Aperiodic Grating Structure for Stable Single-Mode DFB Lasers
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Solution Overview
Problem
Existing diffraction gratings in waveguide devices, such as DFB lasers, suffer from unwanted spectral features and instability due to periodic structures, leading to undesirable lasing modes and reduced single-mode yield, especially when high coupling coefficients or injection levels are reached, affecting stability and efficiency.
Innovation Solution
A synthesized aperiodic grating with non-uniform low and high index profiles is designed to manipulate transmission or reflection spectra, using an iterative method to create aperiodic variations in refractive index, allowing for adjustable stop-bands and transmission peaks to suppress unwanted ripples and achieve stable single or multi-frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a periodic grating structure is used in waveguide devices, then the device can achieve simple manufacturing and basic diffraction function, but unwanted spectral features and spurious lasing modes appear, reducing single-mode yield and stability
Solution Approach 1:
The patent applies asymmetry by transitioning from a periodic grating structure to an aperiodic structure where the grating period varies along the waveguide. This asymmetric variation in periodicity eliminates the formation of spurious spectral features and unwanted lasing modes while maintaining manufacturing feasibility through controlled fabrication processes.
Solution Approach 2:
The patent implements local quality by allowing different regions of the grating to have different local periods. Each section of the grating is designed with specific local periodicity tailored to suppress unwanted modes in particular spectral regions, while the overall structure maintains manufacturability through systematic variation rather than complete randomness.
2Ease of manufacture
If a uniform grating profile is used, then the manufacturing process is simplified, but the transmission spectrum exhibits unwanted ripples and additional lasing modes
Solution Approach 1:
The patent applies local quality by varying the grating period locally along the waveguide structure. This local variation in periodicity allows suppression of unwanted spectral ripples and spurious lasing modes in specific regions without requiring complete redesign of the entire manufacturing process, maintaining ease of fabrication through controlled local modifications.
Solution Approach 2:
The patent implements parameter changes by systematically varying the grating period parameter along the waveguide length. This continuous or discrete variation in the periodicity parameter eliminates the formation of unwanted spectral features while remaining compatible with standard fabrication techniques that can accommodate graded structures.
3Power
If high coupling coefficients are used in periodic gratings, then the diffraction efficiency is improved, but the device becomes unstable and produces unwanted lasing modes
Solution Approach 1:
The patent applies asymmetry to resolve the contradiction between high diffraction efficiency and stability. By using an aperiodic grating structure with varying period, the system maintains strong coupling effects for high diffraction efficiency while the lack of uniform periodicity prevents the formation of unstable spurious modes, allowing operation at high coupling coefficients without stability loss.
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 synthesized aperiodic grating effectively suppresses unwanted spectral features, enhancing side-mode suppression ratio, stability, and production yield of single-mode DFB lasers, enabling precise control over emission wavelengths and frequency operation, suitable for diverse applications including telecommunications and photonic microwave generation.
Implementation Method 1
synthesized aperiodic grating... having non-uniform low and high index profiles that can be adjusted to manipulate the transmission or reflection spectra of the grating
Implementation Method 2
aperiodic variations in refractive index... to suppress unwanted ripples and achieve stable single or multi-frequency operation
Data Source
AI summary
A synthesized grating is provided comprising a substrate/layer, and a plurality of alternating aperiodic non-uniform low and high index profiles on a surface of the substrate/layer defining a transmission/reflection spectrum for one of either single or multi-frequency operation of said grating in an optical cavity. A method is also provided for designing the synthesized grating, comprising determining a grating structure of given profiles through analysis of an optimized weighted sum and mapping the grating profile to said surface with the plurality of alternating non-uniform low and high index profiles. A distributed feedback laser is also provided having top, bottom and two sides, comprising a top electrode, a cladding layer disposed below the top electrode a bottom electrode, a substrate disposed above the bottom electrode, one of either an active or passive waveguide layer, a synthesized aperiodic grating layer providing distributed mirrors, and wherein the waveguide layer and synthesized aperiodic grating layer are disposed between said the substrate and cladding layer and are separated by a spacer layer.