Sensors in optical power meter and its types
Germanium, Silicon, and Indium Gallium Arsenide are the type of major semiconductor sensors. In addition, they can also be used along with attenuation elements for high optical power testing or wavelength selective elements, so they respond only to particular wavelengths. There are many thin film optical coating company in the market which takes help of optical components manufacturer in order to manufacture products and the same procedure is followed by pfg optics also.
These all work under the same type of circuit, although in addition to the response characteristics of their basic wavelength, each one has some other particular characteristics:
- Saturation of Silicon detectors is done at relatively low power levels, and they are useful only in the visible and 850 nm bands, where they generally provide good performance.
- Saturation of the germanium detectors is done at the highest power levels, but they have poor low power performance, are generally temperature-sensitive, and have poor general linearity over the entire power range. They are only marginally accurate for the «1550 nm» test due to the combination of temperature and wavelength, e.g. 1580 nm, although they provide useful performance over the commonly used 850/1300/1550 nm wavelength band, so they are extensively deployed where low accuracy is acceptable. There are some other limitations which include: poor responsivity uniformity across the detector area, and non-linearity at low power levels.
- Saturation of InGaAs detectors is done at intermediate levels. In general, they offer good performance, but they are very wavelength sensitive around 850nm. They are therefore used extensively for testing single-mode fibers at 1270 — 1650 nm.
The fiber optic connector interface is an extremely important part of an optical power meter sensor. A careful optical design is required to avoid significant accuracy problems when used with the wide variety of commonly encountered fiber types and connectors. Sensor input amplifier is another important part. It requires very careful design to avoid reduce in significant performance over a wide range of conditions.
Power Measuring range:
A typical OPM ranges from about 0 dBm (1 milliwatt) to about -50 dBm (10 nanowatts), although the display range can be larger. High power is considered when it is above 0 dBm, and specially adapted units are capable enough to measure 30 dBm (1 Watt).
Irrespective of the specifications of the power meter, tests below approximately -50 dBm are vulnerable to ambient light leakage into the fiber or connector. Therefore when the testing is performed at low power, some sort of linearity verification is suggested.