Direct Side Pumping of Double-Clad Fiber Laser by Laser Diode Array Through the Use of Sub-wavelength Grating Coupler
Journal
IEEE Photonics Journal
Journal Volume
4
Journal Issue
2
Pages
411-421
Date Issued
2012-04
Author(s)
Abstract
An electron-beam-fabricated subwavelength grating coupler for direct side coupling of light emission from a high-power laser diode array (LDA) was studied theoretically and implemented experimentally. A gold-embedded silica-based design for grating coupler was employed to minimize the thermal expansion caused by the accumulated heat from light absorption by metal part of the grating coupler. In addition, with the consideration of the backward diffraction loss and the groove wall nonverticality caused by fabrication distortion, the grating pitch and groove width were optimized for the highest coupling efficiency. According to the experimental results, the grating coupler is capable of coupling light power up to 21 W from a 976-nm continuous-wave-operated LDA into the inner clad of a 400-μm-diameter double-clad fiber with an overall coupling efficiency of 50%. Furthermore, an LDA side-pumped ytterbium-doped DCF laser by using the grating coupler was demonstrated. By fine tuning the slow-axis collimation lens array, the laser-pumping scheme can easily be switched between bidirectional pumping and unidirectional pumping. Compared with the unidirectionally pumped fiber laser of the same gain fiber length, the laser slope efficiency of the bidirectionally pumped fiber laser was increased by 18% because of a better gain distribution over the fiber length. Finally, the signal output power of 10 W with a slope efficiency of 61% was achieved for the bidirectional side-pumped fiber laser.
Subjects
diffractive optics; Diode-pumped lasers; gratings
SDGs
Other Subjects
Bidirectional pumping; Collimation lens; Coupling efficiency; Coupling light; Diffraction loss; Diode pumped lasers; Double clad fiber laser; Double clad fibers; Fiber length; Fine tuning; Gain distribution; Gain fibers; Grating couplers; Grating pitch; Groove width; Laser diode arrays; Metal parts; Side coupling; Side pumping; Side-pumped; Signal output; Slope efficiencies; Slow-axis; Sub-wave length grating; Ytterbium-doped; Diffraction gratings; Diffractive optics; Efficiency; Fiber lasers; Laser Doppler velocimeters; Light absorption; Pumps; Silica; Ytterbium; Electron beam pumping
Type
journal article