Supercontinuum Generation Research Articles

Kilowatt-level supercontinuum generation employing a homemade taper-shaped ytterbium-doped fiber amplifier.

A simple generation method of high-power supercontinuum (SC) based on a homemade long ytterbium-doped taper fiber (T-YDF) amplifier has been demonstrated experimentally and analyzed in this work. The power and spectra of the obtained SC are made adjustable by changing the seed pulse repetition rates. Under a 7.5 MHz seed pulse repetition rate, a SC output is obtained with a spectral range of 1000 nm-1650 nm, maximum output power of 1066 W, and conversion efficiency of 75.7%. The core/clad diameters of the homemade T-YDF are ∼20/400 µm and ∼30/600 µm at the input and output ends, respectively, and the total length is 25 m. Such a long taper fiber can further enhance the properties of the SC while ensuring high power and good beam quality. To the best of the authors' knowledge, this is the first report of directly generating a high average power SC based on the T-YDF amplifier, which provides a proof-of-concept experiment to achieve a high average power SC source and greatly improves the potential application value of the SC source.

Characterizing temporal stability of supercontinuum generation in higher-order modes supported by liquid-core fibers

The generation of tailored supercontinua is essential for studying ultrafast light-matter interactions and for a variety of practical applications requiring broadband light. Liquid-core fibers (LCFs) have emerged as an innovative nonlinear photonic platform, demonstrating high efficiency in nonlinear frequency conversion. In this study, we showcase that LCFs provide a stable platform for ultrafast supercontinuum generation in a selected higher-order vector mode at 1.55μm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.55\\;\\upmu \\hbox {m}$$\\end{document}. Specifically, we demonstrate soliton fission and double-dispersive wave generation using a radially polarized mode in a CS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {CS}_{2}$$\\end{document}-silica liquid-core fiber. The experiments were performed in a temperature-controlled laboratory, showing excellent stability with no evidence of fiber degradation, material degradation, or drift-induced changes in mode excitation over extended periods under standard environmental conditions. Our results confirm that liquid-core fibers are a reliable platform for nonlinear photonics, suitable for applications such as computationally tailored supercontinuum generation, single pulse spxectroscopy, and tailored light sources, all of which rely on consistent and stable nonlinear frequency conversion.

Supercontinuum generation from silver nano species embedded sodium antimony zinc borate glass matrices

Abstract Glass composites that contain metal nanostructures exhibit improved nonlinear properties and ultrafast responses due to their inherent local field effects. In this work, we synthesized glass matrices embedded with diverse silver nano species through the ion exchange method and investigated the generation of supercontinuum from these composites. The formation of silver nano species and their volume fraction were analyzed using the XPS analysis, and their contribution towards supercontinuum broadening was studied. The size of a nanoparticle influences the electron–electron scattering and the frequency of acoustic breathing rate, which influences the extent of supercontinuum broadening. The result indicates the possibility of tuning the nonlinear response of glass nanocomposites by varying the volume fraction of Ag+ and Ag°.

Critical-Layered MoS2 for the Enhancement of Supercontinuum Generation in Photonic Crystal Fibre.

Supercontinuum generation (SCG) from silica-based photonic crystal fibers (PCFs) is of highly technological significance from microscopy to metrology, but has been hindered by silica's relatively low intrinsic optical nonlinearity. The prevailing approaches of filling PCF with nonlinear gases or liquids can endow fibre with enhanced optical nonlinearity and boosted SCG efficiency, yet these hybrids are easily plagued by fusion complexity, environmental incompatibility or transmission mode instability. Here this work presentsa strategy of embedding solid-state 2D MoS2 atomic layers into the air-holes of PCF to efficiently enhance SCG. This work demonstrates a 4.8 times enhancement of the nonlinear coefficient and a 70% reduction of the threshold power for SCG with one octave spanning in the MoS2-PCF hybrid. Furthermore, this work finds that the SCG enhancement is highly layer-dependent, which only manifests for a real 2D regime within the thickness of five atomic layers. Theoretical calculations reveal that the critical thickness arises from the trade-off among the layer-dependent enhancement of the nonlinear coefficient, leakage of fundamental mode and redshift of zero-dispersion wavelength. This work provides significant advances toward efficient SCG, and highlights the importance of matching an appropriate atomic layer number in the design of functional 2D material optical fibers.

