Abstract
Optical coherence tomography (OCT) is a non-invasive technique in biomedical imaging since it provides high axial and lateral resolutions. OCT requires approaching the measurement probe to the sample within the axial range of several millimeters. If there is an initial condition that the distance is unknown; as expected for automatic measurement. In a distance with longer axial range, the time-of-flight (ToF) becomes is useful. In this research, we integrated ToF with sub-millimeter axial resolution and a meter-order axial range; and OCT with micrometer-order axial resolution and a millimeter-order axial measurable range. A spectral-domain (SD-OCT) system composed of a superluminescent diode, optical fibers, and a spectrometer was implemented. ToF system holds a semiconductor laser which is sinusoidally modulated by an electric signal ranging frequency from 0.1 to 1 GHz, a Si PIN photodetector. The ToF and the SD-OCT systems share a common optical path; the phase difference of the sinusoidal signals returning from the sample and reference arms are measured. The importance of the integrated system is that the accuracy of ToF is smaller than the axial measurable range of SD-OCT. The SLD of the SD-OCT system has a central wavelength of 840 nm and a bandwidth of 80 nm. The axial measurable range was 3.7 mm which was calculated from the specifications of the grating and the LSC system. The ToF system has an experimental accuracy of 0.9 mm operating at a frequency of 0.8 GHz. It is enough for the axial resolution measurable in the range of SD-OCT.