Supercontinuum Generation Process Research Articles

Supercontinuum Generation in Naturally Occurring Glass Sponges Spicules

The complex process of supercontinuum generation (SG) is known to be exploitable for designing spatially coherent white light sources emitting light simultaneously in the ultraviolet, visible, and infrared ranges. Herein the first natural material able to generate in laboratory conditions a supercontinuum similar to those known from man‐made photonic crystal fibers is described. The ability resides in siliceous 20–50 cm long spicules of the glass sponge Sericolophus hawaiicus. By shedding into the spicules optical peak intensities ranging from 1 to 100 TW cm−2 the generation of a SG is revealed. The SG involves wavelengths between 650 and 900 nm and shows a maximum spectral spread for excitation at a wavelength of 750 nm. It is hypothesized that the SG is favored by spicules being a biocomposite that incorporates together isotopically pure biogenic silica (δ30Si = −3.28) and 15.2 ± 1.3 μg N‐acetyl‐glucosamine (chitin) per mg of silica. The internal organization of these spicules is distinguished by a solid silica core with a 1 μm wide axial channel as well as a highly ordered silica–chitin composite. Such a composition and organization pattern may be of potential interest for the design of low temperature synthesis of future materials for light guidance.

Effect of Temperature on Supercontinuum Generation in Water-Core Photonic Crystal Fiber

We study the temperature-dependent features of nonlinear pulse propagation in a water-core photonic crystal fiber, which are found to significantly impact the process of supercontinuum generation (SCG). After solving the temperature-dependent fiber parameters, we model pulse propagation with a modified nonlinear Schrodinger equation. The subsequent generated supercontinuum displays a spectral bandwidth that strongly depends on the temperature varied between 55 °C and 75 °C. This could represent an original way to tune SCG, or conversely, make the basis of a temperature sensor.

Tunable Broadband Spectrum Under the Influence of Temperature in IR Region Using CS<inline-formula> <tex-math notation="LaTeX">$_2$</tex-math> </inline-formula> Core Photonic Crystal Fiber

We theoretically demonstrate a bandwidth tunable broadband light spectrum in IR region, using a CS $_2$ core photonic crystal fiber (CSPCF) by varying its temperature. The broadband spectrum is generated via modulation instability (MI) induced supercontinuum (SC) generation process by considering the thermooptic coefficient of CS $_2$ liquid. The temperature-dependent fiber parameters are utilized to solve the nonlinear Schr $\ddot{\mathrm {o}}$ dinger equation, which is modified with the effect of saturable nonlinearity of CS $_2$ . By using numerical simulation, generation of new photons through the process of MI and subsequent evolution of SC spectrum are analyzed under the influence of temperature. The generated SC spectrum shows a variation of a several hundred nanometers in its bandwidth with a change of mere 20 $^\circ$ C in the temperature of CSPCF. It is found that the bandwidth of SC spectrum can be tuned from 688 nm to 1022 nm by varying temperature, saturable parameter, and pump power. The proposed tunable SC spectrum finds application in IR spectroscopy, optical coherence tomography, etc.

Polarization instability of Raman solitons ejected during supercontinuum generation.

We numerically investigate polarization instability of soliton fission and the polarization dynamics of Raman solitons ejected during supercontinuum generation in a photonics crystal fiber using the coupled vector generalized nonlinear Schrödinger equations for both linear and circular birefringent fibers. The evolution of the state of polarizations of the ejected Raman soliton as representated on the Poincaré sphere is affected by both nonlinear and linear polarization rotations on the Poincaré sphere. The polarization dynamics reveal the presence of a polarization separatrix and the emergence of stable slow and unstable fast eigen-polarizations for the Raman solitons ejected in the supercontinuum generation process. Circularly birefringent fiber is investigated and found to simplify the nonlinear polarization dynamics.

Soliton fission and supercontinuum generation in photonic crystal fibre for optical coherence tomography application

We present a practical design of novel photonic crystal fibre (PCF) to investigate the nonlinear propagation of femtosecond pulses for the application of optical coherence tomography (OCT) based on supercontinuum generation (SCG) process. In addition, this paper contains a brief introduction of the physical phenomena of soliton and SCG. Typically, here we discuss how the ultrabroadband radiation in PCF can be generated by SCG through various nonlinear effects of the fibre. To accomplish the proposed aim, we put forth liquid core PCF (LCPCF) structure filled with chloroform for OCT measurements of the eye. From the proposed design, we observe that proposed LCPCFs with liquid material exhibit significant broadened wavelength spectrum with low input pulse energy over small propagation distances for the OCT application.

