1. The selection of optic power meter
According to the specific applications, when we want to choose a suitable optic
power meter, the following things should be concerned:
1.Choose the most suitable probe type and interface type;
2.Evaluating calibration accuracy and calibration procedures should be in
accordance with acquired range of your optical fiber and splice;
3.Ensure the model numbers of these optic power meters correspond to your
measurement range and display resolution;
4.The optic power meter should be equipped with db function(straight insertion and
loss measurement).
Among all the properties of an optic power meter, optical probe should be most
considered. The optical probe is a solid state photodiode which can receive coupling
optics and convert it into electrical signal.The optical probe can be adapted to
exclusive connector interface (used only as one connection type) and general-purpose
interface adapter UCI (connected with screw). UCI can adapt to most kinds of
industry standardized connector. Based on the calibration factor of the selected
wavelength, optic power meter circuit converts the outcoming signals from probe, and
then displays the optical power reading as dBm way (absolute dB equals 1 mW,
0dBm=1mW) on the screen. Chart 1 is a block chart of optic power meter.
The most potent standard of optic power meter’s selection is to make optical probe
types match the expected operating wavelength range. This chart tabulated some basic
choices. It is worth mentioning that InGaAs performs quite well in three transmitting
windows during testing. Compared to Germanium, InGaAs has a more stable
frequency spectrum in all these three windows; InGaAs enjoys a higher measurement
accuracy in 1550nm window; And also, in terms of temperature stability and low
noise, InGaAs is much superior to Germanium.
Optical power measurement is an essential part during manufacturing, mounting,
operating and maintaining of any fiber optic transmission system.
The next factor is closely linked with calibration accuracy. The question is: when
you calibrate an optic power meter, is it matched with your applications? Or as: the
performance standard of optical fiber and connector should be in accordance with
your system requirements. We should analyse what caused the uncertain measured
value while using different Connecting Adapters. The frequency spectrum of similar
optical sources, optical probe types and connectors from different manufacturers is
uncertain, despite that NIST (National Institute of Standards and Technology) has
established American standard, it’s still quite important to take other latent errors into
consideration.
The third step is to ensure those optic power meter model numbers correspond to
your requirements of measurement range. We use dBm as unit. The measurement
range is an all-sided parameter. We will make sure whether application requirements
are to be met by the minimum/maximum magnitude of incoming signal (to make
optic power meter adapt to all accuracies), linearity (BELLCORE made it to be
+0.8dB) and resolution ratio(generally to be 0.1 dB or 0.01 dB).

2. The most important thing in optic power meter selection is that optical probes match
the expected working range.
The fourth thing is that most optic power meters have equipped with dB function
(relative power), as directly reading optical loss is quite practical in measurements.
Optic power meter in at low prices don’t support this. Without dB function,
technologists have to record reference values and measured values respectively, and
calculate their difference values. Because of the relative loss measurement function,
users can raise productivities and reduce manually calculating errors.
Today, the choices of basic characteristics and functions of optic power meters
become decreased for users. But special requests including recording data collecting
history and peripheral interface are made by some users.
stabilized light source
During the process of loss measurement, stabilized light source(SLS) emit the light
whose power and wavelength are already known into light system. Those optic power
meters /optical probes which can calibrate specific wavelength light source(SLS)
receive the light from optical network and convert it into electrical signal. To ensure
the accuracy of loss measurement, the transmission equipments used in light source
simulation should :
1.have same wavelength, and use the same light source(LED, laser);
2.keep the stability of output power and frequency spectrum(the stability of time and
temperature) during measuring.
3.provide the same connecting interfaces and use the same optical fiber;
4.ensure the output power meets system loss at anytime.
The best choice of light source should simulate characteristics and measurement
requirements of systematic optical transmitter and receiver when the transmission
system need a solitary and stabilized light source. In terms of light source selection,
things should be concerned are:
Laser Diode(LD)
The light from Laser Diode has a narrow wavelength bandwidth. And it’s
monochromatic light, that is to say its single wave is long. Compared with LED, laser
which passes through its spectral band is discontinuous, and it emits several wave
lengths whose peak values are low in the two sides of the central wavelength.
Compared with LED light sources, laser light sources are much more expensive than
it despite that laser light sources are proved to be more powerful. Generally Laser
Diodes are used in long distance single-mode systems whose losses are more than
10dB. We should try to not use laser light sources in multimode fiber measurements.
Light Emitting Diode(LED)
LED has a wider spectrum than LD, generally it’s from 50 to 200nm. And its output
power is more stable because LED is a kind of non-interference light. LED light
sources are much cheaper than LD light source, but it’s underpower when the loss
measurement at worst condition. LED light sources are typically used in Local Area
Network(LAN) of short distance networks and multimode fibers. When LED has
enough output power, it can be used in laser light source single mode system to
conduct an accurate loss measurement.