Schematic of the laser diode current driver circuit. The circuit is divided in to separate functions for clarification and easy refrencing.
Noise and drift in the current. In (a) the spectral density of the current noise is shown. The black line represents the spectral density of the current signal when the diode and resistor were driven by the current driver. The thick gray line is the spectral density of the intrinsic noise of the measurement apparatus, measured by disconnecting the current driver from the laser diode. The thin gray lines are the spectral density of the noise data in the original paper on the Hall–Libbrecht design (Ref. 2). In (b) the measured drift of the output current about its mean value is shown as a function of time. In (c) the drift in the temperature at three locations is plotted (all three sets of temperature data are plotted on top of each other).
Accuracy and repeatability of the current set point. The plot in (a) shows the deviation of the actual current data from the set point. The gray lines indicate the LSB points specified in the DAC’s data sheet. Plot (b) show the rms repeatability of the current output, measured as a function of the digitally programed set point.
Temporal response of the current driver. In (a) the Bode plot of the response to the modulation input is displayed. The solid line is the amplitude of the response of the driver normalized to the ideal response for the signal applied to the modulation input. The dashed line is the theoretical high frequency response assuming ideal components and transmission lines given by Eq. (4). In (b) the transient response of the current driver to a total load change of roughly 3% is shown. The black line is the current through the load, and the gray line is the impedance of the load.
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