JP2014230259A - Optical amplifier and photoreceiver using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a feed forward control optical amplifier that is able to exert control such that an output value is constant relative to burst optical signal inputs of different intensities, the optical amplifier being able to widen an input dynamic range by accurately detecting the intensity of the light signal of an input weak burst signal.SOLUTION: In an optical amplifier 42 in which optical amplifiers for amplifying a light signals are connected in series, when an input light signal is equal to or higher than a first identification value set in advance, the first optical amplifier 42-1 connected to the side to which the light signal is input amplifies the input light signal so that this input light signal has a first target value set in advance, and a second optical amplifier 42-2 connected to the one subsequent to the first optical amplifier 42-1 amplifies the first output light signal, output from the first optical amplifier 42-1, to a second target value set in advance.

Description

  The present invention relates to a semiconductor optical amplifier that performs feedforward control that outputs an output optical signal having a constant intensity regardless of the intensity of the input optical signal.

  In an optical subscriber network, a PON (Passive Optical Network) system is widely adopted. In IEEE, standardization of 10G-EPON which is a next generation system as well as G-EPON (Gigabit Ethernet (registered trademark) PON) which has already been commercialized has been completed. In ITU-T, standardization of XG-PON, which is a next-generation system, has been finished as well as B-PON (Broadband PON) and G-PON (Gigabit-capable PON) that have already been commercialized.

  These PONs have a network configuration in which a receiving station and a plurality of subscribers are coupled by a single optical fiber via an optical splitter disposed outside the station. The upstream signal and the downstream signal are the same depending on different wavelengths. It is transmitted in both directions on the optical fiber. The downlink signal is a continuous signal in which a signal for each subscriber is multiplexed using time division multiplexing (TDM) technology, and a transmission / reception device (ONU: Optical Network Unit) arranged in the subscriber is: From the continuous signal branched in the optical splitter, the signal of the time slot required for itself is taken out. The upstream signal is a burst signal that is intermittently transmitted from the ONU, is combined by an optical splitter to become a TDM signal, and is sent to the accommodation station. In this system, the optical fiber from the accommodation station to the optical splitter and the transmission / reception device (OLT: Optical Line Terminal) arranged in the accommodation station can be shared by a plurality of subscribers. Can be provided economically.

  GE-PON, B-PON, and G-PON are commercial systems, but an increase in transmission path loss allowed in the system is one of the problems. If this can be realized, the number of subscribers to be accommodated can be increased by increasing the number of branches of the optical splitter, or the accommodation area can be expanded by extending the transmission distance to improve the accommodation efficiency numerically or planarly. I can expect. In order to solve this problem, a technique has been proposed in which an optical amplifier is used to compensate for the loss of a multi-branch splitter or a lengthened transmission line.

FIG. 1 shows the configuration of a PON system using an optical amplifier. As shown in FIG. 1, the optical repeater 94 is disposed on an optical fiber that couples a transmission / reception apparatus (OLT: Optical Line Terminal) 91 disposed in the accommodation station 95 and an optical splitter 93. When the optical amplifier is disposed outside the accommodating station 95 and used as the repeater 94, it is assumed that the optical amplifier is disposed within the accommodating station 95 and used as a preamplifier. As shown in the illustration, the optical amplifier 42 transmits the bidirectional upstream signal (wavelength λ ₁ ) and the downstream signal (wavelength λ ₂ ) bidirectionally using the two optical multiplexers 41. It is the structure to amplify. As the optical amplifier 42 to be used, an optical fiber amplifier to which rare earth is added, a concentrated amplification type optical fiber Raman amplifier, a semiconductor optical amplifier (SOA), or the like can be used. In particular, SOA has advantages over other optical amplifiers in terms of miniaturization, economy, and power saving, and is a highly expected optical device in an optical subscriber network with strict cost requirements.

