Liquid Crystal Variable Optical Attenuator for Laser Distance Measurement
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Solution Overview
Problem
Current optical attenuators for electronic distance measurement modules fail to achieve the required dynamic range of optical density from OD0 to OD5 or OD6, with existing solutions either being inadequate in range, causing increased scattered light, or being unsuitable for use with laser sources due to diffraction issues.
Innovation Solution
A variable optical attenuation unit using liquid crystals with a polarizer and analyzer, optimized for high contrast and fine adjustment, is employed to achieve a dynamic range of over five orders of magnitude in optical density, specifically designed for use in both the transmission and reception channels of electronic distance measurement modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a gray filter wheel with motor-driven attenuation is used, then the attenuation can be adjusted continuously or discretely, but the device complexity increases and the adjustment range is limited to OD 0-3
Solution Approach 1:
The patent replaces the mechanical gray filter wheel system with an electro-optical liquid crystal shutter system. The liquid crystal shutter uses electrical voltage control to adjust optical attenuation, eliminating mechanical moving parts while achieving continuous attenuation adjustment from OD 0 to OD 5+. This substitution resolves the contradiction by maintaining ease of operation through electrical control while dramatically reducing mechanical complexity.
Solution Approach 2:
The patent changes the physical state and optical properties of liquid crystals through voltage control to achieve variable attenuation. By applying different voltages, the liquid crystal molecules reorient, changing the optical path and attenuation characteristics dynamically. This parameter-based control enables continuous adjustment without mechanical complexity.
2Reliability
If high density black and white photographic film is used, then the optical density can reach OD 3-5, but the films are no longer commercially available and production is discontinued
Solution Approach 1:
The patent uses liquid crystal shutters that change their optical properties through voltage control, achieving OD 0-5+ range without relying on discontinued photographic films. The liquid crystal material can be commercially sourced and manufactured, resolving the availability issue while maintaining the required optical density range through electro-optical parameter changes.
3Reliability
If a line or grating structure is used for attenuation, then higher attenuation ratios can be achieved, but diffraction orders produce discrete beam directions that disturb sensor function
Solution Approach 1:
The patent replaces physical line or grating structures with a liquid crystal shutter system that achieves attenuation through electro-optical effects rather than physical diffraction structures. This substitution eliminates diffraction orders and discrete beam directions, maintaining measurement precision while achieving the required attenuation ratios through voltage-controlled optical property changes.
4Adaptability or versatility
If the distance range is increased from less than 1m to several kilometers, then the measurement range is improved, but the signal dynamic range exceeds 5 orders of magnitude requiring higher attenuation capability
Solution Approach 1:
The patent uses liquid crystal shutters that can dynamically adjust their optical attenuation parameter to handle signals spanning 5+ orders of magnitude. By changing the voltage applied to the liquid crystal, the system can adapt to both weak signals from distant targets and strong signals from close targets, maintaining reliability across the extended distance range.
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 solution enables precise adjustment of signal strength over a wide range, reducing scattered light and mechanical complexity, while maintaining high accuracy and efficiency, thus overcoming the limitations of previous attenuator technologies.
Implementation Method 1
A variable optical attenuation unit using liquid crystals with a polarizer and analyzer, optimized for high contrast and fine adjustment
Implementation Method 2
A variable optical attenuation unit using liquid crystals with a polarizer and analyzer
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
The invention relates to a surveying instrument, in particular a total station, laser scanner, profiler, or laser tracker, with an electronic laser distance measuring module comprising an optical transmit channel and an optical receive channel for laser measurement radiation, wherein a variable optical attenuator (100) for the laser measurement radiation is provided in the optical transmit channel and/or optical receive channel. According to the invention, attenuation of light (101) incident on the attenuator (100) is effected by means of liquid crystals. The attenuator (100) comprises at least one polarizer (P), in particular configured as a polarizing sheet (P), a liquid crystal shutter L, in particular comprising nematic liquid crystals with variable transmission, and a first analyzer (A1), in particular configured as a polarizing sheet (A1).The invention also relates to an electronic distance measuring module with an attenuation unit (100) according to the invention and a method for manufacturing an attenuation unit according to the invention.