Surface-Emitting Laser Hybrid Grating for Efficient Feedback Coupling
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Solution Overview
Problem
Conventional surface emitting distributed feedback (SE-DFB) lasers with second-order grating structures suffer from lower efficiency and require larger areas and higher threshold currents due to simultaneous first-order and second-order diffractions, leading to increased light output coupling loss.
Innovation Solution
A hybrid grating structure is introduced, combining first-order and second-order grating structures in the same grating layer, with the first-order structure acting as a high-efficiency reflection feedback area and the second-order structure near the light-emitting surface, along with a λ/4-Shift phase-shift grating structure to stabilize the laser light field and enhance optical coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a second-order grating structure is used in SE-DFB lasers, then the laser emitting angle is reduced and on-wafer testing becomes feasible, but the diffraction efficiency decreases and threshold current increases
Solution Approach 1:
The grating structure is segmented into two distinct regions: a first-order grating region for high-efficiency feedback and a second-order grating region for controlled emission. This segmentation allows each region to perform its specialized function optimally, resolving the contradiction between emission angle control and diffraction efficiency.
Solution Approach 2:
Different regions of the grating layer are assigned different local properties: the first-order region provides strong feedback with high coupling constant, while the second-order region provides controlled emission with appropriate coupling. This local differentiation enables simultaneous optimization of both efficiency and emission characteristics.
2Ease of operation
If a second-order grating structure is used, then the device can operate with smaller emitting angle, but the device area and threshold current must be increased
Solution Approach 1:
By dividing the grating into functional segments with different orders, the patent achieves effective feedback and emission control without requiring uniform increase in overall device area. The first-order region provides efficient feedback in a compact configuration.
3Reliability
If first-order and second-order diffractions occur simultaneously, then the laser can form in-plane cavity, but the light output coupling loss increases
Solution Approach 1:
The grating layer is segmented spatially so that first-order diffraction occurs primarily in the first-order region for efficient feedback, while second-order diffraction occurs in the second-order region for controlled emission. This spatial segmentation reduces simultaneous interference and coupling loss.
Solution Approach 2:
The hybrid grating structure acts as an intermediary mechanism that mediates between the requirements for in-plane cavity formation and efficient light output coupling. By providing structured regions for different diffraction orders, it enables cavity formation while minimizing unwanted coupling losses.
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 a balance between high slope efficiency and low critical current values, improving the optical coupling efficiency and reducing the threshold current, which is challenging for conventional SE-DFB lasers to attain.
Implementation Method 1
the first-order grating structure is formed at the end-surface of laser to act as a high-efficiency reflection feedback area
Implementation Method 2
the second-order grating structure is formed only at the area near to the middle of the laser emitting surface... the second-order diffraction of the micro-grating structure is used in-plane for coupling the forward and backward modes in the waveguide to form a cavity to emit laser light
Implementation Method 3
a λ/4-Shift phase-shift grating structure can also be introduced in the center of the second-order grating structure area, in order to make the laser light field modal stabilized and to improve the optical coupling efficiency of emitted laser light
Data Source
AI summary
The grating layer of a surface emitting laser is divided into a first grating region and a second grating region along a horizontal direction. The second grating region is located at a middle area of the grating layer, while the first grating region is located in an outer peripheral area of the grating layer. Each of the first and second grating regions comprises a plurality of micro-grating structures. The grating period of the micro-grating structures in the first grating region is in accordance with the following mathematical formula:⋀=mλ2*neff;in addition, the grating period of the micro-grating structures in the second grating region is in accordance with the following mathematical formula:⋀=oλ2*neff.Wherein, Λ is the length of grating period, λ is the wavelength of the laser light, neff is the equivalent refractive index of semiconductor waveguide, m=1, and o=2. The first grating region is a first-order grating region, and the second grating region is a second-order grating region, so as to form a hybrid grating structure in the grating layer. The surface emitting laser emits laser light perpendicularly from a light-emitting surface defined by the second grating region.