Research Of Novel Photonic Devices Based On Microstructure And Their Performances

The concept "Photonics" could be traced back to the year 1960 when the world’s first laser was invented. But it was first proposed by L Poldervaart on Ninth International High Speed Photography Session after ten years. In general, "Photonics" is a subject that mainly concerns about the generation, transportation and interaction between photons and nano-particles. Operating at wavelength of micrometer scale for visible and infrared signals, it has a much higher speed of data transmitting and processing than that of wireless communications. During the decades, with the rapid developments of optical communication systems and electrooptical technology, urgent demands of compact footprint, multiple functionalities, reduced power-consumption and integrated structure make photonic devices significant in every aspect. Under the background of modern science and information, integrated photonics is required to have the ability of processing and switching the real-time and high-speed data stream, which greatly extend its applications of communication technology, information system and biochemical detection.In this dissertation, microstructure based novel photonic devices and their performances were thoroughly investigated. One hand, theoretical models that optimize devices’performances were established (Chapter 2 and 5). On the other hand, novel photonic devices with improved and excellent performances were fabricated and realized (Chapter 3 and 4). The main works and innovative fruits are as follows:First, an optical amplification model based on silicon waveguides was established and their corresponding nonlinear performances were investigated. Considering nonlinear effects such as stimulated Raman scattering (SRS), two-photon absorption (TPA), free-carrier absorption (FCA) and free-carrier dispersion (FCD) together with the intrinsic linear attenuation and chromatic dispersion into an analytical model, an amplitude-coupled model of the pump, signal and idler lights in silicon waveguides could be obtained. The parametric amplification process was investigated with or without SRS effect by setting the values of Raman contribution fraction (RCF). Important dispersive factors such as zero dispersion wavelength, third-order dispersion and fourth-order dispersion coefficients that affect both of the signal amplification and wavelength conversion performances (such as peak value,3 dB bandwidth and flatness) were also investigated. By properly optimizing the parameters of the pump signals (wavelength, bit rate and pulse width), an amplification spectrum from 1457 to 1663 nm with peak gain of 10.2 dB and ripple smaller than 1 dB was reached. Meanwhile, a wavelength conversion spectrum with bandwidth of 1482 to 1617 nm and peak value of 10.1 dB was also reached. Noise figures that were generated during the nonlinear process were analyzed.Second, a novel spectrometer based on photonic crystal structure was investigated. The whole device is composed of a line waveguide and multiple resonant cavities that are critically coupled with each other. By stimulating resonant modes that locate within 1550 nm transmission window, structure parameters of the (line-defect) waveguide and cavities were obtained and further fabricated by nano-fabrication techniques. The line waveguide was designed to introduce the input signal from tapered fiber or ridged waveguide into the device and the coupled structure make most of the resonant photons transmit from waveguide to the resonant cavities. This innovative design improves detection efficiency to 6.36%, which is multiple-order higher compared to those of its counterparts. By slightly shifting side holes of the cavities, precious control of the cavities’ resonances was successfully realized. In the operation mode, an off-shelf camera was employed to collect reflected signals, which could obtain the spectral information of the detected signal at once. The spectrometer was measured to have an operation bandwidth from 1522 to 1545 nm, a spectral resolution of 1 nm, while the footprint is only 60 μm× 8μm.Third, two novel spectrometers (based on tapered fiber and spiral tapered waveguide) were investigated and realized. Based on the fact that multimode waveguides could generate wavelength-dependent pattern of modes dispersion and interference, a model of multimode interference was built to deduce the validation of the idea. The tapered shape (which destroys the total internal reflection condition), body defect and sidewall roughness were employed to scatter the intensity pattern onto the detector. Both of the constituent material and structure parameters were optimized during the fabrication process and the signal processing techniques were improved by algorithm, which resolved the contradictory of compact footprint with broad operation bandwidth and high spectral resolution. By building up a con-focal system and measuring the devices, an operation bandwidth of 400 to 2400 nm and a spectral resolution of 10 ps scale were reached in the tapered fiber spectrometer. In the spiral tapered waveguide spectrometer, an operation bandwidth of 550 to 725 nm and a spectral resolution of 0.02 nm were reached.Fourth, enhanced light-matter interaction was investigated based on resonant structures. Since the monolayer Molybdenum Disulfide (M0S2) has broadband fluorescence around 670 nm, the parameters of metal plasmonic resonators to overlap the fluorescence were stimulated. By establishing a theoretical model that considered modified and suppressed spontaneous emission of MoS2, and building up a con-focal system and a transmission measurement system, the obtained experimental results were: the enhanced fluorescence intensity as a function of polarization direction complies the formula of acos2θ+b, the maximum enhancement factor of ten was reached when both of exciting and collection directions were aligned with the long axis of the resonators. These fundamental results are significant to both of nonlinear investigation and device applications.