Optical modulation device and optical modulation method

1. An optical modulation device configured to operate under a plurality of modulation formats, comprising:

a driving unit adapted to input a modulating signal and for providing a driving signal having a voltage;

a Mach-Zehnder modulator electrically connected to the driving unit, adapted to modulate inputted light in accordance with the driving signal from the driving unit, and adapted to output a modulated signal light;

an oscillator adapted to oscillate a predetermined frequency signal;

a bias controlling unit electrically connected to the Mach-Zehnder modulator and adapted to provide a bias voltage to the Mach-Zehnder modulator in accordance with a frequency component of the predetermined frequency signal in the modulated signal light from the Mach-Zehnder modulator;

a switch adapted to input the predetermined frequency signal from the oscillator, the switch changing an output destination of the predetermined frequency signal to the driving unit or the bias controlling unit; and

a controller configured to receive an external input designating one of the modulation formats, and to control paths of the switch and the voltage of the driving signal in accordance with the modulation format designated by the external input.

2. The optical modulation device of the claim 1 , wherein

the modulation formats are DPSK modulation and NRZ intensity modulation;

the controller controls the switch for providing predetermined frequency to a second path, and controls the voltage of the driving signal of the driving unit in 2V π when the modulation format is DPSK; and

the controller controls the switch for providing predetermined frequency to a first path, and controls the voltage of the driving signal of the driving unit in V π when the modulation format is NRZ intensity modulation.

3. The optical modulation device of the claim 1 , wherein

the modulation formats are RZ modulation and non modulation;

the modulating signal of the driving unit is a clock signal;

the controller controls the switch for providing predetermined frequency to a first path, and controls the voltage of the driving signal of the driving unit in V π when the modulation format is RZ; and

the controller controls the switch for providing predetermined frequency to a second path, and controls the voltage of the driving signal of the driving unit in an off state when the modulation format is non modulation.

4. The optical modulation device of the claim 1 , further comprising a frequency converter converting a frequency of the driving signal, the frequency converter providing the converted driving signal to the driving unit;

wherein

the modulation formats are RZ modulation and CSRZ modulation;

the modulating signal of the driving unit is a clock signal;

the controller controls the switch for providing predetermined frequency to a first path, and controls the voltage of the driving signal of the driving unit in V π when the modulation format is RZ; and

the controller controls the switch for providing predetermined frequency to a second path, and controls the voltage of the driving signal of the driving unit in 2V π when the modulation format is CSRZ.

5. The optical modulation device of the claim 1 , further comprising a differential phase-shift keying modulator that includes:

a first Mach-Zehnder modulator modulating inputted light in accordance with a first driving signal, the first Mach-Zehnder modulator for providing an outputted light itself to the Mach-Zehnder modulator;

a second Mach-Zehnder modulator modulating inputted light in accordance with a second driving signal, the second Mach-Zehnder modulator for providing an outputted light itself to the Mach-Zehnder modulator; and

a first phase controller controlling a phase difference between the first Mach-Zehnder modulator and the second Mach-Zehnder modulator.

6. The optical modulation device of the claim 5 , wherein

the modulation formats are DQPSK and DPSK modulation;

the controller controls the first driving signal and the second driving signal having a voltage 2V π when the modulation format is a changing request to DQPSK; and

the controller controls the first driving signal having a voltage 2V π and the second driving signal having a voltage in absence when the modulation format is DPSK.

7. The optical modulation device of the claim 5 , wherein

the differential phase-shift keying modulator includes a second phase controller for controlling a phase difference between the first driving signal and the second driving signal;

the modulation formats are DQPSK and Duobinary modulation;

the controller for controlling the second phase controller for setting up phase difference between the first driving signal and the second driving signal, and for controlling the first phase controller for setting up in π/2 phase difference between the output light of the first Mach-Zehnder modulator and the second Mach-Zehnder modulator when the modulation format is DQPSK; and

the controller for controlling the second phase controller for setting up in one bit delay between the first driving signal and the second driving signal, the controller for controlling the first phase controller for setting up in nπ between the first Mach-Zehnder modulator and the second Mach-Zehnder modulator when the modulation format is Duobinary.

8. The optical modulation device of the claim 5 wherein

the differential phase-shift keying modulator includes a second phase controller for controlling a phase difference between the first driving signal and the second driving signal;

the modulation formats are DQPSK and AMI modulation;

the controller for controlling the second phase controller for setting up phase difference between the first driving signal and the second driving signal, and for controlling the first phase controller for setting up in π/2 phase difference between the output light of the first Mach-Zehnder modulator and the second Mach-Zehnder modulator when the modulation format is DQPSK; and

the controller for controlling the second phase controller for setting up in one bit delay between the first driving signal and the second driving signal, the controller for controlling the first phase controller for setting up in nπ (n is integer number) between the first Mach-Zehnder modulator and the second Mach-Zehnder modulator when the modulation format is AMI modulation.

9. The optical modulation device of the claim 1 , further comprising a holding unit for holding a bias controlling point information in accordance with the one of the modulation formats; and

wherein the bias controlling unit controls the bias voltage providing to the Mach-Zehnder modulator in accordance with the bias controlling point information held in the holding unit when the Mach-Zehnder modulator changes the modulation format.

10. The optical modulation device of the claim 1 , further comprising:

a receiver receiving information for changing the modulation formats from a communication destination; and

a determining unit determining one of the modulation formats in accordance with the received information from the communication destination, and setting up the one of the modulation formats to the controller.

11. A method for changing a plurality of modulation formats in an optical modulation device having a Mach-Zehnder modulator, the method comprising:

supplying a drive signal to the Mach-Zehnder modulator;

supplying a bias voltage to the Mach-Zehnder modulator;

modulating inputted light with the Mach-Zehnder modulator on the bases of the drive signal and the bias voltage;

receiving an external input designating one of the modulation formats;

selectively superimposing a predetermined frequency signal on the drive signal in accordance with the external input; and

selectively superimposing the predetermined frequency signal on the bias voltage in accordance with the external input.

12. An optical modulation device configured to operate under a plurality of modulation formats, comprising:

a driving means for inputting a modulating signal and for providing a driving signal having a voltage;

a Mach-Zehnder modulator means for modulating inputted light in accordance with the driving signal from the driving means, and adapted to output a modulated signal light;

an oscillator means for oscillating a predetermined frequency signal;

a bias controlling means for providing a bias voltage to the Mach-Zehnder modulator in accordance with a frequency component of the predetermined frequency signal in the modulated signal light from the Mach-Zehnder modulator means;

a switch means for inputting the predetermined frequency signal from the oscillator means, and for changing an output destination of the predetermined frequency signal to the driving means or the bias controlling means; and

a controller means for receiving an external input designating one of the modulation formats, and for controlling paths of the switch means and the voltage of the driving signal in accordance with the modulation format designated by the external input.