In this work, we study the detection of acetylene (C ₂ H ₂ ), carbon dioxide (CO ₂ ) and water vapor (H ₂ O) gases in the near-infrared (NIR) range using an on-chip silicon micro-electro-mechanical system (MEMS) Fourier transform infrared (FT-IR) spectrometer in the wavelength range 1300–2500 nm (4000–7692 cm ⁻¹ ). The spectrometer core engine is a scanning Michelson interferometer micro-fabricated using a deep-etching technology producing self-aligned components. The light is free-space propagating in-plane with respect to the silicon chip substrate. The moving mirror of the interferometer is driven by a relatively large stroke electrostatic comb-drive actuator corresponding to about 30 cm ⁻¹ resolution. Multi-mode optical fibers are used to connect light between the wideband light source, the interferometer, the 10 cm gas cell, and the optical detector. A wide dynamic range of gas concentration down to 2000 parts per million (ppm) in only 10 cm length gas cell is demonstrated. Extending the wavelength range to the mid-infrared (MIR) range up to 4200 nm (2380 cm ⁻¹ ) is also experimentally demonstrated, for the first time, using a bulk micro-machined on-chip MEMS FT-IR spectrometer. The obtained results open the door for an on-chip optical gas sensor for many applications including environmental sensing and industrial process control in the NIR/MIR spectral ranges.

Vertical Bragg grating mirrors are realized by the anisotropic etching of Si using deep reactive ion etching (DRIE), thus producing multiple vertical interfaces between Si and air. The Bragg mirrors are used to realize two optical filter configurations. The first is a tunable Fabry-Peacuterot cavity composed of two mirrors, where tuning is achieved by moving one of the mirrors using silicon-on-insulator (SOI) electrostatic microelectromechanical system (MEMS) actuation. The second is a drop filter, where a tilted Bragg mirror acts as a wavelength selective reflector. The enhanced etching process involving a mix of cryogenic and Bosch DRIE processes is presented. The realized structures, fabrication process, as well as measured performance are also presented

Miniaturized optical benches process free-space light propagating in-plane with respect to the substrate and have a large variety of applications, including the coupling of light through an optical fiber. High coupling efficiency is usually obtained using assembled micro-optical parts, which considerably increase the system cost and integration effort. In this work, we report a high coupling efficiency, monolithically integrated silicon micromirror with controlled three-dimensional (3D) curvature that is capable of manipulating optical beams propagating in the plane of the silicon substrate. Based on our theoretical modeling, a spherical micromirror with a microscale radius of curvature as small as twice the Gaussian beam Rayleigh range provides a 100% coupling efficiency over a relatively long optical path range. Introducing dimensionless parameters facilitates the elucidation of the role of key design parameters, including the mirror's radii of curvature, independent of the wavelength. A micromachining method is presented for fabricating the 3D micromirror using fluorinated gas plasmas. The measured coupling efficiency was greater than 50% over a 200-μm optical path, compared to less than 10% afforded by a conventional flat micromirror, which was in good agreement with the model. Using the 3D micromirror, an optical cavity was formed with a round-trip diffraction loss of less than 0.4%, resulting in one order of magnitude enhancement in the measured quality factor. A nearly 100% coupling was also estimated when matching the sagittal and tangential radii of curvature of the presented micromirror’s surface. The reported class of 3D micromirrors may be an advantageous replacement for the optical lenses usually assembled in silicon photonics and optical benches by transforming them into real 3D monolithic systems while achieving wideband high coupling efficiency over submillimeter distances.

In this paper, a novel Mach-Zhender interferometer for spectroscopy applications is presented. The interferometer is fully integrated on an silicon on insulator wafer using deep reactive ion etching technology, the moving mirror is coupled to a comb drive microelectromechanical systems (MEMS) actuator. Optical propagation inside the MEMS structure is modeled and the diffraction effect is studied. Practical results show the complementary nature of the two outputs and a resolution of 25 nm at 1.55 μm is reported when using the interferometer as an Fourier transform infrared spectrometer. The complementary nature of the interferometer can be further used for source noise reduction.

In this letter, we report a wide tuning range MEMS-based swept laser source using deep reactive ion etching on an SoI substrate. A MEMS Fabry-Pérot filter with a free-spectral range and a tuning range wider than 94 nm is presented. The measured transmission loss of the filter is between -10.2 and -13.6 dB. This filter is used to construct a swept laser source with 85 nm tuning range. These results represent the widest tuning range reported in literature for an in-plane SoI-MEMS based swept laser source using deeply-etched free-standing distributed-Bragg-reflection mirrors. The recorded tuning range enables the use of the in-plane MEMS filter in optical coherence tomography applications.