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This PDF file contains the front matter associated with SPIE Proceedings Volume 7728, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
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As the bit rates of optical networks increase, the ability of accurate monitoring of optical waveforms has become
increasingly important. In recent years, optical sampling has emerged as a technique to perform time-resolved
measurements of optical data signals at high data rates with a bandwidth that cannot be reached by conventional
photodetectors and oscilloscopes. In an optical sampling system, the optical signal is sampled in the optical
domain by a nonlinear optical sampling gate before the resulting samples are converted to an electrical signal.
This avoids the need for high bandwidth electronics if the optical sampling gate is operated with a modest
repetition frequency.
In this paper, we present an optical sampling system using the optical Kerr effect in a highly nonlinear
chalcogenide device, enabling combined capability for femtosecond resolution and broadband signal wavelength
tunability. A temporal resolution 450-fs is achieved using four-wave mixing (FWM) in dispersion-engineered
chalcogenide waveguides: on one hand a 7-cm long planar waveguide (integrated on a photonic chip) and on the
other hand a 5-cm long tapered fiber. The use of a short length, dispersion-shifted waveguide with ultrahigh
nonlinearity (10000/W/km) enables high-resolution optical sampling without the detrimental effect of chromatic
dispersion on the temporal distortion of the signal and sampling pulses, as well as their phase mismatch (which
in turn would degrade the FWM efficiency and the sensitivity of the measurement). Using these chalcogenide
devices, we successfully monitor a 640-Gb/s optical time-division multiplexing (OTDM) datastream, showcasing
its potential for monitoring of signals at bitrates approaching and beyond Tb/s. We compare the advantages
and disadvantages of both approaches and discuss fundamental limitations as well as potential improvements.
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We present a ultra-high repetition-rate passive mode-locked laser with tunable centre wavelength and selectable
repetition-rate between 40 and 640 GHz. The laser is mode-locked by dissipative four-wave mixing and uses a
Fourier-domain programmable optical processor as a spectral filtering element.
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We revisit the use of nonlinear pulse compression for ultrafast pulse train generation in terms of the evolution dynamics
of analytic breather solutions of the nonlinear Schrödinger equation. We discuss to what degree the analytic formalism
of Akhmediev Breather solutions can provide improved insight into the compression process, providing a useful
complement to the more widely employed approach to pulse train optimization using numerical simulations. We also
report experiments where nonlinear reshaping of a directly modulated DFB laser diode signal at 1550 nm in standard
single mode fibre is used to generate a train of sub-20 ps compressed pulses at 11.7 GHz. Characterization using a
Picosolve sampling scope reveals directly the expected compressed pulse and pedestal features.
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A 300 nm× 450 nm× 5mm silicon nanowire is designed and fabricated for a four wave mixing based non-linear optical
gate. Based on this silicon nanowire, an ultra-fast optical sampling system is successfully demonstrated using a freerunning
fiber laser with a carbon nanotube-based mode-locker as the sampling source. A clear eye-diagram of a 320
Gbit/s data signal is obtained. The temporal resolution of the sampling system is estimated to 360 fs.
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Continuously tunable sources with room-temperature operation are required in the mid-infrared region for applications
such as spectroscopy or pollutants monitoring. In this spectral range, optical parametric oscillators (OPOs) are more
versatile than laser diodes.
Guided-wave OPOs constitute a promising perspective, thanks to higher conversion efficiency provided by the
confinement of the interacting waves. While LiNbO3 has been the crystal of choice for a long time, GaAs is a good
alternative thanks to higher nonlinearity, broader transparency range, and optoelectronic integrability. So far, a GaAs
integrated OPO has not yet been demonstrated due to technology induced propagation losses.
Here we present a detailed investigation of the propagation losses in partially oxidized multilayer GaAs/AlAs
waveguides. We have studied the impact of oxidation on the roughness of the multilayer interfaces, via transmission
electron microscopy. While the roughness of our MBE-grown GaAs/AlAs heterostructures is the standard 0.3 nm, it
increases to at least 0.53 nm after AlAs oxidation. Semi-analytical modeling shows that this level of roughness is
responsible for scattering losses, in fair agreement with the measured values. Optimization of the oxidation process is
currently under way with the aim of reaching the OPO oscillation threshold.
