GePD Photodetector Voltage Control for Uniform Sensitivity
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Solution Overview
Problem
In photodetectors, non-uniform sensitivity among GePD groups receiving differential signals leads to a deteriorated common-mode rejection ratio, which affects receiver performance due to manufacturing variations.
Innovation Solution
A photodetector design incorporating sets of two photodiodes with monitors to measure photocurrent and voltage supplies that adjust voltages to equalize photocurrents across the photodiodes, ensuring uniform sensitivity across C and L bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GePD groups are used to receive differential signals in optical communication systems, then the sensitivity and detection capability are improved, but manufacturing variations cause non-uniform sensitivity among the GePD groups which deteriorates the common-mode rejection ratio
Solution Approach 1:
The patent adjusts the reverse bias voltage applied to each GePD group as a controllable parameter to compensate for manufacturing variations. By independently controlling the voltage parameter for each photodiode group, the sensitivity uniformity is improved despite variations in Ge layer thickness and doping concentrations caused by manufacturing processes.
Solution Approach 2:
The patent implements a feedback mechanism where the performance of each GePD group is measured and the reverse bias voltage is adjusted accordingly. This closed-loop control allows the system to automatically compensate for sensitivity variations and maintain a high common-mode rejection ratio by balancing the photocurrents among different photodiode groups.
2Measurement precision
If the Ge layer thickness and doping concentration are increased to improve light absorption and sensitivity, then the detection performance is improved, but the manufacturing variation and difficulty in controlling uniformity increase
Solution Approach 1:
Instead of relying solely on precise control of Ge layer thickness and doping concentration during manufacturing, the patent shifts to controlling the electrical parameter (reverse bias voltage) after manufacturing. This approach maintains high light absorption efficiency while avoiding the manufacturing difficulties associated with precise geometric and compositional control.
Solution Approach 2:
The patent replaces the mechanical/physical control approach (precise control of layer thickness and doping during fabrication) with an electrical control approach (adjusting reverse bias voltage). This substitution allows for easier and more precise control of sensitivity uniformity without requiring extremely tight manufacturing tolerances.
3Reliability
If voltage control is applied to equalize photocurrents among photodiodes, then the common-mode rejection ratio is improved, but the device complexity increases due to additional voltage supply control circuits
Solution Approach 1:
The patent controls the reverse bias voltage parameter of each photodiode to equalize their photocurrents. This simple parameter adjustment approach improves the common-mode rejection ratio without requiring complex additional circuits, as it utilizes the existing voltage supply infrastructure with enhanced control capability.
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 stabilizes the common-mode rejection ratio by maintaining uniform sensitivity, preventing performance degradation in receivers.
Implementation Method 1
when light is incident on the silicon slab 142 from the waveguide layer 141 and is absorbed by the Ge layer 114, a photocurrent flows between an electrode 117 and the electrodes 116 and 118
Data Source
AI summary
A GePD having uniform sensitivity in C and L bands is provided and a photodetector in which deterioration of a common-mode rejection ratio is curbed is provided. A photodetector according to an embodiment includes one or a plurality of sets of two photodiodes to which a differential signal is input, a monitor connected to each of the two photodiodes and configured to measure a photocurrent, and a voltage supply configured to control a voltage applied to each of the two photodiodes, and the voltage supply controls the voltage applied to each of the two photodiodes so that the photocurrent measured by the monitor connected to one of the two photodiodes is equal to the photocurrent measured by the monitor connected to another one of the two photodiodes.