Study On High Quality-factor Resonance Mode Properties Of Infrared Micro-structured Antennas

Electromagnetic waves in the infrared region exhibit unique properties in the fields of thermal radiation,material sensing,and information processing,which open up a large space for explorations in both fundamental studies and device applications.Micro-structured infrared antennas offer an agile way for manipulating the amplitude,phase and polarization of light and for enhancing the light-matter interactions,which hold great promise in emerging applications of wavelength-selective thermal radiation,optical camouflaging,and sensitive molecular detection due to their advantages of compact size and small energy consumption.Conventional metal-based plasmonic microstructured antennas often have large optical loss and thus low quality（Q）factor of less than 20,which limits their device applications.How to realize low loss infrared antenna with high Q factor remains an open question,which deserves further investigations.This dissertation is devoted to studying the microstructure design,resonant mode properties and molecular sensing performance of high Q factor infrared antennas.By using metal-dielectric-metal and metal-dielectric-dielectric structures,we have designed and fabricated metallic strip array antennas and amorphous silicon square patch antennas.High Q factor guided-mode resonance and Fano resonant mode were observed,and their wavelength-selective infrared absorption and thermal emission were measured in experiment.By using these high Q antennas,sensitive refractive index sensing and molecular fingerprint detection were also demonstrated.These results have expanded the fundamental properties and device functionalities available in infrared antennas,which are helpful for further understanding on resonant modes and device development of micro-structured antennas.The main results obtained in this dissertation are as follows:1.By using low loss zenc selenide（Zn Se）material,metal strip array antenna was designed and fabricated,which exhibited high Q factor guided-mode resonance and wavelength-selective infrared absorption and thermal emission.Our fabricated metal strip array antenna consisted of copper film,Zn Se dielectric layer and gold（Au）strip array.Experimental measurements showed that the antenna samples exhibited TE₀guided-mode resonances within the 3-5μm spectral band with Q factors as high as 63.4-77.4.Bandwidths of the guided-mode resonances are 26.3-39.9 nm,and their infrared absorptions and emission intensities are 70.9%-81.6%and 65.5%-72.3%,respectively.As structure size parameters including the Zn Se thickness,width and period of the gold strips were varied,wavelength of the TE₀guided-mode resonance was tuned from 3.10μm to 4.97μm.In addition,as the incident angle increased from 15°to 75°,the TE₀guided-mode resonance was splitted into two modes with redshifted and blue-shifted frequencies,corresponding to the TE₀waveguide mode excited by the-1 and 1 diffraction orders,respectively.Our demonstrated metal strip array antenna exhibits the highest Q factor among reported guided-mode resonance antennas,which suggests that the guided-mode resonance holds great potential for manipulating spectral response in infrared devices.2.Based on the mechanism of mode coupling,amorphous silicon square patch antennas were designed and fabricated,which exhibited Fano resonant mode with both strong light absorption and high Q factor.Our designed amorphous silicon square patch antenna was made of copper substrate,Si O₂dielectric layer and top amorphous silicon square patch array.Coupling between Fabry-Perot cavity mode within the Si O₂film and Mie mode in the silicon square patch led to the formation of a Fano resonant mode.Our measurements indicated that sharp Fano resonant peaks were excited in the antenna samples within the 3-5μm wavelength region.Bandwidths of the Fano resonances are32.5 nm-127.5 nm,and their Q factors and infrared absorptions were 40.2-114.2 and65.8%-86.6%,respectively.As size of the silicon patch was varied,the Fano resonant wavelength was shifted from 3.71μm to 5.03μm.In addition,our analysis also suggested that the theoretical Q factor of the antenna could reach 1488-2234,which was one order of magnitude higher than the measured value.The discrepancy was mainly attributed to the material loss of amorphous silicon used in experiment.These results indicate that thin-film cavity coupling represents a simple and effective scheme for enhancing both Q factor and light absorption in dielectric metasurface antennas.3.By using the high Q guided-mode resonance and Fano mode,molecular fingerprint detection and sensitive refractive index sensing were demonstrated in experiment.Using the special angular sensitivity of the metallic strip array antennas,the guided-mode resonance was scanned in a wide frequency range of 617.4 cm^-1 around the absorption features of polydimethylsiloxane（PDMS）,and symmetric and asymmetric vibrations of CH₂ group were revealed at 2908.7 cm^-1 and 2962.2 cm^-1,respectively.Intensity of the vibration signal depended on the frequency mismatch between the guided-mode resonance and the CH₂vibration line.At a frequency mismatch of 30 cm^-1,maximum vibration signal was measured,whose intensity was enhanced by a factor of2.37.In addition,by using Si O₂ film as analyte in the silicon square patch antenna,we demonstrated refractive index sensing of the high Q Fano resonance mode.Frequency of the Fano resonance redshifted with increasing Si O₂ film thickness.Sensitivity and figure-of-merit（Fo M）of refractive index sensing were measured to be 518.75 nm/RIU and 14.82,which are higher than all-dielectric metasurfaces reported in literature as benefited from the higher Q factor obtained in our antennas.Our above results reveal a great potential of high Q resonant infrared antennas when they are used in optical sensing.