JP2008209266A - Bidirectional optical module and optical pulse tester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bidirectional optical module having high light source stability without generating any ghost. <P>SOLUTION: The bidirectional optical module 100 emits light to an optical fiber, wherein returned light from the optical fiber is incident thereon. The bidirectional optical module 100 includes a plurality of light emitting elements 110, 130 for emitting light to be incident on the optical fiber, a light receiving element 190 for receiving the light emitted from the optical fiber, a multiplexing/demultiplexing element 150 for multiplexing the light emitted from the plurality all light emitting elements 110, 130 and guiding the light to the optical fiber, optical isolators 125, 145 provided between the light emitting elements 110, 130 and the multiplexing/demultiplexing element 150 and transmitting light only in a direction from the sides of the light emitting elements 110, 130 to the side of the multiplexing/demultiplexing element 150, and a combining/splitting element 160 for guiding the light emitted from the optical fiber to the light receiving element 190. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bidirectional optical module, and more particularly to a bidirectional optical module used in an optical pulse tester used for measuring a break point of an optical fiber communication network.

  Optical communication systems and measuring devices such as optical fiber sensors using light include a light source that emits light and a light receiving unit that senses the light. A measuring instrument used for maintenance and management of an optical communication system includes a light source that emits measurement light to a measured optical fiber and a light receiving unit that senses the light transmitted by the measured optical fiber.

  For example, in an optical communication system that performs data communication or the like using an optical signal, an optical pulse called, for example, OTDR (Optical Time Domain Reflectometer) is used in laying or maintaining an optical fiber in order to monitor the state of the optical fiber that transmits the optical signal. A tester is used. The OTDR repeatedly inputs pulsed light into the optical fiber to be measured, and measures the level of the reflected light and backscattered light from the optical fiber to be measured and the light reception time, thereby causing disconnection or loss of the optical fiber to be measured. Measure the state.

  The optical pulse tester includes a bidirectional optical module, a BIDI (Bi-Directional) module, etc., which are modularized as a single unit, with the transmission unit and the reception unit housed in the same case. These modules become low-priced with the recent spread of FTTH (Fiber To The Home), and are often used not only for OTDR but also for other measuring instruments and optical communication systems.

  For example, Patent Document 1 and Patent Document 2 disclose an OTDR configuration using a bidirectional optical module. As shown in FIG. 6, the OTDR includes a bidirectional optical module 10, an LD driving unit 20, a sampling unit 30, a signal processing unit 40, and a display unit 50.

  The bidirectional optical module 10 is a module that outputs pulsed light to the optical fiber 73 to be measured via the measurement connector 60 and senses return light from the optical fiber 73 to be measured. The LD driving unit 20 is a driving unit that drives a light source in the bidirectional optical module 10. The sampling unit 30 is a functional unit that converts an electrical signal (photocurrent) from a light receiving unit in the bidirectional optical module 10 into a voltage and samples it. The signal processing unit 40 is a functional unit that causes the bidirectional optical module 10 to output pulsed light via the LD driving unit 20 and also causes the sampling unit 30 to perform sampling. Further, the signal processing unit 40 performs an arithmetic process on an electrical signal obtained as a result of sampling by the sampling unit 30. The display unit 50 is a functional unit that displays the signal processing result, and for example, a display or the like can be used.

Here, as shown in FIG. 7, for example, the conventional bidirectional optical module 10 includes light emitting elements 11 and 13 that emit light, lenses 12 and 14 that convert light into parallel light, and a plurality of lights into one light. A multiplexing / demultiplexing element 15 for multiplexing, lenses 17 and 18 for condensing light, a multiplexing / branching element 16 for branching light, and a light receiving element 19 for sensing light are configured (for example, Patent Documents). 1-3). The bidirectional optical module 10 includes, for example, a light emitting element 11 that emits light having a wavelength λ _{1 and} a light emitting element 13 that emits light having a wavelength λ ₂ . Lights of wavelengths λ ₁ and λ ₂ emitted from the two light emitting elements 11 and 13 are converted into parallel lights by the lenses 12 and 14, respectively, and are multiplexed by the multiplexing / demultiplexing element 15. The light combined by the multiplexing / demultiplexing element 15 is collected by the lens 17 and enters the optical fiber 71 and then enters the measured optical fiber 73 connected to the optical fiber 71 by the measurement connector 60.

  The light incident on the optical fiber to be measured 73 is reflected at the breaking point or connection point in the optical fiber to be measured 73, and the return light traces the optical fiber to be measured 73 again and is connected by the measurement connector 60. The light enters the bidirectional optical module 10 via 71. The return light is converted into parallel light by the lens 17, and then part or all of the return light is guided to the light receiving element 19 by the coupling / branching element 16. The light reflected by the coupling / branching element 16 toward the light receiving element 19 is collected by the lens 18 and enters the light receiving element 19.

