Conception and realisation of a 1.3 μm grating-based Nd3+-doped optical amplifier

We present the conception and realisation of an optical amplifier for the second telecommunications window, using the 1.3 μm transition of Nd³⁺ ion. A 2 μm thick Nd:LaF₃ active layer is deposited by molecular beam epitaxy over a CaF₂ substrate. Optical pump at 790 nm and signal are injected through end-facets. Parasitic amplified spontaneous emission (ASE) around 1.06 μm is strongly reduced by a periodically etched cap layer (Bragg grating) made of polymerised benzocyclobuten (BCB). This strip structure, realised by an original imprint process, also ensures lateral confinement. The main effects taken into account in our simulation are pump absorption at 790 nm; signal amplification, ASE and excited-state absorption (ESA) at 1.3 μm; parasitic ASE at 860 nm and 1.06 μm. Seven energy levels of the active ion are involved. Simulation of grating bandwidth and rejection efficiency, material characterisation and fabrication process are presented.