Chalcogenide Photonic Crystal Fiber Research Articles

Nanoimprinting and tapering of chalcogenide photonic crystal fibers for cascaded supercontinuum generation.

Improved long-wavelength transmission and supercontinuum (SC) generation is demonstrated by antireflective (AR) nanoimprinting and tapering of chalcogenide photonic crystal fibers (PCFs). Using a SC source input spanning from 1 to 4.2μm, the total transmission of a 15μm core diameter PCF was improved from ∼53% to ∼74% by nanoimprinting of AR structures on both input and output facets of the fiber. Through a combined effect of reduced reflection and redshifting of the spectrum to 5μm, the relative transmission of light >3.5 μm in the same fiber was increased by 60.2%. Further extension of the spectrum to 8μm was achieved using tapered fibers. The spectral broadening dynamics and output power were investigated using different taper parameters and pulse repetition rates.

Numerical investigation on coherent mid-infrared supercontinuum generation in chalcogenide PCFs with near-zero flattened all-normal dispersion profiles**Project supported by the National Natural Science Foundation of China (Grant Nos. 61421002 and 61435003).

We design a novel all-normal flat near-zero dispersion chalcogenide photonic crystal fiber (PCF) for generating mid-infrared (MIR) supercontinuum (SC). The proposed PCF with a core made of As2Se3 glass and uniform air holes in the cladding is selectively filled with As2S5 glass. By carefully engineering the PCF with an all-normal flat near-zero dispersion profile, the anomalous-dispersion soliton effect is reduced, thus enabling broadband highly coherent SC to be generated. We also investigate the influence of the pulse parameters on the SC generation. Broadband SC covering with perfect coherence is achieved by pumping the proposed 3-cm-long PCF with 3- 100-fs pulses. The results provide a potential all-fiber realization of the broadband coherent MIR-SC.

Mid-infrared supercontinuum generation in dispersion-engineered highly nonlinear chalcogenide photonic crystal fiber

An [Formula: see text]-based chalcogenide highly nonlinear photonic crystal fiber (PCF) with concentric rings consisting of air-holes is proposed to achieve extraordinary flat and small chromatic dispersion in mid-infrared region. This is obtained by design and optimization of the PCF cross-sectional structure. The dispersion variation between ±[Formula: see text]5 ps/(nm[Formula: see text]km) is obtained over 800 nm bandwidth. Both the effective mode area and nonlinear coefficient of the proposed PCF within the whole wavelength range from [Formula: see text] to [Formula: see text] are investigated. Furthermore, the output supercontinuum (SC) optical spectra for different pump wavelengths located at the normal and abnormal dispersion region are investigated, respectively. The results show that the broadest SC with −20 dB spectral width of 1034 nm covering from [Formula: see text] to [Formula: see text] is obtained for the pump wavelength of [Formula: see text] with 100 fs secant hyperbolic pulse of the peak power of 10 kW. Our PCF design offers a low-cost SC source, which can find potential application in mid-infrared photonics.

Design and modelling of all-normal dispersion As39Se61 chalcogenide photonic crystal fiber for flat-top coherent mid-infrared supercontinuum generation

Abstract We report numerical investigation of mid-infrared supercontinuum (SC) generation in all-normal dispersion (ANDi) As39Se61 chalcogenide photonic crystal fiber (PCF). Numerical results, obtained by using the Finite-Difference Frequency-Domain (FDFD) method, indicate that desirable dispersion properties can be achieved by adjusting the air holes diameter and ANDi regime is obtained over the entire wavelength range with a PCF pitch and air holes diameter of 1.8 µm and 0.7 µm, respectively. Besides, the optimized design has a nearly zero dispersion wavelength of 3.45 µm and exhibits high Kerr nonlinearity of 5.89 w−1 m−1. By pumping 50 fs duration laser pulses at 3.45 µm, we demonstrate the generation of a broad, ultraflat-top and highly coherent SC spectrum extending from 2.43 µm to 4.85 µm at 4 dB spectral flatness and from 1.95 µm to 6.58 µm at 8 dB, by employing very low energy pulses of 50 pJ and 250 pJ, respectively. Owing to its remarkable optical characteristics, the proposed SC source based on As39Se61 chalcogenide glass PCF is found to be suitable for various potential mid-infrared applications such as optical coherence tomography, mid-infrared spectroscopy and metrology.

