Variable Optical Attenuator Description

High intensity, coherent light beams are used as an increasingly common means of transmitting data. Optical fibers provide higher data rates with lower cost, weight and volume per units of length than cables relying on metallic conductors.

A variety of devices are known for controlling the light beam. Once of these is the fibre attenuator.

An exemplary optical attenuator is described and shown in U.S. NO. 4,192,573 to Brown, Jr.ct al. A flat mirror reflects an input beam of light. A focusing mirror receives the beam of light reflected from the flat mirror, so that the axis of the beam of light reflected by the focusing mirror is offset from and, parallel to, the axis of the input beam of light. A pinhole assembly receives the beam of light reflected from the focusing mirror. The pinhole assembly has a pinhole positioned on the axis of the beam of light reflected by the focusing mirror. A servo-motor actuates the flat mirror and the focusing mirror, in unison, relative to the pinhole assembly in a direction parallel to the axis of the input beam of light. The parallel movement of the mirror acts to vary the proportion of the input beam of light that passes through the pinhole. The servo mechanism is bulky and requires a relatively long period of time to move the mirrors relative to the pinhole assembly.

The present invention is a variable optical attenuator (VOA) which has a semiconductor micro-electro-mechanical device for positioning a reflecting surface in any of a plurality of positions, each providing a respectively different amount of attenuation.

The variable optical attenuator includes a Icns, a first optical waveguide, and a second optical waveguide. A semiconductor micro-electro-mechanical device is positioned on a side of the lens opposite the first and second optical waveguides. The device has a reflecting surface. The reflecting surface has a normal position in which light from the first waveguide reflects off of the reflecting surface and passes through the lens into the second waveguide. The reflecting surface has a plurality of respectively different attenuation positions in which light from the first waveguide reflects off of the reflecting surface and passes through the lens, but an amount of light entering the second optical waveguide is attenuated by respectively different amounts corresponding to the respectively different positions.

According to a further aspect of the invention, a method for controlling a beam of light includes providing a lens, first and second optical waveguides, and a semiconductor micro-electro-mechanical device positioned on a side of the lens opposite the first and second optical waveguides. The devices having a reflecting surface. The reflecting surface is pivoted to a normal position in which light from the first waveguide reflects off of the reflecting surface and passes through the lens into the second waveguide. The reflecting surface is pivoted to a plurality of respectively different attenuating positions in which light from the first waveguide reflects off of the reflecting surface and passes through the lens, but an amount of light entering the second optical waveguide is attenuated by respectively different amounts corresponding to the respectively different positions.
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