JP4912340B2 - Burst optical signal receiving method and apparatus - Google Patents

Description

  The present invention intermittently receives burst optical signals having different intensities, such as an optical transmission system, particularly a PON (Passive Optical Network) system of an optical access network that connects a premises of a communication carrier and a subscriber's home. The present invention relates to a burst optical signal receiving method and apparatus.

  As shown in FIG. 5, the PON system provides a service for an optical transmission line such as an optical fiber 100 or an optical splitter 200, or a subscriber accommodation device 300 (OLT: Optical Line Terminal) installed in a communication company's office building. This is an optical access system that can reduce the cost per person because it can be shared among a plurality of terminal units (ONU: Optical Network Unit). In Japan, PON systems such as B-PON and GE-PON have been deployed, and the number of subscribers has been widespread, exceeding 10 million.

  In the PON system, in order to prevent the signals transmitted from the ONUs from colliding with each other, the transmission timing of each ONU is controlled by the OLT, and the signal transmission for each ONU is performed. A no-signal section called guard time is inserted between the times.

  Therefore, unlike the signal (downstream signal) transmitted from the OLT to the ONU, the upstream signal becomes an intermittent burst signal, and generally, the distance from the OLT to each ONU is small. Therefore, as shown in the strong burst signal 401 and the weak burst signal 402 in FIG. 6, the strength of the signal received by the OLT is different. Reference numeral 403 denotes a guard time.

  Therefore, an upstream optical burst signal receiver for a PON system is required to have high sensitivity characteristics and at the same time have wide dynamic range characteristics.

  As a method for achieving high sensitivity of a burst optical signal receiver, an APD (avalanche photodiode) having a multiplication function when converting an optical signal into an electric signal is used as a light receiving element.

  However, when APD is used, if it is received at an excessively large multiplication factor with respect to the light intensity of the received burst optical signal, a large photocurrent after APD is input exceeding the linear operation region of the preamplifier installed in the subsequent stage. The output waveform is distorted or the APD itself is damaged due to overcurrent.

  For this reason, burst optical signal receivers for PON systems that require a large dynamic range often use an APD with a relatively small multiplication factor to ensure the dynamic range, and the high sensitivity characteristics inherent to the APD. Is not fully utilized.

The method for expanding the dynamic range of a burst optical signal receiving apparatus is to determine the intensity of a burst optical signal from the output voltage of a preamplifier that linearly amplifies and converts the current signal after photoelectric conversion into a voltage signal, A method of controlling the gain of the preamplifier for each received signal by changing the feedback resistance value (Non-Patent Document 1) or a method of controlling the multiplication factor of the APD instead of the gain of the preamplifier (Patent Document) 1).
M. Nakamura et al., "1.25-Gb / s Burst-Mode Receiver ICs With Quick Response for PON Systems", IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL.40, NO.12, Dec. 2005. JP 2007-129639 A

  In a burst optical signal receiving apparatus using APD, it is effective to set the APD multiplication factor and the preamplifier gain to a high value in order to realize high sensitivity characteristics. Here, in order to expand the dynamic range, when the output level of the preamplifier exceeds a preset threshold value, the gain resistance value of the preamplifier is changed to a low value to prevent saturation of the output signal by suppressing the gain. Is proposed in Non-Patent Document 1.

  In this method, as shown in FIG. 7, in the region (A) operating at high gain A, the point where the preamplifier output exceeds the saturation output level is set to X, and the region operating at low gain B (X). In B), the point where the preamplifier output exceeds the saturation output level is set to Y, and the preamplifier gain is further switched to the low gain C, whereby the allowable input light intensity to the APD can be set high.

  However, when an optical signal that is excessively strong with respect to the APD multiplication factor is input, a high-intensity optical signal is received in a high multiplication factor state, and even if the preamplifier is within the linear operation range, the output of the APD The limit level Z is reached, and as a result, the dynamic range is limited by the input light intensity of the APD.

