JP4834164B2 - Optical repeater amplifier, optical communication system, and optical communication method - Google Patents

Description

  The present invention relates to an optical repeater amplifier for extending the length of an optical access system, an optical communication system including the same, and an optical communication method in the optical communication system.

  In recent years, the introduction of optical access systems based on the PON (Passive Optical Network) system has become the mainstream in the world (for example, see Non-Patent Document 1). These PON systems include one terminal device (OLT: Optical Line Terminal) and in-home devices (ONU: Optical Network Unit) installed in a plurality of user homes via an optical splitter installed in the access line. This is an optical access system that can be connected and is very economical. In the PON system, it is difficult to increase the transmission distance because each user shares power with an optical splitter. Also, in low demand areas such as rural areas, it is necessary to expand the area where optical access services can be provided, increase the transmission distance (accommodable area) in the PON system, cover a wider area, and accommodate more users There is. In order to increase the transmission distance in these PON systems, it is generally useful to provide an optical repeater amplifier in the optical access line and compensate for the loss received by the optical fiber or optical splitter.

  FIG. 1 is a configuration example of a long-distance PON system including an optical repeater amplifier 1. The optical repeater amplifier 1 is connected to an OLT 2 which is a device placed in a telecommunications carrier's building and an ONU 3 which is a device placed in the home of each user via respective optical access lines 4. Transmission / reception of the main signal between the user terminal and the communication network installed in the telecommunications carrier building and connected to the connection point is the ONU 3 and the OLT 2, and the optical access line 4 composed of one optical fiber connecting between them, And via the optical repeater amplifier 1. In the signal flow from the ONU 3 to the OLT 2, the ONU 3 has a function of transmitting a main signal from the user terminal as an optical signal to the optical access line 4, and the OLT 2 has a function of receiving an optical signal transmitted from the ONU 3. Conversely, in the signal flow from OLT 2 to ONU 3, ONU 3 functions to receive the optical signal transmitted from OLT 2, and OLT 2 uses the data signal flowing from the communication network in response to a request from ONU 3 as an optical signal. And has a function of transmitting to the optical access section.

  Since the optical signal between the OLT 2 and the ONU 3 is time-division multiplexed, it is possible to connect a plurality of ONUs 3 to one OLT 2. Further, the wavelength bands of the optical signals transmitted by the OLT 2 and the ONU 3 are different, and bidirectional communication is possible with a single optical fiber. The OLT 2 controls the time division multiplexing timing of the optical signal transmitted to each ONU 3 and demultiplexes the optical signal.

  The optical repeater amplifier 1 optically amplifies both the upstream and downstream optical signals transmitted by the OLT 2 and the ONU 3, and compensates the power level of the optical signal attenuated by the transmission loss due to the optical fiber and the loss from the optical splitter. Further, in the upstream signal from the ONU 3 to the OLT 2, the optical amplification device used as the optical repeater amplifier 1 due to the large loss of the used wavelength band from the optical fiber and the influence of the transmitter built in the ONU 3 Remarkably affected by noise.

In an optical repeater system to which an optical amplifier is applied, the entire system is greatly affected by the following four noises.
(1) Shot noise due to optical signal itself (2) Thermal noise in receiver circuit (3) Spontaneously emitted light (ASE) and beat noise due to optical signal (4) Multiple optical amplifiers In addition, it is considered difficult to suppress the influence of beat noise caused by the spontaneous emission light from the optical amplifiers (3) and the spontaneous emission light.

  Due to the influence of these noises, the quality of the optical signal amplified by the amplifying optical repeater deteriorates and becomes a major factor for limiting the transmission distance. For this reason, in order to suppress the influence of these noises and to secure a transmission distance, it is a general configuration to insert an optical bandpass filter after optical amplification. For example, long-distance optical transmission systems used in submarine cables and backbone networks insert an optical bandpass filter with a very narrow transmission bandwidth in order to suppress the influence of beat noise between spontaneously emitted lights in (4). is doing.

ITU-T Recommendation G. 984.6

  However, it is difficult to apply an optical bandpass filter having a narrow transmission bandwidth to the PON system from the viewpoint of system configuration and economy. In addition, the upstream signal wavelength in the PON is assigned a wavelength range of 100 nm from 1260 to 1360 nm, which is the zero dispersion wavelength band of the optical fiber, and further the transmitter signal used in the ONU installed in each user's home. Although it is based on 1310 nm depending on performance and usage environment, it is transmitted to the OLT at a wavelength with variations. For this reason, it is necessary to provide an optical bandpass filter having a wide transmission bandwidth in the PON system. That is, in an optical access system having an optical repeater amplifier for the purpose of extending the transmission distance, due to the above problems, the degree of freedom in network design when noise generated from the optical repeater amplifier constitutes a long distance PON system. There is a problem of restricting.

