High birefringence rectangular-hole photonic crystal fiber

In this paper, the authors describe a new class of silicon photonic crystal fibre (SiPCF) that brings together two powerful optical technologies, the photonic crystal fibre (PCF) and the semiconductor optical fibre. The PCF is now a well established fibre paradigm that has proven to be a very versatile waveguide and has found applications in nonlinear optics, fibre lasers, and sensors. The versatility of the PCF is due to its microstructured cladding which enables complex manipulation of the waveguide's characteristics, and also allows for enhanced light interaction with materials that are infiltrated into the cladding voids. The most typical form of semiconductor optical fibre has a fused silica cladding and guides light in the high refractive index semiconductor core. Although semiconductor optical fibres are a nascent technology, practical applications, such as nonlinear pulse shaping and all optical modulation, have begun to emerge in the last couple of years. However, material losses are currently preventing this fibre type from becoming a major disruptive technology and, with this in mind, the initial steps to decouple the functionality of the semiconductor from its material losses were presented . It was achieved by filling the holes of a modified total internal reflection guiding silica PCF with hydrogenated amorphous silicon (a-Si:H) inclusions. The resulting SiPCF light guide in the low loss core via the antiresonant reflecting optical waveguiding (ARROW) mechanism was shown.

Hollow core photonic crystal fibres (HC-PCFs) have promising applications in high power beam delivery, chemical sensing and gas-based nonlinear optics. According to the waveguide mechanisms they based on, HC-PCFs are typically classified into two kinds. One kind guide light via a two dimensional photonic bandgap while the other through anti-resonant reflection. The former one is so-called hollow core photonic bandgap fibres (HC-PBGFs) while the latter is commonly named hollow core anti-resonant fibres (HAFs).Compared to HC-PBGFs, HAFs can have much broader transmission windows and more flexible fibre designs. As a result, HAFs are currently more popular than HC-PBGFs. Hence the topic of this thesis is focused on HAFs. HAFs have already been demonstrated to have potential on the application of gas filled fibre lasers. As early as 2002, the first demonstration of the Raman scattering emission had been observed with an H2 filled HAF. During the past decades, a lot of efforts have been devoted into the gas filled HAF lasers. However, so far there is no demonstration of any all HAF based fibre laser because there exist two restrictions. The first restriction is that hollow core fibres are favoured in long wavelength regions where solid core glass fibres suffer high material loss, besides, a small cavity cross section (i.e., fibre core size) is preferred to reduce the lasing threshold. However, the confinement loss of a HAF (i.e., cavity loss) increases fastly when core size gets smaller or wavelength gets longer. The second restriction is there is no hollow core fibre based fibre coupler to build an all hollow core fibre based laser ring cavity. Therefore, the task of this thesis is to get rid of these two restrictions to make our contributions to all HAF based fibre lasers. Firstly, I develop the hollow core fibre fabrication technique based on our local facilities. Secondly, I design, fabricate, and characterize a HAF which can have relatively low transmission loss in small core and long wavelength conditions. Thirdly, I design, fabricate, and characterize a HAF based fibre coupler whose power splitting ratio is tunable by adjusting the fibre strain. Thirdly, I use the HAF based fibre coupler to build a ring cavity in a fibre laser system, where the tunable feature of the fibre coupler helps to optimize the conversion efficiency. Moreover, the HAF based fibre coupler is experimentally proved to be able to split and deliver the ultra fast laser pulse without degradation.

While single-mode waveguides are commonly used in integrated photonic circuits, emerging applications in nonlinear and quantum optics rely fundamentally on interactions between modes of different order. Here we propose several methods to evaluate the modal composition of both externally and device-internally excited guided waves and discuss a technique for efficient excitation of arbitrary modes. The applicability of these methods is verified in photonic circuits based on aluminum nitride. We control modal excitation through suitably engineered grating couplers and are able to perform a detailed study of waveguide-internal second harmonic generation. Efficient and broadband power conversion between orthogonal polarizations is realized within an asymmetric directional coupler to demonstrate selective excitation of arbitrary higher-order modes. Our approach holds promise for applications in nonlinear optics and frequency up/down-mixing in a chipscale framework.

