4. Example of tunable lasers: laser diodes

Laser diodes are certainly the most widely used of all tunable lasers. They have the advantage of covering virtually the entire optical spectrum, from the near-ultraviolet to the mid-infrared. For a given material, the spectral gain band is of the order of a few tens of nanometers in the near infrared and up to several micrometers in the mid-infrared (quantum cascade lasers).

There are many ways to wavelength-tune laser diodes.

The tunability of a laser diode can be obtained by modifying its current or temperature. However, this method is not always reproducible, and laser diode emission is often multimode, with several peaks separated by fractions of a nanometer. The orders of magnitude of spectral shifts are given in paragraph