PERFORMANCE OF VCSEL AT 10 Gb/s IN G.655 AND G.652 SSMF IN THE 1310 nm AND 1550 nm TRANSMISSION WINDOWS

Abstract

Vertical cavity surface emitting lasers (VCSELs) are now major optical sources in optical communication and technology. The VCSEL-based transmission systems satisfy the next generation optical fibre access networks requirements such as low output power, no optical amplification and use of single fibre for signal transmission. High speed and long wavelength, 1310 nm and 1550 nm VCSELs, are attractive candidates for use in short distance transmission system due to its cost effectiveness and low current requirements. Direct modulation of VCSEL with separate optical and current apertures enables high modulation bandwidth operating at single mode at low current density. However, dispersion and attenuation is a major hurdle to VCSELs transmission at bit rate of 10 Gb/s and above. This therefore motivates the need to investigate and characterize VCSELs and determine their performance in different fibres at different transmission windows. In this study, a 1310 and 1550 nm VCSEL was directly modulated with 10 Gb/s NRZ PRBS 27-1 and transmitted over 25 km ITU.T G.652 and ITU.T G.655 fibres and optimized for metro-access distances. The VCSELs systems were simulated and verified experimentally using the bit error rate (BER), Q factor and optical signal to noise ratio (OSNR) performance indicators. The power penalty suffered by the system was evaluated at BER=10-9 communication threshold. Power penalty of 1.5 dB was attained experimentally for 1310 nm VCSEL on 25 km G.652 fibre. When a 1550 nm VCSEL was used on G.652 fibre, the system operated on an error floor region without crossing the communication threshold region of BER=10-9 . The high dispersion in 1550 nm VCSEL on G.652 fibre gave rise to high power penalties hence bit errors. However, when a 1550 nm VCSEL was used in G.655 fibre transmission, the error-free receiver sensitivity was measured to be -19.3 dBm for back to back (B2B) and -17.6 dBm after 25 km. The transmission penalty suffered by the system was 1.7 dB. The error floor region occured when a G.652 fibre was used in 1550 nm transmission window. OSNR was observed to vary inversely with fibre length. Small values of OSNR of less than 6 dB were achieved experimentally. OSNR was also observed to reduce with the increase in the received power. The Q factor was used theoretically to quantify the performance of the VCSELs. The Q factor increased with the increase in the output power at the receiver. High Q factor values of 6 and above were achieved when 1310 nm and 1550 nm VCSELs were transmitted over G.652 and G.655 fibres respectively. The results clearly indicates that 1550 nm transmission over G.655 fibre would highly be recommended while 1310 nm is suitable for transmission over G.652 fibre. The findings of this study is significant for high bit rate data transmission for passive optical networks (PON) application. These results show the feasibility of long-wavelength VCSELs in the deployment of enhanced optical access networks