Mid-infrared Supercontinuum Generation Research Articles

Exploiting dispersion of higher-order-modes using M-type fiber for application in mid-infrared supercontinuum generation

M-type fibers have the exceptional property that the higher-order LP0n modes are core-confined and easily excited, while the LP01 and other modes are confined to a high-index ring surrounding the core, so they are not easily excited. This has profound consequences for mid-infrared supercontinuum sources, where the high zero-dispersion wavelength of chalcogenide and ZBLAN fibers means that exotic pump sources have so far been necessary. We show here that in chalcogenide and ZBLAN M-type fibers the lower ZDW of the core-confined higher-order LP02 mode can be in the range of 2 to 3 µm (around 1.55 µm), while the fiber still has a large core diameter and thus supports high average power. This will allow established pump laser technology to be used in future high-power mid-infrared supercontinuum sources.

Mid-infrared two-octave spanning supercontinuum generation in a Ge–Se–Te glass suspended core fiber

We report on both the fabrication and the application of a Ge–Se–Te glass-based suspended core fiber for mid-infrared supercontinuum generation. A two-octave spanning mid-infrared light source (from 3.25 to 13 µm) is experimentally demonstrated by pumping the chalcogenide fiber with sub-100 fs pulses at 8.6 µm. Numerical simulations of nonlinear pulse propagation as well as fiber properties are also provided and support experimental measurements.

Chalcogenide glass fibers with a rectangular core for polarized mid-infrared supercontinuum generation

A step-index chalcogenide fiber with a rectangular core and a circular cladding was fabricated through an approach that combines an extrusion technique and a multiple-stage rod-in-tube method. This fiber has a Ge12As24Se64 glass core with a size of ~2.8 μm × 5.9 μm, and a Ge10As24S66 glass cladding with a diameter of ~220 μm, and shows a relatively large birefringence. When ~10 cm long fiber was pumped at 4.0 μm with 330 fs pulses, ~2.2–9.5 μm supercontinuum with a flatness of 20 dB and a polarization extinction ratio of ~10 dB was generated.

Monolithic all-fiber mid-infrared supercontinuum source based on a step-index two-mode As2S3 fiber**Project supported by the National Natural Science Foundation of China (Grant Nos. 61435009, 61235008, and 61405254).

We demonstrate efficient supercontinuum generation extending into mid-infrared spectral range by pumping a two-mode As2S3 fiber in the normal dispersion regime. The As2S3 fiber is fusion spliced to the pigtail of a near-infrared supercontinuum pump source with ultra-low splicing loss of 0.125 dB, which enables a monolithic all-fiber mid-infrared supercontinuum source. By two-mode excitation and mixed-mode cascaded stimulated Raman scattering, a supercontinuum spanning from to is obtained. Over 70% of the supercontinuum power is converted to wavelengths beyond m. This is the first experimental report with respect to the multimode mid-infrared supercontinuum generation in a step-index two-mode chalcogenide fiber.

Ultra-efficient, 10-watt-level mid-infrared supercontinuum generation in fluoroindate fiber.

A 10-watt-level mid-infrared supercontinuum (SC) spanning 0.8-4.7μm with ultra-high-power conversion efficiency is generated in a piece of fluoroindate (InF3) fiber. The pump laser is a master oscillator power amplifier system seeded by a mode-locked fiber laser operating at 1956nm with pulse repetition rate and pulse duration of 33MHz and 60ps, respectively. A piece of InF3 fiber is fusion spliced to the output end of the pump light source with a low fusion splicing loss of 0.12dB. An endcap made of multimode aluminum fluoride fiber is used to protect the fiber tip from possible optical or thermal damage. Benefiting from the fiber endcap as well as the low-loss splicing joint between silica and InF3 fiber, high-power SC generation is achieved with maximal output power of 11.3W. Furthermore, the long wavelength edge of the obtained SC spectrum is extended to 4.7μm. This Letter, to the best of our knowledge, not only demonstrates the first 10-watt-level SC generation in InF3 fibers, but also achieves record power conversion efficiency of 66.5% among reported 10-watt-level fluoride-fiber-based SC laser sources.

