Enhancement of flip-chip white light-emitting diodes with a one-dimensional photonic crystal.

A design for a one-dimensional photonic crystal (1D PhC) based on thin-film optics is proposed to improve the light extraction efficiency of phosphor-converted flip-chip white-light-emitting diodes (LEDs). The 1D PhC thin film consisting of alternating layers of TiO2 and SiO2 is added between a phosphor layer and sapphire substrate of the LEDs. Monte Carlo simulation method is introduced to analyze performance of the proposed LEDs with a 1D PhC. Results show that the light extraction efficiency is higher than that of conventional LEDs by 16%, and the correlated color temperature becomes lower, below 4000 K. These improvements are attributed to the efficient extraction of backscattered light from the phosphor layer by using the 1D PhC thin film.

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.

Optical properties and residual stress of YbF3 thin films deposited at different temperatures.

The influence of deposition temperature on the optical properties, microstructure, and residual stress of YbF(3) films, deposited by electron-beam evaporation, has been investigated. The increased refractive indices and surface roughness of YbF(3) films indicate that the film density and columnar structure size increase with deposition temperature. At the same time, higher packing density reduces absorption of moisture. The residual stress is related to deposition temperature and to substrate. For the samples deposited on BK7, the residual stress mainly comes from intrinsic stress, however, for those on fused silica, thermal stress is the dominant factor of total residual stress.

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.