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Supercontinuum (SC) generation pumped by fiber lasers with short wavelengths below 2.0 μm is important since it can provide a compact light source for various applications. We review the progress of SC generation in various materials regarding the formation of the waveguides and point out the existing issues in the current investigations and possible solutions in the future. [ABSTRACT FROM AUTHOR]

We investigate a simple structure in which a polarization-maintaining fiber (PMF) is sandwiched between two single-mode fibers (SMFs). By injecting broadband light and observing the modal interference spectrum of the transmitted light in the 870 nm range, we identify a clear shift dependent on the strain applied to the PMF. In addition, we demonstrate that in the same wavelength range, the strain applied to the SMFs before and after the PMF does not influence the interference spectrum. This result confirms that only the PMF segment exhibits strain sensitivity. [ABSTRACT FROM AUTHOR]

Multiple higher-order Stokes of rotational stimulated Raman scattering (SRS) in compressed hydrogen covered the wavelength range from ~1.1 µm to ~1.4 µm using ~1.2 ps pump pulses from a Yb:YAG laser. In this study, the influence of polarization, energy, and the focusing conditions of the pump pulse, as well as gas pressure, on the conversion efficiency and modification of the spectral envelope of rotational and vibrational SRS was investigated. The use of a supercontinuum seed, as well as circular polarization of pump pulses at high hydrogen pressure, made it possible to significantly reduce the threshold for rotational SRS and suppress vibrational Stokes modes. The cascade excitation of rotational SRS, corresponding to a shift of 587 cm−1, ensured a spectrum spanning four Stokes orders withs a conversion efficiency of 52% and an output energy exceeding 3 mJ. The synthesized spectrum corresponded to ~14 fs transform-limited pulses. [ABSTRACT FROM AUTHOR]

We propose and numerically demonstrate chalcogenide based bend M-type fiber for mid-IR supercontinuum (SC) generation through higher order mode (HOM) of LP02. In order to achieve this, we comprise two glass materials such as As2Se3 in core and Ge10As23.4Se66.6 in cladding. M-type index fiber has a special property that the HOM of LP02 is confined into the core region with help of high index ring. The mode field distribution of the proposed fiber is numerically calculated by a finite element method. By optimizing structural dimensions in each bending case, we realize a zero dispersion wavelength, double zero dispersion wavelength effective area and power fraction in core. The simulation results shows the flat anomalous dispersion in the wavelength range of 2.1–2.6µm and 2.5–6.5µm for the core radius 4 and 10 µm, respectively at bending case of 1, 3, and 5 cm. which is important for employing the mature fiber laser technology at mid-IR regions. [ABSTRACT FROM AUTHOR]

We fabricated a core-cladding Ge–Sb–Se glass fiber with a Ge12.5Sb15Se72.5 core and Ge15Sb10Se75 cladding, achieved a supercontinuum spectrum spanning from 2 μm to 9 μm by pumping the Ge–Sb–Se fiber with a core diameter of 11 μm using a femtosecond laser pump at 3.8 μm, and numerically simulated the supercontinuum generation using the generalized nonlinear Schrödinger equation. In particular, we investigate the effect of the different Raman response functions that were calculated using the traditional single Lorentzian model and a multiple vibrational mode model on the evolution of the supercontinuum by comparing the supercontinua obtained from simulation and experimental results. We demonstrate that the Raman response function generated by the multiple vibrational mode model captures the actual response behavior of the material, and the supercontinuum generated using this model has more accuracy. To the best of our knowledge, this is the first reported study on supercontinuum generation in Ge–Sb–Se fiber utilizing a Raman response function calculated using the multiple vibrational mode model. This significant advancement enables more accurate simulation of supercontinuum generation in fibers with a multi-peaked structured Raman gain spectrum and holds great potential for optimizing the performance of various mid-infrared supercontinuum sources. [ABSTRACT FROM AUTHOR]

We experimentally studied the supercontinuum induced by femtosecond filamentation in different liquid media. Using a Mach–Zehnder interferometer, we determined the relative filamentation thresholds (Pth) of these media. Research has shown that the value of the filamentation threshold is greater than that of Pcr (critical power for self-focusing), which can mainly be attributed to the strong dispersion effect. Changing the focal length of the focusing lens affects filamentation dynamics, thereby affecting the measured results regarding the filamentation threshold. With shorter focal lengths, the linear focusing (i.e., geometrical focusing) regime dominates, and the measured values of Pth for different liquid media are almost the same; as the focal length becomes larger, self-focusing starts to play a role, making the values of Pth for different media different from each other. This study presents an efficient method for investigating the femtosecond filamentation phenomenon in liquid media, helpful to provide further insights into the physical mechanism of supercontinuum generation via femtosecond filamentation in liquid media. [ABSTRACT FROM AUTHOR]

