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For the case of the white LED (phosphor converted), the temperature affects phosphor in addition to chip and package. The heat can cause the decrease of the phosphor performance as well as the irreversible damage to the phosphor. In this study, the effect of phosphor thermal configuration on the degradation rate has been investigated experimentally and verified by the theoretical simulations. Two different configurations have been tested. One is die-contact phosphor layer and the other is remote case. The experimental result shows that the LEDs of the die-contact phosphor layers exhibit lower degradation rate than those of the remote phosphor layers. The thermal simulation considering the heat generation from the phosphor (energy converting loss) shows similar results. The temperature of remote phosphor layer is higher than the die-contact case. High temperature causes rapid degradation of phosphor. As the power consumption of LEDs increases, the heat generation from the phosphor becomes no more negligible. For the higher performance and longer lifetime, we have to consider phosphor layer as the heat generator and design the layer with sufficient thermal paths. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We demostrate the efficient p-type reflector for high performance vertical InGaN/GaN light emitting diodes (LEDs) with 1 × 1mm2 chip size. The reflector consists of Indium-Tin-Oxide (ITO) and Ag-Pd-Cu (APC) alloy. The ITO was inserted between p-GaN layer and APC alloy using RF magnetron sputtering to prevent inter-diffusion of APC into GaN layer. Transmission electron microscopy (TEM) result shows that ITO plays an impotant role as a diffusion barrier to APC alloy. In addition, the contact resistivity of ITO to p-GaN layer was measured to be 1.32 × 10-3 Ωcm2 at annealing temperature of 600 °C for 1 minute. APC alloy was adpoted to acheive a higher reflectance for improvement of a light extraction efficiency. The APC alloy reflector appeared to have a higher reflectivity compared to conventional Ni/Ag film reflector. The verical LEDs with ITO/APC alloy reflectors showed the light-output power of 295 mW at an injection current of 350 mA, which is 15% higher than that with Ni/Ag reflectors. The output power enhancement is attributed to the increase of light extraction efficiency due to high reflectivity of APC alloy (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report the first bidirectional optical backplane bus for a high performance multiprocessor system operating at wavelengths of 632.8 nm and 1300 nm. The optical backplane employs an array of multiplexed holograms, in conjunction with a waveguiding plate within which cascaded fanouts are generated. Data transfer rate of 1.2 Gbit/sec at 1300 nm is demonstrated with a single bus line for a system composed of nine processor/memory boards. To provide a reliable system, packaging-related issues, such as the detector size and misalignment effects are addressed. Theoretical treatment to minimize fluctuations among the received power at each processor/memory board is further presented and an optimum design rule is provided. The backplane demonstrated here is for general-purpose. It can support standard multiprocessor buses such as Futurebus+, Multibus II, etc. It also can function as a backplane bus in existing computing systems and significantly reduce the bottlenecks that accompany electrical interconnects.

We discuss the reliability of the oxide VCSELs made by Agilent Technologies (formerly part of Hewlett Packard). Measurements of operating temperature in fiber optic modules are given; these temperatures are higher than generally assumed. General challenges with oxide VCSEL reliability are introduced, and different types of failures are discussed. Long-term oxide VCSEL lifetest results are presented, along with observations about the thermal and current acceleration models. Production monitoring strategies are discussed, and the basic degradation phenomenology is briefly shown.

We review the recent results on the design and implementation of the performance-optimized bidirectional optical backplane bus aimed at high speed multiprocessor systems. It employs an array of multiplexed holograms, in conjunction with a waveguiding plate within which cascaded fanouts are generated. Data transfer rate of 1.2 Gbit/sec at 1300 nm is demonstrated with a single bus line for a system composed of nine boards. Packaging-related issues and misalignment effects are addressed. Theoretical treatment to minimize fluctuations among the received powers at each board was carried out and the overall performance was optimized. We also introduce a hybrid optical backplane with multiple bus lines. The hybrid backplane maintains the same waveguiding structure, and exploits optoelectronic array devices. A new demonstration system is being implemented. The optical backplane that we developed is transparent to higher level bus protocols, thus can support standard backplane buses such as Futurebus+, Multibus II, and VMEbus.

Optical interconnects have potential advantage over electrical methods at the backplane level. In this paper we present a free-space optical connection cube for backplane interconnect applications. The connection cube has a symmetric structure which reduces skew between boards. It can be expanded into a 3-dimensional configuration for parallel communication using vertical-cavity surface-emitting laser (VCSEL) and receiver arrays. Fan-out and fan-in of propagation beams for the connection cube are realized using volume holographic optical elements formed in dichromated gelatin (DCG) emulsion. A four-port communication system has been demonstrated using the connection cube and tested at 500 MHz. In this paper, advantages and detailed implementation of the free-space optical connection cube are presented. Design considerations for fan-out/in holographic gratings and alignment tolerances for the connection cube are discussed. Characteristics of the connection cube are also presented.

The use of optical interconnects for backplane and bus applications in multiboard processor systems has been considered by a number of investigators.1,2 However, most of these analyses have not evaluated the impact of optics on specific bus configurations. In this presentation we evaluate the performance of optics in a Futurebus+backplane, and show that considerable reduction in data transfer delay can be obtained using existing electro-optic interface elements in an optical backplane. The significance of this result is that a substantial improvement of existing bus architectures can be achieved using a straight forward substitution of electro-optic components for electrical transceivers.

We first report on the fabrication of 2 inch wafer-level GaN-based vertical light-emitting diodes (LEDs) by using a multi-functional bonding material system, which is composed of a thick Cu diffusion barrier and a bonding layer. The bonding material system superbly absorbs laser-induced stress and also effectively serves as a barrier to the indiffusion of Sn to the active region. Fully packaged vertical LEDs fabricated with indium tin oxide (ITO)/AgCu contact and the bonding material system give an operating voltage of 3.35 V at 350 mA. After over 1800 h, the operating voltages remain stable, and the reverse currents are in the range 3–8 × 10−7 A at −5 V.

We fabricate blue GaN-based vertical light-emitting diodes (LEDs) using transparent insulating SiO 2 and conducting indium tin oxide (ITO) channel layers connected to the passivation layer by a combined process of electroplated deposition and a laser lift-off technique. It is shown that unlike the SiO 2 layer, the ITO layer effectively serves as current spreading and injection layers. LEDs fabricated with the ITO channel layer exhibit a slightly higher reverse current when the voltage exceeds ―10 V. However, LEDs fabricated with the ITO layer produce higher output power (by ∼20% at 100 mA) compared to LEDs with the SiO 2 layers.