Single Source Optical OFDM Transmitter and Optical FFT Receiver Demonstrated at Line Rates of 5.4 and 10.8 Tbit/s

A novel cost-effective combline generation and cross-talk mitigation in optical OFDM signal using optical iFFT circuits

“…The separated sub-carries were individually modulated employing MZ modulators with data rate equal to comb spacing of 12.5 Gbit/s NRZ signal. The optical modulators were followed by optical attenuators to equalize the power of individual comb lines and phase shifters were used to adjust phases between comb lines [9]. All the modulated comb lines were passively combined by using power combiner as shown in Fig 5. Therefore, the inherently coherent comb lines enable the generation of 87.5 Gbit/s OFDM signals.…”

Single- and multi-carrier techniques to build up Tb/s per channel transmission systems

“…It uses a mode locked laser with a highly nonlinear fibre as comb source to generate the unmodulated subcarriers in the transmitter and a low-complexity all-optical FFT circuit to demultiplex the tributary subchannels in the receiver [7]. This scheme has been demonstrated at OFDM channel net bit rates exceeding 8 Tb/s and has thus been proven to be scalable far beyond the Gb/s per channel regime [8]. There exist various all-optical FFT implementations [23,24], but the lowest complexity for an FFT of any order is achieved by using a cascade of AMZIs and an optical gate, possibly complemented by an optical filter to reduce the necessary FFT order [8].…”

“…This scheme has been demonstrated at OFDM channel net bit rates exceeding 8 Tb/s and has thus been proven to be scalable far beyond the Gb/s per channel regime [8]. There exist various all-optical FFT implementations [23,24], but the lowest complexity for an FFT of any order is achieved by using a cascade of AMZIs and an optical gate, possibly complemented by an optical filter to reduce the necessary FFT order [8]. In this way, an 8-point FFT has been successfully used to extract single subcarriers from a 75-subcarrier OFDM band for analysis [8].…”

“…Whilst analog electronic techniques, such as Kineplex [1] and the related DSP implementation OFDM [3] may theoretically achieve the theoretical maximum capacity of a channel, these techniques themselves do not overcome the electronic bottleneck, and must be combined with ultra-dense WDM, where optical comb generation is often employed to provide a stable channel spacing [4][5][6][7][8], to create Tb/s superchannels with high spectral efficiency. Such optical multiplexing techniques may clearly be employed using conventional modulation of subcarriers either in the time [9,10] or frequency domain [11][12][13][14].…”

“…In the frequency domain, such all-optical techniques may closely approach the capacity limits using matched filtering. This can be achieved by either using Nyquist filtering [13,14] or approximations to the channel orthogonality condition [1] using a one [11,12] or more [7,8] tap optical implementation of the discrete Fourier transform required for OFDM. Inevitably, the filters will not be perfectly matched, and in this case, control of the relative phases of adjacent subcarriers may alleviate any residual penalties [12].…”