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On-chip, all-optical quantization based on pulse spectral broadening in a 6 cm long chalcogenide waveguide and
subsequent filtering is analyzed. Transfer function is obtained for an 8-level quantizer using 2 nm bandwidth filters.
Matrix transformation is used to encode the quantized data into a gray-code. An all-optical implementation of the matrix
transformation encoder is proposed based on all-optical Exclusive-OR (XOR) gate. Broad bandwidth supercontinuum
generation in a chalcogenide waveguide and optical XOR gate based encoder paves the way for ultra-high bandwidth,
high-resolution all-optical analog-to-digital conversion chip.
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At the boundaries between photonics and dynamic systems theory, we combine recent advances in neural networks with opto-electronic nonlinearities to demonstrate a new way to perform optical information processing.
The concept of reservoir computing arose recently as a powerful solution to the issue of training recurrent neural networks. Indeed, it is comparable to, or even outperforms, other state of the art solutions for tasks such as speech recognition or time series prediction. As it is based on a static topology, it allows making the most of very simple physical architectures having complex nonlinear dynamics. The method is inherently robust to noise and does not require explicit programming operations. It is therefore particularly well adapted for analog realizations. Among the various implementations of the concept that have been proposed, we focus on the field of optics.
Our experimental reservoir computer is based on opto-electronic technology, and can be viewed as an intermediate step towards an all optical device. Our fiber optics system is based on a nonlinear feedback loop operating at the threshold of chaos. In its present preliminary stage it is already capable of complicated tasks like modeling nonlinear systems with memory.
Our aim is to demonstrate that such an analog reservoir can have performances comparable to state of the art digital implementations of Neural Networks. Furthermore, our system can in principle be operated at very high frequencies thanks to the high speed of photonic devices. Thus one could envisage targeting applications such as online information processing in broadband telecommunications.
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Nonlinear spectral broadening in two dimensional solid core photonic bandgap fibers is numerically investigated in the
anomalous dispersion regime. A frequency-domain approach is used to simulate supercontinuum generation when
femtosecond pulses are launched into a transmission band of a typical structure. The consequences on the output
characteristics of the strong frequency dependence of the nonlinear parameter, the dispersion and the confinement losses
of this kind of micro-structured fiber are highlighted, and we point out the necessity to include all of them in any
numerical modeling of experiments. This numerical approach allows us to consider also the propagation of field energy
in multiple photonic bandgaps simultaneously, and we show that efficient nonlinear spectral energy transfer is possible
between adjacent and several photonic bandgaps across spectral regions of high attenuation.
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We experimentally and numerically demonstrate the possibility of generating parabolic pulses by propagating
Gaussian pulses in 1.8 m-long normally dispersive tapered microstructured optical fibre (MOF). The modelling
of the MOF and the procedure for the determination of the taper's parameters is presented. The proposed taper
is fabricated and experimentally characterised using linear frequency resolved optical gating (l-FROG) technique,
to measure the output pulse intensity. Numerical simulations are in a good agreement with the experimental
results.
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We present a perturbation analysis that describes the effect of third-order dispersion on the similariton pulse solution
of the nonlinear Schr¨odinger equation in a fibre gain medium. The theoretical model predicts with sufficient
accuracy the pulse structural changes induced, which are observed through direct numerical simulations.
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When ultrashort optical pulses propagate as a soliton inside optical fibers, the presence of higher-order dispersion leads
to transfer of energy from the soliton to a narrowband resonance in the form of dispersive waves (DW). The frequency
of the radiation is determined by a phase-matching condition in the form of a polynomial whose coefficients depend on
the numerical values of the third- and higher-order dispersion coefficients. In this paper we show that there is a striking
correlation between the number of zero-dispersion points (ZDPs) and the generation of DW peaks. Detailed simulations
indicate that the number of ZDPs present in a specific dispersion profile is an excellent predictor of the number of
dispersive peaks created in the output pulse spectrum. A fiber with a single ZDP only has one DW peak, and a fiber
with two ZDPs always exhibits dual DW peaks. Moreover, no DW can be expected in a fiber that has no zero-dispersion
crossings over the entire range of wavelengths. We examine numerically dispersion profiles with as many as six ZDPs
and find that this criterion always holds. Another interesting feature we notice is that, if the frequency of the ZDP is
larger (smaller) than the operating frequency, DWs fall on the higher (lower) frequency side of the operating frequency.