  On the other hand, Patent Document 1 proposes a method of suppressing the photocurrent input to the preamplifier by changing the multiplication factor of the APD to a low value when the output level of the preamplifier exceeds a preset threshold value.

  In this method, as shown in FIG. 8, the preamplifier is always driven in a region (A) operating at a high gain A, and when the preamplifier output reaches a point X where the saturation output level is exceeded, the APD multiplication factor is switched to a low value. Thus, the allowable input light intensity of the APD can be set high.

  However, since the preamplifier gain is always set to a high value, the linear operation input range of the preamplifier is narrowed and the number of times the saturation threshold is reached increases.

  In the current high gain preamplifier, it is necessary to switch the APD multiplication factor at least three times. Since the APD multiplication response is very sensitive to the APD bias voltage, a complicated control circuit is required. In addition, a high-speed response circuit is required so that multiple switching is completed within the burst level adjustment interval.

  Further, in the current high-gain preamplifier, even when PIN-PD is used, it is generally saturated with an optical input of about -10 dBm, and a wide dynamic range can be obtained only by switching the APD multiplication factor. It is difficult to achieve.

  The present invention has been made under such a background, and an object of the present invention is to provide a burst optical signal receiving method and apparatus that can simultaneously and easily realize both high sensitivity and wide dynamic range. .

To achieve the above object, according to a first aspect of the present invention, there is provided a burst optical signal receiving method in which burst optical signals having different intensities are received by an APD, linearly amplified as a current signal by a preamplifier and converted into a voltage signal. And the gain of the preamplifier is a first increase in which the output level of the level detection circuit for detecting the output level of the preamplifier becomes higher than a threshold value when the burst optical signal is low intensity or high intensity. set the magnification and the first gain value, receiving the burst optical signal, wherein when the output level of the level detection circuit exceeds the threshold, the gain of the low second than the first gain value of said pre-amplifier controls the gain value, then, when the output level of the level detection circuit exceeds the threshold value, the low multiplication factor of the APD than the first multiplication factor And controlling the second multiplication factor.
The invention according to claim 2, in the burst optical signal receiving method according to claim 1, wherein the threshold value is characterized by saturation level der Rukoto of the preamplifier.
According to a third aspect of the present invention, in a burst optical signal receiving apparatus that receives burst optical signals having different intensities, an APD that converts the burst optical signal into a current signal, an output current of the APD is linearly amplified, and a voltage signal is generated. The preamplifier to be converted, the level detection circuit for determining the output level of the preamplifier, and the output level of the level detection circuit is higher than the threshold when the burst optical signal is in advance of low intensity or high intensity A multiplication factor / gain switching control circuit for controlling the multiplication factor of the APD set to the first multiplication factor and the first gain value and the gain of the preamplifier based on the output level of the level detection circuit; The multiplication factor / gain switching control circuit increases the gain of the preamplifier when the output level of the level detection circuit exceeds the threshold. Controlled to lower than the value second gain value, then, when the output level of the level detection circuit exceeds the threshold value, to control the multiplication factor of the APD to lower than said first multiplication factor second multiplication factor It is characterized by that.
According to a fourth aspect of the present invention, in the burst optical signal receiving device according to the third aspect, the multiplication factor / gain switching control circuit receives an output signal of the level detection circuit and the level exceeds the threshold value. A first comparator that outputs a first detection signal; and a preamplifier gain controller that controls the gain of the preamplifier to the second gain value when the first comparator outputs the first detection signal; A delay unit that delays the first detection signal output from the first comparator for a predetermined time, and a second unit that receives the first detection signal delayed by the delay unit and whose level exceeds the threshold value. A second comparator that outputs a detection signal of the APD, and an APD multiplication controller that controls the multiplication factor of the APD to the second multiplication factor when the second comparator outputs the second detection signal; characterized by Rukoto equipped with.
The invention according to claim 5 is the burst optical signal receiving apparatus according to claim 3 or 4, wherein the threshold is characterized saturation level der Rukoto of the preamplifier.

