| With the development of micro-and nano-fabrication technology, analysisinstruments with miniaturization, integration and portability are becoming a newtrend. Microfuidic chips can be integrated with the whole laboratory operation suchas sampling, separation, reaction, detection on a single microchip, so the research onthe microfluidic now represents the developing direction in analysis instrumentsfield. After twenty years’ development since the concept was proposed, microfluidichas achieved great improvement. Optical detection is one of the most importantdetection manners. However, due to the larger volume and higher price of externalequipments, microfuidic hasn’t realized so-called optical integrated detectioncompletely. This thesis mainly is about how to improve the sensitivity of opticaldetection and integration of optical system on microfluidic chips. The relatedcontents are as follows:(1) In order to realize highly sensitive and multi-parameter detection for thewhole blood, a multireflection structure based on a quasi Fabry-Perot cavity wasproposed. The optimal condition of the largest optical path and the proper Signal andNoise Ratio (SNR) was analyzed theoretically. The results indicate that thetheoretical maximum path is only inversely proportional to the square of the beamdiameter and the SNR is dependent on the reflectivity of the mirror and the number of the reflection. And a new compensating manner was presented to avoid theuniform error caused by the multireflection. A detection cavity was designed andmethylene blue solutions, albumin and glucose were measured on a centrifugalmicrofluidic chip. The measured results have very good linearity and the optical pathwas proved to be improved by two orders.(2) Filter, as an important optical element in absorption detection, plays the keyrole in detecting different solutions. In order to achieve the miniature and integrationof the optical devices on the microfluidic chips, a novel transmission filter based onsubwavelength metallic grating guided-mode resonance is proposed. The resonancecharacteristics of the filters with symmetric and nonsymmetric waveguide structurewere theoretically analyzed based on planar waveguide theory. The effects of thefilter structural parameters on the transmission spectrum are investigated in detail,such as grating period, filling factor, the incident polarization, and buffer layerthickness. Simulated results show that the novel filters have high transmittance,polarization-independent, and high integration.(3) To improve the integration of the optical detection system and microfluidicchips further, a novel structure that can achieve extraordinary optical absorptionbased on guided-mode resonance effect was proposed. An anti-crossing point can beformed due to the coupling between the cavity mode and the quasi-guided mode atthe maximum absorption peak. The resonant interaction between these two modescan influence the field distribution, which reinforces more power near the metalgrating. From the simulation results, this structure has high absorption efficiency andgood fabrication tolerances. The absorption peak can be readily tuned just by thegrating period. The presented structure may combine the photodiode with the filterefficiently so that the integration of optical detection becomes simpler.(4) If the chips continue to reduce to the nano-scale, the optical path willdecrease simultaneously. So the sensitivity will be very low. To solve this problem, anovel slow light structure was proposed in this thesis. The transmission peak has anarrow transparency window and is associated with a dramatic change in the transmission phase. An extremely slow group velocity of light traversing thestructure can be obtained. The effects of buffer layer thickness and the grating periodon the group index and the phase were investigated with the aid of rigorous couplingwave analysis. The sensitivity will be increase by three orders if we can combine theslow light structure and microfluidic chips. |
PDF Full Text Request