At&t Bell Laboratories

Bell Telephone Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Richard L Panock

Stephen R Forrest

Paul A Kohl

John E Bjorkholm

Richard R Freeman

Robert A Lieberman

William E Cooke

A bidirectional fiber optic system is described in which at one terminal the output radiation of a light source (LED or semiconductor laser) is coupled through a small diameter hole in the active area of a photodiode into the core of a larger diameter transmission fiber. On the other hand, radiation propagating through the fiber in the opposite direction exits from the fiber with a large numerical aperture so that most of it is incident on the active area of the photodiode and little is lost through the hole. Also described are a number of photodiode configurations for use in such a system, as well as dual photodiodes to perform both signal detection and output monitoring functions. Further described are fiber optic sensing systems for monitoring such variables as blood pressure.

Bidirectional fiber optic systems

A single-wavelength, bidirectional fiber optic transmission system is described in which at each terminal the output radiation of a light source (LED or semiconductor laser) is coupled through a small diameter hole in the active area of a photodiode into the core of a larger diameter transmission fiber. On the other hand, radiation propagating through the fiber in the opposite direction exits from the fiber with a large NA so that most of it is incident on the active area of the photodiode and little is lost through the hole. Also described are a number of photodiode configurations for use in such a system, as well as dual photodiodes to perform both signal detection and output monitoring functions.

Photodiodes having a hole extending therethrough

Bidirectional fiber optic transmission systems and photodiodes for use

A procedure is described for electrochemically photoetching n-type and intrinsic compound semiconductors. The process involves applying a potential to the compound semiconductor while it is in contact with an electrolytic solution and irradiating the surface to be etched with light in a certain energy range. By suitable adjustment in the potential, electrolytic solution composition and light energy, the etch rate is made proportional to the light intensity. By suitable variation in light intensity and light-ray direction, various geometrical features can be made on the surface of the compound semiconductor. For example, a hole with straight sides can be made in the compound semiconductor by use of a light spot and parallel (collimated) light rays. An advantageous application of this process is the fabrication of a photodiode with a hole in the center for use in bidirectional communication systems and to monitor power output for optical communication sources. The advantage of this process is that no damage occurs outside etched hole so that a maximum area of the photodiode remains active for detecting incoming radiation. Another advantage of the process is that etching will stop where the material becomes p-type so that etching can be made to stop automatically at a p/n junction.

Electrochemical photoetching of compound semiconductors

The present invention relates to an apparatus for providing second harmonic generation from a single beam in an isotropic medium. An isotropic medium having a two-photon transition between a first level and a second level with a quadrupole moment therebetween is exposed to a beam of laser radiation. The photons in the laser beam have an energy which is substantially equal to one-half the energy difference between the first and second levels.

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Cranford, NJ, United States of America

Richard L Panock