JP2012015866A - Bidirectional optical amplifier, pon system using same, and communication method - Google Patents

Abstract

The present invention relates to a passive double star type PON system, which does not deteriorate upstream signal light in a short-distance area even when accommodating both a long-distance area and a short-distance area subscriber at the same time. An object is to provide an optical amplifier.
A bidirectional optical amplifier according to the present invention includes a first multiplexer / demultiplexer 31 and a second multiplexer / demultiplexer 32 that multiplex and demultiplex a downstream signal light and an upstream signal light, and the intensity of the downstream signal light. A first optical amplifier 33 that amplifies, a second optical amplifier 34 that amplifies the intensity of the upstream signal light, an optical regulator 11 that attenuates or blocks ASE light generated in the second optical amplifier, and an upstream signal And a control circuit 14 that operates the light adjuster 11 when there is light and stops the operation of the light adjuster 11 when there is no upstream signal.
[Selection] Figure 2

Description

  The present invention relates to a bidirectional optical amplifier used in a passive double star PON system, a PON system using the same, and a communication method.

  IEEE (The Institute of Electrical and Electronics Engineers) and ITU-T (International Telecommunication Union Teal to provide high-speed access to the standard service, and the telecommunications service of the ITU-T (International Telecommunition Union Telecom Standard). . IEEE has finished standardization of G-EPON (Gigabit Ethernet (registered trademark) PON) and 10G-EPON of next-generation systems that have already been commercialized, and ITU-T has already commercialized B-E Standardization of PON (Broadband PON) and G-PON (Gigabit-capable PON) has been completed, and standardization of XG-PON of the next generation system is being promoted.

  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 light and the downstream signal light have different wavelengths. The data is transmitted bidirectionally on the same optical fiber. The downlink signal light is a continuous signal in which a signal for each subscriber is multiplexed using a time division multiplexing (TDM) technique, and a transmission / reception apparatus (ONU: Optical Network Unit) arranged in the subscriber is From the continuous signal branched in the optical splitter, the signal of the time slot necessary for itself is taken out. The upstream signal light is a burst signal that is intermittently transmitted from the ONU, is combined by an optical splitter to become a TDM signal, and is transmitted 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 and G-PON are already completed systems, but lengthening of the transmission path is one of the problems. If this can be realized, it can be expected that the accommodation efficiency is improved in terms of number or area by increasing the number of subscribers accommodated by increasing the number of branches of the optical splitter or expanding the accommodation area. In order to solve this problem, there have been proposed optical splitters with an increased number of branches using optical amplifiers and methods for compensating for the loss of the lengthened transmission line (for example, see Non-Patent Documents 1 and 2). ).

FIG. 5 shows the configuration of a PON system using a bidirectional optical amplifier. Shown here is a passive double star type network configuration in which an optical splitter is arranged not only outside but also inside, and among the optical fibers branched from the inside optical splitter, the addition of the long-distance area _AL is shown. A bidirectional optical amplifier 153 is arranged to accommodate the person. Although FIG. 5 shows a case where the bidirectional optical amplifier 153 is arranged in the place, it may be arranged outside the place. As shown in the figure, the bidirectional optical amplifier 153 amplifies bidirectional downstream signal light (wavelength λ ₁ ) and upstream signal light (wavelength λ ₂ ) by separate optical amplifiers using two multiplexers / demultiplexers. It is the structure to do. According to this network configuration, the subscriber of the small number of long-distance area A _L, by accommodating the same OLT52 the subscriber of the near area A _S, it is possible to improve the efficiency of the system housing.

Derek Nesset et al. "Demonstration of 100 km Reach Amplified PONs with Upstream Bit-rates of 2.5 Gb / s and 10 Gb / s", ECOC 2004, We 2.6.3. Ken-Ichi Suzuki et al. , “60 km, 256-split Optically-amplified PON Repeated Transmission using 1.24 Gbit / s Upstream and 2.5 Gbit / s Downstream PON system”, ECOC 2006, Mo4.5.3.

