JP2013061587A - Beam splitter and optical communication module using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a beam splitter that can properly set a branch ratio to branch incident light into transmitted light and reflected light by a simple configuration, and to provide an optical communication module using the same.SOLUTION: A beam splitter 1 that branches incident light into transmitted light and reflected light includes a reflection surface 11 inclined at an angle larger than a critical angle with respect to the optical axis of the incident light, and a transmission surface 12 transmitting a part of the incident light. The transmission surface 12 has the incident angle of a Brewster angle or smaller with respect to the optical axis of the incident light, and is formed on a part of the reflection surface 11.

Description

  The present invention relates to a beam splitter and an optical communication module using the beam splitter, and more particularly a beam splitter capable of appropriately setting a branching ratio and branching incident light into transmitted light and reflected light with a simple configuration. The present invention relates to an optical communication module using the above.

  With the expansion of the Internet and data communication, optical communication systems that transmit signals using optical fibers have become widespread. An optical communication module used in an optical communication system includes a semiconductor laser as a light source, an optical fiber as a transmission medium, and optical elements such as a collimator lens and a condenser lens. In the optical communication module, light emitted from the semiconductor laser passes through optical elements such as a collimator lens and a condenser lens, and is coupled to the end face of the optical fiber with high coupling efficiency.

  It is known that the wavelength of light emitted from a semiconductor laser changes due to the temperature change of the usage environment and the influence of aging. This wavelength variation may cause interference between a plurality of signals transmitted by the optical communication module and reduce the reception sensitivity. To prevent this, a beam splitter is inserted as an optical branching element in the middle of the transmission path so that the light from the semiconductor laser is received by the optical fiber and a part of the light from the semiconductor laser is branched to monitor wavelength fluctuations. doing. By monitoring the wavelength variation, for example, the temperature of the semiconductor laser and the drive current can be adjusted to appropriately control the wavelength of the emitted light. An optical communication module using such a beam splitter is disclosed in Patent Document 1 and Patent Document 2.

  FIG. 10 shows a conventional beam splitter 101 used in an optical communication module. As shown in FIG. 10, the conventional beam splitter 101 includes two triangular prisms 110 a and 110 b having an inclined surface of 45 °, and the inclined surfaces of the prism splitters 110 a and 110 b are interposed via an adhesive layer 109. Are pasted together. The beam splitter 101 having such a configuration is disclosed in Patent Document 3.

  In the conventional beam splitter 101 shown in FIG. 10, when incident light is incident from the X1 direction, transmitted light transmitted in the X2 direction at the interface between the inclined surfaces where the two triangular prisms 110a and 110b are bonded together And the reflected light reflected in the Z1 direction. As described in Patent Document 1, transmitted light and reflected light are usually branched by about 50% and transmitted to an optical fiber or a photodiode.

Japanese Patent Laid-Open No. 5-60937 Japanese Patent Application Laid-Open No. 10-079551 JP 2009-244201 A

  In an optical communication module, wavelength monitoring is usually possible with light having an intensity smaller than that of an optical signal received by an optical fiber. For example, if there is a light intensity of about 10 to 20% of light emitted from a semiconductor laser, monitoring is possible. Is possible. However, as shown in Patent Document 1, when the light from the semiconductor laser is branched using the beam splitter 101, about 50% of the emitted light from the semiconductor laser is branched to the photodiode for wavelength monitoring. Since the branched light is not received by the optical fiber, it does not contribute to signal transmission. Therefore, in the optical communication module using the conventional beam splitter 101, when the reflected light and the transmitted light are branched by about 50%, the light not contributing to the optical communication increases and the light received by the optical fiber. There is a risk that the signal quality will deteriorate due to a decrease in the signal strength.

  In order to adjust the light branching ratio with the conventional beam splitter 101, it is necessary to form a multilayer film made of a dielectric layer or a metal layer on one of the inclined surfaces of the two prisms 110a and 110b. When forming a multilayer film made of a dielectric layer or a metal layer, it is necessary to design each film thickness and configuration of the multilayer film according to the branching ratio using a plurality of materials having different dielectric constants, and the number of stacked layers is several tens. Manufacturing costs increase because they may extend to layers. Furthermore, since the branching ratio changes depending on the thickness of the adhesive layer 109, the thickness accuracy of the adhesive layer 109 is strictly required. In addition, multiple reflection and light absorption occur in the multilayer film between the prisms 110a and 110b and the adhesive layer 109, resulting in a problem that the light efficiency is lowered. Therefore, in the beam splitter 101 having the conventional configuration, it is difficult to appropriately branch the branching ratio between the transmitted light and the reflected light.

