Researches On Novel Wavelength Swept Fiber Laser Sources For OCT Imaging And Biomedical Sensing

Optical coherence tomography(OCT)is based on the technology of the Michelson interferometer's low-coherent imaging technology.It has the advantages of non-invasive,in-body biomedical testing and has become one of the clinical medical imaging detection methods.Swept source optical coherence tomagraphy(SS-OCT)is a newly developed technology for OCT imaging.Compared with the traditional OCT imaging technology,it has the advantages of high speed and sensitivity.The imaging quality of SS-OCT depends on the characteristics of the swept source directly.The swept source with high speed,wide sweep range and narrow instantaneous linewidth plays an important role in improving the imaging performance of SS-OCT.Optical fiber biomedical sensor is a new type of biomedical sensor technology.It is a technology that intercrosses many disciplines such as optical fiber sensing and biomedical detection technology.It has the advantages of anti-electromagnetic interference,small size,and flexibility,which are particularly suitable for in-vivo biomedical detection technique of strong electromagnetic radiation,endoscopic and implantable chips.Swept source has become one of the important choices of the new sources in fiber-optic biomedical sensor demodulation technology due to its advantages of fast speed,and the ability to acquire time-domain information of the measured biomass.Among them,the high speed time-domain demodulation information can greatly improve the detection speed and efficiency of biomedical sensor detection technology.This thesis is dedicated to research on the swept source used for OCT imaging and biomedical sensing.The main works of the thesis are as following:1.A novel Fourier-domain mode-locked(FDML)swept source with narrow instantaneous linewidth based on inverse Four-Wave Mixing(IFWM)effect was proposed and implemented.It was applied to the SS-OCT imaging system and the images of the target and glass slide were obtained.The inverse four-wave mixing effect in the normal dispersion medium can narrow the optical spectrum effectively.Therefore,by combining the inverse four-wave mixing effect with the FDML technique,the swept source with narrow instantaneous linewidth can be obtained.Since the depth of imaging depends on the narrow instantaneous linewidth of the swept source directly,the narrow instantaneous linewidth can improve the imaging depth of the SS-OCT system.In the experiment,a wavelength-swept output with a center wavelength of 1550 nm,a spectral bandwidth of 42.6 nm,a SNR of more than 36 dB,and a sweep rate of 43.115 kHz was obtained and used in the self-built 1550 nm SS-OCT imaging system.The point spread function(PSF)is obtained by taking the total mirror as the sample in the air.A refractive index sensing system for biomedical sensing based on FDML fiber laser and Micro/nano fiber Bragg grating was proposed.Through the time-domain information,the efficiency of sensing and the measured speed was greatly improved.Under the same experimental conditions of the alcohol and water matching liquid,the refractive index sensitivity in the time-domain is two orders of magnitude higher than that of the spectral resolution.Moreover,the sensing identification capability in the time-domain is twice as that in the wavelength domain.2.A swept source based on intracavity mode-locked pulse time-stretching effect using positive-negative dispersion module was realized.The wavelength-swept fiber laser output with a center wavelength of 1555 nm,a sweeping spectral bandwidth of 16 nm,and a sweep rate of 6.17 MHz was obtained.The swept source was used in the 1550 nm SS-OCT imaging system.The result of PSF shows that the imaging depth is 2 mm.The cascaded dispersion compensating fiber(DCF)was placed outside the cavity and the characteristics of different wavelengths corresponding to different time-domains,which can be used to realize the big protide tumor marker p53 protein detection experiment.The specific binding reaction between the p53 protein antigen(10 ng/mL)and antibody is measured by the time-domain pulse shifting curve of the laser source,and the drift time is 5.5 ns.3.A novel intracavity mode-locked pluse time-stretched swept source based on linear chirped fiber Bragg grating(LC-FBG)has been proposed.The wavelength-swept source based on a pair of LC-FBGs was proposed and demonstrated.In the experiment,the wavelength-swept fiber laser output with a center wavelength of 1550 nm,a spectral bandwidth of 6 nm,and a sweep rate of 3.48 MHz was obtained.The bi-directional use of LC-FBG can introduce equivalent negative and positive dispersion simultaneously,which can not only shorten the cavity length,but also solve the problem of dispersion mismatch effectively in the cavity.Another wavelength-swept source based on a single bi-directional used LC-FBG was proposed and demonstrated.LC-FBG was provided as an exact dispersion match in the cavity.Experimental results demostrate a swept fiber laser that exhibits a sweep rate of about 5.4 MHz over a 2.1 nm range at a center wavelength of 1550 nm.The sweep rate is further improved.