However, since the optical amplifier emits spontaneous emission (ASE) light, the problem of signal degradation due to this must be considered. FIG. 6 shows the intensity levels of the upstream signal light in the long-distance area A _L and the short-distance area A _S before and after being coupled by the in-house optical splitter. As shown, the upstream signal light before multiplexing the near area A _S, the second ONU 51 _S group is at the zero level in the non-transmission time which does not transmit any frames. On the other hand, the upstream signal light in the long-distance area A _L is lifted from the zero level even in the non-transmission time of the frame because the ASE is superimposed at all times when the first ONU 51 _L group transmits the frame. When these are combined by the optical splitter, the ASE is also superimposed on the upstream signal light in the short-distance area. As a result, the upstream signal light of the near area A _S which is not amplified by the optical amplifier, the influence of the relatively ASE becomes larger than the upward signal light of the long-distance area A _L, so that the signal is deteriorated.

The present invention, in a passive double star type PON system, even when simultaneously accommodating subscribers distant area A _L and near the area A _S, degrading the upstream signal light of the near area A _S It is an object of the present invention to provide a bidirectional optical amplifier, a PON system using the same, and a communication method.

  In order to achieve the above object, the present invention relates to a PON system using a bidirectional optical amplifier that accommodates ONUs installed in a long-distance area and a short-distance area, and the bidirectional optical amplifier is installed in a long-distance area. The signal from the ONU installed in the long-distance area is not transmitted by determining the time when the signal from the ONU is not transmitted and suppressing the generation of spontaneous emission (ASE) light during the time when the signal is not transmitted. It is possible to eliminate the influence of the ASE light on the signal from the ONU installed in the short distance area in time.

  Specifically, the bidirectional optical amplifier according to the present invention transmits a downstream signal light transmission path for transmitting a downstream signal light having a first wavelength and an upstream signal light having a second wavelength different from the first wavelength. The downstream signal light is input from the upstream optical fiber disposed upstream of the upstream optical signal transmission path, the downstream downstream optical signal transmission path, and the upstream upstream optical fiber, and the downstream downstream optical signal is demultiplexed. Then, the first multiplexed / demultiplexed signal that is output to the downstream optical signal transmission line, is input with the upstream optical signal transmitted through the upstream optical signal transmission path, and outputs the input upstream signal light to the upstream optical fiber. And upstream signal light from a downstream optical fiber disposed downstream of the downstream signal light transmission line and the upstream signal light transmission line, and the upstream signal light is demultiplexed to demultiplex the upstream signal light. Output to the optical transmission line and transmitted through the downstream optical signal transmission line. A second multiplexer / demultiplexer that receives the signal light and outputs the input downstream signal light to the downstream optical fiber, and a first amplifier that is inserted into the downstream signal light transmission path and amplifies the intensity of the downstream signal light. An optical amplifier, a second optical amplifier that is inserted into the upstream optical signal transmission path and amplifies the intensity of upstream optical signal, and ASE (Amplified Spontaneous Emission) light generated in the second optical amplifier is attenuated or A light controller for blocking, a control circuit for determining the presence or absence of upstream signal light, operating the light controller when there is no upstream signal light, and stopping the operation of the light controller when there is upstream signal light; .

  The bidirectional optical amplifier of the present invention includes a downstream optical signal transmission line, an upstream optical signal transmission line, a first multiplexer / demultiplexer, a second multiplexer / demultiplexer, a first optical amplifier, Therefore, the upstream signal and the downstream signal can be amplified. Here, since the bidirectional optical amplifier of the present invention includes the optical regulator and the control circuit, it is possible to prevent the output of the ASE light from the bidirectional optical amplifier in the time zone in which there is no upstream signal light. Therefore, the bidirectional optical amplifier according to the present invention deteriorates the upstream signal light in the short-distance area even in the case where the long-distance area and short-distance area subscribers are accommodated simultaneously in the passive double star PON system. A bidirectional optical amplifier can be provided.

