Metasurfaces have seen a great evolution over the last few years, demonstrating a high degree of control over the amplitude, phase, polarization, and spectral properties of reflected or transmitted electromagnetic waves. Nevertheless, the inherent limitation of static metasurface realizations, which cannot be controlled after their fabrication, engages an ongoing pursuit for reconfigurable metasurfaces with profound tunability. In this paper, we mitigate this grand challenge by demonstrating a new method for free-space rapid optical tunability and modulation, utilizing a planar aluminum nanodisk metasurface coated with indium tin oxide (ITO) on a thin film of lithium niobate (LiNbO) with a chromium/gold (Cr/Au) substrate. Resonance coupling gives rise to an enhanced, confined electromagnetic field residing in the thin film, leading to a narrow and high contrast dip in reflectance of around 1.55 μm. The precise spectral position of this resonance is tuned using the electro-optic Pockels effect by applying an electric bias voltage across the thin film of LiNbO. By doing so, we show that we can likewise modulate the optical reflectance from the metasurface around a wavelength of 1.54 μm. Following that, we experimentally demonstrate a free-space, planar optical modulator with a modulation depth of 40%. The device paves the way for the integration of metasurfaces in applications requiring tunable optical components such as tunable displays, spatial light modulators for advanced imaging, free-space communication, beam scanning LIDARs with no moving parts, and more.
The coupling of atomic and photonic resonances serves as an important tool for enhancing light‐matter interactions and enables the observation of multitude of fascinating and fundamental phenomena. Here, by exploiting the platform of atomic‐cladding wave guides, the resonant coupling of rubidium vapor and an atomic cladding micro ring resonator is experimentally demonstrated. Specifically, cavity‐atom coupling in the form of Fano resonances having a distinct dependency on the relative frequency detuning between the photonic and the atomic resonances is observed. Moreover, significant enhancement of the efficiency of all optical switching in the V‐type pump‐probe scheme is demonstrated. The coupled system of micro‐ring resonator and atomic vapor is a promising building block for a variety of light vapor experiments, as it offers a very small footprint, high degree of integration and extremely strong confinement of light and vapor. As such it may be used for important applications, such as all optical switching, dispersion engineering (e.g. slow and fast light) and metrology, as well as for the observation of important effects such as strong coupling, and Purcell enhancement.
Non-Hermitian systems have recently attracted significant attention in photonics. One of the hallmarks of these systems is the possibility of realizing asymmetric mode switching and omni-polarizer action through the dynamic encirclement of exceptional points (EP). Here, we offer a new perspective on the operating principle of these devices, and we theoretically show that asymmetric mode switching can be easily realized -with the same performance and limitationsusing simple configurations that emulate the physics involved in encircling EP's without the complexity of actual encirclement schemes. The proposed concept of "encirclement emulators" may allow a better assessment of practical applications of non-Hermitian photonics.
We demonstrate the design, fabrication and experimental characterization of long-range dielectric-loaded surface plasmon-polariton waveguides (LR-DLSPPWs) that are compatible with complementary metal-oxide semiconductor (CMOS) technology. The demonstrated waveguide configuration represents a silicon nitride ridge atop a thin strip of metal, which is positioned on a partially oxidized layer of silicon supported by a silicon oxide layer. The demonstrated waveguides feature reasonable mode confinement (~0.5μm2) and show rather long propagation (~700 μm) at telecom wavelengths. Owing to the existence of a metal strip within the structure, one can envision the co-propagation of electrical and photonic signals within the structure, enabling thereby seamless integration of photonic and electronic circuits. Electrical signals in metal strips supporting plasmonic modes can be used for variety of applications, e.g. to control the propagation of radiation via the thermo-optic effect.
