• Optoelectronics is the communication of optics and electronics which involves the study, design and manufacturing of hardware device which converts electrical energy into light and light into energy through semiconductors.
• Made up of semiconductor materials.
• Used in Military services, telecommunications,automatic access control systems and medical equipments.

Types of Optoelectronic devices

• LED
• Photo diode
• Photo transistor

Light Emitting Diode(LED)

• PN- Junction opto-semiconductor
• Emits monochromatic light when operated in forward bais condition
• Converts electrical energy to light energy

Operation

• When sufficient voltage is applied to the leads of the LED, electrons move in one direction across the junction between the p and n regions.
• The electrons recombine with the holes within the device.
• Release energy in the form of photons.
• This effect is called electroluminescence.
  

Advantages of LED

• Consumes less power
• Produces less heat
• Last longer than incandescent lamps

Disadvantages of LED

• Costly
• Temperature sensitivity
• Voltage sensitivity

Application of LED

• Mobile applications
• LED signals
• Automative uses
• Illumination
• Indicators

Photo Diode

• Light sensor made up of semiconductor materials
• When light falls on the junction, voltage or current is generated
• PN- Junction diode, operated in reverse bais
• When a photon(light) strikes a semiconductor, electron- hole pairs are generated through band-band optical absorption
• Electric field is produced when the electron diffuse into the junction
• This electric field across the depletion region is equal to the negative voltage across the unbaised diode. This is known as inner photoelectric effect

Operation

• Optical energy(light) is converted to electrical energy(current/voltage) through optical receivers.
• Refered to as O/E Converter.
• Photodector is the fundamental element of optical receivers.
  

Advantages of Photo diode

• Cost efficient
• Light weight and compact in size
• Wide spectral response
• Quick responce when exposed to light

Disadvantages of Photo diode

• Low illumination levels due to reverse current
• Temperature dependent

Applications of photodiode

• Fire and smoke detectors
• Photo sensors in camera
• Dectectors for computed tomography
• Blood gas monitors

Photo transistor

• Similar to bipolar junction transistor(BJT)
• Only difference is that base current is produced and controlled by light except voltage source
• Converts light energy to electrical signal
• Light sensitive
• Have collector, base and emitter

Operation

• Light sensitive collector base pn junction controls current flow between emitter and collector
• Resistance decreases as intensity increases, creating more emitter-base current
• The small base current controls the larger emitter-collector current

Advantages of Photo transistor

• More sensitive than photodiodes of comparable size
• Produce higher current than photodiodes
• Fast response, compact enough to fit onto single integrated computer chip

Disadvantages of Photo Transistor

• Silicon phototransistors cannot handle voltages above 1000V.
• More susceptible to electricity surges

Applications of Photo Transistor

• Lighting control(Roads,highways,etc.)
• IR Detectors
• Counting systems
• Security systems