According to the present invention, when a burst optical signal is received with the APD multiplication factor and the preamplifier gain set to a high first multiplication factor and a high first gain value, and the light intensity of the burst optical signal increases, When the preamplifier gain is controlled to a second gain value lower than the first gain value and the input light intensity is high even in this state, the APD multiplication factor is then set to a second multiplication factor lower than the first multiplication factor. Since the magnification is controlled, burst optical signal reception with a wide dynamic range characteristic can be easily realized while realizing a high sensitivity characteristic.

  To realize a burst optical signal receiver with high sensitivity characteristics and wide dynamic range characteristics, set the APD multiplication factor in the previous stage of the preamplifier to a high value and detect the weak optical signal by increasing the preamplifier gain. However, when a high-intensity optical signal is received, it is important to secure a dynamic range by switching both the APD multiplication factor and the preamplifier gain.

  FIG. 1 is a block diagram showing a schematic configuration of a burst optical signal receiving apparatus according to an embodiment of the present invention. The burst optical signal receiving apparatus according to the present embodiment includes an APD 20 that converts an incident burst optical signal 10 into a photocurrent signal, a preamplifier 30 that linearly amplifies / voltage converts the photocurrent signal output from the APD 20, A level detection circuit 40 for detecting the input light intensity from the output signal, a multiplication / gain switching control circuit 50 for controlling the APD multiplication factor and preamplifier gain based on the output value of the level detection circuit 40, and the multiplication / gain switching An APD bias power source 60 whose APD bias is controlled by the control circuit 50 and a limiter amplifier 70 that converts the output signal of the preamplifier 30 into a signal of a constant level are formed.

  In the burst optical signal receiving apparatus of this embodiment, the level detection circuit 40 estimates the output value of the preamplifier 30, and the output signal of the preamplifier 30 (that is, the output value estimated by the level detection circuit 40) is a preset threshold value ( When the output exceeds the saturation output level, the multiplication / gain switching control circuit 50 changes the value of the gain resistor Rf in the preamplifier 30 and suppresses the output of the preamplifier 30 from reaching the saturation output level. Thereafter, when the output level from the level detection circuit 40 again exceeds the threshold, the bias value of the APD bias power supply 60 is changed, and the multiplication factor is switched to a low value. The estimation of the output value of the preamplifier 30 is performed using the intermediate point between the peak value and the bottom value of the output voltage of the preamplifier 30 as a reference voltage, and is output from the level detection circuit 40. Since the output voltage of the preamplifier 30 is linear, the level detection circuit 40 estimates the intensity of the burst optical signal input to the APD 20 using this reference voltage.

  FIG. 2 is a block diagram showing an internal configuration of the multiplication factor / gain switching control circuit 50. Reference numeral 51 denotes a first comparator that determines the output level of the level detection circuit 40 based on a preset threshold value (saturated output level of the preamplifier 30), and 52 controls the gain of the preamplifier according to the determination result of the first comparator 51. A preamplifier gain controller 53 for delaying the determination result of the first comparator 41 for a predetermined time, 54 a switch whose on / off is controlled by the output of the delay unit 53, and 55 for the first comparator 41 A second comparator 56 that determines the output level of the level detection circuit 40 that is set with the same threshold and is input from the switch 54 controls the bias value of the APD bias power source 60 according to the determination result of the second comparator 55. It is an APD multiplication factor controller.

  The gain / gain switching control circuit 50 outputs a gain switching signal to the preamplifier gain controller 52 when the output signal from the level detection circuit 40 exceeds the threshold voltage set by the first comparator 51, and the preamplifier The feedback resistance Rf of 30 is switched to a small value, and the gain is switched from high gain to low gain.

