NKT Photonics Koheras ADJUSTIK HP, Product Manual

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Fast wavelength modulation
42
Differential output
If the Wavelength +/- pins are configured as an output, a differential signal will be
present at the pins as shown in
Figure 13
. The differential signal amplitude can
be up to 2x 5 Vpp with a common mode voltage of 2.5 V.
Figure 13 Differential output signal
The differential output signal can be used for example, as the input signal for
other Koheras ADJUSTIK or ADJUSTIK HP lasers.
Wavelength
modulation
coupling
You can select either internal AC or DC coupling of the modulation signal. If AC
coupling is chosen, the laser’s high pass filter function has a cut-off frequency of
1.6 Hz. Setting an X15 variant to DC coupling allows the laser to lock to an
external reference signal that for example, uses the Pound Drever Hall
technique. In this mode, the laser adjusts its wavelength so the differential error
signal level on the Wavelength +/- input leans towards 0 V.
Narrow vs. Wide
modulation range
You can set the wavelength modulation operation to either narrow or wide
range. As detailed in
Table 7
, the operation characteristic of each range depends
on the laser type (X15 or E15/C15/Y15).
Table 7 Narrow vs wide band wavelength modulation
X15 variant E15/C15/Y10 variants
Narrow Very limited modulation can be
obtained, i.e. maximum ~30 MHz.
The extremely low phase noise is
maintained in this mode.
Maximum 0.8 GHz modulation for E15/
C15 and 1 GHz for Y10.
Wide Maximum ~600 MHz modulation,
but the its extremely low phase
noise is NOT maintained in this
mode.
Maximum 8 GHz modulation for E15/
C15 and 10 GHz for Y10. Small
negative impact on low frequency
phase noise.