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Optically Operated Shutter with Fast Recovery

IP.com Disclosure Number: IPCOM000078566D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 20K

Publishing Venue

IBM

Related People

McGroddy, JC: AUTHOR [+2]

Abstract

A passive rugged, optically operated shutter, having a fast recovery time, is proposed. Such a shutter unit is in the form of a thin film of semiconductor material on a transparent substrate.

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Optically Operated Shutter with Fast Recovery

A passive rugged, optically operated shutter, having a fast recovery time, is proposed. Such a shutter unit is in the form of a thin film of semiconductor material on a transparent substrate.

A direct bandgap semiconductor, i.e., InAs(0.2)P(0.8), has an optical absorption edge which rises exponentially above a threshold energy. As seen in the figure, such a semiconductor 2 is grown or deposited on a glass substrate 4, and located adjacent a mode-locked laser 6, placed in an optical cavity, represented by the parallel mirrors 8 and 10. When the laser begins to oscillate, no output is achieved until the laser frequency (about 1.06 mu) emits at an energy value of this threshold energy or above. At this moment, the semiconductor bleaches and becomes transparent to the lasing frequency and emits a sharp pulse at this frequency.

By adjusting the frequency spread of the exciting light of a frequency of 1.06 mu, the recovery time for this bleaching effect can be made as small as one picosecond. Such a shutter does not suffer the degradation effects experienced when organic dyes are used as bleachable shutters. It is believed that this effect is due to the filling up of the final states for transitions to the value 1/2, which essentially eliminates absorption.

If the photon energy spread is delta xi, the recovery time of the semiconductor alloy is the time for an electron or hole to scatter through an energy h delta xi. If aco...