WO2021161382A1

WO2021161382A1 - Optical receiver

Info

Publication number: WO2021161382A1
Application number: PCT/JP2020/005123
Authority: WO
Inventors: 祐太石村
Original assignee: 三菱電機株式会社
Priority date: 2020-02-10
Filing date: 2020-02-10
Publication date: 2021-08-19
Also published as: JP7248154B2; JPWO2021161382A1

Abstract

Provided is an optical receiver with which it is possible to increase the stability of reception sensitivity of an APD module by shortening the response time of bias voltage applied to a light-receiving element in accordance with the light intensity of a received optical signal.　The optical receiver 100 according to the present disclosure comprises: a light-receiving element 1 that generates a current corresponding to the light intensity of the received optical signal; a bias voltage boost circuit 2 that supplies a bias voltage to the light-receiving element 1; a current/voltage conversion amplifier 3 that converts the current generated by the light-receiving element 1 to voltage; a first path 16 that connects the bias voltage boost circuit 2 and the light-receiving element 1, and is connected in parallel to its own bias resistor R and inductor L; a second path 17 connected in parallel to the first path 16 and having lower impedance than the first path 16; and a bias voltage control unit 11 that controls the bias voltage by switching to the first path 16 when the light intensity exceeds a preset light intensity threshold value, and switching to the second path 17 when the light intensity is less than or equal to the light intensity threshold value.

Description

Optical receiver

The present disclosure relates to an optical receiver applied to a PON (Passive Optical Network) system, and in particular, an optical burst signal receiving circuit using a light receiving element APD (Avalanche Photo Diode) is configured. Regarding receivers.

The PON system is an optical splitter that combines a station-side optical line terminal (OLT) installed on the station side and a subscriber-side optical line terminal (ONU: Optical Network Unit) installed in the subscriber's home. It is an optical communication system configured by connecting with an optical fiber via an optical fiber. The PON system has a configuration in which a plurality of ONUs are connected to one OLT.
The uplink and downlink signals between the OLT and the ONU are transmitted by a single optical fiber by optical wavelength division multiplexing communication means. In the downlink communication from the OLT to each ONU, a general continuous signal is used, but the uplink signal from each ONU to the OLT is time-division-multiplexed in a burst-shaped packet signal transmitted individually for each user. The signal is used. Further, since there is a difference in the distance between the OLT and each ONU, the signal strength of the optical signal received by the OLT changes greatly for each ONU.
In the PON system, the optical receiver on the OLT side receives the burst packet signal from each ONU. As an optical receiving module used in an optical receiving circuit of an optical receiver, an APD module having a light receiving element APD and a current-voltage conversion amplifier (TIA: Trans-Impedance Amplifier) in the subsequent stage of the light receiving element APD is known. By applying a bias voltage, the light receiving element APD causes an electron avalanche phenomenon when an optical signal is input, and generates an APD current according to a magnification depending on the bias voltage. The APD current is converted from current to voltage by the current-voltage conversion amplifier TIA in the subsequent stage of the light receiving element APD, and is output as a voltage signal.

In the APD module, it is necessary to change the magnification of the light receiving element APD according to the light intensity of the received optical signal. Since the multiplication factor depends on the bias voltage, the bias voltage control circuit for controlling the bias voltage applied to the light receiving element APD changes the bias voltage according to the light intensity of the optical signal. The weaker the light intensity of the optical signal, the higher the bias voltage is controlled to increase the magnification of the light receiving element APD, and the stronger the light intensity of the optical signal, the lower the bias voltage is used to increase the magnification of the light receiving element APD. It is controlled to lower.

Patent Document 1 proposes a technique for controlling the magnification by changing the bias voltage applied to the light receiving element APD according to the light intensity information of the received optical signal.
When the optical receiver receives optical signals with different optical intensities, the receiving circuit operates by adjusting the gain Gain of the current-voltage conversion amplifier TIA before the data (also called the payload), which is the stable main signal time. An overhead (also called a preamble), which is the time required for stabilization, is provided. In order to maintain stable reception sensitivity, it is necessary to converge the transient response of the bias voltage applied to the light receiving element APD in the overhead.
In the technique according to Patent Document 1, an optical signal is detected by a received light intensity detection unit, and the bias voltage is changed by an APD bias voltage control circuit according to the light intensity of the detected optical signal. However, in the case of high-speed communication. There is a concern that the transient response time of the bias voltage applied to the light receiving element APD in the overhead of the optical signal becomes long. When an optical signal that suddenly changes from a light signal with a weak light intensity to an optical signal with a strong light intensity in a short time of several ns to several tens of ns is received, the excessive response of the bias voltage cannot be converged within the overhead, so that the bias The voltage-dependent change in magnification cannot be converged, and the APD current may not be stable. As a result, the output voltage of the current-voltage conversion amplifier TIA in the subsequent stage of the light receiving element APD continues to change even in the data, and stable reception sensitivity cannot be maintained, so that it may not be possible to receive optical signals having different light intensities.

