Polarization-Stable VCSEL Using External Dielectric Layers
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Solution Overview
Problem
Surface-emitting laser diodes (VCSELs) suffer from polarization instabilities due to their cylindrically symmetrical structure, leading to random and unstable polarization, which limits their use in polarization-dependent optical systems and reduces production yield, as existing solutions like subwavelength gratings and internal polarization-selective elements complicate manufacturing and affect laser properties.
Innovation Solution
A polarization-stable VCSEL is achieved by applying one or more layers with a polarization-dependent refractive index or absorption on the outside of the laser mirrors, using oblique angle vapor deposition of dielectrics, allowing for independent adjustment of the laser wavelength and minimizing losses, thereby stabilizing polarization without complicating the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If subwavelength gratings or internal polarization-selective elements are used to stabilize polarization, then polarization stability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts the polarization-selective function from the internal laser resonator structure and relocates it to external layers applied on the outside of the laser mirrors. This separation allows the laser resonator to maintain its simple cylindrically symmetrical structure while the external polarization-selective layers provide the necessary polarization stabilization, thereby reducing device complexity while maintaining reliability
Solution Approach 2:
The patent introduces dielectric or metallic layers with subwavelength periodic structures as intermediary elements on the external mirror surfaces. These intermediary layers create effective birefringence that stabilizes polarization without requiring complex internal modifications to the laser structure, resolving the contradiction between polarization stability and structural simplicity
2Reliability
If subwavelength gratings are used for polarization stabilization, then polarization stability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the periodicity parameter of the grating structures to be in the subwavelength range (below approximately half a vacuum wavelength). This parameter change enables the gratings to function as effective birefringent elements while being more tolerant to manufacturing variations, as the subwavelength scale reduces sensitivity to precise dimensional control compared to larger-scale optical elements
3Ease of manufacture
If polarization-selective layers are applied on the outside of laser mirrors, then manufacturing complexity is reduced, but polarization selectivity must be maintained
Solution Approach 1:
The patent employs composite structures consisting of dielectric or metallic layers with specific subwavelength periodic patterns on the external mirror surfaces. These composite materials provide effective birefringence and polarization selectivity through their layered and periodic architecture, maintaining high polarization selectivity while enabling application by standard thin-film deposition techniques that simplify manufacturing
4Reliability
If dielectric gratings with subwavelength periodicity are used, then polarization control is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs dielectric materials that can be applied by oblique angle vapor deposition, creating polarization-selective layers that are effective but may have controlled lifetimes or be replaceable. This approach prioritizes polarization control performance while using materials and methods that are relatively simple and cost-effective to manufacture, reducing the burden of extreme manufacturing precision requirements
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 provides deterministic and stable polarization characteristics with high polarization mode/side mode suppression, ensuring the laser is not sensitive to feedback and maintains optimal laser properties, including wavelength stability and reduced noise in optical data transmission.
Implementation Method 1
Because of the electro-optical effect and anisotropies in the component design as well as asymmetries and fluctuations in the manufacturing process, this degeneracy is eliminated and the VCSEL oscillates dominantly only in the preferred polarization mode
Implementation Method 2
one or more polarization-selective layers are provided for stabilizing the polarization in a region which is located on that side of at least one of the laser mirrors that is opposite the active amplifying region
Data Source
AI summary
The present invention relates to a surface-emitting laser diode with an active amplifying region (2) which is bounded by two laser mirrors (1, 3), while one or more polarization-selective layers (4) are provided for stabilizing the polarization in a region that is located on that side of at least one of the laser mirrors (1, 3) that is opposite the active amplifying region (2), these layers (4) extending parallel to the respective mirror (1; 3) and having a polarization-dependent refractive index and/or absorption.