  In order to solve the above problems, the present invention provides an optical repeater amplifier that can use an optical bandpass filter having a narrow-band transmission characteristic and can suppress noise generated in an optical amplification device, and optical communication including the same It is an object to provide a system and an optical communication method of the optical communication system.

  In order to achieve the above object, the optical repeater amplifier according to the present invention monitors the wavelength difference between the transmission bandwidth of the optical bandpass filter to be used and the wavelength of the upstream optical signal from the ONU, and the wavelength difference is predetermined. When the specified value is exceeded, the wavelength is converted into a wavelength that is included in the transmission bandwidth of the optical bandpass filter.

  Specifically, an optical repeater amplifier according to the present invention combines a repeater amplifier for amplifying an input optical signal and the optical signal having a predetermined transmission bandwidth and amplified by the repeater amplifier. An optical bandpass filter, a wavelength determination unit that monitors a wavelength difference between a wavelength of the input optical signal and a center wavelength of a transmission bandwidth of the optical bandpass filter, and the relay amplification unit and the optical bandpass filter. When the wavelength difference monitored by the wavelength determination unit is greater than a predetermined specified value, the wavelength of the optical signal amplified by the relay amplification unit is included in the transmission bandwidth of the optical bandpass filter And a wavelength converter that converts the wavelength of the optical signal.

  In the present optical repeater amplifier, the wavelength converter can convert the wavelength of the optical signal to the center wavelength of the optical bandpass filter, so that the optical bandpass filter can be narrowed. Therefore, the present invention can provide an optical repeater amplifier that can use an optical bandpass filter having a narrow band transmission characteristic and can suppress noise generated in an optical amplifying device.

  The optical repeater amplifier according to the present invention further includes a light intensity adjustment unit that adjusts the light intensity of the optical signal amplified by the repeater amplification unit to be constant and is coupled to the wavelength conversion unit.

  In order to stably convert the wavelength of the optical signal, it is not preferable that the optical intensity of the optical signal input to the wavelength converter varies. In this optical repeater amplifier, since the light intensity adjustment unit makes the light intensity constant, an optical signal with a stable light intensity can be supplied to the wavelength converter, and the wavelength converter can perform a stable wavelength conversion operation. it can.

  The wavelength conversion unit of the optical repeater amplifier according to the present invention includes: a light source that outputs probe light; and wavelength conversion that converts the wavelength of the optical signal amplified by the repeater amplification unit based on the probe light from the light source And a variable attenuator that is disposed between the light source and the wavelength conversion element and transmits and blocks the probe light.

  The optical bandpass filter of the optical repeater amplifier according to the present invention can vary the transmission bandwidth, and the light source of the wavelength converter can vary the wavelength of the probe light.

  This optical repeater amplifier can also be applied to the future when higher-speed optical access services and new services are introduced at different wavelengths.

  The optical communication system according to the present invention is disposed between the OLT, an ONU that transmits an upstream optical signal to the OLT, and the OLT and the ONU, and amplifies the upstream optical signal from the ONU. And an optical repeater amplifier according to any one of 1 to 4.

  Since the optical communication system includes the above-described optical repeater amplifier, it is possible to provide an optical communication system capable of using an optical bandpass filter having a narrow band transmission characteristic and suppressing noise generated in the optical amplification device. .

  In the optical communication method according to the present invention, when the upstream optical signal from the ONU to the OLT is amplified by the optical repeater amplifier, the center wavelength of the transmission bandwidth of the optical bandpass filter in the optical repeater amplifier and the wavelength of the optical signal The wavelength of the optical signal amplified by the relay amplification unit in the optical repeater amplifier is included in the transmission bandwidth of the optical bandpass filter when the wavelength difference is larger than a predetermined specified value. The wavelength of the optical signal is converted so as to be coupled to the optical bandpass filter.

  Since this optical communication method can convert the wavelength of an optical signal into the center wavelength of the optical bandpass filter, the optical bandpass filter can be narrowed. Therefore, the present invention can provide an optical communication method capable of using an optical bandpass filter having a narrow band transmission characteristic and suppressing noise generated in an optical amplification device.

