Optical modulator

1. An optical modulator characterized by comprising:

a 1×2 RZ pulse carver wherein optical phase shifters used for modulation are arranged along two arm waveguides held between a 1×2 coupler and a 2×2 coupler;

two interferometric modulators connected respectively to two output ports of the 2×2 coupler; and

a 2×1 combining coupler for combining the outputs of the interferometric modulators.

2. The optical modulator according to claim 1 , wherein a pulsed signal used to drive the 1×2 RZ pulse carver is a pulsed signal having an amplitude of Vπ and a repetition period CLK, wherein a drive waveform f(t) satisfies a relationship whereof

f ( t −CLK/2)=− f ( t ).

3. The optical modulator according to claim 2 , wherein the pulsed signal is a sine wave.

4. The optical modulator according to claim 1 , wherein the pulsed signal used to drive the 1×2 pulse carver is a pulsed signal having an amplitude of 2Vπ and a repetition period CLK, wherein when a drive waveform f(t) is

F ( t )=Abs{ f ( t )− Vπ/ 2 }−Vπ/ 2, or

F ( t )=Abs{ f ( t )+ Vπ/ 2 }−Vπ/ 2,

the drive waveform f(t) satisfies a relationship whereof

F ( t −CLK/2)=− F ( t ).

5. The optical modulator according to claim 4 , wherein the pulsed signal is a triangular wave with an amplitude center of +Vπ/2 or −Vπ/2.

6. The optical modulator according to claim 1 , wherein the interferometric modulator is a data modulator including phase shifters used for modulation that are arranged along two arm waveguides held between a 1×2 coupler and a 2×1 coupler, and

the optical modulator further comprises:

a delay circuit wherein a propagation delay time difference between output of the 2×2 coupler of the 1×2 RZ pulse carver and input of the 2×1 combining coupler is (k+0.5) times (k is an integer) a pulse carving period; and

a π/2 phase shifters for adjusting to 90° a relative optical phase difference for output light from the individual interferometric modulators during non-modulation.

7. The optical modulator according to claim 1 , wherein:

the 2×1 combining coupler is a polarization beam combiner performing polarization combining for a TE polarized light input from one input port and a TM polarized light input from the other input port;

the interferometric modulator is nest-Mach-Zehnder interferometric modulator including Mach-Zehnder interferometric modulators that are arranged along two arm waveguides held between a 1×2 coupler and a 2×1 coupler and includes a TE/TM polarization converter connected to one output of the Mach-Zehnder interferometric modulator; and

each of the Mach-Zehnder interferometric modulators are data modulators for each of which phase shifters are arranged, along two arm waveguides held between a 1×2 coupler and a 2×1 coupler, and include a π/2 phase shifters for adjusting to 90° a relative optical phase for output light from the 2×1 coupler of the individual Mach-Zehnder interferometric modulators during non-modulation.

8. The optical modulator according to claim 7 , further comprising a delay circuit for which a propagation delay time difference between output of the 2×2 coupler of the 1×2 RZ pulse carver and input of a splitting coupler of each of the interferometric modulators is (k+0.5) times (k is an integer) a pulse carving period.

9. The optical modulator according to claim 7 , wherein a propagation delay time difference between output of the 2×2 coupler of the 1×2 RZ pulse carver to the polarization beam combiner is k times of the pulse carving period.

10. The optical modulator according to claim 6 , wherein, where a delay length of the delay circuit is ΔL, and temperature dependence of a refractive index of a material to be replaced for an optical waveguide is dn/dT, the material has a length dL comp that satisfies

Δ

⁢

⁢

L

·

ⅆ

n

ⅆ

T

-

Δ

⁢

⁢

L

comp

·

ⅆ

n

comp

ⅆ

T

=

0.

11. The optical modulator according to claim 1 , further comprising optical output monitoring devices provided for individual outputs of the interferometric modulator.

12. The optical modulator according to claim 11 , wherein an operating point of the 1×2 RZ pulse carver is adjusted so equal to a temporal mean value for light intensities indicated by the individual optical output monitoring devices.

13. The optical modulator according to claim 1 , further comprising an optical output monitoring device provided for one or both of the outputs of the 2×2 coupler of the 1×2 RZ pulse carver.

14. The optical modulator according to claim 13 , wherein an operating point of the 1×2 RZ pulse carver is adjusted so equal to a temporal mean value for light intensities indicated by the optical output monitoring devices provided at the individual outputs of the 2×2 coupler.

15. The optical modulator according to claim 11 , wherein a very small dither signal is superimposed on a bias value of an operating point of the 1×2 RZ pulse carver, and the operating point of the 1×2 RZ pulse carver is adjusted, so that the amount of change in the optical intensity indicated by the optical output monitoring devices that is based on the dither signal reaches a maximum.

16. The optical modulator according to claim 8 , wherein, where a delay length of the delay circuit is ΔL, and temperature dependence of a refractive index of a material to be replaced for an optical waveguide is dn/dT, the material has a length dL comp that satisfies

Δ

⁢

⁢

L

·

ⅆ

n

ⅆ

T

-

Δ

⁢

⁢

L

comp

·

ⅆ

n

comp

ⅆ

T

=

0.

17. The optical modulator according to claim 13 , wherein a very small dither signal is superimposed on a bias value of an operating point of the 1×2 RZ pulse carver, and the operating point of the 1×2 RZ pulse carver is adjusted, so that the amount of change in the optical intensity indicated by the optical output monitoring devices that is based on the dither signal reaches a maximum.