Supercontinuum Research Articles

Silica-based photonic crystal fiber infiltrated with 1,2-dibromoethane for supercontinuum generation

This study proposes a photonic crystal fiber (PCF) made of fused silica glass with the core infiltrated with 1,2-dibromoethane (C2H4Br2) as a new source of supercontinuum light pulses. Due to the modifications of the PCF's structure geometry, a number of computer simulations investigating their optimized structures has been carried out. This aimed at achieving flat near-zero dispersion and zero dispersion wavelength matching of the pump wavelength for efficient spectral broadening. Based on the obtained results, the structural geometries of two C2H4Br2-core PCFs were optimized using numerical modeling for broadband supercontinuum (SC) generation. The first fiber structure with a lattice constant 1.5 µm and filling factor 0.4 has all-normal dispersion profile. The SC with a broadened spectral bandwidth from 0.64 to 1.70 µm is generated by pump pulses centered at a wavelength of 1.03 µm, 120 fs duration, and energy of 1.5 nJ. The second proposed structure-with lattice constant 1.5 µm and filling factor 0.65-has anomalous dispersion for wavelengths longer than 1.03 µm. We obtained high coherence of the SC pulses in the anomalous dispersion range over wavelengths of 0.7-2.4 µm with the same pump pulse as the first fiber and with input energy of 0.09 nJ. These fibers would be interesting candidates for all-fiber SC sources operating with low-energy pump lasers as cost-effective alternatives to glass core fibers.

Generation of Ultrabroad and Intense Supercontinuum in Mixed Multiple Thin Plates

Supercontinuum (SC) generation using multiple thin plates is demonstrated with a femtosecond laser pulse. We propose an improved technique to obtain larger spectrum broadening and higher spectral intensity by employing mixed multiple thin plates with different thicknesses and materials. Furthermore, the spectrum has good stability, which is superior to that of the spectrum induced by the traditional single filament in bulk material. Our approach offers a route towards simple and stable SC generation for potential applications.

Mid-infrared cascaded stimulated Raman scattering and flat supercontinuum generation in an As-S optical fiber pump at 2 µm.

We demonstrate broadband mid-infrared cascaded stimulated Raman scattering (SRS) and flat supercontinuum (SC) generation in a chalcogenide optical fiber made from As2S5 glass. By using a 2 µm nanosecond laser as the pump source, mid-infrared cascaded SRS up to six orders ranging from 2149 to 3425 nm was experimentally observed, and this all-fiber Raman laser operating at 3.43 µm was realized for the first time to our knowledge. By introducing a 2 µm femtosecond laser as the excited source, the broadband flat mid-infrared SC with the spectral range of ∼10dB (from ∼1030 to 3441 nm) was observed. Our results verify that the As2S5 optical fibers possess promising applications for tunable mid-infrared Raman fiber lasers and SC light sources pumped by 2 µm pulsed lasers.

Experimental study of supercontinuum generation in step-index highly nonlinear fibres

In this work, supercontinuum (SC) generation in three kinds of step-index highly nonlinear fibres (HNLFs) are experimentally investigated. The generated SC spectra are compared with each other by changing the numbers and wavelengths of the pump sources, and also by employing the HNLFs with different refractive-index differences between the core and the cladding. The widest spectral range of generated SC was about 2650 nm covering from 350 to 3000 nm when using the three pump wavelengths of 800, 1400 and 1867 nm. The results demonstrate that the step-index HNLFs have excellent performances for SC generation and great potentials for the realization of all-fibre SC source.

Numerical simulation of all-normal dispersion visible to near-infrared supercontinuum generation in photonic crystal fibers with core filled chloroform

This study proposes a photonic crystal fiber made of fused silica glass, with the core infiltrated with chloroform as a new source of supercontinuum (SC) spectrum. We numerically study the guiding properties of the fiber structure in terms of characteristic dispersion and mode area of the fundamental mode. Based on the results, we optimized the structural geometries of the CHCl3-core photonic crystal fiber to support the broadband SC generations. The fiber structure with a lattice constant of 1 μm, a filling factor of 0.8, and the diameter of the first-ring air holes equaling 0.5 μm operates in all-normal dispersion. The SC with a broadened spectral bandwidth of 0.64 to 1.80 μm is formed by using a pump pulse with a wavelength of 850 nm, 120 fs duration, and power of 0.833 kW. That fiber would be a good candidate for all-fiber SC sources as cost-effective alternative to glass core fibers.

All-fiber high-power supercontinuum laser source over 3.5 µm based on a germania-core fiber.

