JP2005156643A - Optical fiber, optical waveguide, optical apparatus, optical receiver module, optical transmitter and receiver module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber, an optical waveguide, an optical apparatus, or the like wherein the variance of transmitted light intensity caused by interference between higher modes and the fundamental mode is small. <P>SOLUTION: With respect to optical fibers 26, 27, and 28 which are short in the direction of an optical axis, both end faces are inclined to a surface orthogonal to the optical axis, and one and the other of both end faces are arranged forming about 90° angle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical fiber and an optical waveguide used when performing optical communication and sensing, and an optical device, an optical receiving module, and an optical transmitting / receiving module using these.

  In an optical transceiver module used for optical communication, a short optical fiber having a length in the optical axis direction of several millimeters to several centimeters or a waveguide is often used. As such an example, an optical transmission / reception module described in Patent Document 1 below is known.

  FIG. 7 shows a configuration of an optical transceiver module disclosed in Patent Document 1 below. In this optical transceiver module, an optical fiber and a laser diode 11 as a light receiving element or a light emitting element are connected to an optical waveguide 6 via an optical filter 7 and a half mirror 9. That is, in FIG. 7, the substrate is denoted by 1 and the connecting portion is denoted by 2. However, in such a short optical waveguide or optical fiber, if there is a loss in the joint, the higher order mode generated at the input end reaches the output end before being attenuated, and part of it is converted to the fundamental mode here. The interference with the fundamental mode is described in Non-Patent Document 1 below. In joining through a groove or a filter, it is impossible to set the loss to 0 (zero). Therefore, such inter-mode interference always occurs. For this reason, if there is a minute change in the length of the waveguide or optical fiber, the diameter of the waveguide, the refractive index, etc. due to changes in the wavelength of light passing through, temperature changes, etc., the phase difference between the modes changes, The transmitted light intensity may fluctuate greatly.

For example, a cut-off wavelength of a short optical fiber having a length of 1.5 cm is about 1360 nm, and when this optical fiber is inserted into an optical fiber optical system, a short wavelength band (1260 to 1260) of this optical system. The transmission loss at 1360 nm varies by about −0.5 to +0.3 dB depending on the wavelength. As a conventional method for suppressing this fluctuation, an optical fiber structure described in Non-Patent Document 2 below is known.
JP 2000-347050 A Abe, K .; Lacroix, Y .; Bonnell, L .; Jakubczyk, Z .; "Modal interference in a short fiber section: Fiber length, splice loss, cutoff, and wavelength dependences", IEEE Journal of Lightwave Technology, Vol. 10, Issue 4, April, 1992 Renner, H .; "Leaky-Mode Loss in Coated Depressed-Cladding Fibers", IEEE Photonics Technology Letters, Vol. 3, Issue 1, January 1991

The characteristics of the optical fiber in the conventional example are shown in FIG. 8 with the abscissa indicating the radius and the ordinate indicating the refractive index. The core of this optical fiber has a refractive index that decreases from the peripheral edge toward the center, and the cladding is composed of two layers, an inner layer having a lower refractive index than the core and an outer layer having a higher refractive index than the inner layer. Furthermore, the outer surface of the cladding is coated with a dielectric. By making the core like this, the higher-order mode LP ₁₁ tends to leak into the clad, and the clad has a double structure, and the interface with the air is anti-reflective coated, so that the LP ₁₁ mode is clad. It is confined inside and attenuates here.

The conventional method requires an optical fiber having a special structure in which the refractive index of the core is inclined, the clad has a double structure, and the outside of the clad is coated.
An object of the present invention is to suppress fluctuation of transmitted light intensity of an optical system due to interference between a higher-order mode and a fundamental mode without using an optical fiber having a special structure as in the prior art.

In the optical fiber of the present invention, in an optical fiber having a short length in the optical axis direction, both end faces are inclined with respect to an orthogonal plane orthogonal to the optical axis, and one of the two end faces is orthogonal. A deviation angle between a direction inclined with respect to the surface and a direction in which the other surface of the both end surfaces is inclined with respect to the orthogonal surface is approximately 90 degrees.
With this configuration, when an optical fiber is connected to both end faces of the optical fiber, the transmitted light intensity fluctuation of the optical system due to inter-mode interference is suppressed (claim 1).

