Patent ID: 8630551
Filing Date: 2014-01-14
Classification: G01M,H04B

Abstract:
1. Method for characterizing an optical device ( 10 ), which comprises: a 90° optical hybrid unit having a first and a second optical input and at least two optical outputs wherein optical output signals leaving the optical outputs have optical phase differences between each other of 90° or multiple thereof; a first photodetector connected to a first optical output and a second photodetector connected to a second optical output, wherein the first optical output emits a first optical output signal and the second optical output emits a second optical output signal, said second optical output signal having an optical phase difference of 180° relative to the first optical output signal; and a first transimpedance amplifier connected to the first and second optical outputs of the 90° optical hybrid unit; characterized in that a first intensity-modulated optical input signal and a second intensity-modulated optical input signal are generated; the first intensity-modulated optical input signal is inputted into the first optical input and the second intensity-modulated optical input signal is inputted into the second optical input; the optical phase of the second intensity-modulated optical input signal is phase-shifted relative to the first intensity-modulated optical input signal; and characterizing the optical device using the electrical output signal of the first transimpedance amplifier, wherein the optical device comprises a third photodetector connected to a third optical output of the 90° optical hybrid unit, and a fourth photodetector connected to a fourth optical output of the 90° optical hybrid unit, the third optical output emitting a third optical output signal and the fourth optical output emitting a fourth optical output signal, said fourth optical output signal having an optical phase difference of 180° relative to the third optical output signal; wherein the electrical output signals of the third and fourth photodetector are low-pass filtered and the low-pass filtered signals are inputted into an operational amplifier, and the output signal of the operational amplifier is used to control an optical phase shifter which controls the optical phase-difference between the first and second intensity-modulated optical input signals in order to provide that the low-pass filtered signals have the same amplitude.