A 2-Gbit/s optical FSK heterodyne transmission experiment using a 1520-nm DFB laser transmitter

Optical FSK transmission at 2 Gbit/s using a directly modulated DFB laser at 1520-nm wavelength is reported. A receiver sensitivity ofbar{P} = -36.7dBm (etabar{P} = -39.2dBm) at 10^-9BER was achieved for transmission over 101 km of single-mode fiber with no additional penalty attributable to the fiber. The effect of the nonlinear phase of the transmitter FM response, and the system performance for discriminator demodulation, including the impact of laser phase noise, is analyzed and compared with experimental results.     

116 photons/bit in a 565 Mbit/s optical DPSK heterodyne transmission experiment

A 565 Mbit/s DPSK heterodyne experiment is presented. A sensitivity of -50.0 dBm at the receiver input was achieved, which is the best reported value for this data rate. The experimental data match the theory within 1.4 dB.<>     

5 Gbit/s direct optical DPSK modulation of a 1530-nm DFB laser

5 Gb/s direct optical differential-phase-shift-keying (DPSK) modulation of a 1530-nm distributed feedback (DFB) laser is demonstrated using injection current modulation with a bipolar signal format. Delay demodulation is performed using an interferometer with a delay time T equal to the duration of one bit. The input and differentially encoded nonreturn to zero (NRZ) signals are shown. The bipolar modulation current signal is basically the time derivative of the NRZ signal. There was no degradation of the optical DPSK signal due to thermal frequency modulation of the laser. The direct DPSK modulation technique avoids the insertion loss and systems complexity of external DPSK modulators     

Direct modulation 565 Mb/s DPSK experiment with 62.3 dB loss spanand endless polarization control

Optical DPSK at 565 Mb/s is performed by direct modulation of a narrow-linewidth 1.5-μm SL-QW-DFB (strain layer-quantum well-distributed feedback) transmitter laser. The bipolar RZ drive signal has no DC component which allows penalty-free transmission of 2 ²³-1 bit patterns. The heterodyne receiver contains an endless polarization controller with <6.3 or >12 rad/s tracking speed, depending on the tolerable intensity loss. A loss span of 62.3 dB is achieved,without degradation due to stimulated Brillouin scattering     

1.4 Gbit/s optical DPSK heterodyne transmission system experiment

The authors report the performance of a 1.4 Gbit/s differential phase shift keying (DPSK) coherent fibre system experiment using a balanced receiver. They show that the detection sensitivity as a function of local oscillator power follows the same functional dependence as the theoretical prediction     

565 Mbit/s optical DPSK and PSK heterodyne transmission experiment using Nd:YAG lasers at 1.3 mu m

A 565 Mbit/s optical DPSK and PSK transmission experiment is described. Stable monolithic Nd:YAG ring lasers were used as light sources. A PSK demodulation scheme achieved a receiver sensitivity of -53.4 dBm and was found to be 1.3 dB better than DPSK.<>     

Long-span optical FSK heterodyne single-filter detection transmission experiment using a phase-tunable DFB laser diode

High receiver sensitivity (?51.9 dBm) and long span (243 km) transmission expriments have been achieved with a 140 Mbit/s optical FSK heterodyne single-filter detection system, using a phase-tunable DFB laser diode as a transmitter. This has enabled direct FSK modulation without waveform distortion. Also, a 280 Mbit/s 204 km transmission experiment has been carried out successfully.     

200 Mbit/s DPSK heterodyne transmission experiment using colour centre lasers at 2.55 mu m

A 200 Mbit/s DPSK heterodyne transmission experiment has been performed using colour centre lasers operating at 2.55 mu m wavelength for the first time. The minimum received power was 14 dB better than with the previously reported 400 Mbit/s IM-DD system.<>     

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     

FSK heterodyne system experiments at 1.5 ?m using a DFB laser transmitter

140 and 70 Mbit/s FSK heterodyne system experiments are reported using single-filter detection with transmitter laser linewidths of 30 and 60 MHz. The system requirements that must be satisfied to avoid large performance penalties are considered.     