  The present invention provides a beam splitter capable of solving the above-mentioned problems and branching incident light into transmitted light and reflected light with a simple configuration by appropriately setting a branching ratio and an optical communication module using the same. The purpose is to provide.

  The beam splitter of the present invention has a reflection surface formed to be inclined at an angle larger than a critical angle with respect to an optical axis of incident light, and a transmission surface that transmits a part of the incident light, and the transmission The surface is provided on a part of the reflecting surface with an inclination angle equal to or less than the Brewster angle with respect to the optical axis of incident light.

  According to the present invention, the incident light incident on the beam splitter is totally reflected by the reflecting surface having an inclination angle larger than the critical angle. Part of the incident light is transmitted through a transmission surface having an inclination angle equal to or smaller than the Brewster angle. The branching ratio between the transmitted light and the reflected light can be easily set by changing the area ratio between the transmissive surface and the reflective surface without providing a multilayer film made of a dielectric layer or a metal film layer. It can also be set by changing the position of the transmission surface with respect to the intensity distribution of the incident light. Therefore, according to the beam splitter of the present invention, it is possible to branch incident light into transmitted light and reflected light with a simple configuration by appropriately setting a branching ratio.

  The beam splitter of the present invention is preferably configured to have a prism, and the reflection surface and the transmission surface are preferably formed integrally with the prism. According to this, since the reflecting surface and the transmitting surface are formed by one prism without preparing two prisms and bonding them through the adhesive layer, the manufacturing cost can be reduced. Further, it is possible to reduce the multiple reflection and light absorption in the multilayer film and adhesive layer made of the dielectric layer and the metal film layer, and to efficiently split the incident light into the reflected light and the transmitted light.

  It is preferable that an antireflection film is formed on the transmission surface. In this way, it is possible to prevent incident light from being reflected by the transmission surface and returning to the direction of the light source such as a semiconductor laser, and thus it is possible to suppress light loss.

  The beam splitter of the present invention has an incident surface on which the incident light is incident and an exit surface from which the reflected light exits, and an optical functional surface is formed on at least one of the incident surface and the exit surface. Is preferred. Here, the optical function surface is a surface having an optical function such as a function of condensing incident light, a function of converting into parallel light, and a beam shape shaping function. According to this, when an optical functional surface is formed on the incident surface, the incident light travels from the diverging light as parallel light, so that reflection and scattering inside the beam splitter is prevented and the light is branched at an appropriate branching ratio. It becomes possible to do. Further, the light reflected by the reflecting surface is transmitted through the optical function surface of the emitting surface, so that it is efficiently collected on the end surface of the transmission medium such as an optical fiber. Therefore, the light branched by the beam splitter is efficiently transmitted to the outside. Furthermore, when the beam splitter is assembled as an optical communication module, the number of optical elements and the optical path length can be reduced, and the optical coupling efficiency of the optical communication module can be improved. Further, since the number of parts can be reduced, the manufacturing cost can be reduced.

  An optical communication module of the present invention includes a semiconductor laser, an optical fiber that receives light from the semiconductor laser, a light receiving element that receives light from the semiconductor laser, the semiconductor laser, the optical fiber, and the semiconductor laser. And a beam splitter for optically coupling the light receiving element, and the beam splitter is any one of the beam splitters described above. According to this, it is not necessary to provide a multilayer film made of a dielectric layer or a metal film layer as compared with the case of using a conventional beam splitter, and with a simple configuration, an incident light can be set by appropriately setting a branching ratio. It is possible to branch into transmitted light and reflected light. In addition, the branching ratio between the light contributing to the optical communication and the light required for monitoring can be set appropriately, and the optical coupling efficiency between the semiconductor laser and the optical fiber can be improved.

