Optical Waveguide Theory

Curious wave phenomena that occur in optical fibres due to the interplay of instability and nonlinear effects are reviewed.

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Instabilities, breathers and rogue waves in optics

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

Space-division multiplexing (SDM) uses multiplicity of space channels to increase capacity for optical communication. It is applicable for optical communication in both free space and guided waves. This paper focuses on SDM for fiber-optic communication using few-mode fibers or multimode fibers, in particular on the critical challenge of mode crosstalk. Multiple-input–multiple-output (MIMO) equalization methods developed for wireless communication can be applied as an electronic method to equalize mode crosstalk. Optical approaches, including differential modal group delay management, strong mode coupling, and multicore fibers, are necessary to bring the computational complexity for MIMO mode crosstalk equalization to practical levels. Progress in passive devices, such as (de)multiplexers, and active devices, such as amplifiers and switches, which are considered straightforward challenges in comparison with mode crosstalk, are reviewed. Finally, we present the prospects for SDM in optical transmission and networking.

Space-division multiplexing: the next frontier in optical communication

Optical fiber gratings have developed into a mature technology with a wide range of applications in various areas, including physical sensing for temperature, strain, acoustic waves and pressure. All of these applications rely on the perturbation of the period or refractive index of a grating inscribed in the fiber core as a transducing mechanism between a quantity to be measured and the optical spectral response of the fiber grating. This paper presents a relatively recent variant of the fiber grating concept, whereby a small tilt of the grating fringes causes coupling of the optical power from the core mode into a multitude of cladding modes, each with its own wavevector and mode field shape. The main consequence of doing so is that the differential response of the modes can then be used to multiply the sensing modalities available for a single fiber grating and also to increase the sensor resolution by taking advantage of the large amount of data available. In particular, the temperature cross-sensitivity and power source fluctuation noise inherent in all fiber grating designs can be completely eliminated by referencing all the spectral measurements to the wavelength and power level of the core mode back-reflection. The mode resonances have a quality factor of 105, and they can be observed in reflection or transmission. A thorough review of experimental and theoretical results will show that tilted fiber Bragg gratings can be used for high resolution refractometry, surface plasmon resonance applications, and multiparameter physical sensing (strain, vibration, curvature, and temperature).

Tilted fiber Bragg grating sensors

Asymmetric dual-side-grating coupler for high power side-pumping

A simple modal interferometer is proposed, to be produced by splicing a section of a novel ring-core photonic crystal fiber (RPCF) and two segments of single-mode fibers. Owing to the effects of the collapsed region, the ring modes in the RPCF can be effectively activated. This is the first demonstration of an interferometer based on the interference between ring modes, as opposed to previously reported interferometer based on the interference of core modes or cladding modes. The effects of the length of RPCF and the wavelength on the temperature and strain characteristics of the interferometer are investigated. The strain sensitivity increases with RPCF length and with wavelength. Based on the interferometer, a strain sensor with low temperature sensitivity is proposed, which has strain sensitivity of 1.777 pm/(µm/m).

Ring-core photonic crystal fiber interferometer for strain measurement

In this letter, we propose a method to control the wavefront of the graphene plasmons through changing the polarization direction of the circular polarized incidence. Illuminated by the circular polarized incident light, the plasmons are launched through the resonances of a column of nanoantenna pairs beneath graphene. By properly controlling the separation and orientation of antennas in each pair, the propagation direction of plasmons wavefront is no longer perpendicular to the column and the launching angle is also dependent on the circular polarization of incident light. By combining the nanoantenna arrays with their mirroring arrays, two-dimension biconvex or biconcave plasmon lens can be realized. Furthermore, the launching angle can be controlled by the incident wavelength, the phase gradient between adjacent nanoantenna pairs, and the graphene Fermi level. The proposed scheme may provide new possibilities in engineering plasmons wavefront on graphene through launching procedure.

Circular Polarization-Dependent Wavefront Control of Plasmons on Graphene

Suppression of stimulated Brillouin scattering in high-power single-frequency multicore fiber amplifiers

. Anellipticalmultilayer-corefiber(EMCF)withlownonlinearityforwide-banddual-modeoperationwasproposed. The EMCF, in which only the HE 11 and HE 21 modes could be propagated, supported a distinct dual-mode operation. The characteristics of the EMCF, including modal properties, the operating wavelength, thetransmission loss, the effective area, and the bending loss, were systematically investigated. For EMCFs, alarge modal diameter (33.48 μm) was achieved to reduce the fiber nonlinear penalty; meanwhile, the bendingloss could be kept in a lower level. In addition, the single-polarization property in EMCFs could be realized bycombining stress applying elements. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.53.10.105104] Keywords: dual-mode fiber; large mode area; bending loss; single polarization; elliptical multilayer-core fiber.Paper 141171 received Jul. 22, 2014; revised manuscript received Sep. 26, 2014; accepted for publication Sep. 29, 2014; publishedonline Oct. 30, 2014.

Shuisheng Jian

Papers

Asymmetric dual-side-grating coupler for high power side-pumping

Ring-core photonic crystal fiber interferometer for strain measurement

Circular Polarization-Dependent Wavefront Control of Plasmons on Graphene

Suppression of stimulated Brillouin scattering in high-power single-frequency multicore fiber amplifiers

Characteristics of HE11-HE21 mode elliptical multilayer-core fiber with low nonlinearity