| Rapid detection of chemical and biological analytes is of great interest for a variety of applications including quality controlling, disease diagnosis, biological molecule recognition, and environment monitoring. The field is attracting interest globally and many stunning technologies are being developed. However, most of the works reported in the literature use a passive interferometer such as a Mach-Zehnder interferometer, Fabry-Perot cavity, or a ring resonator based on SOI or silica platform as the sensing device. An external light source is used in this case, which leads to complexities in optical coupling and packaging. The goal of the thesis is to realize ultra-compact, potentially low-cost, high-sensitivity and integrated optical sensor which could be achieved in two directions—hybrid integration or monolithic integration.(1) We have investigated theoretically and experimentally a highly-sensitive intensity-interrogated waveguide biosensor based on cascaded FP laser and SOI ring resonator. The detection scheme employs a low-cost easy-to-fabricate FP laser to serve as a reference comb for the sensing ring. Its sharp emission peaks with high spectral power density results in a high sensitivity for the sensor compared to previously investigated all-passive double-ring sensor. Preliminary experiments have demonstrated the operation principle with a sensitivity of1000dB/RIU, more than twice that of the double-ring sensor. Theoretically, an ultrahigh sensitivity in the order of5X104dB/RIU can be achieved with TM mode and10%coupling coefficient between the waveguide and the ring, corresponding to a refractive index detection limit of about2X10-1. With the advancement of Ⅲ-Ⅴ on silicon integration technology and micro-fluidics, the sensing scheme can be extended to large array format for lab-on-a-chip applications.(2) We improved the design based on a FP laser rings by using a monitoring ring with the same waveguide structure to offer temperature compensation. The wavelength instability of the laser and the ring can be monitored and controlled during the detection. Only three detectors are needed to apply the intensity interrogation method. A system detection limit of refractive index in the order of10-6can be achieved which corresponds to a wavelength shift of0.06pm.(3) To explore the potential monolithic integration, we investigated the interface between oxide and non-oxide after oxidation of buried AlGaAs. The vertical oxidation of GaAs or AlGaAs with low Al content activated by a neighboring oxidized Al-rich AlGaAs layer has been demonstrated experimentally. The vertical oxidation causes unexpected oxidation of the adjacent layers and brought additional roughness at the oxide/non-oxide interfaces which is detrimental to the fabrication of optical waveguides. A superlattice structure was proposed in order to limit the vertical oxidation. The superlattice showed a higher resistance against the oxidation through the interface than bulk Al0.34Gao.66As, and even than bulk GaAs. Hydrogen plasma treatment of a dry-etched GaAs surface allowed for the oxidation of bulk GaAs, which showed the key role of hydrogen incorporation in the activation of the oxidation process for GaAs or AlGaAs materials with low Al content.(4) At last, the waveguides with buried oxidation layer were fabricated on stand sample and superlattice sample. A3-period SL was inserted between the bulk Al0.34Gao.66As waveguide core and the lower cladding Al0.34Ga0.66As which is to be oxided. The waveguides were measured by FP method at a long wavelength range (50nm) using broad band SLD source. The propagation loss at1550nm (～18dB/cm) was consistent with the value reported in literature of a similar structure. No significant loss difference was found between standard structure and SL structure at1550nm. However, the loss at830nm was considerably high (in the order of150dB/cm), probably mainly due to the interface scattering loss at short wavelength. In parallel, an FP laser working on TM mode was demonstrated which can be a building block for highly sensitive monolithically integrated circuit... |
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