The proof of concept for a photonic cavity sensor for oil, water and gas detection is reported. The optical design employs an optimized photonic crystal cavity with fluidic infiltration of gas, water or (reservoir) oils. The 3D design and simulation is discussed, followed by the nanofabrication in standard silicon on insulator wafers (SoI). Using an optofluidic cicuit with PDMS channels, the fluid flow to the photonic cavity is controlled with syringe pumps. The variations in dielectric value (refractive index) change with the involved media result in a shift of the cavity resonant wavelength. For fluid change from water to typical oil (refractive index difference of 0.12), we report a wavelenght shift of up to 12 nm at the measurement wavelength of 1550 nm, in very good agreement with the simulations. We follow the optical response at a fixed wavelength, when feeding alternate flows or bubbles of oil/water through the optofluidic chip, and observe the flow pattern on camera. Finally we discuss the outlook and antifouling of the sensor with a special design. This work is supported by Shell Global Solutions.
Appl.Phys.Lett., 106, 031116 (2015)
J.Lightw.Technol., 33, 3672 (2015)
A design of a point-defect cavity in two-dimensional photonic crystal slab with both high Q factor and high transmission
intensity has been achieved by adjusting the radii and position of lattice points in both parallel and perpendicular
directions. Analysis shows that discrete resonant modes have been found in the 1550 wavelength range with Q factors up
to 40,000. Moreover, the cavity was verified to subject to minor intensity decrease of 1.2 dB due to the introducing of
external waveguide access. All these features make the cavity a very promising candidate for light transmission and
detection in practical application. We also demonstrate the potential application of such a cavity being used as a sensitive
index sensor with a high sensitivity of 400nm/refractive index unit.
We demonstrate completely integrated tunable coupled cavity InGaN/GaN lasers with emission wavelength centered on
409 nm. Threshold currents are 650 mA per cavity for 8.7 um wide laser ridges. Experimental tuning map is explained
with estimation of refractive index change due to free carrier injection and the Vernier effect. Multimode laser emission
with the average full width half maximum of 0.3 nm, electronic tuning range of 1.6 nm and thermal tuning range of
2.4nm is observed.
Liquid crystal (LC, Merk 5 CB) is infiltrated into active, InAs quantum dots embedded, InGaAsP membrane type
nanocavities to investigate the possible effect of the LC orientation on active cavity tuning. The tuning is demonstrated
thermally and thermo-optically. The thermal tuning showed that the cavity modes can be tuned in opposite directions and
exhibits a sudden change at the clearing temperature. The mechanism relies on the existence of both ordinary and
extraordinary refractive indices of the liquid crystal due to its molecular alignment inside the voids. It shows that the
electric field distribution of cavity modes can have a substantial component parallel to the LC director. The average
electric field orientation with respect to the LC orientation can be mode dependent, so that different modes can be
dominated by either branch of the LCs refractive index. Thermo-optic tuning of the modes is obtained when the power of
the excitation laser is increased from 40 μW to 460 μW. A large and a reversible blueshift of more than 10 nm of the
cavity modes is observed which is attributed to temperature induced liquid transport. InGaAsP type of nanocavities,
without InAs quantum dots were infiltrated with PbSe colloidal quantum dots to obtain a comparison of internal light
sources either in the semiconductor or in the holes.
The recently introduced helium ion microscope (HIM) is capable of imaging and fabrication of nanostructures thanks to
its sub-nanometer sized ion probe. The unique interaction of the helium ions with the sample material provides very
localized secondary electron emission, thus providing a valuable signal for high-resolution imaging as well as a
mechanism for very precise nanofabrication. The low proximity effects, due to the low yield of backscattered ions
and the confinement of the forward scattered ions into a narrow cone, enable patterning of ultra-dense sub-10 nm structures. This paper presents various nanofabrication results obtained with direct-write, with scanning helium ion beam lithography, and with helium ion beam induced deposition.
Based on the self-collimation effect of light propagating inside a photonic crystal, we demonstrate a novel concept for a
compact Mach-Zehnder interferometer. The properties of these self-collimated beams are such that we can manipulate
them to form the beam splitters and mirrors of the Mach-Zehnder interferometer in a very compact area of 20x20 μm<sup>2</sup>.
We obtain the unidirectional output behaviour characterized by the high contrast in the telecommunication-wavelength
signal at the two outputs of the photonic crystal Mach-Zehnder interferometer. The experiments are done using optical
transmission spectroscopy and far-field optical microscopy. This photonic crystal Mach-Zehnder interferometer holds a
promise for a compact Mach-Zehnder modulator, inspired by recent reports of NEMS-based photonic crystal membrane.
