40 Gbit/s straight-line RZ data transmission over 240 km ofstandard fibre

The authors report straight-line single-channel 40 Gbit/s RZ data transmission over 240 km of standard fibre with periodic dispersion compensation. To the authors' knowledge, this is the longest transmission distance reported in a straight-line transmission experiment, at 40 Gbit/s without any precoding. The back-to-back receiver sensitivity of the system was 18.9 dBm for a BER of 10^-9 . Transmitting data over 240 km of fibre induced a sensitivity penalty of 0.4 dB for a BER of 10^-9     

Demonstration of 20 Gbit/s subcarrier multiplexed transmissionsystem

A 20 Gbit/s subcarrier multiplexed (SCM) optical transmission system is presented. To date, this represents the highest aggregate bit rate SCM transmission that has been demonstrated. Results show that the bit error rate (BER) is less than 10^-12 for a link loss of 29.5 dB, which corresponds to 118 km single mode fibre (SMF). Furthermore, excellent performance is demonstrated after transmission over 82 km of dispersion compensated SMF. Results suggest that the system can support transmission over multiple spans of optical fibre     

Gigabit/s optical receiver sensitivity and zero-dispersion single-mode fiber transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 μm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p+nn- Ge APD. The p+nn- Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55μm and a 10^-9error rate, which was 4 dB better than the receiving level with a p+n Ge APD. Detector performance at 1.3μm was also studied for comparison with performance at 1.55μm. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55μm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) . km at 1.55μm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3μm dispersion-free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.     

10Gbit／s级联光纤放大器通信系统的传输距离

本文数值模拟了强度调制光信号在级联光纤放大器常规ＳＭＦ通信系统中的传输,在模拟中主要考虑了自相位调制、群带色散和ＡＳＥ噪声。我们使用负色散补偿光纤去补偿群速色散和自相位调制。结果表明如果色散得到很好的补偿,当放大器的间距减少到５０ｋＭ时,无误码２０５０ｋｍ传输是可能的。     

BER fluctuation suppression in optical in-line amplifier systemsusing polarisation scrambling technique

The effectiveness of the polarisation scrambling technique for suppressing BER fluctuation is confirmed experimentally with a 2900 km optical in-line amplifier transmission system. The technique suppresses the BER fluctuation by three orders of magnitude, from 10^-5-10^-9 to 10^-810^-9     

Proton implanted VCSEL's for 3 Gb/s data links

Transverse single-mode and multimode intensity modulated butt-coupled InGaAs vertical cavity surface emitting lasers (VCSEL)s are investigated as a light source for optical fiber communication systems. Data transmission at 3 Gb/s with a bit error rate (BER) of less than 10 ^-11 is reported for both 4.3 km of standard fiber, as well as 0.5 km of multimode graded-index fiber, 10-μm active diameter single-mode VCSELs are shown to have lower mode competition noise requiring 3 dB and 6 dB less power at the front end receiver at a BER of 10^-11 compared to 19-μm and 50-μm active diameter devices, respectively. In data transmission with multimode VCSELs, the dispersion penalty is lower than for single-mode sources since the noise at the receiver is mainly determined by transmitter-mode competition noise     

40 Gbit/s return-to-zero transmission over 500 km of standard fibreusing chirped fibre Bragg gratings with small group delay ripples

A 40 Gbit/s return-to-zero transmission has been successfully achieved over 500 km using standard fibres (non-dispersion shifted fibre, singlemode fibre) and chirped fibre Bragg gratings (CFBG). CFBGs were fabricated with small group delay ripples, and error free transmission (BER <1×10^-12) was achieved using these CFBGs for dispersion compensation     

New method analyzing eye patterns and its application to high-speedoptical transmission system

