JP4957567B2 - Optical receiver - Google Patents

Description

  The present invention relates to an optical receiver that does not require a determination threshold for identifying a received digital optical signal to be changed according to a transmission source.

  In a PON optical communication system (PON: Passive Optical Network), high-speed data communication is performed between a station-side terminal device (OLT: Optical Line Terminal) and a plurality of subscriber-side devices (ONU: Optical Network Unit). Sharing the station-side termination device and the optical fiber with a plurality of subscribers by providing an optical splitter in the middle of the optical fiber connecting the station-side termination device and the subscriber-side device and branching the transmission path into a plurality of paths Is possible.

  The downlink signal transmitted from the station-side terminal device is transmitted to all the subscriber-side devices, and each subscriber-side device receives only necessary signals separately. Each subscriber-side device generates a clock signal based on the received downlink signal, and transmits an upstream signal (burst signal) synchronized with the generated clock signal to the station-side terminal device. In order to prevent uplink signals transmitted from each subscriber side apparatus from colliding with each other, a time division multiplexing system is used.

  In such a PON optical communication system, the transmission loss varies depending on the transmission distance between each subscriber-side device and the station-side terminating device, so the strength of the signal transmitted by each subscriber-side device is constant. Even so, the strength of the signal received by the station-side terminal device varies depending on the subscriber-side device as the transmission source.

Therefore, in the station-side terminal device, in order to identify the logical level (1 or 0) of the received signal, it is necessary to change the identification threshold according to the subscriber-side device. Therefore, conventionally, when a burst optical signal is received, the time average of the level at the time of light emission (high level) and the level at the time of extinction (low level) are calculated from the received burst optical signal, and the calculated time average The threshold value is set based on the above.
JP 2003-304202 A Japanese Patent No. 3802232 Japanese Patent No. 3042608

  However, as described above, when the threshold is set based on the time average during the light emission and extinction of the optical signal, when the duty ratio is close to 50%, the threshold is around the central value between the high level and the low level. It is possible to determine the logic level of the signal well, but when the duty ratio deviates from 50%, the optical reception level apparently shifts to the high level side rather than the center between the high level and the low level. Or shift to the low level side. Therefore, when the threshold value is set when the duty ratio is deviated from 50%, the logic level of the signal cannot be correctly determined, and the bit error rate is increased.

  The present invention has been made in view of such circumstances, and the threshold for identifying a digital optical signal is a value between two signal levels corresponding to a high level and a low level. An object of the present invention is to provide an optical receiving apparatus that can reduce the bit error rate by setting the reception sensitivity to be not required to set a threshold according to the transmission source.

An optical receiver according to the present invention includes a receiving unit that receives digital optical signals transmitted from a plurality of optical transmitters , and a photoelectric conversion unit that converts the digital optical signals received by the receiving unit into electrical signals. And an optical receiver for identifying the digital optical signal by comparing the magnitude of the electrical signal converted by the photoelectric conversion means and a preset threshold value, corresponding to the high level and the low level from the electrical signal. detecting means for detecting the two signal levels, means for identifying the reception level and the extinction ratio of the optical signal based on two signal levels detected, on the basis of the reception level and the extinction ratio, the threshold value is the two And a control means for controlling the receiving sensitivity of the photoelectric conversion means so as to be a value between signal levels.

In the present invention, the threshold for identifying the digital optical signal is calculated or selected from the two signal levels such that the threshold value is a value between the two signal levels corresponding to the high level and the low level . Since the reception sensitivity of the digital optical signal is controlled based on the specified reception level and extinction ratio, when the difference between the high level and the low level is small, the reception sensitivity is controlled to increase the high level. It is possible to widen the difference between the level and the low level. As a result, a constant value can be used as a threshold value for identifying the digital optical signal. The threshold value for identifying the received digital optical signal is a value that does not depend on the duty ratio.

