DFB Laser Phase-Shift Grating and AR Coatings for SMSR
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Solution Overview
Problem
Conventional distributed feedback lasers face challenges in achieving high slope efficiency and side mode suppression ratio, particularly in high-speed optical networks, due to issues with laser energy distribution and phase-shift grating designs, which can lead to reduced threshold currents and signal noise ratio.
Innovation Solution
A distributed feedback laser structure with a phase-shift grating structure and a gratingless area in the grating layer, combined with anti-reflection coatings on both lateral sides, is introduced to improve slope efficiency and side mode suppression ratio, featuring a semiconductor-laminated structure with a grating layer and ridge structure, where the phase-shift grating provides a phase-difference distance and the gratingless area maintains consistent phase across micro-grating structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phase-shift grating design is introduced to improve side mode suppression ratio, then SMSR is improved, but random phase problems occur and slope efficiency decreases
Solution Approach 1:
The grating layer is segmented into three distinct regions: a first grating region with micro-grating structures, a phase-shift grating structure in the middle, and a second grating region with micro-grating structures. This segmentation allows each region to perform its specific function independently, resolving the contradiction between SMSR improvement and slope efficiency maintenance.
Solution Approach 2:
Different regions of the grating layer are assigned different local qualities: the first and second grating regions provide feedback for lasing, while the phase-shift grating structure provides a specific phase difference (π phase shift) to suppress side modes. This local differentiation enables simultaneous achievement of high SMSR and high slope efficiency.
2Productivity
If mirrors with anti-reflection coating are applied to improve slope efficiency, then slope efficiency is improved, but lasing occurs easily to Fabry-Perot laser mode under low temperatures
Solution Approach 1:
The invention changes the fundamental parameter of the laser cavity from a Fabry-Perot resonator to a distributed feedback resonator. By introducing periodic micro-grating structures in the first and second grating regions, the laser operates in DFB mode which is inherently more stable across temperature variations, while still allowing AR coating to be applied for high slope efficiency.
3Ease of manufacture
If chip splitting is performed to improve manufacturing, then manufacturing is simplified, but random phase problems occur and SMSR yield is reduced
Solution Approach 1:
The phase-shift grating structure is extracted as a distinct, centrally-located component in the grating layer. This extraction ensures that the critical phase-shift function is preserved and properly positioned regardless of how the chip is subsequently split or packaged, eliminating the random phase problems associated with conventional splitting methods.
4Productivity
If phase-shift grating structure is placed adjacent to HR mirror to improve SE, then slope efficiency is improved, but SMSR yield is reduced due to random phase problems
Solution Approach 1:
The invention creates an asymmetric grating structure where the phase-shift grating is positioned in the center of the laser cavity, equidistant from both output faces. This symmetric positioning of the phase-shift element (despite the overall asymmetric DFB structure) ensures consistent phase relationships and eliminates the random phase problems that occur when the phase-shift grating is placed asymmetrically adjacent to the HR mirror.
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 proposed structure enhances slope efficiency and side mode suppression ratio, achieving improved performance in high-speed optical networks by maintaining consistent phase and reducing random phase issues, thereby addressing the limitations of conventional designs.
Implementation Method 1
a phase-shift grating structure (322), wherein the phase-shift grating structure (322) is located at a junction area of the first grating area (321) and the second grating area (323), and a width of the phase-shift grating structure (322) is equal to one quarter of the laser wavelength
Implementation Method 2
a grating layer (32), located on the semiconductor-laminated structure (31), including a plurality of micro-grating structures arranged in a horizontal direction
Implementation Method 3
a first anti-reflection coating (391), located on the laser-out surface (38); and a second anti-reflection coating (392), located to another lateral side of the semiconductor-laminated structure (31) by opposing to the laser-out surface (38)
Implementation Method 4
a semiconductor-laminated structure (31), generating the laser beam with the laser wavelength upon receiving an electric current
Implementation Method 5
the plurality of micro-grating structures being separated to each other largely by spacing equal to one half of the laser wavelength
Data Source
AI summary
A structure of distributed feedback (DFB) laser includes a grating layer having a phase-shift grating structure and a gratingless area. In addition, both side-surfaces of the DFB laser are coated with anti-reflection coating to improve SMSR and to obtain good slope efficiency (SE). The grating layer is divided by the phase-shift grating structure in a horizontal direction into a first grating area and a second grating area adjacent to a laser-out surface of the DFB laser. The phase-shift grating structure provides a phase-difference distance, such that a shift of phase exists between the micro-grating structures located within the first grating area and the other micro-grating structures located within the second grating area. The gratingless area located within the second grating area contains no micro-grating structure, and moreover, the gratingless area will not change the phase of the micro-grating structures located within the second grating area.