JP4766565B2 - Optical amplifier - Google Patents

Description

  The present invention relates to an optical amplifier installed between an optical subscriber line terminating device and an optical subscriber line network device, and more particularly to an optical amplifier having a characteristic for gain control of an upstream signal optical amplifier.

  In recent years, with the advancement of advanced information technology, in order to transmit a large amount of information at low cost, B using TDM-PON (Time Division Multiplexing Passive Optical Network) technology which is an optical access system capable of transmitting a large amount of information at high speed. -Optical access services using transmission devices such as PON (Broadband Passive Optical Network) and GE-PON (Gigabit Ethernet Passive Optical Network) are provided mainly in urban areas.

  In order to provide these services at a low cost to an area apart from a station where transmission devices other than urban areas are installed, an optical amplifier is required. One of the challenges in providing a wide range of optical access services at low cost using this optical amplifier is to automatically obtain a gain suitable for the service provision range without depending on the characteristics of each network and without human intervention. To control.

  Conventionally, in order to automatically control the gain in the optical amplifier, the light intensity transmitted in the transmission apparatus adjacent to the optical amplifier is compared with the light intensity of the bidirectional signal light incident on the optical amplifier. The light intensity for compensating the signal light incident on the amplifier and the light intensity necessary for transmission to the adjacent transmission device or optical amplifier are obtained, and the gain in the optical amplifier is determined.

On the other hand, in Patent Document 1, a gain control signal generator and a variable attenuator are provided in the transmission apparatus, and the level fluctuation is determined in the optical amplifier, thereby automatically responding to a change in the network configuration. Control is performed.
JP-A-6-69890

  However, even if the method of Patent Document 1 is used for the TDM-PON system currently used in the optical access system, the optical wave from the optical subscriber line network apparatus installed in each subscriber's house If there is no instruction from the optical subscriber line terminating device installed in the network, no signal is transmitted and the transmission control is an asymmetric optical network. Therefore, the gain cannot be determined by the conventional method.

  Further, even if a gain control signal generator or a variable attenuator for generating a gain control signal is provided in the transmission apparatus, it is necessary to modify the conventional apparatus and an increase in cost is inevitable. Moreover, in the area where the apparatus is already installed, it is necessary to replace the transmission apparatus installed in the subscriber's house, and the collection cost is enormous. These are contrary to the purpose of providing optical access services at low cost.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an optical amplifier that can realize an optical access service at a low cost without requiring a complicated configuration. It is in.

In order to achieve the above object, an invention according to claim 1 is installed between an optical subscriber line terminating device and an optical subscriber line network device, and the optical subscriber line network is connected to the optical subscriber line terminating device. An optical amplifier comprising a downstream signal optical amplifier that amplifies downstream signal light to a device, and an upstream signal optical amplifier that amplifies upstream signal light from the optical subscriber line network device to the optical subscriber line termination device, The gain in the upstream signal optical amplifier is controlled to a gain that corrects the difference in transmission line loss due to the wavelength difference between the downstream signal light and the upstream signal light with respect to the gain in the downstream signal optical amplifier. It is characterized by.
The invention according to claim 2 is the invention according to claim 1, wherein the maximum light intensity of the downlink signal light output from the downlink signal optical amplifier is a maximum of an optical subscriber line terminating device that transmits the downlink signal light. The gain in the downlink signal optical amplifier is controlled so as not to exceed the transmission light intensity.
The invention according to claim 3 is characterized in that, in the invention according to claim 1 or 2, gain control in the upstream signal optical amplifier is performed by controlling pumping light intensity of the upstream signal optical amplifier. .
The invention according to claim 4 is the invention according to claim 1 or 2, wherein the uplink signal optical amplifier inputs gain clamp light to the uplink signal optical amplifier, and the gain of the gain clamp light in the uplink signal optical amplifier is increased. The gain clamp type is used to control the gain of the uplink signal optical amplifier, and the gain control in the uplink signal optical amplifier is performed by controlling the gain of the gain clamp light.
The invention according to claim 5 is the invention according to claim 4, wherein the gain of the gain clamp light is controlled by controlling the light intensity of the gain clamp light.
The invention according to claim 6 is characterized in that, in the invention according to claim 4 or 5, ASE light generated in the upstream signal optical amplifier is used as the gain clamp light. The invention according to Item 4, 5 or 6 is characterized in that the gain control in the uplink signal optical amplifier includes control of the pumping light intensity of the uplink signal optical amplifier.

