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Electrically Tunable Optical Filter

IP.com Disclosure Number: IPCOM000034785D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

Dono, NR: AUTHOR [+3]

Abstract

This article describes the use of two simple optical grating filters with an interposed array of electrophotonic gates to achieve an electrically actuated wavelength selective filter in a simple structure. In any wavelength division multiaccess network it is necessary to select a single wavelength band out of a set of possible bands so as either to transmit or to receive one of a comb of wavelengths spaced at intervals along the wavelength axis. This function is usually performed by a tunable optical filter, such as a mechanically adjustable Fabry-Perot Interferometer (FPI) [1,2] or a thermally tuned Periodic Filter (PF) [3]. Mechanical or thermal tuning is often too slow to meet the requirements for speed of reconfiguration (switching).

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Electrically Tunable Optical Filter

This article describes the use of two simple optical grating filters with an interposed array of electrophotonic gates to achieve an electrically actuated wavelength selective filter in a simple structure. In any wavelength division multiaccess network it is necessary to select a single wavelength band out of a set of possible bands so as either to transmit or to receive one of a comb of wavelengths spaced at intervals along the wavelength axis. This function is usually performed by a tunable optical filter, such as a mechanically adjustable Fabry-Perot Interferometer (FPI) [1,2] or a thermally tuned Periodic Filter (PF) [3]. Mechanical or thermal tuning is often too slow to meet the requirements for speed of reconfiguration (switching). It is estimated that even micromachined FPIs (using electrostatic forces to electrically retune) will require hundreds of microseconds to retune, and thermal tuning of PFs is known to take ten times that long. Also, the stability of the readjustment to the new value may prove insufficient, whereupon some means of tracking must be provided. The proposed solution, as shown in the figure, takes two diffraction grating filters and uses the first to demultiplex the incoming comb of N wavelengths, one onto each of N fibers, each of which is an input to an electro-optical switch. The fiber outputs of all N switches are led to the proper inputs of a second grating device operating as a multiplexer. The DEMUX and MUX devices are identical, but face in opposite directions.

The Li wavelength emerging from tap i of the left-hand (DEMUX) grating filter is connected (through the switch) to the same Li input of the right-hand (MUX) grat...