A comparative analysis of short- and long-wavelength multi-chip optical transmitter modules for optical PCBs applications

Abstract

Multichip transmitter modules in which VCSEL chips were packaged on Si-CMOS driver IC chips have been investigated to apply in the optical interconnection using optical printed-circuit board. The modules were prepared using of 1 x 4 bottom-emitting VCSELs which were flip-chip-bonded on a driver IC fabricated by 0.18 μm Si-CMOS technology. Dynamic characteristics and optical crosstalk were compared for two types of VCSELs; 850 nm short-wavelength and 1310nm long-wavelength VCSELs. The two modules showed bit error rate less than 10 -12 with clear eye openings at 2.5 Gbps. The 3-dB bandwidth was 3.2 GHz for the 850 nm module and 3.8 GHz for the 1310 nm module. When the VCSEL aperture was directly contacted with the input port of the fiber, the optical crosstalk within the 3-dB bandwidth showed -53.2 dB for 850 nm module and -57.2 dB for 1310 nm module. These low crosstalk values for both modules might be attributed to the flat surface of the bottom-emitting VCSEL devices allowing tight contact with the fiber surface. This low optical crosstalk performance is an additional advantage of the multichip module, adding to the general advantages in compact packaging and low electrical crosstalk.