Buried Active Grating DFB Laser for Stable Single-Mode Operation
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Solution Overview
Problem
Conventional complex-coupled DFB lasers face issues with variations in complex coupling coefficient due to grating etching depth variations and random facet grating phase variations, leading to unstable single-mode operation and inefficient output power distribution.
Innovation Solution
A complex-coupled DFB laser design with an active multi-quantum-well grating where the grating is entirely buried in the same semiconductor material, eliminating etching depth-induced variations and using asymmetric anti-reflection coated facets to eliminate random facet phase effects, resulting in independent complex coupling coefficients and asymmetric output powers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grating etching is used to create complex-coupled DFB laser, then single-mode operation is improved, but variations in etching depth cause variations in complex coupling coefficient leading to unstable operation
Solution Approach 1:
The patent changes the material parameter by filling etched grooves with regrown semiconductor material having the same refractive index as the surrounding material. This eliminates the refractive index contrast that causes sensitivity to etching depth variations, thereby stabilizing the complex coupling coefficient while maintaining the single-mode operation benefits of the grating structure.
2Reliability
If asymmetric facet coating is applied to eliminate mode degeneracy, then single-mode yield is improved, but random variations of facet grating phase reduce yield
Solution Approach 1:
The patent changes the optical parameter at the facets by applying asymmetric anti-reflection coatings with different reflectivities (R1≠R2). This asymmetric coating configuration eliminates the random phase variation effects by creating a deterministic phase relationship, thereby improving single-mode yield while compensating for manufacturing variations in facet grating phase.
3Reliability
If quarter-wave phase shift is incorporated, then single-mode operation is improved with perfect AR coatings, but yield deteriorates rapidly with non-zero reflectivities
Solution Approach 1:
The patent applies asymmetric anti-reflection coatings with different reflectivities at the two facets (R1 and R2). This asymmetry creates a preferred lasing direction and eliminates the sensitivity to small reflectivity variations that plagues quarter-wave phase-shifted lasers, thereby maintaining high single-mode operation reliability even with non-ideal facet conditions.
4Device complexity
If symmetric output power distribution is used, then laser cavity is simplified, but output power is reduced due to spatial hole-burning
Solution Approach 1:
The patent introduces asymmetric anti-reflection coatings that create an asymmetric standing wave pattern in the laser cavity. This asymmetry shifts the antinodes away from the facets, reducing spatial hole-burning at the output facets while maintaining overall cavity simplicity. The result is enhanced output power without significant increase in device complexity.
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 design achieves stable single-mode operation with high external quantum efficiency and asymmetric power distribution, reducing sensitivity to external optical feedback and enhancing modulation bandwidth.
Implementation Method 1
complex-coupled distributed feedback (DFB) lasers
Implementation Method 2
asymmetric output powers from anti-reflection (AR) coated laser facets
Data Source
AI summary
A distributed feedback semiconductor laser may have (1) a controlled complex-coupling coefficient which is not affected by grating etching depth variation, and (2) facet power asymmetry with no facet reflection which eliminates a random effect of facet grating phase. The device comprises a multiple-quantum-well active region, and a complex-coupled grating formed by periodically etching grooves through a part of the active region. The semiconductor materials for a barrier layer where the groove etching is to be stopped, a regrown layer in the etched groove, and a laser cladding layer, are chosen all the same, so as to form an active grating entirely buried in the same material, providing a complex-coupling coefficient which is defined independently of the etching depth. Facet power symmetry may also be provided by composing the laser cavity of two sections (“front” and “back” sections) having different (“front” and “back”) Bragg wavelengths.