In the bidirectional optical amplifier according to the present invention, the optical modulator is an optical attenuator that is inserted in an optical path between the second optical amplifier and the first multiplexer / demultiplexer, and attenuates the light intensity. An optical branching device that is inserted in an optical path between the second multiplexer / demultiplexer and the optical attenuator and branches the upstream signal light; and the control circuit uses the light intensity branched by the optical branching device. The optical attenuator attenuates the light intensity when there is no upstream signal light, and the optical attenuator does not attenuate the light intensity when there is upstream signal light. Good.
Since the optical adjuster is an optical attenuator, not only can the ASE light be blocked, but also the level of the upstream burst signal having a different intensity can be controlled to be constant, or the optical level of the signal having a high intensity can be reduced. Thereby, it is possible to prevent a strong optical signal from being input to the receiver in the OLT.

In the bidirectional optical amplifier according to the present invention, the optical modulator is an optical blocker that is inserted in an optical path between the second optical amplifier and the first multiplexer / demultiplexer and blocks light, An optical branching device that is inserted in an optical path between the second multiplexer / demultiplexer and the optical attenuator and branches the upstream signal light; and the control circuit uses the light intensity branched by the optical branching device. The configuration may be such that the presence or absence of upstream signal light is determined, the light blocker blocks light when there is no upstream signal light, and the light blocker passes light when there is upstream signal light.
Since the optical regulator is an optical circuit breaker, not only can the ASE light be blocked, but the level of the upstream burst signal having different intensities can be controlled to be constant, or the light level of the signal having a large intensity can be reduced. Thereby, it is possible to prevent a strong optical signal from being input to the receiver in the OLT.

  In the bidirectional optical amplifier according to the present invention, the optical modulator is a pumping light source that supplies pumping light to the second optical amplifier, and is between the second multiplexer / demultiplexer and the second optical amplifier. An optical branching device that branches the upstream signal light, and the control circuit determines the presence or absence of upstream signal light using the light intensity branched by the optical branching device, and there is no upstream signal light The configuration may be such that the supply amount of the excitation light supplied from the excitation light source is decreased, and when the upstream signal light is present, the supply amount of the excitation light supplied from the excitation light source is increased.

  Since the light modulator is an excitation light source, the ASE light can be attenuated without using an optical attenuator or an optical breaker.

  Specifically, in the PON system of the present invention, the first optical splitter that connects the first ONU groups to each other, and the second optical unit that connects the second ONU groups different from the first ONU groups to each other. A splitter, a third optical splitter connecting the first optical splitter and the second optical splitter to the OLT, and an optical path between the third optical splitter and the first optical splitter. A bidirectional optical amplifier according to the present invention, wherein a distance from the third optical splitter to the first ONU group is longer than a distance from the third optical splitter to the second ONU group .

  Since the PON system of the present invention includes the first optical splitter, the second optical splitter, and the third optical splitter, a passive double star PON system can be configured. Here, since the PON system of the present invention includes the bidirectional optical amplifier according to the present invention, the upstream signal light in the short-distance area can be received even when the subscribers in the long-distance area and the short-distance area are accommodated simultaneously. A PON system that does not deteriorate can be provided.

  Specifically, the communication method of the PON system of the present invention is a communication method of a passive double star type PON system in which a plurality of ONU groups having different distances are connected to the OLT by an optical splitter, The downstream signal light transmitted through the optical fiber connecting the ONU group in the long-distance area and the optical splitter is demultiplexed and amplified, and then output to the ONU group in the long-distance area. , Having an amplification procedure for demultiplexing and amplifying the upstream signal light transmitted through the optical fiber and then outputting it to the OLT toward the OLT, and determining whether or not there is upstream signal light in the amplification procedure, When there is upstream signal light, the upstream signal light is demultiplexed and amplified, and then output to the optical fiber toward the OLT. When there is no upstream signal light, Or blocking attenuate the ASE light generated at the time of amplification of the signal light.

  Since the communication method of the PON system of the present invention has an amplification procedure, it is possible to amplify the downstream signal light and the upstream signal light on the optical fiber branched from the optical splitter in the accommodation station. Here, since the ASE light is attenuated or blocked when there is no upstream signal light, the upstream signal light in the short-distance area is deteriorated even when the subscribers in the long-distance area and the short-distance area are accommodated at the same time. It is possible to provide a communication method for a PON system without any problem.

