JP2008304611A - Optical transmitter/receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable optical transmitter/receiver that can suppress optical axis deviation and element destruction caused by change in temperature of a resin for fixing. <P>SOLUTION: The optical transmitter/receiver includes a printed circuit board, one or both of a light emitting element and a light receiving element mounted on the printed circuit board, and an optical waveguide installed between the light emitting and receiving elements in a manner making optical coupling possible with these elements. The optical transmitter/receiver is characterized in that the light emitting and receiving elements and the end of the adjacent optical waveguide are covered with resin having a plurality of layers, and that its outermost resin layer contains a heat-conductive filler. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical transmission / reception device formed by combining a light emitting element, a light receiving element, and an optical waveguide. The optical transmission / reception apparatus of the present invention is used in high-speed communication devices such as supercomputers, server computers and router devices, in-vehicle optical wiring, and small electronic devices such as mobile phones.

  In recent years, optical wiring is being applied to high-speed communication devices such as servers, optical wiring in automobiles, and small electronic devices such as mobile phones. These devices are becoming smaller and lower in cost, and accordingly, there is a strong demand for downsizing and lowering the cost of the optical transceiver. In order to achieve cost reduction and miniaturization, optical transmission / reception apparatuses having various structures have been proposed.

As one of the structures of a conventional optical transmitter / receiver, a structure in which a light emitting element, a light receiving element, and an optical waveguide are covered with a polymer material and fixed has been proposed (for example, see Patent Documents 1 and 2).
Patent Document 1 discloses a structure in which a light receiving element or a light receiving / emitting part of a light emitting element and an optical waveguide end such as an optical fiber are coupled with an ultraviolet curable resin. Thus, the structure in which the light receiving element or the light emitting element and the optical waveguide are covered and integrated with the polymer material is advantageous for downsizing and cost reduction.
Patent Document 2 discloses a structure in which an optical waveguide is fixed to a submount with an adhesive, aligned with a light emitting element mounted on a substrate, and fixed.
Japanese Patent Laid-Open No. 2004-245861 JP 61-231514 A

  However, in the above-described prior arts of Patent Documents 1 and 2, since the linear expansion coefficient of the ultraviolet curable resin or adhesive used for fixing is large, the resin peels off or strong stress is applied to the light receiving element or the light emitting element. May be added. As a result, there is a possibility that the optical axis shifts or the light receiving element or the light emitting element is damaged.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly reliable optical transmission / reception apparatus that can suppress optical axis misalignment, element destruction, and the like due to temperature change of the fixing resin.

  In order to achieve the above object, the present invention provides a printed circuit board, one or both of a light emitting element and a light receiving element mounted on the printed circuit board, and a light emitting element and a light receiving element. The light-emitting element and the light-receiving element, and the end portion of the optical waveguide adjacent to the light-emitting element and the light-receiving element are covered with a plurality of layers of resin, and the outermost thereof. The resin layer contains a heat conductive filler, and provides an optical transceiver.

  In the optical transceiver of the present invention, the light emitting element and the light receiving element are mounted in a direction in which the light emission or light reception direction intersects the mounting surface of the printed circuit board, and at least an end of the optical waveguide is in the light emission or light reception direction It can be set as the structure provided along.

  In the optical transceiver of the present invention, the resin layer may have a two-layer structure of an inner resin layer and an outer resin layer containing a thermally conductive filler.

  In the optical transceiver of the present invention, the resin layer may have a three-layer structure including an inner resin layer, an outer intermediate resin layer, and an outer resin layer containing a heat conductive filler on the outer side. .

  In the optical transceiver of the present invention, it is preferable that a filler that is transparent to communication light is mixed in the inner resin layer or the inner resin layer and the intermediate resin layer.

  In the optical transceiver of the present invention, the optical waveguide is an optical fiber made of quartz glass, and the refractive index at a wavelength of 850 nm of the inner resin layer covering the end of the optical fiber is 1.45 or more and 1.55 or less. preferable.

  In the optical transceiver according to the present invention, the optical waveguide may be a polymer clad fiber.

