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 very high dispersive dual-core photonic crystal fiber is analyzed by the full-vector finite element method. The
dependence of the phase-matching wavelength (PMW) and the full width at half-maximum (FWHM) on the refractive
index of the doped inner core, the diameter of air holes and the hole pitch is demonstrated. The dispersion value is as
large as -1427 ps/(nm km) and the effective mode area of the fundamental mode, 82.06 um 2 are obtained.

Study of the highly dispersive dual-core photonic crystal fiber with large mode area

The fluorescence intensity ratio (FIR) technique for optical fiber-based temperature sensing is discussed in many previous papers. But in the high temperature sensing the FIR technique has been researched a little. In this paper, the temperature dependence of fluorescence in erbium-doped fiber between ∼700 and ∼1300°C is discussed and experimentally demonstrated. 1450nm and 1530nm wavelengths are chosen to calculate the FIR, and the temperature coefficient could achieve - 0.003dB/°C.

http://ieeexplore.ieee.org/iel5/5361200/5405166/05405533.pdf

High temperature sensing characteristics of erbium-doped fiber using fluorescence intensity ratio technology

Twin core erbium-doped fiber is fabricated using a combination of MCVD, solution doping and post processing technique. This paper mainly study the birefringence of twin-core Erbium doped fiber including geometrical and stress birefringence. First we analysis the mode distribution of twin core fiber and geometrical birefringence by supercell lattice orthogonal function method using the structure parameters measured. Then the geometrical birefringence also calculated from the couple theory. The calculated result showed that two elliptical cores would have higher geometrical birefringence than two circular cores. Generally the Er-doped fiber is high Germanium doped to keep high Numerical Aperture (NA), which cause high thermal expansion coefficient difference between the core and the cladding, and the stress birefringence is anisotropic. According the distribution of stress field, we calculated the stress birefringence in the area of assembling of light power, which approximate to 10 -4 . The investigation proved that twin core Erbium doped fiber has high birefringence and good polarization maintaining characteristics.

Fabrication and characteristics of twin core erbium-doped fiber

The random deviation of the periodicity of the gratings will affect the performance of the fiber gratings. The random errors would not accumulate when the gratings were cascaded. But we found a kind of fabricating system errors induced by the method for the side writing of fiber gratings, which would accumulate when cascaded. So laser with the less pulse energy should be used to write the gratings to developing the system's performance.

The non-ideal group delay and reflection characteristics of chirped fiber grating dispersion compensator induced by the method for the side writing

The effect of source wavelength instability on the performance of a system using chirped fiber Bragg gratings as dispersion compensators is numerically investigated, by which it's shown that source wavelength instability will surely induce an additional penalty for the system. And quantified relations of the EOP induced by group delay ripples and reflection ripples with the extent of wavelength instability is given.

Shuisheng Jian

Papers

Study of the highly dispersive dual-core photonic crystal fiber with large mode area

High temperature sensing characteristics of erbium-doped fiber using fluorescence intensity ratio technology

Fabrication and characteristics of twin core erbium-doped fiber

The non-ideal group delay and reflection characteristics of chirped fiber grating dispersion compensator induced by the method for the side writing

Effect of source wavelength instability on the performance of a system using chirped fiber Bragg grating as dispersion compensators