Investigating vibration dyanmics of cross-coupled MEMS resonators for reduced motional resistance

This paper investigates the vibration dynamics of a closed-chain, cross-coupled architecture of MEMS resonators. The system presented here is electrostatically transduced and operates at 1.04 MHz. Curve veering of the eigenvalue loci is used to experimentally quantify the coupling spring constants. Numerical simulations of the motional resistance variation against induced perturbation are used to assess the robustness of the cross-coupled system as opposed to equivalent traditional open-ended linear one-dimensional coupling scheme. Results show improvements of as much as 32% in the motional resistance between the cross-coupled system and its one-dimensional counterpart. © 2013 IEEE.

Demonstration of submicron square-like silicon waveguide using optimized LOCOS process.

We demonstrate the design, fabrication and experimental characterization of a submicron-scale silicon waveguide that is fabricated by local oxidation of silicon. The use of local oxidation process allows defining the waveguide geometry and obtaining smooth sidewalls. The process can be tuned to precisely control the shape and the dimensions of the waveguide. The fabricated waveguides are measured using near field scanning optical microscope at 1550 nm wavelength. These measurements show mode width of 0.4 µm and effective refractive index of 2.54. Finally, we demonstrate the low loss characteristics of our waveguide by imaging the light scattering using an infrared camera.

Acoustic properties of carbon nanotube electrodes in BAW resonators

In this paper the acoustic characterization of a layer of carbon nanotubes (CNT) deposited on AlN solidly mounted resonators is described. The structure of the CNT layer is analyzed by scanning electron microscopy and Raman spectroscopy. The electrical sheet resistance is derived from 4 point probe measurements and from the fitting of the electrical response of the resonators. Values of sheet resistance around 100 Ω/□ are measured. The longitudinal acoustic velocity is derived from the fitting of the electrical response of the resonators using Mason's model, by adjusting the overtones produced in the CNT layer. A mean value of 62000 m·s-1 is obtained, although some devices show values around 90000 m·s -1, close to the theoretical value of 100000 m·s-1. Some results on the deposition of CNT layers on metallic top electrodes and their influence on the performance of the resonator are also presented. © 2013 IEEE.

Analytical formulation of modal frequency split in the elliptical mode of SCS micromechanical disk resonators

This paper presents an analytical formulation of frequency splitting observed in the elliptical modes of single crystal silicon (SCS) micromechanical disk resonators. Taking the anisotropic elasticity of SCS into account, new formulae for computing modal mass and modal stiffness are first derived for accurate prediction of the modal frequency. The derived results are in good agreement with finite element simulation, showing a factor of 10 improvement in the prediction accuracy as compared to using the formula for the isotropic case. In addition, the analysis successfully explains the effect of anisotropy on the modal frequency splitting of primary elliptical modes, for which the maximum modal displacement is aligned with the directions of maximum (1 1 0) and minimum (1 0 0) elasticity respectively on a (1 0 0) SCS wafer. The measured frequency splitting of other degenerate modes is due to the manufacturing imperfections. © 2014 IOP Publishing Ltd.

Numerical study of the impact of process variations on the motional resistance of weakly coupled MEMS resonators

This paper presents a numerical study of the impact of process-induced variations on the achievable motional resistance Rx of one-dimensional, cyclic and cross-coupled architectures of electrostatically transduced MEMS resonators operating in the 250 kHz range. Monte Carlo numerical simulations which accounted for up to 0.75% variation in critical resonator feature sizes were initiated on 1, 2, 3, 4, 5 and 9 coupled MEMS resonators for three distinct coupling architectures. Improvements of 100X in the spread of Rx and 2.7X in mean achievable Rx are reported for the case of 9 resonators when implemented in the cross-coupled topology, as opposed to the traditional one-dimensional chain. © 2013 IEEE.

Low-bias terahertz amplitude modulator based on split-ring resonators and graphene.

Split-ring resonators represent the ideal route to achieve optical control of the incident light at THz frequencies. These subwavelength metamaterial elements exhibit broad resonances that can be easily tuned lithographically. We have realized a design based on the interplay between the resonances of metallic split rings and the electronic properties of monolayer graphene integrated in a single device. By varying the major carrier concentration of graphene, an active modulation of the optical intensity was achieved in the frequency range between 2.2 and 3.1 THz, achieving a maximum modulation depth of 18%, with a bias as low as 0.5 V.

Symmetrical 2-D hermite-gaussian square launch for high bit rate transmission in multimode fiber links

A 2-D Hermite-Gaussian square launch is demonstrated to show improved systems capacity over multimode fiber links. It shows a bandwidth improvement over both center and offset launches and exhibits ±5 ìm misalignment tolerance. © OSA/OFC/NFOEC 2011.