The optical transceiver of the present invention has a structure in which the element and the optical waveguide are fixed by a plurality of resin layers, and the outermost resin layer contains a heat conductive filler, so that heat radiation of the light emitting element or the light receiving element is promoted. It is possible to suppress the temperature rise of the fixing resin, and to suppress the optical axis shift and the element breakage due to the expansion / contraction of the resin due to the temperature change.
Also, by mixing the inner resin layer or the inner resin layer and the intermediate resin layer with a filler that is transparent to communication light, the linear expansion coefficient of the resin that fixes the light receiving element or the light emitting element and the optical waveguide is reduced. It is possible to further suppress optical axis misalignment and element damage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a main part showing a first embodiment of the optical transceiver of the present invention. In FIG. 1, reference numeral 1 denotes an optical transceiver, 2 denotes a printed circuit board, 3 denotes a light emitting element or a light receiving element (hereinafter referred to as a light receiving / emitting element), 4 denotes a light emitting part or a light receiving part (hereinafter referred to as a light receiving / emitting part), 5 is an optical waveguide, 6 is an inner resin layer, 7 is an outer resin layer, and 8 is a thermally conductive filler.

  In the present embodiment, the printed circuit board 2 can be appropriately selected and used from conventionally known various printed circuit boards such as a flexible printed circuit board, a rigid printed circuit board, and a rigid-flexible circuit board. It is preferable that an electrode pad for mounting the light emitting / receiving element 3 is provided at a predetermined mounting position on the surface of the printed board 2. On this printed board 2, not only the light emitting / receiving element 3 is mounted, but also various electronic devices such as driving ICs, LSIs, liquid crystal display elements, and circuits (wirings) for electrically connecting them. Can be provided as appropriate.

  In the present embodiment, the light emitting / receiving element 3 includes a surface emitting laser (hereinafter referred to as VCSEL), a laser diode (hereinafter referred to as LD), a light emitting element such as a light emitting diode (LED), and a photodiode (hereinafter referred to as “light emitting diode”). A light receiving element such as PD can be used.

  In the present embodiment, the light emitting / receiving element 3 is mounted on the upper surface (mounting surface) of the printed circuit board 2 as shown in FIG. 1, and the light emitting / receiving direction of the light emitting / receiving unit 4 is orthogonal to the upper surface of the printed circuit board 2. Or a substantially orthogonal structure. As a light emitting element having such a structure and applicable to a high-speed communication device such as a server, an optical wiring in a car, and a small electronic device such as a mobile phone, for example, there is a VCSEL. The VCSEL having the above-described structure has a feature that it has a low profile in the light emitting / receiving direction and is cheaper than a conventional LD. In addition, due to the element structure, the light emission threshold current is low, and as a result, power consumption is low. In such applications, low cost and low power light sources are a great advantage.

  In the present embodiment, as the optical waveguide 5, a sheet type optical waveguide, a fiber type optical waveguide, or the like can be used. In particular, the fiber-type optical waveguide is advantageous because a long waveguide can be produced and the optical waveguide can be obtained at low cost. As the fiber-type optical waveguide, quartz glass fiber, plastic fiber, or the like can be used. Moreover, although it is a kind of quartz glass fiber, a polymer clad fiber in which a core for guiding light is made of quartz glass and a clad portion around the core is made of a polymer can also be used. A plurality of these fiber-type waveguides can be mounted in a lump by making them into cables or tapes. Moreover, since the diameter of the glass part which comprises a fiber is small, the polymer clad fiber which a clad part consists of a polymer can bend a fiber with a smaller curvature.

  In the present embodiment, the entire light emitting / receiving element 3 mounted on the printed circuit board 2 and the end of the optical waveguide 5 adjacent to the light emitting / receiving portion 4 are covered with the inner resin layer 6 and the inner resin layer 6. The outside is fixed by being covered with an outer resin layer 7 containing a thermally conductive filler 8.

  As the inner resin layer 6, an epoxy resin, an acrylic resin, a silicone resin, a polyimide resin, a polysilane resin, or the like can be used. Curing methods include UV curing, thermosetting, two-component mixed (chemical reaction) curing, and moisture reaction curing. In particular, the UV curable resin is desirable because the curing time is short and the optical waveguide and the light emitting / receiving element are not easily displaced during curing.

Further, by using a resin whose refractive index after curing of the inner resin layer 6 is the same as that of the core of the optical waveguide 5, Fresnel reflection can be prevented and the coupling loss between the light emitting / receiving element 3 and the optical waveguide 5 can be reduced. . For example, when a silica glass optical fiber is used as the optical waveguide 5, the post-curing refractive index of the inner resin layer 6 is in the range of 1.40 to 1.60, more preferably in the range of 1.45 to 1.55. It is desirable to use one.
The inner resin layer 6 can be formed by dropping an uncured resin liquid at a predetermined location and curing it by means such as UV light irradiation. A dispenser or the like can be used for dropping the resin liquid.