Generation of an ultrabroadband supercontinuum in the mid-infrared region using dispersion-engineered GeAsSe photonic crystal fiber

An ultrabroadband mid-infrared (MIR) region supercontinuum (SC) is demonstrated numerically through dispersion-engineered traditional chalcogenide (ChG) photonic crystal fiber (PCF). By varying structural parameters pitch (hole to hole spacing) and air-hole diameter to pitch ratio, a number of 10-mm-long hexagonal PCFs made employing GeAsSe ChG glass as a core and air-holes of hexagonal lattice running through their lengths as a cladding are optimized to predict an efficient mid-infrared region SC spectral emission by pumping them using a tunable pump source between 2.9 and 3.3 µm. Simulations are carried out using an ultrashort pump pulse of 100-fs duration with a low pulse peak powers of between 3 and 4 kW into the optimized designs. It is found through numerical analysis that efficient SC spectral broadening with flattened output can be obtained by increasing the PCF pitch rather than increasing the PCF cladding containing air-hole diameter although a larger nonlinear coefficient could be obtained through increasing air-hole diameter of an optimized design. Simulation results show that the SC spectra can be broadened up to 12.2 µm for a certain design with a peak power of 3 kW. Using a peak power of 4 kW, it is possible to obtain SC spectral broadening beyond 14 µm with an optimized design spanning the wavelength range from 1.8 to 14 µm which covers the electromagnetic spectrum required for MIR molecular fingerprint region applications such as sensing and biological imaging.

Mid-infrared broadband supercontinuum generation in a highly nonlinear rectangular core chalcogenide photonic crystal fiber

Abstract We report the numerical modeling of a highly nonlinear rectangular core Ga-Sb-S chalcogenide photonic crystal fiber for supercontinuum generation in the mid-infrared region. Numerical investigation of linear and nonlinear optical processes has been performed. A finite element method has been employed to study the optical characteristics of confined fundamental mode. Optimization of geometrical parameters i.e., pitch, the diameter of bigger and smaller air-holes has been done in order to achieve small and normal dispersion at the pump wavelength. The proposed design is capable of generating supercontinuum spanning 1–14 µm using a 9 mm long fiber pumped with 90 fs secant hyperbolic pulse of the peak power of 8.19 kW. Such photonic crystal fiber structure in Ga-Sb-S chalcogenide glass is reported the first time and can be proven effective for nonlinear applications of photonic devices.

Effects of a seed pulse on rogue-wave formation for midinfrared supercontinuum generation in chalcogenide photonic crystal fibers

We numerically study the characteristics of optical rogue waves (RWs) in midinfrared supercontinuum (MIR-SC) generation with a femtosecond pump in the anomalous dispersion regime of a chalcogenide photonic crystal fiber. An approach based on seed-induced modulation instability is used to regulate the formation of optical RWs. By carrying out multiple simulations in the presence of noise, we show that optical RWs can be generated in a more controlled manner by providing a seed with an optimum modulation frequency. The redshift range of optical RWs is expanded to a considerable extent in the seed-induced case rather than the noise-induced case. Furthermore, the increase of pump power can facilitate the redshift of optical RWs. These results demonstrate how a seed pulse affects the formation of optical RW for MIR-SC generation with a femtosecond pump in the anomalous dispersion regime of fiber, indicating that optical RW can be used to generate ultra-broadband MIR-SC.

Linearly chirped mid-infrared supercontinuum in all-normal-dispersion chalcogenide photonic crystal fibers.

We demonstrate all-normal dispersion supercontinuum generation in chalcogenide photonic crystal fibers pumped at 2070-2080 nm with a femtosecond fiber laser. At 2.9 kW peak power, the generated supercontinuum has a 3 dB bandwidth of 27.6 THz and -20 dB bandwidth of 75.5 THz. We experimentally investigated the supercontinuum evolution inside our sample fiber at various peak powers and fiber lengths and study the impact of fiber water absorption on the generated supercontinuum spectrum. Multiple tests with fiber length- ranging from 0.34 to 10 cm-provide insight on pulse evolution along fiber length. Our simulations, which utilizes the generalized nonlinear Schrodinger equation model, match perfectly the experiments for all tested pump powers and fiber lengths, and confirm that the output pulse has a linear chirp, allowing linear pulse compression.

Supercontinuum generation at 1.55 μm in As2S3 core photonic crystal fiber.

This paper proposes a design and mathematical study of As2S3 chalcogenide photonic crystal fiber (PCF) for broadband supercontinuum generation. The proposed design offers a large nonlinearity coefficient and ultra-flattened dispersion. The proposed design was analyzed using the full-vectorial finite element method. Through this method, it is shown that an ultra-broad supercontinuum spectrum of 0.8-4.5μm is attained using an As2S3 core PCF design with 20fs pump pulse width and a length of 10mm, having 3kW power at a -40 dB spectral and temporal intensity. The proposed octagonal PCF has shown a low zero dispersion wavelength at the pump wavelength of 1.55μm.