In the communication method of the present invention, in the amplification procedure, the ASE light may be reduced by attenuating light with an optical attenuator.
According to the present invention, not only the ASE light can be attenuated, but also the level of an upstream burst signal having different intensities can be controlled to be constant, or the optical level of a signal having a high intensity can be reduced. Thereby, it is possible to prevent a strong optical signal from being input to the receiver in the OLT.

In the communication method of the present invention, in the amplification procedure, the ASE light may be reduced by blocking light with an optical breaker.
According to the present invention, not only can the ASE light be blocked, but also the level of the upstream burst signal having different intensities can be controlled to be constant, or the optical level of a signal having a high intensity can be reduced. Thereby, it is possible to prevent a strong optical signal from being input to the receiver in the OLT.

In the communication method of the present invention, in the amplification procedure, the ASE light may be reduced by reducing the supply amount of excitation light.
According to the present invention, ASE light can be attenuated without using an optical attenuator or an optical breaker.

  According to the present invention, in a passive double star type PON system, even when a subscriber in a long-distance area and a short-distance area are accommodated at the same time, the bidirectional signal that does not deteriorate the upstream signal light in the short-distance area An optical amplifier, a PON system using the same, and a communication method can be provided.

1 shows an example of a PON system according to a first embodiment. 1 shows a first example of a bidirectional optical amplifier. 3 shows an example of upstream signal light according to the first embodiment. 2 shows a second example of a bidirectional optical amplifier. 1 shows a configuration of a PON system using an optical amplifier. The intensity levels of upstream signal light in the long-distance area and the short-distance area before and after being combined by the optical splitter are shown.

  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.

(Embodiment 1)
FIG. 1 shows an example of a PON system according to this embodiment. The PON system according to the first embodiment is a passive double star PON system in which a plurality of first ONU 51 _L groups and second ONU 51 _S groups having different distances are connected to an OLT 52 by a third optical splitter 55. The first optical splitter 54 _L connects the first ONU 51 _L group to each other. The second optical splitter 54 _S connects a second ONU 51 _S group different from the first ONU 51 _L group to each other. The third optical splitter 55 connects the first optical splitter 54 _L and the second optical splitter 54 _S to the OLT 52. PON system according to the first embodiment, the upward optical signal from the first ONU 51 _L group and the second ONU 51 _S group to OLT52 transmitting, from OLT52 to the first ONU 51 _L group and the second ONU 51 _S group Transmit downstream signal light.

Bidirectional optical amplifier 53 is inserted in the optical path between the third optical splitter 55 and the first optical splitter 54 _L. Here, the distance from the third optical splitter 55 to the first ONU 51 _L group is longer than the distance from the third optical splitter 55 to the second ONU 51 _S group.

The communication method of the PON system according to the first embodiment is a communication method of a passive double star PON system in which the first ONU 51 _L group and the second ONU 51 _S group having different distances are connected by the third optical splitter 55. The bidirectional optical amplifier 53 demultiplexes and amplifies the downstream signal light from the upstream optical fiber 41 and outputs it to the downstream optical fiber 42, and demultiplexes the upstream signal light from the downstream optical fiber 42. And amplifying procedure for outputting to the upstream optical fiber 41 after amplification. In this amplification procedure, the bidirectional optical amplifier 53 determines the presence or absence of upstream signal light. When there is upstream signal light, the bidirectional optical amplifier 53 demultiplexes the upstream signal light, amplifies the upstream signal light, and then outputs the upstream signal light to the upstream optical fiber 41. On the other hand, when there is no upstream signal light, the bidirectional optical amplifier 53 attenuates or blocks the ASE light generated when the upstream signal light is amplified. Hereinafter, a specific example of the amplification procedure will be described.

FIG. 2 shows a first example of a bidirectional optical amplifier. The first example of the bidirectional optical amplifier 53 includes a first multiplexer / demultiplexer 31, a second multiplexer / demultiplexer 32, a first optical amplifier 33, a second optical amplifier 34, and downstream signal light. A transmission path 35, an upstream signal light transmission path 36, an optical adjuster 11, an optical splitter 12, a photodetector 13, and a control circuit 14 are provided. The first multiplexer / demultiplexer 31 is connected to the upstream optical fiber 41 disposed on the third optical splitter 55 side. The second multiplexer / demultiplexer 32 is connected to the downstream optical fiber 42 disposed on the first optical splitter 54 _L side.

