Optical Measuring Device Wavelength Calibration via Periodic Filter
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Solution Overview
Problem
Optical measuring systems face challenges in accurately determining wavelengths, especially when tunable lasers suffer from mode hopping, which can lead to erroneous interpolation and measurement errors due to unpredictable wavelength jumps.
Innovation Solution
An optical measuring device comprising a computation circuit, a periodic optical filter, and a continuous output optical filter that processes signals from detectors to identify wavelengths and correct for mode hops, using quantization and interpolation to provide robust wavelength calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a tunable narrow band reference light source (laser) is used for wavelength calibration, then measurement capability is improved, but the system becomes sensitive to mode hops that cause measurement errors
Solution Approach 1:
A periodic optical filter is introduced as an intermediary component between the tunable laser and the sensing device. This filter provides reference wavelength markers that remain stable even when the laser experiences mode hops, allowing the system to detect and correct for wavelength deviations caused by mode hopping events
Solution Approach 2:
The system implements feedback by continuously monitoring the transmission peaks of the periodic optical filter and comparing them against expected wavelength positions. When deviations are detected (indicating mode hops), the system can compensate for these errors by adjusting the wavelength calibration accordingly
2Ease of manufacture
If broadband light with a low cost tunable narrow band filter is used, then cost is reduced, but wavelength determination accuracy deteriorates when mode hops occur
Solution Approach 1:
The periodic optical filter serves as a reference intermediary that provides known wavelength markers. This allows the low-cost tunable filter system to achieve accurate wavelength determination by referencing these stable markers, even when the tunable filter itself experiences mode hops or drift
Solution Approach 2:
The system changes the operational parameters by scanning the tunable filter across a wavelength range and detecting transmission peaks at specific wavelengths defined by the periodic filter. This allows dynamic wavelength determination that can adapt to and correct for mode hop conditions
3Measurement precision
If interpolation is used to estimate wavelengths between peaks, then measurement resolution is improved, but measurement reliability deteriorates when mode hops cause unpredictable wavelength jumps
Solution Approach 1:
The system uses feedback from the periodic optical filter peaks to detect mode hop events. When a mode hop is detected (by comparing expected vs. actual peak positions), the system can identify that interpolation should not be applied, thereby maintaining reliability while preserving resolution during normal operation
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 accurate wavelength calibration and measurement, even in the presence of mode hops, by using a combination of periodic and continuous filters to quantify and correct for wavelength changes, thereby reducing errors and improving measurement reliability.
Implementation Method 1
a first Fabry-Perot interferometer is dimensioned to provide relatively small differences between successive wavelengths of the comb filter
Implementation Method 2
the resonance wavelength of the tunable filter is scanned
Implementation Method 3
a fibre Bragg based sensor device reflects light in the fibre, with wavelength dependent reflection properties
Data Source
AI summary
An optical measuring device measures a wavelength of a response from a sensing device. The optical measuring device contains a light path coupled to an interface for coupling the light path to the sensing device. A periodic optical filter has an input coupled to the light path, to sample light that is supplied to or received from the sensing device. A continuous output optical filter has an input coupled the light path to sample light that is supplied to or received from the sensing device. A computation circuit is coupled to detectors at the periodic optical filter and the continuous output optical filter. The computation circuit is programmed to process output signals from the detectors obtained during a wavelength scan. The processing involves quantization of data derived from the continuous filter wavelengths associated with respective time points at which the wavelength scan reaches corresponding positions in respective periods of the periodic optical filter. The processing computes a wavelength associated with the response of the sensing device from the identified wavelengths on the basis of a temporal relation between said respective time points and a time point of the response of the sensing device.