How to measure the directivity of an optical splitter

Directivity of an optical splitter is tested by measuring the isolation between the coupled and isolated ports and calculating the ratio of power leakage, using an optical power meter and light source.

Understanding Directivity

Directivity is a measure of how well a directional coupler or splitter isolates the input signal from the isolated port. It is defined as the ratio of the power at the coupled port to the power at the isolated port, and it is closely related to isolation. High directivity indicates minimal signal leakage to the isolated port, which is critical for accurate signal routing in fiber optic networks.

Equipment Needed

Optical light source (appropriate wavelength for the splitter)Optical power meterLaunch and receive reference cablesMatched terminations for unused portsStep-by-Step Testing ProcedureSetup the Source and Reference: Connect a launch reference cable from the optical light source to the input port of the splitter. Calibrate the optical power meter to set a 0 dB reference at the output of the launch cable. Measure Coupled Port Power: Connect a receive cable from the coupled port to the optical power meter and record the power reading.

This represents the intended signal output. Measure Isolated Port Power: Connect the receive cable to the isolated port and measure the power. This reading indicates the leakage or undesired signal at the isolated port.

Calculate Directivity: Directivity (in dB) is calculated as the difference between the power at the coupled port and the power at the isolated port: Directivity (dB) = P_coupled - P_isolated A higher value indicates better isolation and performance. Repeat for All Ports: For splitters with multiple outputs (e.g., 1x4, 1x32), repeat the measurements for each output port. For splitters with multiple inputs (e.g., 2x2), test each input to all outputs in turn.

Optional Tests: You can also test at multiple wavelengths to account for wavelength-dependent behavior and compare outputs to detect variations or crosstalk.

Practical Tips

Ensure all connectors are clean and properly mated to avoid measurement errors. Maintain stable temperature and humidity to reduce test deviations. Use matched terminations on unused ports to prevent reflections that can affect directivity readings.

By following this procedure, you can accurately determine the directivity of an optical splitter, ensuring it meets design specifications and minimizes signal leakage in fiber optic networks.