Hyperspectral Sensor With Filter-Free Diffractive Focusing Pixels
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Solution Overview
Problem
Conventional image sensors suffer from low sensitivity, spatial resolution, and spectral resolution due to the use of absorptive color filters and non-focusing diffractive gratings, leading to inefficiencies in wavelength sensitivity and image quality, particularly in hyperspectral imaging.
Innovation Solution
An image sensor with a diffraction layer and sub-pixels, combined with a trained neural network, that determines spectral bands based on the relative output signals of sub-pixels, allowing for high spectral resolution and sensitivity without the need for color filters, and can be manufactured using CMOS processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If absorptive color filters are used to enable color detection, then wavelength sensitivity is improved, but sensitivity and signal to noise ratio deteriorate
Solution Approach 1:
The patent removes absorptive color filters from the optical path and extracts only the necessary wavelength discrimination function, implementing it instead through diffractive gratings that separate wavelengths spatially without absorbing light. This extraction of the filtering function eliminates the sensitivity penalty while maintaining wavelength discrimination capability.
Solution Approach 2:
The patent replaces the absorptive filtering mechanism (which blocks unwanted wavelengths) with a diffractive optical mechanism that redirects different wavelengths to different spatial locations. This substitution uses interference and diffraction physics rather than absorption, allowing all wavelengths to reach the sensor without loss.
2Measurement precision
If absorptive color filters are used for color detection, then spectral information is improved, but spatial resolution deteriorates
Solution Approach 1:
The patent segments the wavelength discrimination function from the spatial sampling function. Instead of using filters that occupy pixel area and reduce spatial resolution, the diffractive grating segments wavelengths spatially across the sensor array, with each pixel receiving light of a specific wavelength range. This segmentation allows full utilization of pixel area for detection while maintaining spectral discrimination.
Solution Approach 2:
The patent transitions from spectral discrimination in the wavelength domain (using filters) to spatial domain discrimination (using diffractive patterns). By mapping wavelengths to spatial positions through diffraction, the system adds a spatial dimension to spectral measurement, allowing spectral information to be obtained without compromising pixel-level spatial resolution.
3Measurement precision
If non-focusing diffractive gratings are used to determine wavelength characteristics, then color detection capability is improved, but light loss increases
Solution Approach 1:
The patent implements preliminary focusing action by placing a focusing lens between the diffractive grating and the sensor array. This preliminary focusing ensures that diffracted light from each wavelength is concentrated onto the corresponding pixel before detection, maximizing light utilization efficiency and eliminating the light loss associated with non-focusing designs.
4Adaptability or versatility
If color router diffractive elements are used to direct light among pixels, then color routing capability is improved, but device complexity increases
Solution Approach 1:
The patent implements a universal diffractive grating design that performs multiple functions: wavelength separation, spatial mapping, and focusing. Instead of requiring different diffractive element patterns for different colors, a single grating structure handles all wavelength routing simultaneously, greatly simplifying the device while maintaining full color routing capability.
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 enables high sensitivity, spatial resolution, and spectral resolution with a wide spectral range, while maintaining a low stack height, and allows for the classification of light into more spectral bands than the number of sub-pixels, improving image quality and efficiency.
Implementation Method 1
utilize uniform, non-focusing metal gratings, to diffract light in a wavelength dependent manner
Implementation Method 2
each pixel can include a photodiode that generates charge in an amount that is generally proportional to the amount of light (i.e. the number of photons) incident on the pixel
Data Source
AI summary
Methods, sensors, and systems for determining a spectral band of light incident on one or more pixels are provided. Each pixel includes a set of sub-pixels. Light incident on an area of the pixel is diffracted by a set of diffraction elements, producing a diffraction pattern across the sub-pixels. Outputs from the sub-pixels are provided to application programming executed by a processor to produce an output that includes an indication of one of a plurality of spectral bands that the light incent on the pixel belongs. The application programming can implement a neural network that has been trained to assign the light incident on an area of a pixel to one spectral band in the plurality of spectral bands. The number of spectral bands to which light incident on the pixel can be assigned can be greater than the number of sub-pixels included in the pixel.