Optoelectronics and Quantum Theory

Optoelectronics

• Optoelectronics is the study and application of electronic devices and systems that detect, find, and control light.
• It's considered a subfield of photonics.
• It's also known as optronics.
• It's based on quantum mechanical effects of light on electronic materials, especially semiconductors, sometimes in the presence of electric fields.
• It deals with the optical interaction on the electronic responses in some specific optically active semiconducting materials.
• Includes electrical-to-optical or optical-to-electrical transducers, or instruments that use such devices.
• Optoelectronic devices are typically semiconductors.
• Their operation relies on wave theory and quantum mechanics (e.g., the photoelectric effect).
• Light is described as electromagnetic radiation.

Quantum Theory

• Light consists of discrete energy packets called photons.
• Energy (E) = Planck's constant (h) x frequency (f)
• Planck's constant (h) = 6.624 x 10⁻³⁴ J-s
• Frequency (f) is measured in Hertz (Hz).
• Energy (E) is measured in Joules (J).
• Wavelength (λ) = speed of light (c) / frequency (f).
• Speed of light (c) = 3 x 10⁸ m/s
• Wavelength (λ) is measured in meters (m).
• Equation relating energy and wavelength: E = hc/λ
• 1 electron-volt (eV) = 1.6 x 10⁻¹⁹ J
• Converting energy from electron volts (eV) to wavelength (λ): λ = 1.242/E μm

Electromagnetic Spectrum

• The electromagnetic spectrum includes infrared light, visible light, and ultraviolet light.
• Each type of light has a specific range of frequencies and wavelengths.

Visible Light Spectrum

• The spectrum of visible light consists of different colors.
• White light is a mixture of all colors in the visible light spectrum.
• For industrial process control, it's often a diffused type of white light.

Color properties of light

• Red light has the lowest frequency and longest wavelength among visible colors.
• Violet light has the highest frequency and shortest wavelength among visible colors.
• Infrared light has a slightly lower frequency than red light.
• Ultraviolet light has a slightly higher frequency than violet light.
• Units of wavelength measure are defined for convenience.
• 1 micron (µm) = 1 x 10⁻⁶ m
• 1 Angstrom (Å) = 1 x 10⁻¹⁰ m

Light Types

• Incandescent light is produced by heating a source and is often associated with heat production.
• IR & UV light types produce virtually no heat.
• Incandescence describes the ability of a material to radiate light as a consequence of heating.
• Phosphorescence is the ability of a material to emit light both during and after exposure to radiation. The material becomes ionized by the radiation source.
• Fluorescence is the ability of a material to emit light during exposure to radiation. Luminescence only occurs as long as the radiation source exists.

Light Emitting Diode (LED)

• An LED is a semiconductor device that emits light when forward biased.
• It typically uses Gallium Arsenide Phosphide (GaAsP) and Gallium Phosphide (GaP).
• Light is emitted as electrons and holes recombine, releasing energy.
• LED maximum forward voltage ranges from 1.2 V to 3.2 V, depending on the device.
• LED reverse breakdown voltage spans 3 V to 10 V, depending on the device.
• Light output power is directly proportional to the forward current.

LED Applications

• Burglar-alarm systems
• Solid-state video displays
• Image sensing circuits
• Fiber optics
• Data links and remote controllers
• Seven-segment displays
• Numeric displays

Seven-Segment Display

• A seven-segment display comprises seven rectangular LEDs forming alphanumeric figures.
• Common-cathode displays have the diodes' cathodes tied together.
• In common-anode type displays, the anodes are tied together. The ground is used to illuminate the individual segments.

Two-Color LEDs

• Two-color LEDs have two independent LEDs (red and green) within a single package.
• One color illuminates when two specific leads (R and C for red, G and C for green) are forward-biased respectively

Three-Color LEDs

• Three-color LEDs have three independent LEDs within a single package.
• Each color illuminates when the respective leads are forward-biased

Blinking LEDs

• Blinking LEDs combine an oscillator and an LED within one package, creating a blinking light effect.
• These blink at about 3 Hz with a 5 V bias.
• The current when on is about 20 mA and 0.9 mA when off

Liquid Crystal Displays (LCD)

• LCDs either light or dark depending on the voltage applied to a segment.
• The voltage needed for display varies from 2 to 20 V based on the type of display.
• LCDs use less power than LEDs but have slower response times and shorter lifespans.
• A liquid crystal is an organic compound that acts like a liquid at room temperature; its molecular structure has properties usually associated with solids.
• LCDs transmit light through a thin layer of liquid crystal sandwiched between two glass sheets. The glass sheets have transparent electrodes on their inner surfaces.
• A reflective type of LCD has one transparent glass sheet and one with a reflective coating.
• Operates by applying an electric field that causes the liquid crystals to either absorb or scatter incident light, thereby showing areas as either dark or light.

Photodiode

• A photodiode is a semiconductor pn junction device which primarily operates in reverse-bias.
• It measures the current flow when no light is incident.
• The light turns the current on and off in nanoseconds.
• It's one of the fastest photodetectors.

Photoconductive Cells

• A photoconductive cell varies its resistance in direct proportion to the intensity of light.
• Photoconductive cells behave like common resistors but have no polarity limitations regarding circuit placement.
• Commonly made of cadmium sulfide (CdS) and cadmium selenide (CdSe).
• CdS is relatively slow at around 100 ms; CdSe is faster at around 10 ms
• Under no-light conditions, the dark resistance is high (1 MΩ or greater) and goes down to approximately 1 to 100 kΩ varying with light intensity

Phototransistor

• A phototransistor is a light-sensitive transistor similar to an ordinary bipolar junction transistor (BJT).
• It lacks a base terminal connection.
• It works on the principle of photons affecting the collector-base junction.
• Silicon NPNs are commonly used in phototransistors.
• They are typically packaged in a TO-type can with a lens on top.

Photo Darlington

• A photo darlington is a configuration of transistors where the first operates as a photodetector and the second amplifier via the emitter-base coupling.
• It has much greater sensitivity to incident light than a phototransistor, due to the higher amplification provided by the darlington circuit.
• Its switching speed is on the order of 50 ns, which is lower than a photodiode.

IR Emitters

• IR emitters are diodes that emit infrared radiation when forward biased.
• Greater forward bias current leads to greater intensity of emitted radiation.
• The radiation pattern ranges from widely dispersed to tightly focused beams.

Laser Diodes

• Laser diodes have a threshold current, where current exceeds a threshold, it moves from behaving like an LED to a laser.
• The emitted light is coherent and monochromatic with a predictable wavelength.
• The light emitted from a laser diode is collimated, meaning the emitted light waves are parallel

Applications of Optoelectronic Devices

• Laser Printers: Words and figures can be printed rapidly and clearly with laser beams. Components like laser diodes, lenses, rotating mirrors, and photosensitive drums are involved in the process.

• Optical Disks: Optical disk equipment (e.g., for CDs and DVDs) uses laser diodes, lenses, and photodiodes to read and/or store information digitally.

• Solar Cells: These convert light energy into electrical energy; the intensity of the light affects the voltage produced.

• There are many other applications

This quiz explores the fascinating fields of optoelectronics and quantum theory. Discover how electronic devices interact with light and the principles behind photonics. Test your knowledge on the quantum mechanical effects that govern these technologies.