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We demonstrate multifunction operation in a 2D PC slab showing that the same structure may be used for lasing, frequency shifting and switching under appropriate stimulus. Our analytical model, based on a coupled modes nonlinear approach closely describes the main experimental features. The experimental results constitute a first step towards an active reconfiguration of photonic crystal all-optical circuits.

Summary form only given. We experimentally demonstrate nonlinear response of 2D photonic crystal Fano resonance. Phase shifts of 20 times FWHM and gains higher than 7 are measured. An analytical model allows us to describe these outstanding experimental features.

We show that all the structural properties of periodic dielectric multilayers can be accurately determined by a combined measurement of the transmission as a function of the wavelength and of the reflection as a function of the angle of incidence when the wavelength of the incident light is fixed. This method is applied to determine the structural properties of two commercial dielectric mirrors, and the results obtained are compared with a measurement of the same structural parameters by use of another technique based on the more standard optical guiding method.

A Fabry-Perot resonator filled with second-order nonlinear optical material is investigated. Attention is devoted to making the resonator act as a nonlinear mirror for ultralow-intensity light signals that can be switched by a control beam at the second-harmonic frequency. The interaction process is an input-phase-independent parametric downconversion. The theoretical problem is solved through implementation of a dummy variable method optimized for a parametric process. Efficient amplification and bistability of low-intensity signals have been found.

Photonic crystals in 1-dimension constitute a frame that may be used to modify the quadratic nonlinear interaction in much the same way as in the 3-dimensional lattices considered previously in this book. Moreover, the simplicity of a 1-dimensional structure offers several advantages such as for instance to facilitate a controlled introduction of defects, or the study of the nonlinear interaction at resonance. In fact, it was shown that light localization within a defect of a 1 — dimensional multilayer periodic structure could lead to a strong enhancement or inhibition of the second order nonlinear interaction.1 Other 1-dimensional structures have been used to obtain a doubly resonant phase matched second harmonic generation (SHG).2 In such structures one may easily resolve the effective index of refraction dispersion and rigorously show that the phase matching mechanism is provided by the periodicity build into the material.3 More recently, such structures have also been used to induce all-optical changes in the transmission or reflection, when the nonlinear interaction is considered in a cascading configuration.

Second-order nonlinear optical processes in spatially modulated material structures are investigated. In a first part, second harmonic generation in photonic crystals is considered, experimentally and theoretically, in two cases: first, when the nonlinear material is located within a “defect” in a single-dimensional periodic structure; and, second, when the nonlinear material is distributed all along a regular three-dimensional structure. It is also shown in this part that for narrow layers of second-order nonlinear material “momentum non-conserving” interactions can be as important as momentum conserving interactions. Finally, in a second part it is investigated how, in a microcavity, cascading effects induced by an intense second harmonic field can modify the reflectance properties of the structure at the fundamental frequency (nonlinear reflection).

We discuss the effect of second harmonic generation via the Čerenkov-like process in nonlinear bulk media and waveguides. We show that in both schemes the Čerenkov harmonic emission represents in fact a nonlinear Bragg diffraction process. It is therefore possible, for the first time, to describe the bulk and waveguide Čerenkov emission uniformly by considering the spatial modulation of the second-order nonlinear polarization. This is also experimentally illustrated by studying the Čerenkov second harmonic generation at the boundary of a nonlinear quadratic medium via the total internal reflection inside the nonlinear crystal.

We study Čerenkov-type second-harmonic generation in a two-dimensional quasi-periodically poled LiNbO3 crystal. We employ a new geometry of interaction to observe simultaneous emission of multi-directional nonlinear Čerenkov radiation with comparable intensities. This opens a way to control the angle of Čerenkov emission by tailoring the nonlinearity of the material, which is otherwise intrinsically defined by dielectric constants of the medium and their dispersion.

We investigate theoretically the Čerenkov-type second-harmonic generation in two-dimensional bulk nonlinear photonic crystal with longitudinal modulation of the χ(2) nonlinearity. We show that in this scheme the Čerenkov radiation can be achieved simultaneously at multiple directions with comparable intensities. The angles of emission are controllable by the spatial modulation of the nonlinearity. We propose a design of the periodically poled domain pattern, which maximizes the efficiency of the second-harmonic emission.

