The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Graphene plasmons were predicted to possess ultra-strong field confinement and very low damping at the same time, enabling new classes of devices for deep subwavelength metamaterials, single-photon nonlinearities, extraordinarily strong light-matter interactions and nano-optoelectronic switches. While all of these great prospects require low damping, thus far strong plasmon damping was observed, with both impurity scattering and many-body effects in graphene proposed as possible explanations. With the advent of van der Waals heterostructures, new methods have been developed to integrate graphene with other atomically flat materials. In this letter we exploit near-field microscopy to image propagating plasmons in high quality graphene encapsulated between two films of hexagonal boron nitride (h-BN). We determine dispersion and particularly plasmon damping in real space. We find unprecedented low plasmon damping combined with strong field confinement, and identify the main damping channels as intrinsic thermal phonons in the graphene and dielectric losses in the h-BN. The observation and in-depth understanding of low plasmon damping is the key for the development of graphene nano-photonic and nano-optoelectronic devices.

Highly confined low-loss plasmons in graphene-boron nitride heterostructures

We describe the history, guiding mechanism, recent advances, applications, and future prospects for hollow-core negative curvature fibers. We first review one-dimensional slab waveguides, two-dimensional annular core fibers, and negative curvature tube lattice fibers to illustrate the inhibited coupling guiding mechanism. Antiresonance in the glass at the core boundary and a wavenumber mismatch between the core and cladding modes inhibit coupling between the modes and have led to remarkably low loss in negative curvature fibers. We also summarize recent advances in negative curvature fibers that improve the performance of the fibers, including negative curvature that increases confinement, gaps between tubes that increase confinement and bandwidth, additional tubes that decrease mode coupling, tube structures that suppress higher-order modes, nested tubes that increase guidance, and tube parameters that decrease bend loss. Recent applications of negative curvature fibers are also presented, including mid-infrared fiber lasers, micromachining, and surgical procedures. At the end, we discuss the future prospects for negative curvature fibers.

Negative curvature fibers

종격동 종양 및 낭종 27례에 대한 임상적 고찰

The application of topology in optics has led to a new paradigm in developing photonic devices with robust properties against disorder Although considerable progress on topological phenomena has been achieved in the classical domain, the realization of strong light-matter coupling in the quantum domain remains unexplored We demonstrate a strong interface between single quantum emitters and topological photonic states Our approach creates robust counterpropagating edge states at the boundary of two distinct topological photonic crystals We demonstrate the chiral emission of a quantum emitter into these modes and establish their robustness against sharp bends This approach may enable the development of quantum optics devices with built-in protection, with potential applications in quantum simulation and sensing

A topological quantum optics interface

We propose a few-mode erbium-ring-doped fiber laser with high slope efficiency towards an individual transverse vector mode output. Based on the rate equation, specific transverse vector mode output is achieved through numerical investigations of the position and the thickness of the transverse erbium-doped region. Our results show that a thinner erbium-doped region is favorable for increasing the number of available output transverse vector mode, and the position selects desired transverse vector mode to excite. Moreover, high-order vector modes up to the third-order can be excited with appropriate erbium-doped locations. The laser output using the proposed method has merit of high slope efficiency and high mode purity. The slope efficiency and the mode purity can reach 61.25% and 99.99%, respectively. Our work may find potential applications in high-power lasers and high-order transverse mode operation of fiber lasers.

Erbium-ring-doped fiber laser for transverse vector modes output

We present a novel design strategy of single-mode trench-assisted bend-insensitive fibers (SM-TA-BIFs) based on the particle swarm optimization (PSO). A performance index (PI) is defined as the ratio of bending loss to mode-field-diameter to evaluate the fiber performance comprehensively. For the PSO design of SM-TA-BIF, the fitness function is constructed by PI and Gauss weighting function, and cutoff wavelength is applied as the constraint condition. The minimum PI can be achieved by the Gauss weighting fitness function with a target bending radius. With the same trench parameters, but a trench located further away from the center, the average PI of the optimized SM-TA-BIF could be 3.2 times lower than that of a commercial BIF at a bending radius of 5 mm within the entire $C$ -band.

Particle Swarm Optimization of Single-Mode Trench-Assisted Bend-Insensitive Fibers

We propose and experimentally demonstrate a multi-wavelength erbium-doped fiber laser (EDFL) with orbital angular momentum (OAM) mode output. Employing a Mach–Zehnder filter, a Sagnac loop filter, and a mode-selective coupler, the proposed EDFL achieves single-, dual-, triple- and quadruple-wavelength outputs of OAM modes. The tunable range of the output wavelengths is up to 22.64 nm. Besides, the multi-wavelength laser is able to emit OAM modes with its topological charge of $ \pm {1}$±1. The proposed EDFL has the advantages of wide wavelength tunability, good stability, high signal-to-noise ratio (higher than 34 dB), and high mode purity (up to 95%), which may be applied for mode-division-multiplexing optical communication and optical fiber sensing systems.

Multi-wavelength erbium-doped fiber laser with tunable orbital angular momentum mode output

We propose and numerically analyze a kind of terahertz (THz) phase-shifted gratings based on circularly symmetrical subwavelength waveguides. The filtering principle lies in that through introducing periodically structural disturbance to the subwavelength dielectric wire along the THz wave propagation direction, the coupling response are inspired. By modifying the central period unit to introduce a π shift, a THz phase-shifted grating which can operate as a narrowband pass filter is realized. The extinction ratio (ER) and full-width half-maximum (FWHM) of the phase-shifted grating that offers narrow transmission peak are 12.8 dB and FWHM of 2.0 GHz, respectively. Thanks to the circularly symmetrical structure of the waveguides, the proposed gratings are polarization insensitive. Moreover, the application of phase-shifted grating in refractive index sensing is also investigated. The proposed gratings may pave the way for various applications in compact and robust THz sensing, imaging, and communication systems.

Subwavelength waveguide-based THz narrow bandpass filter and application in refractive-index sensing

We report a dual-wavelength fiber laser sensor based on a uniform fiber Bragg grating (UFBG) and a Polyvinyl alcohol (PVA) film-coated long-period grating (LPG) as sensor probe for simultaneous detection of relative humidity (RH) and temperature. Two UFBGs and the LPG were inscribed in three single mode fibers utilizing phase/amplitude mask technology and mobile scanning technique via the 248 nm UV laser. In our experiment, the RH function based on the differential intensity measurement at dual-wavelength output from 30% to 85% is in a quadratic equation, and the RH sensitivity coefficient of 0.358 dB/% shows good linear relationship and stability from 55% to 85%. Meanwhile, the temperature sensitivity coefficients based on wavelength detection and differential intensity detection are 9.1 pm/°C and 0.21 dB/°C, respectively. The structure of dual-wavelength fiber laser sensor with high signal to noise ratio (SNR), narrow spectral width and good stability enables simultaneous measurement of the RH and temperature with high accuracy and good repeatability.

/pdf/wavelength-and-intensity-demodulated-dual-wavelength-fiber-2ud5xbn0o1.pdf

Haisu Li

Papers

Erbium-ring-doped fiber laser for transverse vector modes output

Particle Swarm Optimization of Single-Mode Trench-Assisted Bend-Insensitive Fibers

Multi-wavelength erbium-doped fiber laser with tunable orbital angular momentum mode output

Subwavelength waveguide-based THz narrow bandpass filter and application in refractive-index sensing

Wavelength- and Intensity-Demodulated Dual-Wavelength Fiber Laser Sensor for Simultaneous RH and Temperature Detection