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Bleachable Optical Cell with Variable Recovery Time and Threshold

IP.com Disclosure Number: IPCOM000083315D
Original Publication Date: 1975-Apr-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 28K

Publishing Venue

IBM

Related People

McGroddy, JC: AUTHOR

Abstract

A semiconductor bleachable optical cell is provided that is suitable for Q-switching or mode locking of lasers with variable-recovery time and variable threshold.

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Bleachable Optical Cell with Variable Recovery Time and Threshold

A semiconductor bleachable optical cell is provided that is suitable for Q- switching or mode locking of lasers with variable-recovery time and variable threshold.

A double-heterostructure semiconductor diode is being used as a Q- switching device, serving the same function as is now performed by dye solutions placed in a laser cavity. The semiconductor structure is "bleachable" (its transparency to light changes suddenly from no transmission to high transmission), but the threshold optical power needed to bleach the semiconductor cell can be varied over a wide range. The recovery time of the semiconductor cell following bleaching can also be varied. In both cases, the variations take place by applying an external bias voltage to the bleachable cell.

Fig. 1 is a schematic drawing showing the bleachable semiconductor cell, and Fig. 2 is a diagram of the variation of the direct energy gaps of the respective semiconductor compounds as a function of position in the cell. The cell 2 is composed of a p-type compound of the form AB(x)C(1-x) and an n-type compound of the form AB(x)C(1-x), with an intrinsic layer a few micrometers thick between the two consisting of a compound of the form AB(y)C(1-y).

The dotted line indicates the Fermi level when no bias is applied. If the cell of Fig. 1 were operated without any bias voltage being applied to it, the intrinsic layer serves as a bleachable material.

If a pulse of intense photons of energy h upsilon, slightly in excess of the bandgap of the intrinsic layer, is incident on such layer, the absorption in the layer will be reduced from.a high value to a low value in a few picoseconds. After passage of the pulse, the absorption will recover in a time that depends upon the band structure of the intrinsic layer, its thickness,...