Performance Analysis of Vertical and Horizontal Transmitter Array Modules Using Short- and Long-Wavelength VCSELS for Optical Interconnects

Abstract

For short- and long-wavelength vertical surface-emitting lasers (VCSELs), performances of optical transmitter array modules with vertically and horizontally packaged structures are analyzed for application to on-board optical interconnection. 850 and 1310 nm wavelengths are selected for the short- and long-wavelength light sources. For each wavelength, top- and bottom-emitting VCSELs are used to compare the performances of four different module structures: bottom-emitting types of 850 and 1310 nm for the vertical modules, and top- emitting types of 850 and 1310 nm for the horizontal modules. The horizontal transmitter modules are packaged using the conventional wire-bonding technology for the interconnect between VCSEL and driver chips while the vertical modules are packaged using the flip-chip-bonding technology. Signal crosstalk is investigated using 1 x 4 VCSEL array chips, which are driven using the same Si-CMOS circuits designed for 5 Gb/s operation. The vertical modules show lower crosstalk than the horizontal modules. When the gap distance between the VCSEL aperture and the waveguide input port increases up to 500 mu m for each module, the crosstalk increases in a range -58 to -37 dB. The 3-dB bandwidth performances are sensitively degraded in a range 4.6-2.0 GHz when the gap distance increases. In the crosstalk, the 1310-nm vertical module shows the best performance, while in the 3-dB bandwidth, the 850-nm horizontal module shows the best performance. The four modules shows clear eye openings at 2.5 Gb/s with bit error rate < 10(-12) and can be used for on-board optical interconnections.