Optical multicarrier sources for spectrally efficient optical networks

During the last 30 years the capacity of commercial optical systems exceeded the network traffic requirements, mainly due to the extraordinary scalability of wavelength division multiplexing technology that has been successfully used to expand capacity in optical systems and meet increasing bandwidth requirements since the early 1990’s. Nevertheless, the rapid growth of network traffic inverted this situation and current trends show faster growing network traffic than system capacity. To enable further and faster growth of optical communication network capacity, several breakthroughs occurred during the last decade. First, optical coherent communications, which were the subject of intensive research in the 1980’s, were revived. This triggered the employment of advanced modulation formats. Afterwards, with the introduction of orthogonal frequency division multiplexing (OFDM) and Nyquist WDM modulation techniques in optical communication systems, very efficient utilisation of the available spectral bandwidth was enabled. In such systems the spectral guard bands between neighbouring channels are minimised, at the expense of stricter requirements on the performance of optical sources, especially the frequency (or wavelength) stability. Attractive solutions to address the frequency stability issues are optical multicarrier sources which simultaneously generate multiple phase correlated optical carriers that ensure that the frequency difference between the carriers is fixed. In this thesis, a number of optical multicarrier sources are presented and analysed, with special focus being on semiconductor mode-locked lasers and gain-switched comb sources. High capacity and spectrally efficient optical systems for short and medium reach applications (from 3 km up to 300 km), based on optical frequency combs as optical sources, advanced modulation formats (m-QAM) and modulation techniques (OFDM and Nyquist WDM) have been proposed and presented. Also, certain optoelectronic devices (i.e. semiconductor optical amplifier) and techniques (feed-forward heterodyne linewidth reduction scheme) have been utilised to enable the desired system performance

Flexible terabit/s Nyquist-WDM super-channels using a gain-switched comb source

Terabit/s super-channels are likely to become the standard for next-generation optical networks and optical interconnects. A particularly promising approach exploits optical frequency combs for super-channel generation. We show that injection locking of a gain-switched laser diode can be used to generate frequency combs that are particularly well suited for terabit/s super-channel transmission. This approach stands out due to its extraordinary stability and flexibility in tuning both center wavelength and line spacing. We perform a series of transmission experiments using different comb line spacings and modulation formats. Using 9 comb lines and 16QAM signaling, an aggregate line rate (net data rate) of 1.296 Tbit/s (1.109 Tbit/s) is achieved for transmission over 150 km of standard single mode fiber (SSMF) using a spectral bandwidth of 166.5 GHz, which corresponds to a (net) spectral efficiency of 7.8 bit/s/Hz (6.7 bit/s/Hz). The line rate (net data rate) can be boosted to 2.112 Tbit/s (1.867 Tbit/s) for transmission over 300 km of SSMF by using a bandwidth of 300 GHz and QPSK modulation on the weaker carriers. For the reported net data rates and spectral efficiencies, we assume a variable overhead of either 7\% or 20\% for forward- error correction depending on the individual sub-channel quality after fiber transmission

Performance investigation of 112 Gb/s PDM-QPSK long-haul systems employing discrete mode lasers

International audience100-Gb/s coherent systems based on polarization-division multiplexed quadrature phase shift keying (PDMQPSK), with aggregate wavelength-division multiplexed (WDM) capacities approaching 10 Tb/s per fibre, are being widely deployed due to the benefits provided by coherent detection. The stringent linewidth requirements for lasers used in these systems only allow optical sources with certain phase noise characteristics to be employed. A major challenge is therefore to produce lasers with the requisite performance at low cost. Discrete mode laser diodes (DMLDs) can be designed for narrow linewidth emission and present an economic approach with a focus on high volume manufacturability of monolithic semiconductor lasers. In this paper the performance of a 112 Gb/s long-haul optical transmission system employing PDM-QPSK is investigated using a range of transmitter lasers with linewidth values ranging from 100 kHz to 5 MHz. A linewidth of 100 kHz was obtained from an external cavity laser (ECL) and linewidths ranging from 200 kHz to 5 MHz were obtained from DMLDs. The performance of the system is analysed through experimental measurements and simulations performed by Virtual Photonics Incorporated Transmission Maker (VPI™). Results are presented for back-to-back operation and after transmission through G.654 pure silica core fibre (PSCF) at distances up to 6930 km

5G wireless and wired convergence in a passive optical network using UF-OFDM and GFDM