Therefore there is a possibility to generate two DW peaks on in same side (blue or red side) of the output pulse spectrum
by tailoring the dispersion curve suitably.
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Fiber optical parametric amplifiers (FOPAs) have attracted considerable attention during the last decade because of their
broad bandwidth, high gain and wavelength-flexibility. In comparison to cumbersome bulky systems, they bring the
advantages of all-fiber systems, i.e. reliability, long-term stability and compactness. FOPAs rely on the third-order
susceptibility and are characterized by a quasi-instantaneous nonlinear response that involves pump, signal and idler
waves. Chirped pulse amplification (CPA) allows to get a high energy amplification and its realization in FOPAs would
increase the overall performances of these amplifiers. Such an experimental demonstration has never been reported in the
past. In this work, we show for the first time the experimental feasibility of fiber-based optical parametric chirped pulse
amplification (FOPCPA) with an all-fibered setup. The stretching/compression stages are realized with a single linearly
chirped fiber Bragg grating (LCFBG) used in both directions while the amplification is performed in a CW-pumped
FOPA that uses 500 meters of highly nonlinear fiber (HNLF). Fourier transform limited optical pulses at 1550 nm are
stretched from 6 ps to 70 ps and then amplified by 22 dB without any spectral or temporal distortions. Experiments are
confirmed by simulations carried out by numerical integration of the nonlinear Schrödinger equation with parameters
matching those of the experimental setup. For simplicity, this first experimental demonstration is realized in the
telecommunication window. By using photonic crystal fibers, one can move the working wavelength around 1 μm.
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We propose a novel concept of dual-wavelength microlaser based on the association of a Photonic crystal membrane and
a Fabry-Perot vertical cavity. The goal is to fabricate a surface addressable compact microlaser exhibiting stimulated
emission for two optical modes with about 1THz frequency difference.
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We introduce the concept of energy density flux as a characterization tool for the propagation of ultrashort
laser pulses with spatio-temporal coupling. This energy density flux is calculated in the local frame moving at
the velocity of the envelope of the wave packet under examination, and it can also be extended to the case of
nonlinear propagation. We perform a detailed numerical study of the energy density flux in the particular case
of conical waves. We also experimentally characterize the energy density flux for the cases of Bessel-X pulse in
linear propagation and complex ultrashort pulses generated by filamentation in a nonlinear Kerr medium.
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Optical pulse propagation in nonlinear Kerr media finds an elegant description in terms of particular spacetime
metrics. By adopting the language of general relativity and applying standard reasoning developed in the
context of quantum fields in curved space-time geometries we may expect to observe effects analogous to Hawking
radiation. We discuss recent advances in this field and the application of ultrashort laser pulse filaments for the
production of photons by excitation of the electromagnetic quantum vacuum.
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We study numerically nonlinear pulse propagation in a phase-shifted Bragg grating with a π phase-shift. The phase-shift
acts as a cavity, accumulating the field inside the grating, and hence improving the switching efficiency. Due to material
nonlinearity such cavity can operate in a bistable regime, enabling all-optical switching between high and low
transmission states. We give optimization criteria for grating design that reduce the switching threshold and minimize
the response time of the device. We demonstrate that if the grating and the pulse parameters are chosen carefully, a
temporal reshaping of the transmitted pulse occurs. An asymmetric shape of the output pulse is an indication of the pulse
self-switching between the two states of a bistable Bragg cavity.
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We demonstrate a simple method to measure the evolution of nonlinear effects along a pulse. An all-fiber acousto-optic
modulator is synchronized to the pulse emission and inserted between the laser output and an optical spectrum analyzer.
Thanks to this configuration, the application of a short modulator opening time (10 ns typically) compared to the pulse
width (100 ns typically) forms a spectral measurement window. This window is shifted along the pulse by the use of a
variable trig delay. The optical spectrum is measured for each position of the window. The nonlinear effects evolution
versus the instantaneous power can be characterized. To validate our method, we have analyzed the spectral evolution
along 100 ns pulses from different fiber laser sources. We have observed that the spectral broadening due to Kerr effect
appears first. Raman scattering occurs next for window positions corresponding to highest peak powers. Finally during
the trailing edge course, nonlinear effects disappear in the reverse order of their apparition. This method has also been
extended to measure the power inside and outside a pulse in order to deduce the rate of amplified spontaneous emission.