The optical waveguide of the present invention is an optical waveguide having a short length in the optical axis direction. Both end faces are inclined with respect to an orthogonal plane orthogonal to the optical axis, and one of the two end faces is A deviation angle between a direction inclined with respect to the orthogonal plane and a direction in which the other of the two end faces is inclined with respect to the orthogonal plane is approximately 90 degrees.
With this configuration, when an optical waveguide or an optical fiber is connected to both end faces of the optical waveguide, fluctuations in transmitted light intensity of the optical system due to inter-mode interference are suppressed (claim 2).

In the optical fiber of the present invention, the length in the optical axis direction is short, and a plurality of grooves are provided between both ends. Each of the surfaces including the plurality of grooves is orthogonal to the optical axis. Deviation between a direction inclined with respect to the orthogonal plane, and a direction in which a plane including each of the plurality of grooves is inclined with respect to the orthogonal plane, and a direction in which a plane of a groove adjacent thereto is inclined with respect to the orthogonal plane The angle is approximately 90 degrees.
With this configuration, fluctuations in transmitted light intensity of the optical system due to inter-mode interference of light passing through the two grooves are suppressed (claim 3).

Further, the optical waveguide of the present invention is short in the optical axis direction and includes a plurality of grooves in a portion between both ends, and each of the surfaces including the plurality of grooves is orthogonal to the optical axis. Deviation between a direction inclined with respect to the orthogonal plane, and a direction in which a plane including each of the plurality of grooves is inclined with respect to the orthogonal plane, and a direction in which a plane of a groove adjacent thereto is inclined with respect to the orthogonal plane The angle is approximately 90 degrees.
With this configuration, the transmitted light intensity fluctuation of the optical system due to the inter-mode interference of the light passing through the two grooves is suppressed.

Further, the optical fiber of the present invention has a short length in the optical axis direction, and in an optical fiber having a plurality of grooves in a portion between both ends, both end faces are inclined with respect to a plane perpendicular to the optical axis. And each of the surfaces including the plurality of grooves is inclined with respect to an orthogonal surface orthogonal to the optical axis, and the surface including each of the plurality of grooves is inclined with respect to the orthogonal surface; A surface including a groove adjacent to each of both of the end faces of the plurality of grooves, the angle of deviation in a direction in which the surface of the groove adjacent thereto is inclined with respect to the orthogonal surface is approximately 90 degrees. Is characterized in that the angle of deviation between the direction inclined with respect to the orthogonal plane and the direction in which the end face adjacent thereto is inclined with respect to the orthogonal plane is approximately 90 degrees.
With this configuration, when an optical fiber is connected to one or both end faces of the optical waveguide, fluctuations in transmitted light intensity of the optical system due to inter-mode interference are suppressed (Claim 5).

Also, the optical waveguide of the present invention is short in the optical axis direction, and in the optical waveguide having a plurality of grooves in the portion between both ends, both end faces are inclined with respect to the plane perpendicular to the optical axis. And each of the surfaces including the plurality of grooves is inclined with respect to an orthogonal surface orthogonal to the optical axis, and the surface including each of the plurality of grooves is inclined with respect to the orthogonal surface; A surface including a groove adjacent to each of the two end faces among the plurality of grooves, the angle of deviation in a direction in which the surface of the groove adjacent thereto is inclined with respect to the orthogonal surface is approximately 90 degrees. Is characterized in that the angle of deviation between the direction inclined with respect to the orthogonal plane and the direction in which the end face adjacent thereto is inclined with respect to the orthogonal plane is approximately 90 degrees.
With this configuration, when an optical waveguide or an optical fiber is connected to one or both end faces of the optical waveguide, fluctuations in transmitted light intensity of the optical system due to inter-mode interference are suppressed (Claim 6).

An optical device of the present invention is provided for inserting the tip or the whole of the optical fiber for connecting the optical fiber according to any one of claims 1, 3, and 5 to another optical fiber. And a holding portion having an inner diameter substantially equal to or slightly larger than the diameter of the optical fiber.
With this configuration, the direction of axial misalignment at the tip of the optical fiber is likely to occur in a desired direction to suppress inter-mode interference, and the transmitted light intensity of the optical system due to inter-mode interference of light passing through each end face including the groove The fluctuation is suppressed (claim 7).

An optical device according to the present invention is such that the connection between the optical fiber according to any one of claims 1, 3, and 5 and another optical fiber is light at one or both of the optical fibers at a connection point. This is done through a process of applying pressure in a direction parallel to the axis and facing each other.
With this configuration, the direction of axial misalignment at the tip of the optical fiber is likely to occur in a desired direction to suppress inter-mode interference, and the transmitted light intensity of the optical system due to inter-mode interference of light passing through each end face including the groove Variation is suppressed (claim 8).

