Lixin Xu

Square-wave pulse with ultra-wide tuning range in a passively mode-locked fiber laser

We report the generation of ultrawide tunable square-wave pulse in an erbium-doped mode-locked fiber laser. The pulse width can be tuned in an ultrawide range of more than 1700 ns by simply increasing the pump power. The pulse-width tuning is 5.1 ns/mW. To the best of our knowledge, this is the widest pulse-width tuning range of any square-wave pulse in an all-fiber passively mode-locked fiber laser. Experimental results show that the fiber nonlinearity plays an important role in the tuning range of the output pulse width. The high nonlinearity helps to increase the tuning range of the pulse width.

An all-fiber laser generating cylindrical vector beam

We proposed and demonstrated an all-fiber laser to generate cylindrical vector beam. A pair of fiber-based collimators was used to select the cylindrical vector beam operating. The radially and azimuthally polarized modes can be switchable just by applying pressure to a section of fiber in our fiber laser system. A 70 cm long Yb-doped fiber was used as gain medium and the lasing wavelength was around 1030 nm.

Width and amplitude tunable square-wave pulse in dual-pump passively mode-locked fiber laser

We have proposed and demonstrated a figure-8 dual-pump passively mode-locked fiber laser to generate square-wave pulse tunable by both width and amplitude. Just by simply adjusting the power of the pumps, both the amplitude and width of the output square-wave pulse can be tuned independently and continuously. One pump is used to tune the output pulsewidth while the other is used to tune amplitude.

Wavelength-tunable Yb-doped passively Q-switching fiber laser based on WS 2 saturable absorber

We have fabricated an Yb-doped passively Q-switching fiber laser based on WS(2) saturable absorber. Both the operating wavelength and the repetition rate can be tuned in a wide range. The operating wavelength can be continuously tuned from 1027 nm to 1065 nm under the Q-switching state at a fixed pump power, while the repetition rate increases from 60.2 kHz to 97.0 kHz by varying pump power at a fixed wavelength of 1048.1 nm. The shortest pulse duration of 1.58 µs was observed. To the best of our knowledge, its the first demonstration of WS(2)-based passively Q-switching fiber laser with a wide tunable range at 1.0 μm band.

1/spl times/4 all-optical packet switch at 10 gb/s

We demonstrated a 1/spl times/4 all-optical packet switch with all-optical header processing at a header rate of 5 Gb/s and payload rate of 10 Gb/s using injection-locking in a single Fabry-Pe/spl acute/rot laser diode at each output port of the switch.

Generation of Optical Vortices Using a Helical Fiber Bragg Grating

We present an effective method to generate optical vortices (OVs) by using a helical fiber Bragg grating (H-FBG) written directly on the few-mode fiber. The helical index modulation is obtained by rotating fiber during single-side UV exposure using a phase mask. A set of coupled-mode equations are formulated to analysis reflection characteristics of the H-FBG. We propose that stable OVs can be achieved with a proper design M-fiber, and the order of the OVs can be adjusted by tuning the resonant wavelength and the handedness of the H-FBG.

Optimization of Raman-Assisted Fiber Optical Parametric Amplifier Gain

We studied the gain of Raman-assisted fiber optical parametric amplifiers (RA-FOPAs) both theoretically and experimentally. We investigated the relationship between the overall gain and different combinations of Raman and parametric pump powers using contour maps. We derived a normalized phase-matched model to determine the general behavior the peak gains of RA-FOPAs operating in the small signal region. The contour maps of the combined gain enhancement can be used to optimize both indirect and direct Raman gain of the signal/idler in RA-FOPAs. We showed that, in a given fiber, it is possible to optimize the Raman and parametric pump powers in RA-FOPAs for high gain and high efficiency.

All-optical add–drop node for optical packet-switched networks

We have demonstrated all-optical packet add-drop for all-optical packet-switched networks. Intelligent all-optical add-drop of packets is performed, based on all-optical processing of packet headers. The header and payload rates are 5 and 10 Gbits/s, respectively.

Simultaneous all-optical waveform reshaping of two 10-Gb/s signals using a single injection-locked Fabry-Perot laser diode

All-optical waveform reshaping of a distorted 10-Gb/s nonreturn-to-zero (NRZ) pseudorandom bit sequence (PRBS) signal using two-mode injection locking in Fabry-Perot laser diode (FP-LD) was demonstrated. Simultaneous waveform reshaping of two 10-Gb/s distorted NRZ PRBS signals using a single FP-LD was also demonstrated.

Bi 2 Te 3 based passively Q-switched fiber laser with cylindrical vector beam emission.

We report a passively Q-switched fiber laser with cylindrical vector beam output modes using a few-mode fiber Bragg grating as a polarization-selective output coupler and Bi2Te3 as the saturable absorber. Both radially and azimuthally polarized beams can be readily generated, and the output polarization can be switchable by tuning the polarization controllers inside the laser cavity. The repetition rate of the Q-switched laser can be tuned from 31.54 to 49.40 kHz when the pump power increases from 103.5 to 139.5 mW. The fiber laser operates at a single wavelength of 1557.5 nm with a 3 dB linewidth of <0.04  nm.