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Ultrabroadband Passive Laser Noise Suppression to Quantum Noise Limit via on-chip Second Harmonic Generation

Amir H. Safavi‐Naeini, Geun Ho Ahn, Ziyu Wang, Devin J. Dean, Hubert S. Stokowski, Tae‐Won Park, M. M. Fejer, Jonathan Simon

Published Mar 25, 2026• 0 citations
Publisher

Abstract

Abstract Laser intensity noise limits performance in quantum sensing, metrology, and computing. Existing stabilization methods face a trade-off between bandwidth and complexity: electronic feedback loops are speed-limited, while optical resonators are constrained by narrow linewidths and locking requirements. Here, we demonstrate an all-optical "noise eater" that passively suppresses intensity fluctuations from DC to > 10 gigahertz. By leveraging high-efficiency second-harmonic generation in nanophotonic lithium niobate waveguides, we operate at a pump-depletion stationary point where input fluctuations are decoupled from the output to first order. This passive and nonresonant nanophotonic device suppresses relative intensity noise by 25 to 60 dB over the full measurement bandwidth and stabilizes a noisy fiber amplifier output to the shot-noise limit. Our results establish a scalable, wide-bandwidth paradigm for laser stabilization essential for high-throughput quantum technologies and deployable photonic sensing systems.

DOI
10.21203/rs.3.rs-8727813/v1

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Abstract Laser intensity noise limits performance in quantum sensing, metrology, and computing. Existing stabilization methods face a trade-off between bandwidth and complexity: electronic feedback loops are speed-limited, while optical resonators are constrained by narrow linewidths and locking requirements. Here, we demonstrate an all-optical "noise eater" that passively suppresses intensity fluctuations from DC to > 10 gigahertz. By leveraging high-efficiency second-harmonic generation in nanophotonic lithium niobate waveguides, we operate at a pump-depletion stationary point where input fluctuations are decoupled from the output to first order. This passive and nonresonant nanophotonic device suppresses relative intensity noise by 25 to 60 dB over the full measurement bandwidth and stabilizes a noisy fiber amplifier output to the shot-noise limit. Our results establish a scalable, wide-bandwidth paradigm for laser stabilization essential for high-throughput quantum technologies and deployable photonic sensing systems.
Laser intensity noise limits performance in quantum sensing, metrology, and computing. Existing stabilization methods face a trade-off between bandwidth and complexity: electronic feedback loops are speed-limited, while optical resonators are constrained by narrow linewidths and locking requirements. Here, we demonstrate an all-optical "noise eater" that passively suppresses intensity fluctuations from DC to >10 gigahertz. By leveraging high-efficiency second-harmonic generation in nanophotonic lithium niobate waveguides, we operate at a pump-depletion stationary point where input fluctuations are decoupled from the output to first order. This passive and nonresonant nanophotonic device suppresses relative intensity noise by 25 to 60 dB over the full measurement bandwidth and stabilizes a noisy fiber amplifier output to the shot-noise limit. Our results establish a scalable, wide-bandwidth paradigm for laser stabilization essential for high-throughput quantum technologies and deployable photonic sensing systems.
Abstract Optical amplifiers are fundamental to modern photonics, enabling long-distance communications, precision sensing, and quantum information processing. Erbium-doped amplifiers dominate telecommunications but are restricted to specific wavelength bands, while semiconductor amplifiers offer broader coverage but suffer from high noise and nonlinear distortions. Optical parametric amplifiers (OPAs) promise broadband, quantum-limited amplification across arbitrary wavelengths. However, their miniaturization and deployment has been hampered by watt-level power requirements. Here we demonstrate an integrated OPA on thin-film lithium niobate that achieves > 17 dB gain with < 200 mW input power -- an order of magnitude improvement over previous demonstrations. Our second-harmonic-resonant design enhances both pump generation efficiency (95% conversion) and pump power utilization through recirculation, without sacrificing bandwidth. The resonant architecture increases the effective pump power by nearly an order of magnitude compared to conventional single-pass designs, while also multiplexing the signal and pump. We demonstrate flat near-quantum-limited noise performance over 110 nm. Our low-power architecture enables practical on-chip OPAs for next generation quantum and classical photonics.
Pump power fluctuations are a critical factor in limiting the long-term stability of quantum sensing light sources. However, existing laser power stabilization techniques fail to efficiently address power fluctuations caused by downstream beam-pointing noise coupling. Here, we propose an optimized suppression scheme of pump power fluctuations that integrates a passive second harmonic process and active feedback control, achieving multiple noise suppression of both pointing and intensity noise in the pump field. Within the measurement time of 8.5 hours, we achieve a quantum sensing light source with a squeezing factor of 10.0 dB and its fluctuations below 0.4 dB. The proposed approach effectively boosts the long-term stability of the quantum squeezing source, thus paving a solid way for expanding the utilization of squeezing sources within the realm of quantum precision measurement.
An extremely conspicuous passive power noise stabilization is the first, to the best of our knowledge, discovered in a cavity-enhanced second-harmonic generation (SHG) process. Differing from the SHG as a buffer reservoir, the stronger strength of the nonlinear interaction pushes the power noise suppression level to a higher value and exhibits a broadband noise reduction performance due to the mechanism of dynamic pump suppression in the SHG process. The noise is suppressed to near shot noise limit (SNL) among the kHz to MHz frequency range, accompanied by a maximum noise reduction of 35 dB. A comprehensive demonstration indicates that the nonlinear interaction has no function on the phase noise of fundamental and harmonic waves. A theoretical model is also established that is consistent well with the experimental results. The methodology is beneficial to multiple optical metrology experiments.
High-stability single-frequency fiber lasers typically exhibit relative intensity noise that is far in excess of shot noise across a broad frequency range extending from dc to many tens of megahertz. This excess noise precludes the use of these fiber lasers in a range of precision interferometry and quantum optics applications. We present experimental results using a passive, highQ, fiber ring resonator to filter out up to 26 dB of excess laser intensity noise, resulting in a stabilized laser output that reaches the shot-noise limit over most of its signal spectrum.
The generation and application of squeezed light have long been central goals of quantum optics, enabling sensing below the standard quantum limit, optical quantum computing platforms, and more. Intensity noise squeezing of bright (coherent) states, in contrast to squeezed vacuum, is relatively underdeveloped. Bright squeezing has been generated directly through nonlinear optical processes or ``quietly pumped'' semiconductor lasers. However, these methods suffer from weak squeezing limits, narrow operating wavelength ranges, and have not been explored at large bandwidths. Here, we show how semiconductor lasers with sharp intensity-dependent dissipation can support highly broadband intensity noise squeezing from infrared (IR) to terahertz (THz) wavelengths, the latter of which has remained unexplored in quantum noise studies. Our protocol realizes strongly (>10>10>10 dB) intensity noise-squeezed intracavity quantum states, which could create a new regime for cavity quantum electrodynamics experiments, as well as strong output squeezing surpassing gigahertz bandwidths. Furthermore, we show how the same systems also create self-pulsing and bistable mean field behavior, enabling control of light in both the temporal and noise domains. The existence of these multiple functionalities in both the classical and quantum mechanical domains in a single semiconductor laser platform, from IR to THz wavelengths, could enable advances in on-chip quantum optical communication, computing, and sensing across the electromagnetic spectrum.