  The first multiplexer / demultiplexer 31 receives the downstream signal light from the upstream optical fiber 41 disposed upstream of the downstream signal light transmission path 35 and the upstream signal light transmission path 36, and the received downstream signal light Are demultiplexed and output to the downstream optical signal transmission line 35. The first optical amplifier 33 is inserted into the downstream signal light transmission path 35 and amplifies the intensity of the split downstream signal light. The second multiplexer / demultiplexer 32 receives the downstream signal light amplified by the first optical amplifier 33 by being transmitted through the downstream signal light transmission path 35, and the downstream signal light is input to the downstream downstream optical fiber. Output to 42.

  The second multiplexer / demultiplexer 32 receives the upstream signal light from the downstream optical fiber 42 disposed on the downstream side of the downstream signal light transmission path 35 and the upstream signal light transmission path 36, and receives the upstream signal light input thereto. Are demultiplexed and output to the upstream optical signal transmission line 36. The second optical amplifier 34 is inserted into the upstream signal light transmission path 36 and amplifies the intensity of the upstream signal light. The first multiplexer / demultiplexer 31 receives the upstream signal light that has been amplified by the second optical amplifier 34 by being transmitted through the upstream signal light transmission path 36, and the upstream signal light is input to the upstream optical fiber. 41 is output.

  The optical adjuster 11 is inserted into the upstream signal light transmission path 36 and attenuates or blocks the ASE light generated in the second optical amplifier 34. The optical splitter 12 is inserted into the upstream signal light transmission path 36 and branches a part of the upstream signal light. The photodetector 13 detects the light intensity of the upstream signal light branched by the optical splitter 12. The photodetector 13 is, for example, a photoelectric converter that converts an optical signal into an electrical signal.

  The control circuit 14 determines the presence / absence of upstream signal light. For example, it is determined whether or not the light intensity detected by the photodetector 13 is less than a predetermined value. Then, the control circuit 14 operates the optical adjuster 11 when there is no upstream signal light, and stops the operation of the optical controller 11 when there is upstream signal light. As a result, the upstream signal light is selectively incident on the first multiplexer / demultiplexer 31, and other light including noise such as ASE light is incident on the first multiplexer / demultiplexer 31. prevent.

  For example, the control circuit 14 outputs the control signal at a time when the electric signal level output from the photodetector 13 is low and it is determined as the non-transmission time. When a control signal is sent from the control circuit 14, the optical adjuster 11 attenuates or blocks the ASE light emitted by the second optical amplifier 34 at a time corresponding to the control signal, that is, a time determined as a non-transmission time. To do.

  The optical adjuster 11 is an optical attenuator that is inserted into the optical path between the second optical amplifier 34 and the first multiplexer / demultiplexer 31, for example, and attenuates the light intensity. In this case, the control circuit 14 determines the presence / absence of upstream signal light using the light intensity branched by the optical branching device 12. When there is no upstream signal light, the optical attenuator attenuates the light intensity, and the upstream signal light is In some cases, the optical attenuator does not attenuate the light intensity. Thereby, the ASE light can be attenuated in the amplification procedure.

  The optical adjuster 11 is, for example, an optical blocker that is inserted in an optical path between the second optical amplifier 34 and the first multiplexer / demultiplexer 31 and blocks light. In this case, the control circuit 14 determines the presence / absence of upstream signal light by using the light intensity branched by the optical branching device 12, and when there is no upstream signal light, causes the optical attenuator to block the light so that there is upstream signal light. When light is passed through an optical attenuator. Thereby, the ASE light can be blocked in the amplification procedure.

FIG. 3 shows an example of upstream signal light according to the present embodiment. By using the bidirectional optical amplifier 53, unlike the case of FIG. 6, the upstream signal light far area A _L, since the ASE light is blocked in the non-transmission time, a small short-range area relatively strength upstream signal light a _S can be prevented from being deteriorated by the influence of ASE light.

