DOI: 10.3217/yqhnr-2nq41
title: Measuring the frequency response of an optical microphone system with a fiber based setup

description: The following files contain data to reproduce Figure 2), displaying the measured amplitude a) and phase b) response of the optical microphone at different gain values as a function of modulation frequency f. The difference from the specified input filter (fc = 10 Hz) is indicated in c) for the amplitude and d) for the phase.___________________________________________________________________________________________________The files related to the figure contain the following variables in a column-oriented structure:

Figure_2_raw_data.txt:

Frequency          ... Modulation frequency of the external laser [Hz]

Amplitude 0dB   ... Demodulated amplitude of the microphone output with gain = 0dB [V]

Phase 0dB          ... Demodulated phase angle of the microphone output with gain = 0dB [rad]

Amplitude 20dB ... Demodulated amplitude of the microphone output with gain = 20dB [V]

Phase 20dB         ... Demodulated phase angle of the microphone output with gain = 20dB [rad]

Figure_2_processed_data.txt:

Frequency           ... Modulation frequency of the external laser [Hz]

Amplitude 0dB   ... Demodulated amplitude of the microphone output with gain = 0dB,  normalized and corrected for the frequency response of the laser diode [1]

Phase 0dB          ... Demodulated phase angle of the microphone output with gain = 0dB, corrected for the frequency response of the laser diode [rad]

Amplitude 20dB ... Demodulated amplitude of the microphone output with gain = 20dB, normalized and corrected for the frequency response of the laser diode [1]

Phase 20dB        ... Demodulated phase angle of the microphone output with gain = 20dB, corrected for the frequency response of the laser diode [rad]___________________________________________________________________________________________________

To recreate Figure 2 a) and b), plot the normalized and corrected amplitude and phase contained in "Figure_2_processed_data.txt" for each gain value as a function of modulation frequency. In addition, plot the ideal filter response of a 4th-order Bessel filter with a cut-off frequency of 10 Hz, evaluated at the measured frequency points.  

Figures 2 c) and d) can be recreated by computing the difference between the normalized and corrected data and the ideal filter response, calculated for figures a) and b). This process is repeated for the two evaluated gain values of the amplitude and phase response. ___________________________________________________________________________________________________

The correction and normalization of the data is performed by dividing the raw amplitude measurements given in "Figure_2_raw_data.txt" with the measured frequency response of the laser diode given in "amplitude_phase_correction.csv". The data obtained is normalized by the highest amplitude, observed within a frequency range of 100 Hz to 1 kHz. The phase correction is performed by subtracting the measured phase response of the laser diode from the raw phase measurements, given in  "amplitude_phase_correction.csv" and "Figure_2_raw_data.txt".