Kuei-Huei Lin

Stable Q-switched mode-locked Nd3+:LuVO4 laser by Cr4+:YAG crystal

In use of saturable Cr(4+):YAG crystals, we have demonstrated the stable Q-switched and mode-locked (QML) operation of the Nd:LuVO(4) laser. The operation range of QML in use of the Cr(4+):YAG is larger than that use of SESAM and NLM. The obtained shape of Q-switched envelope, repetition rate and pulse energy are demonstrated to depend on the initial transmittance of the Cr(4+):YAG and reflectivity of the output coupler. Using R = 60% and T(0) = 40%, the highest pulse energy of 77 microJ of each Q-switched envelope, and the highest peak power about 200 kW of Q-switched mode-locked pulses can be obtained at 15 W pump power. It demonstrate the superior characteristic of the Nd:LuVO(4) crystal.

High-power, passively mode-locked Nd:GdVO 4 laser using single-walled carbon nanotubes as saturable absorber

The single-walled carbon nanotubes (SWCNTs) have been widely investigated for making SWCNTs a promising saturable absorber for mode-locking a laser. The SWCNT-SAs have been used for mode-locking lasers operated near 1.0 and 1.5 µm. Until recently, the SWCNT-SAs have been widely used to passively mode-lock the diode-pumped solid-state lasers [1,2]. However, the output power of these lasers is still very low (less than 500 mW) due to the low heat resistance of the polymer material in the SWCNT/polymer composite film. In this paper, the SWCNT-SA film is fabricated without the polymer material by using a vertical evaporation technique [3], and then used in the passive mode-locking of Nd:GdVO4 laser at 1-µm. We obtain the highest output power to our knowledge with the new prepared SWCNT-SA film.

Manipulation of operation states by polarization control in an erbium-doped fiber laser with a hybrid saturable absorber

We propose an operation switchable ring-cavity erbium-doped fiber laser (EDFL) via intra-cavity polarization control. By using a semiconductor saturable absorber mirror in the EDFL cavity, stable Q-switching, Q-switched mode-locking, continuous-wave mode-locking, pulse splitting, and harmonic mode-locking pulses can be manipulated simply by detuning a polarization controller while keeping the pump power at the same level. All EDFL operation states can be obtained under the polarization angles detuning within 180 degrees. Continuous-wave mode-locking of EDFL with 800-fs pulsewidth repeated at 4 MHz has been obtained, for which the output pulse energy is 0.5 nJ and the peak power is 625 W. Interaction between solitons and the accompanied non-soliton component will lead to either pulse splitting or 5th-order harmonic mode-locking at repetition rate of 20 MHz.

Passive mode locking of ytterbium- and erbium-doped all-fiber lasers using graphene oxide saturable absorbers.

Broadband graphene oxide/PVA films were used as saturable absorbers (SAs) for mode locking erbium-doped fiber laser (EDFL) and ytterbium-doped fiber laser (YDFL) at 1.06 μm and 1.55 μm. They provide modulation depths of 3.15% and 6.2% for EDFL and YDFL, respectively. Stable self-starting mode-locked pulses are obtained for both lasers, confirming that the graphene oxide is cost-effective. We have generated mode-locked pulses with spectral width, repetition rate, and pulse duration of 0.75 nm, 9.5 MHz, and 2.7 ps. This is the shortest pulse duration directly obtained from an all-normal-dispersion YDFL with graphene-oxide saturable absorber.

Low threshold and high power output of a diode-pumped nonlinear mirror mode-locked Nd:GdVO4 laser

We demonstrated nonlinear mirror mode-locking of a diode-pumped Nd:GdVO4 laser by using a 10 mm long KTP crystal. The stable CW mode locking can be reached with the relative low threshold pump power as low as 2.3W. The highest output power of 2.65W at the 10 W pump powers are generated with the 121-MHz repetition rate of pulses. It confirms the excellent laser performance of the Nd:GdVO4 for high-peak power of the pulse operation.