JP 2001-305017 A JP-A-4-296812 JP-A-8-166526

  In the bidirectional optical module 10 shown in FIG. 7, the light emitted from the light emitting elements 11 and 13 is passed through the optical fibers through the lenses 12, 14, and 17 so that there is no loss as much as possible for the purpose of increasing the signal level of the OTDR. 71 is incident. However, when the light emitted from the light emitting elements 11 and 13 enters the optical fiber 71 with high efficiency, there is a drawback that the return loss rate obtained by measuring the return light from the measured optical fiber 73 connected to the optical fiber 71 is deteriorated. is there. This is mainly due to multiple reflection of light generated between the break point or the connection point and the light emitting elements 11 and 13.

  FIG. 8 shows an OTDR waveform when the return light from the measured optical fiber 73 is measured by the conventional OTDR. As shown in FIG. 8, the return light from the break point or connection point of the optical fiber 73 to be measured appears as a peak A that first appears in the waveform. However, peaks B and C (ghosts) appear as if there are reflections in spite of the fact that no break point or the like actually exists. The peaks B and C are obtained by detecting light that is multiple-reflected between the breaking point or the connection point and the light emitting elements 11 and 13, and the peak B is about twice as long as the peak A, and the peak C is the peak A. Occurs at a distance of about three times the distance.

  The OTDR is generally provided with a loss light source for loss test. However, when large reflected light (return light) is incident on the light emitting elements 11 and 13, there is a disadvantage that the operation of the OTDR becomes unstable and the light source stability is deteriorated.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a novel and improved bidirectional optical module having high light source stability without generating a ghost and the same. It is to provide an optical pulse tester using the above.

  In order to solve the above problems, according to an aspect of the present invention, there is provided a bidirectional optical module in which light is emitted to an optical fiber and return light is incident from the optical fiber. Such a bidirectional optical module includes a plurality of light emitting elements that emit light incident on an optical fiber, a light receiving element that receives light emitted from the optical fiber, and a light that combines light emitted from the plurality of light emitting elements. An optical isolator that is provided between the light emitting element and the optical multiplexing / demultiplexing element, and that passes light only in the direction from the light emitting element toward the optical multiplexing / demultiplexing element. And a branching / branching element for guiding the light to the light receiving element.

  According to the present invention, the return light from the optical fiber is combined with the light emitting element in order to prevent the light emitted from the light emitting element from entering the light emitting element through the same path as the incident path entering the optical fiber. An optical isolator is provided between the branching element. The optical isolator allows light to pass only in the direction from the light emitting element side toward the multiplexing / demultiplexing element side, and does not allow return light from the optical fiber to pass. Therefore, return light from the optical fiber can be prevented from entering the light emitting element, and the return light is reflected on the surface of the light emitting element to prevent multiple reflection between the light emitting element and the optical fiber. Can do.

  Here, the light receiving surface of the light receiving element includes a first light receiving area and a second light receiving area having a frequency characteristic lower than that of the first light receiving area. At this time, the light receiving element of the present invention may be arranged so that light incident on the light receiving element is defocused from the in-focus position in the first light receiving area. Even in the light receiving element, the return light is reflected slightly. In order to prevent the reflected light from entering the optical fiber again, the light receiving element is disposed at a position away from the focusing position of the lens. Thereby, it is possible to prevent the light reflected by the light receiving element from being reflected in the same direction as the incident path of the incident light.

  Furthermore, you may provide the lens which condenses light between a joint branching element and a light receiving element. By disposing the light receiving element so as to be inclined with respect to a plane perpendicular to the optical axis of the lens, unnecessary light can be prevented from entering the lens again. Thereby, the light incident on the light receiving element is reflected in a direction different from the incident path.

  In order to solve the above problems, according to another aspect of the present invention, an optical pulse tester for testing loss characteristics of an optical fiber is provided. Such an optical pulse tester includes a bidirectional optical module that emits light to an optical fiber and receives return light from the optical fiber, and bidirectional light that drives the bidirectional optical module to generate light at a predetermined timing. A signal processing unit that calculates loss characteristics of an optical fiber based on a module driving unit, an electric signal conversion unit that converts light incident on the bidirectional optical module into an electric signal, and an electric signal converted by the electric signal conversion unit A section. The bidirectional optical module combines a plurality of light emitting elements that emit light incident on an optical fiber, a light receiving element that receives light emitted from the optical fiber, and light emitted from the plurality of light emitting elements. An optical isolator that is provided between the light-emitting element and the optical multiplexer / demultiplexer, and that passes light only in the direction from the light-emitting element toward the optical multiplexer / demultiplexer; And a branching / branching element for guiding the emitted light to the light receiving element.

