Vapor Cell Spectroscopy with Offset Reference Paths for Noise Mitigation
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Solution Overview
Problem
The noise conversion from laser phase noise to amplitude noise in vapor cell-based atomic clocks limits the signal-to-noise ratio, obscuring the resonance feature and increasing costs due to the need for low phase-noise laser sources.
Innovation Solution
A spectroscopy system that transmits an unmodulated reference optical signal and a modulated pump optical signal through a vapor cell with separate, non-crossing optical paths, allowing the control system to detect and mitigate noise by generating a laser adjustment signal for wavelength or frequency adjustments of the optical source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If expensive low phase-noise laser sources are used to mitigate PM to AM noise conversion, then the signal-to-noise ratio improves, but the cost increases significantly
Solution Approach 1:
The patent creates a reference signal that copies the phase noise characteristics of the main laser signal by passing it through the same vapor cell. This reference signal serves as a template for the phase noise, allowing the system to distinguish and remove phase noise artifacts from the absorption measurement without requiring expensive low phase-noise laser sources
Solution Approach 2:
The patent introduces a reference optical signal as an intermediary that carries the phase noise information separately. This reference signal acts as a mediator between the laser phase noise and the absorption measurement, enabling the control system to identify and compensate for phase noise conversion effects through comparison and subtraction operations
2Device complexity
If the optical paths of reference and pump signals cross in the vapor cell, then signal detection is simplified, but phase noise converts to amplitude noise obscuring the resonance feature
Solution Approach 1:
The patent segments the optical paths by using spatially separated propagation paths for the reference signal and pump signal within the vapor cell. This physical segmentation prevents the pump signal from imprinted phase modulation onto the reference signal, allowing independent detection of phase noise effects while maintaining separate measurement channels
Solution Approach 2:
The patent resolves the path crossing issue by utilizing the spatial dimension within the vapor cell - arranging the reference and pump optical paths to propagate through different spatial regions of the vapor cell. This dimensional separation allows both signals to interact with the vapor independently without cross-contamination, preventing unwanted phase noise transfer while still enabling comprehensive noise characterization
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 improves the signal-to-noise ratio by removing noise conversion effects, reducing the reliance on costly low phase-noise laser sources and enhancing the accuracy of vapor cell-based atomic clocks without additional vapor cells.
Implementation Method 1
the wavelength-dependent absorption experienced by the probe beam serves as a discriminant for converting laser phase noise (PM) into amplitude noise (AM)
Implementation Method 2
a control system configured to detect optical signals resulting from the unmodulated reference optical signal and the modulated pump optical signal passing through the vapor cell
Data Source
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AI summary
Embodiments herein describe spectroscopy systems that use an unmodulated reference optical signal to mitigate noise, or for other advantages. In one embodiment, the unmodulated reference optical signal is transmitted through the same vapor cell as a modulated pump optical signal. As such, the unmodulated reference optical signal experiences absorption by the vapor, which converts laser phase noise to amplitude noise like the other optical signals passing through the vapor cell. In one embodiment, the unmodulated reference optical signal has an optical path in the gas cell that is offset (or non-crossing) from the optical path of the modulated pump optical signal. The unmodulated reference optical signal allows removal or mitigation of the noise on the other optical signal.