We study frequency conversion via interaction of two fundamental beams in quadratic nonlinear media with random distribution of the ferroelectric domains. We demonstrate broadband second- and third-harmonic generation, analyse both spatial and polarization properties of the emitted harmonics and show that they closely follow the theoretical predictions.

We analyze second harmonic generation in a generic medium composed of Lorentz oscillators for both the electrical permittivity and magnetic permeability. We discuss conditions where a fundamental beam is tuned in a positive index region and generates second and/or third harmonics in a negative index region. Phase matching condition, phase locking, inhibition of absorption at the harmonic wavelengths, and second and third harmonic lenses are also investigated.

We report a detailed numerical study of phase matched second harmonic generation for narrow beams (of few wavelengths width) in quadratic nonlinear photonic crystals under realistic situations, i.e. considering the dispersion of real materials (in particular Al0.3Ga0.7As), considering experimentally convenient architecture (in particular the planar waveguiding structure) and considering different symmetries of the lattice (the square and rhombic symmetries). We find that in the case of the Al0.3Ga0.7As in planar structures, for the rhombic configuration of the photonic crystal the sign and modulus of the diffraction can be manipulated for the second harmonic wave whereas out-of-plane losses vanish for both fundamental and second harmonic waves, thus making the predicted structure interesting for experiments and applications.

We study experimentally the process of the second harmonic generation by two noncollinear beams in quadratic nonlinear crystals with a disordered structure of ferroelectric domains. We show that the second-harmonic radiation is emitted in the form of two cones as well as in a plane representing the cross-correlation of the two fundamental pulses. We demonstrate the implementation of this parametric process for characterisation of femtosecond pulses, enabling the estimation of pulse width, chirp, and front tilt. This is achieved through monitoring the evolution of the autocorrelation trace inside the nonlinear crystal.

The first observation, to the authors' knowledge, of laser emission in a defect-free deep-etched 2-dimensional photonic crystal is reported. The structure explored here consists in a triangular lattice of 4.5 /spl mu/m-deep air holes drilled in a low index contrast InP-based waveguide. Simultaneous guided and vertical directions laser operation is demonstrated at room temperature. A laser threshold of 15 kW/cm/sup 2/ (average intensity) is measured with a pump diameter corresponding to only 9 periods of the photonic crystal.

In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612nm, using 3 ps pump pulses having peak intensities of the order of 10MW=cm2. We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.

We study parametric frequency conversion in quadratic nonlinear media with disordered ferroelectric domains. We demonstrate that disorder allows realizing broadband third-harmonic generation via cascading of two second-order quasi-phase matched nonlinear processes. We analyze both spatial and polarization properties of the emitted radiation and find the results in agreement with our theoretical predictions.

We demonstrate second and third harmonic generation from a GaAs substrate, well-below the absorption edge, in both transmission and reflection geometries. The pump is tuned at 1064 nm, in the transparency range, while the SH and the TH signals are tuned in the opaque spectral range of GaAs, at 532 nm and 355 nm, respectively. As expected, we find that the polarization of the generated signals is sensitive to the polarization of the pump. In our experiment, we work far from the phase matching condition and we account for both surface and bulk contributions, and show that the surface-generated SH components can be more intense than bulk-generated SH signals. The experimental results are contrasted with numerical simulations that include these two factors, using a hydrodynamic model that accounts for all salient aspects of the dynamics, including surface and bulk generated harmonic components.