Japanese Unexamined Patent Publication No. 2005-45560

The present disclosure has been made to solve the above-mentioned problems, and the excessive response of the bias voltage applied to the light receiving element can be converged within the overhead according to the light intensity of the optical signal received by the APD module. Provided is an optical receiver capable of improving the stability of the reception sensitivity of the APD module by controlling the above and shortening the change time of the magnification of the light receiving element depending on the bias voltage.

The optical receiver according to the present disclosure includes a light receiving element that generates a current corresponding to the light intensity of the received optical signal, a bias voltage boosting circuit that supplies a bias voltage to the light receiving element, and a current generated by the light receiving element. The first path, in which the current-voltage conversion amplifier that converts to Switch to the second path, which has a smaller impedance than the first path, and to the first path when the light intensity exceeds the preset light intensity threshold, and to the second path when the light intensity is less than or equal to the light intensity threshold. A bias voltage control unit for controlling the bias voltage is provided.

According to the optical receiver according to the present disclosure, the bias voltage applied to the light receiving element is controlled by switching the path based on a preset light intensity threshold value. When an optical signal having a light intensity exceeding the light intensity threshold is received, the response time of the bias voltage is controlled to be shortened, and the change time of the magnification of the light receiving element depending on the bias voltage is shortened. The stability of the reception sensitivity of the APD module can be improved.

It is a block diagram of the burst signal receiving circuit of the optical receiver which concerns on Embodiment 1 of this disclosure. It is a timing chart diagram which shows the operation of the burst signal receiving circuit of the optical receiver which concerns on this disclosure. It is a timing chart diagram which shows the operation of the burst signal receiving circuit of the optical receiver which concerns on this disclosure. It is a block diagram of the burst signal receiving circuit of the optical receiver which concerns on Embodiment 2 of this disclosure.

Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. In each of the following embodiments, the same reference numerals are given to the same components.

Embodiment 1.
FIG. 1 is a configuration diagram of an optical receiver according to the first embodiment. The optical receiver 100 composed of a burst signal receiving circuit includes a light receiving element 1 that generates a current corresponding to the light intensity of the received optical signal, a bias voltage boosting circuit 2 that supplies a bias voltage to the light receiving element 1, and a light receiving device. A first path 16 in which a current-voltage conversion amplifier 3 that converts the current generated by the element 1 into a voltage, a bias voltage booster circuit 2 and a light receiving element 1 are connected, and a self-bias resistor R and an inductor L are connected in parallel. , The first path 16 or the second path 17 is switched depending on the light intensity of the optical signal and the second path 17, which is connected in parallel to the first path 16 and has an extremely small impedance as compared with the first path 16. This includes a bias voltage control unit 11 that controls the bias voltage.
Further, the first path 16 is provided with the first transistor 6 which is an open / close switch, and the second path 17 is provided with the second transistor 7 which is an open / close switch. By controlling the opening and closing of the first transistor 6 and the second transistor 7, which are switch elements, the first path 16 and the second path 17 are switched, so that switching at high speed is possible.

The light receiving element 1 is an APD. The bias voltage booster circuit 2 supplies the bias voltage applied to the light receiving element 1. When the light receiving element 1 receives an optical signal having a light intensity Pin while a bias voltage is applied, it generates an APD current Iapd according to a magnification M depending on the bias voltage.
The current-voltage conversion amplifier 3 multiplies the APD current Iapd generated by the light receiving element 1 by impedance, further converts it into a voltage, and outputs it as an output voltage signal Vout.
Here, the light receiving element 1 and the current-voltage conversion amplifier 3 constitute an APD module.

In the optical receiver 100 according to the first embodiment, the bias voltage control unit 11 has a first current mirror circuit 4 that generates a first monitor current Imon 1 that is proportional to the APD current Iapd generated by the light receiving element 1, and a first one. The second current mirror circuit 5 that generates the second monitor current Imon2, which is a current proportional to the monitor current Imon1, and the first monitor current Imon1 and the second monitor current Imon2 are detected and converted into voltages, respectively, and the obtained 2 is obtained. The first path is controlled by controlling the first transistor 6 which is an open / close switch provided in the first path 16 and the second transistor 7 which is an open / close switch provided in the second path 17 based on the potential difference between the two voltages. It has a current detection circuit 8 for switching between 16 and the second path 17.

In order to determine the strength of the received optical signal, the optical intensity threshold value Pmax of the optical signal is set in advance, and the voltage value corresponding to the optical intensity threshold value Pmax is set as the voltage threshold value Vmax. When the current detection circuit 8 in the bias voltage control unit 11 receives the optical signal, the current detection circuit 8 switches between the first path 16 and the second path 17 based on the voltage threshold value Vmax provided corresponding to the light intensity threshold value Pmax. ..