In this Letter, a high-power all-fiber mid-infrared (MIR) supercontinuum (SC) laser source based on 9 cm long germania-core fiber (GCF) pumped by a high-power thulium-doped fiber amplifier is presented. As the pump power was set as 60 W, we obtained a 21.34 W broadband SC source extending from 1742 to 3512 nm with a slope efficiency of 32.5%. The 10 dB spectral bandwidth was over 1000 nm, spanning 1.97 to 3.04 µm. Furthermore, the numerical simulation of SC generation in GCF was in good agreement with the experimental results. As far as we know, this is the highest average output power over 3.5 µm in GCF based on a MIR SC laser source.

Optical characterization of Ge11.5As24S64.5 glass for an on-chip supercontinuum

An on-chip supercontinuum (SC) source spanning from 900 nm to 2000 nm has been experimentally presented and analyzed based on a G e 11.5 A s 24 S 64.5 (GeAsS) planar waveguide at telecommunication wavelength. The nonlinear response parameter ( γ ) of the GeAsS waveguide is estimated to be ∼ 12 / W / m at the pump wavelength using resonant grating waveguide (RGW) nonlinear refractive index ( n 2 = 2 × 1 0 − 18 m 2 / W ), which is measured by the z-scan technique. The dispersion of the waveguide is carefully engineered based on the refractive index of the GeAsS film where the film structure is confirmed by a Raman spectrum exhibiting consistency with the corresponding glass. The results suggest that the GeAsS glass is expected to be an ideal platform for on-chip devices.

Perspective on the next generation of ultra-low noise fiber supercontinuum sources and their emerging applications in spectroscopy, imaging, and ultrafast photonics

A new generation of ultrafast and low-noise supercontinuum (SC) sources is currently emerging, driven by the constantly increasing demands of spectroscopy, advanced microscopy, and ultrafast photonics applications for highly stable broadband coherent light sources. In this Perspective, we review recent progress enabled by advances in nonlinear optical fiber design, detail our view on the largely untapped potential for noise control in nonlinear fiber optics, and present the noise fingerprinting technique for measuring and visualizing the noise of SC sources with unprecedented detail. In our outlook, we highlight how these SC sources push the boundaries for many spectroscopy and imaging modalities and focus on their role in the development of ultrafast fiber lasers and frequency combs with ultra-low amplitude and phase noise operating in the 2 μm spectral region and beyond in the mid-IR.

Coherent ultrabroad orbital angular momentum supercontinuum generation in an AsSe2-As2S5 microstructured fiber with all-normal dispersion

We design and simulate a hollow AsSe2-As2S5 microstructured fiber surrounded by air holes with nearly-zero flattened all-normal dispersion profile. Simulation results show that the coherent first-order orbital angular momentum (OAM1,1) supercontinuum (SC) spectrum extending from 1.3 to 11 μm at −40 dB level, which can be achieved by pumping a chirp-free hyperbolic secant pulse with 100 fs pulse duration and 20 kW peak power at the wavelength of 6 μm into an 11 mm proposed fiber. Due to the flexible controllability for chromatic dispersion of this fiber, several coherent SC spectra generated by different OAM modes are analyzed.

Design of step-index-microstructured hybrid fiber for coherent supercontinuum generation

In this paper, a step-index-microstructured hybrid fiber (SIMHF) with near-zero dispersion at the communication band is proposed. In the SIMHF, a germania-doped core in the center, air holes and germania-doped inclusions arrangement in the cladding are used to control the property of dispersion. Through optimized design, the dispersion of the SIMHF can be maintained within −0.3 to 0 ps/nm/km from 1.49 µm to 1.85 µm wavelength. Taking the advantage of this near-zero-flattened normal dispersion, the SIMHF shows great potential on coherent supercontinuum (SC) generation. By injecting the pulse with peak power of 1 kW and full width at half maximum (FWHM) of 500 fs into the fiber, SC that covers the wavelength range of 1.35– 2.02 µm can be generated.

High-efficiency ultra-compact near-infrared supercontinuum generated in an ultrashort cavity configuration.

We report a novel method to generate near-infrared supercontinuum (SC) in an ultrashort cavity configuration with only 11.5 m. With the continuous laser diode pump, a near-infrared SC with 26.8 W average output power and a spectrum ranging from 900 nm to 2000nm is demonstrated, and the laser diode pump to supercontinuum conversion efficiency is up to 60%. The spectral and power characteristics of the generated SC under different lengths of germanium-doped fiber (GDF) were carefully studied. This near-infrared SC generation method has the advantages of simple structure, low cost and good stability and also possesses the shortest fiber laser cavity length ever reported to the best of our knowledge.

