MEMS Tunable VCSEL for High-Speed Swept Source OCT
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Solution Overview
Problem
Current swept source optical coherence tomography (SSOCT) systems face limitations such as slow wavelength scanning, incomplete wavelength coverage, and limited tuning range, which result in long image acquisition times and shallow depth information due to the use of tunable lasers with mechanical constraints and narrow tuning capabilities.
Innovation Solution
A swept source OCT system employing a vertical cavity surface-emitting laser (VCSEL) with an integrated MEMs tunable mirror, capable of scan rates exceeding 100 kHz and complete wavelength coverage over 100 nm, utilizing a GaAs/Aluminum Oxide mirror and a TiO2/SiO2 dielectric mirror suspended on a deformable membrane, and optically pumped by an edge-emitting laser with multiple quantum wells for broad gain bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional tunable lasers with mechanical constraints are used, then the system structure is simpler, but the wavelength scanning speed is slow and image acquisition time is long
Solution Approach 1:
The patent replaces mechanical tuning mechanisms with a MEMS-based tunable mirror that uses electrostatic actuation to change the cavity length and tuning wavelength. This substitution of mechanical systems with electro-mechanical MEMS devices enables scanning speeds exceeding 100 kHz, dramatically reducing image acquisition time while maintaining tuning functionality.
Solution Approach 2:
The patent implements dynamic tuning capability by using a MEMS mirror that can rapidly adjust the optical cavity length in response to control signals. This dynamic adjustment mechanism allows the laser to sweep through wavelengths at speeds greater than 100 kHz, transforming the static or slowly-changing traditional laser into a dynamically tunable source.
2Adaptability or versatility
If tunable lasers with narrow tuning capabilities are used, then the device complexity is reduced, but the tuning range is limited and spatial resolution is degraded
Solution Approach 1:
The patent achieves a tuning range exceeding 100 nm by changing the effective optical cavity length through MEMS mirror actuation. This parameter change allows the laser to sweep through a broad wavelength range, which directly improves spatial resolution in OCT imaging since resolution is inversely proportional to the tuning range.
Solution Approach 2:
The patent employs a composite cavity structure combining a distributed Bragg reflector (DBR) with a MEMS-tunable mirror. This composite design integrates the high reflectivity and wavelength selectivity of DBR with the dynamic tuning capability of MEMS, enabling both wide tuning range and high resolution performance.
3Speed
If FFP filters are used for wavelength tuning, then the device structure is simpler, but the scan rate is limited to a few kHz
Solution Approach 1:
The patent replaces the mechanical FFP filter tuning mechanism with an electrostatic MEMS mirror that actuates to change the optical cavity properties. This substitution eliminates the mechanical constraints of FFP filters while achieving scan rates exceeding 100 kHz through electrostatic actuation.
Solution Approach 2:
The patent implements rapid dynamic tuning by using a MEMS mirror with high bandwidth electrostatic actuation. The MEMS device can respond to control signals at frequencies greater than 100 kHz, enabling fast wavelength sweeping that is an order of magnitude faster than FFP filter-based systems.
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 system achieves high-speed image acquisition and enhanced spatial resolution with complete wavelength coverage, addressing the limitations of existing SSOCT systems by enabling rapid wavelength scanning and broad tuning range.
Implementation Method 1
Interference between light reflected from the reference mirror and the sample is detected by an optical detector
Implementation Method 2
another mirror is comprised of an alternating dielectric stack of Titanium Dioxide (TiO2) and Silicon dioxide (SiO2) suspended on a deformable membrane
Implementation Method 3
comprises quantum wells of more than one composition or more than one quantum state to broaden the effective gain bandwidth of its active region
Implementation Method 4
the VCSEL is optically pumped by an edge-emitting laser
Data Source
AI summary
A swept source Optical coherence tomography system (SSOCT) comprises a vertical cavity surface-emitting laser with an integrated MEMs tunable mirror movable by electro-static deflection. The MEMs tunable VCSEL offers scan rates greater than 100 khz and tuning ranges approaching 200 nm around 1300 nm and 150 nm around 850 nm. In the preferred embodiment of this invention, a bottom mirror of the VCSEL is comprised of a Aluminum Gallium Arsenide/Aluminum Oxide DBR stack, and a movable top mirror is comprised of a TiO2/SiO2 DBR stack. A MEMs tunable VCSEL at 1300 nm is preferably pumped through the top mirror in a wavelength range between 1050 and 1120 nm, and a MEMs tunable VCSEL at 850 nm is preferably pumped through the top mirror in a wavelength range between 700 nm and 730 nm.