  According to the present invention, the incident light incident on the beam splitter is totally reflected by the reflecting surface having an inclination angle larger than the critical angle. Part of the incident light is transmitted through a transmission surface having an inclination angle equal to or smaller than the Brewster angle. The branching ratio between the transmitted light and the reflected light can be easily set by changing the area ratio between the transmissive surface and the reflective surface without providing a multilayer film made of a dielectric layer or a metal film layer. It can also be set by changing the position of the transmission surface with respect to the intensity distribution of the incident light. Therefore, according to the beam splitter of the present invention, it is possible to branch incident light into transmitted light and reflected light with a simple configuration by appropriately setting a branching ratio.

It is a perspective view of the beam splitter in the 1st embodiment of the present invention. It is a schematic cross section which shows the branch of light in the beam splitter of 1st Embodiment. It is a perspective view showing the 1st modification in a 1st embodiment. It is a perspective view showing the 2nd modification in a 1st embodiment. It is a perspective view which shows the 3rd modification in 1st Embodiment. It is a schematic cross section of the beam splitter in the 2nd Embodiment of this invention. It is a schematic cross section which shows the 1st modification in 2nd Embodiment. It is a schematic cross section which shows the 2nd modification in 2nd Embodiment. It is a schematic plan view of the optical communication module in the 3rd Embodiment of this invention. The transmission perspective view of the beam splitter in a prior art example is shown.

<First Embodiment>
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the beam splitter 1 in the first embodiment, and FIG. 2 is a schematic diagram of the beam splitter 1 for explaining a method of branching incident light into reflected light and transmitted light. A cross-sectional view is shown.

  As shown in FIG. 1, the beam splitter 1 of the present embodiment is configured to include a triangular prism 10. In this embodiment, the triangular prism 10 is formed in a right triangular prism using an optical glass material having a refractive index of about 1.5. The beam splitter 1 includes an incident surface 13 on which incident light is incident (surface on the X1 side), a reflective surface 11 inclined by about 45 ° with respect to the incident surface 13, and light reflected by the reflective surface 11 is transmitted to the outside. And a light exit surface 14 (a surface on the Z1 side). The entrance surface 13 and the exit surface 14 are formed at positions substantially orthogonal to each other.

  A transmission surface 12 that transmits a part of incident light is formed on a part of the reflection surface 11. As shown in FIG. 1, in the present embodiment, the transmission surface 12 is formed such that a part of the reflection surface 11 protrudes in the traveling direction (X2 direction) of the transmitted light. The transmission surface 12 is formed integrally with the triangular prism prism 10 so as to have an incident angle substantially perpendicular to the optical axis of the incident light.

  As shown in FIG. 2, incident light A is incident substantially perpendicular to the incident surface 13 of the beam splitter 1. Incident light A is obtained by making light from a light source such as a semiconductor laser into parallel light by an optical element such as a collimating lens. The incident light A passes through the incident surface 13 and travels toward the reflecting surface 11 and the transmitting surface 12 (X2 direction). Incident light A traveling toward the reflecting surface 11 is reflected by the reflecting surface 11 and its traveling direction is converted in the direction of the exit surface 14 (Z1 direction). Then, the reflected light B emitted from the emission surface 14 to the outside is received by an optical fiber (not shown) through an optical element such as a condenser lens. The reflecting surface 11 is formed so as to be inclined with respect to the incident light A so as to have an incident angle D greater than a critical angle (in this embodiment, it is formed at about 45 °). Thereby, since the incident light A is totally reflected by the reflecting surface 11, the optical loss in the reflecting surface 11 of the beam splitter 1 is reduced, and the intensity of the optical signal transmitted to the optical fiber can be improved.

  In addition, an incident angle shows the angle which the optical axis of the incident light makes and the normal line of the incident surface. The critical angle is the smallest incident angle at which incident light is totally reflected, and is an angle determined by the refractive index of the material. In this embodiment, an optical glass material having a refractive index of about 1.5 is used, and the critical angle for light traveling from glass to air is about 42 °. In addition, when a material having a different refractive index is used, the critical angle also changes. For example, when an optical glass material having a refractive index of 1.7 is used, the critical angle is about 36 °. Therefore, the incident light A is totally reflected by inclining the reflecting surface 11 so as to have an incident angle D larger than the critical angle, not limited to the inclination angle of 45 ° in the present embodiment.

