A Light Source Power Meter Test measures optical power and fiber loss by injecting a known light signal into a fiber and detecting the received power at the other end.

Overview

A Light Source Power Meter (LSPM) Test is essential for evaluating fiber optic links, ensuring they meet performance specifications, and identifying potential issues such as breaks, bends, or faulty connectors . The test uses two main instruments:

• Light Source: Emits a stable optical signal at a specific wavelength (commonly 850 nm, 1300 nm, 1310 nm, or 1550 nm) into the fiber under test .
• Optical Power Meter: Measures the optical power received at the far end of the fiber, displaying results in decibels (dB) for relative loss or decibel-milliwatts (dBm) for absolute power .

Purpose

The test determines insertion loss, which is the amount of light lost as it travels through the fiber. Accurate measurement ensures the fiber link meets industry standards such as TIA-568-3.D and ISO/IEC 14763-3 . It is used for:

• Installation verification
• Maintenance and troubleshooting
• Network upgrades
• Certification of fiber links

Procedure

1. Calibration: Set the power meter to the correct wavelength and calibrate it using a reference fiber or known power level .
2. Connect the Light Source: Attach the light source to one end of the fiber and select the appropriate wavelength for testing .
3. Measure Received Power: Connect the power meter to the opposite end of the fiber. Record the optical power reading.
4. Calculate Loss: Determine the fiber loss by comparing the transmitted power from the light source to the received power at the meter. Loss is typically expressed in dB.
5. Repeat for Multiple Wavelengths: For multimode or singlemode fibers, test at all relevant wavelengths to ensure compliance with specifications .
6. Document Results: Record measurements, including fiber length, wavelength, and loss values, for certification or troubleshooting purposes.

Best Practices

• Use stable, calibrated light sources to ensure accurate readings .
• Perform bidirectional testing when possible to account for connector and splice variations .
• Ensure clean connectors to avoid measurement errors.
• For complex networks, consider using an Optical Loss Test Set (OLTS), which integrates light source and power meter functions and may include duplex testing, length measurement, and pass/fail evaluation .

Field Applications

Portable LSPM kits are widely used in FTTH, enterprise, carrier, and Ethernet networks. They are designed for durability, ease of use, and rapid testing in the field, allowing both novice and experienced technicians to perform accurate measurements efficiently . By following these procedures and best practices, a Light Source Power Meter Test ensures reliable fiber optic network performance and compliance with industry standards.