Newport FPM-8220, Руководство пользователя, Страница: 30 / 84

April 2018 18 FPM-8220
varying the wavelength. The result is a table of detector responses, recorded every 10
nanometers, in A per W. When you input light, the FMH-8700 series of Fiber Optic
Measurement Head measures detector current, then uses your wavelength setting to look up
the conversion factor on the calibration table. Interpolation algorithms are used for wavelengths
between these calibration points. Figure 2.13 is a sample of detector response plotted as a
function of wavelength. The chart is based on data from the FMH-8700 series of Fiber Optic
Measurement Head calibrations that are performed at ILX Lightwave's NIST-traceable
calibration laboratory.
Figure 2.13 – Sample Detector Response
The detector response is shown as photodetector current (amperes) per unit of optical power (watts).
The following are true for all FHM-8700 series Fiber Optic Measurement Heads and are exemplified
in the chart in Figure 2.12.

The highest detector current (greatest sensitivity) is at the longer wavelengths, normally used for
telecom work.

Changes in detector response are significant enough that the meter must know the
wavelength in order to accurately display optical power.

The flatness (or steepness) of the curve at any point is a measure of how much effect an
error in wavelength input will have on the measurement result.

Detector response is less at shorter wavelengths.
Analog Output (BNC)
A BNC output connector is provided on the rear panel to give you direct access to the amplified
photodetector signal. Keep the FPM-8220 in manual range mode when you use the analog output.
This is a very low-noise, stable output that is normalized to 10V to represent percentage of full scale.
For example, 7.1V = 71% of range. This information is represented by the bar graph on the front
panel but with greater resolution. Since the resolution is mostly determined by the instrument that you
connect it to, this output is useful for monitoring small changes. With a typical output impedance of
1000
Ω , you can directly connect the meter to most data loggers or digital voltmeters. The analog
0.0001
0.0003
0.0005
0.0007
0.0009
0.0011
0.0013
0.0015
0.0017
0.0019
800 900 1000 1100 1200 1300 1400 1500 1600
Responsivity
(A/W)
Wavelength (nm)