JP2014038917A - Optical branching device and optical branching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical branching device which can adjust intensity of signal light extracted from an optical transmission line.SOLUTION: An optical branching device comprises: an optical transmission line 10 for transmitting signal light; an extraction section 15 disposed in the vicinity of the optical transmission line 10 to extract evanescent light which is signal light leaked from the optical transmission line 10; an intensity detection section 19 for detecting intensity of the evanescent light extracted by the extraction section 15; and a control section 19 for adjusting the position of the extraction section 15 on the basis of the intensity detected.

Description

  The present invention relates to an optical branching device and an optical branching method.

  When light is incident on a medium having a low refractive index from a medium having a high refractive index, the light is totally reflected when the incident angle is greater than a certain angle. An optical transmission line such as an optical fiber uses such a phenomenon to confine and transmit signal light inside a transmission medium having a higher refractive index than the surroundings. As a method for taking out the signal light confined inside the transmission medium from the optical transmission line, there is a method of branching the signal light using a branching member such as an optical coupler.

  FIG. 3 is an explanatory diagram for explaining the configuration of a branching device that branches signal light using an optical coupler. A branching device 900 shown in FIG. 3 is an optical amplifying device that uses signal light extracted from the optical transmission path to adjust the amplification factor of the signal light.

  The optical branching device 900 includes an optical module unit 910 mainly composed of optical components and a control circuit unit 920 mainly composed of electrical components.

  The optical module unit 910 includes an optical fiber 90 that transmits signal light, an optical connector 91 that is an input interface to which the signal light is input, an optical amplification unit 92 that amplifies the signal light input to the optical connector 91, and an amplification. An optical connector 93 which is an output interface for outputting the signal light, an optical coupler 94 which is connected to the output side of the optical amplifying unit 92 and branches the signal light transmitted through the optical fiber 90, and the branched signal light. And a photodiode 95 that photoelectrically converts the wavelength signal light output from the prism 95 and outputs an electrical signal. The control circuit unit 920 includes a control unit 99 that adjusts the amplification factor of the optical amplification unit 92 based on the electrical signal output from the photodiode 98.

  In this way, signal light can be extracted from the optical transmission line by connecting a branching member such as an optical coupler in the middle of the optical transmission line.

  However, when a branch member is inserted, there is a problem in that a connection loss in which light is lost occurs at a position where the branch member and the optical transmission path are connected, and the intensity of the signal light transmitted through the optical transmission path is significantly reduced. is there. In addition, there is a problem that the signal light cannot be taken out except at a place where the branch member and the optical transmission line are connected, and the flexibility is lacking.

  On the other hand, Patent Document 1 describes a branching method that branches signal light by taking out evanescent light that is signal light leaked from an optical transmission line. When the signal light is totally reflected at the boundary surface between the medium having a high refractive index and the medium having a low refractive index, the vertical component of the wave number with respect to the boundary surface is an imaginary number. Leaks about one wavelength to the medium side having a low refractive index. This leaked signal light is called evanescent light. Since evanescent light leaks from the total reflection point where the signal light is totally reflected to the medium side having a low refractive index and then attenuates without propagating in the direction perpendicular to the boundary between the media, It is localized in a minute area near the reflection point. For this reason, the intensity of the evanescent light is high near the total reflection point on the surface of the optical transmission path, but the intensity of the evanescent light is low except near the total reflection point.

  In the branching method described in Patent Document 1, the optical member is brought into close contact with the optical transmission path to propagate evanescent light localized at each point of the optical transmission path in close contact with the optical member to the optical member. It is taken out with. When the signal light is branched by taking out the evanescent light in this way, it is not necessary to connect the branching member to the optical transmission line, so that the signal light can be taken out from the optical transmission line without causing connection loss.

Japanese Patent Laid-Open No. 3-62021

  However, in the branching method described in Patent Document 1, the evanescent light at each point of the optical transmission line that is in close contact with the optical member is evenly extracted. Therefore, the evanescent light is also emitted from points other than the total reflection point at which the evanescent light is strongest Will be taken out. Therefore, there is a problem that the evanescent light cannot be extracted efficiently.

