JP4644551B2 - Optical communication system and apparatus - Google Patents

Description

  The present invention relates to an optical communication system and apparatus, and more particularly to an optical communication system and apparatus in which a plurality of optical communication apparatuses are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied.

  The Raman amplifier is used to amplify the power of the main signal light using stimulated Raman scattering, which is one of optical nonlinear effects. The gain obtained by the Raman amplifier (Raman gain) is proportional to the optical power injected from the pumping laser into the transmission line. The Raman amplifier uses an optical fiber as a transmission line as an amplification medium, so that the transmission line characteristics ( It is characteristic that the gain varies greatly depending on loss, distance, etc. For this reason, the applicability of the Raman amplifier is determined by the transmission path characteristics. That is, for example, when the transmission line loss is too small, the pump laser of the Raman amplifier has a low output, so that it is difficult to maintain a stable oscillation state, which affects the transmission characteristics of the main signal. This will be specifically described below.

FIGS. 7 and 8 are views (1) and (2) for explaining the prior art, and FIG. 7 (A) shows a typical example of an optical transmission system using a Raman amplifier by backward pumping. In the figure, 10A and 10B are optical transmission apparatuses that perform long-distance transmission of main signal light, 51A and 51B are optical fiber transmission lines to which Raman optical amplification is applied, and 12A and 12B are erbium doped fibers (EDFA) or the like. An optical amplifier (OA), 14 is a wavelength demultiplexer that branches a part of the main signal light, 15 is a photodiode (PD) that detects the power of the branched light, 20 is a Raman amplifier, and 21 is a laser for exciting the Raman amplifier. A diode (LD), 22 is a wavelength multiplexer that injects laser excitation light into the optical fiber transmission line 51A, 16 is an LD controller that performs output control of the LD 21 based on the detection output of the PD 15,
Reference numerals 13A and 13B denote optical amplifiers representing the configuration of the uplink provided in the same manner as that for the downlink.

The LD control unit 16 monitors the signal light power PI input to the optical amplifier 12B, and controls the pumping light output of the LD 21 so that it enters a predetermined input range of the optical amplifier 12B. At that time, as shown in FIG. 7B, the light output corresponding to the bias current obtained by adding a predetermined operation margin to the oscillation threshold of the element is defined as the minimum pumping light output so that the LD 21 operates in the stable region. Then, the LD 21 is operated with a light output equal to or higher than the minimum pumping light output.
JP2003-177440 (summary, figure)

  However, when performing the above-described control, there is a minimum value of the transmission line loss to which the Raman amplifier can be applied, from the relationship between the optical transmission line characteristic and the LD oscillation threshold value. That is, when the transmission line characteristics are good, such as when the loss coefficient (dB / km) of the optical transmission line is small, the pump laser has a low output, and thus the Raman amplifier cannot be applied.

FIG. 8 shows the optical amplification characteristics with respect to the transmission distance of the Raman amplifier. The optical output power PO of the main signal at the transmitting end is uniformly attenuated as the transmission distance increases. If there is no Raman amplifier, the receiving end at the distance L is below the required receiving range as indicated by the dotted line in the figure. The main signal cannot be received normally. In this case, it is possible to obtain a larger optical input power at the receiving end L by providing a Raman amplifier. At this time, if the transmission line loss at the receiving end L is near or below the minimum value of the Raman amplifier application range. If so, the optical input power PI becomes overrange as shown by the solid line in the figure, and as a result of the optical amplifier not operating normally, the reception quality (S / N ratio, etc.) is significantly reduced. Moreover, since the pumping light power is also in the minimum range in this state, the LD 21 cannot be stably operated (oscillated).

  Such a situation is when the actual transmission line loss is smaller than the design value on the desk, or the transmission line loss that appeared to be large in the previous measurement is reduced by precise setting or cleaning when mounting the amplifier. In reality, it can often happen.

  In Patent Document 1, the wavelength multiplexed signal light output from the optical amplifier 12 is monitored, and the Raman amplification excitation light source 13 and the variable light are adjusted so that the power for each wavelength of the wavelength multiplexed signal light is uniform. An optical repeater is described in which a good (flat) gain profile can be obtained by controlling the attenuator 14 regardless of manufacturing variations of components and aging deterioration. However, there is no disclosure or suggestion regarding the above-mentioned problem and its solution.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an optical communication system and apparatus that enable a wider application range of Raman amplification.

