Semiconductor Laser Asymmetric Phase Shift Grating
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Solution Overview
Problem
Semiconductor lasers with diffraction grating structures face challenges in maintaining single-mode operation at high optical output and suffer from modulation characteristic deterioration in the low frequency range due to localized light intensity and spatial hole burning, which affects frequency characteristics and fabrication yield.
Innovation Solution
A semiconductor laser design featuring a diffraction grating structure with a first, second, and third diffraction grating region arranged sequentially, where the second region has a modulated pitch and an asymmetric phase shift, optimized with an anti-reflection and reflection film coating on facets, and an optical coupling coefficient greater than 120 cm^-1, to enhance frequency characteristics and yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform diffraction grating structure is used in a semiconductor laser, then the laser can be fabricated with simple structure, but oscillation occurs with two wavelengths and single-mode operation cannot be maintained
Solution Approach 1:
The patent introduces a quarter-wave phase shift in the diffraction grating structure, creating an asymmetric phase distribution that suppresses one of the two oscillation modes. This phase shift breaks the symmetry of the standing wave pattern, allowing single-mode operation while maintaining the overall simplicity of the DFB laser structure.
Solution Approach 2:
The patent applies a localized phase shift of λ/4 at a specific position within the diffraction grating region. This local modification of the grating phase creates a node in the standing wave pattern that suppresses one oscillation mode, while the rest of the grating maintains its uniform structure for easy fabrication.
2Speed
If optical coupling coefficient is increased to improve transmission speed, then differential gain improves and relaxation oscillation frequency increases, but threshold gain decreases and fabrication yield suffers
Solution Approach 1:
The patent optimizes the optical coupling coefficient κ to be greater than 120 cm^-1, which is a specific parameter change that balances the trade-off between transmission speed and fabrication yield. This parameter optimization ensures high differential gain and relaxation oscillation frequency while maintaining acceptable threshold gain for practical fabrication.
3Speed
If cavity length is shortened to increase transmission speed, then relaxation oscillation frequency increases, but volume of active layer decreases and power handling capability is reduced
Solution Approach 1:
The patent specifies an optimal cavity length range of 150-300 μm that balances the competing requirements of high transmission speed (requiring short length for high relaxation oscillation frequency) and sufficient power handling capability (requiring adequate active layer volume). This parameter optimization resolves the contradiction between speed and volume.
4Stability of the object's composition
If diffraction grating pitch is modulated to reduce light intensity localization, then spatial hole burning is suppressed and single-mode operation is maintained, but device structure becomes more complex
Solution Approach 1:
The patent introduces a quarter-wave phase shift in the diffraction grating structure, creating an asymmetric phase distribution that suppresses one of the two oscillation modes. This phase shift breaks the symmetry of the standing wave pattern, allowing single-mode operation while maintaining the overall simplicity of the DFB laser structure.
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 improves frequency characteristics by suppressing roll-off in the low frequency range and increasing the 3 dB bandwidth, while maintaining high fabrication yield and reliability, enabling high-speed operation with a low threshold current and extended lifespan.
Implementation Method 1
a diffraction grating in which a first diffraction grating region that has a periodic structure with a first pitch, a second diffraction grating region that has a periodic structure with a second pitch different from the first pitch, and a third diffraction grating region that has the periodic structure with the first pitch are arranged sequentially and contiguously side by side along a direction of light propagation
Implementation Method 2
an anti-reflection film that is coated on one facet to the light-emitting side
Implementation Method 3
a reflection film that is coated on the other facet that is opposite the facet to the light-emitting side
Data Source
AI summary
In the semiconductor laser including a diffraction grating in which a first diffraction grating region with a first pitch, a second diffraction grating region with a second pitch and a third diffraction grating region with the first pitch, an anti-reflection film coated on an end facet to the light-emitting side, and a reflection film coated on an opposite end facet, the first diffraction grating region is greater than the third diffraction grating region, and the second diffraction grating region is formed, in such a manner that phases of the first and third diffraction grating regions are shifted in a range of equal to or more than 0.6 π to equal to or less than 0.9 π, phases are successive on a boundary between the first and second diffraction grating regions and the phases are successive on a boundary between the second and third diffraction grating regions.