THORLABS PICO D, User Manual

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2.5.4 Analog control signals
The interface allows settings of wavelength, optical power and the internal (cavity)
temperature through analog signals. The PICO D unit will follow the applied analog
control signals within the specifications.
To reach the specified accuracy, one must correct for small non-linear deviations be-
tween the control signals and their corresponding (wavelength and optical output
power) counterparts. Therefore, setting the optical output to a specified power and
wavelength require a calibration table, see paragraph 3.3.
In order to achieve ultimate performance the control signals must be well defined.
Ideally one would need input signal fidelity to some tenth of a mV to achieve ultimate
performance (concerning wavelength tuning). Resolutions of this order are easily
disturbed by stray ground return potentials that typically can be tenths of volts. In or-
der to ease customer requirements we have incorporated a differential input ampli-
fier, see Figure 2–12, with very high CMRR (Common Mode Reaction Ration).
Note that this is a differential input stage and that, e.g. , both voltages labeled “+” and
“-“ must be connected.
Table 2-6 The analog control signals
Name Short description
WAVELENGTH_TUNING This signal, -10 to +10 V, tunes the wavelength of the laser.
OPTICAL_POWER This signal, -1 to +10 V, sets the optical output power.
MODE_HOP_ADJUST This signal, -10 to +10 V, can be used to move mode hops.
Figure 2–12 Analog input circuitry. Note that this input circuitry has a differen-
tial input stage!
2.5.4.1 Analog control: WAVELENGTH_TUNING
Provided that _TUNING_ENABLE is set TRUE – LOW, the wavelength can be set
and tuned by applying voltage to +WAVELENGTH_TUNING and
-WAVELENGTH_TUNING as shown in Table 2-7 and Figure 2–13.