As a sub-field of photonics, optoelectronics refers to the practice of using and studying electronic devices and systems, which control, source and detect light. Optoelectronics is based on the fundamentals of quantum mechanical effects of light. It focuses on light's effect on semiconductors, and other electronic materials. The different optoelectronic devices are optoisolators, photoresistors, phototransistors, quantum cascade lasers, OLEDs, photomultipliers, light-emitting diodes, etc. Research in this field has enabled scientists to apply principles of optoelectronics in optocoupler and optical fiber communications. This book presents the complex subject of optoelectronics in the most comprehensible and easy to understand language. Such selected concepts that redefine the subject have been presented in it. This extensive book is a vital tool for all researching and studying this field.