is calculated and output to the D / A converter 14d, and the obtained control voltage Vc is applied to the voltage control variable RF attenuator 16. Therefore, by the two-stage processing in the MPU 14c, In addition to correction of optical propagation loss, fine adjustment of gain corresponding to individual circumstances according to the installation location of each light receiving circuit etc. can be performed to eliminate variation in output level of demodulated signal for each slave station device In addition, since the correction voltage Vb is set separately from the calculation process of the optical propagation loss correction voltage value, it can be finely adjusted without affecting the parameter setting of the optical propagation loss correction voltage value processing. There is an effect that can be easily maintained.

  In the light receiving circuits according to the first to third embodiments described above, voltage controlled continuous variable type (analog control) gain variable amplifiers or variable RF attenuators are used as devices for adjusting the RF output level. However, these may be constituted by a digital step variable device whose control value is a serial input or a parallel input. In this case, an A / D conversion unit that converts the voltage output Vc of the control voltage correction unit 13 into a corresponding digital output may be added to the first and second light receiving circuits. In the case of the third light receiving circuit, the correction value output from the MPU may be output to a serial port or parallel port having an appropriate number of bits without being converted into an analog amount by D / A.

Next, an optical transmission system according to a fourth embodiment of the present invention will be described. The optical transmission system according to the fourth embodiment performs additional correction for the optical propagation loss correction voltage in the light receiving circuit of the slave station device based on a remote operation instruction from the master station device on the optical transmission side. is there.
FIG. 5 is a configuration block diagram of an optical transmission system (fourth system) according to the fourth embodiment of the present invention. FIG. 5 shows only the downstream direction of the fourth optical transmission system.
The basic configuration of the fourth system is the same as the general optical transmission system shown in FIG. 7, but the configurations and operations of the master station device and the slave station device are partially different.

  As shown in FIG. 5, the optical transmission unit 51 of the master station apparatus in the fourth system includes an amplifier 52 that amplifies an RF signal to be originally transmitted, and an electrical / optical conversion unit (E) that converts the RF signal into an optical signal. / O) 53, an MPU 55 connected to the setting device 17 'via an input / output interface (I / O), and a modulation unit 54 that modulates output data from the MPU 55.

  In the optical transmitter 51, the setting device 17 'inputs an additional correction value for fine adjustment according to the installation location for the RF output of each slave station, and inputs the additional correction value to an input / output interface (I / O). Is output to the MPU 55 via the. When a plurality of slave station devices are connected to the master station device, the additional correction value is output with an identification number for identifying the slave station device.

The MPU 55 outputs the additional correction value from the setting device 17 'to the modulator 54 as digital data in a format suitable for transmission over the optical fiber section. The MPU 55 may store the additional correction value input from the setting device 17 ′ in the internal work area.
The modulation unit 54 modulates digital data from the MPU 55 using a carrier wave having a frequency f2.
The signal from the modulation unit 54 is multiplexed with an RF signal to be originally transmitted, converted into an optical signal, and transmitted.

The configuration of the optical receiver 60 is substantially the same as the configuration of the third light receiving circuit shown in FIG. 3, but a band pass filter 58 and a demodulator 57 are connected to the integrated automatic correction unit 56. .
The band pass filter 58 passes only a signal in a desired frequency band. Here, a signal of frequency f2 is taken out.
The demodulator 57 demodulates the signal having the frequency f2 input from the band pass filter 58, extracts digital data, and outputs the digital data to the MPU 56c.
The processing in the MPU 56c of the integrated automatic correction unit 56 is the same as the MPU 14c in the third light receiving circuit except that the additional correction value is a value received from the master station device.

The operation in the fourth system will be described.
In the optical transmitter 51 of the master station apparatus, the RF signal (frequency f1) to be originally transmitted is amplified (or attenuated) to an appropriate level for analog optical transmission by the amplifier 52 and input to the electrical / optical converter 53. Is done.

  On the other hand, the data of the additional correction value input from the setting device 17 ′ is input to the MPU 55 via the I / O, converted into digital data of an appropriate format by the MPU 55, output to the modulation unit 54, and modulated. In the unit 54, the signal is modulated by the carrier wave f2 (where f1> f2).

  The f1 signal and the f2 signal are frequency-multiplexed by the multiplexing unit, converted into an optical signal by the electrical / optical conversion unit 53, and transmitted to the slave station apparatus via the optical fiber 62. That is, in the fourth system, the signal to be originally transmitted and the additional correction value data are multiplexed and then converted into an optical signal for transmission.

