JP4648263B2 - Optical amplifier and optical transmission device - Google Patents

Description

  The present invention relates to an optical system using Raman excitation light. Typical examples of the optical system include an optical amplifier, a Raman pumping light emitting device, such as a Raman pumping light source or a Raman pumping light emitting device for performing optical amplification by the stimulated Raman effect in an optical fiber, a light It is a repeater or an optical system using these devices.

  A wavelength division multiplexing (WDW) optical transmission system that performs information transmission by multiplexing a plurality of optical signals having different wavelengths in an optical fiber is an extremely effective technique for increasing the capacity of optical fiber communication. For such optical signal relay / amplification, rare earth-doped optical fiber amplifiers such as EDFAs (Erbium-doped Fiber Amplifiers), and optical fiber amplifiers such as semiconductor optical amplifiers and Raman amplifiers are used. These optical amplifiers are disposed upstream of the optical fiber transmission line and are used as post-amplifiers for amplifying and outputting a transmission optical signal having one wavelength or a plurality of wavelengths to a large optical power. Further, the optical amplifier is arranged on the downstream side of the optical fiber transmission line, and serves as a preamplifier for amplifying and receiving the weakened optical signal after transmission, and amplifies the optical signal after transmission for the next optical fiber. Widely used in applications such as optical repeaters that send out transmission lines.

  These optical amplifiers, especially EDFAs that are already widely used in commercial optical fiber transmission systems, detect the loss of the input optical signal and the release of the output end (connector release and fiber cut) to detect the output of the optical amplifier. A shut-off circuit is provided for shutting off. The method of detecting the disappearance of the input signal and shutting off the optical amplifier is described in, for example, Japanese Patent Application Laid-Open No. 7-240717 (Patent Document 1). Examples of the method of detecting the release of the output connector and shutting off the optical amplifier include, for example, Japanese Laid-Open Patent Publication No. JP-A-07-190887 (Patent Document 2).

  FIG. 2 shows a configuration of a conventional optical amplifier 100 provided with a blocking mechanism based on the disappearance of input light and output release detection. The optical amplifier 100 amplifies the optical signal input from the input optical connector 101 with an optical amplification medium 103 such as EDF (Erbium Doped Fiber) and outputs the amplified optical signal from the output optical connector 105. During a normal optical amplification operation, the optical amplification medium is pumped by pumping light output from the pumping light source 111 to form an optical signal gain. The output intensity of the pumping light is constant, or the output light intensity of the optical amplifier 100 is controlled to be constant (constant output control), or the signal gain of the optical amplifier 100 is controlled to be constant (constant gain control). Is common.

  The blocking mechanism due to the disappearance of the input signal is as follows. A part (approximately several percent) of the optical signal input via the input optical connector 101 is branched by the optical branching device 102 and subjected to photoelectric conversion by the input optical detector 109. The control circuit 110 determines that the input optical signal has disappeared when the photocurrent detected by the input light detector 109 falls below a certain level, controls the drive current of the pumping light source 111, and pumps light supplied to the optical amplifying medium 103. Is reduced or cut off to reduce the gain of the optical amplifier. In general, the constant level is set to a value between the minimum signal input level determined from the S / N ratio of the optical signal and the configuration of the transmission system, and the noise level.

  In addition, the optical amplifier in which the input signal disappears outputs broadband noise light called ASE (Amplified Spontaneous Emission) instead of amplifying the signal light. These noise lights may cause adverse effects such as malfunction of the input signal detection circuit of the subsequent optical amplifier and the optical amplifier with constant gain control or constant output control. To prevent this, the optical amplifier is shut off. There is a case.

  The shut-off mechanism by output release is as follows. The optical branching unit 104 is installed at the output end of the optical amplifier 100 and branches an optical signal 112 output to the optical fiber transmission line and a part (approximately several percent) of the reflected light 113 input from the optical connector 105. Then, they are introduced into the output light detector 107 and the reflected light detector 108, respectively. These signal intensities are photoelectrically converted and input to the control circuit 110. The control circuit determines that the output end is released when the ratio of the reflected light intensity to the output light intensity exceeds a certain level, and determines the drive current of the excitation light source 111. The pumping light supplied to the optical amplifying medium 103 is controlled or reduced or the gain of the optical amplifier is reduced. The above constant level is set between the level of Fresnel reflection that occurs when the connector is released or when the fiber is cut, and the reflection level of the optical signal due to Rayleigh scattering that occurs in the optical fiber transmission line (usually the former is larger). Is common.

JP-A-7-240717 Japanese Patent Application Laid-Open No. 07-190887

  An object of the present invention is to provide an optical amplifier that does not malfunction even when strong excitation light is used. Furthermore, the present invention provides a Raman amplifier that does not malfunction even when strong excitation light is used.

  Furthermore, the present invention provides an optical transmission device or an optical transmission system that does not malfunction even when strong excitation light is used.

  The main technical problems of the present invention will be described as follows.

  The first is to detect the disappearance of the input signal to the optical amplifier with high accuracy even when using strong pumping light, and to cut off or reduce the output of the optical amplifier. . This precise operation of the optical amplifier can prevent an optical surge upon re-incidence of light.

  The second main technical problem of the present invention is to detect the release of the output signal in the optical amplifier with high accuracy and cut off or reduce the output of the optical amplifier even when strong pump light is used. Is to make it possible. This precise operation of the optical amplifier can prevent unnecessary light emission.

  A more preferred object of the present invention is to provide an optical amplifier that can solve both the first and second technical problems. In addition, the optical amplifier of the present invention provides an optical transmission apparatus or an optical system free from malfunction.

  The present invention has three basic forms.

  The first form of the present invention is a form using an excitation light removing means and a removing member such as a filter. Various embodiments are conceivable. Typically, for example, an excitation light removal filter is inserted into the input detection circuit or output detection circuit of an optical device such as an optical amplifier. . By using excitation light removing means for both the input detection circuit and the output detection circuit, both the first and second technical problems can be solved. Alternatively, when detecting reflected light from the output end of Raman excitation light or the like, it is useful to use the same excitation light removing means for the path of the reflected light to the light receiver.

  The excitation light removing means is not limited to a filter, and for example, a multiplexer can be used. In this case, it goes without saying that the multiplexer has a characteristic of removing pumping light such as Raman light and transmitting desired signal light.

  The present multiplexer preferably has a Raman pumping light transmittance that attenuates the intensity of the Raman pumping light reaching the photodetector to ½ or less of the optical signal intensity to be detected.

  The second aspect of the present invention is a form in which the detection threshold value of the input / output detection circuit is changed according to the state of the excitation light, such as ON / OFF of the excitation light. By using a measure for changing the detection threshold for both the input detection circuit and the output detection circuit, both the first and second technical problems can be solved.

  The third form of the present invention is a form for adjusting the intensity of the excitation light itself. The typical form is a form which uses excitation light for the detection of the presence or absence of input / output release.

  Furthermore, in addition to these basic forms, it is possible to use a combination of a startup method of excitation light and a monitoring information transmission method using reverse excitation light, which is useful for the purpose of the present invention.

  Hereinafter, various aspects of the present invention will be described in detail with the above-described three representative forms as axes.

The apparatus and optical system that are the subject of the present invention relate to an optical apparatus or optical system that uses strong excitation light, for example, excitation light that is stronger than signal light. A typical example of this powerful excitation light is Raman light. However, since there are a wide variety of optical devices, members or optical systems to which the present invention can be applied, the main ones are listed and exemplified here. Of the optical devices or optical systems other than those specifically listed here, the optical devices or optical systems to which the inventive idea disclosed herein can be applied are naturally within the scope of the present invention.
(1) Examples of the optical amplifier include an optical fiber amplifier, a semiconductor optical amplifier, an optical fiber Raman amplifier, and a lumped Raman amplifier. Here, the optical fiber / Raman amplifier introduces Raman light into an optical transmission line and an optical fiber, and performs optical amplification by the stimulated Raman effect in the optical transmission line and the optical fiber. In this specification, the means for introducing the Raman light into the optical transmission line, the optical fiber, and the device are referred to as an optical fiber Raman amplifier.
(2) An excitation light source for an optical fiber Raman amplifier.
(3) Various optical amplifiers or optical systems in which optical fiber Raman amplifiers are connected in cascade.
(4) An optical amplifier to which Raman pumping light is input. For example, an optical amplifier having a pumping light input for an optical fiber Raman amplifier.
(5) An optical device, an optical transmission device, and an optical repeater having the optical amplifiers described above.
(6) An optical system having an optical device, an optical transmission device, an optical repeater, and the like using the optical amplifiers described above.

  The basic first technical idea of the present invention is that the wavelength of pumping light used for optical fiber Raman amplification is between an optical detector that detects the intensity of reflected light from the optical signal output end of the optical amplifier and the output end. And an optical filter that transmits the wavelength of the optical signal is inserted. By doing so, disturbance to the photodetector due to Raman excitation light is removed. In addition, an optical filter that blocks the wavelength of the excitation light used for optical fiber Raman amplification and transmits the wavelength of the optical signal is provided between the optical detector that detects the input signal intensity from the input end of the optical signal and the input end. If inserted, it can be similarly applied to input detection.

  Alternatively, the following measures exist to prevent the mixture of the Raman excitation light. The wavelength of the pumping light used for the optical fiber Raman amplification is blocked, and the wavelength of the optical signal is transmitted. That is, the optical signal input section or output section or both are provided with a multiplexer that multiplexes optical fiber Raman amplification pumping light toward the optical fiber transmission line, and this multiplexer is connected to the optical signal input end. The wavelength component of the excitation light can be removed by disposing the input signal intensity between the photodetector and the input end. Alternatively, it is also possible to arrange this multiplexer between the photodetector and the output end for detecting the intensity of the reflected light from the output end of the optical signal, or by arranging both at both. Thus, the wavelength component of the excitation light can be removed. In this case, the multiplexer blocks the wavelength of the pumping light used for the optical fiber Raman amplification, and has characteristics similar to those of the optical filter that transmits the wavelength of the optical signal. It works like a filter.

