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Atomic-referenced Hz-linewidth lasers via fiber interferometric stabilization
Authors:
Changmin Ahn,
Hansol Jeong,
Seoyeon Yang,
Junyong Choi,
Igju Jeon,
Hanseb Moon,
Jungwon Kim
Abstract:
Narrow-linewidth lasers with absolute frequency anchoring are essential for precision metrology, coherent sensing, and emerging quantum technologies beyond laboratory environments. Optical cavities and interferometers provide exceptional short-term spectral purity but lack intrinsic absolute frequency references. Atomic transitions, in contrast, provide stable frequency anchors but offer limited d…
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Narrow-linewidth lasers with absolute frequency anchoring are essential for precision metrology, coherent sensing, and emerging quantum technologies beyond laboratory environments. Optical cavities and interferometers provide exceptional short-term spectral purity but lack intrinsic absolute frequency references. Atomic transitions, in contrast, provide stable frequency anchors but offer limited discrimination sensitivity. Recent hybrid approaches have demonstrated the combination of compact optical resonators with atomic references, yet achieving the Hz-level regime remains challenging. Here, we present a hybrid architecture that enables simultaneous realization of Hz-level linewidth and atomic-referenced frequency stability. An external-cavity diode laser is first stabilized to a fiber interferometer to achieve Hz-level spectral purity, while the interferometer is subsequently anchored to an 87Rb D2 transition via modulation transfer spectroscopy to suppress long-term drift and define the laser frequency relative to the atomic transition. This dual-stabilization scheme realizes a compact atomic-referenced laser with a 3.4-Hz linewidth (1-rad integrated-phase method), a minimum fractional frequency stability of 3.4x10-14 at 0.56 s, and 9x10-13 at 100 s. This architecture establishes a practical and scalable route toward compact and field-deployable atomic-referenced narrow-linewidth lasers for precision metrology and quantum technologies.
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Submitted 25 May, 2026;
originally announced May 2026.
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Scalable Liquid-Crystal Integrated Silicon Nitride Photonic Circuits for Reconfigurable Quantum Interference
Authors:
Chunghyun Ahn,
Yongjin Hwang,
Sangbaek Lee,
Jinil Lee,
Hyunjin Ko,
Sunghyun Moon,
Hojoong Jung,
Hyun-Yong Yu,
Se-Um Kim,
Hyounghan Kwon
Abstract:
Integrated quantum photonics requires compact, efficient, and low-power phase modulators. While silicon nitride (SiN) is a promising platform, existing modulators suffer from high power consumption, thermal crosstalk, or high driving voltages. Liquid crystal (LC) offers a compelling alternative because of the large index changes and industrial maturity. However, their suitability for supporting va…
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Integrated quantum photonics requires compact, efficient, and low-power phase modulators. While silicon nitride (SiN) is a promising platform, existing modulators suffer from high power consumption, thermal crosstalk, or high driving voltages. Liquid crystal (LC) offers a compelling alternative because of the large index changes and industrial maturity. However, their suitability for supporting various applications in the photonic quantum system has not been experimentally confirmed.Here, we report the first experimental demonstration that LC-based phase modulators integrated on a SiN platform show highly visible quantum interference. We fabricated a liquid-crystal integrated Mach-Zehnder interferometer (LC-MZI) that achieved CMOS-compatible performance with V_pi * L < 1 V-mm. In two-photon interference experiments, the devices exhibited high-visibility quantum interference (~98.5%) with voltage-tunable phase control. Furthermore, we validated the scalability of our approach by demonstrating wafer-scale fabrication using stepper lithography. This work establishes LC-integrated SiN photonics as a scalable, reconfigurable, and energy-efficient platform for quantum photonic circuits.
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Submitted 8 May, 2026;
originally announced May 2026.
