6-58
IM AQ6376-01EN
Determining the Level Shift Amount
Even if NA of the optical fiber used is unknown, the level shift amount enabling correct
level measurements can be determined.
1.
Set up a light source such as a DFB-LD with a spectrum width that is narrower
than the instrument’s resolution (with a wavelength of 1310 nm or 1550 nm).
2.
Connect the light source and the instrument using an optical fiber cord and set the
instrument’s resolution to 2.000 nm.
3.
Execute measurement and determine the peak level.
4.
Disconnect the optical fiber cord from the instrument and connect it to a light
power meter to measure the light power.
5.
Calculate the difference between the peak level value obtained from the
instrument and the power value obtained from the light power meter, and set this
amount as the instrument’s level shift.
Explanation
Input Optical Fiber Numerical Aperture (NA) and Level Measurement
Values
The level measurement error of the instrument changes as shown in the figure below,
according to the numerical aperture (NA) of the optical fiber connected to the input
connector. The instrument’s absolute level is calibrated using a 9.5/125 μm single-mode
optical fiber (SSMA type in JIS C6835, with PC polishing, 9.5 μm mode field diameter,
and 0.104 to 0.107 NA). Even if a single-mode optical fiber is used, the level accuracy
will be outside the specifications if the NA is not in the range shown above.
Input optical fiber numerical aperture and level error (typical characteristics)
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.101
0.102
0.103
0.104
0.105
0.106
0.107
0.108
0.109
0.110
0.50
Level error (dB)
Numerical Aperture
6.14 Correcting Displayed Values