  At the same time, the signal passing through the first comparator 51 is input to the delay unit 53, and the switch 54 is turned on after a predetermined time has elapsed. As a result, the output signal from the level detection circuit 40 is also input to the second comparator 55. The delay unit 53 gives a delay until the output signal of the preamplifier 30 after the gain is changed is input again to the multiplication factor / gain switching control circuit 50 via the level detection circuit 40.

  The signal received by the preamplifier 30 whose gain has been changed from high gain to low gain passes through the level detection circuit 40 again, and the detection level is input to the multiplication factor / gain switching control circuit 50. The second comparator 55 has the same threshold value as that of the first comparator 51. When the re-input output level exceeds this threshold value, the second comparator 55 outputs a multiplication factor switching signal to the APD multiplication factor controller 56, and the APD The bias value of the bias power supply 60 is switched, and the APD multiplication factor is switched to a low value.

  The ON operation of the switch 54 in the multiplication / gain switching control circuit 50 and the switching operation of the preamplifier gain controller 52 and the APD multiplication controller 56 are in a state after switching until the reset signal is input after the burst signal ends. Maintained.

  As described above, according to this embodiment, when the preamplifier 30 operates at a high gain and the APD 20 operates at a high gain in the initial state, and the output of the preamplifier 30 reaches a saturation level, the preamplifier gain is first switched to a low value. Thereafter, when the output level of the preamplifier 30 reaches the saturation output level again, the multiplication factor of the APD 20 is switched to a low value (see FIG. 3).

  Therefore, since the switching of the APD multiplication factor is always performed in a state where the gain of the preamplifier 30 is suppressed to a low gain, the linear input operation range of the preamplifier 30 is widened, and it is possible to increase the effect of the APD multiplication factor switching. It is.

  FIG. 4 shows a flowchart of the operation of the burst optical signal receiver of this embodiment. In step S1, the receiving apparatus in which the reset signal is input in the guard time period before the burst optical signal is input initially sets the APD multiplication factor and the preamplifier gain to APD multiplication factor = high value and preamplifier gain = high value. Is done.

  Thereafter, when a burst optical signal is received, the output voltage Vout of the level detection circuit 40 is input to the multiplication factor / gain switching control circuit 50 and compared with a preset threshold value Vth in the first comparator 51 ( Step S2).

  If Vout <Vth is satisfied in step S2, the receiving apparatus receives the burst optical signal as it is in both the gain of the preamplifier 30 and the multiplication factor of the APD 20 (step S6), and prepares for the next burst signal.

  If Vout <Vth is not satisfied in step S2, the gain of the preamplifier 30 is switched from a high value to a low value via the preamplifier gain controller 52 (S3), and the switch 54 is turned on after the delay by the delay unit 53, In the second comparator 55, the output voltage Vout of the level detection circuit 40 is compared with a preset threshold value Vth (step S4).

  In step S4, if Vout <Vth is established, the APD multiplication factor is shifted to step S6 as it is. If Vout <Vth is not established, the APD multiplication factor controller 56 switches the bias value of the APD bias power source 60. Then, after the multiplication factor of the APD 20 is switched from the high value to the low value (step S5), the process proceeds to step S6.

  After the signal determination process in step S6, after the whole is reset, the process proceeds to step S1 again to receive the next burst optical signal.

  As described above, in this embodiment, in a burst optical signal receiving apparatus that receives burst optical signals having different intensities as in the PON system, the preamplifier gain and the APD multiplication factor are set to high values while achieving high sensitivity characteristics. When the preamplifier output level is detected and the preamplifier output level exceeds the preset threshold (preamplifier saturation level), the preamplifier gain is first set to a low value to receive the signal, and the preamplifier output level after changing the preamplifier gain Again exceeds the same threshold value as described above, the signal is received with the APD multiplication factor set to a low value.