  One of the major problems in the PON system using the optical amplifier 42 is the realization of an optical amplifier that amplifies the upstream signal. The upstream signal varies in intensity of the burst signal input to the optical amplifier 42 due to a difference in the distance from the ONU 92 to the optical splitter 93, individual differences in transmitter output in the ONU 92, and the like. The problem here is not a burst signal having a low light intensity but a burst signal having a high light intensity. When a strong burst signal is input to the optical amplifier 42, the output of the optical amplifier 42 naturally increases. When the transmission distance after optical amplification is not so long, the receiver in the OLT 91 exceeds the upper limit of reception sensitivity. There is a problem that a signal is input and the signal cannot be received. When SOA is used as the optical amplifier 42, the response time of the SOA in the amplification process is almost the same as the bit length of the giga-class signal, so that the light intensity of the input burst signal is large and amplified in the saturation region. There is a problem in that signal waveform deterioration called a pattern effect occurs due to excessive optical amplification at the rise of each bit. In other words, in order to apply the SOA-based optical amplifier 42 to the PON, “(1) Make the transmittable distance after optical amplification constant regardless of the input light intensity”, “(2) It is required to expand the input dynamic range in two meanings of “reducing the influence of the SOA pattern effect on the strong signal input”.

  The meaning of (1) can be solved by controlling the light intensity at the output of the optical amplifier 42 to a constant value. Although the purpose is different, a feedforward control optical amplifier capable of controlling the output value to be constant has been proposed in order to relax the requirement for the input dynamic range of the burst receiver (for example, Patent Document 1 and Non-Patent Document). Reference 1).

  FIG. 2 shows a basic configuration according to Non-Patent Document 1. This optical amplifier includes an optical branching device 1, an optical / electrical converter 2, a control circuit 3, a driving circuit 4, and an SOA 5. The optical branching device 1 branches a part of the input burst optical signal. The photoelectric converter 2 converts the branched burst optical signal into an electrical signal. The control circuit 3 stores a relational expression calculated based on input light intensity and output light intensity data with respect to a change in the drive current of the SOA 5 acquired in advance, and is output from the SOA 5 with respect to the input light intensity read from the electrical signal. The drive current at which the light intensity becomes the target value is calculated. The drive circuit 4 sends out the calculated drive signal current. The SOA 5 is driven by the drive signal current, and the gain is adjusted according to the light intensity of the input burst signal. Although not shown, in order to match the timing at which the optical signal whose input light intensity is detected is input to the SOA 5 and the timing at which the SOA 5 is driven by the drive signal current, as described in Patent Document 1, it is necessary. Accordingly, a delay line is arranged between the optical branching device 1 and the SOA 5. As described above, with the configuration using the feedforward control method, the intensity of the input burst optical signal can be controlled to be a constant target value at the output.

  In Patent Document 1, an optical amplifier having an optical amplification function and an optical attenuator for adjusting the light intensity are separated, whereas the structure shown in FIG. Since it is realized with one SOA 5, the number of optical components to be used can be reduced. Further, when a strong burst signal is input, the current for driving the SOA 5 is reduced, so that the SOA 5 is less likely to be saturated compared to the case where the driving current is fixed, and the influence of the pattern effect is alleviated. In meaning, the input dynamic range is expanded.

  However, in the configuration shown in FIG. 2, since the intensity of the input burst optical signal is observed using the branched light, there is a problem that the light intensity cannot be accurately detected with respect to the weak burst optical signal input.

JP 2010-226685 A

N. Cheng, S.M. -H. Yen, J .; Cho, Z .; Xu, T .; Yang, Y. et al. Tang, and L.L. G. Kazovsky, “Long Reach Passive Optical Networks with Adaptive Power Powering Usage Semiconductor Amplifiers,” ACP'2009.

  The present invention accurately detects the optical signal intensity of an input weak burst signal in a feedforward control optical amplifier capable of controlling the output value to be constant with respect to burst optical signal inputs having different intensities. An object of the present invention is to provide an optical amplifier capable of expanding the input dynamic range.

An optical amplifier according to the present invention includes:
An optical amplifier in which optical amplifiers for amplifying optical signals are connected in cascade,
The first optical amplifier connected to the optical signal input side of the optical amplifier, when the input optical signal is greater than or equal to a preset first identification value or more than the first identification value, Amplifying the input optical signal so as to be a first target value set in advance,
The second optical amplifier connected to the subsequent stage of the first optical amplifier among the optical amplifiers detects and detects the light intensity of the first output optical signal output from the first optical amplifier. Amplification is performed so that the second target value is set in advance according to the light intensity.

