19 μm square-wave passively Q-witched mode-locked fiber laser

Abstract

We propose and demonstrate the operation of Q-switched mode-locked square-wave pulses in a thulium-holmium co-doped fiber laser. By using a nonlinear amplifying loop mirror, continuous square-wave dissipative soliton resonance pulse is obtained with 4.4 MHz repetition rate. With the increasing pump power, square-wave pulse duration can be broadened from 1.7 ns to 3.2 ns. On such basis Q-switched mode-locked operation is achieved by properly setting the pump power and the polarization controllers. The internal mode-locked pulses in Q-switched envelope still keep square-wave type. The Q-switched repetition rate can be varied from 41.6 kHz to 74 kHz by increasing pump power. The corresponding average single-pulse energy increases from 2.67 nJ to 5.2 nJ. The average peak power is also improved from 0.6 W to 1.1 W when continuous square-wave operation is changed into Q-switched mode-locked operation. It indicates that Q-switched mode-locked operation is an effective method to increase the square-wave pulse energy and peak power.

Generation of Flat-Top Q-Switched Envelope Dissipative Soliton Resonance Pulse in Passively Mode-Locked Fiber Laser

“…The maximum single envelope width is up to 1.5 times that of the reported in Ref. [26]. Specially, the longest pulse duration can reach as long as 3.5 µs when the pump power is fixed at 266 mW.…”

“…This work has a greater benefit for the deeper understanding of the formation of the Q-switched operation. Furthermore, the average single pulse energy of the 1.9 µm Q-switched mode-locked square-wave fiber laser is three times more than that of continuous dissipative soliton resonance was reported [26]. Nevertheless, it is rarely reported about the technique of combining passively Q-switched mode-locked and the generation of dissipative soliton resonance in the 1.55 µm band.…”

“…In addition, the current technology for manufacturing graphene and carbon nanotubes is still relatively complicated. In recent years, the nonlinear polarization evolution (NPE) and NALM technique as artificial saturable absorber effect are also suitable for the generating of Q-switched pulse in fiber lasers [24]- [26]. It is worth mentioning that a type of peak-power-clamping (PPC) effect in passive Q-switched regime can be achieved in the NPR thulium/holmium co-doped fiber laser by intracavity-incorporating a segment of highly nonlinear fiber (HNLF) and launching high-enough pump power in Ref.…”

Wavelength-Spacing Adjustable Dual-Wavelength Dissipative Soliton Resonance Thulium-Doped Fiber Laser

“…A variety of research reports have been reported on the mode-locked thulium-doped fiber laser, especially passively mode-locked thuliumdoped fiber laser [1]. Various passively mode-locking techniques have been implemented to generate mid-infrared pulses, which can be divided into two categories: utilizing nonlinearity-based equivalent saturable absorption effects, such as nonlinear polarization evolution (NPE) [2]- [4], nonlinear optical loop mirror (NOLM) [5], and nonlinear amplifier loop mirror (NALM) [6], [7], as well as the use of material-based saturable absorbers, such as semiconductor saturable absorbers [8], single-wall carbon nanotubes (CNTs) [9]- [11], and graphene [12]. Nonlinearity-based mode-locked fiber lasers with virtually unlimited lifetime and absence of specific power limitations may deliver relatively high pulse energies directly [13].…”

Generation of 100 nJ pulse, 1 W average power at from an intermode beating mode-locked all-fiber laser

“…Besides these real saturable absorbers (SAs), some other artificial SAs-based passive mode lockers have gradually come into researchers' sight and attracted great attention, e.g., nonlinear polarization rotation (NPR) [11][12][13][14][15][16][17] , nonlinear amplifying loop mirror (NALM) [18][19][20][21] , and self-phase modulation (SPM) [22] . Among them, NPR is the most studied and applied mode locking method.…”