Fiberoptic liquid crystal on-off switch and variable attenuator

Optical waveguides – With optical coupler – Switch

Reexamination Certificate

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Details

C385S016000, C385S033000, C385S140000, C349S196000

Reexamination Certificate

active

06181846

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is related to optical fiber networks, and, in particular, to switches for directing optical signals along fibers of an optical network, or to attenuators for controlling the strength of optical signals in an optical fiber.
In optical fiber networks, switches are often used to direct optical signals along one optical fiber or another. Many, if not most of these switches, are electromechanical devices which have parts moving in response to electrical signals. While miniaturization has desirably reduced the switching speeds of such devices, switch parts are still being accelerated and decelerated with the consequent wear and breakdown. Furthermore, physical movement of parts places an effective limitation on further improvement on switching speeds. Hence it is desirable that fiberoptic devices, including switches, be purely optical, or electro-optical devices. Such devices ideally do not have moving parts.
The present invention provides for a switch which is electro-optical. By applying preselected electrical voltages to the switch corresponding to an On state and an Off state, the switch transmits optical signals between two optical fibers or blocks the signals. Furthermore, by applying electrical voltages intermediate the preselected voltages, the switch operates as an electro-optical attenuator. Attenuators are often used in fiberoptic networks to balance the strength of optical signals along different paths. By controlling the voltage to the device of the present invention, the strength of the signals between two optical fibers may be varied.
SUMMARY OF THE INVENTION
The present invention provides for a fiberoptic liquid crystal on-off switch and variable attenuator comprising a sleeve having a central longitudinal channel and an end face; first and second optical fiber cores fixed in the channel, a birefringent crystal next to the sleeve end face, a quarter-pitch GRIN lens having a first end face next to the sleeve end face and the birefringent crystal, a liquid crystal cell next to the opposite end face of the GRIN lens, and a mirror element next to the liquid crystal cell. End facets of the first and second optical fiber cores, the birefringent crystal, the GRIN lens, the liquid crystal cell and the mirror element are arranged and oriented with respect to each other so that light from the first optical fiber core passes through, and back from, the first birefringent crystal, the GRIN lens, the liquid crystal cell and the mirror element into the second optical fiber core when the liquid crystal cell is in a first state. When the liquid crystal cell is in an opposite second state, light from the first optical fiber core passes through, and back from, the first birefringent crystal, the GRIN lens, the liquid crystal cell and the mirror element, but not into the second optical fiber core.
The first and second states of the liquid crystal cell are the extreme On and Off states so that the operation of the described device is that of a switch. If voltages intermediate to those corresponding to the On and Off states are applied to the liquid crystal cell, the amount of light passing between the first and second optical fiber cores are proportionally controlled. The device operates as an attenuator.


REFERENCES:
patent: 5276747 (1994-01-01), Pan
patent: 5727109 (1998-03-01), Pan et al.
patent: 5742712 (1998-04-01), Pan et al.
patent: 6023542 (2000-02-01), Pan et al.

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