We present some new experiments on self-diffraction in nematic liquid crystals and an extended static theoretical description of this effect. Our model gives some new insights and improvements to calculations carried out before. Using these calculations it was, e.g., possible to determine elastic constants in a pure optic way. For the static and dynamic measurements we designed a computer-controlled optical setup. It allows determination of the most interesting nonlinear optical properties of liquid crystals under variation of many parameters. The layout even allows application for any other nonlinear material. Especially modulation sensitivity, modulation transfer function and distribution of noise measured with just one setup are interesting for later application in optical signal or image processing. Furthermore, we present measurements one some new commercial nematic mixtures which show promising behaviour for future application in nonlinear optics. It was possible to verify our theoretical model with the experimental results.

Photonic-bandgap fibers have had major impact from fundamental studies of photon–atom interactions to new applications in nonlinear optics. While much is known about the optical properties of these fibers, relatively little is known about their optomechanical properties. Here we identify a new form of optomechanical coupling in gas-filled hollow-core fibers. We show that forward Brillouin scattering is produced by air in the core of a photonic bandgap fiber. A single Brillouin resonance is identified at 35 MHz, which corresponds to a guided sound wave within the center of an air-filled hollow-core fiber. A simple analytical model, refined by numerical simulations, is developed that accurately predicts the Brillouin coupling strength and frequency from the gas and fiber parameters, revealing that this optomechanical interaction is highly tailorable. This new mechanism could become the basis for new types of sensing and spectroscopy. Moreover, this previously unknown nonlinearity within hollow core fibers represents a power and noise limitation that requires further consideration.

Photonic crystal fibers (PCFs) have attracted much interests recently mainly because of their unique properties. Based on the light confinement mechanisms, the photonic crystal fibers can be divided into tow classes: the index-guiding PCFs and the photonic bandgap (PBG) PCFs. The former, with multiple air holes periodically arranged around the core, possess numerous unusual properties, such as structure controllable chromatic dispersion, large mode areas, birefringence and stronger optical nonlinenarity.Based on the full vector, semi vector or even the approximate-scalar model, Lots of methods have been used to design the PCFs, such as the effective index approach, the localized function expansion method, the plane wave expansion method, the multipole method, the beam propagation method, the finite difference method, the finite difference time domain method, and the finite element method. Each of theses method mentioned above are accurate and efficient for ideal PCF, however, for the real fabricated PCFs, the geometry structure may not perfect, induced the base mode degeneracy may be destructive, and posses birefringence properties. Sometime the birefringence properties is necessary for special usefulness, such as polarization mode dispersion (PMD) compensation, and PCFs based polarized optical devices. In this paper, a full vector finite element is applied to investigate the mode birefringence, mainly focus on the rectangle lattice PCFs with elliptical or circular holes. It has been demonstrated from the calculated results that high birefringence to the order of 0.01 can be achieved by decreasing both the pitch and the x and y ratio of the elliptical hole. To increase the birefringence of the circular holes rectangle lattice, reduction of the width and height ratio of the lattice is necessary. Based on the simulation results, we conclude that both single polarization transmission and high birefringence polarization maintaining can be achieved by using the proposed structure with suitable parameters respectively. The available high birefringence at relative high frequency regime in the fibers and also the sufficiently broad single mode region would make the fabrication of highly birefringent photonic crystal fibers with novel properties possible.

