Question

Consider the following statements:

(a) LASER diode generates monochromatic coherent light which reduces chromatic dispersion

(b) LASER source is useful for high power long-distance optical communication

(c) LASERs have longer lifetime than LEDs

(d) LASER diodes are less temperature-sensitive than LEDs

Which of the above statements are correct?

1. (a) and (b)
2. (a) and (c)
3. (b) and (d)
4. (b) and (c)

Answer 1

Correct Answer - Option 1 : (a) and (b)

• Monochromatic Dispersion results from the spectral width of the emitter i.e. the spectral width determines the number of different wavelengths that are emitted by the LED or laser.

• One way to reduce chromatic dispersion is to narrow the spectral width.
• A monochromatic laser emits only one wavelength & therefore reduces or does not contribute to chromatic dispersion.(Statement (a) is correct)
• Lasers can produce high output power in fiber optic communications. The laser source is useful for high power i.e. more than 20 mW is available. (Statement (b) is correct)
• LED’s have a longer life than lasers, i.e.

          LED’s: 10⁵ - 10⁸ hours

          Lasers: 10⁵ hours(Statement (c) is wrong)

• In terms of temperature effect, lasers are more temperature-sensitive than LED’s.(Statement (iv) is wrong)