  The means for removing the wavelength component of the pumping light includes, in particular, an optical fiber Raman amplifier or an optical fiber Raman amplification pumping light source using an optical fiber transmission line as a gain medium, and an optical fiber Raman amplification pumping light input unit. It is effective in the provided optical amplifier. In addition, the optical fiber Raman amplifier, the optical fiber Raman amplification pumping light source, or the optical transmission device or the optical transmission system having the optical amplifier provided with the optical fiber Raman amplification pumping light input section is effective.

  The second aspect of the present invention is a form in which the detection threshold value of the input / output detection circuit is changed in accordance with the state of the excitation light such as ON / OFF of the excitation light.

  That is, the reflection intensity or incident intensity of the signal light changes according to the on / off state of the optical fiber Raman amplifier and the output intensity of the pumping light. Therefore, by changing the threshold value for determining input detection or output reflected light detection to a plurality of different values accordingly, the influence of noise light is reduced and more reliable detection of input light or reflected light is achieved. You can do it. For example, when a specific operation is illustrated, when the Raman pump light on / off signal is on, the system uses a large voltage value of the reference voltage source, while the Raman pump light on / off signal is off. In this case, a small voltage value is used. Therefore, malfunction of the optical device and the optical system can be prevented.

  The third aspect of the present invention is a form in which the intensity of the excitation light itself is adjusted, for example, the form in which the excitation light itself is used for detection for input / output release. That is, the pumping light source device for Raman amplification and the optical fiber Raman amplifier also output high-intensity light, so the reflected light intensity from the output end or the ratio of the reflected light intensity from the output end to the output light intensity is measured. If a photodetector is provided, the object of the present invention can be achieved. The excitation light is adjusted based on the detection result of the photodetector.

  As an example of this adjustment, the intensity of the excitation light is detected. If the optical signal level is a certain level or more, it can be confirmed that all the connectors on the upstream side of the light source device are not opened. Therefore, the excitation light is turned on and the excitation light is sent out upstream. Further, when the input signal light drops below a certain level during operation, it is determined that a state such as a connector opening has occurred, and the Raman excitation light is blocked. It is not always necessary to change the threshold value using an on / off binary value, and the threshold value may be continuously variable or set to a plurality of three or more values depending on the intensity of the excitation light.

  At this time, an optical filter that transmits the excitation light wavelength and blocks the amplified signal light wavelength and other disturbance light is arranged between these photodetectors and the output terminal, thereby affecting the influence of the disturbance light. So that more accurate I / O release detection can be performed. This can also be achieved by arranging these photodetectors between a multiplexer that multiplexes the excitation light and the amplified signal light and the excitation light source.

  Furthermore, when the reflected light intensity from the output end or the ratio of reflected light intensity from the output end and the output light intensity exceeds the set value, the excitation light is reduced or blocked, an alarm is displayed, or an alarm or monitoring is performed. By transferring information to another device, it is possible to increase the security of the device.

  Next, it is possible to devise a method for raising the excitation light from the Raman light source. That is, when the excitation light is activated, the excitation light intensity is turned on at a low intensity in advance while measuring the reflected light intensity from the output end or the ratio of the reflected light intensity from the output end to the output light intensity. If this measured value exceeds a certain value, the intensity of the excitation light is fixed, reduced or blocked, an alarm is displayed, alarm / monitoring information is transferred to another device, and the approximate measured value When is below a certain value, the excitation light intensity is increased to a predetermined value. Such a method of starting the excitation light can provide a safer and more reliable method for starting the excitation light.

  In particular, in an optical fiber Raman amplifier, the input and reflection detection at the optical signal wavelength to be amplified and the input and reflection detection at the pumping light wavelength are used in combination, so that the detection for more input / output release is ensured. It becomes possible to increase the sex.

  Next, a method using reverse direction excitation light will be described. In the backward pumping type optical fiber Raman amplifier arranged downstream of the optical fiber transmission line, the Raman pumping light that travels backward with the signal light has a frequency ac (where a is the optical fiber transmission line in the pumping light source). (C is the speed of light.) By modulating the above and detecting the modulation component, the influence of disturbance light is eliminated in the input / output release detection using Raman excitation light, and the transmission characteristics of signal light It becomes possible to avoid the deterioration of.

  Further, the Rayleigh scattering component and the Fresnel reflection component at the connector end can be distinguished, and the input / output release can be more reliably determined. The roughly modulated component can be shared for detecting the input / output release state of the upstream optical transmission apparatus and for information transmission to the upstream optical transmission apparatus.

  When applying the same technique to a translation-type optical fiber Raman amplifier arranged on the upstream side of the optical fiber transmission line, if the modulation amplitude is made sufficiently small, the deterioration of the transmission signal is minimized, The same purpose can be achieved.

  In addition, in an optical amplifier arranged on the upstream side of the optical fiber transmission line, the pumping light intensity of the Raman amplifier arranged on the downstream side of the optical fiber transmission line is measured, and this light intensity falls within a preset light intensity range. In this case, the optical signal output or the pump light of the optical amplifier is turned on, increased or kept constant, and if the light intensity deviates from the above range, the optical signal output or the pump light of the optical amplifier is By reducing or blocking, it is possible to provide a safer and more reliable method of starting and blocking excitation light. This is the same when the optical amplifier on the upstream side is an optical fiber Raman amplifier, and the safety is higher if the Raman pumping light sent from the downstream side at the time of start-up is in a state where the pumping intensity is reduced.

  Conversely, in an optical fiber Raman amplifier arranged downstream of an optical fiber transmission line, the intensity of signal light or Raman pumping light transmitted from the upstream side is measured, and the approximate light intensity is within a preset light intensity range. In this case, the Raman excitation light is turned on, increased, or kept constant, and if the light intensity exceeds the above range, the output of the optical signal is reduced or cut off. A high start-up / shut-off system can be provided.

  The present invention can provide an optical amplifier that does not malfunction even when strong excitation light is used. Furthermore, the present invention can provide a Raman amplifier that does not malfunction even when strong excitation light is used.

  The present invention can further provide an optical transmission device or an optical transmission system that does not malfunction even when strong excitation light is used.

<Consideration of various difficulties that form the basis of the present invention>
Before exemplifying specific embodiments of the present invention, studies, considerations, and the like of the present inventors who have arrived at the present invention will be described.

  As outlined in the section of the prior art, in the conventional optical amplifier, the purpose of detecting the disappearance of the input signal and shutting off the optical amplifier is mainly to prevent an optical surge of the optical amplifier.

  In an optical amplifier using an inversion distribution such as an erbium-doped fiber amplifier (EDFA), when the input signal is lost, the upper level carriers in the EDFA are not consumed and the optical signal gain is increased. It will be in a state of rising. When the optical signal is input again to the optical amplifier in this state, the rising portion of the optical signal sharpens, and there is a possibility that an optical pulse (optical surge) with high peak power is generated. In particular, in a multi-relay optical transmission in which a plurality of optical amplifiers are connected in cascade, such an optical surge grows as the peak power increases each time it passes through the optical amplifier, and finally connects to the receiving end. There is a possibility of destroying an optical device such as an optical receiver and an optical connector. For this reason, when the input signal disappears, the pumping light and pumping current of the optical amplifier may be cut off or reduced to suppress the occurrence of the optical surge.

  Further, as described above, the purpose of detecting the output release and shutting off the optical amplifier is to protect the operator and prevent the connector from burning at the release point. This blocking is particularly important in the recent wavelength division multiplexing transmission because the output signal strength of the optical amplifier reaches several hundred mW. Here, output release means release of a connector, cutting of a fiber, or the like. In addition, there is an effect of preventing an optical surge that occurs when an output released portion (hereinafter abbreviated as an output release point) is connected again.

  However, as a result of various studies on the case where a conventional optical amplifier is used in combination with a Raman amplifier, the present inventors have found that there are the following problems despite having the above-described effects. Based on these viewpoints, the present invention is provided.

In such a conventional optical amplifier, when used in combination with a Raman amplifier, that is, when strong excitation light is used, the blocking mechanism may not operate normally. There are mainly two reasons for this.
(1) Since a Raman amplifier using an optical fiber transmission line as a gain medium inputs strong Raman pumping light to the optical fiber transmission line, the input detection or the above-described input detection used in a conventional optical amplifier such as an EDFA is used by this pumping light. The output release detection or the like malfunctions.
(2) Further, depending on the presence or absence of Raman excitation light, a signal gain is generated and the signal intensity itself changes. This causes the optical amplifier to malfunction.

  These difficulties are due to the specificity based on the use of strong excitation light. This peculiarity will be considered in consideration of the conventional technique shown in FIGS.

  The first problem is that when strong excitation light is used, the reflected light intensity of the signal light and the residual intensity of the excitation light are almost equal, and detection for normal connector release cannot be performed. is there.

  The problem will be described with reference to the example of FIG. For example, in FIG. 2, an optical fiber Raman amplifier 120 is connected to the downstream side of the optical amplifier 100 via an optical fiber transmission line 106. In the optical fiber Raman amplifier 120, the light from the pumping light source 121 is wavelength-multiplexed via the multiplexer 122, and the pumping light 123 output from the pumping light source 121 is guided into the optical fiber transmission line 106. The excitation light 123 is unmodulated light having a wavelength shorter by about 100 nm than the signal light, and travels in the opposite direction to the signal light. Accordingly, the signal light is amplified in the optical fiber transmission line 106 by the stimulated Raman effect.

  As described above, Raman amplification is actually performed in an optical fiber transmission line. In the present specification, an apparatus having a function of combining signal light and Raman pumping light is referred to as an “optical fiber Raman amplifier”. Called. In the drawing, black arrows (112 and the like) indicate optical signals or reflection components of optical signals, and white arrows indicate Raman excitation light (123 and the like) or reflection components thereof. Further, it is assumed that the multiplexer and the demultiplexer are elements having a function of multiplexing and demultiplexing with low loss using the difference in wavelength between the pumping light and the signal light.

