The optocoupling between an optical source and an optical sensor is enhanced while retaining a high dielectric strength by providing a homogeneous medium surrounding the source and the sensor having an inner light transmissive region and an outer light reflective region encapsulated within a substantially opaque body. The homogeneous medium is formed by applying an optically transmissive material to the source and sensor and no more than partially curing said material before applying an optically reflective material which, when fully cured along with the optically transmissive material, does not form an isolation degrading boundary therebetween.

A photo coupler device comprises only one layer having a resin material and addition particles provided for molding a pair of a light emitting element and a light receiving element. The addition particles are made of one from silica of crystal form or amorphous form, glass fibre and the like. The addition particles are suspended in the layer in a certain proportion equal to or below about 70% by weight in comparison with the weight of the resin material. A diameter of the addition particles is in the range of about several tens to about one hundred .mu.m. Preferably, the resin material is made of epoxy resin having phenol as a hardener in the case where the light emitting element provides its electroluminescence of infrared region. In another form of the present invention, an additional layer also having another type of resin material and the addition particles can be formed to mold the first layer containing the pair of the elements.

A high isolation voltage optocoupler includes spaced apart emitter and detector elements coupled to one and the other ends of a bar of light transmissive dielectric material. A reflective coating on the surface of the bar enhances light coupling. An opaque dielectric housing excludes ambient light and provides mechanical support for the coupling elements.

The invention relates to a photocoupler for surface mounting. The device includes a first support (20), a phototransmitter element, a second support (20') having a photoreceiver element, and an electrically insulating assembly housing (1) in which the first and the second supports (20, 20') are assembled together by snap connections (11, 12) in a longitudinal direction of the assembly housing in such a way that the phototransmitter element and the photoreceiver element face on another. The first and the second support (20, 20') have a lateral surface (26) provided with conductor tracks (22, 24) in electrical contact with the said respective elements to enable surface mounting.

A heat sink for optical elements such as semiconductor laser diodes which avoids focussed reflection back to the optical element of stress waves generated within the heat sink by excitation of the elements. The avoidance of this focussed reflection enhances optical performance of such elements and in particular improves the purity of the lasing spectra of semiconductor laser diodes. The heat sink is dimensioned and provided with surface contours to reflect elastic waves in a pattern to avoid focussing the waves at the optical element thus minimizing the disturbance in operation of the element induced by the concentration of focussed stress waves. The element may be mounted off center on the heat sink at a position which avoids concentrations of stress waves. A coating is optionally applied to appropriate heat sink surfaces to dampen the stress waves incident at those surfaces and thus attenuate reflection with the result of reduced disturbance of the optical element. A photodetector body is similarly structured to avoid stress or thermoelastic wave effects.