  The outer resin layer 7 is not particularly limited except that it contains a heat conductive filler 8. For example, a material in which the heat conductive filler 8 is mixed with the same resin as the inner resin layer 6 can be used. . The material and shape of the heat conductive filler 8 are not particularly limited, and for example, a carbon filler can be used. By mixing the heat conductive filler 8 with the outer resin layer 7 in this way, the effect of radiating the heat generated from the light emitting / receiving element 3 to the outside is enhanced. As a result, the temperature change of the inner resin layer 6 caused by the heat generation of the light emitting / receiving element 3 is reduced, and the problems such as the optical axis shift and the damage of the light receiving / emitting element 3 can be solved.

FIG. 2 is a cross-sectional view of a main part showing a second embodiment of the optical transceiver of the present invention. The optical transmission / reception apparatus 11 of this embodiment includes the same components as those of the optical transmission / reception apparatus 1 of the first embodiment shown in FIG. 1 described above, and the same components are denoted by the same reference numerals.
The optical transceiver 11 of the present embodiment covers the entire light emitting / receiving element 3 mounted on the printed circuit board 2 and the end of the optical waveguide 5 adjacent to the light emitting / receiving unit 4 with an inner resin layer 6. The inner resin layer 6 is covered with an intermediate resin layer 9, and the intermediate resin layer 9 is further covered with an outer resin layer 7 containing a heat conductive filler 8 to have a three-layer resin coating.

In the present embodiment, among the three resin layers, the refractive index of the inner resin layer 6 may be higher than that of the intermediate resin layer 9. With this structure, the inner resin layer 6 and the intermediate resin layer 9 form a core / cladding structure, and the coupling efficiency between the light emitting / receiving element 3 and the optical waveguide 5 is improved. Further, by mixing the above-described heat conductive filler 8 with the outer resin layer 7, the effect of radiating the heat generated from the light emitting / receiving element 3 to the outside is enhanced, and the inner resin layer resulting from the heat generation of the light receiving / emitting element 3. 6 and the temperature change of the intermediate resin layer 9 become small.
In this case, like the inner resin layer 6, the intermediate resin layer 9 is made of a resin that is transparent to communication light. The material of the transparent resin is not particularly limited, but an epoxy resin, an acrylic resin, or the like can be used.

  Moreover, in this embodiment, it is good also as a structure which mixed the transparent filler with the inner side resin layer 6 (and intermediate | middle resin layer 9) among the three resin layers. Due to the transparent filler of the inner resin layer 6 (and the intermediate resin layer 9), the linear expansion coefficient of the joint between the light emitting / receiving element 3 and the end of the optical waveguide 5 is reduced, and the optical axis is effectively displaced and the light receiving / emitting element 3 is damaged. Can be solved.

  In this case, needless to say, the refractive index of the transparent filler used for the inner resin layer 6 is preferably the same as or almost the same as the refractive index of the resin used for the inner resin layer 6. When the difference between the refractive indexes of the two becomes large, scattering becomes remarkable and the loss of communication light increases, which is not desirable. The material for the transparent filler is not particularly limited. When the wavelength used for communication is visible light to near infrared light, a quartz glass filler can be used. The shape of the transparent filler is not particularly limited, such as needle-like or granular, but as disclosed in JP-A-2006-257353, it is spherical and the particle size is from a fraction of the wavelength to the wavelength. It is preferable to avoid scattering of communication light by avoiding a region where Mie scattering is likely to occur up to several times.

  When a transparent filler is used also for the intermediate resin layer 9, it is preferable to use a transparent filler having a refractive index close to that of the resin used for the intermediate resin layer 9 as in the case of the inner resin layer 6.

  When a plurality of resin layers are provided as described above, the inner resin layer 6 is desirably provided so as to completely cover at least the entire light emitting / receiving element 3 and the end of the optical waveguide 5. Thereby, the coupling strength between the light emitting / receiving element 3 and the optical waveguide 5 can be improved, and the reliability can be improved. Furthermore, when a transparent filler is mixed in the inner resin layer 6, the linear expansion coefficient of the inner resin layer 6 is lowered, so that it is resistant to temperature changes and the reliability can be further improved.

