Carrier position third and fifth order IMDs of a radio-over-fibre system laser

Abstract

The third order intermodulation distortion (IMD3), instead of the fifth order intermodulation distortion (IMD5), is often thought to limit the performance of the radio-over-fibre system as it tends to fall in-band. A frequency plan based on the Golomb Ruler is suggested to overcome this IMD3 problem. However, its effect on the IMD5 is not known. A laser model is derived based on Volterra Series with electrical parasitics included to simulate the IMD3 and IMD5 appearing at carrier position when the channels to be used are in accordance with the Golomb Ruler’s marks and compare them with those generated by equally spaced carriers at the maximum RF input level supported by a low and high bias current for the number of channels to be used. The IMD5 is found to be more dominant than the IMD3 for the equally spaced frequency plan when the low bias current was employed. The opposite was observed at high bias current. The Golomb Ruler based frequency plan led to no IMD3s but low levels of IMD5 were still present at the channels designated for use when both bias currents were employed but they were lower than those due to the equal frequency spaced channels.