Supercontinuum Generation Research Articles

Sub-cycle pulse revealed with carrier-envelope phase control of soliton self-compression in anti-resonant hollow-core fiber.

The influence of the carrier-envelope phase (CEP) of a pump pulse on the multioctave supercontinuum (SC) generation in a gas-filled anti-resonant hollow-core fiber (AR HCF) by soliton self-compression (SSC) has been explored. We have shown an octave-wide third harmonic generation (THG) in the visible-to-near-infrared range during the pulse compression down to a sub-cycle duration. The CEP of a multi-cycle pump pulse provides control of interference between the third harmonic (TH) and the SC that indicates the coherent synthesis of a sub-cycle pulse with a duration of about 0.4 optical cycles and a peak power of more than 2 GW at the fiber output.

Toward high-speed effective numerical simulation of multiple filamentation of high-power femtosecond laser radiation in a transparent medium

High-power femtosecond laser radiation during propagation in air (and other transparent media) experiences multiple filamentation. Filamentation is a unique nonlinear optical phenomenon, accompanied by a wealth of nonlinear optical effects such as formation of extended plasma channels in the beam wake, generation of higher harmonics and supercontinuum, and generation of THz radiation. The manifestations of laser filamentation can be useful for solving atmospheric optics problems related to remote sensing of the environment as well as directed transmission of laser power. Classical numerical methods used for simulating the nonlinear long-range atmospheric propagation of high-power radiation with a sufficiently large laser beam aperture have almost reached their limit regarding the acceleration of calculations. To solve this problem and speed up the numerical simulations of laser filamentation, we propose an improved numerical technique based on a modified method of phase screens constructed on a sparse spatial grid. Within the framework of this technique, we seek an optimal ansatz (substitution function) to the governing equations using machine learning technology, which provides the best correspondence to the numerical solution of the test problem using a denser spatial grid.

Effect of rotational Raman response on ultra-flat supercontinuum generation in gas-filled hollow-core photonic crystal fibers.

We experimentally and numerically investigate flat supercontinuum generation in gas-filled anti-resonant guiding hollow-core photonic crystal fiber. By comparing results obtained with either argon or nitrogen we determine the role of the rotational Raman response in the supercontinuum formation. When using argon, a supercontinuum extending from 350 nm to 2 µm is generated through modulational instability. Although argon and nitrogen exhibit similar Kerr nonlinearity and dispersion, we find that the energy density of the continuum in the normal dispersion region is significantly lower when using nitrogen. Using numerical simulations, we find that due to the closely spaced rotational lines in nitrogen, gain suppression in the fundamental mode causes part of the pump pulse to be coupled into higher-order modes which reduces the energy transfer to wavelengths shorter than the pump.

Supercontinuum generation based on suspended core fiber infiltrated with butanol

Supercontinuum generation based on suspended core fiber infiltrated with butanol

Broadband supercontinuum generation with low peak power in controllable C7H8-core photonic crystal fibers of characteristic quantities

Broadband supercontinuum generation with low peak power in controllable C7H8-core photonic crystal fibers of characteristic quantities

Tailored supercontinuum generation using genetic algorithm optimized Fourier domain pulse shaping.

We report the generation of a spectrally tailored supercontinuum using Fourier-domain pulse shaping of femtosecond pulses injected into a highly nonlinear fiber controlled by a genetic algorithm. User-selectable spectral enhancement is demonstrated over the 1550-2000-nm wavelength range, with the ability to both select a channel with target central wavelength and bandwidth in the range of 1-5 nm. The spectral enhancement factor relative to unshaped input pulses is typically ∼5-20 in the range 1550-1800 nm and increases for longer wavelengths, exceeding a factor of 160 around 2000 nm. We also demonstrate results where the genetic algorithm is applied to the enhancement of up to four spectral channels simultaneously.

