Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-08-05
2001-04-03
Bovernick, Rodney (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S017000, C385S018000
Reexamination Certificate
active
06212308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical switches. In particular, the invention relates to bistable optical switches that can be implemented in an integrated array.
2. Description of the Related Art
Fiber optics are used in a wide variety of applications. One application is in the area of communication systems. In such application, information signals, in the form of modulations of laser-produced light, are transmitted to, and received from, a plurality of terminals through fiber optic cables. A switching network is provided to selectively direct the information signals to, and from, the terminals. Typically, the switching network converts light emitted by transmitting one of the terminals into corresponding electrical signals. The electrical signals are directed to a selected output port of the switching network by electrical circuitry in the switching network. The electrical signals at the output port are converted into corresponding modulated light for retransmission through fiber optic cables to a receiving one of the terminals. The conversion of the modulated light to electrical signals and then back into modulated light energy, together with the electrical switching circuitry, requires the use of expensive components and/or restricts the potential bandwidth of the data communication system.
Recently, a number of optical switching systems have been developed. As the name implies, in optical switching networks, light emitted by typically any one of the cables is switched to another one of the cables without requiring intermediate conversion of the transmitted light data into electrical signals and then re-conversion of the electrical signal into light data. U.S. Pat. No. 5,255,332, Welch, et al., issued Oct. 19, 1993, entitled “NXN Optical Crossbar Switch Matrix”, (hereinafter “Welch”), describes one such optical switching system and provides a survey of optical switches that employ various schemes to achieve the switching.
One optical switch described in Welch is that of Jackel, et al., U.S. Pat. No. 4,988,157, issued Jan. 29, 1991, entitled “Optical Switch Using Bubbles”, (hereinafter “Jackel”). The Jackel optical switch is particularly useful as a bistable cross-connect matrix. Parallel input waveguides and parallel output waveguides are formed on a substrate at perpendicular angles so as to intersect. A forty-five degree slot is formed across each intersection and is filled with a fluid having a refractive index matching the waveguide material. Electrodes are positioned adjacent the slots and are selectively activated to electrolytically convert the fluid to gaseous bubbles. The bubbles destroy the index matching to the waveguide material and cause light to be reflected by the slot rather than propagate across the slot. In the presence of a catalyst, a pulse of opposite polarity, or of sufficient size and of the same polarity, will destroy the bubble.
Thus, the electrolyte associated with each intersection is selectively activated to alternately form and remove a gaseous bubble in the index-matching fluid at the slot. When the index-matching liquid fills the respective slot, the optical signal simply passes through the intersection. When the gaseous bubble displaces the index-matching liquid however, the index mismatch at the waveguide-slot interface causes the light to be reflected from the side of the slot into the intersecting waveguide. The bubble can be made bistable. That is, once created, the bubble will remain for periods of days.
Although bistable, the switch will ultimately fail when the bubble dissipates. Therefore, the switch must be periodically tested and/or reset to ensure proper operation during long-term periods (i.e., a week or longer). Furthermore, if a liquid that has an index of refraction closely matching that of the waveguides, such as an oil, is employed in the switch, the liquid can crack and oxidize. Thus, over time, the liquid will degrade into a varnish and the switch will not operate properly. On the other hand, water or light alcohols will not decompose when used in the switch. These liquids, however, do not have an index of refraction that closely matches that of the waveguide, thereby introducing reflection-associated crosstalk into the switch. Moreover, using electrolysis to create and remove bubbles can result in an unacceptably slow switching time for some applications.
SUMMARY OF THE INVENTION
A thermal optical switching cell is described that has a channel of either gas or boilable liquid crossing an optical waveguide at a forty-five degree angle. Two or more appropriately placed heater elements use the water/steam/dry states of thermal ink jet technology to quickly insert, or extract, boilable liquid respectively into, or from, the channel. The boilable liquid has an index of refraction close to that of the guide. In the wet state, the channel contains the liquid and nearly all the light of the incoming guide traverses the liquid along the axis of the guide. In the dry state, the channel contains gas. Total internal reflection (TIR) occurs and light is directed at right angles away from the axis of the incoming channel. A cross-bar switch is formed by adding a second waveguide, perpendicular to, and intersecting, the first waveguide at the channel.
These liquid switching cells toggle between the wet and dry states. A monitoring signal is also described that can be used to determine the state of the switch. No power is required to hold the switch in the most recent state.
The dry state of these cells is totally internally reflecting. The wet state, however, is transmissive with a small, but objectionable, amount of reflection. A push-pull optical circuit is formed using paired cells and at least one TIR mirror. One of the cells of the circuit is always in the TIR state to provide good isolation. This circuit also has the property of reporting the state of the switch-pair so that a fault can be detected. If a fault is detected, repeated activation pulses can be applied to force liquid into the correct places to maintain proper operation of the circuit.
REFERENCES:
patent: 4640592 (1987-02-01), Nishimura et al.
patent: 4988157 (1991-01-01), Jackel et al.
patent: 5978527 (1999-11-01), Donald
Agilent Technologie,s Inc.
Bovernick Rodney
Kim Ellen E.
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