  In the bidirectional optical module of the optical pulse tester according to the present invention, the return light from the optical fiber is incident on the light emitting element through the same path as the incident path on which the light emitted from the light emitting element enters the optical fiber. In order to prevent this, an optical isolator is provided between the light emitting element and the multiplexing / demultiplexing element. The optical isolator allows light to pass only in the direction from the light emitting element side toward the multiplexing / demultiplexing element side, and does not allow return light from the optical fiber to pass. Therefore, return light from the optical fiber can be prevented from entering the light emitting element, and the return light is reflected on the surface of the light emitting element to prevent multiple reflection between the light emitting element and the optical fiber. Can do. Thereby, a ghost does not generate | occur | produce in the waveform of the light detected with the optical pulse tester, and the optical pulse tester provided with the bidirectional | two-way optical module which has high light source stability can be provided.

  Furthermore, in order to solve the said subject, according to another viewpoint of this invention, the bidirectional | two-way optical module which radiate | emits light to an optical fiber and in which return light enters from an optical fiber is provided. Such a bidirectional optical module includes a light emitting element that emits light incident on an optical fiber, a light receiving element that receives light emitted from the optical fiber, and a light that is emitted from a plurality of light emitting elements. Are provided between the multiplexing / demultiplexing element side and the multiplexing / demultiplexing element side, and are provided between the multiplexing / demultiplexing element side and the multiplexing / demultiplexing element side. And an optical isolator that allows light to pass only in the direction toward.

  According to the present invention, the return light from the optical fiber prevents the light emitted from the light emitting element from entering the light emitting element through the same path as the incident path entering the optical fiber. And an optical isolator is provided between the coupling element and the branching element. The optical isolator passes light only in the direction from the multiplexing / demultiplexing element side toward the multiplexing / branching element side, and does not allow return light from the optical fiber to pass. Therefore, return light from the optical fiber can be prevented from entering the light emitting element, and the return light is reflected on the surface of the light emitting element to prevent multiple reflection between the light emitting element and the optical fiber. Can do. Further, by disposing an optical isolator at such a position, it is possible to adjust the passage or blocking of light having a plurality of wavelengths with an optical isolator having fewer than the number of light emitting elements.

  Here, the light receiving surface of the light receiving element includes a first light receiving area and a second light receiving area having a frequency characteristic lower than that of the first light receiving area. At this time, the light receiving element can be arranged so that the light incident on the light receiving element is defocused from the in-focus position in the first light receiving area. Or you may further provide the lens which condenses light between a coupling | branching element and a light receiving element. At this time, the light receiving element is disposed so as to be inclined with respect to a plane perpendicular to the optical axis of the lens. Thereby, since the reflection direction of the light reflected in the light receiving element is different from the incident path of the light incident on the light receiving element, it is possible to prevent the reflected light from entering the optical fiber.

  In order to solve the above problems, according to another aspect of the present invention, an optical pulse tester for testing loss characteristics of an optical fiber is provided. Such an optical pulse tester includes a bidirectional optical module that emits light to an optical fiber and receives return light from the optical fiber, and bidirectional light that drives the bidirectional optical module to generate light at a predetermined timing. A signal processing unit that calculates loss characteristics of an optical fiber based on a module driving unit, an electric signal conversion unit that converts light incident on the bidirectional optical module into an electric signal, and an electric signal converted by the electric signal conversion unit A section. The bidirectional optical module combines a light emitting element that emits light incident on an optical fiber, a light receiving element that receives light emitted from the optical fiber, and light emitted from a plurality of light emitting elements. A multiplexing / demultiplexing element that leads to the fiber, a coupling / branching element that guides the light emitted from the optical fiber to the light receiving element, and a coupling / branching element provided between the multiplexing / demultiplexing element and the coupling / branching element. And an optical isolator that allows light to pass only in the direction toward the side.

  As described above, according to the present invention, a bidirectional optical module having high light source stability without generating a ghost and an optical pulse tester using the same can be provided.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(First embodiment)
First, the configuration of the bidirectional optical module 100 according to the first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic configuration diagram illustrating the configuration of the bidirectional optical module 100 according to the present embodiment. FIG. 2 is an explanatory diagram for explaining an example of the arrangement of the light receiving elements 190.

  The bidirectional optical module 100 according to the present embodiment can be used, for example, in the optical pulse tester 1 shown in FIG. As described above, the optical pulse tester 1 repeatedly inputs pulsed light into a measured optical fiber in an optical communication system that performs data communication or the like by a signal, and reflects and backscatters light from the measured optical fiber. This is a device that measures the state of the measured optical fiber, such as disconnection and loss, by measuring the level and the light receiving time. By providing the optical pulse tester 1 with the bidirectional optical module 100 according to the present embodiment, the measurement accuracy of the optical pulse tester 1 can be increased. Hereinafter, the configuration of the bidirectional optical module 100 according to the present embodiment and the operation of the optical pulse tester using the same will be described in detail.

