Embedded v-grooves permit efficient side-pumping of double-cladding amplifiers
A novel approach to coupling light into multimode fibers through notch-like v-grooves allows fiber amplifiers to be side-pumped. Unlike end-pumping through pigtailed diode lasers, side-pumping can be performed with inexpensive diode-laser arrays at multiple points along the fiber, leaving unobstructed fiber ends that can be directly spliced to other fibers. A 90° v-groove embedded in the side of the fiber transverse to the optical axis reaches the inner cladding without disturbing the fiber core. Laser output opposite the groove travels across the fiber, undergoes total internal reflection from the angled wall of the v-groove, and can couple into the inner multimode cladding of the fiber with overall efficiencies as high as 96%.
Lew Goldberg of the Naval Research Laboratory (Washington, DC) will describe this technique at OFC later this month in San Jose, CA (paper WA2). Recently, a 100-µm-wide diode-laser array was used to pump a double-cladding erbium/ytterbium fiber amplifier. A 20-µm-deep v-groove was fabricated in the side of a 8.7-m-long fiber, and 760 mW of collimated, focused diode-array output could be coupled into the cladding with an efficiency of 70%.