Junqiu Liu

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Architecture for integrated RF photonic downconversion of electronic signals

Tobias Kippenberg, Junqiu Liu

Electronic analog to digital converters (ADCs) are run-ning up against the well-known bit depth versus bandwidth trade off. Towards this end, radio frequency (RF) photonic-enhanced ADCs have been the subject of interest for some time. Optical frequency comb technology has been used as a workhorse underlying many of these architectures. Unfor-tunately, such designs must generally grapple with size, weight, and power (SWaP) concerns, as well as frequency ambiguity issues which threaten to obscure critical spec-tral information of detected RF signals. In this work, we address these concerns via an RF photonic downconverter with potential for easy integration and field deployment by leveraging a novel, to the best of our knowledge, hybrid microcomb/electro-optic comb design.(c) 2022 Optica Pub-lishing Group

Optica Publishing Group2023

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Biphoton frequency combs (BFCs) are promising quantum sources for large-scale and high-dimensional quantum information and networking systems. In this context, the spectral purity of individual frequency bins will be critical for realizing quantum networking protocols like teleportation and entanglement swap-ping. Measurement of the temporal autocorrelation function of the unheralded signal or idler photons comprising the BFC is a key tool for characterizing their spectral purity and in turn verifying the utility of the biphoton state for networking protocols. Yet the experimentally obtainable precision for measur-ing BFC correlation functions is often severely limited by detector jitter. The fine temporal features in the correlation function-not only of practical value in quantum information, but also of fundamen-tal interest in the study of quantum optics-are lost as a result. We propose a scheme to circumvent this challenge through electro-optic phase modulation, experimentally demonstrating time-resolved Han -bury Brown-Twiss characterization of BFCs generated from an integrated 40.5-GHz Si3N4 microring, up to a 3 x 3-dimensional two-qutrit Hilbert space. Through slight detuning of the electro-optic drive frequency from the comb's free spectral range, our approach leverages Vernier principles to magnify tem-poral features, which would otherwise be averaged out by detector jitter. We demonstrate our approach under both continuous-wave and pulsed-pumping regimes, finding excellent agreement with theory. Our method reveals not only the collective statistics of the contributing frequency bins but also their temporal shapes-features lost in standard fully integrated autocorrelation measurements.

AMER PHYSICAL SOC2023

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A photonic integrated circuit-based erbium-doped amplifier

Jijun He, Xinru Ji, Tobias Kippenberg, Junqiu Liu, Yang Liu, Anton Lukashchuk, Zheru Qiu, Rui Ning Wang

Erbium-doped fiber amplifiers revolutionized long-haul optical communications and laser technology. Erbium ions could provide a basis for efficient optical amplification in photonic integrated circuits but their use remains impractical as a result of insufficient output power. We demonstrate a photonic integrated circuit-based erbium amplifier reaching 145 milliwatts of output power and more than 30 decibels of smallsignal gain-on par with commercial fiber amplifiers and surpassing state-of-the-art III-V heterogeneously integrated semiconductor amplifiers. We apply ion implantation to ultralow-loss silicon nitride (Si3N4) photonic integrated circuits, which are able to increase the soliton microcomb output power by 100 times, achieving power requirements for low-noise photonic microwave generation and wavelength-division multiplexing optical communications. Endowing Si3N4 photonic integrated circuits with gain enables the miniaturization of various fiber-based devices such as high-pulse-energy femtosecond mode-locked lasers.

AMER ASSOC ADVANCEMENT SCIENCE2022

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