<Configuration of bidirectional optical module>
As shown in FIG. 1, the bidirectional optical module 100 according to the present embodiment includes light emitting elements 110 and 130 that emit light, lenses 120 and 140 that convert light into parallel light, and light that allows light to pass only in one direction. Isolators 125 and 145, a multiplexing / demultiplexing element 150 for multiplexing a plurality of lights into one light, lenses 170 and 180 for condensing the light, a multiplexing / branching element 160 for splitting the light, and a light reception for sensing the light. And an element 190.

  The light emitting elements 110 and 130 are elements that emit light to be incident on the optical fiber 71. For example, laser diodes (Laser Diodes) can be used. Note that the bidirectional optical module 100 according to the present embodiment includes the two light emitting elements 110 and 130, but is not limited to this example, and one or two or more light emitting elements can be provided.

  The lenses 120 and 140 are lenses for converting light into parallel light, and for example, a collimator lens or the like can be used. The lens 120 turns the light emitted from the light emitting element 110 into parallel light, and the lens 140 turns the light emitted from the light emitting element 130 into parallel light.

  The optical isolators 125 and 145 are optical elements that allow light to pass only in one direction. The optical isolators 125 and 145 are provided to prevent the return light from the measured optical fiber 73 from entering the light emitting elements 110 and 130. In this embodiment, the light isolators 110 and a multiplexing / demultiplexing element 150 described later are provided. Are provided between the light emitting element 130 and the multiplexing / demultiplexing element 150. That is, the optical isolator 125 passes the light emitted from the light emitting element 110 to the multiplexing / demultiplexing element 150 side, but the return light from the measured optical fiber 73 passes from the multiplexing / demultiplexing element 150 side to the light emitting element 110 side. I won't let you. Similarly, the optical isolator 145 passes the light emitted from the light emitting element 130 to the multiplexing / demultiplexing element 150 side, but the return light from the measured optical fiber 73 passes from the multiplexing / demultiplexing element 150 side to the light emitting element 130 side. I won't let you. Such optical isolators 125 and 145 have wavelength characteristics corresponding to the corresponding light emitting elements 110 and 130, and in this embodiment, an optical isolator having an isolation of about 30 dB or more is used.

  The multiplexing / demultiplexing element 150 is a wavelength filter that multiplexes the light that has been collimated by the lenses 120 and 140, and for example, a Short Wave Pass Filter, a Long Wave Pass Filter, a Band Pass Filter, or the like can be used. Note that “Wave” is synonymous with “Wavelength”. The light combined by the multiplexing / demultiplexing element 150 is incident on the optical fiber 71 through a coupling / branching element 160 described later.

  The coupling / branching element 160 is an optical element for guiding the return light from the optical fiber 71 to the light receiving element 190. For example, a beam splitter such as a half mirror can be used as the branching element 160. The coupling / branching element 160 reflects part or all of the incident light and causes the return light to enter the light receiving element 190.

  The lenses 170 and 180 are lenses for condensing light, and for example, plano-convex lenses can be used. The lens 170 collects the light incident on the optical fiber 71 via the multiplexing / demultiplexing element 150 and causes the light to enter the optical fiber 71. The lens 180 condenses the return light from the optical fiber 71 branched by the coupling / branching element 160 and makes it incident on the light receiving element 190.

  The light receiving element 190 is an element that senses light. For example, an avalanche photodiode (hereinafter referred to as “APD”) can be used. The APD is a light receiving element that utilizes the avalanche amplification effect, and can detect weak light with high sensitivity. For this reason, APD (especially APD with a small aperture) is suitable for a light receiving element such as OTDR that must detect weak return light with high distance resolution.

  The configuration of the bidirectional optical module 100 according to the present embodiment has been described above. Next, the function of the bidirectional optical module 100 according to the present embodiment will be described together with the operation of the optical pulse tester including the bidirectional optical module 100. Here, the configuration of the optical pulse tester is the same as in FIG. 7, and it is assumed that the bidirectional optical module 100 according to the present embodiment is applied instead of the bidirectional optical module 10.

<Operation of optical pulse tester equipped with bidirectional optical module>
In the optical pulse tester according to the present embodiment, first, the pulse width of the pulsed light is set in advance for the LD drive unit 20 by the signal processing unit 40 of the optical pulse tester 1. Next, a timing signal is transmitted to the LD driving unit 20 at a predetermined interval by a timing generating means (not shown) in the signal processing unit 40. The LD driving unit 20 that has received the timing signal causes the light emitting element 110 or the light emitting element 130 of the bidirectional optical module 100 to output pulsed light so as to be synchronized with the timing signal.

