Optical Readout for Thermal Detector Arrays
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Solution Overview
Problem
Existing thermal detector arrays used for detecting infrared (IR) and terahertz radiation face challenges in sensitivity due to high thermal conductance caused by metallic wires and readout integrated circuits (ROICs).
Innovation Solution
An optical readout system for thermal detector arrays is developed, utilizing waveguide-coupled photonic resonators to optically detect temperature changes without the need for electrical wires or ROICs, thereby reducing thermal conductance and enhancing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If metallic wires and ROICs are used for electrical readout of bolometer elements, then the readout circuitry can measure resistance variation, but the thermal conductance increases and sensitivity decreases
Solution Approach 1:
The patent replaces the electrical readout system (metallic wires and ROICs that measure resistance) with an optical readout system using waveguide-coupled photonic resonators. The resonators detect temperature changes through optical resonance frequency shifts, eliminating the need for electrical connections to each bolometer element. This substitution resolves the contradiction by removing the thermal conduction path introduced by metallic wires while preserving the measurement capability through an alternative physical mechanism (optical resonance instead of electrical resistance measurement).
Solution Approach 2:
The patent introduces waveguide-coupled photonic resonators as intermediary elements between the bolometer elements and the readout system. These resonators serve as mediators that convert temperature changes into optical signals without requiring direct electrical contact with the bolometer elements. The resonators are thermally coupled to the bolometers but optically coupled to the waveguides, creating a thermal-isolated measurement pathway that resolves the sensitivity issue while maintaining measurement precision.
2Temperature
If membrane isolation legs and thin film wiring are used to provide thermal isolation, then the bolometer can be thermally isolated from the substrate, but the wiring contributes to thermal conductance and limits sensitivity improvement
Solution Approach 1:
The patent extracts the readout function from the thermal conduction path by removing metallic wires from the bolometer structure. Instead of using wires that conduct both electrical signals and heat, the invention uses optical resonators that are thermally coupled to the bolometer but read out through optically coupled waveguides. This extraction of the electrical readout function eliminates the parasitic thermal conductance of the wiring while maintaining thermal isolation through the membrane structure.
Solution Approach 2:
The patent substitutes the thin film wiring system with an optical resonator-waveguide system. The resonators are formed without metallic interconnects, using only the membrane material itself or dielectric layers. This substitution eliminates the thermal conduction path through wiring while preserving the electrical isolation benefits of the membrane structure, thereby maximizing thermal isolation and sensitivity.
3Reliability
If fewer, narrower, thinner, and longer isolation legs are used to decrease thermal conductance, then the sensitivity increases, but the structural support and fabrication complexity become challenges
Solution Approach 1:
The patent makes the membrane material serve multiple functions: it provides both the structural support for the bolometer element and the resonator structure for optical readout. The resonators are formed directly from the membrane material or adjacent dielectric layers, eliminating the need for separate support structures and wiring. This multi-functionality allows for simplified fabrication while achieving the desired thermal isolation and sensitivity enhancement.
Solution Approach 2:
The patent changes the physical parameters of the resonators (size, shape, material composition) to optimize both thermal isolation and fabrication ease. By adjusting the resonator dimensions and using standard semiconductor fabrication processes, the invention achieves low thermal conductance without requiring excessively small or complex structures that would be difficult to manufacture. The resonator design allows for scalability across different array sizes and configurations.
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 readout system achieves higher sensitivity for detecting IR and terahertz radiation by minimizing thermal conductance and allowing for more effective thermal isolation, leading to improved performance in thermal detector arrays.
Implementation Method 1
an optical resonator positioned in thermal connection with the absorber, wherein the optical resonator couples a portion of the readout light input at a resonance frequency
Implementation Method 2
a waveguide for receiving the readout light input from the optical light source
Implementation Method 3
an absorber positioned on the membrane to absorb heat from electromagnetic radiation incident on the absorber
Implementation Method 4
the plurality of the membrane isolation legs and the membrane form a first platform suspended in the trench formed by the substrate, wherein the plurality of the membrane isolation legs provide thermal isolation to the membrane
Data Source
AI summary
Embodiments of the present invention relate to an optical detector system capable of detecting in the infrared and terahertz regions of the electromagnetic spectrum with increased sensitivity and simplicity. It includes microbolometers in an array, a waveguide for receiving readout light input from an optical light source, waveguide splitters for splitting the waveguide to output waveguides such that each microbolometer in the array is optically coupled to an output waveguide. The output waveguide is coupled to an optical resonator of the microbolometer at a resonance frequency to generate a readout light output having a characteristic based on a change in a characteristic of the optical resonator. The system further includes a detector for receiving the readout light output from each of the output waveguides to convert the readout light output to an electrical signal.