NKT Photonics Koheras ADJUSTIK, Product Manual

Page: 24 / 105

Laser features
24
Laser features
Thermal tuning
The wavelength of the laser can be controlled using a thermal tuning technique that
changes the temperature of the laser’s fiber. The fiber laser is mounted under tension
on a substrate. When the temperature of the substrate changes, the laser cavity
length also changes due to thermal contraction or expansion. Further, the
temperature of the laser cavity itself also changes such that the laser wavelength
changes in response to both thermo-optic and physical changes in the optical path
length. See
“Tuning the wavelength” on page 82
.
Fast wavelength
modulation
The laser includes the capability to use an external signal to modulate the emission
wavelength using a Piezo. The Piezo allows the modules output wavelength to be
modulated using an external electrical signal.
Input circuits
Section
“Fast wavelength modulation” on page 33
provides examples of fast
wavelength modulation circuits and performance.
Wav/- Signal
To modulate the wavelength, apply an external differential signal to Modulation
connector on the rear panel. See
“Modulation input/output” on page 97
for the
connector’s pin assignment.
As this signal varies and increases its positive potential, the wavelength increases.
Figure 3
shows the frequency response when the fast wavelength modulation
feature is utilized. The graph shows the response for both standard and wide thermal
tuning substrates.
Figure 3 Frequency response using wavelength modulation
The response shown in
Figure 3
is for a laser with a wavelength at 1550 nm. The
response is scaled linearly with the wavelength of the laser. Further, the Narrow
Thermal Tuning module which has less vibration sensitivity, shows resonances that