All-fiber coherent supercontinuum generation in a cascade of silica, fluoride, and chalcogenide fibers

Abstract We present an all-fiber coherent supercontinuum spanning the spectral range of 1.7–5.0 µm from a cascade of silica, ZBLAN, and chalcogenide (ChG) nonlinear fibers (NLFs). Coherence is maintained by the combined use of femtosecond pump pulses as well as by allowing deterministic spectral broadening mechanism at every stage of the cascade. The use of femtosecond pump pulses enables avoiding modulation instability (MI) at the onset of the supercontinuum generation process and thus prevent subsequent MI-seeded random noise. Once in the NLF cascade, the pump pulse is instead converted into a soliton of order maintained at N < 6 in the silica and ZBLAN NLFs, ensuring soliton fission followed by self-frequency shift of a few solitons. Finally, in the ChG NLF, spectral broadening is facilitated through self-phase modulation and dispersive wave generation. The deterministic nature of these nonlinear phenomena results in the generation of a coherent supercontinuum. The supercontinuum delivers an average power of 54 mW from an average pump power of 300 mW, yielding a power conversion efficiency of 18%. The experimental results closely align with numerical simulations, from which coherence is estimated. Such a coherent supercontinuum with a megahertz repetition rate is essential for spectroscopic systems based on optical frequency combs and applications in high-precision optical coherence tomography.

Retraction Note: Design and analysis of inverse tapered silicon nitride waveguide for flat and highly coherent supercontinuum generation in the mid-infrared

Retraction Note: Design and analysis of inverse tapered silicon nitride waveguide for flat and highly coherent supercontinuum generation in the mid-infrared

All-fiber GHz few-cycle pulse generation at 2 µm.

We demonstrate an all-fiber GHz mode-locked laser system with few-cycle duration operating at 2 µm. Based on a dispersion-managed mode-locked oscillator, a multi-stage fiber amplifier, and a nonlinear pulse compressor, the laser system can deliver watt-level few-cycle pulses at a fundamental repetition rate of 1.041 GHz. This 2-µm pulsed laser offers outstanding performance metrics, including a pulse duration of 33 fs (corresponding to ∼5 optical cycles) and an average power of 4.17 W. Moreover, the all-fiber laser system exhibits excellent power stability, and the integrated relative intensity noise (RIN) is only 0.052% (10 Hz-1 MHz). It is anticipated that this new, to the best of our knowledge, laser source is promising for frontier applications, including coherent supercontinuum generation, nonlinear frequency conversion, and laser-material interaction.

Retraction Note: Modulation instability induced supercontinuum generation in defective core photonic crystal fiber

Retraction Note: Modulation instability induced supercontinuum generation in defective core photonic crystal fiber

Highly coherent mid-infrared wideband supercontinuum generation by a silica cladded silicon nitride core buried waveguide

Abstract Optical waveguides with semiconductor cores are drawing considerable research interest in the domain of supercontinuum (SC) generation in recent times. In this work, we design a square-core silicon nitride buried waveguide with a silica-clad, aiming for a wideband spectrum generation in the mid-IR region when operated at the standard telecommunication wavelength of 1550 nm. Among different such silicon nitride square-core buried waveguides, we propose a typical design with dimensions of 400 nm × 400 nm along its height and width, capable of producing a highly coherent broadband intensity spectrum ranging from 810 nm to 5441 nm after propagating through just a few millimeters of the waveguide. The group velocity dispersion maintains minimal value over a broad wavelength range in the mid-IR region, while the nonlinear coefficient is estimated to be sufficiently high. The nonlinear pulse propagation through such a waveguide leads to achieving an SC spanning over 2.76 octaves, sufficiently broader than previously reported silicon nitride-based waveguides. Furthermore, our calculations confirm the highly coherent nature of the generated SC. To the best of our knowledge, this is the first report of SC generation maintaining a high degree of coherence over such a wide wavelength range in the mid-IR zone using a square-core silicon nitride buried waveguide.

Supercontinuum generation in Ga‐Sb‐S chalcogenide‐based PCF using optofluidic approach

AbstractWe report the design and theoretical study of a Ga‐Sb‐S chalcogenide glass‐based photonic crystal fiber (PCF) structure for mid‐infrared supercontinuum generation. The proposed design is engineered by adjusting the diameter of air holes in the cladding region and pitch, giving us control over the dispersion characteristics of the fiber. The optimized structure design offers the Zero Dispersion Wavelength of 5.2 μm. When pumped with 50 fs secant hyperbolic pulses of peak power 4.9 kW, for a fiber of length 8 mm at pump wavelength of 5 μm, the proposed structure design produces an ultra‐broadband supercontinuum spectrum spanning 1.5–14 μm. Proposed PCF design should be helpful in, biomedical imaging, supercontinuum sources, biosesning, and optical coherence tomography.

