Tunable finesse optical filters and resonators are required for some applications when the signal-to-noise ratio and spectral resolution are traded-off to optimize the system performance. They can be used as well to control the amount of energy stored inside the resonator that can be used for optical trapping and atomistic studies. In this work we report a tunable finesse optical MEMS filter in deeply-etched SOI technology. The structure is composed of an optical cavity formed between a multilayer dielectric-coated optical fiber and slotted micromirror, attached to a comb-drive actuator. The cavity length between the multilayer Bragg coated fiber and the slotted micromirror is constant, while the slit width is being varied. The slit width is controlled by the applied voltage on the actuator. Changing the slit width modulates the reflectivity of the micromirror; and hence the finesse of the optical cavity. The obtained finesse is tuned by a factor of 5 across the band of 1330 nm and 1550 nm.
In this work we report a novel optical MEMS deeply-etched mirror with metallic coating and vertical slot, where the later allows reflection and transmission by the micromirror. The micromirror as well as fiber grooves are fabricated using deep reactive ion etching technology, where the optical axis is in-plane and the components are self-aligned. The etching depth is 150 μm chosen to improve the micromirror optical throughput. The vertical optical structure is Al metal coated using the shadow mask technique. A fiber-coupled Fabry-Pérot filter is successfully realized using the fabricated structure. Experimental measurements were obtained based on a dielectric-coated optical fiber inserted into a fiber groove facing the slotted micromirror. A versatile performance in terms of the free spectral range and 3-dB bandwidth is achieved.