Influence of optical amplifiers for on-chip homodyne laser Doppler vibrometers

Photonic integration allows for the development of compact and relatively cheap laser Doppler vibrometers (LDVs). Optical amplification could enhance the performance of these on-chip LDVs, but the intrinsic noise of optical amplifiers could be detrimental for the limit of detection (LOD) of the displacement of the LDV. Recent developments in heterogeneous integration of semiconductor optical amplifiers (SOAs) on the silicon-on-insulator platform allow for compact and relatively cheap development of on-chip LDVs with SOAs. In this paper, we study the influence of an SOA on the LOD of an on-chip homodyne laser doppler vibrometer. We describe the influence of the shot noise and SOA-noise on the LOD of the vibrometer. SOA intrinsic phase noise depends on the optical power in the SOA, causing the position of the SOA to have a large influence on the performance. From the analysis, it is shown that SOAs can improve the performance of an homodyne LDV when there are large losses in the measurement arm. These losses occur due to the coupling of light from the chip towards the target and back into the on-chip waveguides