| Imaging quality of Swept-Source Optical Coherence Tomography(SS-OCT)is closely related with characteristics of the swept source,which is one of the key devices of the SSOCT system.Swept sources based on tunable semiconductor lasers have shown great advantages in good linearity,high speed and fine phase stability,with improvements not only in the system structure,but also in imaging functionality.Phase noise of the tunable semiconductor laser will directly degrade the imaging quality of phase-sensitive SS-OCT application such as angiography and Doppler Imaging.Therefore,it is important to investigate the phase noise of the wavelength tunable semiconductor lasers for SS-OCT application.In this thesis,the phase noise of the Distributed Bragg Reflector(DBR)lasers for SS-OCT application is studied,and specific works are summarized as follow:(1)Static phase noise measurement systems based on phase modulation and based on coherence receivers are established,several types of lasers are tested under continuous-wave mode,and the Frequency Modulation(FM)Noise Spectrum is used to evaluate the level of phase noise.Sources and characteristics of the phase noise of the DBR lasers are focused by experiments.(2)A drive system for swept Digital Supermode DBR(DS-DBR)laser is designed,and related characteristics are measured,including optical spectrum and phase noise under static state.Meanwhile,a wavelength-current look-up table is generated by a large number of static tuning measurements.(3)A scheme of instantaneous phase noise measurement system based on coherence receivers is proposed and a set-up is established.Sweeping dynamics of DS-DBR laser are measured,with a focus on instantaneous frequency and instantaneous phase noise,when the DS-DBR laser is sweeping between channels with 50 GHz and 5GHz frequency interval.The acquisition interval time is determined for phase stability in sweeping dynamic. |
