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Tunable Optical Filter Using a Wedge-Shaped Dispersive Medium

IP.com Disclosure Number: IPCOM000121199D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 1 page(s) / 42K

Publishing Venue

IBM

Related People

Green Jr, PE: AUTHOR [+2]

Abstract

An electrically tunable optical filter is disclosed that introduces, between the mirrors of a Fabry-Perot cavity, a boundary between two regions having different n(g), index as a function of wavelength as shown in Fig. 1.

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Tunable Optical Filter Using a Wedge-Shaped Dispersive Medium

      An electrically tunable optical filter is disclosed that
introduces, between the mirrors of a Fabry-Perot cavity, a boundary
between two regions having different n(g), index as a function of
wavelength as shown in Fig. 1.

      At some particular wavelength, the indices will be equal, the
wedge will be invisible, and the device will act as an ordinary
Fabry-Perot cavity, showing a series of spaced sharp resonance peaks
as shown in Fig. 2.

      As the wavelength of the incident light is changed, two
filtering actions take place, a fine and a coarse wavelength
selectivity.  The fine wavelength selectivity is that of the
Fabry-Perot resonances as shown in Fig. 2.  The coarse filtering
action is due to the fact that, as the wavelength deviates from that
for which the indices of refraction in the two regions are identical,
at the boundary there will be off-angle partial reflections and
transmissions and the ray paths of the light will walk off sideways,
thus destroying the Fabry-Perot cavity resonances.  The overall
effect is schematized in Fig. 3.

      The device is made electrically tunable by making one of the
indices voltage dependent.

      Disclosed anonymously.