NKT Photonics Koheras ADJUSTIK, Product Manual

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Laser features
are higher in frequency. These modules are therefore more suitable for applications
where modulations between 30 and 45 kHz are required.
Note: The frequency response is relatively flat up to 20 kHz, but resonances are seen
at frequencies at and above the first resonance occurring at approximately 30 kHz.
Wavelength modulation can be used for frequencies above 20 kHz, but it is recom -
mended to avoid modulating the laser at the resonance frequencies.
External cavity
stabilization
X15 modules support the use of the Pound-Hall-Drever technique to reduce low
frequency phase noise to an ultra-low level. It requires that the X15 output is
stabilized using an external cavity circuit. Refer to
“External cavity stabilization
(ADJUSTIK X15)” on page 41
for details of the implementation.
Amplitude
modulation
If the laser includes the VOA option, and electrical input signal or the built-in function
generator can be used to modulate the laser output power. Modulation of the output
power ranges from 0 to 100% of the output power.
Am/- Signal
To modulate the power, apply an external differential signal to Modulation connector
on the rear panel. A differential signal applied to these pins varies the VOA
attenuation directly. See
“Modulation input/output” on page 97
for the connector’s
pin assignment.
Setpoint
When amplitude modulation is used, the maximum power output can be limited to a
preset value. This value is known as the “setpoint” and it limits the maximum output to
less than the 100% power level.
Note: For more information on using Amplitude modulation with either an external
signal or the built-in function generator, See
“Amplitude modulation” on page 40
.
.
Operating mode
All modules can operate in Current mode, where the current in the pump feeding the
fiber laser is kept stable. Some variants can operate in Power mode as well, where
the power out of the fiber laser is kept fixed.
•
Current mode – the current in the pump feeding the fiber laser is held stable.
•
Power mode – the power out of the fiber laser is held at a fixed level.
The mode set depends on both the model and the application, refer to
Table 3
for the
recommended mode to use. See
“Setting the operating mode” on page 82
.
Table 3 Recommended power modes
ADJUSTIK
model
Power mode Current mode
C15 & Y10 Better Power Stability Better Frequency Stability
E15 & X15 Better Performance Not Recommended