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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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".

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.

In this article, we discuss the waveguide dimensions optimization aiming to reduce the V_π. For that purpose, various cover materials are investigated leading to a minimum effective core area " A_eff". The index contrast (core-cladding) at λ= 1550 nm, is varying from 0.07 to 0.21. As a result, the A_eff 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.

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.

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.

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.

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.

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 P_Cr and 6 - 60 P_Cr in the f/12 and f/6 focusing geometries, respectively, where the critical power for selffocusing in air is P_Cr = 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.

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.

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.

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.

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.

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.

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.