We demonstrate narrow band spectral intensity switching in dual-core photonic crystal fibers made of highly nonlinear glass under femtosecond excitation. The fibers expressed dual-core asymmetry, thus the slow and fast fiber cores were unambiguously distinguished according to their dispersion profiles. The asymmetry effect on the dual-core propagation in anomalous dispersion region was studied both experimentally and numerically. The experimental study was carried out using femtosecond laser amplifier system providing tunable pulses in range of 1500 nm - 1800 nm. The obtained results unveiled, that it is possible to improve nonlinearly the coupling between the two waveguides by excitation of the fast fiber core. The results were obtained in regime of high-order soliton propagation and were verified numerically by the coupled generalized nonlinear Schrödinger equations model. The spectral analysis of the radiation transferred to the non-excited core revealed the role of effects such as third order dispersion, soliton compression and spectral dependence of the coupling efficiency. The simulation results provide reasonable agreement with the experimentally observed spectral evolutions in the both fiber cores. Under 1800 nm excitation, narrow band spectral intensity switching was registered with contrast of 23 dB at 10 mm fiber length by changing the excitation pulse energy in sub-nanojoule range.
Polarization splitting performance of a special multi-component glass made dual – core microstructure optical fiber (DC MOF) was investigated in the near infrared region. The output dual-core intensity ratio changes were analyzed behind a rotating polarizer both in spectrally resolved and integrated manner under broadband femtosecond pulse excitation of the fiber in the C-band. The polarization angle dependence of the dual-core intensity ratio exhibited similar non-symmetrical character in the case of both camera and spectrometer registration method. The 70 nm broad femtosecond radiation allowed to set an optimal wavelength, at which the extinction ratio difference between the extreme cases was maximized with significantly higher value than by the spectrally integrated method. Non-proper polarization splitting performance was observed with angle distance different than 90° between the extreme cases for the both orthogonal input polarization directions. Afterwards, optimizing the input polarization angle the angle distance became the proper right-angle, which behavior is interpreted in terms of inhomogenously polarized fundamental supermodes supported also by numerical mode analysis of the investigated DC MOF.
Presented work is dedicated to analysis of nonlinear effects in dual core photonic crystal fiber. Both theoretical and
experimental approaches are used. Theoretical analysis includes determination of dispersion and coupling curves.
Simulation of nonlinear propagation is based on coupled generalized nonlinear Schrödinger equations. Modified
numerical model utilizing split-step Fourier method was adapted for dual core fibers. In theoretical part possibility to use
dual core fiber as supercontinuum source or nonlinear coupler is analyzed. Possibility to influence coupling efficiency
and coupling length by intensity was shown in order to propose utilization of dual core fiber as nonlinear coupler.
Experimental analysis was performed with femtosecond laser system in near IR region. Investigation included different
input settings such as polarization, intensity, selective input coupling into each core and selective detection of spectra
from each core. Theoretical and experimental spectra are compared and analyzed.
Nonlinear propagation of femtosecond pulses in double core square lattice PCF made of multicomponent glass was
investigated experimentally at excitation wavelength 1250 nm in the anomalous dispersion region. The obtained results
expressed soliton fission and self frequency shift in the anomalous region, inspected by IR registration, with increasing
complexity by increasing excitation energy. The visible registration, inspecting the normal dispersion region, exhibited
soliton induced dispersive wave generation with blue shifting feature suggesting nonlinear phase change effect on the
phase matching condition. The width of the overall spectral feature approached two octaves at approximately 10 nJ
excitation energy in 6 cm long fiber sample. The knowledge about the evolving processes was extended by numerical
simulation of the nonlinear propagation in the near IR region in reasonable correspondence with the experimental results.
Furthermore, separate registration of the visible spectral features originating from the two fiber cores was ensured
exhibiting significant differences between the multipeak spectra. The two core spectral content differences was possible
to further alternate by rotation of the excitation polarization direction with application potential for polarization switched
directional coupler accompanied by frequency conversion. Finally, single versus double core excitation conditions were
compared. The double core excitation resulted in smoother spectral features, both in the case of IR and visible
registration, at requirement at expense higher excitation energies needed for broadband supercontinuum generation.
