ABSTRACT
We systematically present experimental and theoretical results for the dual-wavelength switching of 1560 nm, 75 fs signal pulses (SPs) driven by 1030 nm, and 270 fs control pulses (CPs) in a dual-core fiber (DCF). We demonstrate a switching contrast of 31.9 dB, corresponding to a propagation distance of 14 mm, achieved by launching temporally synchronized SP-CP pairs into the fast core of the DCF with moderate inter-core asymmetry. Our analysis employs a system of three coupled propagation equations to identify the compensation of the asymmetry by nonlinearity as the physical mechanism behind the efficient switching performance.
ABSTRACT
We present a complex study of pulse-energy-controlled solitonic self-switching of femtosecond pulses at wavelengths of 1700 and 1560 nm in two nonlinear high-index contrast dual-core fibers having different levels of slight asymmetry. In the case of the fiber with higher dual-core asymmetry excited by 1700 nm pulses, the highest switching contrast of 20.8 dB at 40 mm fiber length was demonstrated. It was accompanied by multiple exchanges of the dominant core at the fiber output, which is a strong signature of the soliton-based switching process. In the case of the fiber with lower dual-core asymmetry, excited by 1560 nm pulses, the highest switching contrast of 21.4 dB at 35 mm fiber length was achieved with a broadband character of the switching in the spectral range of 1450-1650 nm. Both demonstrations represent progress in all-optical switching studies at these particular wavelengths thanks to a comparison between their results, which reveals the requirement of a higher level of dual-core symmetry for applicable C-band operation.
ABSTRACT
We experimentally investigate a nonlinear switching mechanism in a dual-core highly nonlinear optical fiber. We focus the input stream of femtosecond pulses on one core only, to identify transitions between inter-core oscillations, self-trapping in the cross core, and self-trapping of the pulse in the straight core. A model based on the system of coupled nonlinear Schrödinger equations provides surprisingly good agreement with the experimental findings.
ABSTRACT
Supercontinuum pulses covering the range from 1100 to 1700 nm with energies >1.0 mJ and excellent beam quality are generated via nonlinear spectral broadening of Cr:forsterite (1240 nm, 110 fs) pulses in pressurized molecular nitrogen. Our spectra, which extend over more than half an octave, offer an attractive alternative to intense few-cycle pulse synthesis in the 1-2 µm range and lend themselves as an important add-on to Cr:forsterite laser technologies.
ABSTRACT
Nonlinear propagation of ultrafast near infrared pulses in anomalous dispersion region of dual-core photonic crystal fiber was studied. Polarization tunable soliton-based nonlinear switching at multiple non-excitation wavelengths was demonstrated experimentally for fiber excitation by 100 fs pulses at 1650 nm. The highest-contrast switching was obtained with the fiber length of just 14 mm, which is significantly shorter compared to the conventional non-solitonic in-fiber switching based on nonlinear optical loop mirror. Advanced numerical simulations show good agreement with the experimental results, suggesting that the underlying dual-core soliton fission process supports nonlinear optical switching and simultaneous pulse compression to few-cycle durations at the level of 20 fs.
ABSTRACT
Our aim is to doubly confine a molecule of coumarin C522 in a host-guest supramolecular complex with ß-cyclodextrin in a reverse sodium dioctyl sulfosuccinate (AOT) micelle using nonpolar n-heptane and polar water solvents. Varying the volumes of coumarin C522 and ß-cyclodextrin dissolved in water allows us to control the water-pool diameters of the reverse micelle in n-heptane with values of w=3, 5, 10, 20, and 40, where w is the ratio of water concentration to AOT concentration in n-heptane. To study the fluorescence dynamics of coumarin C522, the spectral steady-state and time-resolved dependences are compared for the two systems coumarin C522(water)/AOT(n-heptane), denoted C522/micelle, and coumarin C522/ß-cyclodextrin(water)/AOT(n-heptane), referred to as C522/CD/micelle. The formation of the supramolecular host-guest complex CD-C522 is indicated by a blue shift, but in the micelle, the shift is red. However, the values of the fluorescence maxima at 520 and 515 nm are still way below the value of 535 nm representing bulk water. The interpretation of the red shift is based on two complementary processes. The first one is the confinement of CD and C522 by the micelle water pool and the second is the perturbation of the micelle by CD and C522, resulting in an increase of the water polarity. The fluorescence spectra of the C522/micelle and C522/CD/micelle systems have maxima and shoulders. The shoulder intensities at 440 nm, representing the C522 at n-heptane/AOT interface, decrease as the w values decrease. This intensity shift suggests that the small micelle provides a stronger confinement, and the presence of CD shifts the equilibrium from n-heptane towards the water pool even more. The fluorescence emission maxima of the C522/micelle and C522/CD/micelle systems for all w values clearly differentiate two trends for w=3-5, and w=10-40, suggesting different interaction in the small and large micelles. Moreover, these fluorescence maxima result in 7 and 13 nm differences for w=3 and w=5, respectively, and provide the spectral evidence to differentiate the C522 confinement in the C522/micelle and C522/CD/micelle systems as an effect of the CD molecule, which might be interpreted as a double confinement of C522 in CD within the micelle. The ultrafast decay in the case of w=3 ranges from 9.5 to 16 ps, with an average of 12.6 ps, in the case of the C522/micelle system. For C522/CD/micelle, the ultrafast decay at w=3 ranges from 9 to 14.5 ps, with an average of 11.8 ps. Increasing w values (from 10 to 40) result in a decrease of the ultrafast decay values in both cases to an average value of about 6.5 ps. The ultrafast decays of 12.6 and 11.8 ps for C522/micelle and C522/CD/micelle, respectively, are in the agreement with the observed red shift, supporting a double confinement in the C522/CD/micelle(w=3) system. The dynamics in the small and large micelles clearly show two different trends. Two slopes in the data are observed for w values of 3-5 and 10-40 in the steady-state and time-resolved data. The average ultrafast lifetimes are determined to be 12.6 and 6.5 ps for the small (w=3) and the large (w=40) micelles, respectively. To interpret the experimental solvation dynamics, a simplified model is proposed, and although the model involves a number of parameters, it satisfactory fits the dynamics and provides the gradient of permittivity in the ideal micelle for free water located in the centre (60-80) and for bound water (25-60). An attempt to map the fluorescence dynamics of the doubly confined C522/CD/micelle system is presented for the first time.
ABSTRACT
A highly birefringent silicate glass photonic-crystal fiber (PCF) is employed for polarization-controlled nonlinear-optical frequency conversion of femtosecond Cr: forsterite laser pulses with a central wavelength of 1.24 mum to the 530--720-nm wavelength range through soliton dispersion-wave emission. The fiber exhibits a modal birefringence of 1.2.10(-3) at the wavelength of 1.24 mum due to a strong form anisotropy of its core, allowing polarization switching of the central wavelength of its blue-shifted output by 75 nm. Polarization properties and the beam quality of the blue-shifted PCF output are shown to be ideally suited for polarization-sensitive nonlinear Raman microspectroscopy.
