Chalcogenide Fiber Research Articles

Coherent Mid-IR Supercontinuum Generation using Tapered Chalcogenide Step-Index Optical Fiber: Experiment and modelling

Mid-infrared region of electromagnetic spectrum has increased a lot of scientific and technical interest because of its utility to figure out the molecular fingerprints. Current mid-infrared light sources including quantum cascade lasers, thermal-emitters, and synchrotron radiation are not suitable for various potential applications where we require coherent, portable and broadband light sources. During the current decade, several efforts have been put forwarded to extend the spectral range of the supercontinuum. However, the coherent mid-infrared supercontinuum spectrum in the mid-infrared region has been demonstrated rarely. Here, we demonstrate a coherent mid-infrared supercontinuum using a tapered chalcogenide fiber pumped at various wavelength ranging from 2 µm to 2.6 µm. Experimental observations show that the supercontinuum spectrum extending from ~1.6 µm to 3.7 µm can be achieved using a 3 cm long tapered chalcogenide step-index optical fiber pumped with femtosecond laser pulses at 2.6 µm. To the best of our knowledge, using short pump wavelengths at 2 µm to 2.6 µm in an all-normal dispersion engineered chalcogenide glass fiber, the coherent supercontinuum spectrum has been reported first time. Such coherent broadband light source has its key prominence for the various prospective applications in the fields of bio-medical, sensing, and multiplex coherent anti-Stokes Raman scattering microspectroscopy.

Investigation of tellurium-based chalcogenide double-clad fiber for coherent mid-infrared supercontinuum generation

Abstract Considerable investigations have been carried out for chromatic dispersion tailoring of chalcogenide glass fiber with various structures and different material compositions. Here we proposed a tellurium-based chalcogenide glass fiber with a dual-clad structure in a W-type refractive-index profile. The structure of the fiber based on Ge-As-Se-Te glasses was numerically analyzed in detail. The simulation results indicate that an all normal dispersion profile can be realized in this tellurium glass fiber with an optimized dual-cladding structure. Then the optimized tellurium chalcogenide fiber with an all-normal dispersion profile was fabricated by multi-extrusion method. Pumping with a 5 μm ultra-short pulsed laser (150 fs, 1 kHz), abroadband supercontinuum (SC) covering 1.5–11 μm can be generated in the 19 cm-long fiber. The coherence of SC was also investigated by numerical simulation. The result shows that a high coherent SC covering 3.5–10.5 μm can be generated in this all-normal dispersion fiber. In conclusion, all-normal dispersion profile can be realized easily in this tellurium-based glass fiber due to their large materials ZDWs.

Milliwatt-Level Spontaneous Emission Across the 3.5–8 µm Spectral Region from Pr3+ Doped Selenide Chalcogenide Fiber Pumped with a Laser Diode

A spontaneous emission fiber source operating in the mid-infrared (MIR) wavelength range from 3.5 to 8 µm is demonstrated for the first time at output power levels of at least 1 mW. The source is a Pr3+-doped selenide chalcogenide, multimode, glass fiber pumped with commercially available laser diodes operating at 1.470 µm, 1.511 µm and 1.690 µm. This MIR spontaneous emission fiber source offers a viable alternative to broadband mid-infrared supercontinuum fiber sources, which are comparatively complex and costly. The MIR emission wavelength range is significant for molecular sensing applications across biology and chemistry, and in medicine, agriculture, defense, and environmental monitoring.

Triangular pulse generation by using chalcogenide fibers and creation of tunable High frequency oscillations from the Interaction of reshaped pulse pair

Designing few normal dispersion chalcogenide fibers leads to obtain a Normal Dispersion Decreasing Chalcogenide Fiber with a value of group velocity dispersion (β2) varying from ∼ 240.45 ps2/km to 221.52 ps2/km and nonlinear coefficient (γ) within a range from ∼ 62.82 W−1 km−1 to 108.17 W−1 km−1 throughout a fiber length of 75 m. The so designed fiber is preferable for generation of Triangular Pulse at relatively shorter optimum length (Lopt) when compared to previously reported works. Such reshaped pairs of triangular pulses interact as their tails start to overlap while propagating through the fiber and generates high frequency (∼THz) oscillating pulse train. This frequency can be easily altered in a controlled manner by carefully changing the propagation length or the separation between the input pulse pair. The so designed fiber alongwith the optimum input pulse parameters can be potentially applied in the domain of tunable high frequency pulse generators along with many standard applications of TP.