  According to the present invention, the gain in the upstream optical amplifier is controlled on the basis of the gain in the downstream optical amplifier, so that the gain setting of the optical amplifier does not depend on the characteristics of each network and does not involve human intervention. Since it is possible to automatically provide a gain suitable for the service provision range at a low cost without requiring a complicated configuration, it is possible to provide an optical access service in a wide area at a low cost. In addition, by making the upstream signal optical amplifier a gain clamp type and controlling the gain of the gain clamp light, even if the upstream signal light is burst light, an inexpensive optical power meter can be used for the gain observation monitor. It is possible to suppress optical surges.

<Embodiment 1>
FIG. 1 shows a configuration example of an optical access system using an optical amplifier according to the present invention. Here, a single-fiber bidirectional point-to-multipoint optical access system is taken, but the present invention is not limited to this, and can be applied to a multi-core bidirectional or multi-point optical network.

  This optical access system includes an optical subscriber line terminating device 100, a splitter 200, and a plurality of optical subscriber line network devices 300. In order to provide an optical access service to an area away from a station, An optical amplifier 400 is installed between the subscriber line terminating device 100 and the optical subscriber line network device 300.

  In the current optical access network, the downstream signal light S1 from the optical subscriber line terminating device 100 to the optical subscriber line network device 300 is a 1.49 μm band, and from the optical subscriber line network device 300 to the optical subscriber line terminating device 100. Since the upstream signal light S2 has a wavelength band of 1.3 μm and is different from each other, the optical amplifier 400 includes the downstream optical signal amplifier 401, the upstream optical signal amplifier 402, and the downstream optical signal S1 corresponding to each wavelength band. And optical multiplexer / demultiplexers 403 and 404 for multiplexing / demultiplexing the upstream signal light S2.

  Here, as the multiplexers / demultiplexers 403 and 404, a WDM filter for wavelength multiplexing / demultiplexing the upper and lower signal lights S1 and S2 or a circulator using the difference in directionality between the upper and lower signal lights S1 and S2 is used.

  Since the downlink signal optical amplifier 401 and the uplink signal optical amplifier 402 depend on the wavelength band to be used, when an optical fiber amplifier is used, the downlink signal light S1 is compatible with TDFA (Tbulium Doped Fiber Amplifier) and 1.49 band. For SOA (Semiconductor Optical Amplifier) and upstream signal light, PDFA (Praseodymium-Doped Fiber Amplifier) and 1.3 band-compatible SOA are used. However, the present invention is not limited to the type of optical amplification device. When the wavelength band used in the system changes, it is not limited to these optical components.

  In FIG. 1, there is one optical amplifier 400, but an optical access system may be configured by a plurality of optical amplifiers. Further, although there are a plurality of optical subscriber line network devices, a single device may be used.

  FIG. 2 shows a configuration of the optical amplifier 400 according to Embodiment 1 of the present invention. The downstream signal light S 1 is demultiplexed by the multiplexer / demultiplexer 403 toward the downstream signal optical amplifier 401. The demultiplexed downlink signal light S1 is optically amplified in the downlink signal optical amplifier 401 via the monitor 405, and after passing through the monitor 406, is multiplexed in the multiplexer / demultiplexer 404, and is then on the optical subscriber line network device 300 side. Is transmitted to.

  The gain of the downstream signal optical amplifier 401 is controlled using a gain control signal C 1 generated by the gain control circuit 407. The transmission gain A1 of the downstream signal light S1 being transmitted is generated by the gain calculation circuit 408 calculating a signal generated from the optical waves before and after amplification measured by the monitors 405 and 406.

  The gain control circuit 407 generates a gain control signal C1 for performing an ALC (Auto Level Control) operation and an AGC (Auto Gain Control) operation in accordance with specifications required for the optical amplifier. The level value and gain value required for each operation are recorded in the gain control circuit 407.

  The gain control signal C1 is generated by the comparison circuit in the gain control circuit 407 by comparing the transmission gain A1 with the recorded level value and gain value, and is sent to the downstream signal optical amplifier 401. The pumping light intensity of the downstream signal optical amplifier 407 is controlled. The gain of the downstream optical signal amplifier 401 is determined by the characteristics of the gain medium itself and the pumping light intensity.

  At this time, the gain control signal C1 controls the gain of the downstream signal optical amplifier 401 so as not to exceed the maximum transmission light intensity of the optical subscriber line terminating device 100 that transmits the downstream signal light S1. As a result, the failure that occurs when the downstream signal light intensity exceeds the maximum light resistance of the optical subscriber line network device 300 does not occur.

