Dual Wavelength NIR Iris Imaging Lens Assembly
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing iris image acquisition systems for smartphones are limited in their ability to capture in-focus IR images across a wide range of distances without increasing the depth of the smartphone housing, making them ineffective for biometric recognition when the user holds the device at varying distances from their face.
Innovation Solution
A dual wavelength NIR flash system with a fixed focus lens assembly that optimizes axial chromatic aberration to extend the depth of field, using LEDs with specific wavelengths matched to the refractive index of the lens materials, allowing for in-focus iris imaging from 200mm to 350mm without mechanical refocusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated IR lens assembly is used to acquire in-focus IR images, then image quality is improved, but the depth of the smartphone housing must be increased
Solution Approach 1:
The patent combines visible and IR imaging capabilities into a single lens assembly. The lens assembly includes both a visible light lens element and an IR lens element integrated together, allowing the smartphone to capture both visible and IR images without requiring separate lens modules, thus avoiding increased housing depth.
Solution Approach 2:
The lens assembly is designed to perform multiple functions: it can focus visible light for general photography and focus IR light for iris recognition. The system uses wavelength-selective filters and a dual-purpose sensor that can detect both visible and IR wavelengths, making the single lens assembly universal for different imaging modes.
2Adaptability or versatility
If the depth of field is extended to accommodate varying user distances, then adaptability is improved, but the optical system depth must be increased
Solution Approach 1:
The patent implements an autofocus mechanism that dynamically adjusts the focal length of the lens assembly. The system includes a movable lens element that can be positioned at different locations along the optical axis to focus on objects at varying distances, allowing the depth of field to be dynamically extended without permanently increasing the optical system depth.
Solution Approach 2:
The system changes the focal length parameter of the lens assembly to adapt to different object distances. By adjusting the focal length between a first value (for closer objects) and a second value (for farther objects), the system extends its effective depth of field and range of clear imaging without requiring a deeper optical structure.
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 system achieves extended depth of field for iris imaging across a range of distances, maintaining diffraction-limited image quality and accommodating varying user positions without increasing the smartphone's depth, ensuring effective biometric recognition.
Implementation Method 1
The focusing is achieved optically by optimising an axial chromatic aberration of the lens assembly to cover an appropriate distance range, matched with spectral characteristics of the illumination sources.
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
An iris image acquisition system (10) comprises an image sensor (14) comprising an array of pixels including pixels sensitive to NIR wavelengths; at least one NIR light source (16, 18) capable of selectively emitting light with different discrete NIR wavelengths; and a processor (20), operably connected to the image sensor (14) and the at least one NIR light source (16, 18), to acquire image information from the sensor (14) under illumination at one of the different discrete NIR wavelengths. A lens assembly (12) comprises a plurality of lens elements with a total track length of no more than 4.7mm, each lens element comprising a material with a refractive index inversely proportional to wavelength. The different discrete NIR wavelengths are matched with the refractive index of the material for the lens elements to balance axial image shift induced by a change in object distance with axial image shift due to change in illumination wavelength.