High-Power 1.06- $\mu{\hbox {m}}$ Near-Diffraction-Limited Planar Tapered Amplifier Injected With Seed Light Through a Fiber Biconical Microlens

We designed a 1.06-mum single-quantum-well (SQW) InGaAs/AlGaAs planar tapered amplifier that was injected with seed light of a fiber Bragg grating stabilized laser diode through a fiber biconical microlens. To increase the amplifier output, the microlens with approximately 3- and 11-mum radii on vertical and horizontal axes, respectively, provides high coupling efficiency between the laser diode and the amplifier. The microlens also controls propagation in the tapered gain area to suppress the filament formation. In addition, the small radii of the microlens reduce near-end reflection at the amplifier input to prevent parasitic laser oscillation of the amplifier. We demonstrated near-diffraction-limited output of 5.5 W with the beam quality factor M² of 1.5 by using a 3-mm-long amplifier having an optical confinement factor of 1.2%.