In the optical amplifier according to the present invention,
The first optical amplifier is:
A first branching device for branching an input optical signal into a first main signal and a first monitor light;
A first SOA for amplifying the first main signal using a supplied drive current;
A first photoelectric converter for converting the first monitor light into a first electrical signal;
When the amplitude value of the first electric signal is greater than or equal to a first identification value set in advance or greater than the first identification value, the light intensity of the input optical signal using the amplitude value of the first electric signal A first control circuit that calculates the drive current of the first SOA so that the input optical signal of the calculated light intensity becomes a preset first target value;
When the first SOA amplifies the first main signal in which the amplitude value of the first electric signal is greater than or equal to a preset first identification value or exceeds the first identification value, the first SOA A first drive circuit for sending the drive current calculated by the control circuit to the first SOA;
With
The second optical amplifier is:
A second branching device for branching the first output optical signal output from the first SOA into a second main signal and a second monitor light;
A second SOA for amplifying the second main signal using the supplied drive current;
A second photoelectric converter that converts the second monitor light into a second electrical signal;
The light intensity of the first output optical signal is calculated using the amplitude value of the second electrical signal, and the second SOA is driven so that the calculated light intensity becomes a preset second target value. A second control circuit for calculating the current;
A second drive circuit that sends the drive current calculated by the second control circuit to the second SOA when the second SOA amplifies the second main signal;
May be provided.

  In the optical amplifier according to the present invention, the first control circuit has one or more identification values, determines a vertical relationship between an amplitude value of the first electric signal and each identification value, and the first control circuit Each time the amplitude value of the electrical signal exceeds each identification value or exceeds each identification value, a constant driving current smaller than the driving current at the identification value may be calculated.

  In the optical amplifier according to the present invention, the first control circuit and the second control circuit may be configured by a common control circuit.

  In the optical amplifier according to the present invention, the optical signal is a burst optical signal, and the second control circuit calculates a guard time of the burst optical signal of the optical signal from an amplitude value of the second electric signal. The second drive circuit may turn off the second drive current when the guard time determined by the second control circuit passes through the second SOA.

An optical receiver according to the present invention includes:
An optical amplifier according to the present invention, wherein a burst optical signal is input as the optical signal;
An optical reception front end for converting a burst optical signal output from the optical amplifier into an electrical signal;
A signal processing unit that receives a burst optical signal input to the optical amplifier using an electrical signal output from the optical reception front end;
Is provided.

  According to the present invention, in a feedforward control optical amplifier capable of controlling the output value to be constant with respect to burst optical signal inputs having different intensities, the light of a weak burst signal input using cascaded optical amplifiers. An optical amplifier capable of expanding the input dynamic range by accurately detecting the signal intensity can be provided.

1 shows an example of a PON system using an optical amplifier. An example of the related optical amplifier using a feedforward control system is shown. An example of the optical amplifier which concerns on 1st embodiment is shown. An example of the relationship between the input light intensity and the output light intensity of the optical amplifier according to the first embodiment is shown. An example of the relationship between input light intensity and output light intensity when a related optical amplifier is used is shown. An example of the relationship between input light intensity and output light intensity at the time of using the optical amplifier which concerns on 2nd embodiment is shown. An example of the relationship between input light intensity and output light intensity at the time of using the optical amplifier which concerns on 3rd embodiment is shown. An example of the optical amplifier which concerns on 4th embodiment is shown. The structural example of the optical reception front end in the case of performing optical heterodyne detection using polarization diversity is shown. A configuration example of an optical reception front end when optical homodyne detection is performed using polarization diversity and phase diversity will be described.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(First embodiment)
FIG. 3 shows a first embodiment of an optical amplifier according to the present invention. The present optical amplifier 42 includes a first optical amplifier 42-1 and a second optical amplifier 42-2 connected in cascade. The first optical amplifier 42-1 includes a first optical branch 1-1, a first photoelectric converter 2-1, a first control circuit 3-1, a first drive circuit 4-1, and a first optical circuit 42-1. One SOA 5-1 is provided. The second optical amplifier 42-2 includes a second optical splitter 1-2, a second photoelectric converter 2-2, a second control circuit 3-2, a second drive circuit 4-2, Two SOAs 5-2 are provided. In this embodiment, the case where the input optical signal is a burst optical signal will be described. However, the present invention is not limited to the burst signal and can be applied to any optical signal.

