A.J.F. Hollink

Nano-mechanical tuning and imaging of a photonic crystal micro-cavity resonance

We show that nano-mechanical interaction using atomic force microscopy (AFM) can be used to map out mode-patterns of an optical micro-resonator with high spatial accuracy. Furthermore we demonstrate how the Q-factor and center wavelength of such resonances can be sensitively modified by both horizontal and vertical displacement of an AFM tip consisting of either Si(3)N(4) or Si material. With a silicon tip we are able to tune the resonance wavelength by 2.3 nm, and to set Q between values of 615 and zero, by expedient positioning of the AFM tip. We find full on/off switching for less than 100 nm vertical, and for 500 nm lateral displacement at the strongest resonance antinode locations.

Modeling and Experimental Verification of the Dynamic Interaction of an AFM-Tip With a Photonic Crystal Microcavity

We present a transmission model for estimating the effect of the atomic-force microscopy tapping tip height on a photonic crystal microcavity (MC). This model uses a fit of the measured tip-height-dependent transmission above a ¿hot spot¿ in the MC. The predicted transmission versus average tapping height is in good agreement with the values obtained from tapping mode experiments. Furthermore, we show that for the existing, nonoptimized structure, the transmission coefficient can be tuned between 0.32 and 0.8 by varying the average tapping height from 26 to 265 nm. A transmission larger than that of the undisturbed cavity at resonance was observed at specific tip locations just outside the cavity-terminating holes.

Compact integrated optical sensors based on a Si 3 N 4 grated waveguide optical cavity

A grated waveguide (GWG), which is a waveguide with a finite-length grated section, acts as an optical resonator, showing sharp fringes in the transmission spectrum near the stop-band edges of the grating. These oscillations are due to Fabry-Perot resonances of Bloch modes propagating in the cavity defined by the grated section [1]. Any small structural changes in the environment of the GWG, which disturb the evanescent field of the GWG resonant modes, will lead to a shift of its transmission spectrum. Such an effect can be exploited for sensing applications, such as the detection of a bulk refractive index change [2] or nanodisplacements of a cantilever suspended above the GWG [3]. Here we present 3 applications: (1) a concentration sensor, based on the bulk index change of the GWG top cladding; (2) label-free protein sensing (PepN enzyme - the major Suc-LLVY-AMC-hydrolyzing enzyme in Escherichia coli), where the spectral shift of the GWG response is due to the antibody-antigen interaction, leading to growth of an ad-layer on it; and (3) gas sensing, where the GWG detects stress-induced deflections of a doubly-clamped microcantilever (microbridge) with a Pd top layer due to H2 gas absorption by the Pd receptor layer.

Grated waveguide cavity for label-free protein and mechano-optical gas sensing

We demonstrate the versatility of a silicon nitride grated waveguide optical cavity as compact integrated optical sensors for (bulk) concentration detection, label-free protein sensing, and — with an integrated cantilever suspended above it — gas sensing.

On-chip microparticle detection and sizing using a dual-wavelength waveguide laser

An integrated intra-laser-cavity microparticle sensor based on a dual-phase-shift, dual-wavelength distributed-feedback channel waveguide laser in Al2O3:Yb3+ is presented. Real-time detection and accurate size measurement of single microparticles with diameters ranging between 1 μm and 20 μm are achieved, which represent the typical sizes of many fungal and bacterial pathogens as well as a large variety of human cells. The sensing principle relies on measuring changes in the frequency difference between the two longitudinal laser modes, as the evanescent field of the dual-wavelength laser interacts with micro-sized particles on the surface of the waveguide.