Chalcogenide Taper and Its Nonlinear Effects and Sensing Applications.

The nonlinear coefficient of chalcogenide glass is 200–1000 times larger than that of silica glass, and it is transparent in the 1–15 μm wavelength windows, which makes the nonlinear effects happen at much low power with a short length in near- and mid-infrared wavelength window. With tapered chalcogenide fibers, the power density in the core and the waveguide nonlinearity can be enhanced to make nonlinear signal processing unit at a compact size. The threshold of Raman scattering and supercontinuum generation is reduced due to the enhanced Kerr effect and enhanced optical power intensity. Phase-matching condition required in four-wave mixing (FWM) can be realized by tailoring fiber structures to engineer the chromatic dispersion, which enables new wavelengths creation over a large range at mW power and sub-meter length. The guided acoustic waves and longitudinal acoustic waves can be generated and detected in mW power with chalcogenide tapers. The high power density in the microwires and the high photosensitivity of chalcogenide glass in the 1550 nm band enable the inscription of FBGs in the fiber directly. The chalcogenide microwires are fragile and the core diameter cannot be tapered down to sub-microns, which can be mitigated by polymer coating that can provide mechanical strength. Polymers not only provide high mechanical strength as the coating and cladding materials but also bring over 10 times larger thermal expansion than chalcogenide cores, which enhances the sensor prospect of the chalcogenide fibers for temperature, strain, and acoustic sensing. This work reviews the present and emerging trends in investigation of chalcogenide tapers, mainly focusing on the fabrication procedure of chalcogenide microwires, the nonlinear effects, and sensing applications.

A numerical method for pulse propagation in nonlinear fiber Bragg grating with ternary stability nature

Abstract Optical bistability and multistability are often produced in nonlinear media. Although continuous wave (CW) bistability and multistability have widely studied, solution of the nonlinear pulse propagation equations is rarely studied and practiced in bistable and ternary stable systems. In such systems, the history of the pulse should be considered for equation solving. In the present paper, the pulse propagation through the ternary nonlinear chalcogenide fiber Bragg grating is numerically investigated. A novel numerical method is proposed for solving the above mentioned problem using Fourier and inverse Fourier transform as well as dividing the Gaussian input pulse into two intervals which leads to the simplicity of hysteresis and time domain problems. As a result, an algorithm is suggested for solving nonlinear pulse propagation equation in bistable and ternary stable systems and the output pulse is obtained. This method can also be applied on various pulses of different shapes travelling through the other types of Fiber Bragg grating like chirped, phase-shifted, etc. Optical multistability systems are the main building blocks for designing all-optical pulse processing, all-optical memory and all-optical switching.

High-power supercontinuum generation in the mid-infrared pumped by a soliton self-frequency shifted source.

We report the demonstration of a fiber-based supercontinuum source delivering up to 825 mW of average output power between 2.5 and 5.0 µm generated in all-normal dispersion regime. The pumping source consists of an amplified ultrafast Er3+:ZrF4 fiber laser providing high peak power femtosecond pulses at 3.6 µm with an average output power exceeding the watt-level. These pulses are spectrally broadened through self-phase modulation using commercial chalcogenide-based step-index fibers. Al2O3 anti-reflection coatings were sputtered on chalcogenide fiber tips to increase the launching efficiency from 54% to 82%, making this record output power possible, and thus confirming that such coatings can support watt-level pumping with intense femtosecond pulses. To the best of our knowledge, this result represents the highest average output power ever achieved from a As2Se3-based mid-IR supercontinuum source with the potential of a high degree of coherence.

