Silicon-Integrated 2D Grating Coupler PDL Testing with Phase Scanning
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Solution Overview
Problem
Existing methods for characterizing the polarization-dependent loss (PDL) of two-dimensional diffraction grating couplers in photonic integrated circuits are time-consuming and inaccurate, particularly when the polarization state of the input light is variable and unknown, making large-scale testing inefficient.
Innovation Solution
A silicon-integrated test structure with adjustable phase shifters is used to characterize PDL by applying a phase shift between 0 and π to the optical signal, allowing emulation of polarization scans without controlling the input polarization, using a test structure with symmetric couplers and phase modulators to measure transmission variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polarization scanning is performed for each wavelength point to measure PDL, then measurement accuracy is improved, but testing time increases significantly making it incompatible with large-scale testing
Solution Approach 1:
The patent changes the measurement parameter from polarization state scanning to phase difference scanning. By controlling the phase difference between s and p polarized light components through a phase modulator, the system achieves PDL measurement without requiring polarization state scanning, thereby reducing measurement time while maintaining accuracy
Solution Approach 2:
The test structure is pre-configured with symmetric couplers and phase modulators that automatically establish the relationship between phase difference and transmitted power. This preliminary setup eliminates the need for real-time polarization scanning during measurement, enabling rapid large-scale testing
2Measurement precision
If polarization scanning is performed to ensure accurate PDL measurement, then measurement precision is improved, but the complexity of controlling injected power and polarization state increases
Solution Approach 1:
The patent extracts the polarization control requirement from the measurement system. By using a phase modulator to control only the phase difference between polarization components rather than controlling the polarization state itself, the system simplifies the control requirements while maintaining measurement accuracy
Solution Approach 2:
The phase modulator acts as an intermediary that translates electrical phase control signals into optical phase difference adjustments. This intermediary device simplifies the control interface by allowing electrical control of phase difference without requiring complex polarization state control mechanisms
3Productivity
If symmetric coupler test structure is used with phase modulator, then testing speed is improved for large-scale testing, but the device structure becomes more complex
Solution Approach 1:
The patent merges the test structure with the device under test by integrating symmetric couplers and phase modulators directly into the measurement path. This integration allows rapid PDL measurement through phase scanning while using the same optical path for both testing and potential device operation, reducing overall system complexity
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 method enables rapid and precise determination of PDL by scanning phase shifts, bypassing the need for polarization control, thus facilitating efficient large-scale testing of 2DGC couplers.
Implementation Method 1
at least one first adjustable phase shifter which is arranged at the first planar waveguide between the input optical coupler and the 2DGC under test, and which is configured to be driven so as to apply a phase shift determined between 0 and π
Implementation Method 2
an optical coupler with a diffraction grating for achieving optical coupling between the optical fiber(s) and such a photonic integrated circuit
Data Source
Figure 1~2
Figure 3(a)~5B
Figure 6A~7B
AI summary
A silicon-integrated test structure for characterizing the PDL of a 1-to-2 silicon fiber optic coupler with a two-dimensional diffraction grating (2DGC), comprises the 2DGC to be tested (61) configured as an output coupler, mirror-mounted with another 1-to-2 silicon fiber optic coupler configured as an input coupler, via planar waveguides (64,65) coupling their respective guided optical terminals. An adjustable phase shifter (63) is arranged at one of these waveguides (65). A p- or s-polarized optical signal is inserted via the input coupler (62). The adjustable phase shifter is driven to apply a pure phase shift between 0 and π to the optical signal propagating in this waveguide (65). The input signal of the 2DGC under test (61) then scans all mixed polarization states. The variation of the optical transmission in the 2DGC under test (61) during this scan gives the PDL.