Bassam Saadany

Advanced etching of silicon based on deep reactive ion etching for silicon high aspect ratio microstructures and three-dimensional micro- and nanostructures

Abstract Different processes involving an inductively coupled plasma reactor are presented either for deep reactive ion etching or for isotropic etching of silicon. On one hand, high aspect ratio microstructures with aspect ratio up to 107 were obtained on sub-micron trenches. Application to photonic MEMS is presented. Isotropic etching is also used either alone or in combination with anisotropic etching to realize various 3D shapes.

Free-Space Tunable and Drop Optical Filters Using Vertical Bragg Mirrors on Silicon

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

Integrated wide-angle scanner based on translating a curved mirror of acylindrical shape

A wide angle microscanning architecture is presented in which the angular deflection is achieved by displacing the principle axis of a curved silicon micromirror of acylindrical shape, with respect to the incident beam optical axis. The micromirror curvature is designed to overcome the possible deformation of the scanned beam spot size during scanning. In the presented architecture, the optical axis of the beam lays in-plane with respect to the substrate opening the door for a completely integrated and self-aligned miniaturized scanner. A micro-optical bench scanning device, based on translating a 200 μm focal length micromirror by an electrostatic comb-drive actuator, is implemented on a silicon chip. The microelectromechanical system has a resonance frequency of 329 Hz and a quality factor of 22. A single-mode optical fiber is used as the optical source and inserted into a micromachined groove fabricated and lithographically aligned with the microbench. Optical deflection angles up to 110 degrees are demonstrated.

A MEMS-based VOA with very low PDL

In this letter, we study the optical performance of a microelectromechanical system reflection-type variable optical attenuator (VOA). Experimental results of packaged VOA devices show that the proposed architecture exhibits very low polarization dependence within the entire attenuation range (polarization-dependent loss (PDL)<0.1 dB at 30-dB attenuation level).

Fully Integrated Mach-Zhender MEMS Interferometer With Two Complementary Outputs

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.

MEMS tunable Michelson interferometer with robust beam splitting architecture

A new beam splitter [1] is proposed to realize a completely integrated Michelson interferometer, where a single medium interface (Si/Air) is used for optical beam splitting. This offers a stable splitting ratio over a very wide spectral range. Using this technique on SOI wafers, with a moving mirror, a highly robust and tunable interferometer is fabricated. The tunable interferometer is tested experimentally by measuring optical interference versus mirror displacement.

In-plane external fiber Fabry–Perot cavity comprising silicon micromachined concave mirror

Abstract. Light trapping in optical cavities has many applications in optical telecommunications, biomedical optics, atomic studies, and chemical analysis. Efficient optical coupling in these cavities is an important engineering problem that affects greatly the cavity performance. Reported in-plane external fiber Fabry–Perot cavities in the literature are based on flat micromachined mirrors. In this case, the diffraction loss in the cavity is usually overcome by using an expensive-lensed fiber or by inserting a coated lens in the cavity leading to a long cavity with a small free spectral range. In this work, we report a Fabry–Perot cavity formed by a multilayer-coated cleaved-surface single-mode fiber inserted into a groove while facing a three-dimensional concave micromirror; both are fabricated by silicon micromachining. The light is trapped inside the cavity while propagating in-plane of the wafer substrate. Theoretical modeling is carried out, taking into account the effect of asymmetry in the mirror radii of curvature resulting from the micromachining process. A cavity is formed using a concave mirror with 200 and 100 μm in-plane and out-of-plane radii curvature, respectively. The presented cavity has a measured line width of 0.45 nm around 1330 nm showing a quality factor of about 3000, which resembles a one order of magnitude improvement over a flat-mirror cavity.

High aspect ratio nano-structures (HARNS) for photonic MEMS based on vertical DBR architecture

High aspect ratio nano-structures (HARNS), having an aspect ratio of up to 107, were fabricated by DRIE (deep reactive ion etching). Sidewall surface roughness was reduced to a level less than 20 nm peak-to-valley. These technological advances are applied to photonic MEMS based on in-plane, free-space propagation of light. As an illustration, a Fabry-Perot cavity is presented. It uses vertical distributed Bragg reflectors (DBRs), which consist of thin silicon walls separated by small air gaps, the widths being an even multiple of quarter wavelengths of light in silicon and in air, respectively.

Curved Silicon Micromirror for Linear Displacement-to-Angle Conversion With Uniform Spot Size

This paper reports a novel class of deeply etched curved micromirrors enabling linear conversion between the reflection angle of incident light beam and displacement of the beam axis with respect to the curved mirror principal axis. Moreover, the mirror provides phase-transformation of the light beam independent of the inclination angle of the incident light on the mirror surface. The micromirrors are fabricated on SOI substrate by deep reactive ion etching technology. The profile of the curved surface is optimized and controlled precisely, thanks to the photolithographic process. High optical throughput micromirrors exhibiting submillimeter focal lengths are fabricated with 200-μm etching depth and with a sidewall angle deviation from perfect verticality, which is smaller than 0.1°. Optical measurements at wavelengths of 675 and 1550 nm show transformation of the optical beam with high optical spot size stability during a beam steering process with less than ±5% dependence on the inclination/reflection angle over a scanning angle range of 120°. The presented micromirror has applications in MEMS scanners, displacement/rotation sensing, and optical imaging.

Electrostatically-tuned Optical Filter Based on Silicon Bragg Reflectors

A tunable Fabry-Perot cavity composed of two Bragg mirrors is realized using enhanced deep reactive ion etching (DRIE) process. Filter tuning is achieved by moving one of the mirrors using a high resolution electrostatic actuator over SOI. Measured filter response in C&L bands is presented