  An object of the present invention is to provide an optical branching device and an optical branching method capable of efficiently extracting signal light from an optical transmission line.

  An optical branching device according to the present invention includes an optical transmission line that transmits signal light, an extraction unit that is disposed in the vicinity of the optical transmission line and extracts evanescent light that is signal light leaked from the optical transmission line, and the extraction unit And an intensity detection unit that detects the intensity of the evanescent light extracted in step (b), and a control unit that adjusts the position of the extraction unit based on the detected intensity.

  In the optical branching method according to the present invention, an extraction unit is disposed in the vicinity of an optical transmission line that transmits signal light, and evanescent light that is signal light leaked from the optical transmission line is extracted by the extraction unit, and the extracted evanescent light is extracted. The intensity of light is detected, and the position of the extraction portion is adjusted based on the detected intensity.

  According to the present invention, signal light can be efficiently extracted from an optical transmission line.

It is explanatory drawing for demonstrating the structure of the optical amplifier concerning one Embodiment of this invention. It is explanatory drawing for demonstrating the structure by which the optical amplifier concerning one Embodiment of this invention branches signal light from an optical transmission line. It is explanatory drawing for demonstrating the structure of the branch apparatus which branches a signal beam | light using an optical coupler.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in this specification and drawing, the description which overlaps by the same code | symbol may be attached | subjected about the component which has the same function.

  First, an optical amplifying apparatus that is an example of an optical branching apparatus according to an embodiment of the present invention will be described. FIG. 1 is an explanatory diagram for explaining a configuration of an optical amplifying device according to an embodiment of the present invention.

  The optical amplifying apparatus 100 shown in FIG. 1 amplifies the input signal light as light and outputs the amplified signal light. The optical amplification device 100 may be a single device or may be provided in another device (for example, a relay node used in a ROADM (Reconfigurable Optical Add / Drop Multiplexer) system).

  The optical amplification device 100 includes an optical module unit 110 mainly composed of optical components and a control circuit unit 120 mainly composed of electrical components.

  The optical module unit 110 includes an optical fiber 10, an optical connector 11 that is an input interface to which signal light is input, an optical amplification unit 12, an optical connector 13 that is an output interface that outputs signal light, a prism 15, The motor 16, the waveguide 17, and the photodiode 18 are included. The control circuit unit 120 includes a control unit 19 that adjusts the amplification factor of the optical amplification unit 12 and adjusts the position of the prism 15.

  The optical fiber 10 is an example of an optical transmission path that transmits signal light, and connects the optical connector 11 and the optical amplifying unit 12, and connects the optical amplifying unit 12 and the optical connector 13. The signal light transmitted by the optical fiber 10 is assumed to be wavelength multiplexed signal light obtained by multiplexing a plurality of wavelength signal lights having different wavelengths. The signal light includes reference light that is wavelength signal light serving as a reference for controlling the optical output level of the optical amplifying apparatus 100 to be constant. The reference light has a modulation frequency that is considerably smaller than the modulation frequency of the other wavelength signal light.

  The optical fiber 10 transmits the signal light input to the optical connector 11 and inputs it to the optical amplifying unit 12, transmits the signal light output from the optical amplifying unit 12, and outputs it from the optical connector 13.

  The optical amplifying unit 12 amplifies the input signal light as light and outputs it. In the present embodiment, it is assumed that the optical amplifying unit 12 is an optical fiber amplifier that uses an optical fiber to which impurities are added. There are various types of impurities to be added. Here, it is assumed that the optical amplifying unit 12 is an erbium-doped fiber (EDF) to which trivalent erbium ions are added as impurities. The EDF can amplify signal light having a wavelength (1.55 μm band and 1.59 μm band) normally used in an optical communication system. When excitation light having a wavelength of 0.98 μm or 1.48 μm is input to the EDF, erbium ions in the EDF absorb this excitation light and enter an excited state. At this time, when signal light in the 1.55 μm band or 1.59 μm band is input to the EDF, the excited erbium ions become the ground state and stimulated emission occurs, and the input signal light is amplified.

