JP2010164856A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module which has improved heat dissipation efficiency of heat generating component. <P>SOLUTION: The optical module has a substrate which has a level difference between an upper stage and a lower stage in a normal direction on a surface, an optical waveguide circuit which has a waveguide arranged on the upper stage of the substrate, an optical element which is arranged on the lower stage of the substrate, and a reflective element which optically connects the optical waveguide circuit and the optical element. When the optical element is a light receiving element, the optical module is a light receiving module, and, when the optical element is a light emitting element, the optical module is a light emitting module. As the optical element and the optical waveguide circuit are spatially separated, heat is not directly transmitted between the optical element and the optical waveguide circuit. Therefore, heat generated by the optical element and the optical waveguide circuit is dissipated through the substrate, thereby heat dissipation efficiency is improved. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for providing an optical module that transmits or receives an optical signal propagating through an optical waveguide circuit.

  A conventional light receiving module is known to reflect light that has been transmitted through an optical waveguide circuit upward by a reflecting mirror, propagate further through a self-forming optical waveguide circuit, and reach the light receiving element surface to receive light. (For example, see Patent Document 1). In addition, a micro-optical reflective component with a mirror is disposed in the core portion of the optical waveguide circuit film, the light propagating through the core is reflected upward by 45 degrees obliquely, and from the upper part of the clad through the micro lens disposed on the optical axis. A structure that receives light on the light receiving element surface as a focused beam is also known (see, for example, Patent Document 2). Since the minute lens is installed, it is easy to collect the light beam, and the PD having a small light receiving surface can be received.

JP 2007-071951 A JP 2005-164801 A

  The light receiving module as in Patent Document 1 performs optical path conversion with a 45-degree mirror. However, because of the structure in which the light receiving element is mounted on the waveguide substrate, heat radiation of the light receiving element or the light emitting element of the transmitter is an issue. It was. In addition, when a light receiving module such as that disclosed in Patent Document 2 is an ultra-high frequency compatible type, heat generating components such as a light receiving element and a transimpedance amplifier (TIA) must be disposed on the optical waveguide circuit. For example, when the optical waveguide circuit is a polymer material such as fluorinated polyimide, ultraviolet curable epoxy, polymethyl methacrylate (PMMA), the thermal conductivity is 0.24 W / mK, 0.58 W / mK, 0.21 W, respectively. Since it is as small as / mK, the thermal conductivity is poor, and there is a problem in heat dissipation of the heat-generating component. In addition, there are optical waveguide circuits in which quartz glass (thermal conductivity 2 W / mK) or quartz glass with a thickness of several tens of μm is formed on a Si substrate (thermal conductivity 150 W / mK). When a heat-generating component is mounted on a circuit, its thermal conductivity is small and there is a problem in heat dissipation.

  Therefore, an object of the present invention is to provide an optical module with improved heat dissipation efficiency of a heat-generating component.

  In order to achieve the above object, the optical module according to the present invention has a structure in which the heat-generating component is spatially separated from the optical waveguide circuit and can radiate heat independently of the optical waveguide circuit.

  Specifically, an optical module according to the present invention includes a substrate having a surface having upper and lower steps in a normal direction on the surface, an optical waveguide circuit having a waveguide disposed on the upper surface of the substrate, and the substrate And an optical element disposed on the lower surface of the optical waveguide circuit, and a reflective element that optically couples the optical waveguide circuit and the optical element.

  Since the optical element and the optical waveguide circuit are spatially separated, heat is not directly transferred between the two. For this reason, the heat which mutually generate | occur | produces will be thermally radiated through a board | substrate, respectively, and the thermal radiation efficiency will improve. Therefore, the present invention can provide an optical module with improved heat dissipation efficiency of the heat generating component.

  The optical waveguide circuit preferably includes the reflective element on an end face of the waveguide. The optical element can be a light receiving element or a light emitting element.

  The optical module according to the present invention further includes a lens portion between the reflective element and the optical element. If the optical element and the optical waveguide circuit are spatially separated, there is a concern that the light receiving sensitivity may be lowered due to temperature fluctuation, mounting accuracy, and the like. In the optical module according to the present invention, the lens unit collects light on the light receiving surface of the light receiving element, and the lens unit is installed in the middle of the light propagation path. There is little change in sensitivity.

  The optical module according to the present invention has a glass window covering the optical element. By covering the optical element with a glass window, an airtight structure can be obtained, and long-term reliability of the optical element can be ensured. Moreover, since it is glass, even if it has an airtight structure, the optical element can receive or emit light through the glass window.

  The lens unit may be disposed on the glass window. By directly adhering and fixing a lens such as a microlens array to a flat glass window, the lens portion can be easily arranged and mounted.

