The configuration of the swept-source is illustrated in Fig. 1. The SC with a pulse width of 150 ps, output power of 2 W, and spectrum of 460 to 2000 nm provides a broadband pulse train at a repetition rate of 10 MHz and is coupled into a single-mode fiber. Filtered by a circulator and LCFBG 1, the spectrum with a center wavelength of 1550 nm and full width at half maximum bandwidth of 52 nm enters the photonic time stretcher that consists of a circulator and LCFBG 2. The spectrum of each broadband pulse is converted into a temporal waveform by the large group velocity dispersion (GVD) of the LCFBG 2 with a duty cycle . The buffer stages15 are used to fill up the duty cycle to 100% and further increase the swept rate with delayed copies of one scan by . The erbium-doped fiber amplifier (EDFA) is integrated for shaping the spectrum and increasing the power to enhance the SS-OCT sensitivity. The basic parameters of the swept-source, including the bandwidth , time duration , axial depth range , and swept repetition rate , are theoretically obtained.14,16,17 Though the bandwidth of the band-pass filter and the LCFBG 2 is 50 nm, the gain bandwidth of the EDFA is only 40 nm. Therefore, is 40 nm and is revised as 19.8 ns. Thus, the theoretical axial resolution is . The axial depth range is generally limited by the GVD of the dispersive element, the sampling rate of the A/D converter, and the analog bandwidth (B) of the dual-balanced photo-detector, which are , , and 1.6 GHz, corresponding to the axial depth limits of 7.1, 0.59, and 0.47 mm, respectively. Considering all of the above limits, the theoretical axial depth range of our SS-OCT system is 0.47 mm. The buffering further increases the swept rate by , therefore, the swept repetition rate is 40 MHz. The time-stretch interferograms captured by the high-speed oscilloscope are shown in Fig. 2(a). Without any calibrations,12 the temporal swept waveform (short dot line) dramatically shows a good agreement with the spectrum (solid line) captured by an optical spectrum analyzer, as shown in Fig. 2(b). With a total GVD of , the full-swept range of 40 nm is mapped into a time span of 21 ns, which is consistent with the theoretical value of 19.8 ns, corresponding to a duty cycle. The optical power from the LCFBG 1 is , which extremely limits the system sensitivity. Therefore, optical amplification, i.e., EDFA, is necessary. With power input in EDFA, the output of the 40 MHz swept-source is 41.2 mW.