Cavity ring down measurement approach is a promising technique for biosensing as it is insensitive to intensity
uctuations of a laser source. This technique in conjunction with ultra high Q microcavities have a great
potential for ultra sensitive biosensing. Until now, most work on microcavity biosensors has been based on
measurement of the resonant frequency shift induced by binding event on surface of the microcavity. Such
measurements suer from the noise due to intensity
uctuations of the laser source. However, the binding event
will also introduce shift in quality factor of the microcavity, which can be tracked by using cavity ring down
spectroscopy. In this work, we report on experimental demonstration of application of ring down measurement
approach to microcavities for biosensing by tracking disassociation phase of a biotin-streptavidin reaction. These
measurements were performed by using a bioconjugated ultra high Q microtoroidal cavity immersed in a liquid
microacquarium. We found that disassociation curves agree with previously reported results on the protein
In this paper we present an innovative tunable Fabry-Perot cavity micromachined in silicon. A short summary of the
theoretical background of these filters is presented, followed by technical requirements for the design of the dielectric
mirror composing the Fabry-Perot cavity and the cavity itself. Simulations and experimental data are demonstrated to be
in good agreement. An in plane design is used to allow easy fiber alignment. The Fabry-Perot is tuned by an electrostatic
comb drive actuator supported by a set of four springs to achieve a uniform modulation of the air gap of the filter. Only
15.4 V are required to tune the Fabry-Perot over 73nm bandwidth (covering more than the whole C-band) with a FWHM
varying from 6 to 10nm. Transmission losses are -11dB.
In this paper, we propose a solution for simple, fast and easily controllable way of tuning silicon gratings using Micro
Electro Mechanical Systems (MEMS) to deform the grating itself. Basically the idea is to deform mechanically a silicon
grating using electrostatic actuators, enabling pitch tuning over a large proportion (more than 50% is easily achievable
with our approach). Moreover we can change the spacing of individual layers within the grating. A theoretical analysis
and numerical simulations are presented and a first prototype is fabricated. Bragg gratings, springs and actuators are
realized by silicon micro/nano machining on a silicon platform enabling full integration and passive alignment of all
optical components. Applications range from ultra-sensitive displacement sensors, to telecommunications and biology.
This paper extends the modeling of the effect of fringing field, proposed in our recent work, to more generic devices:
electrostatic parallel-plate actuators with deformations. Though these devices can be model as two parallel capacitors with
a variable factor depending on the displacement, it is difficult to determine the analytical expression of such a function.
It is shown that, like the effect of fringing field, the modeling error of the effective actuator due to deformations can
be compensated by introducing a variable serial capacitor. When a suitable robust control is used, the full knowledge
of the introduced serial capacitor is not required, but merely its boundaries of variation. Based on this model, a robust
control scheme is constructed using the theory of input-to-state stability (ISS) and backstepping state feedback design.
This method allows loosening the stringent requirements on modeling accuracy without compromising the performance.
The stability and the performance of the system using this control scheme are demonstrated through both stability analysis
and numerical simulation.
Diffractive MEMS are interesting for a wide range of applications, including displays, scanners or switching elements. Their advantages are compactness, potentially high actuation speed and in the ability to deflect light at large angles.
We have designed and fabricated deformable diffractive MEMS grating to be used as tuning elements for external cavity lasers. The resulting device is compact, has wide tunability and a high operating speed.
The initial design is a planar grating where the beams are free-standing and attached to each other using leaf springs. Actuation is achieved through two electrostatic comb drives at either end of the grating. To prevent deformation of the free-standing grating, the device is 10 μm thick made from a Silicon on Insulator (SOI) wafer in a single mask process.
At 100V a periodicity tuning of 3% has been measured. The first resonant mode of the grating is measured at 13.8 kHz, allowing high speed actuation. This combination of wide tunability and high operating speed represents state of the art in the domain of tunable MEMS filters.
