Yin-Wen Lee

High-Power

We report on the development of novel high-power light sources utilizing a Yb3+-doped phosphate fiber as the gain element. This host presents several key benefits over silica, particularly much higher Yb2 O3 concentrations (up to 26 wt%), a 50% weaker stimulated Brillouin scattering (SBS) gain cross section, and the absence of observable photodarkening even at high population inversion. These properties result in a greatly increased SBS threshold compared to silica fibers, and therefore, potentially much higher output powers out of either a multimode large mode area or a single-mode fiber, which means in the latter case a higher beam quality. To quantify these predictions, we show through numerical simulations that double-clad phosphate fibers should produce as much as ~ 700 W of single-frequency output power in a step index, single-mode core. As a step in this direction, we report a short phosphate fiber amplifier doped with 12 wt% Yb2 O3 that emits 16 W of single-frequency single-mode output. We also describe a single-mode phosphate fiber laser with a maximum output power of 57 W. The laser slope efficiency is currently limited by the fairly high fiber loss ( ~ 3 dB/m). Measurements indicate that 77% of this loss originates from impurity absorption, and the rest from scattering.

\hbox{Yb}^{{\bm 3}{\bm +}}

We report the demonstration of the first, to our knowledge, cladding-pumped continuous-wave Yb(3+)-doped phosphate-glass fiber laser. Phosphate hosts are of interest because they can be much more heavily doped than silica, and because of the possibility that they may have a higher photodarkening threshold. In an 84.6 cm double-clad fiber doped with 12 wt. % of Yb(2)O(3) and laser-diode pumped at 940 nm, nearly 20 W of single-mode 1.07 microm output power was generated with 60.2 W of absorbed pump power. The measured dependence of the output power on pump power is in excellent agreement with simulations.

-Doped Phosphate Fiber Amplifier

We report on a system that produces 19 W of diffraction-limited radiation at 532 nm through single-pass frequency doubling of the output of a 1064 nm Yb3+-doped fiber MOPA in a periodically poled near-stoichiometric lithium tantalate (PPSLT) crystal. The output of the system was stable at the 19 W level for over one hour with no signs of photorefraction. The green power is believed to be limited by infrared-induced thermal dephasing in the PPSLT crystal.

20 W single-mode Yb 3+ -doped phosphate fiber laser

Eye-safe fiber laser sources near 2 μm have attracted a lot of interest in space, defense, medical, and industrial applications. We review our latest developments of various fiber laser sources operating near 2 μm, which include single-frequency CW lasers, wavelength-swept lasers, power-scaled nanosecond pulsed lasers, and various mode-locked lasers. Potential applications of these mid-infrared fiber laser sources are also discussed.

Room-Temperature Stable Generation of 19 Watts of Single-Frequency 532-nm Radiation in a Periodically Poled Lithium Tantalate Crystal

We demonstrate a cascaded Raman fiber laser with a record output power of 104 W at 1480 nm. We achieve this with an 1117 nm Yb-doped fiber laser pumping a cascaded Raman conversion to 1480nm. Enhanced efficiency is achieved in the Raman cavity using a fiber with a long wavelength cut-off which prevents further Raman conversion of 1480 nm light and thus allowing for longer cavity lengths. The output is single mode making it a bright source for core or cladding pumping of erbium-doped fiber lasers.

Development of Eye-Safe Fiber Lasers Near 2 μm

We report the first measurement of the stimulated Brillouin scattering (SBS) gain coefficient of a phosphate fiber. Using single-pass amplification of spontaneous Brillouin scattering noise, we measured an SBS gain coefficient of 2.1 × 10-11 m/W in a 124.5-cm single-mode Yb3+-doped phosphate fiber. This is a factor of two less than the SBS gain coefficient of silica fiber, which puts phosphate glass fiber at an advantage for high-power applications.

Cascaded Raman fiber laser at 1480 nm with output power of 104 W

A multiwavelength linear-cavity laser array for long-distance sensing is designed and experimentally demonstrated. It is a semiconductor optical amplifier (SOA) integrating a 1 × N optical switch, formed by a 2 × 2 fiber loop mirror and fiber Bragg grating (FBG) as cavity ends. We investigate the laser system output characteristics and evaluate the sensor performance for different sensing distances incorporating the FBGs. The results show that this SOA-based laser sensor array possesses a dynamic sensing distance of up to 35 km at a 350-mA injection current. Stress/strain detection and reliable linear-cavity fiber laser sensing operation were successfully achieved.

Measurement of the stimulated Brillouin scattering gain coefficient of a phosphate fiber

We describe the first 10-W single-mode, single-frequency Yb³⁺-doped phosphate fiber amplifier. The fiber is doped with 12 wt% Yb₂O₃ and only 47.5-cm long. A 25-W phosphate fiber laser with 52.7% slope efficiency is also reported.

Multiwavelength Linear-Cavity SOA-Based Laser Array Design for Multiparameter and Long-Haul Sensing

In a crossed-laser-beam accelerator, two properly phased laser beams, forming an interferometric configuration, may provide an adequate particle acceleration field over a phase matching distance. The two laser beams can be obtained by dividing a full, Gaussian laser beam equally in amplitude or in wavefront. We show in this paper that a wavefront-splitting laser-driven accelerator is relatively simple to set up and provides an acceleration gain comparable to that of an amplitude-splitting accelerator under the same laser damage fluence. We also present the noise characteristics measured from various interferometers, which may be useful for implementing interferometric-type accelerators.

10-watt, single-mode, single-frequency, 1.03 μm Yb 3+ -doped phosphate fiber amplifier

We report the measurement of photodarkening in single-mode phosphate fibers with a Yb3+ concentrations of 7.1 × 1026 m-3 and 1.42 × 1027 m-3 (6 wt.% and 12 wt.% Yb2O3).We compare the photodarkening resistance of these phosphate fibers with that of three single-mode Yb3+-doped silica fibers. Our data shows that under strong pumping conditions, phosphate fibers allow Yb3+ concentrations that are least 6 times greater than the most photodarkening-resistant silica fibers to date without the onset of photodarkening at 660 nm.