  The lens unit may be disposed on the end surface of the reflective element. As a method for producing a microlens array, there is a precision molding method using a mold. According to this method, the triangular prism and the microlens array can be manufactured as one body, and there is an effect that the mounting is facilitated by reducing the cost by reducing the number of parts.

  The optical module according to the present invention may further include an electric circuit related to the optical element on the lower surface of the substrate. The electric circuit related to the optical element is, for example, an amplifier circuit that amplifies an electric signal from the light receiving element or a driver of the light emitting element. Heat from such an electric circuit can also be dissipated through the substrate.

  The present invention can provide an optical module with improved heat dissipation efficiency of a heat-generating component. Further, it is possible to provide an optical module in which there is little change in light receiving sensitivity or optical coupling rate to the optical waveguide circuit even when there are temperature fluctuations and mounting accuracy fluctuations.

It is a general-view figure explaining the optical module which concerns on this invention. It is a figure explaining the mode of propagation of a cross section near one end of an optical waveguide circuit, and a light beam. It is a figure explaining the mode of propagation of a cross section near one end of an optical waveguide circuit, and a light beam. It is a figure explaining a micro lens array. It is a figure explaining the micro lens array carrying a GRIN lens. It is a figure explaining a prism micro lens array.

  Hereinafter, the present invention will be described in detail with specific embodiments, but the present invention is not construed as being limited to the following description. In the present specification and drawings, the same reference numerals denote the same components.

(First embodiment)
FIG. 1 is a schematic view illustrating a light receiving module which is an embodiment of an optical module according to the present invention. The light receiving module is composed of two components, an optical waveguide circuit 12 mounted on the substrate 11 and a light receiving package 16. These two components are directly mounted on the substrate 11, but are characterized by being spatially separated. Specifically, the light receiving module of FIG. 1 includes a substrate 11 having a step 11b and a lower step 11a in the normal direction on the surface, and an optical waveguide circuit 12 having a waveguide disposed on the upper surface 11b of the substrate 11. A reflection element 13 that is disposed on the waveguide end face of the optical waveguide circuit 12 and reflects light from the waveguide end face toward the lower stage 11a of the substrate 11, and a lens section 14 that collects input light from the reflection element 13. A light receiving element 15 that receives input light collected by the lens unit 14 and converts it into an electrical signal, and a light receiving package 16 that is disposed on the lower surface 11a of the substrate 11 and on which the light receiving element 15 is mounted. In the present specification, the direction away from the surface of the substrate 11 in the normal direction is described as the top.

  The substrate 11 includes a lower step portion 11a and an upper step portion 11b. The light receiving package 16 is disposed in the lower step portion 11a, and the optical waveguide circuit 12 is disposed in the upper step portion 11b. At this time, the optical waveguide circuit 12 is disposed so that one end thereof is located above the light receiving package 16.

  The optical waveguide circuit 12 is, for example, an arrayed waveguide grating. Wavelength multiplexed communication light incident from the other end is wavelength-separated by the optical waveguide circuit 12 of the arrayed waveguide grating, and is emitted from one end of the optical waveguide circuit 12 as light of ten different wavelengths in this embodiment. A triangular prism which is the reflection element 13 is fixed to the light emitting portion with an adhesive. Since the optical waveguide circuit 12 is thin, one end of the optical waveguide circuit 12 is reinforced by the shield 26 and the reflective element 13 is bonded. The light of ten different wavelengths is changed in direction by about 90 degrees downward and is emitted into the space from the lower surface of the triangular prism. The beam diameters of the ten light beams having different wavelengths gradually increase depending on the propagation distance after exiting the optical waveguide circuit 12.

  The light receiving package 16 has a structure in which electronic components such as a light receiving element 15 and a transimpedance amplifier (TIA) 18 (not shown) are built and hermetically sealed with a window glass 17 (not shown in FIG. 1). The transimpedance amplifier 18 is an amplifying element that amplifies the electric signal from the light receiving element 15. The transimpedance amplifier 18 is disposed at a location close to the light receiving element 15 in order to cope with the ultrahigh frequency modulated light.

  In the present embodiment, ten light receiving packages 16 contain ten sets of light receiving elements 15 and transimpedance amplifiers 18 in order to simultaneously receive light of ten different wavelengths in parallel. A microlens array 21 is fixed with an adhesive or the like directly above the window glass 17 of the light receiving package 16 in order to focus the ten light beams on the ten light receiving elements 15 respectively.

  As shown in FIG. 4, the microlens array 21 has ten lens portions 14 mounted thereon. The lens unit 14 is a convex lens. The microlens array 21 may be equipped with a GRIN lens 24 as shown in FIG. The ten light beams radiated into the space from the reflecting element 13 are collected by the microlens array 21 and reach the light receiving surface of each light receiving element 15.

