Abstract
A 4 × 25 Gb/s ultrawide misalignment tolerance wavelength-division-multiplex (WDM) transmitter based on novel bidirectional vertical grating coupler has been demonstrated on complementary metal-oxide-semiconductor (CMOS)-compatible silicon-on-insulator (SOI) platform. Simulations indicate the bidirectional grating coupler (BGC) is widely misalignment tolerant, with an excess coupling loss of only 0.55 dB within ±3 μm fiber misalignment range. Measurement shows the excess coupling loss of the BGC is only 0.7 dB within a ±2 μm fiber misalignment range. The bidirectional grating structure not only functions as an optical coupler, but also acts as a beam splitter. By using the bidirectional grating coupler, the silicon optical modulator shows low insertion loss and large misalignment tolerance. The eye diagrams of the modulator at 25 Gb/s don’t show any obvious deterioration within the waveguide-direction fiber misalignment ranger of ±2 μm, and still open clearly when the misalignment offset is as large as ±4 μm.
Highlights
The volume of the digital information captured, created, or consumed each year is expected to grow from 538 exabytes to 5.0 zettabytes between 2012 and 2020, and it will double about every two and a half years [1]
The bidirectional grating coupler (BGC) exhibit the advantages of easy fabrication, perfectly vertical coupling and large misalignment tolerance, and potentially enable interfacing with a fiber array or flip-chip-integrated VCSEL laser array for low-cost photonic packaging
We have demonstrated that a Mach–Zehnder-type E-O modulator can be built based on a BGC which functions as a 3 dB power splitter with symmetry grating design [20]
Summary
The volume of the digital information captured, created, or consumed each year is expected to grow from 538 exabytes to 5.0 zettabytes between 2012 and 2020, and it will double about every two and a half years [1]. Several WDM and pulse-amplitude-modulation (PAM) transmitters are proposed to realize high-speed optical links [17,18,19] by different schemes. For these high-speed silicon transmitters based on silicon photonics, coupling a light effectively from a single mode fiber (SMF, typically with core diameter of 9 μm) into the silicon waveguide (typical dimensions of 220 nm × 450 nm) in an economical way is a big challenge. The BGCs exhibit the advantages of easy fabrication, perfectly vertical coupling and large misalignment tolerance, and potentially enable interfacing with a fiber array or flip-chip-integrated VCSEL laser array for low-cost photonic packaging. Eye diagrams don’t show obvious deterioration within the waveguide-direction fiber misalignment ranger of ±2 μm, and still open clearly when the misalignment offset is as large as ±4 μm
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