Patent ID: 7664346

Claim:
A waveguide type broadband optical isolator, comprising: a reciprocal phase shifter which makes a phase difference of 3π/2 between a first light wave propagating through a first waveguide and a second light wave propagating through a second waveguide, with a fundamental operating wavelength λ; and a nonreciprocal phase shifter which provides a phase difference of π/2 for forward propagating waves and a phase difference of −π/2 for backward propagating waves; wherein: said reciprocal phase shifter includes a tapered waveguide in a propagation direction of a light wave and also includes a tapered waveguide in a part of the other one of said first and second waveguides; said first waveguide includes said reciprocal phase shifter; said second waveguide has an adjustment section for adjusting a phase shift by said reciprocal phase shifter; and said adjustment section has an optical path length L 2 and a waveguide propagation constant β 2 satisfying a formula β 1 ×L 1 −β 2 ×L 2 =( x +¾)×2π wherein “L 0 ” is an optical path length between branching/coupling devices of said first waveguide which does not include said reciprocal phase shifter, “β 2 ” is a propagation constant, “L 1 ” is an optical path length of said reciprocal phase shifter, “β 1 ” is a propagation constant, and “x” is an integer of zero or more.