Lecture 8: Laser amplifiers

Coherent optical amplifiers
A coherent optical amplifier is a device that increases the
amplitude of an optical field while maintaining its phase.
If the optical field at the input to such an amplifier is
monochromatic, the output will also be monochromatic with
the same frequency.
The output amplitude is increased relative to the input while
the phase remains unchanged or is shifted by a fixed amount.
In contrast, an incoherent optical amplifier increases the
intensity of an optical wave without preserving its phase.
Coherent optical amplifiers are important, for example, in the
amplification of weak optical pulses that have traveled
through a long length of optical fiber, and as a basis to
understanding laser oscillators.
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