1,721,124 research outputs found
Gap maps and intrinsic diffraction losses in one-dimensional photonic crystal slabs
No full textA theoretical study of photonic bands for one-dimensional (1D) lattices embedded in planar waveguides with strong refractive index contrast is presented. The approach relies on expanding the electromagnetic field onthe basis of guided modes of an effective waveguide, and on treating the coupling to radiative modes by perturbation theory. Photonic mode dispersion, gap maps, and intrinsic diffraction losses of quasi guided modes are calculated for the case of self-standing membranes as well as for silicon-on-insulator structures. Photonic band gaps in a waveguide are found to depend strongly on the core thickness and on polarization, so that the gaps for transverse electric and transverse magnetic modes most often do not overlap. Radiative losses of quasiguided modes above the light line depend in a nontrivial way on structure parameters, mode index, and wave vector. The results of this study may be useful for the design of integrated 1D photonic structures with low radiative losses
Effects of disorder on propagation losses and cavity Q-factors in photonic crystals slabs
No full textA theoretical model of disorder for the etched holes or pillars in a generic two-dimensional photonic crystal slab is presented. This model is employed to calculate the effects of size disorder on propagation losses in linear photonic crystal waveguides, as well as on quality (Q)-factors in photonic crystal nano-cavities. The main results obtained by the present theory and shown in this work are: (a) large single-mode bandwidth and low-loss (< 0. 1 dB/mm) propagation of light is predicted for increased-width membrane-type photonic crystal waveguides, (b) pillar-based lattices show reduced sensitivity to Size fluctuations than hole-based ones, (c) the effects of disorder on cavity Q-factors are quantitatively evaluated. An extension of the model is also introduced in order to take into account the side-wall micro-roughness of the perfectly vertical holes, and preliminary results of this more general approach are discussed
Disorder-induced losses in photonic crystal waveguides with line defects
No full textA numerical analysis of extrinsic diffraction losses in two-dimensional photonic crystal slabs with line defects is reported. To model disorder, a Gaussian distribution of hole radii in the triangular lattice of airholes is assumed.. The extrinsic losses below the light line increase quadratically with the disorder parameter, decrease slightly-with increasing core thickness, and depend weakly on the hole radius. For typical values of the disorder parameter the calculated loss values of guided modes below the light line compare favorably with available experimental results
Single-photon blockade in doubly resonant nanocavities with second-order nonlinearity
Full text linkWe propose the use of nanostructured photonic nanocavities made of chi((2)) nonlinear materials as prospective passive devices to generate strongly sub-Poissonian light via single-photon blockade of an input coherent field. The simplest scheme is based on the requirement that the nanocavity be doubly resonant, i.e., possess cavity modes with good spatial overlap at both the fundamental and second-harmonic frequencies. We discuss the feasibility of this scheme with state-of-the art nanofabrication technology and the possibility to use it as a passive single-photon source on demand
Analog Hawking radiation from an acoustic black hole in a flowing polariton superfluid
No full textWe theoretically study the analog Hawking radiation processes from an analog acoustic black hole in a flowing superfluid of exciton-polaritons in a one-dimensional semiconductor microcavity. Polaritons are coherently injected into the microcavity by a laser pump with a suitably tailored spot profile. An event horizon with a large analog surface gravity is created by inserting a defect in the polariton flow along the cavity plane. Experimentally observable signatures of the analog Hawking radiation are identified in the scattering of phonon wave packets off the horizon, as well as in the spatial correlation pattern of quantum fluctuations of the polariton density. The potential of these tabletop optical systems as analog models of gravitational physics is quantitatively confirmed by numerical calculations using realistic parameters for state-of-the-art devices
Photonic crystal slabs with a triangular lattice of triangular holes investigated using a guided-mode expansion method
No full textL'articolo presenta una formulazione teorica di un metodo originale per calcolare i modi fotonici e le perdite nelle guide d'onda a cristallo fotonico.
