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     

Optical phase-locked PSK heterodyne experiment at 4 Gb/s

A 4 Gb/s phase-locked optical PSK (phase shift keying) heterodyne communication system is demonstrated. The receiver was implemented with a single 100-Ω loaded p-i-n photodiode and a 1320-nm diode-pumped miniature Nd:YAG laser as a local oscillator. For a 2⁷-1 PRBS (pseudorandom bit sequence), the receiver sensitivity was -34.2 dBm or 631 photons/bit. The corresponding power on the surface of the detector was -37.3 dBm or 309 photons/bit. With a 2¹⁵-1 PRBS, a 2.6 dB additional sensitivity degradation was observed due to the nonideal frequency response of the phase modulator and the receiver amplifiers     

560 Mb/s optical PSK synchronous heterodyne experiment

A phase-locked optical heterodyne receiver constructed using a 1320-nm diode-pumped miniature Nd:YAG ring laser is discussed. Using this receiver and a transmitter based on another Nd:YAG laser, a 560-Mb/s phase-shift keying (PSK) synchronous heterodyne transmission was demonstrated over 78 km of single-mode fiber. With an optical phase-locked loop (PLL) natural frequency of 32 kHz and a damping factor of 1.46, the receiver sensitivity, measured at the output of the transmission link, was -48.7 dBm, or 159 photons/b. The corresponding detected sensitivity, measured on the surface of the p-i-n diode, was -51.8 dBm or 78 photons/b. This result suggests that the receiver sensitivity would have been about 82 photons/b if a balanced receiver with 0.2-dB excess coupler loss had been used. The impact of the finite intermediate frequency (IF) on heterodyne system performance was investigated; it was found that an IF of at least twice the bit rate is needed for a negligibly small penalty     

High receiver sensitivity at 10 Gb/s using an Er-doped fiber preamplifier pumped with a 0.98 mu m laser diode

The authors report the realization of an extremely high receiver sensitivity at 10 Gb/s by using an erbium doped fiber (EDF) preamplifier pumped with a 0.98 mu m laser diode. The obtained EDF input sensitivity is -37.2 dBm (147 photons/bit). In addition, the importance of minimizing reflection from amplifier fiber ends is shown.<>     

High-sensitivity two-stage erbium-doped fiber preamplifier at 10Gb/s

An optical preamplifier with a record sensitivity of -38.8 dBm (102 photons/bit) at 10 Gb/s has been demonstrated. When the amplifier is employed in a practical link without an input isolator, the sensitivity is only slightly degraded to -37.6 dBm (135 photons/bit) by input coupling losses and feedback due to Rayleigh backscattering in the transmission fiber. It is predicted that this penalty can be reduced to 0.15 dB with an improved isolator in the composite EDFA     

A 10 Gb/s high sensitivity, monolithically integrated p-i-n-HEMToptical receiver

A high-sensitivity, monolithically integrated optical receiver, composed of a p-i-n-PD and high electron mobility transistors (p-i-n-HEMTs) is described. The receiver sensitivity is -17.3 dBm at a bit error rate of 1×10^-9 for a 10-Gb/s non-return-to-zero (NRZ) lightwave signal. This value is the best result yet reported for 10-Gb/s monolithically integrated receivers. The sensitivity is -30.6 dBm if an erbium-doped fiber amplifier (EDFA) is placed ahead of the p-i-n-NEMT receiver. A transmission experiment using a 150-km dispersion-shifted fiber (DSF) indicates no degradation in the bit error rate characteristics or the eye pattern. This verifies the practicality of the p-i-n-HEMT optical receiver for high-speed transmission systems     

An optical PSK homodyne transmission experiment using 1320 nmdiode-pumped Nd:YAG lasers

A second-order optical phase-locked loop was constructed using 1320-nm diode-pumped miniature Nd:YAG ring lasers. Using the loop, a 140-Mb/s PSK homodyne transmission experiment was demonstrated over 28.6 km of single-mode fiber. With a loop natural frequency of 13 kHz and a damping factor of 0.6, the receiver sensitivity was -62.8 dBm, or 25 photons/bit. The authors believe this is the highest sensitivity obtained to date with any optical communication system     

