Pulse-Mode Miniature Atomic Clock with Shared Optical Servo Loop
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Solution Overview
Problem
Existing CPT atomic micro-clocks operating in pulse mode face challenges with size, cost, and performance, particularly due to the complexity and component requirements of the optical frequency servo loop, which limits size and cost efficiency while compromising performance.
Innovation Solution
The proposed solution simplifies the optical frequency servo loop by using a single alkaline vapor microcell for both microwave and optical frequency feedback, eliminating the need for a second microcell and photodiode, and employing a pulsed control block to generate correction signals during specific durations, allowing for a more compact and cost-effective design without significant performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a second microcell and photodiode are used for optical frequency feedback, then optical frequency control precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the microwave and optical frequency feedback functions into a single alkaline vapor microcell and photodiode system. The microcell simultaneously serves for both microwave CPT measurements and optical frequency stabilization, while the photodiode detects both microwave and optical signals. This consolidation eliminates the need for separate microcell and photodiode dedicated to optical feedback, thereby reducing device complexity and cost while maintaining optical frequency control precision through shared high-precision components.
Solution Approach 2:
The single alkaline vapor microcell and photodiode are designed to perform multiple functions: they serve both for microwave frequency stabilization via CPT and for optical frequency feedback. This multi-functionality approach allows the same components to provide both microwave and optical frequency references, simplifying the overall system architecture and reducing the total component count while maintaining the required precision for both frequency domains.
2Reliability
If continuous mode operation is used, then stability is improved, but pulse mode operation provides better performance with reduced power consumption
Solution Approach 1:
The patent implements periodic pulsed operation for both microwave and optical frequencies using synchronized pulse generators. The microwave pulse generator produces periodic microwave pulses for CPT measurements, while the optical pulse generator produces corresponding optical pulses. This periodic action allows the system to achieve frequency stabilization through repeated measurements while consuming power only during active pulse intervals, thereby maintaining reliability through continuous feedback while significantly reducing average power consumption compared to continuous operation.
Solution Approach 2:
The system employs feedback mechanisms where the photodiode detects both microwave and optical signals during pulse intervals, and the control loops adjust frequencies based on detected errors. The microwave frequency is controlled via a microwave frequency control loop, and the optical frequency is stabilized through an optical frequency control loop, both operating in pulse mode. This feedback ensures frequency stability is maintained despite the intermittent pulsed operation, achieving reliable performance with reduced power consumption.
3Measurement precision
If separate control loops for microwave and optical frequencies are implemented, then control precision is improved, but component count and cost increase
Solution Approach 1:
The patent combines the microwave and optical frequency control functions into shared hardware components. A single alkaline vapor microcell serves both microwave CPT measurements and optical frequency reference, and a single photodiode detects both microwave and optical signals. The control loops are implemented as integrated control circuits that process both frequency domains using the same physical components, thereby maintaining control precision through separate control algorithms while minimizing component count by sharing the microcell and photodiode infrastructure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a smaller, less costly atomic micro-clock with enhanced implementation freedom and reduced component count, maintaining performance while offering a better size/cost compromise, and simplifying manufacturing and implementation.
Implementation Method 1
a dual-frequency laser source (102) receiving an output signal (129) from the local oscillator (125) and having an optical frequency. The frequency difference between the spectral components of the output signal (laser beam) of the dual-frequency laser source (102) is equal to the frequency of the local oscillator (125)
Implementation Method 2
an alkaline vapor microcell (104) receiving (via the optical shaping element (103)) the pulsed laser beam (140) and using population coherent trapping
Implementation Method 3
a photodiode (105) receiving an output signal from the alkaline vapor microcell (104). The photodiode (105) transforms the pulsed light intensity into an electrical signal (106) which also carries the comparison information
Implementation Method 4
a microwave frequency feedback loop (500), receiving a signal (114) (resulting from the filtering of the output signal (106) of the photodiode (105) by a first filter (127)) and configured to control the microwave frequency of the local oscillator (125) to the microwave frequency setpoint (resonance frequency of the hyperfine structure of the alkaline vapor atoms of the microcell (104))
Implementation Method 5
an optical frequency feedback loop (400), configured to control the optical frequency of the dual-frequency laser source (102) to an optical frequency setpoint
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Miniature atomic clock CPT (200) with pulse mode operation, comprising: a local oscillator (125); a dual-frequency laser source (102); means (300) configured to pulse the output signal from the source according to a Ramsey-type interrogation sequence (144) comprising pulses with a duration T1 separated by intervals with a duration T2; an alkaline vapour microcell; a photodiode (105); a feedback control loop (500) for controlling the microwave frequency of the local oscillator; and a feedback control loop (400') for controlling the optical frequency of the source by means of a pulse control block (SERVO_2') receiving the output signal from the photodiode and the interrogation sequence, and providing a correction signal (δ_c_2') to the source. During the period T1, the block (SERVO_2') extracts an error signal from the output signal received from the photodiode and generates the correction signal from the error signal. During the period T2, the block resets the error signal to zero and generates the correction signal by extrapolation.