JP2005269194A - Optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enlarge the dynamic range of an input light level monitor by a simple circuit configuration in an optical receiver having a variable optical attenuator and a photodetecting element. <P>SOLUTION: The optical receiver includes the variable optical attenuator 7 which attenuates input light based on an attenuation amount control value, a photodetecting element 8 which photodetects the output light of the variable optical attenuator 7, a current/voltage converter circuit 9 as a monitor means for monitoring the input light level to the photodetecting element, a variable optical attenuator control circuit 10 which obtains the attenuation amount control value according to the monitor output to output the attenuation amount control value to the variable optical attenuator 7, an attenuation amount calculating circuit 11 for converting the attenuation amount control value inputted from the variable optical attenuator control circuit 10 into a corresponding attenuation amount, and an adder circuit 12 which adds the converted attenuation amount and the monitor output to output the added result as an input light level monitor signal to the optical receiver. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical receiver having a variable optical attenuator and a light receiving element, and more particularly to an optical receiver having a function of monitoring an input light level to the optical receiver.

  In an optical fiber communication system, a variable optical attenuator is used to secure a dynamic range of the system. In particular, in systems using optical amplifiers such as wavelength division multiplexing (WDM) communication and erbium-doped optical fiber amplifiers, which have been applied in recent years with the increase in capacity and distance of systems, the amplification gain between each wavelength of the optical amplifier Since a level difference occurs for each wavelength due to variations in band characteristics and transmitter output levels, it is necessary to insert a variable optical attenuator to ensure a dynamic range.

  When a variable optical attenuator is inserted, there are problems in that the attenuation needs to be adjusted for each wavelength, and that readjustment is required when the wavelength is increased or decreased, or when the wavelength interval is changed. For this reason, an optical receiver in which a variable optical attenuator and a light receiving element are integrated may perform feedback control for adjusting the attenuation amount of the variable optical attenuator according to the input optical signal level.

  As a function of the optical receiver, it is necessary to monitor the input light level in order to monitor the transmission path state of the system. As a method for monitoring the input light level, it is common to monitor the current flowing through the light receiving element.

  For example, in the invention described in Patent Document 1, feedback control is performed to adjust the attenuation amount of the variable optical attenuator according to the input optical signal level, and the current flowing through the light receiving element is monitored in order to monitor the input optical level. ing.

JP 07-79203 A

  When monitoring an input light level in an optical receiver in which a variable optical attenuator and a light receiving element are integrated, in the conventional technique described in Patent Document 1, when the input light level becomes high, the variable optical attenuator operates and the attenuation is performed. Since the input light level to the optical receiver and the input light level to the light receiving element are different by an amount, there is a problem that the dynamic range of the optical input level monitor is narrowed.

  The present invention has been made in view of the above, and an object of the present invention is to obtain an optical receiver that can monitor an input light level with a simple circuit configuration and can also obtain the same dynamic range as the input light level. To do.

  To achieve the above object, an optical receiver according to the present invention includes a variable optical attenuator that attenuates input light based on an attenuation control value, a light receiving element that receives output light from the variable optical attenuator, An optical receiver comprising: monitoring means for monitoring an input light level to an element; and variable optical attenuator control means for obtaining an attenuation amount control value corresponding to a monitor output of the monitoring means and outputting the attenuation amount control value to the variable optical attenuator. The attenuation control value input from the variable optical attenuator control means is converted into a corresponding attenuation amount, the converted attenuation amount and the monitor output of the monitor means are added, and the addition result is sent to the optical receiver. Input light level monitor signal generation means for outputting as an input light level monitor signal.

  According to the present invention, the input light level to the optical receiver can be monitored as the addition result of the input light level to the light receiving element and the attenuation amount of the variable optical attenuator, thereby enabling input with a simple circuit configuration. The dynamic range of the optical level monitor can be expanded, and the transmission path state of the system can be monitored with higher accuracy.