Photonic crystal fibers (PCF) have enlarging application potential in information technology and spectroscopy enabling
different photonic operations in fast and effective manner. The present work was performed on index guiding double
core PCF with square lattice, in which the cores are separated by a single air hole. Femtosecond laser pulses with
wavelengths 1.1-1.5 &mgr;m were utilized to excite the PCF samples and the nonlinear spectral transformations were
registered in the visible-near infrared region. During the manufacturing process the same PCF structure were prepared in
four different sizes allowing to study the influence of the fiber diameter on the spectral transformation. Employing
several nJ femtosecond pulses, polarization tunable narrow spectral features and broadband supercontinuum generation
was observed and tailored by changing the excitation wavelength and polarization, coupling geometry and fiber
diameter. In the case of excitation in anomalous dispersion area the effect of dispersive wave generation is evaluated.
Microstructured fibers with small core are successfully used as a medium for supercontinuum generation. Since light can
be confined in a small core a high density of energy in the fiber is obtained and stimulate nonlinear effects. Use of lead
multicomponent glass allows increasing nonlinear refractive index in the fiber and shape dispersion properties of the
fiber. In this case effective broadening of the spectrum can be obtained with less then 1 m of the fiber. In this paper we
present properties of photonic crystal fibers optimized for supercontinuum generation.
Nonlinear absorption and refraction effects are of particular interest for areas like optical communication (all optical
switching and limiting). Nonlinear parameters of ZnSe, GaAs and polythiophene (polythiophene/zeolite complex) have
been the subject of investigation using an Cr: Forsterite fs laser source with an output wavelength of 1250 nm, i.e. in a
spectral region which plays important role for optical communication systems. The obtained values of nonlinear
refractive index and two photon absorption coefficient are compared to theoretically predicted values. Beside the original
transmittance Z-scan technique a modified Z-scan technique, which allows the sample transmittance and fluorescence
being registered simultaneously was employed. The results are compared with a previously introduced theoretical model15,16.
We demonstrated, that the recently developed low bandgap conductive polymer polythiophene shows
nonlinear absorption followed by the luminescence in the visible. In addition, there is a different behavior of nonlinear
absorption and luminescence for polyalkylthiophene and polythiophene/zeolite complex which may be explained by the
supramolecular complexation of polythiophene in zeolite.
Intermodally phase-matched third harmonic generation (THG) in a multimode microstructured fiber (PCF) accompanied by nonlinear spectral shifts both for fundamental and for third harmonic (TH) was observed. Femtosecond pulses of a Cr:Forsterite laser oscillator with the central wavelength of 1240 nm were used to excite several PCF samples. This wavelength plays important role for actual optical communication systems being in close proximity to the 1.3 μm window. Depending on the coupling geometry, two different high-order third harmonic fiber modes were observed accompanied by spectral shifts in IR. Instead of broadband radiation as in the IR, isolated peaks were generated in the TH region of the spectrum. By the rotation of input polarization, changes in the THG mode patterns were observed and a detailed analysis revealed the intensity and a polarization effects on the sampled spectra. Observed phenomena are interpreted by numerical calculations of modal dispersion properties for the examined PCF. Simulation results confirm the narrow band multi-peak character of the THG radiation and a good agreement was found between experimental and theoretical peak positions. This work is aimed to extend the knowledge about the spectral control of third harmonic signal by tailoring parameters of the fiber.
Since August 2003 the K008 camera /1,2/ being coupled with a MS 3504i monochromator/spectrogaph /3/ has been used in the International Laser Center in Bratislava (Slovak Republic) for investigations in the field of non-stationary spectroscopy, in particular, for the study of fluorescence processes in different dyes. When putting the camera into operation its limiting temporal resolution was prelinarily checked and was found to be 20ps. The results of trial experiments on the study of dynamics of Rhodamin B fluorescence are given below.
Properties of the picosecond supercontinuum generated from water have been studied. We have shown development of a stimulated Raman scattering cross-phase modulation spectrum at the anti-Stokes side of the pump frequency. Supercontinuum diffraction patterns have been recorded and diffraction angles for several wavelengths have been measured. Requirement of the supercontinuum generation power threshold have been found out for different outputs. We have also analyzed defocusing interaction among pulses of the pump train.