Generation of 35 kW peak power 80 fs pulses at 2.9 μm from a fully fusion-spliced fiber laser.

Tunable femtosecond light sources in the short wave and middle wave infrared regions are of utmost importance for various applications ranging from multiphoton microscopy, mid-infrared supercontinuum generation to high-harmonic generation. We report on an all-fusion-spliced fiber laser emitting 80fs pulses up to 2.9μm with 35kW peak power. The laser is based on Raman self-frequency shift effect from 1560nm up to 3000nm in germanium-doped fibers fabricated by the widespread modified chemical vapor deposition process.

Mid-infrared supercontinuum generation and its application on all-optical quantization with different input pulses**Project supported by the National Natural Science Foundation of China (Grant Nos. 61307109 and 61475023).

Supercontinuum generation (SCG) and its application on all-optical quantization of all-optical analog-to-digital conversions (AOADCs) at the mid-infrared region in an AlGaAs strip waveguide are investigated numerically. The simulation results show that when the parabolic pulse is input, not only broader and higher-coherence SCG is obtained and a higher effective number of bits (ENOB) can be achieved, compared with the input pulse with hyperbolic-secant and Gaussian shaping. A four-bit quantization resolution is achieved along with a signal-to-noise ratio of 24.02 dB and an ENOB of 3.99 bit, and the required input peak power is 760 mW.

Ultrabroadband and coherent mid-infrared supercontinuum generation in Te-based chalcogenide tapered fiber with all-normal dispersion.

We demonstrated an ultrabroadband supercontinuum (SC) generation with high coherence property in all-normal-dispersion (ANDi) Te-based chalcogenide tapered fiber. The fibers made of Ge20As20Se15Te45 core and Ge20As20Se20Te40 cladding glasses were fabricated via isolated stacked extrusion. The waist diameter and length can be accurately controlled by a homemade tapering platform. When the core diameter of the waist was ≤14 μm, the fiber showed an ANDi characteristic in the wavelength range of 1.7-14 μm. A coherent SC generation covered 1.7-12.7 μm was generated in a 7-cm-long tapered fiber, pumped at 5.5 μm. To the best of our knowledge, this is the first SC experimental demonstration in Te-based step-index tapered fiber and the broadest SC generation in chalcogenide tapered fiber when pumped in the normal dispersion regime so far.

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.

Mid-infrared supercontinuum generation in chalcogenide optical fibers

The spectral characterization of mid-infrared supercontinuum generation (SC) is studied in a highly nonlinear suspended-core As2S3 microstructure optical fiber pumped by different laser sources (The pulse duration can be ranged from femtosecond to picosecond). Spectra from 1 to 6.5 μm are obtained by using picosecond pulse. The SC generation has been analyzed with different pumping wavelengths. It has been demonstrated that the longer wavelength can be broadened to 7 μm. When the pumping wavelength is around 2.3 μm (near the zero dispersion wavelength), a flat SC spectrum is obtained. We expect these results will help to design a flat mid-infrared SC in real experimental work.

Mid-infrared supercontinuum generation from 2 to 14 μm in arsenic- and antimony-free chalcogenide glass fibers

We demonstrate the fabrication of arsenic-and antimony-free chalcogenide glasses compatible with glass fiber processing. Optical fibers with distinct index profiles are presented and characterized, namely, single-material fibers with or without a suspended core and standard step-index fibers with varying core diameter. In addition, we evidence their potential for nonlinear photonic devices in the mid-infrared spectral region by means of super-continuum generation experiments in the femtosecond regime. Spectral broadenings extend on several octaves in the mid-infrared from 2 to 14 μm.

