Low-Temperature PECVD Growth of Germanium for Mode-Locking of Er-Doped Fiber Laser

Abstract

A low-temperature plasma-enhanced chemical vapor deposition grown germanium (Ge) thin-film is employed as a nonlinear saturable absorber (SA). This Ge SA can passively mode-lock the erbium-doped fiber laser (EDFL) for soliton generation at a central wavelength of 1600 nm. The lift-off and transfer of the Ge film synthesized upon the SiO2/Si substrate are performed by buffered oxide etching and direct imprinting. The Ge film with a thickness of 200 nm exhibits its Raman peak at 297 cm−1, which both the nanocrystalline and polycrystalline Ge phases contribute to. In addition, the Ge thin-film is somewhat oxidized but still provides two primary crystal phases at the (111) and (311) orientations with corresponding diffraction ring radii of 0.317 and 0.173 nm, respectively. The nanocrystalline structure at (111) orientation with a corresponding d-spacing of 0.319 nm is also observed. The linear and nonlinear transmittances of the Ge thin-film are measured to show its self-amplitude modulation coefficient of 0.016. This is better than nano-scale charcoal and carbon-black SA particles for initiating the mode-locking at the first stage. After the Ge-based saturable absorber into the L-band EDFL system without using any polarized components, the narrowest pulsewidth and broadest linewidth of the soliton pulse are determined as 654.4 fs and 4.2 nm, respectively, with a corresponding time–bandwidth product of 0.32 under high pumping conditions.

Synthesis of Nano-Structured Ge as Transmissive or Reflective Saturable Absorber for Mode-Locked Fiber Laser

“…Among the few reports on mode-locking fiber lasers starting with NP saturable absorbers [ 34 , 35 ], the use of Ge NPs with near-infrared absorption [ 36 ] in enabling nonlinear saturable absorption has yet to be explored [ 37 ]. Compared to our previous works [ 37 , 38 ], we proposed a similar metal catalyst method for graphene generation [ 39 ] to fabricate the Ge-NP-on-Au (Ge-NP/Au) film as the saturable absorber. In this work, the Ge-NP/Au film was easily combined with the cooling system to extend the lifetime of the Ge NPs and maintain mode-locking performance during long-term operation in the future.…”

SiO2 Passivated Graphene Saturable Absorber Mirrors for Ultrashort Pulse Generation

“…Ultrashort pulse fiber lasers have attracted tremendous attention due to their excellent flexibility, compactness, stability, efficient heat dissipation, high beam quality, and convenience in coupling the output to fiber systems [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. Among those ultrashort pulse lasers, the passively mode-locked fiber laser based on a saturable absorber (SA) is the most powerful strategy to develop ultrashort pulses because of the benefits of their simple structure, high beam quality, alignment-free compact design, and excellent compatibility [ 8 , 9 , 10 , 11 , 12 , 13 ]. Since graphene was first suggested in 2009 as an optical SA for mode-locked ultrafast fiber lasers [ 14 ], the graphene SA (G-SA) has exhibited outstanding performance, expediting huge prospects for SA in the research field of ultrafast fiber lasers.…”

Editorial for the Special Issue “Applications of Optical Thin Films”

“…Spin-orbit-coupled ZnO single crystals with enhanced orientation-mediated luminescence were developed by Hassan et al [3], and Su et al [4] developed a Cr/n-Si Schottky junction for use in mid-infrared technology. A germanium (Ge) thin film grown using low-temperature plasma-enhanced chemical vapor deposition was developed by Lin et al [5] to mode lock an erbium-doped fiber laser in order to generate a 1600 nm IR light. In Nicoara et al's study [6], crystalline PbS QDs embedded in an inorganic vitreous host matrix formed a nanocomposite material with potential for application in temperature sensor systems.…”