Power Meter Basics
What Does A Power Meter Do?
A power meter performs the most rudimentary fiber optic measurement, which is to measure optical power from the end of a fiber. This measurement allows a user to identify the magnitude of optical power from a source or detect any losses in power before the receiver.
Applications Of A Power Meter
- Fiber optic power meters can be used to determine the continuity of a fiber by checking if the light is successfully travelling from the transmitter to the receiver.
- It can also be used to measure end-to-end attenuation within the fiber. The total signal loss due to the fiber, connectors, splices, or defects can be measured using a fiber optic power meter.
How Do You Use a Power Meter?
First, attach the power meter to the desired fiber optic cable. Then, turn on the source of power or transmitter and read the displayed measurement. Make sure that this reading matches the specified power for the system being measured. It is crucial that these readings match in order for the system to function accurately
Table 1. Typical parameters for various fiber optic applications:
|Wavelength, nm||Power Range, dBm||Power Range, W|
|Telecom||1310, 1550||+3 to -45 dBm||50 nW to 2mW|
|Datacom||650, 850, 1300||0 to -30 dBm||1 to 100uW|
|CATV, DWDM||1310,1550||+20 to -6 dBm||250 uW to 10mW|
Factors That Can Affect Your Selection
- Most fiber optic power meters are available with a choice of 3 different detectors, silicon (Si), Germanium (Ge), or Indium-Gallium-Arsenide (InGaAs), which have a major influence on the performance of the power meter.
- Select an InGaAs (Indium Gallium Arsenide) detector for:
- General and precision measurements over 1000 – 1650 nm up to the maximum meter range.
- Coarse Wavelength-Division Multiplexing (CWDM) or Dense Wavelength-Division Multiplexing (DWDM) bands up to the maximum meter range.
- Single mode-only testing.
- GAO Tek provides a range of InGaAs detector with different features capable of serving multiple functionalities.
- Select a Ge (Germanium) detector for:
- Reasonable accuracy over 850 -1550 nm up to the maximum meter range.
- General single mode & multimode testing
- Avoid a Ge (Germanium) detector for:
- Work on WDM systems above 1550 nm.
- 1550 nm systems if cold temperatures are expected due to temperature sensitive calibration constants.
- Precision or laboratory grade accuracy as Germanium is inherently nonlinear by about 0.04 dB, has some temperature sensitivity, and responsivity is more variable across the detector surface.
- Select a Si (Silicon) detector for:
- Precision measurement at 600 – 1000 nm up to the maximum meter range.
- Plastic Optical Fiber (POF), Hard-Clad Silica and 850nm-only testing.
Determine Limits of the System Power Level
- For LAN or Telecommunication Digital transmission systems, maximum power levels are lower than +5dBm.
- For Radio Frequency or Analog specialist systems, maximum power levels are lower than +15dBm.
- For most standard cases, +18dBm serves as an upper limit, above which special measures and precautions must be taken in order to avoid system failure.
- By using optical power amplifiers, some long distance systems can have a maximum power up to +23dBm.
- For most standard cases, -35dBm serves as a lower limit for system power levels.
- Using power meters on systems below -45dBm can be inaccurate due to noise created by sunlight.
- It is crucial to determine the wavelengths that the devices are running on prior to selecting a power meter.
- Every power meter functions optimally within a certain bandwidth of wavelengths.
- The most commonly used wavelengths range from 800nm-1700nm.
- The power meter must be calibrated to the wavelength of the device in order to get the most accurate measurements