Yanrong Song

High-repetition-rate Q-switched fiber laser with high quality topological insulator Bi 2 Se 3 film

We demonstrated a high-repetition-rate Q-switched fiber laser with topological insulator Bi₂Se₃ absorber. The absorber was made into a film structure by spin-coating method using few-layer Bi₂Se₃ nano-platelets which had regular shape. The uniform film had a low saturable optical intensity of 11 MW/cm(2), which is the lowest saturable optical intensity in the saturable absorbers made by topological insulator till now. By inserting the absorber film into an Erbium-doped fiber laser, a high-repetition Q-switched laser with the repetition rates from 459 kHz to 940 kHz was achieved. The maximum output power was 22.35 mW with the shortest pulse duration of 1.9 μs. To the best of our knowledge, both of the repetition rate and the output power were the highest values among the Q-switched fiber lasers with topological insulator absorber.

Band-Selective Optical Polarizer Based on Gold-Nanowire Plasmonic Diffraction Gratings

We report a plasmonic diffraction grating device as a new kind of optical polarizer. This simple device consists of periodically distributed gold nanowires on top of a transparent glass substrate and is based on the strong polarization dependence of the particle plasmon resonance of the gold nanowires. A high-efficiency secondary diffraction in the same device enhances the polarization extinction ratio significantly. Linearly polarized spectrum in the red with a bandwidth of 53 nm is selectively picked up from the nonpolarized white light, where a polarization extinction ratio higher than 100 at about 650 nm has been achieved. The idea of plasmonic diffraction grating is important for exploiting new detection and sensor techniques.

Mode-locked ytterbium-doped fiber laser based on topological insulator: Bi 2 Se 3

We demonstrated an all-normal-dispersion Yb-doped mode-locked fiber laser based on Bi₂Se₃ topological insulator (TI). Different from previous TI-mode-locked fiber lasers in which TIs were mixed with film-forming agent, we used a special way to paste a well-proportioned pure TI on a fiber end-facet. In this way, the effect of the film-forming agent could be removed, thus the heat deposition was relieved and damage threshold could be improved. The modulation depth of the Bi₂Se₃ film was measured to be 5.2%. When we used the Bi₂Se₃ film in the Yb-doped fiber laser, the mode locked pulses with pulse energy of 0.756 nJ, pulse width of 46 ps and the repetition rate of 44.6 MHz were obtained. The maximum average output power was 33.7 mW. When the pump power exceeded 270 mW, the laser can operate in multiple pulse state that six-pulse regime can be realized. This contribution indicates that Bi₂Se₃ has an attractive optoelectronic property at 1μm waveband.

A 66 fs highly stable single wall carbon nanotube mode locked fiber laser

We demonstrate a highly stable mode locked fiber laser based on single wall carbon nanotubes. The mode locking is achieved by the evanescent field interaction of the propagating light with a single wall carbon nanotube saturable absorber in a microfiber. The pulse width is 66 fs, which, to the best of our knowledge, is the shortest pulse achieved in a carbon nanotube mode locked fiber laser. The maximum average output power is 26 mW, which is about 20 times larger than that of a typical carbon nanotube mode locked fiber laser. The center of the wavelength is 1555 nm, with 54 nm spectral width. The repetition rate is 146 MHz. To investigate the lasers stability, the output pulses are monitored for 120 h and there is no significant degradation of the laser spectral width or shape.

Gain characteristics of the InGaAs strained quantum wells with GaAs, AlGaAs, and GaAsP barriers in vertical-external-cavity surface-emitting lasers

InGaAs strained quantum wells (QWs) with GaAs, AlGaAs, and GaAsP barriers are widely used in optically pumped vertical-external-cavity surface-emitting lasers operating at 1 μm wavelength band. Compared with the reported data, the model-solid theory, which is more suitable for the studied materials, is selected to calculate the band offset. The band structures and the gain characteristics of the three different QWs are computed and compared, and the theoretical results are in good agreement with the recent experimental reports. The numerical simulation shows that the QW with the GaAs barrier has the highest absorption but the lowest peak gain, while for the AlGaAs barrier, it has the lowest absorption but the highest peak gain, and for the GaAsP barrier, it has a moderate absorption and peak gain. GaAsP is the most appropriate candidate for the barrier of InGaAs strained QW when the low-threshold, large-gain, and high-temperature characteristics are demanded simultaneously.

L-band femtosecond fibre laser based on Bi2Se3 topological insulator

We demonstrate a femtosecond erbium-doped fibre laser operating in the long wavelength band (L-band) in which topological insulator Bi2Se3-polyvinyl alcohol film is applied as a saturable absorber. It generates a ~360 fs soliton pulse at 1600 nm with a repetition rate of 35.45 MHz. To the best of our knowledge, this is the shortest pulse duration ever achieved with an L-band design employing Bi2Se3 as a saturable absorber. The result shows topological insulator Bi2Se3 could be a promising candidate to generate L-band ultrafast pulses for practical applications.

Theoretical analysis on the tuning dynamics of the waveguide-grating structures

We investigate theoretically the tuning properties of the resonant mode of the waveguide-grating structures (WGS). This intends to understand how tuning mechanisms of the waveguide resonance mode depend on the structural and the geometric parameters of the WGS device, which can be used as guidance for the design of biosensors and other optoelectronic devices. The device parameters studied here include the angle of incidence, the thickness and refractive index of the waveguide, the period of the grating, and the refractive indices of the substrate and the medium on top of the grating. In particular, the control of the tuning rate and the adjustment of the tuning range by optimizing the combination of the relevant parameters provide a practical route for the design of biosensor and optical switch.

Generation of Q-switched pulse by Bi2Se3 topological insulator in Yb:KGW laser

A Q-switched Yb:KGW solid-state laser using topological insulator Bi2Se3 as a saturable absorber was demonstrated experimentally for the first time. The Bi2Se3 saturable absorber was fabricated in a film on a highly reflective mirror. By inserting this into a Yb:KGW laser, the Q-switched operation was obtained. The highest average output power was 439.4 mW and the corresponding repetition rate, pulse width and pulse energy were 166.7 kHz, 1.6 μs and 2.64 μJ, respectively. To our knowledge, this is the highest output power among topological insulator-modulated lasers with topological insulator absorbers.

Mode-locked ytterbium-doped fiber laser based on tungsten disulphide

We demonstrated an all-normal-dispersion Yb-doped mode-locked fiber laser based on tungsten disulphide (WS2). The saturable absorbers (SA) were made by mixing WS2 solution with polyvinyl alcohol (PVA), and then evaporated on a substrate. The modulation depth of the WS2 film was 2.06% and the saturable optical intensity was 71.6 MW cm−2. When the WS2 film was inserted into the fiber laser, the mode-locked pulses with pulse width of 2.5 ns and repetition rate of 2.84 MHz were obtained. As the pump power increased to 350 mW, the maximum output power was measured to be 8.02 mW. To the best of our knowledge, this is the first time to realize mode-locked pulses based on WS2-SA at 1 μm waveband.

Optically pumped vertical external-cavity surface-emitting lasers

We present an optically pumped vertical external cavity surface emitting lasers using the semiconductor gain chip composed of quantum wells. The dependence of the spectrum of the output on the temperature of the gain chip was measured. The maximum output power reached 40mW at the wavelength of 1015.5nm with the pump power of 1.5W. The optical conversion efficiency reached 2.7%.