In-Plane Optical Beam Collimation Using a Three-Dimensional Curved MEMS Mirror

Abstract

The collimation of free-space light propagating in-plane with respect to the substrate is an important performance factor in optical microelectromechanical systems (MEMS). This is usually carried out by integrating micro lenses into the system, which increases the cost of fabrication/assembly in addition to limiting the wavelength working range of the system imposed by the dispersion characteristic of the lenses. In this work we demonstrate optical fiber light collimation using a silicon micromachined three-dimensional curved mirror. Sensitivity to micromachining and fiber alignment tolerance is shown to be low enough by restricting the ratio between the mirror focal length and the optical beam Rayleigh range below 5. The three-dimensional curvature of the mirror is designed to be astigmatic and controlled by a process combining deep, reactive ion etching and isotropic etching of silicon. The effect of the micromachining surface roughness on the collimated beam profile is investigated using a Fourier optics approach for different values of root-mean-squared (RMS) roughness and correlation length. The isotropic etching step of the structure is characterized and optimized for the optical-grade surface requirement. The experimental optical results show a beam-waist ratio of about 4.25 and a corresponding 12-dB improvement in diffraction loss, in good agreement with theory. This type of micromirror can be monolithically integrated into lensless microoptoelectromechanical systems (MOEMS), improving their performance in many different applications.

Hearing Restoration through Optical Wireless Cochlear Implants

“…Finally, the microelectromechanical device adjusts its optical properties and, thus, steers the beam after receiving the appropriate electrical charge that can be applied during implantation, while in normal operation, the need for adjustment is eliminated, and therefore, the microelectromechanical device operates passively [83,84]. The signal received by the guiding lens presented in ( 1) is forwarded to the microelectromechanical device, which introduces a collimation gain [85].…”

All-Optical Cochlear Implants

“…Moreover, f is the focal length of the MEM and z o is the Rayleigh range of the incident beam. In addition, the beam-waist ratio has a maximum value occurring when the input distance and the focal length are equal and can be evaluated as [48] G…”

Critical analysis of in-plane free-space light beam coupling using photonic curved micromirrors

“…[56][57][58] In addition to the prior work focused on general Gaussian beams in optical fibers or coupling via lenses, there are other works on coupling via microelectromechanical systems (MEMS) involving either optical switches or MEMS mirrors. [59][60][61][62] In this paper, we treat the impact of misalignment between the incident beam, generalized to astigmatic Gaussian beam, and the principal axis of the micromirror with different matrix parameters (i.e., mirror surface profiles) in two orthogonal planes providing a general solution for the coupling efficiency.…”