Browse Prior Art Database

Injection Laser With Polarized Output

IP.com Disclosure Number: IPCOM000077697D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Smith, AW: AUTHOR [+2]

Abstract

A semiconductor laser structure is described which favors the emission of light with a specified polarization through the application or incorporation of a material on one of the reflecting faces of the laser which has different reflecting, scattering, or absorbing properties for light of different polarizations. Lasers with polarized output are desired for magneto-optical reading applications.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 2

Injection Laser With Polarized Output

A semiconductor laser structure is described which favors the emission of light with a specified polarization through the application or incorporation of a material on one of the reflecting faces of the laser which has different reflecting, scattering, or absorbing properties for light of different polarizations. Lasers with polarized output are desired for magneto-optical reading applications.

Conventional injection lasers tend to have randomly polarized emitted light, because the cavity Q for light polarized in or perpendicular to the junction plane is almost the same. This balance can be altered by applying a coating to one face, which makes the Q for the desired polarization higher than that for the other polarization. To estimate the required effect, note that the loss in a complete round-trip traverse of the laser is R(1)R(2) expt-2 Alpha L), where R(1) and R(2) are the reflectivities of the faces, L is the faser length, and Alpha is an effective absorption coefficient. This polarization is achieved by applying a layer of thickness t to one face of the laser, with a difference Delta Alpha in the absorption for light of the two polarization directions. Then t Delta Alpha must be greater than 0.1 in order to change the loss by about 10% for one polarization relative to the other.

If the absorption in the applied layer is strongly polarization-dependent, then the absorption of the desired polarization will be negligible. Furthermore, since the laser will put most of its output into the polarization with the highest Q, there will be little emission with the unfavored polarization, and the efficiency will not be seriously affected. There may be a change in the threshold current of the laser because of the index of refraction change of the applied layer, but this will not have a serious effect on the operation. The layer thickness can be chosen to achieve a wide range of reflectivities, by making appropriate use of multiple reflections within the layer. The index of refraction of the layer should be large, so that as much of the reflection as possible comes from the outer surface of the applied layer rather than the laser-layer interface.

A substance for achieving this structure is one which has greatly different absorption coefficients for light polarized along and perpendicular to the directions of the molecular alignment, i.e., a dichroic material. This alignment can be achieved by extruding the material directly onto the laser surface, or by applying a reverse bias across the laser junction af...