We demonstrate experimentally the realization and the characterization of a chip-scale integrated photodetector for the near-infrared spectral regime based on the integration of a MoSe2/WS2 heterojunction on top of a silicon nitride waveguide. This configuration achieves high responsivity of ~1 A W−1 at the wavelength of 780 nm (indicating an internal gain mechanism) while suppressing the dark current to the level of ~50 pA, much lower as compared to a reference sample of just MoSe2 without WS2. We have measured the power spectral density of the dark current to be as low as ~1 × 10−12 A Hz−0.5, from which we extract the noise equivalent power (NEP) to be ~1 × 10−12 W Hz−0.5. To demonstrate the usefulness of the device, we use it for the characterization of the transfer function of a microring resonator that is integrated on the same chip as the photodetector. The ability to integrate local photodetectors on a chip and to operate such devices with high performance at the near-infrared regime is expected to play a critical role in future integrated devices in the field of optical communications, quantum photonics, biochemical sensing, and more.
Recently, there has been growing interest in integrating alkali vapors with nanoscale photonic structures, such as nanowaveguides, resonators, and nanoantennas. Nanoscale confinement of electromagnetic fields may introduce a longitudinal electric field component, giving rise to circularly polarized modes that are essential for diverse applications involving vapor and light, such as chirality and nonreciprocity. Hereby, we have designed, fabricated, and characterized a miniaturized vapor cell that is integrated with optical waveguides that are designed to generate a peculiar circular-like polarization. Taking advantage of this phenomenon, we demonstrate a spectral shift in the atomic absorption signatures at varying magnetic fields, and significant isolation between forward-and backward-propagating waves in our atomiccladded waveguide. Our results pave the way for the utilization of chip-scale integrated atomic devices in applications such as optical isolation and high spatial resolution magnetometry.Alkali vapors such as rubidium are being used in various research fields such as quantum information [1-3], nonlinear optics [4-6], magnetometry [7][8][9], and atomic clocks [10,11]. In the last few years, there has been a growing interest in miniaturizing rubidium cells from centimeter scale to micro-and nanoscale. On top of the obvious advantages of such integration in reducing footprint and cost, many other great qualities result from such an approach. For example, the high confinement allows one to observe significant nonlinear effects under very low optical power levels (nanowatts) [12][13][14][15]. Several miniaturized rubidium systems have been demonstrated over the last few years, e.g., the atomic-cladded waveguide (ACWG) [15,16], hollow core waveguide [17] and coupled atomic-plasmonic systems [14,18]. The combination of strong nonlinear effects and high confinement pave the way for applications such as few-photons communication systems by alloptical switching [15].Rubidium is a highly dichroic medium due to its strong Zeeman effect, and thus has been used to realize a variety of polarization-selective and unidirectional devices such as optical isolators [19]. Basically, the Zeeman effect generates circular dichroism, i.e., two orthogonal circular polarizations are experiencing a large difference in their absorption spectrum. This effect has also been used for applications such as frequency stabilization [20], memories [2], and magnetometers [7][8][9]. While a rectangular waveguide supports quasi-linear polarized modes, it has been shown in systems combining waveguides and cold atoms that a strong longitudinal electric field is generated due to the strong field confinement. Thus, one can define the quantization axis by applying a magnetic field perpendicular to the propagation direction such that an atom will experience circular polarization interrogation [3]. The absorption lines of such an atom could be controlled by the strength of the magnetic field. This effect has been used for fabricating single-photon ...
Many consumer technologies and scientific methods rely on photodetection of infrared light. We report a Schottky photodetector operating below silicon's band gap energy, through hot carrier injection from a nanoscale metallic absorber. Our design relies on simple CMOScompatible 'bottom up' fabrication of fractally nanostructured aluminium films. Due to the fractal nature of the nanostructuring, the aluminium films support plasmonically enhanced absorption over a wide wavelength range. We demonstrate two orders of magnitude improvements of responsivity, noise-equivalent-power, and detectivity as compared to bulk metal, over a broad spectral and angular range. We attribute this to momentum relaxation processes from the nanoscale fractal geometry. Specifically, we demonstrate a direct link between quantum efficiency enhancement and structural parameters such as perimeter to surface ratio. Finally, our devices also function as bulk refractive index sensors. Our approach is a promising candidate for future cost effective and robust short wave infrared photodetection and sensing applications.
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