Optical receiving device according to the present invention, the photoelectric conversion means comprises an avalanche photodiode which changes the multiplication factor by a bias voltage, said control means comprising means for varying the bias voltage of the avalanche photodiode And

  In the present invention, the reception sensitivity is controlled by changing the bias voltage of the avalanche photodiode.

The optical receiving apparatus according to the present invention is characterized in that the photoelectric conversion means includes an optical amplifier capable of controlling gain, and the control means includes means for controlling the gain of the optical amplifier.

  In the present invention, the reception sensitivity is controlled by controlling the gain of the optical amplifier.

Optical receiving device according to the present invention includes means for determining the reception sensitivity of the photoelectric conversion means for each optical transmission device on the basis of the digital optical signals it receives, the receiver sensitivity was determined identification information for identifying the optical transmission device Storage means for storing the information in association with each other, means for specifying the optical transmission apparatus that is the transmission source of the digital optical signal when receiving the digital optical signal, and reception stored in association with the identification information of the specified optical transmission apparatus characterized in that it comprises means for reading the sensitivity from the storage means, and means for controlling the Ki受 signal sensitivity before based on the reception sensitivity reading.

  In the present invention, since the determined reception sensitivity is stored in association with the optical transmission device, the reception sensitivity can be switched according to the transmission source when a digital optical signal is received.

In the case of the present invention, the threshold value for identifying the digital optical signal transmitted from each of the plurality of optical transmission devices corresponds to the high level and the low level according to the reception level and extinction ratio corresponding to each optical transmission device. Since the reception sensitivity of the digital optical signal is controlled so that the value is between the two signal levels, the reception sensitivity is controlled when the difference between the high level and the low level is small. It is possible to widen the difference between the high level and the low level. As a result, a constant value can be used as a threshold value for identifying the digital optical signal. Further, the threshold value for identifying the received digital optical signal can be a value that does not depend on the duty ratio. As a result, the bit error rate can be kept low regardless of the state when the threshold is set.

  In the case of the present invention, since the reception sensitivity is controlled by changing the bias voltage of the avalanche photodiode, for example, control using a calculation means such as a CPU becomes possible. The method for controlling the reception sensitivity using the ratio between the high level and the low level according to the present invention is a method for controlling the reception sensitivity by detecting a commonly used reception level (average value between the high level and the low level). Since the bias voltage of the avalanche photodiode can be finely controlled as compared with the above, reception sensitivity can be finely controlled.

  In the case of the present invention, since the reception sensitivity is controlled by controlling the gain of the optical amplifier, for example, control using an arithmetic means such as a CPU becomes possible. The method for controlling the reception sensitivity using the ratio between the high level and the low level according to the present invention is a method for controlling the reception sensitivity by detecting a commonly used reception level (average value between the high level and the low level). Since the bias voltage of the avalanche photodiode can be finely controlled as compared with the above, reception sensitivity can be finely controlled.

  According to the present invention, since the determined reception sensitivity is stored in association with the optical transmission device, the reception sensitivity is switched according to the transmission source when a digital optical signal is received. Since the reception level of digital optical signals does not change frequently, the relationship between the transmission source and the reception sensitivity to be set is stored in the memory, and the reception sensitivity can be switched according to the value stored in the memory during operation. The load on the hardware can be reduced. In the present invention, it is not necessary to detect the reception level of high level and low level every time, and the control time of the reception sensitivity is dominant because the time to read from the memory is dominant.

  Hereinafter, an embodiment in which an optical receiving apparatus according to the present invention is applied to a station side terminal apparatus (OLT) of a PON optical communication system will be specifically described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing a schematic configuration of a PON optical communication system according to the present embodiment. In the figure, reference numeral 1 denotes a station-side terminator, and a plurality of subscriber-side devices 3 are connected to the station-side terminator 1 via optical fibers and a plurality of optical splitters 2. For example, a single fiber is used as an optical fiber for connecting the station-side terminal device 1 and the subscriber-side device 3, and two-way communication is performed by using optical signals having different wavelengths in the upstream and downstream directions. Is done. For example, the wavelength of the upstream optical signal is 1.31 μm, and the wavelength of the downstream optical signal is 1.55 μm.