  The first optical branching device 1-1 branches a part of the input burst optical signal and sends it to the first photoelectric converter 2-1 as the first monitor light. The other branched light is sent to the first SOA 5-1 as the first main signal. The first photoelectric converter 2-1 converts the branched first monitor light into a first electrical signal and sends it to the first control circuit 3-1.

  The first control circuit 3-1 stores a relational expression created based on the input light intensity and output light intensity data with respect to the drive current change acquired in advance for the first SOA 5-1. The vertical relationship between the amplitude value of one electrical signal and a preset identification value is determined. If it is determined that the identification value exceeds or exceeds the identification value, the light intensity of the burst optical signal input from the amplitude value is detected.

  Further, the first control circuit 3-1 calculates a drive current in which the light intensity output from the first SOA 5-1 becomes a preset first target value with respect to the detected input light intensity. And sent to the first drive circuit 4-1. In this case, the relational expression created based on the data of the input light intensity and the output light intensity with respect to the drive current change is a relational expression of the drive current for outputting the first target value and the input light intensity. On the other hand, the vertical relationship between the amplitude value of the first electric signal and the preset identification value is determined, and if it is determined to be less than or less than the identification value, this is communicated to the first drive circuit 4-1. The first drive circuit 4-1 sends out the calculated drive current when the amplitude value of the first electric signal exceeds or exceeds the identification value, and the amplitude value of the first electric signal is When it is determined that the value is equal to or less than the identification value, a constant value of drive current (hereinafter referred to as the first drive current) that is continuous with the calculated drive current is transmitted. The first SOA 5-1 is driven by the first drive current, and inputs the amplified optical burst signal to the second optical splitter 1-2. The relationship between the input light intensity and the output light intensity when the output light intensity control is performed is illustrated as the left diagram in FIG.

  The burst optical signal output from the first SOA 5-1 is input to the second optical splitter 1-2. The second optical branching device 1-2 branches a part of the input burst optical signal and sends it to the second photoelectric converter 2-2 as second monitor light. The other branched light is sent to the second SOA 5-2 as a second main signal. The second photoelectric converter 2-2 converts the branched second monitor light into a second electrical signal and sends it to the second control circuit 3-2.

  The second control circuit 3-2 stores a relational expression created based on the data of the input light intensity and the output light intensity with respect to the drive current change acquired in advance for the second SOA 5-2. The light intensity of the burst optical signal input from the amplitude value of the second electric signal is detected, and the light intensity output from the second SOA 5-2 is set to the preset second intensity with respect to the detected input light intensity. Is calculated and sent to the second drive circuit 4-2. In this case, the relational expression created based on the data of the input light intensity and the output light intensity with respect to the driving current change is a relational expression of the driving current for outputting the second target value and the input light intensity. The second drive circuit 4-2 sends out the calculated drive current (second drive current). The second SOA 5-2 is driven by the second drive current, and outputs an optical burst signal that is amplified and controlled to a constant value. The relationship between the input light intensity and the output light intensity when the output light intensity control is performed is illustrated as shown on the right side of FIG. The final output light intensity is shown in the right diagram of FIG. 4 and outputs a constant light intensity with respect to the operation input range of the optical amplifier.

  FIG. 5 shows the relationship between the input light intensity and the output light intensity when the related optical amplifier is used. As shown in FIG. 5, in the configuration of the related optical amplifier, since it is necessary to detect the light intensity of the input light in the entire operation input range, the light intensity detection is not performed for the weak burst signal input. The lower limit value cannot be lowered and the input dynamic range becomes narrow. On the other hand, this optical amplifier employs a two-stage amplification configuration based on SOA, and detects light intensity when a weak burst signal less than or less than a preset identification value is input to the first SOA 5-1. By driving the first SOA 5-1 with a constant drive current without performing the steps, the lower limit value of the operation input range can be lowered and the input dynamic range can be expanded. In addition, when a burst optical signal exceeding the identification value or the following burst optical signal is input, the drive current of the first SOA 5-1 is lowered, and control is performed so that a constant light intensity is output, Mitigates the effects of pattern effects. The second SOA 5-2 controls the optical input intensity in the operation input range so that a constant optical intensity is finally output, and at the same time, increases the output optical intensity by the two-stage amplification configuration. Have.

