Strain-Compensated VCSEL DBR Mirrors for Wider Tuning Range
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing tunable vertical cavity surface emitting lasers (VCSELs) face limitations in tuning range due to the bandwidths of laser cavity mirrors and laser cavity length, particularly in the 1310 nm and 1060 nm bands, which are crucial for optical coherence tomography (OCT) applications, where improved epitaxially-grown mirrors with higher reflectivity, broader spectral width, and fewer layers are needed.
Innovation Solution
Employing semiconductor DBR mirrors with higher refractive index contrast by expanding the material system beyond AlGaAs, using strain-compensated layers such as InGaAs/AlGaAsP or InGaAsN/GaAlAsP, which balance compressive and tensile strain, and incorporate materials lattice-matched to the substrate, such as InGaAsN/Sb, to achieve improved DBR mirror spectral reflection bandwidth and TVCSEL tuning range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If standard GaAs/AlGaAs DBR mirrors are used, then the device structure is simple and manufacturing is easier, but the refractive index contrast is limited and tuning range is restricted to around 100 nm
Solution Approach 1:
The patent employs composite semiconductor materials including InGaAs, InGaAsN, and AlGaAsP to create DBR mirrors with higher refractive index contrast. This composite material approach enables tuning ranges exceeding 100 nm while maintaining device performance, directly resolving the contradiction between limited tuning range and material system simplicity.
Solution Approach 2:
The patent changes material composition parameters by incorporating nitrogen into InGaAs layers (creating InGaAsN) and phosphorus into AlGaAs layers (creating AlGaAsP). These parameter changes increase the refractive index contrast between high and low index layers, thereby expanding the tuning range beyond the limitations of standard GaAs/AlGaAs systems.
2Adaptability or versatility
If DBR mirror bandwidth is increased to extend tuning range, then more layers or higher index contrast is needed, but this increases manufacturing complexity and potential strain-related defects
Solution Approach 1:
The patent modifies material bandgap parameters through composition control in InGaAsN and AlGaAsP layers. By adjusting the nitrogen and phosphorus content, the patent achieves higher refractive index contrast with controlled strain, increasing DBR bandwidth and tuning range while minimizing strain-related defects through optimized material parameters.
Solution Approach 2:
The patent applies different material compositions to different DBR layers, with InGaAsN layers providing high refractive index and AlGaAsP layers providing low refractive index. This local differentiation of material quality across the DBR structure enables higher overall bandwidth while managing strain distribution to reduce defects.
3Reliability
If the number of DBR layers is reduced for simpler manufacturing, then manufacturing precision may suffer and reflectivity may decrease, but if more layers are added to improve reflectivity, then manufacturing complexity increases
Solution Approach 1:
The patent uses composite InGaAsN/AlGaAsP material systems with enhanced refractive index contrast to achieve high mirror reflectivity with fewer DBR layer pairs compared to conventional GaAs/AlAs systems. This reduces manufacturing complexity while maintaining or improving reflectivity performance through superior material properties.
Solution Approach 2:
By changing the refractive index parameters through material composition (InGaAsN and AlGaAsP), the patent increases the optical contrast per layer pair. This allows achieving the same or better reflectivity with fewer total layers, simplifying the device structure and reducing manufacturing complexity while maintaining high reliability.
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 expanded material systems result in increased DBR mirror spectral reflection bandwidth and TVCSEL tuning range, enhancing device reliability and performance by reducing strain-related defects and allowing for larger H/L layer pairs, thereby increasing the laser's tuning capability.
Implementation Method 1
The approach here can include full control over the DBR structure strain either by balancing compressive and tensile strain of alternating mirror layers
Implementation Method 2
semiconductor distributed Bragg reflector (DBR) mirrors supporting tuning ranges on the order of 100 nm
Implementation Method 3
distributed Bragg reflector mirrors with higher refractive index contrast
Data Source
AI summary
Tunable VCSELs (TVCSELs) employing expanded material systems with expanded mechanical/optical design space for semiconductor DBR mirrors on GaAs substrates. One is the InGaAs/AlGaAsP material system. It adds indium In to decrease InGaAs H-layer bandgap for higher refractive index and higher DBR layer refractive index contrast. Adding phosphorus P gives independent control of bandgap and strain of AlGaAsP low refractive index L-layers. The tensile strain of AlGaAsP L-layer compensates compressive strain of InGaAs H-layer and lowers the cumulative strain of the multilayer DBR structure. Another option is the InGaAsN(Sb)/AlGaAsP material system, where both types of layers can be lattice matched to GaAs. It uses indium In and nitrogen N, and possibly antimony Sb, to get independent control of strain and bandgap, and thus refractive index, of dilute nitride InGaAsN(Sb) H-layers, with lower bandgap and higher refractive index than starting GaAs. Using expanded material system enables reliable DBR mirrors with higher reflectivity and spectral bandwidth and tunable VCSELs with wider tuning range.