Optical Wafer-Scale Photodiode Bandwidth Testing Without RF Equipment
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Solution Overview
Problem
Measuring the bandwidth of photodiodes in photonic integrated circuits at high speeds is challenging due to the need for expensive RF equipment and time-consuming calibration, which often precludes inclusion in production, leading to yield loss.
Innovation Solution
An all-optical system using optical signals to test photodiode bandwidth by generating a DC bias, an AC signal, and utilizing an interferometer to detect heat generated by a resistor, correlating the heat to the photodiode's bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If expensive RF equipment and time-consuming calibration are used to measure waveguide PD performance at high speeds, then measurement accuracy is improved, but cost and time increase significantly
Solution Approach 1:
The patent replaces the traditional electrical RF measurement system with an all-optical measurement system. Instead of using electrical probes and RF equipment to measure photodetector bandwidth, the invention uses optical signals throughout the entire measurement process, eliminating the need for electrical connectivity and complex RF calibration while maintaining measurement accuracy at high speeds
Solution Approach 2:
The patent creates an optical copy of the electrical measurement process. By converting the electrical bandwidth measurement problem into an optical domain equivalent, the system replicates the measurement functionality using optical components that are inherently better suited for high-speed photonic applications, avoiding the limitations of electrical measurement systems
2Reliability
If traditional electrical measurement methods are used for photodiode bandwidth testing, then electrical connectivity is established, but cost and calibration time increase
Solution Approach 1:
The patent eliminates electrical connectivity requirements by substituting the electrical measurement system with an all-optical system. The measurement process uses optical signals to probe the photodiode response, removing the need for electrical probes, ground connections, and associated RF calibration procedures, thereby simplifying integration into production lines
Solution Approach 2:
The photodiode under test serves its own measurement function by converting optical input signals to electrical output signals that are then optically detected. The device being measured provides the measurement signal itself through its normal photodetection function, eliminating the need for external electrical test equipment and complex test fixtures
3Productivity
If wafer-level photodiode bandwidth measurement is implemented using optical signals, then cost and time are reduced, but measurement capability must be maintained
Solution Approach 1:
The patent uses periodic optical modulation signals to stimulate the photodiode and measures its frequency response. By sweeping through different optical modulation frequencies and measuring the photodiode's response at each frequency point, the system efficiently characterizes the bandwidth while maintaining precision through the periodic nature of the measurement
Solution Approach 2:
The patent changes the optical signal parameters (frequency, amplitude, wavelength) to probe different aspects of photodiode performance. By varying the optical input parameters and measuring the corresponding output responses, the system extracts bandwidth information without requiring complex electrical measurement setups, enabling fast wafer-level testing
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
Provides a cost-effective and efficient method to measure photodiode bandwidth without electrical connectivity, ensuring accurate and reliable testing of photodiodes in high-speed applications.
Implementation Method 1
a first photodiode to generate a DC bias using a first optical signal
Implementation Method 2
a second photodiode that is biased by the DC bias generated by the first photodiode, wherein the second photodiode generates a varying AC signal based on a tunable optical signal
Implementation Method 3
a resistor where the varying AC signal heats the resistor
Implementation Method 4
an interferometer thermally coupled to the resistor, wherein an optical output of the interferometer changes in response to heat generated by the resistor
Data Source
AI summary
Embodiments herein described an optical system for testing the bandwidth of a photodiode (PD) in a photonic integrated circuit (PIC). In one embodiment, a first optical signal is provided to bias one or more PDs in the PIC which generate a DC bias (e.g., DC voltage) across the PD whose bandwidth is being tested. A second optical signal is directed to the PD being tested, thereby generating an AC signal. The second optical signal can be a tunable optical signal where its frequency/wavelength is varied to test the bandwidth of the PD. The AC signal generated by the PD being tested is passed through a heating element (e.g., a resistor) which generates heat. This heat is then measured by an interferometer. The output of the interferometer can be correlated to a bandwidth of the PD.