Optical interface multichip modules promise to alleviate the bottlenecks of electrical interconnection. Two kinds of optical transmitter multichip module were fabricated for optical printed circuit board (OPCB) based interconnections for performance analysis. Each of the modules consist of 1 x 4 bottom-emitting VCSELs flip-chip bonded on a CMOS driver array IC for optical interconnection; among them one is an 850nm short-wavelength and the other is a 1310nm long-wavelength VCSEL. The short- and long-wavelength VCSELs have -3dB bandwidth of about 3.6 GHz and 2.6 GHz, respectively. Four-channel driver array which has been fabricated in a 0.18μm Si-CMOS technology requires 1.8V of power supply, is used for the both multichip transmitter modules. Short- and long-wavelength multichip modules are bumped with Au/Sn solder and gold stud bump wire respectively using the flip-chip bonding technology. The multichip modules have a dimension of 1.1mm x 1.2mm x 0.5mm for the four channels. The multichip module employing flip-chip bonding technology reduces unwanted crosstalk due to bond wires. The two modules showed BER less than 10<sup>-12</sup> and clear eye openings at 2.5 Gbps. We measured the frequency response and crosstalk of long-wavelength multichip module and will compare them with the short-wavelength multichip module to evaluate which module is preferable for the optical interconnection applications on optical PCBs.
Two kinds of optical transmitter (Tx) modules using an 1310 nm long-wavelength and an 850 nm short-wavelength 4-channel VCSELs have been fabricated and characterized for comparison. 4-channel VCSEL driver has been fabricated by a CMOS 0.18 μm process and used in common for the fabrication of both modules. Both of the modules showed less than 1 x 10<sup>-12 </sup>of bit error rates (BERs) and clear eye openings at the speed of 2.5 Gbps and 3. 5 Gbps. 3dB bandwidths of the two different Tx modules of 850 nm and 1310 nm VCSELs are 3.76 GHz for 850 nm VCSEL and 3.80 GHz for 1310 nm VCSEL. The optical crosstalks of the both transmitter modules are less than -50 dB in common. Crosstalk evaluation of the two optical interconnection systems using these two Tx modules shows that the application of the 1310 nm wavelength VCSEL as well as 850 nm wavelength VCSEL for the optical interconnections is expected to be possible.