High frequency modeling for 10 Gbps DFB laser diode module packaging

In packaging the laser diode several electrical requirements must be satisfied. The conventional packaging method which consists of transmission line, matching resistor and wire bonding interconnect showed good result for the modulation bandwidth requirement of greater than 10 GHz. However the return loss requirement was not content with less than -10 dB. To analyze the effects of package parasitics on return loss, we proposed a small signal circuit model of a laser diode module. From the small signal measurement data, we obtained the small signal circuit model of the laser diode for each bias current, which contains package parasitics and intrinsic laser diode characteristics. Considering both the intrinsic laser diode characteristics and total parasitic effects of the packaged module, the overall frequency response of the laser diode module was simulated and compared to the experimental results. The simulation results on the small signal modulation bandwidth and return loss showed a good agreement with measurements. However, the return loss does not meet the requirement for 10 Gbps laser diode module. Therefore, the wire bonding effect on the return loss was analyzed. The characteristics of wire bonding inductance which affect the return loss were simulated using an interconnect analysis program. As a result, shorter wire bonding length would be the best step to reduce the package induced inductance.