INTEGRATION OF VCSEL WITH MODULATED RAMAN PUMP FOR DATA AND CLOCK TRANSMISSION IN OPTICAL COMMUNICATION

Abstract

The evolution of ultrafast optical technologies has led to the realization of low cost, low latency and high speed optical networks. Existing telecommunication infrastructure does not provide sufficient capacity to satisfy future demands in terms of extend of coverage, bandwidth and number of served customers. Fibre-optic technology for data transmission is subject to dynamic development fueled by the increasing demand for large bandwidth and reach extension. High capacity VCSELs are the most desired transmitters for data transmission but, they are limited to short distances. Since high powered Raman lasers are compatible with VCSELs, integration of the two unlocks the puzzle of enhanced data and RF clock signal distribution system. First, a 1550 nm VCSEL was directly modulated with 8.5 Gbps data to counter-propagate with modulated backward Raman pump carrying 8.5 Gbps data over a 50.7 km True Wave Reach fibre to realize enhanced full-duplex bidirectional data transmission system. We report error free data transmission with receiver sensitivity of -14.42 dBm, -14.38 dBm and -13.00 dBm for signal analysis with unmodulated backward Raman, modulated backward Raman pump analysis and signal analysis with modulated backward Raman respectively at BER threshold of 10-9. Secondly, unidirectional data transmission system was realized by employing modulated forward Raman pump instead of modulated backward Raman. Modulated Raman pump simultaneously amplifies the VCSEL channel and transmits data over the transmission link, therefore maximizing the network efficiency. Minimum receiver sensitivity of −14.38 dBm was attained for a transmission configuration with un-modulated forward Raman pump. Thirdly, performance of DFB laser on 2 GHz, 4 GHz and 6 GHz RF clock signal distribution was investigated. At 10 kHz offset frequency lowest phase noise of -119.93 dBc/Hz was recorded for 2 GHz signal. Fourthly, we realized a technique of exploiting forward and backward Raman pumping to both disseminate clock tones and amplify data signal simultaneously. 10 Gbps data from directly modulated VCSEL was coupled into a 50.7 km fibre to counter propagate with 4 GHz modulated Raman pump and repeated the same for forward pumping where the data co-propagated with 4 GHz clock. Amplified errorfree data transmission with minimum receiver sensitivity of -14.8 dBm for modulated forward Raman and distributed stable clock signal over 50.7 km True Wave Reach fibre was achieved. A maximum phase noise of -100.6 dBc/Hz at 10 kHz offset frequency was experimentally measured for 50.7 km fibre transmission with backward Raman pumping. Finally, long term stability measurement on RF clock signal was analyzed using Allan deviation for DFB laser. Allan deviation of 1.49e-12 /s and 1.63 e-12 /s was obtained for B2B and 24.69 km fibre respectively at 100 s averaging time for 2 GHz clock signal. The results show the suitability of VCSEL light source and Raman amplification for application in integrated optical transmission links. This work offers an integrated VCSEL-based transmission system which satisfy the requirements for the next generation optical fibre networks regarding long reach, enhancement, duplex data/clock dissemination with a single fibre upstream and downstream transmissions.