The effect of a lower index oxide layer inclusion within a highly doped silica glass slot waveguide is investigated for optimized supercontinuum generation at telecom wavelengths. By controlling the thickness of the oxide slot, it is demonstrated that one can engineer the waveguide dispersion profile in order to obtain supercontinua with vastly different spectral broadening dynamics and bandwidths. Using this approach, a waveguide with a low and flat dispersion profile of less than 43 pskm−1nm−1$\rm ps\ km^{-1}\ nm^{-1}$ across a wavelength range spanning over 1000 nm is designed and fabricated. It is shown that, when pumped at the telecom C‐band, a supercontinuum that spans over 1.5 octaves can be generated from 817 to 2183 nm. The numerical simulations, whose parameters are derived from the measured waveguide dimension and material indices, exhibit good agreement with experimental measurements, where one can observe both a qualitative and quantitative match in the supercontinuum overall spectrum and specific features (e.g., soliton and dispersive wave locations). This study represents an important step forward in the control and manipulation of dispersive and nonlinear dynamics in highly doped silica glass waveguides, paving the way toward advanced on‐chip broadband light manipulation. [ABSTRACT FROM AUTHOR]

The work is devoted to the study of the problem of using laser radiation in the supercontinuum mode in fiber optical gyroscopes. To achieve this goal, the following tasks were solved in the work. The physics of the process of measuring the angular velocity of an object based on the Sagnac effect is described. The factors influencing the resolution of the gyroscope are analyzed. These factors include fractional noise, unavoidable noise, and noise due to backscatter in the fiber, which can be minimized by using photonic crystal fibers and a broadband radiation source. It is proposed to use an optical supercontinuum (optical comb) as such a source. Thanks to its ultra-wide radiation spectrum, precision frequency reproduction accuracy, high radiation stability and femtosecond pulse duration, supercontinuum is considered as a promising radiation source in ranging, hyperspectral spectroscopy and imaging, tomography, and low-coherence white light interferometry. In the work of Lpischan, the physics of the supercontinuum generation process, its main characteristics. An analysis of the possibility of using an optical comb in optical gyroscopy has been carried out. Mathematical modeling of the influence of optical fiber characteristics and supercontinuum parameters on the sensitivity of a fiber gyroscope was carried out. The results of the work indicate the promise of further research on the creation of a photonic crystal fiber-optic gyroscope using supercontinuum laser radiation. [ABSTRACT FROM AUTHOR]

Supercontinuum (SC) generation pumped by fiber lasers with short wavelengths below 2.0 μm is important since it can provide a compact light source for various applications. We review the progress of SC generation in various materials regarding the formation of the waveguides and point out the existing issues in the current investigations and possible solutions in the future.

The supercontinuum generation and manipulation of Airy-Gaussian pulses in a photonic crystal fiber with three zero-dispersion points are studied using the split-step Fourier method. Firstly, the spectral evolution of Airy-Gaussian pulses in four photonic crystal fibers with different barrier widths was discussed, and the optimal fiber was determined after considering the factors of width and flatness. By analyzing the mechanism of supercontinuum generation in photonic crystal fibers with single, double and three zero-dispersion points, it is found that the photonic crystal fiber with three zero-dispersion points have a larger spectral width due to the component of tunneling solitons. Then, the effects of four characteristic parameters (truncation factor a, distribution factor χ0, initial chirp C and central wavelength λ) on forming the supercontinuum spectrum of Airy-Gaussian pulses are analyzed in detail. The results show that the spectral width and energy intensity of the dispersive wave and tunneling soliton generation can be well controlled by adjusting the barrier width and initial parameters of the pulse. These research results provide a theoretical basis for generating and manipulating high-power mid-infrared supercontinuum sources. [ABSTRACT FROM AUTHOR]

The Sixth Generation (6G) networks have identified the use of frequency range between 95 GHz and 3 THz with a targeted data rate of 1 Terabytes/second at the access network for holographic video applications. As is demands broadening of spectrum at the core network, this paper proposes a Supercontinuum Generation (SCG) through photonic crystal fiber (PCF) as it provides excellent broadening of the optical spectrum. Discussed in the paper is supercontinuum generation at high pumping power as per the standards specified by the International Telecommunications Union. The proposed PCF is designed with silicon nanocrystal core and the cladding microstructures is arranged in a fusion approach to effectively optimize the optical parameters such as dispersion, nonlinearity, birefringence, group‐velocity dispersion, and confinement loss. The fused cladding comprises of a flower‐cladding assembly in which air‐holes arrangement is inspired from petals in a pleated structure. Such arrangement is shown here to provide high nonlinearity and negative dispersion for high power supercontinuum generation. The novel nanocore assembly with improved structural constraints delivers a non‐linearity of 6.37 × 106 W−1 km−1 and a negative dispersion of −142.1 (ps/nm‐km) at 1,550 nm. Moreover, a supercontinuum spectrum is generated using different pulse widths ranging from 350 to 650 ps with 25 kW pump power for PCF lengths of 10 and 15 mm. Key Points: A Supercontinuum Generation through photonic crystal fiber (PCF) is proposed which provides excellent broadening of the optical spectrumPCF designed with silicon nanocrystal core and cladding microstructures is arranged in fusion approach to optimize the optical parametersThe structural analysis of nano‐core PCF with fused cladding provides a baseline for designing the 6G architecture [ABSTRACT FROM AUTHOR]