Naturally grown ferroelectric crystals such as Strontium Barium Niobate (SBN) often exhibit an irregular multidomain structure with rod-like domains [1]. These disordered nonlinear quadratic crystals have attracted a considerable attention in recent years due to their potential benefits for nonlinear parametric processes [2]. Despite being usually considered as disadvantageous in typical nonlinear optical phenomena due to the low efficiency of the NL process, the randomness of the nonlinear media offers potential applications in broadband frequency generation [3] and ultra-short pulse monitoring [4]. These applications utilize the fact that the crystal with disordered anti-parallel domains forms, in fact, a two-dimensional photonic nonlinear structure with an infinite number of ¿2 reciprocal vectors corresponding to various local nonlinear gratings. Consequently, such structure enables phase matching of various parametric processes at the same time, over an ultra-broad spectral range and in different spatial directions [5]. Fig. 1 represents a schematic illustration of such type of random crystal placed in a typical experimental set-up where the fundamental beam shines the crystal and the SH spatial distribution is recorded. In Fig. 1b a numerically generated random distribution of up and down ferroelectric domains is represented by bright and dark colors, respectively. However, recent experiments with random domain SBN crystals also demonstrated that the emission pattern of the generated waves may differ drastically from sample to sample, going from a spatially homogeneous pattern to exhibiting distinct intensity peaks [3][4][5][6][7][8]. This behavior points towards the existence of significant differences in the actual distributions of ferroelectric domains in different samples. In fact, observations of random domains ranging from tens of nanometers to few microns have been reported in the literature [1].

Missatge de l'editorial: "This paper was published in Optical letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/ol/fulltext.cfm?uri=ol-38-14-2376&id=258441. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law." We experimentally demonstrate full two-dimensional focalization of light beams at visible frequencies by a three-dimensional woodpile photonic crystal. The focalization (the flat lensing) with focal distances of the order of 50–70 µm is experimentally demonstrated. Experimental results are compared with numerical calculations and interpreted by harmonic expansion studies.

Periodic inversion of ferroelectric domains is realized in a lithium niobate crystal by focused femtosecond near-infrared laser beam. One and two-dimensional domain patterns are fabricated. Quasi-phase matched frequency doubling of 815nm light is demonstrated in a channel waveguide with an inscribed periodic domain pattern with conversion efficiency as high as 17.45%.

We study transverse non-collinear second harmonic generation in a nonlinear crystal with random ferroelectric domain structure and demonstrate that it provides a simple and robust method for characterizing femtosecond optical pulses.

Copyright 2015 AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. An approach to switching between different patterns of light beams transmitted through the woodpile photonic crystals filled with liquid crystals is proposed. The phase transition between the nematic and isotropic liquid crystal states leads to an observable variation of the spatial pattern transmitted through the photonic structure. The transmission profiles in the nematic phase also show polarization sensibility due to refractive index dependence on the field polarization. The experimental results are consistent with a numerical calculation by Finite Difference Time Domain method.

We report experimental results on a two dimensional Al/sub 0.3/Ga/sub 0.7/As photonic crystal slab which exhibits a 1.6 nm full width at half maximum resonance around 1.5 /spl mu/m in reflectivity at normal incidence with respect to the plane of periodicity. The slab is supported by an AlO/sub x/ low index thick layer that plays the role of an efficient heat sink. Light with peak intensity greater than 10 GW/cm/sup 2/ can be incident on the slab without damaging the sample.

We study how the phase-locked SH component is localized and enhanced inside a highly absorbing cavity. We report that the efficiency can be proportional to the square of the quality factor.

Photonic crystals (PCs), are famous due to their well-known temporal dispersion properties as well as recently discovered spatial dispersion properties, allowing to manage spatial propagation properties of light. The peculiarities of the spatial propagation in PCs consist in vanishing of diffraction (self-collimation [1,2], negative-refraction and super-refraction of light [3]). The above listed effects refer to the propagation of the beams inside the PCs. Less is understood about the behavior of the beams behind the crystals with nontrivial dispersion properties. The ideas have been promoted that the PCs should show super-lensing effects [4], however, these effects are not well understood theoretically, nor convincingly demonstrated experimentally. We concentrate on the beam propagation behind the PCs and report an experimental observation of the formation of well collimated beam behind the 3D PC of a woodpile type.

We employ a classical, nonlinear Lorentz-Duffing oscillator model to predict third harmonic conversion efficiencies in the ultrafast regime, from a variety of metal nanostructures, including smooth, isolated metal layers, a metal-dielectric photonic band gap structure, and a metal grating. As expected, the plasmonic grating yields the largest narrow-band conversion efficiencies. However, interference phenomena at play within the multilayer stack yield comparable, broadband conversion. The method includes both linear and nonlinear material dispersions that in turn sensitively depend on linear oscillator parameters. Concurrently, and unlike other techniques, the integration scheme is numerically stable. By design, one thus avoids the introduction of explicit, third-order nonlinear coefficients and also takes into account linear and nonlinear material dispersions simultaneously, elements that are often necessary to fully understand many of the subtleties of the interaction of light with matter.

