We demonstrate direct diode-bar side pumping of a Yb-doped fiber laser using embedded-mirror side pumping (EMSP).
In this method, the pump beam is launched by reflection from a micro-mirror embedded in a channel polished into the
inner cladding of a double-clad fiber (DCF). The amplifier employed an unformatted, non-lensed, ten-emitter diode bar
(20 W) and glass-clad, polarization-maintaining, large-mode-area fiber. Measurements with passive fiber showed that
the coupling efficiency of the raw diode-bar output into the DCF (ten launch sites) was ~84%; for comparison, the net
coupling efficiency using a conventional, formatted, fiber-coupled diode bar is typically 50-70%, i.e., EMSP results in a
factor of 2-3 less wasted pump power. The slope efficiency of the side-pumped fiber laser was ~80% with respect to
launched pump power and 24% with respect to electrical power consumption of the diode bar; at a fiber-laser output
power of 7.5 W, the EMSP diode bar consumed 41 W of electrical power (18% electrical-to-optical efficiency). When
end pumped using a formatted diode bar, the fiber laser consumed 96 W at 7.5 W output power, a factor of 2.3 less
efficient, and the electrical-to-optical slope efficiency was lower by a factor of 2.0. Passive-fiber measurements showed
that the EMSP alignment sensitivity is nearly identical for a single emitter as for the ten-emitter bar. EMSP is the only
method capable of directly launching the unformatted output of a diode bar directly into DCF (including glass-clad
DCF), enabling fabrication of low-cost, simple, and compact, diode-bar-pumped fiber lasers and amplifiers.