  Here, an optical fiber amplifier will be described as an example, but the optical amplifying unit 12 may be of any type as long as it is an optical amplifier that amplifies signal light as it is. The optical amplifying unit 12 is also an example of an optical transmission path that transmits signal light. Hereinafter, when simply referred to as an optical transmission line, both the optical fiber 10 and the optical amplifying unit 12 are included.

  The prism 15 is an example of an extraction unit that extracts evanescent light that is signal light leaked from the optical transmission path. The prism 15 is a demultiplexing element that demultiplexes the extracted evanescent light into a plurality of wavelength signal lights and outputs each wavelength signal light. The prism 15 is disposed in the vicinity of the optical fiber 10 connected to the output side of the optical amplification unit 12. Here, the state in which the prism 15 is disposed in the vicinity of the optical fiber 10 means that the prism 15 and the optical fiber 10 are not in contact with each other, and the prism 15 is disposed in a range where the evanescent light on the surface of the optical fiber 10 exists. State. The range in which the evanescent light exists is usually a distance of several tens to several hundreds of nanometers from the surface of the optical fiber 10.

  The motor 16 is a prime mover that moves the prism 15 along the longitudinal direction of the optical transmission path. The motor 16 moves the prism 15 along the longitudinal direction of the optical transmission path while keeping the distance between the prism 15 and the optical transmission path constant. The motor 16 is driven in accordance with a switch signal for driving the motor 16. For example, the motor 16 is driven while the switch signal is input, and the motor 16 stops driving when the switch signal is not input.

  The waveguide 17 transmits the wavelength signal light output from the prism 15 and inputs it to the photodiode 18. In FIG. 1, only one waveguide 17 is shown for simplicity, but in reality, the waveguide 17 is provided for each of the wavelength signal lights output from the prism 15. The waveguide 17 is, for example, an optical fiber.

  The photodiode 18 is an example of an intensity detection unit that detects the intensity of the evanescent light extracted by the prism 15 by detecting the intensity of the wavelength signal light input from the waveguide 17. Specifically, the photodiode 18 detects the intensity of the input wavelength signal light and generates an electrical signal corresponding to the intensity. The photodiode 18 inputs the generated electrical signal to the control unit 19. A photodiode 18 is provided for each waveguide 17 and each photodiode 18 is connected to one of the waveguides 17 in a one-to-one correspondence.

  The control unit 19 is an analog / digital mixed circuit using a CPU (Central Processing Unit) and an A / D (Analog / Digital) converter.

  The control unit 19 adjusts the amplification factor of the optical amplification unit 12 based on the intensity of the wavelength signal light detected by the photodiode 18. Specifically, the control unit 19 adjusts the amplification factor based on the intensity of the reference light among the wavelength signal light. For example, the control unit 19 adjusts the amplification factor of the optical amplification unit 12 so that the intensity of the reference light becomes constant.

  Since the reference light has a modulation frequency that is considerably smaller than the modulation frequency of the other wavelength signal light, it is less susceptible to noise. For this reason, if the amplification factor is adjusted using the reference light, the amplification factor can be adjusted appropriately compared to the case where the amplification factor is adjusted using wavelength signal light other than the reference light.

  Further, the control unit 19 drives the motor 16 to adjust the position of the prism 15. For example, the control unit 19 adjusts the position of the prism 15 by inputting a switch signal for driving the motor 16 to the motor 16. At this time, the control unit 19 adjusts the position of the prism 15 based on the intensity detected by the photodiode 18. For example, the control unit 19 adjusts the position of the prism 15 so that the intensity detected by the photodiode 18 becomes higher. More specifically, the control unit 19 adjusts the position of the prism 15 so that the intensity detected by the photodiode 18 becomes a predetermined threshold value or more.

  As triggers for the controller 19 to adjust the position of the prism 15, for example, the following may be considered. For example, when the user performs an input operation for adjusting the position of the prism 15, the control unit 19 adjusts the position of the prism 15 according to the input operation. Further, the control unit 19 may periodically adjust the position of the prism 15. The control unit 19 can also monitor the intensity of the detected evanescent light and adjust the position of the prism 15 when the intensity of the evanescent light falls below a predetermined threshold.

  The configuration of the optical amplifying device 100 according to the present embodiment has been described above. The configuration described here is an example, and various modifications can be made.