Specifically, the current detection circuit 8 detects the first monitor current Imon 1 and the second monitor current Imon 2, and converts the first monitor current Imon 1 and the second monitor current Imon 2 into voltages by separate resistors or the like. The potential difference between the two converted voltages and the voltage threshold Vmax are compared.
When the light intensity Pin of the received optical signal becomes excessive, the light receiving element 1 shows a high value of the APD current Iapd, and the first monitor current Imon1 proportional to the APD current Iapd and the second monitor current Imon1 proportional to the first monitor current Imon1. The monitor current Imon2 also becomes a high value.
When the potential difference between the two voltages converted by the first monitor current Imon1 and the second monitor current Imon2 exceeds a predetermined voltage threshold Vmax, the light intensity Pin of the received optical signal exceeds the light intensity threshold Pmax. (Light intensity Pin of optical signal> light intensity threshold Pmax). In this case, the current detection circuit 8 controls the first transistor 6 to be in the ON state, and switches the path of the bias voltage applied to the light receiving element 1 to the first path 16. The self-bias resistor R and the inductor L in the first path 16 operate so as to reduce the bias voltage applied to the light receiving element 1.

When the potential difference between the two voltages converted by the first monitor current Imon1 and the second monitor current Imon2 is equal to or less than the predetermined voltage threshold Vmax, the light intensity Pin of the received optical signal is equal to or less than the light intensity threshold Pmax (light). It is determined that the signal light intensity Pin ≦ light intensity threshold Pmax). In this case, the current detection circuit 8 controls the second transistor 7 to be in the ON state, and switches the path of the bias voltage applied to the light receiving element 1 to the second path 17. The second path 17, whose impedance is extremely smaller than that of the first path 16, does not lower the bias voltage applied to the light receiving element 1 and maintains the magnification of the light receiving element 1.
In the optical receiver 100 according to the first embodiment, the second path 17 is a path in which no resistor is inserted with respect to the first path 16 in which the self-bias resistor R and the inductor L are connected in parallel.

The self-bias resistor R is inserted to change the bias voltage applied to the light receiving element 1, and is applied to the light receiving element 1 when the light intensity Pin of the optical signal becomes excessive and exceeds the light intensity threshold Pmax. It has the effect of lowering the bias voltage. However, since the response time for changing the bias voltage due to the self-bias resistor R becomes longer due to the influence of the parasitic capacitance against a sudden current change, the self-bias resistor is used for the purpose of shortening the response time for changing the bias voltage. The R and the inductor L are connected in parallel. As a result, the response time of the bias voltage applied to the light receiving element 1 can be shortened, and it can be ensured that the bias voltage converges within the overhead.

Next, the operation of the burst signal receiving circuit of the optical receiver 100 configured as described above will be described.
FIG. 2 shows a timing chart in the operation of the burst signal receiving circuit of the optical receiver 100 according to the first embodiment. In FIG. 2, the horizontal axis represents time t, and an example is shown in which the optical receiver 100 continuously receives optical signals having different light intensities.

FIG. 2A shows the light intensity Pin of each optical signal received by the light receiving element 1. The light receiving element 1 receives the optical signal ONU1, the optical signal ONU2, the optical signal ONU3, the optical signal ONU4, and the optical signal ONU5 having different light intensities in this order. The light intensity Pins of the optical signal ONU1 and the optical signal ONU3 are smaller than the light intensity threshold value Pmax, but the light intensity Pins of the optical signal ONU2, the optical signal ONU4 and the optical signal ONU5 are values exceeding the light intensity threshold value Pmax. That is, the voltage signal corresponding to the light intensity Pin of the optical signal ONU1 and the optical signal ONU3 becomes a value smaller than the predetermined voltage threshold value Vmax, and the voltage corresponding to the light intensity Pin of the optical signal ONU2, the optical signal ONU4 and the optical signal ONU5. The signal has a value that exceeds a predetermined voltage threshold Vmax.

As shown in FIG. 2A, after receiving the light signal ONU1, the light signal ONU2 having a light intensity stronger than the light intensity of the light signal ONU1 and exceeding the light intensity threshold value Pmax is received. After receiving the light signal ONU2, the light signal ONU3 which is weaker than the light intensity of the light signal ONU2 and has a light intensity equal to or less than the light intensity threshold value Pmax is received. After receiving the light signal ONU3, the light signal ONU4 having a stronger light intensity and a light intensity exceeding the light intensity threshold value Pmax is received. After receiving the light signal ONU4, the light signal ONU5 is received, which has a weaker light intensity but has a light intensity exceeding the light intensity threshold value Pmax.

When receiving each optical signal, an overhead, which is the time required for stable operation, is provided before the data, which is the time when the operation of the receiving circuit is stable. FIG. 2A shows the data 102 of the optical signal ONU1, the

overhead

201 and 202 of the optical signal ONU2, the overhead 301 and data 302 of the optical signal ONU3, and the overhead of the optical signal ONU4 in the traveling direction of time from left to right. The overhead 501 and data 502 of 401 and data 402 and the optical signal ONU5 are shown. Further, X2 to Y2 are the times of the overhead 201 of the optical signal ONU2, X3 to Y3 are the times of the overhead 301 of the optical signal ONU3, X4 to Y4 are the times of the overhead 401 of the optical signal ONU4, and X5 to Y5. Is the time of the overhead 501 of the optical signal ONU5. The time of the overhead 101 of the optical signal ONU1 is not shown in the figure.