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This paper presents a new optical circuit that performs both pulse compression and frame synchronization and retiming.
Our design aims at directly multiplexing several 10G Ethernet data packets (frames) to a high-speed OTDM link. This
scheme is optically transparent and does not require clock recovery, resulting in a potentially very efficient solution. The
scheme uses a time-lens, implemented through a sinusoidally driven optical phase modulation, combined with a linear
dispersion element. As time-lenses are also used for pulse compression, we design the circuit also to perform pulse
compression, as well. The overall design is: (1) Pulses are converted from NRZ to RZ; (2) pulses are synchronized,
retimed and further compressed at the specially designed time-lens; and (3) with adequate optical delays, frames from
different input interfaces are added, with a simple optical coupler, completing the OTDM signal generation. We
demonstrate the effectiveness of the design by laboratory experiments.
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A novel solution for all-optical packets buffering in OPS nodes is proposed. Variable delays are performed by exploiting
a low-loss optically controlled fiber-based loop configuration. XGM in SOAs allows polarization and wavelength
independent operation in the whole C-band. A packet delay resolution of 5 μs is obtained as well as a storage time of
50 μs with moderate signal degradation. Performances are evaluated in terms of bit error rate measurements for 10 Gb/s
NRZ data payload, providing an OSNR penalty lower than 3 dB after 10 circulations. The proposed solution is
particularly attractive in slotted OPS nodes architectures where packet contention would be managed entirely in the
optical domain.
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An experimental analysis of the dynamics of optical patterns emerging from a photorefractive two-wave mixing
geometry is investigated. The dynamics appears in the system, when a tilted single feedback mirror gives rise to an
advection-like effect. Depending on the nonlocal coupling (introduced by the tilting angle) between the two
counterpropagating beams, the strength of the nonlocal response of the nonlinear photorefractive bulk medium and the
distance mirror-crystal, we report on: the seeding of new pattern geometry, the inversion of pattern transverse phase
velocity and the bifurcation from convective to absolute instabilities.
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We study the process of sum-frequency generation of femtosecond laser pulses in a strontium barium niobate
crystal with a random distribution of ferroelectric domains. The random domain structure allows for broadband
quasi-phase matching of wavelengths over the whole visible spectrum. We analyze sum-frequency generation
in the wavelength range 460nm - 630 nm, which is emitted on a cone with angles between 30 • and 55 •. We
measure the effective angular width of the sum-frequency intensity profile which is related to the spectral pulse
width and directly visualizes the spectral pulse broadening due to self-phase modulation.
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We investigate optical switching based on stimulated Raman scattering. The circuit consists of two fiber stages
connected in series with a spectral filter rejecting a signal inserted between them. When both pump and signal are
launched to the input, the pump is saturated because of the signal amplification in the first stage; the amplified signal is
rejected by the filter, so that only the low-power pump enters the second stage and no signal pulses appear at the output.
Second stage is fed by 1-mW power at signal wavelength. When pump only enters at the input, it passes through the first
stage without saturation, enters the second stage and amplifies the signal entering this stage; strong signal pulses appear
at the output. The on-off contrast is deteriorated by the pulse shape because the pump saturation is observed in the
central part of pulses, by fiber GVD, etc. These effects were not considered before. We used 2-ns pulses at 1528 nm as
the pump and a 1620-nm cw as the signal. We used in the first stage both fibers with normal and anomalous dispersion.
In fibers with anomalous dispersion pump saturation was affected by modulation instability. We found that the contrast
may be improved using fibers with normal and anomalous dispersion connected in series in the first stage provided that
the ratio between the lengths of the fibers with normal and anomalous dispersion is appropriately selected. The best
achieved contrast was 15 dB at 6-W pump peak power.
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Nonlinear action is known for its ability to create unusual phenomena and unexpected
events. Optical rogue waves-freak pulses of broadband light arising in nonlinear fiber-testify to
the fact that optical nonlinearities are no less capable of generating anomalous events than those in
other physical contexts. In this paper, we will review our work on optical rogue waves, an ultrafast
phenomenon counterpart to the freak ocean waves known to roam the open oceans. We will discuss
the experimental observation of these rare events in real time and the measurement of their heavytailed
statistical properties-a probabilistic form known to appear in a wide variety of other
complex systems from financial markets to genetics. The nonlinear Schrödinger equation predicts
the existence of optical rogue waves, offering a means to study their origins with simulations. We
will also discuss the type of initial conditions behind optical rogue waves. Because a subtle but
specific fluctuation leads to extreme waves, the rogue wave instability can be harnessed to produce
these events on demand. By exploiting this property, it is possible to produce a new type of optical
switch as well as a supercontinuum source that operates in the long pulse regime but still achieves a
stable, coherent output.
