Takeshi Komiyama

VCSEL-based optical transceiver module for high-speed short-reach interconnect

Interconnects have been more important in high-performance computing systems and high-end servers beside its improvements in computing capability. Recently, active optical cables (AOCs) have started being used for this purpose instead of conventionally used copper cables. The AOC enables to extend the transmission distance of the high-speed signals dramatically by its broadband characteristics, however, it tend to increase the cost. In this paper, we report our developed quad small form-factor pluggable (QSFP) AOC utilizing cost-effective optical-module technologies. These are a unique structure using generally used flexible printed circuit (FPC) in combination with an optical waveguide that enables low-cost high-precision assembly with passive alignment, a lens-integrated ferrule that improves productivity by eliminating a polishing process for physical contact of standard PMT connector for the optical waveguide, and an overdrive technology that enables 100 Gb/s (25 Gb/s × 4-channel) operation with low-cost 14 Gb/s vertical-cavity surfaceemitting laser (VCSEL) array. The QSFP AOC demonstrated clear eye opening and error-free operation at 100 Gb/s with high yield rate even though the 14 Gb/s VCSEL was used thanks to the low-coupling loss resulting from the highprecision alignment of optical devices and the over-drive technology.

Structure of 25-Gb/s Optical Engine for QSFP Enabling High-Precision Passive Alignment of Optical Assembly

We propose a novel structure for optical assembly that enables high-precision passive alignment assembly process for our flexible printed circuit -- based optical engine. The optical engines are fabricated with less than 7 μm of misalignment between optical devices and polymer waveguides. This high-precision alignment suppresses the optical coupling losses to an average of 2.9 dB for the transmitter side and, 1.6 dB for the receiver side. The optical engines are installed to a high-volume product of 100 Gb/s quad small form-factor pluggable (QSFP) optical transceivers. The QSFP demonstrated clear eye opening and error-free operation at 100Gb/s with high yield rate thanks to the low-coupling loss resulting from the high-precision alignment of optical devices.