  The optical communication method according to the present invention converts the wavelength of the optical signal after adjusting the optical intensity of the optical signal amplified by the relay amplification unit to be constant.

  In this optical communication method, the optical repeater amplifier can supply an optical signal with a stable optical intensity to the wavelength converter because the optical intensity adjustment unit keeps the optical intensity constant, and the wavelength converter stabilizes the wavelength. Conversion operations can be performed.

  In the optical communication method according to the present invention, the probe light input to the wavelength conversion element is transmitted or blocked by the variable attenuator, and the wavelength of the optical signal is converted or not converted.

  The optical repeater amplifier monitoring method according to the present invention is characterized in that a transmission bandwidth of the optical bandpass filter is varied, a wavelength of the probe light is varied, and a wavelength band of an amplifiable optical signal is changed. .

  This optical communication method can also be applied when a higher-speed optical access service at a different wavelength or a new service is introduced in the future.

  The present invention makes it possible to use an optical bandpass filter having a narrow-band transmission characteristic, and an optical repeater amplifier capable of suppressing noise generated in an optical amplification device, an optical communication system including the same, and optical communication of the optical communication system A method can be provided.

It is a figure explaining the optical communication system provided with the conventional optical repeater amplifier. It is a figure explaining an optical communication system provided with the optical repeater amplifier concerning the present invention. It is a figure explaining the structure of the optical repeater amplifier which concerns on this invention. It is a flowchart explaining the optical communication method which concerns on this invention. It is a figure explaining the structure of the optical repeater amplifier which concerns on this invention. It is a figure explaining the structure of the optical repeater amplifier which concerns on this invention. It is a figure explaining the propriety flow of the wavelength conversion by wavelength determination.

  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.

  FIG. 2 is a diagram illustrating the optical communication system according to the present embodiment. The optical communication system includes an OLT 2, an ONU 3 that transmits an upstream optical signal to the OLT 2, and an optical repeater amplifier 1 that is disposed between the OLT 2 and the ONU 3 and that amplifies the upstream optical signal from the ONU 3.

  The optical repeater amplifier 1 includes a repeater amplifier 5 that amplifies an input optical signal, an optical bandpass filter 6 that has a predetermined transmission bandwidth and to which the optical signal amplified by the repeater amplifier 5 is coupled, A wavelength determination unit 9 that monitors the wavelength difference between the wavelength of the optical signal to be transmitted and the center wavelength of the transmission bandwidth of the optical bandpass filter 6, and is disposed between the relay amplification unit 5 and the optical bandpass filter 6. When the wavelength difference monitored by the determination unit 9 is larger than a predetermined specified value, the wavelength of the optical signal so that the wavelength of the optical signal amplified by the relay amplification unit 5 is included in the transmission bandwidth of the optical bandpass filter 6. And a wavelength conversion unit 8 for converting.

  The ONU 3 and the optical repeater amplifier 1 and the OLT 2 and the optical repeater amplifier 1 are connected by an optical fiber that is an optical access line 4. The control circuit 10 is connected to the wavelength conversion unit 8 and transmits a signal for controlling the wavelength conversion unit 8.

  FIG. 4 is a flowchart for explaining the optical communication method of this embodiment. In the optical communication method of the present embodiment, when the upstream optical signal from the ONU 3 to the OLT 2 is amplified by the optical repeater amplifier 1, the center wavelength of the transmission bandwidth of the optical bandpass filter 6 in the optical repeater amplifier 1 and the light The wavelength difference with the wavelength of the signal is monitored, and when the wavelength difference is larger than a predetermined specified value, the wavelength of the optical signal amplified by the relay amplifying unit 5 in the optical repeater amplifier 1 is an optical bandpass filter. The wavelength of the optical signal is converted so as to be included in the transmission bandwidth of 6 and coupled to the optical bandpass filter 6.

  The operation of the optical communication system and the optical communication method will be described with reference to FIGS. An optical directional coupler 7 is inserted between the ONU 3 and the relay amplification unit 5, and the optical signal from the ONU 3 is split into two. One of the optical signals is coupled to the relay amplification unit 5. The other of the optical signals is coupled to the receiver (PD) 12 (step S01). The optical signal input to the PD 12 is converted into an electric signal and input to the wavelength determination unit 9. The wavelength determination unit 9 monitors the wavelength of the optical signal (step S02), and the wavelength difference between the center wavelength of the transmission bandwidth of the optical bandpass filter 6 connected to the wavelength determination unit 9 and the wavelength of the optical signal from the ONU 3 Is derived (step S03). The wavelength determination unit 9 is also connected to the control circuit 10 and notifies the derived wavelength difference.

