Passively q-switched fiber laser employing graphene and carbon nanotubes saturable absorber

Abstract

Pulse laser has charmed photonic properties due to its high photon energy, broad absorption bandwidth and easy thermal management. These advantages allow it to be widely used in various applications especially in the area of electronic devices, scientific research, industrial, military and medical treatment. Q-switched fiber laser which has the ability to generate an energetic short pulse from a laser by modulating the intra-cavity losses and Q factor of the laser resonator. This Q-switched technique is practical for obtaining high energy and peak power with solid-state bulk lasers from microsecond to nanosecond pulses. These criteria make the research on Q-switched fiber laser is highly demanding. There are numerous techniques to generate the Q-switched fiber laser such as semiconductor saturable absorption mirror (SESAM), nonlinear polarization rotation (NPR), nonlinear optical loop mirror (NOLM), and nonlinear amplifying loop mirror (NALM). These techniques have drawbacks in terms of complex design and high fabrication cost. For instance, SESAM needs additional optical components such as lens, mirror or U-bench. To overcome these drawbacks, passively Q-switched erbium doped fiber laser (EDFL) employing carbon based saturable absorber (SA) is proposed in view of its advantages of ultrafast recovery time, simple fabrication process and easy to incorporate in the cavity. In this research, the passively Q-switched EDFL was generated by using graphene and carbon nanotubes (single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT)) based SA. The fabrication of graphene and CNT SAs was done by using dip coating and drop casting method. Polyvinyl alcohol (PVA) was used as the host polymer due to its excellent film-forming, very high flexibility and water-solubility. SWCNT SA solution was combined with PVA solution with the ratio of 1:1, 2:3 and 3:2, whereas MWCNT SA solution was mixed with PVA solution with the ratio of 1:1 and 2:3. Next, SAs were characterized for optical and physical spectroscopic characterization. For optical spectroscopic characterization, SAs were characterized by using Raman characterization and surface morphology, and for physical characterization was done by observing the thickness of the SA materials. The performance of Q-switched EDFL was analyzed in the same ring cavity configuration by using graphene, SWCNT and MWCNT based SA. The properties of passively Q-switched EDFL namely the output spectrum, repetition rate, pulse width, pulse energy, output power, pulse train, and signal to noise ratio were analyzed. When the performance of the three SAs was compared, the SWCNT 2:3 ratio SA had the best pulse width of 3.31μs, repetition rate of 134.4 kHz, and SNR value of 52 dB. The SWCNT with the ratio of 3:2 attained the highest pulse energy of 29.98 nJ. The findings of this research provide significant steps toward the development of future research in the advanced pulse laser technology especially in the application of industrial, military and medical area.