Bandpass Filter With Chirped Grating And Absorber
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Solution Overview
Problem
Current radiation sources require tailoring for specific applications, such as mid-infrared emitter applications, and there is a need for a bandpass transmission filter that offers a combination of a narrow transmission band and a spectrally broad stop-band, while maintaining low structural complexity and cost-effectiveness.
Innovation Solution
The implementation of a bandpass transmission filter with a spectrally broad stop-band and a narrow transmission band at the center wavelength, combined with a broadband emitter, creates a narrowband radiation source. This filter utilizes a waveguide structure with a chirped grating and a radiation absorbing structure to achieve the desired spectral characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bandpass transmission filter is designed with a narrow transmission band, then the spectral selectivity is improved, but the stop-band width is reduced
Solution Approach 1:
The filter is segmented into multiple functional zones: a first grating region with initial pitch for wavelength selection, a second grating region with modified pitch for stop-band extension, and intermediate transition zones. This segmentation allows independent optimization of narrow transmission band and broad stop-band characteristics without mutual interference.
Solution Approach 2:
Different regions of the filter are assigned different local properties: the first grating region has uniform pitch for sharp wavelength selection, while the second grating region has progressively modified pitch to extend the stop-band. The intermediate zones have gradient transitions to maintain performance throughout the structure.
2Ease of manufacture
If the filter structure is simplified to reduce fabrication complexity, then manufacturing cost is reduced, but achieving both narrow transmission band and broad stop-band becomes more difficult
Solution Approach 1:
The invention achieves complex spectral characteristics by changing geometric parameters (grating pitch, zone lengths) rather than introducing complex materials or structures. The pitch modification follows simple mathematical relationships that can be implemented through standard lithographic processes, maintaining ease of manufacture while achieving precise spectral control.
Solution Approach 2:
The filter design incorporates preliminary calculation and optimization of grating parameters before fabrication. The pitch modification zones are pre-designed with specific length and pitch change characteristics to ensure the desired spectral performance is achieved without requiring complex real-time adjustments during manufacturing.
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 proposed solution effectively creates a narrowband radiation source with a narrow transmission band and a broad stop-band, suitable for various applications, including optical sensors, while maintaining low fabrication costs and complexity.
Implementation Method 1
a grating structure (120) having changing grating pitch values (Λi) for diffracting a radiation R propagating in the waveguide structure (110) having a wavelength λ1 which is lower than a center wavelength λ0
Implementation Method 2
a radiation absorbing structure (130) for absorbing a radiation R guided by the waveguide structure (110) having a wavelength λ3 which is higher than the center wavelength λ0
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
According to an aspect, a bandpass transmission filter having a center wavelength λ0 of transmission comprises: a waveguide structure, a grating structure in the waveguide structure, the grating structure having changing grating pitch values Λi for diffracting a radiation in the waveguide structure having a wavelength λ1 which is lower than the center wavelength λ0 (λ1 < λ0), and for reflecting, e.g. a Bragg reflection, a radiation in the waveguide structure having a wavelength λ2 which is higher than the center wavelength λ0 (λ2 >λ0), and a radiation absorbing structure, which is an integrated part of the waveguide structure or is formed as a layer arranged adjacent to the waveguide structure, for absorbing a radiation guided by the waveguide structure having a wavelength λ3 higher than the wavelength λ2, with λ0 < λ2 < λ3.