Optoelectronics Notes Module 4 PDF

**Optoelectronics** - The **study** and **application** of **electronic devices and systems that source**, **detect** **and control light.** It focuses on light emitting or light detecting devices - Two types of optoelectronics are Light Emitting Device and Light Detecting Device...

**Optoelectronics** - The **study** and **application** of **electronic devices and systems that source**, **detect** **and control light.** It focuses on light emitting or light detecting devices - Two types of optoelectronics are Light Emitting Device and Light Detecting Device **[Light Emitting Device]** - use voltage and current **to produce electromagnetic radiation** (i.e., light). Such light-emitting devices are commonly used for purposes of illumination or as indicator lights **[Light Detecting Device]** are designed to **convert received electromagnetic** **energy into electric current or voltage.** Light-detecting devices can be used for light sensing and communication. Examples of these include darkness-activated switches and remote controls. In general terms, light-detecting devices **work** by **using photons** to liberate bound electrons within semiconductor materials **Photons** - **fundamental** **units** of **electromagnetic** **radiation** - The **human eye** **is sensitive to optical EMR**, which is further categorized into colors. Color is not an inherent property of photons; rather, **photons have frequency**, and human beings interpret these **different frequencies as different color** - A **photon** with a **longer wavelength** (i.e., a lower frequency) has less energy than a photon with a shorter wavelength (i.e., a higher frequency) (y na baliktad equals to v(**m/s**)/f in units meters) **LED devices** 1. **Lamps** are devices that **convert electric current** **into visible light energy** 2. **Incandescent lamp** is a filament made from **tungsten wire**, have short lifetimes compared with other types of lighting; around 1,000 hours for home light bulb. 3. **Halogen Lamp** commonly known for both their **brilliant** **light** and **their very hot-to-the touch bulbs** which are also considered as **advanced form of the incandescent bulb** and its **glass is stronger than incandescent lamp's**. It is much **less efficient than LED**. 4. **Fluorescent lamp** consists of a **mercury vapor--filled glass tube** whose inner wall is coated with a material that fluoresces. It is **10,000 hours lifespan** 5. **LED Lamp** is an **electric light for use in light fixtures** that produces light **using one or more light-emitting diodes.** It has a lifespan **many times longer than equivalent incandescent lamps**, and are **significantly more efficient** than most fluorescent lamps most efficient commercially available. **20k to 30h hrs. life span** 6. **Light emitting diode** is a **semiconductor diode** that **emits incoherent narrow spectrum** light when electrically biased in the **forward direction of a p-n junction** Sample Applications are **comms**, **Remote Control, Display and Solid-State Lighting** 7. **LASER Diodes** (Light Amplification by Stimulated Emission of Radiation) **semiconductor laser device** that is very **similar**, in both form and operation, **to a light-emitting diode (LED).** It is a device that **emits light through a process of optical amplification** based on the stimulated emissions of electromagnetic radiation. It is much faster response compared to LED. Applications are;; laser points and bar code scanners, CD ROM and CD Players, and Molecular Identification **Light Detecting Devices** 1. **Photoresistors** is a light variable controlled resistor**, AKA LIGHT DEPENDENT RESISTORS.** When photoresistor is in the dark, the resistance is high and not if otherwise. Its resistance depends on the intensity of light. Application: 1. LDR Switch 2. **Photodiode** is **two-lead semiconductor devices** that **convert light energy** **directly into electric current** and functions as a **photodetector** 3. **Solar Cells** are **simply photodiodes but it has exceptional large areas.** These larger areas allow the solar cells to be more sensitive to incoming light as well as more powerful---in terms of both voltage and current---than photodiodes Commonly used in solar panels, but they are also often used as light-sensitive elements in detectors of visible light. 4. **Phototransistors** is a transistor which base current is produced when light strikes the photosensitive semiconductor base region. The collector-- base pn junction is exposed to incident light through lens opening in the transistor package **Phototransistor are not sensitive to all light** but **only to light within a certain range** of **wavelength**. The LEDs are semiconductor devices that emit light at an intensity determined by the forward current through the devices. 5. **Photodarlington,** it consists of phototransistor connected in a **darlington arrangement** with a conventional BJT Because of higher current gain, this device has a much higher collector current and exhibits a greater light sensitivity than does a regular phototransistor 6. **Optical couple** or also known as **opto isolator or opto coupler** are electrical devices that **interconnect two circuits** by means of an optical interface composed of an **LED and a phototransistor,** both of which are encased in a light-tight enclosure LED portion of an opto isolator is connected to a driver circuit, and the phototransistor is the output device typical application of an optoisolator is to provide electrical isolation between two separate circuits 1. **Isolation voltage** -- the **maximum** **voltage** that **can exist between the input and output** terminals **without** **dielectric breakdown** occurring. **Typical** values are about **7500 V ac peak** 2. **DC Transfer** **Ratio**-- This parameter is the **ratio** of the **output current** to the **input current** **through** the LED. It is **usually** expressed as a **percentage**. For a phototransistor output, typical values range from 2 percent to 100 percent. For a photodarlington output, typical values range from 50 percent to 500 percent 3. **LED trigger current**-- This parameter applies to **LASCR output coupler** and the **phototriac output device.** The trigger current is the value of current required to trigger the thyristor output device. Typically, the trigger current is in the mA range 4. **Transfer gain**-- This parameter applies to the optically isolated ac linear coupler. The transfer gain is the ratio of **output voltage to input current**, and atypical value is 200 mV/mA **Fiber optic** --- **Uses light pulses** to **transmit information** through fiber optic cables about the diameter of human hair, which is about 100 microns(1 millionth of a meter) Have several advantages over copper wires: **Faster speed**, **higher signal capacity**, **longer transmission distances without amplification**, **less** **susceptibility** **to interference** and **more economical** to maintain **Basic operation** \- When light is introduced into one end of a fiber optic cable, it "bounces" along until it emerges from the other end. The fiber is generally made of pure glass or plastic that is surrounded by a highly reflective cladding so that it can be move around bends in the fiber with essentially no loss. As the light moves along the fiber, it is reflected off the cladding so that it can movearoundbendsinthefiber with essentially no loss. Parts of a Fiber optic cable 1\. Core -- the glass fiber itself 2\. Cladding-- surrounds the fiber and provides reflective surface 3\. Outer coating or jacket-- Provides protection. Figure 19. Simplified structure and operation of a fiber optic cable Angle of incidence-- The angle at which a light ray strikes the surface Critical angle-- The angle that defines whether a light ray will be reflected or refracted when it strikes the surface If the angle of incidence is greater than the critical angle, the light ray is then reflected back into the core at an angle of reflection scattering loss- If the angle of incidence is less than the critical angle, the light ray is refracted and passes into the cladding, causing energy to be loss. Absorption loss-- Caused by the interaction of the light photons and the molecules of the cor