Optical Coherence Tomography: System Design and Noise Analysis

The basic properties of an Optical Coherence Tomography (OCT) system, such as coherence and interference are presented. A 1.3µm light source and a 1.5µm source is examined and used in OCT imaging for comparison of penetration depth. No improvement was shown with the 1.5µm system, but is expected theoretically. A simple inexpensive 1.5µm source was also examined for use in OCT, and shows promising results, based on a spectral analysis. Noise in unbalanced and balanced detection is examined theoretically. The noise and SNR is measured experimentally for a given system, showing that the theoretical model does not give a good estimate. A model is therefore constructed using the experimental noise measurements, and shown to give better estimations of the SNR than the theoretical model. Using the new model, it is shown that attenuation of the reference power does not improve the SNR in the examined system when using unbalanced detection, as expected when using the theoretical model. It is also found that using a 25/75 coupler split ratio instead of 50/50 in balanced detection, should improve the SNR. A 50Hz noise was found to be picked up after filtering, and is shown to limit the SNR when no amplification of the measured signal is used.