In a passively mode-locked Erbium-doped fiber laser with large anomalous-dispersion, we experimentally demonstrate the formation of noise-like square-wave pulse, which shows quite different features from conventional dissipative soliton resonance (DSR). The corresponding temporal and spectral characteristics of a variety of operation states, including Q-switched mode-locking, continuous-wave mode-locking and Raman-induced noise-like pulse near the lasing threshold, are also investigated. Stable noise-like square-wave mode-locked pulses can be obtained at a fundamental repetition frequency of 195 kHz, with pulse packet duration tunable from 15 ns to 306 ns and per-pulse energy up to 200 nJ. By reducing the linear cavity loss, stable higher-order harmonic mode-locking had also been observed, with pulse duration ranging from 37 ns at the 21st order harmonic wave to 320 ns at the fundamental order. After propagating along a piece of long telecom fiber, the generated square-wave pulses do not show any obvious change, indicating that the generated noise-like square-wave pulse can be considered as high-energy pulse packet for some promising applications. These experimental results should shed some light on the further understanding of the mechanism and characteristics of noise-like square-wave pulses.

Topological insulators have been theoretically predicted as promising candidates for broadband photonics devices due to its large bulk band gap states in association with the spin-momentum-locked mass-less Dirac edge/surface states. Unlike the bulk counterpart, few-layer topological insulators possess some intrinsic optical advantages, such as low optical loss, low saturation intensity and high concentration of surface state. Herein, we use a solvothermal method to prepare few-layer Bi₂Te₃ flakes. By sandwiching few-layer Bi₂Te₃ flakes with polymethyl methacrylate (PMMA) polymer, a novel light modulation device had been successfully fabricated with high chemical and thermal stabilities as well as excellent mechanical durability, originating from the contribution of PMMA acting as buffer layers that counteract excessive mechanical bending within the fragile Bi₂Te₃ flakes. The incorporation of the as-fabricated PMMA-TI-PMMA as saturable absorber, which could bear long-term mechanical loadings, into the fiber laser cavity generated the stable dissipative soliton mode-locking with a 3-dB spectral bandwidth up to 51.62 nm and tunable wavelength range of 22 nm. Our work provides a new way of fabricating PMMA-TI-PMMA sandwiched composite structure as saturable absorber with promising applications for laser operation.

We experimentally demonstrated a stable, high-average-power, continuous-wave (CW) passively mode-locked ${\mathrm{Er}}^{3+}$-doped ZBLAN fiber laser at 2.8 μm based on a semiconductor saturable absorber mirror. A stable mode-locked laser with a signal-to-noise ratio of 52 dB and a slope efficiency of 14% was obtained. The highest average output power in excess of 1 W was generated at the incident pump power of 8.2 W, with a pulse repetition rate of 22.56 MHz and pulse duration of 25 ps. To the best of our knowledge, this is the highest average output power of a CW mode-locked ZBLAN fiber laser in the mid-infrared wavelength regime up to now.

Ultrathin topological insulator bismuth telluride (Bi₂Te₃) nanosheets with uniform hexagonal nanostructure have been synthesized by cost-effective solvothermal method. Broadband spatial self-phase modulation phenomena of these topological insulator nanosheets have been observed with 400 nm, 800 nm, and 1070 nm ultrafast lasers. The experimental results suggest that this coherent light scattering is due to the broadband, ultrafast, and large third-order optical nonlinearity of Bi₂Te₃. With the pulsed laser excitation, the nonlinear refractive index (n₂) of Bi₂Te₃ dispersion solution was measured to be ∼10⁻¹² m²/W, and the third-order nonlinear susceptibility ∼10⁻⁷ esu. Our work may provide an inroad for developing the nonlinear optical applications based on topological insulators.

By using evanescent field optical deposition method, we had successfully fabricated an effective optoelectronic device based on multi-layer black phosphorus (BP), which is been heavily investigating 2 dimensional (2D) semiconducting material with similar structure as graphene and thickness dependent direct band-gap. By placing this BP-based optoelectronic device inside a highly compact all-anomalous dispersion fiber laser cavity, stable passive mode-locking operation could be ensured and eventually a record 280 fs transmission limited soliton pulse with tunable central wavelength had been obtained through finely tailoring the cavity length. Other operation states, like bound soliton and noise-like state, had also been observed as well. This work demonstrates the enormous potential of BP for ultra-short pulse generation as an effective optoelectronic device.

We demonstrated a passively Q-switched 2.8-μm Er ^3± -doped ZBLAN fiber laser with topological insulator Bi ₂ Te ₃ nanosheets prepared by the solvothermal method. Enabled by the gold mirror with self-assembled Bi ₂ Te ₃ nanosheets film sandwiched by polymethyl methacrylate polymer, the Q-switched fiber laser can deliver a maximum average power of 856 mW with corresponding pulse energy of 9.3 μJ and a pulse width of 1.3 μs at a repetition rate of 92 kHz under the pump power 5.9 W. To the best of our knowledge, this is the highest output power for the pulsed fluoride fiber laser around 2.8 μm modulated by the two-dimensional Dirac material. This letter reveals that the topological insulator can be a kind of promising nonlinear modulator for a mid-infrared laser.