ECE 3121 Optoelectronic Devices Lecture Notes PDF

ECE 3121 LECTURE 2: Optoelectronic Devices Optoelectronics The term optoelectronics means the interaction of light or optics with electrons Optoelectronic devices and optical fiber sensors have bought a revolution in the field of communication, signal processing, industrial instrumentat...

ECE 3121 LECTURE 2: Optoelectronic Devices Optoelectronics The term optoelectronics means the interaction of light or optics with electrons Optoelectronic devices and optical fiber sensors have bought a revolution in the field of communication, signal processing, industrial instrumentation and measurement. Photosensitive devices (photoconductive cells, photovoltaic cells, photoresistors, photodiodes, light—activated SCR 's, photofets, photo— transistors) convert the energy in light into electrical energy. PHOTOEMISSIVE devices (light—emitting diodes) convert electrical energy into light energy. Applications of Optoelectronics Telecommunications: Fiber optic communication systems rely on lasers, modulators, and photodetectors to transmit data over long distances. Displays: LEDs and OLEDs are used in various types of displays, such as TVs, smartphones, and digital signage. Medical Imaging: Lasers are used in medical imaging techniques like laser scanning microscopy and laser therapy. Sensing: Optical sensors are employed in environmental monitoring, biometric identification, and industrial process control. Data Storage: Laser diodes are used in optical storage devices like DVDs and Blu-ray discs. Defense and Security: Optoelectronic devices are used in night vision systems, laser rangefinders, and missile guidance systems. Optical Communication System Working Principle Information source gives the measurand to be measured of the information to be transmitted, which is electrical in nature Electrical Transmitter/modulator modulates some parameter or characteristic of light wave such as wavelength, frequency or amplitude with respect to the information Optical Source converts electrical signal into optical signal. Ex. LED, LASER etc. Working Principle Optical Fiber Cable carries the modulated light wave through multiple total internal reflections to the destination. Optical detector re-converts the incoming light signal into electrical signal. Ex. Photodiodes, photomultipliers, photoconductors, photovoltaic cells etc. Electrical Receiver/Demodulator demodulates/extracts the original modulated information carrying content from the signal and sends it to the required destination. Advantages of Optoelectronic Devices High Immunity to noise and electromagnetic interference High speed and bandwidth Non-interference of light/optical signals Easy integration of light and electrons Optical fibers are of small size and occupy less space as compared to their metallic counterparts. Power loss and transmission loss is less in fiber cables as compared to their metallic cables. Optical communication has high degree of signal security Disadvantages of Optoelectronic Devices Optoelectronics Sensors, devices and optical fibers are very expensive Optoelectronic devices are very fragile and delicate It requires trained and skilled personnel to handle and operate these systems. Photosensitive Devices 1. Photoresistor - a device in which the internal resistance changes according to the intensity of the light striking it. Applications Automatic Lighting Control Burglar Alarms Automated Blinds and Curtains Display Brightness Control Photosensitive Devices 2. Photovoltaic cell - The photovoltaic device is also known as a SOLAR CELL. because it has a PN junction, it directly converts light energy into electrical energy. Applications Residential Solar Energy Systems Remote Power Supply: Portable Electronic Devices Agricultural Applications Space Applications Photosensitive Devices 3. Photodiode A PN-junction diode that consumes light energy to produce an electric current. They are also called a photo-detector, a light detector, and a photo-sensor. Photodiodes are designed to work in reverse bias condition. Applications Optical Communication Systems Light Sensors Barcode Scanners and QR Code Readers Industrial Automation Smoke and Fire Detection Photosensitive Devices 5. Photofets - The combination of light detection and signal amplification makes photofets versatile devices that find applications in diverse fields, including telecommunications, sensing, medical imaging, and scientific research. Applications Optical Communication Receivers Light Detection and Ranging (LiDAR): Photosensitive Devices 6. LASCR - is an optoelectronic device that combines the properties of a thyristor with light sensitivity. LASCRs can be triggered into conduction by light, making them useful in various applications where light control of electrical switching is required. Applications Light-Activated Switching Remote Control Systems Photoemissive Devices 1. Light-Emitting Diode - A Light Emitting Diode (LED) is a semiconductor device, which can emit light when an electric current passes through it. Applications Illumination Automotive Lighting Decoration and Architectural Lighting Traffic and Transportation Photoemissive Devices 2. Optical Coupler - devices used to split or combine optical signals in optical fiber communication systems. They play a crucial role in various applications that involve transmitting, distributing, or combining optical signals.