Structured active fiber fabrication and characterization of a chemically high‐purified Dy3+‐doped chalcogenide glass

AbstractBy conventional melt‐quenching techniques, a series of Dy3+‐doped (0.1 to 1.0 wt%) Ga5Ge20Sb15S60 bulk glasses were fabricated and their potential for developing mid‐infrared fiber laser beyond 4 μm were evaluated, in which the optimal Dy3+ doping concentration was found to be 0.3 wt% and the largest laser quality factor value (σe × τmea = 2.62 × 10−23 cm2 s) among all of the Dy3+‐doped chalcogenide glass was obtained. On this basis, through using the chemical purification methods with chlorine gas combined with the dynamic distillation process, the high‐purity GGSS glasses with low O–H and S–H absorptions were successfully fabricated, which was confirmed by the optimized mid‐infrared linear transmittance and improved fluorescent lifetimes of Dy3+: 6H13/2, 6H11/2 levels. Furthermore, for the first time to the best of our knowledge, the Dy3+‐doped, single‐mode, and double‐cladding chalcogenide fibers with the core/cladding ratios of 125:60:11 and 125:66:11.5 were achieved by a multistage rod‐in‐tube fiber drawing process and extrusion methods, respectively. The GeS2‐based fiber exhibits excellent transmission performance at 1.0‐5.0 μm: 3.0 dB/m at 2.9 μm (O–H), 2.4 dB/m at 4.1 μm (S–H). Combining the advantages of high‐purity, high doping concentration and single‐mode double‐cladding structure, the optimized active fiber should be an ideal efficient and low‐threshold medium toward mid‐infrared fiber laser beyond 4 μm.

All-Optical Ternary Stability in Uniform Nonlinear Chalcogenide Fiber Bragg Gratings

All-Optical Ternary Stability in Uniform Nonlinear Chalcogenide Fiber Bragg Gratings

Numerical study on mid-infrared optical parametric amplification around 5 µm by injecting signal vector beams in As2Se3 MOFs

The influence of the core diameter and pump wavelength on the phase-matching conditions when different signal vector beams are injected is analyzed numerically in a suspended-core ${{\rm As}_2}{{\rm Se}_3}$As2Se3 microstructured optical fiber (MOF). The idler wavelengths satisfying the phase-matching conditions with different signal vector beams can reach wavelengths of 4.8–5.9 µm in the ${{\rm As}_2}{{\rm Se}_3}$As2Se3 MOFs with different core diameters. By changing the signal vector mode field and adjusting the corresponding signal wavelength, the idler wavelength can be tuned in 754.8 nm from 4.9182 to 5.6730 µm with the pump wavelength changing from 2.80 to 2.90 µm. The influence on signal gain and the idler conversion efficiency is calculated in the ${{\rm As}_2}{{\rm Se}_3}$As2Se3 MOFs with different lengths when injecting different signal vector beams. The peak gain of signal and idler conversion efficiency can reach $\sim{28}\,\, {\rm dB}$∼28dB and $\sim{24}\% $∼24%, respectively, when the different signal vector beams are injected. The simulated results demonstrate that the optical parametric oscillation with wavelengths longer than 5 µm can be realized in chalcogenide fibers with signal vector beam injection.

All-solid mid-infrared chalcogenide photonic crystal fiber with ultralarge mode area.

In this Letter, we report, to the best of our knowledge, the largest effective single-mode mid-infrared chalcogenide (ChG) fiber. Two thermally matched ChG glasses with a large index contrast of ∼0.35 are chosen for constructing all-solid photonic crystal fiber (PCF) with two rings of "holey" microstructured cladding. Single-mode operation is confirmed in the fabricated ChG PCF with a core diameter of 91.2μm, from both near-field and far-field observation at 4μm. Ultralow numerical aperture of <0.025 has been observed at wavelengths between 2.5 and 4.0μm. The fundamental mode area is calculated to be 5200 μm2 at 4μm, where the propagation loss of the ChG PCF is measured to be 5.2dB/m. Broadband 3.5 and 7.5μm supercontinuum has been generated in a 35-cm-long ultralarge-mode-area PCF.

1.2-15.2 μm supercontinuum generation in a low-loss chalcohalide fiber pumped at a deep anomalous-dispersion region.