The above problem is solved by the configuration of FIG. That is, the optical communication system of the present invention (1) has a plurality of optical communication devices 50A through the optical fiber transmission path 51A to which the Raman amplification, 50B is a optical communication system interconnecting said main signal a variable attenuator 69 for attenuating the light, the detection means 55 for detecting the reception level of the main signal light received through the optical fiber transmission line, the Raman pumping to amplify the main signal light of the optical fiber transmission path A predetermined reception level is detected by the detection means 55 in a state in which the laser 61, the monitor means 63 for monitoring the light output of the Raman excitation laser, and the monitor means are detecting a light output exceeding a predetermined value. as that, in which a control unit 56 for controlling the amount of loss of the variable attenuator 69.

  In the present invention (1), not only a predetermined reception level is obtained, but if necessary, the gain required by the Raman amplifier is increased by increasing the attenuation amount of the variable attenuator provided in the main signal transmission line. Therefore, the excitation laser can be stably operated. Therefore, even if the optical fiber transmission line is near or below the minimum value of the Raman amplifier application range, the Raman amplifier can be stably applied, and the application range of the Raman amplifier is greatly expanded.

  Further, the optical communication system of the present invention (2) is the same as the above-mentioned present invention (1). For example, as shown in FIG. 1, the optical transmission side 50A includes a variable attenuator 69 and the optical reception side 50B includes a Raman excitation laser 61. Is. This configuration is suitable for application to the backward excitation method.

The optical communication system of the present invention (3), in the present invention (1), for example as shown in FIG. 5, comprises a Raman pump laser 61 to the optical transmitting side 50A, the detection means definitive on the light receiving side 50B A variable attenuator 69 is provided in the preceding stage . This configuration is suitable for application to the forward excitation method.

Further, the receiving side device of the present invention (4) is, for example, as shown in FIG. 4, a receiving side device 50B of an optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman light amplification is applied. A Raman excitation laser 61 for amplifying the main signal light in the optical fiber transmission line 51A, a monitor means 63 for monitoring the optical output of the Raman excitation laser, and excitation to the optical fiber transmission line A variable attenuator 69 which is provided in a subsequent stage of the light injection unit and attenuates the main signal light received via the optical fiber transmission line; and a detection means 55 for detecting the reception level of the main signal light after passing through the variable attenuator; The loss amount of the variable attenuator 69 is adjusted so that a predetermined reception level is detected by the detection unit 55 in a state where the monitor unit detects a light output exceeding a predetermined level. In which and a Gosuru control unit 56. In this way, the present invention can be realized by a single receiving apparatus.

The transmission side device of the present invention (5) is a transmission side device 50A of an optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied, for example, as shown in FIG. And a variable attenuator 69 for attenuating the main signal light to be transmitted to the optical fiber transmission line, and pumping light from the subsequent stage of the variable attenuator to amplify the main signal light in the optical fiber transmission line 51A. A Raman excitation laser 61, a monitor means 63 for monitoring the light output of the Raman excitation laser, a reception means 67 for receiving information on the reception level of the main signal light detected by the opposing device 50B, and the monitoring means The loss amount of the variable attenuator 69 is controlled so that information of a predetermined reception level is received by the receiving means in a state where a light output exceeding a predetermined value is detected. In which a control unit 56. This way, the present invention can be implemented in the transmitting apparatus with the addition of a simple configuration to the receiving device.

  As described above, according to the present invention, the application area of the Raman amplifier is expanded, which greatly contributes to the spread of long-distance / high-quality transmission.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings.

