Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Advances in chip-scale atomic frequency references at NIST

Svenja A. Knappe, Vishal Shah, Alan S. Brannon, Vladislav P. Gerginov, H. G. Robinson, Zoya B. Popovic, Leo W. Hollberg, John E. Kitching

Published Aug 29, 2007• 9 citations
Publisher

Abstract

Coherent population trapping (CPT) resonances usually exhibit contrasts below 10% when interrogated with frequency modulated lasers. We discuss a relatively simple way to increase the resonance contrast to nearly 100% generating an additional light field through a nonlinear four-wave mixing interaction in the atomic vapor.1 A similar method can also be used to create a beat signal at the CPT resonance frequency that can injection-lock a low-power microwave oscillator at 3.4 GHz directly to the atomic resonance.2 This could lead to chip-scale atomic clocks (CSACs) with improved performance. Furthermore, we introduce a miniature microfabricated saturated absorption spectrometer3 that produces a signal for locking a laser frequency to optical transitions in alkali atoms. The Rb absorption spectra are comparable to signals obtained with standard table-top setups, although the rubidium vapor cell has an interior volume of only 1 mm3 and the volume of the entire spectrometer is around 0.1 cm3.

DOI
10.1117/12.735024

Related papers

Passive atomic frequency standard based on coherent population trapping in ^87Rb using injection-locked lasers

Han Seb Moon, Sang Eon Park, Young‐Ho Park +2 more

We present a microwave frequency standard based on coherent population trapping (CPT) in the 87Rb D1 line. The CPT spectrum is obtained using two Raman lasers with a 6.8 GHz frequency offset by injection locking of a master laser to a slave laser. We have constructed an atomic clock employing a 5 cm long Rb vapor cell confined with 6.67 kPa neon buffer gas at 70 °C. Using this system, we improve the CPT contrast through the elimination of undesired off-resonant fields created by the direct modulation method. We measured the frequency shift of the CPT signal as a function of the temperature of the Rb cell and estimated it to be approximately 1.3 ×10−9/K. The frequency of a 10 MHz crystal oscillator has been stabilized to the CPT spectrum between the two ground states in 87Rb. The relative frequency stability is approximately 2.3×10−12 for an average time of 68 s.

Journal of the Optical Society of America B•Nov 1, 2006•23 citations

Microfabricated Atomic Clocks at NIST

Svenja A. Knappe, Peter D. D. Schwindt, Vladislav P. Gerginov +5 more

This paper presents the latest progress in the development, fabrication, and characterization of microfabricated atomic frequency references at NIST. With volumes below 10 mm3 the physics packages contain the complete integrated assembly for probing the ground-state hyperfine splitting frequency of the alkali atoms by coherent population trapping (CPT). This technique allows for a simple and compact device containing a vertical-cavity surface-emitting laser (VCSEL), optics to shape the laser beam, a vapor cell containing the atoms, and a detector. We present an improved technique for microfabricating the miniature alkali vapor cells. When integrated into a CPT clock, a clear reduction of long-term frequency drifts is observed. This leads to a fractional frequency instability of less than 10-11 at one hour of integration, a more than one order of magnitude improvement over previous results. We identify the remaining sensitivities of the clock frequency to environmental influences and propose ways to reduce them.

•Dec 1, 2004•3 citations

Stabilization method for atomic clocks to detect the maximum coherent-population-trapping resonance signal

Yusuke Odagiri, Satoshi Hatano, Yuichiro Yano +3 more

Abstract Chip-scale atomic clocks based on coherent population trapping (CPT) face challenges due to miniaturized gas cells, which reduces the CPT resonance signal and the absorption signals of alkali atoms. To overcome this, we propose a method that simultaneously stabilizes the laser wavelength and microwave modulation frequency without relying on absorption line detection. Our approach enables stabilization at the point where the amplitude of the CPT resonance signal is maximized, making it suitable for compact atomic clocks. The system uses three lock-in amplifiers: one is used to stabilize the RF modulation frequency, and the other two are used for detecting the amplitude of the CPT resonance and stabilizing the laser wavelength. The Allan deviation measurements demonstrate a 1.4-fold improvement in short-term stability compared to conventional methods, suggesting that the proposed technique is a promising solution for enhancing the performance of small gas-cell atomic clocks.

