Because plasmonic modes have no cut-off, we are able to demonstrate downscaling

Effective manipulation of cavity resonant modes is crucial for emission control in laser physics and applications. Using the concept of parity-time symmetry to exploit the interplay between gain and loss (i.e., light amplification and absorption), we demonstrate a parity-time symmetry-breaking laser with resonant modes that can be controlled at will. In contrast to conventional ring cavity lasers with multiple competing modes, our parity-time microring laser exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth. Thresholdless parity-time symmetry breaking due to the rotationally symmetric structure leads to stable single-mode operation with the selective whispering-gallery mode order. Exploration of parity-time symmetry in laser physics may open a door to next-generation optoelectronic devices for optical communications and computing.

*These authors contributed equally to this work.Plasmon lasers create and sustain coherent surface plasmon polaritons, collective electronic oscillations of metal-dielectric interfaces (1-5). These intense, coherent and confined optical fields have the unique ability to drastically enhance light-matter interactions bringing fundamentally new capabilities to bio-sensing, data storage, photolithography and optical communications (5-7). However, these important applications require sub-diffraction limited lasers operating at room temperature, which remains a major hurdle (1, 2). There are two critical challenges: high absorptive loss of metals and low cavity feedback. Recent efforts in semiconductor plasmon lasers have resulted in two approaches: devices capped in metal provide good feedback, but suffer high metal loss resulting in limited mode confinement (2). On the other hand, nanowire lasers on planar metal substrates achieve strong confinement with low metal loss, but the open configuration limits feedback imposing a minimum nanowire length (1). While the merits of capped and planar metallic devices remain mutually exclusive, plasmon lasers must rely on cryogenic temperatures to attain sufficient gain to combat losses. Therefore, room temperature plasmon laser operation below the diffraction limit demands low metal loss, effective cavity feedback and high gain; all within a single nanoscale device.We report here a room temperature semiconductor plasmon laser with both strong cavity feedback and λ/20 optical confinement. The device consists of a 45 nm thick, 1 μm length single crystal Cadmium Sulfide (CdS) square atop a Silver surface separated by a 5 nm thick Magnesium Fluoride gap layer, shown in Fig. 1A. We achieve strong

Electro-optic modulators have been identifi ed as the key drivers for optical communication and signal processing. With an ongoing miniaturization of photonic circuitries, an outstanding aim is to demonstrate an on-chip, ultra-compact, electro-optic modulator without sacrifi cing bandwidth and modulation strength. While silicon-based electro-optic modulators have been demonstrated, they require large device footprints of the order of millimeters as a result of weak non-linear electro-optical properties. The modulation strength can be increased by deploying a high-Q resonator, however with the trade-off of signifi cantly sacrifi cing bandwidth. Furthermore, design challenges and temperature tuning limit the deployment of such resonance-based modulators. Recently, novel materials like graphene have been investigated for electro-optic modulation applications with a 0.1 dB per micrometer modulation strength, while showing an improvement over pure silicon devices, this design still requires device lengths of tens of micrometers due to the ineffi cient overlap between the thin graphene layer, and the optical mode of the silicon waveguide. Here we experimentally demonstrate an ultra-compact, silicon-based, electro-optic modulator with a record-high 1 dB per micrometer extinction ratio over a wide bandwidth range of 1 μm in ambient conditions. The device is based on a plasmonic metal-oxide-semiconductor (MOS) waveguide, which efficiently concentrates the optical modes ' electric fi eld into a nanometer thin region comprised of an absorption coefficient-tuneable indium-tin-oxide (ITO) layer. The modulation mechanism originates from electrically changing the free carrier concentration of the ITO layer which dramatically increases the loss of this MOS mode. The seamless integration of such a strong optical beam modulation into an existing silicon-on-insulator platform bears signifi cant potential towards broadband, compact and effi cient communication links and circuits.Keywords: Modulator; silicon-on-insulator; ultra-compact.A waveguide-integrated electro-optical modulator can be perceived as a transistor with an optical source and drain and an electrical gate [1]. This waveguide receiving a continuous wave laser beam converts electrical data arriving at the gate electrode into an optical encoded data stream. A widely used modulation mechanism is to change the free carrier concentration of the material overlapping with the propagating optical mode, which leads to a shift of the plasma frequency of the dispersion relation [2]. This modifi es both the real and imaginary parts of the refractive index of the material, and henceforth alters the index and loss of the optical propagating mode. While a Mach-Zehnder type modulator utilized a refractive index change in the real part [3], an electro-absorption type modulator deploys the altered loss of the optical mode [4]. With the promise of silicon-on-insulator (SOI) technology [5] for on-chip integrated photonics, the Intel team demonstrated a Mach-Zehnder modulator by c...

Levitated optomechanics has great potential in precision measurements, thermodynamics, macroscopic quantum mechanics, and quantum sensing. Here we synthesize and optically levitate silica nanodumbbells in high vacuum. With a linearly polarized laser, we observe the torsional vibration of an optically levitated nanodumbbell. This levitated nanodumbbell torsion balance is a novel analog of the Cavendish torsion balance, and provides rare opportunities to observe the Casimir torque and probe the quantum nature of gravity as proposed recently. With a circularly polarized laser, we drive a 170-nm-diameter nanodumbbell to rotate beyond 1 GHz, which is the fastest nanomechanical rotor realized to date. Smaller silica nanodumbbells can sustain higher rotation frequencies. Such ultrafast rotation may be used to study material properties and probe vacuum friction.