Distributed Feedback Laser Diode With Graded Grating Coupling
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Solution Overview
Problem
Existing distributed feedback laser diodes face challenges in achieving high output power with narrow linewidth due to conflicting requirements of grating strength and optical coupling efficiency, which are exacerbated by manufacturing tolerances and saturation effects, particularly in high-order gratings.
Innovation Solution
A laser diode design with a high-order surface grating that adapts its coupling strength to the optical power density by varying parameters such as trench depth, width, and refractive index along the resonator axis, using a coupling parameter that decreases from the back to the front facet, reducing interaction in high-power regions to minimize losses and saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a strongly interacting grating is used to achieve narrow laser emission, then the linewidth is reduced, but the output coupling efficiency decreases and optical losses increase
Solution Approach 1:
The grating structure implements local quality variations by having different trench depths at different positions along the resonator. The trenches have maximum depth at the rear facet and progressively shallower depth toward the front facet, creating position-dependent coupling strength that optimizes both linewidth and output coupling efficiency at different locations within the laser diode
Solution Approach 2:
The invention applies parameter changes by systematically varying the trench depth parameter along the resonator length. This continuous parameter variation allows the grating coupling strength to be adapted to the local optical power density distribution, achieving optimal performance for both narrow linewidth and high output coupling efficiency
2Ease of manufacture
If high-order gratings are used to reduce processing requirements, then lithography complexity is reduced, but manufacturing tolerances for grating depth become extremely small
Solution Approach 1:
The grating design uses local quality variations with different trench depths at different positions, which provides robustness against manufacturing tolerances. The position-dependent depth profile ensures that even with variations in fabrication, the overall apodization function is maintained, reducing sensitivity to depth errors compared to uniform high-order gratings
3Measurement precision
If uniform gratings are used to achieve narrow linewidth, then the spectral purity is improved, but the thermal tuning window and conversion efficiency are limited
Solution Approach 1:
The invention implements parameter changes by varying the trench depth parameter along the resonator length, creating a graded apodization profile. This parameter variation enables the grating to maintain narrow linewidth while providing enhanced thermal tuning characteristics and broader operational flexibility compared to uniform gratings
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 achieves improved optical coupling efficiency and reduced saturation effects, allowing for higher output power with narrower linewidth and enhanced thermal tuning stability, while minimizing the impact of manufacturing fluctuations.
Implementation Method 1
distributed feedback laser diodes (DFB laser diodes) are monolithically constructed, frequency-stabilized laser light sources
Implementation Method 2
The frequency-selective element is usually a Bragg grating located in the immediate vicinity of the active layer
Implementation Method 3
a wave-guiding region at least partially surrounding the active layer
Data Source
Figure 1~2
Figure 3a
Figure 3b
AI summary
The invention relates to a laser diode (100) comprising: an active layer (10); a wave guiding region (12) which surrounds the active layer (10) at least in part; a rear facet (14); a front facet (16) designed for decoupling laser radiation, wherein the active layer (10) extends, at least in part, along a first axis (X) between the rear facet (14) and the front facet (16); and a grid (18) which is operatively connected to the wave-guiding region (12), wherein the grid (18) comprises a plurality of webs (22) and trenches (24), characterized in that the plurality of trenches (24) is designed such that an average rise of a coupling parameter P is not equal to zero for the plurality of trenches (24) along the grid (18), wherein the coupling parameter P of a trench (24) is defined by the formula (I), wherein d res is a distance of the trench (24) to the active layer (10), wis a width of the trench (24) and Δn is the refractive index difference between a refractive index of the trench (24) and a refractive index of a material surrounding the trench (24). The invention in particular relates to a laser diode in which a distributed feedback occurs over a surface grid of high order while radiation is decoupled on one side and in which the coupling strength of the grid is matched to the power density of the wave guided in the laser diode.