Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-03-17
2001-08-14
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Switch
C385S039000
Reexamination Certificate
active
06275625
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical mirror switch and, more particularly, to an optical mirror switch based upon an optical implementation of a Michelson interferometer.
Conventional electro-optical switches can be realized using a number of different waveguide, electrode, and substrate implementations. Two different designs are used in commercially available electro-optical switches; the Mach-Zehnder and the &Dgr;&bgr; directional coupler. The Mach-Zehnder design is similar to that of a free-space, conventional Mach-Zehnder interferometer, except that the beam splitters/combiners are replaced by 3-dB directional couplers. Similar to the Mach-Zehnder, the first 3-dB coupler splits the incident signal into two signals, ideally of equal intensity. If a differential phase shift is introduced between these signals, then when they re-combine in the second 3-dB coupler, the ratio of power in the two outputs will be altered. Contrast ratios greater than 20 dB (e.g., 100:1) are routinely achieved in commercial devices. In the &Dgr;&bgr; directional coupler switch, electrodes are placed directly over (or immediately next to) the coupler and an applied electric field functions to alter the power transfer between the two adjacent waveguides. The contrast ratios achieved with the &Dgr;&bgr; directional coupler switch are comparable to those of the 3-dB coupler arrangement.
A “mirror” switch can be defined as an arrangement including a pair of bidirectional ports. In a first state of the mirror switch, the ports are directly coupled to each other (a “pass” state). In a second state (hereinafter referred to as the “reflective” state), the ports are de-coupled so that an input signal is directly reflected and then returned back through the same port, that is, an optical signal input into the first port would be reflected back into the first port and, optionally, an optical signal input into the second port would be reflected back into the second port.
SUMMARY OF THE INVENTION
The present invention relates to an optical mirror switch and, more particularly, to an optical mirror switch based upon an optical implementation of a Michelson interferometer.
In accordance with the present invention, the optical mirror switch comprises a conventional beam splitter, defined as including a set of four optical ports. One opposing pair of ports are defined as the “signal” ports for the mirror switch and are used to provide optical communication between these ports for the first, “pass through” state of the optical mirror switch. The remaining, opposing pair of ports are mirrored to form reflective surfaces at these locations, used to form the second, “reflective” state of the optical mirror switch. In general, an optical signal input at a first signal port will be “split” in half by the beam splitter, a first half directed to the first reflective port and the second half directed to the second reflective port. When the optical path lengths associated with the first reflective port and the second reflective port are equal (or differ by a multiple number of whole wavelengths), the two reflected optical signals will again pass through the beam splitter and thereafter “constructively” interfere with each other as they are coupled forward into the second (“exit”) signal port of the device. Alternatively, if the path lengths between the signal port and reflective ports differ by n&lgr;/2 (n=±1, +3, ±5, . . . ), “destructive” interference will occur in the forward direction, thus essentially “blocking” transmission between the two signal ports. However, “constructive” interference will occur back along the reflected path at the entrance to the first signal port, thus allowing the original input signal to be “reflected” back into its signal port of origin (thus providing the “reflective” state of the mirror switch).
In one embodiment the optical mirror switch may comprise a pair of optical fibers and associated focusing/collimating elements disposed along the two opposing paths of a beam splitter. A suitably oriented mirror element may be disposed along each remaining signal path of the beam splitter to form the complete device. The change in optical signal path length required to switch the device from its first, “pass through” state to its second, “reflective” state may be accomplished in a number of different ways, including but not limited to, physically moving one or both of the mirrors with respect to the beam splitter, tilting the beam splitter, or inserting an additional (transparent) element in one or both optical signal paths (functioning to either “speed up” or “slow down” the propagation of the optical signal along the path). In general, as long as the optical signal path lengths can be changed between “equal” (associated with the first, “pass through” state) and “n&lgr;/2”, n=±1, ±3, ±5, . . . , (associated with the second, “reflective” state), switching in accordance with the present invention will occur.
An alternative embodiment of the present invention comprises planar waveguides and an optical path length alteration arrangement disposed in the top surface of an optical substrate.
A complete understanding of these and other embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.
REFERENCES:
patent: 5647032 (1997-07-01), Jutamulia
Agere Systems Optoelectronics Guardian Corp.
Font Frank G.
Koba Wendy W.
Nguyen Tu T.
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