Moreover, the optical receiver of the present invention is placed at different locations in the plurality of light receiving elements, the optical fiber according to any one of claims 1, 3, and 5 and the groove of the optical fiber, Each of the plurality of light receiving elements includes two or more wavelength selection filters that reflect light in a specific wavelength range out of the optical fiber transmission light.
With this configuration, even if the distance between the filters is shortened, intensity variation due to inter-mode interference between transmitted light and light reflected by the filter is suppressed, so a small and stable output receiver is realized ( Claim 9).

Moreover, the optical receiver of the present invention is placed in different locations in the plurality of light receiving elements, the optical waveguide according to any one of claims 2, 4, and 6, and the groove of the optical waveguide, Each of the plurality of light receiving elements includes two or more wavelength selection filters that reflect light in a specific wavelength range out of the optical waveguide transmission light.
With this configuration, even if the distance between the filters is shortened, intensity variation due to inter-mode interference between transmitted light and light reflected by the filter is suppressed, so a small and stable output receiver is realized ( Claim 10).

Moreover, the optical transceiver module of the present invention is placed at different locations in the plurality of light receiving elements, the optical fiber according to any one of claims 1, 3, and 5 and the groove of the optical fiber, For each of the plurality of light receiving elements, two or more wavelength selection filters that transmit light in a specific wavelength range of the optical fiber transmission light by reflection, or one or more wavelength selection filters and half mirrors, and the light A light emitting element for sending light to one end of the fiber is provided.
With this configuration, even if the distance between the filters is shortened, fluctuations in the intensity of the received light and the output light of the module due to inter-mode interference are suppressed, so a compact and stable optical transceiver with a stable transmission / reception signal level is realized. (Claim 11).

Moreover, the optical transceiver module of the present invention is placed at different locations in the plurality of light receiving elements, the optical waveguide according to any one of claims 2, 4, and 6, and the groove of the optical waveguide, For each of the plurality of light receiving elements, two or more wavelength selective filters that transmit light in a specific wavelength range out of the optical waveguide transmission light by reflection, or one or more wavelength selective filters and a half mirror, and the light A light emitting element for transmitting light is provided at one end of the waveguide.
With this configuration, even if the distance between the filters is shortened, fluctuations in the intensity of the received light and the output light of the module due to inter-mode interference are suppressed, so a compact and stable optical transceiver with a stable transmission / reception signal level is realized. (Claim 12).

An optical transceiver module according to the present invention is placed in a light receiving element, the optical fiber according to any one of claims 1, 3, and 5, and a groove of the optical fiber, and the light receiving module. A device includes a wavelength selection filter that transmits light in a specific wavelength range by reflection in the optical fiber transmission light, and a light emitting device that transmits light to one end of the optical fiber.
With this configuration, even if the distance between the optical output end and the wavelength selection filter is shortened, intensity variation due to inter-mode interference between the received light and the output light of the module is suppressed, so the transmission / reception signal level is small and stable. An optical transceiver is realized (claim 13).

An optical transceiver module according to the present invention is placed at different locations in a light receiving element, the optical waveguide according to any one of claims 2, 4, and 6, and a groove of the optical waveguide. Each of the light receiving elements includes a wavelength selection filter that sends out light in a specific wavelength range of the optical waveguide transmission light by reflection, and a light emitting element that sends light to one end of the optical waveguide.
With this configuration, even if the distance between the optical output end and the wavelength selection filter is shortened, intensity variation due to inter-mode interference between the received light and the output light of the module is suppressed, so the transmission / reception signal level is small and stable. An optical transceiver is realized (claim 14).

  In order to achieve the above object, in the optical fiber of the present invention, both end faces are inclined with respect to an orthogonal plane orthogonal to the optical axis, and one end face and the other end face of both end faces are in an angular relationship of approximately 90 degrees. Therefore, it is possible to suppress the transmitted light intensity fluctuation of the optical system due to the interference between the higher-order mode and the fundamental mode without using an optical fiber having a special structure as in the conventional example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a schematic diagram showing a basic configuration of an optical transceiver module according to the first embodiment of the present invention. Moreover, the schematic diagram of the example which provided the holding member in the basic composition is shown to FIG. 1B. The optical transceiver module having the basic configuration shown in FIG. 1A has three optical fibers each having a short length in the optical axis direction, that is, first to third optical fibers 26, 27, and 28. These first to third optical fibers 26, 27, and 28 are connected in series so as to be in a straight line along the same optical axis. Each of the first to third optical fibers 26, 27, and 28 has both end faces inclined with respect to an orthogonal plane orthogonal to the optical axis, and one end and the other end of both end faces are approximately 90 degrees. They are arranged in an angular relationship.

