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Results are presented on the use of InGaAsP photonic crystal nanobeam slot waveguides for refractive index sensing. These sensors are read remote-optically through photoluminescence, which is generated by built-in InGaAs quantum dots. The nanobeams are designed to maximize the electromagnetic field intensity in the slot region, which resulted in record-high sensitivities in the order of 700 nm/RIU (refractive index unit). A cavity, created by locally deflecting the two beams towards each other through overetching, is shown to improve the sensitivity by about 20%.

A large and reversible all-optical tuning effect is demonstrated for liquid crystal (LC) infiltrated InGaAsP photonic crystal membrane nanocavities. The tuning is based on the change in the refractive index of the LC due to the large local heating caused by absorption of laser light by the semiconductor. Compared to opto-thermal tuning based on semiconductor heating alone, the effects with the LC are an order of magnitude larger and can be either redshifting or blueshifting, depending on the spatial distribution of the cavity mode’s polarization direction.

We demonstrate the independent lithographic mode tuning by changing the holes around the defect area of photonic crystal nanocavities containing light-emitting quantum dots. The data have been verified by the three- dimensional finite-difference time domain simulation. These findings can be applied to realize encoded particles with large coding capability (>105) for biosensing.

We present the design, fabrication, and photoluminescence experiment of InGaAsP photonic crystal slot nanobeam slow light waveguides with embedded InAs quantum dots. The strong confinement of electric field in the slot region is confirmed by the measured record high sensitivity of 7 x 10 (2) nm per refractive index unit RIU to the refractive index change of the environment. A cavity, formed by locally deflecting the two beams toward each other, gives an even higher sensitivity of about 9x10(2) nm/RIU.

The sensitivities of resonant wavelengths of photonic crystal (PhC) membrane nanocavities with embedded InAs quantum dots to the ambient refractive index are reported for use in (bio) chemical sensing. The resonances for the different modes of several point-defect type cavities are obtained by photoluminescence measurements. Systematic trends of the variation of sensitivity with increase of the overlap of the modes with the PhC holes are observed for varying cavity type as well as for a given mode within a cavity type. A maximum sensitivity of approximately 300 nm/RIU (refractive index unit) is observed, corresponding to approximately 25% mode overlap with the holes and complete infiltration with the aqueous solution.

We demonstrate the control of the mode degeneracy when a liquid crystal (LC) is infiltrated into an InGaAsP membrane photonic crystal nanocavity with embedded InAs quantum dots. Mode splitting exists in the anisotropic nematic LC state, and not in the unfilled or isotropic LC state. The degeneracy lifting of the quadrupole mode is attributed to the different interactions of the two orthogonal basis modes of the degenerate mode with the two components of the refractive index of the LC. The interpretation is supported by the quantitative agreement between the experimental results and the three-dimensional finite-difference time-domain computations.

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 defectcavity, 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 defectcavity. 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 defectcavity 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.

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.

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.

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.

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 blueshifting and subsequent red-shifting the

A high-contrast-ratio (30 dB) photonic band gap in the near-infrared transmission of hole-type GaN two-dimensional photonic crystals(PhCs) is reported. These crystals are deeply etched in a 650 nm thick GaN layer grown on sapphire. A comparison of the measured spectrum with finite difference time domain simulations gives quantitative agreement for the dielectric band and qualitative agreement for the air band. The particular behavior of the air band arises from the relatively low index contrast between the GaN layer and the sapphire substrate. Our results call for extension of the operation of GaNPhCs to the visible range.

An extensive investigation has been performed on inductively coupled plasmaetching of InP. An important motivation for this work is the fabrication of high-aspect-ratio holes for photonic crystals. The essential chemistry is based on Cl₂ with the addition of N₂ or O₂ for sidewall passivation. The influence of different process parameters such as gas flows, temperature,pressure, ion energy, and inductively coupled plasma power on the hole geometry is presented. It is concluded that photonic crystals can be etched with Cl₂ only; however, temperature and pressure control is critical. Adding passivation gases largely broadens the window in the parameter space for hole etching. Most importantly, etching of narrow holes can be carried out at higher temperatures where the etching is mass limited and spontaneous etching of InP by Cl₂ occurs.