  Although the excitation light 123 is lost by the optical fiber transmission line 106, a part of the excitation light 123 reaches the connector 105 and reaches the reflected light detector 108 together with the reflected light 113 of the signal light. For example, assuming that the output level of the pumping light is 25 dBm and the loss of the optical fiber transmission line is 30 dB, the light intensity input to the output connector 105 is −5 dBm. On the other hand, if the signal light output of the optical amplifier 100 is 10 dBm and the Fresnel reflectivity of the signal light is −14 dB, the Fresnel reflected light intensity and the remaining intensity of the excitation light are almost equal, and detection for normal connector release is possible. The problem of being unable to do so arises.

  Next, the second problem is that when a Raman amplifier is used in cascade with another optical amplifier, it is difficult to detect an input signal or output release in both the conventional optical amplifier and the Raman amplifier. It is.

  Consider the configuration of FIG. 3 shows an optical amplifier 100-1 and an optical fiber Raman amplifier (translation pumping type) 130 on the upstream side of the optical fiber transmission line 106, and an optical fiber Raman amplifier (reverse pumping type) 120 and an optical fiber amplifier on the downstream side. This is an example in which 100-2 is arranged.

  For example, the reflected light detector 108 should detect the reflected light 113 originally generated by the optical connectors 105, 134, 135, and the like. However, the Rayleigh scattered light of the Raman excitation light 133 and the residual portion 133 ′ of the Raman excitation light 123 from the downstream side may pass through the multiplexer 132 and leak into the reflected light 113. As the multiplexer 132, one having a wavelength separation of about 30 dB to 40 dB is usually used. However, since the light intensity of the Raman excitation light is extremely high, the reflected light detector 108 may be malfunctioned when the number of wavelengths of the optical signal is small and the optical signal intensity is low. Further, depending on the Raman amplification method, a method of arranging a pumping light reflection grating that reflects pumping light in the middle of the optical fiber transmission line 106 is known in order to improve pumping efficiency. In such a case, the reflectance of the excitation light becomes stronger, so that malfunction is likely to occur.

  Although omitted in each of the above-described drawings, it is conceivable that the optical fiber Raman amplifiers 130 and 120 are also provided with input detection and output release detection. However, these circuits may malfunction due to the other Raman optical amplifier as well.

  Similarly, the input detection circuit 109 of the optical amplifier 100-2 may malfunction due to Raman pumping light.

  The identification threshold value of the presence or absence of an input signal at the input detector 109 is usually a low value of −20 dBm to −40 dBm, depending on the system configuration. For this reason, even if the wavelength separation in the multiplexer 122 is high, there is a high possibility of malfunction due to reflection of excitation light and residual components. In particular, when the optical fiber Raman amplifier 120 is not used, it becomes a big problem.

  In addition, when an optical fiber Raman amplifier is used, the level of the signal light varies depending on whether the Raman pumping light sources 131 and 121 are turned on or off, which may cause a malfunction.

<Embodiments of the main invention>
Based on these studies by the inventors of the present application, the present application is based on an input detection method and output release detection of an optical amplifier (note that the optical amplifier here includes the Raman amplifier). The present invention provides new inventions relating to a method and a method for starting up and shutting down an optical amplifier in consideration of the specificity of a Raman amplifier.

  Hereinafter, since the present invention is diverse, the main embodiments are listed.

  In the first embodiment of the present application, in an optical amplifier that amplifies an optical signal having one wavelength or wavelength multiplexing, an optical signal is detected between an optical detector that detects the intensity of reflected light from the output end of the optical signal and the output end. This is an optical amplifier characterized by inserting an optical filter that blocks the wavelength of the pumping light used for fiber Raman amplification and transmits the wavelength of the approximate optical signal. As the Raman excitation light removing member, any optical filter such as a dielectric multilayer film, an optical fiber grating, or a glass waveguide can be used as long as it has a function of transmitting signal light and removing Raman excitation light. The Raman excitation light removing member is handled as an individual part. However, if there is a similar function, there is no problem even if the function is incorporated into a part of another part. This aspect is the same in the following examples.

  In the second embodiment of the present application, in an optical amplifier that amplifies an optical signal having one wavelength or wavelength multiplexing, an optical signal is detected between an optical signal input terminal from the optical signal input terminal and the input terminal. This is an optical amplifier characterized by inserting an optical filter that blocks the wavelength of the pumping light used for fiber Raman amplification and transmits the wavelength of the approximate optical signal.

  The third embodiment of the present invention is an optical amplifier that amplifies an optical signal of one wavelength or wavelength multiplexed, and an optical fiber Raman amplification toward an optical fiber transmission line at an input portion and / or an output portion of the optical signal. Including a multiplexer that multiplexes the excitation light for use, and the multiplexer is disposed between the photodetector and the input end that detects the input signal intensity from the input end of the optical signal, or The optical amplifier is characterized in that it is arranged between a photodetector for detecting the intensity of reflected light from the output end of the optical signal and the output end, or both.

  The fourth embodiment of the present application includes the first, second, and third optical amplifiers, and an optical fiber Raman amplifier, an optical fiber Raman amplification pumping light source, or an optical fiber Raman amplification amplifier that uses an optical fiber transmission line as a gain medium. An optical amplifier, an optical transmission device, and an optical transmission system, each including an excitation light input unit.

  According to the fifth embodiment of the present application, in the first, second, third, and fourth optical amplifiers, the optical transmission device, and the optical transmission system, depending on the on / off state of the optical fiber Raman amplifier and the output intensity of the pumping light. The optical amplifier, the optical transmission apparatus, or the optical transmission system is characterized in that the threshold value for determination of input detection or output reflected light detection is changed to a plurality of different values.

  In the sixth embodiment of the present application, in an excitation light source device that transmits excitation light for Raman amplification, or an optical fiber Raman amplifier that transmits excitation light for Raman amplification to an optical fiber transmission line, from the output end of the excitation light An excitation light source device or an optical fiber Raman amplifier comprising a photodetector that measures the reflected light intensity of the light or the ratio of the reflected light intensity from the output end of the excitation light to the output light intensity.

  In a seventh embodiment of the present application, in the sixth excitation light source device or the optical fiber Raman amplifier, a photodetector for detecting reflected light intensity from an output end of excitation light or light detection for detecting output light intensity And an optical filter that transmits the wavelength of the pumping light and blocks the wavelength of the signal light to be amplified or the pumping light wavelength of other optical fiber Raman amplifier or other disturbance light Or the reflected light intensity detector and / or the approximate output light detector are arranged between the excitation light source and the multiplexer that combines the excitation light and the amplified signal light. An excitation light source device or an optical fiber Raman amplifier.

  In the eighth embodiment of the present application, in the pumping light source device or optical fiber Raman amplifier of 6 to 7, the reflected light intensity from the output end or the reflected light intensity from the output end and the output light intensity ratio exceeds the set value. The pumping light source device or the optical fiber Raman amplifier is characterized by reducing or blocking the pumping light, displaying an alarm, or transferring the alarm or monitoring information to another device. is there.

  In the ninth embodiment of the present application, when the excitation light of the sixth, seventh, or eighth optical fiber Raman amplifiers is raised, the reflected light intensity from the output terminal, or the reflected light intensity from the output terminal and the output light intensity. The excitation light intensity is lit at a low intensity in advance while measuring the ratio, and if this measured value exceeds a certain value, the excitation light intensity is fixed, reduced or blocked, an alarm is displayed, or an alarm is displayed. A pumping light source device or an optical fiber Raman amplifier characterized by transferring monitoring information to another device, and increasing the pumping light intensity to a predetermined value when the measured value is a predetermined value or less. It is.

  In a tenth embodiment of the present application, in the sixth, seventh, eighth, or ninth optical fiber Raman amplifier, the first, second, third, fourth, or fifth optical signal wavelength input detection or reflected light. An optical fiber Raman amplifier characterized by having both detection and both.

  An eleventh embodiment of the present application is an optical fiber Raman amplifier that is disposed downstream of an optical fiber transmission line and that sends out pumping light toward the upstream side of the optical fiber transmission line to perform optical signal amplification. Is an optical fiber Raman amplifier characterized in that the intensity is modulated at a frequency ac (a is the loss coefficient of the optical fiber transmission line in the pumping light source, c is the speed of light) or more.

  In a twelfth embodiment of the present application, in the eleventh embodiment, the modulation component is used for input / output release detection of an optical fiber Raman amplifier or an optical transmission device arranged on the upstream side, or on the upstream side. An optical fiber Raman amplifier or an optical transmission device characterized by transmitting information to the transmission device.

  A thirteenth embodiment of the present application is an optical fiber Raman amplifier that is arranged upstream of an optical fiber transmission line and that sends out pumping light toward the downstream side of the optical fiber transmission line to perform optical signal amplification. The frequency ac (a is the loss factor of the optical fiber transmission line in the pumping light source, c is the speed of light) is modulated by a small signal intensity, and the open state of the output is detected by detecting the approximate modulation component, or on the downstream side. An optical fiber Raman amplifier, or an optical transmission device, characterized in that input release detection is performed by an optical transmission device arranged.

  In a fourteenth embodiment of the present application, in an optical amplifier arranged on the upstream side in the optical signal transmission direction of the optical fiber transmission line, the pumping light intensity of the Raman amplifier arranged on the downstream side of the optical fiber transmission line is measured. When the light intensity is within the preset light intensity range, the optical signal output or the excitation light of the optical amplifier is turned on, increased or kept constant, and when the approximate light intensity deviates from the above range An optical amplifier characterized by reducing or blocking optical signal output or pumping light of an optical amplifier.

