Design of flexible ultrahigh-Q microcavities in diamond-based photonic crystal slabs

We design extremely flexible ultrahigh-Q diamond-based double-heterostructure photonic crystal slab cavities by modifying the refractive index of the diamond. The refractive index changes needed for ultrahigh-Q cavities with $Q ~ 10^7$, are well within what can be achieved ($\Delta n \sim 0.02$). The cavity modes have relatively small volumes $V<2 (\lambda /n)^3$, making them ideal for cavity quantum electro-dynamic applications. Importantly for realistic fabrication, our design is flexible because the range of parameters, cavity length and the index changes, that enables an ultrahigh-Q is quite broad. Furthermore as the index modification is post-processed, an efficient technique to generate cavities around defect centres is achievable, improving prospects for defect-tolerant quantum architectures.Comment: 9 pages, 4 figures (1 in colour

Propagation effects in optical waveguides, fibres and devices

This thesis consist of a theoretical study of propagation effects in optical waveguides, fibres and photonic crystals, with some comparison with experiment. ¶ ..

First-principles method for high-QQ photonic crystal cavity mode calculations

We present a first-principles method to compute radiation properties of ultra-high quality factor photonic crystal cavities. Our Frequency-domain Approach for Radiation (FAR) can compute the far-field radiation pattern and quality factor of cavity modes $\sim 100$ times more rapidly than conventional finite-difference time domain calculations. It also provides a simple rule for engineering the cavity's far-field radiation pattern

Comparison of the sensitivity of air and dielectric modes in photonic crystal slab sensors

Optical cavities provide a route to sensing through the shift of the optical resonant peak. However, effective sensing with optical cavities requires the optimization of the modal quality factor, Q, and the field overlap with the sample, f. For a photonic crystal slab (PCS) this figure of merit, M =fQ, involves two competing effects. The air modes usually have large f but small Q, whereas the dielectric modes have high-Q and small f. We compare the sensitivity of air and dielectric modes for different PCS cavity designs and account for loss associated with absorption by the sensed sample or its host liquid. We find that optimizing Q at the expense f is the most beneficial strategy, and modes deriving from the dielectric bands are thus preferred. ©2009 Optical Society of America

Broadband and robust optical waveguide devices using coherent tunnelling adiabatic passage

We numerically demonstrate an optical waveguide structure for the coherent tunnelling adiabatic passage of photons. An alternative coupling scheme is used compared to earlier work. We show that a three rib optical waveguide structure is robust to material loss in the intermediate waveguide and variations to the waveguide parameters. We also present a five rib optical waveguide structure that represents a new class of octave spanning power divider

MONITORING OF EMG TO FORCE RATIO USING NEW DESIGNED PRECISE WIRELESS SENSOR SYSTEM

This work is focused on problematic of biopotential signals measurements (EXG) using powerful SMART sensor system, composed of portable units, intended for in-time wireless measurement and evaluation of electrical activity, produced by skeletal muscles, human heart or brain. Here, we discuss very precise measurement features, which characterize this device (high gain, low noise, wireless data transfer, multi-probe measuring), some special features as low voltage and ultra-low power consumption were reached by application of the described amplifier in order to achieve its longer performance for daily use. It brings a lot of advantages to biomedical electronics and medical care. In order to optimize the performance of novel proposed smart biomedical instrument in our experimental part we have focused on measurement of surface electromyography (sEMG) signal to force ratio. These sEMG signals can illuminate our understanding of how the brain controls muscles to generate force and produce movement and can be used in such applications like as training of athletes, controlling robots, monitoring the physical capabilities of patients with motor disorders etc

Slow-light switching in nonlinear Bragg-grating coupler

We study propagation and switching of slow-light pulses in nonlinear couplers with phase-shifted Bragg gratings. We demonstrate that power-controlled nonlinear self-action of light can be used to compensate dispersion-induced broadening of pulses through the formation of gap solitons, to control pulse switching in the coupler, and to tune the propagation velocity.Comment: 3 pages, 4 figure

Material Limitations on the Detection Limit in Refractometry

We discuss the detection limit for refractometric sensors relying on high-Q optical cavities and show that the ultimate classical detection limit is given by min{Dn} > eta with n+i*eta being the complex refractive index of the material under refractometric investigation. Taking finite Q factors and filling fractions into account, the detection limit declines. As an example we discuss the fundamental limits of silicon-based high-Q resonators, such as photonic crystal resonators, for sensing in a bio-liquid environment, such as a water buffer. In the transparency window of silicon the detection limit becomes almost independent on the filling fraction, while in the visible, the detection limit depends strongly on the filling fraction because silicon absorbs strongly.Comment: Published in Special Issue "Laser Spectroscopy and Sensing", Edited by Prof. M.W. Sigris