Modelling of Supercontinuum Generation in the Germanium-on-Silicon Waveguided Platform

The influence of high-order susceptibilities on the supercontinuum generation process in germanium-on-silicon waveguides has been investigated in detail in the midinfrared. The frequency dispersion of both the three-photon absorption coefficient and the real part of the fifth-order susceptibility has been investigated in order to develop a self-consistent modeling based upon a generalized nonlinear Schrodinger equation. Numerical results demonstrate that germanium-on-silicon waveguides can be used to induce supercontinuum generation over 1.34-μm-wide bandwidth with 200-fs input pulses pumped at a wavelength of 4 μm with peak pump powers of 89 W and waveguide lengths of 4.6 mm. The soliton fission process has also been observed as it is the main mechanism behind the supercontinuum generation.

Generation of a compact high-power high-efficiency normal-dispersion pumping supercontinuum in silica photonic crystal fiber pumped with a 1064-nm picosecond pulse

Broadband normal dispersion pumping supercontinuum (SC) generation in silica photonic crystal fiber (PCF) is investigated in this paper. A 1064-nm picosecond fiber laser is used to pump silica PCF for the SC generation. The length of PCF is optimized for the most efficient stimulated Raman scattering process in the picosecond pump pulse region. The first stimulated Raman Stokes peak is located in the anomalous dispersion regime of the PCF and near the zero dispersion wavelength; thus the SC generation process can benefit from both a normal dispersion pumping scheme and an anomalous dispersion pumping scheme. The 51.7-W SC spanning from about 700 nm to beyond 1700 nm is generated with an all-fiber configuration, and the pump-to-SC conversion efficiency is up to 90%. In order to avoid the output fiber end face damage and increase the stability of the system, an improved output solution for the high power SC is proposed in our experiment. This high-efficiency near-infrared SC source is very suitable for applications in which average output power and spectral power density are firstly desirable.

A colloquium on the influence of versatile class of saturable nonlinear responses in the instability induced supercontinuum generation

We investigate the modulational instability induced supercontinuum generation (MI-SCG) under versatile saturable nonlinear (SNL) responses. We identify and discuss the salient features of saturable nonlinear responses of various functional forms such as exponential, conventional and coupled type on modulational instability (MI) and the subsequent supercontinuum (SC) process. Firstly, we analyze the impact of SNL on the MI spectrum and found both analytically and numerically that MI gain and bandwidth is maximum for exponential nonlinearity in comparison to other types of SNL’s. We also reported the unique behavior of the SNL system in the MI dynamics. Following the MI analysis, the proceeding section deals with the supercontinuum generation (SCG) process by virtue of MI. We examine exclusively the impact of each form of SNL on the SC spectrum and predicted numerically that exponential case attains the phase matching earlier and thus enable to achieve broad spectrum at a relatively shorter distance of propagation than the other cases of SNL’s. Thus a direct evidence of SCG from MI is emphasized and the impact of SNL in MI-SCG is highlighted. To analyze the quality of the output continuum spectrum, we performed the coherence analysis for MI-SCG in the presence of SNL.

Investigation of hundred-watt-level supercontinuum generation in photonic crystal fiber

A 101 W all-fiber supercontinuum soure is demonstrated by seeding a piece of photonic crystal fiber with a high-power pulse-repetition-rate-tuning picosecond fiber laser. By performing a series of comparative experiments, influences of the pump pulse repetition rate and the photonic crystal fiber length on the supercontinuum generation process are investigated in detail. How to improve the power level of the supercontinuum soure is analyzed and discussed. The research results will make a contribution to the further development of high-power supercontinuum soure.

Tip‐enhanced broadband CARS spectroscopy and imaging using a photonic crystal fiber based broadband light source

We report tip‐enhanced broadband coherent anti‐Stokes Raman scattering (CARS) spectroscopy and imaging based on a broadband light source using a photonic crystal fiber. Multiplexing from 900 cm–1 to 2200 cm–1 is achieved by optimizing the supercontinuum generation process at a high numerical aperture focus. By combining this system with a shear‐force microscope, semiconducting carbon nanotubes are imaged with a spatial resolution of 60 nm. Our results show that tip‐enhanced broadband CARS image exhibits a positive contrast even though the enhancement effect has not been fully optimized. Analyses of delay‐dependent tip‐enhanced broadband CARS spectra suggest the possibilities of multiple carrier interactions that uniquely occur at high intensities within the nanotubes. Copyright © 2012 John Wiley & Sons, Ltd.

