We developed a method to easily transfer optical structures from a semiconductor substrate to a fiber-tip facet without the need for glues and preserving the pristine or functionalized condition of the structure surface. An opening is etched on the back of the fabrication wafer and the structure is suspended via breakable support. The transfer is achieved by mechanical contact with the fiber facet. Using a photonic crystal structure designed for high vertical coupling at the Gamma point a reflectance fiber-tip sensor with refractive index sensitivity of 120 nm/RIU has been assembled and could be further functionalized for application in biosensing.
Due to their deterministic nature and efficiency, devices based on quantum dots (QD) are currently replacing traditional single-photon sources in the most complex quantum optics experiments, such as boson sampling protocols. Embedding these emitters into photonic crystal (PhCs) cavities enables the creation of an array of Purcell-enhanced single photons required to build quantum photonic integrated circuits. So far scaling of the number of these cavity-emitters nodes on a single chip has been hampered by practical problems such as the lack of post-fabrication methods to control their relative detuning and the complexity involved with their optical excitation. Here, we present a tuneable single-photon source combining electrical injection and nano-opto-electromechanical cavity tuning. The device consists of a double-membrane electromechanically tuneable PhC structure. A vertical p-i-n junction, hosted in the top membrane, is exploited to inject current in the QD layer and demonstrate a tunable nano LED whose cavity wavelength can be reversibly varied over 15 nanometers by electromechanically varying the distance between membranes. Besides, electroluminescence from single QD lines coupled to PhC cavities is reported for the first time. The measurement of the second-order autocorrelation function from a cavity-enhanced line proves the anti-bunched character of the emitted light. Since electrical injection does not produce stray pump photons, it makes the integration with superconducting single-photon detectors much more feasible. The large-scale integration of such tuneable single-photon sources, passive optics and waveguide detectors may enable the implementation of fully-integrated boson sampling circuits able to manipulate tens of photons.
Andrea Fiore, Zarko Zobenica, Rob van der Heijden, Maurangelo Petruzzella, Francesco Pagliano, Rick Leijssen, Ewold Verhagen, Tian Xia, Leonardo Midolo, YongJin Cho, Frank van Otten
Nanophotonic structures with narrow optical resonances, such as high-quality factor photonic crystal cavities, in principle enable spectral sensing with high resolution. This can also result in high-sensitivity displacement and/or acceleration sensing if a part of the cavity is compliant. However, the control of the resonance and its optical read-out are complex and usually not integrated with the sensing part. In this talk we will introduce a novel nano-opto-electromechanical system (NOEMS), where actuation, sensing and read-out are integrated in the same device. It consists of a double-membrane photonic crystal cavity, where the resonant wavelength is tuned by electrostatically controlling the separation between the membranes. The output current signal provides direct information about either the wavelength of the incident light or the cavity resonance. This nanophotonic sensing system can be employed to measure the spectrum of incident light, to determine the wavelength of a laser line with pm-range resolution, or equivalently to measure tiny displacements.
As a result of the continuously shrinking features of the integrated circuit, the overlay budget requirements have become very demanding. Historically, overlay has been performed using metrology targets for process control, and most overlay enhancements were achieved by hardware improvements. However, this is no longer sufficient, and we need to consider additional solutions for overlay improvements in process variation using computational methods. In this paper, we present the limitations of third-order intrafield distortion corrections based on standard overlay metrology and propose an improved method which includes a prediction of the device overlay and corrects the lens aberration fingerprint based on this prediction. For a DRAM use case, we present a computational approach that calculates the overlay of the device pattern using lens aberrations as an additional input, next to the target-based overlay measurement result. Supporting experimental data are presented that demonstrate a significant reduction of the intrafield overlay fingerprint.
In this paper we present the limitations of 3rd order distortion corrections based on standard overlay metrology and propose a new method to quantify and correct the cold-lens aberration fingerprint. As a result of continuous shrinking features of the integrated circuit, the overlay budget requirements have become very demanding. Historically, most overlay enhancements were achieved by hardware improvements. However there also is a benefit in the computational approach, and so we looked for solutions for overlay improvements in process variation with computational applications.
Photonic crystal (PhC) cavities made in broadband luminescent material offer attractive possibilities for flexible active
devices. The luminescence enables the cavity to operate as an autonomous entity. New applications of this property are
demonstrated for cavities made in the InGaAsP underetched semiconductor membrane with embedded InAs Quantum
Dots that emit in the range of 1400-1600 nm.
Planar photonic crystal membrane nanocavities were released from the parent chip by mechanical nanomanipulation.
The released cavity particle could be bonded on an arbitrary surface, which was exploited to make a novel fiber-optic tip
sensor with a PhC cavity attached to the tip.
A single mode from a short cavity is shown to couple simultaneously to at least three cavity modes of a long cavity, as
concluded from level anticrossing data when the small cavity was photothermally tuned.
Reconfigurable and movable cavities were created by locally varying the infiltration status by liquid oil near a PhC
waveguide or defect cavity. Liquid was displaced locally on a micron scale using capillary force effects or laser-induced
evaporation and condensation phenomena.
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%.
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.
Hexagonal symmetry InGaAsP membrane type cavities with embedded InAs quantum dots as active emitters were investigated by room temperature photoluminescence experiments at wavelengths near 1.50 µm. Cavities consisting of simple defects of just removing one or seven air holes were studied as well as modified cavities with additional holes decreased in size and shifted in position. The latter include the H0 cavity, in which only two adjacent holes were modified, but none removed. Low-Q cavity modes were observed for the simple cavities while high-Q modes were observed after modification of the surrounding holes. The resonant frequencies were varied over a large range of lithographic parameters both by changing the lattice spacing or the size of the modified holes. More than 15 nm reversible dynamic optical tuning of the resonance modes was observed by changing the applied laser power up to 5 mW. For thermo-optic tuning, this corresponds to a heating of up to 200 °C.
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.
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 N2+Cl2 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 SiNX mask. The next main
effort is InP pattern transfer in Cl2+N2 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 N2+Cl2 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 in situ 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
measurements.
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 in situ 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
measurements.
Mischa S. Andriesse, Carl-Fredrik Carlström, Emile van der Drift, Erik-Jan Geluk, Rob van der Heijden, A. Karouta, Peter Nouwens, Y. Siang Oei, Tjibbe de Vries, Huub Salemink
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.
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