16 quadrature amplitude modulation optical signal transmitter

1. 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.

2. The optical transmitter according to claim 1 , wherein voltage value of the I components of the first and second signals is smaller than a half wave voltage of its respective optical modulator.

3. The optical transmitter according to claim 1 , wherein for 100 Gbit/s 16QAM signal generation out of the combining optical coupler the bit rate for the I and Q components each is 25 Gbit/s.

4. The optical transmitter according to claim 1 , wherein at least one of the I components the Q components are synchronized in a time domain.

5. The optical transmitter according to claim 1 , wherein the modulators are dual arm modulators being one of a LiNbO3 mach-Zehnder modulator and a InP mach-Zehnder modulator.

6. A method for generating an optical signal comprising the steps of:

dividing a lightwave onto optical paths;

modulating the lightwave on a first of the optical paths responsive to an I component of a first signal and a I component of a second signal, a DC biasing of the modulating of the I components being at a quadrature point;

modulating the lightwave on a second of the optical paths responsive to a Q component of the first signal and a Q component of the second signal, a DC biasing of the Q components being at the quadrature point;

generating a 90 degree phase shift in the modulated Q components; and

combining the modulated I components and the phase shifted Q components for generating a quadrature amplitude modulated signal;

wherein the generating step generates an optical ray length of approximately one quarter of 1550 nm if the lightwave divided onto the optical paths has a wavelength of nearly 1550 nm.

7. The method according to claim 6 , wherein a voltage value of the I components of the first and second signals is smaller than a half wave voltage of its respective optical modulator.

8. The method according to claim 6 , wherein for 100 Gbit/s 16QAM signal generation out of the combining step the bit rate for the I and Q components each is 25 Gbit/s.

9. The method according to claim 6 , wherein at least one of the I components the Q components are synchronized in a time domain.

10. The method according to claim 6 , wherein the modulating steps are carried out by dual arm modulators being one of a LiNbO3mach-Zehnder modulator and a InP mach-Zehnder modulator.