More Related Content Similar to Industrial optically pumped cesium beam clock (20) Industrial optically pumped cesium beam clock1. 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
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Outline
Motivation
Design
Performance
Conclusion
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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
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Outline
Motivation
Design
Performance
Conclusion
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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
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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
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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)
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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
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Industrial product OSA-3300 HP
19’’ rack, 3U (450 x 133 x 460 mm3)
35 W
23 kg (battery included)
10 years lifetime
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Outline
Motivation
Design
Performance
Conclusion
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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)
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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)
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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)
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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
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Outline
Motivation
Design
Performance
Conclusion
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• 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
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