The hybrid integration of passive and optoelectronic devices has been widely researched. One of the main applications of this technique is for the fiber to the home (FTTH) network. In bi-directional transceivers, integrated WDM filters have been used to separate or combine the optical signals. Thin film filter (TFF) embedded waveguide type is effective for an application requiring wide bandwidth and low loss.
Although the insertion loss of TFF itself is quite low, significant loss occurs at the trench and it depends on the geometrical structure and fabrication errors of the trench waveguide. The conventional sawing method and deep reactive ion etching technique were used for trench fabrication. In the case of using DRIE process, fabrication error was reduced and position error of the trench was controlled within 1um. This method could also enhance the platform design flexibility. To reduce the coupling loss between input and reflection waveguides with high tolerance of filter position, a few mode waveguide and horn waveguide were proposed. The insertion losses of transmission and reflection were less than 0.5dB and 0.7dB respectively. The 1dB tolerance of filter position was improved to be nearly twice than that of the conventional waveguide.
A simple method for fabricating fiber-embedded boards using a grooving technique is described that is quite cost effective and fully compatible with conventional printed circuit board (PCB) processes with no necessity for a specially designed wiring machine. FR-4 plates are grooved using a dicing saw machine and followed by placing optical fibers into the grooves. The fiber-embedded PCBs are laminated by conventional PCB processes at a temperature of 180°C for 1 h under 47 kg/cm2 of pressure. The 50/125-µm glass fibers, and the polyimide-coated glass fibers are laminated successfully. In the fiber-embedded boards with a length of 10 cm, the variation of center positions of the embedded glass fibers is about ±5 µm. The transmitted optical power through the fiber-embedded boards shows a good uniformity of less than ±0.5 dB variation from the average value for the 12 fiber channels. Data transmission through the board at data rates of 2.5 Gbits/s is achieved. After confirming the successful laminations and the data transmission with the small-scale fiber-embedded boards, a large-scale prototype of the fiber-embedded board for a backplane application is successfully fabricated.
Device parameters, like center frequency, polarization dependent loss (PDL), and optical crosstalk in silica-based waveguide device, are determined by the refractive index (RI) and its uniformity across the wafer, thermal expansion coefficient (TCE), and biaxial elastic modulus of silica film. In this study the optical and thermo-mechanical properties of plasma enhanced CVD silica films with different compositions were investigated before and after thermal annealing. RI of deposited films decreased sharply with N2O/SiH4 ratio up to 40, and increased slowly when this ratio was larger than 60. The minimum RI of deposited film was found slightly higher than that of thermal oxide. CTE and elastic modulus of silica film were obtained by measuring the film stress with temperature. Growth stresses of deposited films were increased with N2O/SiH4 ratio. Due to the porous structure, the CTE and elastic modulus of deposited films at low temperature range (<400°C) were different from those of pure silica. Sharp rise in stress due to gas evolution from film was observed around 500°C. The amount of stress increase and the origin of evolved gas are dependent on the film composition. When silica films were fully annealed (1100°C for 4hour), their CTE and elastic modulus were the same as those of thermal oxide. Upon annealing at high temperature (~800°C), however, cracks were generated on sub-oxide film, which was deposited at low N2O/SiH4 ratio. RI of annealed films changed with the composition of deposited film, the annealing temperature, and the cooling rate after anneal.
The objective of this study was to find the relationship between process parameters and responses in deep silica etching for hybrid integration. The process parameters were the wafer temperature, oxygen addition, clamp material and process pressure. The responses to these parameters were sidewall roughness, profile of etched waveguide, the morphology of etched surface and critical dimension change. When the process parameters were varied, the change in responses could be interpreted by analyzing sidewall polymer thickness and selectivity. Polymer thickness and selectivity also have positive correlation. To investigate which parameter is dominant in determining the coupling efficiency between waveguide end facet and active device in application for hybrid integration, the propagation loss of waveguide with or without deep trenches were measured and analyzed.