This study proposes a novel supercontinuum (SC) shaping method using an all-fiber structure with little influence on the time domain and frequency domain of the SC spectrum. An SC is a type of laser source with a broad spectrum. However, its pump wavelength has a much greater intensity than other wavelengths, limiting the application of the SC. Our approach takes advantage of a hollow core anti-resonance fiber to attenuate the power density at the pump wavelength appropriately, thus flattening the SC spectrum. Simulation and experimental results both support the effectiveness of this method in reducing the wavelength at the pump. In our experiment, the use of a hollow core anti-resonant fiber decreased the intensity at the pump wavelength of the SC by 9 dB. By employing this method, the energy threshold can be lowered, allowing the SC to be applied to a larger range of experimental setups or applied scenarios with fewer energy requirements. [ABSTRACT FROM AUTHOR]

The control of rogue waves in mid-infrared SC generated by pumped femtosecond pulses in chalcogenic optical fibers abnormal dispersion has been studied. And the control effect of the time delay between the seed light and the pump light on the rogue wave in the mid infrared supercontinuum is numerically studied. A seed is emitted into the photonic crystal fiber with an appropriate time delay to control the soliton trajectory. The results show that the appropriate negative time delay will increase the possibility of the formation of rogue waves in the mid-infrared supercontinuum, while the appropriate positive time delay will inhibit the formation of rogue waves. In addition, we also numerically study the influence of the peak power of the pump light on the formation of rogue waves. With the change of peak power, rogue waves will be promoted or suppressed. We believe that this study will provide new insights into the control of rogue waves. [ABSTRACT FROM AUTHOR]

High-precision electro-optic distance measurement (EDM) is essential for deformation monitoring. Although sub-ppm instrumental accuracy is already feasible with state-of-the-art commercial technology, the practically attainable accuracy on distances over more than a few hundred meters is limited by uncertainties in estimating the integral refractive index along the propagation path, which often results in measurement errors of several ppm. This paper presents a new instrumental basis for high-accuracy multispectral EDM using an optical supercontinuum to enable dispersion-based inline refractivity compensation. Initial experiments performed on two spectrally filtered bands of 590 and 890 nm from the supercontinuum show measurement precision better than 0.05 mm over 50 m for an acquisition time of around 3 ms on the individual bands. This represents a comparable performance to our previously reported results on 5 cm by over a range of 3 orders of magnitude longer, which can still be improved by increasing the acquisition time. The preliminary results indicate a relative accuracy of about 0.1 mm at 50 m on each wavelength. Improvement is possible by calibration and by implementing a self-reference scheme that mitigates slow drifts caused by power-to-phase coupling. The results reported herein thus indicate that the presented approach can be further developed for achieving sub-ppm accuracy of refractivity compensated distance measurements on practically useful ranges and under outdoor conditions. [ABSTRACT FROM AUTHOR]

Over the last decade, intense interest in both basic science and industry has been generated by the physics and uses of fiber-based supercontinuum (SCG) sources. Here, we present our findings about the design and characterization of PCFs based on Tellurite, which combines the following benefits: high nonlinearity, high Birefringence (BR), formation of supercontinuum, coherent normal dispersion profile, and optical range transmission potential with flattened chromatic dispersion profile equal 0.5327 ps/nm km up to a wavelength of around 1.65 μm. Optical properties such as Birefringence, confinement losses (CL), effective refractive index (Neff) and effective mode area (Aeff) are comprehensively examined and explored using the Finite element method (FEM) while employing the solution of nonlinear Schrödinger equations (GNLSE) to profile the temporal and spectral wave propagation. The simulation results show that zero-dispersion is achieved in the proposed PCF design at 1.5 to 1.65 μm. The chosen fiber topology can produce a large supercontinuum spectrum from approximately (1200–2000) nm covering S–C–L bands. The designed PCF will be a good fit for various applications, including biophotonics, Spectroscopy, biosensing, biomedical imaging, and ultra-broadband signal amplification. [ABSTRACT FROM AUTHOR]

