A CMOS A nalogue Predistortion Driver Circuit for Wideband Optical Fibre Links

1. A CMOS Analogue Predistortion Driver Circuit for Wideband Optical Fibre Links Fu-Chuan Lin and David M Holburn Department of Engineering, University of Cambridge, U.K. Abstract Access Network Interfaces The laser is a major source of non-linearity for optical fibre communication systems. In this research, we demonstrate a CMOS analogue predistortion circuit to reduce laser non-linearity for wideband optical fibre links. The circuit uses a non-linearity having the inverse transfer characteristic of the directly modulated vertical cavity surface emitting laser (VCSEL). It has been shown by measurement that the predistortion circuit gives 8.9 dB improvement of IIP3 in the optical fibre system. The optical fibre transmitter front-end with predistortion lineariser was implemented using austriamicrosystems (AMS) 0.35 mm CMOS technology. • Optical access key providing up to 24x51.84 Mb/s to end users. • Able to meet future high bandwidth demands using a cost-effective, flexible and evolutionary solutions. • Integration with present-day APON and future WDM-based transport networks as well as with the substantial network of copper-drop to the home. Important Features of this Approach Distribution Point Function Node • Graceful evolution from current copper infrastructure, enabling an evolutionary upgrade path. • Common downstream/upstream optical path to the DP, with reuse of common optoelectronic components. • Down- and up-conversion carrier signals delivered optically from the access node, hence eliminating the need for stable local oscillator at the DP. • Use of low-cost, low-power commercially-available components such as VCSELs. • Use of a low-power design to minimise thermal management. Integration in a single technology - CMOS Analogue Predistortion Circuit Microphotograph of the CMOS Transmitter The voltage controls (VISS(L) and VISS(N)) are controlled to generate a reverse curve transfer characteristic that corresponds closely to the directly modulated VCSEL laser. Conclusions • A low-power optical transmitter front-end with clipping distortion suppression has been presented. • A CMOS analogue predistortion circuit has been developed for linearisation of the directly modulated VCSEL laser in optical fibre transmitters. • Measurement results show that the IIP3 was improved by 8.9 dB at the centre frequency of 700 MHz. • The SFDR3 improvement obtained was 3.6 dB/Hz2/3 at a system bandwidth of 40 MHz with centre frequency of 700 MHz. • This approach can provide a substantial improvement compared with conventional designs.