OCT Light Source Coherence Length for Wide-Area Fundus Imaging
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Solution Overview
Problem
The existing OCT apparatuses with wavelength-variable light sources have a short coherence length, leading to varying interference signal intensity with measurement position, making it difficult to acquire accurate information on wide areas with a single scan due to significant optical-path length variations in the spherical eyeball.
Innovation Solution
An imaging apparatus with a light-source unit using a surface-emitting laser with a coherence length of 14 mm or longer, capable of sweeping frequencies, and a scanning unit that scans the fundus at an angle of 47 degrees or greater, ensuring consistent interference signal intensity across the wide area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a wavelength-variable light source with short coherence length is used to scan a wide area of the fundus, then the angle of view is widened, but the interference signal intensity varies with measurement position due to optical-path length variations
Solution Approach 1:
The patent changes the key parameter of coherence length from short (conventional) to long (14mm or more). This is achieved by using a surface-emitting laser with a Fabry-Perot resonator having a specific cavity length and refractive index, which fundamentally alters the light source characteristics to maintain consistent interference signal intensity across wide-area measurements
2Area of moving object
If multiple tomographic images are connected to obtain a wide-area image, then the observable area is widened, but the image processing becomes time-consuming and troublesome
Solution Approach 1:
The patent merges multiple measurement positions into a single coherent measurement by using a long coherence length light source. This allows simultaneous acquisition of interference signals from different optical path lengths within the coherence range, enabling wide-area imaging through a single scan rather than requiring sequential imaging and post-processing concatenation
3Adaptability or versatility
If the optical path length varies significantly across the fundus due to the spherical shape of the eyeball, then wide-area imaging is enabled, but the interference signal intensity becomes position-dependent when using a short coherence length light source
Solution Approach 1:
The patent changes the coherence length parameter from short to long (14mm or more) to accommodate the optical path length variations inherent in wide-area fundus imaging. This parameter change stabilizes the interference signal intensity across different measurement positions by ensuring that the coherence length exceeds the maximum optical path difference encountered in the imaging field
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
Enables high-accuracy information acquisition on wide areas with a single scan by maintaining interference signal intensity, improving image quality and clinical value in ocular disease diagnosis.
Implementation Method 1
The light-source unit includes a surface-emitting laser, the surface-emitting laser including a first reflector, a second reflector, and an active layer provided between the first reflector and the second reflector. When at least one of the first reflector and the second reflector is driven, a distance between the first reflector and the second reflector changes and the frequency of the light emitted changes.
Implementation Method 2
an interference unit configured to separate the light emitted from the light-source unit into illuminating light to be applied to a fundus and reference light, and to generate interfering light formed of reflected light, which is light applied to the fundus and reflected by the fundus, and the reference light
Implementation Method 3
The scanning unit is configured such that an angle of linear scanning of the fundus with the illuminating light is 47 degrees or greater in the air
Data Source
AI summary
To acquire information on sections of an object with high accuracy even if the area to be imaged with a single scan is wide. A scanning unit is configured such that an angle of linear scanning of a fundus with illuminating light is 47 degrees or greater in the air. A light-source unit 10 includes a MEMS-VCSEL 601 whose coherence length during the sweeping of the frequency of the light is 14 or longer.