In order to improve diffraction efficiency and to expand the usable wavelength range, a blazed version of the deformable MEMS grating has been designed. A key issue is maintaining the mechanical properties of the original device while providing optically smooth blazed beams. Using a process based on anisotropic KOH etching, blazed gratings have been obtained and preliminary characterization is promising.
The National Science Foundation Center for Adaptive Optics (CfAO) is coordinating a program for the development of spatial light modulators suitable for adaptive optics applications based on micro-optoelectromechanical systems (MOEMS) technology. This collaborative program is being conducted by researchers at several partner institutions including the Berkeley Sensor & Actuator Center, Boston Micromachines, Boston University, Lucent Technologies, the Jet Propulsion Laboratory, and Lawrence Livermore National Laboratory. The goal of this program is to produce MEMS spatial light modulators with several thousand actuators that can be used for high-resolution wavefront control applications that would benefit from low device cost, small system size, and low power requirements. The two primary applications targeted by the CfAO are astronomy and vision science. In this paper, we present an overview of the CfAO MEMS development plan along with details of the current program status.
We present a 1xN switch for single mode fiber optical communication systems, which is composed of an array of fibers, an achromatic lens, and an adaptive membrane mirror. The working principle of the optical switch is as follows: the center fiber of the array delivers the input signal, this signal is collimated by the lens, back reflected on the membrane mirror and refocused by the lens to an other fiber. The addressing of the receiving fiber is made by lateral displacement of the lens. However, using the achromatic lens under off-axis conditions introduces aberrations, which cause coupling losses to the receiving single-mode fibers. The deformable membrane mirror is used to adaptively correct these aberrations. The optimization of the coupling efficiency is made with the help of a genetic algorithm. For each position of the lens, the optimized voltages on the electrodes of the membrane mirror can be stored during the calibration procedure and afterwards recalled during operation of the switch. A demonstrator has been set up with a commercially available linear array of 32 single-mode fibers disposed in V-grooves, an achromatic lens mounted on a two-dimensional translation stage, and a membrane mirror made of silicon nitride coated with aluminum and electro-statically activated by thirty-seven electrodes. To demonstrate the capabilities of the aberration correction we used the first fiber in the array as input fiber and optimized the coupling efficiency to all the other fibers in the array. We obtained insertion losses of less than 3 dB and a cross talk below 30 dB. These results prove the feasibility to build a switch with a two-dimensional array of more than 1000 addressable fibers.
The alignment of optical elements in a MOEMS, is of prime importance in order to realize a reliable and low loss system. Fabrication errors or temperature changes deteriorate the alignment accuracy. These errors can be compensated with the aid of an active alignment system. The aim of the paper is to investigate an active system in order to align microlenses and fibers within a system. A high lateral precision is required for single mode fiber injection, typically better than 1 micrometers . With the active alignment system we can correct a misalignment of +/- 6 micrometers .
The alignment of optical elements in a Micro-Opto-Electro- Mechanical System, is of prime importance in order to realize a reliable and low loss system. Fabrication errors or temperature changes deteriorate the alignment accuracy. These errors can be compensated with the aid of an active alignment system. The aim of the paper is to investigate an active system in order to align microlenses and fibers. A high lateral precision is required for single mode fiber injection, typically better than 1 micrometers . The alignment along the optical axis is less critical. Our system consists of a microlens placed between one input fiber and one output fiber. The fibers are held in V-grooves and the microlens is mounted on an XY-stage. The lens is fabricated by melting resist technology and subsequent etching in quartz. The mechanical parts are realized by wire electro-discharge machining (wire-EDM). Two piezo-electrical actuators move the flexible bearings of the stage in the X and Y direction. We will present the results obtained with this system and we will discuss its potential.
Two different applications of micro-opto-electro-mechanical systems (MOEMs) are described in this paper. The first one is a Q-switched fiber laser using a micro-mirror as switching element. We present the general concept, the latest experimental setup with results and simulations on the behavior of the pulsed laser. The second application is an opto-mechanical switch for telecommunication ring networks. We describe a free-space optical switch using a micro-mirror, micro-optical elements and a fiber bundle.