Photodetector Circuit Saturation Current and Optical Filtering
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Solution Overview
Problem
Photodiodes experience photocurrent saturation and reduced bandwidth due to the charge screening effect caused by high light intensities, which leads to increased recombination of electron-hole pairs and reduced output current.
Innovation Solution
The use of multiple optical input ports or a truncated multi-mode interferometer (MMI) to distribute light uniformly across the photodiode, reducing peak intensity and local electron-hole pair density, combined with optical waveguides and delay elements to induce a frequency-dependent phase shift and reduce out-of-band frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high light intensity is applied to the photodiode to increase photocurrent output, then the photocurrent output increases, but the charge screening effect increases causing reduced bandwidth and increased recombination
Solution Approach 1:
The optical waveguide is divided into multiple propagation modes (first mode and second mode) that illuminate different regions of the photodiode. This segmentation distributes the light intensity across multiple zones, preventing excessive local intensity that would cause charge screening, while maintaining high total photocurrent output through combined signal detection
2Power
If multiple optical signals are used to increase photocurrent, then the dynamic range improves, but out-of-band frequency response increases
Solution Approach 1:
Different propagation modes are assigned different temporal characteristics through delay elements. The first propagation mode carries the in-band signal with minimal delay, while the second propagation mode carries out-of-band signals with intentional delay. This creates local quality differences in the temporal domain, allowing selective enhancement of in-band signals while suppressing out-of-band responses through controlled interference
Solution Approach 2:
Delay elements introduce periodic time delays between different propagation modes. This periodic action creates frequency-dependent phase shifts that result in constructive interference for in-band frequencies and destructive interference for out-of-band frequencies, effectively filtering the frequency response while maintaining high dynamic range
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 enhances the dynamic range of signal detection, mitigates the charge screening effect, and improves the frequency response of the photodetector by increasing the output photocurrent while reducing recombination and saturation.
Implementation Method 1
A multi-mode interferometer (MMI) is a waveguide with multiple guided propagation modes that propagate along the waveguide independently from each other. The multiple guided propagation modes propagate at different velocities to result in an interference pattern that changes along the length of the MMI.
Implementation Method 2
Detection of light in a photodiode involves the generation of electron-hole pairs.
Implementation Method 3
The first optical waveguide is coupled to the at least one side via a plurality of delay elements, the plurality of delay elements comprise a delay difference that induces a frequency dependent phase shift of the first optical signal and the second optical signal
Data Source
AI summary
A photodetector circuit is disclosed. The photodetector circuit includes an optical input configured to receive a source optical signal for detection by the photodetector circuit, an optical waveguide for coupling the optical input and at least one side of a plurality of sides of a photodiode, wherein the optical waveguide is configured to generate a first optical signal and a second optical signal from the source optical signal, and the photodiode coupled to the first optical waveguide, where the photodiode is illuminated on the at least one side by the first and second optical signals at different locations on the photodiode, where the photodiode generates a photocurrent based on the first and second optical signals reducing photocurrent saturation. Providing a delay between the first and second optical signals reduces an out-of-band frequency response of the photodiode circuit.