Repeaterless Systems Research Articles

Finite-key analysis for memory-assisted decoy-state quantum key distribution

Memory-assisted quantum key distribution (MA-QKD) systems are among novel promising solutions that can improve the key-rate scaling with channel loss. By using a middle node with quantum storage and measurement functionalities, they offer the same key-rate scaling with distance as a single-node quantum repeater. However, the distance at which they can surpass the nominal key rate of repeaterless systems, in terms of bits per second, is typically long, owing to the efficiency and/or interaction time issues when one deals with quantum memories. This crossover distance can be a few hundred kilometres, for instance, when one relies on the exchange of infinitely many key bits for the key-rate analysis. In a realistic setup, however, we should account for the finite-key effects in our analysis. Here, we show that accounting for such effects would actually favour MA-QKD setups, by reducing the crossover distance to the regime where realistic implementations can take place. We demonstrate this by rigorously analysing a decoy-state version of MA-QKD, in the finite-key regime, using memory parameters already achievable experimentally. This provides us with a better understanding of the advantages and challenges of working with memory-based systems.

Analytical solution of transmission performance improvement in fiber spans with forward Raman gain and its application to repeaterless systems

A simple analytical expression for the optical signal-to-noise ratio (SNR) benefit expected from adding forward Raman gain to backward Raman gain in a fiber transmission span is derived. This result is then applied to modify the stimulated Brillouin scattering (SBS) threshold for the case of a signal experiencing forward Raman gain. These concepts are applied to demonstrate repeaterless transmission of 10 and 40 Gb/s data rates over standard single mode fiber (SSMF).

Locally-pumped repeatered and remotely-pumped repeaterless 1.55 [micro sign]m CATV video lightwave systems over 127 km standard singlemode fibre

1.55 /spl mu/m 80 channel AM CATV video lightwave systems are investigated using 1480 nm locally- and remotely-pumped amplified techniques far the first time. Satisfactory CNR performances of 45 dB with CSO/CTB of 61:70 dB are achieved for a locally-pumped repeatered system over a standard 127 km singlemode fibre. Based on the repeatered technique. System design and operation considerations of the remotely-pumped repeaterless system are also discussed. Repeaterless systems may find important applications for inter-islands and island-hopping with no active components allowed.

Bit-dependent degradation caused by stimulated Brillouin scattering in CPFSK coherent optical repeaterless systems with booster amplifiers

An interesting phenomenon due to stimulated Brillouin scattering (SBS) is experimentally found in a CPFSK heterodyne system with a booster amplifier. We find that the demodulated waveform amplitudes of just a few distinguished bits are strongly suppressed leading to a significant increase in BER. It is confirmed that the BER degradation can be reduced by adjusting the threshold voltage bias of the receiver decision circuit. >

Future Directions for Undersea Communications

Technologies used in undersea systems have changed radically in the last five years, driven primarily by the emergence of the erbium-doped fiber amplifier (EDFA). EDFAs have enabled long, transoceanic systems to offer significantly higher capacities (5 gigabits per second [Gbits/s] per fiber pair) and much longer lengths in repeaterless systems. The opportunities offered by EDFAs, combined with other technological advances, extend far beyond those used in currently planned systems. This paper describes the new technologies that are expected to play a role in future undersea systems, and the opportunities for applying those technologies.

Remote postamplifiers in repeaterless transmission systems

Three schemes for remotely pumping postamplifiers in a repeaterless system are investigated: Raman gain, Raman and EDFA, and separate fibre pumping of an EDFA. Using a dedicated pump fibre, 6 dB of budget improvement is predicted for 1000 mW of 1485 nm pump power. Experiments agree with the theoretical predictions within 0.75 dB.

Achievable budget improvement with Raman amplification and remotely pumped postamplification at transmit side of 622 Mbit/s and 2.5 Gbit/s repeaterless systems

This paper investigates Raman amplification and remotely pumped postamplification in repeaterless systems based on standard fiber. Design rules taking into account self phase modulation are presented along with the achievable power budget improvements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performace Evaluation of ASK and DPSK Optical Coherent Systems affected by Chromatic Dispersion and Polarization Mode Dispersion

We present theoretical estimates on performances of ASK and DPSK coherent systems employing optical fibers affected by both chromatic dispersion and polarization mode dispersion. Results of simulations in terms of error probability show that, at the same bit rate, repeaterless ASK systems are intrinsically less sensitive than DPSK systems to dispersion effects.

Bright prospects for erbium-doped fiber amplifiers in future lightwave communication systems

Abstract In the light of achievable component performance from both a theoretical and an experimental point of view, the applications of erbium-doped fiber amplifiers (EDFA) in long distance repeaterless digital transmission and analog cable TV distribution is discussed. In digital repeaterless systems, EDFA postamplifiers are capable of output powers over + 15 dBm; preamplifiers and remotely pumped amplifiers improve system budgets by more than 7 dB and 13 dB, respectively, when compared to a conventional APD (avalanche photodiode) receiver. In analog AM-VSB TV distribution networks, EDFA postamplifiers improve the power budget by more than 10 dB, and cascaded EDFA repeaters hold promise for power budgets over 35 dB, allowing large splitting ratios in the network.

1.7 Gb/s-419 km transmission experiment using a shelf-mounted FSK coherent system and packaged fiber amplifier modules

Experiments to assess the commercial viability of long-span FSK coherent systems with fiber amplifiers were performed. Transmission spans of 253, 365, and 419 km with integrated shelf-mounted modules have been demonstrated in repeaterless systems and in single-fiber and two-fiber amplifier repeatered systems, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Repeaterless undersea lightwave systems

A repeaterless undersea lightwave system connects two terrestrial locations separated by the sea without the need for undersea regeneration of the optical signal. To achieve the longest span length possible, the system combines terrestrial terminals containing superior-performance optoelectronic devices with ultrareliable undersea cable technology. The lightwave technology used to achieve cost-effective, long-span repeaterless undersea lightwave systems is discussed. This includes undersea fiber and cable, lasers and receivers, and terminal equipment. The first application of this technology, Taiwan's Tainan to Peng-Hu system, is described. The possibilities for increasing the maximum attainable span length of high-capacity repeaterless undersea systems are examined. Key elements are higher-output transmitters, more sensitive receivers, and improved optical fibers. >