Closure of the stop-band in photonic wire Bragg gratings.

Photonic Wire Bragg Gratings, made by periodic insertion of lateral rectangular recesses into photonic wires in silicon-on-insulator, can provide large reflectivity with short device lengths because of their large index contrast. This type of design shows a counter-intuitive behaviour, as we demonstrate - using experimental and numerical data - that it can have low or null reflectance, even for large indentation values. We provide physical insight into this phenomenon by developing a model based on Bloch mode theory, and are able to find an analytical expression for the frequency at which the grating does not sustain the stop-band. Finally we demonstrate that the stop-band closing effect is a general phenomenon that may occur in various types of periodic device that can be modeled as transmission line structures.

Far-field scattering microscopy applied to analysis of slow light, power enhancement, and delay times in uniform Bragg waveguide gratings.

A novel method is presented for determining the group index, intensity enhancement and delay times for waveguide gratings, based on (Rayleigh) scattering observations. This far-field scattering microscopy (FScM) method is compared with the phase shift method and a method that uses the transmission spectrum to quantify the slow wave properties. We find a minimum group velocity of 0.04c and a maximum intensity enhancement of ~14.5 for a 1000-period grating and a maximum group delay of ~80 ps for a 2000-period grating. Furthermore, we show that the FScM method can be used for both displaying the intensity distribution of the Bloch resonances and for investigating out of plane losses. Finally, an application is discussed for the slow-wave grating as index sensor able to detect a minimum cladding index change of 10(-8), assuming a transmission detection limit of 10(-4).

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.