Overcoming the near-infra-red spectral range limit with Fabry-Perot silicon microcavity enabled by slotted micromirrors

In this work we report, a novel Fabry-Perot architecture and its implementation on silicon leading to an ultra-wideband spectral range, where the latter is not limited to the infrared range, but extended below 1100 nm and even to the visible range. The microcavity is constructed of two flat slotted mirrors. The microcavity is fabricated using deep reactive ion etching (DRIE) of silicon wafer. The structure is metalized with Aluminum to improve the mirrors reflectivity, while the mirror is partially transmitting; thanks to the slots in the mirrors. The characterization is carried out using tunable laser sources (TLS) around 1575 nm and 914 nm. The measured free spectral range (FSR) is 6.7 nm around 1575 nm and 2.2 nm around 914 nm. Two microcavities are characterized having 2-pm and 4-pm slot widths, and their quality factor is about 1300 and 2000, respectively at 1575 nm. The quality factor is 2555 for the 2 pm slotted mirrors structure at 914 nm demonstrating the operation below 1100 nm. The reported results open the door for MEMS microcavity operating below 1100 nm, which is a range of high interest for biomedical and food spectroscopy applications.