  The downlink signal transmitted from the station-side terminal device 1 is transmitted to all the subscriber-side devices 3, and each subscriber-side device 3 separates and receives only the necessary signals. The subscriber side device 3 generates a clock signal based on the received downlink signal, and transmits an upstream signal (burst signal) synchronized with the generated clock signal to the station side terminal device 1. In order to prevent the uplink signals transmitted from the subscriber side apparatuses 3 from colliding with each other, a time division multiplexing system is used as the transmission system.

  FIG. 2 is a block diagram illustrating an internal configuration of the station-side termination device according to the first embodiment. The station side termination device 1 includes an upper layer circuit unit 10, a level conversion circuit 21, an LD driver 22 (LD: Laser Diode), an LD 23, a monitor photodiode 24 (hereinafter referred to as a monitor PD 24), and an APC circuit 25 (APC: Automatic). Power Control), WDM coupler 30 (WDM: Wavelength Division Multiplexing), avalanche photodiode 31 (hereinafter referred to as APD 31), preamplifier 32, post amplifier 33, signal level detector 34, APD bias voltage controller 41, APD bias power supply 42 is provided.

  The downstream transmission signal is given to the level conversion circuit 21 via the frame buffer 11 and the PHY 12 in the upper layer circuit unit 10, and after the signal level is stabilized by the level conversion circuit 21, it is input to the LD driver 22. The The LD driver 22 drives the LD 23 according to the output signal of the level conversion circuit 21, and an optical signal is input from the LD 23 to the WDM coupler 30. In addition, an APC circuit 25 is provided to stabilize the optical signal output from the LD 23. After a part of the output optical signal of the LD 23 is detected by the monitor PD for monitoring and converted into a DC electric signal, it is compared with a reference value in the APC circuit 25, and the output of the LD driver 22 is set so that the output optical signal becomes constant. Take control. Thereby, the optical signal output from LD23 can be stabilized. The WDM coupler 30 transmits the optical signal from the LD 23 to the subscriber side device 3 as a downlink transmission signal.

  An upstream signal (burst signal) received from the subscriber side device 3 is provided to the WDM coupler 30 via an optical fiber. The APD 31 converts the burst signal (optical signal) from the WDM coupler 30 into a current signal. The current signal converted by the APD 31 is converted by the preamplifier 32 into voltage signals corresponding to two levels of digital data “1” and “0”. The voltage signal output from the preamplifier 32 is amplified by a postamplifier 33 having an AGC (automatic gain control) function, and decoded by the PHY 12 of the upper layer circuit unit 10 for communication with other devices. The decoded signal is once buffered by the frame buffer 11, and the timing is adjusted by the upper layer circuit unit 10 and outputted to the outside.

  The station-side terminal device 1 according to the present embodiment is configured to detect a signal level of a received optical signal and control reception sensitivity based on the detected signal level. Specifically, the voltage signal output from the preamplifier 32 is input to the signal level detection unit 34, and the CPU 13 of the upper layer circuit unit 10 controls the APD bias voltage based on the signal level detected by the signal level detection unit 34. The reception sensitivity is controlled by controlling the unit 41 and controlling the bias voltage applied to the APD 31 by the APD bias power source 42.

  FIG. 3 is an explanatory diagram for explaining an example of control of the APD bias voltage by the station-side terminating device 1. FIG. 3A shows the reception level before the APD bias voltage is controlled. Since the reception level of the optical signal received by the station-side terminal device 1 differs for each subscriber-side device 3, a determination threshold value for identifying “1” or “0” of the digital signal is originally set as the subscriber-side device 3. It is necessary to set every time. In the example of FIG. 3A, the determination thresholds are set to Va, Vb, and Vc for the respective subscriber side devices, and the signal is identified.

