As2Se3 Photonic Crystal Fiber Research Articles

Characteristics of vector beams in mid-infrared waveband in an As2Se3 photonic crystal fiber with small hollow core

Abstract Characteristics of vector beams in mid-infrared waveband are analyzed numerically in an As2Se3 photonic crystal fiber (PCF) with small central hollow core (SCHH), including the mode fields, confinement loss, effective refractive index and chromatic dispersion. In the PCFs with the SCHH diameter d0 of 0–1.5 μm, the confinement losses of the four vector beams (HE11, TM01, TE01, and HE21) are smaller than 1.0 dB/m for the wavelengths up to ~5 μm. For the SCHH diameter d0 of 0.5–1.5 μm, the field enhancement of the HE11 mode occurs in the SCHHs in the central area for the wavelengths ≥5 μm. This happens because the evanescent light penetrates into the SCHH. With d0 increasing, the effective refractive index separations (δneff) between the HE11 mode and high-order modes (TM01, TE01, and HE21) decreases, while the δneff among the high-order modes increases. At the wavelength of 5 μm, the δneff of HE11-TE01, TE01-HE21, and HE21-TM01 is 0.03098, 0.03960, and 0.06867, respectively, when d0 is 1.5 μm. The second ZDWs of TE01, HE21 and TM01 mode are blueshifted with the increase of d0, but they are longer than 5 μm. The negative dispersion regions of the high-order modes (TE01, HE21, and TM01) are much wider than the HE11 modes. With the increase of d0, the HE11 mode dispersion curves have no obvious change, while the high-order modes (TE01, HE21, and TM01) dispersion curves become steep at the longer wavelength, the TM01 mode changes most obviously, and the depression appears. The transmission property for the waveband of 5–10 μm could be improved by increasing the ring number or core diameter of the fiber. The fiber losses at 10 μm are 4.81, 7.65, 5.95 and 2.47 dB/m for the four kinds of vector beams, respectively, when the diameters of the central area and SCHH are increased to 15.09 and 5.25 μm. Our simulated results will be useful for the optical applications in mid-infrared waveband, such as the generation of cylindrical vector mode and orbital angular momentum (OAM) and the particle manipulation by optical fields.

Stimulated Brillouin scattering by the interaction between different-order optical and acoustical modes in an As2Se3 photonic crystal fiber

Brillouin gain spectra (BGS) in an As2Se3 photonic crystal fiber (PCF) are investigated numerically. The profiles of the BGS are simulated by calculating the characteristics of different-order optical and acoustic waves in the PCFs with different core diameters. For the small-core PCF, there are two peaks in BGS, but there is only one peak for the large-core PCF. We also reveal that in the small-core PCF, the difference of Brillouin frequency shift between the LP01 and LP11 modes is obvious, while it is not obvious in the large-core PCF. The Brillouin threshold increases with the core diameter increasing.

Raman competition from ultra-broadband modulation instability gain in the As2Se3 glass photonic crystal fiber filled with argon gas

Based on the As2Se3 glass photonic crystal fiber (PCF) filled with Argon gas, pressure- and power-dependent modulation instability(MI) gain properties are studied. Two narrow MI gain bandwidths in the Stokes or anti-Stokes region expand gradually with the increasing light power, and merge into an ultra-broadband gain profile eventually by increasing the pump power from 1 W to 9000 W at a fixed gas pressure. Further increasing pump power will result in the reduction of the gain bandwidth and the formation of a constant narrow-band gain peak, which is a novel phenomenon and observed in our work for the first time. When the argon gas pressure is changed from 1 P0 to 400 P0, a similar gain characteristic is also found. However, their maximum gain bandwidths are reduced from 5065 nm to 3833 nm with the increase of the gas pressure, and their pump power required to generate the narrow-band gain spectrum are reduced from 8450 W to 3060 W. These results indicate that the formation of the ultra-broadband MI gain mainly depends on some nonlinear effects rather than stimulated Raman scattering (SRS) effect, while the single gain peak with a narrow bandwidth mainly results from the SRS effect. And they also show that, it is feasible to control the MI gain characteristic in the mid-infrared region by changing the Argon gas pressure in the As2Se3 PCF, and this scheme can also be used in optical communication and spectral shaping in the future.

Mid-infrared supercontinuum generation using As2Se3 photonic crystal fiber and the impact of higher-order dispersion parameters on its supercontinuum bandwidth

A dispersion engineered As2Se3chalcogenide hexagonal photonic crystal fiber which can produce a mid-infrared supercontinuum (SC) spectral evolution spanning from 2 μm to beyond 15 μm with a low peak power of 3 kW is numerically designed and demonstrated. Numerical analysis is carried out to investigate the impact of higher-order dispersion (HOD) parameters on the output SC bandwidth and shows that the SC spectral broadening at the output of the proposed design depends on the convergence of the Taylor approximation with increasing fitting parameters, which implies a sufficient number of HOD parameters must be included during numerical simulations. Four designs with different structural parameters are optimized for pumping, each operating at a different pump wavelength to test the convergence of output SC by the successive addition of HOD parameters. To realize spurious free SC spectral evolution by the proposed designs, HOD terms up to the sixteenth-order are included during all SC simulations. The proposed design can be used in molecular finger print spectroscopy, bio-medical imaging as well as various mid-infrared region applications.

