Single photons generated by spontaneous parametric down conversion are often utilized in heralded schemes, in which case the heralded photon purity must be maximized to preserve the indistinguishability of the photons that carry out quantum computing. In this work, we present software designed for accurate calculation of such purity, which was optimized to minimize computational resources and time, allowing for maximum purity searches in broad wavelength ranges. Lithium niobate and potassium titanyl phosphate (KTP) were studied in three phase-matching conditions, and an ultra-high purity configuration was found. The configuration was experimentally realized through an ion-exchanged KTP waveguide, exploiting flexibility in pump and phase matching temperature to compensate fabrication deviations, and purities as high as 0.923 were found, with very high generation rate of 40.7 MHz/mW. The experimental purity is significantly degraded by the multimode guiding at the desired wavelengths, which we propose to address by engineering with femtosecond laser writing, of which preliminary results are presented.
Light-matter interaction is crucial in many application domains of nanophotonics, including biosensing, trapping at the nanoscale, nonlinear optics, and lasing. Many approaches, mainly based on photonic and plasmonic resonant structures, have been investigated to enhance and tailor the interaction, but those based on all-dielectric metasurfaces have several unique advantages: low loss, easy excitation and readout, possibility of engineering the optical field distribution with many degrees of freedom, and electric tuning. Here we show that properly designed all-dielectric metasurfaces can support silicon-slot quasi-bound states in the continuum modes resonating in the near-infrared, strongly confining light in air and, consequently, enhancing light-matter interaction. Some samples of the designed metasurface have been fabricated in a silicon-on-sapphire wafer by e-beam lithography and reactive ion etching. The optical characterization of the chip has confirmed the excitation of the quasi-bound state in the continuum resonant modes, with measured Q-factor values exceeding 700.
The advent of 300mm fabrication tools and immersion lithography for photonics may change the game and the practical use of ring resonator based devices. We implemented such ring resonators on our 300 mm SOI platform for Silicon photonics using immersion lithography. We show that such technology offers unprecedented level of uniformity and reproducibility within a die but also from die to die. Such performances allowed us to combine and cascade ring resonators to fabricate high rejection filters in Coupled Resonator Optical Waveguide (CROW) configurations. Such high rejection filters are thus very promising candidates for quantum photonics, and more particularly in circuits based on photons pair generation, where pump rejection filters with over 100dB of rejection are needed.
Silicon photonics based on CMOS technology is a very attractive platform to build compact, low-cost and scalable quantum photonics integrated circuits addressing the requirements of quantum key distribution protocols. We show record low propagation losses below 0.5 dB/cm and below 0.05 dB/cm for silicon and silicon nitride waveguides respectively. We will present our results on integrated components such as hybrid III-V on silicon lasers for weak coherent pulse generation, high-quality microresonators for entangled photon pair generation and we will show our recent developments on high crystalline quality NbN thin films with improved critical temperature for waveguide-integrated superconducting single photon detectors.
We experimentally demonstrate the feasibility of the use of integrated linearly uncoupled resonators, which are coupled solely through the nonlinear interaction, to selectively enhance or suppress nonlinear processes. This is exploited to selectively enhance dual-pump spontaneous four-wave mixing while suppressing the parasitic noise associated with single pump spontaneous four-wave mixing processes. A signal-to-noise ratio characterizing the generation of identical photon pairs of more than four orders of magnitude is reported, opening the way to a new class of integrated devices exploiting the unique properties of identical photon pairs in the same optical mode.
Integration density, channel scalability, low switching energy and low insertion loss are the major prerequisites for on-chip WDM systems. A number of device geometries have already been demonstrated that fulfill these criteria, at least in part, but combining all of the requirements is still a difficult challenge. I will present our recent work on photonic crystal enhanced light sources, modulators and detectors for silicon photonics, that promise to give the ultimate in low energy and area consumption.
Four-wave mixing can be stimulated or occur spontaneously: the latter effect, also known as parametric fluorescence,
can be explained only in the framework of a quantum theory of light, and it is at the basis of many
protocols to generate nonclassical states of the electromagnetic field. In this work we report on our experimental
study of spontaneous four wave mixing in microring resonators and photonic crystal molecules integrated on a
silicon on insulator platform. We find that both structures are able to generate signal and idler beams in the
telecom band, at rates of millions of photons per second, under sub-mW pumping. By comparing the experiments
on the two structures we find that the photonic molecule is an order of magnitude more efficient than the
ring resonator, due to the reduced mode volume of the individual resonators.