  On the other hand, in the present embodiment, the signal level (high level) corresponding to the light emission is related to the optical signal transmitted from each subscriber apparatus 3 so that the determination threshold value does not have to be changed for each subscriber apparatus 3. ) And the signal level (low level) corresponding to the time of extinction are detected, and the reception sensitivity is controlled so that the determination threshold value to be set is a value between the two detected signal levels. More specifically, the reception level and extinction ratio of the optical signal are calculated based on the two detected signal levels, and the bias voltage applied to the APD 31 is controlled according to the calculated reception level and extinction ratio.

  FIG. 3B shows an example of control performed by the APD bias voltage control unit 41 and the APD bias power source 42. Regardless of the signal level of the optical signal transmitted from each subscriber side device 3, the APD is set so that the determination threshold value takes a value between a high level corresponding to “1” and a low level corresponding to “0”. The bias voltage control unit 41 controls the bias voltage applied to the APD 31. In the example shown in FIG. 3B, when the light reception level is strong and the extinction ratio is large, the bias voltage of the APD 31 is set to a small value. When the light reception level is weak and the extinction ratio is small, the bias voltage of the APD 31 is set to a large value.

  FIG. 3C shows the relationship between the reception level and the determination threshold value after the bias voltage of the APD 31 is controlled. By controlling the bias voltage of the APD 31 and setting the optical signal reception sensitivity for each subscriber side device 3 as described above, the optical signal reception level can be made approximately constant. The signal can be identified using V0.

  Regarding the bias voltage to be set, a rule may be set in advance with respect to the optical reception level and extinction ratio, and when receiving an optical signal, the rule may be applied to determine the bias voltage of the APD 31. Table 1 below shows an example of rules applied when determining the bias voltage of the APD 31.

  In the example shown in Table 1, the optical reception level and the extinction ratio are classified into three according to strength (magnitude), and the APD bias voltage is determined according to the strength of the optical reception level and the magnitude of the extinction ratio. ing. For example, when the optical reception level of the received optical signal is weak and the extinction ratio is small, the bias voltage of the APD 31 is set to V1. Further, when the optical reception level of the received optical signal is strong and the extinction ratio is large, the bias voltage of the APD 31 is determined to be V5. The bias voltage of the APD 31 is similarly determined when optical signals having other optical reception levels and extinction ratios are received. It should be noted that the strength of the light reception level and the magnitude of the extinction ratio can be classified using threshold values determined for each. That is, in the example shown in Table 1, it is possible to classify the optical reception level and the extinction ratio by using two threshold values.

  In Table 1, the bias voltage applied to the APD 31 is determined in advance so as to satisfy the relationship of V1> V2> V3> V4> V5. By controlling the reception sensitivity of the APD 31 using the bias voltage determined in this way, it is possible to perform control so as to widen the “eye” when creating an eye pattern of an optical signal. Regardless of 3, a constant determination threshold can be used.

  The rules as shown in Table 1 are stored as a table in the memory 14 of the upper layer circuit unit 10, for example. The CPU 13 of the upper layer circuit unit 10 reads this table from the memory 14 and determines the bias voltage to be applied to the APD 31 by applying it to the received signal (the detection result of the signal level detection unit 34), thereby controlling the APD bias voltage. The unit 41 can be controlled.

  In this embodiment, the APD bias voltage is determined by classifying the optical reception level and the extinction ratio into three according to strength (magnitude), respectively. However, the classification is not limited to three. That is. In this embodiment, the value of the APD bias voltage to be applied is determined in advance. However, the increase / decrease value may be set based on the current bias voltage.

  FIG. 4 is a flowchart for explaining a procedure of processing executed by the station-side terminal device 1 according to the first embodiment. When the station-side terminating device 1 receives an optical signal transmitted from each subscriber-side device 3, the received optical signal is converted into a current signal by an APD 31 to which a bias voltage is applied from an APD bias power source 42, and then by a preamplifier 32. Conversion into a voltage signal (step S11).

  The signal level detector 34 detects a signal level corresponding to a high level (referred to as Pon) and a signal level corresponding to a low level (referred to as Poff) from the voltage signal converted by the preamplifier 32 (step S12). . The detection result by the signal level detection unit 34 is notified to the CPU 13 and temporarily stored in the memory 14.