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.
This article analyzes the efficacy of the light sources and their limitations in theory and in technology. The LED's spectra were simulated by a Gaussian model to calculate the efficacy. The conventional light sources have been compared with LEDs; the results show that significant increase of LEDs' internal quantum efficiency and extraction efficiency is essential for LED application in general lighting.
We have developed a reliable process to fabricate high quality 2D air-hole and dielectric column InP photonic crystals
with a high aspect ratio on a STS production tool using ICP N<sub>2</sub>+Cl<sub>2</sub> plasma. The photonic crystals have a triangular
lattice with lattice constant of 400 nm and air-hole and dielectric column radius of 120 nm. Large efforts have been
devoted on developing a proper mask. We obtained a perfect, clean and vertical profiled SiN<sub>X</sub> mask. The next main
effort is InP pattern transfer in Cl<sub>2</sub>+N<sub>2</sub> plasma. Etching selectivity, smooth sidewall and etch profile are directly related
to plasma process condition, besides the quality of SiNX mask. We have optimized the N<sub>2</sub>+Cl<sub>2</sub> plasma condition to obtain
high aspect ratio, vertical profile and smooth sidewall InP structures. Cylindrical holes (2 micron depth) and rodlike
pillars (2.4 micron height) are uniformly fabricated. An aspect ratio of 18 for 100nm trench lines has been obtained.
AFM measurement evidences that etched surfaces are smooth. The root mean square roughness of pillar and hole is 0.7
nm and 0.8 nm, respectively. The optical transmission characterization of ridge waveguides has been carried out.
Transmission spectrum of 1 micron wide waveguide has been obtained.
The filling is reported of the air holes of an InP-based two-dimensional photonic crystal with solid polymer and with liquid crystal 5CB. The polymer filling is obtained by thermal polymerization of an infiltrated liquid monomer, trimethylolpropane triacrylate. The filling procedure for both the monomer and liquid crystal relies on the capillary action of the liquid inside the ~ 200 nm diameter and < 2.5 μm deep air holes. The solid polymer infiltration result was directly inspected by cross-sectional scanning electron microscopy. It was observed that the holes are fully filled to the bottom. The photonic crystals were optically characterized by transmission measurements around the 1.5 μm wavelength band both before and after infiltration. The observed high-frequency band edge shifts are consistent with close to 100% filling, for both the polymer and the liquid crystal. No differences were observed for filling under vacuum or ambient, indicating that the air diffuses efficiently through the liquid infiltrates, in agreement with estimates based on the capillary pressure rise.
Polymer filling of the air holes of indiumphosphide based two-dimensional photonic crystals is reported. The filling is
performed by infiltration with a liquid monomer and solidification of the infill <i>in situ </i>by thermal polymerization.
Complete hole filling is obtained with infiltration under ambient pressure. This conclusion is based both on cross-sectional
scanning electron microscope inspection of the filled samples as well as on optical transmission
Chlorine-based inductively coupled plasma etching processes are investigated for the purpose of etching two-dimensional photonic crystals in InP-based materials. Etch rates up to 3.7 mm/min and selectivity’s to the SiN mask up to 19 are reported. For the removal of indiumchloride etch products both the application of elevated temperatures and high ion energy’s are investigated. The reactor pressure is an important parameter, as it determines the supply of reactive chlorine. It is shown, that N2 passivates feature sidewalls during etching, improving the anisotropy. Ions that impact onto the sidewalls, either directly or after scattering with the SiN-mask or hole interior, cause sidewall etching. Highly directional ion bombardment and vertical sidewalls in the SiN-mask are therefore crucial for successful etching of fine high aspect ratio structures.
ihe (1 10) face in Ill-V binaiy compounds is a non-polar surface and allows the determination of valence and conduction hand edges as well as energy gap at the clean ultra-high vacuum cleaved surface. In epitaxial 111-V semiconductor multilayers this (1 10) face forms a cross section to the preferential 001 growth direction. With scanning tunneljng microscopy we have been able to observe the atomic arrangement in MBE-grown GaAs and A1GaAs layers as well in their interfaces. The binary and ternary cornpoupds can be clearly distinguished and we also find indications for composition fluctuations in the ternary. The atomic resolution images show that the material transition occurs over 2 unit cells. From the current-voltage characteristics across the GaAs-AlGaAs interface the valence band edge is determined and compared with theoretical calculations. The electronic valence band transition occurs over a length scale of less than 4 urn.