Simulation of Brillouin gain properties in a double-clad As2Se3 chalcogenide photonic crystal fiber

The Brillouin gain properties in a double-clad As2Se3 photonic crystal fiber (PCF) are simulated based on the finite-element method (FEM). The results indicate that the Brillouin gain spectrum (BGS) of our proposed chalcogenide PCF exhibits a multipeaked behavior and has a high Brillouin gain coefficient. We also find that a larger size of inner cladding air holes will lead to a more pronounced second peak in the BGS. On the other hand, the size of the outer cladding has nearly no effect on the BGS behavior. Through these results, one can tailor the Stimulated Brillouin scattering effect in PCFs for a wide range of applications.

Single gain peak from modulation instability in As2Se3 chalcogenide glass photonic crystal fiber

With the As2Se3 photonic crystal fiber (PCF), the effect of pump power and wavelength on modulation instability (MI) gain is studied in detail. Due to high Raman scattering effect and high nonlinearity of As2Se3 PCF, ultra-broadband MI gain is obtained when appropriate pump power and wavelength is chosen, and the optimal MI gain bandwidth reaches 2812 nm. More importantly, competing between Raman scattering and four-wave mixing results in a single gain peak observed in the anti-Stokes region of As2Se3 PCF when pump power is higher than about 3000 W, while there is no gain spectrum in the fiber Stokes region. The phenomenon is found for the first time, and the obtained single gain peak mainly results from Raman scattering effect.

Coherent mid-infrared supercontinuum generation with As2Se3 photonic crystal fiber and femtosecond Airy pulses

We discuss a novel method for generating hyper-broadband mid-infrared (MIR) supercontinua (SC) with coherent bandwidth from ~2 μm to ~10 μm by using As2Se3 photonic crystal fiber (PCF) and a 4.1 μm pump with femtosecond (fs) Airy pulse profile. Our simulations confirm that, when pumping in the normal dispersion region, the deceleration and self-healing properties of the Airy pulse can suppress the incoherent noise in modulational instability (MI) induced SC generation and maintain the pulse coherence over a long propagation distance. We also find that fs Airy pulse can generate an MIR SC with a broader coherent bandwidth than these can be achieved with fs parabolic secant pulse.

2–10 μm mid-infrared supercontinuum generation in As2Se3 photonic crystal fiber

For the first time, we demonstrate that a hyper-broadband output from 2 to 10 μm can be generated with a high spectral flatness by using a ∼4 μm pump and an As2Se3 photonic crystal fiber. The broad and flat dispersion profile and the low guiding loss of the endlessly single-mode As2Se3 photonic crystal fibers, combined with the high nonlinearity and the wide mid-infrared transparent window of As2Se3 chalcogenide glass, are essential for this high performance mid-infrared laser source.

Generation of a mid-infrared broadband polarized supercontinuum in As2Se3 photonic crystal fibers

A simplified structure of birefringent chalcogenide As2Se3 photonic crystal fiber (PCF) is designed. Properties of birefringence, polarization extinction ratio, chromatic dispersion, nonlinear coefficient, and transmission are studied by using the multipole method, the finite-difference beam propagation method, and the adaptive split-step Fourier method. Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm, we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail, with femtosecond pulses at a wavelength of 4 μm as the pump pulses. Especially, mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm. Their spectral width at −20 dB reaches up to 12 μm. In the birefringent PCF, we find that the supercontinuum generation changes with the pump alignment angle. Research results show that no coupling between eigenpolarization modes are observed at the maximum average power (i.e., 37 mW), which indicates that the polarization state is well maintained.

Study of Self Phase Modulation in Chalcogenide Glass Photonic Crystal Fiber

In this paper, Self Phase Modulation (SPM) in chalcogenide As2Se3 glass Photonic Crystal Fiber (PCF) is numerically studied by combining the fully vectorial effective index method (FVEIM) and Split Step Fourier Method (SSFM). The FVEIM is used to calculate the variation of effective refractive index of guided mode (neff), effective area (Aeff), dispersion and non-linear coefficient (γ) with wavelength for different designs of chalcogenide As2Se3 PCF. The FVEIM solves the vector wave equations and SSFM solves non linear Schrödinger Equation (NLSE) for the different designing parameter of As2Se3 PCF. In case of Self Phase Modulation (SPM), spectral width of the obtained output pulse at d/Λ=0.7 is 1.5 times greater than width of the output pulse obtained at d/L=0.3 using SSFM. Thus we can get the desired spectral broadening just by tailoring the design parameters of the PCF.