All-Fiber, Optically Controlled Optical Switch

National Security Agency, Ft. George G. Meade, Maryland

An optical switch is a device where information-bearing light may be directed to one of several outputs. Prior art optical switches have mainly been integrated optical waveguide structures such as titanium-diffused (Ti) waveguides in lithium-niobate (LiNbO₃) or gallium-arsenide (GaAs) structures, or other compound semiconductors.

One problem with integrated optic switches is that they may be connected to an optic fiber since such fibers are the primary carriers of optical communications. Coupling between integrated optic switches and optical fiber is an inefficient process because the modal fields of these two elements are not compatible, and large differences in the indices of refraction lead to large reflection losses.

The prior art optical switches have been controlled, primarily, by electro-optic or acousto-optic techniques. In such an arrangement, the waveguides of the optical switch are separated or surrounded by electro-optic or acousto-optic material that controls the coupling between the waveguides. Such control is not the fastest control possible because coupling in such devices occurs through the electro-optic or acousto-optic material. Also, such control does not provide a system optimized with respect to the number of elements contained therein.

A two-fiber optical switch exists where one of the fibers is replaced with a slab waveguide. Although the slab waveguide provides benefits such as providing couplings between more modes than can a two-fiber optical switch, a slab-fiber optical switch still suffers from the problems listed above for a two-fiber optical switch.

The invention described here is an optical switch that includes two optic fiber waveguides, and a third optical waveguide. The three waveguides are in the same plane. The third optical waveguide may be an optic fiber or a slab waveguide. The other two optic fiber waveguides are close enough to exhibit evanescent wave coupling under noninterference conditions. The second optic fiber waveguide is between the other two waveguides and closer to the third optical waveguide. The first and second optic fiber waveguides have identical propagation constants.

An information-bearing optical signal is applied to the first optic fiber waveguide. An optical control signal applied to the third optical waveguide controls its propagation constant and, therefore, controls whether switching occurs between the first and second fiber optic waveguides. The optical switch may be made to be normally on or normally off.

The optical switch may utilize standard communication-sized optic fibers for signal transport in and out of the switch so that the signal-bearing materials of the switch match materials to which the switch may be connected. Matching signal-bearing materials minimizes the loss of optical power. The switch is optically controlled so that switching speed is maximized. Control of the switch is separated from the signal transport medium to eliminate interference between a control signal and an information-bearing signal, and to facilitate the matching of signal-bearing materials.

For more information, contact the NSA Technology Transfer Program at This email address is being protected from spambots. You need JavaScript enabled to view it.; 866-680-4539.