Soliton-induced supercontinuum generation in liquid-filled photonic crystal fibre

We aim to study the nonlinear optical phenomena with ultra-broadband radiation in photonic crystal fibre (PCF). While PCFs with cores made from different glasses are well studied in previous works, in this paper, it is planned to investigate the dynamics of nonlinear processes of supercontinuum generation (SCG) in liquid-filled PCF (LCPCF) to understand the physical phenomena of femtosecond pulse propagation, particularly, the temporal and spectral changes of the pulse propagating through specific PCFs. Since the CS2-filled LCPCF has complex nonlinear phenomena, we intend to analyse the role of saturable nonlinear response and slow nonlinear response on SCG in detail. For the physical explanation, soliton fission and modulational instability techniques will be implemented to investigate the impact of slow nonlinear response and saturable nonlinear response respectively, in SCG process.

Broad and ultra-flattened supercontinuum generation in the visible wavelengths based on the fundamental mode of photonic crystal fibre with central holes

By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti: sapphire laser into the fundamental mode of photonic crystal fibre (PCF) with central holes fabricated through extracting air from the central hole, the broad and ultra-flattened supercontinuum (SC) in the visible wavelengths is generated. When the fundamental mode experiences an anomalous dispersion regime, three phases in the SC generation process are primarily presented. The SC generation (SCG) in the wavelength range from 470 nm to 805 nm does not emerge significant ripples due to a higher pump peak power and the corresponding mode fields at different wavelengths are observed using Bragg gratings. The relative intensity fluctuations of output spectrum in the wavelength ranges of 530 nm to 640 nm and 543 nm to 590 nm are only 0.028 and 0.0071, respectively.

Design of all-normal dispersion microstructured optical fibers for pulse-preserving supercontinuum generation

Recently, the generation of coherent, octave-spanning, and recompressible supercontinuum (SC) light has been demonstrated in optical fibers with all-normal group velocity dispersion (GVD) behavior by femtosecond pumping. In the normal dispersion regime, soliton dynamics are suppressed and the SC generation process is mainly due to self-phase modulation and optical wave breaking. This makes such white light sources suitable for time-resolved applications. The broadest spectra can be obtained when the pump wavelength equals the wavelength of maximum all-normal GVD. Therefore each available pump wavelength requires a specifically designed optical fiber with suitable GVD to unfold its full power. We investigate the possibilities to shift the all-normal maximum dispersion wavelength in microstructured optical fibers from the near infra red (NIR) to the ultra violet (UV). In general, a submicron guiding fiber core surrounded by a holey region is required to overcome the material dispersion of silica. Photonic crystal fibers (PCFs) with a hexagonal array of holes as well as suspended core fibers are simulated for this purpose over a wide field of parameters. The PCFs are varied concerning their air hole diameter and pitch and the suspended core fibers are varied concerning the number of supporting walls and the wall width. We show that these two fiber types complement each other well in their possible wavelength regions for all-normal GVD. While the PCFs are suitable for obtaining a maximum all-normal GVD in the NIR, suspended core fibers are well applicable in the visible wavelength range.

Modal four-wave mixing supported generation of supercontinuum light from the infrared to the visible region in a birefringent multi-core microstructured optical fiber

We experimentally studied the process of supercontinuum generation in a birefringent multi-core microstructured optical fiber. By selecting the excitation of the fundamental mode, or by combining the first and the second order modes of a particular core, it was possible to emphasize the role of four-wave mixing on the transfer of power from the infrared to the visible region of the spectrum. We carried out an in-depth analysis of the effects of input light polarization on the generated supercontinuum spectral features. The measured polarization properties of the output Stokes and anti-Stokes bands confirmed the strong vector nature of the four-wave mixing processes. The experimental spectra exhibit excellent agreement with numerical simulations of the nonlinear mode interactions.