Near-infrared nanospectroscopy using a low-noise supercontinuum source

Unlocking the true potential of optical spectroscopy on the nanoscale requires development of stable and low-noise laser sources. Here, we have developed a low-noise supercontinuum (SC) source based on an all-normal dispersion fiber pumped by a femtosecond fiber laser and demonstrate high resolution, spectrally resolved near-field measurements in the near-infrared (NIR) region. Specifically, we explore the reduced-noise requirements for aperture-less scattering-type scanning near-field optical microscopy (s-SNOM), including inherent pulse-to-pulse fluctuation of the SC. We use our SC light source to demonstrate the first NIR, spectrally resolved s-SNOM measurement, a situation where state-of-the-art commercial SC sources are too noisy to be useful. We map the propagation of surface plasmon polariton (SPP) waves on monocrystalline gold platelets in the wavelength region of 1.34–1.75 μm in a single measurement, thereby characterizing experimentally the dispersion curve of the SPP in the NIR. Our results represent a technological breakthrough that has the potential to enable a wide range of new applications of low-noise SC sources in near-field studies.

Supercontinuum-illumination for long-working-distance microscopic imaging of air–liquid mixed sprays in the near-nozzle region

We demonstrate the optical diagnosis of air–liquid mixed sprays in the near-nozzle region using the supercontinuum (SC)-illumination long-working-distance microscopic imaging method, enabling the imaging of microdroplets, ligament structures, and cavities. In addition, SC-illumination long-working-distance microscopic imaging effectively suppresses speckles and reveals the ligament structures in the sprays more accurately. Finally, analysis of the droplet size distribution of the sprays under different air and liquid flow rates indicates that SC-illumination long-working-distance microscopic imaging offers several advantages for studying spray dynamics at the small structure level.

Mid-infrared single-Mode As-S-Se glass fiber and its supercontinuum generation

Two kinds of single-mode (SMF) step-index(SIF) chalcogenide fibers based on S-rich and S-poor As-S-Se glass have been fabricated successfully by an isolated extrusion method. We experimentally explored the effects of S and Se weights on the IR light transmission in the infrared area of the waveguide medium. By exploring the infrared transmission. It is found that the As-S-Se system has a transmission varied range between full S-based (As2S3) and full Se-based (As2Se3) glasses. The results show that with the addition of selenium, the red-shift is observed in both the short-wavelength absorption edge and long-wave cut-off wavelength. This phenomenon can be sourced from the varying of optical band gaps and phonon energies. Simultaneously, single-mode fibers was employed to evaluate the attenuation and supercontinuum(SC). We found that S-rich fiber shows a lower optical loss of 0.67–1.5 dB/m in 4.1–5.9 μm region, with a minimum value of 0.67 dB/m at 4.6 μm than that of S-poor fiber does. Yet, the SC results of S-poor fiber shows a flatter and broader spectrum region than that of S-rich fiber does.

Higher order mode supercontinuum generation in tantalum pentoxide (Ta2O5) channel waveguide

We fabricated tantalum pentoxide (Ta2O5) channel waveguides and used them to experimentally demonstrate higher-order mode supercontinuum (SC) generation. The Ta2O5 waveguide has a high nonlinear refractive index which was in an order magnitude of 10–14 cm2/W and was designed to be anomalously dispersive at the pumping wavelength. To the best of our knowledge, this is the first time a higher-order mode femtosecond pump based broadband SC has been measured from a nonlinear waveguide using the phase-matching method. This enabled us to demonstrate a SC spectrum spanning from 842 to 1462 nm (at − 30 dB), which corresponds to 0.83 octaves, when using the TM10 waveguide mode. When using the TE10 mode, the SC bandwidth is slightly reduced for the same excitation peak power. In addition, we theoretically estimated and discussed the possibility of using the broadband higher-order modes emitted from the Ta2O5 waveguide for trapping nanoparticles. Hence, we believe that demonstrated Ta2O5 waveguide are a promising broadband light source for optical applications such as frequency metrology, Raman spectroscopy, molecular spectroscopy and optical coherence tomography.

Fourier transform and grating-based spectroscopy with a mid-infrared supercontinuum source for trace gas detection in fruit quality monitoring.