  In order to receive modulated light of about 10 Gbps, the light receiving surface diameter of the light receiving element 15 is as small as about 10 to 30 μm, but the light is smaller than the light receiving surface diameter of the light receiving element 15 by the lens portion 14 or the GRIN lens 24 of the microlens array 21. It is possible to focus the beam. Since the light receiving package 16 is directly mounted on the lower stage 11 a of the substrate 11, heat from the light receiving element 15 and the transimpedance amplifier 18 can be exhausted directly through the substrate 11. On the other hand, the optical waveguide circuit 12 is often provided with an optical circuit such as a variable optical attenuator using a thermo-optic (TO) effect. Since the optical waveguide circuit 12 is directly mounted on the upper stage 11 b of the substrate 11, heat from the optical circuit can also be exhausted directly through the substrate 11. Here, a metal material with good thermal conductivity is used as the substrate material (for example, CuW, KOVAR, INVAR, etc., the thermal conductivity is 255 W / mK, 18 W / mK, 13 W / mK), and the bottom surface of the light receiving package is used. Uses CuW or alumina laminated ceramics (thermal conductivity 17 W / mK), and therefore has excellent heat exhaustion of the heating element.

  FIG. 2 is a diagram for explaining a cross section near one end of the optical waveguide circuit 12 and a state of propagation of the light beam. The light propagated through the core 12b of the optical waveguide circuit 12 is emitted from the output end 12a. Hereinafter, the emitted light will be described as a light beam. The light beam is emitted as a Gaussian beam having a certain cone angle determined by the aperture angle (NA) of the output end 12a. This light beam spreads and enters the adhesive layer of the optical waveguide circuit 12 and the reflective element 13 and the reflective element 13 that is a triangular prism, and further spreads and is reflected by the total reflection on the 45-degree inclined surface of the reflective element 13. The direction is changed to 90 degrees. Further, the light beam spreads to the lower surface of the reflecting element 13 and is emitted to the space.

  The diameter of the light beam at this time is determined by the propagation distance and the NA of the output end 12a of the optical waveguide circuit 12, but spreads to about several hundred microns between the lower surface of the reflecting element 13 and the surface of the lens portion 14 (gap). A microlens array 21 having 10 lens portions 14 having an effective diameter sufficiently larger than the light beam diameter was prepared and directly attached to the window glass 17 disposed on the upper surface of the light receiving package 16. For example, the effective lens diameter of the lens unit 14 is 500 μmφ. For example, the diameter of the light receiving surface of the light receiving element 15 is 25 μmφ. The light beam is applied to the light receiving surface of the light receiving element 15 by the lens unit 14 as a sufficiently small beam spot of about 6 to 7 μmφ.

  In many cases, the optical waveguide circuit 12 is slightly warped in either direction. For example, if it is assumed that one end of the optical waveguide circuit 12 has a warp of about 10 μm at the maximum (warping in the direction perpendicular to the paper surface in FIG. 2 and the output end 12a is arranged like a bow), the output end 12a of the optical waveguide circuit 12 The position is shifted in the vertical direction by the amount of warpage, and the incident point where the light beam enters the reflecting element 13 is displaced approximately 10 μm in the vertical direction. When the incident point incident on the reflecting element 13 is displaced by about 10 μm in the optical arrangement of FIG. 2, the irradiation spot on the light receiving surface of the light receiving element 15 is found to be displaced by about 5 μm.

  When the beam spot diameter is 7 μmφ and the center is shifted by 5 μm, the irradiation area of the light beam spreads to a position that is at most 8.5 μm away from the center of the light receiving surface. Since the diameter of the light receiving surface of the light receiving element 15 is 25 μmφ, even if the optical waveguide circuit 12 is warped, it does not deviate from the light receiving surface of the light receiving element 15. That is, the light receiving sensitivity of the present light receiving module has a sufficient margin even when the warp of the optical waveguide circuit 12 is 10 μm at the maximum.

  When the optical waveguide circuit 12 warps, the distance between the reflective element 13 and the lens unit 14 also changes. A change in the light beam position and the diameter in the case where the gap between the reflecting element 13 and the lens unit 14 is changed to 0.3 mm due to warpage of the optical waveguide circuit 12 with respect to 0.2 mm in design will be described.

  When the gap increased 0.1 mm from 0.2 mm to 0.3 mm, the light beam spot diameter on the light receiving surface of the light receiving element 15 increased to 11 to 12 μmφ, and the light beam center shift was 5 μm. The light beam irradiates the light beam at a maximum distance of 11 μm from the center of the light receiving surface of the light receiving element 15, but all the light beam spots exist within the light receiving surface of the light receiving element 15. The light sensitivity of the module does not change.

  As described above, the light receiving module has a large warp of the optical waveguide circuit 12 and a large mounting tolerance at the time of mounting, and a stable light receiving sensitivity can be obtained. Further, since the light receiving module has a large dimensional tolerance, the light receiving sensitivity hardly decreases even when the environmental temperature changes (−5 ° C. to 75 ° C.).