  Specifically, in the first optical fiber 26, one end face is inclined by 8 degrees with respect to a plane orthogonal to the optical axis, and the other end face is inclined by 30 degrees with respect to a plane that is also orthogonal to the optical axis. In the second optical fiber 27, one end face connected to the first optical fiber 26 is 30 degrees with respect to the plane perpendicular to the optical axis, and the other end face connected to the third optical fiber 28 is the same light. It is inclined 30 degrees with respect to a plane perpendicular to the axis. In the third optical fiber 28, one end face connected to the second optical fiber 27 is 30 degrees with respect to a plane orthogonal to the optical axis, and the other end face is 8 degrees with respect to a plane that is also orthogonal to the optical axis. Inclined.

  First to third ferrules 29, 30, and 31 having these optical fibers 26, 27, and 28 and having the same inclination as that of the optical fiber having a built-in end face are provided. The wavelength selection filter 24 is inserted between the first optical fiber 26 and the second optical fiber 27, and the half mirror 25 is inserted between the second optical fiber 27 and the third optical fiber 28. . Furthermore, the light emitting element 21 that outputs light having the first wavelength λ2 (1.31 μm) is disposed on the end face side of the third optical fiber 28 inclined at 8 degrees. Further, the first light receiving element 22 is disposed in the traveling direction of the received light having the second wavelength λ2 (1.55 μm) reflected by the wavelength selection filter 24, and the second light receiving element 23 is formed by the half mirror 25. The reflected light is disposed in the traveling direction of the received light having the first wavelength λ1 (1.31 μm).

  The wavelength selection filter 24 and the half mirror 25 are formed by laminating a dielectric multilayer film on a polyimide substrate, a glass substrate, or the like, and are fixed between corresponding optical fibers by a UV curable resin or a thermosetting resin. ing. Each of the light receiving elements 22 and 23 is resin-fixed on the notch of the corresponding ferrule. The first to third optical fibers 26, 27, and 28 are inserted into a cylindrical sleeve (not shown) provided with a notch in the light receiving element portion, and are fixed by the resin.

  FIG. 1B shows an example in which the holding member 70 is provided in the optical transceiver module having the basic configuration shown in FIG. 1A. In this example, the holding member 70 is configured to hold the ferrules 29, 30, 31, and 33. Yes. In addition, as shown in part in FIG. 1C, a holding member 72 that directly holds the optical fiber may be provided instead of the ferrule. The holding members 70 and 72 are preferably made of a material having a coefficient of thermal expansion substantially equal to that of quartz, such as zirconia or phosphor bronze. The holding members 70 and 72 are configured to be coaxial with the optical fiber and / or the ferrule, but the cross-sectional shape is not a complete cylindrical annular shape, but has a slit 74 in part as shown in the cross section of FIG. 1D. That is, a so-called split sleeve may be used. In the case of such a split sleeve, the inner diameters of the holding members 70 and 72 are smaller than the outer diameter of the optical fiber or ferrule to be attached when not attached to the optical fiber or ferrule. It becomes larger and is the same as or slightly larger than the outer diameter of the optical fiber or ferrule to be attached.

  FIG. 1E is a cross-sectional view showing in detail a portion connecting the optical fibers. FIG. 1E shows an example in which the end faces of the optical fibers are butted and connected, but the same applies to the case where the end faces of the ferrules into which the optical fibers are inserted are butted. The connection between the optical fiber and another optical fiber applies pressure to one or both of the optical fibers in the direction parallel to the optical axis at the connection point and facing each other, as indicated by two arrows in FIG. 1E. It goes through the process.

  The wavelength selection filter 24 and the half mirror 25 are inserted into a groove 36 provided in a portion between both ends (not shown) of the optical fiber 34 and the ferrule 35 as in the wavelength selection filter 37 shown in FIG. Alternatively, as in the wavelength selection filter 42 shown in FIG. 3, the light guide 40 may be inserted into a groove 41 provided in a part of the optical waveguide 40 and the optical waveguide substrate 39 constituting the light guide. In FIG. 2, the light receiving element is indicated by 38, and in FIG. 3, the light receiving element is indicated by 43. Further, the end face polished so as to be inclined by 8 degrees from the plane perpendicular to the optical axis of the optical fiber 34 may be a vertical end face.