Japanese Journal of Applied Physics•Jun 1, 2025•2 citations

The Microfabricated Alkali Vapor Cell with High Hermeticity for Chip-Scale Atomic Clock

Shuo Jia, Zhiyuan Jiang, Binbin Jiao +4 more

Herein, a microfabricated millimeter-level vapor alkali cell with a high hermeticity is fabricated through a wet etching and single-chip anodic bonding process. The vapor cell, containing Rb and N2, was investigated in a coherent population trapping (CPT) setup for the application of a chip-scale atomic clock (CSAC). The contrast of CPT resonance is up to 1.1% within the only 1 mm length of light interacting with atom. The effects of some critical external parameters on the CPT resonance, such as laser intensity, cell temperature, and buffer gas pressure, are thoroughly studied and optimized. The improved microfabricated vapor cell also exhibited great potential for other chip-scale atomic devices.

Applied Sciences•Jan 3, 2022•20 citations

Experimental study of the application feasibility of a novel chip-scale atomic clock scheme

Huifang Lin, Yuan Tian, Jie‐Hua Chen +1 more

Rb vapor cell with differential detection. Elliptically polarized light is used to interact with alkali atoms to generate coherent population trapping (CPT) resonance, and the CPT signal is obtained by detecting the Faraday rotation effect with differential detection technology. To move closer to an actual chip-scale atomic clock (CSAC), we reduce the volume of the experimental apparatus and use a divergent laser beam to interact with the atoms. We obtain the short-term frequency stability of the CSAC based on the differential detection scheme and compare it with that of a conventional CSAC. The results show that the frequency stability is more than two times better than that of current commercial CSAC devices with the same power consumption and volume.