(Example)
An optical transceiver having the structure shown in FIG. 2 was produced. As the light emitting element 3, a VCSEL having an emission center wavelength of 850 nm was used. For the inner resin layer 6, an ultraviolet curable epoxy resin having a refractive index after curing of 1.457 and mixed with 10% by mass of quartz glass filler whose refractive index was adjusted was used. For the intermediate resin layer 9, an ultraviolet curable epoxy resin having a refractive index after curing of 1.452 and 10% by mass of a quartz glass filler whose refractive index was adjusted was used. For the outer resin layer 7, an ultraviolet curable resin mixed with 10% by mass of carbon filler as the heat conductive filler 8 was used. A quartz glass optical fiber was used for the optical waveguide 5.

(Comparative example)
For comparison, an optical transceiver that uses the epoxy resin that does not contain a filler in each of the inner, middle, and outer resin layers, and is otherwise similar to the above-described example, was also manufactured.

(Heat cycle test)
A heat cycle test was performed on each sample of the manufactured examples and comparative examples. The test was performed while the VCSEL was made to emit light with a light emission output of 0.3 mW. The cycle shown in FIG. 3 was set to one cycle, and 500 cycles were performed. The joint between the VCSEL, the resin layer, and the optical fiber of each sample after the treatment was observed with an optical microscope.

In the comparative example (no filler), a small number of samples were found where the joint between the VCSEL and the resin and the joint between the optical fiber and the resin were peeled off.
On the other hand, in the example in which a filler was added to the resin layer, almost no joint peeling was found. As a result, it was found that the example in which the filler was added to the resin layer was resistant to thermal cycling.

  In this example, a commercially available filler was used as the quartz glass filler. When it is difficult to adjust the refractive index with a commercially available quartz glass filler, the quartz glass filler can be synthesized using a vapor phase synthesis method and used. As a raw material, for example, silicon tetrachloride can be used. A spherical quartz glass filler can be obtained by mixing silicon tetrachloride vapor with a carrier gas such as argon or nitrogen and oxygen, transporting the mixture to a synthesis chamber, and heating to about 800 ° C to 1500 ° C. In order to adjust the refractive index of the quartz glass filler, for example, vapor such as germanium tetrachloride or aluminum trichloride may be mixed with vapor of silicon tetrachloride and synthesized. By adding elements such as germanium and aluminum to quartz glass, the refractive index of quartz glass can be increased. The amount of increase in refractive index can be adjusted according to the amount to be added.

It is principal part sectional drawing which shows 1st Embodiment of the optical transmission / reception apparatus of this invention. It is principal part sectional drawing which shows 2nd Embodiment of the optical transmitter / receiver of this invention. It is a graph which shows the temperature conditions of the heat cycle test done in the Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,11 ... Optical transmitter / receiver, 2 ... Printed circuit board, 3 ... Light emitting / receiving element, 4 ... Light emitting / receiving part, 5 ... Optical waveguide, 6 ... Inner layer resin layer, 7 ... Outer layer resin layer, 8 ... Thermally conductive filler, 9 ... intermediate resin layer.

Claims (7)

A printed circuit board, one or both of a light emitting element and a light receiving element mounted on the printed circuit board, and an optical waveguide provided between the light emitting element and the light receiving element so as to be optically coupled to these elements. And
The light emitting element and the light receiving element, and an end portion of the optical waveguide adjacent to the light emitting element and the light receiving element are covered with a plurality of layers of resin, and the outermost resin layer contains a heat conductive filler. An optical transceiver.   The light emitting element and the light receiving element are mounted in a direction in which the light emission or light reception direction intersects the mounting surface of the printed circuit board, and at least an end portion of the optical waveguide is provided along the light emission or light reception direction. The optical transmission / reception apparatus according to claim 1.   The optical transmission / reception device according to claim 1 or 2, wherein the resin layer has a two-layer structure of an inner resin layer and an outer resin layer containing a thermally conductive filler.   The said resin layer consists of a 3 layer structure of the inner side resin layer, the intermediate | middle resin layer of the outer side, and the outer side resin layer containing the heat conductive filler of the outer side, The Claim 1 or 2 characterized by the above-mentioned. Optical transceiver.   The optical transmission / reception apparatus according to claim 3 or 4, wherein a filler that is transparent to communication light is mixed in the inner resin layer or the inner resin layer and the intermediate resin layer.   The optical waveguide is an optical fiber made of quartz glass, and an inner resin layer covering the end of the optical fiber has a refractive index of 1.45 or more and 1.55 or less at a wavelength of 850 nm. The optical transceiver according to any one of the above.   The optical transceiver according to claim 1, wherein the optical waveguide is a polymer clad fiber.

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