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Laser Mode Selection by Shift of Optical Absorption Edge

IP.com Disclosure Number: IPCOM000092401D
Original Publication Date: 1967-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 23K

Publishing Venue

IBM

Related People

Wieder, H: AUTHOR

Abstract

The scanlaser is a device in which an active medium is placed in a conjugate concentric cavity. The cavity is angularly degenerate, that is, The scanlaser is a device in which an active medium is placed in a conjugate concentric cavity. The cavity is angularly degenerate, that is, many laser modes are supported in the cavity. The laser oscillations are destroyed or spoiled by changing their plane of polarization. Individual modes can be selected by overcoming the change in polarization. Such is usually accomplished by including an electro-optic crystal whose birefringence is changed by the applied charge.

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Laser Mode Selection by Shift of Optical Absorption Edge

The scanlaser is a device in which an active medium is placed in a conjugate concentric cavity. The cavity is angularly degenerate, that is, The scanlaser is a device in which an active medium is placed in a conjugate concentric cavity. The cavity is angularly degenerate, that is, many laser modes are supported in the cavity. The laser oscillations are destroyed or spoiled by changing their plane of polarization. Individual modes can be selected by overcoming the change in polarization. Such is usually accomplished by including an electro-optic crystal whose birefringence is changed by the applied charge.

In this method of sequentially selecting modes in the scanlaser, use is made of the shift in the wavelength position of the optical absorption edge of a material with applied electric field.

This is the Franz-Keldysh F-K effect. A typical transmission spectrum of a semiconductor material is shown in the drawing. The region of interest is in the vicinity of the bandgap of the material.

The optical absorption edge without any applied electric field is represented by the solid line. Application of an external electric field shifts the edge as shown by the dotted line.

If the operating wavelength of the laser is lambda(o), then the transmission of the material can be caused to decrease locally by the application of a local electric field. Conversely, if the field is removed locally as, for example, by secondary emission of electrons, then the operating point of the laser can be adjusted so that only the mode for which the local transmission of the material has been increased is above threshold. The semiconductor material can be extremely thin, in the form of a thin crystal or film, coated on one side with a transparent conductor and on the other with a highly reflecting dielectric. Switching can be accomplished by applying the field...