JP5066591B2 - Bidirectional optical amplifier, PON system, and communication method for PON system - Google Patents

Description

  The present invention relates to a bidirectional optical amplifier using a semiconductor optical amplifier (SOA: Semiconductor Optical Amplifier), a PON system, and a communication method of the PON system.

  IEEE and ITU-T are working on standardization of PON (Passive Optical Network) in order to provide a high-speed access service economically. IEEE has finished standardization of G-EPON (Gigabit Ethernet (registered trademark) PON) and 10G-EPON of next-generation systems that have already been commercialized. ITU-T has already standardized B-PON (Broadband PON) and G-PON (Gigabit-capable PON), which are already commercialized, and is proceeding with standardization of XG-PON for the next generation system. . 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, B-PON, and G-PON are systems that have already been completed, but one of the problems is to increase the allowable transmission path loss. 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 and a method of compensating for the loss of the lengthened transmission path using a bidirectional optical amplifier. FIG. 10 shows a configuration of a PON system using a bidirectional optical amplifier. As shown in the figure, the bidirectional optical amplifier 153 is disposed on an optical fiber 67 that couples the OLT 52 and the optical splitter 54. As shown in the figure, the bidirectional optical amplifier 153 uses the two multiplexer / demultiplexers 61 and 62 to separate the bidirectional upstream signal light (wavelength λ ₁ ) and downstream signal light (wavelength λ ₂ ). In this configuration, the amplifiers 163 and 164 amplify bidirectionally.

  As the optical amplifiers 163 and 164 used in the PON, an optical fiber amplifier to which rare earth is added, a concentrated amplification type optical fiber Raman amplifier, a semiconductor optical amplifier, or the like can be used. In particular, SOA has advantages over other optical amplifiers in terms of miniaturization, economy, and power saving. However, since the SOA response time in the amplification process is about the same as the bit length of a giga-class signal, when the light intensity of the input signal is large and amplified in the saturation region, an optical surge occurs at the rising edge of each bit. There is a problem that occurs. The occurrence of an optical surge not only deteriorates the signal waveform but also causes a failure of the receiver due to excessive input.

FIG. 11 shows an application area of the bidirectional optical amplifier considering the influence of the optical surge. The horizontal axis and the vertical axis are the ONU-to-optical amplifier distance and the OLT-to-optical amplifier distance, respectively. The signal bit rate, the extinction ratio of signal light, the gain of the optical amplifier, and the 32-branch optical splitter loss are 10.3125 Gb / s, 6 dB, 20 dB, and 17.5 dB, respectively. The ONU output is 4 dBm, the ONU reception sensitivity is −28.5 dBm, the OLT output is 2 dBm, and the OLT reception sensitivity is −28 dBm. Furthermore, the upper limit of the input light intensity (P _LIM ) to the SOA corresponding to the boundary between the saturated region and the unsaturated region, that is, the input light intensity to the SOA due to the light surge was set to -13 dBm. In PON defined by IEEE and ITU-T, λ ₁ and λ ₂ are near 1300 nm and 1500 nm, respectively, and therefore, the optical fiber loss is greatly different between upstream signal light and downstream signal light. Here, as typical values of the single mode optical fiber, the upstream signal light loss is 0.35 dB / km and the downstream signal light loss is 0.25 dB / km.

The loss limit shown in the figure indicates a boundary line in which the intensity of the signal light input to the receiver is lower than the reception sensitivity, even in the case where the optical amplifier is used, in a region exceeding the loss limit. Since the uplink signal light loss is larger than the downlink signal light loss, it is the loss limit of the uplink signal light that limits the application area of the optical amplifier. On the other hand, the light surge limit indicates a boundary line where the input light intensity to the SOA exceeds P _LIM . In the figure, the optical surge limit of the downstream signal light is illustrated, but the optical surge limit of the upstream signal light is not illustrated. This is because the intensity of the upstream signal light is greatly attenuated by the optical splitter before the signal transmitted from the ONU reaches the optical amplifier. As a result, the application area of the optical amplifier is defined by the area partitioned by the loss limit of the upstream signal light and the optical surge limit of the downstream signal light. In the figure, the application area is shown when the distance between the OLT and the optical amplifier is 72 km or more. However, from a different viewpoint, it can be said that this bidirectional optical amplifier cannot be applied in a region where the distance between the OLT and the optical amplifier is smaller than 72 km.

