Abstract
We present a novel phase generated carrier (PGC) demodulation technique for homodyne interferometers which is robust to modulation depth variations and source intensity fluctuations. By digitally mixing the waveform with a multitone synthetic function (a linear combination of harmonics of the modulating signal), distortion can become negligible even in presence of large variations of the modulation depth. The technique only requires two mixers and can also provide the DC component of the phase in real time, without needing any previously recorded data or ellipse-fitting algorithms. We validate the technique with simulated waveforms and with experimental data from a wavelength metering experiment using an integrated unbalanced interferometer on-chip, showing that the technique corrects distortion without increasing the noise with respect to the standard PGC technique.
Highlights
Optical interferometry is currently the most accurate technique to measure certain physical magnitudes such as displacement, vibrations, and wavelength, among others
We have evaluated the performance of the phase-generated carrier (PGC)-multitone mixing (MTM) algorithms for a nominal modulation depth of Cnom = 0.84π, but we can calculate the coefficients of the mixing signals f 1 and f 2 for other nominal values
In the latter it can be appreciated that the PGC-std algorithm has visible non-linearities in the form of an undulation that occurs every π/2 shift, or every quarter of the free spectral range of the Mach-Zehnder interferometer (MZI), whereas for PGC-MTM up to 3ω and up to 4ω there are no visible non-linearities when compared to the trace obtained with the commercial wavemeter, demonstrating the robustness of the PGC-MTM algorithms to modulation depth deviations
Summary
Optical interferometry is currently the most accurate technique to measure certain physical magnitudes such as displacement, vibrations, and wavelength, among others. Other techniques apply active modulation of the interferometer, either to keep it in quadrature with a feedback loop [2] or dithering it constantly and applying phase demodulation techniques such as pseudo-heterodyne [3], serrodyne modulation with quadrature sampling [4] or phase-generated carrier (PGC) modulation [5]. The latter method is the most popular, and consists in introducing a sinusoidal modulation in the interferometer, and extracting the cosine (in-phase, I) and the sine (quadrature, Q) components from the different harmonics (most typically the first and the second) of the interferometric signal. Once the I and the Q are known, the phase can be calculated either by applying an arc-tangent function [6] or a cross-difference multiplication algorithm (CDM) [5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
