Hhje Harm Kicken

Wavelength tuning of planar photonic crystals by local processing of individual holes

Tuning of the resonant wavelength of a single hole defect cavity in planar photonic crystals was demonstrated using transmission spectroscopy. Local post-production processing of single holes in a planar photonic crystal is carried out after selectively opening a masking layer by focused ion beam milling. The resonance was blue-shifted by enlargement of selected holes using local wet chemical etching and red-shifted by infiltration with liquid crystals. This method can be applied to precisely control the resonant frequency, and can also be used for mode selective tuning.

Birefringence-induced mode-dependent tuning of liquid crystal infiltrated InGaAsP photonic crystal nanocavities

Mode-dependent shifts of resonant frequencies of cavities in liquid crystal (LC) infiltrated planar photonic crystals (PhC) are experimentally observed when the temperature is varied across the LC ordering transition. The shifts can be in opposite directions, even for two very similar nearly degenerate modes. The behavior is attributed to the different interactions of the modes with the two components of the refractive index of the LC infill and directly demonstrates that at least a substantial amount of the LC is oriented perpendicular to the PhC-hole axis.

Wavelength-sized, tunable nanocavity in deeply etched InP /InGaAsP /InP photonic crystals

Wavelength-sized point defect cavities coupled to access waveguides are reported for deeply etched InP/InGaAsP/InP two-dimensional photonic crystals. The observed quality factor of 60 is comparable to those found for one-row defect Fabry-Perot cavities and for simple point defect cavities in membranes. The quality factor was changed by varying the number of rows of holes. Upon infiltration of the holes with liquid crystal, frequency tuning was demonstrated.

Modeling the fs Demagnetization: Laser-Induced Reversal in an Applied Magnetic Field

A novel model for ultrafast laser-induced magnetization dynamics is analyzed. Equilibration of the magnetic system is described by including electron-phonon scattering events with a finite spin flip probability. Recently, we demonstrated that such a model predicts a direct relation between the demagnetization time and the Gilbert damping. Here we present numerical simulations based on the same Hamiltonian, but including the presence of an external applied field. Thereby, reversal of the magnetization after heating above the Curie temperature (TC) can be modeled. We demonstrate that magnetization reversal can be achieved even if the lattice temperature stays below TC.

Local digital etching and infiltration for tuning of a H1-cavity in deeply etched InP/InGaAsP/InP photonic crystals

Local post-production processing of single holes in a planar photonic crystal is demonstrated by selectively opening a masking layer by focused ion beam milling. Local tuning was optically demonstrated by both blue-shifting and subsequent red-shifting the resonance frequency of a point defect cavity. Since only a few holes of the PC are affected by the post-processing, the Q-factor is not significantly changed. This method can be applied to precisely control the resonant frequency, and can also be used for mode selective tuning.

Tuning of narrow-bandwidth photonic crystal devices etched in InGaAsP planar waveguides by Liquid Crystal infiltration

Photonic crystal (PC) devices in the InP/InGaAsP/InP planar waveguide system exhibiting narrow bandwidth features were investigated for use as ultrasmall and tunable building blocks for photonic integrated circuits at the telecom wavelength of 1.55 μm. The H1 cavity, consisting of a single PC-hole left unetched, represents the smallest possible cavity in a dielectric material. The tuning of this cavity by temperature was investigated under the conditions as etched and after the holes were infiltrated with liquid crystal (LC), thus separating the contributions of host semiconductor and LC-infill. The shift and tuning by temperature of the MiniStopBand (MSB) in a W3 waveguide, consisting of three rows of holes left unetched, was observed after infiltrating the PC with LC. The samples finally underwent a third processing step of local wet underetching the PC to leave an InGaAsP membrane structure, which was optically assessed through the ridge waveguides that remained after the under etch and by SNOM-probing.

Wavelength-sized cavities in high aspect InP/InGaAsP/InP photonic crystals

The photonic properties of two classes of wavelength-sized cavities are reported for deeply etched InP/InGaAsP/InP planar photonic crystals. The high aspect, deeply etched structures are studied as potential building blocks for nonmembrane type photonic devices in standard InP photonic integrated circuits. The first class consists of cavities of one unit cell in one direction and varying size in the other planar direction. The studied class includes a Fabry–Perot type cavity with one row of missing holes, a simple single missing hole defect cavity, and a cavity consisting of two holes which have been slightly shifted and reduced in hole radius. The best observed quality factor of 65 in this class is obtained for a single hole defect cavity. The second class is comprised of cavities which are derived from a three missing row defect in one direction and varying size in the other direction. This includes a Fabry–Perot type cavity with three rows of missing holes, a point defect cavity consisting of seven unetched holes and a six hole ring cavity. The best observed quality factor of 300 is obtained for the ring cavity in this second class of structures, which is adequate for applications.