12 GHz passive harmonic mode-locking in a 1.06 μm semiconductor optical amplifier-based fiber laser with figure-eight cavity configuration

We report the generation of passively harmonic mode-locked pulses using a 1.06 μm semiconductor optical amplifier (SOA) in a figure-eight laser configuration operated in the all-normal-dispersion regime. Different orders of harmonic mode-locking can be obtained from 30 MHz to 12.02 GHz by changing the injection current of the SOA from 80 to 660 mA together with the adjustment of polarization controllers. The highest pulse repetition rate increases almost linearly with the SOA current. As SOA current is set to 660 mA, we obtain the intracavity power of 46 mW at the highest repetition rate of 12.02 GHz, corresponding to the 1202th harmonic of the fundamental mode-locking frequency. To our best knowledge, this is the lowest intracavity power to generate the highest repetition rate with a passively mode-locked laser in the all-normal-dispersion regime.

Switchable mode-locking states in an all-fiber all-normal-dispersion ytterbium-doped laser

Multi-operation state in an all-normal-dispersion ytterbium-doped fiber laser is obtained by introducing nonlinear polarization or hybrid mode-locking mechanism in the laser cavity. In addition to operating the laser at continuous-wave mode-locking, various operation states including continuous-wave, Q-switched mode-locking, pulse-splitting, and harmonic mode-locking can be achieved by tuning the laser pump power or an intracavity polarization controller. Insertion of a semiconductor saturable absorber mirror in the cavity helps to shorten the output pulsewidth of the hybrid mode-locked laser. When the pump power is rapidly adjusted, a strong asymmetric hysteresis behavior can be observed during the manipulation between different orders of harmonic mode-locking.

Characteristics of Q-switched and mode-locked pulses generation in c-cut Nd:LuVO4 laser by acousto-optic modulator

The characteristics of Q-switched and mode-locked operation in c-cut Nd:LuVO4 laser has been first time investigated by using an acousto-optic modulator. In our study, higher pulse energy and shorter width of Q-switched envelope can be generated using output coupler with R = 80% as compared to those of R = 60%. However, deeper modulation depth and shorter pulsewidth of mode-locked pulses can be generated by using R = 60% instead of R = 80%. In our laser, the pulsewidth of QML pulses are measured by the FROG method and pulsewidth of about 212 ps was produced in the c-cut Nd:LuVO4 laser.

Multiple pulsing and harmonic mode-locking in an all-normal-dispersion Nd:GdVO4 laser using a nonlinear mirror

Harmonic mode-locking (HML) in a diode-pumped Nd:GdVO4 laser was experimentally demonstrated by nonlinear mirror mode-locking (NLM-ML) using a KTP crystal and a dichroic output coupler (OC). By varying the distance between the KTP and the OC, fifth-order HML was demonstrated to generate picosecond pulses with a repetition rate of 576 MHz and supermode suppression larger than 30 dB. Group velocity mismatch between the fundamental wave and second-harmonic wave as well as cascaded second-order nonlinearity in KTP was recognized as the reason for pulse splitting. Transient depletion and recovery gain dynamics acted to push the adjacent split pulses into either equal or unequal spacing, resulting in either HML or multiple pulsing.

Investigation of Graphene Dispersion From Kelly Sideband in Stable Mode-Locked Erbium-Doped Fiber Laser by Few-Layer Graphene Saturable Absorbers

In this paper, stable passively mode-locked fiber lasers (MLFLs) constructed using graphene saturable absorbers (SAs) with different layer numbers of ~1 to ~15 have been reported. The flat linear transmission spectrum in the range from 1540 to 1580 nm without any distinct absorption peak implies that the graphene SAs exhibit low dispersion in this region. Therefore, stable soliton-like pulses are generated because of negative dispersion provided by the fiber laser cavity, which requires no additional single-mode fiber (SMF) for dispersion compensation. Power-dependent transmission measurements show that the saturation intensity ranges from 1.2 to 3.2 MW/cm2 and that the modulation depth (MD) of the graphene SAs increases with the number of graphene layers. All the samples were observed to easily mode-lock the laser with a stable mode-locking state persistently operated over hours. By analyzing the soliton Kelly sidebands, we deduced the group delay dispersion (GDD) for different layers of the graphene. The calculated results show that the variation of sample GDD is within the calculation error, indicating that the GDD of graphene is small to be negligible. This result is consistent with the experimental results reported by Chang et al. [Appl. Phys. Lett. 97, 211102 (2010)] using the phase-shift method. This study demonstrates that different layers graphene SAs have different MD contributions to the generation of laser pulses with different pulse widths.