  FIG. 1 is a diagram showing a configuration of a Raman amplifier control system according to the first embodiment, and shows a case where a Raman amplifier is a backward pumping system and a variable attenuator is on the transmission side. In the figure, 50A and 50B are optical transmission devices (terminal station devices, optical repeaters, etc.) that transmit the main signal light over a long distance, 51A and 51B are optical fiber transmission lines to which Raman optical amplification is applied, and 52A and 52B are EDFAs. Etc., 54 is a wavelength demultiplexer that branches a part of the main signal light, 55 is a photodiode (PD) that detects the power of the branched light, 60 is a Raman amplifier, and 61 is a Raman amplifier. A laser diode (LD) for excitation, 62 is a wavelength multiplexer for injecting laser excitation light into the optical fiber transmission line 51A, and 63 is a photodiode for detecting the operating state (light output) of the LD 61 based on the back light of the LD 61. PD), 64, 67 are OSC communication units for exchanging uplink monitoring signals through an optical supervisory channel (OSC) between the optical transmission apparatuses 50A, 50B, 65, 6 is a wavelength multiplexer / demultiplexer for multiplexing / branching control signal light having a wavelength different from that of the main signal light to the optical fiber transmission line 51B, 69 is a variable attenuator (ATT) for attenuating the power of the main signal light, and 68 is The variable attenuator control unit 56 is a control unit that controls the output of the LD 61 based on the detection outputs of the PD 55 and PD 63, and 53A and 53B are light representative of the configuration of the uplink 51B provided in the same manner as that for the downlink 51A. It is an amplifier.

  Based on the detection output PID of the PD 55, the control unit 56 not only obtains a reception level PID within a predetermined range at the input of the optical amplifier 52B, but also within a range where the predetermined reception level PID is detected, and Raman. The loss amount of the variable attenuator 69 is controlled so that the excitation LD 61 operates in a stable oscillation state. Therefore, the Raman amplifier can be stably applied even when the optical fiber transmission line 51A is near or below the minimum value of the Raman amplifier application range, and thus the application range of the Raman amplifier is greatly expanded.

Next, an example of a preferable control method by the control unit 56 will be specifically described. FIG. 2 is a flowchart of the attenuator control process according to the embodiment, and is executed by the control unit 56. In step S11, the loss of the variable ATT 69 is minimized via the OSC communication units 64 and 67. In step S12, the optical output LP of the excitation LD 61 is increased by a predetermined amount ΔP (mW). In step S13, it is determined whether or not the input power PI of the optical amplifier 52B has reached the target value (within a predetermined reception range) based on the detection output PID of the PD 55. If not, the process returns to step S12.

  Thus, when the input power PI of the optical amplifier 52B reaches the target value in the determination in step S13, the optical output power LP of the pumping LD 61 becomes a predetermined minimum pumping light power based on the detection output of the PD 63 in step S14. It is determined whether or not it has been reached. If not, the loss of the variable ATT 69 is increased by a predetermined amount Δx (dB) in step S15, and the process returns to step S12.

  Thus, the pumping light power of the LD 61 is increased until the input of the optical amplifier 52B reaches the target value again in the determination in step S13. When the target value is reached, the pumping light output at that time is the minimum pumping light in step S14. It is determined whether or not the output has been reached.

  Therefore, it is possible to efficiently achieve both the predetermined reception level and the stable laser oscillation state. In addition, although the said control method specifically described the thing with respect to 1st Embodiment of FIG. 1, this control method is applicable also to other embodiment mentioned later.

  FIG. 3 is a diagram for explaining optical transmission characteristics according to the embodiment. According to the above prior art, when the optical output at the transmission end is PO, even if the LD 61 is driven with the minimum excitation light or the excitation light is stopped, the reception level at the reception end L is the required level of the optical amplifier 52B. Although the dynamic range (for example, 6 to 7 dB) was not entered, when the variable ATT 69 is controlled according to the present invention and the optical output at the transmission end is attenuated to PO-α, the LD 61 is excited with a power higher than the minimum excitation light. The optimum reception level can be obtained.

  FIG. 4 is a diagram showing the configuration of the Raman amplifier control system according to the second embodiment, and shows a case where the present invention can be realized by the receiving apparatus 50B alone. Here, the Raman amplifier 60 is configured to be backward pumped, the variable ATT 69 is provided in the subsequent stage of the Raman amplifier 60, and the wavelength demultiplexer 54 is provided in the subsequent stage. Even in such a configuration, a required main signal input to the optical amplifier 52B and a stable oscillation operation of the LD 61 can be secured by the control method of FIG.

  FIG. 5 is a diagram showing the configuration of the Raman amplifier control system according to the third embodiment, and shows a case where the Raman amplifier is a forward pumping system and the variable attenuator is on the receiving side. In the figure, reference numerals 70 and 71 denote wavelength multiplexers / demultiplexers for multiplexing / branching control signal light having a wavelength different from that of the main signal light into the optical fiber transmission line 51A. Here, the control unit 56 is provided on the transmitting device 50A side, receives the reception level detection signal PID from the receiving side PD 55 via the uplink 51B, and controls the remote variable ATT 69 via the downlink 51A. It is the composition to do. Even in such a configuration, a required main signal input to the optical amplifier 52B and a stable oscillation operation of the LD 61 can be secured by the control method of FIG.