We theoretically investigated the properties of the ultraviolet secondary radiation generated under the action of three-color ionizing pulses obtained from parametric light generators. We show that the combination components in the spectrum of electron currents generated under the action of such three-color pulses can form a strictly exponentially decreasing sequence. For moderately short pump pulse durations (30 fs at 800 nm main field) with the use of this effect, it is possible to generate a smooth broadband supercontinuum in the 800–100 nm range. [ABSTRACT FROM AUTHOR]

The ghost imaging technique allows us to recover information about an object in conditions of noisy transmission channels, commensurate with the intensity of the speckle structures involved in the reconstruction. One of the main disadvantages of this technique is relatively slow reconstruction speed. This limits its applicability for study of dynamic processes or fast-moving objects. In this paper, we propose a modification of the computational ghost imaging technique that allows us to overcome this limitation. It is shown that the spectral multiplexing of the speckle patterns speeds up the image reconstruction. Increase in the number of spectral channels from 4 to 10 leads to the increase of the signal-tonoise ratio by the factor of 6. Simultaneously, under the same conditions and with the same number of measurements classical monochrome ghost imaging does not reconstruct the picture at all. This makes the proposed technique attractive for high-speed demanding applications such as communications and remote sensing.

The object of the research is deleting the interaction of the higher order soliton interaction by introducing the third and fourth order dispersions inside an optical fiber. The results are obtained by the simulation of the nonlinear Schrödinger equation, which models the propagation of solitons in the optical fiber using the method of Fast Fourier Transform. The interaction of two higher order solitons due to the attraction of their electric field can lead to losing the solitons’ properties. Hence, this can prevent the use of solitons in high-bit-rate optical fiber communication systems because it increases the bit error rate, significantly limiting the potential of the communication system. To resolve this problem, we should diminish the bit rate error by avoiding the interaction of the co-propagative solitons when they are too close. It is well known that, during higher order soliton propagation in the presence of the third order dispersion, the irregular shape of the higher order soliton disappears, and a splitting towards its fundamental constituents occurs after a considerable propagation. As for the fourth order, dispersion gives rise to two dispersive wave sidebands on the red or blue side. Our results reveal that bringing two higher order solitons together in the presence of the fourth order dispersion, a series of interactions between the components generated after their fission is obtained. In the third-order distribution, besides the fourth-order diffusion, the rare form and the supercontinuum generated by the fission of the higher-order solitons disappear, and we get two fundamental solitons propagating in parallel with a temporal shift and some inconsiderable dispersive waves. The most important aspect is that both higher-order dispersions are able to suppress the interactions of higher-order solitons thanks to the time shift induced by the third-order distribution and the intermittent compression caused by the fourth-order scattering. These results can be obtained in practice inside the dispersion-engineered photonic crystal waveguide (PhC-wg), which allows for manipulating the high order dispersion. [ABSTRACT FROM AUTHOR]

Supercontinuum (SC) has opened up possibilities for numerous applications in optical communications, signal processing, metrology, and spectroscopy. Supercontinuum generation (SCG) in the integrated nonlinear platforms has attracted much interest recently, due to its fundamental advantages in terms of complementary metal oxide semiconductor compatibility, low power consumption, compact size, and cost‐effectiveness. In this paper, the latest progress on various types of nanophotonic waveguides for SCG is reviewed. The material properties of silicon, germanium, silicon–germanium alloy, silicon nitride, silica, chalcogenide, III–V materials, lithium niobate, and other materials, which are used as nonlinear media for SCG are discussed. The wavelength‐dependent nonlinear Kerr index, material, and nonlinear loss of the waveguides are taken into account. This review mainly focuses on the SCG resulting from the cubic χ(3) nonlinearity processes pumped by the femtosecond pulse. The recent representative SCG works based on the integrated optical waveguides are summarized, and further classified according to the dispersion characteristics. Furthermore, different types of spectra broadening mechanisms in details according to the classifications are analyzed. Perspectives on the SC spectral coverage, the realization of various dispersion curves, and the novel materials, which are the key aspects of the SCG in nanophotonic waveguides are provided. [ABSTRACT FROM AUTHOR]

We present a compact and cost-effective mJ-level femtosecond laser system operating at a center wavelength of approximately 2.15 µm. An affordable two-stage ytterbium-doped yttrium aluminum garnet (Yb:YAG) chirped pulse amplifier provides more than 10 mJ, approximately 1.2 ps pulses at 1030 nm to pump a three-stage optical parametric chirped pulse amplifier (OPCPA) based on bismuth borate crystals and to drive the supercontinuum seed in the YAG crystal. The energy of the amplified pulses in the wavelength range of 1.95-2.4 µm reached 2.25 mJ with a pump-to-signal conversion efficiency of approximately 25% in the last OPCPA stage. These pulses were compressed to 38 fs in a pair of Suprasil 300 glass prisms. [ABSTRACT FROM AUTHOR]

