Cavity optomechanics have become a promising route towards the development of ultrasensitive sensors for a wide range of applications including mass, chemical and biological sensing. In this study, we demonstrate the potential of Very Large Scale Integration (VLSI) with state-of-the-art low-loss performance silicon optomechanical microdisks for sensing applications. We report microdisks exhibiting optical Whispering Gallery Modes (WGM) with 1 million quality factors, yielding high displacement sensitivity and strong coupling between optical WGMs and in-plane mechanical Radial Breathing Modes (RBM). Such high-Q microdisks with mechanical resonance frequencies in the 10<sup>2</sup> MHz range were fabricated on 200 mm wafers with Variable Shape Electron Beam lithography. Benefiting from ultrasensitive readout, their Brownian motion could be resolved with good Signal-to-Noise ratio at ambient pressure, as well as in liquid, despite high frequency operation and large fluidic damping: the mechanical quality factor reduced from few 10<sup>3</sup> in air to 10’s in liquid, and the mechanical resonance frequency shifted down by a few percent. Proceeding one step further, we performed an all-optical operation of the resonators in air using a pump-probe scheme. Our results show our VLSI process is a viable approach for the next generation of sensors operating in vacuum, gas or liquid phase.
A comparative study of the gain achievement is performed in a waveguide optical amplifier whose active layer is constituted by a silica matrix containing silicon nanograins acting as sensitizer of either neodymium ions (Nd<sup>3+</sup>) or erbium ions (Er<sup>3+</sup>). Due to the large difference between population levels characteristic times (ms) and finite-difference time step (10<sup>−17</sup>s), the conventional auxiliary differential equation and finite-difference time-domain (ADE-FDTD) method is not appropriate to treat such systems. Consequently, a new two loops algorithm based on ADE-FDTD method is presented in order to model this waveguide optical amplifier. We investigate the steady states regime of both rare earth ions and silicon nanograins levels populations as well as the electromagnetic field for different pumping powers ranging from 1 to 10<sup>4</sup> mW/mm<sup>2</sup> . Furthermore, the three dimensional distribution of achievable gain per unit length has been estimated in this pumping range. The Nd<sup>3+</sup> doped waveguide shows a higher gross gain per unit length at 1064 nm (up to 30 dB/cm<sup>-1</sup>) than the one with Er<sup>3+</sup> doped active layer at 1532 nm (up to 2 dB/cm<sup>-1</sup>). Considering the experimental background losses found on those waveguides we demonstrate that a significant positive net gain can only be achieved with the Nd<sup>3+</sup> doped waveguide. The developed algorithm is stable and applicable to optical gain materials with emitters having a wide range of characteristic lifetimes.