Development Of Wide Bandwidth Swept Source With Narrow Instantaneous Linewidth

Optical coherence tomography (OCT) is a non-invasive, non-contact biomedical optical imaging technique with high speed. OCT can divide into two kinds, one is Time Domain Optical Coherence Tomography (TD-OCT), the other is Optical Frequency Domain Imaging (OFDI). The Optical Frequency Domain Imaging based on swept source is a new kind of OCT and has great advantage over TD-OCT in imaging speed, imaging range, sensitivity and so on. The key component of swept source OCT is swept laser source whose performance index influence that of swept source OCT. So, our research and induction focus on the swept laser source.In our project, we mainly research the theory and construction of swept laser source, survey the development of swept laser source in recent years, design a few kinds of swept laser source, and build a swept laser source with wide bandwidth and narrow line width at last. In swept laser source, optical tunable filter has the effect of tuning the laser and it is very important. However, to an optical filter, its spectral resolution (the instantaneous line width of swept laser source) and free spectral range (the spectrum range of swept laser source) are inverse relationship. To obtain a swept laser source with narrow instantaneous line width and wide spectrum range, we present a ring swept laser source based on Grating/Polygon-scanner filter and Fabry-Perot Tunable Filter (FFP-TF). It has both the narrow instantaneous line width of Grating/Polygon-scanner filter and wide spectrum range of FFP-TF. On the base of existing instruments, we put a telescope system into Grating/Polygon-scanner filter to expand the spot size on the grating, as a result, we expand the free spectral range and improve the spectral resolution of the Grating/Polygon-scanner filter. After designing the system and selecting the instruments, we build the wide bandwidth and narrow instantaneous line width swept laser source based on combined tunable filters. The output spectrum were detected by the single-point detector and linked to oscilloscope to obtain the timing diagram of the swept laser. When the output spectrum were linked to the spectrometer, we get the wave sequence diagram of the swept laser. The thesis can be divided into five chapters:1. In this chapter, we introduce the principle and development of OCT. Then we focused on the swept laser source which is the key instrument of SS-OCT. At last, we elaborate the importance, content and innovation of our research.2. Firstly, we introduce the principle theory of the swept laser source. Then we analysis the major index of the swept source, including center wavelength, spectrum range, instantaneous line width, tuning speed and power.3. This chapter is about the designing of the system, including the optical system and synchronization device. In the designing of optical system, we present program of the wide bandwidth and narrow instantaneous line width swept laser source based on combined tunable filters and propose a few methods to improve the spectral resolution and narrow the free spectral range of the Grating/Polygon-scanner filter. We analysis the principle, advantages and disadvantage of all these methods. Then we determine the design parameters of the instruments and get the theory wave sequence diagram. To make the wave tuning of Grating/Polygon-scanner filter and FFP-TF consistence, we design a synchronization device.4. After designing the system and choosing the instruments, we build the swept laser source. Firstly, we measure the amplified spontaneous emission spectrum of the SOA. Then we put the Grating/Polygon-scanner filter and FFP-TF into the ring laser successively. We get the wave sequence diagram and timing diagram by spectrometer and oscilloscope. At last, we analysis the experimental results.5. In this chapter, we summary our work and innovation of this research. Then we present the points need to be improved, next work and outlook.