Broadband mid-infrared supercontinuum generation in dispersion-engineered silicon-on-insulator waveguide

In this paper, we numerically investigate near- and mid-infrared supercontinuum (SC) generation in dispersion-engineered silicon-on-insulator (SOI) waveguides employing a novel side-slotted core structure. The effect of waveguide parameters on the dispersion is studied to achieve optimum dispersion profiles for SC generation in the anomalous and normal dispersion regimes. Numerical results show that by applying an input pump pulse with 200 fs width and 400 W peak power at 2.1 μm wavelength in a 10-mm-long SOI waveguide, SC spectra as wide as 2.8 μm and 2.0 μm can be obtained in the anomalous and normal dispersion regimes, respectively. These waveguides are useful as compact on-chip silicon photonic sources for spectroscopic applications in mid-infrared wavelengths.

Ultrafast mid-infrared high harmonic and supercontinuum generation with n2 characterization in zinc selenide.

Polycrystalline ZnSe is an exciting source of broadband supercontinuum and high-harmonic generation via random quasi phase matching, exhibiting broad transparency in the mid-infrared (0.5-20μm). In this work, the effects of wavelength, pulse power, intensity, propagation length, and crystallinity on supercontinuum and high harmonic generation are investigated experimentally using ultrafast mid-infrared pulses. Observed harmonic conversion efficiency scales linearly in propagation length, reaching as high as 36%. For the first time to our knowledge, n2 is measured for mid-infrared wavelengths in ZnSe: n2(λ=3.9μm)=(1.2±0.3)×10-14cm2/W. Measured n2 is applied to simulations modeling high-harmonic generation in polycrystalline ZnSe as an effective medium.

Mid-infrared flattened supercontinuum generation in all-normal dispersion tellurium chalcogenide fiber.

We have prepared a well-structured tellurium chalcogenide (ChG) fiber with a specialized double cladding structure by an improved extrusion method, and experimentally demonstrated an ultra-flat mid-infrared (MIR) supercontinuum (SC) generation in such a fiber. The step-index fiber had an optical loss of <1 dB/m in a range from 7.4 to 9.7 μm with a minimum loss of 0.69 dB/m at 7.87 μm. Simulation showed that an all-normal dispersion profile can be realized in this double cladding tellurium fiber. An ultra-flat MIR SC spectrum (~3.2-12.1μm at -10 dB, ~2-14 μm at -30 dB) was generated from a 22-cm long fiber pumped with a femtosecond laser at 5 μm (~150 fs, 1 kHz). Then the degree of coherence was calculated out based on a simulation, showing that a high coherent MIR SC (from 2.9 to 13.1 μm) can be generated in this double-cladding tellurium fiber.

Numerical investigation of a broadband coherent supercontinuum generation in Ga8Sb32S60 chalcogenide photonic crystal fiber with all-normal dispersion

All normal dispersion (ANDi) and highly nonlinear chalcogenide glass photonic crystal fiber (PCF) is proposed and numerically investigated for a broad, coherent and ultra-flat mid-infrared supercontinuum generation. The proposed PCF consists of a solid core made of Ga8Sb32S60 glass surrounded by seven rings of air holes arranged in a triangular lattice. We show by employing the finite difference frequency domain (FDFD) method that the Ga8Sb32S60 PCF dispersion properties can be engineered by carefully adjusting the air holes diameter in the cladding region and ANDi regime is achieved over the entire range of wavelengths with a zero chromatic dispersion around 4.5 μm. Moreover, we demonstrate that injecting 50 fs width and 20 kW peak power laser pulses (corresponding to a pulse energy of 1.06 nJ) at a pump wavelength of 4.5 μm into a 1 cm long ANDi Ga8Sb32S60 PCF generates a broad, flat-top and perfectly coherent SC spectrum extending from 1.65 μm to 9.24 μm at the 20 dB spectral flatness. These results make the proposed Ga8Sb32S60 PCF an excellent candidate for various important mid-infrared region applications including mid-infrared spectroscopy, medical imaging, optical coherence tomography and materials characterization.

