Coherent Bi-Color Light Source for Atomic Clocks
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Solution Overview
Problem
Existing CPT atomic clocks face low contrast and stability issues due to the majority of atoms being populated at energy levels with minimum or maximum magnetic quantum number, and the presence of useless frequency sidebands in the laser beam, which affects the output frequency of the crystal oscillator.
Innovation Solution
A device and method for producing a coherent bi-color light source using an array substrate, two laser tubes, a half wave plate, a birefringent crystal, and quarter wave plates, which inter-injection-lock to produce inter-perpendicular polarized laser beams, counteracting optical pumping effects and reducing non-participating sidebands, resulting in a high-quality CPT signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single laser tube with FM modulation is used, then the device structure is simple, but the CPT signal contrast is low due to useless frequency sidebands and improper atomic population distribution
Solution Approach 1:
The single laser tube is segmented into two separate laser tubes: a first laser tube producing monochromatic light and a second laser tube producing FM modulated multi-chromatic light. This segmentation allows each tube to perform a specific function, eliminating the harmful sidebands while maintaining the beneficial carrier wave, thereby improving CPT signal contrast without significantly increasing overall device complexity
Solution Approach 2:
The harmful frequency sidebands are extracted and removed from the system by using a separate monochromatic laser tube for the carrier frequency. Only the useful carrier wave from the second laser tube and the monochromatic light from the first laser tube are combined, while the useless sidebands are excluded, improving signal quality
2Reliability
If left-handed or right-handed circularly polarized light is used to act on atomic vapor, then the optical pumping effect populates atoms at minimum or maximum magnetic quantum number energy levels, but the population at magnetic quantum number zero levels remains small which is necessary for clock transition
Solution Approach 1:
Instead of using symmetric circular polarization (which creates symmetric population distribution at maximum/minimum magnetic quantum numbers), the invention uses asymmetric linear polarization. This asymmetric approach creates an asymmetric population distribution that preferentially populates the magnetic quantum number zero levels, which are necessary for clock transition
Solution Approach 2:
The conventional approach uses circular polarization to achieve optical pumping, but this produces the opposite of the desired effect (populating extreme magnetic quantum numbers). The invention inverts this approach by using linear polarization, which produces the complementary effect of populating the central magnetic quantum number zero levels needed for clock transition
3Measurement precision
If inter-injection-locking between two laser tubes is implemented, then coherent bi-color light with perpendicular polarization is produced improving CPT signal quality, but the device complexity and production cost increase
Solution Approach 1:
The output beams from the first monochromatic laser tube and the second FM modulated laser tube are merged using a beam combining technique. The linearly polarized monochromatic light and the circularly polarized multi-chromatic light are combined to form a coherent bi-color light beam with perpendicular polarization directions, achieving high CPT signal quality while managing device complexity through efficient optical integration
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
The solution achieves a high-quality CPT signal by populating a majority of atoms at the required energy levels, improving the stability of the output frequency and reducing non-essential sidebands, while also minimizing production costs and device size.
Implementation Method 1
a birefringent crystal, a first quarter wave plate, a partially reflecting plane mirror, and a second quarter wave plate are disposed in sequence in an emission direction of a laser beam emitted by the first laser tube
Implementation Method 2
The laser signal passes through the quarter wave plate and outputs a left-handed or right-handed circularly polarized light
Implementation Method 3
an included angle between an optical axis direction of the half wave plate and a polarization direction of the laser beam emitted by the first laser tube is 45°
Implementation Method 4
a partially reflecting plane mirror
Implementation Method 5
a first laser tube, a second laser tube... The first laser tube is driven by a first direct current (DC) signal. The second laser tube is driven by a modulation signal coupled by a microwave signal and a second DC signal
Implementation Method 6
inter-injection-lock to produce inter-perpendicular polarized laser beams, counteracting optical pumping effects and reducing non-participating sidebands
Data Source
AI summary
A device for producing a coherent bi-color light source, including: an array substrate, a first laser tube driven by a first direct current signal, a second laser tube driven by a modulation signal coupled by a microwave signal and a second DC signal, a half wave plate, a birefringent crystal, a first quarter wave plate, a partially reflecting plane mirror, and a second quarter wave plate. The first laser tube and the second laser tube are fixed on the array substrate. The half wave plate, the birefringent crystal, the first quarter wave plate, the partially reflecting plane mirror, and the second quarter wave plate are disposed in sequence in an emission direction of a laser beam emitted by the first laser tube. The second laser tube is disposed opposite to the birefringent crystal.