Uncertainty principle limit for swept source OCT.

Swept source optical coherence tomography (OCT) technology makes use of dispersive Fourier transformation (DFT) methods. We theoretically and experimentally look at the distortions in the measurement of a 2-GHz wide Lorentzian optical filter. While accurate at low sweep rates, the measurement is distorted at high rates. The cross-over point is delimited by a time-bandwidth inequality reminiscent of the uncertainty principle. There are limitations at very high GHz/ns sweep rates, R. Unless ΔνΔt is much less than 1, the measurement is unreliable, where Δν = RΔt. This occurs because an attempt is made to measure the filter bandwidth in less than its ring-down time. Then we extrapolate as to what happens in swept source OCT where the Lorentzian filter is replaced with a Mach-Zehnder filter in the imaging and clock interferometers. We find that there is indeed a resolution limitation at very high sweep rates, but that the limit is not significant for current-day swept sources, such as a MEMS tunable VCSEL.