Abstract: A signal transmission system includes an interface unit that monitors the operating condition of each device. The signal transmission system also includes a simulator that simulates the transmission quality of the system in response to the operating condition of each device, and controls each device so as to optimize the transmission quality.

Abstract: A polarization-independent optical wavelength filter uses a polarization splitter to divide an optical input signal into first and second signals with mutually perpendicular planes of polarization. The first signal propagates via a first optical path to a first end of an optical device, such as a TE-TM mode converter or a polarization-dependent filter, that acts selectively on the desired wavelength, then returns via a second optical path from a second end of the optical device to the polarization splitter. The second signal propagates via the second optical path to the second end of the same optical device, and returns from the first end via the first optical path to the polarization splitter. The polarization splitter recombines the returning signals into an optical output signal consisting only of the desired wavelength.

Abstract: A waveguide-type optical switch having a Y-branch structure composed of a Y-waveguide and branched waveguides provided with electrodes for electrically controlling the guide asynchronism thereof characterized in that the branched waveguides arranged at a converging angle of .theta..sub.1, and the Y-waveguide having a branching angle .theta..sub.2 (.theta..sub.2 >.theta..sub.1) connected to the branched waveguides. It is possible to shorten the length of the device of the Y-structured arrangement having the electrodes capable electrically of controlling the asynchronism of the branched waveguides.

Abstract: Waveguide-type optical switch comprising a substrate, branched first and second waveguide routes provided thereon, and an electrode(s) provided on the substrate for controlling the propagation-constant difference or refractive index difference between the first and second waveguide routes. The interval between the first and second waveguide routes is extended towards the terminal end sides from the branch point side of the waveguide routes. The first and second waveguide routes are provided with a branched part. The first and second waveguide routes are provided with at least one part of the bending portions (II) connected to the branch part, respectively. The local branch angle between the first and second waveguide routes on the side of starting ends of the bending portions (II) is enlarged while the local branch angle between the first and second waveguide routes on the side of terminal ends at the bending portions (II) is reduced.

Abstract: A waveguide type photoswitch has a substrate on which a plurality of waveguide paths are provided in close proximity to each other. Electrodes are arranged along the waveguide paths in a coupling region of the paths. The distance between the waveguide paths is greater at the center of the coupling region than at opposite ends of the region, so that the coupling coefficient can be reduced at the central part of the coupling region and the coupling region itself can be shortened. The electrodes each is shorter than the coupling region to allow the operating voltage to be noticeably lowered and the operation speed to be increased.

Abstract: In an electro-optic distributed coupler switch having a parallel rib geometry, a coupling enhancement region formed of the same material as the upper cladding layers but of lower step height is located between the ribs. By increasing the electric field strength, the coupling enhancement region enables the coupling length L.sub.c to be reduced.

Abstract: An optical switch matrix for selecting an optical propagation route between input ports and output ports by electric control. A first directional coupler is disposed on the input port side of a crosspoint of the matrix. A second directional coupler is disposed on the output port side of the crosspoint. A corner reflector is formed at a joint of the first and second directional coupler.