1. Technical Field
The present invention relates to an optically coupled device and a method of manufacturing the same.
2. Related Art
Optically coupled device has a light emitting element which accepts input of electric signals, a light receiving element which outputs electric signals, and an optical waveguide allowing therethrough transmission of optical signals from the light emitting element to the light receiving element.
The optically coupled device may be exemplified by those disclosed in Published Japanese Translation of PCT International Publication for Patent Application No. H09-510835, Japanese Laid-Open Patent Publication No. H06-37352, and Japanese Laid-Open Patent Publication No. 2000-40839.
The optically coupled device of Published Japanese Translation of PCT International Publication for Patent Application No. H09-510835 has, as illustrated in FIG. 7, a light emitting element 101, a light receiving element 102, a light-transmissive flat waveguide 103 as an optical waveguide which allows therethrough transmission of optical signals from the light emitting element to the light receiving element, a plurality of holographic elements 104 for reflecting light (g, h, i), provided along the waveguide 103, and a package 105 which covers these components. This publication describes that “the package 105 is unnecessarily composed of a reflective material, since the light is reflected only on the holographic elements 104, and there is no need of refection of light on the interface between the waveguide 103 and the package 105”.
Japanese Laid-Open Patent Publication No. H06-37352 discloses, as illustrated in FIG. 11 of the Publication, an optically coupled device configured to have a light emitting element and a light receiving element, which are disposed in an insulating cup-like case and encapsulated by a light-transmissive encapsulation layer (equivalent to an optical waveguide), a light-transmissive optical waveguide plate disposed on the light-transmissive encapsulation layer, and a light interceptor which covers the light-transmissive optical waveguide plate and the light-transmissive encapsulation layer. In the optically coupled device of the Publication, a reflective surface, which is formed by plating or by printing of a highly-reflective resin, is provided to the lower surface of the light interceptor (the surface opposed to the upper surface of the light-transmissive optical waveguide plate).
The optically coupled device of Japanese Laid-Open Patent Publication No. 2000-40839 is configured as illustrated in FIG. 1 of the Publication, so that a light emitting element and a light receiving element are opposed so as to optically couple with each other, an inert gas is filled in a hollow component which surrounds the light emitting element and the light receiving element opposed as described in the above, and the outer circumference of the hollow component is molded by a light-intercepting resin. In the optically coupled device, the inner space of the hollow component behaves as an optical waveguide.
The technique disclosed in Published Japanese Translation of PCT International Publication for Patent Application No. H09-510835 is necessarily provided with the expensive holographic elements 104, and is therefore suffering from a problem such that the material cost is high, or such that it is difficult to provide the optically coupled device at a low price.
The technique disclosed in Japanese Laid-Open Patent Publication No. H06-37352 needs preliminary formation of the plated layer or the resin layer on the light interceptor, and consequently needs an increased number of steps of manufacturing. Therefore, a problem of difficulty in providing the optically coupled device at a low price remains.
In recent years, there has been a growing trend of downsizing of various equipment, such as those for FA (Factory Automation). In association with the trend, there have been growing demands of downsizing and thinning also on the semiconductor components (including optically coupled devices) mounted thereon. The technique disclosed in Japanese Laid-Open Patent Publication No. 2000-40839 is, however, suffering from a problem in that thinning of the optically coupled device is difficult, because the hollow space is necessarily formed between the light emitting element and the light receiving element opposed to each other.
As described in the above, it has been difficult to provide thin optically coupled devices at low costs.