High Dynamic Range Fiber Optic Link Measurements With Traveling Wave Linearized Directional Coupler Modulators

An important figure of merit for all high frequency analog transmission links is the spur free dynamic range (SFDR) which is the ratio of the largest to smallest signal that the link can transmit and receive without introducing distortion. The two factors which limit the dynamic range in fiber optic links are the system noise, predominantly from the laser relative intensity noise and the photodetector shot noise, and the non-linearity of the modulation process. The noise level of fiber optic systems has been reduced as much as possible for now through the use of high-power solid state or DFB lasers and attention has turned to improving the linearity of the modulation.