Twenty years after Dr. Holonyak's invention, a compact disc (CD) was introduced to the market in 1982. A laser diode is always in the heart of optical storage systems and a variety of other industrial applications. Innovations in laser diode technologies have brought optical storage evolutions from CD to digital versatile disc (DVD) and then Blu-ray disc (BD) every ten years. Since the most important reason for our success in laser development is our choice of metalorganic chemical vapor deposition (MOCVD) for growing these semiconductor alloys, MOCVD equipment, growth conditions, material properties, and phenomena associated with MOCVD and various alloy lasers grown by MOCVD are described in detail. Reviewing the development history would tell us how the laser diode has created a huge market and why recent innovations will predict future applications.

To improve the lifetime of high-power pure-blue InGaN-based laser diodes, the need to reduce the number of newly created structural defects in active regions, consisting of multiple quantum well structures, is inevitable. We first report on detailed structural analyses of these new types of defects and discuss their formation mechanisms and reduction methodologies. We then fabricated laser diodes with current-injection free regions near the laser facets and confirm that this is an effective method for the suppression of degradation by catastrophic optical damage. Based on the analyses of aged devices by using fluorescence microscopy, we also discuss the degradation mechanisms of GaN-based laser diodes.

In this paper, robust force control of a flexible arm is considered. We derive the dynamic equations of the joint angle and vibration of the flexible arm and its contact force. On the basis of a finite-dimensional model of distributed-parameter systems, an LQ controller, an optimal controller with low-pass property and a robust N/sub /spl infin// controller are constructed. A set of simulations has been carried out and responses for three controllers are compared.>

In this paper, task understanding and optimal strategies for handling flexible beams by using N-link manipulators are discussed. We consider the planning of the input torque and the trajectory of the manipulator as not to excite the vibration of the flexible beam. First, the equations of the motion of a general type of N-link manipulators with a flexible beam are derived. On the basis of the dynamic equations, the optimal input torque, which accomplishes the desired end-position of the manipulator and the diminution of the vibration of the flexible beam, is calculated by employing an iterative numerical algorithm. As the equation of the vibration of the flexible beam implies that the acceleration of the end-point of the manipulator excites the vibration, we consider an optimal trajectory planning so as to minimize the end-point acceleration of the manipulator. The validity of the optimal input torque and the optimal trajectory are demonstrated by computer simulations and experiments for an air-driven robot arm, respectively.>