Silicon oxynitride (SiOxNy) grown by plasma enhanced chemical vapor deposition (PECVD) is well-suited for the realized application of high contrast waveguides for the range of the refractive index can be largely tuned (1.45-2.0). SiOxNy AWG device with 3% refractive index difference (Δ) and the transmission spectrum of AWG's device indicated the insertion loss, crosstalk and side-lobe were lower than -3 dB, -15 dB and -40 dB, respectively, by 3D beam propagation method were investigated in this study. The chip size of the whole device is smaller than 4 cm x 1.5 cm, and the highest coupling loss of the rib waveguide for single mode fiber was about -1.6 dB. Based on the simulation results, the device can be really fabricated by thin-film deposition, photo-lithography and dry-etching processes.
Microstructural evolution analysis revealed over-supplied silicon atoms would form silicon nano-crystallized structure in the amorphous optical films for lower N2O/(N2+NH3) ratio, and resulted in higher refractive index and extinction coefficient. From the scanning electron microscopy (SEM) features of rib-type silicon oxynitride waveguide, we found the profile, and the roughness of side- and top-walls of waveguide reached to the manufacturing criteria of AWG device. We had successfully fabricated an AWG device with 8 channels and 1.6nm channel spacing, and the coupling loss and propagation loss were about -2.24 dB and -0.15 dB/cm, respectively. While, the AWG device performances need further improvements by modified design, uniform thin film deposition, and accurate dry-etching processes.
Polyimides and polyimide-silica hybrid AWG device with 2.2% and 1.6% refractive index difference (□), and the transmission spectrum of AWG's device indicated the insertion loss were -3.12 dB and -3.16 dB, crosstalk were -20 dB and -15 dB, and side-lobe were both lower than -60 dB, respectively, by 2D beam propagation method were investigated in this study. The smallest chip size of the whole device is smaller than 3.4 cm x 1.8 cm, and the highest coupling loss of the rib waveguide for single mode fiber was about -1.02 dB. Based on the 3D simulation results, the devices will be really fabricated by thin-film deposition, photolithography and dry-etching processes.
Optical measurements of polyimides and polyimide-silica hybrid materials formed on quartz glass indicated, the refractive indexes of top cladding/core/bottom cladding layers at 1550 nm wavelength were 1.522/1.546/1.522 and 1.4907/1.53/1.4907, respectively. The extinction coefficients of all samples indicated approximately zero at 1550 nm wavelength. We will adopt these polyimides and polyimide-silica hybrid materials to perform real AWG fabrication. From atomic force microscopy (AFM) analysis of polyimides and polyimide-silica hybrid materials revealed, the surface average roughness was 0.236 nm and 0.364 nm, respectively. The structures of polyimides and polyimide-silica hybrid materials were identified by fourier transform infar ray (FTIR). High-resolution transmission electron microscopy (HRTEM/EDAX) was used to study the localized interface structure and compositional distribution. The morphology of rib structure waveguides, polyimides and polyimide-silica hybrid films were examined by scanning electron microscopy (SEM).
Ion beam assisted deposition (IBAD) technique had widely used for improving stacking density and atomic mobility of thin films in many applications, especially adopted in optical film industries. Tantalum pentaoxide (Ta2O5) and silicon oxides (SiO2) optical thin films were deposited on the quartz glass substrate by using argon ion beam assisted deposition, and the influences of the residual argon gas and thermal annealing processes on the optical property, stress, compositional and microstructure evolution of the thin films were investigated in this study.
Ta2O5 thin films were analyzed by XPS indicated that the ratio value of oxygen to tantalum was insufficient, at the same time, the residual argon gas in the thin films might result in film and device instabilities. Adopting oxygen-thermal annealing treatment at the temperature of 425°C, the thin films not only decreased the residual argon gas and the surface roughness, but also provided the sufficient stoichiometric ratio. Simultaneously, microstructure examination indicated few nano-crystallized structures and voids existed in Ta2O5 thin films, and possessed reasonable refractive index and lower extinction coefficient. By the way, we also suggested the IBAD system using the film compositional gas ion beam to replace the argon ion beam for assisting deposited optical films. The designed (HL)6H6LH(LH)6 multi-layers indicated higher insertion loss than the designed (HL)68H(LH)6 multi-layers. Therefore, using the high refractive index as spacer material represented lower insertion loss.
Amorphous silicon SOI-AWG device with 59% extra high refractive index difference (Δ) and the transmission spectrum of AWG's device indicated the insertion loss, crosstalk and side-lobe were lower than -3.5 dB, -25 dB and -45 dB, respectively, by 3D beam propagation method were investigated in this study. The smallest chip size of the whole device is smaller than 4.5 cm x 1.2 cm, and the highest coupling loss of the rib waveguide for single mode fiber was about -1.68 dB. Based on the simulation results, the device will be really fabricated by thin-film deposition, photolithography and dry-etching processes.
Optical measurements of amorphous silicon films indicated, the more refractive index of a-Si films indicated possessing less point defects, dangling bonds, voids, and more hydrogen content and silicon nano-crystallized structures. Meanwhile, the more point defects, dangling bonds, silicon nano-crystallized structures, and less voids and hydrogen content result in larger extinction coefficient. Therefore, we adopted the suitable deposition rate and refractive index at 1550nm wavelength were 0.6 nm/s and 3.5012, respectively, to perform real AWG fabrication. From atomic force microscopy (AFM) analysis revealed the increased argon/silane flow rate and RF power wattage, and decreased operating vacuum would increase surface roughness. High-resolution transmission electron microscopy (HRTEM) analysis indicated amorphous silicon films mainly had amorphous structure with few silicon nano-crystallized structures, point defects and voids might affect the value of the refractive index and reliability. The structures of the a-Si films all indicated amorphous structure by x-ray diffraction (XRD) analysis.
To avoid potential large bending losses, the technique of high index contrast (HIC) has been developed. Silicon-oxynitride possess the priorities of the low residual stress, variations of the refractive index controlled by processing gas, and low absorption phenomena for infrared region, result in excellent promise and can provide key practical devices in dense wavelength division multiplexing (DWDM). The purpose of this study is to investigate and develop the rib shape, detail scale, reasonable selection of the waveguide material for silicon-oxynitride arrayed waveguide grating (AWG) design, processing parameters, and optical properties. Selecting index of 1.50 and 1.45 silicon-oxynitride as core and top/bottom cladding layers with reasonable design parameters represented very low loss, crosstalk, and side-lobe transmission spectral by 2D and 3D simulations. Based on the design results, we will perform the actual device fabrication. Silicon-oxynitride films optical measurements indicated, the refractive index and the extinction coefficient were 1.45~1.89 and 1x10-4~4.3x10-4 respectively by varying N2O/N2 ratio at 1550nm wavelength. From compositional analysis revealed the increased N/O ratio would increase refractive index and extinction coefficient, meanwhile the more Si-H and N-H bonds would increase extinction coefficient Microstructure analysis indicated silicon-oxynitride had amorphous structure with some voids might reduce the refractive index and reliability.