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Optical frequency comb integration in radio telescopes: advancing signal generation and phase calibration
Authors:
Minji Hyun,
Changmin Ahn,
Junyong Choi,
Jihoon Baek,
Woosong Jeong,
Do-Heung Je,
Do-Young Byun,
Jan Wagner,
Myoung-Sun Heo,
Taehyun Jung,
Jungwon Kim
Abstract:
Very long baseline interferometry (VLBI) enables high-angular-resolution observations in astronomy and geodesy by synthesizing a virtual telescope with baselines spanning hundreds to thousands of kilometres. Achieving high instrumental phase stability in VLBI relies on the generation of high-quality, atomic-referenced RF local oscillator (LO) and RF-comb signals for the effective downconversion of…
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Very long baseline interferometry (VLBI) enables high-angular-resolution observations in astronomy and geodesy by synthesizing a virtual telescope with baselines spanning hundreds to thousands of kilometres. Achieving high instrumental phase stability in VLBI relies on the generation of high-quality, atomic-referenced RF local oscillator (LO) and RF-comb signals for the effective downconversion of celestial RF signals and precise phase calibration, respectively. As observing frequencies move into higher ranges with wider bandwidth, conventional electronic methods face significant challenges in maintaining the quality of these signals. Here, we demonstrate that an optical frequency comb (OFC) can be used as a versatile tool to generate and distribute low-noise and atomic-referenced RF-comb and RF-LO signals in the VLBI telescope. Hydrogen maser-stabilized optical pulses are transmitted over a timing-stabilized fibre link from the observatory building to the VLBI receiver system at the telescope, where photodetection converts them into the required RF-comb and RF-LO signals. In VLBI test observation, we successfully detected VLBI fringes and extracted the RF-combs characteristics in a format suitable for VLBI instrumental phase calibration. These results highlight the high potential of OFC-based technology for enhancing next-generation broadband VLBI measurements, advancing astrophysical research and facilitating intercontinental clock comparison.
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Submitted 9 January, 2025;
originally announced January 2025.
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10$^{-15}$-level laser stabilization down to fiber thermal noise limit using self-homodyne detection
Authors:
Igju Jeon,
Woosong Jeong,
Changmin Ahn,
Jungwon Kim
Abstract:
We demonstrate a self-homodyne detection method to stabilize a continuous-wave 1550-nm laser to a 1-km optical fiber delay line, achieving a frequency instability of 6.3x10<sup>-15</sup> at a 16-ms averaging time. This result, limited by fiber thermal noise, is achieved without the need for a vacuum system, highlighting the potential of our approach for ultra-stable laser systems in non-laboratory…
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We demonstrate a self-homodyne detection method to stabilize a continuous-wave 1550-nm laser to a 1-km optical fiber delay line, achieving a frequency instability of 6.3x10<sup>-15</sup> at a 16-ms averaging time. This result, limited by fiber thermal noise, is achieved without the need for a vacuum system, highlighting the potential of our approach for ultra-stable laser systems in non-laboratory environments. The system utilizes only a few passive fiber optic components and a single balanced photodetector, significantly simplifying the laser stabilization process while maintaining high performance. The entire optical setup is compactly packaged in a portable metal air-tight case.
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Submitted 7 February, 2025; v1 submitted 6 September, 2024;
originally announced September 2024.
