Patent ID: 8331798

Claim:
An optical m-ary modulator, comprising: an optical loop forming a polarization maintaining closed loop path; a loop input-output unit for receiving linearly polarized input signal light, splitting the input signal light into a first signal component and a second signal component, the first signal component and the second signal component also being linearly polarized, feeding the first signal component and the second signal component into the optical loop in mutually opposite directions, and recombining the first signal component and the second signal component after the first signal component and the second signal component have traveled around the optical loop to generate a returning optical signal including the first signal component and the second signal component; a first phase modulator disposed in the optical loop, for modulating an optical phase of the first signal component responsive to a first control signal representing a first binary data sequence; a second phase modulator disposed in the optical loop, for modulating an optical phase of the second signal component responsive to a second control signal representing a second binary data sequence; and an optical phase bias unit optically connected to the loop input-output unit, for creating a relative optical phase difference between the first signal component and the second signal component; wherein after the first signal component and the second signal component have passed through the optical phase bias unit and been recombined into the returning optical signal, the returning optical signal is output as an m-ary modulated optical signal; the first control signal and the second control signal are intensity modulated linearly polarized optical signals differing in wavelength from the input signal light; the optical loop includes a nonlinear polarization maintaining optical fiber; the first phase modulator includes a first optical coupler for inserting the first control signal into the nonlinear polarization maintaining optical fiber so that the first control signal and the first signal component propagate in identical directions through the nonlinear polarization maintaining optical fiber and the first control signal modulates the first signal component by an optical Kerr effect; and the second phase modulator includes a second optical coupler for inserting the second control signal into the nonlinear polarization maintaining optical fiber so that the second control signal and the second signal component propagate in identical directions through the nonlinear polarization maintaining optical fiber and the second control signal modulates the second signal component by the optical Kerr effect.