  As shown in FIG. 2, part of the incident light A travels toward the transmission surface 12 and is emitted from the transmission surface 12 as transmitted light C in the X2 direction. The transmitted light C is received by a light receiving element such as a photodiode (not shown) in order to monitor the wavelength variation of the light of the semiconductor laser. The transmission surface 12 preferably has an inclination angle equal to or less than the Brewster angle with respect to the optical axis of the incident light A. If it carries out like this, it can suppress that incident light A is reflected by the transmissive surface 12, and can permeate | transmit the transmissive surface 12 efficiently.

  The Brewster angle is an angle at which the reflectance of p-polarized light, which is a polarization component parallel to the incident surface, becomes 0. When the incident angle is increased from 0 °, the reflectance of p-polarized light gradually increases. And the reflectivity becomes 0 at the Brewster angle. When the Brewster angle is exceeded, the reflectance of p-polarized light tends to increase rapidly. For s-polarized light, which is a component perpendicular to the incident surface, the reflectance gradually increases as the incident angle is increased from 0 °, and the reflectance increases above the Brewster angle. Both p-polarized light and s-polarized light are totally reflected at an angle of incidence greater than the critical angle. Therefore, by setting the angle of the transmission surface 12 with respect to the incident light A to be equal to or less than the Brewster angle, it is possible to efficiently extract the transmission light C while suppressing an increase in reflectance on the transmission surface 12. For example, in the case of an optical glass material having a refractive index of about 1.5, the Brewster angle is about 33 °, and in the case of an optical glass material having a refractive index of 1.7, the Brewster angle is about 30 °.

  In the beam splitter 1 of the present embodiment, the branching ratio between the reflected light B and the transmitted light C is easily set by changing the area ratio between the transmitting surface 12 and the reflecting surface 11 in the region irradiated with the incident light A. can do. It can also be set by changing the position of the transmission surface 12 with respect to the intensity distribution of the incident light A. It is known that a beam of a semiconductor laser as a light source has an intensity distribution according to a Gaussian distribution. The beam intensity is large near the center of the cross-sectional shape perpendicular to the optical path of the incident light A, and the beam intensity decreases toward the peripheral edge. Therefore, when the transmission surface 12 is formed near the center of the incident light A, the necessary transmitted light C can be extracted with a smaller area. Further, when the transmission surface 12 is formed in the vicinity of the outer edge of the incident light A, it is necessary to form the transmission surface 12 with a relatively large area. In this case, light near the central portion where the beam intensity is high is used as reflected light B. Since it can be coupled to a fiber or the like, the quality of the optical signal can be improved. Thus, the branching ratio between the reflected light B and the transmitted light C is appropriately determined by determining the area ratio between the reflecting surface 11 and the transmitting surface 12 and the position of the transmitting surface 12 in consideration of the beam intensity distribution of the incident light A. It becomes possible to set to. Therefore, according to the beam splitter 1 of the present invention, the incident light A can be transmitted through the light by appropriately setting the branching ratio with a simple configuration without designing and forming a multilayer film made of a dielectric layer or a metal layer. It is possible to branch into C and reflected light B.

  As shown in FIG. 1, in the beam splitter 1 of the present embodiment, the transmission surface 12 is formed so as to be located closer to the Z1 side than the vicinity of the center of the reflection surface 11, and extends in the Y1-Y2 direction. Is provided. However, the present invention is not limited to this mode, and the shape and area of the transmission surface 12 can be appropriately set according to the beam diameter and beam shape of the incident light A or the branching ratio of the light to be branched.

  In the conventional beam splitter 101, incident light is branched by being transmitted or reflected through a multilayer film made of an adhesive layer 109 or a dielectric layer between two prisms 110a and 110b. In this case, multiple reflections or light absorption may occur in the adhesive layer 109 or the multilayer film, and light loss may occur, resulting in a decrease in optical signal output. In addition, if an air layer is interposed at the bonding interface between the two triangular prisms 110a and 110b, there is a risk that light loss occurs and the transmitted signal is deteriorated. In addition, when an air layer is present at the bonding interface, there arises a problem that the adhesive strength is lowered and a problem that environmental resistance cannot be sufficiently obtained due to intrusion of moisture in the air. Therefore, advanced bonding technology is required in manufacturing the beam splitter 101.