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Palm-sized, vibration-insensitive and vacuum-free all-fiber-photonic module for 10-14-level stabilization of CW lasers and frequency combs
Authors:
Igju Jeon,
Changmin Ahn,
Chankyu Kim,
Seongmin Park,
Wonju Jeon,
Lingze Duan,
Jungwon Kim
Abstract:
Compact and robust frequency-stabilized laser sources are critical for a variety of fields that require stable frequency standards, including field spectroscopy, radio astronomy, microwave generation, and geophysical monitoring. In this work, we applied a simple and compact fiber ring-resonator configuration that can stabilize both a continuous-wave laser and a self-referenced optical frequency co…
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Compact and robust frequency-stabilized laser sources are critical for a variety of fields that require stable frequency standards, including field spectroscopy, radio astronomy, microwave generation, and geophysical monitoring. In this work, we applied a simple and compact fiber ring-resonator configuration that can stabilize both a continuous-wave laser and a self-referenced optical frequency comb to a vibration-insensitive optical fiber delay-line. We could achieve a thermal-noise-limited frequency noise level in the 10 Hz - 1 kHz offset frequency range for both the continuous-wave laser and the optical frequency comb with the minimal frequency instability of 2.7x10-14 at 0.03-s and 2.6x10-14 at 0.01-s averaging time, respectively, in non-vacuum condition. The optical fiber spool, working as a delay reference, is designed to be insensitive to external vibration, with a vibration sensitivity of sub-10-10 [1/g] and volume of 32 mL. Finally, the ring-resonator setup is packaged in a palm-sized aluminum case with 171-mL volume with a vibration-insensitive spool, as well as an even smaller 97-mL-volume case with an ultra-compact 9-mL miniaturized fiber spool.
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Submitted 24 November, 2023;
originally announced November 2023.
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Imaging through random media using coherent averaging
Authors:
Byungjae Hwang,
Taeseong Woo,
Cheolwoo Ahn,
Jung-Hoon Park
Abstract:
We propose and demonstrate a new phase retrieval method for imaging through random media. Although methods to recover the Fourier amplitude through random distortions are well established, recovery of the Fourier phase has been a more difficult problem and is still a very active research area. Here, we show that by simply ensemble averaging shift-corrected images, the Fourier phase of an object ob…
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We propose and demonstrate a new phase retrieval method for imaging through random media. Although methods to recover the Fourier amplitude through random distortions are well established, recovery of the Fourier phase has been a more difficult problem and is still a very active research area. Here, we show that by simply ensemble averaging shift-corrected images, the Fourier phase of an object obscured by random distortions can be accurately retrieved up to the diffraction limit. The method is simple, fast, does not have any optimization parameters, and does not require prior knowledge or assumptions about the sample. We demonstrate the feasibility and robustness of our method by realizing all computational diffraction-limited imaging through atmospheric turbulence as well as imaging through multiple scattering media.
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Submitted 12 May, 2021;
originally announced May 2021.
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Highly ordered lead-free double perovskite halides by design
Authors:
Chang Won Ahn,
Jae Hun Jo,
Jong Chan Kim,
Hamid Ullah,
Sangkyun Ryu,
Younghun Hwang,
Jin San Choi,
Jongmin Lee,
Sanghan Lee,
Hyoungjeen Jeen,
Young-Han Shin,
Hu Young Jeong,
Ill Won Kim,
Tae Heon Kim
Abstract:
Lead-free double perovskite halides are emerging optoelectronic materials that are alternatives to lead-based perovskite halides. Recently, single-crystalline double perovskite halides were synthesized, and their intriguing functional properties were demonstrated. Despite such pioneering works, lead-free double perovskite halides with better crystallinity are still in demand for applications to no…
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Lead-free double perovskite halides are emerging optoelectronic materials that are alternatives to lead-based perovskite halides. Recently, single-crystalline double perovskite halides were synthesized, and their intriguing functional properties were demonstrated. Despite such pioneering works, lead-free double perovskite halides with better crystallinity are still in demand for applications to novel optoelectronic devices. Here, we realized highly crystalline Cs2AgBiBr6 single crystals with a well-defined atomic ordering on the microscopic scale. We avoided the formation of Ag vacancies and the subsequent secondary Cs3Bi2Br9 by manipulating the initial chemical environments in hydrothermal synthesis. The suppression of Ag vacancies allows us to reduce the trap density in the as-grown crystals and to enhance the carrier mobility further. Our design strategy is applicable for fabricating other lead-free halide materials with high crystallinity.
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Submitted 29 June, 2020;
originally announced June 2020.
