Cascaded DFB Laser for Broadband Swept Source OCT
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Solution Overview
Problem
Current tunable lasers for swept-source optical coherence tomography (SS-OCT) are either limited in tuning range, speed, or cost, failing to meet the requirements for high-speed, real-time imaging with a broad spectral range.
Innovation Solution
A cascaded multi-DFB semiconductor laser with band-gap engineered sections along a single waveguide, allowing for continuous tuning of multiple wavelengths, enabling a broad spectral range and high-speed operation at a lower cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single DFB laser is used for SS-OCT, then the device complexity is low, but the tuning range is limited (typically 5 nm to 10 nm)
Solution Approach 1:
The patent divides the laser system into multiple DFB laser sections (typically 3-5 sections) with different center wavelengths, each contributing to a portion of the overall tuning range. This segmentation allows the system to achieve a broad tuning range (50 nm or more) while keeping each individual section relatively simple and well-established in technology.
Solution Approach 2:
The patent combines multiple DFB laser sections into a single integrated device by coupling them through a common waveguide structure. The individual laser sections are merged spatially and optically, allowing them to operate simultaneously or sequentially to provide continuous wavelength tuning across the desired spectral range.
2Speed
If mechanically tunable lasers are used for SS-OCT, then the tuning range can be broad, but the sweep speed is slow and the cost is high
Solution Approach 1:
The patent replaces mechanical tuning mechanisms with an electronically controlled system. Each DFB laser section is tuned using electrical current injection and temperature control, eliminating the need for mechanical moving parts. This substitution enables sweep speeds exceeding 20 kHz while reducing device complexity and cost compared to mechanically tunable lasers.
3Productivity
If the wavelength sweep rate is increased for real-time imaging, then the imaging speed improves, but the signal-to-noise ratio may deteriorate
Solution Approach 1:
The patent employs multiple DFB laser sections that can be activated continuously or in sequence to maintain uninterrupted wavelength sweeping. This continuous operation ensures that the full spectral range is covered at high sweep rates without gaps or interruptions, preserving signal-to-noise ratio while achieving real-time imaging speeds.
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 solution provides a high-speed, continuously tunable laser with a broad spectral range, suitable for SS-OCT applications, offering improved axial resolution and signal-to-noise ratio while reducing costs compared to mechanically tunable lasers.
Implementation Method 1
distributed feedback (DFB) laser sections, each having a different center wavelength and different gain curve
Implementation Method 2
band-gap engineered sections along a single waveguide
Implementation Method 3
cascaded multi-DFB semiconductor laser with band-gap engineered sections along a single waveguide
Data Source
AI summary
The present invention is a tunable semiconductor laser for swept source optical coherence tomography, comprising a semiconductor substrate; a waveguide on top of said substrate with multiple sections of different band gap engineered multiple quantum wells (MQWs); a multiple of distributed feedback (DFB) gratings corresponding to each said band gap engineered MWQs, each DFB having a different Bragg grating period; and anti-reflection (AR) coating deposited on at least the laser emission facet of the laser to suppress the resonance of Fabry-Perot cavity modes. Each DFB MQWs section can be activated and tuned to lase across a fraction of the overall bandwidth as is achievable for a single DFB laser and all sections can be sequentially activated and tuned so as to collectively cover a broad bandwidth, or simultaneously activated and tuned to enable a tunable multi-wavelength laser. The laser hence can emit either a single lasing wavelength or a multiple of lasing wavelengths and is very suitable for swept-source OCT applications.