We present experimental analysis of supercontinuum generation obtained for highly birefringent and highly nonlinear dual-mode fiber. A specific difference between the zero dispersion wavelength of fundamental mode and higher order mode in such fiber gives possibility of a normal and an anomalous dispersion regime pumping, depending on the mode, which is excited. The nonlinear effects responsible for the generation of broadband spectrum of the light are analyzed when the fiber is pumped by the pulse pump source operating at the wavelength of 1064nm. Full Text: PDF References J. M. Dudley, G. Goëry, and C. Stéphane, "Supercontinuum generation in photonic crystal fiber", Reviews of modern physics 78(4), 1135 (2006). CrossRef J. C. Knight, and D. V. Skryabin, "Nonlinear waveguide optics and photonic crystal fibers", Opt. Express, 15(23), 15365-15376 (2007). CrossRef Z. Holdynski et al., "Experimental study of dispersion characteristics for a series of microstructured fibers for customized supercontinuum generation", Opt. Express 21(6), 7107-7117 (2013). CrossRef M. Napierala et al., "Influence of photonic crystal fiber manufacturing inaccuracies on supercontinuum generation", SPIE Photonics Europe, International Society for Optics and Photonics, p. 91361M-91361M-6 (2014). CrossRef J. M. Dudley, and J. R. Taylor: Supercontinuum generation in optical fibers (Cambridge University Press, 2010). CrossRef P. Falk, M. H. Frosz, and O. Bang, "Supercontinuum generation in a photonic crystal fiber with two zero-dispersion wavelengths tapered to normal dispersion at all wavelengths", Opt. Express 13(19), 7535?7540 (2005). CrossRef A. Hartung, A. M. Heidt, and H. Bartelt, "Design of all-normal dispersion microstructured optical fibers for pulse-preserving supercontinuum generation", Opt. Express, 19, 7742-7749 (2011). CrossRef B. Jinendra, K. Ranka, R. S. Windeler, and A. J. Stentz, "Optical properties of high-delta air?silica microstructure optical fibers", Opt. Lett., 25, 796-798 (2000). CrossRef J. C. Knight et al., "Anomalous dispersion in photonic crystal fiber", IEEE Photon. Technol. Lett. 12(7), 807?809 (2000). CrossRef T. Tenderenda et al., "Fibre Bragg Gratings written in highly birefringent microstructured fiber as very sensitive strain sensors", SPIE Photonics Europe, International Society for Optics and Photonics, p. 84260D-84260D-8 (2012). CrossRef T. Tenderenda et al., "Highly birefringent dual-mode microstructured fiber with enhanced polarimetric strain sensitivity of the second order mode", Opt. Express, 20, 26996-27002 (2012). CrossRef K. Stepien et al., "Fiber Bragg gratings in hole-assisted multicore fiber for space division multiplexing", Opt. Lett., 39, 3571-3574 (2014). CrossRef http://www.lumerical.com/tcad-products/mode/. DirectLink

A highly birefringent and nonlinear photonic crystal fiber with a V-shape simplified structure is proposed and analyzed by the fully vectorial finite element method. It will have important applications in the nonlinear optics and biophotonics.

We present a compressed hexagonal photonic crystal fiber (CH-PCF) based on a simple structure with ultra-flattened dispersion, high birefringence and nonlinearity. The propagation characteristics are studied accurately by utilizing full vector finite-element method (FEM). Numerical results indicate that the birefringence of 1.59 × 10−2 was obtained with high nonlinear coefficient of 42.58 W−1 km−1(X) and 52.80 W−1 km−1(Y) at an effective wavelength of 1.55 μm. Furthermore, CH-PCF presents an ultra-flattened dispersion with variation of ± 3.4 ps/nm/km(X) and ± 1.6 ps/nm/km(Y) over 1.3 μm to 1.8 μm (0.5 μm bandwidth), respectively. In addition, this circular-hole structure can be fabricated conveniently at most easy compared with complex designs, which is an advantage for practical applications such as dispersion compensation and nonlinear optics application.

We present and demonstrate a novel method for engineering the radial-variant polarization on the incident field to achieve a needle of transversally polarized field without any pupil filters. We generate a new kind of localized linearly-polarized vector fields with distributions of states of polarization (SoPs) describing by the radius to the power p and explore its tight focusing, nonparaxial focusing, and paraxial focusing properties. By tuning the power p, we obtain the needle-like focal field with hybrid SoPs and give the formula for describing the length of the needle. Experimentally, we systematically investigate both the intensity distributions and the polarization evolution of the optical needle by paraxial focusing the generated vector field. Such an optical needle, which enhances the light-matter interaction, has intriguing applications in optical microma-chining and nonlinear optics.

All-dielectric metasurfaces are unique component to control optical wavefront with high transmission or reflection coefficient. Recently, accelerating beam, which propagates along curved arbitrary trajectories, has been realized with conventional diffractive optical elements (DOE). However, DOE suffer from low sampling ratio of rapid phase gradients and its diffraction efficiency drops quickly when the wavelength is switched to another wavelength which is different than the designed wavelength.. In this study, we show accelerating beam which is generated by highly efficient and polarization insensitive all-dielectric metasurfaces in the visible wavelength. The acceleration beam is numerically generated with the proposed metasurfaces which are composed of TiO2 nanopillars residing on glass substrate using finite difference time-domain computational method. It is shown that this beam has the ability to propagate curved trajectories in air medium. Transmission efficiency of the proposed structure is above 65% and desired arbitrary trajectories have been achieved. Generating highly efficient accelerating beam can be used in photonic applications in optical imaging, spectroscopy, optical micromanipulation and nonlinear optics.