Changes in the multiplier M, the APD current Iapd, the TIA gain Gain of the current-voltage conversion amplifier 3, and the output voltage signal Vout are shown in FIGS. 2 (b) and 2 (c), respectively, according to changes in the light intensity of the received optical signal. , 2 (d) and 2 (e).
FIG. 3 is a part of FIG. 2, and is a diagram for explaining in detail the operation when the optical signal ONU1 and the optical signal ONU2 are continuously received in the timing chart shown in FIG. After receiving the optical signal ONU1, changes in the multiplier M, the APD current Iapd, the TIA gain Gain of the current-voltage conversion amplifier 3, and the output voltage signal Vout are shown in FIGS. 3 (b) and Vout, respectively, according to the light intensity of the optical signal ONU2. 3 (c), FIG. 3 (d) and FIG. 3 (e).

First, the operation of the burst signal receiving circuit of the optical receiver 100 will be described with reference to FIG.
As shown in FIG. 3, after the light receiving element 1 receives the light signal ONU1 having a light intensity equal to or lower than the light intensity threshold value Pmax, the light intensity of the light signal ONU1 is stronger and the light intensity exceeds the light intensity threshold value Pmax. Receives the optical signal ONU2 to have.
When the optical signal ONU2 is received, the APD current Iapd corresponding to the light intensity Pin of the optical signal ONU2 becomes high, and the first monitor current Imon1 and the second monitor current Imon2, which are proportional to the APD current Iapd, also become high values. The potential difference between the two voltages converted from the first monitor current Imon1 and the second monitor current Imon2 exceeds the voltage threshold Vmax corresponding to the light intensity threshold Pmax. It is determined that the light intensity Pin of the light signal exceeds the light intensity threshold value Pmax, and the current detection circuit 8 controls the first transistor 6 to be in the ON state, and switches from the second path 17 to the first path 16. The bias voltage booster circuit 2 applies a bias voltage to the light receiving element 1 from the first path 16 in which the self-bias resistor R and the inductor L are connected in parallel.

Since the inductor L tends to have a higher impedance than the self-bias resistor R with respect to a sudden increase in current from the time X2 when the optical signal ONU2 is received, the bias applied to the light receiving element 1 from the bias voltage booster circuit 2 The voltage is reduced by the self-bias resistor R. Since the impedance of the inductor L decreases with the passage of time, the bias voltage applied to the light receiving element 1 gradually transitions to the state immediately after receiving the optical signal ONU2. As the impedance of the inductor L becomes smaller than the self-bias resistor R, the bias voltage changes from a decrease to a rapid increase.

The magnification M depends on the bias voltage. FIG. 3B shows the change in the magnification M. In FIG. 3B, the magnification M1 shown by the solid line is a response image of the magnification in which the change converges in the overhead 201 by the first path 16. In the overhead 201 from X2 that received the optical signal ONU2 to Y2 that the operation of the receiving circuit is stable, the multiplying factor M1 is once lowered by the decrease of the bias voltage. With the passage of time, the impedance of the inductor L decreases, and the magnification M1 changes from decreasing to increasing from Z2 in the overhead 201. That is, the magnification M1 decreases from X2 to Z2 of the overhead 201, and the magnification M1 increases from Z2 to Y2. In the data 202 after the overhead 201, the magnification M1 becomes a stable value as before receiving the optical signal ONU2. As described above, the magnification M1 decreases immediately after receiving the optical signal ONU2 with the change of the bias voltage, and has a characteristic of rapidly increasing from the decrease, and the change of the magnification M1 can be converged within the overhead 201.
By connecting the self-bias resistor R of the first path 16 and the inductor L in parallel, the response time of the bias voltage can be shortened, and the change time of the multiplication factor depending on the bias voltage can also be shortened.

In the overhead 201, the time point Z2 when the bias voltage reverses from the decrease to the increase is also the time point when the impedance of the inductor L and the self-bias resistance R become the same value. Depending on the set values of the impedance of the inductor L and the self-bias resistor R, the time position of Z2 at which the bias voltage reverses from a decrease to an increase is changed, and the response of the bias voltage is accelerated to ensure convergence in the overhead. ..

In FIG. 3B, the magnification M2 shown by the broken line is a response image of the magnification by a method of inserting a self-bias resistor between the bias voltage booster circuit 2 and the light receiving element 1 to reduce the bias voltage. .. The Magnification M2 decreases as the bias voltage decreases, but the change cannot converge within the overhead, and the change continues even at the head portion "A" of the data from Y2 to W2.
Further, the alternate long and short dash line in the overhead 201 of FIG. 3B shows a response image of the multiplication factor M3 when the bias voltage booster circuit 2 and the light receiving element 1 are directly connected without inserting the self-bias resistor. Since the bias voltage is not controlled, the multiplying factor M3 does not change.