  In the fifteenth embodiment of the present application, in the optical fiber Raman amplifier arranged on the downstream side of the optical fiber transmission line, the intensity of the signal light or Raman pumping light transmitted from the upstream side is measured, and the light intensity is set in advance. When the light intensity is within the range, the Raman excitation light is turned on, increased, or kept constant, and when the light intensity deviates from the above range, the optical signal output is reduced or blocked. An optical fiber Raman amplifier.

<Embodiment of the present invention>
The first embodiment is an example of a form using a filter for removing excitation light. FIG. 1 is a block diagram showing a first embodiment of the present invention. In particular, this example shows a configuration example of the optical amplifier 140 according to the present invention. That is, in this example, the optical amplifier 140 and the optical fiber Raman amplifier 120 that generates pumping light are connected by the optical fiber transmission line 106. Here, the abbreviations in the figure are briefly described. These abbreviations are used interchangeably in all figures. LD stands for Laser Diode, PD stands for Photo Diode, CTL, CTRL stands for Control Circuit, EDF stands for Erbium Doped Fiber, and BPF stands for Band-Pass Filter.

  The signal light 200 is amplified by the optical amplifier 140 and then amplified again by the optical fiber transmission line 106 by the Raman pumping light 123 from the optical fiber Raman amplifier 120. The amplified signal light 201 is output from the output end 211 of the optical fiber Raman amplifier 120.

  An optical branching device 102 is disposed on the input side of the optical amplification medium 103, and the branched light of the input light 200 is input to the input light detector 109 that detects the input light. The detection result by the input light detector 109 is transmitted to the control circuit 110 to control the output of the excitation light source 111 and the like. On the other hand, an optical splitter 104 is arranged on the output side of the optical amplifying medium 103, transmits an optical signal to the output terminal 105, and inputs the light branched from the optical splitter 104 to the output photodetector 107. . The light branching ratio is several percent, for example, about 1% to 10%. Then, the detection result by the input light detector 107 is transmitted to the control circuit 110 to control the output of the excitation light source 111 and the like. Further, the reflected light 113 from the output terminal 105 is input to the reflected light detector 108 through the optical splitter 104. Then, the detection result by the input light detector 108 is transmitted to the control circuit 110 to control the output of the excitation light source 111 and the like. Thus, the optical amplifier 140 controls the output intensity of the pumping light to be constant, controls the output intensity of the optical amplifier 140 to be constant, or controls the signal gain of the optical amplifier 140 to be constant. It is controlled as desired. A specific example of the control circuit 110 will be described later, but general control of such a control system is sufficient in accordance with a usual method, and thus detailed description thereof is omitted here.

  The features of the present invention are as follows. The optical amplifier 140 amplifies the optical signal 200 input from the input optical connector 101 by the optical amplification medium 103 and outputs the amplified optical signal 200 from the output optical connector 105 to the optical fiber transmission line 106. After this output optical connector 105, an optical fiber Raman amplifier 120 is connected. Therefore, the optical signal 112 reaches the output optical connector 105, but the reflected light 113 is generated. Immediately before the reflected light detector 108, a filter for removing Raman excitation light (hereinafter, this filter is abbreviated as a Raman excitation light removing filter) 142 is disposed, and residual Raman excitation light leaking into the reflected light 113. 123 is removed.

  The Raman excitation light removal filter 142 has a function of transmitting an optical signal having a wavelength to be amplified by the optical amplifier 140 and removing the Raman excitation light. Therefore, even when the Raman amplifier 120 is used, it is possible to accurately measure the intensity of the reflected light 113 of the signal light 112 and perform correct output release detection. In addition, since the excitation light normally used for Raman amplification is about 100 nm shorter than the signal wavelength, the two can be easily separated by wavelength filtering. For example, when the wavelength of the optical signal is 1550 nm, the wavelength of the Raman excitation light is approximately 1450 nm. Even when the Raman amplifier is not used, the operation as a normal optical amplifier is not affected.

  In this example, the Raman excitation light removal filter 141 is also disposed between the input light detector 109 and the input connector 101. In this embodiment, only the signal for backward pumping from the downstream side of the optical fiber is specifically shown, but in this way, the Raman pumping light is previously applied to the input light detection unit and the reflected light detection unit in the optical amplifier. If an optical filter to be removed is inserted, there is an advantage that the same optical amplifier can be shared in the future when an optical fiber Raman amplifier is used or in different system configurations.

  In the present embodiment, an example having both functions of input light detection and reflected light detection has been described, but the present invention can be applied without any problem in either case. In addition, since the required specifications differ between the input light detection and the reflected light detection depending on the system form and the like, the present invention may be applied to only one of them depending on the system specifications.

  In the case of amplification of a broadband wavelength division multiplexed signal, there are cases where a plurality of wavelength multiplexed optical signals are used as signal wavelengths, and a plurality of pump lights having different wavelengths are also used as an excitation light source. Even in such a case, the present invention can be applied without any problem.

  As the gain medium 103, in addition to the most widely used 1550 nm band EDFA, a long wavelength band EDFA such as a 1580 nm band, an optical fiber amplifier having a different wavelength such as a 1.3 μm band, or a semiconductor optical amplifier, a highly nonlinear fiber, etc. The present invention can be applied to any optical amplifier as long as it is a lumped-constant type Raman amplifier using an optical amplifier and an optical amplifier having an input light / reflected light detection function. In addition, regarding the optical fiber Raman amplifier using the optical fiber transmission line itself as a gain medium, an embodiment in consideration of its peculiarity is shown separately.

  As the Raman excitation light removing filters 141 and 142, any optical filter such as a dielectric multilayer film, an optical fiber grating, or a glass waveguide can be used as long as it has a function of transmitting signal light and removing Raman excitation light. be able to. A multiplexer that combines the wavelength of the signal light and the excitation light can also be applied to this application.

  Since the Raman excitation light is generally very strong as several hundred mW, the light intensity to be removed by the filter may be very strong depending on the position of the optical filter. Even in such a case, there is no problem because the destruction of the filter can be prevented by using a non-absorption type optical filter or by sufficiently expanding the cross-sectional area of the optical signal. In the present invention, the Raman excitation light removal filter is handled as an individual part. However, if there is a similar function, there is no problem even if the function is incorporated into a part of another part. For example, even if a function to block the Raman excitation wavelength or an optical filter is added to the photodetector itself, or an optical branching unit that performs input detection or reflection detection is given a blocking characteristic at the Raman excitation wavelength, basically, It should be noted that it is included in the present invention.

  The insertion positions of the Raman excitation light removal filters 141 and 142 do not necessarily need to be immediately before the input light detector 109 and the reflected light detector 108 as long as this function is satisfied. For example, it may be arranged in the middle of the input connector 101 and the optical splitter 102, in the middle of the optical splitter 104 and the output optical connector 105, and the like. In this case, although the loss of the signal light slightly increases, there is an advantage that the leaked Raman excitation light hardly affects the amplification operation of the optical amplifying medium 103.

  In addition, a multiplexing method that does not necessarily depend on the wavelength can be applied to the portion that is a multiplexer in the present invention as long as it has a function of combining the excitation light and the signal light. For example, if a loss of about 3 dB is permissible for the signal light / pumping light, a 1: 1 optical coupler type optical branching unit is used, or if the traveling direction and polarization of the pumping light and the signal light are different. It is also possible to combine with low loss by an optical circulator or a polarization beam splitter. Even in such a case, the present invention is effective when the degree of separation between the excitation light and the signal light in the input light detector and the reflected light detector cannot be sufficiently obtained.

  Another example using the excitation light removing member is shown as a second embodiment. FIG. 4 is a block diagram showing a second embodiment of the present invention. The figure shows an example in which optical fiber Raman amplifiers of signal light, translational pumping, and backward pumping are applied to both the upstream side and the downstream side of the optical fiber transmission line.

  FIG. 4 shows only main parts directly related to the present invention. As desired, the optical amplifier controls the output intensity of the pumping light to be constant, or the output intensity of the optical amplifier 140 is controlled to be constant, or the signal gain of the optical amplifier 140 is controlled to be constant. Controlling is as exemplified in the first embodiment. Detailed description of these points will be omitted. In the following embodiments, only main parts directly related to the present invention are displayed.

  The optical signal amplified by the optical amplifier 140-1 is input to the optical fiber Raman amplifier 130. The optical signal is combined with the excitation light 133 output from the Raman excitation light source 131 by the multiplexer 132 and then input to the optical fiber transmission line 106.

  At the other end of the optical fiber transmission line 106, the pumping light 123 output from the Raman pumping light source 121 inside the optical fiber Raman amplifier 120 is input via the multiplexer 122 in the opposite direction to the signal light. The optical signal that has passed through the optical fiber Raman amplifier 120 is further amplified by the optical amplifier 140-2.

  In the present embodiment, Raman excitation light removal filters 142 and 141 are inserted immediately before the reflected light detector 108 of the optical amplifier 140-1 and the input light detector 109 of the optical amplifier 140-2, and leaked. The malfunction of the optical amplifier cutoff circuit due to Raman pumping light is prevented. For example, the excitation light removal filter 141 removes the residual component of the Raman excitation light 133 and the reflection component of the Raman excitation light 123 that have passed through the optical fiber transmission line from the optical signal leaking into the input photodetector 109.

In this configuration, the multiplexer 122 that multiplexes the excitation light has the effect of reducing the leakage light of the excitation light, but this value is usually about −30 to −40 dB, which is not necessarily sufficient. I can not say. For example, if the pumping light output is +25 dBm, the light reflectivity due to Rayleigh scattering in the optical fiber transmission line 106 is −24 dB, and the pumping light removal effect of the multiplexer is −35 dB, the pumping light input to the optical fiber amplifier 100-2. The strength is -34 dBm. This value corresponds to, for example, reception sensitivity (error rate 10 ⁻¹² ) of a 10 Gbit / s optical receiver using an optical preamplifier. In a system using a system configuration or an error correction circuit, this value may be close to the input level of the optical signal itself. If the present invention is not applied, the input photodetection circuit 109 may malfunction. Further, when the output release detection circuit is not attached to the optical fiber Raman amplifier 120, or when the output release detection circuit malfunctions, if the input connector 124 or the like is released, the input photodetection circuit 109 is stronger by about 10 dB. Reflected light is input. In either case, when there is no signal light input, it is mistakenly recognized as being present, and the optical amplifier 100-2 is not normally cut off. In the present invention, the excitation light level can be further reduced by several tens of dB by the excitation light removal filter, and this situation can be prevented.

