MEMS Tunable VCSEL for Swept Source OCT
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current tunable VCSELs for OCT applications face limitations in wavelength tuning range due to insufficient DBR reflectivity bandwidth and complex wafer bonding processes required for growing InP-based active regions and GaAs-based DBRs on different substrates.
Innovation Solution
A MEMS tunable quantum dot VCSEL design featuring a GaAs-based DBR with high reflection bandwidth and an active region of quantum dots epitaxially grown on a GaAs substrate, allowing for continuous wavelength tuning without the need for wafer bonding, utilizing an upper vertically movable mirror and a bottom half VCSEL part with a gap that can be adjusted via electrostatic force for increased axial resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If InP-based active region and GaAs-based DBR are grown on different substrates, then the DBR reflectivity bandwidth is sufficient, but the manufacturing process becomes complex due to wafer bonding requirements
Solution Approach 1:
The patent combines the InP-based active region and GaAs-based DBR into a single epitaxial structure grown on a common GaAs substrate. This merging eliminates the need for separate wafer bonding processes while maintaining the high reflectivity bandwidth of the GaAs-based DBR and the performance of the InP-based active region.
Solution Approach 2:
The patent introduces an InGaAs intermediate layer that serves as a buffer between the GaAs substrate and the InP-based active region. This intermediary layer facilitates lattice matching and reduces dislocation density, enabling the growth of high-quality InP structures on GaAs substrates without complex bonding processes.
2Ease of manufacture
If InP-based active region is grown on GaAs-based DBR, then the manufacturing process is simplified, but the wavelength tuning range is limited by insufficient DBR reflectivity bandwidth
Solution Approach 1:
The patent changes the material composition parameters of the DBR by using GaAs-based materials with higher refractive index contrast. This parameter change increases the reflectivity bandwidth of the DBR, thereby extending the wavelength tuning range of the VCSEL while maintaining a simplified epitaxial growth process.
3Device complexity
If fixed cavity length is used in VCSEL, then the device structure is simple, but the axial resolution in OCT is limited
Solution Approach 1:
The patent introduces a movable mirror that can dynamically adjust the cavity length of the VCSEL. This dynamic adjustment capability allows the system to vary the axial resolution according to different imaging requirements, achieving high measurement precision without significantly increasing device complexity.
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 design achieves a wide tuning range greater than 100 nm, enhancing axial resolution and sample detection sensitivity in SS-OCT systems, while simplifying the manufacturing process by eliminating the need for complex wafer bonding.
Implementation Method 1
The cavity length of the cavity formed between the upper DBR and the bottom DBR can be changed by changing the gap distance through application of an electrostatic force to the membrane
Implementation Method 2
an active region consisting of quantum dots which are epitaxially grown on top of the bottom DBR
Implementation Method 3
a MEMS tunable quantum dot VCSEL design featuring a GaAs-based DBR with high reflection bandwidth
Implementation Method 4
a bottom mirror consisting of a lower DBR composed of multiple alternating layers of AlGaInAs and InP
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) with the use of micro-electromechanical system (MEMS) technology is provided as a swept source for Optical Coherence Tomography (OCT). The wavelength-tunable VCSEL comprises a bottom mirror of the VCSEL, an active region, and a MEMS tunable upper mirror movable by electrostatic deflections. The bottom mirror comprising a GaAs based distributed Bragg reflector (DBR) stack, and the active region comprising multiple stacks of GaAs based quantum dot (QD) layers, are epitaxially grown on a GaAs substrate. The MEMS tunable upper mirror includes a membrane part supported by suspension beams, and an upper mirror comprising a dielectric DBR stack. The MEMS tunable quantum dots VCSEL can cover an operating wavelength range of more than 100 nm, preferably with a center wavelength between 250 and 1950 nm, and the sweeping rate can be from a few kHz to hundreds of kHz, and up to a few MHz.