| Surface-enhanced Raman Scattering(SERS)is widely used in various fields such as food detection,medical inspection and environmental monitoring due to its high specificity,fast detection speed and ability to provide detailed component information.Compared with conventional SERS sensing technology based on spatial optical path configuration,the optical waveguide integrated SERS sensing technology has attracted more and more attention in recent years.This is due to its advantages of small size,high integration,strong stability,portability and easy operation.The current researches mainly focus on improving the structures of optical fiber integrated SERS sensors.However,many current sensors are complicated to fabricate and lack stable sensing environments,making them vulnerable to damage.With the development of integrated photonics,the on-chip waveguide integrated SERS sensing technology has become a future research direction,but there is currently limited research on it.Therefore,this thesis optimizes the optical fiber integrated SERS sensor and corresponding sensing system,experimentally studies the on-chip waveguide integrated SERS sensing technology,and proposes on-chip waveguide integrated SERS sensors with other multiplexing functions such as notch filtering and optical capture.The main research contents and results of this thesis are as follows:(1)A simple and easy-to-fabricate optical fiber integrated SERS sensor is proposed to overcome the difficulties in fabricating micro-structured optical fibers that are vulnerable to damage.The proposed sensor relies on exciting the outer cladding mode via depressed double cladding fiber.To protect the sensor and provide a closed sensing environment,the corresponding optical fiber embedded microfluidic chip is manufactured.Furthermore,an optical fiber integrated Raman detection system is constructed,realizing real-time detection of 10 μM Rhodamine 6G aqueous solution.The combination of optical fiber integrated SERS sensor,microfluidic chip embedding package and all-fiber connection results in a more stable,portable and user-friendly all-fiber integrated SERS sensing system.(2)Considering that the size of optical fiber is relatively large and the curved surface is not conducive to the low-cost mass production of gold micro-nano structure,this thesis further explores the application of more compact,integrated and mass-produced on-chip waveguides in SERS sensing.A SERS sensor based on hybrid plasmonic deep slot waveguide caspable of intense light-matter interaction is proposed along with corresponding mode conversion waveguide elements.An edge-coupled Raman detection system is also constructed for detecting of a 4-nitrophenylmercaptan monolayer.For the strategy of exciting and collectting scattered light with the waveguide itself,the process exploration and experimental verification for slot waveguide integrated SERS sensing are provided.(3)To address the issue that the conventional enhancement factor only reflects the electric field enhancement and fail to fully characterize the SERS performance of the sensor,a total enhancement factor comprehensively considering the electric field enhancement,sensing volume and collection efficiency of scattered light is proposed.According to this factor,the proposed hybrid plasmonic nano-cavity is simulated and optimized.The built-in grating in the cavity can filter the pump light from the output light and increase the total enhancement factor to 3.52 times.The proposed scheme not only improves the SERS performance of the sensor,but also economize the external notch filter,which helps the development of the on-chip waveguide integrated SERS sensor chip to be more compact,integrated and miniaturized.(4)In view of the bulky volume and complicated operation of the traditional Raman tweezer system based on objective lens and spatial optical path configuration,a hybrid plasmonic nano-focusing waveguide is proposed for on-chip waveguide integrated tweezer enhancing Raman in situ.Utilizing asymmetric mode coupling in a stack of silicon nitride-thin silicon and tapered mode conversion structure,the mode field can be compressed and thereby realizing the nano-focusing in the plasmonic gap.In theory,a polystyrene sphere with a diameter of 20 nm can be trapped at the pump power of 19.77 m W,and a point electric field enhanced by 9.16 times is generated at the center of the potential well.The proposed nanofocusing waveguide provides an on-chip integration scheme for stable trapping and accurate detection of a single nanoparticle in on-chip microsystems without the assisting of off-chip devices. |
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