  Embodiments of an optical receiver according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 shows a configuration of a wavelength division multiplexing (WDM) optical fiber communication system as an example to which an optical receiver according to the present invention is applied. In FIG. 1, a plurality of optical transmitters 1 (1-1 to 1-n) are connected to an input terminal of a multiplexer 2. The output end of the multiplexer 2 is connected to the input end of one optical fiber 5 as an optical transmission line, and is connected to the optical amplifier 6 at every relay interval. The output end of the optical fiber 5 is connected to the duplexer 3, and the output end of the duplexer 3 is connected to a plurality of optical receivers 4 (4-1 to 4-n).

  The plurality of optical transmitters 1-1 to 1-n output optical modulation signals having predetermined optical output wavelengths λ1 to λn according to the transmission path and communication method, respectively. The multiplexer 2 multiplexes a plurality of optical modulation signals from the optical transmitters 1-1 to 1-n in order to enable transmission of a plurality of optical modulation signals through one optical fiber 5. The optical fiber 5 transmits the multiplexed optical modulation signal. Each optical amplifier 6 amplifies the optical modulation signal attenuated by the optical fiber 5. The duplexer 3 separates the multiplexed optical modulation signal received via the optical fiber 5 for each wavelength. The optical receivers 4-1 to 4-n demodulate the input optical modulation signal for each wavelength.

  FIG. 2 shows an internal configuration of the optical receiver 4 (4-1 to 4-n) shown in FIG. The optical receiver 4 includes a variable optical attenuator 7, a light receiving element 8, a current-voltage conversion circuit 9, a variable optical attenuator control circuit 10, an attenuation calculation circuit 11, and an addition circuit 12.

  The variable optical attenuator 7 can vary the attenuation amount according to the variable optical attenuator control value from the variable optical attenuator control circuit 10, and is, for example, a mechanical type, a magneto-optical system, or a micro electro mechanical system (MEMS). There are methods. In particular, since the MEMS system can be easily downsized, a small optical receiver can be realized.

  The light receiving element 8 is configured by a photodiode (PD) or an avalanche photodiode (APD), and a current proportional to the input light level flows. The light receiving element 8 has a characteristic that the current increases as the input light level increases, and the current decreases as the input light level decreases.

  The current-voltage conversion circuit 9 is configured by a resistor, for example. The current flowing through the light receiving element 8 is converted into a voltage by the current-voltage conversion circuit 9, a voltage proportional to the input light level is output, and the input light level to the light receiving element 8 is monitored. Hereinafter, the output of the current-voltage conversion circuit 9 is referred to as a light receiving element input light level monitor signal.

  The variable optical attenuator control circuit 10 uses the light receiving element input light level monitor signal output from the current-voltage conversion circuit 9 to change the input light level to the light receiving element 8 within the operating range of the light receiving element 8. This circuit determines an optical attenuator control value, and is realized by, for example, an error amplifier circuit using an operational amplifier. Since the variable optical attenuator control value is determined so that the error signal between the reference voltage and the light receiving element input light level monitor signal becomes 0, when the input light level to the light receiving element 8 increases, the variable optical attenuator attenuates. When the amount of light input to the light receiving element 8 is reduced, the amount of light input to the light receiving element 8 is within the operating range of the light receiving element 8 by reducing the attenuation of the variable optical attenuator. It is controlled as follows.

  The attenuation amount calculation circuit 11 is a circuit that calculates the attenuation amount of the variable optical attenuator 7 using the variable optical attenuator control value output from the variable optical attenuator control circuit 10, and is a voltage using an operational amplifier, for example. This is realized by a level conversion circuit. The attenuation amount of the variable optical attenuator 7 is monitored from the output voltage of the attenuation amount calculation circuit 11. Hereinafter, the output of the attenuation calculation circuit 11 is referred to as a variable optical attenuator attenuation monitor signal. For example, in the case of the variable optical attenuator 7 having such a characteristic that the amount of attenuation increases when the variable optical attenuator control value increases, the output of the attenuation amount calculation circuit 11 increases as the variable optical attenuator control value increases. When the voltage is increased and the attenuation becomes smaller when the variable optical attenuator 7 has a larger variable optical attenuator control value, the attenuation calculation circuit 11 increases as the variable optical attenuator control value increases. Reduce the output voltage.

