Optical Power Meter Measurement of OLT Emission Selective Wavelength

Accurate measurement of OLT optical power at selective wavelengths requires a wavelength-selective optical power meter or filtered PON tester to isolate the specific service wavelength, avoiding errors from multiple simultaneous signals.

Principles of Measurement

An optical power meter (OPM) measures the optical power in fiber systems using a calibrated photodiode sensor, typically made of Si, Ge, or InGaAs, depending on the wavelength range.

Standard OP

Ms are wavelength-dependent, meaning the detector's response varies with wavelength. For accurate measurements, the meter must either be set to the correct wavelength or use a wavelength-selective head that automatically compensates for spectral responsivity.

In PO

N systems, OLT emissions often include multiple wavelengths simultaneously (e.g., 1490 nm for G-PON downstream, 1550 nm for broadcast video, 1577 nm for XGS-PON). Using a broadband power meter in such cases can produce incorrect readings because it sums the power from all wavelengths. Therefore, filtered or wavelength-selective meters are essential to isolate the target wavelength.

Equipment OptionsWavelength-Selective Optical Power Meters Instruments like the OMM-6810B with Power/Waveheads can measure both optical power and wavelength simultaneously. These heads self-calibrate for wavelength-dependent detector response, providing accurate power readings without manual wavelength entry. They are suitable for lab or production testing of OLT lasers and fiber links.

Field PO

N Testers Devices such as the VIAVI SmartPocket V2 OLP-39 allow simultaneous selective measurement of G/E-PON (1490 nm) and XGS-PON (1577 nm) wavelengths with a single fiber connection. These testers use optical filters to separate wavelengths, ensuring accurate power readings even when multiple services coexist on the same PON.

Measurement Procedure

Connect the meter to the OLT output using the appropriate fiber connector (SC, LC, etc.). Select the target wavelength on the meter or ensure the wavelength-selective head is in use. Calibrate the meter if necessary, using a reference source or transfer standard to account for detector responsivity.

Record the optical power displayed, ensuring the meter is not saturated and the fiber is properly aligned. Repeat for other wavelengths if multiple services are present, using either separate filtered measurements or a multi-wavelength tester.

Key Considerations

Avoid broadband meters when multiple wavelengths are present, as they cannot distinguish between signals. Use wavelength-selective or filtered meters to prevent measurement errors. Account for connector losses and fiber attenuation to ensure accurate absolute power readings.

Verify calibration periodically, especially for high-precision or production measurements. By following these practices, technicians can accurately measure OLT emission power at selective wavelengths, ensuring proper PON performance and service quality.