Apparatus and method for optical modulation and demodulation

A Mach-Zehnder optical modulator in which an optical waveguide having first and second light paths is provided on a substrate having electro-optical effect and in which a signal electrode is placed in the first light path to cause a phase difference between light that is transmitted through the first light path and light that is transmitted through the second light path, said Mach-Zehnder optical modulator comprising:

• at least one phase modulation electrode which provides phase modulation to light being transmitted through at least one of the first and second light paths provided in the Mach-Zehnder optical modulator;
• and
• at least one driving circuit, coupled to said at least one phase modulation electrode, supplying a first driving signal to light passing through the first light path that imparts chirping with a phase offset to substantially cancel the chirping after the light passing through the first light path and light passing through the second light path are coupled by the optical waveguide, thereby increasing dispersion tolerance.

A Mach-Zehnder optical modulator in which an optical waveguide having first and second light paths is provided on a substrate having electro-optical effect and in which first and second signal electrodes are placed in the first and second light paths, respectively, to receive first and second driving signals causing a phase difference between light that is transmitted through the first light path and light that is transmitted through the second light path, said Mach-Zehnder optical modulator comprising:

• a third electrode which provides phase modulation to light being transmitted through one or both of the first and second light paths provided in the Mach-Zehnder optical modulator;
• and
• a driving circuit coupled to supply a third driving signal to said third electrode so that chirping imparted by the first, second and third driving signals to light passing through the first and second light paths are offset by each other after the light passing through the first light path and the light passing through the second light path are coupled by the optical waveguide, thereby increasing dispersion tolerance.

A method for optical modulation using a Mach-Zehnder optical modulator in which an optical waveguide having first and second light paths is provided on a substrate having electro-optical effect and in which a first signal electrode is placed in the first light path so as to cause a phase difference between light that is transmitted through the first light path and light that is transmitted through the second light path, said method comprising:

• providing phase modulation to light being transmitted through one or both of the first and second light paths provided in the Mach-Zehnder optical modulator so that chirping imparted by a first driving signal to light passing through the first light path is offset after the light passing through the first light path and light passing through the second light path are coupled, thereby increasing dispersion tolerance.

A method for optical modulation using a Mach-Zehnder optical modulator in which an optical waveguide having first and second light paths is provided on a substrate having electro-optical effect and in which first and second signal electrodes are placed in the first and second light paths, respectively, so as to cause a phase difference between light that is transmitted through the first light path and light that is transmitted through the second light path, said method comprising:

• providing phase modulation to light being transmitted through one or both of the first and second light paths provided in the Mach-Zehnder optical modulator so that chirping imparted by a first driving signal to light passing through the first light path and chirping imparted by a second driving signal to light passing through the second light path are offset by each other after the light passing through the first light path and the light passing through the second light path are coupled, thereby increasing dispersion tolerance.

An optical transmitter using a Mach-Zehnder optical modulator in which an optical waveguide having first and second light paths is provided on a substrate having electro-optical effect and in which a signal electrode is placed in the first light path to cause a phase difference between light that is transmitted through the first light path and light that is transmitted through the second light path, said optical transmitter comprising:

• at least one phase modulation electrode which provides phase modulation to light being transmitted through at least one of the first and second light paths provided in the Mach-Zehnder optical modulator;
• and
• at least one driving circuit, coupled to said at least one phase modulation electrode, supplying a first driving signal to light passing through the first light path that imparts chirping with a phase offset to substantially cancel the chirping after the light passing through the first light path and light passing through the second light path are coupled by the optical waveguide, thereby increasing dispersion tolerance.

An optical transmitter using a Mach-Zehnder optical modulator in which an optical waveguide having first and second light paths is provided on a substrate having electro-optical effect and in which first and second signal electrodes are placed in the first and second light paths, respectively, to receive first and second driving signals causing a phase difference between light that is transmitted through the first light path and light that is transmitted through the second light path, said optical transmitter comprising;

• a third electrode which provides phase modulation to light being transmitted through one or both of the first and second light paths provided in the Mach-Zehnder optical modulator;
• and
• a driving circuit coupled to supply a third driving signal to said third electrode so that chirping imparted by the first, second and third driving signals to light passing through the first and second light paths are offset by each other after the light passing through the first light path and the light passing through the second light path are coupled by the optical waveguide, thereby increasing dispersion tolerance.