Peifu Gu

Freeform LED lens for uniform illumination

Light flux from LED must be redistributed to meet the needs of lighting in most cases, a new method is proposed for its secondary optic design. Based on refractive equation and energy conservation, a set of first-order partial differential equations which represent the characters of LED source and desired illumination were presented. The freeform lens was constructed by solving these equations numerically. The numerical results showed that we can get a freeform lens for the illumination of uniformity near to 90%, with considerable high computation speed. This method can shorten the designing time of the freeform lens with high accepted tolerance.

Damage thresholds of (ZrO 2 –Y 2 O 3 )/SiO 2 reflectors used for XeCl lasers

An excimer laser reflector at the wavelength of 308 nm (XeCl) consisting of materials of ZrO(2)-Y(2)O(3) and SiO(2) is prepared. The reflectance reaches ~99.5% and the laser-induced damage threshold is raised to ~8.5 J/cm(2). The ZrO(2)-Y(2)O(3) mixture is proven to be a film material with a high laser damage resistance.

Omnidirectional narrow bandpass filter based on metal-dielectric thin films.

We show that a metal-dielectric Fabry-Perot (FP) structure can exhibit an omnidirectional transmission for p-polarized light, which means a passband is independent of the incidence angle of light. The omnidirectional passband occurs when the sum of the reflection phase shift at the metal-spacer interface and the propagation shift in the spacer region is almost 2pi for every incidence angle. We numerically and experimentally demonstrate such an omnidirectional narrow bandpass filter in an air/Ag/ZnS/Ag/glass structure. Moreover, we introduce an antireflection coating on both sides of the metal-dielectric FP structure. The transmittance will increase obviously, while the omnidirectional property remains the same.

Design and fabrication of a novel reflection filter.

Reflection filters are useful in optical communication, display, and other systems. A novel reflection filter is designed and fabricated. Analytical design formulas have been put forward and show good agreement with the measured maximum reflectance as well as with the bandwidth at the central wavelength. The effective admittance and distribution of the electrical field intensity are also calculated to analyze the properties of the filter. This novel filter with high peak reflectance, narrow bandwidth, and deep cutoff, is simple to design, easy to fabricate and convenient to integrate, compared with the conventional dielectric multilayer reflection filters.

Design of non-polarizing color splitting filters used for projection display system

Abstract Optical thin films used at oblique incidence exhibit inevitable polarization dependent properties. In reflective projection display systems, Philips prisms with color splitting filters are widely used. Generally, illuminating light at different polarization components passes the color splitting filters twice in such Philips prism. Color splitting filters operate as color separation for s-polarization and as color recombination for p-polarization, and thus performances of the color splitting filters for s- and p-polarization are equally important. In order to reduce stray light, it is necessary to design non-polarizing thin film edge filters for color separation and recombination system in projectors. The novel design method is based on a broad-band Fabry–Perot interference filter in which both sides of transmittance band can be used as initial designs for long-wave-pass filter or short-wave-pass filters, and through suitable refinement to reduce the transmittance ripples, it is possible to achieve zero separation between two polarization components.

Wavelength-division multiplexed thin-film filters used in tilted incident angles of light

The properties of wavelength-division multiplexed (WDM) narrowband filters used in tilted collimated light are described. The wavelength shift for s polarization in a low-index-spacer filter is larger than that for p polarization when the filter is tilted, but it is smaller in a high-index-spacer filter. Therefore the passbands of the tilted filter can be centered at the same wavelength for two polarization modes by use of high- and low-index materials, as appropriate, as spacers or by selection of a moderate-index material instead of a spacer. With such spacers, WDM filters used for incident angles of 20 degrees or even greater are constructed. Experimental results agree with the computed ones.

Laser-induced damage resistance of thin-film polarizers prepared by ion-assisted deposition

An investigation of the effects of ion-assisted deposition on the laser-induced damage threshold of thin-film polarizers has been carried out. It shows that the laser-induced damage threshold of polarizers with 50–100-eV oxygen-ion bombardment during deposition is improved considerably.

Graded wavelike two-dimensional photonic crystal made of thin films

A filling-factor-graded wavelike two-dimensional photonic crystal (2DPC) possessing a light-path bending effect that is polarization dependent is theoretically studied by using a qualitative analysis of the isofrequency curves. The numerical simulation results obtained by using the finite-difference time-domain method demonstrate that such a graded 2DPC has potential applications in a polarization splitter and a parallel-plane resonant cavity. A new kind of waveguide structure that combines a filling-factor-graded wavelike 2DPC and one-dimensional multilayer thin films is also discussed.

Optical modified signed-digit addition module based on Boolean polarization-encoded logic algebra

The modified signed-digit (MSD) number system satisfies the requirements of totally parallel addition using identical units and enables the addition of any two numbers in three sucessive steps. We show a simple and compact design of the parallel optical addition module based on MSD number representation using Boolean polarization-encoded logic algebra (BPLA). The four transforms of MSD addition are ex- pressed mathematically and the realization of the transform module us- ing liquid crystal devices (LCDs) are also given.

Properties of dielectric coatings produced by ion assisted deposition

Some metal oxides, fluorides, and ZnS films deposited by ion assisted deposition are investigated as a function of ion energy, ion variety, and ion source type. Both optical and mechanical properties, such as optical stability, absorption and scattering losses, laser damage threshold, and durability, are examined for samples deposited with the assistance of four kinds of ion source and various preparation conditions.