  In the beam splitter 1 of the present embodiment, the transmission surface 12 is formed integrally with the triangular prism 10. Therefore, since the reflecting surface 11 and the transmitting surface 12 are formed by one prism 10 without preparing two prisms and bonding them via an adhesive layer, a multilayer film composed of a dielectric layer or a metal layer, and Multiple reflections and light absorption at the adhesive layer 109 can be reduced, and the reflected light B and transmitted light C can be emitted efficiently.

  In the present embodiment, as shown in FIGS. 1 and 2, the transmission surface 12 is formed to have an angle substantially perpendicular to the incident light A (incident angle D = 0 °). In this way, it is possible to suppress the reflection of the incident light A on the transmission surface 12 and reduce the light returning to the inside of the prism 10, and efficiently transmit the incident light A incident on the transmission surface 12. It is possible to make it. Similarly, it is preferable that the incident surface 13 is formed substantially perpendicular to the incident light A and the output surface 14 is formed substantially perpendicular to the reflected light B. By so doing, it is possible to improve the optical coupling efficiency by preventing the reflection of the incident light A on the incident surface 13 and suppressing the reflection of the reflected light B on the exit surface 14.

  The beam splitter 1 in this embodiment can be formed by press molding using an optical glass material having a refractive index of about 1.5. Therefore, the same process as the process for manufacturing the triangular prisms 110a and 110b shown in the conventional example can be performed on the transmission surface 12 protruding from a part of the reflection surface 11 by changing the mold used for press molding. Thereby, it can shape | mold integrally. Further, according to the beam splitter 1 of the present embodiment, unlike the conventional beam splitter 101, it is not necessary to prepare and bond the two triangular prisms 110a and 110b, so that the manufacturing cost can be reduced. .

  In the present embodiment, the beam splitter 1 in which the transmission surface 12 is formed integrally with the prism 10 is shown. However, the reflection surface 11 and the transmission surface 12 may be provided separately. In this case, the transmission surface 12 is provided on a part of the reflection surface 11 by preparing and bonding two prisms having different sizes. Even in such an embodiment, it is not necessary to provide a multilayer film composed of a dielectric layer or a metal film layer, and therefore, with a simple configuration, the incident light A is appropriately set to the transmitted light C and the reflected light with the branching ratio set appropriately. It is possible to branch to B. Further, even if the reflection surface 11 and the transmission surface 12 are provided separately, the reflected light B is totally reflected by the reflection surface 11 without being affected by the adhesive layer, so that light loss is reduced. Can do. That is, the reflected light B that is branched to transmit the optical communication signal is efficiently branched.

  Further, in the beam splitter 1 of the present embodiment, the triangular prism 10 is used, but it is not limited to such a mode. Even in the case of prisms of other shapes such as a flat plate shape and polygonal shape, incident light can be set with a simple configuration and a suitable branching ratio by providing a transmission surface on a part of the reflection surface as in this embodiment. Can be branched into transmitted light and reflected light.

  3 to 5 are perspective views of a beam splitter 1, which is a modification of the present embodiment. In the first modification shown in FIG. 3, the transmission surface 12 is not provided with a length equal to the width of the prism 10 in the Y1-Y2 direction, but is provided in a part of the Y1-Y2 direction. Therefore, the area of the transmission surface 12 can be reduced compared to the beam splitter 1 of FIG. 1, and the branching ratio of the transmitted light C can be reduced. Further, when the incident light A has a Gaussian intensity distribution, an equivalent branching ratio of the transmitted light C can be obtained with a smaller area of the transmission surface 12 if the transmission surface 12 is formed closer to the center.

  Further, in the beam splitter 1 in the second modification shown in FIG. 4, a plurality of transmission surfaces 12 extending in the Y1-Y2 direction are formed at intervals in the Z1-Z2 direction. In this manner, by providing a plurality of transmission surfaces 12, it is possible to increase the area of the transmission surface 12 and increase the branching ratio of the transmitted light C. In this case, since the incident light A in the vicinity of the central portion having a large light intensity is reflected by the reflecting surface 11 and received by the optical fiber, a decrease in signal intensity is suppressed.