Low peak power broadband supercontinuum spectra generated in a square lattice toluene-core photonic crystal fiber with different air hole diameters

This study shows that it is possible to achieve a very large supercontinuum spectral broadening with a peak power hundreds of times lower than in previous publications. We can achieve by using a square lattice toluene-core photonic crystal fiber. With the heterogeneity in the diameter of air holes, our new design allows simultaneous optimization of characteristic quantities to ensure flat near-zero dispersion, small effective mode area, and low attenuation for efficient spectral broadening. Supercontinuum generation (SC) of proposed PCFs has been numerically simulated and studied under different pump source parameters. The first fiber with a lattice constant of 1.0 μm and filling factor of 0.65 operates in all-normal dispersion. It generates broadband of 1.045 μm by a pump pulse with a central wavelength of 1.3 μm, 40 fs duration, and energy of 18 pJ (corresponding peak power of 0.45 kW). Besides, two octave-spanning of the SC spectrum in the wavelength range of 0.775–4.3 μm are formed in the second fiber with an input pulse whose optical properties are 1.55 μm wavelength, 100 fs duration, and energy of 55 pJ (0.45 kW of the peak power). The lattice constant of second fiber is 2.0 μm and the filling factor is 0.3. They would be good candidates for all-fiber SC sources operating with low-power pump lasers. This would be a as cost-effective alternatives to glass core fibers.

Wafer-scale inverted gallium phosphide-on-insulator rib waveguides for nonlinear photonics.

We report a gallium phosphide-on-insulator (GaP-OI) photonic platform fabricated by an intermediate-layer bonding process aiming to increase the manufacture scalability in a low-cost manner. This is enabled by the "etch-n-transfer" sequence, which results in inverted rib waveguide structures. The shallow-etched 1.8 µm-wide waveguide has a propagation loss of 23.5 dB/cm at 1550 nm wavelength. Supercontinuum generation based on the self-phase modulation effect is observed when the waveguides are pumped by femtosecond pulses. The nonlinear refractive index of GaP, n2, is extracted to be 1.9 × 10-17 m2/W, demonstrating the great promise of the GaP-OI platform in third-order nonlinear applications.

Generation of Mid‐Infrared Noise‐Like Pulses from a Polarization‐Maintaining Fluoride Fiber Oscillator

Noise‐like pulses (NLPs) are becoming increasingly attractive for a variety of applications such as supercontinuum generation, materials processing, and low‐coherence spectral interferometry. Related research in the near‐infrared region is extensive, yet few studies have been reported in the mid‐infrared (MIR) region. Herein, a systematic investigation of MIR NLPs is made for the first time. An approach is presented by exploiting a polarization‐maintaining fluoride fiber in the mode‐locked oscillator to cause a polarization‐dependent delay between the orthogonal‐polarized components of intracavity circulating pulses, thus generating a series of ultrashort pulses which will eventually form a stable wave packet, namely, NLP. Numerical simulations based on the extended coupled nonlinear Schrödinger equations predict the generation of NLPs, and reveal key aspects of the pulse evolution. Experiments yield linearly polarized NLPs at 2.8 μm with a maximum average power of 498 mW and a spike width of 4.3 ps, corresponding to a pulse energy of 12 nJ. The experimental results are in good agreement with the simulation results. This work constitutes a major step toward the development of MIR ultrafast fiber lasers with NLPs output.

Photonic molecule state transition by collision.

We investigate the impact of collisions with two-frequency photonic molecules aiming to observe internal dynamic behavior and challenge their strong robustness. Versatile interaction scenarios show intriguing state changes expressed through modifications of the resulting state such as temporal compression and unknown collision-induced spectral tunneling. These processes show potential for efficient coherent supercontinuum generation and all-optical manipulation.

Optimization of dispersion in hollow-core photonic crystal fibers filled with toluene

In this work, we thoroughly investigated the dispersion in SiO2-based photonic crystal fibers with a C7H8-infiltrated hollow core. By cleverly modifying the air hole diameters and lattice constants in the structural design, we achieved ultra-flat near-zero dispersion as small as 0.462 ps·nm–1·km–1 and diverse dispersion properties of PCFs, very beneficial for supercontinuum generation. Based on the simulation results, we propose three optimal structures with small and flat dispersion capable of generating a broad and smooth supercontinuum spectrum. The results of our study can be advantageous for fabricating fibers in low-cost all-fiber laser systems.

