Video Endoscope Optical System with Interference Filter for Fluorescence Imaging
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Solution Overview
Problem
Video endoscopes with short optical systems and CMOS sensors face challenges in reliable fluorescence imaging due to the steep chief ray angle of the micro-lens array, which prevents the effective positioning of conventional interference filters, leading to contamination of fluorescence signals by excitation wavelengths.
Innovation Solution
An optical system with a filter coating positioned within the system to minimize the angle of incidence of image light on the filter, allowing for efficient absorption or blocking of excitation radiation and enabling reliable fluorescence imaging, even with high chief ray angles, by adapting the filter's position and design to match the CMOS sensor's requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional interference filter is positioned in a short optical system with a CMOS sensor, then the filter can block excitation radiation, but the steep chief ray angle causes the filter transmission band to shift towards shorter wavelengths, allowing excitation light to pass through and contaminate the fluorescence signal
Solution Approach 1:
A meniscus lens is introduced as an intermediary optical element between the objective lens and the interference filter. This meniscus lens redirects the chief rays to strike the filter at near-perpendicular angles, preventing the wavelength shift that would otherwise allow excitation light to pass through. This intermediary element resolves the contradiction by maintaining filter effectiveness despite the short optical path required by CMOS sensors.
Solution Approach 2:
The patent changes the angular parameter of light incidence on the interference filter by introducing the meniscus lens. Instead of the filter receiving rays at steep angles (inherent to short optical systems with CMOS sensors), the meniscus lens modifies the ray paths so that chief rays strike the filter at near-zero angles, maintaining the filter's transmission characteristics and blocking effectiveness.
2Volume of moving object
If a short optical system is used with a CMOS sensor to meet space constraints, then the endoscope fits within limited space, but the steep chief ray angle progression prevents proper interference filter positioning for fluorescence imaging
Solution Approach 1:
The meniscus lens serves as a space-efficient intermediary that reconciles the short optical path requirement with the need for proper filter positioning. By redirecting rays within the constrained space, it enables fluorescence imaging without requiring a longer optical system, thus maintaining both compactness and signal purity.
Solution Approach 2:
The meniscus lens introduces a dimensional transformation by changing the spatial orientation of light rays. It takes the steep chief rays inherent to short optical systems and redirects them to strike the filter perpendicularly, effectively adding an angular dimension control mechanism that resolves the contradiction between short path length and proper filter positioning.
3Ease of manufacture
If mass-produced CMOS sensors with steep chief ray angles are used, then cost and availability improve, but the optical system cannot properly position interference filters to prevent excitation light contamination
Solution Approach 1:
The meniscus lens acts as a corrective intermediary that compensates for the inherent steep chief ray angle of mass-produced CMOS sensors. This allows the use of inexpensive, readily available sensors while maintaining fluorescence imaging reliability through proper filter positioning, thus resolving the contradiction between cost-effectiveness and imaging reliability.
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
This solution enables reliable fluorescence imaging without contamination by excitation radiation, allowing for high-resolution imaging of both visible and fluorescent light, enhancing the fluorescence functionality of endoscopes and optimizing the use of CMOS sensors in endoscope systems.
Implementation Method 1
efficient absorption or blocking of excitation radiation
Implementation Method 2
at least one filter coating is located at and/or on a support element for forming an interference filter
Implementation Method 3
a lens system with at least one lens, a second lens, a third lens and/or further lenses to receive an image light from an object field and to direct the image light to the at least one image sensor
Implementation Method 4
fluorescence imaging (FI)... radiation emitted by the excited fluorophore
Data Source
AI summary
The invention concerns an optical system, and a video endoscope therefor, with at least one electronic active pixel image sensor with a progressive offset micro-lens array, and a lens system with a plurality of lenses in order to receive image light from an object field and direct it to the image sensor. The optical system has at least one interference filter coating located within the optical system, such that the angle of incidence of the image light on the filter coating is minimized, minimizing thereby the filtration characteristics of the coating that are angularly dependent. This minimization improves the reliability of fluorescence imaging with short optical systems. The location for the filter coating may be on a curved surface, such as a lens, or on a properly positioned flat element within the optical system.