In this paper we describe the fabrication of a periodic, two-dimensional arrangement of gold square patches on a Silicon
substrate, and highlight technological limitations due to the roughness of the metal layer. Scanning Electron Microscope
(SEM) and Atomic Force Microscope analyses are also reported showing that the geometrical parameters obtained are
almost identical to the nominal parameters of the simulated structure.
The device is functionalized by means of a conjugated rigid thiol forming a very dense, closely packed, reproducible 18
Å–thick, self-assembled monolayer. The nonlinear response of the 2D array is characterized by means of a micro-Raman spectrometer and it is compared with a conventional plasmonic platform consisting of a gold nano-particles ensemble on Silicon substrate, revealing a dramatic improvement in the Raman signal. The SERS response is empirically investigated using a laser source operating in the visible range at 633 nm. SERS mapping and estimation of the provided SERS enhancement factor (EF) are carried out to evaluate their effectiveness, stability and reproducibility as SERS substrate.
Moreover, we take advantage of the simple geometry of this 2D array to investigate the dependence of the SERS
response on the number of total illuminated nano-patches.
We experimentally demonstrate the possibility to implement an optical bio-sensing platform based on the shift of the
plasmonic band edge of a 2D-periodic metal grating. Several 2D arrangements of square gold patches on a silicon
substrate were fabricated using electron beam lithography and then optically characterized in reflection. We show that
the presence of a small quantity of analyte, i.e. isopropyl alcohol, deposited on the sensor surface causes a dramatic red
shift of the plasmonic band edge associated with the leaky surface mode of the grating/analyte interface, reaching
sensitivity values of ~650nm/RIU. At the same time, dark field microscopy measurements show that the spectral shift of
the plasmonic band edge may also be detected by observing a change in the color of the diffracted field. Calculations of
both the spectral shift and the diffracted spectra variations match the experimental results very well, providing an
efficient mean for the design of sensing platforms based on color observation.
Colloidal nanocrystals, i.e. quantum dots synthesized trough wet-chemistry approaches, are promising nanoparticles for
photonic applications and, remarkably, their quantum nature makes them very promising for single photon emission at
room temperature. In this work we describe two approaches to engineer the emission properties of these nanoemitters in
terms of radiative lifetime and photon polarization, drawing a viable strategy for their exploitation as room-temperature
single photon sources for quantum information and quantum telecommunications.
In this paper we present a reliable process to fabricate GaN/AlGaN one dimensional photonic crystal (1D-PhC)
microcavities with nonlinear optical properties. We used a heterostructure with a GaN layer embedded between two
AlGaN/GaN Distributed Bragg Reflectors on sapphire substrate, designed to generate a λ= 800 nm frequency downconverted
signal (χ(2) effect) from an incident pump signal at λ= 400 nm. The heterostructure was epitaxially grown by
metal organic chemical vapour deposition (MOCVD) and integrates a properly designed 1D-PhC grating, which
amplifies the signal by exploiting the double effect of cavity resonance and non linear GaN enhancement. The integrated
1D-PhC microcavity was fabricate combing a high resolution e-beam writing with a deep etching technique. For the
pattern transfer we used ~ 170 nm layer Cr metal etch mask obtained by means of high quality lift-off technique based
on the use of bi-layer resist (PMMA/MMA). At the same time, plasma conditions have been optimized in order to
achieve deeply etched structures (depth over 1 micron) with a good verticality of the sidewalls (very close to 90°).
Gratings with well controlled sizes (periods of 150 nm, 230 nm and 400 nm respectively) were achieved after the pattern
is transferred to the GaN/AlGaN heterostructure.