  The control circuit 10 compares the notified wavelength difference with the set specified value, and determines whether it is necessary to convert the wavelength of the optical signal from the ONU 3 (step S04). When the wavelength conversion is not necessary, the control circuit 10 does not cause the wavelength conversion unit 8 to perform the wavelength conversion operation and transmits the optical signal to the optical bandpass filter 6. On the other hand, when wavelength conversion is necessary, the control circuit 10 causes the wavelength conversion unit 8 to perform wavelength conversion so as to compensate for the wavelength difference derived by the wavelength determination unit 9 (step S05).

  FIG. 3 is a diagram illustrating the configuration of the optical repeater amplifier 1 of the present embodiment. The wavelength conversion operation of the wavelength converter 8 will be described with reference to FIG. The wavelength conversion unit 8 includes a wavelength conversion element 8a and a light source 8b. In general, wavelength conversion of an optical signal is realized by a nonlinear optical effect of light in an optical fiber. Non-linear optical effects are physical phenomena due to nonlinearity of light, such as four-wave mixing (FWM), cross phase modulation (XPM), and cross gain modulation (XGM). is there. When performing these wavelength conversions, a wavelength conversion element having strong light nonlinearity is generally used. In addition, since strong optical input power is required to cause the nonlinear optical effect, it is necessary to input light that has been intensified by a high-power semiconductor laser or a high-power optical amplifier to the wavelength conversion element. Since the optical repeater amplifier 1 is provided with the repeater amplifier 5 in front of the wavelength converter 8, an optical signal having sufficient optical power can be input to the wavelength converter 8.

  An important parameter for determining the wavelength after wavelength conversion at the time of wavelength conversion is probe light input to the wavelength conversion element 8a separately from the optical signal. When it is determined that the input optical signal needs to be wavelength-converted, the control circuit 10 causes the light source 8b to make the probe light incident on the wavelength conversion element 8a. The light source 8b is, for example, a laser diode (LD).

  The optical repeater amplifier 1 further includes an optical intensity adjuster (ALC) 11 that adjusts the optical intensity of the optical signal amplified by the repeater amplifier 5 to be constant and is coupled to the wavelength converter 8.

  At the time of wavelength conversion, it is not preferable that the input signal intensity to the wavelength conversion unit 8 varies. In order for the wavelength converter 8 to perform a stable wavelength conversion operation, it is necessary to supply an optical signal having a stable light intensity. For this reason, the ALC 11 is connected to the subsequent stage of the relay amplification unit 5. The ALC 11 has a function of attenuating the optical signal amplified by the relay amplification unit 5 at a high speed, and can input an optical signal with uniform light intensity to the wavelength conversion unit 8.

  As described above, in the optical communication system according to the present embodiment, the wavelength of the optical signal is transmitted through the optical bandpass filter 6 by the wavelength converter 8 even when there is a variation in wavelength in the optical signal transmitted from the ONU 3. It can be converted to a wavelength that matches the wavelength. As a result, the transmission bandwidth of the optical bandpass filter 6 can be narrowed, the influence of beat noise between spontaneously emitted lights, which has been difficult in the conventional optical access system, can be suppressed, and the transmission distance can be greatly reduced. Stretching is possible.

  In addition, the optical communication system according to the present embodiment improves the economic efficiency and accommodation efficiency of an optical access system such as a long-distance PON system, enables elimination of digital divide in urban and rural areas, and enables long-distance transmission of optical fiber communication. Is possible.

  Furthermore, in the optical communication system of the present embodiment, the wavelength converter 8 converts the optical signal into a single wavelength, so that the requirements (minimum reception sensitivity and reception) at the receiver of the OLT 2 in the upstream and the ONU 3 in the downstream are as follows. (Sensitivity dynamic range) can be relaxed, and it is possible to contribute to the economics of system component devices.

(First embodiment of optical repeater amplifier)
FIG. 5 is a diagram for explaining a first embodiment of the optical repeater amplifier 1. The wavelength conversion unit 8 of the optical repeater amplifier 1 in FIG. 6 has a light source 8b that outputs probe light and a wavelength conversion element that converts the wavelength of the optical signal amplified by the relay amplification unit 5 based on the probe light from the light source 8b. 8a, and a variable attenuator 8c that is disposed between the light source 8b and the wavelength conversion element 8a and that transmits and blocks the probe light.

