An optical switch having an input waveguide and two output waveguides separated by and disposed around a trench. The input waveguide and a first output waveguide have respective optical paths defined by their respective cores which are coaxial with each other. Those waveguides are also
An optical phase shifter including a constant phase shift element or a variable phase shift element, each introducing a desired and predetermined phase shift into an optical signal passing through the phase shifter. The phase shifter has coaxial first and second waveguides each with a co
