LED vs Laser diode | Difference between LED and Laser diode
Both LED and Laser are used as optical transmitters for various applications. The following section describes them and mention difference between LED and Laser.
What is LED
An LED is a junction diode made from semiconductor compound gallium arsenide phosphide. LEDs used as optical fiber transmitters emit infrared radiation at a wavelength of about 850 nm (0.85 µm).
Pulse code modulated signals from the coder supply input current to the LED. This will produce equivalent stream of infrared pulses for transmission along the optical fiber system. The spectral spread of wavelengths in the output is about 30-40 nm.
LEDs are very cheap and convenient source of light. They are usually used with multimode fibers due to their low output intensity. They are employed in low data rate digital transmission systems upto speed of about 30 Mbps where in spreading of output pulses because of dispersion is not a big problem. Lens between LED and fiber system will improve light energy transmission between them. This page mentions what is led and provides links to terminologies on electronic devices or components. Figure-1 depicts LED diode circuit symbol and pins. As shown in LED, long lead is anode (positive) and short lead is cathode (negative).
What is Laser Diode
Laser is derived from Light Amplification by the Stimulated Emission of Radiation.
It produces a very intense beam of light or infrared radiation which is having following properties.
• Monochromatic ( meaning consists of one wavelength)
• Coherent (meaning all parts are in phase)
• Collimated (meaning all parts travel in one and same direction)
Laser diode used in optical fiber systems are made of gallium arsenide phosphide. The laser having size of grain of sand can produce power output of about 10 mWatt.
ON/OFF switching speed of laser is faster than LED. Spectral spreading is less than LED about 1 to 2 nm or even less. Hence dispersion is not a problem with laser compare to LED. Hence lasers are more suitable for optical fiber systems used for monomode and high bit rate systems. The figure-2 depicts Laser diode rear view and circuit symbols. The circuit symbol of Laser diode is same as LED diode.
This explaination on LED and Laser helps one compare difference between LED and Laser. Also refer following links on various electronic components.
Following table compares LED and Laser with respect to various comparison factors/specifications.
|specification||Light Emitting Diode||Laser Diode|
|Output power||Linearly proportional to drive current||Proportional to current above the threshold|
|Current||Drive Current (50 to 100 mA) (Peak)||Threshold current (5 to 40 mA)|
|Fiber Type||Multimode only||Singlemode and multimode|
|Ease of use||Easier||Harder|
|Spectral width||Wider, 25 to 100 nm
(10 to 50 THz)
|Narrower, <10-5 to 5 nm
(<1 MHz to 2 MHz)
|Modulation Bandwidth||Moderate, Tens of KHz to tens of MHz||High, Tens of MHz to tens of GHz|
|Available Wavelength||0.66 to 1.65 mm||0.78 to 1.65 mm|
|E/O Conversion Efficiency||10 to 20 %||30 to 70 %|
|Eye Safety||Generally considered eye-safe||Must be rendered eye-safe, especially for λ < 1400 nm|
|Cost||Low||Moderate to High|
Electronic components ralated links
Transformer basics and types
BJT vs FET
Diac vs Triac
JUGFET vs MOSFET
Analog vs Digital Multimeter
LED vs Laser
Microphone basics and types
Photo Diode vs Photo Transistor Battery SCR or thyristor Op-Amp Halfwave rectifier vs Fullwave rectifier
What is Difference between
difference between FDM and OFDM
Difference between SC-FDMA and OFDM
Difference between SISO and MIMO
Difference between TDD and FDD
Difference between 802.11 standards viz.11-a,11-b,11-g and 11-n
OFDM vs OFDMA
CDMA vs GSM
Bluetooth vs zigbee
Fixed wimax vs mobile
wibro vs mobile wimax
Microcontroller vs microprocessor
FDM vs TDM