| In recent years there has been an explosion in data traffic due to the prevailing Internet. A technique called wavelength division multiplexing (WDM) promises to accommodate the increased traffic without replacing the existing fiber networks. Wavelength sensitive devices such as tunable filters, detectors, and lasers are key components in the WDM system. Surface micromachining is one of the most promising technologies to fabricate such devices.; A typical surface micromachined wavelength-tunable device was demonstrated by integrating a deformable membrane of dielectric mirror stack to optoelectronic devices. These devices have been applied to different fields such as communications, parameter extraction, etc. As the number of WDM channels increases, these devices have to contend with narrower channel linewidths. This is especially important for the passive devices where the linewidth is determined largely by the cavity finesse. To achieve this, a top mirror with high reflectivity and wide bandwidth is desired. Another important issue is how to lower the tuning voltage of devices. In this work, we focus on building a tunable optoelectronic filter with low actuation voltage, narrow linewidth, and wide tuning range.; To design an optimal structure, I establish an opto-mechanical model which can evaluate the micromachined structure easily and accurately. Through this model, we can quantify the optical diffraction loss caused by the curved surface and thus facilitate the design of high finesse tunable filters. A comprehensive mechanical method, called the “area moment method,” is used to provide an accurate surface profile of the mirror under actuation. This profile is then input into to a second-order perturbation model to estimate optical loss. The linewidth broadening effect can be directly obtained from the loss.; From the above analysis, a less stiff top movable structure is accomplished using Al2O3/GaAs as the distributed Bragg reflector material. A tunable optical filter is grown, processed and measured. Its surface profile matches our mechanical analysis and it demonstrates 64 nm tuning range under a 12-volt swing. The tuning characteristics of this device can also be changed by additional silicon nitride etching. This new design of tunable devices will be attractive for future generation of optical communication systems. |