  Here, the ALC operation is an operation in which the light intensity of the downstream signal light S1 after amplification is automatically set to a constant value. Further, the AGC operation is an operation in which the gain of the downstream signal light S1 before and after amplification is always set to a constant value.

  The gain control signal C1 is transferred to the uplink signal gain automatic control circuit 409. The uplink signal gain automatic control circuit 409 corrects a difference in transmission conditions such as a transmission line loss due to the wavelength difference between the upper and lower signal lights S1 and S2 with respect to the gain control signal C1, and generates an uplink signal gain automatic control signal C2. Generated and transferred to the gain control circuit 410.

  The upstream signal light S2 is demultiplexed by the multiplexer / demultiplexer 404 to the upstream signal optical amplifier 402 side. The demultiplexed upstream signal light S2 is optically amplified by the upstream signal optical amplifier 402 via the monitor 411, and after passing through the monitor 412, is multiplexed by the multiplexer / demultiplexer 403, and the optical subscriber line terminating device 100 To the side.

  The gain of the upstream signal optical amplifier 402 is controlled using a gain control signal C 3 generated by the gain control circuit 410. The transmission gain A2 of the upstream signal light S2 being transmitted is generated by the gain calculation circuit 413 calculating a signal generated from the optical waves before and after amplification measured by the monitors 411 and 412. Since the uplink signal gain control signal C2 indicates the gain necessary for transmitting the signal light in the present optical access system, the gain control circuit 410 uses the transmission gain A2 and the uplink signal gain control signal C2. A gain control signal C3 that satisfies the required gain is generated. The gain control signal C3 controls the pumping light intensity of the upstream signal optical amplifier 402.

  The gain in the upstream signal optical amplifier 402 is determined by the intensity of the signal light and the intensity of the pumping light. When the signal light intensity is weak, the gain is large, and when it is strong, the gain is small. That is, the gain control signal C3 generated by the gain control circuit 410 changes depending on the maximum gain required by the optical access system.

  As described above, in the first embodiment, the uplink signal gain automatic control circuit 409 transmits the gain control signal C1 for the downlink signal optical amplifier 401, such as a transmission line loss due to the wavelength difference between the upper and lower signal lights S1 and S2. The uplink signal gain automatic control signal C2 is generated by correcting the difference in conditions, and the gain control signal C3 is further generated by the gain control circuit 410 in consideration of the transmission gain A2 of the upstream optical signal S2. The gain of the upstream optical signal amplifier 402 is controlled by the signal C3. Therefore, the setting of the gain control signal C3 does not depend on the characteristics of each network, does not require manual intervention, does not require a complicated configuration, and is automatically and inexpensively suitable for the service provision range. There is.

<Embodiment 2>
FIG. 3 shows a configuration of an optical amplifier according to Embodiment 2 of the present invention. In the first embodiment described with reference to FIG. 2, the transmission gain A2 of the upstream signal light S2 is generated by monitoring the upstream signal light S2 by the monitors 411 and 412 before and after the upstream signal optical amplifier 402. In the second embodiment, as shown in FIG. 3, the uplink signal optical amplifier 402 is a gain clamp type optical amplifier, and the transmission gain A2 is generated using the light intensity before and after the optical amplification of the gain clamp light.

  For accurate gain control of the upstream signal light S2, feedback control using observation of light intensity by a monitor is indispensable. However, when the upstream signal light S2 is a burst signal, the upstream signal light intensity is accurately determined. It is difficult to observe. In gain-clamped optical amplifiers, when gain-clamped light is input to an optical amplifying medium, the inversion distribution state of the amplifying medium is stabilized, and the gain is constant even when the input signal optical power of the burst signal is changed. Observation of light intensity using a simple optical power meter becomes easy.

  Further, in the gain clamp type optical amplifier, the gain clamp light is always incident on the downstream signal optical amplifier 402, so that the band with a flat gain can be expanded and the optical surge can be suppressed. Here, the band with a flat gain is a width of the signal light intensity with a flat gain, regardless of the input signal light intensity.

  The gain clamp light S3 oscillated from the gain clamp laser diode 414 having a wavelength different from that of the upstream signal light S2 passes through the monitor 415, and is then combined with the upstream signal light S2 by the multiplexer / demultiplexer 416, and the upstream signal optical amplifier 402 To enter. The gain clamp light S3 amplified by the upstream signal optical amplifier 402 is demultiplexed from the upstream signal light C2 by the multiplexer / demultiplexer 417 and is input to the monitor 418.

