what is tunable laser
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A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range. There are many types and categories of tunable lasers.
Tunable lasers are of paramount importance in modern telecom systems as they can be used to populate different channel slots and reduce laser inventory. In addition, they can also provide a route to reconfigurable WDM systems. The response times are in the 0.1 ms–1 s range, depending on the actuator and tuning mechanism utilized. The lower limit is imposed by the acoustic velocity of strain waves in the fibers. Fiber DFB lasers can be tuned effectively by heating, stretching, and/or compressing uniformly the grating cavity. Continuous tuning over 27 nm has been demonstrated in Er3+/Yb3+ all-fiber, DFB lasers using a simple tuning mechanism for axial extension and compression. The demonstrated devices operated with powers up to 10 dBm and remain operating in single mode over the full tuning range [50].