  In this way, in addition to preventing preamplifier saturation by switching the preamplifier gain, the allowable light input can be improved by switching the APD multiplication factor. A burst optical signal receiver having a wide dynamic range characteristic can be easily realized.

It is a block diagram which shows schematic structure of the burst optical signal receiver of the Example of this invention. FIG. 2 is a block diagram showing an internal configuration of a multiplication factor / gain switching control circuit of the burst optical signal receiving device of FIG. 1. FIG. 2 is an operational characteristic diagram of the burst optical signal receiving device of FIG. 1. 3 is a flowchart of the operation of the burst optical signal receiving device of FIG. It is a block diagram of a PON system. It is explanatory drawing of the upstream optical signal of a PNO system. It is an operating characteristic figure of the conventional burst optical signal receiver. It is an operating characteristic figure of the burst optical signal receiver of another conventional example.

Explanation of symbols

100: optical fiber, 200: optical splitter, 300: OLT, 400: ONU
10: burst optical signal, 20: APD, 30: preamplifier, 40: level detection circuit, 50: multiplication factor / gain switching control circuit, 60: APD bias power supply, 70: limiter amplifier 51: first comparator, 52: preamplifier Gain controller, 53: delay device, 54: switch, 55: second comparator, 56: APD multiplication controller

Claims (5)

In a burst optical signal receiving method in which burst optical signals having different intensities are received by an APD and linearly amplified as a current signal by a preamplifier and converted into a voltage signal,
The APD multiplication factor and the gain of the preamplifier are set such that the output level of the level detection circuit for detecting the output level of the preamplifier is higher than a threshold when the burst optical signal is low intensity or high intensity. multiplication factor and is set to the first gain value, receiving the burst optical signal, when the output level of the level detection circuit exceeds the threshold, the gain of the preamplifier is lower than the first gain value The gain value is controlled to a gain value of 2, and thereafter , when the output level of the level detection circuit exceeds the threshold value, the multiplication factor of the APD is controlled to a second multiplication factor lower than the first multiplication factor. Burst optical signal receiving method. The burst optical signal receiving method according to claim 1,
The threshold value, the burst optical signal receiving method comprising saturation level der Rukoto of the preamplifier. In burst optical signal receiving apparatus for receiving a different burst optical signal intensity,
An APD that converts the burst optical signal into a current signal;
A preamplifier that linearly amplifies the output current of the APD and converts it into a voltage signal;
A level detection circuit for determining the output level of the preamplifier;
When the burst optical signal has a low intensity or a high intensity, the output level of the level detection circuit is set to a first gain and a first gain value that are higher than a threshold value. A gain and gain switching control circuit for controlling the gain and the gain of the preamplifier based on the output level of the level detection circuit,
The gain / gain switching control circuit controls the gain of the preamplifier to a second gain value lower than the first gain value when the output level of the level detection circuit exceeds the threshold, and then the level when the output level of the detection circuit exceeds the threshold value, the burst optical signal receiving apparatus characterized that you control the multiplication factor of the APD to lower than said first multiplication factor second multiplication factor. In the burst optical signal receiving device according to claim 3 ,
The multiplication factor / gain switching control circuit is
A first comparator that inputs an output signal of the level detection circuit and outputs a first detection signal when the level exceeds the threshold;
A preamplifier gain controller that controls the gain of the preamplifier to the second gain value when the first comparator outputs the first detection signal;
A delay device for delaying the first detection signal output from the first comparator by a predetermined time;
A second comparator that receives the first detection signal delayed by the delay unit and outputs a second detection signal when the level exceeds the threshold;
An APD multiplication controller for controlling the multiplication factor of the APD to the second multiplication factor when the second comparator outputs the second detection signal;
Burst optical signal receiving apparatus according to claim Rukoto equipped with. In the burst optical signal receiver according to claim 3 or 4,
The threshold value, the burst optical signal receiving apparatus, wherein the saturation level der Rukoto of the preamplifier.

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