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While being the most precise measurement tool in physics, high precision laser spectroscopy is still limited to
wavelengths in the range between the infrared and the near ultraviolet. The generation of XUV frequency combs might
be a route to extend optical frequency metrology into extreme ultraviolet (XUV) spectral region where many elements
have fundamental transitions. The method of choice for XUV frequency comb generation has been cavity-assisted high
harmonic generation, where an infrared frequency comb is converted into the XUV inside a femtosecond enhancement
cavity at the full repetition rate of the oscillator. Our recent efforts have been directed towards a significant improvement
of the average power of XUV combs. To this end, we experimentally investigated the process of non-collinear high
harmonic generation (NCHHG) and proved it to be useful as a combined method for efficient generation and outcoupling
of XUV radiation. Also, we developed a high repetition rate single-pass amplifier which has the potential to boost the
available power for intracavity HHG.
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We consider various aspects of supercontinuum generation in the quasi-CW regime through analysis, numerical
simulations and experiments. A new interpretation of certain features of the developing spectrum in terms of localized
periodic structures known as "Akhmediev Breathers" is proposed. We also briefly consider the role of breather
collisions and turbulence in the presence of higher order dispersion and show that they lead to the formation of very large
amplitude localized structures that may be analogous to the infamous oceanic rogue waves.
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We demonstrate here that it is possible to fabricate 1D and 2D diffraction gratings on the (001) surface of RbTiOPO4
(RTP) and KTiOPO4 (KTP) single crystals. We analyzed the linear and nonlinear optical properties of 1D and 2D
nonlinear photonic crystals. We show enhanced second harmonics when the samples were illuminated with a pulsed
Nd:YAG laser, when compared to non-structured surface of the same materials and mainly there exists an asymmetry on
the diffraction patterns of the second harmonic generated light, showing higher intensity in diffraction orders different to
the zero order in the reflection configuration.
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Random nonlinear photonic crystal (NPC) structures formed by as-grown domains in a non-ferroelectric strontium
tetraborate (SBO) are investigated. The domain shape and orientation are similar to those in ferroelectric KTP. Nonlinear
diffraction is the simplest way to detect, evaluate and characterize these structures. Reciprocal superlattice vectors
spectra of NPC in SBO are very wide and enable broadband efficiency enhancement of nonlinear optical processes.
Second harmonic (SH) generation of femtosecond Ti:sapphire oscillator radiation with 1.9% efficiency is obtained using
nonlinear diffraction geometry. Random quasi phase matched generation at the wavelengths of fourth harmonic of
Ti:sapphire laser is obtained with average power up to 1μW.
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We present our latest findings on the nature and behavior of CARS in active Raman devices, such as Raman converters
and Raman lasers, which operate at exact Raman resonance. We demonstrate that the CARS mechanism in these devices
actually comprises two opposite and competing interactions, which respectively create and annihilate phonons in the
Raman-active medium. Furthermore, we show that both the phase mismatch of the CARS process and the level of pump
depletion determine which of these two interactions takes place along the fields' propagation path in the Raman devices.
Finally, we compare this CARS model with the model used by the CARS spectroscopy community, and explain that the
difference between both models is mainly due to the fact that "CARS" in the context of Raman devices refers to Ramanresonant
four-wave mixing, whereas "CARS" in the context of spectroscopy often denotes a two-step Raman interaction.
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The total reflection effect of the weak signal pulse from the high-power reference pulse with another frequency is first
demonstrated in the dispersive nonlinear medium. It is shown that as a result of the binary collision, signal pulse
frequency shift occurs, propagation velocity changes and time delay takes place. The conditions of total internal
reflection from moving inhomogeneity induced by pump pulse in nonlinear medium are found. The expression for the
reflected wave frequency shift is obtained. The possibility of pulse reflection from bright solitons in cubic medium is
considered.