  In the case where the optical fiber Raman amplifier 120 is not used, the residual component of the Raman pumping light 133 is input to the optical fiber amplifier 140-2. Also in this case, the excitation light removal filter 141 can prevent malfunction. As described above, the optical amplifier to which the present invention is applied has an advantage that the input detection circuit always operates normally even in a system configuration in which the position and number of Raman amplifiers are different.

  Although common to all the embodiments, not all of the optical amplifiers and optical Raman amplifiers shown in the drawings are necessarily required for application of the present invention. The illustrated figure illustrates the connection state of an optical amplifier, an optical Raman fiber amplifier, or the like.

  For example, in the second embodiment, there may be a configuration in which one of the optical amplifiers 140-1 and 140-2 does not exist, or one or both of the Raman amplifiers 120 and 130 do not exist. On the contrary, a configuration in which other optical amplifiers are connected in multiple stages, or a configuration in which a plurality of optical fiber transmission lines are relayed are conceivable, but there is no problem in applying the present invention. For example, even when there is no Raman amplifier at all, by arranging the Raman pumping light removal filters 141 and 142 in the optical amplifiers 140-1 and 140-2 in advance, when the Raman amplifier is applied in the future, The cutoff circuits of the amplifiers 140-1 and 140-2 can be provided so as not to malfunction. Further, this embodiment has an advantage that the device configuration can be unified and shared.

  The third embodiment is another example using an excitation light removal filter. FIG. 5 shows a configuration of an optical transmission system according to a third embodiment of the present invention, which transmits a plurality of bands of optical signals by dividing the band.

  In this embodiment, two wavelength bands of 1.3 μm and 1.5 μm bands are assumed. The optical signal in the 1.5 μm band is amplified by optical amplifiers 140-1 and 140-2 such as EDFA, and the optical signal in the 1.3 μm band is amplified by optical fiber Raman amplifiers 130 and 120, respectively. That is, in this case, light is amplified by the stimulated Raman effect in the optical fiber 106 or the like. The optical signals of both wavelengths are multiplexed by the multiplexer / demultiplexer 143-1, transmitted through the optical fiber transmission line 106, and again demultiplexed by the multiplexer / demultiplexer 143-2. The wavelengths of the excitation light sources 121 and 131 used for amplification in the 1.3 μm band are approximately 1.2 μm. When the wavelength demultiplexing characteristics of the multiplexer / demultiplexers 143-1 and 143-2 are not necessarily designed so that sufficient wavelength separation characteristics can be obtained in the 1.2 μm band, as in the other embodiments, Raman excitation is performed. Light may affect the input light and output reflected light detection circuit of the optical amplifiers 140-1 and 140-2. In this embodiment, Raman excitation light removal filters 142 and 141 for removing the vicinity of the wavelength of 1.2 μm are inserted immediately before the reflected light detection circuit 108 and the input light detection circuit 109 to prevent malfunction.

  The combination of wavelength bands and the wavelength band to which Raman amplification is applied are not necessarily limited to this example. In FIG. 5, for example, a 1.3 μm band amplification may be performed with a 1.3 μm band optical fiber amplifier such as a PDFA, and an optical fiber Raman amplifier may be further applied before and after the 1.5 μm band optical amplifier. In these cases, the present invention can be applied in exactly the same manner. In this case, since the wavelength of the Raman excitation light is close to the middle of both bands of 1.4 μm, it becomes difficult to perform sufficient wavelength separation using only the multiplexer / demultiplexers 143-1 and 143-2. Increases nature.

  The example using the excitation light removal filter has been described so far, but a configuration example of the control circuit 110 will be exemplified. A case of application to an example using the excitation light removal filter will be described.

  FIG. 6 shows an example in which the control circuit 110 according to the present invention is configured by an electronic circuit. The control circuit of this example corresponds to the embodiment of FIG. 1 and receives an input light intensity signal 150, a reflected light intensity signal 151, and an output light intensity signal 152 measured by three photodetectors. The input light intensity signal 150 is input to the comparator 154-1. When this value is larger than the reference input level set in the reference voltage source 153-1, that is, when there is a signal light input, the comparator 154 Output has a logical value of 1. The reflected light intensity signal 151 and the output light intensity signal 152 are input to the divider 155, and the ratio between them is calculated. This value is input to the comparator 154-2 and compared with the reference reflection level set in the reference voltage source 153-2. When the ratio between the two is below a certain level, that is, when the reflected light intensity is sufficiently small, the comparator 154-2 The output is set to logical value 1. The output signals of these two comparators 154-1 and 154-2 are input to the AND circuit 156, and the excitation light source current source 157 is turned on only when the logical product is a logical value 1, and the excitation light source driving current 158 is output. Is done. That is, in other cases, the excitation current 158 is turned off, and the optical amplifier is cut off.

  In this example, only the basic operation is shown, but in an actual circuit, hysteresis is given to the operation of the comparator to prevent the influence of noise and the occurrence of optical surges, and a certain delay is applied to the startup of the excitation current source. In some cases, a plurality of excitation light sources may be controlled simultaneously or only a part thereof. Further, this example is merely an example of realization, and almost all operations can be realized by a program by, for example, an A / D converter, a combination of a D / A converter and a CPU.

  The fourth embodiment is an example in which the detection threshold value of the input / output detection circuit is changed according to the state of the excitation light according to the second embodiment of the present invention described above. FIG. 7 is a diagram showing a fourth embodiment of the present invention. In this example, the excitation light source current 158 from the excitation light source current source 157 is controlled by the control circuit 110 in accordance with the state of the Raman excitation light.

  In this example, the control circuit 110 receives the Raman pumping light on / off signal 160, switches 153-1 and 153-2 to different reference voltage sources by the switch 159, and changes the discrimination threshold. The input signal strength signal 150 and the signal of the reference voltage value are input to the comparator 154-1. For example, it is assumed that the reference voltage source 153-1 has a large voltage value, and the reference voltage source 153-2 has a small voltage value. The output signal from the comparator 154-1 and other signals for the control circuit 110 are input to the AND circuit 156, and this output controls the excitation light source current source 157. Various optical amplifiers can be used. For example, the basic configuration of FIG. 1 can be used. Furthermore, the present invention can be applied to the optical amplifier exemplified in this specification. Of course, in such various configurations, the object of the present invention can be achieved by using the control circuit of this example without using the filters 141 and 142 in FIG. The same applies to other examples.

  In Raman amplification using an optical fiber transmission line as a gain medium, the gain of the signal wavelength changes in the optical fiber by turning on and off the Raman pumping light. The magnitude of the light changes. For example, when backward pumping is performed from the downstream side of the optical fiber transmission line, the Raman gain received by the signal wavelength reaches 10 to 20 dB, and the magnitude of the input light intensity signal 150 and the magnitude of the noise light are correspondingly increased. Change.

  Therefore, when the Raman pumping light is on, it is possible to appropriately cut off the optical amplifier and suppress the optical surge by raising the input light detection level. That is, when the Raman excitation light on / off signal 160 is on, the Raman excitation light is connected to the reference voltage source 153-1 having a large voltage value. On the other hand, when the Raman excitation light on / off signal 160 is off, the Raman excitation light is connected to a reference voltage source 153-2 having a small voltage value. If the pumping light drops due to a failure of the Raman pumping light source or the like, if the input detection level of the downstream optical amplifier is lowered, the downstream optical amplifier is not necessarily cut off, so that signal degradation is equivalent to one Raman amplifier. It is also possible to suppress only the minimum SN degradation and prevent unnecessary signal disconnection.

  The Raman pumping light on / off signal may be obtained or transmitted as long as it is on / off information of the pumping light involved in signal amplification. For example, logical information may be transmitted between devices or across an optical fiber transmission line as electrical information on a board, a cable between devices, or a monitoring signal. Further, as will be described later, an optical detector having a wavelength of Raman excitation light may be provided separately, and the reflection intensity and input intensity of the Raman excitation light may be detected and generated using this. It is not always necessary to change the threshold value in an on / off binary manner, and the threshold value may be continuously variable or a plurality of three or more values depending on the intensity of the excitation light. Moreover, although the example applied only to the input detection part was shown in the said embodiment, you may apply to a reflected light detection part.

  The fifth embodiment is an example of adjusting the intensity of the excitation light itself, which is the third embodiment of the present invention. FIG. 8 is a diagram showing a fifth embodiment of the present invention. In this example, an optical fiber Raman amplifier is provided with a mechanism for detecting and blocking the input intensity or output reflection intensity of signal light.

  In the example of FIG. 8, an optical fiber Raman amplifier 136 and an optical fiber Raman amplifier 126 are connected to both ends of the optical fiber transmission line 106. The signal light 200 is output as an amplified output light 210. In FIG. 8, Raman excitation light sources 131 and 121 are provided, and these are controlled by control circuits 110-1 and 110-2. In accordance with this control, control signals are input to the control circuits based on the detection light from the output light detectors 107 and 109 and the reflected light detector 108. The optical fiber Raman amplifier 136 includes an optical splitter 102 and detects input light by the input photodetector 109.

  In the optical fiber Raman amplifier used in the present invention, since the optical fiber transmission line is a gain medium and the gain medium is not included in the portion shown as the optical fiber Raman amplifier, the input intensity and the output intensity of the signal light are the same. It is consistent with excluding loss of waver. Therefore, in the following, only one of them is measured without particularly distinguishing between the two.

