High-Density Optical Digital Datalink with Double-Sided Packaging

A fiber optic receiver is apt to be disturbed by electromagnetic interference by adjacent circuits because of its low input power level. Therefore, in a duplex optical datalink consisting of a transmitter and a receiver, the crosstalk from the transmitter to the receiver may become an obstacle in increasing the packaging density. An approach to fabricating a transmitter on one side of an FR-4 four-layer printed wiring board (PWB) and a receiver on the other side, thus suppressing the interference between the two circuits and realizing a compact and low-cost optical digital datalink, is described. The receiver using this new packaging technique achieved an optical sensitivity of -- 32 dBm for a 10-9 bit error rate (BER) at a transmission rate of 8.192 Mb/s for the CMI data format. Since the output optical power of the transmitter is -15 dBm or more, this optical datalink provides transmission over a 700 m distance using a 15 dB/km loss optical fiber.