Transparent and Efficient Wavelength Conversion with Interferometric Pump Recycling

ABSTRACT Expanding wavelength bands is crucial for telecommunications and other photonic areas. Wavelength conversion via optical nonlinear processes provides a versatile approach to generating and modulating light waves in new bands. To increase the nonlinear efficiency, resonators are commonly used, however, the wavelength transparency is constrained due to resonance filtering. In this study, we stress the trade‐off between the wavelength transparency and efficiency by harnessing the unique interferometric property of a linearly decoupled Mach‐Zehnder Interferometer (MZI). By integrating the MZI with a high‐quality microresonator, pump recycling for nonlinear enhancement and non‐resonant transmission for wavelength transparency are realized simultaneously. We experimentally demonstrate a 14 dB conversion efficiency enhancement over equivalent‐length waveguides and transparent wavelength conversion covering 110 nm bandwidth. Finally, wavelength conversion of a 20 Gbit/s optical data stream with open eye diagrams is demonstrated, with a clear waveform confirmed from C‐band to L‐band conversion, showcasing its potential for wavelength band expansion. This research paves the way for efficient and flexible wavelength converters, broadband parametric amplifiers, and regenerators essential for advanced optical networks. The ability to manipulate light in new wavelength bands without resonance constraints may also benefit sensing, imaging, and quantum technologies.