Patent ID: 7233714
Filing Date: 2007-06-19
Classification: G02B,G02F

Abstract:
1. A planar optical waveguide circuit variable attenuator having a substrate and an optical waveguide layer having cores and a clad formed on the substrate, which comprises: a Mach-Zehnder interferometer circuit having, in the cores, at least one input optical waveguide, an optical branch portion for causing branching of a light beam inputted from the input optical waveguide, at least one output optical waveguide, an optical coupling portion provided on the input side of the output optical waveguide, and two connection optical waveguides connecting the optical coupling portion with the optical branch portion and arranged being spaced from and in parallel with each other; phase adjusting means provided in at least one of the two connection optical waveguides, for adjusting a phase of a transmitted light beam; a slit formed in the optical waveguide layer, in a direction which crosses a longitudinally intermediate part of at least one of the input optical waveguide and the output optical waveguide; a liquid index matching medium charged in a part of the slit and having a refractive index approximated to that of the cores; and a matching medium displacing means for displacing the index matching medium to either a position which includes an optical path of a light beam in at least one of the input optical waveguide and the output optical waveguide, or a position which is retracted from the optical path, wherein one of the two connection optical waveguides which are spaced from and in parallel with each other is a first connection optical waveguide, and the other one of the two connection optical waveguides is a second connection optical waveguide, the first connection optical waveguide is formed therein with first and fourth phase adjusting means serving as the phase adjusting means, which are spaced from each other in the longitudinal direction and are arranged in that order, the second connection optical waveguide is formed therein with second and third phase adjusting means serving as the phase adjusting means, which are spaced from each other in the longitudinal direction and are arranged in that order, the first phase adjusting means has the same configuration as that of the third phase adjusting means, the second phase adjusting means has the same configuration as that of the fourth phase adjusting means, a first recess is formed as the optical waveguide removal portion on one side of the first phase adjusting means, at a first distance therefrom, a third recess is formed as the optical waveguide removal portion on one side of the third phase adjusting means, at a third distance therefrom, which is substantially equal to the first distance, a second recess is formed as the optical waveguide removal portion on one side of the second phase adjusting means at a second distance therefrom, which is different from the first distance, and a fourth recess is formed as the optical waveguide removal portion on one side of the fourth phase adjusting means at a fourth distance therefrom, which is substantially equal to the second distance.