Bidirectionally pumped optical amplifier

An optical amplifier (200) comprises an active fiber (201), a first pump source (202) and a second pump source (203). The amplifier further comprises a first and a second coupling device (210, 211) having at least two input ports and at least two output ports. Said first and second coupling devices, said first and second pump sources and said active fiber are connected in such a manner as: the first input ports of said first and seconed coupling devices are connected to said first and second pump sources, respectively; the first output ports of said first and second coupling devices are connected to a first and a second end of said active fiber, respectively; the second output port of said first coupling devices is connected to the second input port os said second coupling device; the second output port of said second coupling device is connected to the second input port of said first coupling device

Bidirectionally pumped optical amplifier

An optical amplifier (200) comprises an active fiber (201), a first pump source (202) and a second pump source (203). The amplifier further comprises a first and a second coupling device (210, 211) having at least two input ports and at least two output ports. Said first and second coupling devices, said first and second pump sources and said active fiber are connected in such a manner as: the first input ports of said first and seconed coupling devices are connected to said first and second pump sources, respectively; the first output ports of said first and second coupling devices are connected to a first and a second end of said active fiber, respectively; the second output port of said first coupling devices is connected to the second input port os said second coupling device; the second output port of said second coupling device is connected to the second input port of said first coupling device

16x125 Gb/s Quasi-Nyquist DAC-Generated PM-16QAM Transmission Over 3590 km of PSCF

We report on a transmission experiment over high-performance pure silica core fiber (PSCF) of 16 Nyquist wavelength-division-multiplexed (Nyquist-WDM) channels at a symbol rate of 15.625 GBaud, using polarization-multiplexed (PM) 16 symbols quadrature amplitude modulation (16QAM), resulting in a per-channel raw bit rate of 125 Gb/s. The channel spacing is 16 GHz, corresponding to 1.024 times the symbol rate. The interchannel crosstalk penalty is drastically reduced through the confinement of the signal spectrum within a near-Nyquist bandwidth, achieved with digital filtering and digital-to-analog converters (DACs) operating at 1.5 samples/symbol. The optical line is a recirculating loop composed of two spans of high-performance PSCF with erbium-doped fiber amplifiers only. The transmission distance of 3590 km at a target line bit-error rate (BER) of 1.5 10^-2 is achieved at a raw spectral efficiency (SE) of 7.81 b/s/Hz. Assuming a commercial hard forward error correction with 20.5% redundancy, capable of handling the target BER, the net SE is 6.48 b/s/Hz, the highest so far reported for multithousand kilometer transmission of PM-16QAM at ≥ 100 Gb/s per channel. These results demonstrate the feasibility of very high SE DAC-enabled ultra-long-haul quasi-Nyquist-WDM transmission using PM-16QAM with current technologies and manageable digital signal processing complexit

Experimental Investigation of Nonlinear Interference Accumulation in Uncompensated Links

Noise due to nonlinear effects in uncompensated links has recently been shown to be Gaussian and additive. We experimentally investigate the law governing its accumulation. Our results suggest a mild super-linear accumulation versus number of spans, compatible with coherent accumulation model

Multilevel Nyquist-WDM Ultra-Long-Haul Coherent Optical Transmission Systems

The continuous expansion of multimedia terminals, like smart-phones, besides the introduction of new multimedia services, like the high-definition streaming television, determines a constant increase in the demand of high-speed connectivity. This scenario requires a permanent update of the data capacity in local access networks. Nevertheless, a proper capacity upgrades plan, with new optical links deployment, has required for back-bone optical networks in order to avoid possible networks congestions. Such effect has theoretically forecast as probable in actual networks within next few tenths years, particularly in US if some network segments will reach their saturation. Nowadays, the most promising technology for future optical communication networks has proven to be coherent detection. Rather than intensity modulation direct detection systems, such solution enables to implement new multilevel transmission systems, allowing a more efficient use of the optical transmission bandwidth. These novel coherent optical communication systems have been made possible thanks to the availability of high-speed (gigabit-per-second) analog and digital opto-/electronic devices. Such new devices have allowed the introduction of real-time digital signal processing (DSP) in coherent receivers, so overcoming the practical limitations that were experienced in coherent optical system experiments in the early 1990s. In this thesis, four main topics have been investigated to assess the feasibility and behaviour of spectrally efficient multichannel coherent optical communication systems for the highest data channel capacity in ultra-long-haul links. More in details, Nyquist filtered multilevel optical modulation formats (QPSK, 8QAM and 16QAM) have been investigated as candidates for the efficient transmission of information (toward the Shannon limit). Wavelength division multiplexed (WDM) systems assembled with these modulation formats have proven to support high spectral efficiency for data transmission over distances ranging from 3000~km to 10000~km. Besides the report of state-of-the-art transmission experiments, some practical and theoretical limitations have been discussed to motivate choices for laboratory experimental solutions as well as devices characteristics, DSP parameters, etc. The introduction of a novel mathematical model, accounting for non-linear interference (NLI) accumulations in optical lines optimized for systems based on coherent detection, has required an experimental validation through ad-hoc Nyquist-WDM transmission experiments. Reliability of the NLI model in performance predictions, enables to derive analytical expressions of transmission quantities as: the Figure of Merit of optical fibers, the non-linear channel capacity, etc. Furthermore, a simulative study to investigate the potentiality of a digital back-propagation (DBP) technique has been performed. The application of a digital non-linear compensation technique to data of a Nyquist-WDM transmission experiment has been carried out. Such analysis confirmed a loss in efficiency of DBP based on single channel processing to improve transmission distance in ultra-dense WDM systems as Nyquist-WDM. Finally, a simulative study about the polarization dependent loss (PDL) impact on system performances has been reported. Results from this analysis have justified the introduction in the DSP of the coherent receiver algorithms for the continuous channel parameters monitor. This DSP upgrade allowed to improve and speed-up laboratory measurements. The thesis is organized as follows: in the first chapter, it is reported a brief review of motivations, advantages and drawbacks in reintroducing coherent detection based systems in optical networks. Thereafter, novel DSP-based coherent optical systems are briefly introduced with some references about DSP algorithms reported in Appendix A. Theoretical foundations about the application of Nyquist theory to achieve ultra-dense WDM systems are reported in the second chapter. Chapters three to six have been dedicated to separately report each of the four investigated topics mentioned above. The final chapter contains a conclusive analysis, and it has followed by a reference bibliography and a complete list of the papers published within the three-year PhD period (2010-2012

Digital signal processing for FDMA-PON: Evaluation of processing complexity of three different architectures

In this paper, we present an estimation of the digital signal processing (DSP) computational complexity for some specific optical line terminal (OLT) architectures for passive optical network (PON) applications, based on electrical frequency division multiplexing (FDM) of user data channels. The complexity and feasibility estimations is a key task in any DSP based transmission solution investigation also in relation to cost constraints, which are much tighter for PONs than for many other optical transmission applications. We derived the DSP complexity of three different architectures implementing frequency division multiple access (FDMA) and orthogonal frequency division multiple access (OFDMA) transmission systems, and we discussed them with respect to the today available application-specific integrated circuit (ASIC) and field-programmable gate array (FPGA) technologie

Temperature Dependent Dynamic Gain Tilt in EDFAs

A “black box” model for the EDFAs’ prediction of the spectral gain change due to temperature variations is described and experimentally verified. The model is based on a dynamic gain tilt technique and predicts the amplifier spectral gain curve shape at any temperature starting from the measurement of the gain curve shape at two different temperature values. The proposed temperature model is also tested over a laboratory submarine line composed of real amplifier units