Optical power meters can measure very low powers like -50 dBm and -70 dBm, but require highly sensitive sensors and careful calibration.

Understanding Optical Power Levels

Optical power is often expressed in dBm, a logarithmic unit relative to 1 milliwatt. A reading of -50 dBm corresponds to 10 picowatts, and -70 dBm corresponds to 0.1 picowatts. These are extremely low power levels, typically encountered in long-haul fiber optic systems, low-power laser testing, or sensitive photonic experiments.

Sensor Requirements

To measure such low powers accurately, you need high-sensitivity photodiode sensors or low-noise detectors. Common sensor types include:

• InGaAs photodiodes: Suitable for near-infrared wavelengths (900–1700 nm) with high sensitivity and low noise, ideal for fiber optic communications .
• Silicon photodiodes: Used for visible wavelengths but less sensitive in the infrared range.
• Thermopile sensors: Typically for higher power levels; not suitable for -50 dBm or -70 dBm. Low-power sensors often have femtowatt to picowatt resolution, enabling detection of signals in the -50 to -70 dBm range .

Meter Types

• Benchtop meters: Provide the highest sensitivity and stability, often with multiple channels and advanced calibration options. They are ideal for laboratory or production testing where low-power measurement is critical .
• Handheld meters: Portable and convenient, but their sensitivity may be limited. Some high-end handheld meters can still measure down to -70 dBm with appropriate sensors .

Calibration and Wavelength Considerations

Optical power meters are wavelength-dependent, meaning the sensor must be calibrated for the specific wavelength of the light source. Using the wrong wavelength setting can result in significant measurement errors, especially at very low powers . NIST-traceable calibration ensures accuracy and repeatability.

Practical Tips

• Minimize ambient light and reflections to avoid noise interference.
• Use short, clean fiber connections to reduce insertion loss.
• Ensure the meter and sensor are thermally stable, as low-power measurements are sensitive to temperature fluctuations.
• For dynamic measurements, choose meters with high sampling rates and low latency to capture transient signals .

Summary

Measuring -50 dBm and -70 dBm optical power is feasible with modern optical power meters, provided you use high-sensitivity sensors, proper wavelength calibration, and maintain a low-noise environment. Benchtop meters with InGaAs sensors are generally preferred for these ultra-low power levels, while some advanced handheld meters can also achieve these measurements in field applications .