Waveguide Depletion Tuning for Low-Astigmatism Laser Emission
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Solution Overview
Problem
Astigmatic light output profiles in gain-guided or quasi-gain-guided solid-state light emitters, such as semiconductor lasers, are challenging due to lateral carrier spreading and surface recombination, which complicates optical beam shaping and increases threshold current, leading to inefficient device performance.
Innovation Solution
The use of electrically tunable depletion regions and optical loss structures in the vicinity of carrier flow and optical mode propagation, created by highly resistive Schottky contacts or metal-insulator-semiconductor structures, reduces lateral carrier diffusion and astigmatism without complex fabrication processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If gain-guiding is used to achieve optical mode guiding in the junction plane, then optical mode confinement is improved, but lateral carrier spreading increases causing astigmatic beam output
Solution Approach 1:
A depletion region is introduced as an intermediary structure between the gain-guided active region and the lateral carrier flow. This depletion region, created by a Schottky contact or MIS structure, acts as a mediator that blocks lateral carrier diffusion while allowing the optical mode to remain confined by gain-guiding, thus eliminating astigmatism without sacrificing mode confinement
Solution Approach 2:
The patent applies local quality by creating a depletion region with specific electrical properties in a localized area adjacent to the waveguide. This localized depletion region selectively blocks carriers in the lateral direction while maintaining the optical guiding properties in the vertical direction, achieving different functional qualities in different spatial regions
2Ease of operation
If etching through the active region is performed to achieve full index-guiding, then astigmatism is eliminated, but surface recombination increases and threshold current rises
Solution Approach 1:
The patent extracts the carrier blocking function from the waveguide structure itself and places it in a separate depletion region created by a Schottky contact or MIS structure. This allows the waveguide to maintain its full index-guiding structure without etching through the active region, while still achieving the desired carrier confinement to eliminate astigmatism
Solution Approach 2:
The patent segments the carrier confinement function from the optical guiding function. The index-guiding waveguide structure handles optical confinement, while a separate depletion region handles lateral carrier blocking. This segmentation allows each function to be optimized independently without the trade-offs inherent in combined approaches
3Reliability
If multiple epitaxial growth steps are used to fabricate double buried heterostructure, then surface recombination is reduced and heat removal is improved, but fabrication complexity increases
Solution Approach 1:
The patent merges the carrier blocking function into a single epitaxial growth step by forming a Schottky contact or MIS structure on the existing waveguide structure. This combines the benefits of carrier confinement and thermal management into a unified structure that can be fabricated in a single growth run, eliminating the need for separate overgrowth steps
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 approach enhances device performance by reducing astigmatism, lowering threshold current, and improving heat transport, enabling efficient light coupling and modulation, particularly in photonic applications like telecommunications and sensing.
Implementation Method 1
A depletion region is disposed in the epitaxial layers under each of the first and second metal contact pads, extending from the first and second metal contact pads to the active region
Implementation Method 2
utilization of an electrically tunable depletion region and/or (ii) additional optical loss structures in the vicinity of carrier flow and optical mode propagation
Implementation Method 3
optical mode guiding in the junction plane (epitaxial layer plane) is achieved by gain-guiding
Implementation Method 4
an active region comprising at least one active layer configured to allow carrier recombination and light generation
Implementation Method 5
An anti-reflective coating is disposed on the at least one output mirror, the anti-reflective coating being configured to prevent self-lasing
Implementation Method 6
the crystal lattice surrounding the active region is unhindered, and heat transport by phonon interaction remains very effective
Data Source
AI summary
Solid-state optical devices (10) enable tuning of an electrically tunable depletion region (200) to reduce and block lateral (in-junction) carrier spreading. This capability reduces the negative effects of gain-guiding in the junction plane and reduces an astigmatism of an emitted light beam. The tunable depletion region is created by forming a highly resistive Schottky contact (105, 110) or metal-insulator-semiconductor (MIS) structure (205, 210) next to a waveguide (optical mode propagation) and current injection region (215), where lateral spread due to diffusion is expected. The depletion region area is tuned by applying a bias to the highly resistive Schottky contact or the MIS contact structure. Such contacts or similar lossy structures reduce in-junction plane gain-guiding also when unbiased by creating additional optical loss for the mode, thus reducing the effective carrier density participating in light generation, thereby reducing astigmatism.