The optical signal transmitted through the optical fiber 62 is incident on a photodiode module (light receiving element) 61 of the optical receiver 60 of the slave station apparatus, and is restored to an RF signal in which f1 and f2 are frequency multiplexed. . This frequency multiplexed signal can be separated by an appropriate constant filter circuit or the like. For example, if f1 is 1 GHz and f2 is 1.2 kHz, if the value of capacitor 2 is selected as 56 pF as an example, f1 passes through capacitor 2, but f2 has a very high impedance. Therefore, it cannot pass.
Then, the signal of f1 is amplified by the amplifiers 10 and 15, and finally gain-adjusted by the voltage control variable RF attenuator 16, and output as an RF output.

  In addition, since the circuit portion including the inductor 4 and the capacitor 5 is a low-pass filter, the frequency component f1 can be sufficiently attenuated by an appropriate constant and supplied to the detection resistor 8. Then, the potential difference between both ends of the detection resistor 8 is amplified to an appropriate level by the DC amplifier circuit (differential amplifier) 56a of the integrated automatic correction unit 56, converted into digital data by the A / D conversion unit 56b, and then MPU 56c. However, similarly to the third light receiving circuit, the correction amount (light propagation loss correction voltage value) corresponding to the optical loss is determined using the DC component.

  Further, in the optical receiving unit in the fourth system, the output of the differential amplifier 56 a is branched and input to the demodulator 57 through the bandpass filter 58, and the digital data of the additional correction value is restored in the demodulator 57. The MPU 56c inputs this via the I / O port, performs additional correction on the optical propagation loss correction voltage value with the input additional correction value, and obtains a final correction voltage value.

  In the configuration of the optical receiver 60 in FIG. 5 and the above description, a so-called voice band modem is assumed as the modulator 54 on the master station side, but the modulation method is not limited to this, and other than that, Frequency multiplexing (FDM) that is modulated by a high-frequency signal having a frequency different from the frequency f1 of the RF signal to be transmitted, code area multiplexing that is multiplexed at the same frequency, or multiplexing with the baseband serial bit string as it is Multiplexing with various electric signals is possible.

  Further, as indicated by a dotted line in FIG. 5, the setting device 17 is directly connected to the I / O port of the integrated automatic correction unit 56 of the optical receiver 60 of the slave station apparatus, and the third embodiment is used. The remote operation from the master station device and the local operation at the slave station device can be used properly according to the situation at that time.

  According to the optical transmission system of the fourth embodiment of the present invention, in the optical transmitter 51 of the master station device, the additional correction value corresponding to each slave station device input from the setting device 17 ′ is set to I / O. The MPU 55 is input via the O port and converted into an appropriate data format. The modulation unit 54 modulates the frequency f2 and frequency-multiplexes it with the signal to be transmitted at the frequency f1, and the electric / optical conversion unit 53 The optical receiver 60 of the slave station device converts the optical signal into an RF signal by the light receiving element 61, amplifies the components other than the high frequency component by the DC amplification circuit 56a of the integrated automatic correction unit 56, The output is branched, and on the one hand, a light propagation loss correction voltage value is calculated based on the detected voltage value corresponding to the average received light power. F2 is taken out by the band pass filter 58 from the other branched one, and demodulated by the demodulator 57. MP for additional correction value The MPU 56c further corrects the light propagation loss correction voltage value based on the additional correction value, and outputs the final correction value to the D / A converter 56d. The obtained control voltage Vc is variable in voltage control. Since it is applied to the RF attenuator 16, it is possible to perform individual additional correction according to the installation conditions for each slave station by remote control from the master station device, and to output a demodulated signal for each slave station device. The level variation can be eliminated, and the setting of the correction voltage Vb is performed separately from the calculation process of the light propagation loss correction voltage value, so that the parameter setting of the processing of the light propagation loss correction voltage value is not affected. Fine adjustment is possible, and there is an effect that maintenance during operation can be facilitated.

Next, an optical transmission system (fifth system) according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 6 is a configuration block diagram of an optical transmission system (fifth system) according to the fifth embodiment of the present invention. FIG. 6 shows only the downstream direction of the fifth optical transmission system.
Similar to the fourth system described above, the fifth system transmits additional correction value information from the master station apparatus side. However, WDM (Wavelength Division Multiplex: wavelength), which is one of optical transmission methods, is used. (Region multiplexing) method is used. The basic configuration of the fifth system is the same as that of the general optical transmission system shown in FIG. 7, but the configurations and operations of the master station device and the slave station device are partially different from each other.

