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Improvement of Franz Keldysh Light Modulator

IP.com Disclosure Number: IPCOM000096567D
Original Publication Date: 1963-Jul-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Levitt, RS: AUTHOR [+2]

Abstract

This relates to an improved version of the Franz-Keldysh light modulator, based on the Franz-Keldysh effect. Such effect is the change of the intrinsic optical absorption edge of a semiconductor caused by application of an electric field. The absorption coefficient for light which excites electrons across the forbidden energy gap of the semiconductor is, in turn, changed by the change in the gap.

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Improvement of Franz Keldysh Light Modulator

This relates to an improved version of the Franz-Keldysh light modulator, based on the Franz-Keldysh effect. Such effect is the change of the intrinsic optical absorption edge of a semiconductor caused by application of an electric field. The absorption coefficient for light which excites electrons across the forbidden energy gap of the semiconductor is, in turn, changed by the change in the gap.

The difficulties present with the Franz-Keldysh light modulator have previously been indicated to be due to the conductivity imparted to the semiconductor by the excitation of electrons across the energy gap. The conductivity leads to very large electrical power dissipation by the high electric field used to change the gap and consequent-undesirable heating of the modulating semiconductor crystal.

The improvement here is based on the observation that the energy of certain relatively sharp absorption lines, the exciton lines, at energies somewhat less than the intrinsic gap energy can be expected to vary with electric field in the same way as the gap energy. This expectation is based on physical theory and on the fact that energy levels near a band edge generally closely follow the energy of the band edge when the gap is changed in other ways. Thus, the absorption coefficient at a wavelength on the shoulder of an exciton line can be varied by the application of an electric field. The use of this effect as a light modulator is d...