Shamil Appaturai, Derek Nesset, Russell Davey, “Measurement of tolerance to non-uniform burst powers in SOA amplified GPON systems 30-75”.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a bidirectional optical amplifier, a PON system, and a communication method for the PON system, in which the application area is expanded by relaxing the optical surge limit of the SOA with respect to downstream signal light in the PON system. And

  In order to achieve the above object, the bidirectional optical amplifier, the PON system, and the communication method of the PON system according to the present invention include a downlink input to the bidirectional optical amplifier in the PON system to which the bidirectional optical amplifier including the SOA is applied. When the light intensity of the signal light is measured and the light intensity exceeds a predetermined value, the input light intensity is attenuated by using an attenuator, or the clamp light is increased by using the optical gain clamp method. By mitigating the optical surge limit determined by the signal light, the applicable range of the bidirectional optical amplifier in the PON system is expanded, and the extension of the PON system can be realized.

Specifically, the bidirectional optical amplifier according to the present invention includes an upstream optical signal transmission path for transmitting upstream optical signal, a downstream optical signal transmission path for transmitting downstream optical signal having a wavelength different from the upstream optical signal, and the downstream optical signal. Upstream signal light is input from a downstream optical fiber disposed downstream of the upstream optical signal transmission path and the upstream optical signal transmission path, and the incoming upstream signal light is demultiplexed and output to the upstream optical signal transmission path A first multiplexer / demultiplexer that receives the downlink signal light transmitted through the downlink signal optical transmission line and outputs the input downlink signal light to the downstream optical fiber, the downlink signal optical transmission line, and Downstream signal light is input from an upstream optical fiber disposed on the upstream side of the upstream signal light transmission path, and the received downstream signal light is demultiplexed and output to the downstream signal light transmission path, and the upstream signal Upstream signal light transmitted through the optical transmission line is input and input A second multiplexer / demultiplexer that outputs the upstream signal light to the upstream optical fiber, and a first SOA (Semiconductor Optical Amplifier) that is inserted into the upstream signal light transmission line and amplifies the intensity of the upstream signal light. ), A second SOA that is inserted into the downlink signal light transmission path and amplifies the intensity of the downlink signal light, and the light intensity of the downlink signal light is less than or equal to an upper limit value of an unsaturated region of the second SOA Determining whether the optical intensity of the downstream signal light input to the second SOA exceeds the upper limit value of the unsaturated region of the second SOA, A control circuit that causes the optical adjuster to adjust when it is determined that the value exceeds the upper limit value, and is connected between an input port for inputting the drive current of the second SOA and a drive power supply of the second SOA And the above A branch unit for branching the electrical signal output from the power port, and the control circuit uses the electrical signal branched from the branch unit to determine the light intensity of the downstream signal light input to the second SOA. It is determined whether or not the upper limit value of the unsaturated region of the second SOA is exceeded .

  An upstream signal optical transmission line, a downstream signal optical transmission line, a first multiplexer / demultiplexer, a second multiplexer / demultiplexer, a first SOA, and a second SOA are provided. Light and downstream signal light can be amplified. Since the optical adjuster and the control circuit are provided, the light intensity of the downstream signal light input to the second SOA can be adjusted to be equal to or lower than the upper limit value of the unsaturated area of the second SOA. Therefore, the bidirectional optical amplifier of the present invention can be expanded in the PON system by relaxing the SOA optical surge limit for downstream signal light.

In the bidirectional optical amplifier according to the present invention, when the control circuit determines that the upper limit value is exceeded, the light intensity of the downstream signal light input to the second SOA is an unsaturated region of the second SOA. The light adjuster may be adjusted so that the upper limit value is reached.
When the light intensity of the downstream signal light reaches the upper limit value of the unsaturated area of the second SOA, the application area of the second SOA is maximized. Therefore, according to the present invention, the application area of the bidirectional optical amplifier can be maximized.

  Specifically, the PON system of the present invention is a PON (Passive Optical Network) system in which a plurality of ONUs (Optical Network Units) and OLTs (Optical Line Terminals) are connected by an optical splitter, And the OLT, the first multiplexer / demultiplexer is disposed on the optical splitter side, and the second multiplexer / demultiplexer is disposed on the OLT side. An optical amplifier is inserted.

