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 proposed a simple method for fabricating high-birefringence nonlinearly chirped fiber Bragg grating by writing into a high-birefringence photosensitive tapered fiber through a linearly chirped phase mask. Its performance as PMD compensator is demonstrated experimentally.

http://ieeexplore.ieee.org/iel5/8671/27470/01224318.pdf

A simple method for fabricating high-birefringence nonlinearly chirped Bragg grating as a PMD compensator

The invention relates to a wave-front measurement device for a laser diode linear array or planar array, which belongs to the field of adaptive optics and can be used for wave-front measurement on a high-power laser diode linear array or planar array. A support flat plate (5) of the wave-front measurement device is movably connected onto a cylindrical bulge at the center of an angle measurement dial disc (8). A light barrier (3) with a pinhole (a) is arranged at the position of the diameter of the angle measurement dial disc. A precise three-dimensional adjustment platform (1) is arranged in front of the light barrier with the pinhole (a), and the laser diode linear array or planar array (2) is arranged on the precise three-dimensional adjustment platform. A condenser lens (4), a light barrier (6) with a pinhole (b) and a photoelectric detector (7) are fixed on the support flat plate in sequence. By adjusting the precise three-dimensional adjustment platform along the fast-axis direction and the slow-axis direction of the laser diode linear array or planar array, the front-wave measurement can be carried out on a whole luminous zone. The wave-front measurement device for the laser diode linear array or planar array has a simple structure, is easy to install and adjust and is capable of carrying out high-precision wave-front measurement on the laser diode linear array or planar array within a range of -80 degrees-80 degrees.

Wave-front measurement device for laser diode linear array or planar array

The proposed methods of Polarization Mode Dispersion (PMD) mitigation can be divided into three main approaches: (i) electrical PMD compensation, (ii) optical PMD compensation, and (iii) mitigation by use of robust modulation formats, increased power margin etc. In this paper, we discussed each of these sententiously, with less emphasis on comparing the first and the second, but with more emphasis on the third. We quantify the benefits of using different techniques for compensation of PMD in fiber-optic communication systems by means
of numerical simulations. This is done both with respect to PMD-induced pulse broadening and in terms of system outage probability for different data formats [nonreturn-to-zero (NRZ) and return-to-zero (RZ)]. With our experimental results, we find that RZ performs better than NRZ, furthermore, it is comparable with 2-3 DOF
PMD compensator, and can be expected to be a practical alternative in particular if used in combination with error correcting codes. We also study the trade-off between power margin and acceptable PMD. Moreover, it is generally believed that a PMD compensator with a polarization controller and a variable delay line can only
compensate the PMD to the first order. Our experimental results show that, the counterintuitive fact that this scheme can also partially compensate for higher order PMD. We also investigate the benefit of using a polarizer as compensation element where the optical average power can be used as a feedback signal.

A comparison among various PMD mitigation approaches

A new near-elliptic inner cladding (NEIC) structure of polarization-stable highly birefringent photonic crystal fiber (HB-PCF)
is proposed and analyzed by using a full-vector finite element method (FEM) with anisotropic perfectly matched
layers. From the numerical results it is confirmed that, with the diameter of air hole A varied by ~10%, the modal
birefringence degradations of the three proposed NEIC-PCFs are less than 4.2 × 10 -5 , 6 × 10 -5 and 1.17 × 10 -4 ,
respectively, while the average birefringence is of the order of 2 × 10 -3 at 1.55μm, which strongly proves that the
proposed structure is highly polarization-stable. Especially, the MFDs in x-direction and y-direction of NEIC-PCF with
three holes diminished in the center are measured as 5.8 μm and 2.6 μm, respectively, which are very attractive in the
application field of fiber optic sensor, e.g. fiber optic gyros.

Polarization-stable highly birefringent photonic crystal fiber with near-elliptic inner cladding structure

The dispersion properties of the index-step higher order mode dispersion-compensating fibers (HOM-DCFs) are
simulated using an unequal interval finite difference method in this paper. Large negative dispersion of the first few
higher order modes (HOMs) near cutoff are studied comparatively, which is helpful for designing the dispersion
compensator based HOM-DCFs.

Shuisheng Jian

Papers

A simple method for fabricating high-birefringence nonlinearly chirped Bragg grating as a PMD compensator

Wave-front measurement device for laser diode linear array or planar array

A comparison among various PMD mitigation approaches

Polarization-stable highly birefringent photonic crystal fiber with near-elliptic inner cladding structure

Higher order mode-based large negative dispersion in step-index fibers for dispersion compensation