  From the gain clamp light intensity before and after amplification measured by the monitors 415 and 418, the gain calculation circuit 413 obtains the transmission gain A2 of the gain clamp light S3. Since the uplink signal gain control signal C2 indicates the gain necessary for transmitting the signal light in this optical access system, the gain control circuit 410 uses the transmission gain A2 and the uplink signal gain control signal C2 to request Gain control signals C3 and C4 that satisfy the gain to be generated are generated. The gain control signal C3 controls the pumping light intensity of the upstream signal optical amplifier 402, and the gain control signal C4 controls the light intensity of the gain clamp light S3.

  The gain in the upstream optical signal amplifier 402 is determined by the intensity of the signal light, the intensity of the excitation light, and the gain clamp light intensity. When the signal light intensity is weak, the gain is large, and when it is strong, the gain is small. When the gain clamp light intensity is high, the gain is small, but a flat band of gain is widened. That is, the gain control signals C3 and C4 generated by the gain control circuit 410 change depending on the maximum gain and the gain flat band required by the optical access system.

  In FIG. 3, the gain of the upstream optical amplifier 402 is controlled by the gain control signals C3 and C4. However, it is not always necessary to use both gain control signals, and the gain is controlled by using only one or both signals. Just do it.

  In FIG. 3, the monitor 415 is located in front of the gain clamp laser diode 414, but it may be installed behind the gain clamp laser diode and observe the rear emission of the gain clamp laser diode 414. Further, although the gain clamp light S3 is a front input type of the upstream signal optical amplifier 402, the present invention is not limited thereto, and as shown in FIG. 4, the rear input type, that is, the gain clamp light S3 is combined with the multiplexer / demultiplexer 417. The signal may be input to the upstream optical amplifier 402 in the direction from the side to the multiplexer / demultiplexer 416 side. Further, the present invention can also be applied to a bidirectional input type in which gain clamp light having different wavelengths is input from both sides of the upstream optical signal amplifier 402 and observed.

  As described above, in the second embodiment, the gain of the gain clamp light is used for observing the gain of the upstream signal optical amplifier 402. Therefore, even when the upstream signal light S2 is a burst signal, the monitors 415 and 418 are inexpensive. Not only can an optical power meter be used, but there is an advantage that optical surge can be suppressed.

<Embodiment 3>
FIG. 5 shows a configuration of an optical amplifier according to Embodiment 3 of the present invention. 3 and FIG. 4, the dedicated gain clamp laser diode 414 is used as the gain clamp light. However, in the third embodiment shown in FIG. 5, a part of the amplified upstream signal is variable optical attenuator 419. And a loop-back gain clamp type optical amplifier that is input to the upstream optical signal amplifier 402 again.

  The upstream signal light S2 is optically amplified by the upstream signal optical amplifier 402 via the multiplexer / demultiplexer 420, and transmitted to the optical subscriber line terminating device 100 side via the multiplexers / demultiplexers 421 and 403.

  A part of the upstream signal light S 2 is demultiplexed by the multiplexer / demultiplexer 420, the light intensity is adjusted by the variable optical attenuator 419 via the monitor 422, and then the upstream / downstream optical amplifier 402 side of the multiplexer / demultiplexer 421. Looped back. This looped back light acts as gain clamp light.

  The multiplexers / demultiplexers 420 and 421 multiplex / demultiplex ASE (Amplified Spontaneous Emission) light S4 generated from the upstream signal optical amplifier 402 excluding the wavelength band of the upstream signal light S2.

  Since the ASE light S4 generated from the upstream signal optical amplifier 402 is oscillated in both the forward and backward directions, the direction of the ASE light S4 is set to one direction in order to facilitate control of the ASE light S4 that is looped back. The optical isolators 423 and 424 are installed.

  The ASE light intensity P1 is obtained from the light intensity of the ASE light S4 measured by the monitor 422. When the upstream signal S2 is not input to the upstream signal optical amplifier 402, the ASE light intensity P1 becomes a constant value. When the upstream signal S2 is input to the upstream signal optical amplifier 402, the ASE light intensity P1 varies. The relationship between the ASE light intensity P1 and the gain of the upstream signal optical amplifier 402 is measured in advance and recorded in the gain control circuit 410 as a gain table. Since the upstream signal gain control signal C2 indicates a gain necessary for transmitting signal light in the present optical access system, gain control signals C3 and C5 satisfying the required gain are generated. The variable optical attenuator 419 is controlled by the gain control signal C5, and the pumping light intensity in the upstream signal optical amplifier 402 is controlled by the gain control signal C3.

