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Semiconductor Element Acting as a Light Modulator

IP.com Disclosure Number: IPCOM000095396D
Original Publication Date: 1965-Dec-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Folberth, OG: AUTHOR

Abstract

For the phase modulation of light by the linear, transversal electro-optical Pockels effect semiconductor crystals including a PN junction are used. The field existing in the depletion layer of the PN junction causes birefringence for a beam propagating along the junction plane and a phase shift of the component rays polarized perpendicularly with respect to one another. However in such elements the small aperture which is due to the small thickness of the PN junction is of disadvantage.

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Semiconductor Element Acting as a Light Modulator

For the phase modulation of light by the linear, transversal electro-optical Pockels effect semiconductor crystals including a PN junction are used. The field existing in the depletion layer of the PN junction causes birefringence for a beam propagating along the junction plane and a phase shift of the component rays polarized perpendicularly with respect to one another. However in such elements the small aperture which is due to the small thickness of the PN junction is of disadvantage.

An optically active region of a larger width is produced by intercalating between the P- and N-regions of the crystal a layer with a high resistivity i.e. (S a semi-insulating layer). With a large thickness e.g., > 200 mu , of the latter layer it is also possible to use PSP or NSN structures.

Light from source 1 is transmitted through collimator 2 and polarizer 3 to the electro-optical element 4 consisting of a GaP crystal. Element 4 consists of PSN structure extending in parallel to the direction of light transmission therethrough. Such structure is reverse biased by the voltage applied to electrodes 5 and 6. Due to the field so produced in the S-region, this is rendered birefringent with different indices of refraction in directions perpendicular to one another. When the applied voltage reaches a suitable level the polarization plane of the light which is restricted to the field region by shutter 7, is rotated 90 degrees. In thi...