Modulation of LED
- 1. PRESENTED BY: ANNI PRIYANKA Topic: Modulation of LED Satellite and Optical Communication
- 2. Requireme nt of Optical Source Output power must be high, using lowest possible current and less heat High output directionali ty, narrow spectral width. Bandwidth should be wide enough Low distortion
- 3. LED It is a semi-conductor and has polarity Light emitters converts the electrical signal into a corresponding light signal that can be injected into the fibre.
- 4. LEDs are of interest for fibre optics because of five inherent characteristics They are small They possess high radiance The emitting area is small They have a very long life They can be modulated
- 5. How it works? When current flows across a diode Negative electrons move one way and positive holes move the other way
- 6. How it works? Here, the holes exist at a lower energy level than the free electrons So, when a free electrons falls, it losses energy
- 7. How it works? This energy is emitted in a form of a photon, which causes light The color of the light is determined by the fall of the electron and hence energy level of the photon
- 8. Inside a LED
- 9. Spectrum of an LED LED Density -15 to -25 dBm 60-100nm λ Different frequency = different wavelength = different colors
- 10. Modulation of LED In order to code information as pulses, it is necessary to modulate the output of the LED This is done by switching the current on and off
- 11. Modulation of LED • The frequency response of an LED depends on: 1- Doping level in the active region 2- Injected carrier lifetime in the recombination region, . 3- Parasitic capacitance of the LED • If the drive current of an LED is modulated at a frequency of 𝜔 the output optical power of the device will vary as: • Electrical current is directly proportional to the optical power, thus we can define electrical bandwidth and optical bandwidth, separately. 2 0 )(1 )( i P P
- 13. LED Vs. Laser diode
- 14. The disadvantages lower output optical power is coupled into a fiber lower modulation bandwidth harmonic distortion
- 15. Thank You..