One of the basic functionalities of photonic devices is the ability to manipulate the polarization state of light. Polarization components are usually implemented using the retardation effect in natural birefringent crystals and, thus, have a bulky design. Here, we have demonstrated the polarization manipulation of light by employing a thin subwavelength slab of metamaterial with an extremely anisotropic effective permittivity tensor. Polarization properties of light incident on the metamaterial in the regime of hyperbolic, epsilon-near-zero, and conventional elliptic dispersions were compared. We have shown that both reflection from and transmission through λ/20 thick slab of the metamaterial may provide nearly complete linear-to-circular polarization conversion or 90° linear polarization rotation, not achievable with natural materials. Using ellipsometric measurements, we experimentally studied the polarization conversion properties of the metamaterial slab made of the plasmonic nanorod arrays in different dispersion regimes. We have also suggested all-optical ultrafast control of reflected or transmitted light polarization by employing metal nonlinearities.

We demonstrate experimentally and theoretically a broad-band enhancement of the spontaneous two-photon emission from AlGaAs at room temperature by plasmonic nanoantenna arrays fabricated on the semiconductor surface. Plasmonic structures with inherently low quality factors but very small effective volumes are shown to be optimal. A 20-fold enhancement was achieved for the entire antenna array, corresponding to an enhancement of nearly 3 orders of magnitude for charge carriers emitting at the near field of a plasmonic antenna.KEYWORDS Semiconductors, two-photon emission, nanoparticles, plasmonic enhancement O ver the past decade, a growing interest has been focused on exploiting the tight confinement of the electromagnetic field achievable in the vicinity of a metal-dielectric boundary, commonly referred to as surface plasmon polariton (SPP), for enhancing the efficiency of spontaneous emission in semiconductors, 1-3 and it has been shown that such enhancement is highly significant for very inefficient emitters. 4 These endeavors follow the success of using SPPs for the enhancement of nonlinear phenomena, including the surface enhancement of Raman scattering by many orders of magnitude, 5 surface-enhanced second-harmonic generation, 6 and the recent demonstration of high-harmonic generation by coupling to bow-tie nanoantennas. 7 It was also shown that SPPs preserve many key quantum properties of the photons used to excite them, including entanglement, 8,9 and the quantization theory of surface plasmon fields was developed 10 and experimentally demonstrated, 11 allowing an array of new applications in quantum information processing. Two-photon emission (TPE) is a nonlinear process with unique quantum properties, important in different realms of science. TPE from a semiconductor results from electronhole recombination with the simultaneous emission of two photons. Semiconductor TPE was recently observed 12 and theoretically analyzed, 13 and current-induced two-photon transparency was demonstrated, 14 paving the way for the realization of room-temperature miniature devices, including semiconductor two-photon lasers 15 and photon pair sources. 16 However, TPE is an inherently weak second-order process, and therefore enhancing mechanisms could significantly widen the range of its applications. Since the emission spectrum of spontaneous TPE is very wide band due to the large energy uncertainty of the virtual state, regular dielectric optical cavities with a very high qualityfactor, Q, and thus very narrow bandwidth 17 may enhance emission at specific wavelengths; 18 however, they are unable to enhance the broad spectrum of TPE. Plasmonic cavities, on the other hand, enhancing the field by significantly reducing the mode volume at low Q, 19 are optimal.Here we report the first experimental observation of plasmon-enhanced spontaneous TPE from semiconductors, by coupling the emission to bow-tie nanoantenna arrays, having efficient radiative coupling of plasmons to far-field light. 20 The broad band TPE from AlGaA...

A method for designing plasmonic particles with desired resonance spectra is presented. The method is based on repetitive perturbations of an initial particle shape while calculating the eigenvalues of the various quasistatic resonances. The method is rigorously proved, assuring a solution exists for any required spectral resonance location. Resonances spanning the visible and the near-infrared regimes, as designed by our method, are verified using finite-difference time-domain simulations. A novel family of particles with collocated dipole-quadrupole resonances is designed, demonstrating the unique power of the method.Such on-demand engineering enables strict realization of nano-antennas and metamaterials for various applications requiring specific spectral functions.

Semiconductor photonics is an advanced field, both from fundamental and applicative points of view, aimed at the integration of the unique features of optical communications and quantum optics with the miniaturization and controllability of semiconductors. Many classical and quantum applications may benefit from interaction between optical signals, usually implemented by nonlinear optical processes of various orders. The efficiency of such processes in semiconductors is being constantly enhanced, assisted by the progress in ultrashort laser pulses and ultra-sensitive detectors, enabling practical devices. In this review, the lowest order of nonlinear interactions-the two-photon processes in semiconductors-are discussed, and their applications to a variety of novel classical and quantum configurations are reviewed.

We describe systematic measurements of the gain and delay spectra in a slow light system based on stimulated Brillouin scattering in optical fibers. The measurements yield the system complex transfer function with which delays and signal distortion can be calculated for any input signal. The theoretical predictions are confirmed experimentally for single pulses as well as 50 Mb/s data streams in a system which employs pump modulation to modify the gain and delay spectra of the SBS process.