  FIG. 6 is a diagram showing a configuration of a Raman amplifier control system according to the fourth embodiment, and shows a case where the Raman amplifier is a forward excitation system and a variable attenuator is on the transmission side. Here, the control unit 56 is provided on the side of the transmitting device 50A, receives the reception level detection signal PID from the receiving side PD 55 via the uplink 51B, and at the Raman amplifier 60 in the own device 50A and the preceding stage. The variable ATT 69 provided is controlled. Even in such a configuration, a required main signal input to the optical amplifier 52B and a stable oscillation operation of the LD 61 can be secured by the control method of FIG.

Although not shown, the present invention can be applied to a forward-pumping and backward-pumping Raman amplifier by, for example, combining the configurations of FIGS. 4 and 6 and omitting the overlapping configuration. In the control of FIG. 2 in this case, for example, in step S12, the optical outputs of the two LDs 61 on the transmission / reception side are alternately increased by ΔP (or ΔP / 2) to equalize the excitation load sharing. Also in step S14, the operating states of the two LDs 61 are monitored, and the loop processing of FIG. 2 is repeated until both of them reach a required operating state.

  Further, although the main signal light is not described in detail in each of the above embodiments, the present invention is particularly suitable when applied to a wavelength division multi / demultiplexing (WDM) system. In this case, both the main signal light and the excitation light include a plurality of types of wavelengths (also referred to as wavelength multiplexing excitation methods). The wavelength demultiplexer 54 may branch only signal light of a specific wavelength, but may be a so-called beam splitter that branches signal light of all wavelengths uniformly.

  In the above embodiment, the operating state of the Raman excitation LD 61 is monitored by the optical power of the backlight, but the present invention is not limited to this. For example, it may be monitored by the magnitude of the bias current applied to the LD 61.

  Moreover, although several embodiment suitable for the said invention was described, it cannot be overemphasized that the structure of each part, control, a process, and these combination can be variously changed within the range which does not deviate from this invention. .

  (Supplementary note 1) A Raman amplifier control method for an optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied, comprising: a variable attenuator for attenuating main signal light; A variable attenuator, comprising: a detection means for detecting a reception level of the signal light; a Raman excitation laser for amplifying the main signal light in the optical fiber transmission line; and a monitor means for monitoring an operating state of the Raman excitation laser. A first step of minimizing the amount of attenuation, a second step of increasing the output of the Raman excitation laser until the reception level of the main signal light reaches a predetermined range, and the reception level of the main signal light A third step of determining whether or not the Raman excitation laser when reaching the predetermined range has reached a predetermined operating state or higher capable of stably maintaining the oscillation state; Since the determination has not reached the predetermined operating state, a fourth step of increasing the attenuation amount of the variable attenuator by a predetermined amount and then returning to the second step; A Raman amplifier control method comprising: a fifth step of stopping a series of controls by reaching the first step.

  According to the invention of appendix 1, not only a predetermined reception level can be obtained, but at this time, if the Raman excitation laser is not in a stable oscillation state, the predetermined amount of reception can be increased by increasing the loss amount of the variable attenuator. Both the level and the stable laser oscillation state can be achieved efficiently.

  (Supplementary Note 2) An optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied, and a variable attenuator for attenuating main signal light, and a reception level of main signal light Detecting means for detecting the Raman signal, a Raman excitation laser for amplifying the main signal light in the optical fiber transmission line, a monitoring means for monitoring the operating state of the Raman excitation laser, and a predetermined reception level detected by the detection means An optical communication system comprising: control means for controlling a loss amount of the variable attenuator so that the Raman excitation laser operates in a stable oscillation state within a range to be operated.

  (Supplementary note 3) The optical communication system according to supplementary note 2, wherein a variable attenuator is provided on the optical transmission side, and a Raman excitation laser is provided on the optical reception side.

  (Supplementary note 4) The optical communication system according to supplementary note 2, wherein a Raman pumping laser is provided on the optical transmission side, and a variable attenuator is provided on the optical reception side.

