Heterodyne Interferometer Using Dual-Frequency Beams to Eliminate Nonlinearity
Solution Overview
Problem
Traditional heterodyne interferometers face limitations in achieving high resolution and high speed measurements due to frequency and polarization mixing effects, which restrict their accuracy and resolution, making them unsuitable for high precision and competitive production demands.
Innovation Solution
A high speed high resolution heterodyne interferometric method and system that uses spatially separated measurement and reference beams with different frequencies, employing a polarizing beam splitter, quarter wave plate, and photodiodes to generate and process measurement signals, allowing for selective phasemeter selection based on target movement direction and speed, thereby eliminating periodic nonlinearity and utilizing a low beat frequency laser source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional heterodyne interferometer is used, then measurement precision is improved, but measurement speed is limited by beat frequency of laser source
Solution Approach 1:
The patent divides the measurement process into two separate measurement beams with different frequencies (f1 and f2), each interfering with the other's reference beam. This segmentation allows independent optimization of each measurement channel and enables high-speed measurement by selecting the appropriate frequency combination based on target speed
Solution Approach 2:
The patent changes the frequency parameters of the laser beams by using two different frequencies (f1 and f2) instead of a single frequency. By adjusting the frequency difference and selecting appropriate photodetectors, the system can measure both high-speed and low-speed targets while maintaining high precision
2Device complexity
If frequency and polarization mixing effects are present, then device configuration is simplified, but measurement accuracy and resolution are reduced
Solution Approach 1:
The patent extracts and eliminates the frequency and polarization mixing effects by using two distinct frequencies (f1 and f2) for the measurement beams. The spatial separation of beams and frequency differentiation prevent the mixing effects that plague single-frequency interferometers, thereby improving measurement accuracy
Solution Approach 2:
The patent introduces frequency as an intermediary parameter to distinguish between measurement beams and reference beams. By using different frequencies (f1 and f2) and detecting them with appropriate photodetectors, the system can separate and process signals without frequency mixing, maintaining configuration simplicity while improving accuracy
3Measurement precision
If spatially separated measurement and reference beams are used, then frequency and polarization mixing effects are eliminated, but device complexity increases
Solution Approach 1:
The patent makes the beam splitter and optical path serve multiple functions: they not only separate measurement and reference beams spatially to eliminate mixing effects, but also enable dual-frequency operation and high-speed measurement capability. This multi-functionality reduces the need for additional complex components
4Measurement precision
If low beat frequency laser source is used, then measurement resolution is improved, but measurement speed is limited
Solution Approach 1:
The patent introduces dynamic frequency selection by using two different frequencies (f1 and f2) and allowing the system to adaptively choose the appropriate measurement channel based on target speed. This dynamic approach enables the system to maintain high resolution with low beat frequency while achieving high measurement speeds when needed
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 high resolution and high accuracy measurements by eliminating frequency and polarization mixing effects, allowing for high speed target measurement with a low beat frequency laser source, and simplifies the measurement circuit using ordinary electric clock signals, making it cost-effective and applicable for industrial engineering.
Implementation Method 1
dividing the other portion of each of the two laser beams into a reference beam and a measurement beam by a polarizing beam splitter
Implementation Method 2
directing the two measurement beams with different frequencies f1 and f2 respectively through a quarter wave plate
Implementation Method 3
detecting one portion of each of the two laser beams by a photodiode
Implementation Method 4
the measurement beam with frequency f1 interferes with the reference beam with frequency f2 whereby a first measurement signal Im1 of frequency fb+Δf is generated
Data Source
AI summary
A high speed high resolution heterodyne interferometric method and system are provided. The invention uses two spatially separated beams with slightly different frequencies and has two measurement signals with opposite Doppler shift. The switching circuit selects one of the two measurement signals for displacement measurement according to the direction and speed of the target movement. In this invention, the measurement is insensitive to the thermal variation; the periodic nonlinearity is essentially eliminated by using two spatially separated beams; the measurable target speed of the interferometer is no longer limited by the beat frequency of the laser source.