Ethanol-infiltrated circular photonic crystal fiber for low peak power supercontinuum generation from near-infrared to mid-infrared region

Ethanol-infiltrated circular photonic crystal fiber for low peak power supercontinuum generation from near-infrared to mid-infrared region

Polarization effects on PPLN waveguide: Supercontinuum, second harmonic, and disperssive wave generations

Polarization effects on PPLN waveguide: Supercontinuum, second harmonic, and disperssive wave generations

Plasma-based optical fiber tapering rig

Optical fiber tapers have been widely proposed and demonstrated as reliable optical fiber structures for sensing, lasers, and supercontinuum generation applications. This paper proposes an innovative approach to fabricating optical fiber tapers using plasma as the heat source. From our literature review, and to the best of our knowledge, this is the first time that plasma has been used as the heat source for producing optical fiber tapers. The system is not intricate and simple to replicate. Moreover, the elements involved make this machine attractive to research groups devoted to optical fibers. The setup consistently generates robust biconical optical fiber tapers. A typical waist of ∼8 μm and taper lengths ranging from 3 to 15 mm are achieved. Our results showed tapers with interference fringes up to 12 dB, from 1465 nm to 1599 nm. Furthermore, the statistical evaluation presented demonstrates a good level of reproducibility in our tapering process.

Chalcogenide Ge20Sb5Se75 photonic crystal fiber with seven air-hole rings for ultraflat mid-infrared supercontinuum generation

Supercontinuum (SC) generation in solid-core circular photonic crystal fibers (PCFs) made of Ge20Sb5Se75 is numerically analyzed. A large core is projected to increase light coupling efficiency into selected PCFs as well as raise coupling to standard silica fibers. High nonlinear coefficient and near-zero flat dispersion allow ultraflat SC spanning 1.5–4.6 μm in an all-normal dispersion regime. This requires 3 kW of peak power with 180 fs of pulse duration. The fiber with one zero-dispersion wavelength (ZDW) generates SC bandwidth in the range of 1.54–7.39 μm at 3.5 μm using peak power of 10 kW. For the same input power, the SC spectral covers from 1.39 to 7.36 μm in 10 cm of fiber with two ZDWs. These are wider SC bandwidths than those of previous chalcogenide fibers reached with lower peak powers. Therefore, the proposed Ge20Sb5Se75 PCFs are excellent candidates for the broadband ultraflat mid-infrared SC spectra used in high-speed nonlinear imaging and frequency measurement.

Supercontinua from integrated gallium nitride waveguides

Supercontinua are broadband spectra that are essential to optical spectroscopy, sensing, imaging, and metrology. They are generated from ultrashort laser pulses through nonlinear frequency conversion in fibers, bulk media, and chip-integrated waveguides. For any generating platform, balancing the competing criteria of strong nonlinearity, transparency, and absence of multiphoton absorption is a key challenge. Here, we explore supercontinuum generation in integrated gallium nitride (GaN) waveguides, which combine a high Kerr nonlinearity, mid-infrared transparency, and a large bandgap that prevents two- and three-photon absorption in the technologically important telecom C-band, where compact erbium-based pump lasers exist. Using this type of laser, we demonstrate tunable dispersive waves and gap-free spectra extending to almost 4 µm in wavelength, which is relevant to functional group chemical sensing. Additionally, leveraging the material’s second-order nonlinearity, we implement on-chip f-to-2f interferometry to detect the pump laser’s carrier-envelope offset frequency, which enables precision metrology. These results demonstrate the versatility of GaN-on-sapphire as a platform for broadband nonlinear photonics.

Extreme bandwidths via stochastic self-phase-modulation

We examine the spectral broadening of stochastic laser pulses experiencing self-phase modulation (SPM) in a medium with Kerr nonlinearity. The statistics of extreme bandwidths emerging from such a process is shown to converge, in the large-sample-size limit, to a generalized Poisson distribution whose mean is given by the exponent of the respective extreme-event statistics. In striking contrast to the SPM spectral broadening of deterministic laser pulses, the properties of spectral broadening in stochastic SPM depend not only on the field intensity and the propagation path, but also on the signal-to-noise ratio a of laser pulses and the sample size N. For N >> 1 laser pulses with a high signal-to-noise ratio, the upper bound of SPM-broadened spectra shifts as (lnN/a2)δs, δs being the deterministic SPM bandwidth. The parameter Na=exp(a2/2) is shown to provide an important benchmark, setting a borderline between deterministic and stochastic SPM. These findings offer useful insights into the extreme-event properties of supercontinuum generation.