  In the present embodiment, the case where the first control circuit 3-1 and the second control circuit 3-2 are separated has been described. However, even if the above operation is realized by a common control circuit and the single control circuit. Good.

(Second embodiment)
FIG. 6 shows an example of the relationship between the input light intensity and the output light intensity when the second embodiment of the optical amplifier according to the present invention is used. The configuration of the optical amplifier according to this embodiment is the same as that of the first embodiment. The control mechanism of the first SOA 5-1 is the same as that of the first embodiment. The difference is the control mechanism of the second SOA 5-2.

  The burst optical signal output from each ONU 92 is transmitted with the light intensity during the non-transmission time turned off in order to prevent optical interference with burst optical signals output from other ONUs 92. When optical amplification is performed by the amplifier 42, spontaneous emission light noise emitted by the optical amplifier 42 is added at all times including the non-transmission time. After optical amplification, it is not a problem if it is transmitted and received as it is in the receiver of OLT 91. However, when multiple branches are combined again via optical splitter 93 and then received in the receiver of OLT 91, other branches are connected. A problem arises in that spontaneous emission light noise is superimposed on the burst optical signal that has passed through, and the SNR (Signal-to-Noise Ratio) of the signal deteriorates.

  In order to avoid this, in the optical amplifier according to the present embodiment, the second control circuit 3-2 receives an optical signal less than the preset non-transmission time identification value OG or less than the non-transmission time identification value OG. If it is determined, the drive current output from the second drive circuit 4-2 is turned off.

  For example, it is preferable not to amplify the burst signal at the guard time. Therefore, the second control circuit 3-2 determines the guard time of the burst signal from the amplitude value of the second electric signal. The non-transmission time identification value OG is used for the guard time determination. Then, the second drive circuit 4-2 turns off the second drive current at the guard time determined by the second control circuit 3-2.

  With the configuration of the present embodiment, it is possible to prevent the spontaneous emission light from being superimposed on the burst optical signal that has passed through another branch at that time.

  Note that it is very difficult to perform this control in the first SOA 5-1 because the non-transmission time identification value becomes an extremely low value. In contrast, if the non-transmission time is detected when the second SOA 5-2 is controlled, the light intensity of the burst optical signal is amplified by the first SOA 5-1, and the non-transmission time identification value OG is increased. Since it can be set, it can be easily realized.

(Third embodiment)
FIG. 7 shows an example of the relationship between the input light intensity and the output light intensity when the third embodiment of the optical amplifier according to the present invention is used. The configuration of the optical amplifier according to this embodiment is the same as that of the first embodiment. The control mechanism of the second SOA 5-2 is the same as that of the first embodiment. What is different is the control mechanism of the first SOA 5-1.

  The first control circuit 3-1 has one or more identification values IT <b> 1 and IT <b> 2 set in advance, and determines the vertical relationship between the amplitude value of the first electrical signal and each identification value. Each time the first drive circuit 4-1 determines that the amplitude value of the first electrical signal exceeds each identification value IT1 or IT2, or the amplitude value of the first electrical signal is greater than or equal to each identification value IT1 or IT2. In addition, a driving current having a constant value LO, which is smaller than the driving current at the identification value, is sent out.

  For example, the first SOA 5-1 outputs an output light intensity that linearly increases from OL to OC1 according to the input light intensity when the input light intensity to the first SOA 5-1 is greater than IL and less than IT1. If the input light intensity to the first SOA 5-1 is not less than IT and less than IT2, an output light intensity that linearly increases from OL to OC1 according to the input light intensity is output, and the first SOA 5-1 is output. When the input light intensity to IT2 is greater than or equal to IT2 and less than IH, an output light intensity that linearly increases from OL to OC1 according to the input light intensity is output. Thereby, the first SOA 5-1 outputs an optical signal having a light intensity of OL or more and OC1 or less.

  Similarly to the first embodiment, the optical amplifier drive mechanism also detects the light intensity when a weak burst signal of less than or equal to the preset minimum identification value is input to the first SOA 5-1. By not driving the first SOA 5-1 with a constant drive current, the lower limit value of the operation input range can be lowered to widen the input dynamic range. Similarly to the first embodiment, when the minimum discriminating value is exceeded or the following burst optical signal is input, the influence of the pattern effect is reduced by lowering the driving current of the first SOA.

