Research On High Performance On-chip Optical Waveguide Biosensor

Biochemical sensors play a very important role in the field of medical treatment,industrial production,bioengineering,homeland security,food safety,environmental protection,etc.Optical biochemical sensors have attracted extensive attention because of their advantages such as immunity to electromagnetic interference,remote sensing,and multiplex detection.The optical biochemical sensors based on the interaction between light and analyte can realize label-free sensing and real-time dynamic monitoring for analyte,which is an important sensing mechanism to realize selective,rapid,sensitive,direct,and low-cost biochemical sensor.Nowadays,with the rapid development of integrated optics,the application of planar optical waveguides in the field of biochemical sensing has attracted more and more attention.In addition to the advantages of these conventional optical sensors,planar optical waveguide biochemical sensors also have some unique advantages,including fabrication material diversity,compact and flexible structure,and integration capability,and so on.Moreover,compared with optical fiber sensors,planar optical waveguide biochemical sensors offer the advantages of on-chip integration,device miniaturization and portability,etc.In the past few decades,various highly sensitive planar optical waveguide biochemical sensors based on sensing the refractive index of analyte have been widely studied and reported.The configurations of these reported sensor include Mach-Zehnder interferometer（MZI）,microring resonator,dual-mode interferometer（TMI）,Bragg grating,long period grating,directional coupler,etc.The methods to achieve high sensitivity include using sensing waveguides with high waveguide sensitivity to enhance the interaction between light and the analyte,and optimizing the sensor configuration based on the waveguide dispersion engineering,Fano effect or vernier effect to further increase the change of output light signal caused by the analyte.In addition to high sensitivity,the cost of sensor fabrication and measurement are also important factors that need to be considered when promoting the application of the planar optical waveguide biochemical sensors.Considering the needs for high-performance biochemical sensor,this dissertation focuses on the development of high-performance planar optical waveguide sensors with ultra-high sensitivity,simple and compact configuration,flexible design,low cost,and easy to implement.The main research work of this dissertation is summarized as follows:1.A highly sensitive MZI liquid refractive index sensor is proposed.The proposed sensor achieves high sensitivity by designing an appropriate length of the reference arm to optimize the optical path difference（OPD）between the two arms of the MZI.As a proof of concept,five MZI liquid refractive index sensors with different reference arm lengths are designed and fabricated using polymer traditional rectangular waveguide.These five sensors have different reference arm lengths of 7900.0,7942.5,7950.9,7962.2,and 7969.5μm,respectively,but the same sensor arm lengths of 7900.0μm.Their sensitivity,measured with sucrose solution at different concentrations,are 5151.1,10598.9,12110.8,24218.6,and 33662.8 nm/RIU,respectively.And they have almost the same detection range（DR）of 0.0041±0.0002 RIU.The above research shows that even using traditional rectangular waveguide as sensing waveguide,ultra-sensitive MZI liquid refractive index sensors without reducing the DR can be realized based on the proposed design scheme.2.Research on the integration of germanium doped silicon dioxide（SiO₂-Ge）waveguide and nanoporous material（ZIF-8）,and design of a MZI sensor for volatile organic compound（VOC）sensing based on the integrated waveguide.The integration of the SiO₂-Ge waveguide and ZIF-8 is realized by assembling a nanoscale high quality ZIF-8 film on the surface of the SiO₂-Ge waveguide using in situ self-assembly method.As a proof of concept,an asymmetric MZI sensor for VOC sensing is designed employing the above integrated waveguide as the sensing waveguide and using the above scheme to optimize the reference arm length.The fabricated sensor has a sensing arm length of 7mm and its output spectrum shows a high extinction ratio of 28.6 d B.And for sensing ethanol gas,it shows a large detection range of 1.6-1000 ppm,a high sensitivity of 41pm/ppm（at least 19 pm/ppm over the range of 1.6-50 ppm）,and a low detection limit of1.6 ppm.3.An ultra-compact embedded dual-ring liquid refractive sensor based on the vernier effect is proposed.The proposed sensor features that the sensing ring is embedded in the reference ring,which reduces markedly the footprint of the microring sensor based on the vernier effect.As a proof of concept,the proposed embedded dual-ring sensor is designed and fabricated with polymer traditional rectangular waveguide.The fabricated sensor has a sensing ring length of 2504μm and a footprint of 1500μm×850μm.And its sensitivity,measured with sucrose solution at different concentrations,is as high as7390 nm/RIU,which is about 114 times higher than that of a single-ring sensor.Moreover,a further theoretical investigation indicates that our proposed embedded dual-ring sensor is capable of achieving an ultra-high sensitivity of 19704 nm/RIU if a silicon-polymer composite waveguide is used to replace the polymer waveguide to construct the sensing ring waveguide.4.A high-sensitivity MZI liquid refractive index sensor using a polymer horizontal slot waveguide as sensing waveguide is proposed.The remarkable confinement for light of slot waveguide can greatly increase the strength of the interaction between light and the analyte,which helps to achieve high waveguide sensitivity.However,fabricaton of these reported vertical slot waveguides are difficult and expensive,and it is difficult to obtain high-quality slot,while horizontal slot waveguide is able to overcome these shortcomings.Calculated result shows that optimized polymer horizontal slot waveguide achieves a waveguide sensitivity of 0.18,which is about three times higher than that of the traditional rectangular waveguide.Subsequently,a MZI liquid refractive index sensor based on the above polymer horizontal slot waveguide is designed,which has a sensing length of 7900μm and can achieve an ultra-high sensitivity of 4.6×10⁴nm/RIU.Further,the sensor fabrication process and its impact on the performance of the sensor are also investigated,and based on the investigation,the proposed sensor is further optimized to ensure a successful fabrication,and the further optimized sensor can still achieve an ultra-high sensitivity of 3.5×10⁴nm/RIU.