We propose and generate a class of structured light fulfilling the mathematical form of a SU(2) coherent state based on a set of circular Airy vortex modes. Such wave packets possess strong focus with both radial and angular self-accelerations, which exploit more general 3D inhomogeneous velocity control with global spatial symmetry of multilayer rotation akin to galactic kinematics, termed galaxy waves. Galaxy waves are endowed with higher degrees of freedom to control strong focusing and acceleration, which opens a direction of multi-dimensional accelerating of 3D structured light field, promising numerous applications in optical trapping, manufacturing, and nonlinear optics.

In the present work, a good-quality nickel sulfate hexahydrate (NSH) single crystal measuring 30 × 20 × 15 mm3 was grown via a slow evaporation solution technique (SEST). NSH single crystal is an inorganic material and is widely used in optical applications, UV sensors, and missile detection systems, among others. The grown crystal was characterized using powder x-ray diffraction (PXRD), UV-visible spectroscopy, microhardness test and etching analysis. Photoacoustic spectroscopy (PAS) was used to identify the thermal diffusivity of the grown crystal. The thermal diffusivity of the NSH crystal was found to be superior to that of various common nonlinear optical (NLO) materials, and is thus suitable for use in optical and sensor applications. Differential scanning calorimetry (DSC) was utilized to determine the material decomposition at a certain temperature. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed to identify the melting point of the grown crystal. The dielectric analysis showed that the crystal has low dielectric loss, fewer defects, and better optical properties, and is suitable for NLO applications. Thermal analysis showed that the grown crystal can be utilized for a wide array of applications including optical communications, UV bandpass filters, UV sensors, harmonic generation, and missile detection systems.

This study explores the dynamics of highly dispersive optical solitons in nonlinear Schrödinger equations (NLSE) with non-local self-phase modulation (SPM) and polarization-mode dispersion (PMD). These nonlinear effects significantly influence soliton propagation and stability in advanced optical communication systems. Employing the Improved Modified Extended Tanh-Function Method (IMETFM), we derive exact soliton solutions, including bright, dark, singular, and combo solitons, under specific parametric conditions. The IMETFM effectively handles the complexity of the NLSE, incorporating higher-order dispersion terms (up to sixth-order) and non-local nonlinearities. Additionally, we perform a modulation instability (MI) analysis to examine the stability of steady-state solutions. This analysis uncovers the conditions under which instabilities emerge due to the interplay between dispersion and nonlinearity. The MI study offers critical insights into the growth of wave perturbations, thereby advancing the understanding of soliton stability dynamics. Graphical representations of the solutions illustrate their behavior, emphasizing the impact of non-local SPM, PMD, and MI on soliton dynamics. These findings offer valuable insights for optimizing high-capacity optical communication systems and fiber laser technologies, with broader implications for nonlinear wave phenomena in birefringent fibers and other nonlinear physical systems. This work advances the theoretical framework for soliton dynamics and lays a foundation for future experimental validations and practical applications in nonlinear optics.

Experimental investigations of microstructured fibers filled with liquid crystals (LCs) have so far been performed only by using host fibers made of the silica glass. In this paper, the host photonic crystal fiber (PCF) was made of the PBG08 high-refractive index glass (approximately 1.95) that is much higher than silica glass index (approximately 1.46) and also higher then both ordinary and extraordinary refractive indices of the majority of LCs. As a result, low-loss and index-guiding propagation is observed regardless of the LC molecules orientation. Attenuation of the host PCF was measured to be approximately 0.15 dB/cm and for the PCF infiltrated with 5CB LC was slightly higher (approximately 0.19 dB/cm), resulting in a significant reduction to approximately 0.04 dB/cm of the scattering losses caused by the LC. Moreover, an external transverse electric field applied to the effective photonic liquid crystal fiber (PLCF) allowed for continuous phase birefringence tuning from 0 to 2.10(-4).