  In addition, since the optical adjuster 11 is an optical attenuator or optical interrupter, not only the ASE light is blocked, but the level of the upstream burst signal having different intensities is controlled to be constant, or the optical level of a signal having a large intensity is controlled. By weakening, it is possible to prevent a strong optical signal from being input to the receiver in the OLT 52.

(Embodiment 2)
The PON system according to this embodiment includes a second example of the bidirectional optical amplifier 53. FIG. 4 shows a second example of the bidirectional optical amplifier. In the second example of the bidirectional optical amplifier 53, instead of the optical adjuster 11, the optical splitter 12 and the control circuit 14 described in the first example of the bidirectional optical amplifier, the optical adjuster 21, the optical splitter 22 and A control circuit 24 is provided.

  The communication method according to the present embodiment reduces the ASE light by reducing the supply amount of the excitation light in the amplification procedure. For example, an optical fiber amplifier to which rare earth is added is used for the second optical amplifier 34. The light controller 21 is a pumping light source that supplies pumping light to the second optical amplifier 34. The second optical amplifier 34 amplifies the upstream signal light with the pumping light supplied from the optical regulator 21.

  The optical splitter 22 is inserted in the optical path between the second multiplexer / demultiplexer 32 and the second optical amplifier 34, and branches a part of the upstream signal light. The light detector 13 detects the light intensity of the upstream signal light branched by the light branching device 22. The control circuit 24 determines the presence / absence of upstream signal light using the light intensity branched by the optical branching device 22. For example, it is determined whether or not the light intensity detected by the photodetector 13 is less than a predetermined value. When there is no upstream signal light, the control circuit 24 decreases the supply amount of the excitation light supplied by the excitation light source. At this time, the control circuit 24 may stop supplying the excitation light. On the other hand, when there is upstream signal light, the control circuit 24 increases the supply amount of excitation light supplied by the excitation light source. Thereby, ASE light can be reduced in an amplification procedure.

The second example of the bidirectional optical amplifier 53, the upstream signal light far area A _L shown in FIG. 1, it is possible to attenuate the ASE light in the non-transmission time. Accordingly, the upstream signal light small short-range area A _S relatively strength can be prevented from being deteriorated by the influence of ASE light.

  Further, the optical adjuster 21 may not only attenuate the ASE light but also have an AGC (Auto Gain Control) function for controlling the gain of the second optical amplifier 34 to be constant. For example, when the light intensity detected by the photodetector 13 is high, the control circuit 24 increases the supply amount of pumping light until a desired gain is obtained. On the other hand, when the light intensity detected by the photodetector 13 is low, the control circuit 24 reduces the supply amount of the excitation light or stops the supply until a desired gain is obtained. Thereby, the gain of the second optical amplifier 34 can be maintained at a desired constant value.

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

DESCRIPTION OF SYMBOLS 11, 21: Optical regulator 12, 22: Optical splitter 13: Photo detector 14, 24: Control circuit 31: 1st multiplexer / demultiplexer 32: 2nd multiplexer / demultiplexer 33: 1st optical amplifier 34: second optical amplifier 35: downstream optical signal transmission path 36: upstream optical signal transmission path 41: upstream optical fiber 42: downstream optical fiber 51 _L : first ONU
51 _S : Second ONU
52: OLT
53, 153: bidirectional optical amplifier 54 _L : first optical splitter 54 _S : second optical splitter 55: third optical splitter 100: accommodation station

Claims (9)