Discrete spectral incoherent solitons in nonlinear media with noninstantaneous response

We show theoretically that nonlinear optical media characterized by a finite response time may support the existence of discrete spectral incoherent solitons. The structure of the soliton consists of three incoherent spectral bands that propagate in frequency space toward the low-frequency components in a discrete fashion and with a constant velocity. Discrete spectral incoherent solitons do not exhibit a confinement in the space-time domain, but exclusively in the frequency domain. The kinetic theory describes in detail all the essential properties of discrete spectral incoherent solitons: A quantitative agreement has been obtained between simulations of the kinetic equation and the nonlinear Schrodinger equation. Discrete spectral incoherent solitons may be supported in both the normal dispersion regime or the anomalous dispersion regime. These incoherent structures find their origin in the causality condition inherent to the nonlinear response function of the material. Considering the concrete example of the Raman effect, we show that discrete incoherent solitons may be spontaneously generated through the process of supercontinuum generation in photonic crystal fibers.

An efficient method for supercontinuum generation in dispersion-tailored Lead-silicate fiber taper

In this paper we theoretically study the broadband mid-IR supercontinuum generation (SCG) in a lead-silicate microstructured fiber (the glass for simulation is SF57). The total dispersion of the fiber can be tailored by changing the core diameter of the fiber so that dispersion profiles with two zero dispersion wavelengths (ZDWs) can be obtained. Numerical simulations of the SCG process in a 4 cm long SF57 fiber/fiber taper seeded by femto-second pulses at telecommunications wavelength of 1.55 µm are presented. The results show that a fiber taper features a continuous shift of the longer zero dispersion wavelength. This extends the generated continuum to a longer wavelength region compared to fibers with fixed ZDWs. The phase-matching condition (PMC) is continuously modified in the fiber taper and the bandwidth of the generated dispersive waves (DWs) is significantly broadened.

Infrared Supercontinuum Generation in Cladding of a Hollow-Core Fiber Pumped with a 1-ns 1.06-µm Nd3+:YAG/Cr4+:YAG Microchip Laser

We present an experimental treatment for the super-continuum (SC) generated through a hollow-core fiber by a nanosecond pulse launched from a Q-switched microchip Nd 3+ :YAG/Cr 4+ :YAG laser. The SC spectrally spans over a half-octave in near IR (~1.0-1.5 � m) and is attainable yet at fairly moderate fiber length (tens of cm). The SC generation process is shown to originate from silica nodes of the fiber cladding (secondary cores), where the pump radiation is tightly focused, and to be triggered out by a four-wave mixing process, which is boosted up by the Raman response in the fiber.

Generation of 045-138 μm visible to near-infrared widely broadened supercontinuum using Er-doped ultrashort-pulse fiber laser system

Visible to near-infrared, widely broadened supercontinuum generation is demonstrated using an ultrashort-pulse fiber laser system. A 229 mW, 83 fs high-power ultrashort pulse was generated at 1550 nm in an Er-doped fiber-chirped pulse amplification system. An almost pedestal-free 107 fs second-harmonic pulse was generated at 780 nm using periodically poled LiNbO3. A 0.45-1.38 μm widely broadened supercontinuum was generated in a highly nonlinear photonic crystal fiber. In terms of spectral flatness, the total modulation bandwidth was within 14 dB. All of the fiber devices were fusion spliced so that the system showed good stability. The effect of a pulse-trapping phenomenon in the supercontinuum generation process was discussed from experimental considerations.

Toward a thermodynamic description of supercontinuum generation

We consider the incoherent nonlinear regime of the supercontinuum generation process in optical fibers. We show that, under certain conditions, the phenomenon of spectral broadening inherent to the supercontinuum generation may be described by simple thermodynamic arguments based on the kinetic wave theory. Accordingly, the supercontinuum generation process may be regarded as a thermalization process, which is characterized by an irreversible evolution of the optical field toward a thermodynamic equilibrium state, i.e., the state of maximum nonequilibrium entropy.

Coherence Degradation in the Process of Supercontinuum Generation in an Optical Fiber

Changes in coherence during the process of supercontinuum generation in a dispersion-shifted fiber (DSF), a dispersion-flattened fiber (DFF) and a dispersion-decreasing fiber (DDF) have been investigated in detail for the first time. It is shown that both time and frequency coherence are greatly degraded in DSF and DFF. This is due to the four wave mixing effect caused by self-phase modulation and group velocity dispersion in the presence of amplified spontaneous emission. Such a light pulse may be unsuitable for long-distance, high-speed transmission because it contains timing jitter and amplitude fluctuations. On the other hand, DDF can maintain its coherence as the spectral broadening occurs coherently through adiabaticN=1 soliton compression. This fiber is useful for ultra-high-speed communication.