Review of Scientific Instruments•May 1, 2019•6 citations

VCSELs for atomic clocks

Darwin K. Serkland, Gregory M. Peake, K.M. Geib +4 more

The spectroscopic technique of coherent population trapping (CPT) enables an all-optical interrogation of the groundstate hyperfine splitting of cesium (or rubidium), compared to the optical-microwave double resonance technique conventionally employed in atomic frequency standards. All-optical interrogation enables the reduction of the size and power consumption of an atomic clock by two orders of magnitude, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources due to their low power consumption and circular output beam. Several research teams are currently using VCSELs for DARPA's chip-scale atomic clock (CSAC) program with the goal of producing an atomic clock having a volume < 1 cm^3, a power consumption < 30 mW, and an instability (Allan deviation) < 1x10^-11 during a 1-hour averaging interval. This paper describes the VCSEL requirements for CPT-based atomic clocks, which include single mode operation, single polarization operation, modulation bandwidth > 4 GHz, low power consumption (for the CSAC), narrow linewidth, and low relative intensity noise (RIN). A significant manufacturing challenge is to reproducibly obtain the required wavelength at the specified VCSEL operating temperature and drive current. Data are presented that show the advantage of operating at the D1 (rather than D2) resonance of the alkali atoms. Measurements of VCSEL linewidth will be discussed in particular, since atomic clock performance is especially sensitive to this parameter.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Feb 9, 2006•60 citations
Coherent population trapping (CPT) resonances usually exhibit contrasts below 10% when interrogated with frequency modulated lasers. We discuss a relatively simple way to increase the resonance contrast to nearly 100% generating an additional light field through a nonlinear four-wave mixing interaction in the atomic vapor.1 A similar method can also be used to create a beat signal at the CPT resonance frequency that can injection-lock a low-power microwave oscillator at 3.4 GHz directly to the atomic resonance.2 This could lead to chip-scale atomic clocks (CSACs) with improved performance. Furthermore, we introduce a miniature microfabricated saturated absorption spectrometer3 that produces a signal for locking a laser frequency to optical transitions in alkali atoms. The Rb absorption spectra are comparable to signals obtained with standard table-top setups, although the rubidium vapor cell has an interior volume of only 1 mm3 and the volume of the entire spectrometer is around 0.1 cm3.
We present a microwave frequency standard based on coherent population trapping (CPT) in the 87Rb D1 line. The CPT spectrum is obtained using two Raman lasers with a 6.8 GHz frequency offset by injection locking of a master laser to a slave laser. We have constructed an atomic clock employing a 5 cm long Rb vapor cell confined with 6.67 kPa neon buffer gas at 70 °C. Using this system, we improve the CPT contrast through the elimination of undesired off-resonant fields created by the direct modulation method. We measured the frequency shift of the CPT signal as a function of the temperature of the Rb cell and estimated it to be approximately 1.3 ×10−9/K. The frequency of a 10 MHz crystal oscillator has been stabilized to the CPT spectrum between the two ground states in 87Rb. The relative frequency stability is approximately 2.3×10−12 for an average time of 68 s.
This paper presents the latest progress in the development, fabrication, and characterization of microfabricated atomic frequency references at NIST. With volumes below 10 mm3 the physics packages contain the complete integrated assembly for probing the ground-state hyperfine splitting frequency of the alkali atoms by coherent population trapping (CPT). This technique allows for a simple and compact device containing a vertical-cavity surface-emitting laser (VCSEL), optics to shape the laser beam, a vapor cell containing the atoms, and a detector. We present an improved technique for microfabricating the miniature alkali vapor cells. When integrated into a CPT clock, a clear reduction of long-term frequency drifts is observed. This leads to a fractional frequency instability of less than 10-11 at one hour of integration, a more than one order of magnitude improvement over previous results. We identify the remaining sensitivities of the clock frequency to environmental influences and propose ways to reduce them.
Abstract Chip-scale atomic clocks based on coherent population trapping (CPT) face challenges due to miniaturized gas cells, which reduces the CPT resonance signal and the absorption signals of alkali atoms. To overcome this, we propose a method that simultaneously stabilizes the laser wavelength and microwave modulation frequency without relying on absorption line detection. Our approach enables stabilization at the point where the amplitude of the CPT resonance signal is maximized, making it suitable for compact atomic clocks. The system uses three lock-in amplifiers: one is used to stabilize the RF modulation frequency, and the other two are used for detecting the amplitude of the CPT resonance and stabilizing the laser wavelength. The Allan deviation measurements demonstrate a 1.4-fold improvement in short-term stability compared to conventional methods, suggesting that the proposed technique is a promising solution for enhancing the performance of small gas-cell atomic clocks.
Herein, a microfabricated millimeter-level vapor alkali cell with a high hermeticity is fabricated through a wet etching and single-chip anodic bonding process. The vapor cell, containing Rb and N2, was investigated in a coherent population trapping (CPT) setup for the application of a chip-scale atomic clock (CSAC). The contrast of CPT resonance is up to 1.1% within the only 1 mm length of light interacting with atom. The effects of some critical external parameters on the CPT resonance, such as laser intensity, cell temperature, and buffer gas pressure, are thoroughly studied and optimized. The improved microfabricated vapor cell also exhibited great potential for other chip-scale atomic devices.
Rb vapor cell with differential detection. Elliptically polarized light is used to interact with alkali atoms to generate coherent population trapping (CPT) resonance, and the CPT signal is obtained by detecting the Faraday rotation effect with differential detection technology. To move closer to an actual chip-scale atomic clock (CSAC), we reduce the volume of the experimental apparatus and use a divergent laser beam to interact with the atoms. We obtain the short-term frequency stability of the CSAC based on the differential detection scheme and compare it with that of a conventional CSAC. The results show that the frequency stability is more than two times better than that of current commercial CSAC devices with the same power consumption and volume.
The spectroscopic technique of coherent population trapping (CPT) enables an all-optical interrogation of the groundstate hyperfine splitting of cesium (or rubidium), compared to the optical-microwave double resonance technique conventionally employed in atomic frequency standards. All-optical interrogation enables the reduction of the size and power consumption of an atomic clock by two orders of magnitude, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources due to their low power consumption and circular output beam. Several research teams are currently using VCSELs for DARPA's chip-scale atomic clock (CSAC) program with the goal of producing an atomic clock having a volume < 1 cm^3, a power consumption < 30 mW, and an instability (Allan deviation) < 1x10^-11 during a 1-hour averaging interval. This paper describes the VCSEL requirements for CPT-based atomic clocks, which include single mode operation, single polarization operation, modulation bandwidth > 4 GHz, low power consumption (for the CSAC), narrow linewidth, and low relative intensity noise (RIN). A significant manufacturing challenge is to reproducibly obtain the required wavelength at the specified VCSEL operating temperature and drive current. Data are presented that show the advantage of operating at the D1 (rather than D2) resonance of the alkali atoms. Measurements of VCSEL linewidth will be discussed in particular, since atomic clock performance is especially sensitive to this parameter.