Quan Sheng

Single-frequency fiber laser at 1950 nm based on thulium-doped silica fiber.

A single-frequency fiber laser operating at 1950 nm has been demonstrated in an all-fiber distributed Bragg reflection laser cavity by using a 1.9 cm commercially available thulium-doped silica fiber, for the first time, to the best of our knowledge. The laser was pumped by a 793 nm single-mode diode laser and had a threshold pump power of 75 mW. The maximum output power of the single longitudinal mode laser was 18 mW and the slope efficiency with respect to the launched pump power was 11%. Moreover, the linewidth and relative intensity noise at different pump power have been measured and analyzed.

5.2-W high-repetition-rate eye-safe laser at 1525 nm generated by Nd:YVO 4 –YVO 4 stimulated Raman conversion

We report herein an efficient eye-safe Raman laser, which is based upon Nd:YVO₄₋YVO₄ and in-band pumped by a wavelength-locked laser diode array at 878.6 nm. By virtue of mitigated thermal load and improved pump absorption, a maximum average output power of 5.2 W at 1525 nm is obtained under the incident pump power of 30.6 W with the pulse repetition frequency of 140 kHz, corresponding to an optical efficiency of 17.0%.

Continuous-wave mid-infrared intra-cavity singly resonant PPLN-OPO under 880 nm in-band pumping

We report herein a continuous-wave mid-infrared intra-cavity singly resonant optical parametric oscillator (ICSRO) which is the first example of ICSRO that utilize in-band pumped Nd-doped vanadate laser as pump source. A 1064 nm Nd:YVO₄ laser in-band pumped by 880 nm LD and a periodically poled lithium niobate (PPLN) crystal are employed as the parent pump laser and the nonlinear medium, respectively. The idler output wavelength tuning range is 3.66-4.22 µm. A maximum output power of 1.54 W at 3.66 µm is obtained at absorbed pump power of 21.9 W, with corresponding optical efficiency being 7.0%. The control experiment of ICSRO under 808 nm traditional pumping is also carried out. The results show that in-band pumped ICSRO has better performance in terms of threshold, power scaling, efficiency and power stability than ICSRO traditionally pumped at 808 nm.

Passive Q-switching of an all-fiber laser induced by the Kerr effect of multimode interference.

A novel passively Q-switched all-fiber laser using a single mode-multimode-single mode fiber device as the saturable absorber based on the Kerr effect of multimode interference is reported. Stable Q-switched operation of an Er(3+)/Yb(3+) co-doped fiber laser at 1559.5 nm was obtained at a pump power range of 190-510 mW with the repetition rate varying from 14.1 kHz to 35.2 kHz and the pulse duration ranging from 5.69 μs to 3.86 μs. A maximum pulse energy of 0.8 μJ at an average output power of 27.6 mW was achieved. This demonstrates a new modulation mechanism for realizing Q-switched all-fiber laser sources.

Dual-wavelength fiber laser operating above 2 μm based on cascaded single-mode-multimode-single-mode fiber structures.

A stable dual-wavelength Tm3+:Ho3+ co-doped fiber laser operating above 2 μm based on cascaded single-mode-multimode-single-mode (SMS) fiber structures is proposed and experimentally demonstrated. Based on the theoretical analysis of the transmission properties of the SMS fiber structure, two cascaded SMS fiber devices with different multimode fiber (MMF) lengths were used in our laser system, where one acted as a long-pass filter to suppress the competitive laser below 2 μm, and the other worked as a band-pass filter to select the specific operating wavelengths of the laser. Dual-wavelength operation of the fiber laser at 2002.8 and 2016.1 nm has been achieved in the experiment with a signal to a noise ratio up to 50 dB.

High-Power All-Fiber Single-Frequency Erbium–Ytterbium Co-Doped Fiber Master Oscillator Power Amplifier

We report herein an all-fiber single-frequency master oscillator power amplifier (MOPA) at 1550 nm with Er/Yb-codoped active fiber and wavelength-stabilized 976-nm LD pump source. A pump-limited maximum continuous-wave output power of 56.4 W was achieved under the pump power of 150 W, with corresponding slope efficiency being 37.0%. Via the self-heterodyne method, the evolution of spectrum linewidth during the amplification was investigated for the high-power MOPA-based single-frequency fiber laser. The linewidth and relative intensity noise at the maximum output power are 4.21 kHz and -110 dBm/Hz, respectively.

12.45 W wavelength-locked 878.6 nm laser diode in-band pumped multisegmented Nd:YVO 4 laser operating at 1342 nm

A multisegmented Nd:YVO4 laser operating at 1342 nm that is in-band pumped by a wavelength-locked 878.6 nm laser diode is reported here. We achieve an output power of 12.45 W at 1342 nm for an absorbed pump power of 35.6 W, corresponding to an optical-to-optical efficiency of 34.9% and a slope efficiency of 36.1%. To the best of our knowledge, it is the highest optical-to-optical efficiency of Nd:YVO4 lasers operating at 1342 nm with an output power more than 10 W.

Optical tuning of dielectric properties of SrTiO3:Fe in the terahertz range

Tuning of the dielectric permittivity spectra of iron-doped strontium titanate (SrTiO3:Fe) single crystals in an external optical field is investigated at room temperature by means of terahertz time-domain spectroscopy. Application of the optical field leads to an appreciable tuning of the permittivity, which reaches up to 3.8%. The observed behavior is interpreted in terms of soft-mode hardening due to the anharmonic character of its potential. We also find that the change of refractive index has a linear relationship on scale with the applied light power. These findings are attributed to the internal space charge field of photorefraction caused by the excited free carriers.

Continuous-wave intra-cavity singly resonant optical parametric oscillator with resonant wave output coupling

We report herein the enhancement in both power and efficiency performance of a continuous-wave intra-cavity singly resonant optical parametric oscillator (ICSRO) by introducing finite resonant wave output coupling. While coupling out the resonant wave to useful output, the output coupling increases the SRO threshold properly thus suppresses the back-conversion under high pump power. Therefore, the down-conversion efficiency is maintained under high pump without having to raise the threshold by defocusing. With a T = 9.6% signal wave output coupler used, the SRO threshold is 2.46 W and the down-conversion efficiency is 72.9% under the maximum pump power of 21.4 W. 1.43 W idler power at 3.66 μm and 5.03 W signal power at 1.5 μm are obtained, corresponding to a total extraction efficiency of 30.2%. The resonant wave out coupling significantly levels up the upper limit for the power range where the ICSRO exhibits high efficiency, without impeding its advantage of low threshold.

Efficient Eye-Safe Nd:YVO 4 Self-Raman Laser In-Band Pumped at 914 nm

An efficient Q-switched eye-safe Nd:YVO4 self-Raman laser, which we believe to be the first one in-band pumped at 914 nm, is presented, and 2.58 W of 1525-nm Stokes output was generated under the absorbed pump power of 10.2 W with a high repetition rate of 100 kHz, corresponding to a conversion efficiency of 25.3%. The optical efficiency with respect to incident pump also reached 16.4%. Influences of crystal temperature and dopant concentration on the performance of the eye-safe self-Raman laser were experimentally investigated.