Abstract
Microcombs—optical frequency combs generated in microresonators—have advanced tremendously in the past decade, and are advantageous for applications in frequency metrology, navigation, spectroscopy, telecommunications, and microwave photonics. Crucially, microcombs promise fully integrated miniaturized optical systems with unprecedented reductions in cost, size, weight, and power. However, the use of bulk free-space and fiber-optic components to process microcombs has restricted form factors to the table-top. Taking microcomb-based optical frequency synthesis around 1550 nm as our target application, here, we address this challenge by proposing an integrated photonics interposer architecture to replace discrete components by collecting, routing, and interfacing octave-wide microcomb-based optical signals between photonic chiplets and heterogeneously integrated devices. Experimentally, we confirm the requisite performance of the individual passive elements of the proposed interposer—octave-wide dichroics, multimode interferometers, and tunable ring filters, and implement the octave-spanning spectral filtering of a microcomb, central to the interposer, using silicon nitride photonics. Moreover, we show that the thick silicon nitride needed for bright dissipative Kerr soliton generation can be integrated with the comparatively thin silicon nitride interposer layer through octave-bandwidth adiabatic evanescent coupling, indicating a path towards future system-level consolidation. Finally, we numerically confirm the feasibility of operating the proposed interposer synthesizer as a fully assembled system. Our interposer architecture addresses the immediate need for on-chip microcomb processing to successfully miniaturize microcomb systems and can be readily adapted to other metrology-grade applications based on optical atomic clocks and high-precision navigation and spectroscopy.
Highlights
Optical microcombs, generated in micro and nanophotonic resonators, have substantially broadened the reach of applications of optical frequency combs[1]
The convergence of nanophotonic resonators with scalable integrated photonics inherently supports the promise of creating integrated microcomb-based systems, with immediate applications in optical frequency synthesis[10,11,12], optical atomic clocks[13,14], optical distance ranging[15,16,17], optical spectroscopy[18,19,20], microwave and radiofrequency photonics[21,22,23], astronomy[24,25], and telecommunications[26,27,28]
We experimentally demonstrate the constituent passive elements of the proposed interposer, i.e., octave-wide dichroic couplers, resonant filters, and multimode interferometers (MMIs), and confirm that their performance agrees with our electromagnetic simulations via short-loop tests
Summary
Optical microcombs, generated in micro and nanophotonic resonators, have substantially broadened the reach of applications of optical frequency combs[1]. Filter, route, and interface light between many such active and passive devices are essential to realize the improvements in cost, size, weight, and power, performance, and scalability, offered by microcombs and integrated photonics, and will promote further system-level innovation using frequency combs. Such interposers need to integrate multiple broadband high-performance photonic elements, manage octave-wide light, and maintain modal and polarization purity in a low-loss and high damage threshold photonics platform while pragmatically balancing heterogeneous integration and chip-to-chip coupling on a system-level architecture
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