Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-04-05
2003-12-16
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S017000, C359S222100
Reexamination Certificate
active
06665461
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to optical switches and, more specifically, to a total internal reflection (TIR) optical switch and method of operating the switch to selectively guide beams of light.
BACKGROUND OF THE INVENTION
In today's rapidly expanding optical network, a critical need exists for a fast reversing optical bypass switch to redirect an optical signal from one path to another. Optical switches of this type find use in a network having a number of communication nodes connected sequentially to form a ring, one or more nodes may require temporary removal from the network. To achieve this removal, the optical fibers interconnecting the network must be able to “switch” the node(s) from an active (transmit/receive) state to a passive (bypass) state. Optical switches of this type find further use in wavelength division multiplexing (WDM) transmission systems, in which a need exists for add/drop switches to add and drop traffic along the route.
Currently, several different technologies are used to make optical fiber switches (exclusive of the integrated optical switch). One technology is known as “moving fiber.” In this technology, either the input optical fibers, the output optical fibers, or both, are physically moved relative to one another to switch the light path between outputs.
Another technology is known as “moving prism” or “moving mirror.” In this technology, a refractive or reflective medium (i.e., a prism or a mirror) positioned in the optical path between input and output optical fibers is reoriented to switch the light path between outputs; the fibers themselves do not move.
Examples of moving prism optical switches are set forth in U.S. Pat. Nos. 2,565,514; 4,303,303; 4,322,126; 4,589,726; 4,927,225 (which employs a gradient index of refraction, or GRIN, lens to bend the light path); and 5,647,033. Examples of moving mirror optical switches are set forth in U.S. Pat. Nos. 3,611,436; 3,716,804; 4,208,094; 4,304,460; 4,626,066; 4,932,745; 5,000,534; 5,042,889; 5,221,987; 5,436,986; 5,444,801; 5,555,558; 5,566,260; and 5,875,271.
Still other technologies employ liquid crystal, bubble or micro-electromechanical systems (MEMS) switches to switch light paths. Examples of such optical switches will not be set forth here.
In contrast to the above-described technologies, frustrated total internal reflection (FTIR) switching technology provides a virtual solid state optical switching ability that overcomes the limitations of the previously listed switches.
FTIR optical switches, in general, go back to at least 1947. In almost all cases, FTIR optical switch designs feature an air gap between two solid bodies of similar material. A disparate index of refraction caused by the air gap produces total internal reflection in the bodies. By various mechanical means, a movable one of the two bodies of material (called the “switch plate”) is selectively moved toward the other of the two bodies to drive the air gap between the two bodies to less than {fraction (1/10)}
th
of a wavelength (of the light to be switched) in thickness. This frustrates the total internal reflection in the other of the two bodies, changes the optical path in the other of the two bodies, and lends the technology its name.
Unfortunately, In many of these conventional FTIR optical switches, the reflection does not go to zero, a fact that most corresponding patents acknowledge. Examples of conventional FTIR optical switch designs suffering these disadvantages are found in U.S. Pat. Nos. 2,997,922; 3,338.656; 3,376,092; 3,514,183; 3,559,101; 3,649,105; and 4,249,814. Although these patents fail to address the underlying reason why, all of these FTIR optical switches have difficulty closing the gap to less than {fraction (1/10)}
th
wavelength.
U.S. Pat. Nos. 5,221,987; 5,555,327 and 5,909,301 purport that the problem in closing the air gap to less than {fraction (1/10)}
th
wavelength is caused by air being trapped in the air gap, owing to the rate at which the air gap is closed during operation of the optical switch. As a result, these patents teach that, by forming the switch plate of a thin material and exerting a peel force to lift the edges of the switch plate first, less force is required than the shear force that would otherwise be required to lift the switch plate all at once.
Despite all efforts to the contrary, the problem of closing the air gap inexplicably remains in FTIR optical switches employing peel-force thin switch plates. What is needed in the art is a recognition of what is causing the problem of closing the air gap reliably. What is needed in response to that recognition is a fundamentally different structure for a TIR optical switch that reliably closes and opens its air gap to switch optical signals reliably. What is further needed in the art is a wholly new reversing optical switch architecture.
SUMMARY OF THE INVENTION
It has been discovered that the failure to close the air gap to less than {fraction (1/10)}
th
wavelength is caused by surface irregularities and transient dimpling due to uneven application of force to a thin switch plate, which causes the switch plate to deform transiently. The deformation usually takes the form of dimpling. Though transient, the dimpling remains long enough to hamper suitably high speed switching.
Thin switch plates are subject to deformation due to shock waves created as they are suddenly moved. Shock waves, particularly those created at the edge of a switch plate, cause transient deformations that, in turn, causes a gap that results in a transient partial reflection, from the interface. In the case of U.S. Pat. No. 5,909,301, the gap is in the center, the active area of the switch. Many of the above-described FTIR optical switches drive in such a manner that the shockwave produced by the transducer reaches the outer edges before reaching the center. This causes a gap to form at the center and hinders closing of the optical switch.
To address these and other deficiencies of the prior art, the present invention provides novel architectures of optical switches and N×N cross bar optical switches. In one embodiment, an optical switch constructed according to the principles of the present invention includes: (1) a primary refracting body having a total internal reflecting surface and capable of transmitting optical energy therethrough, (2) a frustrating refracting body having a frustrating surface located proximate the total internal reflecting surface and (3) an actuator, coupled to the primary refracting body and the frustrating refracting body, that drives at least a center portion of the frustrating refracting body. In another embodiment, the actuator can drive the frustrating refracting body between (1) an open state, in which a collimated beam emanating from the first collimating lens reflects off the total internal reflecting surface and travels toward the second collimating lens, and (2) a closed state, in which the collimated beam emanating from the first collimating lens reflects off the angled mirror and travels back toward the first collimating lens.
The present invention introduces the broad concept of providing an optical switch in which opposing optical beams are launched at each other and selectively reflected by the total internal reflecting surface associated with the primary refracting body or the mirror associated with the frustrating refracting body. The actuation, which reduces the total internal reflection of the total internal reflecting surface, changes the path such that the input optical beams are reflected almost back upon themselves to the collimating lens that launched them.
In one embodiment of the present invention, actuation of the center portion of the frustrating refract body initiates a shock wave in the frustrating refracting body that emanates outward from the center portion to edges thereof thereby to frustrate a reflection of the total internal reflecting surface. The total internal reflection can be reduced by a shock wave that propagates first to
Sanghavi Hemang
Song Sarah N
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