L.D. Tzeng

Performance evaluation of waveguide phase modulators for coherent systems at 1.3 and 1.5 µm

This article describes the fabrication and performance evaluation of X -cut and Z -cut Ti:LiNbO 3 traveling wave waveguide phase modulators designed for coherent systems applications at 1.3 and 1.5 μm. Details of device fabrication and measurements of phase shift as a function of optical wavelength, input polarization, modulation voltage, and modulation frequency are reported. Phase modulator performance in a 40-Mbit/s self-heterodyne coherent DPSK experiment is also discussed.

A 5 Gb/s repeaterless transmission system using erbium-doped fiber amplifiers

A fully engineered 5 Gb/s repeaterless long-span transmission system with excellent long term performance is introduced. The transmitting power from an optical power booster was +15.5 dBm with SBS suppression, and an optical preamplifier receiver provided a receiver sensitivity of -38 dBm for 10/sup -9/ BER (or -35 dBm for 10/sup -15/ BER). A Ti:LiNbO/sub 3/ external modulator transmitter allowed dispersion limited repeaterless transmission through 226 km non-DSF (a total dispersion of 4100 ps/nm).<<ETX>>

2.488 Gb/s-318 km repeaterless transmission using erbium-doped fiber 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:LiNbO/sub 3/ 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/sup -9/ BER. To the authors 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 approximately -44 dBm ( approximately -124 photons/bit) for 2.5 Gb/s optical preamplifier detection.<<ETX>>

Effect of transmitter speed and receiver bandwidth on the eye margin performance of a 10-Gb/s optical fiber transmission system

We calculated the effect of the transmitter speed and receiver bandwidth on the electrical eye margin performance of a 10-Gb/s NRZ optical fiber transmission system. The transmitter under consideration used a 1.5 /spl mu/m DFB-laser externally modulated by a zero-chirp LiNbO/sub 3/ modulator with NRZ, 2/sup 7/-1 PRBS data. The receiver was a pin-diode based direct detection receiver. Main results are (1) near optimum system performance is achieved when the 10-90% rise/fall-time of the transmitter output is 40 ps, only small improvement is obtained by using faster speeds and, (2) the optimum bandwidth of the receiver is at 10 GHz (the baudrate) for both the back-to-back and the 120-km transmission configuration. Thus, the optimum receiver bandwidth is at the baudrate (10 GHz) which is in conflict with accepted practice which suggests approximately 0.6/spl times/ baudrate (6 GHz). The reason for this discrepancy is that we considered an optically amplified NRZ transmission system where the optical power level at the receiver input is well above the receiver sensitivity. Therefore, the impact of thermal noise is negligible and the system is dominated by ISI, which can be reduced by increasing the receiver bandwidth.

A high-sensitivity APD receiver for 10-Gb/s system applications

In this paper, we will report the performance of a high-sensitivity (-28.7 dB) avalanche photodiode (APD) receiver, constructed with a low-noise superlattice APD, for l0-Gb/s applications. This receiver sensitivity value is only about 4-5 dB away from that of a commercially realizable optical pre-amplifier receiver at this bit-rate. Using this receiver and a transmitter with an output optical power of only -4 dB, we are able to transmit data over 61 km of standard fiber, including system operational margins, without using any optical amplifiers.

Densely Spaced FDM Optical Coherent System With Near Quantum-Limited Sensitivity and Computer-Controlled Random Access Channel Selection

We report the results obtained with a densely spaced FDM coherent optical fiber star network utilizing monolithic frequency-tunable lasers to generate optical signals FSK at 200 Mb/s, which provides an optical receiver sensitivity of 74 photons/bit at a BER of 10-9 and random access channel selection by computer control of the receiver LO laser frequency. The results indicate that this system has the potential to provide a throughput of 2000 Gb/s.

Field demonstration of 10-Gb/s line-rate transmission on an installed transoceanic submarine lightwave cable

We report the successful field demonstration of 10 Gb/s NRZ line rate transmission on the installed TransPacific Cable (TPC-5) Segment G. Using prototype transmitters, receivers and a bit-synchronous 10-GHz polarization scrambler, we achieved long-term error-free transmission with a bit-error rate below 10 on a 4230-km-long installed fiber cable. We also obtained a bit-error-rate as low as 10/sup -15/ for 8460-km transmission. The measured Q-values for 4230-, 8460-, and 12 690-km transmission are 20, 16.5, and 12.5 dB, respectively.

1.3 mu m semiconductor laser power amplifier

The performance of a 3.4-Gb/s system using a low-power 1.318- mu m distributed-feedback (DFB) laser transmitter and a traveling-wave semiconductor laser power amplifier is studied. The -14.5-dBm, input from a directly modulated DFB laser is boosted to +10.3 dBm, of which +4.8 dBm is coupled into the transmission fiber. The penalty, caused by amplifier noise and pattern effects due to gain saturation, is less than 0.5 dB.<<ETX>>

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/sup -9/ bit error rate (BER) were between -38 and -40 dBm. An error rate below 6*10/sup -15/ (less than one error per day) was achieved at received optical powers of -33 approximately -35 dBm.<<ETX>>

Densely spaced FDM coherent optical system with random access digitally tuned receiver

The authors report the results obtained with a densely spaced FDM (frequency division multiplexing) coherent optical fiber star network utilizing monolithic frequency-tunable lasers to generate optical signals frequency-shift-keyed at 200 Mb/s, which provides an optical receiver sensitivity of 74 photons/b at a bit error rate of 10/sup -9/ and random access channel selection by a computer-controlled digitally tuned receiver. The demonstration system consists of six optical channels spaced by 2.2 GHz, the minimum frequency interval possible without adjacent channel interference. The channels are generated by multiple-quantum-well distributed-Bragg-reflector lasers operating at a wavelength of 1.53 mu m. These lasers provide a narrow linewidth (2-4 MHz) that is small enough for coherent detection application.<<ETX>>