Dispersion-engineered silicon nitride waveguides for mid-infrared supercontinuum generation covering the wavelength range 0.8–6.5 μm

We numerically demonstrate the generation of a mid-infrared supercontinuum (SC) through the design of an on-chip complementary metal oxide semiconductor compatible 10 mm-long air-clad rectangular waveguide made using stoichiometric silicon nitride (Si3N4) as the core and MgF2 glass as the lower cladding. The proposed waveguide is designed for pumping in both the anomalous and all-normal dispersion regimes. A number of waveguide geometries are tailored for pumping at 1.55 m with ultrashort pulses of 50 fs duration and a peak power of 5 kW. By initially keeping the thickness constant at 0.8 m, four different structures are engineered with varying widths between 3 m and 6 m. The largest SC spectral evolution covering a region of 0.8 m to beyond 6.5 m could be realized by a waveguide geometry with a width of 3 m. Numerical analysis shows that increasing width beyond 3 m while keeping thickness constant at 0.8 m results in a reduction of the SC extension in the long wavelength side. However, the SC spectrum can be enhanced beyond 6.5 m by increasing the waveguide thickness beyond 0.9 m with the same peak power and pump source. To the best of our knowledge, this is the first report of a broad SC spectral evolution through numerical demonstration in the mid-infrared region by the Si3N4 waveguide. In the case of all-normal dispersion pumping, a flatter SC spectra can be predicted with the same peak power and pump pulse but with a reduced bandwidth spanning 950–2100 nm.

Scaling power, bandwidth, and efficiency of mid-infrared supercontinuum source based on a GeO2-doped silica fiber

We demonstrate a supercontinuum source with a 20 dB bandwidth from ∼1 to ∼3 μm with output power exceeding 6 W based on a GeO2-doped silica fiber. This is the highest output power reported for a 3 μm supercontinuum source based on germania-doped silica fiber in an all-fiberized and compact size device. We further demonstrate a spectrum spanning from ∼1.7 to ∼3.4 μm (∼10 dB bandwidth from ∼1.8 to ∼3.2 μm) at a low power of tens of milliwatts with more than 50% power fraction above 2400 nm, which makes this source suitable for several applications where a broadband source at low power is required to avoid damage of the samples. Our investigations reveal the unexploited potential of germania-doped fiber for mid-infrared supercontinuum generation and surpass the current state-of-the-art results.

Flattened and broadband mid-infrared super-continuum generation in As2Se3 based holey fiber

By using an As2Se3 based holey fiber (HF) with a normal flat dispersion profiles, a flattened and broadband mid-infrared super-continuum generation is analysed. The transmission of an ultra-short pulse in the HF is numerically simulated by solving the generalized nonlinear Schrodinger equation under various parameters. The simulation results show that, by launching a pulse with a width of 50 fs and a peak power of 4.25 kW at 4375 nm into the 6 mm-long HF, a flat and broadband super-continuum at 3 dB level is successfully generated. The super-continuum covers the wavelengths from 3866 to 5958 nm which is the largest flat bandwidth reported in such a short fiber.

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.

Dispersion-Engineered Step-Index Tellurite Fibers for Mid-Infrared Coherent Supercontinuum Generation from 1.5 to 4.5 μm with Sub-Nanojoule Femtosecond Pump Pulses

Mid-infrared supercontinuum generation from 1.5 to 4.5 µm with sub-nanojoule femtosecond pump pulses is demonstrated by using a short segment of dispersion-engineered step-index tellurite fiber with very low OH content. Distinct group-velocity dispersion regimes in a simple design of step-index tellurite fiber are also reported, which allows to choose the nonlinear pulse propagation regime according to the required tailoring of the supercontinuum source. Numerical simulations based on the generalized nonlinear Schrödinger equation are used to determine optimized fiber parameters before experimental demonstrations. We also analyse the coherence properties of the resulting supercontinuum sources.