The Development And Application Of The Recirculation Loops Swept Source Optical Coherence Tomography

Optical coherence tomography (OCT) is a high-resolution, non-invasive, non-destructive optical imaging technique. OCT can not only obtain structure and functional image of the biological internal tissues, but also be used for non-destructive testing of industrial areas. However, due to the limited image depth for conventional OCT system, the conventional OCT cannot be applied in the industrial areas which needs greater imaging depth. Therefore, we have developed the recirculation loops swept source OCT (SS-OCT) system, which can achieve more than 30 mm measurement range. The main contents are listed as bellow:1. Firstly, the theory of SS-OCT is studied, and three-dimensional SS-OCT system at 1297.2 nm central wavelength is developed, which is consisted of a main interferometer and a high speed swept source (SL1310V1) of 122.4 nm 10dB bandwidth. In addition, we have developed the real time two-dimensional imaging software based on GPU acceleration. The constructed SS-OCT system realizes high speed A-Scan rate of 100 kHz compared to previous 20 kHz SS-OCT system. The axial resolution and lateral resolution of the system are 16 μm and 8.7 μm, respectively. The imaging depth range is 12 mm supported by the optical clock in the swept source. We obtain successfully the high speed three-dimensional OCT images for 1951 USAF resolution test target and finger, respectively.2. The measurement of center thickness and airgaps along the optical axis of the mounted optical system, such as the lens system for microscopy, photography or lithography, is critical for optics manufacturing industry and modern optical instrumentation. Based on the conventional SS-OCT technology, we have developed the recirculation loops SS-OCT system, which have equipped the recirculation loops in reference arm and sample arm, respectively. In addition, phase-sensitive approach based on phase-comparison between measurement signal and reference signal is proposed to distance determination without wavenumber calibration. Corresponding to the conventional SS-OCT system, more than 30 mm measurement range for the proposed system can be implement, and submicron precision about a range of 30 mm is confirmed.3. We have improved the recirculation loops SS-OCT system applied to the extent range distance measurement. The repeated measurements for the same lateral location can be achieved with shifting the sample measurement into the recirculation loop in sample arm. The enhanced sensitivity for the measurement of optical thin film thickness is confirmed by using poly (s-caprolactone) PCL film layer deposited on a Si substrate as the sample. In addition, the thin film thickness can be precisely obtained by fitting the improved analytical model for nonlinear phase of thin film.