We perform spatially dependent tuning of a GaInP photonic crystal cavity using a continuous wave violet laser. Local tuning is obtained by laser heating of the photonic crystal membrane. The cavity resonance shift is measured for different pump positions and for two ambient gases: He and N 2 . We find that the width of the temperature profile induced in the membrane depends strongly on the thermal conductivity of the ambient gas. For He gas a narrow spatial width of the temperature profile of 2.8 µm is predicted and verified in experiment.Photonic crystal (PhC) cavities are widely studied because of their fascinating applications 1-3 . Arrays of PhC cavities can form coupled resonator optical waveguides (CROW), which are very promising for slow light applications 4 and the study of light localization 5 . Various fabrication imperfections can cause a disorder in a CROW structure which leads to a detuning of cavities from the intended resonance and reduces the waveguide throughput and bandwidth. Tuning each cavity independently can restore cavities in resonance and counteract the disorder. There is a variety of methods to change the refractive index of a PhC cavity, including free-carrier injection 6 , the nonlinear Kerr effect 7 , thermal effects 8,9 , oxidation 10-12 and chemical processes 13 . Of these methods, thermal tuning through local laser heating is easy, reversible and can give a steady-state control of the resonance properties of the system. However due to the diffusion of heat in the PhC membrane thermal control of one cavity will affect the neighbor cavities. The width of the temperature profile is determined by the sample material and the surrounding media. Therefore one can expect that by carefully selecting the sample material and ambient medium one can control the width of the temperature profile.In this work we use the semiconductor alloy Ga 0.51 In 0.49 P as a sample material and two gases, nitrogen and helium, as a surrounding media. Ga 0.51 In 0.49 P has a thermal conductivity 14 of 4.9 W/(m·K) which is quite small in comparison to other semiconductor materials 15 . The thermal conductivity of gases is often assumed to be negligible compared to semiconductors, such as Si. However, the effect of the gas on the width of the thermal profile depends strongly on the ratio of the thermal conductivity of the gas and the semiconductor. Helium has a high thermal conductivity 16 of 0.153 W/(m·K), which is more than 6 times higher than of a) s.sokolov@utwente.nl; http://cops.nano-cops.com nitrogen 16 (0.024 W/(m·K)) and only 32 times smaller that that of Ga 0.51 In 0.49 P. Therefore the combination of Ga 0.51 In 0.49 P and He should have a high thermal exchange efficiency and small width of the temperature profile in comparison with other materials. To investigate the width of the temperature profile in PhC membranes we measured the response of the resonance of a H0-type cavity to a spatially scanned continuous wave (CW) heating laser focused on the membrane. pump 405 nm SLM (b) L1 IR camera CW IR laser ...

Near the band edge of photonic crystal waveguides, localized modes appear due to disorder. We demonstrate a new method to elucidate spatial profile of the localized modes in such systems using precise local tuning. Using deconvolution with the known thermal profile, the spatial profile of a localized mode with quality factor (Q) > 10 5 is successfully reconstructed with a resolution of 2.5 µm.

Weakly coupled high-Q nanophotonic cavities are building blocks of slowlight waveguides and other nanophotonic devices. Their functionality critically depends on tuning as resonance frequencies should stay within the bandwidth of the device. Unavoidable disorder leads to random frequency shifts which cause localization of the light in single cavities. We present a new method to finely tune individual resonances of light in a system of coupled nanocavities. We use holographic laser-induced heating and address thermal crosstalk between nanocavities using a response matrix approach. As a main result we observe a simultaneous anticrossing of 3 nanophotonic resonances, which were initially split by disorder. a) s.a.sokolov@uu.nl; http://www.nanolinx.nl/ 1 arXiv:1608.01257v3 [physics.optics]

We measure and analyze reflection spectra of directly coupled systems of waveguides and cavities. The observed Fano lines offer insight in the reflection and coupling processes. Very different from side-coupled systems, the observed Fano line shape is not caused by the termini of the waveguide, but the coupling process between the measurement device fiber and the waveguide. Our experimental results and analytical model show that the Fano parameter that describes the Fano line shape is very sensitive to the coupling condition. A movement of the fiber well below the Rayleigh range can lead to a drastic change of the Fano line shape.