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We investigate the interaction of two optical beams at different frequencies in an optical gradient waveguide. The index
has a parabolic profile, and the nonlinearity belongs to a defocusing type. The total reflection of a tilted signal beam
from a negative inhomogeneity induced by pump-beam occurs while both beams are trapped in the refractive index
trough is considered. We derive the equation for the rays, taking into account cubic nonlinearity and transverse
inhomogeneity. Trajectories of the signal beam at different ratios of the values of the nonlinearity, heterogeneity and the
initial angle of inclination are plotted. The critical angle of total reflection in a gradient waveguide with negative
nonlinearity is found. The interaction of co-axis beams is also discussed. The waveguiding propagation of a pump beam
under the balance between defocusing with negative nonlinearity and focusing with parabolic inhomogeneity is
presented. The wide signal beam can split by narrow pump beam.
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Here had been analyzed the coupling of microring resonators in the presence of Kerr effect. The effects of nonlinear
coupling on optical bistability of microring resonators are investigated too. This result provides a technique to designing
an "all-optical flip-flop circuit".
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As the semiconductor materials have strong nonlinear optical effects, they have a great deal of attention in ultrafast alloptical
data processing. In semiconductors, the free carriers (FC) density change with field intensity in process of Two
Photon Absorption (TPA), and leads to second order intensity dependant in refractive index and loss. In this paper, in
addition to Kerr effect, the nonlinear optical effects (TPA) and free carriers is studied theoretically in nonlinear
directional couplers by starting from Maxwell's equations and perturbation method. As results show that TPA and FC
limit the field transmission between waveguides stronger than Kerr effect and the threshold of filed intensity decreases
one order of magnitude. This phenomenon has important applications in switching operation when coupling and
decoupling optical wave is needed.
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In this article, we discuss the waveguide dimensions optimization aiming to reduce the Vπ. For that purpose, various
cover materials are investigated leading to a minimum effective core area " Aeff". The index contrast (core-cladding) at
λ= 1550 nm, is varying from 0.07 to 0.21. As a result, the Aeff decreases from 12 μm2 down to 2.3 μm2, the total
thickness of the waveguide is thus reduced and consequently the Vπ. Optimal parameters were calculated at λ= 1550 nm
for single mode inverted-rib waveguides structure. The PAS1 a new polymer is used as electro-optic material for the
core. An analytical model taking account the losses by tunnelling, allowed us to estimate the optimum distance between
electrodes to reduce the Vπ which could be about 1.6V ( 0.8 V in a push-pull configuration). Related with the bandwidth
of the modulator, permittivity measurements were carried out on core and cladding polymers as well. The process of
waveguides fabrication is described in details and several waveguides are performed. Finally, a new experimental
technique for precision measurements of the propagation losses in waveguides is presented. The principle is simple, and
the propagation losses measured is found to be independent of coupling conditions.
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We demonstrate all-optical NOR logic operation of four data signals in one SOA. Exploiting XGM, wavelength
multiplexing and optical filtering for signal discrimination, we purpose an implementation in which an all-one optical
probe signal is modulated by the optical sum of four different data signals at 10 Gbps each. Data signals act as pump and
reduce the gain of the SOA producing on-off keying of the probe and, hence, the NOR behavior. We derive the
feasibility of a multiple-bit NOR from a simple XGM setup working at a wide range of pump power by means of a
characterization with all-one RZ streams. High-resolution measures of the signals are presented to illustrate nonlinear
effects and wavelength management. Signals traces are showed to prove logic functioning and 4-bit gate quality is
reported by means of eye diagrams of the output signal for different input powers.
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We present the results of experimental studies of physical properties of the detection process of GaAs Schottky diodes
for terahertz frequency radiation. The development of technology in the THz frequency band has a rapid progress
recently. Considered as an extension of the microwave and millimeter wave bands, the THz frequency offers greater
communication bandwidth than is available at microwave frequencies. The Schottky barrier contact has an important role
in the operation of many GaAs devices. GaAs Schottky diodes have been the primary nonlinear device used in
millimeter and sub millimeter wave detectors and receivers. GaAs Schottky diodes are especially interesting due to their
high mobility transport characteristics, which allows for a large reduction of the resistance-capacitance (RC) time
constant and thermal noise.