(Second Embodiment)
FIG. 3 is a diagram for explaining a cross section near one end of the optical waveguide circuit 12 and a state of propagation of the light beam in a light receiving module which is another embodiment of the optical module according to the present invention. A difference between the light receiving module and the light receiving module of FIG. 2 is that the lens unit 14 is arranged on the emission end face of the reflecting element 23 without using the microlens array 21.

  The reflective element 23 is, for example, a prism microlens array in which a prism 31 and a lens unit 14 as shown in FIG. 6 are integrated. The prism microlens array can be produced by a precision glass mold method. Since the light beam can be condensed on the light receiving surface of the light receiving element 15 by the lens portion 14 of the reflecting element 23, the optical characteristics of the light receiving module are almost the same as those of the light receiving module of FIG. Obtainable. Furthermore, by using the reflective element 23, it is not necessary to adjust the optical axis between the reflective element 13 and the microlens array 21, which is necessary in the light receiving module of FIG. For this reason, the light receiving module is easy to mount and the number of parts is reduced, so that a low price can be realized.

(Third embodiment)
The optical module of the present invention can also be applied to an optical module equipped with a variable attenuator that generates a lot of heat. For this reason, this optical module is, for example, as an integrated light receiving module for optical multiplexed communication light that can receive light with high sensitivity while wavelength-separating wavelength multiplexed communication light and adjusting the attenuation of light of each wavelength to an optimum light receiving amount. Is available.

(Fourth embodiment)
The optical module of the present invention may be a light emitting module equipped with a light emitting element. There are two types of light emitting elements: edge emitting LDs and surface emitting LDs. In the case of a light emitting module using a surface emitting LD, the light emitting module is replaced with a surface emitting LD as an alternative to the light receiving element, and is replaced with an LD driver as an alternative to TIA. For this reason, the light emitting module using surface emitting LD becomes the same as the structure of the light receiving module of 1st Embodiment and 2nd Embodiment. In the case of the light emitting module, the coupling efficiency can be increased by adjusting the radiation angle of the surface emitting LD at the lens portion.

  On the other hand, in an end surface light emitting LD (direct modulation LD, LD with an EA modulator, etc.), the end surface needs to face upward. In the case of a light emitting module using an end surface light emitting LD, the configuration is the same as that of the surface light emitting LD except that the end surface light emitting LD is mounted not on the lower surface of the substrate but on the side surface and the light emitting portion faces upward.

  In the case of a light emitting module using a light emitting element, the light emitting element is easily affected by heat, but since the optical waveguide circuit and the light emitting element are separated, the optical waveguide circuit uses the thermo-optic effect (TO effect). Even so, the light emitting element is hardly affected by the heat of the optical waveguide circuit.

(Fifth embodiment)
In the first and second embodiments, the structure in which the reflective element 13 is attached to the output end 12a of the optical waveguide circuit 12 has been described. However, a mirror may be provided in the optical waveguide circuit 12. Specifically, a structure in which the core 12b is penetrated from the surface of the optical waveguide circuit 12 by reactive ion etching (RIE) or the like, is dug down to the lower part of the cladding layer, and the reflecting element 13 is embedded therein. With such a structure, light can be extracted downward in the middle of the optical waveguide circuit 12. This light passes through the substrate 11 made of a material such as Si or quartz glass and irradiates the lower surface of the substrate 11. When the lower surface of the substrate 11 is not optically polished, loss due to scattering occurs. Therefore, it is preferable to optically polish the lower surface of the substrate 11 and further apply a non-reflective coating.

11: Substrate 11a: Lower stage 11b: Upper stage 12: Optical waveguide circuit 12a: Output end 12b: Core 13: Reflective element 14: Lens unit 15: Light receiving element 16: Light receiving package 17: Window glass 18: Transimpedance amplifier (TIA)
21: Micro lens array 23: Reflecting element 24: GRIN lens 26: Short 31: Prism

Claims (7)

A substrate having upper and lower steps in the normal direction on the surface;
An optical waveguide circuit having a waveguide disposed on an upper surface of the substrate;
An optical element disposed on a lower surface of the substrate;
A reflective element that optically couples the optical waveguide circuit and the optical element;
An optical module comprising:   The optical module according to claim 1, wherein the optical waveguide circuit includes the reflective element on an end face of the waveguide.   The optical module according to claim 1, wherein the optical element is a light receiving element or a light emitting element.   The optical module according to claim 1, further comprising a lens portion between the reflective element and the optical element. A glass window covering the optical element;
The optical module according to claim 4, wherein the lens unit is disposed on the glass window.   The optical module according to claim 4, wherein the lens unit is disposed on an end surface of the reflective element.   The optical module according to claim 1, further comprising an electric circuit related to the optical element mounted on a lower surface of the substrate.

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