High-speed Broad Bandwidth Swept Source At 1μm

Optic coherence tomography(OCT) is an optic imaging technology. As it can realize noninvasive, noncontact and real-time imaging, many scholars both domestic and overseas pay a lot of attention to it, and the technology develops fast. Swept source OCT(SS-OCT) is a latest generation OCT, which belongs to Fourier domain OCT(FD-OCT), it has the advantages over time domain OCT(TD-OCT) in imaging speed and sensitivity and been widely used in biological tissue imaging and so on. The key device of SS-OCT system is the swept laser source, which can determines the performance of SS-OCT. This paper is focused on swept source at 1.0μm, including the method of building the swept source and improving the performance of the swept source. The main work and results are summarized as follows:1. We have built a swept laser source at 1.0μm. The swept laser source is comprised of gain medium, tunable filter and resonant cavity. In this system, semiconductor optical amplifier(SOA) is used as gain medium for the laser and is coupled to the filter via one port of the 50:50 optical coupler as resonant cavity. The tunable filter is a compact telescope-less polygon scanner filter in Littrow arrangement. One port of the 50:50 OC is used as the output port of the laser. The measured tuning range of the laser, the center wavelength, the repetition rate and the output power are 90nm(994nm~1084nm), 1040 nm, 43 kHz, 2.8mW, respectively.2. In order to analyze the specific impact of the parameter in the cavity on the performance of the swept laser source, we have done three groups of experiments: different cavity length, different rotating speed of polygon mirror and different coupling ratio. We can get the following conclusions by analysising of the results of these experiments: 1) The bandwidth becomes more narrow and the sweep frequency becomes lower when the length of the cavity becomes longer; 2) The bandwidth becomes wider and the sweep frequency becomes faster when the speed of polygon mirror becomes lower; 3) The bandwidth becomes wider when the ratio of light entering the cavity becomes larger.3. In order to improve the sweep frequency, we have added a buffered structure in the swept laser source system, which includes 2 kilometers of single-mode fiber. The time of delay is half period of swept laser source. After add the buffered structure, we have built a swept source laser,the sweep wavelength range is 90 nm from 990 nm to 1080 nm centered at1040 nm, the output power is about 550μW and the repetition rate is about 86 kHz. It can be seen that the sweep frequency has been doubled while the output power decreased obviously. In order to improve the output power, we have added a booster amplifier(BOA) behind buffered structure and the output power is 18 mW.