A high-performance optical receiver for 622 Mb/s direct-detectionsystems

A report is presented on the measurement of receiver sensitivity and noise characteristics of a high-performance optical receiver using a low-noise InGaAs avalanche photodiode (APD) and a low-noise high-electron mobility transistor (HEMT). At a bit rate of 622.08 Mb/s and a wavelength of 1.297 μm, the measured receiver sensitivity is -48.3 dBm. This is equivalent to a sensitivity of 155 photons/b and is about 12 dB away from the quantum limit of 10 photons/b     

1 Gbit/s PSK homodyne transmission system using phase-lockedsemiconductor lasers

Homodyne detection of 1 Gb/s pilot-carrier (BPSK) optical signals using phase-locked 1.5 μm external-cavity semiconductor lasers is discussed. After 209 km fiber transmission of a 2¹⁵-1 pseudorandom binary sequence (PRBS), the measured receiver sensitivity is 52.2 dBm or 46 photons/bit. Experimental evidence of the data-to-phase-lock crosstalk that potentially limits the usable ratio of linewidth to bit rate in pilot-carrier PSK homodyne systems is presented     

High-sensitivity receiver optical preamplifiers

High-receiver sensitivities of -40.9, -44.3, -46.2, -49.0, and -51.3 dBm are reported at 2.4, 1.8, 1.2, 0.62, and 0.14 Gb/s, respectively, using a low-noise, 980-nm diode-pumped, erbium fiber amplifier in the receiver preamplifier configuration with all field usable components. This corresponds to a best sensitivity of 156 photons/bit at the input of the optical amplifier (96 photons/bit at the input of the erbium-doped fiber). Selection of a low-chirp laser-diode transmitter, an optical filter with a bandwidth appropriate for filtering the signal, and a low-noise electrical amplifier with appropriate bandwidth in the post detection stage are all critical to achieve very high-receiver sensitivities     

High-sensitivity direct-detection receiver with a 1.5 ?m optical preamplifier

A 1.5 ?n optical preamplifier was used to improve the sensitivity of a PINFET receiver by 12dB. The resonant optical amplifier provided 17dB of fibre-to-fibre gain including coupling losses in an isolator and a narrowband optical filter. The achieved sensitivity, -45.6 dBm at 500 Mbit/s, or 420 photons/bit, is the best reported for any direct-detection receiver and a factor of two better than previous results using optical amplifiers. However, the results are virtually identical to the best APD receiver results.     

REAP: recycled erbium amplifier pump

We report a novel erbium doped fiber preamplifier design with a combination of high gain (>40 dB) and low noise figure (3 dB) at 1556 nm for 80 mW of 980 nm pump power. The co-directional single pumped amplifier employs a composite two stage arrangement in which the second stage is pumped with recycled pump not used in the first stage. In addition, we contrast the amplifier performance trade-offs with the insertions of an isolator or a band pass filter or both in between the two amplifier sections. Finally, we demonstrate a receiver sensitivity of -37 dBm (156 photons/bit) with a 10 Gb/s optical preamplifier regenerator     

Optimum system parameters for multigigabit CPFSK optical heterodynedetection systems

To obtain a multigigabit continuous-phase frequency-shift-keying (CPFSK) system with a high receiver sensitivity, we theoretically and experimentally investigated the optimum modulation index parameter and IF center frequency, considering the modulation and demodulation baseband widths and the IF bandwidth. In a 6-Gb/s CPFSK experiment, we achieved a receiver sensitivity of -41.6 dBm, or 89 photons/bit. To use the 4- to 13-GHz IF band efficiently, we set the IF center frequency f _IF to 8.7 GHz, or 1.45 times the bit rate. To compensate for the insufficient 5-GHz FM-modulation bandwidth in the transmitter, we set the modulation index parameter β to 1.38, that is, a modulation index m of 0.8     

Rayleigh scattering influence on performance of 10 Gb/s opticalreceiver with Er-doped optical fiber preamplifier

