Low Negative Dispersion Research Articles

Single-laser-based simultaneous four-wavelength excitation source for femtosecond two-photon fluorescence microscopy.

Multicolor labeling of biological samples with large volume is required for omic-level of study such as the construction of nervous system connectome. Among the various imaging method, two photon microscope has multiple advantages over traditional single photon microscope for higher resolution and could image large 3D volumes of tissue samples with superior imaging depth. However, the growing number of fluorophores for labeling underlines the urgent need for an ultrafast laser source with the capability of providing simultaneous plural excitation wavelengths for multiple fluorophores. Here, we propose and demonstrate a single-laser-based four-wavelength excitation source for two-photon fluorescence microscopy. Using a sub-100 fs 1,070-nm Yb:fiber laser to pump an ultrashort nonlinear photonic crystal fiber in the low negative dispersion region, we introduced efficient self-phase modulation and acquired a blue-shifted spectrum dual-peaked at 812 and 960 nm with 28.5% wavelength conversion efficiency. By compressing the blue-shift near-IR spectrum to 33 fs to ensure the temporal overlap of the 812 and 960 nm peaks, the so-called sum frequency effect created the third virtual excitation wavelength effectively at 886 nm. Combined with the 1,070 nm laser source as the fourth excitation wavelength, the all-fiber-format four-wavelength excitation source enabled simultaneous four-color two-photon imaging in Brainbow AAV-labeled (TagBFP, mTFP, EYFP, and mCherry) brain samples. With an increased number of excitation wavelengths and improved excitation efficiency than typical commercial femtosecond lasers, our compact four-wavelength excitation approach can provide a versatile, efficient, and easily accessible solution for multiple-color two-photon fluorescence imaging in the field of neuroscience, biomolecular probing, and clinical applications with at least four spectrally-distinct fluorophores.

Two Sides Rhombus Shaped Cladding Hexagonal PCF with Low Confinement Loss and Negative Dispersion

A novel design of solid core photonic crystal fiber (PCF) has been proposed with seven rings rhombus inside eight rings hexagonal structure. Waveguide properties have been numerically investigated by utilizing the full vectorial finite element method (FEM). Here the paper elaborates PCF characteristic like confinement loss, dispersion properties, normalize frequency, mode field diameter, effective area, and nonlinear coefficient with asymmetric cladding designed and investigated. Silica is used as background material. The calculated value shows the ultra-low confinement loss in 1.1 µm to 1.7 µm, low negative dispersion -400ps/km-nm achieved in solid core. The high nonlinear coefficient 3.1661762 W-1km-1 and 3.141089 W-1km-1 at 1.55 µm in xpolarization and y-polarization mode respectively achieved. PCF achieved low confinement loss and better mode field diameter for remote sensing application.

Dispersion tailoring of silicon nanowire optical rectangular waveguide (SNORW)

Dispersion analysis on silicon nanowire optical rectangular waveguide (SNORW) has been presented in this paper by guiding light inside low refractive index region. Dispersion engineering is an essential study to utilize any photonic integrated circuit-based waveguide in linear and nonlinear optical devices. This paper exhibits distinctive dispersion characteristics recognized in the wavelengths of S, C and L bands by tailoring physical parameters of SNORW. Modal investigation and numerical analysis have been carried out by finite element method (FEM), which shows that SNORW configuration enables the flat and low negative dispersion behavior. This paper also demonstrates the utilization of cladding materials and structural parameters of SNORW to tune the magnitude and behavior of dispersion for flat dispersion profile.