A downstream optical signal transmission path for transmitting downstream optical signal having a first wavelength;
An upstream optical signal transmission line for transmitting upstream optical signal having a second wavelength different from the first wavelength;
Downstream signal light is input from an upstream optical fiber disposed upstream of the downstream signal light transmission path and the upstream signal light transmission path, and the downstream signal light transmission path is demultiplexed by dividing the input downstream signal light. A first multiplexer / demultiplexer that receives the upstream signal light transmitted through the upstream optical signal transmission line and outputs the upstream signal light to the upstream optical fiber;
Upstream signal light is input from a downstream optical fiber disposed downstream of the downstream signal light transmission path and the upstream signal light transmission path, and the upstream upstream signal light transmission path is demultiplexed. A second multiplexer / demultiplexer that receives the downstream signal light transmitted through the downstream optical signal transmission path and outputs the input downstream signal light to the downstream optical fiber;
A first optical amplifier that is inserted into the downlink signal light transmission line and amplifies the intensity of the downlink signal light;
A second optical amplifier which is inserted into the upstream signal light transmission line and amplifies the intensity of the upstream signal light;
An optical regulator for attenuating or blocking ASE (Amplified Spontaneous Emission) light generated in the second optical amplifier;
A control circuit that determines the presence or absence of upstream signal light, operates the optical regulator when there is no upstream signal light, and stops the operation of the optical regulator when there is upstream signal light;
A bidirectional optical amplifier. The optical adjuster is an optical attenuator that is inserted in an optical path between the second optical amplifier and the first multiplexer / demultiplexer and attenuates light intensity,
An optical branching device that is inserted in an optical path between the second multiplexer / demultiplexer and the optical attenuator and branches the upstream signal light;
The control circuit determines the presence / absence of upstream signal light using the light intensity branched by the optical branching unit. When there is no upstream signal light, the optical attenuator attenuates the light intensity, and when there is upstream signal light. The bidirectional optical amplifier according to claim 1, wherein the optical attenuator does not attenuate the light intensity. The optical adjuster is an optical interrupter inserted in an optical path between the second optical amplifier and the first multiplexer / demultiplexer to block light;
An optical branching device that is inserted in an optical path between the second multiplexer / demultiplexer and the optical attenuator and branches the upstream signal light;
The control circuit determines the presence / absence of upstream signal light by using the light intensity branched by the optical branching unit. When there is no upstream signal light, the optical circuit breaks the light, and when there is upstream signal light. The bidirectional optical amplifier according to claim 1, wherein light is allowed to pass through the optical breaker. The light regulator is a pumping light source that supplies pumping light to the second optical amplifier;
An optical branching device that is inserted in an optical path between the second multiplexer / demultiplexer and the second optical amplifier and branches the upstream signal light;
The control circuit determines the presence or absence of upstream signal light using the light intensity branched by the optical branching unit, and when there is no upstream signal light, reduces the supply amount of pumping light supplied by the pumping light source, The bidirectional optical amplifier according to claim 1, wherein when there is light, the supply amount of excitation light supplied from the excitation light source is increased. A first optical splitter for connecting a first ONU (Optical Network Unit) group to each other;
A second optical splitter for connecting a second ONU group different from the first ONU group to each other;
A third optical splitter connecting the first optical splitter and the second optical splitter to an OLT (Optical Line Terminal);
The bidirectional optical amplifier according to any one of claims 1 to 4, wherein the bidirectional optical amplifier is inserted in an optical path between the third optical splitter and the first optical splitter.
A PON (Passive Optical Network) system, wherein a distance from the third optical splitter to the first ONU group is longer than a distance from the third optical splitter to the second ONU group. A communication method of a passive double star type PON system in which a plurality of ONU groups having different distances are connected to an OLT by an optical splitter,
The downstream signal light transmitted through an optical fiber connecting the ONU group in the long-distance area of the ONU group and the optical splitter is demultiplexed and amplified, and then the light is directed toward the ONU group in the long-distance area. An amplification procedure of outputting to the optical fiber toward the OLT after demultiplexing and amplifying the upstream signal light transmitted through the optical fiber, and outputting to the fiber;
In the amplification procedure,
Determine the presence or absence of upstream signal light,
When there is upstream signal light, the upstream signal light is demultiplexed, the upstream signal light is amplified, and then output to the optical fiber toward the OLT,
A communication method for a PON system, characterized in that when there is no upstream signal light, the ASE light generated when the upstream signal light is amplified is attenuated or blocked.   The PON system communication method according to claim 6, wherein in the amplification procedure, the ASE light is attenuated by attenuating light with an optical attenuator.   The communication method of the PON system according to claim 6, wherein, in the amplification procedure, the ASE light is blocked by blocking light with an optical breaker.   The PON system communication method according to claim 6, wherein, in the amplification procedure, the ASE light is attenuated by decreasing a supply amount of excitation light.

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