The pulsed light of wavelength λ ₁ emitted from the light emitting element 110 is converted into parallel light by the lens 120, and the pulsed light of wavelength λ ₂ emitted from the light emitting element 130 is converted into parallel light by the lens 140, and each is an optical isolator. 125 and 145 and enter the multiplexing / demultiplexing device 150. The multiplexing / demultiplexing element 150 transmits the light having the wavelength λ ₁ emitted from the light emitting element 110, while reflecting the light having the wavelength λ ₂ emitted from the light emitting element 130, so that both are directed to the coupling / branching element 160. Guide the light to. Then, the light of wavelength λ ₁ emitted from the light emitting element 110 and the light of wavelength λ ₂ emitted from the light emitting element 130 pass through the branching element 160 and enter the lens 170. The lens 170 collects the incident light and makes it incident on the optical fiber 71.

  The light incident on one end of the optical fiber 71 enters the measured optical fiber 73 that is a measurement target such as disconnection or loss via the measurement connector 60 connected to the other end of the optical fiber 71. Here, Rayleigh scattering may occur inside the optical fiber 73 to be measured. Part of the scattered light travels in the direction opposite to the traveling direction of the pulsed light, and returns to the optical pulse tester 1 as backscattered light. Further, light incident from the bidirectional optical module 100 is Fresnel reflected at the connection point or break point of the optical fiber 73 to be measured, and the reflected light also returns to the optical pulse tester 1.

  These return lights from the measured optical fiber 73 enter the bidirectional optical module 100 via the measurement connector 60 and the optical fiber 71. The return light is converted into parallel light by the lens 170, and then branched so as to enter the light receiving element 190 by the coupling / branching element 160. Here, a part of the return light is not branched to the light receiving element 190 side by the coupling / branching element 160 but passes through the coupling / branching element 160 and proceeds to the light emitting elements 110 and 130 side. When the return light is incident on the light emitting elements 110 and 130, it is reflected by the surface thereof and travels again toward the optical fiber 73 to be measured. When such a phenomenon is repeated, that is, when multiple reflection occurs, a ghost appears in the OTDR waveform of the optical pulse tester 1.

  In the bidirectional optical module 100 according to the present embodiment, optical isolators 125 and 145 are provided between the light emitting elements 110 and 130 and the multiplexing / demultiplexing element 150 in order to prevent such a phenomenon. As described above, the optical isolators 125 and 145 pass light from the light emitting elements 110 and 130 toward the multiplexing / demultiplexing element 150, but return light from the measured optical fiber 73 passes or reflects through the multiplexing / demultiplexing element 150. Thus, it functions to prevent the light from entering the light emitting elements 110 and 130. Therefore, by providing the optical isolators 125 and 145, it is possible to prevent the return light from passing through the optical isolators 125 and 145 and entering the light emitting elements 110 and 130, so that the light emitting elements 110 and 130 and the light to be measured Multiple reflections with the fiber 73 can be prevented.

  On the other hand, of the return light of the optical fiber 73 to be measured, the light branched to the light receiving element 190 side by the coupling / branching element 160 is collected by the lens 180 and enters the light receiving element 190. Here, there is a small amount of light that is reflected on the light incident surface of the light receiving element and that travels toward the lens 180 again. When such reflected light passes through the lens 180 and enters the measured optical fiber 73 again by the coupling / branching element 160, multiple reflection occurs between the light emitting elements 110 and 130 and the measured optical fiber 73. Cause it. In order to prevent such a phenomenon, the light receiving element 190 of the present embodiment is disposed at a position where the focused position of the light condensed by the lens 180 is defocused. This is because the incident direction and the reflection direction are the same when reflected at the in-focus position, and the incident direction and the reflection direction are different when reflected at a position different from the in-focus position. is there.

  As shown in FIG. 2, the return light 100 a from the optical fiber 73 to be measured is collected on the lens 180 and enters the light receiving element 190. At this time, the light receiving element 190 is disposed so that the focusing position of the light by the lens 180 is located a predetermined distance away from the light receiving surface 191 of the light receiving element 190. For example, as illustrated in FIG. 2, when the light receiving surface 191 of the light receiving element 190 is disposed on the opposite side of the lens 180 with respect to the light focusing position by the lens 180, the return light 100 a is transmitted by the lens 180. After being condensed, the light enters the light receiving surface 191 in a diffused state again. As described above, by arranging the light receiving element 190 so that the in-focus position is defocused, the light 100 b reflected on the light receiving surface 191 of the light receiving element 190 can be advanced in a direction not entering the lens 180. Therefore, the reflected light 100b incident on the lens 180 can be reduced, and the reflected light 100b can be prevented from entering the measured optical fiber 73 again.

  The light receiving surface 191 of the light receiving element is located outside the first light receiving area 191a and the first light receiving area 191a, which is an effective light receiving area, and has a frequency characteristic worse than that of the first light receiving area 191a. It consists of area 191b. For this reason, the light receiving element 190 is disposed so that the light focused by the lens 180 enters the first light receiving area 191a. In FIG. 2, the focused position of the light collected by the lens 180 is defocused so that it is behind the focal point. However, the present invention is not limited to this example, and the defocusing is performed ahead of the focal point. May be.

