Nd-doped waveguide amplifiers for heterogeneous integration in optical backplanes

The optical amplifier performance of Nd3+-doped polymer and amorphous Al2O3 channel waveguides with single-mode and multi-mode behavior around 880 nm is compared. Internal net gain in the wavelength range 865-930 nm is investigated under continuous-wave excitation near 800 nm, for Nd3+ dopant concentrations typically in the range of 0.6- 1.0 × 1020 cm-3. A peak gain of 2.8 dB at 873 nm is obtained in a 1.9-cm-long polymer waveguide at a launched pump power of 25 mW. The small-signal gain measured in a 1-cm-long sample is 2.0 dB/cm. In Al2O3, a peak gain of 1.57 dB/cm in a short and 3.0 dB in a 4.1-cm-long waveguide is obtained at 880 nm. Tapered multi-mode Nd3+-doped amplifiers are embedded into an optical backplane and a maximum 0.21 dB net gain is demonstrated in a structure consisting of an Al2O3:Nd3+ amplifier placed between two passive polymer waveguides on an optical backplane. The gain can be further enhanced by increasing the pump power and improving the waveguide geometry, and the wavelength of amplification can be adjusted by doping other rare-earth ions.