Xu-Wu Zheng

2 GHz passively harmonic mode-locked fiber laser by a microfiber-based topological insulator saturable absorber

We report on the generation of passive harmonic mode locking of a fiber laser using a microfiber-based topological insulator (TI) Bi(2)Te(3) saturable absorber (SA). The optical deposition method was employed to fabricate the microfiber-based TISA. By virtue of the excellent nonlinear optical property of the proposed TISA, the fiber laser could operate at the pulse repetition rate of 2.04 GHz under a pump power of 126 mW, corresponding to the 418th harmonic of fundamental repetition frequency. The results demonstrate that the microfiber-based TI photonic device can operate as both the high nonlinear optical component and the SA in fiber lasers, and could also find other applications in the related fields of photonics.

Femtosecond pulse generation from a topological insulator mode-locked fiber laser

We reported on the generation of femtosecond pulse in a fiber ring laser by using a polyvinyl alcohol (PVA)-based topological insulator (TI), Bi2Se3 saturable absorber (SA). The PVA-TI composite has a low saturable optical intensity of 12 MW/cm2 and a modulation depth of ~3.9%. By incorporating the fabricated PVA-TISA into a fiber laser, mode-locking operation could be achieved at a low pump threshold of 25 mW. After an optimization of the cavity parameters, optical pulse with ~660 fs centered at 1557.5 nm wavelength had been generated. The experimental results demonstrate that the PVA could be an excellent host material for fabricating high-performance TISA, and also indicate that the filmy PVA-TISA is indeed a good candidate for ultrafast saturable absorption device.

Microfiber-based few-layer MoS2 saturable absorber for 2.5 GHz passively harmonic mode-locked fiber laser.

We reported on the generation of high-order harmonic mode-locking in a fiber laser using a microfiber-based molybdenum disulfide (MoS(2)) saturable absorber (SA). Taking advantage of both the saturable absorption and large third-order nonlinear susceptibilities of the few-layer MoS(2), up to 2.5 GHz repetition rate HML pulse could be obtained at a pump power of 181 mW, corresponding to 369th harmonic of fundamental repetition frequency. The results provide the first demonstration of the simultaneous applications of both highly nonlinear and saturable absorption effects of the MoS(2), indicating that the microfiber-based MoS(2) photonic device could serve as high-performance SA and highly nonlinear optical component for application fields such as ultrafast nonlinear optics.

Dual-Wavelength Harmonically Mode-Locked Fiber Laser With Topological Insulator Saturable Absorber

Dual-wavelength passively harmonic mode locking (HML) operation is demonstrated in an erbium-doped fiber laser with a microfiber-based topological insulator (TI) saturable absorber. It was found that the dual-wavelength pulse-trains possess different HML orders due to the different cavity nonlinear effects experienced by the two wavelengths. By properly adjusting the cavity parameters, dual-wavelength HML pulses with repetition rates of 388 and 239 MHz were achieved. Moreover, wavelength switchable operation of dual-wavelength HML pulses was also obtained. The experimental results reveal that the microfiber-based TI could indeed be employed as a high-performance dual-function photonic device with the saturable absorption and high nonlinear effects for the applications in fields of ultrafast and nonlinear photonics.

Dual-wavelength rectangular pulse Yb-doped fiber laser using a microfiber-based graphene saturable absorber.

We reported on the generation of dual-wavelength rectangular pulses in a Yb-doped fiber laser (YDFL) by using a microfiber-based graphene saturable absorber (GSA). The duration of dual-wavelength rectangular pulse could be varied from 1.41 ns to 4.23 ns with the increasing pump power. With a tunable bandpass filter, it was found that the characteristics of the rectangular pulses centered at 1061.8 nm and 1068.8 nm are similar to each other. Moreover, the dual-wavelength switchable operation was also realized by properly rotating the polarization controllers (PCs). The demonstration of the dual-wavelength rectangular pulses from a YDFL would open some applications for fields such as spectroscopy, biomedicine and sensing research.

Vector nature of multi-soliton patterns in a passively mode-locked figure-eight fiber laser.

The vector nature of multi-soliton dynamic patterns was investigated in a passively mode-locked figure-eight fiber laser based on the nonlinear amplifying loop mirror (NALM). By properly adjusting the cavity parameters such as the pump power level and intra-cavity polarization controllers (PCs), in addition to the fundamental vector soliton, various vector multi-soliton regimes were observed, such as the random static distribution of vector multiple solitons, vector soliton cluster, vector soliton flow, and the state of vector multiple solitons occupying the whole cavity. Both the polarization-locked vector solitons (PLVSs) and the polarization-rotating vector solitons (PRVSs) were observed for fundamental soliton and each type of multi-soliton patterns. The obtained results further reveal the fundamental physics of multi-soliton patterns and demonstrate that the figure-eight fiber lasers are indeed a good platform for investigating the vector nature of different soliton types.

High-energy noiselike rectangular pulse in a passively mode-locked figure-eight fiber laser

We report on the generation of a high-energy noiselike rectangular pulse in a mode-locked figure-eight fiber laser. The noiselike pulse appeared to have a rectangular shape on the oscilloscope. The pulse duration increased with increasing pump power, while the peak amplitude remained constant, which is very similar to the pulse evolution of dissipative soliton resonance. However, the pulse type is confirmed as a noiselike pulse using an autocorrelator. With the maximum pump power of 350 mW, the 135 nJ noiselike rectangular pulse with 76 ns duration was achieved. The results provide a new guideline for clarifying an alternative formation mechanism of the high-energy rectangular pulses in fiber lasers.

Microfiber-Based Highly Nonlinear Topological Insulator Photonic Device for the Formation of Versatile Multi-Soliton Patterns in a Fiber Laser

We reported on the observation of versatile multi-soliton patterns in an erbium-doped fiber laser with a microfiber-based topological insulator (TI) photonic device. Taking advantage of both the high third-order nonlinear susceptibility and excellent saturable absorption of TI, various multi-soliton formations, such as soliton molecules, bound solitons, and soliton rains could be easily obtained at a low pump power. These results might deepen the understanding of nonlinear dynamics of multi-soliton patterns, and further demonstrate that the TI deposited microfiber could operate as a high-performance photonic device with both highly nonlinear effect and saturable absorption for the related optics applications.

Noise-like pulse trapping in a figure-eight fiber laser.

We report on the trapping of noise-like pulse in a figure-eight fiber laser mode locked by nonlinear amplifier loop mirror (NALM). After achievement of noise-like vector pulse, it was found that the wavelength shift of the two resolved polarization components responsible for the pulse trapping was very sensitive to the cavity birefringence. By properly rotating the polarization controllers (PCs), the wavelength shift could be up to 4.8 nm, which is much larger than that of conventional soliton trapping. The observed results would shed some light on the fundamental physics of noise-like pulse as well as its vector features in fiber lasers.

Generation of Multiwavelength Noise-Like Square-Pulses in a Fiber Laser

The generation of multiwavelength square pulses is demonstrated in a passively mode-locked figure-eight fiber laser. The multiwavelength square pulses were found to be structured by superposing the square pulses centered at different wavelengths, whose pulse duration broadens with the increasing pump power. The square pulse was confirmed as the noise-like pulse by using an autocorrelator. By properly rotating the PCs, the dual- or triple-wavelength square pulse could be achieved. The obtained results provide a new viewpoint for understanding the formation mechanism of the multiwavelength pulses with noise-like square profiles in fiber lasers.