High birefringence and broadband dispersion compensation photonic crystal fiber

We propose a perfectly square lattice photonic crystal fiber (PCF) which shows high birefringence and negative dispersion. To set up high asymmetry in the core, dual line imperfection is considered where the fill fraction ratio and defect air hole diameter exhibit significant impact on dispersion and birefringence. Numerical analyses of guiding properties of the proposed PCF are done using finite element method with perfectly matched layer boundary condition from 1.2 to 1.8 μm wavelength. The optimized square lattice PCF presents high birefringence of 2.48 × 10−2 and dispersion of −777.66 (ps/nm.km) at 1.55 μm wavelength. In addition, the proposed PCF offers ultra-low confinement and insertion loss at 1.55 μm wavelength. Moreover, −0.45 (ps/nm2.km) dispersion slope and 0.0045 nm−1 relative dispersion slope are observed at 1.55 μm wavelength. Additionally, the proposed PCF maintains dispersion and birefringence variation of ±30 (ps/nm.km) and ±0.00001 between 1.5 and 1.6 μm wavelength ranges, respectively. Furthermore, the proposed PCF shows high quality factor and low bit error rate at 10 dBm input power. We believe the proposed square lattice PCF can be deployed in wavelength division multiplexing based optical fiber transmission system for wide-band dispersion compensation.

Influence of dispersion slope on soliton spectral tunneling in photonic crystal fiber

We report a numerical investigation of how the dispersion slope affects the soliton spectral tunneling (SST) in a photonic crystal fiber with three zero dispersion wavelengths. It is discovered that a larger dispersion slope makes group-velocity mismatch between the initial soliton and the transferred wave thereby suppressing the SST effect, while a proper decrease of the dispersion slope enhances the SST effect to widen a supercontinuum range. Besides, we find a soliton-like leaking dispersion wave, which can sustain information and energy for a short time within a particular spectral range.

High-Order Analytical Formulation of Soliton Self-Frequency Shift

<div>We derive an analytical formulation of the Raman-induced frequency shift experienced by a fundamental soliton. By including propagation losses, self-steepening, and dispersion slope, the resulting formulation is a high-order (HO) extension of the well-known Gordon's formula for soliton self-frequency shift (SSFS). The HO-SSFS formula closely agrees with numerical results of the generalized nonlinear Schrödinger equation, but without the computational complexity and required computation time. The HO-SSFS formula is a useful tool for the design and validation of wavelength conversion systems and supercontinuum generation systems.</div>

High-Order Analytical Formulation of Soliton Self-Frequency Shift

<div>We derive an analytical formulation of the Raman-induced frequency shift experienced by a fundamental soliton. By including propagation losses, self-steepening, and dispersion slope, the resulting formulation is a high-order (HO) extension of the well-known Gordon's formula for soliton self-frequency shift (SSFS). The HO-SSFS formula closely agrees with numerical results of the generalized nonlinear Schrödinger equation, but without the computational complexity and required computation time. The HO-SSFS formula is a useful tool for the design and validation of wavelength conversion systems and supercontinuum generation systems.</div>

Measurements of the dispersion, the dispersion slope and nonlinear coefficients of photonic crystal fibers based on degenerate four-wave mixing (FWM)

A simple and accurate method based on degenerate four-wave mixing (FWM) to evaluate optical fiber dispersion and nonlinearity is presented. We investigated the continuous wave degenerate FWM characteristics of two photonic crystal fibers (PCFs) and a SMF28 fiber. Simply by measuring and analyzing the continuous wave degenerate FWM conversion efficiency as a function of the wavelength difference between pump and signal waves, fitting between experimental data and analytical FWM conversion efficiency expression is carried out to determine the dispersion, dispersion slope and nonlinear coefficient of the fiber. The fiber parameters simultaneously obtained from a single set of FWM measurement for Single Mode Fiber 28 (SMF28) are found to be agreement with the manufacturer specifications for this fiber, thus validating the PCF results and, more generally, the acceptable accuracy of the simple method proposed here.

Ultrasonic liver steatosis quantification by a learning-based acoustic model from a novel shear wave sequence

Background An efficient and accurate approach to quantify the steatosis extent of liver is important for clinical practice. For the purpose, we propose a specific designed ultrasound shear wave sequence to estimate ultrasonic and shear wave physical parameters. The utilization of the estimated quantitative parameters is then studied. Results Shear wave attenuation, shear wave absorption, elasticity, dispersion slope and echo attenuation were simultaneously estimated and quantified from the proposed novel shear wave sequence. Then, a regression tree model was utilized to learn the connection between the space represented by all the physical parameters and the liver fat proportion. MR mDIXON quantification was used as the ground truth for liver fat quantification. Our study included a total of 60 patients. Correlation coefficient (CC) with the ground truth were applied to mainly evaluate different methods for which the corresponding values were − 0.25, − 0.26, 0.028, 0.045, 0.46 and 0.83 for shear wave attenuation, shear wave absorption, elasticity, dispersion slope, echo attenuation and the learning-based model, respectively. The original parameters were extremely outperformed by the learning-based model for which the root mean square error for liver steatosis quantification is only 4.5% that is also state-of-the-art for ultrasound application in the related field. Conclusions Although individual ultrasonic and shear wave parameters were not perfectly adequate for liver steatosis quantification, a promising result can be achieved by the proposed learning-based acoustic model based on them.