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This chapter presents a brief review of the sensing techniques and interrogation methods used in optical micro-electro-mechanical-system (MEMS) and nanophotonic accelerometers. Most micromachined accelerometers work on the same basic principle. The proof mass attached to a compliant suspension experiences inertial force in response to acceleration of the body/frame. The deflection of the proof mass or the deformation of the suspension are transduced and form the metric for acceleration measurement. Special purpose satellites orbiting Earth enable determination of any object with a high degree of precision. Invention and evolution of MEMS technology has resulted in miniaturization of these position tracking devices such that they are hand-held and can be carried around. The resolution of an accelerometer depends on the noise floor of the system, including both mechanical and electrical noise. Optical sensing techniques involve change in properties of light signal due to deflection of proof mass due to inertial force.

Design and analysis of high-sensitivity optical MEMS accelerometer based on waveguide Bragg grating integrated with Crab-leg beam for low frequency applications is presented in this paper. Crab-leg beam are used to suspend the proof-mass to decrease spring stiffness with low device footprint. A waveguide Bragg grating is positioned on the shin of crab-leg to maximize strain sensitivity. To compensate for the temperature dependence of Bragg spectral properties, a reference grating positioned on the proof-mass is used. Due to excellent linear response, high-sensitivity of 184 pm/g and low fundamental frequency, the proposed accelerometer is suitable for microgravity and seismometry applications.

In this article, we present classification of integrated optical MEMS devices as being free-space or guided-wave based on light propagation method. Free-space optical MEMS devices are limited in performance by precision of micromachining and alignment of optical components. To fully leverage the capacity of the free-space devices, integration of photonic or electronic signal processing on chip is a relevant and ongoing research work. Guided-wave optical MEMS devices where all optical, electrical and mechanical components are integrated are more reliable and have lower costs. Grating coupler based free-space optical MEMS accelerometer with potential for integration of detection circuit is discussed. Waveguide Bragg grating based guided-wave optical MEMS widely tunable filters with potential for integration of electronic channel selectivity circuit to improve the device performance is also presented. Waveguide Bragg gratings based guided-wave optical MEMS accelerometers with potential for integration of optical spectral detection using unbalanced Mach–Zehnder modulators on chip is also discussed in this work. In the conclusion, we argue for development of integrated electronic or photonic integrated devices for both classes of optical MEMS devices to enhance their functionality and improve performance.

A novel lateral dual-axis a-Si/SiO2 waveguide Bragg grating based quad-beam accelerometer with high-resolution and large linear range has been presented in this paper. The sensor consists of silicon bulk micromachined proof mass suspended by silica beams. Three ridge gratings are positioned on the suspending beam and proof mass to maximize sensitivity and reduce noise. Impact of external acceleration in the sensing direction on the Bragg wavelength of gratings and MEMS structure has been modelled including the effects of strain, stress and temperature variation. Acceleration induces stress in the beam thus modifying the grating period and introducing chirp. The differential wavelength shift with respect to reference grating on the proof mass is the measure of acceleration. To compensate for the effect of the weight of the proof mass and increase the sensitivity of the sensor, electrostatic force of repulsion is applied to the proof mass. For the chosen parameters, the designed sensor has a linear response over a large range and a sensitivity of 30 pm/g. The temperature of surroundings, which acts as noise in sensor performance is compensated by taking differential wavelength shift with respect to reference grating. By design and choice of material, low cross-axis sensitivity is achieved. The proposed design enables a high-resolution well below 1 &mu, g/ Hz and is suitable for inertial navigation and seismometry applications.

An electrostatically actuated MEMS cantilever beam-based waveguide Bragg grating tunable optical filter has been designed and simulated. The tunable filter is obtained by shifting the reflected wavelength of the waveguide Bragg grating located on the electrostatically actuated cantilever beam. An approach to increasing the electrostatic actuation of the beam by having an electrode underneath the beam is used and a large wavelength tuning range for the optical filter is achieved. Dimensions of the device are chosen such that full-width-half-maximum is 0.75 nm, thus capable of filtering adjacent channels of the dense wavelength division multiplexing (DWDM) network. The filter has a tuning range of 10.65 nm (1552.52 to 1563.17 nm) providing add/drop functionality for 14 adjacent DWDM channels.

A simulation model of temperature insensitive waveguide grating based SOI MOEMS accelerometer is presented. The sensor consists of two waveguide gratings are placed on the beams suspending silicon micromachined proof mass. The gratings are placed on the beams suspending the micromachined silicon proof mass such that they have different linear chirp coefficient depending on their position on the beam. For small range of acceleration and temperature variations, the cross-sensitivity terms are ignored and by measuring the shift in Bragg wavelength of both gratings the external acceleration can be accurately measured. The resolution for the sensor is 0.001g with range of measurement of 1g.