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CeiKNSBN is a new photorefractive material in the KNSBN family, which has some advantages compared to other crystals. Based on two-wave mixing theory, different methods are used to investigate the photorefractvie properties of the Ce:KNSBN crystal. Most parameters of the CeiKNSBN crystal are in the same orders with those of Cu:KNSBN crystal. The diffraction efficiency from the CeiKNSBN crystal is affected by the applied electric field. The applied field increases the response rate of the grating formation and enhances the diffraction efficiency. There exists an optimum applied field and grating spacing related to the maximum diffraction efficiency, and the history of applied field influences the value of diffraction efficiency. Fanning loss and thermal effects should be considered in the diffraction theory for the CeiKNSBN crystal. The phase conjugate properties of the CeiKNSBN crystal are demonstrated in the four-wave mixing configuration and in the SPPC CAT conjugator. The experimental results agree with the analytical solution under some conditions. The He-Ne laser generates higher SPPC in the CeiKNSBN crystal than that by the argon-ion laser. The Doppler frequency detuning technique is first, to our knowledge, applied in the SPPC CAT configuration. The SPPC reflectivity is enhanced and the uniformity of the reflectivity is improved by this technique.

archives@tulane.edu / The sharing of quantum resources between multiple parties allows for the creation of quantum networks. Traditional four-wave mixing creates twin correlated beams of light. More complex four-wave mixing schemes can create a multitude of correlated beams for use in quantum communication, helping pave the way toward future quantum networks. These correlations can be seen in the intensity-difference squeezing between output modes. In this dissertation, we examine a variety of multi-mode quantum systems. I begin in chapters 2 and 3 by using the noise figure, which compares the signal-to-noise ratios of output modes to input modes, to calculate intensity-difference squeezing and make predictions about phase-sensitivity. In chapter two, I analyze a dual-pump four-wave mixing system yielding three output modes for cases in which a single seed, two asymmetric seeds, and two symmetric seeds are used. In chapter 3, I perform similar calculations for three different cascaded four-wave mixing configurations. Various intensity-difference squeezing combinations are compared for two variations of two cascaded four-wave mixing cells and for three cascaded four-wave mixing cells. Chapter 4 describes a dual pump four-wave mixing scheme with four output modes created experimentally and chapter 5 shows that when only one input mode is seeded this process is phase-insensitive. Interestingly, I find that when only two of the input modes are seeded the system becomes phase-sensitive. Finally, in chapter 6, I describe the simulated and experimental results of using a deep neural network to improve the bit error rates in a classical free-space optical on-off keying scheme, that will eventually be expanded into the quantum regime. / 1 / Sara K Wyllie