The CPU 13 calculates the reception level and extinction ratio of the received optical signal using the two signal levels (that is, Pon and Poff) detected by the signal level detection unit 34 (step S13). The value of Pon itself can be used as the reception level. The extinction ratio can be calculated by 10 × log ₁₀ (Pon / Poff). The extinction ratio indicates that the higher the ratio, the greater the margin for the code error rate BER (bit error rate).
The extinction ratio can be read out by creating a table in which the calculation result is written on the memory 14 at the address corresponding to the values of Pon and Poff according to the above formula. Further, as one embodiment of the present invention, a high level and a low level are detected from an electric signal output from the preamplifier 32 using a peak hold circuit and a bottom hold circuit, respectively, and a ratio value between the high level and the low level is detected. May be classified as shown in Table 1 (comparing a high level value and a low level value by a comparator circuit or the like). In this case, the system can be configured without calculating the value by directly applying the extinction ratio formula, and the circuit can be simplified and the scale can be reduced.

  Next, the CPU 13 reads a rule to be applied to the calculated light reception level and extinction ratio from the memory 14 and determines an APD bias voltage to be set (step S14). Then, the CPU 13 controls the APD bias voltage control unit 41 according to the determined value of the APD bias voltage, so that the bias voltage applied to the APD 31 by the APD bias power source 42 is the same as the APD bias voltage determined in step S14. Control is performed (step S15).

  As described above, in the present embodiment, the signal level (high level) corresponding to the light emission and the signal level (low level) corresponding to the extinction are detected for the optical signal transmitted from each subscriber side device 3, and the signal Since the reception sensitivity of the optical signal is controlled so that the determination threshold value for identifying the signal becomes a value between two detected signal levels, it is not necessary to change the determination threshold value for each subscriber apparatus 3. .

Embodiment 2. FIG.
In the first embodiment, the reception sensitivity is controlled by controlling the bias voltage applied to the APD 31 when an optical signal transmitted from each subscriber side device 3 is received. The reception level of the received optical signal does not change frequently. Therefore, a control period for controlling the reception sensitivity is provided, and the value of the bias voltage controlled in the control period is set for each subscriber unit 3. The reception sensitivity may be controlled according to the stored bias voltage value for each subscriber apparatus 3 during actual operation.

  Note that the configuration of the PON optical communication system and the internal configuration of the station-side termination device 1 are exactly the same as those in the first embodiment, and thus the description thereof is omitted. In this embodiment, it is assumed that the optical signal transmitted from each subscriber side device 3 includes identification information for identifying each subscriber side device 3.

  FIG. 5 is a flowchart for explaining a procedure of processing executed by the station-side terminal device 1 according to the second embodiment. First, the station-side terminal device 1 determines whether or not the present is the control period (step S21). The determination of whether or not it is the control period is made by determining whether or not the control period is designated by an external device (not shown) such as a personal computer connected to the upper layer circuit unit 10. Further, a switch for switching between the control period and the non-control period may be provided in the station-side terminal device 1, and it may be specified that the control period is set by this switch.

  When it is determined that the station-side terminal device 1 is in the control period (S21: YES), an instruction signal for transmitting a predetermined signal to the station-side terminal device 1 is transmitted to each subscriber-side device 3 (step) S22).

  When receiving the optical signal transmitted from a certain subscriber-side device 3, the station-side terminal device 1 converts the received optical signal into a current signal by the APD 31 to which a bias voltage is applied from the APD bias power source 42, and the preamplifier 32. Is converted into a voltage signal (step S23).

  A part of the voltage signal converted by the preamplifier 32 is amplified by the postamplifier 33, decoded by the PHY 12 of the upper layer circuit unit 10, and buffered in the frame buffer 11. The CPU 13 acquires identification information for identifying the transmission source of the optical signal from the signal buffered in the frame buffer 11 (step S24).