Multiple higher-order Stokes of rotational stimulated Raman scattering (SRS) in compressed hydrogen covered the wavelength range from ~1.1 µm to ~1.4 µm using ~1.2 ps pump pulses from a Yb:YAG laser. In this study, the influence of polarization, energy, and the focusing conditions of the pump pulse, as well as gas pressure, on the conversion efficiency and modification of the spectral envelope of rotational and vibrational SRS was investigated. The use of a supercontinuum seed, as well as circular polarization of pump pulses at high hydrogen pressure, made it possible to significantly reduce the threshold for rotational SRS and suppress vibrational Stokes modes. The cascade excitation of rotational SRS, corresponding to a shift of 587 cm−1, ensured a spectrum spanning four Stokes orders withs a conversion efficiency of 52% and an output energy exceeding 3 mJ. The synthesized spectrum corresponded to ~14 fs transform-limited pulses.

We fabricated a core-cladding Ge–Sb–Se glass fiber with a Ge12.5Sb15Se72.5 core and Ge15Sb10Se75 cladding, achieved a supercontinuum spectrum spanning from 2 μm to 9 μm by pumping the Ge–Sb–Se fiber with a core diameter of 11 μm using a femtosecond laser pump at 3.8 μm, and numerically simulated the supercontinuum generation using the generalized nonlinear Schrödinger equation. In particular, we investigate the effect of the different Raman response functions that were calculated using the traditional single Lorentzian model and a multiple vibrational mode model on the evolution of the supercontinuum by comparing the supercontinua obtained from simulation and experimental results. We demonstrate that the Raman response function generated by the multiple vibrational mode model captures the actual response behavior of the material, and the supercontinuum generated using this model has more accuracy. To the best of our knowledge, this is the first reported study on supercontinuum generation in Ge–Sb–Se fiber utilizing a Raman response function calculated using the multiple vibrational mode model. This significant advancement enables more accurate simulation of supercontinuum generation in fibers with a multi-peaked structured Raman gain spectrum and holds great potential for optimizing the performance of various mid-infrared supercontinuum sources.

We experimentally studied the supercontinuum induced by femtosecond filamentation in different liquid media. Using a Mach–Zehnder interferometer, we determined the relative filamentation thresholds (Pth) of these media. Research has shown that the value of the filamentation threshold is greater than that of Pcr (critical power for self-focusing), which can mainly be attributed to the strong dispersion effect. Changing the focal length of the focusing lens affects filamentation dynamics, thereby affecting the measured results regarding the filamentation threshold. With shorter focal lengths, the linear focusing (i.e., geometrical focusing) regime dominates, and the measured values of Pth for different liquid media are almost the same; as the focal length becomes larger, self-focusing starts to play a role, making the values of Pth for different media different from each other. This study presents an efficient method for investigating the femtosecond filamentation phenomenon in liquid media, helpful to provide further insights into the physical mechanism of supercontinuum generation via femtosecond filamentation in liquid media.

Miniaturization of frequency-comb sources could open a host of potential applications in spectroscopy, biomedical monitoring, astronomy, microwave signal generation, and distribution of precise time or frequency across networks. This review article places emphasis on an architecture with a semiconductor mode-locked laser at the heart of the system and subsequent supercontinuum generation and carrier-envelope offset detection and stabilization in nonlinear integrated optics.

We present a compact and cost-effective mJ-level femtosecond laser system operating at a center wavelength of approximately 2.15 μm. An affordable two-stage ytterbium-doped yttrium aluminum garnet (Yb:YAG) chirped pulse amplifier provides more than 10 mJ, approximately 1.2 ps pulses at 1030 nm to pump a three-stage optical parametric chirped pulse amplifier (OPCPA) based on bismuth borate crystals and to drive the supercontinuum seed in the YAG crystal. The energy of the amplified pulses in the wavelength range of 1.95–2.4 μm reached 2.25 mJ with a pump-to-signal conversion efficiency of approximately 25% in the last OPCPA stage. These pulses were compressed to 38 fs in a pair of Suprasil 300 glass prisms.

Herein, a tellurite multimode optical fiber with a rectangular step‐index core to combine easy coupling of the pump power with the exceptionally cubic nonlinearity of such type of glass is developed. An alkali‐free composition (TeO2–ZnO–La2O3) is prepared to produce a preform with the use of both the stack‐and‐draw and the direct‐bonding methods. The linear and nonlinear optical responses of the fiber are characterized and are then used to generate a homogeneous supercontinuum (SC) in the near‐infrared domain. The spectral broadening, which is obtained in this work in a short fiber sample, is used for imaging mouse kidney cells, labeled with three different fluorochromes, by means of two‐photon absorption (2PA) and three‐photon absorption (3PA). Despite the multimode nature of the output beam, clear images of tubules, actin, and nucleus are collected with a spatial resolution down to 1.2 μm. Although image acquisition at better resolution has already been reported in the literature using relatively long spans of graded‐index silica multimode fibers, here, the combination of high third‐order susceptibility of the glass and the large Raman gain in short segments of tellurite fiber is exploited to obtain nonlinear imaging with adequate spatial resolution.

