Junqing Zhao

Tunable and switchable multi-wavelength dissipative soliton generation in a graphene oxide mode-locked Yb-doped fiber laser

We report the generation of tunable single-, switchable and tunable dual-, and stable triple-wavelength dissipative solitons (DSs) in an all-normal-dispersion mode-locked Yb-doped fiber laser based on a graphene-oxide saturable absorber (GOSA) without additional components (such as optical filter, or fiber grating). The tunable single-wavelength DS have a wide wavelength-tunable range of 16.4 nm. The dual-wavelength DSs not only have a wavelength-tunable range (about 10 nm) but also have variable wavelength spacing (3.8-13.8 nm). The formation dynamics of the triple-wavelength DSs was also investigated experimentally. The different operations of tunable single-, switchable and tunable dual-, and stable triple-wavelength DSs depend on the strength of the cavity birefringence. The simple, compact all-fiber DS laser with lasing wavelength tunability and flexibility can meet great potential for applications.

Double Cladding Seven-Core Photonic Crystal Fibers With Different GVD Properties and Fundamental Supermode Output

We fabricated three kinds of double cladding nonlinear seven-core photonic crystal fibers (PCFs) with different group velocity dispersion (GVD) properties and fundamental supermode output. Pumped by a 150 ps polarization maintaining a ytterbium-doped fiber laser based on the gain-switched technique, octave-spanning supercontinua were generated within the wavelengths from 450 to at least 2000 nm in these fibers with a high spatial quality.

Polarization dependent visible supercontinuum generation in the nanoweb fiber

We have fabricated a novel nanoweb fiber with web-like bundle of the fused-silica membranes with different thickness in its cross section. We pumped the 0.55-μm-thick membrane with 200-fs laser pulse at 800-nm just adjacent to its second-zero-dispersion wavelength, and demonstrated the polarization dependent visible supercontinuum (SC). The mode patterns were recorded in detail and analyzed at different polarization angles of incident pulse. The broadband spectrum range from ~350 nm to 950 nm is achieved for TM mode excitation. The tunable visible SC in the nanoweb fiber may be used in the substrate integrated waveguide for sensing.

100 W dissipative soliton resonances from a thulium-doped double-clad all-fiber-format MOPA system.

In this paper, we first achieve nanosecond-scale dissipative soliton resonance (DSR) generation in a thulium-doped double-clad fiber (TDF) laser with all-anomalous-dispersion regime, and also first scale the average power up to 100.4 W by employing only two stage TDF amplifiers, corresponding to gains of 19.3 and 14.4 dB, respectively. It is noted that both the fiber laser oscillator and the amplification system employ double-clad fiber as the gain medium for utilizing the advantages in high-gain-availability, high-power-handling and good-mode-quality-maintaining. DSR mode-locking of the TDF oscillator is realized by using a nonlinear optical loop mirror (NOLM), which exhibits all-fiber-format, high nonlinear and passive saturable absorption properties. The TDF oscillator can deliver rectangular-shape pulses with duration ranging from ~3.74 to ~72.19 ns while maintaining a nearly equal output peak power level of ~0.56 W, namely peak power clamping (PPC) effect. Comparatively, the two stage amplifiers can scale the seeding pulses to similar average power levels, but to dramatically different peak powers ranging from ~0.94 to ~18.1 kW depending on the durations. Our TDF master-oscillator-power-amplifier (MOPA) system can provide a high power 2-μm band all-fiber-format laser source both tunable in pulse duration and peak power.

Cladding-filled graphene in a photonic crystal fiber as a saturable absorber and its first application for ultrafast all-fiber laser

Abstract. We demonstrate a saturable absorber (SA) based on cladding-filled graphene in a specially designed and manufactured photonic crystal fiber (PCF) for the first time. The saturation absorption property is achieved through the evanescent coupling between the guided light and the cladding-filled graphene layers. To boost the mutual interaction, the PCF is designed to contain five large air holes in the cladding and small-core region. Employing this graphene-PCF SA device, we construct an erbium-doped all-fiber laser oscillator and achieve mode-locked operation. This device can pave the way for high power and all-fiber applications of photonics with graphene with some unique advantages, such as single-mode operation, nonlinearity enhancement, high-power tolerance, environmental robustness, all-fiber configuration, and easy fabrication.

