1：Experimental Design and Method Selection:

The method involves designing a test element with two input couplers, an interferometer, waveguides of different lengths, and a photodetector to measure propagation loss without being affected by manufacturing errors in grating couplers and PDs. The interferometer's branching ratio has wavelength dependence, allowing extraction of insertion loss differences.

2：Sample Selection and Data Sources:

Test elements were fabricated with long waveguide lengths of 1, 2, 3, and 5 cm on a silicon wafer, using a Ge PD integrated on the Si waveguide.

3：List of Experimental Equipment and Materials:

The test element includes grating couplers, an interferometer, waveguides, and a germanium photodetector. Specific models or brands are not mentioned.

4：Experimental Procedures and Operational Workflow:

Light is coupled into the test element via grating couplers, propagates through waveguides of different lengths, and is detected by the PD. The photo current is monitored, and wavelength dependence of optical power is measured to derive propagation loss.

5：Data Analysis Methods:

The amplitude of the output power (difference between peak and dip) is used to extract insertion loss for different waveguide lengths, from which propagation loss is calculated (e.g., 3.4 dB/cm).