  For example, in the above embodiment, the optical amplifying unit 12 has one optical amplifier, but the present invention is not limited to such an example. For example, the optical amplifying unit 12 may include optical amplifiers connected in a plurality of stages. Further, the optical amplifying unit 12 may be configured to include an optical device for maintaining the signal quality of signal light such as an optical signal gain equalizer and an optical dispersion compensator.

  In the above embodiment, the prism 15 is shown as an example of the extraction unit that extracts the evanescent light. However, the extraction unit may be an optical member such as a diffraction grating.

  In the above embodiment, the prism 15 is disposed in the vicinity of the optical fiber 10 on the output side of the optical amplifying unit 12, but the initial position and the adjusted position of the prism 15 are on the input side of the optical amplifying unit 12. The optical fiber 10, an amplification fiber that is an amplification medium included in the optical amplification unit 12, and an optical transmission line including the optical fiber 10 on the output side of the optical amplification unit 12 may be used.

  Moreover, in the said embodiment, although the motor 16 was shown as an example of the motor | power_engine for changing the position of the extraction part which takes out evanescent light, the structure for changing the position of an extraction part is not restricted to said example. The above embodiment is also an example of a method for controlling the motor 16, and any control method may be used as long as the evanescent light can be extracted with high intensity.

  In the above embodiment, a photodiode is shown as an example of the intensity detection unit. However, any element may be used as long as it can detect the intensity of signal light.

  Next, the operation of the optical amplification device 100 will be described. FIG. 2 is an explanatory diagram for explaining a configuration in which the optical amplifying apparatus according to the present embodiment branches signal light from the optical transmission line. This will be described below with reference to FIGS.

  The optical transmission line 50 shown in FIG. 2 is an optical fiber 10 or an amplification fiber of the optical amplification unit 12. Although only the transmission medium portion of the optical transmission line 50 is shown here, the optical transmission line 50 may actually be covered with a clad. The clad may be further covered with a coating. The transmission medium portion of the optical transmission line 50 is composed of a medium having a higher refractive index than the outside of the transmission medium. For this reason, when the signal light is incident on the transmission medium at an angle greater than a predetermined critical angle, total reflection occurs at the point where the signal light contacts the boundary of the transmission medium, and the signal light travels through the optical transmission line while repeating total reflection. move on. A point where total reflection occurs is hereinafter referred to as a total reflection point TRP.

  Here, at the total reflection point TRP, part of the signal light leaks to the outside of the optical transmission line 50 as evanescent light EL. If the prism 15 is disposed in a region where the evanescent light EL exists, the evanescent light EL can be extracted.

  The prism 15 that has extracted the evanescent light EL demultiplexes the extracted evanescent light EL into a plurality of wavelength signal lights, and inputs the wavelength signal light to the waveguide 17.

  The waveguide 17 transmits the input wavelength signal light and inputs it to the photodiode 18. The photodiode 18 detects the intensity of the input wavelength signal light and generates an electrical signal corresponding to the intensity. The photodiode 18 inputs the generated electrical signal to the control unit 19.

  The control unit 19 adjusts the amplification factor of the optical amplification unit 12 based on the intensity of the wavelength signal light indicated by the input electrical signal. For example, the control unit 19 adjusts the amplification factor of the optical amplifying unit 12 based on an electrical signal indicating the intensity of the reference light included in the evanescent light EL so that the intensity of the reference light becomes constant.

  Further, the control unit 19 adjusts the position of the prism 15 based on the intensity of the wavelength signal light indicated by the input electric signal. The control unit 19 adjusts the position of the prism 15 so that the detected intensity becomes high. Specifically, the control unit 19 generates a switch signal and inputs it to the motor 16 when the detected intensity falls below a predetermined threshold. The motor 16 starts driving according to the input switch signal. When the motor 16 is driven, the prism 15 moves. While the prism 15 is moving, the control unit 19 continues to monitor the intensity of the evanescent light EL extracted by the prism 15. The control unit 19 stops the input of the switch signal to the motor 16 when the detected intensity is equal to or greater than a predetermined threshold value. When the control unit 19 adjusts the position of the prism 15 in this way, the prism 15 can extract the evanescent light EL with high intensity.