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Electromagnetic Characteristics of a Superconducting Magnet for 28GHz ECR Ion Source according to the Series Resistance of a Protection Circuit
Authors:
Hongseok Lee,
Young Kyu Mo,
Onyou Lee,
Junil Kim,
Seungmin Bang,
Jong O Kang,
Jonggi Hong,
Seokho Nam,
Sukjin Choi,
In Seok Hong,
Min Chul Ahn,
Hyoungku Kang
Abstract:
A linear accelerator, called RAON, has been being developed as a part of Rare Isotope Science Project (RISP) by Institute for Basic Science (IBS) [1]. The linear accelerator utilizes an electron cyclotron resonance (ECR) ion source for providing intense highly charged ion beams to the linear accelerator. 28GHz ECR ion source can extract heavy ion beams from proton to uranium. A superconducting mag…
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A linear accelerator, called RAON, has been being developed as a part of Rare Isotope Science Project (RISP) by Institute for Basic Science (IBS) [1]. The linear accelerator utilizes an electron cyclotron resonance (ECR) ion source for providing intense highly charged ion beams to the linear accelerator. 28GHz ECR ion source can extract heavy ion beams from proton to uranium. A superconducting magnet system for 28GHz ECR ion source is composed of hexapole coils and four solenoid coils made with low Tc superconducting wires of NbTi [2]. The electromagnetic force acts on the superconducting magnets due to the magnetic field and flowing current in case of not only normal state but also quench state [3]. In case of quench on hexapole coils, unbalanced flowing current among the hexapole coils is generated and it causes unbalanced electromagnetic force. Coil motions and coil strains in quench state are larger than those in normal state due to unbalanced electromagnetic force among hexapole coils. Therefore, analysis on electromagnetic characteristics of superconducting magnet for 28GHz ECR ion source according to the series resistance of protection circuit in case of quench should be conducted. In this paper, analysis on electromagnetic characteristics of superconducting hexapole coils for 28GHz ECR ion source according to the series resistance of protection circuit in case of quench is performed by using finite elements method (FEM) simulation.
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Submitted 11 August, 2015;
originally announced August 2015.
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Active silicon integrated nanophotonics: ferroelectric BaTiO3 devices
Authors:
Chi Xiong,
Wolfram H. P. Pernice,
Joseph H. Ngai,
James W. Reiner,
Divine Kumah,
Frederick J. Walker,
Charles H. Ahn,
Hong X. Tang
Abstract:
The integration of complex oxides on silicon presents opportunities to extend and enhance silicon technology with novel electronic, magnetic, and photonic properties. Among these materials, barium titanate (BaTiO3) is a particularly strong ferroelectric perovskite oxide with attractive dielectric and electro-optic properties. Here we demonstrate nanophotonic circuits incorporating ferroelectric Ba…
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The integration of complex oxides on silicon presents opportunities to extend and enhance silicon technology with novel electronic, magnetic, and photonic properties. Among these materials, barium titanate (BaTiO3) is a particularly strong ferroelectric perovskite oxide with attractive dielectric and electro-optic properties. Here we demonstrate nanophotonic circuits incorporating ferroelectric BaTiO3 thin films on the ubiquitous silicon-on-insulator (SOI) platform. We grow epitaxial, single-crystalline BaTiO3 directly on SOI and engineer integrated waveguide structures that simultaneously confine light and an RF electric field in the BaTiO3 layer. Using on-chip photonic interferometers, we extract a large effective Pockels coefficient of 213 plus minus 49 pm/V, a value more than six times larger than found in commercial optical modulators based on lithium niobate. The monolithically integrated BaTiO3 optical modulators show modulation bandwidth in the gigahertz regime, which is promising for broadband applications.
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Submitted 4 February, 2014; v1 submitted 16 January, 2014;
originally announced January 2014.