  Since a plurality of ONUs, OLTs, optical splitters, and bidirectional optical amplifiers are provided, upstream signal light and downstream signal light can be amplified in the PON system. Since the bidirectional optical amplifier according to the present invention is provided, the optical surge limit of the SOA for the downstream signal light can be relaxed. Therefore, the application range of the PON system of the present invention can be expanded by relaxing the SOA optical surge limit for downstream signal light.

Specifically, the communication method of the PON system according to the present invention is a communication method of the PON system in which a plurality of ONUs (Optical Network Units) and OLTs (Optical Line Terminals) are connected by an optical splitter. And the downstream signal light transmitted through the optical fiber connecting between the optical splitter and demultiplexing the amplified signal light, and then output the optical signal toward the optical splitter to the optical fiber and the upstream signal light transmitted through the optical fiber. And then amplifying the downstream signal light by using an SOA (Semiconductor Optical Amplifier), and amplifying the downstream signal light. Downlink signal input to the SOA before amplification It is determined whether the light intensity of the light exceeds the upper limit value of the unsaturated region of the SOA. If it is determined that the light intensity exceeds the upper limit value, the light intensity of the downstream signal light input to the SOA is equal to that of the SOA. An electrical signal output from an input port for inputting the drive current of the SOA is branched at the time of the determination in the amplification procedure, and adjusted to be equal to or lower than the upper limit value of the unsaturated region, and the branched electrical signal is used. Then, it is determined whether or not the light intensity of the downstream signal light input to the SOA exceeds the upper limit value of the unsaturated region of the SOA .

  Since the amplification procedure is included, upstream signal light and downstream signal light can be amplified in the PON system. Here, according to the communication method of the PON system of the present invention, in the amplification procedure, the light intensity of the downstream signal light input to the SOA is adjusted so as to be equal to or lower than the upper limit value of the unsaturated region of the SOA. Therefore, the communication method of the PON system of the present invention can expand the application area of the SOA by relaxing the optical surge limit of the SOA for the downstream signal light in the PON system.

  The above inventions can be combined as much as possible.

  According to the present invention, in the PON system, it is possible to provide a bidirectional optical amplifier, a PON system, and a communication method for the PON system, in which the application area is expanded by relaxing the optical surge limit of the SOA with respect to the downstream signal light. .

1 shows an example of a PON system according to a first embodiment. The relationship between the input light intensity and gain to the first SOA and the second SOA according to the first embodiment is shown. A first example of the bidirectional optical amplifier 53 is shown. A second example of the bidirectional optical amplifier 53 is shown. A third example of the bidirectional optical amplifier 53 is shown. The application area | region of the bidirectional | two-way optical amplifier 53 concerning this embodiment is shown. An application area of the bidirectional optical amplifier 53 when the attenuation amount X is expanded to 10 dB is shown. A fourth example of the bidirectional optical amplifier 53 will be described. The relationship between the input light intensity and gain to the first SOA and the second SOA according to the second embodiment is shown. 1 shows a configuration of a PON system using a bidirectional optical amplifier. The application area of the bidirectional optical amplifier considering the effect of optical surge is 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 this embodiment is a PON system in which a plurality of ONUs 51 and an OLT 52 are connected by an optical splitter 54, and a bidirectional optical amplifier 53 is inserted in an optical path between the optical splitter 54 and the OLT 52. Yes.

In the communication method of the PON system according to the present embodiment, the downstream signal light having the wavelength λ ₂ transmitted through the optical fiber 67 connecting the OLT 52 and the optical splitter 54 is demultiplexed and amplified, and then directed to the optical splitter 54. In addition to being output to the optical fiber 67, the optical fiber 67 has an amplification procedure of demultiplexing and amplifying the upstream signal light having the wavelength λ ₁ and then outputting it to the optical fiber 67 toward the OLT 52. In the amplification procedure, the upstream signal light and the downstream signal light are amplified using the bidirectional optical amplifier 53 provided with the SOA.

FIG. 2 shows the relationship between the input light intensity and the gain to the first SOA and the second SOA according to the first embodiment. As shown in the figure, the amplification region can be divided into two depending on the magnitude of the input light intensity. One has a small input light intensity P _B, an area where automatic gain amplifier (linear amplifier) is made, the other is a large input light intensity P _A, a region where the gain is saturated. The SOA response time in the amplification process is comparable to the bit length of a giga-class signal. Thus, rectangular light pulses having an input light intensity P _A which corresponds to the saturation amplification region, is input to the SOA, the light surge is generated in the rise of the bit.

