Fiber Optic Transceivers in Surface Mount Technology for High Performance and Low Cost Optical Interconnects

Abstract

We have developed plastic molded fiber optic transceiver (FOT) modules for surface mounting. The transmitter contains a vertical-cavity surface emitting laser (VCSEL) light source operating at 850nm wavelength, an electronics driver chip, and some passive components. The package is suitable for surface mounting. It shows good stability during reflow soldering in an infrared oven with a peak temperature of 250degC. With a special designed heat shield, the SMT module shows a stable optical alignment before and after the reflow soldering process. The SMT technology enables very low cost component mounting on PCB using automatic pick&place machines. The right material selection and package design is crucial for the stability of the optoelectronic module during the surface mount soldering process. The SMT module is a technology extension of our through-hole mounting FOTs. The output power of the transmitter module is limited to 0.7mW to meet eye-safety class 1 requirements. The transmitter has an internal control circuit to stabilize the optical output of VCSEL and an integrated coupling optics to provide loose alignment tolerances of plusmn70um in lateral axis for a working distance of 500um to polymer cladded silica (PCS) optical fiber with 200um core diameter. The optical coupling power from the transmitter to the PCS fiber has a variation within 1 dB over the wide ambient temperature range from -40deg C to +105degC This enables the usage of very low cost plastic molded connector ferrules. The receiver module contains a high speed MSM photodetector. The special design of the MSM photodetector enables high speed operation up to 5Gb/s in combination with a large active area for easy alignment. With two pairs of the fiber optic transceiver modules, we demonstrate a 1Gb/s video transmission over up to 15m of PCS fiber. The video link consists of a camera with an electrical S800 LVDS interface and a high resolution monitor. A pair of fiber optic cable connects the two ports replacing and extending the regular electrical cable. In contrast to the electrical cable the optical fiber is thin, light weight, and highly flexible. The high power budget margin of the link allows 3 in-line connectors for the 10-15m link length. For other applications a longer link length is feasible using higher bandwidth optical fiber. The SMT fiber optic transceivers enable new low cost applications in automotive, industrial control, and home networking. The technology can compete with electrical solutions on performance and cost and can outperform it on cable flexibility and EMI immunity