The generation of quantum light based on the nondeterministic process of spontaneous parametric down-conversion (SPDC) is usually performed by using bulky conventional nonlinear crystals and waveguides. However, these structures require strict momentum conservation for the involved photons, which strongly limits the versatility of the single photon emission they produce. In addition, the entangled state emission can only be obtained with a certain probability that is usually very small due to the inherent extremely weak nature of nonlinear optical processes. Quantum optical metasurfaces help to overcome these constraints due to their subwavelength thickness leading to relaxed momentum conservation (or phase-matching) requirements and increased optical nonlinear efficiencies. In our talk, we demonstrate compact quantum plasmonic metasurfaces to efficiently generate entangled and correlated single-photon pairs with unprecedently high SPDC generation rates.
Surfaces with high directional electromagnetic absorption or emission in the infrared (IR) region of the electromagnetic spectrum have numerous potential applications, however many of the relevant surfaces suffer from extremely narrow bandwidth and/or polarization dependence. Here we demonstrate broadband directional emissivity in the mid-infrared range of 7.5 to 14 μm, that is not dependent on polarization. This was achieved with angled micro-scale structures that are overlaid with nano-scale features on stainless steel 304 produced using an emerging fabrication technique known as femtosecond laser surface processing (FLSP). FLSP is an advanced surface functionalization technique that produces hierarchical micro- and nano-scale quasi-periodic surface features in a single laser processing step. Here we report a surface with peak emission for an angle of 55° using FLSP to create fin-shaped micro- and nano-scale surface features that are tilted at a 55° angle. Cross sectioning of the fin-shaped structures using focused ion beam milling was performed to understand the morphology and subsurface microstructure. Cross-sectional images and energy dispersive X-ray spectroscopy analysis show the structure consists of a thin redeposited oxide layer and the bulk of the fin structure is consistent with the original stainless-steel alloy. The emission results are verified by full-wave electromagnetic simulations which consider all the diffraction-orders performed utilizing the finite element method software, COMSOL Multiphysics, that predicts with reasonable accuracy the resulting directional emissivity of the laser processed surface.
Chiral light-matter interactions have an extremely weak nature, are difficult to be controlled and enhanced, and cannot be made tunable. Here, we experimentally realize and theoretically verify spectrally tunable, extremely large, and broadband circular dichroism by designing new nanohelical metamaterial configurations (U. Kılıç et. al., Advanced Functional Materials 31(20), 2010329, 2021). The currently presented bottom-up fabricated hybrid helical metamaterials can be used in a plethora of diverse emerging classical and quantum optical applications, such as in the design of ultrathin polarization filters, chiral sensors, circular polarized single- or multi-photon radiation sources, and directional spin-dependent nanophotonic waveguides.
In this study, by using glancing angle deposition technique, subsequent and repeated depositions of silicon(Si) and silver(Ag) lead to nanometer-dimension chiral subsegments, and thereby, we successfully fabricated spatially coherent, highly porous, super lattice type helical heterostructure thin films. We theoretically and experimentally investigate the chiro-optical properties of this new type plasmonic metamaterial via finite element modeling calculations and Mueller matrix spectroscopic ellipsometry method, respectively. The systematic changes in the morphology of helical structures by incorporating the plasmonic subsegments reveal an extra-ordinary chiro-optical response with fine spectral tunability over the entire visible spectral range into the ultra-violet.
We demonstrate a simple bias-free self-induced nonreciprocal device of an ultrathin bifacial dielectric metasurface. It is composed of two passive silicon-based metasurfaces exhibiting Fano and Lorentzian resonances, respectively. The narrowband resonant response, as well as the boosted field enhancement, lead to very low required input intensity values to obtain significant nonreciprocal transmission. Cascaded metasurface designs are also presented to further improve the geometric asymmetry and self-induced nonreciprocal performance. This work is expected to have several applications, such as nonreciprocal ultrathin coatings for the protection of sources or other sensitive equipment from external pulsed signals, circulators, and isolators.