  FIG. 7 shows a case where the maximum output light intensity of the first SOA 5-1 is controlled to be the same OC1 as in the first embodiment, but the number of identification values such as IT1 and IT2 is increased. Thus, by reducing the drive current of the first SOA 5-1 at the same input light intensity, the influence of the pattern effect can be further alleviated.

(Fourth embodiment)
FIG. 8 shows a fourth embodiment of the optical receiver using the optical amplifier according to the present invention. The configuration and control mechanism of the optical amplifier used in this embodiment are the same as those in the first to third embodiments. The optical receiver according to the present embodiment receives an optical reception front end 43, an analog / digital converter (ADC) 44, and a digital signal processing circuit (DSP: Digital) in order to receive a burst optical signal. Signal Processor) 45 is provided.

  In the present embodiment, not only the intensity modulation signal normally used in the PON, but also a modulation signal having two or more values used in so-called optical coherent communication in which information is superimposed on the phase and frequency is not limited to the amplitude. The optical reception front end 43 plays a role of converting an optical signal into an electric signal. For example, when receiving an intensity modulation signal, the optical reception front end 43 uses a normal photoelectric converter. When receiving a modulated signal used in optical coherent communication, the optical reception front end 43 performs polarization diversity and phase diversity, and thus an optical circuit that realizes the function is provided before the photoelectric converter.

  FIG. 9 shows an example of a circuit configuration of the optical reception front end 43 when optical heterodyne detection is performed using polarization diversity. FIG. 10 shows an example of a circuit configuration of the optical reception front end 43 when optical homodyne detection is performed using polarization diversity and phase diversity. When optical coherent detection is performed, local light is used to improve reception sensitivity and demodulate a multilevel modulation signal.

  The optical heterodyne detection shown in FIG. 9 uses local light whose optical frequency is shifted by at least the symbol rate with respect to the optical frequency of the optical signal, whereas the optical homodyne detection shown in FIG. 10 uses the optical frequency of the optical signal. And local light with the same optical frequency is used. Polarization diversity is used when optical heterodyne detection and optical homodyne detection are performed. In the polarization separator 33, an optical signal is separated into mutually orthogonal polarization components, and local light of the same polarization is coupled to each. Thus, it serves to prevent the signal from becoming unreceivable due to the difference in the polarization state between the optical signal and the local light.

  The polarization rotator 34 is for matching the polarization-separated optical signal with the polarization of the local light. In FIG. 9, the polarization of the local light is rotated by 90 degrees. On the other hand, phase diversity is used when optical homodyne detection is performed, and plays a role of preventing signals from becoming unreceivable due to a difference in optical phase between an optical signal and local light. The phase delay devices 39X and 39Y are for shifting the phase of the branched local light from each other. In FIG. 10, the optical phase of the local light is delayed by 90 degrees.

  Note that FIG. 8 shows a case where the output of the photoelectric converter provided in the optical reception front end 43 is one assuming the case of receiving an intensity modulation signal, but in the case of performing polarization diversity or phase diversity As shown in FIGS. 9 and 10, a plurality of photoelectric converters to be used are required, and the same number of analog electrical signals are output. Note that the circuit configurations illustrated in FIGS. 9 and 10 are merely examples, and various circuit configurations have been proposed.

  The output analog electric signal is sampled by the ADC 44, converted into a digital signal, processed by the DSP 45, and received. When using polarization diversity or phase diversity, an ADC 44 is connected to the subsequent stage of each photoelectric converter provided in the optical reception front end 43, and a digital signal output from each ADC 44 is sent to the DSP 45. An advantage of using the DSP 45 at the time of signal reception is that a waveform that has deteriorated due to demodulation of a multi-modulation signal, wavelength dispersion of a transmission line, or the like can be easily realized. However, when receiving a burst optical signal, analog electrical signals corresponding to different light intensities are input to the ADC 44. For this reason, if the quantization of the amplitude direction of the ADC 44 is optimized for a strong burst optical signal, a weak burst optical signal cannot be detected. Conversely, if the ADC 44 is optimized for a weak burst signal, the strong burst optical signal cannot be detected. Occurs. For this reason, the optical amplifier 42 according to the present invention is arranged before the optical reception front end 43 converts the optical signal into an electrical signal, so that a burst optical signal controlled to a constant light intensity can be obtained. Therefore, this problem can be avoided. Further, since the present optical amplifier 42 can operate even for weak burst signal input, if it is used as a preamplifier, it can receive signals with high sensitivity. The optical receiver according to the present embodiment can be used not only as an upstream optical receiver in the PON system but also as an downstream optical receiver in the PON system.