FIG. 3 (c) shows the change in the APD current Iapd. In FIG. 3C, the solid line APD current I1 is a response image of the APD current Iapd whose change converges in the overhead 201 by the first path 16.
As shown in FIG. 3C, the APD current I1 increases in response to the optical signal ONU2 having a light intensity exceeding the light intensity threshold value Pmax. In the time zone from X2 to Z2 of the overhead 201, the APD current I1 does not increase sharply as the magnification M1 decreases, but gradually increases. As the impedance of the inductor L decreases with the passage of time, the APD current I1 exhibits a characteristic of rapidly increasing in the time zone from Z2 to Y2 of the overhead 201. The change in the APD current I1 exhibits a characteristic of converging within the overhead 201.
In FIG. 3C, the APD current I2 shown by the broken line is a response image of the APD current Iapd by a method of inserting a self-bias resistor between the bias voltage booster circuit 2 and the light receiving element 1 to lower the bias voltage. be. The APD current I2 does not increase sharply as the magnification M2 decreases, but gradually increases, but the change cannot converge within the overhead and continues to change at the head "A" of the data from Y2 to W2. It will be.
Further, in the overhead 201 of FIG. 3C, the APD current I3 shown by the alternate long and short dash line is the response of the APD current Iapd when the bias voltage booster circuit 2 and the light receiving element 1 are directly connected without inserting the self-bias resistor. It is an image. The APD current I3 increases sharply as the optical signal ONU2 is received.

The gain Gain of the current-voltage conversion amplifier 3 is adjusted based on the value of the APD current Iapd. As shown in FIG. 3D, in the overhead 201, the gain Gain shows a characteristic that gradually decreases as the APD current Iapd increases.

The output voltage signal Vout by the current-voltage conversion amplifier 3 changes depending on the APD current Iapd and the gain Gain of the current-voltage conversion amplifier 3. In FIG. 3E, the output voltage signal V1 shown by the solid line is a response image of the output voltage signal Vout that gradually increases and converges in the overhead 201 by the first path 16.
When the light receiving element 1 receives the optical signal ONU2 having a light intensity exceeding the light intensity threshold value Pmax, the output voltage signal V1 gradually increases from the time X2 when the optical signal ONU2 is received, as shown in FIG. 3 (e). do. Since the change in the APD current I1 converges in the overhead 201, the change in the output voltage signal V1 also converges in the overhead 201. Immediately after receiving the optical signal ONU2, the gain Gain of the current-voltage conversion amplifier 3 is still high, but since the APD current I1 is not rapidly increased by the first path 16, the output voltage signal V1 is The output does not suddenly become excessive.
In FIG. 3E, the output voltage signal V2 shown by the broken line is the response of the output voltage signal Vout by a method of inserting a self-bias resistor between the bias voltage booster circuit 2 and the light receiving element 1 to lower the bias voltage. It is an image. The output voltage signal V2 does not suddenly become an excessive output, but the change cannot converge in the overhead, and the change continues even at the head portion "A" of the data from Y2 to W2.
Further, in the overhead 201 of FIG. 3 (e), the output voltage signal V3 shown by the alternate long and short dash line is suddenly excessive when the bias voltage booster circuit 2 and the light receiving element 1 are directly connected without inserting the self-bias resistor. It is a response image of the output voltage signal Vout which becomes an output.

Here, the multiplication factor M, the APD current Iapd, the TIA gain Gain of the current-voltage conversion amplifier 3 and the TIA gain Gain when the optical signal ONU2 is received from the optical signal ONU1 by the burst signal receiving circuit of the optical receiver 100 according to the first embodiment. The response of the output voltage signal Vout is shown in the same results in FIGS. 2 and 3.
As shown in FIGS. 2 and 3, changes in the multiplication factor M, the APD current Iapd, and the output voltage signal Vout have a characteristic of converging within the overhead 201, and in the data 202 after the completion of the overhead 201, the multiplication factor M and the APD current Iapd, gain Gain, and output voltage signal Vout are stable values, respectively.

Next, with reference to FIG. 2, changes in the multiplication factor M, the APD current Iapd, the TIA gain Gain of the current-voltage conversion amplifier 3, and the output voltage signal Vout when the optical signal ONU5 is received from the optical signal ONU2 will be described.
As shown in FIG. 2, after the light receiving element 1 receives the light signal ONU2, the light intensity of the light signal ONU2 is weaker, and the light signal ONU3 having a light intensity equal to or lower than the light intensity threshold value Pmax is received. When the optical signal ONU3 is received, the APD current Iapd corresponding to the light intensity of the optical signal ONU3 is lower than that when the optical signal ONU2 is received. The first monitor current Imon1 and the second monitor current Imon2, which are proportional to the APD current Iapd, also have lower values than when the optical signal ONU2 is received. The potential difference between the two voltages converted from the first monitor current Imon1 and the second monitor current Imon2 is equal to or less than the voltage threshold Vmax corresponding to the light intensity threshold Pmax.
The current detection circuit 8 controls the second transistor 7 to be in the ON state, and switches to the second path 17, which has an extremely small impedance as compared with the first path 16.