A fiber optic refractive index sensor based on Fabry-Perot interferometer formed by two Chirped Fiber Bragg Gratings on a seven-core fiber is successfully demonstrated. A small part of the fiber cladding is etched to expose the outer 6 cores to the ambient environment. While optical modes supported by the outer 6-cores are affected by both temperature and refractive index changes of the surrounding liquid, the optical mode in the central core is affected by the temperature changes only. Because only a small part of the cladding is removed, the sensor maintains excellent mechanical strength and stability.
The active and nonlinear graphene properties are limited due to weak light-matter interaction between the ultrathin graphene and the incident light. In this work, we present enhanced nonlinear effects at the low terahertz (THz) range by designing a new patterned graphene hyperbolic metamaterial (GHMM). More specifically, it is demonstrated that the third harmonic generation (THG) can be significantly enhanced by the proposed GHMM due to the field enhancement at the resonance as well as the supported slow-light response that fosters strong light–matter interaction.
Nonreciprocal transmission is the fundamental process behind unidirectional wave propagation phenomena. In our work, a compact and practical parity-time (PT) symmetric metamaterial is designed based on two Silicon Carbide (SiC) media separated by an air gap and photonically doped with gain and loss defects. We demonstrate that an exceptional point (EP) is formed in this PT-symmetric system when SiC operates as a practical epsilon-near-zero (ENZ) material and by taking into account its moderate optical loss. Furthermore and even more importantly, strong self-induced nonreciprocal transmission is excited due to the nonlinear Kerr effect at a frequency slightly shifted off the EP but without breaking the PT-symmetric phase. The transmittance from one direction is exactly unity while the transmittance from the other direction is decreased to very low values, achieving very high optical isolation. The proposed active nonlinear metamaterial overcomes the fundamental physical bounds on nonreciprocity compared with a passive nonlinear nonreciprocal resonator. The strong self-induced nonreciprocal transmission arises from the extreme asymmetric field distribution achieved upon excitation from opposite incident directions. The significant enhancement of the electric field in the defects effectively decreases the required optical power to trigger the presented nonlinear response. This work can have a plethora of applications, such as nonreciprocal ultrathin coatings for the protection of sources or other sensitive equipment from external pulsed signals, circulators, and isolators.
We will demonstrate that the incorporation of active media with extremely small gain coefficients inside epsilon-near-zero (ENZ) plasmonic waveguides will cause the formation of exceptional points and spectral singularities (light amplification). Note that the realization of these points with symmetric reciprocal plasmonic configurations is still elusive mainly due to the weak light-matter interaction at the nanoscale. These intriguing effects will lead to several novel functionalities, such as reflectionless ENZ response, slow light, and nanolasing. Moreover, we will demonstrate that the entanglement of two or multiple emitters placed inside the ENZ nanochannels, even without incorporating gain (lossy ENZ case), will be enhanced over extended areas, which are comparable or even longer than the wavelength of the emitted radiation. Our findings can be applied to improve the response of optical quantum computers, such as the efficient control of long distance entanglement between qubits.
Graphene is a two-dimensional layer of carbon atoms arranged in a honeycomb lattice, whose outstanding properties makes it an excellent material for future electronic and photonic terahertz (THz) devices. In this work, we design hybrid graphene metasurfaces by using a monolayer graphene placed over a metallic grating, operating in the THz frequency range. Perfect absorption can be achieved at the resonance, where the electric field is greatly enhanced due to the coupling between the graphene and the grating plasmonic responses. The enhancement of the electric field along the graphene monolayer, as well as the large nonlinear conductivity of graphene, can dramatically boost the nonlinear response of the proposed THz device. In addition, the presented enhanced nonlinear effects can be significantly tuned by varying the doping level of graphene. The proposed structure can be used in the design of THz-frequency generators and all-optical processors.
We demonstrate a way to coherently control light at the nanoscale and achieve coherent perfect absorption (CPA) by using epsilon-near-zero (ENZ) plasmonic waveguides. The presented waveguides support an effective ENZ response at their cut-off frequency, combined with strong and homogeneous field enhancement along their nanochannels. The CPA conditions are perfectly satisfied at the ENZ frequency, surprisingly by a subwavelength plasmonic structure, resulting in strong CPA under the illumination of two counter-propagating plane waves with appropriate amplitudes and phases. In addition, we investigate the nonlinear response of the proposed ENZ plasmonic configuration as we increase the input intensity of the incident waves. We demonstrate that the CPA phenomenon can become both intensity- and phasedependent in this case leading to new tunable all-optical switching and absorption devices.