  In the optical fiber Raman amplifier 136 of the present invention on the upstream side of the optical fiber transmission line, the intensity of the signal light input from the input connector 134 and the intensity of the reflected light are detected by the photodetectors 107 and 108, and the release detection of the output connector 135 is detected. It is carried out.

  In this example, the optical filter for removing the excitation light is not required by arranging the multiplexer 132 for multiplexing the Raman excitation light between the reflected light detector 108 from the output end of the optical signal and the output connector 135. Yes. In the case of an optical fiber Raman amplifier, this arrangement is possible because there is always a pumping light multiplexer. When the wavelength separation degree of the multiplexer 132 is low, when Raman excitation light of other wavelengths may leak, or when the positions of the multiplexer 132 and the optical splitter 104 are reversed, the light detection is performed. It is necessary to insert a Raman excitation light removal filter in front of the devices 108 and 107.

  As described above, when the signal light is used for output connector release detection, it is possible to determine whether to release the connector and turn on the excitation light source 131 before turning on the Raman excitation light source whose output is extremely higher than that of the signal light. Therefore, it is advantageous in terms of worker safety and protection of connectors and optical components. In addition, by shutting off the excitation light source 131 even when the input signal light is cut off during operation, it is possible to improve safety and prevent malfunction of downstream equipment.

  On the other hand, in the optical fiber Raman amplifier 126 of the present invention downstream of the optical fiber transmission line 106, the input light intensity is detected at the signal light wavelength. In this example, the excitation light multiplexer 122 is disposed between the input light detection unit 109 and the input end, and a Raman excitation light removal filter 142 is further inserted. In particular, since the threshold value for determining the presence or absence of an input signal to the input light detection unit 109 is low, this arrangement relaxes the specification of the wavelength separation degree for the Raman excitation light removal filter 142 and the wavelength multiplexer 122. It becomes possible. The position of the excitation light removal filter 142 may be between the splitter 102 and the input photodetector 109.

  As described above, if the signal light is used for the determination of the presence / absence of input, it can be confirmed that there is no connector release portion up to the upstream side before the high-power excitation light source 121 is turned on. It becomes possible to raise.

  In addition, since the input photodetector 109 can measure the signal gain before and after the Raman excitation light source 121 is turned on, it can be used for detecting an abnormality in the amplification operation. In particular, in this configuration, even if an abnormality occurs during operation and the signal light is interrupted, the Raman amplifier amplifies noise light such as ASE of the upstream optical amplifier and misidentifies that there is an input signal. there is a possibility. In such a case, the problem can be avoided by making the input detection level variable as described in the previous embodiment.

  Conversely, when the input signal light is strong to some extent, abnormal situations such as incorrect connections and situations where the transmission path is short and Raman amplification is unnecessary are conceivable, so that other devices and optical elements can be protected. Measures such as not turning on the excitation light source are effective. Furthermore, by applying feedback control to the pumping light intensity so that the signal light power is constant, the input range to the subsequent optical receiver and optical amplifier is not deviated, and the protection of components and the wavelength gain difference of the gain are prevented. Occurrence can be suppressed.

  FIG. 9 shows a sixth embodiment of the present invention. This example shows a configuration of a backward pumping type optical fiber Raman amplifier 126 that uses Raman pumping light itself for connector release detection. The reverse excitation type Raman amplifier is a type of Raman amplifier that advances Raman excitation light in a direction opposite to the traveling direction of signal light. In FIG. 9, only the circuit portion of the optical fiber Raman amplifier is shown. Although the optical fiber transmission line is connected to the input optical connector 124, the illustration is omitted.

  Therefore, in the reverse excitation type Raman amplifier, since strong Raman excitation light is output toward the optical signal input connector 124, it is necessary to detect reflected light from the signal input side.

  In this example, an optical splitter 104-1 is provided between the multiplexer 122 that combines the excitation light and the amplified signal light and the Raman excitation light source 121, and a part of the output light and reflected light of the excitation light is provided. The excitation light reflected light detector 171 and the excitation light output light detector 170 detect it. In this way, a part of the Raman excitation light and the excitation light reflected light are detected, and further, a part of the input light detector 109 signal light is detected, and the control circuit 110 is controlled based on these signals.

With such a configuration, for example, when the reflected light 202 detects that the Raman excitation light at the output end 124 has reached a predetermined value or more, the Raman excitation light is reduced or blocked. Similarly, in the case of signal light, it is possible to detect a part of the signal light of the input light detector 109 and perform operations such as maintaining, reducing or blocking excitation light. However, in this example, detection and control can be performed more accurately by using Raman excitation light for connector release detection.

  That is, in this example, the signal light 200 incident from the input optical connector 124 is sufficiently attenuated by the multiplexer 122 before reaching the excitation light reflected light detector 171, thereby eliminating the influence of the signal light. Release detection can be performed only by the reflected light 202 of the Raman excitation light.

  As will be described later, the application of the signal light removal filter is particularly effective when the intensity of the excitation light is weak, such as when lighting is performed while increasing the Raman excitation light stepwise.

  In the reverse excitation type Raman amplifier, when the Raman excitation light is used for input release detection, the reflection loss can be accurately measured at the excitation light wavelength as compared with the case where the incident signal light is used. In the case of connection, release detection can be reliably performed. further. Since the excitation light intensity is as high as 100 to 10,000 times the signal light, there is an advantage that it is not easily affected by noise light or disturbance light. Further, there is a case where an input signal sufficient for input detection cannot be secured unless the excitation light is turned on and signal amplification is performed. In this case, input detection using signal light cannot be applied. Further, when signal light is used, there is a problem that it becomes impossible to distinguish between signal interruption due to failure and input release detection.

  Normally, the intensity of excitation light used for Raman amplification is as extremely high as several hundred mW, so that even for the purpose of detecting reflected light as described above, damage to equipment that has been misconnected or the operator at the time when the excitation light is turned on. May cause problems. In this example, a Raman pumping light removal filter 142 and an input light detector 109 are additionally provided to measure the optical signal intensity. First, after checking the range of the input signal, the pumping light is turned on, so that at least the input connector It avoids problems such as misconnections and radiation of strong excitation light to the outside. As described above, the input signal detection and the double detection of the reflection of the Raman excitation light enable highly reliable input release detection.

  If the output light from the output connector 125 is dangerously strong, a reflected light detector may also be provided here. In the present embodiment, the excitation light output light detector 170 is also provided separately. For example, a monitor photodiode incorporated in the excitation light source 121, a relationship curve between the drive current and the excitation light output, or the like. Can be substituted.

  FIG. 10 is a block diagram showing a seventh embodiment of the present invention. This example shows a configuration of a translational pump type optical fiber Raman amplifier 136 that uses Raman pumping light itself for output release detection. FIG. 10 shows only the circuit portion of the optical fiber Raman amplifier. Although the optical fiber transmission line is connected to the output optical connector 135, the illustration is omitted.

  The translational excitation type Raman amplifier is a type of Raman amplifier that advances Raman excitation light in the same direction as the traveling direction of signal light. Therefore, in the translational excitation type, it is necessary to detect the reflected light from the output connector 135 side.

  In this example, an optical splitter 102-3 is provided between the multiplexer 132 that combines the pump light and the amplified signal light and the Raman pump light source 131 to extract a part of the reflection component of the pump light, The reflected light intensity is measured by the excitation light reflected light detector 171. Thus, in this example, the signal light part 211, the excitation light reflected light part 212, and the excitation light part 213 are detected, and the control circuit 110 is controlled based on these signals. Reference numeral 109 is an input light detector, 171 is an excitation light reflected light detector, and 170 is an excitation light output detector. The signal light 200 is output as the output light 214 of the translational excitation type Raman amplifier 136 and transmitted to the optical waveguide. On the other hand, the Raman excitation light 215 is transmitted to the optical waveguide as output light 216 from the output end 135 of the translational excitation type Raman amplifier 136. The signal light 214 is amplified in the optical waveguide by the stimulated Raman effect by the Raman light 216.

  By the way, in this example, it has an optical branching device, a multiplexer, and a signal light removal filter. That is, the reflected light of the excitation light from the output connector 135 passes through the optical branching unit 102-2, the multiplexer 132, and the optical branching unit 102-3, and is used as a part 212 of the reflected light of the excitation light as the excitation light. The reflection detector 171 is reached. The wavelength component of the signal light 200 is set so as to be sufficiently attenuated by the multiplexer 132, and the influence of the signal light component on release detection using the excitation light component can be prevented.

  As described above, the advantage of using the excitation light component itself is that more reliable release detection can be performed compared to the case of using signal light wavelengths having different wavelengths, and the light intensity is several times to several tens of times stronger than the signal light. By using the excitation light, it is difficult to be mixed with noise light or other disturbance light.

  Further, in the present embodiment, an example is shown in which the pumping light output light detector 170 measures the intensity of the pumping light component 213 extracted separately from the optical splitter 102-2 and extracted by the signal light removal filter 172.

  The position of the output light detector 170 is not necessarily limited to this. For example, the output light detector 170 may be disposed in an empty port of the light splitter 102-3 as in the previous embodiment.

  Unlike the case of the reverse excitation described above, in this embodiment, the release of the output connector 135 to which the excitation light is output cannot be detected by the presence or absence of the input signal light.

  For this reason, in the present invention, the pump light is gradually increased from the weak intensity while monitoring the ratio of the reflected light detector and the output detector of the excitation light. That is, the monitor of the ratio between the reflected light detector and the output detector is, for example, calculating the ratio between the reflected light intensity 151 and the output light 152 using a divider as shown in FIG.

  As a result, it is possible to detect the release of the output connector without causing danger to the output connector or the operator. Note that there is no problem even if this means is applied to the case of backward excitation. When release of the connector is detected during excitation light operation or during operation, the excitation light is cut off, or the reflected light intensity is continuously monitored while the light is maintained at low intensity in preparation for reconnecting the connector. These measures are effective.