  The adder circuit 12 is a circuit that adds the light receiving element input light level monitor signal output from the current-voltage conversion circuit 9 and the variable optical attenuator attenuation amount monitor signal output from the attenuation amount calculation circuit 11, for example, an operational amplifier This is realized by an adder circuit using.

  An operation example in the first embodiment will be described with reference to FIGS. 3-1 to 3-3. 3A, the input light level to the light receiving element 8 is indicated by a solid line, the attenuation amount of the variable optical attenuator 7 is indicated by a broken line, and the horizontal axis indicates the input light level to the optical receiver 4. . 3-2, the light receiving element input light level monitor signal is indicated by a solid line, the variable optical attenuator attenuation amount monitor signal is indicated by a broken line, and the horizontal axis indicates the input light level to the optical receiver 4. In FIG. 3C, the vertical axis indicates the input light level monitor signal, the horizontal axis indicates the input light level to the optical receiver 4, the solid line indicates the monitor value according to the present invention, and the broken line indicates the monitor according to the prior art. The value is shown.

  In the region where the input light level to the optical receiver 4 is low, the attenuation amount of the variable optical attenuator 7 is 0 as shown by the broken lines in FIGS. 3A and 3B. The input light level to the detector 4 and the input light level to the light receiving element 8 are the same.

  In the region where the input light level to the optical receiver 4 is higher, the attenuation amount of the variable optical attenuator 7 increases as the input light level to the optical receiver 4 becomes higher. As indicated by the solid line in FIG. 3B, the input light level to the light receiving element 8 is constant. That is, in this region, the optical input light level to the optical receiver 4 and the input light level to the light receiving element 8 are different by the attenuation amount of the variable optical attenuator 7. Therefore, in the conventional input light level monitor signal, as shown by the broken line in FIG. 3C, the signal is constant in the region where the input light level to the optical receiver 4 is high.

  On the other hand, in the first embodiment, the light receiving element input light level monitor signal output from the current-voltage conversion circuit 9 and the variable optical attenuator attenuation monitor signal output from the attenuation calculation circuit 11 by the adder circuit 12. Therefore, as shown by the solid line in FIG. 3C, the monitor value of the input light level monitor signal increases as the input light level to the optical receiver 4 increases. Therefore, in the first embodiment, the input light level to the optical receiver 4 can be monitored with high accuracy by the input light level monitor signal that is the output of the adder circuit 12.

  As described above, in the first embodiment, the result of adding the light receiving element input light level monitor signal output from the current-voltage conversion circuit 9 and the variable optical attenuator attenuation monitor signal output from the attenuation calculation circuit 11. Is used as the input light level monitor signal, so that the input light level to the receiver can be reliably monitored even when the input light level is high and the input light level is attenuated by the variable optical attenuator 7. With this, the dynamic range of the input light level monitor can be expanded with a simple circuit configuration.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a diagram illustrating an internal configuration of the optical receiver 4 according to the second embodiment.

  4, a microcomputer 13 is provided in place of the attenuation calculation circuit 11 and the addition circuit 12 in the configuration of the first embodiment shown in FIG. In the constituent elements shown in FIG. 4, the same reference numerals are given to the constituent elements that basically perform the same operations as the constituent elements in FIG.

  The microcomputer 13 includes a memory that stores and holds information and a CPU that performs various controls and calculations. As shown in FIG. 5, the memory stores and holds the relationship between the variable optical attenuator control value and the attenuation amount of the variable optical attenuator 7 in advance. The CPU reads the attenuation amount corresponding to the input variable optical attenuator control value from the memory, and adds the read attenuation amount to the light receiving element input light level monitor signal.

  That is, the microcomputer 13 reads the variable optical attenuator control value output from the variable optical attenuator control circuit 10, refers to the memory in the microcomputer 13, and the variable optical attenuator 7 corresponding to the corresponding variable optical attenuator control value. Attenuation amount, that is, a variable optical attenuator attenuation monitor signal is derived, and the derived variable optical attenuator attenuation monitor signal is added to the light receiving element input light level monitor signal output from the current-voltage conversion circuit 9, The addition result is output as an input light level monitor signal.

