Interferometer with NCO Phase Control for Large Range High Resolution Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Interferometers have limited use due to their short operating ranges, high Size, Weight, and Power (SWaP) requirements, and high costs, which restrict their acceptance in many applications, and existing methods for linearizing sensor output, such as using linear translation stages or optical heterodyne methods, introduce noise and offset errors.
Innovation Solution
The implementation of phase locked lasers, optical heterodyne detection, and a novel method involving direct phase control of a numerically controlled oscillator (NCO) to generate a sensing beat signal, which is proportional to the displacement of an object, avoiding frequency control and thus reducing noise and common mode errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If basic interferometer is used, then high resolution measurement is achieved, but operating range is limited to nanometer scale
Solution Approach 1:
The patent segments the measurement task into two independent parts: a coarse measurement channel using a long reference arm for large displacement measurement, and a fine measurement channel using the interferometer for high-resolution measurement. The total displacement is calculated by combining results from both channels, effectively extending the operating range while maintaining high resolution.
Solution Approach 2:
The patent introduces a coarse measurement channel as an intermediary system that handles the large displacement component. This intermediary system uses a long reference arm to provide coarse positioning information, which then guides the high-resolution interferometer measurement, allowing the system to achieve both large range and high precision.
2Length of stationary object
If linear translation stage is used to linearize sensor output, then operating range is extended, but Size, Weight, and Power increase
Solution Approach 1:
The patent extracts the linearization function from the mechanical translation stage and implements it through signal processing. By using digital signal processing algorithms to compensate for the sinusoidal output characteristics, the system achieves linear output without requiring heavy mechanical components, thus reducing weight while extending operating range.
Solution Approach 2:
The patent replaces the mechanical translation stage with an electronic/software-based linearization system. Instead of using physical mechanical components to achieve linear output, the system uses digital signal processing and algorithmic compensation to achieve the same effect, eliminating the need for heavy mechanical structures.
3Length of stationary object
If AOM frequency shifter is used for optical heterodyne method, then operating range is extended, but device size and power consumption increase
Solution Approach 1:
The patent extracts the frequency shifting function from the AOM device and implements it through electronic signal processing. By using digital frequency modulation and mixing algorithms, the system achieves the necessary frequency differentiation for heterodyne measurement without requiring high-power optical modulators, thus reducing power consumption while maintaining extended operating range.
Solution Approach 2:
The patent replaces the optical AOM frequency shifter with an electronic signal processing system. Instead of using optical modulators that consume significant power, the system uses electronic frequency modulation and digital signal processing to achieve the same measurement function, dramatically reducing power consumption.
4Length of stationary object
If frequency measurement is integrated to obtain displacement, then operating range is extended, but noise and offset errors cause random walk and saturation
Solution Approach 1:
The patent implements feedback mechanisms to continuously monitor and correct measurement drift. By using the long reference arm to provide stable reference information and digital signal processing to compensate for noise and offset errors, the system maintains measurement stability over extended ranges without the random walk and saturation problems of integration-based methods.
Solution Approach 2:
The patent performs preliminary calibration and compensation using the long reference arm before actual measurements. By establishing stable reference conditions in advance and using digital signal processing to pre-compensate for potential noise and offset errors, the system ensures measurement reliability throughout the extended operating range without drift or saturation.
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 interferometers with large linear output ranges and high displacement sensitivity while being compact, low-power, and cost-effective, providing a high signal-to-noise ratio and minimizing common mode errors.
Implementation Method 1
light from a laser is split into two beams, one that is sent along the sensing leg to the object and the other that sent along a reference leg
Implementation Method 2
With a Michelson interferometer, light from a laser is split into two beams
Implementation Method 3
A retro-reflector on the object reflects the measurement beam back into the opposite direction, where it is reflected again by the beam splitter/combiner and sent to a photodetector
Data Source
AI summary
An interferometer including a master laser, a slave laser and optical elements is provided. The optical elements direct and combine a master laser beam and a slave laser beam into a sensing phase measurement loop to provide a sensing beat signal and a reference phase lock loop to provide a reference beat signal. An electronic circuit portion is coupled to receive the sensing and reference beat signals. The electronic circuit portion includes a clock, at least one numerically controlled oscillator, at least one mixer and an interferometer output. The at least one numerically controlled oscillator has a clock input coupled to the clock. The at least one mixer has a first input to receive the sensing beat signal and a second input to receive an output of the at least one numerically controlled oscillator. The interferometer output is coupled to receive an output of the at least one mixer.