Bright and Dark Square Pulses Generated From a Graphene-Oxide Mode-Locked Ytterbium-Doped Fiber Laser

The observation of the bright pulses and dark square pulses in a graphene-oxide saturable absorber (GOSA) passively mode-locked ytterbium-doped fiber laser has been investigated experimentally. Bright pulses are achieved at a pump power of ~ 200 mW. However, the dark-square-pulse generation starts at a much higher pump power of ~ 450 mW. At the maximum pump power of 600 mW, the dark-square-pulse bunches and harmonic mode locking (HML) can be also obtained by tuning the polarization controller (PC) to different orientations. It is the first demonstration of the bunches and HML of dark square pulses in a GOSA passively mode-locked ytterbium-doped fiber laser with large normal dispersion cavity.

Passively harmonic mode locking in ytterbium-doped fiber laser with graphene oxide saturable absorber

Abstract. We have demonstrated the dissipative solitons generated in an ytterbium-doped fiber laser cavity using graphene oxide as the saturable absorber. The lasing light, centered at 1077.2 nm, has a 3 dB spectral bandwidth of ∼1.12  nm. Under different launched pump powers and appropriate polarization orientations, harmonic mode-locked of second- and third-order pulse trains have been achieved; the corresponding 3-dB bandwidth and pulse duration have been detected.

70-W Graphene-Oxide Passively Q-Switched Thulium-Doped Double-Clad Fiber Laser

We report on a graphene-oxide (GO) passively Q-switched thulium-doped double-clad fiber laser with two-stage amplifiers that can deliver >70 W average power at ~1950.27 nm wavelength. The achieved highest average power is ~73 W, corresponding to ~1.5 μs pulse duration, ~0.877 mJ pulse energy, and ~585 W peak power. To our best knowledge, this is the first high-power pulsed output by using passive method to generate Q-switched pulses, especially by using GO as the saturable absorber, paving the way toward practical application of GOSA in high power pulsed double-clad fiber laser system.

Mid-infrared Spectral Intensity Enhanced Supercontinuum Generation Based on Nanosecond Thulium-Doped Fiber Laser

We report a mid-infrared (MIR) spectral intensity-enhanced supercontinuum (SC) generation from a ZrF4-BaF 2-LaF3-AlF3-NaF fiber pumped by a nanosecond thulium-doped fiber laser. The spectral region covered from 1930 to 3500 nm with an average output power of 5.23 W. The average power ratio of the MIR SC for the wavelength > 2200 and > 2500 nm were 91.81% and 74.29% with respect to the total output power, respectively. The 1950-nm nanosecond seed pulses were generated from a long ring cavity based on semiconductor saturable absorber mode locker. The pulse repetition rate was 3.02 MHz with a tunable pulse duration of about 1.0 ns-3.9 ns. In addition, a 69.5-W short-wave infrared SC was obtained through a two-stage thulium-doped fiber amplifier with the spectrum extending from 1930 to 2500 nm. To the best of our knowledge, this is the first time such a spectral intensity-enhanced MIR SC directly pumped by a high-pulse-energy nanosecond thulium-doped fiber laser has been achieved.

Silicon Wafer: a Direct Output Coupler in Tm:YLF Laser*

We present a high power diode-pumped continuous-wave Tm:YLF (Tm3+-doped lithium yttrium fluoride) laser with apiece of silicon wafer as the output coupler (Si-OC laser) directly. Under the pump power of 40 W at 793 nm, a maximum output power of 12.1 W is obtained with a beam quality of M2 ≤ 1.55 at 1887 nm, corresponding to an optical-to-optical efficiency of 30.25% and a slope efficiency of 33.21%. To the best of our knowledge, this is the first report on directly utilizing silicon as an output coupler (Si-OC) in the solid Tm:YLF laser system. Due to the intriguing characteristics of silicon, such as negligible absorption in the wavelength region around 2 μm, high damage threshold, low cost and long-pass filter properties, double-side polished monocrystalline silicon wafer is considered as an outstanding candidate output coupler in the high-power laser system 2 μm spectral region, which may dramatically reduce the total manufacturing costs of the 2 μm laser system.