A scaling methodology for optically pumped waveguide amplifiers is presented as a function of their core-cladding index contrast. Increasing index contrast results in two crucial advantages: 1) an increase in gain efficiency and 2) a decrease in the areal footprint of a planar structure. Increasing index contrast is observed to have no effect on the output noise figure. A figure of merit summarizing these advantages demonstrates the powerful role of index contrast as an enabler for improving planar amplifier performance. Design rules are presented in the form of performance maps, allowing waveguide designers to optimize amplifier length and footprint. Using the Er-doped waveguide amplifier as a case study, we design an optical amplifier with >3-dB/cm gain within a 300 × 300-µm2 area, powered by a single 1-mW pump source. This work represents a design rule approach for making a scalable microphotonic optical amplifier.
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