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A fast acting, low insertion loss switch for use in an optical fiber communication system includes a small diameter waist region incorporating a Bragg grating which is precisely tuned by tensioning to be reflective at a selective wavelength band. By a small physical shift of the waist, as by lateral

A fast acting, low insertion loss switch for use in an optical fiber communication system includes a small diameter waist region incorporating a Bragg grating which is precisely tuned by tensioning to be reflective at a selective wavelength band. By a small physical shift of the waist, as by lateral displacement of an attached small magnetic element with a magnetic field, the periodicity of the grating is varied so that the selected wavelength is passed through the waist with virtually no loss. The incremental motion required can be introduced by a variety of devices, selected in accordance with cost, size and response time requirements. Modules having a number of such switches in close juxtaposition offer distinct advantages for wavelength division multiplexed systems.

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1. A switch for selectively diverting throughput optical signals in one of a number of spaced apart predetermined wavelength bands of defined wavelength width from a throughput path to a drop path, the wavelength bands being spaced apart by preestablished separation bands, comprising:an optical sign

1. A switch for selectively diverting throughput optical signals in one of a number of spaced apart predetermined wavelength bands of defined wavelength width from a throughput path to a drop path, the wavelength bands being spaced apart by preestablished separation bands, comprising:an optical signal coupler including a multi-terminal optic device incorporating a periodic grating in a length that is extensible within elastic limits, the terminals including an input port, a throughput port and a drop port, and wherein the grating periodicity diverts a selected wavelength band from the input port to the drop port; a temperature compensating support structure mounted to suspend at least the periodic grating length of the coupler with a tension to provide periodicity responsive to a selected wavelength band within a selected temperature range, and a deflecting device in adjacent and orthogonal spaced apart relation to the suspended length of the coupler and effective to deflect the grating length and change the tension on the grating length such that the grating periodicity shifts to be responsive to optical signals in a different separation band without affecting the temperature compensation in the selected temperature range.