Transmissive Diffraction Grating for High Resolution Spectroscopy

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Solution Overview

Problem

Reflective diffraction gratings face challenges in achieving high wavelength resolution and diffraction efficiency simultaneously, particularly in spectroscopic applications like Raman spectroscopy, where high resolution and efficiency are needed across a wide wavelength band, and polarization-dependent optical characteristics complicate signal detection.

Innovation Solution

A transmissive diffraction grating design incorporating a polarization conversion layer and refractive index modulation structures in two diffractive layers, where TE polarized light has high diffraction efficiency and TM polarized light is transmitted, optimizing light use efficiency and wavelength resolution through specific refractive index modulation patterns and inclined surfaces.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the grating period is shortened to improve wavelength resolution, then wavelength resolution is improved, but the wavelength band capable of obtaining high diffraction efficiency becomes very narrow

Engineering Contradiction:

Improvewavelength resolutionVSAvoidwavelength band

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The invention divides the incident light into two polarization components (TE and TM) and processes them separately through the diffraction grating. The TE-polarized light component is diffracted with high efficiency, while the TM-polarized light component is transmitted. This segmentation allows the system to achieve high wavelength resolution through the diffracted component while maintaining a wide wavelength band by preserving the transmitted component, thus resolving the contradiction between resolution and wavelength band coverage.

Inventive Principle:

Principle #1Segmentation

2Loss of energy

If the cross-sectional shape is blazed to increase diffraction efficiency, then diffraction efficiency is improved, but it becomes difficult to obtain high diffraction efficiency when the grating period is shortened

Engineering Contradiction:

Improvediffraction efficiencyVSAvoidwavelength resolution

Core Design Contradiction:

Loss of energyVSMeasurement precision

Solution Approach 1:

The invention applies different optical properties to different polarization components locally. The diffraction grating is designed with specific groove shapes that create strong diffraction for TE-polarized light while allowing TM-polarized light to transmit. This local differentiation of optical interaction enables high diffraction efficiency for the TE component even with short grating periods, while the TM component maintains transmission, thus achieving both high efficiency and high resolution.

Inventive Principle:

Principle #3Local quality

3Loss of energy

If a reflective diffraction grating is used to achieve high diffraction efficiency, then diffraction efficiency is improved, but it is difficult to achieve both high wavelength resolution and high diffraction efficiency simultaneously

Engineering Contradiction:

Improvediffraction efficiencyVSAvoidwavelength resolution

Core Design Contradiction:

Loss of energyVSMeasurement precision

Solution Approach 1:

The invention introduces dynamic polarization control by placing a polarization controller before the diffraction grating. This allows the polarization state of the incident light to be adjusted dynamically, enabling optimization of the TE-polarized light component for high-diffraction efficiency applications while maintaining the capability for high wavelength resolution when needed. The polarization controller provides adaptability to switch between prioritizing efficiency or resolution based on application requirements.

Inventive Principle:

Principle #15Dynamics

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 design achieves high diffraction efficiency and improved wavelength resolution across a wide wavelength band, reducing polarization-dependent noise and enhancing signal detection in spectroscopic applications, particularly in Raman spectroscopy.

Implementation Method 1

a polarization conversion layer; a first diffractive layer disposed on one surface side of the polarization conversion layer; and a second diffractive layer disposed on the other surface side of the polarization conversion layer

Methodology Applied

Scientific EffectPolarization conversion: Polarisation

Implementation Method 2

both the first diffractive layer and the second diffractive layer include refractive index modulation structures arranged with a period P in a first direction

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 3

refractive index modulation structures

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS9041924B2Transmissive diffraction grating and detection apparatus

Publication Date: 2015.05.26 SEIKO EPSON CORP

AI summary

A transmissive diffraction grating includes a polarization conversion layer, a first diffractive layer disposed on one surface side of the polarization conversion layer, and a second diffractive layer disposed on the other surface side of the polarization conversion layer. Both the first diffractive layer and the second diffractive layer include refractive index modulation structures arranged with a period P in a first direction, and diffraction efficiency for a TE polarized light component is higher than a diffraction efficiency for a TM polarized light component.