We measured the divergence angles of supercontinuum fiber sources from various types of silica fibers in the spectral range from 0.5 to 2.3 μ m, covering almost the entire range of supercontinuum that can be generated from silica fibers. The divergence angle of the supercontinuum directly output from the photonic crystal fibers (PCFs) increases monotonously with the increase of the wavelength. The divergence angle of the supercontinuum after transmitting through single-mode fibers, including HI1060, SMF-28 and 10/130 fibers, increases firstly and decreases then with the increase of the wavelength. The turning point is different for the three kinds of fibers. The beam parameter product (BPP) increases monotonously with wavelength for both the PCF and the single-mode fibers. Theoretical calculations are also made for the mentioned four types of fibers. The divergence angle of supercontinuum after transmitting through multimode fibers with 50, 100 and 200 μ m core diameters is also measured, which varies in a certain range without obvious rules depending on the wavelength. [ABSTRACT FROM AUTHOR]

A nitrobenzene liquid-core photonic crystal fiber (NLC-PCF) with eight elliptical air-holes in the innermost ring of the cladding is proposed in this work, and this fiber structure can contribute to flexibly adjusting dispersion and constraining the fiber core. The appreciable dispersion is realized by adjusting the structural parameters of NLC-PCF, which is characterized by three zero-dispersion wavelengths (ZDWs), flat dispersion with the fluctuation of fewer than 40 ps nm−1 km−1, and high nonlinearity as high as 5500 W−1 km−1. The propagation of femtosecond pulse and supercontinuum generation (SCG) in NLC-PCF is studied numerically when the pump wavelength is located in the normal and abnormal dispersion region near different ZDW through solving the generalized nonlinear Schrödinger equation (GNLSE) by the split-step Fourier method. The numerical results show that a highly coherent supercontinuum (SC) spanning from 1.3 to 2.8 µm is obtained when the pump pulse with the center wavelength of 1810 nm, the peak power of 1000 W, and pulse width of 50 fs propagated in the 5 cm long NLC-PCF. This research can find applications in the fields of novel liquid-core PCF design and ultrashort pulse propagation. [ABSTRACT FROM AUTHOR]

Multiband supercontinuum generation covering the bandwidth from 0.65 μm to 3.3 μm was demonstrated in a gas-filled hollow-core silica fiber pumped by chirped ultrashort pulses at 1.03 μm. The development of the SC spectrum into the mid-IR was initiated by cascade stimulated Raman scattering in gaseous D2, which was used as an active medium filling the hollow core. The influence of the Kerr nonlinearity was studied by changing the linear chirp of the pump pulses. The influence of gas pressure and pump pulse energy on the SC generation was investigated. As high as 14% of pump quanta were converted to the wavelength range above 2 μm. [ABSTRACT FROM AUTHOR]

The step-index heavily germanium-doped silica fibers with all normal dispersion (ANDi) are promising candidates for highly coherent supercontinuum (SC). These ANDi step-index silica fibers are easier to fabricate, splice and handle than silica photonic crystal fibers (PCFs). 40% GeO2 doped step-index silica fiber of 3 μm core diameter has flat and near-zero dispersion which is between −5.5 and 0 ps/nm/km from 1.4 to 2.4 μm. Highly coherent SC spanning from 1050 nm to 2100 nm generated from the ANDi step-index heavily germanium-doped silica fiber pumped at 1560 nm. All-fiber coherent SC source from 1200 nm to 2200 nm is achieved by splicing the ANDi silica fiber with a 1560 nm femtosecond fiber laser of 90% couple efficiency. Moreover, the step-index ANDi germania-core silica fiber of 2.2 μm core diameter is proposed to generate coherent mid-infrared SC from 1.7 to 3 μm. The ANDi step-index silica fibers not only can generate highly coherent broadband SC at near infrared or mid-infrared region but also can easily achieve all-fiber structure coherent SC source. And the experiment of supercontinuum generation in UNNA4 and UHNA7 fibers with different pump wavelengths indicates that the pump of 1064 nm is not suitable for coherent supercontinuum generation in the fiber of UNNA4 and UHNA7.