  In the beam splitter 1 shown in FIG. 1 to FIG. 4, a transmission surface 12 is formed by projecting a part of the reflection surface 11 of the triangular prism 10. However, the present invention is not limited to this, and the transmission surface 12 may be formed by indenting part of the reflection surface 11 toward the incident surface 13 like the beam splitter 1 of the third modification shown in FIG. . Even in such an embodiment, the area and position of the transmission surface 12 can be changed as in FIGS. 3 and 4, and the branching ratio between the reflected light B and the transmitted light C can be set appropriately. Can do.

Further, it is preferable to provide an antireflection film 20 on the transmission surface 12. Accordingly, it is possible to suppress the incident light A from being reflected by the transmission surface 12 and returning to the inside of the beam splitter 1. Magnesium fluoride (MgF ₂ ) can be used as the antireflection film 20 and is formed by a thin film method such as a vapor deposition method. Magnesium fluoride (MgF ₂ ) is a low-refractive material having a refractive index of about 1.38, can suppress reflected light with a single layer, and has low light absorption and loss.

  Note that the antireflection film 20 can be similarly formed on the incident surface 13 and the exit surface 14. In this way, it is possible to prevent the incident light A from being reflected by the incident surface 13 and returning to the light source side. In addition, the reflected light B is reflected from the exit surface 14 and the light returning to the inside of the prism 10 is suppressed.

<Second Embodiment>
In FIG. 6, the schematic cross section of the beam splitter 2 in 2nd Embodiment is shown. In addition, about the same component as the beam splitter 1 in 1st Embodiment, the same code | symbol is attached | subjected and the detailed description is abbreviate | omitted.

  As shown in FIG. 6, in the beam splitter 2 in the second embodiment, the reflection surface 11 that reflects the incident light A is formed and a part of the incident light A is obtained as in the first embodiment. A transmitting surface 12 that transmits light is provided on a part of the reflecting surface 11. Thereby, the incident light A can be branched into the reflected light B and the transmitted light C by appropriately setting the branching ratio.

  As shown in FIG. 6, in this embodiment, an optical function surface 22 is formed on a part of the incident surface 13. In the present embodiment, the optical functional surface 22 is a collimating lens that converts divergent light into parallel light. As shown in FIG. 6, when divergent light from the semiconductor laser 31 is incident as incident light A and passes through the optical function surface 22, it travels as parallel light inside the beam splitter 2. The parallel light is reflected by the reflecting surface 11 and emitted to the outside as reflected light B, and a part of the parallel light is transmitted through the transmitting surface 12 and branched as transmitted light C. If the divergent light from the semiconductor laser 31 is incident on the beam splitter 2 without being converted into parallel light, unnecessary reflection inside the beam splitter 2 increases and the light loss increases. According to the beam splitter 2 of the present embodiment, divergent light is converted into parallel light by the optical function surface 22, so that internal reflection can be suppressed and light loss can be suppressed. Further, the incident light A is converted into parallel light and travels to the reflecting surface 11 and the transmitting surface 12, so that the branching ratio can be set appropriately and the reflected light B and the transmitted light C can be branched. .

  The optical function surface 22 is preferably formed to have a shape larger than the cross-sectional shape of the incident light A on the incident surface 13. By so doing, light loss at the incident surface 13 can be reduced, and most of the incident light A is converted into parallel light.

  In addition, when the beam splitter 2 of the present embodiment is incorporated into an optical communication module, it is not necessary to provide an optical element such as a collimator lens between the semiconductor laser 31 and the beam splitter 2, thereby reducing optical components. Manufacturing costs can be reduced. In addition, the optical path length between the semiconductor laser 31 and the beam splitter 2 can be shortened, which is advantageous for improving the optical coupling efficiency and reducing the size of the optical communication module.

  The beam splitter 2 in the present embodiment can be formed by press molding using an optical glass material, similarly to the beam splitter 1 in the first embodiment. That is, even when the optical function surface 22 is provided on the incident surface 13, the prismatic prism 10, the optical function surface 22, and the protruding surface 12 are integrally formed in the same process, so that the manufacturing cost is suppressed. .