This light surge increases as the input light intensity increases. The input light intensity corresponding to the boundary between these regions is defined as _PLIM . The light surge can be quantified by b / a using the physical quantities a and b representing the amplitude shown in the illustration in the figure. In practice, it is difficult to accurately distinguish P _LIM by distinguishing linear amplification region and saturation amplification region as defined. _{Thus, the} determination of _{P LIM,} the value of b / a can tolerate a light surge, 0.5 dB or less and, as hereinafter become value 1 dB, is left to the person designing the system.

  Here, considering the case of FIG. 11, it is assumed that the bidirectional optical amplifier 53 needs to be arranged at a position on the optical fiber 52 km away from the OLT 52. As shown in the figure, in the range where the distance between the OLT 52 and the bidirectional optical amplifier 53 is smaller than 72 km, there is no application area of the bidirectional optical amplifier 53 due to the optical surge limit of downstream signal light.

If you place the bidirectional optical amplifier 53 to the position on the distant optical fibers 52km from OLT52, for example, downstream signal light having an input light intensity P _A corresponds to a case where input to the SOA. Here, before the SOA, the light intensity of the downstream signal light is attenuated by X dB so that the input light intensity P _B is input to the SOA. Since the input light intensity P _B is equal to or less than P _LIM and is the input light intensity corresponding to the linear amplification region of the SOA, it is possible to prevent the occurrence of an optical surge. However, when the input light intensity is reduced by X dB, the gain is reduced by the same amount.

  Therefore, in the communication method of the PON system according to the present embodiment, before the downstream signal light is amplified in the amplification procedure, the light intensity of the downstream signal light input to the SOA exceeds the upper limit value of the unsaturated region of the SOA. It is determined whether or not. If it is determined that the value exceeds the upper limit value, the light intensity of the downstream signal light input to the SOA is adjusted to be equal to or lower than the upper limit value of the SOA unsaturated region. Hereinafter, a specific example of the amplification procedure will be described.

  FIG. 3 shows a first example of the bidirectional optical amplifier 53. The first example of the bidirectional optical amplifier 53 has a configuration for amplifying downstream signal light and upstream signal light. For example, the first example of the bidirectional optical amplifier 53 includes an upstream signal light transmission path 65, a downstream signal light transmission path 66, a first multiplexer / demultiplexer 61, a second multiplexer / demultiplexer 62, 1 SOA 63 and a second SOA 64.

The first demultiplexer 61, the upstream signal light is inputted from the downstream-side optical fiber 67 _D arranged on the downstream side of the downstream signal light transmission path 66 and upstream signal light transmission path 65, the input uplink signal The light is demultiplexed and output to the upstream signal light transmission path 65. The upstream signal light transmission path 65 transmits upstream signal light. The first SOA 63 is inserted into the upstream signal light transmission path and amplifies the strength of the upstream signal light. The second demultiplexer 62 is supplied with the upward optical signal transmitted by the uplink signal optical transmission line 65, and outputs the upstream signal light inputted to the upstream side optical fiber 67 _U.

The second demultiplexer 62 is downstream signal light transmission path 66 and the upstream side optical fiber downstream signal light from the 67 _U which is disposed upstream of the upstream signal optical transmission line 65 is input, the input downstream signal The light is demultiplexed and output to the downstream signal light transmission path 66. The downstream signal light transmission path 66 transmits downstream signal light having a wavelength different from that of the upstream signal light. The second SOA 64 is inserted into the downstream signal light transmission path 66 and amplifies the intensity of the downstream signal light. The first demultiplexer 61, the downstream signal light transmitted by the downstream signal light transmission path 66, and outputs the input downstream signal light in the downstream side optical fiber 67 _D.

  In the amplification procedure, before the downstream signal light is further amplified, the control circuit 13 determines whether the light intensity of the downstream signal light input to the second SOA 64 exceeds the upper limit value of the unsaturated region of the second SOA 64. Determine whether or not. When it is determined that the upper limit value is exceeded, the optical intensity of the downstream signal light is more preferably set to the upper limit value of the unsaturated area of the second SOA 64 so as to be equal to or lower than the upper limit value of the unsaturated area of the second SOA 64. Thus, the light intensity of the downstream signal light is adjusted.

