Characterization of nematic liquid crystals for nonlinear optical applications

While single-mode waveguides are commonly used in integrated photonic circuits, emerging applications in nonlinear and quantum optics rely fundamentally on interactions between modes of different order. Here we propose several methods to evaluate the modal composition of both externally and device-internally excited guided waves and discuss a technique for efficient excitation of arbitrary modes. The applicability of these methods is verified in photonic circuits based on aluminum nitride. We control modal excitation through suitably engineered grating couplers and are able to perform a detailed study of waveguide-internal second harmonic generation. Efficient and broadband power conversion between orthogonal polarizations is realized within an asymmetric directional coupler to demonstrate selective excitation of arbitrary higher-order modes. Our approach holds promise for applications in nonlinear optics and frequency up/down-mixing in a chipscale framework.

High birefringence rectangular-hole photonic crystal fiber

The growth and overlap of research in the fields of photonic crystals (PhCs) and nonlinear optics should lead to new exciting, active functions and high-efficiency nonlinear optical applications because nonlinear optical effects in PhCs may allow for significant advances in various optical processes by using resonantly stored light and anomalous band dispersions, in combination with nonlinear optical host materials. To show the experimental and theoretical evidences of great potentials of the nonlinear PhCs for the realization of the high-efficient and very compact nonlinear optical devices and applications, we have examined the typical second- and third-order nonlinear optical responses and the photonic band structure of the nonlinear two-dimensional (2D) PhC waveguides. We have demonstrated for the first time the second harmonic generation (SHG), the sum-frequency mixing (SFM) in the ultraviolet (UV) region, and the strong enhancement of the SHG intensity originating from the photonic band resonance in this waveguide. Moreover, by probing the nonlinear optical changes of the band resonances in angle-resolved reflectivity,we have shown direct evidence that the nonlinear optical changes arising from modifications of the photonic bands by purely optical means are dominated by the dispersion nature and the group velocity of the photonic bands, which are essential for the realization of desirable nonlinear applications, such as practical all-optical switching devices with very low operational power and ultra-small dimensions. These results agree well with the bhavior predicted from band structures, indicating that the design of nonlinear optical properties of material systems is realistically possible by band dispersion and group velocity engineering.

We present and demonstrate a novel method for engineering the radial-variant polarization on the incident field to achieve a needle of transversally polarized field without any pupil filters. We generate a new kind of localized linearly-polarized vector fields with distributions of states of polarization (SoPs) describing by the radius to the power p and explore its tight focusing, nonparaxial focusing, and paraxial focusing properties. By tuning the power p, we obtain the needle-like focal field with hybrid SoPs and give the formula for describing the length of the needle. Experimentally, we systematically investigate both the intensity distributions and the polarization evolution of the optical needle by paraxial focusing the generated vector field. Such an optical needle, which enhances the light-matter interaction, has intriguing applications in optical microma-chining and nonlinear optics.

All-dielectric metasurfaces are unique component to control optical wavefront with high transmission or reflection coefficient. Recently, accelerating beam, which propagates along curved arbitrary trajectories, has been realized with conventional diffractive optical elements (DOE). However, DOE suffer from low sampling ratio of rapid phase gradients and its diffraction efficiency drops quickly when the wavelength is switched to another wavelength which is different than the designed wavelength.. In this study, we show accelerating beam which is generated by highly efficient and polarization insensitive all-dielectric metasurfaces in the visible wavelength. The acceleration beam is numerically generated with the proposed metasurfaces which are composed of TiO2 nanopillars residing on glass substrate using finite difference time-domain computational method. It is shown that this beam has the ability to propagate curved trajectories in air medium. Transmission efficiency of the proposed structure is above 65% and desired arbitrary trajectories have been achieved. Generating highly efficient accelerating beam can be used in photonic applications in optical imaging, spectroscopy, optical micromanipulation and nonlinear optics.

We propose and generate a class of structured light fulfilling the mathematical form of a SU(2) coherent state based on a set of circular Airy vortex modes. Such wave packets possess strong focus with both radial and angular self-accelerations, which exploit more general 3D inhomogeneous velocity control with global spatial symmetry of multilayer rotation akin to galactic kinematics, termed galaxy waves. Galaxy waves are endowed with higher degrees of freedom to control strong focusing and acceleration, which opens a direction of multi-dimensional accelerating of 3D structured light field, promising numerous applications in optical trapping, manufacturing, and nonlinear optics.