Mid-infrared dual-rhombic air hole Ge20Sb15Se65 chalcogenide photonic crystal fiber with high birefringence and high nonlinearity

We propose a mid-infrared dual-rhombic air hole hexagonal lattice photonic crystal fiber with high birefringence and large nonlinearity based on Ge20Sb15Se65 chalcogenide glass. The properties of birefringence, dispersion, nonlinearity, and confinement loss were investigated in the 3 µm~5 µm mid-infrared range by using the Finite Difference Time Domain (FDTD) method with perfectly matched layer (PML) absorption boundary conditions. The results indicate that for the optimized structural parameters of Λ= 2.0 µm, D= 1.932 µm, d= 0.8 µm, and H= 0.8 µm, an ultrahigh birefringence of 0.041, a very low confinement loss of 0.0013 dB/km (for x-polarization modes) and 0.0342 dB/km (for y-polarization modes), and the maximum nonlinearity coefficient of 4375 w−1km−1 (for x-polarization modes) and 3960 w−1km−1 (for y-polarization modes) were achieved, respectively. The proposed PCF has a lower confinement loss and higher birefringence than an elliptical-hole PCF with the same air-filling fraction. Thus, it will be an excellent candidate for mid-infrared optical fiber sensing, precision optical instruments and nonlinear optics.

Mid-infrared multispectral tissue imaging using a chalcogenide fiber supercontinuum source.

We present, to the best of our knowledge, the first demonstration of mid-infrared supercontinuum (SC) tissue imaging at wavelengths beyond 5μm using a fiber-coupled SC source spanning 2-7.5μm. The SC was generated in a tapered large-mode-area chalcogenide photonic crystal fiber in order to obtain broad bandwidth, high average power, and single-mode output for diffraction-limited imaging performance. Tissue imaging was demonstrated in transmission at selected wavelengths between 5.7 (1754 cm-1) and 7.3μm (1370 cm-1) by point scanning over a sub-millimeter region of colon tissue, and the results were compared to images obtained from a commercial instrument.

All-Normal Dispersion Chalcogenide PCF for Ultraflat Mid-Infrared Supercontinuum Generation

We numerically study the dispersion-engineered chalcogenide photonic crystal fiber (PCF), which allows us to generate ultraflat broadband supercontinuum (SC) spectra in all-normal dispersion regime. A 1-cm-long chalcogenide hexagonal PCF made using Ge11.5As24Se64.5 glass pumped at $1.55~\mu \text{m}$ produced an SC bandwidth 700 nm at a peak power of 1 kW. By shifting pump at $2~\mu \text{m}$ , SC spectra can be extended with a bandwidth of 1900 nm at the same peak power level. In both cases, nonuniform spectral power distribution observes over the entire output bandwidth owing to the lower dispersion slop on the long wavelength side of the dispersion curve. To spanning SC further in the mid-infrared as well as to reduce the spectral asymmetry, we optimize another design for pumping at 3.1 $\mu \text{m}$ in such a way that the pump source can be employed vicinity to the peak of the dispersion curve. Employing the largest pump peak power up to 5 kW, SC can be extended up to 6 $\mu \text{m}$ (1.5 octaves), and the power distribution among the spectral components over the entire SC bandwidth can be improved significantly by this design. To enhance the spectral flatness, we optimize a second PCF geometry by reducing its pitch length, and it is possible to obtain ultraflat coherent SC spanning from 2 to 5.5 $\mu \text{m}$ (>1 octave) by this structure maintaining nearly symmetric power distribution between both side of its spectral components.

Increased mid-infrared supercontinuum bandwidth and average power by tapering large-mode-area chalcogenide photonic crystal fibers.

The trade-off between the spectral bandwidth and average output power from chalcogenide fiber-based mid-infrared supercontinuum sources is one of the major challenges towards practical application of the technology. In this paper we address this challenge through tapering of large-mode-area chalcogenide photonic crystal fibers. Compared to previously reported step-index fiber tapers the photonic crystal fiber structure ensures single-mode propagation, which improves the beam quality and reduces losses in the taper due to higher-order mode stripping. By pumping the tapered fibers at 4 μm using a MHz optical parametric generation source, and choosing an appropriate length of the untapered fiber segments, the output could be tailored for either the broadest bandwidth from 1 to 11.5 μm with 35.4 mW average output power, or the highest output power of 57.3 mW covering a spectrum from 1 to 8 μm.

Mid-infrared supercontinuum generation in multimode As2 Se3 chalcogenide photonic crystal fiber.

We rigorously investigated the mid-infrared supercontinuum generation in a multimode As2Se3 chalcogenide photonic crystal fiber (PCF). We studied the impact of the intermodal nonlinear effects on the nonlinear propagation of the fundamental and high-order modes. By solving the multimode generalized nonlinear Schrödinger equation, we have predicted the generation of a very broadband supercontinuum in both polarizations of the fundamental mode spanning from 2 to 11μm at -20 dB in only 5cm PCF length. The proposed study confirms that the energy transfer occurs only between the optical degenerate modes when propagating in the multimode chalcogenide PCF in the mid-infrared region.