  As shown in FIG. 6, the optical transmission unit 51 of the master station device in the fifth system converts an RF signal to be originally transmitted and an RF signal to be originally transmitted into an optical signal having a wavelength λ1. A first electric / optical converter (E / O (1)) 53, an MPU 55 connected to a setting device 17 'via an input / output interface (I / O), and modulation for modulating output data from the MPU 55 Unit 54, a second electrical / optical converter (E / O (2)) 66 for converting data from modulator 54 into an optical signal with wavelength λ2, an optical signal with wavelength λ1, and an optical signal with wavelength λ2 And a WDM multiplexing coupler 65 for synthesizing the two. When a plurality of slave station devices are connected to the master station device, the setting device 17 ′ adds an identification number for identifying the slave station device to the additional correction value and outputs the added correction value. It has become.

  The optical receiving unit 60 of the slave station apparatus in the fifth system is substantially the same as the optical receiving unit in the fourth system, but the combined optical signal input from the optical fiber 62 is converted into wavelengths λ1 and λ2. A WDM demultiplexing coupler 67, a second optical / electrical converter (O / E (2)) 68 that converts an optical signal having a wavelength λ2 into an electrical signal, and a second optical / electrical converter (O / E (2)) 68 is provided.

  That is, in the fifth system, the signal including the transmission data and the signal including the data of the additional correction value are converted into optical signals of different wavelengths, synthesized, and transmitted to the slave station device. The optical receiving unit separates and demodulates each wavelength, and corrects the optical propagation loss correction voltage value based on the demodulated additional correction value.

The operation in the fifth system will be described with reference to FIG.
In the optical transmission unit of the master station apparatus of the fifth system, the RF signal to be originally transmitted is amplified by the amplifier 52 with a predetermined amplification factor, and the first electric / optical conversion unit (E / O (1)) 53 is obtained. Is converted to an optical signal of wavelength λ1.

On the other hand, the additional correction value data input from the setting device 17 is input to the MPU 55 of the optical transmission unit 51 via the I / O, converted into a data format suitable for optical transmission, and then modulated by the modulator 54. Then, the second electrical / optical conversion unit (E / O (2)) 66 converts the optical signal into an optical signal having a wavelength λ2.
Then, the λ1 optical signal and the λ2 optical signal are combined by the WDM multiplexing coupler 65 of the optical transmission unit 51 and transmitted to the optical reception unit 60 of the slave station apparatus through the optical fiber 62.

  The transmitted optical signal is separated into λ1 and λ2 optical signals by the WDM demultiplexing coupler 67, and converted into electrical signals by conversion units corresponding to the wavelengths. That is, similarly to the fourth light receiving circuit, the optical signal of λ1 is photoelectrically converted by the optical / electrical converter (light receiving element) 61, and the optical signal of λ2 is converted into an electrical signal by the second optical / electrical converter 68. Is converted to

  The signal including the transmission data converted by the optical / electrical converter 61 is amplified by the amplifiers 10 and 15 through the capacitor 2 as in the fourth system, and finally gain adjustment is performed by the voltage controlled variable RF attenuator 16. And output as an RF output.

  On the other hand, the signal converted by the second optical / electrical converter 68 is demodulated by the demodulator 57 and restored to the data of the additional correction value, and is input to the MPU 56c of the integrated automatic controller 56 via the I / O. The Then, the MPU 56c corrects the additional correction value with respect to the light propagation loss correction voltage value obtained based on the level of the DC component input from the A / D conversion unit 56b in the same manner as the third light receiving circuit. An operation is performed to obtain a final correction voltage value. The control voltage Vc based on the final correction voltage value is applied to the voltage control variable RF attenuator 16 to finely adjust the gain according to the installation conditions of the slave stations.

In these procedures, a communication protocol related to control signal transmission between the master station device and the slave station device is determined in advance, and a program is provided in the MPU of both devices so that the operation according to the protocol is performed. is there.
Similarly to the fourth system, the setting device 17 is connected to the MPU 56c of the integrated automatic correction unit 56 of the slave station device so that both remote control from the master station and local control at the slave station can be performed. You may be able to do it.

