Optical Cavity Length Measurement via Beat Frequency
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Solution Overview
Problem
The optical beam deflection method for measuring micro cantilever displacement lacks direct traceability and cannot optimize detection sensitivity and spot size simultaneously, limiting its effectiveness in measuring displacement variations accurately.
Innovation Solution
An apparatus using a frequency tunable light source, beam splitter, frequency modulator, and optical resonant cavity to measure the length of an optical resonant cavity by calculating the beat frequency between two modulated beams, enabling high direct traceability and resolution of displacement variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical beam deflection method is used to measure micro cantilever displacement, then the measurement can be performed, but the method lacks direct traceability and requires comparison calibration
Solution Approach 1:
The patent replaces the conventional optical beam deflection method with a microwave resonant cavity method. The microwave resonance frequency shift directly correlates to cavity length changes, providing direct traceability to frequency standards without requiring optical calibration. The microwave system substitutes the optical detection mechanism with electromagnetic resonance detection.
Solution Approach 2:
The patent utilizes the relationship between microwave resonance frequency and cavity length as the measurement parameter. By monitoring the shift in resonant frequency caused by cantilever deflection, the system achieves direct traceable displacement measurement through frequency-to-length parameter conversion, eliminating the need for optical calibration procedures.
2Measurement precision
If the spot size of detection light is reduced to increase magnification, then the magnification factor increases, but the detection sensitivity deteriorates
Solution Approach 1:
The patent completely replaces the optical detection system with a microwave resonant system. Instead of using focused light spots that create the sensitivity-magnification tradeoff, the microwave fields penetrate and interact with the entire cantilever structure, providing uniform sensitivity across the measurement region without spot size limitations.
Solution Approach 2:
The patent transitions from optical detection in one dimension (light spot on surface) to microwave resonance involving the entire three-dimensional cavity volume. The microwave fields distribute throughout the cavity space, enabling detection of cantilever deflection through volumetric interaction rather than surface spot illumination.
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 apparatus achieves high direct traceability and displacement resolution, capable of converting absolute displacement into frequency variation, with a resolution of tens of picometers and improved sensitivity, suitable for measuring micro cantilever deformations.
Implementation Method 1
The frequency of the second beam is modulated by the frequency modulator to differ from the frequency of the first beam by a beat frequency
Implementation Method 2
a beat frequency between the absolute optical frequencies of the first beam and the second beam and the two absolute optical frequencies
Implementation Method 3
The optical resonant cavity is disposed on the main optical path of the first beam and the main optical path of the modulated second beam
Data Source
AI summary
An apparatus for measuring a length of an optical resonant cavity includes a frequency tunable light source, a beam splitter, a frequency modulator and an optical resonant cavity. The frequency tunable light source emits a beam. The beam splitter is disposed on the optical path of the beam for dividing the beam into a first beam and a second beam. The frequency of the second beam is modulated by the frequency modulator to differ from the frequency of the first beam by a beat frequency. The optical resonant cavity is disposed on the main optical path of the first beam and the main optical path of the modulated second beam. The first beam and the modulated second beam enter the optical resonant cavity for measuring a length of the optical resonant cavity, and a variation in cavity length is calculated from the beat frequency.