Development of organic nonlinear optical materials has become progressively more important due to their emerging applications in new-generation photonic devices. A novel series of chromophores based on innovative thiophene and furan-fused cyclopentadienyl bridge with various powerful donor and acceptor moieties were designed and theoretically investigated for applications in nonlinear optics. To unravel the structure-property relationship between this new push-pull conjugated systems and their nonlinear optical property, multiple methods, including density of states analysis, coupled perturbed Kohn-Sham (CPKS) method, sum-over-states (SOS) model, the two-level model (TSM), hyperpolarizability density analysis, and the (hyper)polarizability contribution decomposition, were performed to comprehensively investigated the nonlinear optical and electronic properties of this new π-system. Due to excellent charge transfer ability of new bridge and distinctive structure of donor and acceptor, the designed chromophores exhibit deep HOMO levels, low excitation energy, high dipole moment difference and large hyperpolarizability, indicating the appealing air-stable property and remarkable electrooptic performance of them. Importantly, THQ-CS-A3 and PA-CS-A3 shows outstanding NLO response properties with βtot value of 6953.9 × 10-30 and 5066.0 × 10-30 esu in AN, respectively. The influence of the push-pull strength, the heterocycle and the π-conjugation of new bridge on the nonlinear optical properties of this novel powerful systems are clarified. This new series of chromophores exhibit remarkable electro-optical Pockels and optical rectification effect. More interestingly, PA-CS-A3 and THQ-CS-A2 also show appealing SHG effect. This study will help people understand the nature of nonlinear optical properties of innovative heteroarene-fused based cyclopentadienyl chromophores and offer guidance for the rational design of chromophores with outstanding electrooptic (EO) performance in the future.

Nonlinear optics, a research area that is emerged after the invention of laser in 1960, continues to be widely explored with a broad range of applications from optical communication and spectroscopy to quantum photonics. A long-standing goal is to realize nonlinear optical structures at progressively low optical power down to quantum regime and electrically-tunable, which is difficult given the small nonlinear coefficients of bulk materials. Currently, there arises a new type of 2D nonlinear optical materials with fascinating properties such as broadband saturable absorption and ultrafast carrier dynamics with a large nonlinear refractive index. Graphene with the ease of fabrication, compatibility with CMOS technology and silicon photonics is a strong contender for a new class of optoelectronic and photonic devices and circuits. In this talk, I will first review graphene's relevant physics for its application in nonlinear optics complemented by our theoretical work on the quantum treatment of its nonlinear Kerr coefficient. This includes how the Kerr coefficient can be electrically-tuned for device operation as well as new physics of anomalous optical saturation. I will then present our systematic experimental investigation of measuring Kerr coefficient through optical self modulation effect, with an emphasis on its wavelength dependence and temporal evolution via combined z-scan and pump-probe measurements. Finally, I will present our experimental work on ultrafast optical modulation/switching and bistability in a hybrid graphene-silicon photonic crystal nanocavities providing a world-record of modulation/switching speed and depth with the lowest optical power for an integrated nonlinear silicon-based photonic devices.

In the present work, a good-quality nickel sulfate hexahydrate (NSH) single crystal measuring 30 × 20 × 15 mm3 was grown via a slow evaporation solution technique (SEST). NSH single crystal is an inorganic material and is widely used in optical applications, UV sensors, and missile detection systems, among others. The grown crystal was characterized using powder x-ray diffraction (PXRD), UV-visible spectroscopy, microhardness test and etching analysis. Photoacoustic spectroscopy (PAS) was used to identify the thermal diffusivity of the grown crystal. The thermal diffusivity of the NSH crystal was found to be superior to that of various common nonlinear optical (NLO) materials, and is thus suitable for use in optical and sensor applications. Differential scanning calorimetry (DSC) was utilized to determine the material decomposition at a certain temperature. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed to identify the melting point of the grown crystal. The dielectric analysis showed that the crystal has low dielectric loss, fewer defects, and better optical properties, and is suitable for NLO applications. Thermal analysis showed that the grown crystal can be utilized for a wide array of applications including optical communications, UV bandpass filters, UV sensors, harmonic generation, and missile detection systems.