The absorption of sound by helmholtz resonators with and without flow

Helmholtz resonators are commonly used as absorbers of incident acoustic power. Theoretical and experimental investigations have been performed in the four cases of no mean flow, grazing mean flow, bias mean flow and a combination of grazing and bias mean flows. In the absence of a mean flow, the absorption coefficient (deflned as the proportion of incident energy absorbed) is a non-linear function of the acoustic pressure and high incident acoustic pressures are required before the absorption becomes signiflcant. In contrast, when there is a mean flow present, either grazing or bias, the absorption is linear and thus absorption coefficient is independent of the magnitude of the acoustic pressure, and absorption is obtained over a wider range of frequencies. Non-linear effects are only discernible very close to resonance and at very-high amplitude. With grazing mean flow, there is the undesirable effect that sound can be generated over a range of frequencies due to the interaction between the unsteadily shed vorticity waves and the downstream edge of the aperture. This production is not observed when there is a bias flow because here the vorticity is shed all around the rim of the aperture and swept away by the mean flow. When there is both a grazing mean flow and a mean bias flow, we flnd that only a small amount of bias mean flow, compared with grazing mean flow, is required to destroy the production of acoustic energy. © 2002 by the author(s). Published by the American Institute of Aeronautics and Astronautics, Inc.

Realization of submicron-scale square-like silicon waveguide via optimized LOCOS process

We demonstrate the design, fabrication and experimental characterization of submicron-scale silicon waveguide fabricated by local oxidation of silicon and provide guidelines for controlling its profile. Near field measurements shows submicron confinement of the optical mode. © 2010 Optical Society of America.

Terahertz optical modulator based on metamaterial split-ring resonators and graphene

The integration of quantum cascade lasers with devices capable of efficiently manipulating terahertz light represents a fundamental step for many different applications. Split-ring resonators, subwavelength metamaterial elements exhibiting broad resonances that are easily tuned lithographically, represent the ideal route to achieve such optical control of the incident light. We have realized a design based on the interplay between metallic split rings and the electronic properties of a graphene monolayer integrated into a single device. By acting on the doping level of graphene, an active modulation of the optical intensity was achieved in the frequency range between 2.2 and 3.1 THz, with a maximum modulation depth of 18%. © 2014 Society of Photo-Optical Instrumentation Engineers.

Graphene-based optical modulator realized in metamaterial split-ring resonators operating in the THz frequency range

The integration of quantum cascade lasers with devices capable of efficiently manipulating terahertz light, represents a fundamental step for many different applications. Split-ring resonators, sub-wavelength metamaterial elements exhibiting broad resonances that are easily tuned lithographically, represent the ideal route to achieve such optical control of the incident light. We have realized a design based on the interplay between metallic split rings and the electronic properties of a graphene monolayer integrated into a single device. By acting on the doping level of graphene, an active modulation of the optical intensity was achieved in the frequency range between 2.2 THz and 3.1 THz, with a maximum modulation depth of 18%.

Mode Simulation for Midinfrared Microsquare Resonators With Sloped Sidewalls and Confined Metals

EQUILATERAL-TRIANGLE; MU-M; LASERS; MICROLASERS; MICRODISK Abstract: Mode characteristics for midinfrared microsquare resonators with sloped sidewalls and confined metal layers are investigated by finite-difference time-domain (FDTD) techniques. For a microsquare with a side length of 10 mu m, the mode quality (Q)-factors of 8329, 4772, and 2053 are obtained for TM5,7 mode at wavelength 7.1 mu m by three-dimensional FDTD simulations, as the tilting angles of the side walls are 90 degrees, 88 degrees, and 86 degrees, respectively. Furthermore, microsquare resonators laterally surrounded by SiO2 and metal layers are investigated by the two-dimensional FDTD technique for the metal layers of Au, Ti-Au, Ag-Au, and Ti-Ag-Au, respectively.

Silicon-Based Asymmetric Add-Drop Microring Resonators with Ultra-Large Through-Port Extinctions

We theoretically simulate and experimentally demonstrate ultra-large through-port extinctions in silicon-based asymmetrically-coupled add-drop microring resonators (MRs). Through-port responses in an add-drop MR are analyzed by simulations and large extinctions are found when the MR is near-critically coupled. Accurate fabrication techniques are applied in producing a series of 20 mu m-radii add-drop microrings with drop-side gap-widths in slight differences. A through-port extinction of about 42.7 dB is measured in an MR with through-and drop-side gap-width to be respectively 280 nm and 295 nm. The large extinction suggests about a 20.5 dB improvement from the symmetrical add-drop MR of the same size and the through-side gap-width. The experimental results are finally compared with the post-fabrication simulations, which show a gap-width tolerance of > 30 nm for the through-port extinction enhancement.

Investigation of mode radiation loss for microdisk resonators with pedestals by FDTD technique

Mode radiation loss for microdisk resonators with pedestals is investigated by three-dimensional (3D) finite-difference time-domain (FDTD) technique. For the microdisk with a radius of 1 mu m, a thickness of 0.2 mu m, and a refractive index of 3.4, on a pedestal with a refractive index of 3.17, the mode quality (Q) factor of the whispering-gallery mode (WGM) quasi-TE7,1 first increases with the increase of the radius of the pedestal, and then quickly decreases as the radius is larger than 0.75 mu m. The mode radiation loss is mainly the vertical radiation loss induced by the mode coupling between the WGM and vertical radiation mode in the pedestal, instead of the scattering loss around the perimeter of the round pedestal. The WG M can keep the high Q factor when the mode coupling is forbidden.