  Next, the operation of this optical module will be briefly described. The light of wavelength λ1 emitted from the light emitting element 21 enters the third optical fiber 28, passes through the half mirror 25, the second optical fiber 27, the wavelength selection filter 24, and the first optical fiber 26, and then is transmitted externally. The optical fiber 32 is sent out. On the other hand, the light having the wavelength λ 2 input from the optical transmission path passes through the first optical fiber 26 and reaches the wavelength selection filter 24, where it is reflected and enters the first light receiving element 22. In addition, light of wavelength λ1 input from the optical transmission path passes through the first optical fiber 26, the wavelength selection filter 24, and the second optical fiber 27, and reaches the half mirror 25, where a part of the light is reflected. Is incident on the second light receiving element 23. The light emitting element 21 is disposed at a position slightly away from the first and second light receiving elements in order to reduce electrical crosstalk.

  The coupling efficiency of the optical fiber is 100% because the traveling direction of the light to be coupled and the optical axis of the optical fiber coincide, and the beam waist of the light to be coupled is on the end face of the optical fiber, and the intensity distribution here Is completely consistent with the intensity distribution of the fundamental mode of the optical fiber. This is because when two optical fibers whose core shape, core refractive index, and clad refractive index completely match each other are connected with an optical axis offset of 0 (zero) and an end-to-end distance of 0 (zero), This corresponds to the case where laser light is condensed on the end face of the optical fiber by a coupling lens.

  However, when optical fibers are joined with another optical member such as a filter or when a groove is provided in the optical waveguide, it is very difficult to satisfy this condition, and mode conversion occurs at the coupling portion. .

  An example of mode conversion is shown in FIG. FIG. 6A shows an example in which the optical axes of the two optical fibers are shifted in a direction perpendicular to the optical axis, and FIG. 6B shows the angles of the optical axes of the two optical fibers. This is an example when tilted. In any case, a new standing wave different from the fundamental mode is generated in the direction in which the optical axis is shifted. This standing wave reaches the next connection point without being attenuated if the length of the optical fiber is short. At the next connection point, as in the previous connection point, a new standing wave that is different from the fundamental mode is generated in the direction in which the optical axis is shifted, so that one of the higher-order modes that have reached the connection point without being attenuated. The unit returns to the basic mode, interferes with the original basic mode, and causes fluctuations in the output light.

  In the optical system of FIG. 1A, the coupling part where such mode conversion occurs frequently is between the first optical fiber 26 and the second optical fiber 27 in which the filter is inserted, and the half mirror is inserted. The second optical fiber 27 and the third optical fiber 28 and the end of the third optical fiber 28 where the light emitting element 21 is placed. Both are places where the coupling loss is large. However, since the length of the third optical fiber 28 is increased to reduce electrical crosstalk, mode conversion at the end of the third optical fiber 28 does not couple with other modes at other junctions. . Therefore, the mode of light transmitted through the optical system in FIG. 1 is considered to be equivalent to an optical system in which the second optical fiber 27 is inserted in a normal single mode optical transmission line in which the higher-order mode attenuates during transmission. .

  In this embodiment, in order to suppress inter-mode interference, the inclination directions of both end faces of the second optical fiber 27 are set as follows. That is, both end faces are inclined with respect to a plane orthogonal to the optical axis (referred to as an orthogonal plane), the optical axis direction is the Z axis, and the plane is a plane parallel to both the X axis and the Y axis. In this case, one of both end surfaces is a surface substantially parallel to the X axis, and the other of both end surfaces is a surface substantially parallel to the Y axis. That is, the angle formed by the inclined rotation axis with respect to the orthogonal surface of one surface and the inclined rotation axis with respect to the orthogonal surface of the other surface is approximately 90 degrees. This angle is referred to as a tilt angle in the tilt direction with respect to the orthogonal plane. The reason why the inter-mode interference can be suppressed by this configuration will be described below.

  The light passing between the end faces of the optical fiber is refracted at the interface of media having different refractive indexes, such as optical fiber, adhesive, each layer of the dielectric multilayer film, and the substrate for the multilayer film. The point at which the light intensity is maximum at the side end face and the point at which the light intensity is maximum at the incident side end face are slightly shifted. The direction of deviation is the X-axis direction when the end face is perpendicular to the optical axis in the YZ sectional view, and the Y-axis direction when the end face is perpendicular to the optical axis in the XZ sectional view. In this configuration, since the boundary surfaces of the refractive indexes are substantially parallel to each other, the incident angle shift to the optical fiber hardly occurs. Therefore, when the end face is perpendicular to the optical axis in the YZ cross-sectional view, the light traveling direction and intensity distribution immediately after incidence on the incident side end face are shifted in the X-axis direction between the optical fibers on the vertical end faces. When the end face is perpendicular to the optical axis in the XZ sectional view, the traveling direction and intensity distribution of the light immediately after incidence on the incident side end face is such that the optical axis between the optical fibers on the vertical end face is the Y axis. It is almost the same as when it is displaced in the direction. If the traveling direction and intensity distribution of the light immediately after incidence on the incident side end face are the same, the coupling efficiency and the higher order mode to be generated are also equal.