The provision of both wireless and wired services in the optical access domain will be an important function for future passive optical networks (PON). With the emergence of 5th generation (5G) mobile communications, a move toward a dense deployment of small cell antenna sites, in conjunction with a cloud radio access network (C-RAN) architecture, is foreseen. This type of network architecture greatly increases the requirement for high capacity mobile fronthaul and backhaul links. An efficient way of achieving such connectivity is to make use of wavelength division multiplexed (WDM) PON infrastructure where wireless and wired services may be converged for distribution. In this work, for the first time, the convergence of 5G wireless candidate waveforms with a single-carrier wired signal is demonstrated in a PON. Three bands of universally filtered orthogonal frequency division multiplexing (UF-OFDM) and generalized frequency division multiplexing (GFDM), are transmitted at an intermediate frequency in conjunction with a digital 10Gb/s pulse amplitude modulation (PAM-4) signal in the downlink direction. Orthogonal frequency division multiplexing (OFDM) is also evaluated as a benchmark. Results show, for each waveform, how performance varies due to the 5G channel spacing - indicating UF-OFDM's superiority in terms of PON convergence. Successful transmission over 25km of fibre is also demonstrated for all waveforms

Converged wired and wireless services in next generation optical access networks

5G communications will require the effective transmission of new radio signals through fiber networks, in order to facilitate the proliferation of antenna sites as well as greater pooling of resources. Next generation optical access networks can provide an efficient platform for mobile x-haul. Techniques discussed in this paper shows how both wired and 5G wireless services may be converged over a single fiber infrastructure, and how optical networking can be harnessed in order to provide flexible millimeter-wave radio-over-fiber

25-Gb/s OFDM 60-GHz Radio Over Fiber System Based on a Gain Switched Laser

[EN] A 25-Gb/s OFDM 60-GHz radio over fiber (RoF) transmission system employing a gain switched DFB laser for millimeter-wave generation is demonstrated. Transmission performance below the 7% FEC limit is achieved over 50 km of fiber initially by employing precompensation. This precompensation overcomes phase noise caused by the optical phase decorrelation induced by chromatic dispersion on the two optical channels separated by 60 GHz. An externally injected gain switched laser is subsequently employed to eradicate the need for the precompensation, thus reducing phase noise and increasing the tolerance to the induced time delay between the optical tones. Transmission performance below the 7% limit is achieved over 25 km of fiber with 2-m wireless transmission in this case.This work was supported by the Higher Education Authority through PRTLI 4 and 5, the International Centre for Graduate Education in Micro- and Nanoengineering, and Science Foundation Ireland through the following programs: Principle Investigator under Grant 09/IN.1/I2653, CTVR under Grant 10/CE/I1853, and IPIC under Grant 12/RC/2276.Martin, EP.; Shao, T.; Vujicic, V.; Anandarajah, PM.; Browning, C.; Llorente, R.; Barry, LP. (2015). 25-Gb/s OFDM 60-GHz Radio Over Fiber System Based on a Gain Switched Laser. Journal of Lightwave Technology. 33(8):1635-1643. doi:10.1109/JLT.2015.2391994S1635164333

Chromatic dispersion-induced optical phase decorrelation in a 60 GHz OFDM-RoF system

We propose and demonstrate a 25-Gb/s 16-quadrature amplitude modulation orthogonal frequency division multiplexing 60-GHz radio over fiber transmission system based on a gain-switched optical comb source. The impact of the phase noise caused by the optical phase decorrelation due to the chromatic dispersion is theoretically studied and experimentally investigated by employing a high linewidth comb source and transmitting over a 50-km standard single-mode fiber reel. A time delay precompensation is deployed based on the study of phase noise in order to reduce the phase noise impact, and thereby improve system performance.This work was supported in part by the Science Foundation Ireland through the Principal Investigator Programme under Grant 09/IN.1/I2653 and Grant 10/CE/I1853 and in part by the Higher Education Authority PRTLI 4 INSPIRE Programs.Shao, T.; Martin, E.; Anandarajah, PM.; Browning, C.; Vujicic, V.; Llorente Sáez, R.; Barry, LP. (2014). Chromatic dispersion-induced optical phase decorrelation in a 60 GHz OFDM-RoF system. IEEE Photonics Technology Letters. 26(20):2016-2019. doi:10.1109/LPT.2014.2344314S20162019262