Second-Order Diffraction Correction in Fiber-Optic Spectrometers

Solution Overview

Problem

Miniature spectrometers face accuracy issues due to second-order diffraction, where light of different wavelengths mixes at detector pixels, leading to errors in intensity measurement, which conventional methods attempt to mitigate by using costly linearly-graded high-pass filters.

Innovation Solution

A method to correct for second-order diffraction errors by determining the relationship between first-order and second-order light outputs, calculating the expected contribution of second-order light, and subtracting it from the spectrometer output, thereby eliminating the need for costly optical filters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If linearly-graded high-pass filters are used to block second-order light, then measurement precision is improved, but manufacturing cost increases and alignment complexity increases

Engineering Contradiction:

Improvemeasurement precisionVSAvoidmanufacturing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent extracts and removes the harmful second-order diffraction component from the detected light signal through mathematical processing. By measuring the second-order component separately (using the relationship between first and second order intensities) and subtracting it from the total signal, the harmful effect is isolated and eliminated without requiring physical filters.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/optical filtering system with a computational/mathematical system. Instead of using linearly-graded high-pass filters to physically block second-order light, the invention uses mathematical relationships and signal processing to identify and remove the second-order contribution from the measured spectrum.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If linearly-graded high-pass filters are used to block second-order light, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvemeasurement precisionVSAvoidalignment complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts and removes the harmful second-order diffraction component from the detected light signal through mathematical processing. By measuring the second-order component separately (using the relationship between first and second order intensities) and subtracting it from the total signal, the harmful effect is isolated and eliminated without requiring physical filters.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/optical filtering system with a computational/mathematical system. Instead of using linearly-graded high-pass filters to physically block second-order light, the invention uses mathematical relationships and signal processing to identify and remove the second-order contribution from the measured spectrum.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If the wavelength range is restricted to avoid second-order diffraction, then measurement precision is improved, but adaptability decreases

Engineering Contradiction:

Improvemeasurement precisionVSAvoidwavelength range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent converts the harmful second-order diffraction effect into a useful measurement. By establishing the mathematical relationship between first and second-order intensities, the second-order component that was previously a source of error becomes a measurable quantity that can be used to correct the spectrum, allowing full wavelength range operation with high precision.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 effectively removes second-order light signals from the spectrometer output, improving measurement accuracy across the entire wavelength range without the expense and alignment challenges of linearly-graded filters, resulting in accurate intensity measurements similar to those with filters in place.

Implementation Method 1

Most miniature spectrometers use diffraction gratings to spread out the light to be analyzed into its constituent wavelengths

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS8908177B2Correction of second-order diffraction effects in fiber-optic-based spectrometers

Publication Date: 2014.12.09 KLA CORP

AI summary

Embodiments described herein correct errors in spectrometer outputs due to the presence of second-order light. Embodiments determine a relationship between first-order light and second-order light of the spectrometer output. The relationship is a function of wavelength and an output of the spectrometer due to the first-order light. The relationship is used to determine an estimated contribution of the second-order light to the output. Spectrometer errors introduced by the second-order light are corrected by adjusting the spectrometer output according to the estimated contribution of the second-order light.