**2. Q-switched TYDFL using multi-walled carbon nanotubes passive saturable absorber**

There are growing interests in compact Q-switched laser sources that operate in the midinfrared spectral region around 2 microns. This is mainly driven by the applications in spectroscopy, communication, material processing, manufacturing, sensing, medicine, and nonlinear optical research [18, 19]. Nowadays, another type of nanotube called multi-walled carbon nanotubes (MWCNT) has been examined in the field of nonlinear optics because its production cost is 50–80% lower than SWNTs [9]. MWCNTs also have higher mechanical strength, higher photon absorption per nanotube, and higher mass density which leads to better stability [20].

We successfully demonstrated, a Thulium-Ytterbium co-doped fiber (TYDF) Q-switched laser using a laboratory made saturable absorber based on MWCNTs implanted in polyvinyl alcohol (PVA) composite for the first time [2]. A homemade double clad Thulium-Ytterbium codoped fiber (TYDF) drawn from a preform which was manufactured based on the modified chemical vapor deposition (MCVD) and solution doping processes is used as a lasing medium. The fabricated MWCNT-PVA film (SA) is attached within the laser cavity by sandwiching it between two fiber connectors. Similarly, a modelocked TYDFL is also demonstrated using graphene PVA film as a saturable absorber.