  FIG. 5 shows an example of the relationship between the variable optical attenuator control value and the attenuation amount of the variable optical attenuator 7 stored in advance in the memory. FIG. 6 shows an example of the variable optical attenuator control value and the attenuation amount of the variable optical attenuator 7.

  As shown in FIG. 6, since the relationship between the variable optical attenuator control value and the attenuation amount of the variable optical attenuator 7 is generally not linear, the voltage level conversion circuit using the operational amplifier shown in the first embodiment is used. When the attenuation calculation circuit 11 is configured, a compensation circuit is further required to monitor the input light level with high accuracy. Further, since there is a component variation in the relationship between the variable optical attenuator control value and the attenuation amount of the variable optical attenuator 7, it is necessary to cope with this variation during mass production.

  In the second embodiment, even if the relationship between the variable optical attenuator control value and the attenuation amount of the variable optical attenuator 7 is not linear or varies by rewriting the in-memory data 14 of the microcomputer 13 as described above. Therefore, it is possible to easily obtain a highly accurate input light level monitor.

  As described above, in the second embodiment, the light receiving element input light level monitor signal output from the current-voltage conversion circuit 9 and the variable optical attenuator control value output from the variable optical attenuator control circuit 10 are used. Since the input light level monitor signal is formed in the microcomputer 13, even when the input light level is high and the input light level is attenuated by the variable optical attenuator 7, it is possible to accurately monitor the input light level. The dynamic range of the input light level monitor can be expanded with a simple circuit configuration, and a highly accurate input light level monitor can be obtained.

  As described above, the optical receiver according to the present invention is an optical receiver having a variable optical attenuator and a light receiving element in a system to which an optical amplifier such as wavelength division multiplexing (WDM) communication or an erbium-doped optical fiber amplifier is applied. Useful for.

It is a block diagram which shows the structure of the WDM optical fiber communication system as an example to which this invention is applied. It is a block diagram which shows the internal structure of Embodiment 1 of the optical receiver of this invention. It is a figure which shows the relationship between the input light level to a light receiving element, the attenuation amount of a variable optical attenuator, and the input light level to an optical receiver. It is a figure which shows the relationship between a light receiving element input light level monitor signal, a variable optical attenuator attenuation amount monitor signal, and the input light level to an optical receiver. It is a figure which shows the relationship between the input light level monitor signal by this invention, and the input light level of the optical receiver 4. FIG. It is a block diagram which shows the internal structure of Embodiment 2 of the optical receiver of this invention. 6 is a diagram illustrating an example of in-memory data according to Embodiment 2. FIG. It is a figure which shows an example of the variable optical attenuator control value and the attenuation amount of a variable optical attenuator.

Explanation of symbols

1 Optical transmitter,
2 multiplexer,
3 duplexer,
4 Optical receiver,
5 optical fiber,
6 Optical amplifier,
7 Variable optical attenuator,
8 light receiving element,
9 Current-voltage conversion circuit,
10 Variable optical attenuator control circuit,
11 Attenuation calculation circuit,
12 adder circuit,
13 Microcomputer (microcomputer),
14 Data in memory.

Claims (3)

A variable optical attenuator that attenuates the input light based on the attenuation control value;
A light receiving element that receives the output light of the variable optical attenuator;
Monitoring means for monitoring the input light level to the light receiving element;
A variable optical attenuator control means for obtaining an attenuation control value corresponding to the monitor output of the monitor means and outputting the attenuation control value to the variable optical attenuator;
In an optical receiver comprising:
The attenuation control value input from the variable optical attenuator control unit is converted into a corresponding attenuation amount, the converted attenuation amount and the monitor output of the monitor unit are added, and the addition result is sent to the optical receiver. An optical receiver comprising input light level monitor signal generation means for outputting as an input light level monitor signal. The input light level monitor signal generating means; an attenuation amount calculating means for converting the attenuation amount control value into a corresponding attenuation amount;
Adding means for adding the converted attenuation amount and the monitor output of the monitoring means;
The optical receiver according to claim 1, further comprising: The attenuation amount calculating means includes
A memory storing the attenuation control value and attenuation;
Means for reading out the attenuation corresponding to the attenuation control value input from the variable optical attenuator control from the memory;
The optical receiver according to claim 2, further comprising:

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