Experimental evaluation and improvement methods for low cost transmitters in long reach PONs

An extensive experimental research of an optical access network behaviour has been realized, in the framework of studying distance enhancement of long reach passive optical networks (PONs), while maintaining low cost and high performance. The network system has been implemented with low cost transmitters - operated at low driving voltage, without the use of electrical amplification, at 10 Gb/s - and with colourless optical network units (ONUs) as receivers. Although studied for variable lengths, error-free transmission (target bit-error rate at 10−9) over 100 km reach has been achieved in several ways. The performance of extended PONs, when low cost transmitters operated at low driving voltage are utilized, is improved by the application of optical dispersion compensation and electronic equalization techniques. The chirp of the transmitter has been shown to have an important effect on the behaviour of the system because of the dispersion phenomenon. It is observed however, that the combined use of optical dispersion compensation and electronic equalization gives a reduction of 5-10 dB of the required optical signal to noise ratio (OSNR) for an error-free transmission. Moreover, it significantly reduces the heterogeneity of the system performance for several distances, yielding a predictable behaviour, while at the same time permits the use of handy, inexpensive and integrated transmitters.