Xianyu Ao

Polarization beam splitter based on a two-dimensional photonic crystal of pillar type

Negatively and positively refractive behaviors are achieved in a two-dimensional photonic crystal of pillar type for TE and TM polarizations, respectively, at the same frequency. The photonic cry ...

Polarization beam splitters based on a two-dimensional photonic crystal of negative refraction.

A two-dimensional metallo-dielectric photonic crystal of negative refraction was designed for the application of polarization beam splitters. To match the refractive index of air, the effective refractive index of the designed photonic crystal is -1 for TE polarization and +1 for TM polarization. Two types of polarization beam splitter are presented.

Three-dimensional photonic crystal of negative refraction achieved by interference lithography

A three-dimensional bicontinuous photonic crystal of a bcc lattice with all-angle negative refraction that can be achieved at optical frequencies by interference lithography is proposed. A numerical simulation of the focusing imaging of a slab of this crystal was performed to verify the property of all-angle negative refraction. The dependence of the negative-refraction frequency range on the threshold of photoresist development and on the dielectric constant is also discussed.

Negative refraction of left-handed behavior in porous alumina with infiltrated silver at an optical wavelength

Porous alumina with infiltrated silver is suggested to achieve a negative refraction of left-handed behavior at an optical wavelength. Numerical simulations of subwavelength focusing by a slab lens are performed for both H and E polarizations. Beam refraction by a wedge is also simulated to verify the left-handed behavior.

High-efficiency polarization beam splitters based on a two-dimensional polymer photonic crystal

We present a design for a high-efficiency polarization beam splitter based on a two-dimensional hexagonal polymer photonic crystal, which can be fabricated directly in SU-8 photoresist using interference lithography. Computer simulations show that more than 99.9% of TM-polarized light is reflected by the polarization beam splitter, whereas 98.9% of TE-polarized light propagates through the polarization beam splitter over the wavelength range 1.53?1.62??m (C and L bands for optical communication) with good angular insensitivity of about 10?. The present polarization beam splitter has a reasonably good tolerance of fabrication errors.

General properties of N x M self-images in a strongly confined rectangular waveguide

General properties of N x M self-images in a strongly confined rectangular waveguide are given. Analytical formulas are derived for the positions, amplitudes, and phases of the N x M images at the end of multimode interference section. The formulas are verified with numerical simulation of a three-dimensional semivectorial beam propagation method.

Two-stage design method for realization of photonic bandgap structures with desired symmetries by interference lithography.

Interference lithography for the fabrication of photonic crystals is considered. A two-stage design method for realization of photonic bandgap structures with desired symmetries is developed. An optimal photonic crystal with a large bandgap is searched by adjusting some parameters while keeping some basic symmetry of the unit cell unchanged. A nonlinear programming method is then used to find the optimal electric field vectors of the laser beams and realize the desired interference pattern. The present method is useful for a rational and systematical design of new photonic bandgap structures.

Broadband Metallic Absorber on a Non-Planar Substrate

Absorbers for visible and near-infrared light are realized by depositing a thin iron layer on arrays of cones which are replicated from a porous template. The replicated conic structure itself is of several micrometers and ineffective at antireflection, but the subsequent deposition of iron on top generates nano-meter-size columnar structures, and thus broadband absorption enhancement is achieved.

Hybrid nanostructures of mixed-phase TiO2 for enhanced photoelectrochemical water splitting

Mixed-phase TiO2 nanostructures are synthesized by hydrothermal treatment of anodized TiO2 nanotubes. The growth of rutile nanorods on the anatase nanotubes can greatly expedite the electron–hole separation and transportation, enhance the light absorption, and also increase the surface area. When used for photocatalytic water splitting, more than three-fold enhancement in photocurrent density is observed for mixed-phase TiO2 nanostructures, relative to pristine TiO2 nanotubes.

Black silicon film with modulated macropores for thin-silicon photovoltaics

We present a kind of “one-step strategy” to produce black silicon film where the antireflection/light-trapping structures and the silicon film itself are fabricated simultaneously and directly from a silicon wafer. We first demonstrate that the macroporous black silicon has better light harvesting capability and longer lifetime of minority carriers than silicon nanowires of the same thickness, leading to higher efficiency when assembled into liquid junction photoelectrochemical solar cells. A free-standing macroporous black silicon film is further detached from the substrate and the measured absorption in the near infrared region is close to the theoretical limit without the help of back reflectors. FDTD simulations reveal that the modulation on the micrometer scale can scatter strongly and thus enhance the absorption of the originally weakly absorbed light.