An advanced method of analyzing eye patterns is proposed which plots the eye pattern as a function of the error rate. The method is applied to high-speed optical-transmission systems and its usefulness is confirmed. Degradation of eye opening due to noise and intersymbol interference is investigated quantitatively using the 10^-10 BER eye. An automatic gain-control system is evaluated from a viewpoint of eye margin, and a gain control system having an improved eye margin performance is proposed. Low-probability abnormal phenomena, such as turn-on fluctuations and mode partitioning in directly modulated distributed feedback (DFB) lasers, are observed using this method     

High-speed optical pulse transmission at 1.29-µm wavelength using low-loss single-mode fibers

Optical-fiber transmission experiments in the 1.3-μm wavelength region are reported. GaInAsP/InP double-heterostructure semiconductor laser emitting at 1.293 μm is modulated directly in nonreturn-to-zero (NRZ) codes at digit rates tanging from 100 Mbit/s to 1.2 Gbit/s. Its output is transmitted through low-loss GeO2-doped single-mode silica fibers in 11-km lengths. Transmitted optical signals are detected by a high-speed Ge avalanche photodiode. Overall loss of the 11-km optical fibers, including 11 splices, is 15.5 dB at 1.3 μm. Average received optical power levels necessary for 10^-9error rate are -39.9 dBm at 100 Mbit/s and -29.1 dBm at 1.2 Gbit/s. In the present system configuration, the repeater spacing is limited by loss rather than dispersion. It seems feasible that a more than 30 km repeater spacing at 100 Mbit/s and a more than 20 km even at 1.2 Gbit/s can be realized with low-loss silica fiber cables, whose loss is less than 1 dB/km. Distinctive features and problems associated with this experimental system and constituent devices are discussed.     

Remote-control signal of optical loopback for supervision of long-haul fiber-optic undersea cable systems

A remote-control signal for repeater supervision to be used in a remote-controlled optical loopback method of a long-haul optical undersea cable system is proposed on out-of-service basis and the results of its transmission experiment by a field trial system are theoretically analyzed. The remote-control signal is basically composed of a pseudo-random sequence with a periodicity corresponding to a repeater selection frequency. 500 repeater selection frequencies will be available using a monolithic crystal filter (MCF) as a detection filter. By a field trial experiment, the controllability was shown to be maintained even at a bit error rate (BER) of up to 10^-1with a control signal level which, being decreased by 1.9 dB, is still more than 30 dB over a filtered noise level due to random bit errors.     

A field demonstration of 1.7 Gb/s coherent lightwave regenerators

Four 1.7-Gb/s frequency-shift keying (FSK) coherent regenerators that were successfully operated in a typical field environment using installed fiber cables connected between Roaring Creek and Sunbury, PA (a distance of 35 km) are discussed. Each regenerator is housed in a standard AT&T repeater shelf and consists of five separate plug-in subsystem modules including a polarization diversity receiver, a FSK transmitter, and a cold-start automatic frequency control (AFC) circuit. During one month of continuous operation, the received optical powers for 10^-9 bit error rate (BER) were between -38 and -40 dBm. An error rate below 6×10^-15 (less than one error per day) was achieved at received optical powers of -33~-35 dBm     

Fiber-optic transmissions of microwave 8-phase-PSK and 16-aryquadrature-amplitude-modulated signals at the 1.3-μm wavelengthregion

Transmissions of a 6-GHz 8-phase phase-shift-keyed (8φ-PSK) signal over a 12.5-km single-mode fiber with a 5-dB power margin and bit-error-rate (BER) of 10^-10 and a 6-GHz 16-ary quadrature-amplitude-modulated (QAM) signal over the same distance with a 2-dB power margin and BER of 10^-12 were demonstrated. The 8φ-PSK digital modem operated at 78Mb/s and the 16-QAM digital modem operated at 90 Mb/s. A high-speed multimode InGaAsP laser diode and a high-speed p-i-n diode were used in both fiber-optic transmission systems. Floor characteristics and power penalties observed in the BER performances of both systems were found to be caused by the intensity noise of the laser diode, particularly the reflection-induced intensity noise     

