arXiv subjects

Rajesh V. Nair

Publications and source records attributed to Rajesh V. Nair.

7 recordsLinked to original sources

arXiv2022

Deterministic single photon source enabled by coherent superposition of Mie-scattering moments in a NV- center coupled dipolar antenna

Generation of an ultra-bright, deterministic, solid-state single photon source with high photon collection rate is an imperative requirement for quantum technologies. In this direction, various nanophotonic systems coupled with single quantum emitters are being implemented, but results in low decay rate enhancement and MHz photon collection rate. Here, we unravel coherent superposition of excited Mie-scattering moments in a dipolar antenna, coupled with a single nitrogen-vacancy (NV-) center, to achieve bright single photon source with GHz collection rate. Such balancing of Mie-scattering moments, especially higher-order multi-polar moments, provide strong forward light scattering with null backward scattering at the generalized Kerker condition. This results in strong field intensity localization that can be used to shape the emission from an embedded NV- center in the dipolar antenna. A relative decay rate enhancement of more than 300 times with collection efficiency exceeding 75% is achieved that result in photon collection rate of ~ 5 GHz. The calculated intensity-intensity correlation confirms bright single photon emission with enhanced rate and collection efficiency.

quant-ph↗

arXiv2016

Observation of wavelength-dependent Brewster angle shift in 3D photonic crystals

The interaction of polarized light with photonic crystals exhibit unique features due to its sub-wavelength nature on the surface and the periodic variation of refractive index in the depth of the crystals. Here, we present a detailed study of polarization anisotropy in light scattering associated with three-dimensional photonic crystals with face centered cubic symmetry over a broad wavelength and angular range. The polarization anisotropy leads to a shift in the conventional Brewster angle defined for a planar interface with certain refractive index. The observed shift in Brewster angle strongly depends on the index contrast and lattice constant. Polarization-dependent stop gap measurements are performed on photonic crystals with different index contrast and lattice constants. These measurements indicate unique stop gap branching at high-symmetry points in the Brillouin zone of the photonic crystals. The inherited stop gap branching is observed for TE polarization whereas that is suppressed for TM polarization as a consequence of Brewster effect. Our results have consequences in the polarized light-scattering from plasmonic structures and dielectric meta-surfaces and are also useful in applications like nano-scale polarization splitters and lasers.

physics.optics↗

arXiv2016

Polarization-selective branching of stop gaps in three-dimensional photonic crystals

We study the direction- and wavelength-dependent polarization anisotropy in light scattering at the air-photonic crystal interface as a function of angle of incidence for TE and TM polarized light. This is done using optical reflectivity measurements at high-symmetry points in the Brillouin zone of a three-dimensional photonic crystal with fcc symmetry. Polarized reflectivity measurements indicate the presence of stop gap branching for TE polarization, which is absent for TM polarization till the Brewster angle at K point. In contrast, stop gap branching is present for both TE and TM polarizations at W point due to the intricate mixing of crystal planes. This characteristic behavior signifies the inevitable role of energy exchange in the stop gap branching. The measured polarization anisotropy shows a prominent shift in the Brewster angle for on-resonance wavelength as compared to the off-resonance along both K and W points, and that, in accordance with theory. Our results have implications in polarization-induced light scattering in sub-wavelength photonic structures like plasmonic crystals, and meta-materials.

physics.optics↗

arXiv2014

Interaction between dual cavity modes in a planar photonic microcavity

We theoretically study the interaction between dual cavity modes in a planar photonic microcavity structure in the optical communication wavelength range. The merging and splitting of cavity mode is analyzed with realistic microcavity structures. The merging of dual cavity resonance into a single cavity resonance is achieved by changing the number of layers between the two cavities. The splitting of single cavity resonance into dual cavity resonance is obtained with an increase in the reflectivity of mirrors in the front and rear side of the microcavity structure. The threshold condition for the merging and splitting of cavity mode is established in terms of structural parameters. The physical origin of the merging of dual cavity modes into a single cavity resonance is discussed in terms of the electric field intensity distribution in the microcavity structure. The microcavity structure with dual cavity modes is useful for the generation of entangled photon pairs, for achieving the strong-coupling regime between exciton and photon, and for high resolution multi-wavelength filters in optical communication.

physics.optics↗

arXiv2011

Observation of sub-Bragg diffraction of waves in crystals

We investigate the diffraction conditions and associated formation of stopgaps for waves in crystals with different Bravais lattices. We identify a prominent stopgap in high-symmetry directions that occurs at a frequency below the ubiquitous first-order Bragg condition. This sub-Bragg diffraction condition is demonstrated by reflectance spectroscopy on two-dimensional photonic crystals with a centred rectangular lattice, revealing prominent diffraction peaks for both the sub-Bragg and first-order Bragg condition. These results have implications for wave propagation in 2 of the 5 two-dimensional Bravais lattices and 7 out of 14 three-dimensional Bravais lattices, such as centred rectangular, triangular, hexagonal and body-centred cubic.

physics.optics↗

arXiv2011

Engineering disorder in three-dimensional photonic crystals

We demonstrate the effect of introducing controlled disorder in self-assembled three-dimensional photonic crystals. Disorders are induced through controlling the self-assembling process using an electrolyte of specific concentrations. Structural characterization reveals increase in disorder with increase in concentrations of the electrolyte. Reflectivity and transmittance spectra are measured to probe the photonic stop gap at different levels of disorder. With increase in disorder the stop gap is vanished and that results in a fully random photonic nanostructure where the diffuse scattered intensity reaches up to 100%. Our random photonic nanostructure is unique in which all scatters have the same size and shape. We also observe the resonant characteristics in the multiple scattering of light.

physics.optics↗

arXiv2011

Signature of a three-dimensional photonic band gap observed on silicon inverse woodpile photonic crystals

We have studied the reflectivity of CMOS-compatible three-dimensional silicon inverse woodpile photonic crystals at near-infrared frequencies. Polarization-resolved reflectivity spectra were obtained from two orthogonal crystal surfaces corresponding to 1.88 pi sr solid angle. The spectra reveal broad peaks with high reflectivity up to 67 % that are independent of the spatial position on the crystals. The spectrally overlapping reflectivity peaks for all directions and polarizations form the signature of a broad photonic band gap with a relative bandwidth up to 16 %. This signature is supported with stopgaps in plane wave bandstructure calculations and with the frequency region of the expected band gap.

physics.optics↗