The invention relates to an envelope for a photodiode which serves as a detector of light signals.
For optical communication, an avalanche breakdown diode is often used as a detector of light signals. The light signals are presented to the detector via a glass fiber. The distance between the end of the fiber and the photodiode should be very small so as to obtain an efficient optical coupling. When this distance is larger than approximately 0.1 mm, a considerable part of the light presented by the fiber will fall beyond the photosensitive part of the detector. Obtaining this small distance in a reproducible manner is difficult in practice.
As is known, it is desirable for the avalanche breakdown diode to have a dark current which is as small as possible. In order to avoid an increase in the dark current, the avalanche breakdown diode should be incorporated in a hermetic envelope. However, this in turn adds to the problems which occur in realizing an efficient optical coupling between the detector and the optical fiber.