Results 1 - 10 of 11
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[en] This paper reports a novel micromachined stationary lamellar grating interferometer for Fourier transform (FT) based spectroscopy applications. The interferometer employs a set of tilted interdigitated light reflecting beams to produce an interferogram with spatially varying optical path difference (OPD) recorded by a line photodetector array. Due to the advantages including robustness and the absence of mechanical moving parts and optical beam splitters, the proposed spectrometer may be built in a relatively small volume and with moderate cost for wide-band radiation spectra measurement, fast time-resolved spectroscopy and for field use. The proposed stationary lamellar grating FT spectrometer was implemented using a silicon-on-insulator (SOI) micromachining process. The prototype spectrometer demonstrated a full width at half maximum (FWHM) spectral resolution of 2 nm at a wavelength of 532 nm and of 2.6 nm at 632.8 nm
[en] The Alvarez lens offers variable focal lengths through lateral shifting of two lens elements. Imaging characteristics and alignment tolerances of the Alvarez lens are studied, and one analytic method for optimal coefficient selection is proposed. Results show that the performance of the Alvarez lens decays with increasing element displacements, and dominant optical aberrations are spherical aberrations, defocus and coma. The lens performance is most sensitive to misalignments in the y direction. If the tolerance is defined as a 10% rise of normalized RMS spot radius, the misalignment should be smaller than 0.01 mm and the tilt angle about any axis can never exceed 1°. By adopting the new coefficient-selection method, lens performance is improved evidently and the degrading trend with increasing displacements is mitigated markedly. In addition, alignment tolerance is increased as well. (paper)
[en] 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
[en] A novel method for detecting the in-plane movement of MEMS devices has been presented, in which a scanning grating structure has been adopted. One end of the grating is directly connected to the movable platform under test, while the other end is fixed to a substrate, both by a suspending beam. Due to this structure design, any in-plane movement of the platform will be finally translated into grating rotation. When a laser beam is incident onto the grating, the direction of diffracted light as well as its spot position on a photosensitive device (PSD) will be changed accordingly due to the grating rotation. From the output of the PSD, the movement amplitude can be finally determined. With this novel sensing mechanism, not only static and dynamic movements, but also the transient structure response have been experimentally demonstrated.
[en] 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 wafer's 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°
[en] A novel nano-tribometer is developed to characterize the friction on the sidewall of several hundreds of nanometers thickness for NEMS applications. A sub-micron electrostatic comb-drive actuator is adopted to provide the required driving force as well as the movement for device operation. At the same time, a new displacement-sensing mechanism, demonstrating excellent integration capability and easy operation, is also proposed, exploiting the high sensitivity of the coupling of light between waveguides on their alignment. With this device, the kinetic coefficient of friction and the adhesion force appearing on the sidewall are experimentally measured to be 0.208 ± 0.005 and 25.3 ± 1.2 nN, respectively. Owing to its versatility, additional information about the air damping (6.06 ± 0.01 × 10"−"8 kg s"−"1) imposed on the current device is also successfully extracted
[en] Fano resonance is a prevailing interference phenomenon that stems from the intersection between discrete and continuum states in many fields. We theoretically and experimentally characterize the asymmetric Fano lineshape in side-coupled waveguide Fabry–Pérot and photonic crystal nanobeam cavities. The measured quality-factor of the Fano resonance before tuning is 28 100. A nanoelectromechanical systems bidirectional actuator is integrated seamlessly to control the shape of the Fano resonance through in-plane translations in two directions without sacrificing the quality-factor. The peak intensity level of the Fano resonance can be increased by 8.5 dB from 60 nW to 409 nW while the corresponding dip intensity is increased by 12.8 dB from 1 nW to 18 nW. The maximum recorded quality-factor throughout the tuning procedure is up to 32 500. Potential applications of the proposed structure include enhancing the sensitivity of sensing, reconfigurable nanophotonics devices, and on-chip intensity modulator
[en] In this Letter, we report a hybrid system consisting of nano-optical and nano-mechanical springs, in which the optical spring effect works to adjust the mechanical frequency of a nanoelectromechanical systems resonator. Nano-scale folded beams are fabricated as the mechanical springs and double-coupled one-dimensional photonic crystal cavities are used to pump the “optical spring.” The dynamic characteristics of this hybrid system are measured and analyzed at both low and high input optical powers. This study leads the physical phenomenon of optomechanics in complex nano-opto-electro-mechanical systems (NOEMS) and could benefit the future applications of NOEMS in chip-level communication and sensing
[en] In this letter, a nano-electro-mechanical-systems (NEMS) mechanism is proposed to drive the in-plane rotation of the doubly coupled photonic crystal (PhC) nanobeam cavities. The corresponding interactions between optical resonances and rotations are investigated. This is the first in-plane rotational tuning of the PhC cavities, which benefits from the flexible design of NEMS actuators. In experiments, more than 18 linewidths of the third order TE even mode corresponding to 0.037 mrad of the shrinking angle between the two nanobeam cavities are demonstrated; this study provides one more mechanical degree of freedom for the practical optomechanical interactions. (letter)
[en] We report the experimental observation of lateral shearing optical gradient forces in nanoelectromechanical systems (NEMS) controlled dual-coupled photonic crystal (PhC) nanobeam cavities. With an on-chip integrated NEMS actuator, the coupled cavities can be mechanically reconfigured in the lateral direction while maintaining a constant coupling gap. Shearing optical gradient forces are generated when the two cavity centers are laterally displaced. In our experiments, positive and negative lateral shearing optical forces of 0.42 nN and 0.29 nN are observed with different pumping modes. This study may broaden the potential applications of the optical gradient force in nanophotonic devices and benefit the future nanooptoelectromechanical systems.