In This work are investigated the electrical and photoelectric properties of GaAs Schottky diodes. Samples were obtained
by deposition of different metals (Au, Ni, Pt, Pd, Fe, In, Ga, Al) on semiconductor. For fabrication metal-semiconductor
(MS) structures is used original method of metal electrodepositing. In this method electrochemical etching of
semiconductor surface occurs just before deposition of metal from the solution, which contains etching material and
metal ions together. For that, semiconductor surface cleaning processes and metal deposition carries out in the same
technological process. In the experiments as the electrolyte was used aqueous solution of chlorides. Metal deposition was
carried out at room temperature.
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We present a comprehensive review of the nonlinear optical (NLO) properties of various phthalocyanines
studied by our group over the last few years. The NLO coefficients obtained in the continuous wave (cw), nanosecond
(ns), picosecond (ps), and femtosecond (fs) regimes are summarized and important conclusions drawn from these studies
are highlighted. Wherever possible the figures of merit in different pulse domains are evaluated and discussed for
possible applications in the field of photonics. Various schemes to identify and exploit the potential of these molecules
are proposed. Necessary measures required for the realization of practical devices out of these molecules are delineated.
The performance of these molecules vis-à-vis other phthalocyanines and related compounds is evaluated.
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We present the simulation results of the optical parametric amplification in the composite chalcogenide-tellurite
microstructured fiber driven by a single wavelength. Further, by applying dual pumping scheme, with two equal power
pumps with different wavelengths, lying on opposite sides of the zero dispersion wavelength (ZDWL), we achieve a
relatively flat gain spectrum over a wider bandwidth than that possible for single pump. The two pumps in the dual
pumping scheme have the power half that of the pump power in single pumping scheme. The composite microstructured
fiber designed here not only shows zero dispersion in the telecommunication band but also has two ZDWLs (one in the
telecommunication band at 1.51 μm and the other at 2.19 μm) with anomalous dispersion between the two ZDWLs. In
addition, the composite fiber has high nonlinearity (of the order of 16 W-1m-1). With a single pump at the first ZDWL,
1.51 μm, the parametric gain over more than 1000 nm wide wavelength band, starting from 1.14 to 2.21 μm, is achieved
with a 11.13 dB gain difference between the gains near the pump and optimal wavelengths. In the dual pumping scheme,
the difference between the gains at optimal wavelengths and pump wavelength is only 2.45 dB; while the difference
between the maximum and minimum gain is 3.43 dB. The maximum value of the gain at the optimal wavelengths, in
both single pumping and dual pumping schemes are same. We further show that by selecting proper pump wavelengths
ultra-broadband gain can be achieved.
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We present the evolution of supercontinuum emission (SCE) from tightly focused fs laser pulses propagating in air.
45 fs laser pulses at 806 nm, 10 Hz repetition rate, from Ti:Sapphire laser (Thales Laser, Alpha 10) with a
nanosecond contrast ratio better than 10-6: 1 are focused in air by a lens to an f/12 focusing geometry in one case,
and by an off-axis parabolic mirror leading to an f/6 focusing in another. The laser input power is varied in the range
of 10 - 90 PCr and 6 - 60 PCr in the f/12 and f/6 focusing geometries, respectively, where the critical power for selffocusing
in air is PCr = 3 GW for 806 nm. The effect of the tight focusing condition on the SCE spectrum and the
dependence on the input laser polarization are studied. Within the input power range used in the study, the blue edge
(the maximum positive frequency shift) of the SCE spectrum is found to decrease continuously when the laser
energy is increased. This result is in contrast with previous measurements of SCE in condensed matter and gases
with loose focusing geometry, for which a constant blue edge was interpreted as due to intensity clamping. We
propose a model, which show that for tight focusing conditions, external focusing prevails over the optical Kerr
effect annihilating plasma defocusing and self-focusing, thereby giving access to a new propagation regime featured
by an efficient laser energy deposition in fully ionized air and intense 1015 W/cm2 pulses at the focus.
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Many nonlinear systems exhibiting wave propagation, support solitons, nonlinear excitations that propagate unchanged,
due to a balance of nonlinearity and dispersion. Of particular interest, both as a subject within photonics, as well as a
topic of basic research, is their interaction with periodic structures, such as photonic crystals or gratings. Optical fibers
and fiber gratings are rich experimental environments for nonlinear physics. The propagation of light in such a fiber is
described approximately by the nonlinear Schrödinger equation. Here we demonstrate, both in experiment and
simulation, that the process of soliton excitation, which is inherently discrete, profoundly changes the high power
transmission properties of pulses through a Fiber Bragg grating for frequencies close to the band-edge. The quantization
manifests itself in a characteristic staircase shape of the transmission spectrum at high powers. This behaviour is
analyzed by a systematic study of the temporally resolved transmission spectra, which allows us to identify gap solitons
as causing the transmission quantization. They act as discrete, self-induced transmission channels, because only solitons
are able to propagate through the otherwise "forbidden" band-gap.
