Optical Switch
Corporation's technology is based upon both Frustrated Total Internal Reflection
(FTIR),
and Total Internal Reflection (TIR). TIR is based on the critical angle defined in Snell's
law, where optical rays beyond some critical angle are totally and perfectly reflected
with no polarization dependence. This is the same optical physics utilized to constrain
the optical energy in the optical fibers of today's network. A fiber-to-Gradient Index
Lens (GRIN), is utilized to launch a collimated beam into prism, which reflects the beam
at the hypotenuse. When a switch plate is brought into contact with The surface of the
prism at the point of Total Internal Reflection, the beam is frustrated (FTIR) and travels
into the switch plate where it is again reflected from the rear surface of the switch
plate by TIR. As a result, the angular position of the light beam is changed, (a different
angle is encoded) causing the focusing GRIN to shift the beam from the primary to
secondary fiber.
When multiple switch plates are used within a sequence of prisms, multiple output light
beams can be coupled into a larger GRIN Lens fiber array, to support as many as 256 output
fibers. Therefore, 1XN switching matrices or back-to-back 1XN matrices can be fabricated
to create true non-blocking optical switches in configurations of 1X2, 2X2, 1X4, 4X4,
etc., or as large as 256X256 and beyond. Each switch plate is capable of switching an
incoming beam into either primary or secondary light beam coupled into either output
fiber. Both the optical and switch performance characteristics are superb. The FTIR
optical switch is both bit rate and wavelength independent and the actual switch
transition time of the FTIR switch is less than 2msec. Optical performance is optimized,
yielding low insertion loss across any NXN connection (2dB for an 8X8 matrix, as an
example), superior optical channel isolation and excellent optical reflectance
characteristics with negligible polarization components.
Because the beam is switched by intimate contact of the switch plate, which is under
positive pressure to the prism surface, FTIR technology can be subjected to extreme
environmental conditions such as temperature, shock and vibration, without degradation of
the optical signal.
The basic FTIR switch is composed of a prism and switch plate as the centerpiece of the
switch. In order to couple incoming light from the fiber into the prism, a Graded Index
Lens (GRIN is used to convert to the light from the fiber into a collimated beam that is
transmitted in to the prism and reflected off of the reflective surface (hypotenuse).
Likewise, the focusing lens is used to focus the collimated beams of light back into the
fibers. The switch plate, positioned on the
top of the prism's reflecting surface at the collimated beam, is a circular plate of glass
with the back (reflecting surface) ground at an angle to the front (contacting surface).
This switch plate is actuated by a Piezoelectric Bimorph Transducer. When the Switch Plate
is not engaged, a total internal reflection of the Input light to the primary output
occurs. When the Switch Plate is engaged, the circular switch plate makes intimate contact
(less than 100 angstroms) with the surface of the prism thus "frustrating the beam of
light to the secondary output.
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