  FIG. 3 shows an OTDR waveform when the return light from the optical fiber 73 to be measured is measured by the conventional OTDR by the optical pulse tester 1 having such a bidirectional optical module 100. As shown in FIG. 3, the peak appearing in the waveform is only peak A, which is a ghost compared to the result measured by the optical pulse tester 1 including the conventional bidirectional optical module 10 shown in FIG. Peaks B and C do not appear. As described above, by using the bidirectional optical module 100 according to the present embodiment, multiple reflections generated between the light emitting elements 110 and 130 and the multiplexing / demultiplexing element 150 can be prevented, and a normal waveform can be displayed. . In addition, since large reflected light is not incident on the surfaces of the light emitting elements 110 and 130, the bidirectional optical module 100 with high light source stability can be provided.

  The operation of the bidirectional optical module 100 according to the first embodiment and the optical pulse tester using the same has been described above. In the bidirectional optical module 100 according to the first embodiment, in order to prevent multiple reflections that occur between the light emitting elements 110 and 130 and the optical fiber 73 to be measured, the light emitting elements 110 and 130 and the multiplexing / demultiplexing element 150 are connected to each other. There are provided optical isolators 125 and 145 that allow only light traveling from the light emitting elements 110 and 130 to the multiplexing / demultiplexing element 150 to pass therethrough. Thereby, it is possible to prevent the return light from the optical fiber 73 to be measured from entering the light emitting elements 110 and 130, thereby suppressing the occurrence of multiple reflections and displaying a normal waveform without ghost as the OTDR waveform. it can. In addition, since there is no return light to the light emitting elements 110 and 130, a stabilized light source with high light output stability can be provided. Further, the light receiving element 190 receives the defocused light, so that the light reflected on the light incident surface of the light receiving element 190 enters the measured optical fiber 73 again through the same path as the incident light incident path. Can be prevented.

(Second Embodiment)
Next, a bidirectional optical module 200 according to the second embodiment of the present invention will be described with reference to FIG. The bidirectional optical module 200 of this embodiment is different from the bidirectional optical module 100 of the first embodiment in that only one optical isolator is provided instead of providing a plurality of optical isolators corresponding to each light emitting element. Is different. Hereinafter, differences from the first embodiment will be mainly described, and detailed description of the same configuration and the same operation will be omitted. FIG. 4 is a schematic configuration diagram illustrating the configuration of the bidirectional optical module 200 according to the present embodiment.

  As shown in FIG. 4, the bidirectional optical module 200 according to the present embodiment includes light emitting elements 110 and 130 that emit light, lenses 120 and 140 that convert light into parallel light, and light that allows light to pass only in one direction. An isolator 155, a multiplexing / demultiplexing element 150 that combines a plurality of lights into one light, lenses 170 and 180 that collect the light, a multiplexing / branching element 160 that splits the light, and a light receiving element 190 that senses the light. With.

In the bidirectional optical module 200 of the present embodiment, one optical isolator 155 is provided between the multiplexing / demultiplexing element 150 and the coupling / branching element 160. The optical isolator 155 allows light to pass only from the multiplexing / demultiplexing element 150 side to the coupling / branching element 160 side, and even if return light from the optical fiber 73 to be measured passes through the coupling / branching element 160 and enters the optical isolator 155. Do not pass. The optical isolator 155 of this embodiment needs to have characteristics corresponding to the two light emitting elements 110 and 130 that emit light of different wavelengths in order to prevent the return light from entering both the light emitting elements 110 and 130. . As such an optical isolator 155, for example, an optical isolator 155 corresponding to a substantially intermediate wavelength between the wavelength λ ₁ of light emitted from the light emitting element 110 and the wavelength λ _{2 of} light emitted from the light emitting element 130 can be used.

In such a bidirectional optical module 200, the pulse light of the wavelength lambda ₁ emitted from the light emitting element 110 is collimated by the lens 120, the pulse light of the wavelength lambda ₂ emitted from the light emitting element 130, a lens 140 The light is converted into parallel light and enters the multiplexing / demultiplexing device 150. The light of wavelength λ _{1 and} the light of wavelength λ ₂ guided to the optical isolator 155 side by the multiplexing / demultiplexing element 150 are transmitted through the optical isolator 155 and the coupling / branching element 160 and are incident on the lens 170. The light incident on the lens 170 is collected and incident on the optical fiber 71.

  Light that has entered one end of the optical fiber 71 enters the optical fiber 73 to be measured via the measurement connector 60. Of the light incident on the optical fiber 73 to be measured, the light that has been Rayleigh scattered inside the optical fiber 73 to be measured, or the light that has been Fresnel reflected at the connection point or break point of the optical fiber 73 to be measured, And enters as return light.