  Also in this embodiment, the signal light intensity is measured by the input light detector 109. If the signal light is below a certain level, an abnormal condition such as an input signal disconnection, and if it exceeds a certain level, it is considered a connection error, so the excitation light is blocked or an alarm is generated, It is effective to notify the abnormal state to such as.

  In the following example, a multiplexer is used, and this characteristic is given the role of an excitation light removal filter. FIG. 11 shows an eighth embodiment of the present invention. This example is a configuration of an optical amplifier 180 in which a multiplexer for multiplexing Raman pumping light is built in front of the input / output terminals of the optical amplifier. This example is an example having a backward pumping Raman amplifier. A reverse pumping Raman amplifier introduces Raman pumping light in a direction opposite to the traveling direction of signal light in an optical transmission line, and amplifies the light by the stimulated Raman effect in this region.

  In the example of FIG. 11, the input light 200 is amplified by the optical amplification medium 103. An excitation light source 111 is disposed on the optical amplification medium 103. The light source 111 is controlled by the control circuit 110. Further, in this example, Raman pumping lights 221 and 223 are introduced from the input / output ends 101 and 105 of the optical amplifier 180 into optical transmission paths such as optical fibers connected thereto. Thus, in the optical system of this example, light is further amplified by the stimulated Raman effect even in the optical transmission line.

  The Raman pumping light 220 for backward pumping is input (220) from the Raman pumping light input 181 and is combined with the signal light path by the multiplexer 132, and then connected to the input connector 101 side. It is output (221) to the transmission line. The Raman pumping light for translation pumping is input (222) from the Raman pumping light input 182 and combined with the signal light by the multiplexer 122, and then output to the optical fiber transmission line connected to the output connector 105 side. (223). In this manner, by combining the Raman excitation multiplexer in the input / output end in advance, the multiplexers 132 and 122 serve as excitation light removal filters. Therefore, it is possible to prevent leakage of Raman excitation light to the input photodetector 109, the reflection detector 108, the optical amplification medium 103, etc., regardless of whether or not Raman excitation is performed in this optical repeater. Also in this configuration, an excitation light removal filter 141 can be provided as necessary for a part that affects the operation even when a slight amount of excitation light leaks, such as the input photodetector 109. In addition, such a configuration with a built-in multiplexer in advance may be applied to a preamplifier, a postamplifier, or the like, or it may have only a built-in multiplexer for either backward or translational Raman pumping light. Absent.

  Next, an example of a wavelength multiplex excitation light source is shown. Such a light source can be configured separately from the optical amplifier and used as the excitation light source of the optical amplifier described so far. FIG. 12 shows the configuration of the excitation light source device 183 according to the ninth embodiment of the present invention in such an example. This light source is used by being connected to the excitation light source inputs 181 and 182 of FIG. 11, for example.

  This example shows a configuration of wavelength multiplexing excitation. The Raman pumping light sources 121-1 and 121-2 having different wavelengths are combined. The output lights 300 and 301 are combined by a Raman pumping light combiner 184, and then passed through an optical branching unit 104 to be Raman. An excitation light output 185 is connected. A part 302 of the Raman pumping light is guided to the pumping light output light detector 170, and a part 303 of the reflected light returning from the Raman pumping light output 185 is guided to the pumping light reflected light detector 171. Here, these lights 302 and 303 are wavelength-multiplexed lights. The control circuit 110 monitors the ratio of the output signals of both photodetectors and has a function of blocking the excitation light when the intensity of the reflected light exceeds a certain value. Further, when the excitation light is started up, the excitation light is turned on step by step while monitoring the reflected light intensity.

  When this apparatus is connected to the excitation light input 181 of the optical amplifier of FIG. 11, not only the excitation light output 185 but also the reflected light of the excitation light generated at points such as the excitation light input 181 and the input connector 101 can be detected without problems. . Furthermore, when it is desired to avoid leakage of signals in other wavelength bands, an optical filter that removes light of these wavelengths may be incorporated.

  In this way, by incorporating a reflected light detector with the excitation light source as a separate device, it is possible to add an expensive Raman excitation light source only when necessary, and it can also be replaced during operation of the device. There are advantages. In multi-relay transmission using a plurality of optical repeaters, a failure of one Raman amplifier does not necessarily cause fatal SN degradation of all optical signals. There are advantages. In addition, since reflection detection can always be performed between the excitation light and signal light combined portion and the excitation light source, there is an advantage that the configuration can be simplified by removing an extra optical filter. Furthermore, since the control part of the excitation light source and the control part of the signal light can be completely separated, it is possible to simplify the signal transfer and control algorithm between the apparatuses.

  In addition, the input / output part and the connector part of the optical signal and the pumping light are not limited to the present embodiment, and each of the optical fiber connectors is collimated in a means such as a configuration for splicing fiber strands or in space. There may be a portion that couples the optical signal with the lens system. In any case, if there is an abnormal reflection or loss at these points, the reflection detection means of the present invention operates without any problem.

  In addition to the present embodiment, the number of Raman excitation light sources and the intensity ratio may be arbitrarily set as necessary. In general, the number and intensity of the light sources affect the Raman gain and the wavelength dependence of the gain. Therefore, by setting these appropriately, the gain can be flattened or automatic gain equalization can be performed. The reflection / output intensity detection of the excitation light may be performed by measuring the sum of a plurality of excitation lights as in this example, or may be performed for a specific excitation light source. The latter can be easily realized by changing the position of the optical splitter 104 between the specific light source and the multiplexer 184.

  FIG. 13 shows a tenth embodiment of the present invention. In this example, sinusoidal intensity modulation is applied to the Raman pumping light of the backward pumping type optical fiber Raman amplifier 126 at the frequency f.

  This optical fiber Raman amplifier 126 has a pumping light source 121, and the pumping light 310 is emitted (312) from the input connector 124. A part 313 of the excitation light 310 is detected by the excitation light output detector 170 and a part 314 of the reflected light from the excitation light input connector 124 is detected by the excitation light reflected light detector 171 and controlled based on each signal. The circuit 110 is controlled as desired. In the figure, reference numeral 104 denotes an optical splitter, and 122 denotes a multiplexer.

  In this example, a signal from the sine wave generator 190 is added to the drive current of the excitation light source 121, and sine wave AM modulation is superimposed on the output excitation light. The frequency f of the sine wave is smaller than the effective length of the nonlinear effect of the optical fiber transmission line (Leff = 1 / a, where a is the loss factor of the optical fiber transmission line in the pumping light source). For example, it is set to several MHz or the like. That is, the relationship f> ac (where c is the speed of light) is established. Since the signal light and the pumping light travel in opposite directions, if the frequency f is sufficiently larger than the above value even if the pumping light is modulated, the Raman gain felt by the signal light is spatially averaged, and the signal There is no degradation in the light. In the case of excitation light that translates with signal light, if such modulation is performed, intensity modulation occurs in the signal light and transmission characteristics deteriorate, so the modulation component is extremely small (for example, 10% or less). There is a need.

  In this way, if the Raman pumping light is modulated, the intensity and reflectance of the pumping light can be accurately known even if there is disturbance light by extracting the modulation component from the output signal of the photodetector. .

  In this example, the signal light and the excitation light are received by the excitation light output light detector 170 and the excitation light reflected light detector 171, respectively. At this time, the detection signal is converted into an electric signal, and only the modulation component of the frequency f is extracted in the region of the electric signal by using the bandpass filters 191-1 and 191-2 having the center frequency f. For this reason, even when the signal light or the pumping light component from the upstream is mixed, it is possible to extract only the backward pumping light component without providing an optical filter. In addition, although the component reflected by Fresnel at the open end in the middle of the fiber retains the modulation component, the modulation component is spatially averaged and becomes extremely small when it is distributed in a distributed manner such as Rayleigh scattering. . Therefore, the detection threshold can be lowered as compared with the conventional case, and the open end (Fresnel reflection) can be detected with high accuracy.

  The modulation signal does not need to be a sine wave as long as the minimum frequency component satisfies the above conditions. For example, the modulation signal may be modulated with an information signal. It can be used to transfer monitoring information and alarms to the optical transmitter. In this case, since it is not necessary to provide a transmitter / receiver dedicated to monitoring information, the apparatus configuration can be simplified.

  FIG. 14 shows an eleventh embodiment of the present invention. This example is an example in which the upstream optical amplifier of the optical fiber transmission line detects the lighting state of the pump light of the downstream Raman amplifier by receiving the modulation component of the downstream pump light.

  In detecting output open using the reflection intensity of signal light, if the distance from the output end to the release point is several kilometers or more and a loss of several dB occurs between the two points, the reflected light level becomes too small. There was a problem that it was impossible to detect the output release. However, in wavelength division multiplex transmission and high power transmission, the intensity of signal light and excitation light is sufficiently strong even at several kilometers away, and it may be at a level that requires open detection. In this embodiment, in order to perform more reliable output open detection, the optical amplifier on the downstream side of the optical fiber transmission line indicates the presence or absence of signal light from the upstream, and the optical amplifier on the upstream side performs Raman excitation from the downstream side. Detect light.

  In this example, the upstream optical fiber Raman amplifier 136, the optical fiber transmission line 106, and the downstream optical fiber Raman amplifier 126 are connected in cascade. The upstream optical fiber Raman amplifier 136 has a pumping light source 131, and the pumping light 310 is emitted from the output connector 181. A part of the pumping light 310 is detected by the pumping light output detector 170, and a part of the reflected light 313 from the pumping light output connector 181 is detected by the pumping light reflected light detector 171, and the control circuit is based on these signals. 110-1 is controlled as desired. In this example, signal light removal filters 172-1 and 172-2 and a bandpass filter 191 are provided. The downstream optical fiber Raman amplifier 126 has a pumping light source 121, and the pumping light 330 is emitted from the input connector 182. The signal light 340 is output (341) from the output end 183. A part of the signal light 342 is detected by the input light detector 109, and the control circuit 110-2 is controlled based on this signal. In this example, light from the excitation light source 121 is modulated at a frequency f by a sine wave generator 190. In addition, a Raman light removal filter 141 is provided in front of the input light detector 109.

