Industrial optically pumped cesium beam clock

1. Industrial optically pumped cesium beam clock Precise Time and Time Interval Meeting, January 23-26, 2023, Long Beach, CA, USA P. Berthoud, M. Haldimann, F. Kroll, V. Dolgovskiy

3. © 2023 ADVA. All rights reserved. 3 Improve performance while keeping lifetime and compactness Telecommunication network reference • Telecom operators, railways, transport, power, … Enterprise / Data-centers (ICPs) / Finance • Synchronization of distributed databases, • Speed trading PNT market • Multi verticals GNSS backup Defense • Secured telecom, inertial navigation Space • Satellite mission tracking, GNSS systems Science • Astronomy, nuclear and quantum physics, … Metrology • Time scale, fundamental unit measurement Markets for cesium clocks

5. © 2023 ADVA. All rights reserved. 5 Cs tube • Produce a cesium atomic beam • Provide mechanical means to measure Cs resonance frequency Optical bench • Provide laser beams to the Cs tube for the optical pumping and optical detection processes Electronics • Control the laser • Control the Cs tube • Provide an output signal to the user based on the Cs atom reference frequency Optically-pumped cesium clock architecture Collector Cs Oven Collector Ramsey cavity C-field coil + magnetic shields Vacuum enclosure Laser FM sinus ADC A A B Demod Laser source DAC ADC FM square + time sequencer Demod RF synth. DAC RF pwr OCXO DAC RF freq DAC C-field C-field source Output frequency

6. © 2023 ADVA. All rights reserved. 6 Cesium tube Collector Cs Oven Collector Ramsey cavity C-field coil + magnetic shields Vacuum enclosure Laser A A B Cesium oven • Temperature = 100°C • Compatible with 10 yr lifetime Ramsey cavity • Dark fringe (p pulse between arms) • Loaded quality factor = 500 Atomic fluorescence collectors • Efficiency >50% • Laser light trap (50 dB) Magnetic C-field and shields • Static and uniform • Amplitude = 100 mG

7. © 2023 ADVA. All rights reserved. 7 Optical bench Collector Cs Oven Collector Ramsey cavity C-field coil + magnetic shields Vacuum enclosure Laser A A B Simplest optical setup • Single laser frequency (D2:3→4’) for atomic preparation and detection • DFB laser module • Free space optics • No acousto optic modulator • No optical isolator Beams (3) • A: laser frequency lock (50 mW) • A’: optical pumping completion (1.5 mW) • B: clock transition detection (50 mW)

8. © 2023 ADVA. All rights reserved. 8 Laser lock loops • Sine wave FM (20 kHz) • Optical frequency by current and temp. • Optical power by current and temp. Clock lock loops • Square wave FM (10 Hz) • Time sequencer for multiple loops • Quartz oscillator frequency • RF field power • Magnetic C-field amplitude • Light shift compensation • All error signals come from atomic signals and are differential Processing • Real time • Fully digital (FPGA) Electronics Collector Cs Oven Collector Ramsey cavity C-field coil + magnetic shields Vacuum enclosure Laser FM sinus ADC A A B Demod Laser source DAC ADC FM square + time sequencer Demod RF synth. DAC RF pwr OCXO DAC RF freq DAC C-field C-field source Output frequency

11. © 2023 ADVA. All rights reserved. 11 Symmetric spectrum Dark fringe behavior • Minimum signal at resonance Contrast: 50% Linewidth: 740 Hz (FWHM) Signal-to-noise ratio: 15’000 Hz1/2 Fringes per sub-level: 1 • Large destructive fringe interference by the wide atomic velocity distribution Open loop performances (Ramsey fringes)

12. © 2023 ADVA. All rights reserved. 12 Test setup: • Phase comparision of cesium clock vs. active hydrogen maser • Active maser frequency monitored versus GPS • Carrier frequency: 10 MHz • Measurement time: 50 days • Sampling period: 10 s • Standard lab conditions Frequency stability • Overlapping Allan deviation sy(t) • White FM noise (t-1/2 slope) • sy(t) = 4E-12 t-1/2 (0.004 ppb @1s) • Not limited by any flicker FM noise @4E-15 Frequency stability (Allan deviation)

13. © 2023 ADVA. All rights reserved. 13 Test setup • Identical as before (same data) Cesium clock vs. active hydrogen maser Time interval error • ± 6 ns over 50 days in free running mode Time interval error (TIE) Good candidate to hold time during long GNSS outages (PNT)

14. © 2023 ADVA. All rights reserved. 14 3300 SHP experimental batch Test setup • Cesium clocks vs. active hydrogen maser Repeatability • Statistics over 10 clocks • About ±25% stability dispersion between clocks • All clocks comply with HP standard, with a 10 years lifetime basis

16. © 2023 ADVA. All rights reserved. 16 • Design description of an industrial and compact optically-pumped thermal cesium beam clock (19’’, 3U rack) • High performance frequency stability demonstration using optical pumping technology (long lifetime) • Good industrial ground-based back-up solution for PNT architecture (in case of GNSS outages) Conclusions

17. Thank you IMPORTANT NOTICE ADVA is the exclusive owner or licensee of the content, material, and information in this presentation. Any reproduction, publication or reprint, in whole or in part, is strictly prohibited. The information in this presentation may not be accurate, complete or up to date, and is provided without warranties or representations of any kind, either express or implied. ADVA shall not be responsible for and disclaims any liability for any loss or damages, including without limitation, direct, indirect, incidental, consequential and special damages, alleged to have been caused by or in connection with using and/or relying on the information contained in this presentation. Copyright © for the entire content of this presentation: ADVA. info@oscilloquartz.com

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Industrial optically pumped cesium beam clock

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