  For example, the first example of the bidirectional optical amplifier 53 includes the optical regulator 11, the optical branching unit 12, and the control circuit 13, and operates as follows. At the time of determination in the amplification procedure, the optical branching unit 12 is inserted in the preceding stage of the second SOA 64 in the downstream signal light transmission path 66, branches a part of the downstream signal light, and controls the branched light to the control circuit 13. To enter. The control circuit 13 uses the light branched by the optical branching unit 12 to determine whether the light intensity of the downstream signal light input to the second SOA 64 exceeds the upper limit value of the unsaturated region of the second SOA 64. judge. For example, the control circuit 13 photoelectrically converts the input light and measures the light intensity.

  When the control circuit 13 determines that the upper limit value is exceeded, the control circuit 13 causes the light adjuster 11 to adjust. For example, the control circuit 13 causes the optical attenuator to attenuate the downstream signal light. Thereby, at the time of adjustment in the amplification procedure, the optical adjuster 11 adjusts the light intensity of the downstream signal light to be equal to or lower than the upper limit value of the unsaturated region of the second SOA 64. On the other hand, if the control circuit 13 determines that the value is equal to or lower than the upper limit value, the control circuit 13 stops the adjustment of the light adjuster 11. For example, the control circuit 13 does not attenuate the downstream signal light in the optical attenuator. Thereby, at the time of adjustment in the amplification procedure, the optical adjuster 11 does not adjust the light intensity of the downstream signal light below the upper limit value of the unsaturated region of the second SOA 64.

For example, the input light intensity to the second SOA 64 is converted in consideration of the measurement value of the control circuit 13, the branching ratio of the optical branching unit 12, and the intrinsic loss of the optical attenuator, and the converted value is the input light intensity P _LIM . If so, the control signal is transmitted to the optical attenuator. The optical attenuator transmitted with the control signal attenuates the light intensity of the downstream signal light so that the light intensity input to the second SOA 64 becomes P _LIM .

  FIG. 4 shows a second example of the bidirectional optical amplifier 53. The second example of the bidirectional optical amplifier 53 includes an optical adjuster 21, an optical branching unit 22, and a control circuit 23 instead of the optical adjuster 11, the optical branching unit 12, and the control circuit 13. The optical branching unit 22 is different from the optical branching unit 12 in that the optical branching unit 22 is arranged at the subsequent stage of the second SOA 64. For example, the optical branching unit 22 is inserted into the optical path between the second SOA 64 and the first multiplexer / demultiplexer 61. The control circuit 23 stores in advance the relationship between the output light intensity and the input light intensity to the second SOA 64, and converts the input light intensity of the second SOA 64 using the stored relationship. As a result, the control circuit 23 determines whether or not the light intensity of the downstream signal light input to the second SOA 64 exceeds the upper limit value of the unsaturated region of the second SOA 64.

  FIG. 5 shows a third example of the bidirectional optical amplifier 53. The third example of the bidirectional optical amplifier 53 is the first example of the bidirectional optical amplifier 53 in that it is arranged on an electric circuit between the current input port 35 for driving the second SOA 64 and the current source 34. And the configuration of the second example is different. When the downstream signal light is input to the second SOA 64 with the drive current applied, a current proportional to the input light intensity flows out from the input port 35. From this current value, the input light intensity to the second SOA 64 can be converted.

  Specifically, in the third example of the bidirectional optical amplifier 53, instead of the optical adjuster 11, the optical branching unit 12, and the control circuit 13, the optical adjuster 31, the branching unit 32, the control circuit 33, and the current A source 34. The current source 34 drives the second SOA 64. The branch unit 32 is connected between the input port 35 of the second SOA 64 and the current source 34 of the second SOA 64, and branches an electrical signal output from the input port 35. As the branching unit 32, not only an intensity branching unit but also a circulator or a bias T can be used as shown in the illustration.

  And in the determination in an amplification procedure, the branch part 32 branches the electric signal output from the input port 35 which inputs the drive current of 2nd SOA64. Then, the control circuit 33 uses the electrical signal branched by the branching unit 32 to determine whether the light intensity of the downstream signal light input to the second SOA 64 exceeds the upper limit value of the unsaturated region of the second SOA 64. Determine whether.

  The optical adjuster 31 is, for example, an optical attenuator that is inserted into an optical path between the second SOA 64 and the second multiplexer / demultiplexer 62 and attenuates light. In this case, the control circuit 33 causes the optical attenuator to attenuate the downstream signal light when it is determined that the upper limit value is exceeded, and causes the optical attenuator to stop the attenuation of the downstream signal light when determined to be equal to or less than the upper limit value.

