Comparison of dispersion characteristics of hollow-core photonic crystal fibers filled with aromatic compounds

In this paper, hollow-core photonic crystal fibers (PCFs) infiltrated with benzene and nitrobenzene are designed and investigated. Their dispersion characteristics are numerically simulated. The results show that using the aromatic-compounds-filled hollow core of PCFs makes dispersion curves flat. In addition, the dispersion curves approach the zero-dispersion line closer than previously published dispersion curves of PCFs with toluene, thus significantly improving the supercontinuum generation to create the ultra-flat spectrum expansion

Noise-related polarization dynamics for femto and picosecond pulses in normal dispersion fibers

We report how the complex intra-pulse polarization dynamics of coherent optical wavebreaking and incoherent Raman amplification processes in all-normal dispersion (ANDi) fibers vary for femto and picosecond pump pulses. Using high temporal resolution vector supercontinuum simulations, we identify deterministic polarization dynamics caused by wavebreaking and self-phase modulation for femtosecond pulses and quasi-chaotic polarization evolution driven by Raman amplification of quantum noise for picosecond pulses. In contrast to cross-phase modulation instability, the Raman-based polarization noise has no power threshold and is reduced by aligning the higher energy polarization component with the lower index axis of the fiber. The degree of polarization stability is quantified using new time domain parameters that build on the spectrally averaged degree of coherence used in supercontinuum research to quantify the output spectral stability. We show that the spectral coherence is intrinsically linked to polarization noise, and that the noise will occur in both polarization maintaining (PM) and non-PM fibers, spanning a broad range of pulse energies, durations, and fiber birefringence values. This analysis provides an in-depth understanding of the nonlinear polarization dynamics associated with coherent and incoherent propagation in ANDi fibers

Hybrid soliton dynamics in liquid-core fibres

The discovery of optical solitons being understood as temporally and spectrally stationary optical states has enabled numerous innovations among which, most notably, supercontinuum light sources have become widely used in both fundamental and applied sciences. Here, we report on experimental evidence for dynamics of hybrid solitons—a new type of solitary wave, which emerges as a result of a strong non-instantaneous nonlinear response in CS2-filled liquid-core optical fibres. Octave-spanning supercontinua in the mid-infrared region are observed when pumping the hybrid waveguide with a 460 fs laser (1.95 μm) in the anomalous dispersion regime at nanojoule-level pulse energies. A detailed numerical analysis well correlated with the experiment uncovers clear indicators of emerging hybrid solitons, revealing their impact on the bandwidth, onset energy and noise characteristics of the supercontinua. Our study highlights liquid-core fibres as a promising platform for fundamental optics and applications towards novel coherent and reconfigurable light sources

Carbon chloride-core fibers for soliton mediated supercontinuum generation

We report on soliton-fission mediated infrared supercontinuum generation in liquid-core step-index fibers using highly transparent carbon chlorides (CCl4, C2Cl4). By developing models for the refractive index dispersions and nonlinear response functions, dispersion engineering and pumping with an ultrafast thulium fiber laser (300 fs) at 1.92 μm, distinct soliton fission and dispersive wave generation was observed, particularly in the case of tetrachloroethylene (C2Cl4). The measured results match simulations of both the generalized and a hybrid nonlinear Schrödinger equation, with the latter resembling the characteristics of non-instantaneous medium via a static potential term and representing a simulation tool with substantially reduced complexity. We show that C2Cl4 has the potential for observing non-instantaneous soliton dynamics along meters of liquid-core fiber opening a feasible route for directly observing hybrid soliton dynamics

Third harmonic generation in liquid core optical fibres

The objective of this thesis is to investigate third harmonic generation in liquid core fibres. Such fibres are formed by injection of liquid into a hollow, solid cladding by capillary forces. Carbon disulphide and tetrachloroethylene are identified as most promising liquid candidates. Such liquids offer a strong nonlinearity whose major contribution is non-instantaneous arising from the molecular structure. The effect of this material response during harmonic generation is investigated numerically by solving coupled evolution equations and causes distinct spectral shifts and broadening of both harmonic and fundamental wave. Both liquids offer excellent transparency and a high index of refraction enabling intermodal phase matching in a step-index geometry without requiring a complex microstructure. Aspects of fibre design and experimental realisation are presented in detail. Using sub-picosecond pump pulses of different duration the harmonic is generated in a higher order fibre mode and resulting signals are analysed in the spectral domain. Modification of the fibre cross-section towards an elliptical core is investigated. Besides the induced birefringence, harmonic generation in further sets of higher order modes is possible due to their transformation of electric fields. Design considerations of spatially modified fibres were confirmed experimentally and adaptive phase matching by controlling fibre temperature could be realised. Feasibility of long term exposure of liquid filled fibres to high average powers of femtosecond pulses is demonstrated underpinning that liquid core fibres withstand practical applications beyond laboratory use. Finally, possible routes to enhance the currently achieved conversion efficiencies for tetrachloroethylen of 2 ∙ 10^-5, and carbon disulphide of 10^-7, are identified and future prospects of this fibre platform are discussed