  Further, when joining the optical fibers built in the ferrule, a method is often adopted in which the ferrule is inserted into the sleeve, and the adhesive is fixed by applying force from both sides toward the connection point. If this method is used, the end face is perpendicular to the optical axis in the YZ cross-sectional view due to slight misalignment between the ferrule and the sleeve, and the end face is the optical axis in the XZ cross-sectional view. If it is perpendicular to the optical axis, the optical axis tends to shift from the Y axis. Also in this case, the point at which the light amount on the exit surface and the entrance surface peaks is shifted in the above-described direction.

  Considering the above, the mode of light transmitted through the optical system of FIG. 1 is such that the second optical fiber 27 is inserted into a normal single mode optical transmission line in which the higher-order mode attenuates during transmission. It may be considered that the direction of the axis deviation of the optical fiber before and after the fiber 27 is the same as the state where they are different from each other by 90 degrees with respect to the optical axis.

  By the way, Harris DO, Throckmorton RA, "Azimuthal dependence of modal interference in closely spaced single-mode fiber joints", IEEE Photonics Technology Letters, Vol. 6, Issue 10, Oct. 1994 In addition, in a coupling system consisting of three optical fibers into which a short (for example, 17 mm) single-mode optical fiber is inserted, if the directions of axial misalignment of the two joints differ from each other by 90 degrees with respect to the optical axis, It has been shown that the wavelength dependence of the transmitted light intensity, which is the result of interfering interference, is extremely small. The reason why the inter-mode interference is reduced in this manner is that the direction in which the node of the standing wave in the direction perpendicular to the optical axis of the optical fiber increases or decreases by the mode conversion is different between the two junction points. This is because the fundamental mode converted to the higher-order mode at this junction point is not converted to the fundamental mode at the second junction point.

  Since the optical system of FIG. 1 corresponds to the state in which the inter-mode interference is the smallest as described in the above-mentioned document, it is possible to suppress the interference between the higher-order mode and the fundamental mode, and the output light intensity of the optical module. , Fluctuations in received signal strength are suppressed.

In addition, when the loss at the joint between the first optical fiber 26 and the external transmission line optical fiber 32 is large, the distance between the adjacent joints, that is, the first optical fiber 26 and the second optical fiber 26 is the same. The distance between the joint portion of the optical fiber 27 and the joint portion of the second optical fiber 27 and the third optical fiber 28 must be equal to or greater than the distance at which the higher-order mode attenuates while passing through the joint portion. Specifically, the length connecting the first optical fiber 26 and the second optical fiber 27 is set so that the cutoff wavelength of the LP ₁₁ in this optical fiber series is shorter than the wavelength of the transmitted light. There is a need to. If this condition is satisfied, the higher mode generated at the first junction will not be coupled to the fundamental mode at the next adjacent junction, so only inter-mode interference between two adjacent junctions will occur. You should consider it. Since the two joints correspond to the state in which the inter-mode interference described in the document is the smallest, interference between the higher-order mode and the fundamental mode can be suppressed, and the output light intensity of the optical module, the received signal Variation in strength is suppressed. In this case, compared with the case where the inclination direction of the end face of the optical fiber is not changed as in the present embodiment, even if the length of one optical fiber is halved, only the same level of inter-mode interference occurs. The optical path length can be set short, and the optical transceiver module can be miniaturized.

  The first embodiment is an example of an optical transmission / reception module including two light receiving elements, but the present invention includes only one light receiving element as in the second embodiment shown in FIG. An optical transmission / reception module in which end faces of the external transmission line optical fiber 50 and the first optical fiber 47 are obliquely polished may be used. In this case, only when the loss at the joint between the external transmission line optical fiber 50 and the first optical fiber 47 is large, the higher-order mode generated at one of the two joints of the optical fiber becomes the fundamental mode at the other. It is possible to suppress fluctuations in the output light intensity and the received signal intensity that occur due to the combination.