Performance analysis of photonic crystal fiber structure based on different highly nonlinear materials

Generally, fiber with a large mode area is desired for fiber laser and beam delivery applications. But the use of these fiber types is restricted to linear optical applications due to the lower value of the nonlinear coefficient. This paper investigates a single material-based photonic crystal fiber (PCF) with improved optical characteristics, applicable for linear and nonlinear optics. The light propagation in the structure is explored by applying finite element solver-based COMSOL multiphysics software. Five nonlinear optical materials are utilized as background material to get the optimized material with high performance PCF. Using this PCF, the improved optical properties of PCF such as moderate effective mode area of 115.85 [Formula: see text], chromatic dispersion, confinement loss of 10[Formula: see text] dB/m, the nonlinear coefficient of 543W[Formula: see text]Km[Formula: see text], splicing loss of 2.013 dB, and numerical aperture are numerically analyzed. This single-mode PCF also shows the low bending loss for the bending radius of 7[Formula: see text]mm. The amended PCF structure is found to be suitable for high-power fiber laser, supercontinuum generation, wavelength conversion, and slow-light generation.

Design and Optimization of C6H5NO2‐Core Photonic Crystal Fibers for Broadband Supercontinuum Generation with Low Peak Power

AbstractThis study presents a new square‐lattice photonic crystal fiber (PCF) with a nitrobenzene core. Considering the non‐uniformity of the air hole diameter, this new design allows the characteristic quantities to be optimized simultaneously to ensure near‐zero dispersion, a small effective mode area, and low loss for efficient spectral broadening. The spectrum broadens significantly at peak powers many times lower than in previous studies. Based on the obtained results, two optimal PCFs are proposed and validated in detail for supercontinuum generation (SCG). The first fiber #F1 operates in an all‐normal dispersion regime with a pump wavelength of 1.3 µm.It produces a spectral supecontinuum (SC) from 0.726 to 1.649 µm with a pulse duration of 90 fs and a peak power of 133 W. Meanwhile, the second fiber #F2 operates in anomalous dispersion regime with a pump wavelength of 1.61 µm. With a low peak power of 300 W and a pulse duration of 150 fs, the fiber #F2 provides SC generation with bandwidth from 0.805 µm to 3.970 µm. The proposed fibers are suitable for all‐fiber SC light sources, respectively, and may lead to new low‐cost all‐fiber optical systems.

Optimization of Dispersions in GeO2-doped Photonic Crystal Fibers with Square Lattice

Germanium doped photonic crystal fibers with differences in the layers' air hole diameters in the cladding are presented to obtain flat dispersion, small effective mode area, and low attenuation property for supercontinuum generation applications. The flatness and small value of the dispersion depend on the lattice geometry when the fibers have the same germanium doping concentration. The dispersion of the square lattice fibers is a flatter and smaller value at the pump wavelength than the circular lattice fibers. Square lattice fibers with Ʌ = 0.9 µm, d1/Ʌ = 0.4 and Ʌ = 1.0 µm, d1/Ʌ = 0.45 are proposed for supercontinuum generation which has anomalous and all-normal dispersion, respectively. Their small dispersion values of 0.449 ps /nm.km and −1.096 ps/nm.km are suitable for broad spectrum supercontinuum generation. The small effective mode area and low attenuation of the two fibers of 3.221 µm2, 2.361 µm2 and 1.805×10−7 dB/m, 1.322×10−15 dB/m, respectively are favorable conditions for choosing a laser pump sources with low peak power. The proposed fibers can be new supercontinuum generation source replacing traditional glass core fibers.

Maximizing supercontinuum bandwidths in gas-filled hollow-core fibers using artificial neural networks

Machine learning has been used to accelerate studies in the dynamics of optical pulses. In this study, we use machine learning to investigate the optimal design of supercontinuum-generating hollow-core antiresonant fibers (HC-ARFs) pressurized and filled with methane. Artificial neural networks (ANNs) are trained to replace the numerical solvers, accelerate the simulation of fibers, and provide a more rapid fiber design procedure. We first use an analytical model to approximate the dispersion and loss of the methane-filled silica HC-ARF. This approximation is used by the generalized unidirectional pulse propagation equation solver to simulate the pulse propagation and generate training data for our ANNs by varying design parameters including the pump center wavelength, fiber hollow-core radius, fiber length, cladding strut thickness, and gas pressure. We evaluate the performance of different spectral-predicting ANN architectures and use the trained ANN along with a custom fiber performance function to search the full parameter space. Subsequently, the regions with design parameters with predicted high performance are identified, and these high-performance HC-ARF designs are further optimized for supercontinuum generation at target supercontinuum bandwidths. We also extend our effort to maximizing the total spectral energy outside of the input pump wavelength by integrating the ANN with a global optimization technique for the search of an optimal HC-ARF design.

