Edge emitting LED

Light emitting diode (LED) is an extensively used device in electronic circuits. GaAs is used for the fabrication of LED. A simple p-n junction of GaAs can be used as an LED. This type of LED is called planar LED. In hemispheric LED, a hemisphere of n-type GaAs is surrounded by a diffused p-type region. Truncated ellipsoid LED couples with a truncated spherical microlens made from oxides of silica and titanium with the InGaAsP surface emitting LED. Low output, low bandwidth and presence of harmonic distortion are the main disdavantages of LED. Buthey have advantages like high reliability, economical and linearity. Edge emitting LED is a diode based on double heterostructure LED. This LED can provide an increase in order-of-magnitude in radiome from a very small emission area. GaAs in 5 layers can act as an edge emitting LED. This diode gives more output power from a small active area. Here self absorption of photon is very less since the active region is very thin. The structure of this LED is similar to that of stripe edge type laser diode.

Types of navigation

Navigation is the method of determining the position and velocity of a physical body and then directing the course of the body, relative to some reference co-ordinate grid, such that the destination is achieved. The different types of navigation are celestial navigation, X-ray pulser navigation, dead reckoning navigation, inertial navigation, satellite navigation and integrated navigation. The celestial navigation is an old format, where stars are chosen as inertial reference frame. Modified version of celestial navigation is stellar navigation where the star sensors and sun sensors provide accurate direction. X-ray pulsers navigation provides an alternative means for interplanetary missions and for spacecraft tracking. Here accuracy is independent of the distance between earth and the spacecraft. In dead reckoning navigation, the position is derived from the measurements of vehicle speed, reading and elapsed time from the starting point. A set of inertial sensor and a computer is used in inertial navigation. Inertial navigation makes use of dead reckoning principle for tracking the position of a spacecraft. Electronic instruments are used in radio navigation. Satellite navigation is a modern navigation system where artificial satellites are used to provide information. Integration navigation is another navigation tool where data from complementary navigation sensors are used to improve the navigation accuracy.