Avalanche Photodiode Filter for Crosstalk Reduction
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Solution Overview
Problem
Avalanche photodiode detector arrays in LADAR systems experience photon crosstalk due to secondary photon emissions, leading to reduced image quality and increased component failures, especially when operating near breakdown voltage for high sensitivity.
Innovation Solution
Incorporating a filter with a bandgap between the absorber and multiplier bandgaps in the photodiode detector array to absorb secondary photon emissions, thereby reducing crosstalk between pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the APD pixels are biased close to or beyond the nominal breakdown voltage to achieve high sensitivity, then the sensitivity to incident photons is improved, but photon crosstalk between adjacent pixels increases due to secondary photon emissions
Solution Approach 1:
An optical filter is introduced as an intermediary component between adjacent APD pixels. This filter selectively absorbs secondary photons emitted during avalanche breakdown while allowing primary signal photons to pass through, thereby blocking crosstalk without compromising the sensitivity achieved through high bias operation
Solution Approach 2:
The optical filter is designed with specific optical parameters (bandpass characteristics) that match the emission spectrum of the laser source. By changing the optical parameters of the filter to transmit only the laser wavelength and block secondary photons, the system maintains high sensitivity while reducing crosstalk
2Measurement precision
If the APD pixels are biased beyond breakdown voltage to achieve single-photon level detection, then the detection capability is improved, but ghosting images and component failures increase
Solution Approach 1:
The optical filter converts the harmful secondary photon emissions into a beneficial filtering mechanism. By absorbing these secondary photons that would otherwise cause ghosting images and pixel saturation, the filter protects the detector array from damage while operating at high bias voltages necessary for single-photon detection
Solution Approach 2:
The optical filter serves as a protective intermediary between the high-voltage biased APD pixels and the optical environment. It allows the pixels to operate at breakdown voltage for enhanced detection capability while preventing the harmful effects of secondary photon emissions from degrading component reliability
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 effectively minimizes ghosting images and enhances the quality of 3D images generated by LADAR systems, reducing component failures and improving system performance.
Implementation Method 1
A filter is positioned between the window and the active region. The filter is configured to have a bandgap between an absorber bandgap and a multiplier bandgap.
Implementation Method 2
With such an electric field, a single carrier injected into a depleted multiplication layer of the APD pixel may trigger an avalanche breakdown, producing electrons and/or holes, resulting in an avalanche current.
Implementation Method 3
The LADAR system projects a laser beam onto a surface of a target to enable a 3D image of the surface to be generated.
Data Source
AI summary
A laser detection and ranging (LADAR) system is provided for generating a three-dimensional image of an object. The LADAR system includes a laser source configured to project a laser beam onto the object, and a photodiode detector array configured to detect a reflection of the laser beam projected onto the object. The photodiode detector array includes a back interface, a front interface positioned opposite the back interface, and a passivation region disposed between the back interface and the front interface. The back interface includes at least one window, and the front interface includes at least one active region oriented to detect a photon associated with the reflection. The at least one active region includes an absorber and a multiplier. The filter is configured to have a bandgap between an absorber bandgap and a multiplier bandgap.