| CPC G01D 5/35364 (2013.01) [G01K 11/322 (2021.01); G01L 1/242 (2013.01)] | 15 Claims |

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1. An apparatus for digitizing an optical signal, comprising:
an optical detector to detect an optical signal and to generate an electric signal corresponding to the optical signal;
an envelope curve detector to determine the amplitude of the electric signal or a modified electric signal resulting from the electric signal, and to supply an amplitude signal corresponding to the amplitude;
an analog to digital converter to digitize the amplitude signal and to supply a corresponding digitized amplitude signal; and
a variable voltage source to generate a variable voltage signal to calibrate the envelope curve detector, wherein the variable voltage signal has the same or a similar frequency as the electric signal generated from the optical signal.
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