SiON is a suitable material for the implementation of photonic integrated circuits with a middle refractive index contrast
for the visible and near infrared region. The paper presents the design, fabrication and characterization of SiON/SiO2/Si
structures for passive optical waveguides realization with designed refractive index contrast 0.13. This refractive index
contrast allows fabrication of strip SiOx/SiON/SiO2/Si waveguides with waveguide band losses bellow 0.01dB/cm at
150um waveguide radius. SiON and SiOx layers were fabricated by plasma-enhanced chemical vapor deposition
techniques. The plasma-enhanced chemical vapor deposition technological parameters were tuned and optimized
for designed refractive index contrast 0.13 and designed waveguide thickness 2.5 m. The refractive index of fabricated
SiON layers were measured by optical ellipsometry.
In this paper we report on the fabrication of a non-symmetric double core microstructured fiber made of in-house
synthesized silicate glass. The micro-structured fiber uses three rings of holes around two cores separated with a single
hole. This fiber has a birefringence of about 10<sup>-3</sup> at 1.5 μm and zero dispersion wavelengths at 1.3- 1.5 nm range.
For experimental verification of nonlinear properties of the fiber we use a femtosecod Ti:Sapphire oscillator emitting in
the range of 750-900 nm in the normal dispersion regime of the pumped fiber. Measurements we performed with
excitation of one of the core and readout at the output from both cores separately. Registered spectra show a strong
coupling between cores and there is no evident difference between signals for excited or other core. Generated spectrum
is flat and relatively narrow, which is a result of pumping in normal region of fiber dispersion as we predicted with
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.
Efficient confinement of laser radiation in the core of a photonic crystal fiber (PCF) enhances the nonlinear processes
resulting in supercontinuum generation. The technique of adaptive pulse shaping using an evolutionary algorithm
provides a method to gain control over nonlinear processes. Adaptive pulse shaping of the driving laser radiation
passing through the photonic crystal fiber was employed to modify the shape and composition of the output
supercontinuum. Amplified pulses of a Ti:Sapphire laser system were coupled into a high air fill factor (cobweb) PCF
sample. Alternatively a Cr:Forsterite master oscillator was used as the pump source. Supercontinua acquired with
unshaped pulses are compared for both pump sources. Amplitude and phase shaping of the amplified Ti:Sapphire pulses
was then used to optimize the emission between 500 and 700 nm, as well as a soliton centered at 935 nm. The originally
separated spectral regions near 700 nm eventually merged into a smoother and broader supercontinuum. The intensities
of the broadband emission and of the soliton driven by a shaped laser pulse increased in comparison to unshaped pulses
by factors of 4 and 3, respectively. In addition, the suppression of self-steepening effects in supercontinuum spectra was
demonstrated using a shaped laser pulse.
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 model<sup>15,16</sup>.
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.