Q-Switched and mode-locked Erbium doped fiber laser using cadmium selenide based passive saturable absorber

To date, various Q-switched and mode-locked Erbium doped fiber lasers (EDFL) have been demonstrated using various types of nanomaterials based saturable absorber (SA) such as graphene, topological insulators and transition metal dichalcogenides. In this dissertation, cadmium selenide (CdSe) quantum dots (QD) is proposed and demonstrated for Q-switching and mode-locking pulse generation in Erbium doped fiber laser (EDFL) cavity. A Q-switched EDFL is demonstrated using a CdSe doped PMMA microfiber, which was obtained using direct drawing technique. The CdSe microfiber is placed between two cutting microfiber tips which are connected to an EDFL cavity to produce a Q-switching pulse train operating at 1533 ran. The repetition rate of the pulse train is tunable within 37 kHz to 64 kHz while the corresponding pulse width reduces from 7 \is to 4 (is as the pump power is varied from 34 mW to 74 mW. The maximum pulse energy of 1.16 nJ is obtained at the pump power of 74 mW. The RF spectrum of the pulse train shows signal to noise ratio of about 47dB, which indicates the stability of the laser. The mode-locked EDFL is demonstrated by using Manganese-doped CdSe QD based SA in a 202m long laser cavity with anomalous fiber dispersion of-4.265 ps2. The laser produces a soliton pulse train operating at 1561.1 nm with a repetition rate of 1 MHz and pulse duration of 480 ns as the pump power is increased above the threshold of 113 mW. At the maximum pump power of 250 mW, the maximum pulse energy of 6.2 nJ is obtained. Better mode-locking performance is expected by optimizing the dispersion parameter of the laser cavity and reducing the cavity loss.