Microcavity-Enhanced Optical Bolometer for Thermal Imaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current uncooled thermal imagers, particularly those using VOx bolometers, are limited by noise sources such as 1/f noise and thermal fluctuation noise, which restrict their detectivity and require significant thermal mass, leading to increased system size, weight, and power consumption.
Innovation Solution
The development of resonant microcavity bolometers with wavelength-scale microcavities and engineered absorbers, which use optical resonators for thermal readout, eliminating electrical noise and allowing for thermal fluctuation-limited performance without increasing thermal mass or pixel pitch, and incorporating waveguides for evanescent light coupling to reduce system complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If VOx bolometers are used for thermal imaging, then thermal detection capability is achieved, but electrical noise (1/f noise) limits detectivity
Solution Approach 1:
The patent replaces the electrical readout mechanism with an optical readout mechanism. Instead of measuring resistance changes electrically (which introduces 1/f noise), the invention uses optical interferometry to detect temperature-induced refractive index changes in a microcavity, thereby eliminating electrical noise from the measurement system.
Solution Approach 2:
The patent introduces a microcavity as an intermediary between the thermal sensing element and the readout system. The microcavity converts temperature changes into optical phase shifts through refractive index changes, allowing indirect measurement that avoids direct electrical contact and associated noise.
2Measurement precision
If thermal mass is increased to reduce noise, then detectivity improves, but system size, weight, and power consumption increase
Solution Approach 1:
The patent changes the measurement parameter from electrical resistance to optical refractive index. This allows detection of temperature changes without requiring large thermal mass, as the optical interferometric readout can detect minute refractive index changes that correspond to small temperature variations, enabling lightweight design.
Solution Approach 2:
The patent utilizes optical resonance in a microcavity structure, where the cavity is designed to resonate at specific wavelengths. This resonance enhances the sensitivity of the measurement by amplifying the optical signal in response to temperature-induced refractive index changes, improving detectivity without increasing thermal mass.
3Measurement precision
If VOx bolometers are used, then thermal detection is achieved, but 1/f noise and thermal fluctuation noise restrict detectivity
Solution Approach 1:
The patent replaces the electrical measurement system with an optical measurement system. By using optical interferometry to detect temperature changes through refractive index variations in a microcavity, the invention eliminates the photoconductive readout mechanism that generates 1/f noise and thermal fluctuation noise, achieving superior detectivity.
4Object-generated harmful factors
If optical resonators are used for thermal readout, then electrical noise is eliminated, but device complexity increases
Solution Approach 1:
The patent merges the thermal sensing function and the readout function into a single integrated microcavity structure. The microcavity serves both as the thermal isolation element and as the optical resonator for readout, eliminating the need for separate electrical contacts and readout circuitry, thereby reducing overall device complexity despite the sophisticated optical mechanism.
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 approach enables thermal fluctuation-limited detectivity, potentially surpassing the performance of VOx bolometers while reducing system size, weight, and power consumption, and eliminating electrical noise, thereby improving imaging capabilities.
Implementation Method 1
Each pixel in the array of pixels comprising an absorbing material to absorb incident thermal infrared radiation
Implementation Method 2
a photonic crystal cavity in thermal communication with the absorbing material. Absorption of the incident thermal infrared radiation by the absorbing material causes a shift in a resonance of the photonic crystal cavity
Implementation Method 3
These hollow pillars support the array of pixels above the substrate and thermally isolate the array of pixels from the substrate
Data Source
AI summary
Optical microcavity resonance measurements can have readout noise matching the fundamental limit set by thermal fluctuations in the cavity. Small-heat-capacity, wavelength-scale microcavities can be used as bolometers that bypass the limitations of other bolometer technologies. The microcavities can be implemented as photonic crystal cavities or micro-disks that are thermally coupled to strong mid-IR or LWIR absorbers, such as pyrolytic carbon columns. Each microcavity and the associated absorber(s) rest on hollow pillars that extend from a substrate and thermally isolate the cavity and the absorber(s) from the rest of the bolometer. This ensures that thermal transfer to the absorbers is predominantly from radiation as opposed to from conduction. As the absorbers absorb thermal radiation, they shift the resonance wavelength of the cavity. The cavity transduces this thermal change into an optical signal by reflecting or scattering more (or less) near-infrared (NIR) probe light as a function of the resonance wavelength shift.