  FIG. 6 shows an application area of the bidirectional optical amplifier 53 according to this embodiment. The attenuation amount X of the input light intensity to the second SOA 64 was set to 5.1 dB. As shown in the figure, the optical surge limit of the downstream signal light is relaxed, and the application area of the bidirectional optical amplifier 53 is expanded to a range where the distance between the OLT 52 and the second SOA 64 is 52 km or more. Thereby, the bidirectional optical amplifier 53 can be disposed at a position on the optical fiber 67 52 km away from the OLT 52. At the same time, since the gain of the second SOA 64 decreases from 20 dB to 14.9 dB, the loss limit of the downlink signal light moves to the lower left of the figure, but the uplink signal light is still the limiting factor for the loss limit. no change.

FIG. 7 shows an application area of the bidirectional optical amplifier 53 when the attenuation amount X is expanded to 10 dB. As shown in the figure, the optical surge limit of the downstream signal light is relaxed to a range where the distance between the OLT 52 and the second SOA 64 is 32 km or more. On the other hand, since the gain of the second SOA 64 decreases from 20 dB to 10 dB at the same time, the loss limit of the downstream signal light becomes a limiting factor of the application area instead of the upstream signal light, and a part of the application area is a non-application area. Will be converted. Therefore, it is desirable to keep the attenuation amount X to a minimum so that the input light intensity to the second SOA 64 becomes equal to P _LIM .

(Embodiment 2)
The PON system according to this embodiment includes a fourth example of the bidirectional optical amplifier 53. The fourth example of the bidirectional optical amplifier 53 is characterized in that the gain clamp method is applied to the second SOA 64 that amplifies the downstream signal light. The gain clamp method is a technique for expanding a linear amplification region by causing light (clamp light) having a wavelength different from that of the amplified signal light to enter the optical amplifier simultaneously with the signal light.

  FIG. 8 shows a fourth example of the bidirectional optical amplifier 53. In the fourth example of the bidirectional optical amplifier 53, the light intensity of the downstream signal light input to the second SOA 64 is equal to or lower than the upper limit value of the unsaturated region of the second SOA 64 during the adjustment in the amplification procedure. The clamp light C is increased. For example, the fourth example of the bidirectional optical amplifier 53 includes a clamp light source 41 as an optical adjuster, an optical branching unit 42, and a control circuit 43.

  The clamp light source 41 supplies the clamp light C to the second SOA 64. The control circuit 43 increases the supply amount of the clamp light C to the clamp light source 41 when it is determined that the upper limit value is exceeded, and decreases the supply amount of the clamp light C to the clamp light source 41 when it is determined that it is equal to or less than the upper limit value. The arrangement and operation of the optical branching unit 42 and the control circuit 43 are the same as in the first example of the bidirectional optical amplifier 53.

  Thus, the point which arrange | positions the clamp light source 41 differs from the structure of Embodiment 1. FIG. In the figure, the output of the clamp light source 41 is illustrated as being incident from the output side of the second SOA 64, but an optical filter is disposed on the output side of the second SOA 64, and the signal light and the clamp light C are transmitted. If means such as separation is used, the light may enter from the input side of the second SOA 64.

FIG. 9 shows the relationship between the input light intensity and the gain to the first SOA and the second SOA according to the second embodiment. By supplying the clamp light C to the second SOA 64, the linear amplification region of the second SOA 64 can be expanded. Thus, the input light intensity of an input light intensity P _LIM boundaries can be increased to a new input light intensity P _{LIM _N.}

However, since the clamping beam C at the same time the wavelength lambda ₃ with downstream signal light having a wavelength lambda ₂ is amplified, the gain of the downstream signal light is reduced. If you place a bidirectional optical amplifier 53 to the position on the optical fiber 67 away 52km from OLT52, for example, downstream signal light having an input light intensity _{P A} corresponds to a case where input to the second SOA64. Input light intensity P _A, so corresponds to the saturation amplification region, the light surge is generated in the rising portion of the bit of the amplified signal.

Here, the clamp light C incident on the second SOA 64 is output, or if it has already been output, its output is increased. As a result, the linear amplification region of the second SOA 64 is expanded, and linear amplification is possible for the same input light intensity. For example, the light intensity of the downstream signal light is not changed remains P _A, moves to point B point A located in the saturation amplification region is located in the linear amplification region. As a result, generation of an optical surge of the amplified signal can be prevented, and the bidirectional optical amplifier 53 can be arranged at a position on the optical fiber 67 closer than 72 km from the OLT 52.