  As described above, according to the present embodiment, the extraction unit disposed in the vicinity of the optical transmission line that transmits the signal light extracts the evanescent light that is the signal light leaked from the optical transmission line. Then, the intensity of the extracted evanescent light is detected, and the position of the extraction unit is adjusted based on the detected intensity. As a result, it becomes possible to efficiently extract signal light from the optical transmission line.

  Moreover, in this embodiment, the position of the extraction part is adjusted so that the detected intensity | strength becomes high. As a result, it is possible to extract high intensity signal light from the optical transmission line.

  Moreover, in this embodiment, the position of an extraction part is adjusted by moving an extraction part to the longitudinal direction of an optical transmission path. As a result, the extraction portion can be moved to the vicinity of the total reflection point, and signal light with high intensity can be extracted from the optical transmission line more reliably.

  In this embodiment, the optical transmission line has an optical amplification unit, and the amplification factor of the optical amplification unit is adjusted based on the evanescent light. For this reason, the signal light extracted from the optical transmission line by extracting the evanescent light can be used to adjust the amplification factor of the optical amplification unit.

  Further, in the present embodiment, the signal light transmitted through the optical transmission line includes reference light having a predetermined frequency, the evanescent light extracted from the optical transmission line is demultiplexed, and among the demultiplexed evanescent light The intensity of the reference light is detected, and the amplification factor is adjusted based on the intensity of the reference light. Thus, if an appropriate frequency is used for the reference light, the reference light is not easily affected by noise, and the amplification factor can be adjusted appropriately.

  While the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  For example, in the above embodiment, as an example of an optical branching device, an optical amplifying device that uses signal light branched from an optical transmission line for adjusting an amplification factor has been described. However, the present invention is not limited to such an example. The technique of the present invention can be applied to all uses regardless of the use of the signal light branched from the optical transmission line.

  Moreover, in the said embodiment, although the optical amplification apparatus adjusted the gain based on the reference light among wavelength signal lights, this invention is not limited to this example. The technology of the present invention can also be applied to a configuration in which the optical amplification device adjusts the amplification factor based on wavelength signal light other than the reference light.

  In the above embodiment, the position of the extraction portion is adjusted by moving the extraction portion along the longitudinal direction of the optical transmission path, but the present invention is not limited to this example. The direction in which the extraction portion is moved is not limited to the longitudinal direction of the optical transmission path.

DESCRIPTION OF SYMBOLS 100 Optical amplification apparatus 110 Optical module part 10 Optical fiber 11, 13 Optical connector 12 Optical amplification part 15 Prism (extraction part)
16 Motor 17 Waveguide 18 Photodiode (Intensity detector)
50 Optical transmission line 120 Control circuit unit 19 Control unit

Claims (6)

An optical transmission line for transmitting signal light;
An extraction unit that is arranged in the vicinity of the optical transmission line and extracts evanescent light that is signal light leaked from the optical transmission line;
An intensity detection unit for detecting the intensity of the evanescent light extracted by the extraction unit;
And a control unit that adjusts the position of the extraction unit based on the detected intensity.   The optical branching device according to claim 1, wherein the control unit adjusts a position of the extraction unit so that the detected intensity becomes high.   The optical branching device according to claim 1, wherein the control unit adjusts a position of the extraction unit by moving the extraction unit along a longitudinal direction of the optical transmission path. The optical transmission line includes an optical amplification unit that amplifies the signal light,
The optical branching device according to claim 1, wherein the control unit adjusts an amplification factor of the optical amplification unit based on the intensity. The signal light includes reference light having a predetermined frequency,
The extraction section extracts and demultiplexes the evanescent light,
The optical branching device according to claim 4, wherein the intensity detection unit detects an intensity of the reference light among the demultiplexed evanescent light. An optical branching method using an optical branching device in which an extraction unit that extracts evanescent light that is signal light leaked from an optical transmission line that transmits signal light is disposed in the vicinity of the optical transmission line,
Detecting the intensity of the evanescent light extracted by the extraction unit;
An optical branching method for adjusting a position of the extraction portion based on the detected intensity.

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