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

The cylindrical waveguide (optical fiber ) with a metal outer clad were analysed. The propagation constant of core mode and clad mode were derived from vector method and then solved by numerical method. And some characteristics of the mode in metal clad fiber were studied. We also analysied the effect of metal clad to the long-period fiber grating.

Mode property of metal-coated fiber and long-period fiber grating

Polarization-related impairments have become a critical issue for high-data-rate optical systems, particularly when considering polarization-mode dispersion (PMD). Consequently, compensation of PMD, especially for the first-order PMD is necessary to maintain adequate performance in long-haul systems at a high bit rate of 10 Gb/s or beyond. In this paper, we successfully demonstrated automatic and tunable compensation for first-order polarization-mode dispersion. Furthermore, we reported the statistical assessment of this tunable compensator at 10 Gbit/s. Experimental results, including bit error rate measurements, are successfully compared with theory, therefore demonstrating the compensator efficiency at 10 Gbit/s. The first-order PMD was max 274 ps before PMD compensation, and it was lower than 7ps after PMD compensation.

Compensation for first-order polarization-mode dispersion by using a novel tunable compensator

Hole-assisted lightguide fiber (HALF) is a microstructured fiber composed of a high index core, a low index cladding and a small number of air holes surrounding the core. The characteristics of HALF are studied by using the full-vector finite element method. The contour lines of power flow intensity and transverse electric distributions are plotted for the fundamental mode and the first four higher order modes. The effect of the structural parameters, such as hole-to-core spacing and relative size of air holes to the cutoff wavelengths of fundamental mode and higher order mode, core power confinement factor, and mode field diameter is analyzed. Due to these holes, there are variations between HALF and conventional step-index fiber. It's found that when the distance between the air holes and core is shorter or the relative size of air holes becomes larger, the effect of air hole on the HALF turns greater: core power confinement factor becomes larger; mode diameter becomes smaller; the cutoff wavelengths of fundamental mode and higher order mode move to shorter wavelength. In terms of waveguide design, the structural parameters of erbium-doped HALF are optimized to obtain high-efficiency operation of a fiber laser or amplifier.

Research on the characteristics of hole-assisted lightguide fiber

A new near-elliptic cladding Polarization-maintaining photonic crystal fibre (PM-PCF) with four different hole diameters was proposed. Since the refractive index decreases gradually from x-axis to y-axis, less polarization coupling and high extinction ratio were obtained compared to the conventional PM-PCFs. Secondly, every hole diameter of near-elliptic cladding was optimized to get good performance, considering proper mode field diameter of x-axis and y-axis for better coupling to SLD and smaller confinement loss of the new PCF, high birefringence and high extinction ratio, especially the effects of disturbance on extinction ratio stability. According to series of comparison on different hole diameters and correlation between different holes, the optimum parameters of this new PCF of Λ=2.2μm, d 1 =2μm, d 2 =1.1μm, d 3 =1.7μm and d 4 =1.2μm were derived. The optimized near-elliptic cladding PCF can obtain both high extinction ratio (>29dB) and good extinction ratio stability (<2dB with ±10% transverse disturbance of d 3 ) which is useful for practical use.

Design and optimization of a near-elliptic cladding photonic crystal fiber with high extinction ratio stability

A universal scaling law to describe dispersion relation of plasmon modes in graphene-coated nanowire (GNW) is presented, which could be applied to obtain the dispersion relation of GNW with any radius without further extensive calculation.

Shuisheng Jian

Papers

Mode property of metal-coated fiber and long-period fiber grating

Compensation for first-order polarization-mode dispersion by using a novel tunable compensator

Research on the characteristics of hole-assisted lightguide fiber

Design and optimization of a near-elliptic cladding photonic crystal fiber with high extinction ratio stability

Universal Dispersion Relation for Plasmon Modes in Graphene-Coated Nanowire