The family of III-V semiconductors is of high significance in photonics for two main reasons. First, not only they are the most practical material platforms for active photonic devices but also they are suitable for monolithic integration of passive and active photonic devices. Second, some III-V compounds exhibit high values of second and third-order nonlinear coefficients – the property useful in all-optical signal processing and wavelength conversion. This Ph.D. thesis explores the above perspectives with two candidates from the group III-V family, namely AlGaAs and InGaAsP. The dissertation consists of two main parts. The first part is dedicated to the theoretical modelling of nonlinear bianisotropic AlGaAs metasurfaces, while the second part focuses on the experimental studies of the nonlinear optical performance of InGaAsP waveguides. Concerning the first part, due to the high confinement of light supported by the Mie resonances, AlGaAs nanoantennas and metasurfaces with both high refractive index and high nonlinear susceptibility have found a unique place in planar nonlinear optics, where not only the presence of high intensity of light is of significant matter, but also the optically thin thickness of the entities releases the device from phase matching. We first describe the linear optical properties of AlGaAs meta-atoms and metasurfaces such as relatively high scattering cross-sections and the bianisotropic effect. Also, we derive and explain all required analytic formulas for this purpose. Bianisotropic metasurfaces with magnetoelectric coupling and asymmetric optical properties have sparked considerable interest in linear meta-optics. However, further in this thesis, we explore the nonlinear features of bianisotropic AlGaAs metasurfaces. In particular, we explore a second-harmonic generation in a bianisotropic AlGaAs metasurface based on the multipolar interference inside the meta-atoms and the nonlinear polarization current. We theoretically demonstrate that it is possible to obtain several orders of magnitude secondharmonic power differences for the forward and backward illuminations by adjusting the geometrical parameters of the meta-atoms in such a way that quasi-bound states in the continuum (quasi-BICs) are achievable. This research paves the way for the generation of directional higher-order waves. Concerning the second part, the research is focused on exploring nonlinear material platforms for monolithic integration of active and passive devices on the same chip. In this regard, we explore InGaAsP/InP waveguides of different geometries. First, we provide the theoretical background such as the nonlinear Schrodinger equation and four-wave mixing (FWM) equations in a nonlinear waveguide, then we solve the set of FWM equations using MATLAB to observe the qualitative behavior of the signal, idler, and the pump inside a nonlinear waveguide. Furthermore, we design and employ two waveguide geometries i.e. half-core and nanowire waveguides. We first design these waveguides so that achieving zero group velocity dispersion is possible through a suitable material composition and certain geometrical dimensions. However, for the rest of the work, we continued with the waveguides of different dimensions compared to the designed ones (due to some limitations in fabrication). We demonstrate self-phase modulation (SPM) and FWM for the half-core waveguides. For the case of the nanowire waveguides, we also demonstrate the FWM effect. We measured and extracted the effective value of the nonlinear refractive index of InGaAsP/InP waveguides to be n2 = 1.9 × 10−13 cm2/W through the relation between the idler and the pump power when the phase mismatch is negligible. Finally, we experimentally observe the two-photon absorption effect in our waveguides through the nonlinear characteristics of input and output powers of the waveguides from which the two-photon absorption coefficient of 19 cm/GW is calculated.

Estudamos os efeitos não lineares em cristais dopados com Cr+3 como o Rubi (Al2O3: Cr+3) e o Aluminato de Gadolínio (GdAlO3: Cr+3), acrescentados através de um índice de refração dependente da intensidade de luz incidente, que caracteriza os meios tipo Kerr (n= n0+n2I, com n2= n2´+in2´). As propriedades não lineares desses cristais se devem à diferença de susceptibilidades do estado excitado e do estado fundamental dos íons de Cr+3. Este modelo é amplamente conhecido, e explica muito bem os efeitos não lineares do Rubi. Porém, para o GdAl O3: Cr+3 há um efeito que não pode ser explicado por esse modelo simplificado: a dependência da razão r= n2\"/n2\' com a intensidade, cuia observação experimental foi feita utilizando a técnica de Mistura de Duas Ondas (MDO). A explicação para esse efeito foi apresentada recentemente e propõe que seja devido à interação de pares de Cr, presente quando a concentração de íons de Cr no material é alta. Neste trabalho verificamos a dependência de r com a intensidade por MDO e utilizando uma nova técnica, a MDO transiente. Esta última possui a grande vantagem de fornecer a razão r de forma direta, enquanto que na MDO, r é obtido pelo ajuste de uma curva de ganho. Como resultado, observamos que a MDO transiente fornece uma dependência de r com a intensidade que está de acordo com a prevista pela interação de pares de Cr e é superior à obtida por MDO. Também apresentamos os parâmetros determinados via MDO (n2\', a intensidade de saturação do meio, r e o tempo de resposta do meio) para 488 nm no GdAlO3: Cr+3, cujos valores ainda não são conhecidos na literatura / We have studied the nonlinear properties of Chromium doped crystals such as ruby (Al2O3: Cr+3) and Gadolinium aluminate (GdAlO3: Cr+3), given by the intensity dependent refractive index characteristic of Kerr media, where n= n0+n2I and n2= n2´+in2´. The nonlinear properties of these crystals are due to the difference between the excited and the ground state susceptibilities. This model is widely used and explains the nonlinearity of ruby. However, GdAlO3: Cr+3 presents an effect that cannot be explained by that simplified approach: the intensity dependence of the parameter r=n2\"/n2\'. The experimental observation of such dependence was achieved using the Two Wave Mixing technique. An explanation for this effect was recently proposed using the interaction between Chromium ions that occurs when their concentration is high enough. In this work we observed the intensity dependence of r via two wave mixing and using a new technique, transient Two wave mixing. The last one gives the parameter r in a direct way, while the two waves mixing gives r by the fitting of a gain curve. As a result, we observed that transient two wave mixing shows greater intensity dependence than two wave mixing and agree with the interaction of Chromium ions. Also, we present the Two wave mixing parameters (n2\', the saturation intensity and response time of the medium) at 488nm, that were never reported before