Super-flat coherent supercontinuum source in As38.8Se61.2 chalcogenide photonic crystal fiber with all-normal dispersion engineering at a very low input energy.

We numerically report super-flat coherent mid-infrared supercontinuum (MIR-SC) generation in a chalcogenide As38.8Se61.2 photonic crystal fiber (PCF). The dispersion and nonlinear parameters of As38.8Se61.2 chalcogenide PCFs by varying the diameter of the air holes are engineered to obtain all-normal dispersion (ANDi) with high nonlinearities. We show that launching low-energy 50 fs optical pulses with 0.88 kW peak power (corresponding to pulse energy of 0.05 nJ) at a central wavelength of 3.7 μm into a 5 cm long ANDi-PCF generates a flat-top coherent MIR-SC spanning from 2900 to 4575 nm with a high spectral flatness of 3 dB. This ultra-wide and flattened spectrum has excellent stability and coherence properties that can be used for MIR applications such as medical diagnosis of diseases, atmospheric pollution monitoring, and drug detection.

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.

SBS based slow-light generation in rectangular lattice graded-index photonic crystal fiber: Design and analysis

Theoretical analysis of stimulated Brillouin scattering based slow-light in As2Se3 based chalcogenide photonic crystal fiber has been reported. A maximum time-delay of 252.8ns has been achieved for 1m long fiber at input pump power of 9.8mW. A maximum gain of 99dB/m has been obtained for the same input pump-power. The simulated results indicate that the time-delay can be tuned by varying the input pump-power and the size of the air holes to obtain tunable features. We feel that the comprehensive theoretical investigation carried out in this paper have potential impact in the design and development of slow-light based photonic devices.

Circular Lattice Photonic Crystal Fiber for Mid-IR Supercontinuum Generation

This letter introduces specific design features of a proposed chalcogenide photonic crystal fiber for ultra-wideband supercontinuum generation in the mid-infrared region. The fiber is optimized to include a circular photonic crystal lattice having tremendous potential in the fields of spectroscopy, food quality control, pulse compression, gas sensing, and various nonlinear applications. By tailoring the zero-dispersion wavelength up to 2 and 2.5 μm, we have reached supercontinuum generation in the anomalous dispersion regime with the entire design hinging upon fibers based on two types of chalcogenide glass-arsenic-selenide and arsenic-sulfide, where supercontinuum broadening from 1.2 to 9.3 μm is made possible.

Numerical Investigation of Mid-Infrared Supercontinuum Generation in GeAsSe Based Chalcogenide Photonic Crystal Fiber Using Low Peak Power

We numerically investigate the use of photonic crystal fiber (PCF) through dispersion engineering of its cladding containing air-holes for supercontinuum (SC) generation in the mid-infrared region using low peak power. A 3.6-cm-long PCF made using Ge11.5As24Se64.5 chalcogenide (ChG) glass with a hexagonal array of air-holes was optimized for obtaining zero-dispersion wavelength through dispersion tailoring around the pump wavelength of 4 μm. We have performed numerical simulations for such dispersion tailored ChG PCF with the peak power range between 0.25 kW and 2 kW. It was found through rigorous numerical simulations that an ultrabroadband mid-infrared SC spectra covering the wavelength range 2-8 μm which is equivalent to 2 octaves could be generated using pump pulses of 320 fs duration at a wavelength of 4 μm with a relatively low peak power of 2 kW by using our proposed ChG PCF design.

Characterization and modeling of microstructured chalcogenide fibers for efficient mid-infrared wavelength conversion.

We experimentally demonstrate wavelength conversion in the 2 µm region by four-wave mixing in an AsSe and a GeAsSe chalcogenide photonic crystal fibers. A maximum conversion efficiency of -25.4 dB is measured for 112 mW of coupled continuous wave pump in a 27 cm long fiber. We estimate the dispersion parameters and the nonlinear refractive indexes of the chalcogenide PCFs, establishing a good agreement with the values expected from simulations. The different fiber geometries and glass compositions are compared in terms of performance, showing that GeAsSe is a more suited candidate for nonlinear optics at 2 µm. Building from the fitted parameters we then propose a new tapered GeAsSe PCF geometry to tailor the waveguide dispersion and lower the zero dispersion wavelength (ZDW) closer to the 2 µm pump wavelength. Numerical simulations shows that the new design allows both an increased conversion efficiency and bandwidth, and the generation of idler waves further in the mid-IR regions, by tuning the pump wavelength in the vicinity of the fiber ZDW.