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Thermal emissions and climate change: Cooler options for future energy technology
Authors:
Nick E. B. Cowern,
Chihak Ahn
Abstract:
Global warming arises from 'temperature forcing', a net imbalance between energy fluxes entering and leaving the climate system and arising within it. Humanity introduces temperature forcing through greenhouse gas emissions, agriculture, and thermal emissions from fuel burning. Up to now climate projections, neglecting thermal emissions, typically foresee maximum forcing around the year 2050, fo…
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Global warming arises from 'temperature forcing', a net imbalance between energy fluxes entering and leaving the climate system and arising within it. Humanity introduces temperature forcing through greenhouse gas emissions, agriculture, and thermal emissions from fuel burning. Up to now climate projections, neglecting thermal emissions, typically foresee maximum forcing around the year 2050, followed by a decline. In this paper we show that, if humanity's energy use grows at 1%/year, slower than in recent history, and if thermal emissions are not controlled through novel energy technology, temperature forcing will increase indefinitely unless combated by geoengineering. Alternatively, and more elegantly, humanity may use renewable sources such as wind, wave, tidal, ocean thermal, and solar energy that exploit energy flows already present in the climate system, or act as effective sinks for thermal energy.
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Submitted 12 December, 2008; v1 submitted 4 November, 2008;
originally announced November 2008.
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Photonic quantum-corral ring laser: A fermionic phase transition
Authors:
O'Dae Kwon,
B. H. Park,
J. Y. Kim,
J. Bae,
M. J. Kim,
J. C. Ahn,
O. H. Kwon
Abstract:
Extensive Bose-Einstein condensation research activities have recently led to studies of fermionic atoms and optical confinements. Here we present a case of micro-optical fermionic electron phase transition. Optically confined ordering and phase transitions of a fermionic cloud in dynamic steady state are associated with Rayleigh emissions from photonic quantum ring manifold which are generated…
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Extensive Bose-Einstein condensation research activities have recently led to studies of fermionic atoms and optical confinements. Here we present a case of micro-optical fermionic electron phase transition. Optically confined ordering and phase transitions of a fermionic cloud in dynamic steady state are associated with Rayleigh emissions from photonic quantum ring manifold which are generated by nature without any ring lithography. The whispering gallery modes, produced in a semiconductor Rayleigh-Fabry-Perot toroidal cavity at room temperature, exhibit novel properties of ultralow thresholds open to nano-ampere regime, thermal stabilities from square-root-T-dependent spectral shift, and angularly varying intermode spacings. The photonic quantum ring phenomena are associated with a photonic field-driven phase transition of quantum-well-to-quantum-wire and hence the photonic (non-de Broglie) quantum corral effect on the Rayleigh cavity-confined carriers in dynamic steady state. Based upon the intra-cavity fermionic condensation we also offer a prospect for an electrically driven few-quantum dot single photon source from the photonic quantum ring laser for quantum information processors.
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Submitted 18 April, 2002;
originally announced April 2002.
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Photonic quantum ring laser
Authors:
J. C. Ahn,
K. S. Kwak,
B. H. Park,
H. Y. Kang,
J. Y. Kim,
O'Dae Kwon
Abstract:
We report a quantum ring-like toroidal cavity naturally formed in a vertical-cavity-like active microdisk plane due to Rayleigh's band of whispering gallery modes. The $\sqrt{T}$-dependent redshift and a square-law property of microampere-range threshold currents down to 2 $μ$A are consistent with a photonic quantum wire view, due to whispering gallery mode-induced dimensional reduction.
We report a quantum ring-like toroidal cavity naturally formed in a vertical-cavity-like active microdisk plane due to Rayleigh's band of whispering gallery modes. The $\sqrt{T}$-dependent redshift and a square-law property of microampere-range threshold currents down to 2 $μ$A are consistent with a photonic quantum wire view, due to whispering gallery mode-induced dimensional reduction.
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Submitted 20 December, 1998; v1 submitted 28 November, 1998;
originally announced November 1998.