  Further, the present invention may be an optical receiver module of the type inserted into a transmission line as in the third embodiment shown in FIG. In this case, only when the loss at the junction between the external transmission path optical fiber 59 and the first optical fiber 55 and the junction between the external transmission path optical fiber 60 and the third optical fiber 57 is small, the third optical fiber It is possible to suppress fluctuations in the output light intensity and the received signal intensity, which are generated when the higher-order mode generated at one end of 57 is coupled to the fundamental mode at the other end. If the loss is large, the influence of mode conversion at the end of the optical fiber on the external optical transmission line cannot be ignored, so the effect of suppressing fluctuation is considered to be small.

  Although the said embodiment was demonstrated as an optical receiver module or an optical transmission / reception module, this invention can be grasped | ascertained as an optical fiber in these embodiments, an optical waveguide, or an optical apparatus. The optical device referred to in the present invention includes an optical component as a part of an optical device having a certain function.

  According to the present invention, it is possible to suppress fluctuations in transmitted light intensity of the optical system due to interference between the higher-order mode and the fundamental mode without using an optical fiber having a special structure. Useful for.

Schematic diagram of the basic configuration of the optical transceiver module according to the first embodiment of the present invention. Schematic diagram showing an example in which a holding member is provided in the basic configuration of FIG. 1A Schematic diagram showing an example in which the holding member directly holds the optical fiber instead of the configuration of FIG. 1B Sectional drawing of the split sleeve which can be used as a holding member of FIG. 1B and FIG. 1C Sectional drawing which shows in detail the part which connects optical fibers in the optical transmission / reception module in the 1st Embodiment of this invention Filter implementation example Example of filter mounting on a waveguide The block diagram of the optical transmission / reception module in the 2nd Embodiment of this invention The block diagram of the optical receiver module in the 3rd Embodiment of this invention (A) is explanatory drawing which shows mode conversion which arises by position shift of an optical axis, (b) is explanatory drawing which shows mode conversion which arises by angle shift of an optical axis. Structure diagram of conventional optical transceiver module Characteristics of conventional optical fiber that suppresses higher-order modes

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 1a Step part 2 Connection part 2a Guide groove 3 1st receiving part 4 Transmitting part 5 2nd receiving part 6 Optical waveguide 6a Lower clad layer 6b Core layer 6c Upper clad layer 7 Reflective optical filter 9 Half mirror 10 Photo Diode 11 Laser diode 12 Photodiode for monitoring 21, 44 Light emitting element 22, 51 First light receiving element 23, 52 Second light receiving element 24, 37, 42, 46 Wavelength selection filter 25 Half mirror 26, 47, 55 First Optical fiber 27, 48, 56 Second optical fiber 28, 57 Third optical fiber 29 First ferrule 30 Second ferrule 31 Third ferrule 32, 50, 59, 60 External transmission line optical fiber 33 External Ferrule for transmission line 34, 61 Optical fiber 35, 49, 58 Ferrule 36 Groove 38, 4 3, 45 Light receiving element 39 Optical waveguide substrate 40 Optical waveguide 41 Groove 53 First wavelength selection filter 54 Second wavelength selection filter 62 Core 63 Clad 70, 72 Holding member 74 Slit

Claims (14)