A novel low-loss selenium-based chalcohalide fiber, with a low zero-dispersion wavelength, was prepared by an innovative preparation process. The composition optimized fiber has a wide transmission range of up to 11.5μm, a lowest fundamental mode zero-dispersion wavelength of 4.03μm, and a minimum optical loss of 1.12dB/m at 6.4μm, which provides a possibility to replace As2S3 and As2Se3 in a cascade of ZrF4-BaF2-LaF3-AlF3-NaF(ZBLAN)-As2S3-As2Se3 fiber in the practical all-fiberized supercontinuum (SC) source. Meanwhile, the broadest SC spectrum, ∼1.2 to 15.2μm, was achieved by pumping a 12-cm-long fiber with a femtosecond laser at a deep anomalous-dispersion region. Furthermore, simulations are adopted to interpret the results as well as to demonstrate spectral evolution along the fiber. To the best of our knowledge, this is the broadest SC spectrum reported in any selenium-based chalcogenide fiber.

Dy3+ doped GaGeSbSe fiber long-wave infrared emission

We report on the mid-wave infrared (MWIR) and long-wave infrared (LWIR) emissions of a 1000 ppm Dy3+ doped Ga5Ge20Sb10Se65 chalcogenide fiber. Following a short-wave infrared (SWIR) optical pumping at 0.92, 1.12 and 1.32 μm using commercial laser diodes, LWIR luminescence around 7.3 μm (6H7/2 → 6H9/2 transition) was recorded for the first time to the best of our knowledge along with MWIR emissions around 4.3 μm and 5.4 μm with a Dy3+ doped Ga5Ge20Sb10Se65 fiber. Frequency dependent spectroscopic investigation clearly shows that this LWIR luminescence originates from the 6H7/2 manifold. Spectroscopic properties of this Dy3+ doped material and the comparison with its equivalent sulfide Dy3+:Ga5Ge20Sb10S65 glass are presented.

Fabrication and characterization of multimaterial Ge25Se10Te65/As2S3 chalcogenide fiber with a high value of the numerical aperture

The design and fabrication of a novel multimaterial Ge25Se10Te65/As2S3 chalcogenide glass fiber with ultra-high numerical aperture (NA) by using the rod-in-tube method was reported. The NA of fiber of approximately 2.2 is the maximum NA of step-index chalcogenide fibers obtained experimentally. The Ge25Se10Te65 glass was selected as the core material, and its mechanical and thermal properties were investigated. The optical properties and bending strength were measured to investigate fiber performance. The low bending loss of fiber was demonstrated through a simulation and an experiment. The fundamental dispersion characteristic, effective-mode-area, and nonlinear coefficient of fiber were simulated numerically.

Midinfrared Compatible Tunable Bandpass Filter Based on Multimode Interference in Chalcogenide Fiber

We demonstrate a mid-infrared compatible tunable bandpass filter that consists of a singlemode-multimode-singlemode fiber structure, made from chalcogenide fibers. Experiments have been carried out using step-index multimode fibers with small core radius, resulting in a continuous wavelength tunability >52 nm and a hop wavelength tunability of 84 nm, via mechanical bending. Core to core lateral offsets at input and output interfaces between singlemode fibers and multimode fiber are optimized to maximize the extinction ratio and set a desired transmission wavelength. Transmission characteristics of the multimode interference effect and design rules of a widely tunable filter are also presented.

Simulation and Comprehensive Analysis of Fluoride Fiber SPR Sensor With Multilayer Variants of 2D Materials (Graphene and MoS2) Under Optimum Radiation Damping in NIR

The performance of multiple variants of fluoride fiber plasmonic sensor is simulated and analyzed under optimum radiation damping (ORD) in terms of coordinated tuning of Ag layer thickness ( $\text{d}_{\mathbf {Ag}}$ ) and near infrared (NIR) wavelength ( $\lambda $ ). The sensor variants are in terms of number of monolayers (N: 1 – 5) of graphene and MoS2. The dispersion relations of all constituent layers along with the transfer matrix method are utilized for sensor simulation. The sensor’s performance is evaluated in terms of figure of merit (FOM) that takes into account the shift and width of fiber power loss resonance curves originating under the plasmonic modulation. Further totality is added to performance evaluation by combining the FOM with signal scattering and power loss ratio factors. The simulation results and their comprehensive analysis indicate that a combination of $\lambda =925.3$ nm, $\text{d}_{\mathbf {Ag}} =48.4$ nm, and MoS2 monolayer can provide considerably enhanced performance in terms of maximum FOM, small light signal scattering (and analyte photodamage), and large power loss ratio (with respect to the reference resonance curve). The FOM achievable with this sensor is 4.5 times better than the previously reported chalcogenide fiber plasmonic sensor under its corresponding ORD. A deeper analysis of the proposed fluoride sensor predicts that even smaller signal scattering (and photodamage) along with nearly identical power loss ratio and FOM can be achieved with the sensor variant based on MoS2 bilayer.