  The present invention can be applied to the information communication industry.

DESCRIPTION OF SYMBOLS 1, 1-1, 1-2: Optical splitter 2, 2-1, 2-2: Photoelectric converter 3, 3-1, 3-2: Control circuit 4, 4-1, 4-2: Drive Circuits 5, 5-1, 5-2: SOA
31: Local light source 32, 37, 38X, 38Y: Branch device 33: Polarization separator 34: Polarization rotator 35X, 35Y: Coupler 36X, 36Y: Photoelectric converter 39X, 39Y: Phase delay device 41: Multiplexer / demultiplexer 42: optical amplifier 42-1: first optical amplifier 42-2: second optical amplifier 43: optical reception front ends 44, 44X, 44Y: analog / digital converter 45: digital signal processing circuit 91 : OLT
92: ONU
93: Optical splitter 94: Optical repeater 95: Accommodating station

Claims (6)

An optical amplifier in which optical amplifiers for amplifying optical signals are connected in cascade,
The first optical amplifier connected to the optical signal input side of the optical amplifier, when the input optical signal is greater than or equal to a preset first identification value or more than the first identification value, Amplifying the input optical signal so as to be a first target value set in advance,
The second optical amplifier connected to the subsequent stage of the first optical amplifier among the optical amplifiers detects and detects the light intensity of the first output optical signal output from the first optical amplifier. Amplified to become a second target value set in advance according to the light intensity
Optical amplifier. The first optical amplifier is:
A first branching device for branching an input optical signal into a first main signal and a first monitor light;
A first SOA for amplifying the first main signal using a supplied drive current;
A first photoelectric converter for converting the first monitor light into a first electrical signal;
When the amplitude value of the first electric signal is greater than or equal to a first identification value set in advance or greater than the first identification value, the light intensity of the input optical signal using the amplitude value of the first electric signal A first control circuit that calculates the drive current of the first SOA so that the input optical signal of the calculated light intensity becomes a preset first target value;
When the first SOA amplifies the first main signal in which the amplitude value of the first electric signal is greater than or equal to a preset first identification value or exceeds the first identification value, the first SOA A first drive circuit for sending the drive current calculated by the control circuit to the first SOA;
With
The second optical amplifier is:
A second branching device for branching the first output optical signal output from the first SOA into a second main signal and a second monitor light;
A second SOA for amplifying the second main signal using the supplied drive current;
A second photoelectric converter that converts the second monitor light into a second electrical signal;
The light intensity of the first output optical signal is calculated using the amplitude value of the second electrical signal, and the second SOA is driven so that the calculated light intensity becomes a preset second target value. A second control circuit for calculating the current;
A second drive circuit that sends the drive current calculated by the second control circuit to the second SOA when the second SOA amplifies the second main signal;
Comprising
The optical amplifier according to claim 1.   The first control circuit has one or more identification values, determines a vertical relationship between the amplitude value of the first electric signal and each identification value, and the amplitude value of the first electric signal is each identification value. 3. The optical amplifier according to claim 2, wherein a driving current having a constant value smaller than the driving current at the identification value is calculated every time the value exceeds or exceeds each identification value.   4. The optical amplifier according to claim 2, wherein the first control circuit and the second control circuit are configured by a common control circuit. 5. The optical signal is a burst optical signal;
The second control circuit determines a guard time of the burst optical signal among the optical signals from the amplitude value of the second electric signal,
5. The second drive circuit turns off the second drive current when the guard time determined by the second control circuit passes through the second SOA. 6. An optical amplifier according to any one of the above. The optical amplifier according to any one of claims 1 to 5, wherein a burst optical signal is input as the optical signal;
An optical reception front end for converting a burst optical signal output from the optical amplifier into an electrical signal;
A signal processing unit that receives a burst optical signal input to the optical amplifier using an electrical signal output from the optical reception front end;
An optical receiver comprising:

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