Design of externally tuned asymmetric fibre Fabry-Perot electroabsorption optical modulators

The authors present design criteria for a fibre-matched, externally tunable, asymmetric Fabry-Perot, electroabsorption optical modulator. The theoretical analysis includes the effects of angular distribution of the incident power, optical bandwidth of the source, cavity finesse, and the power-coupling loss for both singlemode and multimode step-index fibre devices. The results indicate that, for a laser source, fibre with standard numerical aperture of 0.2 and a fibre front-end reflectivity of 0.6, a cavity length less than four times of the working wavelength is required to obtain 10 dB contrast for both singlemode- and multimode-fibre devices, while an optimum cavity length exists for minimum insertion loss. A theoretical analysis of degradation of device performance with mirror-surface roughness, mirror mismatch and mirror misalignment is also presented, showing that such devices have high tolerance to these deviations