WAVEGUIDE BENDS AND DEVICES INCLUDING WAVEGUIDE BENDS

摘要

Waveguide bends are specially designed according to a matching condition in order to suppress mode distortion and other undesirable effects. Generally, an optical field in a waveguide bend (58) is describable by first and second bend modes which are in phase at the start of the bend, but which propagate at different velocities through the bend, thereby coming out of phase and into phase with each other in beats. According to the teaching of the invention, the bend (58) is structured having regard to its length and curvature (1, R, &thetas;) to ensure that at its end the first and second bend modes are substantially in phase with each other having completed approximately an integer number of beats. By being in phase at the end of the bend, the two modes are able to properly reconstruct the first mode of the straight waveguide and propagate on with a minimum of distortion, whether it be into a straight section, a further curved section of arbitrary curvature, into a free space propagation region or whatever. This approach can be used to suppress mode distortion, transition losses and other negative effects of waveguide bends, without inserting small lateral jumps as proposed in the prior art. A number of device applications are discussed, including couplers, Y-branches and Mach-Zehnder interferometers, all of which include waveguide bends.