  In an optical fiber having a short length in the optical axis direction, both end faces are inclined with respect to an orthogonal plane orthogonal to the optical axis, and one of the two end faces is inclined with respect to the orthogonal plane. And an angle of deviation in a direction in which the other of the two end faces is inclined with respect to the orthogonal plane is approximately 90 degrees.   In an optical waveguide having a short length in the optical axis direction, both end faces are inclined with respect to an orthogonal plane orthogonal to the optical axis, and one of the two end faces is inclined with respect to the orthogonal plane. And an angle of deviation in a direction in which the other of the two end faces is inclined with respect to the orthogonal plane is approximately 90 degrees.   In an optical fiber having a short length in the optical axis direction and having a plurality of grooves in a portion between both ends, each of the surfaces including the plurality of grooves is inclined with respect to an orthogonal plane orthogonal to the optical axis. The angle of deviation between the direction in which the surface including each of the plurality of grooves is inclined with respect to the orthogonal surface and the direction in which the surface of the groove adjacent thereto is inclined with respect to the orthogonal surface is approximately 90 degrees. An optical fiber characterized by   In an optical waveguide having a short length in the optical axis direction and having a plurality of grooves in a portion between both ends, each of the surfaces including the plurality of grooves is inclined with respect to an orthogonal plane orthogonal to the optical axis. The angle of deviation between the direction in which the surface including each of the plurality of grooves is inclined with respect to the orthogonal surface and the direction in which the surface of the groove adjacent thereto is inclined with respect to the orthogonal surface is approximately 90 degrees. An optical waveguide characterized by   In an optical fiber having a short length in the optical axis direction and provided with a plurality of grooves in a portion between both ends, both end faces are inclined with respect to a plane orthogonal to the optical axis, and the plurality of grooves are provided. Each of the included surfaces is inclined with respect to an orthogonal surface orthogonal to the optical axis, and a direction in which the surface including each of the plurality of grooves is inclined with respect to the orthogonal surface, and a surface of the groove adjacent thereto are provided. The angle of deviation in the direction inclined with respect to the orthogonal plane is approximately 90 degrees, and a plane including the grooves adjacent to each of the two end faces is inclined with respect to the orthogonal plane. An optical fiber characterized in that the angle of deviation between the direction and the direction in which the end face adjacent to the direction is inclined with respect to the orthogonal plane is approximately 90 degrees.   In an optical waveguide having a short length in the optical axis direction and provided with a plurality of grooves in a portion between both ends, both end faces are inclined with respect to a plane perpendicular to the optical axis, and the plurality of grooves are Each of the included surfaces is inclined with respect to an orthogonal surface orthogonal to the optical axis, and a direction in which the surface including each of the plurality of grooves is inclined with respect to the orthogonal surface, and a surface of the groove adjacent thereto are provided. The angle of deviation in the direction inclined with respect to the orthogonal plane is approximately 90 degrees, and a plane including the grooves adjacent to each of the two end faces is inclined with respect to the orthogonal plane. An optical waveguide characterized in that an angle between a direction and a direction in which an end face adjacent to the direction is inclined with respect to the orthogonal plane is approximately 90 degrees.   A diameter substantially equal to the diameter of the optical fiber for inserting the tip or the whole of the optical fiber for connecting the optical fiber according to any one of claims 1, 3, and 5 to another optical fiber. Or an optical device having a holding part with a slightly larger inner diameter.   A direction in which the connection between the optical fiber according to any one of claims 1, 3, and 5 and another optical fiber is parallel to the optical axis at a connection point and faces each other with respect to one or both of the optical fibers. The optical device according to claim 7, wherein the optical device is subjected to a step of applying pressure to the optical device.   A plurality of light receiving elements, the optical fiber according to any one of claims 1, 3, and 5, and a groove in the optical fiber, are placed at different locations, and for each of the plurality of light receiving elements, An optical receiver module comprising two or more wavelength selective filters that transmit, by reflection, light in a specific wavelength range of optical fiber transmission light.   A plurality of light receiving elements, the optical waveguide according to any one of claims 2, 4, and 6, and a groove in the optical waveguide, are placed at different locations, and each of the plurality of light receiving elements, An optical receiver module comprising two or more wavelength selective filters that transmit, by reflection, light in a specific wavelength range out of optical waveguide transmission light.   A plurality of light receiving elements, the optical fiber according to any one of claims 1, 3, and 5, and a groove in the optical fiber, are placed at different locations, and for each of the plurality of light receiving elements, Two or more wavelength selection filters that transmit light in a specific wavelength range by reflection among optical fiber transmission light, or one or more wavelength selection filters and a half mirror, and a light emitting element that transmits light to one end of the optical fiber Optical transmission / reception module.   A plurality of light receiving elements, the optical waveguide according to any one of claims 2, 4, and 6, and a groove in the optical waveguide, are placed at different locations, and each of the plurality of light receiving elements, Two or more wavelength selective filters that transmit light in a specific wavelength range by reflection in the optical waveguide transmission light, or one or more wavelength selective filters and a half mirror, and a light emitting element that transmits light to one end of the optical waveguide Optical transmission / reception module.   A light receiving element, the optical fiber according to any one of claims 1, 3, and 5, and a groove in the optical fiber, are placed at different locations, and the optical fiber transmission light is placed on the light receiving element. An optical transmission / reception module comprising: a wavelength selection filter that transmits light in a specific wavelength range by reflection; and a light emitting element that transmits light to one end of the optical fiber. A light receiving element, the optical waveguide according to any one of claims 2, 4, and 6, and the optical waveguide disposed in different locations in the groove of the optical waveguide, and each of the plurality of light receiving elements An optical transmission / reception module comprising: a wavelength selection filter that transmits, by reflection, light in a specific wavelength range of transmitted light; and a light emitting element that transmits light to one end of the optical waveguide.