Method for modulating signal quality of an optical modulation communication system

A method for modulating signal quality of an optical modulation communication system, the optical modulation communication system comprising an optical fiber, an receiving device, and an optical modulating device, the optical modulating device being a Mach-Zehnder modulator (MZM), the method comprising:

• splitting an inputting optical signal by an optical splitting ratio with an optical splitter of the optical modulating device, which is adapted to receive the inputting optical signal;
• generating a first split optical signal and a second split optical signal;
• modulating the phase of the first split optical signal and the second split optical signal with an optical phase modulator of the optical modulating device being coupled to the optical splitter to receive the first split optical signal and the second split optical signal and respectively generating a first modulated optical signal and a second modulated optical signal;
• combining the first modulated optical signal and the second modulated optical signal by a combining ratio using an optical combiner of the optical modulating device that is coupled with the optical phase modulator and receives the first modulated optical signal and the second modulated optical signal, and
• generating an outputting optical signal having a desired chirp, and
• transmitting the outputting optical signal to the optical receiving device via the optical fiber, and
• demodulating the outputting optical signal with the optical receiving device, the method further comprising:
• selecting the desired chirp of the outputting optical signal according to a dispersion amount of the optical fiber, and
• setting the combining ratio being equal to the optical splitting ratio at a predetermined value, which corresponds to the desired chirp, wherein the predetermined value being a positive number, and the predetermined value being less than one or more than one, to make the outputting optical signal have a maximized optical modulation amplitude at the desired chip.