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

Strict dual-mode large-mode-area fiber with multicore structure

Highly nonlinear fibers with nearly zero flattened dispersion over a wide band range has very wide applications in future
high-capacity, all-optical networks. Because of its flexibility of structure design and much larger index contrast between
the core and effective cladding than the conventional fibers, photonic crystal fibers (PCFs) are becoming to be an
attractive candidate to form this kind of highly nonlinear fibers. Based on quantitative analysis on the effect of the
difference of hole-sizes between the first ring and the other's, and the effect of Ge-doped concentration in the core region
on the PCF's dispersion curve, a new way to design PCF with high nonlinear coefficient and nearly zero flattened
dispersion is proposed. Based on this, a PCF is designed, which has dispersion values between ±0.8ps/nm/km over
S+C+L wavelength bands, and the dispersion slope of 0.005ps/nm 2 /km, nonlinear coefficient of 46.6W -1 km -1 at 1.55μm.

Design of highly nonlinear photonic crystal fibers with flattened dispersion over S+C+L wavelength bands

Double-grating coupler based on two fiber Bragg gratings(FBGs) has the advantages of compact structure and enhanced filtering efficiency. The influences of different gratings' position in the coupling region and grating length on the filtering spectra were investigated based on the unified coupled-mode theory. The results show that, the coupling region on the left of the graing mostly affects the drop channel characteristic; the length of the grating mostly affects the drop efficiency; the transmission characteristic is best with the whole length of the coupling region Lc integral multiple of coupling length π/(2Kf ). A coupler with uniform coupling region making of two photoconductive fibers was fabricated by improved fused taper technology, then two Bragg gratings were written in the coupling region with 248nm ultraviolet laser, and a grating reflecton coupler with maximum drop reflectivity 20dB and bandwidth 0.8nm was achieved.

Study and fabrication of add/drop filter based on Bragg gratings reflection coupler

A fully vectorial effective index method and multiple-cladding method (FVEIM&MCM) is developed for modeling photonic crystal fibers. The large negative dispersion and nearly zero flattened dispersion in highly nonlinear photonic crystal fibers are analyzed numerically.

Analysis of dispersion properties in highly nonlinear photonic crystal fibers

In this paper, a new type of photonic crystal fiber with high birefringence is proposed and analyzed with a full-vector model based on the super-lattice and the plane-wave expansion model. Due to the two different sizes of the holes introduced into the cladding of the PCF, the fiber is two-fold rotational symmetry and appears to be with high birefringence. Numerical results demonstrate that a modal birefringence at wavelength 1.31 μm is 1.8×10−3 in the PCF with Λ=2.55 μm,d 1/Λ=0.3 andd 2/Λ=0.833. A near 200 nm SPSM region within the wavelength range from 1.4 μm to 1.6 μm is obtained.

Shuisheng Jian

Papers

Strict dual-mode large-mode-area fiber with multicore structure

Design of highly nonlinear photonic crystal fibers with flattened dispersion over S+C+L wavelength bands

Study and fabrication of add/drop filter based on Bragg gratings reflection coupler

Analysis of dispersion properties in highly nonlinear photonic crystal fibers

A new type photonic crystal fiber with high birefringence