How much should the optical power meter display when the light source is 0Hz

If the light source is 0 Hz (i.e., no optical signal), the optical power meter should display a reading corresponding to zero optical power, typically around negative infinity in dBm or the lowest measurable value of the meter.

Explanation

An optical power meter measures the optical power arriving at its detector, expressed in dBm (decibels relative to 1 milliwatt) or milliwatts. A reading of 0 dBm equals 1 milliwatt of optical power, while negative dBm values indicate less than 1 milliwatt, and positive values indicate more than 1 milliwatt . When the light source is 0 Hz, it effectively emits no photons, meaning no optical power reaches the meter. In this case:

• The meter detects no signal, so the reading corresponds to 0 mW.
• In dBm, this is mathematically negative infinity, because dBm = 10 × log10(P/1 mW), and log10(0) is undefined. Practically, the meter will display its lowest measurable value, often around -50 dBm to -70 dBm, depending on the meter's sensitivity .
• Some meters may display “OL” (overload) or “under-range” if the input is below the detection threshold.

Practical Considerations

• Zeroing the meter: Before taking measurements, the meter is usually zeroed or calibrated with no light input to establish a baseline. This ensures that any subsequent readings reflect actual optical power rather than electronic noise .
• Noise floor: Even with no light, the meter may show a small nonzero reading due to detector noise. This is normal and should be considered when interpreting very low power measurements .
• Wavelength setting: The meter must be set to the correct wavelength for accurate readings. At 0 Hz, the wavelength is irrelevant, but incorrect settings can affect baseline noise readings .

Summary

With a 0 Hz light source, the optical power meter essentially measures no optical power. The display will show either the lowest detectable power (negative dBm) or a zeroed baseline if the meter has been calibrated. This reading represents the absence of light, which is critical for establishing reference levels in fiber optic testing and loss measurements .