Most common optical power meters can detect optical signals as low as –50 dBm, equivalent to about 1 microwatt or less.

Measurement Range and Sensitivity

A typical fiber optic power meter measures optical power in the range of +3 dBm to –50 dBm, depending on the detector type and calibration . The threshold, or minimum detectable power, is usually around –50 dBm, which corresponds to approximately 1 microwatt. This sensitivity is sufficient for most fiber optic communication systems, including singlemode and multimode networks .

Units and Calibration

Optical power meters report measurements in dBm, a logarithmic scale referenced to 1 milliwatt. For example:

• 0 dBm = 1 mW
• –10 dBm = 0.1 mW
• –20 dBm = 0.01 mW
• –30 dBm = 0.001 mW (1 microwatt) The meter's calibration is traceable to national standards, ensuring consistent readings across different instruments .

Detector Types

Common detectors in optical power meters include Silicon (Si), Germanium (Ge), and Indium Gallium Arsenide (InGaAs). The choice of detector affects the wavelength range and sensitivity, with InGaAs detectors typically used for long-wavelength singlemode fibers (1310–1550 nm) and offering high sensitivity down to the –50 dBm range .

Practical Considerations

• Lasers: Typical output powers are 0 to –10 dBm for short-range systems, and higher for long-haul or CATV applications.
• LEDs: Lower output powers, often –10 to –20 dBm, are still detectable by standard power meters.
• Loss Measurement: Power meters are often used with a light source to measure fiber loss, where the sensitivity threshold ensures accurate detection even after significant attenuation . In summary, the threshold of a common optical power meter is around –50 dBm, allowing reliable measurement of very low optical powers typical in fiber optic communication systems.