Single Plastic Optical Fiber, Multiple Channel Data Link for Sensing Applications With PCB Implemented Transmitter and Receiver

Abstract

The limited physical bandwidth of optical data links can be utilised better using pulse amplitude modulation (PAM) schemes. PAM can also be used to implement multiple channels on a single fibre to reduce the fibre count. In this paper, PAM is used with an additional amplitude level transmitting the clock associated with the data. This allows a direct detection of the clock from the signal. Frequent returns to this additional peak level are used to determine the signal strength at the receiver. The paper presents a very compact PCB implemented transmitter achieving a data rate of up to 400 Mbps. Furthermore, three PCB implemented receiver designs that cover different speed (20-400 Mbps) and cost/complexity ranges are presented including measurement results. The proposed solutions are compared to various industry standard solutions in terms of their achievable sampling rate and measurement delay resulting from connected sensors. It is concluded that PAM based data links represent an attractive alternative to the usual time domain multiplexing based 8b/10b encoded no-return-to-zero (NRZ) data links. They lead to an increase of the possible sampling rate (278 %) of the sensor and a decrease of the measurement delay (20 %), while keeping the same signal bandwidth and number of fibres.