  Further, the signal level detection unit 34 detects a signal level corresponding to a high level (referred to as Pon) and a signal level corresponding to a low level (referred to as Poff) from the voltage signal converted by the preamplifier 32 (step S). S25). The detection result by the signal level detection unit 34 is notified to the CPU 13 and temporarily stored in the memory 14.

  The CPU 13 calculates the reception level and extinction ratio of the received optical signal using the two signal levels (that is, Pon and Poff) detected by the signal level detection unit 34 (step S26), and calculates the calculated optical reception level and A rule to be applied for the extinction ratio is read from the memory 14, and the APD bias voltage to be set is determined (step S27).

  Next, the CPU 13 stores the identification information acquired in step S24 and the APD bias voltage determined in step S27 in the memory 14 in association with each other (step S28). Table 2 below shows an example of a table storing the identification information of the subscriber side device 3 and the association of the APD bias voltage.

  In the example shown in Table 2, the bias voltage of the APD 31 is set to V1, V3, V5,... With respect to the subscriber side device 3 having identification information (ID) of “AA0001”, “AA0002”, “AA0003”,. Shown to set.

  Next, the CPU 13 determines whether or not the control period has ended (step S29). Whether or not the control period has ended is determined by determining whether or not the APD bias voltage has been determined for all the subscriber apparatuses 3. When it is determined that the control period has not ended (S29: NO), the processing of the station-side terminal device 1 returns to step S23.

  If it is determined in step S21 that it is not the control period (S21: NO), or if it is determined in step S29 that the control period has ended (S29: YES), a signal to permit transmission is sent to each subscriber side device 3. (Step S30).

  Next, the CPU 13 reads the value of the APD bias voltage set for each subscriber device 3 from the memory 14 in accordance with the reception timing of the transmission signal from each subscriber device 3 (step S31). Then, the CPU 13 controls the APD bias voltage control unit 41 according to the value of the read APD bias voltage, so that the bias voltage applied to the APD 31 by the APD bias power supply 42 becomes the read APD bias voltage. Control (step S32).

  Thus, in this embodiment, a control period for controlling the reception sensitivity of the optical signal is provided, and the reception sensitivity can be controlled using the APD bias voltage stored in the memory 14 in actual operation. It is not necessary to perform control every time an optical signal is received, and the load on the upper layer circuit unit 10 is reduced.

  In the first and second embodiments, the CPU 13 calculates the extinction ratio of the optical signal. However, the extinction ratio detection unit that detects the extinction ratio based on the voltage signal output from the preamplifier 32 may be separately provided. Good.

Embodiment 3 FIG.
In the first and second embodiments, the reception sensitivity is controlled by controlling the bias voltage applied to the APD 31, but the upstream optical signal input to the WDM coupler 30 is amplified by an optical amplifier. A configuration may be adopted in which reception sensitivity is controlled by controlling the gain of the optical amplifier.

  FIG. 6 is a block diagram illustrating an internal configuration of the station-side termination device 1 according to the third embodiment. The station-side termination device 1 according to the third embodiment includes an upper layer circuit unit 10, a level conversion circuit 21, an LD driver 22, an LD 23, a monitor PD 24, an APC circuit 25, a WDM coupler 30, a preamplifier 32, a post amplifier 33, a signal level. The detector 34, the optical amplifier 51, and the photodiode 52 are provided.

  The transmission procedure of the optical signal by the station side terminal device 1 is exactly the same as in the first embodiment. The upstream signal (burst signal) received from the subscriber side device 3 is applied to the WDM coupler 30 via an optical fiber, and the burst signal (optical signal) from the WDM coupler 30 is amplified by the optical amplifier 51. The As the optical amplifier 51, for example, an erbium-doped optical fiber amplifier (EDFA) can be used.

