Patent ID: 8761612

Claim:
An optical transmitter comprising: a dividing optical coupler for dividing a lightwave onto optical paths; a first optical modulator in a first of the optical paths and driven by an I component of a first signal and a I component of a second signal for modulating the lightwave, a DC bias of the first optical modulator being at a quadrature point; a second optical modulator in a second of the optical paths and driven by a Q component of the first signal and a Q component of the second signal for modulating the lightwave, a DC bias of the second optical modulator being at the quadrature point; a phase shifter for generating a 90 degree phase shift in the Q components of the first and second signals that are modulated by the second optical modulator; and a combining optical coupler for combining the modulated lightwave from the first optical coupler and the phase shifted Q components of the first and second signals for generating a quadrature amplitude modulated signal; wherein the phase shifter generates an optical ray length of approximately one quarter of 1550 nm if the lightwave has a wavelength of near 1550 nm.