Wideband tuning of four-wave mixing in solid-core liquid-filled photonic crystal fibers

We present an experimental study of parametric four-wave mixing generation in photonic crystal fibers that have been infiltrated with ethanol. A silica photonic crystal fiber was designed to have the proper dispersion properties after ethanol infiltration for the generation of widely spaced four-wave mixing (FWM) bands under 1064 nm pumping. We demonstrate that the FWM bands can be tuned in a wide wavelength range through the thermo-optic effect. Band shifts of 175 and over 500 nm for the signal and idler bands, respectively, are reported. The reported results can be of interest in many applications, such as CARS microscopy

Nonlinear optics Pulse propagation in fiber optics filled with gases, liquids, and organic dyes.

The characterization of nonlinear optical material properties, such as nonlinear refractive index and nonlinear absorption coefficient, is one of the most important subjects in nonlinear optics due to its application in many fields such as spectroscopy, material processing, biophysics, atmospheric sensing and metrology, among others. Besides the possibility of creating new technology. In this thesis, the Z-scan technique was implemented and calibrated. It remains one of the most widely used techniques to obtain both nonlinear refractive index and the absorption coefficient of a material. Moreover, nonlinear phenomena inside optical fiber is well known due to their applications and advantages like the low input energy required to generate supercontinuum, four wave mixing, dispersive wave, among others. In this work, several simulations were performed with new fiber geometries, material responses and different noble gases infiltrated in fiber. Different simulation regimes were considered as well by varying input power, pulse width and pressure. Nonlinear parameters for organic dyes, multi-walled carbon nanotubes, and CS2 were reported, pointing out the main reasons behind each result and addressing possible new phenomena involved. The nonlinear output response in both time and frequency domains was reported for several simulations, obtaining the nonlinear pulse output for the new CS2 response function. A novel consideration was proposed in which the final pulse depends on the propagation distance for non-instantaneous materials and the nonlinear constant (γ) must be recalculated at each step. It was demonstrated how the output pulse can be controlled by changing the fiber length. Among the most important results, it was found there exists a possibility to change between modulation instability and four wave mixing by only varying the propagation distance. Finally, it was also found that a special type of fiber, namely negative curvature hollow core fiber, can be used to obtain a broad band spectrum when it is filled with noble gases and they can be tuned with pressure from linear behavior up to a super critical zone.Resumen: a caracterización de propiedades ´ópticas no lineales, como lo son el ´índice de refracción y el coeficiente de absorción no lineal, es uno de los temas más importantes en ´óptica no lineal debido a su aplicación en muchos campos como la espectroscopia, procesamiento de materiales, biofísica, sensado atmosférico, metrología, entre otros. Además de la posibilidad de creación de nueva tecnología. En esta tesis se implemento y calibro la técnica Z-Scan, una de las técnicas más utilizadas para obtener tanto el ´índice de refracción no lineal como el coeficiente de absorción de un material. Asimismo, los fenómenos no lineales dentro de la fibra ´óptica son bien conocidos debido a sus aplicaciones y ventajas tales como la baja energía de entrada requerida para generar fenómenos de supercontinuo, mezclado de cuatro ondas y ondas dispersivas. En este trabajo se realizaron varias simulaciones con nuevas geometrías de fibras, respuestas de material y gases nobles dentro de la fibra. Se consideraron diferentes regímenes de potencia de entrada, ancho de pulso y presión. Se reportaron los parámetros no lineales para las sustancias orgánicas usadas, nanotubos de carbono de paredes múltiples y CS2, indicando la razón principal detrás de cada resultado y abordando los posibles nuevos fenómenos involucrados. La respuesta de salida no lineal tanto en el dominio del tiempo como en el de frecuencia se reportó en varias simulaciones, obteniendo el pulso no lineal de salida para la nueva función de respuesta del CS2, se propuso una nueva consideración donde el pulso final depende de la distancia de propagación para materiales no instantáneos y la constante no lineal (γ) se deben recalcular en cada paso. Se demostró como se puede controlar el pulso de salida cambiando la longitud de la fibra; entre los resultados más importantes se encontró la posibilidad de cambiar entre la inestabilidad de la modulación y el mezclado de cuatro ondas solo variando la distancia de propagación. Finalmente, se encontró que un tipo especial de fibra, a saber, la fibra de núcleo hueco de curvatura negativa, se puede usar para obtener un amplio espectro de banda cuando se llena con gases nobles y se sintoniza con la presión, desde el comportamiento lineal hasta la zona supercríticaMaestrí

