Interferometric Distance Sensing with Parallel Optical Branch Paths
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Solution Overview
Problem
Interferometric distance sensing devices with common path architectures are limited by environmental disturbances and coherence length, affecting accuracy and reliability in distance measurements.
Innovation Solution
The use of parallel optical branch paths and a three-way coupler allows for accurate distance measurement by computing distance representations from intensities detected at the coupler outputs, independent of path length differences, and employing a pulsed light source for time-based determination of path lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If parallel beam paths are introduced to increase measurement distance beyond coherence length, then the measurable distance is improved, but part of the common path architecture advantage is lost
Solution Approach 1:
The optical path is segmented into multiple parallel beam paths with different lengths. By dividing the single common path into multiple segments that recombine at the N-way coupler, the system can measure distances beyond the coherence length while maintaining environmental stability through the common path architecture.
Solution Approach 2:
Multiple parallel beam paths are merged at the N-way coupler to recombine the light beams. This combining of separate paths allows the system to achieve extended measurement range while preserving the benefits of common path architecture through the interference of recombined beams.
2Reliability
If conventional common path architecture is used to eliminate environmental disturbances, then reliability is improved, but measurement precision is limited by coherence length
Solution Approach 1:
The system transitions from a single-path architecture to a multi-dimensional parallel path architecture. By introducing multiple beam paths with different lengths that interfere at the N-way coupler, the system adds a new dimension to the common path architecture, enabling sub-wavelength precision measurements beyond the traditional coherence length limitation while maintaining environmental disturbance resistance.
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 configuration enhances measurement accuracy and reduces dependence on environmental factors, enabling sub-wavelength precision in distance determination beyond the coherence length limitations.
Implementation Method 1
a light source, optical fibers coupled to the light source that guide light from the light source to a beam splitter
Implementation Method 2
a beam splitter that receives the light from the optical fibers and provides a reference beam and a sensing beam respectively by partial reflection and transmission of the light
Implementation Method 3
an interferometric distance sensing device detects interference between a reference beam and a sensing beam that has been reflected from a target
Implementation Method 4
Both the sensing beam and the reference beam travel through each of the parallel optical branch paths. Light from the common path is fed to distinct input terminals of an N way coupler by parallel optical branch paths
Data Source
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Figure 2
AI summary
Distance to a target is sensed using a common path interferometer, wherein a first fraction of light from a light source is collected after reflection by a partially reflective element together with reflection from a target of a second fraction of light from the light source that has been transmitted by the partially reflective element. The collected light is split in two parts, both containing a part of the first fraction and part of the reflection from the target. The parts are fed through a first and second optical branch path to an input side of a three-way optical coupler respectively. Light from at three terminals on a second side of the N way coupler is fed to respective light intensity detectors. Information representing an excess distance traveled by the first fraction from detection signals determined by the least three light intensity detectors.