Mid-infrared supercontinuum generation in chalcogenide fibers with high laser damage threshold.

Laser damage thresholds (Ith) at 1.03 µm, as well as third-order nonlinear refractive indices (n2) and two photon absorption coefficients (β) at 1.55 µm of a number of Ge-As-S glasses were measured and systematically studied. The glass with the composition Ge0.12As0.24S0.64 showed a high Ith and the maximum figure of merit (fm= n2/(β·λ)), and therefore was selected as the core material for the fabrication of a step-index fiber. A compatible glass with the composition Ge0.18As0.1S0.72 was chosen as the cladding material. Based on the dispersion calculations, the fiber with a core diameter of ∼7-10 µm was designed. The designed fiber was fabricated by a multiple step rod-in-tube method. When the fiber with a core diameter of ∼9 µm and a length of ∼13.5 cm was pumped by ∼170 fs pulses (1 MHz) at 4.5 µm, the mid-infrared supercontinuum (SC) covering 1.3-8.1 µm was generated. These results demonstrate the good potential of Ge-As-S chalcogenide fibers for producing high-brightness broadband mid-infrared SC light sources.

Numerical demonstration of widely tunable femtosecond soliton generation in chalcogenide microstructured fibers

We numerically investigated widely tunable femtosecond solitons spanning from 4.1 to 7.2 µm in designed chalcogenide fibers with two rings of air holes. The core was made of Ge15Sb15Se70 glass and the cladding glass was composed of Ge20As15S65. By using a 4.1 µm fiber laser with a pulse width of 100 fs as the pump light and 1 m long chalcogenide microstructured fibers as the nonlinear media, widely tunable femtosecond solitons spanning from 4.1 to 7.2 µm were observed, and the pulse width of these tunable Raman solitons remained below 150 fs. The efficiencies of the mid-infrared soliton could be up to over 80%, ranging from 4.1–6.8 µm. Through numerical simulations, we also observed red-shifted dispersive waves varying from 10.2 to 8.9 µm. Our simulated results show that the designed chalcogenide microstructured fibers are promising nonlinear media for generating tunable mid-infrared light sources.

Efficient coupling of a quantum cascade laser to a few-mode chalcogenide fiber.

We report efficient coupling of a quantum cascade laser (QCL) into step-index chalcogenide fibers (As 2S 3). Mechanically robust and low-loss chalcogenide fibers were fabricated using a hybrid, multi-material thermal drawing process. With suitable free-space optics, more than 160 mW of optical power was coupled into the fiber with predominantly single-mode excitation. Antireflection coatings on the fiber facets enabled 88.9% transmission with strong core confinement. By accurately tailoring the core diameter and antireflection-coating thickness, these fibers offer a versatile platform for high-power and low-loss transmission across the infrared spectrum. This work introduces an attractive alternative to the use of hollow-core fibers or multimode solid-core fibers for diffraction-limited infrared beam delivery.

Extruded seven-core tellurium chalcogenide fiber for mid-infrared

A novel tellurium chalcogenide (ChG) multicore fiber has been fabricated via extrusion for the first time. The fiber has seven cores in a hexagonal structure, with one center core surrounded by six other ones. The loss of the fiber is less than 3.5 dB/m in a range of 5-11 µm, and the minimum optical loss is 0.38 dB/m at 6 µm. When light is coupled to each core, the maximum transmission power is up to 1.1 W at 10.6 µm. Supercontinuum spectrum covering 2-12 µm at a bandwidth of -30 dB has been demonstrated. This tellurium ChG multicore fiber shows great potential in the field of high-power laser propagation and wide supercontinuum generation in the mid-infrared.