Towards integrated photonic interposers for processing octave-spanning microresonator frequency combs

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.

Surpassing the nonlinear conversion efficiency of soliton microcombs

“…The DKS conversion efficiency scales inversely with the number of lines generated 16 , leading to a fundamental trade-off between the spectral density and power per line. The low conversion efficiency places stronger requirements in the performance of on-chip lasers, interposers and frequency doublers for realizing self-referencing 18 —a key ingredient in modern frequency synthesis and metrology. Improving the conversion efficiency is instrumental to leveraging advances in photonic integration 19 – 21 and realizing fully integrated microcomb-based systems on-chip.…”

Perspective on Lithium-Niobate-on-Insulator Photonics Utilizing the Electro-optic and Acousto-optic Effects

“…46 Frequency Combs. Deep EO modulation also enables the frequency combs, which have many applications in frequency metrology, 47 microwave photonics, 48 optical clocks, 49 and precision navigation, 50 etc. Unlike the Kerr comb using χ (3) , the EO comb utilizes χ (2) to generate new frequency lines.…”

2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments

“…The microcomb source, which is generated by dissipative Kerr solitons in a laser-driven integrated microresonator [251], provides an excellent LO for an integrated spectrometer (for bright objects), as it delivers a series of comb lines with a precise and fixed FSR. Innovations such as battery-operated integrated comb generators [252], octave-spanning microcombs [57,253], and frequency stabilization [215,254] have recently been demonstrated experimentally.…”