Design and analysis of an integrated optical sensor for scanning force microscopies

Abstract

In this paper, a novel probe for displacement sensing will be introduced. It is based on a conventional GaAs cantilever, integrated with a Bragg grating as a photo-elastic strain sensor. The deflection of the cantilever is measured directly from the intensity modulation of the reflected light. The principle of the experimental setup and the sensor, as well as the theoretical investigation of the force and displacement sensitivity of the probe, is presented. Finite-element method simulations were performed to get the optimum sensor design. Transfer matrix method simulation of the waveguide grating have been described in detail. In order to enhance the sensitivity, different types of grating structures are discussed. Using this new design, it should be possible to achieve sensitivities, defined as the fractional change in detected optical power per unit displacement of the cantilever, as high as 10-4 Å-1 of cantilever deflection. © 2005 IEEE

Demonstration of microcantilever array with simultaneous readout using an in-plane photonic transduction method

“…In our case, the average sensitivity is 2.3ϫ 10 −4 nm −1 . This is comparable to the sensitivity obtained with optical beam deflection 31,32 and two orders of magnitude larger than for piezoresistive readout, 14,[33][34][35] which are the two most widely used microcantilever readout techniques. Hence, in-plane photonic transduction is attractive in that it maintains the sensitivity of optical beam deflection while being scalable to readout arrays of microcantilevers.…”

A novel optical waveguide microcantilever sensor for the detection of nanomechanical forces

“…In general, the systems using PSD work very well. The typical value of sensitivity defined as a fractional change in the detected output signal per unit displacement of the cantilever is about 10 −3 nm −1 [3]. The typical value of deflection noise density (DND) is in the range of 100-1000 fm/ √ Hz.…”

“…Integrated optical sensor systems are small, relatively easy to produce, sensitive and versatile tools [3], [8]- [10]. Integrated optics sensors with cantilevers have been realized before based on the following: 1) a fiber cantilever used to detect displacements with 600 fm/ √ Hz DND [9], 2) optical microcantilevers integrated with multimode interferometer [10], and 3) a conventional GaAs cantilever integrated with a Bragg grating as a photoelastic strain sensor with a sensitivity of 10 −3 nm −1 [3].…”

Ultrasensitive nanomechanical photonic microsensor

“…This value is 4 orders of magnitude higher than the typical sensitivity exhibited by state-of-the-art microcantilver sensors [6,7]. The estimated deflection detection limit of the slot-waveguide disk resonator sensor would be ∆d min =∆n eff,min / S slot = 10 -6 (RIU) / 1.15×10 -3 (RIU/nm) = 8.7×10 -4 nm, which is two orders of magnitude smaller than that shown by waveguide microcantilever sensors [7].…”