Supercontinuum generation by nonlinear polarization rotation mode-locked fiber laser with pulse type switchable

We report on the generation of a supercontinuum (SC) by nonlinear polarization-rotating (NPR) mode-locked fiber laser, which includes a pulsed switchable NPR mode-locked fiber laser, an Er-doped fiber amplifier, and high nonlinear fiber (HNLF). In the experiment, by adjusting the polarization controller (PC) angle and pump power, we obtained three different pulses. They are traditional soliton bunch pulses, the coexistence of soliton bunch pulses and square pulses, and multi-longitudinal mode noise like square pulses. All three pulses can generate SC with spectrum width be about of 1000 nm. We fixed the pump power in the laser and observed the influence of amplifier power on the spectrum width and output power of SC. The SC width of soliton bunch pulse reaches 950.9 nm, the SC of soliton bunch pulse and square pulse coexisting pulse is 1009.7 nm, and the SC spectrum width of multi-longitudinal mode noise like square pulse is 887.1 nm. Our results demonstrate the generation of SC with three types of switchable pulses, opening up possibilities for various application requirements.

Watt-level ultra-flat wideband supercontinuum generation in GeO2 fiber by femtosecond pulse

The high-power ultra-flat supercontinuum (SC) sources play an important role in various fields. In this letter, we experimentally demonstrated an all-fiber, high-power, ultra-flat SC source in GeO2 highly nonlinear fiber (HNLF) pumped by a femtosecond fiber laser system. The system is mode-locked by a semiconductor saturable absorber mirror with an all-polarization-maintaining (PM) structure. Based on the technology of chirped pulse amplification, a maximum power of 3.12 W was realized with a repetition rate of 80 MHz at 1.56 μm, and the pulse duration was compressed to 124 fs in a segment of PM single-mode fiber. Furthermore, by optimizing the length of the HNLF, a wideband SC spectrum of nearly 700 nm was obtained at10 dB with a maximum power of 1.82 W, and the flatness of the spectrum was better than 5 dB in the range of 1600–2200 nm. We observed that the pulse evolved into a noise-like pulse with a narrowest pulse duration of 62 fs. Thanks to the all-PM structure of the fiber laser, the long-term stability of SC power was manifested with a relative fluctuation as low as 0.53 % over 6 h.

Mid-infrared supercontinuum generation in As2S3-circular photonic crystal fibers pumped by 4.5 µm and 6 µm femtosecond lasers

A study on As2S3 chalcogenide photonic crystal fiber (PCF) and its potential in supercontinuum generation (SCG) applications is presented. The designed fibers exhibit near-zero flattened chromatic dispersion, facilitating coherent and broad SCG utilizing femtosecond lasers at 4.5 and 6 µm wavelengths. A continuous spectrum spanning from 1.5 to 8 µm is achieved when the initial fiber is stimulated with an input power of 20 kW. With a pulse width of 100 fs and input power of 6 kW, the second fiber provides soliton-induced SCG with 2 to 15 µm spectral bandwidth. Furthermore, the integration of these large core diameter PCFs with high-power laser pulses guarantees the preservation of optical fiber integrity without damage. Consequently, these fibers hold promise for delivering SC spectra characterized by high power density, catering to a diverse range of practical applications including optical communications, spectroscopy, sensing, metrology, and calibration.

High-energy noise-like pulsing in a thulium/holmium co-doped fiber laser with watt-level average output power

A Thulium/Holmium co-doped fiber laser with high-energy noise-like rectangular pulses at the central wavelength of 1985 nm is experimentally demonstrated. The experimental setup is based on a 298-m long nonlinear optical loop mirror. By varying the pump power from 3 to 10 W, the noise-like rectangular pulse width can be tuned from 2.8 to 15.2 ns, respectively, and under a maximum pump power of 10 W, 1.45 W of average output power is obtained. The pulse repetition rate is 671 kHz. Consequently, highly energetic optical pulses with 2.16 µJ pulse energy and an estimated peak power of 142 W are achieved. To the best of our knowledge, these pulses, which are generated directly from the laser cavity, possess the highest average output power and pulse energy for noise-like pulse emission in the near 2 µm wavelength region. The proposed laser source has the most straightforward all-fiber cavity design that has been proposed for generating high-energy noise-like rectangular pulses, and as such has potential applications in scientific research and as a pump source for mid-infrared supercontinuum generation.