  (Supplementary Note 5) An optical communication device of an optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied, and amplifies main signal light in the optical fiber transmission line A Raman excitation laser, a monitoring means for monitoring the operating state of the Raman excitation laser, a variable attenuator provided at a subsequent stage of the Raman excitation laser injection unit, and attenuating the received main signal light, and passing through the variable attenuator Detecting means for detecting the reception level of the subsequent main signal light; and the variable attenuator so that the Raman excitation laser operates in a stable oscillation state within a range in which a predetermined reception level is detected by the detecting means. An optical communication apparatus comprising: a control unit that controls a loss amount.

(Supplementary Note 6) An optical communication device of an optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied, and a variable attenuator that attenuates main signal light to be transmitted; A Raman pumping laser provided after the variable attenuator for amplifying the main signal light in the optical fiber transmission line, a monitoring means for monitoring the operating state of the Raman pumping laser, and a reception level detected by the opposing device Receiving means for receiving the information,
Control means for controlling a loss amount of the variable attenuator so that the Raman excitation laser operates in a stable oscillation state within a range in which a predetermined reception level is obtained with respect to the received reception level information. An optical communication device.

It is a figure which shows the structure of the Raman amplifier control system by 1st Embodiment. It is a flowchart of the attenuator control process by embodiment. It is a figure explaining the optical transmission characteristic by embodiment. It is a figure which shows the structure of the Raman amplifier control system by 2nd Embodiment. It is a figure which shows the structure of the Raman amplifier control system by 3rd Embodiment. It is a figure which shows the structure of the Raman amplifier control system by 4th Embodiment. It is a figure (1) explaining a prior art. It is a figure (2) explaining a prior art.

Explanation of symbols

50A, 50B Optical transmission device 51A, 51B Optical fiber transmission line 52A, 52B Optical amplifier (OA)
54 Wavelength demultiplexer 55, 63 Photodiode (PD)
56 Control unit 60 Raman amplifier 61 Laser diode (LD)
62 Wavelength multiplexer 64, 67 OSC (Optical Supervisory Channel) communication unit 65 Wavelength multiplexer 66 Wavelength demultiplexer 68 Variable attenuator control unit 69 Variable attenuator (ATT)

Claims (5)

An optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied,
A variable attenuator for attenuating the main signal light;
Detecting means for detecting the reception level of the main signal light received via the optical fiber transmission line;
A Raman excitation laser for amplifying main signal light in the optical fiber transmission line;
Monitoring means for monitoring the optical output of the Raman excitation laser;
Control means for controlling a loss amount of the variable attenuator so that a predetermined reception level is detected by the detection means in a state in which the monitor means detects a light output exceeding a predetermined value. Optical communication system. 2. The optical communication system according to claim 1, wherein the variable attenuator is provided on the transmission side of the main signal light, and the Raman excitation laser is provided on the reception side of the main signal light. 2. The optical communication system according to claim 1, wherein the Raman pumping laser is provided on the main signal light transmitting side, and the variable attenuator is provided in front of the detecting means on the main signal light receiving side. A receiving- side device of an optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied,
A Raman excitation laser for amplifying main signal light in the optical fiber transmission line;
Monitoring means for monitoring the optical output of the Raman excitation laser;
A variable attenuator provided downstream of the pumping light injection unit to the optical fiber transmission line, for attenuating the main signal light received via the optical fiber transmission line;
Detection means for detecting the reception level of the main signal light after passing through the variable attenuator;
Control means for controlling a loss amount of the variable attenuator so that a predetermined reception level is detected by the detection means in a state in which the monitor means detects a light output exceeding a predetermined value. receiving device for. A transmission side device of an optical communication system in which a plurality of optical communication devices are connected to each other via an optical fiber transmission line to which Raman optical amplification is applied,
A variable attenuator for attenuating the main signal light transmitted to the optical fiber transmission line;
A pump for Raman excitation for injecting pumping light from the latter stage of the variable attenuator, and amplifying main signal light in the optical fiber transmission line;
Monitoring means for monitoring the optical output of the Raman excitation laser;
Receiving means for receiving information of the reception level of the main signal light detected by the opposite device;
Control means for controlling the amount of loss of the variable attenuator so that information of a predetermined reception level is received by the reception means in a state where the monitor means detects a light output exceeding a predetermined value. transmitting device, wherein.

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