We present a multi-species trace gas sensor based on a fast, compact home-built Fourier transform spectrometer (FTS) combined with a broadband mid-infrared supercontinuum (SC) source. The spectrometer covers the spectral bandwidth of the SC source (2 - 4 µm) and provides a best spectral resolution of 1 GHz in 6 seconds. It has a detection sensitivity of a few hundred of ppbv Hz-1/2 for different gas species. We study the performance of the developed spectrometer in terms of precision, linearity, long-term stability, and multi-species detection. We use the spectrometer for measuring fruit-produced volatiles under different atmospheric conditions and compare the performance with a previously developed scanning grating-based spectrometer.

Ultra-flat, low-noise, and linearly polarized fiber supercontinuum source covering 670-1390 nm.

We report an octave-spanning coherent supercontinuum (SC) fiber laser with excellent noise and polarization properties. This was achieved by pumping a highly birefringent all-normal dispersion photonic crystal fiber with a compact high-power ytterbium femtosecond laser at 1049 nm. This system generates an ultra-flat SC spectrum from 670 to 1390 nm with a power spectral density higher than 0.4 mW/nm and a polarization extinction ratio of 17 dB across the entire bandwidth. An average pulse-to-pulse relative intensity noise down to 0.54% from 700 to 1100 nm was measured and found to be in good agreement with numerical simulations. This highly stable broadband source could find strong potential applications in biomedical imaging and spectroscopy where an improved signal-to-noise ratio is essential.

Super continuum generation in water doped with Homeopathic medicines

We have carried out systematic studies to investigate the effect on supercontinuum generation in water using 40 fs laser pulses when doped with Homeopathic medicines. We perform these studies using five series of medications with different levels of dilution (10-30 to 10-100000). We measure supercontinuum spectra that span from 400-1050 nm. We monitor the area under the curve in the range 450-750 nm for each sample at a fixed incident laser energy. Our observations indicate that the yield of supercontinuum generation, in water containing Homeopathic medicine is significantly different from that obtained in water containing plain ethanol. The measurement for different dilutions shows up to 7 times standard deviation variation in the yield of supercontinuum generation? Even though linear absorption in the UV-visible region does not show any significant difference for different Homeopathic medicines, the supercontinuum yield which depends on the effective nonlinear refractive index changes with different samples.

Programmable Supercontinuum Laser Spectrum Generator Based on a Liquid-Crystal on Silicon Spatial Light Modulator

Supercontinuum (SC) lasers combine a broadband light spectrum with the unique properties of single-mode lasers. In this work we present an optical system to spectrally filter a SC laser source using liquid-crystal on silicon (LCoS) spatial light modulators (SLM). The proposed optical system disperses the input laser and the spectrally separated components are projected onto the LCoS-SLM, where the state of polarization of each wavelength is separately modulated. Finally, recombining the modulated spectral components results in an output laser source where the spectrum can be controlled dynamically from a computer. The system incorporates two branches to independently control the visible (VIS) and the near infrared (NIR) spectral content, thus providing a SC laser source from 450 to 1,600 nm with programmable spectrum. This new ability for controlling at will the wide spectra of the SC laser sources can be extremely useful for biological imaging applications.

Supercontinuum generation in photonic crystal fibers infiltrated with tetrachloroethylene

This study proposes a photonic crystal fiber made of fused silica glass, with the core infiltrated with tetrachloroethylene (C2Cl4) as a new source of supercontinuum (SC) spectrum. We studied numerically the guiding properties of the several different fiber structures in terms of characteristic dispersion, mode area, and attenuation of the fundamental mode. Based on the results, the structural geometries of three C2Cl4-core photonic crystal fibers were optimized in order to support the broadband SC generations. The first fiber structure with lattice constant 1.5 μm and filling factor 0.4 operates in all-normal dispersion. The SC with a broadened spectral bandwidth of 0.8–2 μm is generated by a pump pulse with a central wavelength of 1.56 μm, 90 fs duration and energy of 1.5 nJ. The second proposed structure, with lattice constant 4.0 μm and filling factor 0.45, performs an anomalous dispersion for wavelengths longer than 1.55 μm. With the same pump pulse as the first fiber, we obtained the coherence SC spectrum in an anomalous dispersion range with wavelength range from 1 to 2 μm. Meanwhile, the third selected fiber (lattice constant 1.5 μm, filling factor 0.55) has two zero dispersion wavelengths at 1.04 μm and 1.82 μm. The octave-spanning of the SC spectrum formed in this fiber was achieved in the wavelength range of 0.7–2.4 μm with an input pulse whose optical properties are 1.03 μm wavelength, 120 fs duration and energy of 2 nJ. Those fibers would be good candidates for all-fiber SC sources as cost-effective alternatives to glass core fibers.