  For example, although the wavelength band used for optical access differs slightly depending on each carrier, such as GE-PON currently commercialized in Japan, there is no significant difference within the carrier. For example, in GE-PON, a wavelength of 1310 nm is assigned to the upstream signal wavelength band, and all ONUs transmit upstream signals using the wavelength as a reference. When only one type of system is accommodated on such a network, a fixed wavelength light source is sufficient as the light source 8b for outputting the probe light to the wavelength conversion element 8a. For example, in the GE-PON system, a fixed wavelength light source having a center wavelength of 1310 nm is selected.

  When wavelength conversion is not necessary, it is necessary to stop the supply of probe light to the wavelength conversion element 8a. For this reason, the variable attenuator 8c is inserted between the light source 8b and the wavelength conversion element 8a. Only when the wavelength determination unit 9 determines that there is no need for wavelength conversion, the variable attenuator 8c increases the attenuation value and blocks the input of the probe light. The wavelength conversion element 8a couples the optical signal to the optical bandpass filter 6 while maintaining the wavelength.

  On the other hand, when it is necessary to convert the wavelength of the optical signal input to the wavelength conversion element 8a, the variable attenuator 8c switches the attenuation value to 0 at high speed and inputs the probe light having a wavelength of 1310 nm to the wavelength conversion element 8a. The wavelength conversion element 8 a performs wavelength conversion of the optical signal based on the probe light, and couples the optical signal after wavelength conversion to the optical bandpass filter 6.

(Second embodiment of optical repeater amplifier)
In the future, an optical access system is constructed so that it will coexist with existing facilities and systems when a higher-speed optical access service or a new service is developed. For example, 10GE-PON, which is 10 times faster than the current GE-PON, is assigned with wavelengths that can coexist in upstream and downstream for the purpose of coexistence with GE-PON. As for the upstream wavelength, 1310 nm is assigned by GE-PON, and 1270 nm is assigned by 10G-EPON. In addition to the above example, it is fully considered to use a new wavelength when developing a new service after video, and the optical access system is required to flexibly cope with them.

  FIG. 6 is a diagram for explaining a second embodiment of the optical repeater amplifier 1. In the optical repeater amplifier 1 of FIG. 6, the optical bandpass filter 6 can change the transmission bandwidth, and the light source 8b of the wavelength converter 8 can change the wavelength of the probe light in order to meet the above requirement.

  In the optical repeater amplifier 1 of FIG. 6, a variable bandpass filter is used for the optical bandpass filter 6 and a variable wavelength LD is applied to the light source 8b. The wavelength determination unit 9 monitors the wavelength of the optical signal and the transmission wavelength of the optical bandpass filter 6 to determine which wavelength band the optical signal is in. Then, the transmission wavelength of the optical bandpass filter 6 is switched as necessary. Further, the wavelength difference between the center wavelength of the transmission wavelength bandwidth of the optical bandpass filter 6 after switching and the wavelength of the optical signal is determined. The control circuit 10 determines the wavelength of the probe light based on the determination result of the wavelength difference so that the optical signal after the wavelength change has a desired wavelength, and instructs the light source 8b. Further, the control circuit 10 controls the attenuation value of the variable attenuator 8c to an optimum value. As a result, even when GE-PON, 10G-EPON, or a new wavelength after them is used, the influence of spontaneous emission light is suppressed by transmitting each signal from the relay amplification unit at the specified wavelength. However, long-distance transmission is possible.

FIG. 7 is a diagram for explaining the flow of wavelength determination in wavelength conversion. The center wavelength of the transmission bandwidth of the optical bandpass filter 6 connected to the latter stage of the ALC 11 is W _BPFCenter , the 3 dB transmission bandwidth is W _BPF3 dB, and the wavelength of the optical signal is W _signal . The 3 dB transmission bandwidth is a point at which the spectrum intensity of the signal is halved from the peak power, and is also called a full width at half maximum.

この時、波長変換の可否を判断する判定式として数２及び数３を用いる。

In this example, a criterion for determining whether or not wavelength conversion is necessary is a case where the center wavelength of the optical signal deviates from the 3 dB transmission bandwidth of the optical bandpass filter 6. In this case, the wavelength difference WaveDiff between the center wavelength of the optical signal and the center wavelength of the transmission bandwidth of the optical bandpass filter 6 is expressed by Equation 1 from the optical signal wavelength and the center transmission wavelength.

At this time, Equations 2 and 3 are used as determination formulas for determining whether or not wavelength conversion is possible.

