12-Channel optical transmitter on an organic substrate for optical interconnections

We fabricated a newly designed 12-channel optical transmitter has a butt coupling possibility. An organic FR4 printed circuit board (PCB) was used as a substrate for integrating a 850 nm vertical cavity surface emitting laser (VCSEL) array with an electrical driver integrated circuit (IC). The substrate whose dimensions are 6.0 mm x 6.0 mm x 0.5 mm serves as a packaging platform which can provide the advantages of shorter signal routing, smaller size, and so on. Since the VCSEL array is attached on the sidewall of an organic substrate, this structure is the direct coupling-capable that has high optical coupling efficiency, which doesn´t require 45deg mirror and lens. This simple structure reduces the complexity of implementation and the cost. To analyze microwave characteristics of the optical transmitter, we have designed electrical transmission line from a driver IC to a VCSEL array. The circuit simulation was accomplished with the CST microwave studio, which uses the method of finite-difference time-domain (FDTD) algorithm for full wave electromagnetic characteristics. Through the simulation of the quasi-CPW line structure optimization, this transmission line is proved to be applicable to high frequency signal transmission. Simulation of temperature distribution in the embedded VCSEL array and driver IC modules was also achieved. The optical transmitter has been characterized using optical coupling into multimode fiber array. This transmitter showed a clear eye diagram of 5Gbps optical transmission.