  According to the optical transmission system of the fifth embodiment of the present invention, in the optical transmission unit 51 of the master station apparatus, the first electrical / optical conversion unit 53 transmits the RF signal including the data to be transmitted to the wavelength λ1. The MPU 55 receives the additional correction value corresponding to each slave station apparatus input from the setting unit 17 ′ and converts it into an appropriate data format, and the second electrical / optical converter 66. Is converted into an optical signal of wavelength λ2, and the WDM multiplexing coupler 65 combines and transmits the optical signal of wavelength λ1 and the optical signal of wavelength λ2, and the optical receiver 60 of the slave station apparatus demultiplexes the WDM signal. The coupler 67 separates the optical signal of λ1 and the optical signal of λ2, converts the optical signal of λ1 into an electrical signal by the light receiving element 61, and based on the DC component, the MPU 56c of the integrated automatic correction unit 56 performs optical propagation loss. While calculating the correction voltage, the optical signal of λ2 is converted to the second optical / electrical The signal is converted into an electric signal by the conversion unit 68, demodulated by the demodulator 57, and the additional correction value is input to the MPU 56c. The MPU 56c further corrects the optical propagation loss correction voltage value based on the additional correction value, and the final correction value Is output to the D / A converter 56d, and the obtained control voltage Vc is applied to the voltage controlled variable RF attenuator 16. Therefore, the remote station can remotely control the installation conditions for each slave station. Individual additional corrections can be performed in accordance with the output level of the demodulated signal for each slave station device, and the correction voltage Vb can be set separately from the optical propagation loss correction voltage value calculation process. Therefore, there is an effect that fine adjustment can be performed without affecting the parameter setting of the processing of the light propagation loss correction voltage value, and maintenance during operation can be facilitated.

  The present invention provides a light receiving circuit and an optical transmission system capable of easily and finely adjusting a correction value for controlling a gain of an output level of a demodulated signal based on an optical propagation loss according to an installation condition for each slave station. Is suitable.

FIG. 1 is a block diagram showing a configuration of a light receiving circuit (first light receiving circuit) according to the first embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a light receiving circuit (second light receiving circuit) according to the second embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of a light receiving circuit (third light receiving circuit) according to the third embodiment of the present invention. FIG. 4 is a flowchart showing processing in the MPU 14c of the integrated automatic correction unit 14 of the third light receiving circuit. FIG. 5 is a configuration block diagram of an optical transmission system (fourth system) according to the fourth embodiment of the present invention. FIG. 6 is a configuration block diagram of an optical transmission system (fifth system) according to the fifth embodiment of the present invention. FIG. 7 is a schematic configuration diagram of an analog optical transmission system for mobile communication.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Light receiving element, 2 ... Capacitor 3, 7, 9 ... RF load resistance, 4 ... Inductor, 5, 6 ... Capacitor, 8 ... Detection resistance, 10 ... First stage amplifier, 11 ... Voltage control type variable gain amplifier, 12 ... Optical propagation loss correction unit, 13 ... Control voltage correction unit, 14 ... Integrated automatic correction unit, 15 ... Fixed gain amplifier, 16 ... Voltage controlled variable RF attenuator, 17, 17 '... Setting device, 21 ... Optical transmission master station device , 22, 31 ... Electric / optical converter, 23, 30 ... Optical / electric converter, 24, 25, 32, 33 ... Amplifier, 26 ... Radio modulator / demodulator, 27, 28 ... Optical fiber, 29 ... Optical transmission slave station Device 34: antenna duplexer 35 ... antenna 36 mobile radio terminal 51 optical transmission unit 52 amplification unit 53 (first) electrical / optical conversion unit 54 modulation unit 55 MPU , 56 ... Integrated automatic correction unit 57 ... Demodulation unit 58 ... Band pass filter 61 ... First optical / electrical conversion unit 62 ... Optical fiber 65 ... WDM multiplexing coupler 66 ... Second electrical / optical conversion unit 67 ... WDM demultiplexing coupler, 68 ... second optical / electrical converter

Claims (2)

An optical / electrical converter that converts the received optical signal into an electrical signal;
An amplifying unit that amplifies and outputs a high-frequency component of the electrical signal converted by the optical / electrical conversion unit with a gain based on an applied control voltage;
Detecting an average received light level based on a direct current component of the electrical signal converted by the optical / electrical converter, and obtaining a light propagation loss correction voltage for adjusting a gain in the amplifying unit according to the average received light level; A light receiving circuit including a correction unit that outputs a control voltage,
The light receiving circuit, wherein the correction unit is a correction unit that additionally corrects the light propagation loss correction voltage based on an external setting and outputs the correction voltage as a control voltage. An optical transmission system comprising: a master station device having an optical transmitter that transmits an optical signal; and a slave station device having the light receiving circuit according to claim 1,
Light that is transmitted from the same optical fiber by the optical transmission unit of the master station device multiplexed from the original transmission signal with a signal including an additional correction value that is set by an external setting device and specifies the correction amount of additional correction A transmission unit,
The light receiving circuit of the slave station device receives the optical signal transmitted from the master station device, separates and demodulates the original transmission signal and the signal including the additional correction value, and in the correction unit, An optical transmission system, which is a light receiving circuit that additionally corrects an optical propagation loss correction voltage based on a demodulated additional correction value and outputs it as a control voltage.

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