Fiber-Optic Encoder Using Nested Optical Path for Compact High Resolution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical encoders are either too large for compact applications or lack the necessary resolution and accuracy, particularly for interferometric-type encoders which are not sufficiently compact and often limited by electronic detectors.
Innovation Solution
An ultra-compact interferometric optical encoder utilizing fiber-optic detector channels with a light source, source grating, and interference field generating grating to achieve high resolution and accuracy, with features like s-polarized light and suppression of higher order diffraction orders to enhance measurement precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interferometric-type optical encoders are used to achieve high resolution and accuracy, then measurement precision is improved, but device size becomes too large for compact applications
Solution Approach 1:
The patent implements a nested optical path configuration where the return beam travels through the same optical components (source grating, mirrors, interference field generating grating) as the outgoing beam. This nesting of optical paths allows the encoder to achieve interferometric measurement precision while minimizing the physical volume required, as the same components serve dual purposes for both outgoing and returning light paths.
Solution Approach 2:
The patent utilizes polarization dimensions to encode measurement information. By employing s-polarized light and controlling polarization states through the optical path, the system achieves high-resolution measurement in a compact configuration that doesn't require additional spatial dimensions, thus resolving the contradiction between precision and size.
2Measurement precision
If electronic detectors are used in interferometric encoders, then measurement capability is improved, but operation speed is limited
Solution Approach 1:
The patent replaces electronic detection systems with an all-optical detection approach. The fiber-optic detector channels directly detect optical interference patterns without requiring electronic conversion, thereby maintaining high measurement capability while enabling operation at much higher speeds that exceed electronic detector limitations.
Solution Approach 2:
The optical system serves its own detection function through the fiber-optic channels that directly measure the interference pattern of the return beam. This self-service optical detection eliminates the need for separate electronic detection components, enabling higher operating speeds while maintaining measurement precision.
3Volume of moving object
If crude fiber-optic encoders are used to reduce size, then device volume is reduced, but measurement precision becomes insufficient
Solution Approach 1:
The patent changes the operational parameters of the fiber-optic system by implementing interferometric measurement principles. By controlling the phase of light through the optical path and using polarization states, the system achieves high measurement precision that would normally require larger electronic detector systems, while maintaining the compact fiber-optic form factor.
Solution Approach 2:
The patent applies specific local optical properties (polarization states, interference patterns) at critical points in the optical path to enhance measurement precision. By optimizing the local optical characteristics at the scale grating and detector interfaces, the system achieves high resolution and accuracy within a compact fiber-optic configuration.
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 encoder provides unprecedented size, resolution, and accuracy while operating with fine scale grating pitches, offering economical fabrication and high-speed displacement measurement capabilities.
Implementation Method 1
a source grating that diffracts and splits the source light into at least +/− 1 st order source light beams
Implementation Method 2
a pair of mirrors that are arranged to receive and reflect the +/− 1 st order source light beams to converge toward the scale grating
Implementation Method 3
receive and reflect +/− 1 st order scale light beams diffracted by the scale grating
Implementation Method 4
an interference field generating grating that receives and diffracts the converging +/− 1st order scale light beams, to produce an interference illumination field
Implementation Method 5
Movement of the fringes in the interference illumination field corresponds to relative displacement between the scale and the readhead and is sensed by the fiber-optic detector channels
Data Source
AI summary
An ultra-miniature interferometric fiber-optic encoder readhead for sensing displacement of a very fine pitch scale grating is disclosed. The readhead includes a source grating that diffracts diverging source light into +/− 1st order beams, a pair of mirrors that reflect the +/− 1st order beams to converge toward the scale grating. The +/− 1st order scale light beams are reflectively diffracted back from scale grating to return to the mirrors, and are then reflected to converge back toward the light source and a set of adjacent fiber-optic receiver channels. An interference field generating grating positioned in front of the receiver channels produces interference fringes having a desired pitch. Movement of the interference fringes is sensed by the fiber-optic receiver channels to provide displacement information. The readhead may be configured so that primarily or only +/− 1st order light reaches the receiver channels.