  In Equations 2 and 3, it is determined whether the wavelength difference WaveDiff is located within the 3 dB transmission bandwidth of the optical bandpass filter 6. In Equation 2, since the wavelength difference WaveDiff is within the 3 dB transmission bandwidth, the control circuit 10 determines not to perform wavelength conversion. On the other hand, in Equation 3, since the wavelength difference WaveDiff is equal to or greater than the 3 dB transmission bandwidth, the control circuit 10 determines to perform wavelength conversion. As a result, a signal with different wavelengths is shaped within the transmission bandwidth of the optical bandpass filter 6 by wavelength conversion. In this example, the 3 dB transmission bandwidth is used as a threshold for determination. However, it can be changed by system design or the like, such as a 10 dB transmission bandwidth or a 20 dB transmission bandwidth.

  The optical repeater amplifier 1 described in the present embodiment can suppress the influence of noise that has been a problem in the conventional optical amplification technique, and is a narrow-band optical bandpass filter that has been used in a long-distance transmission system. Unlike the insertion method, it can be applied to an optical access system represented by a PON system. In addition, the optical repeater amplifier 1 as shown in FIG. 6 contributes to the construction of an access system that can be accommodated flexibly even when the speed of the future PON system is increased or when a new service is introduced.

1: Optical repeater amplifier 2: OLT
3: ONU
4: optical access line 5: repeater amplifier 6: optical bandpass filter 7: optical directional coupler 8: wavelength converter 8a: wavelength converter 8b: light source 8c: variable attenuator 9: wavelength determiner 10: control circuit 11 : ALC
12: PD

Claims (9)

A relay amplifier for amplifying an input optical signal;
An optical bandpass filter having a predetermined transmission bandwidth, to which the optical signal amplified by the relay amplification unit is coupled;
A wavelength determination unit that monitors the wavelength difference between the wavelength of the input optical signal and the center wavelength of the transmission bandwidth of the optical bandpass filter;
When the wavelength difference monitored between the repeater amplifier and the optical bandpass filter and monitored by the wavelength determiner is larger than a predetermined value, the wavelength of the optical signal amplified by the repeater amplifier is A wavelength converter that converts the wavelength of the optical signal so as to be included in the transmission bandwidth of the optical bandpass filter;
An optical repeater amplifier comprising:   2. The optical repeater amplifier according to claim 1, further comprising a light intensity adjustment unit that adjusts a light intensity of the optical signal amplified by the relay amplification unit to be constant and is coupled to the wavelength conversion unit. The wavelength converter is
A light source that outputs probe light;
Based on the probe light from the light source, a wavelength conversion element that converts the wavelength of the optical signal amplified by the relay amplification unit;
A variable attenuator that is disposed between the light source and the wavelength conversion element and transmits and blocks the probe light;
The optical repeater amplifier according to claim 1 or 2, characterized by comprising: The optical bandpass filter can vary the transmission bandwidth,
The optical relay amplifier according to claim 3, wherein the light source of the wavelength conversion unit can change a wavelength of the probe light. OLT (Optical Line Terminal),
An ONU (Optical Network Unit) for transmitting an upstream optical signal to the OLT;
The optical repeater amplifier according to any one of claims 1 to 4, wherein the optical repeater amplifier is disposed between the OLT and the ONU and amplifies an upstream optical signal from the ONU.
An optical communication system comprising: When the upstream optical signal from the ONU to the OLT is amplified by the optical repeater amplifier,
Monitor the wavelength difference between the center wavelength of the transmission bandwidth of the optical bandpass filter in the optical repeater amplifier and the wavelength of the optical signal, and repeat the relay in the optical repeater amplifier when the wavelength difference is greater than a predetermined specified value. An optical communication method for converting the wavelength of the optical signal so that the wavelength of the optical signal amplified by the amplifying unit is included in the transmission bandwidth of the optical bandpass filter and coupling the optical signal to the optical bandpass filter.   The optical communication method according to claim 6, wherein the wavelength of the optical signal is converted after the light intensity of the optical signal amplified by the relay amplification unit is adjusted to be constant.   8. The optical communication method according to claim 6, wherein probe light input to the wavelength conversion element is transmitted or blocked by a variable attenuator to convert or not convert the wavelength of the optical signal.   9. The optical communication method according to claim 8, wherein the wavelength band of the optical signal that can be amplified is changed by changing the transmission bandwidth of the optical bandpass filter and changing the wavelength of the probe light.

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