Self-phase modulation and dispersion in high data rate fiber-optictransmission systems

The theoretical transmission limits imposed by the interaction of first- and second-order group velocity dispersion and intensity-dependent self-phase modulation (SPM) effects for a range of wavelengths around the zero dispersion wavelength (λ₀) for fibers in which polarization dispersion is negligible are investigated. It is found that increasing the peak input power to 30 mW reduces the transmission distance for data rates greater than 50 Gb/s, if operating at wavelengths shorter than λ₀. Operating at wavelengths longer than λ₀ improves the performance due to the cancellation of first-order dispersion by self-phase modulation. For example, at 50 Gb/s and 30 mW peak input power, the maximum transmission distance is 255 and 162 km, if operating at wavelengths 1 nm longer or shorter than λ₀, respectively. Above 100 Gb/s, higher-order dispersion limits the transmission distance even at wavelengths equal to, or longer than, λ₀. Linear dispersion compensation using a grating-telescope combination can significantly improve system performance for wavelengths where first-order dispersion dominates     

Full-Field Electronic Dispersion Compensation of a 10 Gbit/s OOK Signal Over 4$,times,$ 124 km Field-Installed Single-Mode Fibre

We experimentally demonstrate the use of full-field electronic dispersion compensation (EDC) to achieve a bit error rate of 5times10^{- 5} at 22.3 dB optical signal-to-noise ratio for single-channel 10 Gbit/s on-off keyed signal after transmission over 496 km field-installed single-mode fibre with an amplifier spacing of 124 km. This performance is achieved by designing the EDC so as to avoid electronic amplification of the noise content of the signal during full-field reconstruction. We also investigate the tolerance of the system to key signal processing parameters, and numerically demonstrate that single-channel 2160 km single mode fibre transmission without in-line optical dispersion compensation can be achieved using this technique with 80 km amplifier spacing and optimized system parameters.     

256 QAM Modem for Multicarrier 400 Mbit/s Digital Radio

This paper describes the performance of a 256 QAM modem with 400 Mbit / s transmission capacity. A variety of novel techniques are introduced as ways to achieve good performance. Key techniques include 1) an accurate 256 QAM modulator employing a new monolithic multiplier IC, 2) a carrier recovery circuit which satisfies such requirements: good phase jitter performance and no false lock phenomenon, 3) a highly stable high-level decision circuit, and 4) a forward error correcting code. As an overall modem performance, BER characteristics and signatures are presented. The equivalent CNR degradations of 1 dB(at BER of 10^-4) and 2 dB (at BER of 10^-9)are obtained using a single Lee-error correcting code and a seven-tap baseband transversal equalizer. The residual bit errors are decreased below the order of 10^-10. The performance of a 256 QAM multicarrier modem has given prospect for the development of 400 Mbit/s digital microwave radio system.     

2.488 Gb/s-318 km repeaterless transmission using erbium-dopedfiber amplifiers in a direct-detection system

The authors have achieved a 2.488 Gb/s, 318 km repeaterless transmission without any fiber dispersion penalty through a nondispersion-shifted fiber in a direct detection system. The system was loss limited with a T-R power budget of 57 dB. Three key components enabled the authors to achieve this result: (1) a Ti:LiNbO₃ external amplitude modulator enabling a dispersion-free transmission, (2) erbium-doped fiber amplifiers increasing the transmitting power to +16 dBm, and (3) an erbium-doped fiber preamplifier enabling a high-receiver sensitivity of -4.1 dBm for 10^-9 BER. To the author's knowledge, this result is the longest repeaterless transmission span length ever reported for direct detection at this bit rate. From the experimental results and a theoretical model, the authors identified the sources of the receiver sensitivity degradation from the quantum limit (-48.6 dBm) and estimated the practically achievable receiver sensitivity of ~-44 dBm (~-124 photons/bit) for 2.5 Gb/s optical preamplifier detection     

