Image sensors and optical devices

Which correctly describes the difference between a semiconductor laser and an LED?

  1. AAn LED has a narrower wavelength spread and better monochromaticity
  2. BA semiconductor laser uses stimulated emission and an optical resonator to emit highly directional light with uniform wavelength and phase
  3. CA semiconductor laser emits light without current
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Answer: B. A semiconductor laser uses stimulated emission and an optical resonator to emit highly directional light with uniform wavelength and phase

An LED emits light by spontaneous emission, with a spread of wavelengths, in many directions. A semiconductor laser causes stimulated emission in an optical resonator formed by cleaved facets or similar, emitting highly directional light with uniform wavelength and phase. It is used in optical communication, optical discs and laser processing.

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