In this work, we design and numerically investigate a silica-cladded Germania-doped ring-core fiber (RCF) that supports orbital angular momentum (OAM) modes with all-normal dispersion. By optimizing the structure parameters of the designed RCF, an all-normal and flat dispersion with a total variation of 1,1 mode. A 1.3-octave supercontinuum spectrum of the OAM1,1 mode is generated numerically after launching a 40-fs 200-kW chirp-free hyperbolic secant pulse train centered at 1700 nm into a 2-cm long designed fiber with 50 mol% Ge-doped ring-core, covering 1290-nm bandwidth from 885 nm to 2175 nm at −40 dB power level. The coherence of the generated supercontinuum of the OAM1,1 mode depicts nearly perfect property over the whole spectral range. This design can serve as an efficient way to extend the spectral coverage of beams carrying OAM modes in various applications.

An all-fiber supercontinuum (SC) laser source with 50.7 W average output power and spectrum ranging from 500 nm to 2400 nm is demonstrated. With the generation of high peak power nanosecond pulses and photonic crystal fiber (PCF) in the self-Q-switched fiber laser, the output SC shows good spectral width and flatness which has a 20 dB bandwidth of 1900 nm except the 1064 nm peak. The effect of the PCF length on the spectral characteristics and output power of SC were carefully studied. To the best of our knowledge, this is the highest power of SC generated in a single-stage fiber laser with such a broadband spectrum. This ultra-compact SC generation method has the merits of simple structure, low cost and good robustness, which provide an easily available SC generation method for various practical applications.

This paper presents the first systematic study on second harmonics generation based on a supercontinuum source. We analyzed the effect of the supercontinuum beam diameter and the crystal length to generate second harmonics. The walk-off effect on the second harmonics was also investigated; the efficiency was limited by the walk-off, and the beam of the second harmonic was out of shape. A tunable ultraviolet in the range of 285–340 nm is obtained with the pump of a visible supercontinuum, which is generated by a laser with an all-fiber device. The results provide a theoretical basis for the improvement of the second harmonic power and optimization of the crystal and beam diameters. A potentially tunable ultraviolet with a power exceeding 10 mW can be obtained by a high-power supercontinuum pump.

• Elevated the average power of linearly polarized supercontinuum to over 300 watts, while preserving good beam quality. • A spectral subtraction method is introduced in detail and demonstrate that it can measure the polarization extinction ratio of hundred-watt level linearly-polarized supercontinuum and accurately reflect the polarization state at each wavelength range. • An interesting four-wave mixing phenomenon between the two orthogonal polarization states is observed. We report an all-fiber linearly-polarized supercontinuum laser source with 322.5 W average output power and spectrum covering 800 nm to 2200 nm. A spectral subtraction method is utilized to measure the polarization extinction ratio (PER) of the laser source, which can directly measure the PER of each single wavelength within a wide spectral range. Through detail observation of the PER distribution along wavelengths, an interesting four-wave mixing (FWM) phenomenon between the two orthogonal polarization states is found in the laser system. [ABSTRACT FROM AUTHOR]

• An efficient hybrid network for supercontinuum generation prediction proposed. • Wasserstein generative adversarial network augments the original dataset. • Deep neural network with a TCN layer predicts supercontinum spectrum accurately. In this paper, a Hybrid Network is reported for predicting the output pulse shape parameters of the supercontinuum in optical fibers. The network incorporates the Wasserstein generative adversarial network (WGAN) and the deep neural network (DNN) with a TCN layer. The WGAN augments a limited set of original data, while the designed DNN accurately predicts supercontinuum. The simulation results show the spectra agreement (A gm) of the predictions by individual DNN is 89% and the root mean square error (RMSE) is 0.1092. After retraining with WGAN's extended dataset, the A gm of DNN predictions is improved to 98% and the RMSE is reduced to 0.0513. The input pump power corresponding to the appearance of the fourth soliton peak can be predicted by the retrained DNN. Numerical analysis demonstrates the effectiveness and generalization ability of a Hybrid Network in predicting pulse parameters. The network fits the propagation dynamics in the spectral domain of SC, which provides a promising tool for further research in this field. [ABSTRACT FROM AUTHOR]

The supercontinuum generation and manipulation of Airy-Gaussian pulses in a photonic crystal fiber with three zero-dispersion points are studied using the split-step Fourier method. Firstly, the spectral evolution of Airy-Gaussian pulses in four photonic crystal fibers with different barrier widths was discussed, and the optimal fiber was determined after considering the factors of width and flatness. By analyzing the mechanism of supercontinuum generation in photonic crystal fibers with single, double and three zero-dispersion points, it is found that the photonic crystal fiber with three zero-dispersion points have a larger spectral width due to the component of tunneling solitons. Then, the effects of four characteristic parameters (truncation factor a, distribution factor χ0, initial chirp C and central wavelength λ) on forming the supercontinuum spectrum of Airy-Gaussian pulses are analyzed in detail. The results show that the spectral width and energy intensity of the dispersive wave and tunneling soliton generation can be well controlled by adjusting the barrier width and initial parameters of the pulse. These research results provide a theoretical basis for generating and manipulating high-power mid-infrared supercontinuum sources.