A novel application of chirped dielectric mirrors for narrow beam focalization is proposed and demonstrated numerically and experimentally. Analogy to temporal dispersion compensation by chirped dielectric mirrors is discussed.

The efficiency of second harmonic generation for very narrow beams with diameter of few wavelengths is limited by two basic physical mechanisms: 1) the diffraction which will give rise to a broadening of both fundamental and second harmonic waves leading to a decreasing of their top intensities and eventually, of their nonlinear coupling; 2) the phase mismatch since all Fourier components of the narrow parametrically beams can never be simultaneously phase matched.

When a fundamental beam propagates perpendicular to the optical axis of a nonlinear crystal with randomly distributed ferroelectric domains showing inverted sign of 2nd order nonlinearity (χ2), the generated second harmonic (SH) signal is spatially distributed in a plane, perpendicular to the optical axis [1]. Because the angular distribution of the SH intensity in this plane depends on the particular domain size and distribution, the characterization of the angular emission pattern could bring information about these parameters, which is difficult to be obtained by imaging methods since the domain size can be very small (few hundreds of nm). The domain statistics of such nonlinear materials was considered in the study of the SH diffraction pattern in a one-dimensional (1D) model by Le Grand et al. [2-4]. However, this model yields some discrepancies between the theoretical fits and experimental results [4]. In this work we compare experimental results of the SH angular distribution with the predictions of a more precise 2D model for extracting domain statistics.

This paper reports on numerical and experimental observation of a beam focusing behind a flat 3D woodpile PhC. The work demonstrates this idea using paraxial approximation model, as well as using a conventional Finite-Difference Time-Domain (FDTD) method.

A method for generating second-harmonic light from silica glass by doping its surface layer with ions is presented. When anions CO32−, OH− or Cl− are introduced from the cathodic surface during poling, the second-harmonic signal generated near that surface is enhanced by two orders of magnitude with respect to the case of poling without doping. The penetration depths of CO32−, OH− and Cl− have been measured by the etching technique. In contrast, by doping the anodic surface with cations Li+, Na+ or K+, the second-harmonic signal drops to one tenth of that corresponding to the case of poling without doping. This indicates that in the anodic surface the main charges are negative, and the positive charges neutralize them to decrease the strength of the electric field that is at the origin of the second-order susceptibility. Secondary ion mass spectroscopy detection shows the concentration distribution of the injected lithium in the surface layer. The second-harmonic signal from the anodic surface decreases m...

A novel use of chirped mirrors for narrow beam focalization is proposed. Focusing in reflection from flat chirped mirror has been demonstrated numerically and experimentally. Analogy to temporal dispersion mirrors is discussed.

The precise characterization of femtosecond laser pulses is as challenging as their generation and a topic of intense research. Dispersion-scan (d-scan) [1] is a recently established technique where the spectrum of a nonlinear signal, e.g., second-harmonic generation (SHG), is measured as a function of dispersion applied to the pulse. The spectral phase of the pulse can then be retrieved from the resulting 2D trace using an iterative algorithm. An important implementation of d-scan, based on a chirped mirror and wedge compressor, involves progressively moving one of the wedges around the maximum compression point and acquiring the resulting SHG spectrum for each insertion with a standard spectrometer. This robust and fully inline approach, which does not require any beamsplitting or temporal delays, has enabled the simultaneous compression and measurement of pulses down to single-cycle durations [2-4], but its scanning nature precludes single-shot operation. A single-shot d-scan variant that explores the spatially dependent dispersion of a glass prism was successfully demonstrated with 3.2 fs pulses [5], but the relatively small amount of dispersion that can be introduced by a single prism limits its use to few-cycle pulses.

We study experimentally second-harmonic generation by two noncollinear beams in disordered ferroelectric crystals and demonstrate implementation of this process in a novel approach for fs-pulse reconstruction, enabling full retrieval of pulse profile, phase, and front-tilt.