The nonlinear optical response of low-temperature (LT) grown GaAs were studied using four-wave mixing techniques. Through measurements of the four-wave mixing response as a function of pulse delay and photon energy, a strong optical response was identi ed associated with the fundamental band gap exciton. These experiments therefore demonstrated the importance of the exciton in understanding the ultrafast nonlinear optical response of LT-GaAs despite the absence of any evidence of the exciton in past linear absorption studies in this material. Measurement of the fourwave mixing response as a function of pulse delay and the polarization states of the two excitation pulses shows that the dominant contribution to the exciton signal is tied to excitation-induced dephasing. Four-wave mixing experiments in which the sample is exposed to an additional laser pulse indicate that the exciton signal may be strongly diminished due to a combination of screening and a reduction in the total dephasing time. The short temporal duration of the above e ect provides evidence of an ultrashort (< 100 fs) electron trapping time in this system tied to arsenic related defects introduced during low-temperature growth. These ndings are of importance to the understanding of the optical properties of LT-GaAs and will aid in the development of optoelectronic devices using this material system.

Estudamos os efeitos não lineares em cristais dopados com Cr+3 como o Rubi (Al2O3: Cr+3) e o Aluminato de Gadolínio (GdAlO3: Cr+3), acrescentados através de um índice de refração dependente da intensidade de luz incidente, que caracteriza os meios tipo Kerr (n= n0+n2I, com n2= n2´+in2´). As propriedades não lineares desses cristais se devem à diferença de susceptibilidades do estado excitado e do estado fundamental dos íons de Cr+3. Este modelo é amplamente conhecido, e explica muito bem os efeitos não lineares do Rubi. Porém, para o GdAl O3: Cr+3 há um efeito que não pode ser explicado por esse modelo simplificado: a dependência da razão r= n2\"/n2\' com a intensidade, cuia observação experimental foi feita utilizando a técnica de Mistura de Duas Ondas (MDO). A explicação para esse efeito foi apresentada recentemente e propõe que seja devido à interação de pares de Cr, presente quando a concentração de íons de Cr no material é alta. Neste trabalho verificamos a dependência de r com a intensidade por MDO e utilizando uma nova técnica, a MDO transiente. Esta última possui a grande vantagem de fornecer a razão r de forma direta, enquanto que na MDO, r é obtido pelo ajuste de uma curva de ganho. Como resultado, observamos que a MDO transiente fornece uma dependência de r com a intensidade que está de acordo com a prevista pela interação de pares de Cr e é superior à obtida por MDO. Também apresentamos os parâmetros determinados via MDO (n2\', a intensidade de saturação do meio, r e o tempo de resposta do meio) para 488 nm no GdAlO3: Cr+3, cujos valores ainda não são conhecidos na literatura / We have studied the nonlinear properties of Chromium doped crystals such as ruby (Al2O3: Cr+3) and Gadolinium aluminate (GdAlO3: Cr+3), given by the intensity dependent refractive index characteristic of Kerr media, where n= n0+n2I and n2= n2´+in2´. The nonlinear properties of these crystals are due to the difference between the excited and the ground state susceptibilities. This model is widely used and explains the nonlinearity of ruby. However, GdAlO3: Cr+3 presents an effect that cannot be explained by that simplified approach: the intensity dependence of the parameter r=n2\"/n2\'. The experimental observation of such dependence was achieved using the Two Wave Mixing technique. An explanation for this effect was recently proposed using the interaction between Chromium ions that occurs when their concentration is high enough. In this work we observed the intensity dependence of r via two wave mixing and using a new technique, transient Two wave mixing. The last one gives the parameter r in a direct way, while the two waves mixing gives r by the fitting of a gain curve. As a result, we observed that transient two wave mixing shows greater intensity dependence than two wave mixing and agree with the interaction of Chromium ions. Also, we present the Two wave mixing parameters (n2\', the saturation intensity and response time of the medium) at 488nm, that were never reported before