In this paper, the nonlinear properties of photonic crystal fibers (PCF) with As2S3 substrate were analyzed numerically. With the suspended-core design, we achieve an anomalous dispersion regime with one or two zero-dispersion wavelengths, which is flat and has a small value at the investigated wavelength. The high nonlinear coefficient and very low confinement loss in the wavelength range of 1–3 µm, in comparison with other publications, are the outstanding advantages of these suspended-core PCFs. The highest nonlinear coefficient (28,527.374 W–1·km–1), smallest effective mode area (0.593 µm2), and low confinement loss (6.050 × 10–17 dB·m–1) at the wavelength of 1.55 µm were observed in the PCFs with a fiber diameter of 16.07 μm. Based on the numerical simulation results, we proposed two optimal structures suitable for supercontinuum generation.

We review methods for precision transfer of frequencies across broad optical wavelength ranges. Single-branch supercontinuum generation allows for a frequency transfer stability of < 1 × 10−17 in 1 s across an octave. With supercontinuum stitching, highly coherent supercontinuum spectra spanning across more than two octaves are generated. With noise cancellation techniques a relative frequency transfer stability of ≈ 2 × 10−18 in 1 s can be achieved. Highly stable frequency transfer along with a maximization of power per mode at multiple freely selectable frequency bands is further enabled via pulse shaping techniques. We also include a brief review of general fiber combs and research aimed at frequency extension of frequency combs covering the whole spectral range from the XUV to the mid IR, power scaling of frequency combs as well as low noise microwave and mmwave technology enabled with frequency combs.

We investigate the input and propagation characteristics and geometric parametric instability of the partial Gaussian beam limited by the fiber face area in a graded-index multimode fiber. The theoretical simulation shows that the energy of the partial Gaussian beam and the coupling efficiency of the fiber face are restricted by the fiber face area for the different powers and spot sizes of the input Gaussian beam. The spot intensity pattern of the partial Gaussian beam exhibits a standard oscillating distribution in space as the beam undergoes periodic oscillations with propagation. Also, the dynamic evolution process from parametric sidebands to a supercontinuum is affected by the peak power, the spot size of the partial Gaussian beam, and the fiber length. Finally, the experimental output spectra with different powers of the partial Gaussian beam and fiber lengths in a graded-index multimode fiber confirm the prediction of theoretical simulations. This work provides practical guidance for optimizing supercontinuum source expansion and spectral power density.

We designed a structure of dual-coupled ridge waveguide in thin-film lithium-niobate-on-insulator (LNOI) and numerically studied the highly efficient, broadband, and flattened dispersive wave-enhanced supercontinuum generation in the mid-infrared region. By leveraging the mode coupling of the proposed dual-coupled waveguide structure, one of the supermodes, namely the anti-symmetric mode, can produce additional zero-dispersion wavelengths in the mid-infrared region, and consequently multiple normal dispersion regions for dispersive wave emission. Given the rich geometrical degrees of freedom powered by this dual-coupled LNOI waveguide structure, we can tailor the dispersion profile so that a well-established mode-locked fiber laser in the telecommunication band can serve as the pump. Thus, the whole system can potentially be fiber-to-chip integrated and packaged, enabling a compact, cost-effective, and low system-complexity platform. We numerically show that the broadband dispersive wave covering the wavelength range of 1.92~3.55 μ m (−20 dB level, near octave-spanning) with spectral flatness of 6.31 dB can be achieved using a 1550 nm, 190 pJ femtosecond pump seed. When the dual hump-shaped spectrum is obtained, the conversion efficiency of the mid-infrared dispersive wave can be up to 19.31%. The influence of the pumping conditions on the performance of mid-infrared dispersive wave generation was also studied. This work provides a competitive candidate for efficient, broadband, and flattened mid-infrared spectrum generation, which can find important applications in spectroscopy, metrology, and communication. [ABSTRACT FROM AUTHOR]

In this paper, we design a silica-cladded Germania-doped ring-core fiber (RCF) that supports orbital angular momentum (OAM) modes. By optimizing the fiber structure parameters, the RCF possesses a near-zero flat dispersion with a total variation of <±30 ps/nm/km over 1770 nm bandwidth from 1040 to 2810 nm for the OAM1,1 mode. A beyond-two-octave supercontinuum spectrum of the OAM1,1 mode is generated numerically by launching a 40 fs 120 kW pulse train centered at 1400 nm into a 12 cm long designed 50 mol% Ge-doped fiber, which covers 2130 nm bandwidth from 630 nm to 2760 nm at −40 dB of power level. This design can serve as an efficient way to extend the spectral coverage of beams carrying OAM modes for various applications. [ABSTRACT FROM AUTHOR]