Qingxin Zhang

High-speed, high-optical-efficiency laser scanning using a MEMS-based in-plane vibratory sub-wavelength diffraction grating

In this paper, we report the modeling, fabrication and characterization of a microelectromechanical systems (MEMS)-based sub-wavelength diffraction grating under in-plane motion for high-optical-efficiency high-speed laser-scanning applications. The scanner utilizes in-plane rotational vibration of a planar microstructure to change the orientation of the diffraction grating, hence causing a diffracted laser beam to scan with less dynamic wavefront deformation as compared with conventional scanning micromirrors. An optical efficiency of more than 75% is experimentally achieved with a simple gold-coated binary sub-wavelength grating. When operated in air and electrostatically driven by 45 V dc bias and 84 V peak-to-peak ac voltages, the 1 mm diameter grating is capable of scanning an optical scan angle of 13.7° with a 632.8 nm wavelength incident laser beam at a resonant frequency of 20.35 kHz. The measured optical resolution is around 310 pixels per unidirectional scan.

Double-Layered Vibratory Grating Scanners for High-Speed High-Resolution Laser Scanning

A novel micromachined electrostatic double-layered vibratory grating scanner has been successfully developed for high-speed high-resolution laser scanning applications. This paper presents its design, modeling, fabrication, and measurement results. A comprehensive dynamic model considering the geometric nonlinearity of the platform suspension flexures is also proposed to predict the dynamic performance of the device at large scanning amplitudes. Compared with previously reported single-layered vibratory grating scanners, double-layered scanners - in which the diffraction grating and its driving actuator are located in different layers - have the potential to scan at large amplitudes and at high scanning speeds with large aperture sizes. We have demonstrated a prototype with a 2-mm-diameter diffraction grating which is capable of scanning at 23.391 kHz with an optical scan angle of around 33° and a resulting θopticalD product (product of the optical scan angle and diameter of the diffraction grating) of 66 deg mm.

A 2-DOF Circular-Resonator-Driven In-Plane Vibratory Grating Laser Scanner

In this paper, we present the design, modeling, fabrication, and measurement results of a microelectromechanical systems (MEMS)-based in-plane vibratory grating scanner driven by a two-degree-of-freedom (2-DOF) comb-driven circular resonator for high-speed laser scanning applications. Diffraction grating driven by a 2-DOF circular resonator has the potential to scan at large amplitudes compared with those driven by a one-degree-of-freedom (1-DOF) comb-driven circular resonator or a 2-DOF electrical comb-driven lateral-to-rotational resonator. We have demonstrated that our prototype device, with a 1-mm-diameter diffraction grating is capable of scanning at 20.289 kHz with an optical scan angle of around 25deg. A refined theoretical model with fewer assumptions is proposed, which can make the prediction of dynamic performance much more accurate.

Hyperspectral imaging using a microelectrical-mechanical-systems-based in-plane vibratory grating scanner with a single photodetector

We present a single-photodetector-based hyperspectral imaging system that utilizes a microelectrical-mechanical-systems-driven diffraction grating for fast spatial scanning and two synchronized steering mirrors for slow spectral scanning. This configuration allows high-speed scanning without degradation in optical performance resulting from dynamic non-rigid-body deformation of the platform. The proposed operational principle is demonstrated with a prototype device developed using silicon microfabrication technology. The proposed spectral imaging system has the potential to achieve low cost, small form factor, and high-speed operation.

A high-speed MEMS grating laser scanner with a backside thinned grating platform fabricated using a single mask delay etching technique

A novel micro-electromechanical system (MEMS) technology-based grating laser scanner with a backside thinned grating platform has been successfully developed for high-speed laser scanning applications. The grating platform is thinned by a round cavity and reinforced by a circular frame, which are fabricated using a single mask delay etching (SMDE) technique. The SMDE technique, which utilizes the well-know loading effects of the deep reactive ion etching (DRIE) process, is a simple and low-cost methodology to regulate the etching rate of a prescribed area. It can be used in a silicon-on-insulator (SOI) micromachining process to form multilevel structures in a silicon device layer through a multi-step DRIE process from a wafers backside. This paper presents the design, simulation, fabrication process and characterization of the high-speed MEMS grating scanner as well as the principle and applications of the SMDE technique. When illuminated with a 635 nm wavelength incident laser beam, the prototype scanner with a 1 mm diameter diffraction grating is capable of scanning at 50.192 kHz with an optical scan angle of 14.1°.

A high-speed electrostatic double-layered vibratory grating scanner with very high optical resolution

This paper demonstrates the design, fabrication and characterization of a micromachined electrostatic double-layered vibratory grating scanner for high speed, high optical resolution laser scanning applications. The prototype scanner with a 2mm diameter diffraction grating is capable of scanning a laser beam at around 21.591kHz with an optical scan angle of 33.5°, resulting a θopticalD product (product of optical scan angle and diameter of the diffraction grating) of 67 deg·mm. The optical resolution of the prototype scanner is measured to be 916 pixels per-unidirectional-scan while scanning in atmosphere. While scanning in vacuum condition, the optical resolution can be estimated to be 1460 pixels per-unidirectional-scan, which is suitable for SXGA (1280×1024) resolution scanned beam displays.

Synchronized laser scanning of multiple beams by MEMS gratings integrated with resonant frequency fine tuning mechanisms

This paper presents an effective method to achieve synchronized laser scanning of multiple beams by using MEMS diffraction gratings with their resonant frequency fine tuning mechanisms. Multiple gratings are actuated in-plane by a common electrostatic comb-driven resonator and their resonant frequencies can be fine-tuned to compensate the micromachining process errors. Continuous and reversible resonant frequency tuning was achieved. The resonant frequency of one diffraction grating gradually dropped from 19870 Hz to 19588 Hz with its tuning voltages increased from 0V to 5V. Finally, synchronized laser scanning of multiple beams was demonstrated using stroboscopic method.

Dynamic characterization of a 2-DOF circular resonator-driven vibratory grating scanner with geometric nonlinearity

A micro-sized 2-DOF grating laser scanner which is made to vibrate in-plane by an electrical comb-driven circular resonator drive is fabricated and tested. The frequency response of the prototype scanner in atmosphere to different driving voltages and the variations of its natural frequency with scanning amplitude are measured. The results are compared with those from finite element simulations using a comprehensive dynamic model, including the effects of geometric nonlinearity of the flexural beams under large deformations. The comparison shows that the predictions made by the developed nonlinear model are generally valid.

A micromachined vibratory sub-wavelength diffraction grating laser scanner

A novel MEMS based in-plane vibratory sub-wavelength diffraction grating scanner is reported. Diffraction efficiency of more than 75%, optical scan angle of 13.7deg and scanning frequency of 20.35 kHz are experimentally achieved.