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Although ultrafast lasers have demonstrated much success in structuring and ablating dielectrics on the micrometer scale
and below, high aspect ratio structuring remains a challenge. Specifically, microfluidics or lab-on-chip DNA sequencing
systems require high aspect ratio sub-10 μm wide channels with no taper. Micro-dicing also requires machining with
vertical walls. Backside water assisted ultrafast laser processing with Gaussian beams allows the production of high
aspect ratio microchannels but requires sub-micron sample positioning and precise control of translation velocity.
In this context, we propose a new approach based on Bessel beams that exhibit a focal range exceeding the Rayleigh
range by over one order of magnitude. An SLM-based setup allows us to produce a Bessel beam with central core
diameter of 1.5 μm FWHM extending over a longitudinal range of 150 μm. A working window in the parameter space
has been identified that allows the reliable production of high aspect ratio taper-free microchannels without sample
translation. We report a systematic investigation of the damage morphology dependence on focusing geometry and
energy per pulse.
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The novel propagation characteristics of Bessel beams have been widely applied to optical manipulation and harmonic
generation, and have provided new perspectives on fundamentals of ultrashort laser pulse propagation in nonlinear
media. Fully exploiting their many unique properties, however, requires the development of techniques for the
generation of high quality Bessel beams with flexible adjustment of the beam parameters. Moreover, long working
distances are needed to produce Bessel beams inside bulk samples. In this paper, we report on the development of a
novel spatial light modulator based setup that combines the properties of parameter flexibility, long working distance,
high throughput and operation on micron-scale. We report both on the general characterization of the beam properties as
well as a specific application in surface nanoprocessing.
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Over the last 15 years, many groups have analyzed terahertz generation by optical rectification and
subsequently many different expressions are present in the literature. The theory has been developed
for the (100), (110), (111) and more recently the (112) crystal faces and compared to experimental
results. A recent paper by Hargreaves, Radhanpura and Lewis (HRL) deals with optical rectification
in zinc blende crystals for arbitrary excitation conditions. The current paper analyzes expressions
from the literature to reconcile any differences. In most cases, we have found that the generalized
theory reproduces the results published in previous papers with some phase shift in azimuthal angle.
However, these phase shifts not only differ between papers but also, within the one paper, between
different crystal orientations. As notations tend to differ between papers, the need for a generalized
and agreed definition of co-ordinates and angles becomes apparent. Identifying where these
corrections originate is made more difficult with some of the papers missing explicit definitions of
co-ordinate systems and azimuthal angles. It has been found that the differences originate from the
definition of the azimuthal angle and direction of rotation. With these differences reconciled, the
general theory is able to reproduce the azimuthal angle dependence of terahertz generation by optical
rectification.
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Liquid crystals are candidate materials for optical devices operating in the Terahertz (THz) frequency region of the
electromagnetic spectrum. Proposed devices include THz phase shifters and THz quarter wave plates. To assist in
designing for these applications, the fundamental properties of the materials should be determined. Fundamental optical
properties to be determined over the frequency range of interest are the refractive index n and the absorption coefficient
α. According to the orientation of the liquid crystals relative to the polarisation of the light field, ordinary and
extraordinary values for the refractive index may be distinguished. In early work, employing time-domain spectroscopy,
a rise in both no and ne with optical frequency in the THz region was reported. Later work, employing two-colour
generation of THz radiation, indicated the values of no and ne were both relatively constant in the THz region. We have
now made measurements of the two common nematic liquid crystals K15 and E7 using time-domain THz spectroscopy
and confirm that no and ne show little change over the spectral region 0.15 to 1 THz.
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Inverse Faraday effect and optical Kerr effect are measured in antiferromegnetic NiO using pump-probe method.
The magnetic field is induced by the illumination of 100 fs intense circularly polarized wave, which is detected
by the Faraday rotation of probe beam.
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