  The return light is converted into parallel light by the lens 170, and then branched so as to enter the light receiving element 190 by the coupling / branching element 160. Here, a part of the return light is not branched to the light receiving element 190 side by the coupling / branching element 160 but passes through the coupling / branching element 160 and proceeds to the light emitting elements 110 and 130 side. However, the optical bidirectional module 200 according to the present embodiment includes an optical isolator 155 that does not allow light to pass between the multiplexing / demultiplexing element 160 and the multiplexing / demultiplexing element 150 from the multiplexing / demultiplexing element 160 side. Is provided. Thereby, most of the return light from the measured optical fiber 73 is blocked by the optical isolator 155, and the amount of return light incident on the light emitting elements 110 and 130 can be reduced. Therefore, the occurrence of multiple reflections between the light emitting elements 110 and 130 and the measured optical fiber 73 can be suppressed.

  On the other hand, of the return light of the optical fiber 73 to be measured, the light branched to the light receiving element 190 side by the coupling / branching element 160 is collected by the lens 180 and enters the light receiving element 190. Here, there is a small amount of light that is reflected on the light incident surface of the light receiving element and that travels toward the lens 180 again. In order to prevent multiple reflections between the light emitting elements 110 and 130 and the optical fiber 73 to be measured due to such reflected light, light collected by the lens 180 by the lens 180 as in the first embodiment. The in-focus position should be arranged at a position where defocusing is performed.

  When the optical pulse tester 1 including the bidirectional optical module 200 according to the present embodiment detects a break point or a connection point of the optical fiber 73 to be measured, the bidirectional optical module 100 according to the first embodiment is used. It is considered that a slight multiple reflection occurs as compared with the case of the above. This is because one optical isolator 155 allows light of different wavelengths to pass or be blocked. However, since the number of components of the bidirectional optical module 200 can be reduced, the cost required for manufacturing the module can be suppressed, and the module can be easily manufactured.

  The bidirectional optical module 200 according to the second embodiment has been described above. The bidirectional optical module 200 according to the second embodiment is provided between the multiplexing / demultiplexing element 150 and the coupling / branching element 160 in order to prevent multiple reflections that occur between the light emitting elements 110 and 130 and the optical fiber 73 to be measured. In addition, an optical isolator 155 that passes only light traveling from the multiplexing / demultiplexing element 150 side to the coupling / branching element 160 side is provided. Thereby, it is possible to prevent the return light from the optical fiber 73 to be measured from entering the light emitting elements 110 and 130, thereby suppressing the occurrence of multiple reflections and displaying a normal waveform without ghost as the OTDR waveform. it can. In addition, since there is no return light to the light emitting elements 110 and 130, a stabilized light source with high light output stability can be provided. Further, the light receiving element 190 receives the defocused light, so that the light reflected on the light incident surface of the light receiving element 190 enters the measured optical fiber 73 again through the same path as the incident light incident path. Can be prevented.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the above embodiment, the light receiving element of the bidirectional optical module is disposed at a position where the in-focus position is defocused in a range where incident light enters the effective light receiving surface, but the present invention is not limited to such an example. The light receiving surface of the light receiving element may be inclined with respect to the optical axis of the lens that collects the light incident on the light receiving element. Generally, the light receiving element is arranged so that its light receiving surface is perpendicular to the optical axis of the lens. At this time, as described above, the light reflected by the light receiving surface is reflected along the same path as the incident path of the incident light, which causes multiple reflection. Therefore, for example, as shown in FIG. 5, the light receiving surface 191 of the light receiving element is arranged to be inclined by several degrees with respect to a surface perpendicular to the optical axis of the lens 180 that collects the incident light 100a. Thereby, even if the incident light 100a is reflected by the light receiving surface 191, the reflected light 100b travels in a direction different from the incident path, so that the possibility that the reflected light 100b enters the lens 180 is reduced. In this way, multiple reflections can be prevented from occurring due to the light reflected on the light receiving surface of the light receiving element.

  Moreover, although the bidirectional module of the said embodiment was provided with two light emitting elements, this invention is not limited to this example, and can provide one or two or more light emitting elements. When there is one light emitting element, the multiplexing / demultiplexing element may not be provided, and the optical isolator may be arranged between the light emitting element and the coupling / branching element.

  Furthermore, in the first embodiment, one optical isolator is provided corresponding to each light emitting element, and in the second embodiment, the present invention is not limited to this example, and the number of optical isolators and The installation position can be changed as appropriate.

1 is a configuration schematic diagram showing a configuration of a bidirectional optical module according to a first embodiment of the present invention. It is explanatory drawing for demonstrating an example of arrangement | positioning of a light receiving element. It is a graph which shows a waveform when the reflected light in a breaking point or a connection point is detected with the optical pulse tester using the bidirectional | two-way optical module concerning this embodiment. It is a structure schematic diagram which shows the structure of the bidirectional | two-way optical module concerning the 2nd Embodiment of this invention. It is explanatory drawing for demonstrating the example of other arrangement | positioning of a light receiving element. It is a block diagram which shows the structure of an optical pulse tester. It is the structure schematic which shows the structure of the conventional bidirectional | two-way optical module. It is a graph which shows a waveform when the reflected light in a fracture | rupture point or a connection point is detected with the optical pulse tester using the conventional bidirectional | two-way optical module.