Since the bias voltage applied to the light receiving element 1 is not lowered by passing through the second path 17, the magnification M is also maintained without being lowered as shown in FIG. 2 (b).
As shown in FIG. 2C, the APD current Iapd receives a light signal ONU3 weaker than the light intensity of the light signal ONU2, and the APD current Iapd decreases according to the light intensity of the light signal ONU3 in the overhead 301.
As shown in FIG. 2D, since the gain Gain of the current-voltage conversion amplifier 3 is adjusted based on the value of the APD current Iapd, the overhead 301 shows a characteristic of gradually increasing as the APD current Iapd decreases. ..
The output voltage signal Vout by the current-voltage conversion amplifier 3 changes depending on the APD current Iapd and the gain Gain of the current-voltage conversion amplifier 3. As shown in FIG. 2E, the output voltage signal Vout shows a characteristic of gradually decreasing in the overhead 301.

In the data 302 after the end of the overhead 301, the magnification M, the APD current Iapd, the gain Gain, and the output voltage signal Vout are stable values, respectively.

Next, after the light receiving element 1 receives the optical signal ONU3, the light receiving element 1 receives the optical signal ONU4 having a stronger light intensity and a light intensity exceeding the light intensity threshold value Pmax.
When the optical signal ONU4 is received, the APD current Iapd corresponding to the light intensity of the optical signal ONU4 becomes high, and the first monitor current Imon1 and the second monitor current Imon2, which are proportional to the APD current Iapd, also become high values. The potential difference between the two voltages converted from the first monitor current Imon1 and the second monitor current Imon2 exceeds the voltage threshold Vmax corresponding to the light intensity threshold Pmax.

Similar to the case where the optical signal ONU2 is received from the optical signal ONU1, the current detection circuit 8 controls the first transistor 6 to be in the ON state, and switches from the second path 17 to the first path 16.
The bias voltage booster circuit 2 applies a bias voltage to the light receiving element 1 from the first path 16 in which the self-bias resistor R and the inductor L are connected in parallel. The bias voltage applied to the light receiving element 1 is initially lowered by the self-bias resistor R. Since the impedance of the inductor L decreases with the passage of time, the bias voltage applied to the light receiving element 1 gradually transitions to the state immediately after receiving the optical signal ONU4. As the impedance of the inductor L becomes smaller than the self-bias resistor R, the bias voltage changes from a decrease to a rapid increase.

The multiplying factor M changes with a change in the bias voltage. As shown in FIG. 2B, in the overhead 401 from X4 which received the optical signal ONU4 to Y4 where the operation of the receiving circuit is stable, the magnification M is once lowered by the decrease of the bias voltage. With the passage of time, the impedance of the inductor L decreases, and the magnification M changes from decreasing to increasing from Z4 in the overhead 401. That is, X4 to Z4 of the overhead 401 are in a state in which the magnification M is decreased, and Z4 to Y4 are in a state in which the magnification M is increased.
By connecting the self-bias resistor R of the first path 16 and the inductor L in parallel in this way, the response time for changing the bias voltage is shortened, so that the change in the multiplication factor M changes with the change in the bias voltage overhead 401. Can converge within.

As shown in FIG. 2C, in X4 to Z4 of the overhead 401, the APD current Iapd increases in response to the optical signal ONU4, but does not increase sharply as the magnification M decreases, but gradually increases. Shows the characteristics of As the impedance of the inductor L decreases with the passage of time, the APD current Iapd shows a characteristic of rapidly increasing from Z4 to Y4 of the overhead 401. The change in APD current Iapd shows the characteristic of converging in the overhead 401.

The gain Gain of the current-voltage conversion amplifier 3 is adjusted based on the value of the APD current Iapd. As shown in FIG. 2D, in the overhead 401, the gain Gain shows a characteristic that gradually decreases as the APD current Iapd increases.

As shown in FIG. 2E, the output voltage signal Vout by the current-voltage conversion amplifier 3 gradually increases from the time X4 when the optical signal ONU4 is received. The change in the output voltage signal Vout shows the characteristic of converging in the overhead 401.
In the data 402 after the end of the overhead 401, the magnification M, the APD current Iapd, the gain Gain, and the output voltage signal Vout are stable values, respectively.

Next, after the light receiving element 1 receives the optical signal ONU4, the light receiving element 1 receives the optical signal ONU5 having a light intensity that is weaker but exceeds the light intensity threshold value Pmax.
When the optical signal ONU5 is received, the first monitor current Imon1 and the second monitor current Imon2, which are proportional to the APD current Iapd corresponding to the light intensity of the optical signal ONU5, are detected and converted into a voltage. The potential difference between the two voltages converted from the first monitor current Imon1 and the second monitor current Imon2 exceeds the voltage threshold Vmax corresponding to the light intensity threshold Pmax.

Since the current detection circuit 8 controls the first transistor 6 in the ON state and the bias voltage booster circuit 2 remains connected to the first path 16, the bias voltage applied to the light receiving element 1 does not change.
As shown in FIG. 2B, in the overhead 501 that received the optical signal ONU5, the multiplying factor M does not change with the bias voltage.

As shown in FIG. 2C, the APD current Iapd gradually decreases from the time X5 when the optical signal ONU5 is received, in accordance with the light intensity of the optical signal ONU5.
In order to continue to receive the optical signal ONU4 and the optical signal ONU5 having the light intensity exceeding the light intensity threshold Pmax, as shown in FIG. Is already small, so it shows a characteristic that is maintained at a low value. Therefore, the APD current Iapd does not increase sharply, and the change in the APD current Iapd can converge within the overhead 501.