Abstract: According to a recent proposal [S. Takayama et al., Appl. Phys. Lett. 87, 061107 (2005)], the triangular lattice of triangular air holes may allow us to achieve a complete photonic band gap in two-dimensional photonic crystal slabs. In this work we present a systematic theoretical study of this photonic lattice in a high-index membrane, and a comparison with the conventional triangular lattice of circular holes, by means of the guided-mode expansion method whose detailed formulation is described here. Photonic mode dispersion below and above the light line, gap maps, and intrinsic diffraction losses of quasiguided modes are calculated for the periodic lattice as well as for line and point defects defined therein. The main results are summarized as follows: (i) The triangular lattice of triangular holes does indeed have a complete photonic band gap for the fundamental guided mode, but the useful region is generally limited by the presence of second-order waveguide modes; (ii) the lattice may support the usual photonic band gap for even modes (quasi-TE polarization) and several band gaps for odd modes (quasi-TM polarization), which could be tuned in order to achieve doubly resonant frequency conversion between an even mode at the fundamental frequency and an odd mode at the second-harmonic frequency; (iii) diffraction losses of quasiguided modes in the triangular lattices with circular and triangular holes, and in line-defect waveguides or point-defect cavities based on these geometries, are comparable. The results point to the interest of the triangular lattice of triangular holes for nonlinear optics, and show the usefulness of the guided-mode expansion method for calculating photonic band dispersion and diffraction losses, especially for higher-lying photonic modes
Enhanced nonlinear properties of photonic crystal nanocavities
No full textPhotonic crystal cavities in silicon-on-insulator platforms have been designed to achieve very high quality factors and/or far-field input/output coupling. In this paper I will review our works on the use of these cavities to realize: record-high-Q resonators by genetic optimization of the holes, and bright light emission in an electrically pumped light-emitting diode. Finally, I will discuss theoretical predictions for the realization of quantum photonic devices, such as single-photon sources and diodes, in all-silicon or hybrid photonic crystal platforms
Single-photon nonlinear optics with Kerr-type nanostructured materials
No full textIn this work, it is described a quantum theory of the nonlinear optical response from an actual solid-state material possessing an intrinsic bulk contribution to the third-order nonlinear susceptibility (Kerr-type nonlinearity). This material is assumed to be arbitrarily nanostructured to achieve diffraction-limited electromagnetic
field confinement.
By calculating the zero-time delay second-order correlation of the cavity field, the conditions are identified for using semiconductor or insulating materials with near-infrared energy gaps as efficient means to obtain single-photon nonlinear behavior in prospective solid-state integrated devices, alternative to ideal sources of quantum radiation such as, e.g., single two-level emitters.
Thus, future quantum photonics applications can strongly benefit from
the capability of nanostructuring ordinary Kerr-type materials to achieve sub-diffraction limited electromagnetic field confinement.
The growing interest in integrated quantum photonics, and the possibility of fully exploiting the mature CMOS-based technology to build room-temperature and intrinsically flexible single-photon devices are likely to produce new research avenues based on
the present proposal in the near future
Theory of exciton-polariton condensation in gap-confined eigenmodes
Full text linkExciton-polaritons are bosonic-like elementary excitations in semiconductors,
which have been recently shown to display large occupancy of topologically
protected polariton bound states in the continuum in suitably engineered
photonic lattices [Nature {\bf 605}, 447 (2022)], compatible with the
definition of polariton condensation. However, a full theoretical description
of such condensation mechanism that is based on a non equilibrium
Gross-Pitaevskii formulation is still missing. Given that the latter is well
known to account for polariton condensation in conventional semiconductor
microcavities, here we report on its multi-mode generalization, showing that it
allows to fully interpret the recent experimental findings in patterned
photonic lattices, including emission characteristics and condensation
thresholds. Beyond that, it is shown that the polariton condensation in these
systems is actually the result of an interplay between negative mass
confinement of polariton eigenstates (e.g., due to the photonic gap originated
from the periodic pattern in plane) and polariton losses. We are then able to
show that polariton condensation can also occur in gap-confined bright modes,
i.e., coupling of QW excitons to a dark photonic mode is not necessarily
required to achieve a macroscopic occupation with low population threshold
Low-loss guided modes in photonic crystal waveguides
No full textWe study disorder-induced propagation losses of guided modes in photonic crystal slabs with line-defects. These losses are treated within a theoretical model of size disorder for the etched holes in the otherwise periodic photonic lattice. Comparisons are provided with state-of-the-art experimental data, both in membrane and Silicon-on-Insulator ( SOI) structures, in which propagation losses are mainly attributed to fabrication imperfections. The dependence of the losses on the photon group velocity and the useful bandwidth for low-loss propagation are analyzed and discussed for membrane and asymmetric as well as symmetric SOI systems. New designs for further improving device performances are proposed, which employ waveguides with varying channel widths. It is shown that losses in photonic crystal waveguides could be reduced by almost an order of magnitude with respect to latest experimental results. Propagation losses lower than 0.1 dB/mm are predicted for suitably designed structures, by assuming state-of-the-art fabrication accuracy
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