Photonic integration and all-optical signal processing are promising solutions to the increasing demand for high-bandwidth and high-speed communication systems. III-V semiconductor materials, specially AlGaAs, have shown potentials for photonic integration and efficient nonlinear processes due to their low nonlinear absorption, flexibility at controlling the refractive index, and mature fabrication technology. In this thesis, we report the designs of AlGaAs microring resonators optimized for efficient four-wave mixing. Four-wave mixing (FWM) is a nonlinear optical phenomenon which can be used to realize many optical signal processing operations such as optical wavelength conversion and optical time division multiplexing and demultiplexing. Our designed AlGaAs microring resonators are expected to have good optical confinement, transmission characteristics, and efficient coupling between the ring and waveguide. Here we also present our fabrication efforts to fabricate the microring resonators device and the insights gained in the process. The microring resonators devices have a potential to be used in optical communication networks for all-optical signal processing operations.

Two experimental methods, optical limiting and degenerate four-wave mixing, are employed to study the nonlinear optical properties of various novel fullerenes structures. Optical limiting refers to decreased transmittance of a material with increased incident light intensity. Detailed measurements of the wavelength-dependence of fullerene optical limiters have illustrated several key features of reverse saturable absorption. Most important among these is the requirement of weak but non-negligible ground state absorption. We have shown that the optical limiting performance of C₆₀ can be extended into the near infrared range by appropriate modifications of the structure such as higher cage fullerenes or derivatization of the basic C₆₀ molecule. The higher cage fullerene C₇₆ shows improved optical limiting behavior compared to C₆₀, for wavelengths higher than 650 nm, but becomes a weak limiter in the 800 nm range. C₈₄, even at high concentrations in [alpha]-chloronaphthalene, does not reach the good performance of C₆₀, but instead shows weak optical limiting in the 800 nm range. We also demonstrate that by attaching various groups to the C₆₀ molecule, we can extend the optical limiting performance in the near infrared regime. The C₆₀ derivatives studied, (C₆₀ cyclic ketone, C₆₀ secondary amine, C₆₀CHC₆H₄CO₂H, and C₆₀C₄H₄(CH₃)CH₂O₂C(CH₂)CO₂H), have a similar characteristic: the attached groups cause a symmetry-breaking of the C₆₀ sphere and, therefore, there are new allowed transitions that appear as absorption features up to 750 nm. The optical limiting measurements show that these materials, even for low input energies, have an exceptionally strong optical limiting response in the 640 to 750 nm spectral region. For wavelengths higher than 800 nm, however, they become transparent and no optical limiting is observed. Excited state absorption cross-sections obtained from analysis of the optical limiting data reveal that the C₆₀ derivatives have a maximum triplet-triplet absorption cross-section at 700 nm, which is shifted from the 750 nm value for the C₆₀ molecule. For the first time, optical limiting measurements are performed on five separate C₈₄ isomers. These intriguing results show that the optical limiting behavior is strongly dependent on the cage symmetry. It is also found that the most abundant isomer does not have the strongest optical limiting performance, but is in fact one of the weaker optical limiters of the isomers isolated so far. The endohedral metallofullerenes are a unique class of fullerene materials and consist of one or more metal atoms encapsulated inside the buckyball cage. An important characteristic of these materials is the charge-transfer from the dopant atoms to the fullerene cage, which has a high electron affinity. The charge-transfer is similar to the optical excitation in a material, but although the electrons are placed in the lowest unoccupied molecular orbital (LUMO), there are no holes produced in the highest occupied molecular orbital (HOMO). This is an important analogy, since it has been previously shown that optical excitation enhances the nonlinear optical properties of a material. The nonresonant degenerate four-wave mixing experiments performed on the endohedral metallofullerene Er₂@C₈₂, at 1064 nm, show that the third order nonlinear susceptibility value is increased by orders of magnitude relative to the empty cage fullerenes, thus, confirming the charge-transfer process from the encapsulated atoms to the fullerene cage. We obtain a value [gamma]_xyyx⁽³⁾( &#173 [omega]; [omega], [omega], &#173 [omega])= &#173 8.65 &#215 10⁻³² esu for the molecular second order hyperpolarizability, which is almost three orders of magnitude larger than the values reported in literature for an empty cage fullerene. / Ph. D.