We fabricated Au nanoparticles on the surface of TiO2 by photo-reduction method. The structural property of film is investigated using transmission electron microscopy technique. The surface plasmon resonance absorption peaks of TiO2 and Au-TiO2 were recorded using Shimadzu (UV-2450) UV-visible spectrophotometer. The work function of films was measured by scanning Kelvin probe microscopy (SKP5050) from KP technology, United Kingdom. The nonlinear optical refractive index and nonlinear optical absorption coefficient of Au-TiO2 nanocomposites were simultaneously measured using z-scan technique. The nonlinear optical response of Au-TiO2 nanocomposites is due to pure electronic transfer effects in Au nanoparticles. The observed nonlinearity is due to the dielectric constant of Au, which is due to the surface plasmon resonance and surface polarization between Au nanoparticles and TiO2. The dielectric constant of Au shows maximum value at 532 nm wavelength (2.33 eV). Surface plasmon resonance effect of Au nanoparticles is directly related to the metal dielectric constant, therefore it is increased. The increase in surface plasmon rsonance of Au-TiO2 nanocomposites can be observed from UV-visible absorption spectra. The optical nonlinearity depends strongly on the dielectric constant of Au. Therefore, the optical nonlinearity increases with the increase in surface plasmon resonance peak. The absorption peak of surface plasmon resonance at 544 nm is inversely proportional to the work function. Therefore, we can say that the Au dopant decreases the work function that effectively increases the surface plasmon resonance absorption peak at 544 nm, so that the nonlinear response is enhanced. The systematic change in the work function with Au concentration plays a major role in optical nonlinearity. The estimated optical nonlinearity was found to increase from 3.80×10-6 to 9.69×10-6 esu with increase in Au concentrations from 0 to 1.0x10-2 mole. This observed increment in nonlinearity is due to the enhancement of local electric field created by excitation of surface plasmon resonance that affects the work function. Therefore, the surface plasmon resonance and work function help in tuning the optical nonlinearity. The tunable nonlinear optical response of the Au-TiO2 nanocomposites may find applications in nonlinear optics at wavelength 532 nm and the development of materials for generating the higher order harmonics.

Nonlinear optical responses of carbon quantum dots anchored on graphene oxide hybrid in solid-state transparent monolithic silica gel glasses

In this paper, we consider a class of N-th order lattice filter with gains as an extension to the traditional lattice filter structures and develop analysis and synthesis of such filters. In the analysis-synthesis parts, we present recursive methods to derive the input-output transfer function of the filter in terms of parameters of the lattice structure such as the time delay, gains, transmission and reflection coefficients and vice versa. Stability of the filter is analyzed and an algorithm to test the stability is proposed. This class of MIMO lattice filters with adjustable gains models integrated photonic devices under development in our labs for optical communication and high speed signal processing applications. Our signal processing approach to characterizing this type of lattice structures can also be used in filter realization by VLSI, FPGA, or programmable processors for acoustic or speech applications

Synthesis, characterization, linear and nonlinear optical features of novel organic compound Pyridylcarboxamide chalcone for nonlinear optical applications

Synthesis, Structural Analysis and Investigation of Photoluminescence Properties of Mixed Metal Cation Borates

Organic nanocrystals are occupied in an intermediate state between single molecule and the corresponding molecular crystal in a bulk state, which are fabricated in common by using the reprecipitation method. The crystal size is in the range of several tens nanometer to sub-micrometer. In particular, linear optical properties such as excitonic absorption spectrum and fluorescence emission spectrum are evidently dependent on crystal size, owing to thermally soften nanocrystal lattice with increasing specific surface area. Core–shell-type hybridization between organic nanocrystals and novel metal nanoparticles is of too much interest in current material science. In this chapter, creation of polydiacetylene nanocrystal fibers hybridized with gold nanoparticles will be introduced in details toward nonlinear optics applications. Polydiacetylene is typically one-dimensional π-conjugated polymer, and one of the most promising organic nonlinear optical materials. It is expected that nonlinear optical properties would be enhanced because of peculiar optoelectronic interaction between exciton in polydiacetylene and localized surface plasmon resonance effect in gold nanoparticles.