  In this example, considering the characteristics of the Raman amplifier, for example, the following startup procedure is taken. First, the Raman pumping light is blocked on both the upstream side and the downstream side, and on the downstream side of the optical fiber Raman amplifier 126, the input signal light that has passed through the pumping light removal filter 141 is detected by the input photodetector 109, and the optical signal is detected. If the level is above a certain level, it can be confirmed that all the upstream connectors are not opened. The control circuit 110-2 turns on the excitation light 121 and sends out the modulated excitation light toward the upstream side. Further, when the input signal light drops below a certain level during operation, the Raman excitation light is blocked.

  Next, in the optical fiber Raman amplifier 136 on the upstream side, the intensity of pumping light input from the optical fiber transmission line 106 side by the branching unit 104-1, the signal light removal filter 172-2, and the pumping light reflected light detector 171. Is observed. In particular, since the component modulated at the frequency f by the band pass filter 191 is extracted, the intensity of the excitation light from the downstream side can be determined from the intensity. If this level is above a certain level, it can be confirmed that all the downstream connectors are not open. In response to this, the control circuit 110-1 turns on the excitation light 131. Further, when the modulation component falls below a certain level during operation, the Raman excitation light is blocked. With the above procedure, the startup operation of the excitation light with extremely high reliability can be performed. FIG. 16 shows an example of the rising state of the excitation light.

  Depending on the loss of the optical fiber transmission line and the level of the transmission signal, the signal level is too low unless either the upstream, downstream, or both optical fiber Raman amplifiers are started up. May not be possible. In such a case, first, a technique is effective in which one or both of the Raman excitation lights are raised at a safe weak intensity and the reflection is detected.

  In this example, in order to avoid signal light deterioration due to Raman pumping light modulation, an example is shown in which only downstream Raman pumping light is modulated. If a certain degree of signal light degradation can be tolerated, the upstream Raman pumping light can also be modulated. In this case, if encoding is performed with a modulation frequency or code different from that on the downstream side, it is possible to distinguish between upstream and downstream excitation light. This upstream modulation component can be applied to detection of connector open as in the downstream modulation.

  FIG. 15 shows a twelfth embodiment of the present invention. This example shows a configuration in the case where an optical amplifier 140 other than a Raman amplifier is arranged on the upstream side of the optical transmission line with respect to the previous embodiment. The optical amplifier 140 has an optical amplification medium (for example, EDF) 103, and the EDF 103 is excited by the excitation light source 111. The signal light 400 is amplified by the optical amplifying medium 103 and emitted (401) from the output optical connector 105 to the optical transmission line 106. In this example, the input signal 400 is branched by the optical splitter 102, and a part thereof is detected by the input photodetector 109. Further, a part 403 of the amplified signal light is detected by the output light detector 107, and a part 402 of the amplified reflected light 404 reflected by the optical splitter 104 is detected by the reflected light detector 108. The On the other hand, a part 405 of the Raman excitation light from the Raman excitation light source existing on the downstream side is incident on the optical amplifier 140. Then, a part 405 thereof is detected by the excitation light input photodetector 193 via the multiplexer 192. Thus, the control circuit 110 controls the excitation light based on the detection results of the detectors 109, 108, 107, and 193.

  In this example, a multiplexer 192 that combines the Raman pumping wavelength and the signal light wavelength is disposed at the output portion of the optical amplifier 140 using EDF, and a pumping light input photodetector 193 is disposed immediately thereafter. Thus, the intensity of the excitation light transmitted from the downstream side can be detected. In this example, it is assumed that the multiplexer 192 is set to a characteristic that serves as an excitation light removal filter, and an excitation light removal filter is provided in front of the output light / reflected light detectors 108 and 107 of the signal light. Not placed.

  When the signal level output from the optical amplifier 140 is dangerously high as it is, at the time of start-up, the pumping light source 111 is first weakly pumped and the signal light is transmitted at a low output. If the optical fiber Raman amplifier (this amplifier is not shown) on the downstream side of the optical fiber transmission line 106 detects this signal, it transmits Raman pumping light from the downstream side. The pumping light input detector 193 detects the Raman pumping light from the downstream side, and if this is above the specified level, the light intensity ratio between the reflected light detector 108 and the output light detector 107 is below a certain level. In this case, the control circuit 110 increases the excitation light source 111 to a normal specified output. Thus, it is possible to perform open detection with higher certainty by confirming both the reflection from the upstream side and the presence or absence of excitation light from the downstream side.

  According to the present invention, even when an optical amplifier is used in combination with an optical fiber Raman amplifier, the detection of the input signal and the output release detection mechanism can be normally operated. Also, the above function can be added to the optical fiber Raman amplifier. Further, the safety can be further improved by the method of starting and shutting down the optical amplifier in consideration of the peculiarity of the Raman amplifier.

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 is a configuration diagram of a conventional optical amplifying device. FIG. 3 is a configuration diagram of a conventional optical amplifying device. FIG. 4 is a block diagram showing a second embodiment of the present invention. FIG. 5 is a diagram showing a third embodiment of the present invention. FIG. 6 is a configuration diagram illustrating an implementation example of the control circuit. FIG. 7 is a block diagram showing a fourth embodiment of the present invention. FIG. 8 is a block diagram showing a fifth embodiment of the present invention. FIG. 9 is a block diagram showing a sixth embodiment of the present invention. FIG. 10 is a block diagram showing a seventh embodiment of the present invention. FIG. 11 is a block diagram showing an eighth embodiment of the present invention. FIG. 12 is a block diagram showing a ninth embodiment of the present invention. FIG. 13 is a block diagram showing a tenth embodiment of the present invention. FIG. 14 is a block diagram showing an eleventh embodiment of the present invention. FIG. 15 is a block diagram showing a twelfth embodiment of the present invention. FIG. 16 is a time chart showing an example of excitation light startup.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Conventional optical amplifier, 101 ... Input optical connector, 102 ... Optical branching device, 103 ... Optical amplification medium, 104 ... Optical branching device, 105 ... Output optical connector, 106 ... Optical fiber transmission line, 107 ... Output light detector, 108 ... Reflected light detector, 109 ... Input light detector, 110 ... Control circuit, 111 ... Excitation light source, 112 ... Output light, 113 ... Reflected light, 120 ... Optical fiber Raman amplifier (reverse pump), 121 ... Raman pump light source, 122 ... Multiplexer, 123 ... Raman pump light , 124, input optical connectors, 125, output optical connectors, 126, optical fiber Raman amplifier of the present invention (reverse pump), 130, optical fiber Raman amplifier (translational pump), 131,. .Raman excitation light source, 132 .. Multiplexer, 133 ... Raman pumping light, 134 ... Input optical connector, 135 ... Output optical connector, 136 ... Optical fiber Raman amplifier of the present invention (translational pumping), 140 ... Invention of the present application 141 ... Raman excitation light removal filter, 142 ... Raman excitation light removal filter, 143 ... multiplexer, 150 ... input light intensity signal, 151 ... reflected light intensity signal , 152 ... Output light intensity signal, 153 ... Reference voltage source, 154 ... Comparator, 155 ... Divider, 156 ... AND circuit, 157 ... Excitation light source current source, 158 ... Excitation light source drive current, 159 ... switch, 160 ... Raman excitation light on / off signal, 161 ... other control signals, 170 ... excitation light output photodetector, 171 ... excitation light Reflected light detector 172... Signal light removal filter, 180... Optical repeater of the present invention, 181... Raman pumping light input, 182... Raman pumping light input, 183. ... Raman excitation light multiplexer, 185 ... Raman excitation light output 190 ... Sine wave generator (frequency f), 191 ... Bandpass filter (center frequency f), 192 ... Multiplexer 193 ... excitation light input photodetector.

Claims (10)

  An optical amplifier disposed upstream of the optical fiber transmission line in the optical signal transmission direction, the pumping light intensity of a Raman amplifier disposed downstream of the optical fiber transmission line is measured, and this light intensity is set in advance. If it is within the light intensity range, the optical signal output or the pumping light of this optical amplifier is turned on, increased or kept constant, and if the light intensity deviates from the above range, the optical signal output or this light is output. An optical amplifier characterized by reducing or blocking the pumping light of the amplifier.   2. The optical amplifier according to claim 1, wherein the pump light source is intensity-modulated at a frequency ac (where a is a loss factor of an optical fiber transmission line in the pump light source, and c is the speed of light).   3. The optical amplifier according to claim 2, wherein the optical amplifier amplifies an optical signal by sending pumping light toward a downstream side of the optical fiber transmission line, and detects the modulation component, An optical amplifier characterized in that the release state of the output of the excitation light can be detected.   3. The optical amplifier according to claim 2, wherein the optical amplifier amplifies an optical signal by sending pumping light toward a downstream side of the optical fiber transmission line, and detects the modulation component, An optical amplifier characterized in that input release detection can be performed by a light detection means arranged on the downstream side of the optical fiber transmission line.   An optical transmission device comprising the optical amplifier according to claim 1. An optical amplifier arranged downstream of the optical fiber transmission line, the pumping light intensity of a Raman amplifier arranged upstream of the optical fiber transmission line is measured, and the light intensity falls within a preset light intensity range. In this case, the optical amplifier is characterized in that the Raman pumping light is turned on, increased, or kept constant, and the optical signal output is reduced or blocked when the light intensity deviates from the above range. .   7. The optical amplifier according to claim 6, wherein the intensity of the pump light source is modulated at a frequency ac (where a is a loss factor of an optical fiber transmission line in the pump light source and c is the speed of light).   8. The optical amplifier according to claim 7, wherein the modulation component is used for input release detection of the optical amplifier or an optical transmission device arranged on the upstream side.   8. The optical amplifier according to claim 7, wherein the modulated component transmits information to an upstream optical transmission device. An optical transmission device comprising the optical amplifier according to claim 6.

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