  The gain in the upstream optical signal amplifier 402 is determined by the intensity of the signal light, the intensity of the excitation light, and the gain clamp light intensity. When the signal light intensity is weak, the gain is large, and when it is strong, the gain is small. When the gain clamp light intensity is high, the gain becomes small, but the band where the gain is flat increases. That is, the gain control signals C3 and C5 generated by the gain control circuit 410 vary depending on the maximum gain and gain flat band required by the optical access system.

  In FIG. 5, the gain of the upstream optical amplifier 402 is controlled by the gain control signals C3 and C5. However, it is not always necessary to use both gain control signals, and only one or both signals are used as necessary. The gain may be controlled.

  In FIG. 5, the ASE light S4 is input to the upstream optical signal amplifier 402 by the optical isolators 423 and 424 in the direction opposite to the traveling direction of the upstream signal light S2, but is transmitted in the forward direction. An optical amplifier may be used.

  As described above, in the third embodiment, since the ASE light generated in the upstream signal optical amplifier 402 is used as the gain clamp light forming the gain clamp type optical amplifier, the number of parts can be reduced and the service is performed at low cost. There are advantages that can be made.

1 is a configuration diagram of an optical access system using an optical amplifier according to the present invention. FIG. It is a block diagram of the optical amplifier which concerns on Embodiment 1 of this invention. It is a block diagram of the optical amplifier which concerns on Embodiment 2 of this invention. It is a block diagram of the modification of the optical amplifier which concerns on Embodiment 2 of this invention. It is a block diagram of the optical amplifier which concerns on Embodiment 3 of this invention.

Explanation of symbols

100: Optical subscriber line termination device 200: Splitter 300: Optical subscriber line network device 400: Optical amplifier 401: Downstream signal optical amplifier 402: Upstream signal optical amplifier 403, 404: Multiplexers / demultiplexers 405, 406: Monitor 407: Gain control circuit 408: Gain calculation circuit 409: Upward signal gain automatic control circuit 410: Gain control circuit 411, 412: Monitor 413: Gain calculation circuit 414 :: Gain clamp laser diode 415: Monitor 416, 417: Multiplexer 418 : Monitor 419: variable optical attenuator 420, 421: multiplexer / demultiplexer 422: monitor 423, 424: optical isolator S1: downstream signal light S2: upstream signal light S3: gain clamped light S4: ASE light C1: gain control signal C2 : Uplink signal gain automatic control signal C3, C4, C5: Gain control signal A1, A2: Transmission gain P1: ASE light intensity

Claims (7)

A downstream optical signal amplifier installed between an optical subscriber line termination device and an optical subscriber line network device, for amplifying downstream signal light from the optical subscriber line termination device to the optical subscriber line network device; In an optical amplifier comprising an upstream optical signal amplifier that amplifies upstream optical signal from an optical subscriber line network device to the optical subscriber line termination device
Gain in the uplink signal optical amplifier, for the gain in the downlink signal optical amplifier, and the difference in transmission path loss associated with wavelength difference of the said downstream signal light upstream signal light to be controlled in gain to correct An optical amplifier characterized by that. Maximum light intensity of the downlink signal light output from the downstream signal optical amplifier, so as not to exceed the maximum transmission light intensity of the optical network unit originating the downlink signal light, the gain in the downlink signal optical amplifier 2. The optical amplifier according to claim 1, wherein the optical amplifier is controlled. It said gain control in the upstream signal optical amplifier, according to claim 1 or 2, wherein the optical amplifier is characterized in that it has to be performed by controlling the excitation light intensity of the upward optical signal amplifier. The upstream signal optical amplifier is a gain clamp type in which gain clamp light is input to the upstream signal optical amplifier, and the gain of the upstream signal optical amplifier is controlled using the gain of the gain clamp light in the upstream signal optical amplifier. the gain control in the upstream signal optical amplifier, according to claim 1 or 2, wherein the optical amplifier is characterized in that so as to be performed by the control of the gain of the gain clamped optical. 5. The optical amplifier according to claim 4 , wherein the gain of the gain clamp light is controlled by controlling the light intensity of the gain clamp light. Wherein the gain clamp light, according to claim 4 or 5, wherein the optical amplifier is characterized by using an ASE light generated in the upward optical signal amplifier. Said gain control in the upstream signal optical amplifier, according to claim 4, characterized in that it has to include also the control of the excitation light intensity of the upward optical signal amplifier, 5 or 6, wherein the optical amplifier.

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