Further, as shown in FIG. 2E, the output voltage signal Vout by the current-voltage conversion amplifier 3 gradually decreases from the time X5 when the optical signal ONU5 is received, as the APD current Iapd changes. The change in the output voltage signal Vout also shows the characteristic of converging within the overhead 501.
In the data 502 after the end of the overhead 501, the magnification M, the APD current Iapd, the gain Gain, and the output voltage signal Vout are stable values, respectively.

According to the optical receiver according to the first embodiment, the bias voltage applied to the light receiving element is controlled by switching the path based on a preset light intensity threshold value. When an optical signal having a light intensity exceeding the light intensity threshold is received, the response time of the bias voltage is controlled to be shortened, and the change time of the magnification of the light receiving element depending on the bias voltage is shortened. The stability of the reception sensitivity of the APD module can be improved.
Further, since the bias voltage control unit can switch between the first path and the second path at high speed by the switch element according to the light intensity of the optical signal, the optical signal whose light intensity suddenly differs significantly. Since it is possible to ensure that the change in magnification depending on the bias voltage is converged within the overhead even when the light is continuously received, the stability of the reception sensitivity of the APD module can be improved.

Embodiment 2.
In the second embodiment, the same reference numerals are used for the same components as those in the first embodiment of the present disclosure, and the description of the same or corresponding parts will be omitted. Hereinafter, the optical receiver 200 according to the second embodiment will be described with reference to the drawings.

FIG. 4 is a configuration diagram of the optical receiver 200 according to the second embodiment. As shown in FIG. 4, the optical receiver 200 configured by the burst signal receiving circuit has a light receiving element 1 that generates a current corresponding to the light intensity of the received optical signal and a bias that supplies a bias voltage to the light receiving element 1. The voltage booster circuit 2, the current-voltage conversion amplifier 3 that converts the current generated by the light receiving element 1 into a voltage, the bias voltage booster circuit 2 and the light receiving element 1 are connected, and the self-bias resistor R and the inductor L are connected in parallel. The connected first path 16 and the second path 17 which is connected in parallel to the first path 16 and whose impedance is extremely smaller than that of the first path 16 and the first path 16 according to the light intensity of the optical signal. Alternatively, it has a bias voltage control unit 21 that controls the bias voltage by switching the second path 17.

Further, it has a first transistor 6 which is an open / close switch of the first path 16 and a second transistor 7 which is an open / close switch of the second path 17. By controlling the opening and closing of the first transistor 6 and the second transistor 7, which are switch elements, the first path 16 and the second path 17 are switched, so that switching at high speed is possible.

The optical intensity of an optical signal is determined by the distance between the station-side optical network unit (OLT) and the subscriber-side optical network unit (ONU). The shorter the distance between the OLT and the ONU, the stronger the light intensity of the optical signal transmitted from the ONU.
In the optical receiver 200 according to the second embodiment, the bias voltage control unit 21 transfers the memory 9 in which the information regarding the optical intensity of the optical signal transmitted from each ONU to the OLT is stored, and the determined ONU to the OLT. Based on the transmission timing of the uplink signal, the information on the light intensity of the ONU stored in the memory 9 and the preset light intensity threshold value Pmax are compared with the first path 16 before the reception time of the OLT. It has a switching control unit 10 for switching the second path 17.
Also in the optical receiver 200 according to the second embodiment, the second path 17 is a path in which no resistor is inserted with respect to the first path 16 in which the self-bias resistor R and the inductor L are connected in parallel.

The components other than the bias voltage control unit 21 of the optical receiver 200 according to the second embodiment are the same as those of the optical receiver 100 of the first embodiment.
The switching control unit 10 of the bias voltage control unit 21 switches the path of the bias voltage applied to the light receiving element 1 by comparing the light intensity Pin of the transmitted optical signal with the preset light intensity threshold value Pmax. When the light intensity Pin of the optical signal exceeds the light intensity threshold Pmax, it is connected to the first path 16, and when the light intensity Pin of the optical signal is equal to or less than the light intensity threshold Pmax, it is connected to the second path 17 to bias. Control the voltage.
That is, in the first embodiment, the intensity of the light intensity is determined based on the voltage threshold value corresponding to the light intensity threshold value of the optical signal. On the other hand, in the second embodiment, the light intensity of the light signal for each ONU is stored and compared with the light intensity threshold value to determine the strength of the light intensity to be received.

Further, in the optical receiver 200 according to the second embodiment, the determined transmission timing of the uplink signal from the ONU to the OLT is also determined in advance and stored in the memory 9. The switching control unit 10 compares the information on the light intensity of the ONU stored in the memory 9 with the light intensity threshold value Pmax before the reception time of the OLT based on the predetermined transmission timing from each ONU to the OLT. As a result, the switching control unit 10 controls to switch between the first path 16 and the second path 17.