  The optical signal amplified by the optical amplifier 51 is converted into a current signal by the photodiode 52. The current signal converted by the photodiode 52 is converted into a voltage signal corresponding to two levels of digital data “1” and “0” by the preamplifier 32. The voltage signal output from the preamplifier 32 is amplified by a postamplifier 33 having an AGC (automatic gain control) function, and decoded by the PHY 12 of the upper layer circuit unit 10 for communication with other devices. The decoded signal is temporarily buffered by the frame buffer 11, and the timing is controlled by the CPU 13 to be output to the outside.

  The voltage signal output from the preamplifier 32 is input to the signal level detection unit 34, and the CPU 13 of the upper layer circuit unit 10 controls the gain of the optical amplifier 51 based on the signal level detected by the signal level detection unit 34. Thus, the reception sensitivity of the optical signal is controlled.

  The control method is the same as in the first embodiment, and for the optical signal transmitted from each subscriber side device 3, the signal level (high level) corresponding to light emission and the signal level (low level) corresponding to light extinction are set. The reception sensitivity is controlled so that the determination threshold value to be detected is set to a value between the two detected signal levels. More specifically, the optical signal reception level and extinction ratio are calculated based on the two detected signal levels, and the gain of the optical amplifier 51 is controlled according to the calculated reception level and extinction ratio. Controls signal reception sensitivity.

It is a schematic diagram which shows schematic structure of the PON optical communication system which concerns on this embodiment. 3 is a block diagram illustrating an internal configuration of a station-side termination device according to Embodiment 1. FIG. It is explanatory drawing explaining the example of control of the APD bias voltage by a station side termination | terminus apparatus. 6 is a flowchart illustrating a procedure of processing executed by a station-side terminal device according to the first embodiment. 6 is a flowchart for explaining a procedure of processing executed by a station-side terminal device according to the second embodiment. FIG. 10 is a block diagram illustrating an internal configuration of a station-side termination device according to a third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Station side termination | terminus apparatus 2 Optical splitter 3 Subscriber side apparatus 10 Upper layer circuit part 11 Frame buffer 12 PHY
13 CPU
14 Memory 21 Level conversion circuit 22 LD driver 23 LD
24 Monitor Photodiode (Monitor PD)
25 APC circuit 30 WDM coupler 31 Avalanche photodiode (APD)
32 Preamplifier 33 Postamplifier 34 Signal Level Detection Unit 41 APD Bias Voltage Control Unit 42 APD Bias Power Supply 51 Optical Amplifier 52 Photodiode

Claims (4)

Receiving means for receiving digital optical signals transmitted from a plurality of optical transmission devices , and photoelectric conversion means for converting digital optical signals received by the receiving means into electrical signals, and converted by the photoelectric conversion means In the optical receiver for identifying the digital optical signal by comparing the magnitude of the electrical signal and a preset threshold value,
Detecting means for detecting two signal levels corresponding to a high level and a low level from the electrical signal;
Means for determining the reception level and extinction ratio of the optical signal based on the two detected signal levels;
Based on the reception level and the extinction ratio, so that the threshold is a value between the two signal levels, the optical receiving apparatus, characterized in that it comprises a control means for controlling the reception sensitivity of the photoelectric conversion means. The photoelectric conversion means includes an avalanche photodiode whose multiplication factor is changed by a bias voltage ,
Before SL control means includes this comprises means for varying the bias voltage of the avalanche photodiode
Optical receiving apparatus according to claim 1, wherein the. The photoelectric conversion means includes an optical amplifier capable of gain control ,
Before SL control means includes this comprises means for controlling the gain of the optical amplifier
Optical receiving apparatus according to claim 1, wherein the. Means for determining the reception sensitivity of the photoelectric conversion means for each optical transmitter based on the received the digital optical signal,
Storage means for storing the determined was boss receiving sensitivity in association with the identification information for identifying the optical transmission device,
When receiving the digital optical signals, means for identifying the source of the optical transmitter of the digital optical signal,
Means for reading a reception sensitivity which is stored associated with the specific identification information of the optical transmission apparatus from said storage means,
Means for controlling the Ki受 signal sensitivity before based on the reception sensitivity read
Optical receiving device according to any one of claims 1 to 3, characterized in that it comprises a.

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