부산대학교 도서관

Optical coherence tomography (OCT) uses a low coherence interferometry to acquire the micron-scale cross-sectional image non-invasively. Fourier domain OCT has many advantages over the conventional time domain OCT, such as a higher acquisition speed without mechanical delay line and a higher signal-to-noise ratio. A promising method to high-speed imaging is offered by swept source (SS) OCT [1-5]. The performance of high-speed and high-resolution SS-OCT imaging depends on the effective sweep rate and tuning spectral range of wavelength-swept laser source. Generally, most of the wavelength-swept laser for SS-OCT has been employed by the use of a semiconductor optical amplifier (SOA) as gain medium [1-4]. Since the sweep rate and the spectral range are limited by the carrier relaxation times and the entire gain band of the gain medium, respectively, the typical carrier relaxation time of the SOA is known for several nanoseconds and the gain band of it usually provides a bandwidth of less than 100 nm. Fourier domain mode-locked (FDML) techniques have been also demonstrated to increase the sweeping speed of the wavelength-swept lasers by using additional delayed length of optical fiber in the laser cavity [2]. However, the long length of optical fiber over ~ km induces an additional insertion loss of cavity, which is not helpful for lasing operation. Recently, we propose that the additional delayed length of optical fiber can be used as a gain medium instead of loss medium when a fiber Raman amplification is generated by using high power of pump light [6,7]. In this research, novel broadband wavelength-swept Raman laser is demonstrated using multi-wavelength optical pumping scheme to implement a FDML SS-OCT imaging. It is the first experimental demonstration of a broadband SS-OCT based on a fiber Raman amplifier, instead of SOA, as a broad gain medium over 50 nm. As high power optical pump sources became commercially available, a fiber Raman amplification based on stimulated Raman scattering in silica optical fibers has been widely studied especially in the wavelength-division-multiplexed (WDM) telecommunication system applications [8-13]. The fiber Raman amplifier has various merits, such as low noise, arbitrary gain band determined on the band of the optical pump sources, high temperature stability and the instantaneous carrier relaxation times of the order of several femto-seconds for silica [9]. It is expected that the application of fiber Raman amplifier can be extended to the biomedical imaging area based on the experimental result of this research because the demands for higher-speed and wider-gain band are required for the real time and high resolution OCT imaging, respectively.