Bell Telephone Laboratories

Other

Bernard Collins De Loach, Jr

Bertram Schwartz

Richard C Miller

Mauro DiDomenico, Jr

A system (FIG. 1) for interrogating the ON-OFF status of an electrical switch (31) comprises a semiconductor body (4) containing a PN junction and means (5) for electrically connecting an auxiliary switch (32) coupled to the interrogated switch, or alternately (FIG. 2) the interrogated switch (32), across the PN junction. Light (7) of a first wavelength incident on the semiconductor body causes light of a second wavelength (11) to be emitted from the body when the switch is open (OFF), whereas no light is emitted from the body when the switch is closed (ON). Therefore, photoelectric detection of the emission vs. non-emission of light of the second wavelength from the semiconductor body indicates the OFF vs. ON status of the switch.

Optical system for interrogation of the status of a switch

Circuits for selectively operating redundant light sources (lasers or LEDs) in lightwave communication systems are described.

Redundant light source circuit

The proper utilization of that portion of the millimeter wave spectrum that is particularly highly absorbed by the atmosphere is shown in conserve frequency spectrum while permitting a high density of users operating in relatively close proximity.

Electromagnetic wave communication systems

A particularly important factor limiting the reliability of diode lasers is the catastrophic mirror damage which occurs when the radiated output exceeds a critical value. Experience has shown that this occurs as a result of fluctuations in the drive current, especially in high efficiency diodes. To avoid such damage, a portion of the output radiation from a diode laser, located in the collector circuit of a common emitter drive transistor, is coupled back to a photodetector, located in the base-emitter circuit of the transistor. The resulting negative feedback tends to stabilize the overall operation of the device and maintain the maximum radiated power within safe limits.

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Murray Hill, NJ, United States of America

Bernard Collins De Loach, Jr