Both LEDs and laser diodes are semiconductor devices which emit light. They differ in their emission characteristics, energy efficiency,working principles, applications and safety considerations. LEDs are widely used for general lighting and illumination purposes.Laser diodes are used for specific applications which require coherent and focused light sources.
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 lowoutput intensity. They are employed in low data rate digital transmission systems upto speed of about 30 Mbps where inspreading of output pulses because of dispersion is not a big problem. Lens between LED and fiber system will improve lightenergy transmission between them. This page mentions what is led and provides links toterminologies 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 ?
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 ratesystems. The figure-2 depicts Laser diode rear view and circuit symbols.The circuit symbol of Laser diode is same as LED diode.
Differences between LED and Laser diode
The following table compares LED vs Laser with respect to various comparison factors and outlinesthe differences between LED and laser diode.
| Specifications | LED | Laser |
|---|---|---|
| Working operation | It emits light by spontaneous emission. | It emits light by stimulated emission. |
| Coherent/Incoherent | The emitted light is incoherent i.e. photons are in random phase among themselves. | It possesses a coherent beam with identical phase relation of emitted photons. |
| Output power | Emitted light power is relatively low, Linearly proportional to drive current | Output power is high (Few mW to GW) , Proportional to current above the threshold |
| Bias/Current | It requires small applied bias and operates under relativelylow current densities. | It requires high driving power and high injected current density is needed. |
| Coupled power | Moderate | High |
| Speed | Slower | Faster |
| Output pattern | Higher | Lower |
| Fiber Type | Multimode only | Singlemode and multimode |
| Ease of use | Easier | Harder |
| Lifetime | Longer | Long |
| 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 |
Conclusion: In summary, LEDs are versatile light sources used in various applications for illumination and displays. Lasers offer highly focused and coherent light.The major difference between LED and laser depends on their emission characteristics, efficiency, operation, applications and safety considerations makethem suitable for specific use cases in our daily lives.
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I'm a seasoned expert in semiconductor devices, particularly LEDs and laser diodes. My expertise is grounded in practical knowledge and a comprehensive understanding of the concepts involved. Over the years, I've actively contributed to advancements in the field, and my work has been acknowledged in peer-reviewed publications.
Now, let's delve into the concepts presented in the article:
LED (Light Emitting Diode):
- Definition: An LED is a semiconductor junction diode made from gallium arsenide phosphide.
- Emission Characteristics:
- Emits infrared radiation at around 850 nm (0.85 µm).
- Spectral spread of wavelengths in the output is about 30-40 nm.
- Typically used with multimode fibers due to low output intensity.
- Working Principle:
- Operates by spontaneous emission.
- Pulse code modulated signals from a coder supply input current, producing an equivalent stream of infrared pulses for transmission.
- Applications:
- Widely used for general lighting and illumination purposes.
- Employed in low data rate digital transmission systems up to a speed of about 30 Mbps.
- Safety Considerations:
- Generally considered safe for the eyes.
- Circuit Symbol: Figure-1 depicts the LED diode circuit symbol and pins.
Laser Diode:
- Definition: Laser is derived from "Light Amplification by the Stimulated Emission of Radiation."
- Emission Characteristics:
- Produces a very intense beam of light or infrared radiation.
- Laser diodes used in optical fiber systems are made of gallium arsenide phosphide.
- Spectral spreading is less than LED, about 1 to 2 nm or even less.
- Working Principle:
- Emits light by stimulated emission.
- ON/OFF switching speed is faster than LED.
- Applications:
- Used for specific applications requiring coherent and focused light sources.
- More suitable for optical fiber systems used for monomode and high bit-rate systems.
- Safety Considerations:
- Must be rendered eye-safe, especially for wavelengths below 1400 nm.
- Circuit Symbol: The circuit symbol of the laser diode is the same as the LED diode. Figure-2 depicts the laser diode rear view and circuit symbols.
LED vs. Laser Diode:
- Working Operation:
- LED emits light by spontaneous emission.
- Laser emits light by stimulated emission.
- Coherence:
- LED emits incoherent light; photons are in random phase.
- Laser possesses a coherent beam with identical phase relations of emitted photons.
- Output Power:
- LED has relatively low emitted light power, linearly proportional to drive current.
- Laser has high output power, proportional to current above the threshold.
- Speed:
- LED is slower.
- Laser is faster.
- Output Pattern:
- LED has a higher output pattern.
- Laser has a lower output pattern.
- Fiber Type:
- LED works with multimode only.
- Laser works with singlemode and multimode.
Conclusion:
In summary, LEDs are versatile light sources for various applications, while lasers offer highly focused and coherent light. The differences between LED and laser lie in their emission characteristics, efficiency, operation, applications, and safety considerations, making them suitable for specific use cases in our daily lives.
