Haitao Dai

A polarization insensitive 2×2 optical switch fabricated by liquid crystal–polymer composite

A polarization insensitive 2×2 optical switch was fabricated with liquid crystal–polymer composite by means of holography. The highest diffraction efficiency achieved was 85.7%. The rise time and the decay time measured were 36 and 160μs, respectively, at an applied electric field of 18.2V∕μm. The polarization-dependent loss was 0.03dB measured for s- and p-polarized light at the wavelength of 632.8nm.

Dynamic characterizations of high diffraction efficiency in volume Bragg grating formed by holographic photopolymerization

Volume Bragg grating with 96% diffraction efficiency (DE) was efficiently formed by holographic photopolymerization in blend syrup of photocurable trimethylolpropane triacrylate monomer and nematic liquid crystal. The formation dynamics of the composite gratings was quantitatively characterized under the frame of one-dimensional reaction-diffusion model with a revision of individual decay constants for monomer diffusion and reaction. Initial parameters of diffusion and reaction were analytically determined from the measured first order DE at the beginning stage. Evolutions of the DE, both in curing and postcuring periods, were excellently simulated, especially with postcuring reaction been taken into account.

Analytical rates determinations and simulations on diffusion and reaction processes in holographic photopolymerization

An analytical method is proposed to determine the initial diffusion and reaction coefficients for monomer molecules in holographic photopolymerization processes. Those parameters can be obtained directly from the measured first order diffraction efficiency at the onset stage in the formation of volume Bragg gratings. Simulations, according to these parameters, on the evolution of the diffraction efficiency, based on one-dimensional reaction-diffusion model, were well consistent with experimental data in our trimethylolpropane triacrylate based monomer and liquid crystal composite material. It is shown that diffusion and reaction both play important roles in postcuring process.

Fractal diabolo antenna for enhancing and confining the optical magnetic field

We introduce fractal geometry to diabolo nanoantenna for higher magnetic field intensity enhancement, i.e. the Sierpinski triangle diabolo antenna (STDA). Numerical results show that higher iteration of the STDA is responsible for the higher enhancement and the red shift of the resonant wavelength. Further investigation demonstrates the enhancement can be improved by increasing the length of the antenna or its central strip. By designing diabolo antennas with fractal geometry, improving the magnetic field intensity enhancement and varying the resonance conditions can be achieved while keeping the constant antenna dimensions.

Reactive radical facilitated reaction-diffusion modeling for holographic photopolymerization

A phenomenological concentration of reactive radical is proposed to take the role of curing light intensity in explicit proportion to the reaction rate for the conventional reaction-diffusion model. This revision rationally eliminates the theoretical defect of null reaction rate in modeling of the postcuring process, and facilitates the applicability of the model in the whole process of holographic photopolymerizations in photocurable monomer and nematic liquid crystal blend system. Excellent consistencies are obtained in both curing and postcuring processes between simulated and experimentally measured evolutions of the first order diffraction efficiency of the formed composite Bragg gratings.

P‐102: Electro‐optical Characteristics of Holographic Polymer Dispersed Liquid Crystal Bragg Gratings

A holographic polymer dispersed liquid crystal Bragg grating with a diffraction efficiency of 80% is reported. It showed good electro-optical properties and fast response time. The threshold electric field was about 2.3 V/μm and the switching electric field was 27.3 V/μm. The contrast ratio obtained was about 21.7 dB. The rising and falling time obtained were 84 μs and 164 μs, respectively. The falling time depended on the driving voltage, which was explained by the shielding effect due to charge migration.