In the burst signal receiving circuit of the optical receiver 200 according to the second embodiment, the bias voltage control unit 21 sets the light intensity Pin in advance before the OLT reception time according to the change in the light intensity of the received optical signal. The first path 16 and the second path are connected to the first path 16 when the set light intensity threshold value Pmax is exceeded, and connected to the second path 17 when the light intensity pin is equal to or less than the light intensity threshold value Pmax. The bias voltage is controlled by switching between 17 and 17.
Therefore, for example, when the optical signal ONU1, the optical signal ONU2, the optical signal ONU3, the optical signal ONU4, and the optical signal ONU5 shown in FIG. The changes in the TIA gain Gain and the output voltage signal Vout of No. 3 are the same as the response images shown in FIGS. 2 (b), 2 (c), 2 (d), and 2 (e), respectively. That is, as shown in FIGS. 2 and 3, the burst signal receiving circuit of the optical receiver 200 according to the second embodiment shortens the excessive response time of the bias voltage for each optical signal, and increases the magnification M and the APD current. The changes in Iapd and the output voltage signal Vout can be converged within each overhead, and the data after the overhead ends have the characteristics of stable values.

In the burst signal receiving circuit of the optical receiver 200 according to the second embodiment, the same effect as that of the first embodiment can be obtained. Since it is the same as the timing chart in the burst signal receiving circuit of the optical receiver according to the first embodiment, the description thereof will be omitted.

According to the optical receiver according to the second embodiment, the bias voltage applied to the light receiving element is controlled by switching the path based on a preset light intensity threshold value. When an optical signal having a light intensity exceeding the light intensity threshold is received, the response time of the bias voltage is controlled to be shortened, and the change time of the magnification of the light receiving element depending on the bias voltage is shortened. The stability of the reception sensitivity of the APD module can be improved.
Further, the bias voltage control unit switches the first path or the second path before the reception time of the OLT based on the transmission timing of the uplink signal from the ONU to the OLT according to the light intensity of the optical signal. Even when optical signals with significantly different intensities are continuously received, it is possible to ensure that the change in magnification depending on the bias voltage is converged within the overhead, so that the stability of the reception sensitivity of the APD module can be improved. ..

The configuration shown in the above-described embodiment shows an example of the contents of the present disclosure, can be combined with another known technique, and is configured without departing from the gist of the present disclosure. It is also possible to omit or change a part of.

1 light receiving element, 2 bias voltage booster circuit, 3 current / voltage conversion amplifier, 4 1st current mirror circuit, 5 2nd current mirror circuit, 6 1st transistor, 7 2nd transistor, 8 current detection circuit, 9 memory, 10 switching Control unit, 11, 21 Bias voltage control unit, 16 1st path, 17 2nd path, 100, 200 Optical receiver

Claims

A light receiving element that generates a current corresponding to the light intensity of the received light signal,
A bias voltage booster circuit that supplies a bias voltage to the light receiving element,
A current-voltage conversion amplifier that converts the current generated by the light-receiving element into a voltage,
A first path in which the bias voltage booster circuit and the light receiving element are connected and the self-bias resistor R and the inductor L are connected in parallel.
A second path, which is connected in parallel to the first path and has a lower impedance than the first path,
The bias voltage is controlled by switching to the first path when the light intensity exceeds a preset light intensity threshold value, and switching to the second path when the light intensity is equal to or less than the light intensity threshold value. Bias voltage control unit and
An optical receiver equipped with.
A first transistor, which is an open / close switch, is provided in the first path.
A second transistor, which is an open / close switch, is provided in the second path.
The optical reception according to claim 1, wherein the bias voltage control unit switches between the first path and the second path by controlling the opening and closing of the first transistor and the second transistor. vessel.
The bias voltage control unit
The light according to claim 1 or 2, wherein a current detection circuit for switching between the first path and the second path is provided based on a voltage threshold value provided corresponding to the light intensity threshold value. Receiver.
The bias voltage control unit
A first current mirror circuit that generates a first monitor current that is proportional to the current that is generated according to the light intensity, and
A second current mirror circuit that generates a second monitor current, which is a current proportional to the first monitor current, is further provided.
The current detection circuit detects the first monitor current and the second monitor current, converts them into voltages, respectively, and compares the potential difference between the two obtained voltages with the voltage threshold value. When the potential difference exceeds the voltage threshold, it is determined that the light intensity exceeds the light intensity threshold, and the path is switched to the first path. When the potential difference is equal to or less than the voltage threshold, the light intensity is said. The optical receiver according to claim 3, wherein the optical receiver is determined to be equal to or less than the light intensity threshold and switched to the second path.
The bias voltage control unit
A memory that stores the optical intensity of the optical signal transmitted from each subscriber side optical network unit (ONU) to the station side optical network unit (OLT), and
A switching control unit that switches between the first path and the second path by comparing the light intensity with the light intensity threshold value.
The optical receiver according to claim 1 or 2, wherein the optical receiver comprises the above.
The switching control unit
Based on a predetermined transmission timing from each subscriber-side optical network unit (ONU) to the station-side optical network unit (OLT), the above is performed before the reception time of the station-side optical network unit (OLT). The optical receiver according to claim 5, wherein the first path and the second path are switched by comparing the light intensity stored in the memory with the light intensity threshold value.