A highly-compact optical amplifier for densely-integrated communications systems

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We propose to develop a new very-small-form-factor (VSFF) optical amplifier on a chip. Current VSFF amplifiers are limited to semiconductor optical amplifiers (SOAs), which use costly materials and are hampered by high noise and nonlinearities which induce signal crosstalk. The leading alternative technology, erbium-doped fiber amplifiers (EDFAs) offer low noise and high gain for high performance in optical systems. However, the silica optical fiber used to build such amplifiers is on the order of meters long and cannot be bent too tightly when wrapped up, thereby imposing a limit on the overall size of the device. A potential alternative is the erbium-doped waveguide amplifier (EDWA), in which an erbium-doped waveguide is fabricated on a low-cost silicon substrate, allowing for large-scale production and orders of magnitude reduction in size because of the use of thin film materials with high refractive index and which allow for higher erbium dopant concentrations than silica. We have recently improved EDWAs using a novel platform based on hybrid erbium-doped tellurite glass and silicon nitride waveguides. Our platform removes past challenges with EDWAs which have prevented their commercialization, including reproducible fabrication methods using well-established silicon nitride technology, and high gain in a compact form factor enabled by the high refractive index doped tellurite glass. We have demonstrated optical gain of up to 5 dB using this platform, showing its viability. The remaining challenges to be addressed in this project include a) demonstrating higher optical gain of up to 20 dB in longer spiral waveguides; b) reducing the fiber-chip coupling loss to < 1 dB for optical pump and signal light to improve efficiency and noise performance; c) demonstrating a packaged component with optical pump and signal multiplexing on the same chip and input and output ports in a compact form factor. Such compact EDWAs will have wide-ranging applications in optical communications networks, data centers, high-performance computing, AI, space communications, and detection and ranging in self-driving vehicles.