Endoscope Optical Unit Ghost Reduction via Aperture and Filter Geometry
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Solution Overview
Problem
Endoscopes face challenges in reducing periodic pattern ghosts due to intense light reflections from laser therapy, which hinder observation and cause discomfort, especially when using infrared and laser light cut-off filters in conjunction with CCD image pickup devices.
Innovation Solution
An optical unit design incorporating a multi-layer interference film coating that transmits visible light and cuts off specific laser wavelengths, with specific F number, maximum image height, and distance relationships between optical components to minimize ghost formation, including an aperture diaphragm and solid-state image pickup device, effectively reducing periodic pattern ghosts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a multi-layer interference film (cut-off coat) is used as a laser light cut-off filter, then laser light is effectively blocked, but periodic pattern ghosts are generated due to light reflection from the coating surface
Solution Approach 1:
The patent applies parameter changes by carefully controlling the optical parameters of the system including the F number (FNO), maximum image height (IH), and the distance relationship (Δd) between the aperture diaphragm and the coating surface. By satisfying specific mathematical relationships among these parameters, the patent reduces the intensity of periodic pattern ghosts while maintaining effective laser light cut-off functionality.
Solution Approach 2:
The patent introduces an aperture diaphragm as an intermediary element that controls the light path. By positioning the aperture diaphragm at a specific distance from the coating surface and controlling its size relative to the maximum image height, it mediates the interaction between incident light and the coating surface, thereby reducing ghost image formation while preserving the laser cut-off function.
2Reliability
If an infrared light cut-off filter and laser light cut-off filter are arranged in the optical unit, then proper color reproduction and laser therapy observation are achieved, but the observation screen becomes extremely bright making object image observation difficult
Solution Approach 1:
The patent controls the brightness of the observation screen by managing the geometric parameters of the optical system. By controlling the F number, maximum image height, and the distance between the aperture diaphragm and coating surface, the patent limits the intensity of reflected light reaching the screen, thereby preventing excessive brightness while maintaining accurate color reproduction through the infrared and laser cut-off filters.
3Volume of moving object
If the distance between optical components is reduced to compact the optical unit, then device size is minimized, but ghost light reflection intensity increases
Solution Approach 1:
The patent establishes specific mathematical relationships among the F number, maximum image height, and the distance Δd between the aperture diaphragm and coating surface. By controlling these parameters to satisfy the given relationships, the patent achieves compact optical unit design while simultaneously controlling ghost light intensity, thus resolving the contradiction between miniaturization and ghost reduction.
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 optical unit design significantly reduces periodic pattern ghost intensity and visibility, improving observation by diffusing ghost light and preventing erroneous recognition of ghost images as affected body parts, while maintaining optical system efficiency and functionality.
Implementation Method 1
an optical member disposed on the image plane side relative to the aperture diaphragm, the optical member including a coating surface resulting from a multi-layer interference film that transmits visible light and cuts off light having a particular wavelength being formed thereon
Data Source
AI summary
An optical unit includes: a plurality of lenses that form an object image on an image plane that is a light-receiving surface of a CCD; an aperture diaphragm; and an infrared absorption filter disposed on the image plane side relative to the aperture diaphragm, the infrared absorption filter including coating surfaces resulting from a YAG laser cut-off film and an LD laser cut-off film that each cut off predetermined laser light being formed respectively, and an F number FNO, a maximum image height IH, and a distance Δd between a paraxial image formation position in a ghost optical path on which a light beam emitted from the aperture diaphragm BI is reflected by the image plane and further reflected by the coating surface and reaches the image plane again and the image plane satisfy (Expression 1):0.75<|FNO·IH/Δd|<2.0 (Expression 1).