The achievement of -30.8 dBm (630 photon/bit) receiver sensitivity at 10 Gb/s, with an Er³⁺-doped optical fiber preamplifier, is discussed. This is an 8.3-dB sensitivity improvement over the avalanche-photodiode/FET receiver. Power penalties caused by a noise increase due to Rayleigh backscattering by the transmission optical fiber have been evaluated. Approximately -30-dB Rayleigh scattering from a 20-km optical fiber resulted in a 3.5-dB power penalty for a 25-dB-gain optical amplifier     

2．4Gb／s50kmMach－Zehnder外调制／直接检测型光纤传输系统

本文介绍了国内首次利用国产Ｍａｃｈ－Ｚｅｈｎｄｅｒ型Ｔｉ：ＬｉＮｂＯ３外调制器进行２．４Ｇｂ／ｓ伪随机码信号光纤传输的系统实验。经过５０．７ｋｍ传输后接收机灵敏度为－３０．３ｄＢｍ。     

Practical implementation of a highly sensitive receiver using an erbium-doped fiber preamplifier

A practical erbium-doped fiber preamplified direct detection receiver is demonstrated with which receiver input sensitivities of -46.5 dBm at 622 Mb/s and -40.7 dBm at 2.3 Gb/s have been achieved. There is no penalty from the transmission fiber Rayleigh backscattering. The bit error ratio measurements with 2/sup 23/-1 NRZ PRBS (pseudorandom bit sequence) show highly stable characteristics with no apparent error floor, owing to the polarization insensitivity of the preamplifier and to an active locking of the receiver optical filter. The tradeoff between preamplifier and avalanche gain is shown, and the influence of optical filter bandwidth and decision threshold setting is measured.<>     

10 Gbit/s optical PSK homodyne transmission experiments using external cavity DFB LDs

10 Gbit/s optical PSK homodyne transmission experiments using a modified decision-driven optical phase locked loop with 1.55 mu m external cavity laser diodes were conducted. A receiver sensitivity of -34.2 dBm or 297 photon/bit was experimentally achieved. There was no degradation in receiver sensitivity after signal transmission through 151 km of dispersion shifted fibre.<>     

Over 300 km CPFSK transmission experiment using 67 photon/bit sensitivity receiver at 2.5 Gbit/s

A nonrepeated fibre transmission experiment over 308 km of conventional optical fibre is reported at 2.5 Gbit/s in a CPFSK heterodyne detection system. The system has a sensitivity of -46.7 dBm or 67 photons/bit at 10/sup -9/ BER and has the maximum allowable attenuation of 55.1 dB without an optical amplifier.<>     

1 Gbit/s bipolar optical FSK transmission experiment over 121 km offibre

Bipolar direct modulation has been used to overcome the nonuniform low-frequency modulation response of a DFB laser transmitter in a 1 Gbit/s optical FSK transmission system. The heterodyne receiver sensitivity (nP¯) was -39 dBm for a 2²³-1 bit pseudorandom pattern, with no degradation in receiver sensitivity after transmission through 121 km of fibre     

Receiver Design for Digital Fiber Optic Transmission Systems Using Manchester (Biphase) Coding

An analysis of the sensitivity of an optical receiver in a digital communication system using Manchester (biphase) coding is performed. Both cases of p-i-n and avalanche photodiodes are considered. Experimental results for the sensitivity of a Manchester receiver operating at 250 Mbits/s are reported. Two types of low noise receiver amplifiers, namely the high impedance and the transimpedance amplifier, are designed and implemented for use in the receiver. A receiver sensitivity of -49.8 dBm in terms of detected optical power is obtained (at a 10^-9bit error rate and 0.1 laser extinction ratio), which corresponds to only 175 average photons per bit. It is shown that in contrast to the NRZ code, the Gaussian approximation theory tends to underestimate the Manchester receiver sensitivity. Tradeoffs between Manchester and NRZ coding are also discussed in terms of receiver sensitivity and ease of implementation. It is shown that Manchester coding is an attractive alternative to NRZ coding for optical transmission systems, particularly when an avalanche photodiode is used.