Propagation behaviors of light in index-tunable photonic crystals were analyzed by calculating the directions of the group velocity of light in the photonic crystals. Simulation results reveal that the band structures of tunable photonic crystals are highly anisotropic and the equifrequency surface curves in the wave-vector space of photonic crystals can show acute variation corresponding to an index change when operation frequency and incident angle are carefully selected. In the case of a triangular system composed of ferroelectric background and circular airholes, “on/off” switching can be operated when operation frequency a/λ is 0.4205 and the incident angle falls into a window of 32°–49°. Light can deflect 40° when the operation frequency a/λ and incident angle are 0.5372 and 23°, respectively. Two types of optical switches based on the anisotropic characteristics of index-tunable photonic crystals are proposed, which will find great potential applications in optical communications.

Light extraction efficiency is key to the performance of solid-state light sources such as the light-emitting diode. The reflectance of the bottom mirror has a significant impact on the light extraction efficiency because a large difference in the refractive index between the light source and air leads to multiple internal reflections and optical loss. Therefore, efficiency can be drastically improved with even a slight increase in the bottom mirror reflectance. This paper focuses on wide angular light incidences. An omnidirectional reflector (ODR) is then designed that included a low-index thick layer (MgF 2 ), a pair of quarter-wavelength-thick layers (Ta 2 O 5 /MgF 2 ), and a metal layer (Ag) on a solid-state light source with n ¼ 2.4. The first thick layer works as a perfect reflector for wide angular and broadband incident light since total internal reflection (TIR) occurs at the interface. In the simulations, the angular integrated reflectance for our designed reflector (TI-ODR) reaches 99.7%. The reflectance is higher than the typical ODR that is composed of a quarter-wavelength-thick layer and Ag (98.6%) or an Ag reflector alone (97.9%). The TI-ODR is then fabricated onto a gallium nitride (GaN)-based light-emitting diode and obtained a light extraction efficiency enhancement factor of approximately 1.1.

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Solid‐State Light Source In article number http://doi.wiley.com/10.1002/pssa.201700775 Kazuyuki Yamae, Hiroshi Fukshima, and Kozo Fujimoto develop novel omnidirectional reflector with total internal reflective interface (TI‐ODR) which realizes higher reflectance compared to conventional reflector for solid‐state light source (SSL). The authors then fabricate the TI‐ODR onto a gallium nitride (GaN) ‐ based light emitting device (LED) and obtain a light extraction efficiency enhancement factor of approximately 1.1.

High performance reflector is significant structure for efficiency improvement of organic and inorganic solid-state light emitting devices because a large difference in the refractive index between the light source and air leads to multiple internal reflections at the reflector. Then we focused on wide angular light incidence and designed a total internal omnidirectional reflector (TI-ODR) based on transparent oxide layers. The simulation results showed that light extraction structure with TI-ODR gives 17% and 4% efficiency enhancement compared to typical Ag based mirror for organic LED (n=1.8) and inorganic LED (n=2.4), respectively. Then the TI-ODR on blue LED structure was fabricated and that showed enhancement effect of about 8%. The layers are composed of conductive layer for current distribution, low-index thick layer for total internal reflection (TIR) of wide angular light, and high-index layer for the reinforcement of adhesion of layers.