Vector FWM in optical fibers: tuning techniques and applications

Recientemente, el efecto no lineal de mezcla de cuatro ondas (FWM) en fibras ópticas ha atraído un gran interés para el desarrollo de nuevas fuentes de luz de fibra óptica debido a la emisión de luz múltiple producida por este efecto no lineal. En los últimos años, estas fuentes de luz basadas en FWM han demostrado una gran utilidad en áreas como la óptica cuántica y la microscopía avanzada basada en efecto Raman. Además, según el estado de polarización de la luz de bombeo responsable del efecto FWM y la birrefringencia de la fibra, la luz producida por FWM puede presentar diferentes propiedades de polarización dada la naturaleza vectorial de FWM. Esto posibilita el diseño y desarrollo de fuentes de luz polarizada con emisión múltiple que pueden ser de gran interés en diferentes estudios o aplicaciones de la fotónica. Además, el efecto FWM es relativamente sensible a los cambios en las propiedades ópticas del medio en el que se genera. En el caso de una fibra óptica, la dispersión cromática y la birrefringencia de la fibra son los parámetros más relevantes en la condición de ajuste de fase de FWM. De esta forma, se pueden medir determinadas magnitudes físicas mediante sensores de fibra óptica basados ​​en FWM aprovechando la susceptibilidad de la fibra a cambios en las propiedades ópticas de la propia fibra. En esta tesis proporcionamos el estudio teórico y experimental de FWM vectorial producido en fibras ópticas débilmente birrefringentes. En particular, hemos centrado nuestra atención en un proceso específico de FWM vectorial conocido como modulación por inestabilidad debido a la polarización (PMI). En este trabajo proporcionamos métodos simples y prácticos para generar y sintonizar la emisión de intensas bandas de luz producidas por PMI/FWM en un amplio rango de longitudes de onda. Dada la alta eficiencia de las fibras ópticas microestructuradas (MOF) para generar efectos no lineales como FWM, la mayoría de nuestros experimentos se llevaron a cabo en MOFs con diferentes propiedades de guiado. En este trabajo mostramos la generación de PMI/FWM en fibras con perfiles de dispersión tipo ANDi, fibras con 1 o 2 longitudes de onda de dispersión cero y MOF híbridos infiltrados con líquidos cuyas propiedades permiten generar y sintonizar PMI/FWM. En esta tesis hemos demostrado la sintonización de banda ancha de bandas de luz de alta intensidad producidas por PMI. La sintonización de este efecto se logra explotando la sensibilidad de la condición de ajuste de fase de PMI a los cambios de dispersión y birrefringencia de la fibra óptica. Para ello, se han empleado técnicas sencillas para controlar la dispersión y birrefringencia de las fibras basadas en el efecto elasto-óptico de la sílice fundida o bien en el efecto termo-óptico de los líquidos infiltrados en las fibras. Además, se ha demostrado por primera vez la generación y la sintonización simultánea de FWM y PMI en MOF. En este estudio hemos demostrado experimentalmente la sintonización de las bandas de luz generadas por ambos efectos en un amplio rango de longitudes de onda, cubriendo una gran parte del espectro infrarrojo cercano.Recently, the nonlinear four-wave mixing (FWM) effect in optical fibers has attracted great interest for the development of new optical fiber light sources due to the multiple light emission produced by this nonlinear effect. In recent years, such FWM-based light sources have demonstrated great utility in areas such as quantum optics and advanced Raman-based microscopy. Additionally, according to the polarization state of the pump light responsible for the FWM effect and the birefringence of the fiber, the light produced by FWM can exhibit different polarization properties given the vector nature of the FWM. Thus, this enables the design and development of polarized light sources with multiple emission which can be of great interest in different studies or applications of photonics. In addition, FWM effect is relatively sensitive to changes in the optical properties of the medium in which it is generated. In the case of an optical fiber, the chromatic dispersion and birefringence of the fiber are the most relevant parameters in the phase-matching condition of FWM. In such a way, certain physical quantities can be measured by means of FWM-based fiber optic sensors taking advantage of the susceptibility of the fiber to changes in the optical properties of the fiber itself. In this thesis we provide the theoretical and experimental study of vector FWM produced in weakly birefringent optical fibers. In particular, we have focused our attention on a specific process of vector FWM known as polarization modulation instability (PMI). In this work we provide simple and practical methods to generate and tune the emission of intense bands of light produced by PMI/FWM over a wide wavelength range. Given the high efficiency of microstructured optical fibers (MOFs) to generate nonlinear effects such as FWM, most of our experiments were carried out with MOFs with different guiding properties. In this work, we show the generation of PMI/FWM in fibers with ANDi dispersion profiles, fibers with 1 or 2 zero-dispersion wavelength, and hybrid MOFs infiltrated with optical liquids whose properties enables PMI/FWM generation and tuning. In this thesis we have demonstrated broadband tuning of intense light bands produced by PMI. Tunability is achieved by exploiting the sensitivity of the PMI phase-matching condition to changes of dispersion and birefringence of the optical fiber. To this end, simple techniques have been employed to control fiber dispersion and birefringence based on either the elasto-optic effect of fused silica or the thermo-optic effect of the liquids infiltrated into the fibers. In addition, simultaneous generation and tuning of FWM and PMI in MOFs has been demonstrated for the first time. This required a fine control of the optical guiding properties of the fibers. In this study we have experimentally demonstrated tunability of the light bands generated by both effects over a wide wavelength range, covering a large part of the near-infrared spectrum