  FIG. 7 is a schematic cross-sectional view of the beam splitter 2 showing a first modification of the second embodiment. In this modification, an optical function surface 23 is formed on the emission surface 14. The optical function surface 23 is not particularly limited, but can be a condensing lens for receiving the reflected light B on the end surface of the optical fiber 33. In this case, the optical function surface 23 is preferably an aspheric lens that corrects spherical aberration. The optical function surface 23 is preferably formed in a shape larger than the cross-sectional shape of the reflected light B. According to this, the light loss at the emission surface 14 is suppressed, and the reflected light B branched at the reflection surface 11 is efficiently coupled to the end surface of the optical fiber 33.

  Further, when such a beam splitter 2 is incorporated into a communication module, there is no need to separately provide a condensing lens for condensing the reflected light B onto the end face of the optical fiber 33. The optical path length with the beam splitter 2 can be shortened, leading to improvement in optical coupling efficiency and downsizing of the optical communication module. Moreover, since only the alignment between the reflected light B and the optical fiber 33 is required when installing each optical member, it is easy to improve the optical coupling efficiency.

  Further, in the beam splitter 2 shown in FIGS. 6 and 7, it is possible to provide the optical function surface 22 on the entrance surface 13 and also provide the optical function surface 23 on the exit surface 14. In this way, when an optical communication module is used, optical members such as a collimating lens and a condenser lens can be omitted, and the communication module can be downsized. In addition, since the optical length from the semiconductor laser 31 as the light source to the optical fiber 33 as the light receiving unit can be shortened, it is possible to improve the optical coupling efficiency.

  In FIG. 8, the schematic cross section of the beam splitter 2 which is the 2nd modification of 2nd Embodiment is shown. As in this modification, the optical function surface 24 may be provided on the transmission surface 12. When the transmitted light C is received by the light receiving surface of the photodiode 32, it is possible to efficiently receive the light by providing the optical function surface 24 such as a condenser lens. Even when a plurality of transmission surfaces 12 are formed, the transmitted light C is efficiently received by the light receiving surface of the photodiode 32 by forming the optical function surface 24 for each.

<Third Embodiment>
FIG. 9 shows a schematic plan view of an optical communication module 3 using the beam splitter 1 of the first embodiment. The optical communication module 3 includes a semiconductor laser 31 as a light source, an optical fiber 33 as a transmission medium, a photodiode 32 for monitoring wavelength fluctuations, a beam splitter 1 for branching light from the semiconductor laser 31, and the like in a package 50. Arranged and configured. The divergent light emitted from the semiconductor laser 31 passes through the collimator lens 41 and is converted into parallel light. The parallel light transmitted through the collimator lens 41 is incident on the incident surface 13 of the beam splitter 1 as incident light A, and a part of the incident light A is reflected by the reflecting surface 11 and travels toward the emitting surface 14 to be reflected light. It is emitted as B. The reflected light B is collected by the condenser lens 42 and coupled to the end face of the optical fiber 33. In this manner, the optical signal from the semiconductor laser 31 is coupled to the optical fiber 33 via the beam splitter 1, and optical communication using the optical fiber 33 as a transmission medium can be realized.

  In addition, the wavelength of light emitted from the semiconductor laser 31 may change due to the influence of temperature and aging. When the wavelength variation occurs, crosstalk and reception sensitivity may be reduced, and transmission characteristics may be deteriorated. In order to prevent such a problem, a part of the light from the semiconductor laser 31 is monitored to control the wavelength of the light from the semiconductor laser 31.

  As shown in FIG. 9, in the optical communication module 3 of the present embodiment, a part of the incident light A is transmitted through the transmission surface 12 and is coupled to the photodiode 32 for monitoring the wavelength variation. A band pass filter 43 is disposed between the transmission surface 12 and the photodiode 32, and only light in a predetermined wavelength region is transmitted and coupled to the photodiode 32. The bandpass filter 43 has a characteristic of transmitting a certain range of light with the wavelength of the semiconductor laser 31 as the center wavelength, for example. The photodiode 32 is an element that generates a current according to the amount of light received. Therefore, when the wavelength variation of the light from the semiconductor laser 31 occurs, a part of the transmitted light C that passes through the bandpass filter 43 is limited, and the amount of light received by the photodiode 32 changes. The change in the current of the photodiode 32 caused thereby is transmitted to a wavelength control unit (not shown), and the wavelength of the light of the semiconductor laser 31 is controlled based on the change in the current signal.

