DFB Semiconductor Laser Waveguide Layout for Stable Single-Mode Output
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Solution Overview
Problem
Existing semiconductor laser elements face a tradeoff between single mode characteristics and optical output (gain), with reducing the waveguide width improving single mode characteristics but decreasing gain, and increasing the width for higher gain leading to deteriorated single mode characteristics and increased power consumption, which affects resolution in gas analysis.
Innovation Solution
A semiconductor laser element with a diffraction grating portion and a broader flat portion connected by a continuously changing width, combined with high-reflection and anti-reflection films on opposite ends, to stabilize single mode output and increase gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser beam is focused tightly on the sample to improve measurement precision, then the measurement precision is improved, but the beam quality deteriorates due to contamination from the sample surface
Solution Approach 1:
The optical system is segmented into separate functional zones: a first objective lens for delivering the laser beam to the sample, and a second objective lens for collecting the Raman signal. This segmentation allows the measurement path to be separated from the contamination-prone area, maintaining beam quality while achieving tight focusing for high measurement precision.
Solution Approach 2:
A beam splitter serves as an intermediary element that directs the laser beam from the first objective lens toward the sample while allowing the Raman signal to be collected by the second objective lens. This intermediary component enables the separation of the excitation and collection paths, preventing contamination of the laser beam while maintaining measurement precision.
2Measurement precision
If the laser beam is delivered close to the sample surface to improve measurement precision, then the measurement precision is improved, but contamination occurs on the sample surface
Solution Approach 1:
The system segments the optical paths by using separate objective lenses for beam delivery and signal collection. The first objective lens delivers the laser beam at a controlled distance from the sample, while the second objective lens collects the Raman signal from a different spatial position, reducing contamination while maintaining measurement precision.
Solution Approach 2:
The beam splitter acts as an intermediary that separates the laser beam path from the Raman signal collection path. This allows the laser to be delivered close to the sample for high measurement precision while the collected signal is routed through a different path that avoids contamination from the sample surface.
3Measurement precision
If a high numerical aperture objective lens is used to improve measurement precision, then the measurement precision is improved, but the depth of field decreases
Solution Approach 1:
The system uses two separate objective lenses with potentially different numerical apertures optimized for their respective functions. The first objective lens can have a high numerical aperture for precise beam delivery, while the second objective lens is optimized for signal collection with an appropriate depth of field, thus resolving the contradiction between measurement precision and depth of field.
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
Stable single mode light output with increased gain is achieved, reducing unintended reflections and lowering chirp rate, thereby improving resolution in gas analysis devices.
Implementation Method 1
a first objective lens delivers a laser beam to a sample, and a second objective lens collects light emitted from the sample
Data Source
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AI summary
The present invention enables single mode light to be stably output while also enabling the intensity thereof to be increased, and is a distributed feedback type of semiconductor laser element (3) in which a diffraction grating (3M) is formed on a waveguide (3L). The waveguide (3L) includes a diffraction grating portion (301) where the diffraction grating (3M) is formed, and a flat portion (302) having a region where the diffraction grating (3M) is not formed and whose width is broader than the diffraction grating portion (302). The flat portion (302) has a connecting portion (303) having a region whose width changes continuously approaching a connection location with the diffraction grating portion (301), and a high-reflection film (HR) is provided on an end surface of the flat portion (302) that is on an opposite side from the connecting portion (303), while an anti-reflection film (AR) is provided on an end surface of the diffraction grating portion (301) that is on an opposite side from the connecting portion (303).