Terahertz One Dimensional Photonic Crystal Cavity And Applications

With rapid development of terahertz source, detection, imaging, spectrum, communications and other areas, the demand for high performance and low cost terahertz devices becomes more and more urgent, The high quality factor (Q) of one dimensional photonic crystal has important applications in filter, modulator and gas detection. The traditional methods of preparing one-dimensional photonic crystal are photo lithography, chemical etching and thin film growth. Because of the large size of terahertz device, the traditional methods of preparing terahertz device are difficult, complicated and expensive. Therefore, searching for a superior performance terahertz device which is cheap and simple is the urgent need for the terahertz development. In this paper, the author writes a Matlab program using transfer matrix to simulate photonic crystal cavity transmission spectrum characteristics. With the method of dielectric material paste, we have fabricated a high performance terahertz one dimensional photonic crystal filter. The high performance terahertz one dimensional photonic crystal filter can be used in tunable filter, gas detection and terahertz modulation. This paper is divided into four parts.(1) We have wrote a Matlab program using transfer matrix to simulate photonic crystal cavity transmission spectrum to simulate the characteristic of one-dimensional photonic crystal. We have fabricated two kinds of one dimensional photonic crystal cavity based on quartz and air, silicon and air. We can change the thickness of quartz and air layers, the thickness of silicon and air layers in order to get high Q cavity theoretically. To design bandstop and bandpass filters in theory is important for our experiment.(2) We have prepared a terahertz one-dimensional photonic crystal band-pass and bandstop filter based on quartz crystal. The bandstop is about30GHz, and the six period filter transmission of bandstop is2.1%. Change the thickness of the middle air cavity, we can get a high performance narrowband tunable filter. The tunable range of the filter is310-340GHz, and the full width at half maximum is less then1GHz. It has a very high quality factor of about300.(3) We have prepared a terahertz one-dimensional photonic crystal bandpass filter based on silicon crystal. By coordinated the length of cavity, we realized that the transmission and quality factor are both high when the interference period is six. The full width at half maximum is less then200MHz. The quality factor is approximately1580. Change the length of the cavity, we can get a tunable filter. The tunable range is285GHz-350GHz.(4) Based on the high Q terahertz photonic crystal cavity, we realized a gas detector. By mixing different ratio of CO2gas on the cavity experimentally, we found that the peak position was changed obviously, that we can get cavity gas concentration according to the change of frequency. Using808nm semiconductor laser irradiated the outside silicon layer in order to change the potency of carrier and realize a terahertz switch. The maximum modulation is up to80%, the modulation speed depends on the lifetime of carrier.