Optical Waveguide Theory

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

/pdf/instabilities-breathers-and-rogue-waves-in-optics-252ilwzt4i.pdf

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

We experimentally demonstrate a multiwavelength fiber ring laser with tunable orbital angular momentum (OAM) beam output The laser is embedded with a few-mode fiber Bragg grating and a mode selective coupler (MSC) The mode conversion from LP01 mode to LP11 mode is realized by using the MSC as a mode converter By rotating a polarizer set at the output end of the MSC, the topological charge of the OAM beam can be tuned from l = −1 to l = +1 and thus a tunable OAM beam is obtained By adjusting the polarization controllers (PCs), the laser can operate under single-, dual- and triple-wavelength lasing conditions

https://iopscience.iop.org/article/10.1088/1612-202X/aacb48/pdf

Few-mode fiber Bragg grating-based multi-wavelength fiber laser with tunable orbital angular momentum beam output

In this paper we propose a method of unidirectional excitation of graphene plasmons via metal nanoantenna arrays and reveal its application in a circular polarization analyzer. For nanoantenna pairs with orthogonal orientations, the graphene plasmons are excited through antenna resonances with the direction of propagation can be controlled by incident polarization. On the other hand, based on the spiral shape distribution of antenna arrays, a circular polarization analyzer can be obtained via the interaction of geometric phase effect of antenna arrays and the chirality carried by incident polarization. By utilizing the unidirectional excitation of plasmons, the extinction ratio of analyzer can be improved to over 103, which is at least an order of magnitude larger than the result of antenna pairs with same orientations or antenna arrays with closed circular shape formation. The proposed analyzer may find applications in analyzing chiral molecules using different circularly polarized waves.

Graphene circular polarization analyzer based on unidirectional excitation of plasmons.

A novel design, two-layer low-index trench fiber with parabolic-profile core, is proposed and investigated numerically in this paper. Based on scalar FD-BPM algorithm, the excellent performance over other types of structures and great potential in mode area enlargement are demonstrated. The effective mode area of our design (D = 100μm) is approximately 890 μm2. Both the high order mode (HOM) suppression and bending resistance of our design are better than that of Multi-Trench Fiber (MTF). The mode loss ratio and effective mode area are independent on the bending radius. Due to the circular symmetry of our proposed configuration design, the bending property is not varied with the changing of bending directions.

Novel bending-resistant design of two-layer low-index trench fiber with parabolic-profile core

Low-threshold wavelength-switchable fiber laser based on few-mode fiber Bragg grating

We conduct both analytical and numerical investigations of the giant gradient force for nanoparticle trapping in the coupled graphene strips waveguides system. An analytical model based on coupled slab waveguides has been adopted in the analysis of mode performance and gradient force, and good agreement is obtained with numerical simulations. Both theoretical modeling and numerical simulations have shown that the gradient force can be as high as 8 nN/ $\mu \text{m}\,\cdot \,$ mW at a gap size of 10 nm, which is at least one order of magnitude higher than the previously reported hybrid plasmonic waveguide. Meanwhile, the giant gradient force leads to an ultrahigh trapping force and potential of $1.5\times 10^{\mathrm {\mathbf {6}}}$ fN/W and $2.4\times 10^{\vphantom {R^{G}}\mathrm {\mathbf {3}}}~\text{k}_{\mathrm {\mathbf {B}}}\text{T}$ /W, which are three orders of magnitude larger than the hybrid plasmonic waveguides. This enables the efficient trapping of nanoparticles with diameters as small as 2 nm. This coupled graphene strips system opens up new possibilities of tunable nanoscale mechanical devices and various potential applications, such as manipulating biomolecules.

Shuisheng Jian

Papers

Few-mode fiber Bragg grating-based multi-wavelength fiber laser with tunable orbital angular momentum beam output

Graphene circular polarization analyzer based on unidirectional excitation of plasmons.

Novel bending-resistant design of two-layer low-index trench fiber with parabolic-profile core

Low-threshold wavelength-switchable fiber laser based on few-mode fiber Bragg grating

Giant Gradient Force for Nanoparticle Trapping in Coupled Graphene Strips Waveguides