Variable-Wavelength Laser Grating Layout for Mode-Hop Suppression
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Solution Overview
Problem
Variable-wavelength lasers face the challenge of mode hop, where light oscillates at a wavelength different from the desired wavelength due to significant differences in refractive indices between gain and wavelength control regions, leading to unstable operation.
Innovation Solution
A variable-wavelength laser design with diffraction gratings in gain and wavelength control regions, and a region without diffraction gratings at the ends, where the length of this region is between 5% and 30% of the respective region's length, to suppress mode hop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If diffraction gratings are arranged in both gain region and wavelength control region, then wavelength control function is improved, but mode hop occurs due to significant refractive index differences
Solution Approach 1:
The patent extracts the diffraction grating from the wavelength control region, leaving only the gain region with diffraction grating. This removes the source of harmful refractive index discontinuities while preserving the essential wavelength selection function through the gain region grating alone.
Solution Approach 2:
The patent applies different structural qualities to different regions: the gain region contains a diffraction grating for wavelength selection, while the wavelength control region has a uniform refractive index without diffraction grating. This local differentiation optimizes each region's function while avoiding mode hop.
2Reliability
If diffraction grating is removed from wavelength control region, then mode hop is suppressed, but wavelength control precision may be reduced
Solution Approach 1:
The patent uses the gain region diffraction grating as an intermediary element that performs both wavelength selection and stabilization functions. The grating in the gain region acts as a distributed feedback mechanism that compensates for the absence of grating in the wavelength control region, maintaining precision without causing mode hop.
3Reliability
If region without diffraction grating is made larger, then mode hop suppression is improved, but device length increases
Solution Approach 1:
The patent removes the diffraction grating completely from the wavelength control region rather than partially, creating a fully uniform refractive index zone. This excessive removal of grating structure ensures complete elimination of refractive index discontinuities and mode hop, while the resulting device length increase is acceptable for achieving reliable 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 design effectively suppresses mode hop, allowing the laser to oscillate at a desired wavelength by controlling the refractive index of the wavelength control region, ensuring stable operation and reducing unwanted sub-peaks in reflectance spectra.
Implementation Method 1
a diffraction grating arranged in each of the gain region and the wavelength control region
Implementation Method 2
a wavelength control function as an optical device... controlling the refractive index of the wavelength control region
Data Source
AI summary
A variable-wavelength laser includes a gain region and a wavelength control region alternately arranged along a propagation direction of light, a diffraction grating arranged in each of the gain region and the wavelength control region, and a region located at least one of an end of the gain region and an end of the wavelength control region at a boundary between the gain region and the wavelength control region, the region being without the diffraction grating, wherein a length of the region without the diffraction grating is 5% or more and 30% or less of a length of the gain region or the wavelength control region to which the region belongs.