Editing Tunable laser (section)

===Narrowband tuning===
For some types of lasers, the laser's cavity length can be modified, and thus they can be continuously tuned over a significant wavelength range. [[Distributed feedback laser|Distributed feedback]] (DFB) [[semiconductor laser]]s and [[vertical cavity surface emitting laser|vertical-cavity surface-emitting laser]]s (VCSELs) use periodic [[distributed Bragg reflector]] (DBR) structures to form the mirrors of the optical cavity. If the [[temperature]] of the laser is changed, then the index change of the DBR structure causes a shift in its peak reflective wavelength and thus the wavelength of the laser. The tuning range of such lasers is typically a few nanometres, up to a maximum of approximately 6&nbsp;nm, as the laser temperature is changed over ~50 [[Kelvin|K]]. As a rule of thumb, the wavelength is tuned by 0.08&nbsp;nm/K for DFB lasers operating in the 1,550&nbsp;nm wavelength regime. Such lasers are commonly used in optical communications applications, such as [[DWDM]]-systems, to allow adjustment of the signal wavelength. To get wideband tuning using this technique, some such as [[Santur Corporation]] or [[Nippon Telegraph and Telephone]] (NTT Corporation)<ref>{{cite journal | last1 = Tsuzuki | first1 = K. | last2 = Shibata | first2 = Y. | last3 = Kikuchi | first3 = N. | last4 = Ishikawa | first4 = M. | last5 = Yasui | first5 = T. | last6 = Ishii | first6 = H. | last7 = Yasaka | first7 = H. | year = 2009 | title =  Full C-Band Tunable DFB Laser Array Copackaged with InP Mach–Zehnder Modulator for DWDM Optical Communication Systems| journal =   IEEE Journal of Selected Topics in Quantum Electronics| volume = 15 | issue = 3 | pages = 521–527 | doi=10.1109/jstqe.2009.2013972| bibcode = 2009IJSTQ..15..521T | s2cid = 27207596 }}</ref> contain an array of such lasers on a single chip and concatenate the tuning ranges.