A 2D MEMS grating based CMOS compatible poly-SiGe variable optical attenuator

Abstract

A variable optical attenuator based on a 2D MEMS grating is described. The device is a perforated and suspended poly-SiGe membrane with fixed islands within the perforations. It specularly reflects light in the non-actuated state, whereas after actuation the membrane deflects downwards forming a grating which diffracts light in higher orders reducing the intensity of the specular reflection. Using a laser of 400 nm wavelength, we could obtain an attenuation level of 20 dB with 0.11 dB of polarization dependent loss. A close match was obtained between the experimental and simulated mechanical behavior of the device showing the possibility of efficiently extending its use in the NIR regime. Additionally, as the device is made of poly-SiGe deposited at low temperature, it can be monolithically integrated with CMOS in the future. Dear Editorial Board of Microelectronic Engineering,Please find enclosed the manuscript named "A 2D MEMS grating based CMOS compatible poly-SiGe variable optical attenuator" by S. Rudra et al. All co-authors have seen and agreed with the contents of the manuscript. We certify that the submission is original work and is not under review at any other publication.This work deals with novel 2D MEMS gratings made of Poly-SiGe, a novel material which can help in monolithically integrating MEMS directly on top of CMOS. It can appreciably reduce the cost and device dimension though the functionality increases manifold. We used the concept of 2D gratings in forming variable optical attenuators with applications mainly targeted towards optical communication. We showed a maximum attenuation level of ~20 dB at an applied voltage of 1.6 V. As the devices are based on symmetric 2D gratings, there is no polarization sensitivity for the diffracted light and hence we could obtain a maximum PDL of 0.11 dB at the highest attenuation level. We also tailored the design parameters to obtain a critical damped response for the devices showing a fast response time of 3.3 µs. Though the characterizations were performed with 400 nm laser, with proper simulations and explanations we support the efficient extension of its working range in the NIR regime. Supported by the SiGe technology, this can be a step forward in efficiently integrating large arrays of VOAs on a single silicon chip.To our knowledge, this is the first 2D MEMS grating based VOA discussed thoroughly in literature. Hence, we hope that the editorial board and the reviewers will agree to the interest of this study. The authors report an alternative design for a Variable Optical Attenuator based on a MEMS structure. The device consists of a suspended poly-SiGe membrane with fixed islands within the holes of the photonic device. The reflectivity of the membrane can be tuned by electrostatic actuation of the membrane, which deflects downwards. This deflection forms a diffraction grating, reducing the specular reflection. Here are my comments:-The paper is divided into different sections, after a brief introduction the authors introduce a conceptua...