  In place of the optical branching unit 42 and the control circuit 43, the optical branching unit 22 and the control circuit 23 shown in FIG. 4 may be used, or the branching unit 32 and the control circuit 33 shown in FIG. The same effect as the embodiment can be obtained.

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

11, 21, 31, 41: Optical regulators 12, 22, 42: Optical branching units 13, 23, 33, 43: Control circuit 32: Branching unit 34: Current source 35: Input port 51: ONU
52: OLT
53, 153: bidirectional optical amplifier 54: optical splitter 61: first multiplexer / demultiplexer 62: second multiplexer / demultiplexer 63: first SOA
64: Second SOA
65: upstream signal optical transmission line 66: downstream signal light transmission line 67: optical fiber 67 _D: downstream optical fiber 67 _U: upstream optical fiber 100: receiving station 163, 164: optical amplifier

Claims (4)

An upstream optical signal transmission path for transmitting upstream optical signal;
A downstream optical signal transmission path for transmitting downstream optical signal having a wavelength different from upstream optical signal;
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 first multiplexer / demultiplexer that receives the downlink signal light transmitted through the downlink signal optical transmission line and outputs the input downlink signal light to the downstream optical fiber;
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 second multiplexer / demultiplexer that receives the upstream signal light transmitted through the upstream optical signal transmission path and outputs the input upstream signal light to the upstream optical fiber;
A first SOA (Semiconductor Optical Amplifier) that is inserted into the upstream signal light transmission path and amplifies the intensity of the upstream signal light;
A second SOA that is inserted into the downstream signal light transmission path and amplifies the intensity of the downstream signal light;
An optical adjuster that adjusts the light intensity of the downstream signal light to be equal to or lower than the upper limit value of the unsaturated region of the second SOA;
It is determined whether the light intensity of the downstream signal light input to the second SOA exceeds the upper limit value of the unsaturated region of the second SOA, and if it is determined that the light intensity exceeds the upper limit value, the light A control circuit for adjusting the regulator;
With
A branch unit connected between an input port for inputting a drive current of the second SOA and a drive power supply of the second SOA, and for branching an electric signal output from the input port;
Whether the light intensity of the downstream signal light input to the second SOA exceeds the upper limit value of the unsaturated region of the second SOA using the electric signal branched by the branching unit Bidirectional optical amplifier that determines whether or not. When the control circuit determines that the value exceeds the upper limit value, the light intensity of the downstream signal light input to the second SOA becomes the upper limit value of the unsaturated region of the second SOA. The bidirectional optical amplifier according to claim 1, wherein the optical regulator is adjusted. A PON (Passive Optical Network) system in which a plurality of ONUs (Optical Network Units) and OLTs (Optical Line Terminals) are connected by an optical splitter,
The optical path between the said light splitter OLT, in a state where the first demultiplexer is disposed on the optical splitter side, the second demultiplexer is arranged in the OLT, claim 1 Or a PON system, wherein the bidirectional optical amplifier according to 2 is inserted. A communication method of a PON system in which a plurality of ONUs (Optical Network Units) and OLTs (Optical Line Terminals) are connected by an optical splitter,
The downstream signal light transmitted through the optical fiber connecting between the OLT and the optical splitter is demultiplexed and amplified, and then output to the optical fiber toward the optical splitter and transmitted through the optical fiber. An amplification procedure for demultiplexing and amplifying the signal light and then outputting it to the optical fiber toward the OLT;
In the amplification procedure,
The downstream signal light is amplified using SOA (Semiconductor Optical Amplifier),
Before amplifying the downstream signal light, it is determined whether the light intensity of the downstream signal light input to the SOA exceeds the upper limit value of the unsaturated region of the SOA,
If it is determined that the upper limit value is exceeded, the light intensity of the downstream signal light input to the SOA is adjusted to be equal to or lower than the upper limit value of the unsaturated region of the SOA,
During the determination in the amplification procedure, the electrical signal output from the input port for inputting the SOA drive current is branched, and the downstream signal light input to the SOA is split using the branched electrical signal. A communication method of the PON system that determines whether or not the strength exceeds the upper limit value of the unsaturated region of the SOA.

Images