Radiation detector with built-in test capability

A device for detecting external electromagnetic radiation and generating electrical signals in response thereto comprising:

• a base member having a plurality of electrical terminals;
• an opaque enclosure mounted on said base member, said enclosure including a transparent window for admitting light from a source outside of said enclosure;
• a photodetector mounted on the base member and inside of said enclosure in a position to respond to light directed to it from said external source;
• a light emitter also mounted on the base member and inside of said enclosure in a position offset from the photodetector and having electrical circuit connections to some of said electrical terminals;
• a prismatic light conduit extending between the emitter and a selected small portion only of the photodetector;
• and
• selective actuation means connected to said light emitter to provide a built-in test capability for the device.

The method of testing a photodetector device which has a photodetector mounted on a base member and inside of an enclosure with a transparent window for admitting light from a source located outside said enclosure, said photodetector mounted in a position to receive light from said external source and generate electrical signals in response thereto and an internal light source also mounted on the base member and inside said enclosure in substantially coplanar relationship with but displaced from the photodetector, said method comprising the steps of:

• selectively energizing the internal light source;
• directing substantially all of the light from the internal light source through a prismatic light conduit to only a selected minimum portion of the active surface of the photodetector in order to stimulate the photodetector to generate an output signal without substantially interfering with the light path for external light to the photodetector;
• and
• monitoring the electrical signals from the photodetector responsive to the internal light source to ascertain the operability thereof.

The method of fabricating a photodetector device having a built-in test capability, which device is located inside an opaque enclosure having a window for admitting light from an external source located outside of the enclosure, which photodetector is responsive to light from said external source, comprising the steps of:

• affixing on the upper surface of a base member having a plurality of electrical terminals, a pair of ceramic pads, each of which has a gold plated layer deposited on its upper surface, one of said pads being affixed in a generally central location on the base member;
• mounting a photodiode of generally planar configuration on the gold plated layer of the centrally positioned pad by means of conducting epoxy;
• mounting a light emitting diode of generally planar configuration on the gold plated layer of the other ceramic pad by means of conducting epoxy;
• establishing electrical connections to the photodiode and the light emitting diode by ball bonding individual wire leads respectively to the gold plated layers of the two pads and to the upper surfaces of the two diodes;
• forming a bridge member into a prismatic element by developing selectively shaped end surfaces thereof;
• applying clear epoxy to the upper surface of the light emitting diode and to only a corner surface of the photodiode;
• and
• positioning the prismatic element against the upper surfaces of the two diodes so that one end overlies the light emitting diode and the other end overlies a corner portion only of the photodiode.