Explanation of symbols

100, 200 Bidirectional optical module 110, 130 Light emitting element 120, 140 Lens 125, 145, 155 Optical isolator 150 Multiplexing / demultiplexing element 160 Multiplexing / branching element 170, 180 Lens 190 Light receiving element 191 Light receiving surface

Claims (8)

A bi-directional optical module that emits light to an optical fiber and receives return light from the optical fiber,
A plurality of light emitting elements emitting light incident on the optical fiber;
A light receiving element for receiving light emitted from the optical fiber;
A multiplexing / demultiplexing element that multiplexes light emitted from the plurality of light emitting elements and guides the light to the optical fiber;
An optical isolator that is provided between the light emitting element and the multiplexing / demultiplexing element and allows light to pass only in a direction from the light emitting element side toward the multiplexing / demultiplexing element side;
A coupling / branching element for guiding light emitted from the optical fiber to the light receiving element;
A bidirectional optical module comprising: The light receiving surface of the light receiving element includes a first light receiving area and a second light receiving area having a frequency characteristic lower than that of the first light receiving area.
2. The bidirectional optical module according to claim 1, wherein the light receiving element is arranged so that light incident on the light receiving element is defocused from a focus position in the first light receiving area. 3. . A lens for condensing light between the coupling / branching element and the light receiving element;
The bidirectional optical module according to claim 1, wherein the light receiving element is disposed so as to be inclined with respect to a plane perpendicular to the optical axis of the lens. An optical pulse tester for testing loss characteristics of an optical fiber,
A bidirectional optical module that emits light to the optical fiber and in which return light is incident from the optical fiber;
A bidirectional optical module driving unit that drives the bidirectional optical module to generate light at a predetermined timing;
An electrical signal converter that converts light incident on the bidirectional optical module into an electrical signal;
Based on the electrical signal converted by the electrical signal converter, a signal processor that calculates loss characteristics of the optical fiber;
With
The bidirectional optical module includes:
A plurality of light emitting elements emitting light incident on the optical fiber;
A light receiving element for receiving light emitted from the optical fiber;
A multiplexing / demultiplexing element that multiplexes light emitted from the plurality of light emitting elements and guides the light to the optical fiber;
An optical isolator that is provided between the light emitting element and the multiplexing / demultiplexing element and allows light to pass only in a direction from the light emitting element side toward the multiplexing / demultiplexing element side;
A coupling / branching element for guiding light emitted from the optical fiber to the light receiving element;
An optical pulse tester comprising: A bi-directional optical module that emits light to an optical fiber and receives return light from the optical fiber,
A light emitting element for emitting light incident on the optical fiber;
A light receiving element for receiving light emitted from the optical fiber;
A multiplexing / demultiplexing element that multiplexes the light emitted from the plurality of light emitting elements and guides the light to the optical fiber;
A coupling / branching element for guiding light emitted from the optical fiber to the light receiving element;
An optical isolator that is provided between the multiplexing / demultiplexing element and the coupling / branching element, and allows light to pass only in a direction from the multiplexing / demultiplexing element side toward the coupling / branching element;
A bidirectional optical module comprising: The light receiving surface of the light receiving element includes a first light receiving area and a second light receiving area having a frequency characteristic lower than that of the first light receiving area.
6. The bidirectional optical module according to claim 5, wherein the light receiving element is arranged so that light incident on the light receiving element is defocused from a focus position in the first light receiving area. . A lens for condensing light between the coupling / branching element and the light receiving element;
6. The bidirectional optical module according to claim 5, wherein the light receiving element is disposed so as to be inclined with respect to a plane perpendicular to the optical axis of the lens. An optical pulse tester for testing loss characteristics of an optical fiber,
A bidirectional optical module that emits light to the optical fiber and in which return light is incident from the optical fiber;
A bidirectional optical module driving unit that drives the bidirectional optical module to generate light at a predetermined timing;
An electrical signal converter that converts light incident on the bidirectional optical module into an electrical signal;
Based on the electrical signal converted by the electrical signal converter, a signal processor that calculates loss characteristics of the optical fiber;
With
The bidirectional optical module includes:
A light emitting element for emitting light incident on the optical fiber;
A light receiving element for receiving light emitted from the optical fiber;
A multiplexing / demultiplexing element that multiplexes the light emitted from the plurality of light emitting elements and guides the light to the optical fiber;
A coupling / branching element for guiding light emitted from the optical fiber to the light receiving element;
An optical isolator that is provided between the multiplexing / demultiplexing element and the coupling / branching element, and allows light to pass only in a direction from the multiplexing / demultiplexing element side toward the coupling / branching element;
An optical pulse tester comprising:

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