Enhancement of blue and ultraviolet components in PCF-based supercontinuum generation through inter-modal dispersive-wave radiation.

Broadband supercontinuum (SC) light sources generated through nonlinear effects in solid-core photonic crystal fibers (PCFs) have been widely used in spectroscopy, metrology, and microscopy, leading to great application successes. The short-wavelength extension of such SC sources, a longstanding challenge, has been the subject of intensive study over the past two decades. However, the exact mechanism of blue and ultraviolet light generation, especially for some resonance spectral peaks in the short-wavelength regime, is not yet fully understood. Here, we demonstrate that the effect of inter-modal dispersive-wave radiation, which results from phase matching between pump pulses at the fundamental optical mode and packets of linear waves at some higher-order modes (HOMs) propagating in the PCF core, might be one of the critical mechanisms that can result in some resonance spectral components with wavelengths much shorter than that of the pump light. We observed in an experiment that several spectral peaks resided in the blue and ultraviolet regimes of the SC spectrum, whose central wavelengths can be tuned by varying the PCF-core diameter. These experimental results can be interpreted well using the inter-modal phase-matching theory, providing some useful insights into the SC generation process.

Supercontinuum generation in a square-lattice photonic crystal fiber using carbon disulfide infiltration

This study proposed new liquid-filled photonic crystal fiber structures as a new supercontinuum source with low pumping energy. The designed fiber has square lattices on its cross-section and its core being infiltrated by carbon disulfide. We studied numerically optical properties of the square lattice fiber with the modification of its structural parameters including lattice constant (Λ) and hole diameter (d). From the simulated results, two PCF structures supporting the best broadband supercontinuum generations were selected. The first optimized fiber #F1 having lattice pitch Λ = 1.0 µm and filling factor d1/Λ = 0.7 provides an all-normal dispersion. This fiber offers the supercontinuum spectrum broadening from 860 nm to 1738 nm (resulting in a bandwidth of 878 nm) by pumping at a wavelength of 1300 nm, 80 fs pulse duration and input energy of 1.5 nJ, corresponding to the input power of 18.75 kW. The second fiber #F2 (lattice pitch Λ = 1.5 µm, filling factor d1/Λ = 0.3) exhibits mostly anomalous dispersion region. In this fiber, the octave-spanning of the supercontinuum spectrum was formed with a bandwidth of 1935 nm from 594 nm to 2529 nm for an input pulse are 1670 nm pump wavelength, 80 fs duration and energy of 0.5 nJ, corresponding to the input power of 6.25 kW. The proposed fibers are good candidates for low-cost all-fiber sources for potential application in the fields of telecommunications and mid-infrared detection.

KGW and YVO4: two excellent nonlinear materials for high repetition rate infrared supercontinuum generation.

We present an experimental investigation of supercontinuum generation in potassium gadolinium tungstate (KGW) and yttrium vanadate (YVO4) crystals pumped with 210 fs, 1030 nm pulses from an amplified Yb:KGW laser operating at 2 MHz repetition rate. We demonstrate that compared to commonly used sapphire and YAG, these materials possess considerably lower supercontinuum generation thresholds, produce remarkable red-shifted spectral broadenings (up to 1700 nm in YVO4 and up to 1900 nm in KGW) and exhibit less bulk heating due to energy deposition during filamentation process. Moreover, durable damage-free performance was observed without any translation of the sample, suggesting that KGW and YVO4 are excellent nonlinear materials for high repetition rate supercontinuum generation in the near and short-wave infrared spectral range.

(Invited) control of supercontinuum generation due to soliton propagation in fibers with varying dispersion

We demonstrate experimental and numerical studies of supercontinuum generation for silica fibers with longitudinally varying diameter and dispersion. The significant difference in the spectral and temporal transformations of the pump pulse depending on the direction of propagation in the researched fiber samples is shown. Numerical simulations demonstrate the possibility of the supercontinuum spectra management by controlling the longitudinal profile of the fiber. Ways to optimize the output in terms of spectral flatness and efficient energy transfer to the desired wavelength region are presented.

Collision off-axis position dependence of relativistic nonlinear Thomson inverse scattering of an excited electron in a tightly focused circular polarized laser pulse

This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron’s initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum’s harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings, when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought.