Start date: Nov 1, 2014,
End date: Oct 31, 2019
"This project aims at pushing the limits of optical sensing on a microchip by orders of magnitude, thereby allowing for ultra-high sensitivity in optical detection and enabling first-time-ever demonstrations of several optical sensing principles on a microchip. My idea is based upon our distributed-feedback lasers in rare-earth-ion-doped aluminum oxide waveguides on a silicon chip with ultra-narrow linewidths of 1 kHz, corresponding to Q-factors exceeding 10^11, intra-cavity laser intensities of several watts over a waveguide cross-section of 2 micrometer, and light interaction lengths reaching 20 km. Optical read-out of the laser frequency and linewidth is achieved by frequency down-conversion via detection of the GHz beat signal of two such lasers positioned in the same waveguide or in parallel waveguides on the same microchip.The sensitivity of optical detection is related to the laser linewidth, interaction length, and transverse mode overlap with the measurand; its potential of optically exciting ions or molecules and its optical trapping force are related to the laser intensity. By applying novel concepts, we will decrease the laser linewidth to 1 Hz (Q-factor > 10^14), thereby also significantly increasing the intra-cavity intensity and light interaction length, simplify the read-out by reducing the line-width separation between two lasers to the MHz regime, and increase the mode interaction with the environment by either increasing its evanescent field or perpendicularly intersecting a nanofluidic channel with the optical waveguide, thereby allowing for unprecedented sensitivity of optical detection on a microchip. We will exploit this dual-wavelength distributed-feedback laser sensor for the first-ever demonstrations of intra-laser-cavity (ILC) optical trapping and detection of nano-sized biological objects in an optofluidic chip, ILC trace-gas detection on a microchip, ILC Raman spectrometry on a microchip, and ILC spectroscopy of single rare-earth ions."
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