Optical Frequency Shift Measurement via Time Delay Conversion
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Solution Overview
Problem
Current methods for measuring small changes in the centroid of a light field's power spectrum, such as those required for detecting low concentrations of molecular impurities, are limited by the low resolution of optical spectrometers, which are orders of magnitude too coarse for detecting frequency shifts of the order of 500 Hz needed for nanomole concentrations.
Innovation Solution
The method involves directing light through an optically dispersive system, where changes in the center optical frequency are converted into time delays, allowing for the measurement of these shifts by measuring the difference in transit times, enhancing sensitivity beyond the limitations of existing Raman sensing techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical spectrometers are used to measure frequency shifts, then the measurement can be performed with standard equipment, but the resolution is orders of magnitude too coarse (maximum 1 GHz) to detect small frequency shifts of about 500 Hz required for nanomole concentration detection
Solution Approach 1:
The invention changes the measurement parameter from direct optical frequency measurement to time delay measurement. By passing light through an optically dispersive system, small frequency shifts are converted into measurable time delays, enabling detection of 500 Hz shifts that would be impossible with standard spectrometers
Solution Approach 2:
The invention introduces an optically dispersive system as an intermediary between the light source and detector. This dispersive system acts as a frequency-to-time converter, transforming the difficult-to-measure frequency shifts into easily measurable time delays without requiring complex direct frequency measurement equipment
2Quantity of substance
If Raman interactions are used for molecular detection, then high spatial resolution imaging is achieved, but the weak Raman interactions limit detection to relatively high concentration levels
Solution Approach 1:
The invention changes the detection parameter from intensity-based Raman scattering to frequency shift measurement. By measuring the centroid of the power spectrum and converting frequency shifts to time delays, the system achieves sensitivity to nanomole concentrations, overcoming the limitation of weak Raman interactions
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 enables significantly higher sensitivity in detecting small changes in the centroid of the power spectrum, allowing for the detection of nanomole concentrations by converting optical frequency shifts into measurable time delays, thereby overcoming the resolution limitations of traditional spectrometers.
Implementation Method 1
directing the light from the light source into an optically dispersive system, whereby the center frequency experiences a first transit time through the dispersive system
Data Source
AI summary
An apparatus and method for measuring small changes in the centroid of the spectrum of a light field by conversion of optical frequency centroid shifts into time delays are described. A time delay for a particular frequency of light is created by directing the light into an optically dispersive system that converts the change in center frequency to a change in transit time through the system as the dispersive element causes different colors to travel at different speeds. Examples of such dispersive elements include, but are not limited to, optical fibers, bulk materials, volumetric or fiber Bragg gratings, and grating or prism based pulse stretchers. This time delay can be measured, by detecting the change in transit time (or time of flight through the dispersive element) by using a detector such as a photodiode, PMT, etc. that converts the incident optical pulse train into an electronic pulsed signal. The phase of the periodic electronic signal provides a measure of the timing delay of the pulse, and can be determined by adapting standard methods of electronic oscillator phase detection relative to a reference electronic oscillator clock.