This paper explores the challenges of signal processing when using optical coherence tomography (OCT) imaging instruments driven by asymmetric MHz bidirectional sweeping lasers. A downconversion master-slave (DMS) method is proposed as a viable alternative to the traditional OCT protocol. Unlike conventional swept source OCT, which requires a separate calibration for each sweep, the DMS approach does not require calibration of the acquired channeled spectra; its operation is independent of the tuning direction. We demonstrate the practicality of the DMS method with en-face OCT images obtained with an OCT instrument equipped with a fast bidirectional swept laser (tuning speed 1.6 MHz) and a slow acquisition card of only 2.5 MS/s sampling rate.