We present a SOI ring based sensor read-out system. The novelty of the architecture lies in the capability to sense the shifts of multiple peaks simultaneously with an integrated AWG spectrometer.

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In the past decade, there has been a surge in research at the boundary between photonics and phononics 1 . Most efforts centered on coupling light to motion in a high-quality optical cavity 2 , typically geared towards observing the quantum state of a mechanical oscillator 3 . It was recently predicted that the strength of the light-sound interaction would increase drastically in nanoscale silicon photonic wires 4 . Here we demonstrate, for the first time, such a giant overlap between nearinfrared light and gigahertz sound co-localized in a small-core silicon wire. The wire is supported by a tiny pillar to block the path for external phonon leakage, trapping 10 GHz phonons in an area below 0.1 µm 2 . Since our geometry can be coiled up to form a ring cavity, it paves the way for complete fusion between the worlds of cavity optomechanics and Brillouin scattering. The result bodes well for the realization of low-footprint optically-pumped lasers/sasers 5 and delay lines 6 on a densely integrated silicon chip.The diffraction of light by sound was first studied by Léon Brillouin in the early 1920s. Therefore such inelastic scattering has long been called Brillouin scattering 7 . On the quantum level, the process annihilates pump photons while creating acoustic phonons and redshifted Stokes photons. The effect is known as stimulated Brillouin scattering (SBS) when the sound is generated by a strong modulated light field. This sets the stage for a self-sustaining feedback loop: the beat note between two optical waves (called the pump and the Stokes) generates sound that reinforces the initial beat note.In a seminal experimental study 8 , Brillouin scattering was viewed as a source of intense coherent sound. Later, the effect became better known as a noise source in quantum optics 9 and for applications such as spectrally pure lasing 10-12 , microwave signal processing 13,14 , slow light 15 , information storage 6 and phononic band structure mapping 16 .Traditionally 5-20 , the photon-phonon interaction was mediated by the material nonlinearity. Electrostriction drove the phonon creation, and phonon-induced permittivity changes lead to photon scattering. This conventional image of SBS as a bulk effect, without reference to geometry, breaks down in nanoscale waveguides. The impressive progress in engineering radiation pressure in micro-and nanoscale systems [21][22][23][24][25] recently inspired the * raphael.vanlaer@intec.ugent.be theoretical prediction of enormously enhanced photonphonon coupling 4,26-28 in silicon nanowires. In such waveguides, boundary effects can no longer be neglected. Thus both electrostriction and radiation pressure create phonons. Equivalently, the new theory takes into account not only bulk permittivity changes but also the shifting material boundaries. The strong photon confinement offered by these waveguides boosts both types of optical forces. However, destructive interference between the two contributions may still completely cancel the photon-phonon coupling. The giant light-sound overlap...

Nanophotonic waveguides and components are promising for use in the large-scale integration of photonic circuits. Coupling light between nanophotonic waveguides and a single-mode fiber is an important problem and many different solutions have been proposed and demonstrated in recent years. In this paper, we discuss a grating coupler approach. Grating couplers can be placed anywhere on a circuit and can easily be integrated. We have experimentally demonstrated >30% coupling efficiency with a 1 dB bandwidth of 40 nm on standard wafers. Theoretically, the coupling efficiency can be improved to >90% using an optimized grating design and layer stack. The fabrication of the couplers in silicon-on-insulator and in indium phosphide membranes is also discussed.