We present a study on the design, growth and optical characterization of a GaN/AlGaN microcavity for the enhancement
of second order non linear effects. The proposed system exploits the high second order nonlinear optical response of
GaN due to the non centrosymmetric crystalline structure of this material. It consists of a GaN cavity embedded between
two GaN/AlGaN Distributed Bragg Reflectors designed for a reference mode coincident with a second harmonic field
generated in the near UV region (~ 400 nm). Critical issues for this target are the crystalline quality of the material,
together with sharp and abrupt interfaces among the multi-stacked layers. A detailed investigation on the growth
evolution of GaN and AlGaN epilayers in such a configuration is reported, with the aim to obtain high quality factor in
the desiderated spectral range. Non linear second harmonic generation experiments have been performed and the results
were compared with bulk GaN sample, highlighting the effect of the microcavity on the non linear optical response of
We analyze in this work the second harmonic amplification of χ(2) nonlinear process in membrane type GaAs circular
photonic crystal. This unconventional kind of photonic crystal is well suited for the generation of whispering gallery
modes due to the circular symmetric periodic pattern. The Gaussian beam of a fundamental pump signal at 1.55 μm
defines a whispering gallery mode resonance and generates a second harmonic mode at 0.775 μm in the central missing
hole micro-cavity. The periodic pattern and the micro-cavity are tailored and optimized in order to generate a second
harmonic conversion efficiency of 50 %. We predict the resonances by an accurate 2D time domain model including χ(2)
nonlinearity and also by a 3D Finite Element Method FEM. Moreover, by using a 3D membrane configuration, we
predict a quality factor of the second harmonic mode of the order of 35000.
Colloidally synthesized CdSe/ZnS core/shell semiconductor nanocrystals (NCs) show highly efficient, narrow-width and size-tunable luminescence. Moreover, they can be incorporated in polymer matrices and deposited on solid substrates by means of spin-coating techniques. When embedded between two mirrors a NCs/polymer blends microcavity is realised, thus allowing to tailor the photoluminescence spectrum of these emitters. By virtue of the quantized photonic and electronic density of states, colloidal quantum dots embedded in a single mode vertical microcavity are good candidates for the fabrication of high-efficiency emitting devices with high spectral purity and directionality.
In this paper, we have applied a new organic-inorganic hybrid technology for the fabrication by imprint lithography (IL) of vertical microcavities that embed colloidal quantum dots.
Two dielectric distributed Bragg reflectors (DBR) are evaporated on two different substrates. The active organic layer (NCs/polymer blend) is spin coated on the first DBR, whereas a lithographic pattern is realized on the second DBR, used as the IL mold. The two parts are then assembled together in an IL process in order to create a vertical microcavity. The fine control of the thickness of the active material waveguide layer can be achieved through the mold patterning depth and the IL process parameters. All the fabrication steps have been engineered in order to decrease the thermal stress of the active layer.
The effectiveness of this technology is demonstrated by the room temperature photoluminescence (PL) spectra, recorded on the fabricated microcavity, which show a sharp emission peak with a line width of 4.15 nm.
In this paper we propose the design and the fabrication of 90° bend ridge waveguide (WG) assisted by a two-dimensional photonic crystal (2D-PC). 2D-PCs act as efficient mirrors along the boundaries of the bend ridge thus reducing the in-plane losses. The ridge waveguide consists of a 3 μm x 0.75 μm titanium dioxide core on a silica bottom cladding. The 2D-PC structure surrounding the bend waveguide is composed of a triangular array of circular dielectric pillars having a height of 0.75 μm. The titanium dioxide waveguiding core layer is covered with PMMA in order to create a quasi-symmetric structure. A photonic band gap centered around 1.3 μm is obtained by a PC radius r = 0.33a and lattice period a = 0.450 μm. The design of the whole structure is subsequently optimized by using a 3D Finite Difference Time Domain based computer code. The ridge waveguide assisted by a 2D-PC has been fabricated by using electron beam lithography and reactive ion etching. For the pattern transfer we have used about 50 nm thin layer Cr metal etch mask obtained by means of a lift-off technique based on the use of bi-layer resist (PMMA/MMA).
The presence of the 2D-PC around the bend waveguide leads to a sharp increase of the transmission efficiency around 1.3 μm for curvature radius of 2.5 μm. The bend transmission results to be in the range between 0.76 and 0.85 when the thickness of the ridge WG and of the 2D-PC pillars is between 0.75 and 1.3 μm. This value is more than twice with respect to the bend waveguide without 2D-PC.