144 8163A/B, 8164A/B, 8166A/B User’s Guide
5 Tunable Lasers
How to Set a Relative Wavelength
You use a relative wavelength for heterodyning, for example, when you are
measuring the linewidth of DFB (distributed feedback) lasers.
The output wavelength, λ, is set from the base wavelength,
λ
0
, and the
frequency offset, df. The formula for calculating the output wavelength is:
where c is the speed of light in a vacuum (2.998×10
8
ms
-1
).
To set a frequency offset of 1.000 THz from a base wavelength of 1545 nm:
1 Move to the Tunable Laser channel and press [Details].
2 Press [Menu]. The menu appears.
3Move to <Wavelength Mode> in the menu and press Enter. A menu
appears.
4Move to <Offset>, by using the cursor key, press Enter, and press
Close. You see the screen in Figure 83 on page -145.
λ
cλ
0
λ
0
df c+
--------------------
=
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