Optical phase modulator design incorporating pre-emphasis

Abstract

An optical modulator ( ) that operates as a phase modulator at high frequency and as a frequency modulator at low frequencies to provide a suitable signal-to-noise ratio over a wide frequency band. The modulator ( ) includes an optical waveguide and opposing RF electrodes ( ) formed in the waveguide ( ). An RF input signal is applied to the electrodes ( ) to create an electric field that changes the index of refraction of the waveguide ( ) to affect the propagation speed of an optical carrier signal ( ), and thus provide the modulation. The electrodes ( ) are long velocity-matched electrodes that provide the RF loss versus RF frequency needed to produce the desired V&pgr; versus RF frequency over the entire bandwidth. The lower V&pgr; at lower RF frequencies will emphasize the lower frequencies and improve the low-frequency fidelity of the optical link by boosting the low-frequency signals above the excess link noise generated in the demodulator ( ).