We demonstrate electrically pumped silicon nano-light source at room temperature,
having very narrow emission line (<0.5nm) at 1500nm wavelength, by enhancing the
electroluminescence (EL) via combination of hydrogen plasma treatment and Purcell
effect. The measured output power spectral density is 0.8mW/nm/cm2, which is
highest ever reported value from any silicon light emitter.
During the last years, much attention has been paid to photonic crystals (PC) for different applications, but
only recently they have been proposed and showed useful for applications in solar cells. Little work has been
done in the actual manufacture and characterization of a complete solar cell with a two-dimensional photonic
crystal (2D-PC) on its front surface, conceived as a periodic distribution of the dielectric constant in the plane
(the surface of the solar cell) and involving sub-wavelength motifs. In this case, the photonic crystal effect is
different from the one happening in slabs or suspended membranes. Despite the partial vertical confinement,
there may be some reasons that can justify the use of photonic crystal front surface with sub-wavelength
motifs. Experimental results on actual devices with a photonic crystal nanopatterned layer will be shown,
along with reflectivity studies on PC lattices with different symmetries and shapes.
Bloch Surface Waves (BSWs) are propagation modes that exist at the interface between a homogeneous medium and a
photonic crystal (PhC). The confinement at the interface of the media relies on total internal reflection in the
homogeneous medium and on the photonic band gap in the PhC. The dispersion relation of BSWs can be easily tailored
through the design of the PhC. This makes BSWs extremely flexible and suitable for applications in the field of optical
sensors, light emitters, and photovoltaic devices, where the capability to confine and amplify the electromagnetic field in
micro- and nano-structures allows for the enhancement of the light-matter interaction. In particular, we present two
different configurations for the detection of Bloch surface waves in silicon nitride multilayers: attenuated total
reflectance and photoluminescence measurements. In the first, we measured a 50-fold enhancement of the diffraction
signal by a protein grating printed on the multilayer when the incident light beam is coupled to the surface waves. In the
second, we observe a significant modification of the spontaneous emission by a monolayer of rhodamine molecules
bonded to the photonic crystal surface. These results may found application in the field of optical sensors, particularly
for biosensing.
Artificial opals are a simple and cheap playground to manipulate the propagation of light. The interest in these kind of
photonic crystals is further increased by the possibility to be infiltrated with highly polarisable media like organic
semiconductors, i.e. conjugated polymers, push-pull molecules and multipolar chromophores.
In this work, we report on the optical properties of polystyrene opals infiltrated with a heteroaromatic quadrupolar
derivative endowed with strong nonlinear optical properties (two-photon absorption) in solution. The insertion of
tris(ethylene glycol)monomethyl ether chains on the conjugated skeleton allows the molecule to be soluble in water, a
non-solvent for polystyrene. This condition is fundamental in order to attempt opal infiltration.
Variable angle transmittance and photoluminescence spectroscopy are used to characterize the system. The bathochromic
shift of the opal stop band upon immersion in the chromophore solution confirms that the infiltration process easily takes
place preserving a dielectric contrast suitable for further investigations.
Photoluminescence spectra recorded at different emission angle with respect to the normal of the sample for both the
chromophore solution and opals infiltrated with such solution show interesting characteristics. The presence of opal
modifies the chromophore emission spectrum by filtering the light for wavelengths corresponding to those of the stop
band and according to its dispersion.
Photonic modes in 1-D and 2-D silicon-on-insulator photonic
crystal waveguides periodic or containing line-defects, are fully
explored by means of angle- and polarization-resolved
micro-reflectance measurements. Both quasi-guided and truly guided
photonic modes are probed with a frequency-wave vector range that
is greatly expanded under attenuated total reflectance
configuration. It is shown that the presence of a supercell
repetition in the direction perpendicular to a line defect leads
to the simultaneous excitation of defect and bulk modes folded in
a reduced Brillouin zone. Consequently, the group-velocity
dispersion of the defect modes corresponding to different
polarizations of light can be fully determined. We show also that
the measured dispersion is in good agreement with full 3D
calculations based on expansion in the waveguide modes.
Bulk polystyrene opals have been grown. Variable incidence angle reflectance spectroscopy is used to probe their photonic band structures. Several different structures are observed and accounted for by theoretical calculations of photonic bands and density of states. The results yield a clear distinction between diffraction in the direction of propagation by the (111) family planes (leading to the formation of the stop band) and diffraction in other directions by higher-order planes (corresponding to excitation of photonic modes in the crystal).
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