Reconstruction-Equivalent-Chirp DFB Laser Grating Fabrication
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Solution Overview
Problem
The existing manufacturing processes for DFB semiconductor lasers face challenges in achieving high-performance, complex grating structures efficiently, particularly due to the difficulty in fabricating uniform Bragg gratings, which results in low product yield and high costs, and the need for advanced techniques like electron-beam lithography.
Innovation Solution
The use of reconstruction-equivalent-chirp (REC) technology allows for the design and fabrication of DFB lasers with equivalent gratings using ordinary holographic exposure and sub-micron precision, replacing conventional Bragg gratings with sampled Bragg gratings that have equivalent chirps and phase shifts, enabling the creation of complex grating structures without the need for precise facet control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Bragg gratings are used in DFB lasers, then single-longitude-mode operation can be achieved, but the manufacturing precision and product yield are low due to the difficulty in fabricating uniform gratings
Solution Approach 1:
The patent uses sampled Bragg gratings that replicate the essential feedback function of conventional Bragg gratings through sampling. The sampled grating structure copies the wavelength selection capability while being manufacturable with lower precision requirements using standard holographic exposure techniques
Solution Approach 2:
The patent changes the grating structure parameters from continuous conventional Bragg gratings to discrete sampled gratings with specific sampling periods. This parameter change enables equivalent wavelength selection functionality while significantly reducing manufacturing precision requirements
2Manufacturing precision
If advanced fabrication techniques like electron-beam lithography are used to create complex grating structures, then manufacturing precision improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent employs standard holographic exposure masks instead of expensive electron-beam lithography systems. The sampling period can be controlled by simple mask design rather than complex fabrication processes, dramatically reducing equipment cost and process complexity
Solution Approach 2:
The patent segments the continuous grating structure into discrete sampled points. This segmentation allows the complex grating function to be achieved through simple periodic sampling that can be implemented with basic holographic techniques rather than advanced lithography
3Ease of manufacture
If facet reflections are present in practical DFB lasers, then manufacturing ease improves, but single mode yield decreases due to uncertain reflection phase
Solution Approach 1:
The patent extracts the wavelength selection function from the facet reflections and concentrates it in the sampled Bragg grating structure. By taking out the critical feedback function from the uncertain facet reflections and placing it in the controllable sampled grating, single-mode operation is achieved regardless of facet reflection conditions
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 simplifies the grating fabrication process, reduces costs, and enhances the performance of DFB lasers by allowing control over lasing wavelengths and achieving dynamic single-longitude-mode operation, even under high-speed modulation, while maintaining high side-mode suppression ratios.
Implementation Method 1
Bragg gratings in the semiconductor laser waveguide to select a wavelength longitude mode for lasing
Implementation Method 2
the light can be amplified during the feedback
Implementation Method 3
at least one facet of the two facets is provided with an anti-reflection coating
Data Source
AI summary
Using sampled Bragg grating structure, the present invention proposes a distributed feedback (DFB) semiconductor laser based on reconstruction-equivalent-chirp technology. Namely, the Bragg grating in the said DFB semiconductor laser cavity is a sampled Bragg grating, in which there is an equivalent grating corresponding to the original ordinary DFB grating as feedback for lasing. The laser wavelength of the said semiconductor laser located within the operation bandwidth of the said equivalent grating. The said equivalent grating is designed and fabricated using REC technology and has equivalent chirps, one equivalent phase shift or multiple equivalent phase shifts. The said sampled Bragg grating has multiple ghost gratings and the wavelength spacing between neighboring ghost gratings is inversely proportional to the sampling period and the effective refractive index of the said semiconductor laser. Only one ghost grating except the ghost grating related to the center wavelength is selected to be as equivalent grating. In semiconductor laser fields, only based on sub-micron precision, the present invention provides a method to realize various complex equivalent chirps and equivalent phase shifts in the resonant cavity of the said semiconductor laser. These equivalent chirps and equivalent phase shifts have the same functions with the corresponding true chirps and true phase shifts, so as to avoid the processes of fabrication of grating structure with complex true chirps and true phase shifts.