Integrated Metamaterial Interfaces for Self-Aligned Fiber-to-Chip Coupling in Volume Manufacturing
Improving the scalability and cost efficiency of photonic packaging is central to fulfilling the silicon photonic promise of low-cost devices with unprecedented optical complexity. A key enabler toward this goal is an efficient, large-mode, integrated fiber coupler and mode converter. Using standard fiber modes at fiber-to-chip junctions avoids expensive in-fiber mode conversion and relaxes alignment tolerances for low-cost assembly and improved reliability. Metamaterial waveguides, also called subwavelength gratings, are particularly useful for such structures. They provide unmatched design flexibility and, counter-intuitively, are more forgiving to fabrication tolerances than solid-core waveguides. Here, we summarize our work on interfacing self-aligned, standard cleaved fibers to rectangular Si routing waveguides. Fiber V-grooves are integrated on chip with metamaterial converters embedded in suspended oxide membranes to prevent coupler-mode leakage to the substrate. We show optical results from first integration of V-grooves with metamaterial converters to commercial structures fabricated in 300 mm CMOS production facilities. We demonstrate a peak transmission of -0.7 dB on the TE polarization and -1.4 dB on the TM polarization with a respective spectral roll-off of 0.3 and 0.4 dB over the 60 nm bandwidth measured.