Fiber-to-fiber gain in Nd-doped aluminium oxide waveguide amplifiers

Fiber-to-fiber gain is demonstrated in waveguide amplifiers fabricated from Al₂O₃:Nd³⁺ films. The Nd-doped aluminium oxide film is deposited using reactive sputtering, resulting in a polycrystalline film with an approximate ion concentration of 2.2 × 10²⁰ ions/cm³. An amplifier with a length of 5.5 cm is optically pumped at 805 nm, following a bi-directional pumping scheme. For an incident signal input power of -14.9 dBm, the amplifier shows an external gain at a signal wavelength of 1064 nm as large as 14.5 dB, limited by the available pump power. Under those conditions, a noise figure of 8.5 dB was measured. These results pave the way towards on-chip amplification for applications including biomedical imaging, spectroscopy, atmospheric LiDAR, and quantum technologies.