Reconfiguration of silicon photonic integrated circuits relying on the weak, volatile thermo-optic or electro-optic effect of silicon usually suffers from a large footprint and energy consumption. Here, integrating a phase-change material, Ge 2 Sb 2 Te 5 (GST) with silicon microring resonators, we demonstrate an energy-efficient, compact, non-volatile, reprogrammable platform. By adjusting the energy and number of free-space laser pulses applied to the GST, we characterize the strong broadband attenuation and optical phase modulation effects of the platform, and perform quasi-continuous tuning enabled by thermooptically-induced phase changes. As a result, a non-volatile optical switch with a high extinction ratio, as large as 33 dB, is demonstrated.

We experimentally demonstrate a wide band near perfect light absorber in the mid-wave infrared region using multiplexed plasmonic metal structures. The wide band near perfect light absorber is made of two different size gold metal squares multiplexed on a thin dielectric spacing layer on the top of a thick metal layer in each unit cell. We also fabricate regular nonmultiplexed structure perfect light absorbers. The multiplexed structure IR absorber absorbs above 98% incident light over a much wider spectral band than the regular non-multiplexed structure perfect light absorbers in the mid-wave IR region.Anomalous light absorption in metal structures was first observed a century ago by Wood [1]. The interest of light absorption in structured metals resurfaced in the 1960s, 1970s, and 1990s [2-8]. Today, it is well understood that anomalous light absorption in metal structures is due to the excitation of surface plasmon-polaritons (SPPs). Recently, perfect electromagnetic energy absorptions in structured metamaterials have been demonstrated in the gigahertz and terahertz regimes [9][10]. Perfect absorbers at optical frequencies have also been reported by several groups [11][12][13][14][15][16]. However, all the metamaterial perfect absorbers reported have very narrow spectral widths limited by the line-widths of the electromagnetic resonances in the structures. In many applications, it is desirable to have perfect absorption over broader spectral bands. Expansion of absorption band has been proposed using structures combining multiplexed subwavelength apertures [13], however, the proposed structure is polarization dependent and experimentally has not been demonstrated. In this paper, we report an experimental demonstration of a wide spectral band perfect absorber using a multiplexed surface plasmon resonance structure. In the multiplexed surface plasmon resonance structure, two gold metal squares are multiplexed in the unit cell of the periodic structure. The multiplexed plasmonic structure metamaterial, operating in the mid-wave infrared regime, near perfectly absorbs photons over a wider spectral range than previously reported.Figure 1 (a) shows the regular non-multiplexed narrow band perfect light absorber structure. In this structure, gold thin film squares are patterned periodically on the top of a thin dielectric layer deposited on top of a thick gold metal layer. The thick metal layer is thick enough that no transmission can occur when light is incident from above the structure. Due to electromagnetic resonance in the metal-dielectric subwavelength structure, the effective impedance of the structured metamaterial surfaces can match the impedance of the vacuum; therefore reflections from the surface can be completely eliminated. Fig. 1 (b) shows the multiplexed perfect light absorber structure. The period of the multiplexed structure is the same as the period of the non-multiplexed perfect light absorber structure.However, in the multiplexed structure there are two metal squares of different sizes in the un...

Single defects in monolayer WSe2 have been shown to be a new class of single photon emitters and have potential applications in quantum technologies. Whereas previous work relied on optical excitation of single defects in isolated WSe2 monolayers, in this work we demonstrate electrically driven single defect light emission by using both vertical and lateral van der Waals heterostructure devices. In both device geometries, we use few layer graphene as the source and drain and hexagonal boron nitride as the dielectric spacer layers for engineered tunneling contacts. In addition, the lateral devices utilize a split back gate design to realize an electrostatically defined p-i-n junction. At low current densities and low temperatures (∼5 K), we observe narrow spectral lines in the electroluminescence (EL) whose properties are consistent with optically excited defect bound excitons. We show that the emission originates from spatially localized regions of the sample, and the EL spectrum from single defects has a doublet with the characteristic exchange splitting and linearly polarized selection rules. All are consistent with previously reported single photon-emitters in optical measurements. Our results pave the way for on-chip and electrically driven single photon sources in two-dimensional semiconductors for quantum technology applications.

We present a paradigm for encoding strain into two-dimensional materials (2DMs) to create and deterministically place single-photon emitters (SPEs) in arbitrary locations with nanometer-scale precision. Our material platform consists of a 2DM placed on top of a deformable polymer film. Upon application of sufficient mechanical stress using an atomic force microscope tip, the 2DM/polymer composite deforms, resulting in formation of highly localized strain fields with excellent control and repeatability. We show that SPEs are created and localized at these nanoindents and exhibit single-photon emission up to 60 K, the highest temperature reported in these materials. This quantum calligraphy allows deterministic placement and real time design of arbitrary patterns of SPEs for facile coupling with photonic waveguides, cavities, and plasmonic structures. In addition to enabling versatile placement of SPEs, these results present a general methodology for imparting strain into 2DM with nanometer-scale precision, providing an invaluable tool for further investigations and future applications of strain engineering of 2DM and 2DM devices.

We study arrays of silver split-ring resonators operating at around 1.5-µm wavelength coupled to an MBE-grown single 12.7-nm thin InGaAs quantum well separated only 4.8 nm from the wafer surface. The samples are held at liquid-helium temperature and are pumped by intense femtosecond optical pulses at 0.81-µm center wavelength in a pump-probe geometry. We observe much larger relative transmittance changes (up to about 8%) on the split-ring-resonator arrays as compared to the bare quantum well (not more than 1-2%). We also observe a much more rapid temporal decay component of the differential transmittance signal of 15 ps for the case of split-ring resonators coupled to the quantum well compared to the case of the bare quantum well, where we find about 0.7 ns. These observations are ascribed to the evanescent coupling of the split-ring resonators to the quantum-well gain. All experimental results are compared with a recently introduced analytical toy model that accounts for this evanescent coupling, leading to excellent overall qualitative agreement.