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
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).