Nima Dabidian

Plasmonic Nanolaser Using Epitaxially Grown Silver Film

Going Green with Nanophotonics Plasmons are optically induced collective electronic excitations tightly confined to the surface of a metal, with silver being the metal of choice. The subwavelength confinement offers the opportunity to shrink optoelectronic circuits to the nanometer scale. However, scattering processes within the metal lead to losses. Lu et al. (p. 450) developed a process to produce atomically smooth layers of silver, epitaxially grown on silicon substrates. A cavity in the silver layer is capped with a SiO insulating layer and an AlGaN nanorod was used to produce a low-threshold emission at green wavelengths. An atomically smooth layer of silver enhances the performance of nanophotonic devices. A nanolaser is a key component for on-chip optical communications and computing systems. Here, we report on the low-threshold, continuous-wave operation of a subdiffraction nanolaser based on surface plasmon amplification by stimulated emission of radiation. The plasmonic nanocavity is formed between an atomically smooth epitaxial silver film and a single optically pumped nanorod consisting of an epitaxial gallium nitride shell and an indium gallium nitride core acting as gain medium. The atomic smoothness of the metallic film is crucial for reducing the modal volume and plasmonic losses. Bimodal lasing with similar pumping thresholds was experimentally observed, and polarization properties of the two modes were used to unambiguously identify them with theoretically predicted modes. The all-epitaxial approach opens a scalable platform for low-loss, active nanoplasmonics.

Experimental Demonstration of Phase Modulation and Motion Sensing Using Graphene-Integrated Metasurfaces

Strong interaction of graphene with light accounts for one of its most remarkable properties: the ability to absorb 2.3% of the incident lights energy within a single atomic layer. Free carrier injection via field-effect gating can dramatically vary the optical properties of graphene, thereby enabling fast graphene-based modulators of the light intensity. However, the very thinness of graphene makes it difficult to modulate the other fundamental property of the light wave: its optical phase. Here we demonstrate that considerable phase control can be achieved by integrating a single-layer graphene (SLG) with a resonant plasmonic metasurface that contains nanoscale gaps. By concentrating the light intensity inside of the nanogaps, the metasurface dramatically increases the coupling of light to the SLG and enables control of the phase of the reflected mid-infrared light by as much as 55° via field-effect gating. We experimentally demonstrate graphene-based phase modulators that maintain the amplitude of the reflected light essentially constant over most of the phase tuning range. Rapid nonmechanical phase modulation enables a new experimental technique, graphene-based laser interferometry, which we use to demonstrate motion detection with nanoscale precision. We also demonstrate that by the judicious choice of a strongly anisotropic metasurface the graphene-controlled phase shift of light can be rendered polarization-dependent. Using the experimentally measured phases for the two orthogonal polarizations, we demonstrate that the polarization state of the reflected light can be by modulated by carrier injection into the SLG. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.

Electrical tuning of the polarization state of light using graphene-integrated anisotropic metasurfaces

Plasmonic metasurfaces have been employed for moulding the flow of transmitted and reflected light, thereby enabling numerous applications that benefit from their ultra-thin sub-wavelength format. Their appeal is further enhanced by the incorporation of active electro-optic elements, paving the way for dynamic control of lights properties. In this paper, we realize a dynamic polarization state generator using a graphene-integrated anisotropic metasurface (GIAM) that converts the linear polarization of the incident light into an elliptical one. This is accomplished by using an anisotropic metasurface with two principal polarization axes, one of which possesses a Fano-type resonance. A gate-controlled single-layer graphene integrated with the metasurface was employed as an electro-optic element controlling the phase and intensity of light polarized along the resonant axis of the GIAM. When the incident light is polarized at an angle to the resonant axis of the metasurface, the ellipticity of the reflected light can be dynamically controlled by the application of a gate voltage. Thus accomplished dynamic polarization control is experimentally demonstrated and characterized by measuring the Stokes polarization parameters. Large changes of the ellipticity and the tilt angle of the polarization ellipse are observed. Our measurements show that the tilt angle can be changed from positive values through zero to negative values while keeping the ellipticity constant, potentially paving the way to rapid ellipsometry and other characterization techniques requiring fast polarization shifting. This article is part of the themed issue ‘New horizons for nanophotonics’.

Switching of Mid-Infrared Light Using Plasmonic Fano-Resonant Meta-Surfaces Integrated with Graphene

We experimentally demonstrate that graphene can strongly modulate the scattered light from Fano-resonant plasmonic metasurfaces. The Modulation depth of 1000% is achieved at around 7μm as the graphene carrier concentration changes.

Diffraction-Unlimited Plasmonic Nanolaser

Up to now, significantly reducing the size of semiconductor lasers in all three dimensions is the ultimate challenge for the development of nanolasers, which is a key component for long-waited on-chip optical communications and computing systems. However, the minimum size of conventional semiconductor lasers utilizing dielectric resonators is governed by the optical diffraction limit (λ/2n)3. Recently, we have published the world’s smallest semiconductor laser [1] based on a new concept in laser feedback mechanism. We report on the low-threshold, continuous-wave operation of a sub-diffraction nanolaser based on surface plasmon amplification by stimulated emission of radiation (spaser ) [2]. The plasmonic nanocavity is formed between an atomically smooth epitaxial silver film and a single optically pumped nanorod consisting of an epitaxial gallium nitride shell and an indium gallium nitride core acting as gain medium.

Amplitude and Phase Modulation of Light Using Fano-Resonant Meta-Surfaces Integrated with Graphene

We experimentally demonstrate amplitude and phase modulation in graphene-integrated Fano-resonant plasmonic metasurfaces. Order of magnitude modulation depth is achieved in mid-IR. Strong coupling between trapped graphene and metallic plasmons is predicted in high-mobility graphene.

Dynamic inductive tuning of fano-resonant meta-surfaces using plasmonic response of graphene in mid-infrared

We demonstrate theoretically and experimentally that electrically gated single-layer graphene can be used to inductively tune the infrared optical response of Fano-resonant meta-surfaces. Several implementations will be introduced: graphene of the meta-surface, graphene directly under the meta-surface, and graphene separated by a thin spacer from the meta-surface. Both electrostatic and chemical doping of graphene will be discussed and supporting experimental results presented. Finally, we will demonstrate how the spectral shifts of metamaterials resonances introduced by the graphene can be utilized to extract graphenes electronic properties such as the complex-valued resistivity.

Fano-resonant electrically connected meta-surfaces with high quality factors

We introduce electrically connected Fano-resonant metasurfaces consisting of a periodic array of antennas connected to wires. Possibility of the direct interaction among the antennas by the charge transfer allows for robust high quality Fano resonances.