Swept Light Source Dynamic Gain Control
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Solution Overview
Problem
Conventional swept light sources struggle to maintain a long coherence length across an entire wide sweep wavelength range, leading to reduced image quality and detection sensitivity in SS-OCT devices due to a wide unsaturated gain range and excessive optical gain near the center wavelength.
Innovation Solution
A swept light source with a laser resonator, optical gain control, and wavelength control mechanisms that dynamically adjust the optical gain to remain slightly above the lasing threshold across the entire wavelength sweep, using a diffraction grating and optical deflector to optimize the SOA current waveform and maintain a narrow linewidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional swept light source uses a temporally constant injected current into the gain medium, then the device structure is simple and easy to operate, but the unsaturated gain range becomes wide near the center wavelength, causing the coherence length to be short and reducing image quality
Solution Approach 1:
The patent applies dynamics by transitioning from a static, temporally constant injected current to a dynamic, time-varying injected current that changes according to the swept wavelength. The current is modulated to track the gain spectrum peak across the wavelength range, ensuring optimal coherence length at each wavelength point while maintaining system operability through automated control.
Solution Approach 2:
The patent implements parameter changes by varying the injected current magnitude as a function of swept wavelength. The current parameter is dynamically adjusted to match the changing gain spectrum characteristics, narrowing the unsaturated gain range at each wavelength and thereby extending the coherence length across the entire swept range.
2Adaptability or versatility
If the swept light source operates with a wide unsaturated gain range, then more wavelengths can be swept, but the coherence length becomes short due to excessive optical gain, reducing detection sensitivity
Solution Approach 1:
The patent uses dynamics to continuously adapt the injected current to the instantaneous swept wavelength, enabling the system to maintain optimal performance across a wide wavelength range. The dynamic current modulation ensures that the gain spectrum peak tracks with the swept wavelength, preventing excessive optical gain and maintaining long coherence length throughout the sweep, thereby preserving detection sensitivity.
Solution Approach 2:
The patent implements feedback by using the swept wavelength information to control the injected current magnitude. The system monitors the current wavelength point in the sweep and adjusts the current accordingly to maintain the gain spectrum peak at the desired wavelength, ensuring both wide wavelength coverage and high detection sensitivity through closed-loop control.
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 ensures a constant long coherence length during wavelength sweeps, enhancing the point spread function strength and image detection sensitivity of SS-OCT devices by maintaining optimal optical gain and wavelength control.
Implementation Method 1
a gain medium configured to amplify a beam
Implementation Method 2
means for changing a lasing wavelength... using a diffraction grating
Implementation Method 3
an optical deflector configured to change an angle of incidence of a laser beam on the diffraction grating
Data Source
AI summary
A swept light source of the present invention keeps a coherence length of an output beam long over an entire sweep wavelength range. A gain of a gain medium is changed with time in response to a wavelength sweep and the coherence length is kept maximum. The gain of the gain medium is kept close to a lasing threshold and an unsaturated gain range of the gain medium is narrowed over the entire sweep wavelength range. An SOA current waveform data acquiring method of driving while keeping the coherence length long, a novel coherence length measuring method, and an optical deflector suitable for the swept light source are also disclosed.