  In the optical communication module 3 of the present embodiment, it is the reflected light B received by the optical fiber 33 among the incident light A that contributes to the transmission of the optical signal, and is transmitted from the incident light A that is branched and used for monitoring. The light C is not used for optical communication signals. Therefore, when the amount of transmitted light C increases, the amount of reflected light B received by the optical fiber 33 relatively decreases, causing a problem that the quality of the optical signal deteriorates. In the present embodiment, by using the beam splitter 1, the branching ratio between the reflected light B and the transmitted light C can be appropriately set with a simple configuration. Thereby, since the light quantity required for monitoring can be branched as transmitted light C, the light quantity of the reflected light B received by the optical fiber 33 can be sufficiently secured. In the beam splitter 101 of the conventional example, light absorption and loss occur due to the adhesive layer 109 and the multilayer film provided on the joint surfaces of the two triangular prisms 110a and 110b. Since it is composed of the two prisms 10, the incident light A is efficiently branched. Therefore, according to the optical communication module 3 of the present embodiment, the optical coupling efficiency between the semiconductor laser 31 and the optical fiber 33 can be improved.

  The branching ratio of the transmitted light C used for monitoring is determined by the light intensity of the semiconductor laser 31, the light receiving sensitivity of the photodiode 32, and the like. For example, 10% to 20% of the light emitted from the semiconductor laser 31 When about% is branched as transmitted light C, the wavelength can be monitored. In the present embodiment, by appropriately providing the position and area of the transmission surface 12 on the reflection surface 11, the light can be branched at a branching ratio of 10% to 20%, and 80% to 90% of the light of the semiconductor laser 31. Are coupled to the optical fiber 33.

  In the optical communication module 3, the beam splitter 2 shown in the second embodiment can also be used. According to this, since the optical function surfaces 22 and 23 are formed on at least one of the entrance surface 13 and the exit surface 14, the functions of the collimator lens 41 and / or the condensing lens 42 are added to the beam splitter 2. The Therefore, it is possible to omit at least one of the collimating lens 41 and the condensing lens 42 among the optical members, and the optical communication module 3 can be reduced in size and cost. Furthermore, since the optical path length from the semiconductor laser 31 to the optical fiber 33 can be shortened, the optical communication module 3 can be downsized and the optical coupling efficiency can be improved.

  In the optical communication module 3 of the present embodiment, the reflected light B is coupled to the optical fiber 33 and the transmitted light C is used for wavelength monitoring. However, the present invention is not limited to this mode. The configuration may be such that the reflected light B is used for wavelength monitoring by being coupled to the fiber 33.

DESCRIPTION OF SYMBOLS 1, 2 Beam splitter 3 Optical communication module 10 Prism 11 Reflecting surface 12 Transmitting surface 13 Incident surface 14 Outgoing surface 20 Antireflection film 22, 23, 24 Optical functional surface 31 Semiconductor laser 32 Photodiode 33 Optical fiber 41 Collimating lens 42 Condensing Lens 43 Bandpass filter 50 Package A Incident light B Reflected light C Transmitted light D Incident angle

Claims (5)

In a beam splitter that splits incident light into reflected light and transmitted light,
A reflective surface formed at an angle greater than the critical angle with respect to the optical axis of the incident light;
A transmission surface that transmits a part of the incident light,
The beam splitter, wherein the transmission surface has an inclination angle equal to or less than a Brewster angle with respect to an optical axis of incident light and is provided on a part of the reflection surface.   The beam splitter according to claim 1, wherein the beam splitter is configured to include a prism, and the reflection surface and the transmission surface are formed integrally with the prism.   The beam splitter according to claim 1, wherein an antireflection film is formed on the transmission surface. Having an incident surface on which the incident light is incident and an exit surface from which the reflected light is emitted;
The beam splitter according to any one of claims 1 to 3, wherein an optical functional surface is formed on at least one of the incident surface and the exit surface. Optically connecting a semiconductor laser, an optical fiber that receives light from the semiconductor laser, a light receiving element that receives light from the semiconductor laser, the semiconductor laser, the optical fiber, the semiconductor laser, and the light receiving element A beam splitter to be coupled,
5. The optical communication module according to claim 1, wherein the beam splitter is the beam splitter according to any one of claims 1 to 4.