Patent ID: 7738527

Claim:
A semiconductor laser comprising: a first optical ring resonator comprising a first optical waveguide, at least a portion of said first optical waveguide being sandwiched between a pair of electrodes for injecting an electrical current to provide optical gain, a second optical ring resonator comprising a second optical waveguide, at least a portion of said second optical waveguide being sandwiched between a pair of electrodes for injecting an electrical current to provide optical gain, whereas the first and the second optical ring resonators have different round-trip optical path lengths, and are coupled to each other through a 2×2 optical coupler, said 2×2 optical coupler having predetermined cross-coupling coefficients that are substantially less than self-coupling coefficients and cross-coupling phases that are substantially equal to an integer multiple of π relative to self-coupling phases for achieving an optimal single-mode selectivity of the laser.