| dc.description.abstract | In this dissertation, the researches focus on the development of the components and modules under a miniaturized silicon-based optical interconnect configuration. The component part can be further divided into two research topics, including inter-chip and intra-chip photonics elements, respectively. The former researches contain the development of the silicon 45° micro-reflectors and a monolithic integration of a diffractive optical element on the silicon 45° micro-reflectors; the latter researches comprise the wide-angle SOI-based waveguide bend combined with a phase-compensated microprism, and two types of SOI-based waveguide filters aiming to narrow and widely-flattened bandwidths, respectively, in spectra response. Regarding the research in module application, a miniaturized optical transceiver module is realized by using silicon optical bench (SiOB) technology.
With respect to the researches on the inter-chip optical interconnect components, we first demonstrate a silicon 45° micro-reflector with a deep depth and smooth slant quality. By using the KOH/IPA mixed etchant, the silicon 45° micro-reflector can be fabricated on the common (100) silicon wafers. The etching depth of this 45° slant can be over than 200 μm with the etching depth inaccuracy less than 5% and the slant RMS roughness under 20 nm. Therefore, this 45° slant can act as a great micro- reflector, which makes the light beams propagating on the SiOB deflect to the non-coplanar direction. Then, we further extending this technique to monolithically integrate a diffractive optical element (DOE) lens onto the silicon 45° micro-reflector. This novel optical element can make light beams simultaneously deflect and focus to the specific position in the non-coplanar direction. In addition, this DOE lens with an elliptic-symmetry shape can effectively eliminate the off-axis aberration within this optical system. Under the 600-μm working distance, the experimental results reveal that a diverged light beam can be deflected to the non-coplanar direction and focused with a spot size of only 15 μm, which would facilitate the single-/multi-mode fiber coupling issues.
Regarding the intra-chip photonics components, the waveguide bends and waveguide filters are developed in this research topic. These components can be monolithically integrated onto the SOI-based rib waveguide platform. In addition, the sizes of these components are only a couple of micrometer squares, which can fit the high-density integration expectation for the intra-chip photonics. For the wide-angle waveguide bend, a phase-compensated microprism is introduced into the SOI rib waveguides in order to correctly tilt the wavefront of the waveguide eigen-mode and effectively suppress the radiation loss. The bending angles with 10°, 20°, 30°, and 40° cases are demonstrated to examine the effects of the arbitrary optical paths. Under filling the BCB material to the microprism area, the compact bending radius and bending loss are only 15.4 μm and 3.43 dB, respectively. After improving the interface Fresnel losses in the next design, the bending losses could be effectively suppressed to only 1 dB. For the waveguide filters, we theoretically investigate a silicon sub-wavelength grating, possessing the guided-mode resonance (GMR) effects, on the SOI rib waveguide. Based on the design of a strongly-modulated effect, a finite-sized waveguide mode passing this grating can converge with an extinction ratio of 14.93 dB in optical spectral response. In addition, the transmissive flattened bandwidth can be available to over 40 nm in 0.5-dB degradation. We also apply the distributed Bragg reflectors (DBR) grating to design a 3-nm narrow bandwidth in full width at half maximum (FWHM). Less than the bandwidth with 1-nm FWHM could be expected by properly increasing the DBR layers. Both mentioned waveguide filters can serve the future requirements of the ultra-high-speed optical interconnects by introducing the wavelength-division multiplexing (WDM) approaches.
Finally, compact and passive-alignment 4-channel ? 2.5-Gbps optical interconnect modules including transmitting and receiving parts are developed based on the SiOBs of 5 ? 5 mm2. A silicon-based 45° micro-reflector and V-groove arrays are fabricated on the SiOB using anisotropic wet etching. Moreover, 2.5-GHz high-frequency transmission lines with 4 channels, and bonding pads with Au-Sn eutectic solder are also deposited on the SiOB using evaporating. The vertical-cavity surface-emitting laser (VCSEL) array and photo-detector (PD) array are flip-chip assembled on the intended positions. The multi-mode fiber (MMF) ribbons are passively aligned and mounted onto the V-groove arrays using UV curing. Without the assistance of additional optics, the coupling efficiencies of VCSEL-to-MMF in the transmitting part and MMF-to-PD in the receiving part can be as high as -5.65 and -1.98 dB, respectively, under an optical path of 180 μm. The 1-dB coupling tolerance of greater than ±20 μm is achieved for both transmitting and receiving parts. Eye patterns of both parts are demonstrated using 15-bit PRBS at 2.5 Gbps.
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