The optical nonlinear effects can provide different advanced electromagnetic functionalities, such as wave mixing and phase conjugation, which can be applied in a variety of new applications. However, these effects usually suffer from extremely weak nature and require high input intensity values in order to be excited. Interestingly, the large third order nonlinearity of graphene, along with the strong field confinement stemming from its plasmonic behavior, can be utilized to enhance several relative weak nonlinear effects at infrared (IR) and terahertz (THz) frequencies. Towards this goal, various nonlinear graphene metasurfaces are presented in this work to effectively increase the efficiency of different optical nonlinear effects and, as a result, decrease the required input intensity needed to be excited. In particular, we will show that the efficiency of four-wave mixing (FWM) can be improved by several orders of magnitude by using a nonlinear metasurface composed of patterned graphene ribbons, a dielectric interlayer, and a metallic reflector acting as substrate. We also demonstrate that the self-phase modulation (SPM) nonlinear process can be enhanced by using an alternative graphene nonlinear metasurface, operating as coherent perfect absorber, leading to a pronounced shift in the resonant frequency of the coherent perfect absorption (CPA) effect of this structure as the input intensity of the impinging incident waves is increased. This property will provide a robust mechanism to dynamically tune and switch the CPA process. Furthermore, it will be presented that strong negative reflection and refraction can be achieved by a single graphene monolayer film due to the enhancement of another nonlinear process, known as phase conjugation. This nonlinear process is envisioned to be used in the construction of a perfect imaging device with subwavelength resolution.
The investigation of hyperbolic metamaterials, shows that metal layers that are part of graphene structures, and also types I and II layered systems, are readily controlled. Since graphene is a nicely conducting sheet it can be easily managed. The literature only reveals a, limited, systematic, approach to the onset of nonlinearity, especially for the methodology based around the famous nonlinear Schrödinger equation [NLSE]. This presentation reveals nonlinear outcomes involving solitons sustained by the popular, and more straightforward to fabricate, type II hyperbolic metamaterials. The NLSE for type II metatamaterials is developed and nonlinear, non-stationary diffraction and dispersion in such important, and active, planar hyperbolic metamaterials is developed. For rogue waves in metamaterials only a few recent numerical studies exist. The basic model assumes a uniform background to which is added a time-evolving perturbation in order to witness the growth of nonlinear waves out of nowhere. This is discussed here using a new NLSE appropriate to hyperbolic metamaterials that would normally produce temporal solitons. The main conclusion is that new pathways for rogue waves can emerge in the form of Peregrine solitons (and near-Peregrines) within a nonlinear hyperbolic metamaterial, based upon double negative guidelines, and where, potentially, magnetooptic control could be practically exerted.
The concept of broadband extraordinary optical transmission (EOT) through metallic gratings at the plasmonic Brewster
angle has recently been introduced. It is based on the ultrabroadband impedance matching between guided modes
supported by ultranarrow slits in a one-dimensional (1D) metallic grating and an incident transverse magnetic (TM)
wave. The overall mechanism results in total transmission through such a corrugated plasmonic screen. This concept was
first demonstrated in 1D metallic gratings and it can also be extended to two-dimensional (2D) periodic metallic gratings
made by either multiple rectangular or cylindrical rods. In this contribution, we review this concept and we demonstrate
that this phenomenon can be applied to semiconductor gratings, whose materials have plasmonic properties at THz
frequencies. This may open several opportunities to develop low-loss, broadband optical metamaterials for energy
harvesting and concentrators.
In this paper, we discuss anomalous and enhanced nonlinear effects available when combining nonlinear optical
materials with plasmonic metamaterials. Narrow periodic apertures filled with Kerr nonlinear materials are carved in a
plasmonic screen. Large field enhancement confined inside each slit may be obtained, in particular when we operate at
the cut-off of this array of plasmonic channels. This ensures a significant boosting of nonlinear optical effects, leading to
strong optical bistable performance. New exciting venues for applications are opened with the aforementioned novel
nonlinear devices.
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