Germanium Photodetector SWIR Imaging Dark Current Control
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Solution Overview
Problem
Existing SWIR imaging systems face challenges with high dark current in photodetectors, which affects the quality of detection signals and are often expensive to manufacture, limiting their integration into electronics and applications such as short-wave infrared imaging.
Innovation Solution
An active SWIR imaging system using Germanium photodetectors with a pulsed illumination source and a passively Q-switched laser, along with a controller to manage integration time and reduce dark current noise, and a method to compensate for dark current effects using voltage-controlled current circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Germanium photodetectors with high dark current are used, then the photodetector can detect SWIR radiation effectively, but the dark current noise degrades the signal-to-noise ratio and detection quality
Solution Approach 1:
The patent applies periodic pulsed illumination instead of continuous illumination. The illumination source emits light pulses at specific intervals, and the photodetector integrates signal only during the pulse duration. This periodic action limits the integration time to the pulse width, preventing dark current from accumulating over extended periods while still capturing the SWIR radiation signal effectively.
Solution Approach 2:
The patent changes the integration time parameter to match the illumination pulse duration. By setting the integration time equal to the pulse width and using fast readout circuits, the system optimizes the balance between capturing sufficient signal and minimizing dark current noise. This parameter adjustment transforms the high dark current from a detrimental factor into an acceptable trade-off for effective SWIR detection.
2Quantity of substance
If the integration time is extended to improve signal accumulation, then more SWIR radiation can be detected, but dark current noise accumulates and exceeds readout noise
Solution Approach 1:
The pulsed illumination source emits light at specific intervals with a defined pulse width. The photodetector is activated only during these pulse intervals, creating a periodic detection cycle. This ensures that integration time is naturally limited to the pulse duration, preventing excessive dark current accumulation while still allowing sufficient signal accumulation during each pulse.
Solution Approach 2:
The system maintains continuous detection capability by rapidly sequential scanning of multiple photodetector elements. While individual elements have short integration times limited by pulse width, the array as a whole maintains continuous monitoring of the SWIR scene through rapid readout cycles, ensuring no useful signal is lost.
3Reliability
If InGaAs-based photodetectors are used for SWIR imaging, then detection performance is achieved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent employs Germanium photodetectors that can be manufactured using standard CMOS processes, replacing expensive InGaAs-based detectors. These Ge photodetectors are cheaper to fabricate and can be integrated directly into CMOS circuits, reducing overall system cost while maintaining adequate SWIR detection performance for the intended applications.
Solution Approach 2:
The patent merges the photodetector array with CMOS readout circuitry in a single integrated chip. The Ge photodetectors are fabricated using CMOS-compatible processes, allowing direct integration with amplifiers, analog-to-digital converters, and control logic. This merging eliminates the need for separate discrete components and reduces system complexity while lowering manufacturing costs.
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 improved signal-to-noise ratio by limiting dark current noise, reducing the impact of dark current on detection signals, and provides a cost-effective solution for SWIR imaging, enabling integration into various electronic systems.
Implementation Method 1
an imaging receiver comprising a plurality of Germanium (Ge) PDs operative to detect the reflected SWIR radiation, wherein the imaging receiver produces for each Ge PD a respective detection signal representative of the reflected SWIR radiation impinging on the respective Ge PD
Implementation Method 2
a pulsed illumination source operative to emit SWIR radiation pulses towards a target, the radiation pulses impinging on the target resulting in reflected SWIR radiation pulses reflected from the target
Data Source
AI summary
Systems and methods for imaging in the short wave infrared (SWIR), photodetectors with low dark current and associated circuits for reducing dark currents and methods for generating image information based on data of a photodetector array. A SWIR imaging system may include a pulsed illumination source operative to emit radiation pulses in the SWIR band towards a target resulting in reflected radiation from the target; (b) an imaging receiver including a plurality of Ge PDs operative to detect the reflected SWIR radiation and a controller, operative to control activation of the receiver for an integration time during which the accumulated dark current noise does not exceed the time independent readout noise.