Serial Photodetector Array for High-Bandwidth Free-Space Optical Communication
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Solution Overview
Problem
Current free-space optical communication systems face limitations in mobility, bandwidth, and size, weight, and power (SWAP) requirements, with photodetectors experiencing trade-offs between bandwidth and field of view due to their RC time constant and capacitance, leading to impracticality for dynamic and mobile applications.
Innovation Solution
The implementation of a serial array of photodetectors with flood illumination and a trans-impedance amplifier, where the photodetectors are connected in series and uniformly illuminated, allowing for high-bandwidth operation while maintaining sensitivity and expanding the field of view without sacrificing other performance metrics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the photodetector area is increased to detect wider incident angle or larger beam size, then the field of view is improved, but the bandwidth is reduced due to increased capacitance
Solution Approach 1:
The photodetector is divided into multiple segments (first photodetector segment, second photodetector segment, third photodetector segment) connected in series. Each segment has a smaller area and lower capacitance than a single large-area photodetector, enabling high bandwidth operation while collectively covering a wide field of view through the series configuration.
2Speed
If a lens system is used to focus a large beam onto a small area photodetector, then the bandwidth is improved, but the field of view is decreased due to the law of etendue
Solution Approach 1:
Instead of using a lens to focus light onto a small photodetector (which limits FoV), the patent segments the photodetector into multiple small-area segments arranged to collectively receive light from a large beam area. The series connection maintains high bandwidth while the distributed segments capture a wide field of view without requiring optical focusing elements.
3Speed
If the series resistance is reduced to improve bandwidth, then the bandwidth is improved, but the sensitivity is reduced
Solution Approach 1:
The photodetector is segmented into multiple sections with individually optimized resistance values. The series connection allows the total resistance to be distributed across segments, enabling bandwidth improvement through reduced individual segment capacitance while the cumulative sensitive area of all segments maintains high sensitivity for detecting incident light.
Solution Approach 2:
Different segments of the photodetector can have different local properties (different areas, different resistance values) optimized for their specific function. This allows each segment to contribute optimally to the overall performance, with the series connection combining these local optimizations into a high-bandwidth, high-sensitivity device.
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 configuration enhances bandwidth and sensitivity, overcoming the trade-offs between these parameters, enabling high-bandwidth and high-sensitivity operation with increased field of view, suitable for dynamic and mobile applications in free-space optical communication systems.
Implementation Method 1
an amplifier connected to the array of photodetectors, where the amplifier is configured to amplify an electrical signal generated by the array of photodetectors in response to illumination
Implementation Method 2
an amplifier connected to the array of photodetectors, where the amplifier is configured to amplify an electrical signal generated by the array of photodetectors
Data Source
AI summary
An optical receiver may include multiple photodetectors connected in serial and an amplifier connected to the photodetectors, where the amplifier is configured to amplify an electrical signal generated by the photodetectors in response to illumination. The receiver may further include one or more optical elements to receive signal light and direct the signal light to a subset of the plurality of photodetectors. The receiver may further include an illumination source to illuminate the plurality of photodetectors with flood illumination during operation. An optical modulator may include multiple modulators connected in serial and driven by a common voltage driver.