Estimated performance of 2.488 Gb/s CPFSK optical non-repeateredtransmission system employing high-output power EDFA boosters

The configuration of a practical nonrepeatered coherent optical transmission system and its performance are reported. The practicability of combining continuous-phase frequency-shift keying (CPFSK) with erbium-doped fiber amplifier (EDFA) boosters is verified by laboratory and field experiments. A system gain of 60.8 dB is achieved at a BER at 10^-11; the EDFA's optical output power is +18 dBm and the receiver sensitivity is -42.8 dBm. The stimulated Brillouin scattering (SBS) effect is examined to estimate the dependence of error rate characteristics on the bit sequence length. No power penalty is observed for a pseudorandom bit sequence (PRBS) of more than 2⁵-1 or STM-16 patterns containing a 30-byte block of consecutive identical digits. The power penalty of 1.3 dB caused by the 310-km non-dispersion-shifted transmission fiber is successfully compensated by installing a chromatic dispersion compensator in each orthogonal polarization branch. During a four month field experiment, error-free operation was observed over a 30 day period, and the long-term error rate is under 6×10^-16     

Gigabit/s Optical Receiver Sensitivity and Zero-Dispersion Single-Mode Fiber Transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 µm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p/sup +/nn/sup -/ Ge APD. The p/sup +/nn/sup -/ Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55 µm and a 10/sup -9/ error rate, which was 4 dB better than the receiving level with a p/sup +/n Ge APD. Detector performance at 1.3 µm was also studied for comparison with performance at 1.55 um. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55 µm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) /spl dot/ km at 1.55 µm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3 µm dispersion free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.     

Test Method for Measuring Bit Error Rate of Pulsed Transceivers in Presence of Narrowband Interferers

The popularity of pulse-based transceivers can be attributed to the high information rates that can be achieved in such systems compared to traditional narrowband systems. However, such systems are usually low-power and transmission efficiency is severely affected by the interference signals from other moderate to high-power narrowband transmitters. Hence, during manufacturing, pulse-based systems must be characterized and tested for bit error rate (BER) performance in the presence of narrowband interferers. Usually, at large interference levels, the BER is moderate (10^-4) to high (10^-2). However, at low interference levels when very few bits are in error, the BER is low (10^-6 - 10^-10 ) and testing for the BER becomes time consuming. We propose a new measurement technique employing sinusoidal pulses such that the BER value obtained is significantly large (10^-3 - 10^-4 ) even at low interference levels. BER values obtained using sinusoidal pulses are highly correlated to the actual BER values. Hence, the actual BER can be accurately estimated in a much smaller time without actually performing the standard test. This method was implemented in hardware using an Altera field-programmable gate-array development board. From the measurements, BER estimation error was less than 3%. In addition, significant reduction (up to 100 x) in test time was obtained using the proposed method.     

The influence of cross-phase modulation on optical FDM PSK homodynetransmission systems

A combination of optical frequency division multiplexing (FDM) and phase-shift-keying (PSK) homodyne detection can increase transmission capacity. However, phase sensitive transmission systems, especially repeatered ones, suffer from data-dependent optical amplitude fluctuation that is converted to phase fluctuation by fiber nonlinearity. The authors discuss how this data-dependent amplitude fluctuation affects the error rate performance of optical FDM PSK homodyne detection systems. If only the optical amplitude fluctuation induced by phase modulators is taken into account, the allowable power fluctuation to keep the power penalty at 0.5 dB at a bit error rate (BER) of 10^-10 is below 0.17 mW for BPSK homodyne detection and 0.09 mW for QPSK homodyne detection. However, if only the amplitude fluctuation induced by the fiber chromatic dispersion is taken into account, the allowable number of repeaters to keep a 0.5-dB power penalty due to XPM at a BER of 10^-10 is 1 for BPSK homodyne detection and below 5 for QPSK homodyne detection