Guangya Zhou

A liquid-filled tunable double-focus microlens

A novel microlens design with tunable double-focus is presented. It is fabricated by adding only one SU-8 photolithography step to the well-developed liquid-filled microlens fabrication process. The thickness of this layer determines the thickness difference between the central and peripheral region of the membrane, the deformation of which is used to define the surface profile of the microlens. The stepped thickness variation is finally manifested as the difference in deformation contour at two different regions of the membrane when subjected to uniform applied pressure, thereby causing two focal lengths to appear. Experimental and simulation results are presented, from which the tunability of the focal lengths of the double-focus microlens is demonstrated to be effective over a wide range through combining the structural design with pressure control. The successful demonstration of this unconventional microlens design concept will potentially extend t application of liquid-filled microlens technology.

Tunable liquid-filled lens integrated with aspherical surface for spherical aberration compensation.

A novel liquid-filled lens design is presented. During fabrication, high precision single point diamond turning (SPDT) is introduced into standard soft lithography process to fabricate an aspherical surface constituting one end of lens. This enables the spherical aberration associated with the operation of the conventional liquid-filled lenses to be compensated for. Through flexibly optimizing this surface contour, it can be designed to work within particular working regions with improved optical quality. At the same time, the deformable elastic membrane is still adopted at the other end of the lens, thus preserving the high focal length tunability. This proof of concept and the performance of the proposed lens have been demonstrated using the lateral shearing interferometry experiment..

Dynamic tuning of an optical resonator through MEMS-driven coupled photonic crystal nanocavities

We present dynamic tuning of optical resonance using microelectromechanical systems (MEMS)-driven coupled photonic crystal (PhC) nanocavities. The device consists of an air-suspended one-dimensional PhC nanocavity coupled to input and output waveguides and a perturbing nanocavity attached to a submicrometer MEMS comb drive. Resonance tuning is achieved through varying the gap between the two coupled cavities. We demonstrate experimentally that resonance can be tuned up to 8nm with no significant deterioration in the Q factor. The proposed mechanism potentially enables a new platform of on-chip photonic devices that can achieve a large tuning range with low power and small footprint and may find useful applications in tunable optical/photonic devices.

An in-plane nano-mechanics approach to achieve reversible resonance control of photonic crystal nanocavities

Control of photonic crystal resonances in conjunction with large spectral shifting is critical in achieving reconfigurable photonic crystal devices. We propose a simple approach to achieve nano-mechanical control of photonic crystal resonances within a compact integrated on-chip approach. Three different tip designs utilizing an in-plane nano-mechanical tuning approach are shown to achieve reversible and low-loss resonance control on a one-dimensional photonic crystal nanocavity. The proposed nano-mechanical approach driven by a sub-micron micro-electromechanical system integrated on low loss suspended feeding nanowire waveguide, achieved relatively large resonance spectral shifts of up to 18 nm at a driving voltage of 25 V. Such designs may potentially be used as tunable optical filters or switches.

Liquid tunable diffractive/refractive hybrid lens

We present a liquid tunable diffractive/refractive hybrid lens fabricated through what we believe to be a novel process that combines single-point diamond turning with soft lithography techniques. The hybrid lens achieves focal length tunability by changing its shape and, at the same time, utilizes the unique dispersion property of diffractive surfaces to enhance its spectral performance within a wide tuning range.

Micromachined in-plane vibrating diffraction grating laser scanner

In this letter, we present a novel micromachined vibrating diffraction-grating laser scanner that utilizes in-plane angular vibration of a planar diffraction grating causing the diffracted laser beam to scan. The proposed micromachined diffraction-grating laser scanner can operate with low voltage and has the potential to scan at high frequencies without the optical performance degradation due to dynamic nonrigid-body deformation, which is prevalent in conventional high-speed out-of-plane torsional micromirror scanners. A prototype grating scanner has been developed using micromachining technology to demonstrate this new microscanner principle. The tested device is capable of scanning an optical angle of 15.9/spl deg/ with virtually bow-free scan-line at a resonant frequency of 8.34 kHz for a 635-nm wavelength incident laser beam, electrostatically driven by 15-V dc bias and 15-V ac voltages.

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.

Design of the diffractive optical elements for synthetic spectra

We present a novel efficient gradient-based optimization algorithm for the design of diffractive optical elements (DOEs) for synthetic spectra applications. Two design examples are given. The results demonstrate that the DOEs obtained by the proposed algorithm can accurately produce the desired intensity spectra at a predetermined diffraction angle.

On-chip integrated optofluidic complex refractive index sensing using silicon photonic crystal nanobeam cavities

Complex refractive index sensing is proposed and experimentally demonstrated in optofluidic sensors based on silicon photonic crystal nanobeam cavities. The sensitivities are 58 and 139 nm/RIU, respectively, for the real part (n) and the imaginary part (κ) of the complex refractive index, and the corresponding detection limits are 1.8×10(-5) RIU for n and 4.1×10(-6) RIU for κ. Moreover, the capability of the complex refractive index sensing method to detect the concentration composition of the ternary mixture is demonstrated without the surface immobilization of functional groups, which is impossible to realize with the conventional refractive index sensing scheme.

Micromachined Vibratory Diffraction Grating Scanner for Multiwavelength Collinear Laser Scanning

This paper presents an effective method to achieve multiwavelength collinear laser scanning using micromachined vibratory grating scanners, which have the potential to scan at high frequencies without the optical performance degradation resulting from dynamic nonrigid-body deformation. An optical simulation model has been developed to predict the scanning patterns of the vibratory grating scanners. The proposed multiwavelength collinear scanning method was studied both analytically with the optical simulation model and experimentally with a prototype device fabricated by the MUMPS polysilicon surface micromachining process. The experimental results agree very well with the simulation data. The prototype scanner demonstrated collinear scanning of 532 nm (green) and 632.8 nm (red) wavelengths laser beams and achieved an optical scan angle of 12.7 degrees with virtually bow-free scan-line at a resonant frequency of 9.9 kHz when driven by electrostatic comb-drive resonators with 60 V dc bias and 32 Vpp ac voltages