565 Mbit/s 219 km transmission experiment using four gain controlled packaged semiconductor laser amplifiers

A 565 Mbit/s 219 km optical transmission system is investigated, using four gain controlled travelling wave semiconductor laser amplifier packages. The addition of gain control caused little deterioration in system performance, and allowed stable operation against changes in signal polarisation and device temperature. Residual system output power fluctuations of less than 0.5 dB were observed over a 7 degree temperature range.<>     

Balanced phase diversity receiver in 565 Mbit/s DPSK transmission system

565 Mbit/s DPSK optical transmission experiments with a balanced phase diversity receiver are reported. by employing a bulk optical 90 degrees hybrid in the input stage and a silicon bipolar multiplier IC in the demodulator and AFC stages, a system with a receiver sensitivity of -48.5 dBm and long-term stability was realised.<>     

Laser diode pumped Er3+-doped fiber amplifier in a 565Mbit/s DPSK coherent transmission experiment

A laser-diode-pumped erbium-doped fiber amplifier, exhibiting 9-dB gain, has been operated as an in-line optical repeater in a 565-Mb/s coherent optical communications system. A sensitivity penalty of 0.4 dB was observed when the amplifier was positioned 35 dB away from the receiver, thus indicating a system improvement of 8.6 dB. By progressively reducing the coupling loss between amplifier and receiver, the noise figure of the contradirectionally pumped amplifier was calculated to be 5.4 dB, a value which is consistent with simple noise theory     

1.8 Gbit/s 65 km optical transmission experiment using a 1.478 ?m DFB laser and Ge APD receiver

A 1.8 Gbit/s optical transmission system trial has been conducted over 65 km of conventional monomode fibre using a 1.478 ?m DFB laser and p+n Ge APD receiver. Using a 215 ?1, NRZ, PRB test sequence, a long-term BER of 2×10?10 was achieved. Dispersive effects introduced a 1 dB penalty after 65 km transmission.     

279 km, 591 Mb/s direct detection transmission experiment usingfour in-line semiconductor optical amplifiers

The authors realized a direct detection intensity-modulation system experiment with four cascaded in-line semiconductor optical amplifiers. Using optical isolators between the amplifiers, they transmitted a NRZ 2²³-1 message over a distance of 279 km at a bit rate of 591.2 Mb/s. A comparison of this result with parallel experiments without optical isolators indicates that for a realistic implementation of long distance systems with semiconductor optical amplifiers, interamplifier optical isolators will be needed unless the residual facet reflectivity of the optical amplifiers is brought to a very low value (<1×10^-4)     

Spectral characteristics of a DFB laser under high-speed direct modulation

Characteristics of a DFB laser under high-speed direct modulation are studied with an emphasis on the spectral analysis. A stable single-longitudinal-mode oscillation was confirmed up to 8.4 GHz direct modulation. The possibility of reducing the frequency chirping by device parameter optimisation is predicted on the basis of the experimental results obtained.     

Field demonstration of 565 Mbit/s DPSK coherent transmission systemover 176 km of installed fibre

Reports the results of a 565 Mbit/s coherent system field trial over 176 km of installed SM fibre. Fully automated endless polarisation control was employed using a novel method and error free operation was achieved with BER readings of better than 10^-13     

16 Gbit/s transmission experiments using a directly modulated 1.3μm DFB laser

A 16 Gb/s electrically time-division-multiplexed lightwave link is discussed. The 16 Gb/s electronic signal was generated by multiplexing together eight copies of the 2-Gb/s pseudorandom sequence (length 2¹⁵-1) produced by a commercial BER test set. A 22-km transmission distance was achieved using a directly modulated, 1.3-μm wavelength DFB laser and a 50-Ω p-i-n receiver. Receiver sensitivity for a BER of 10^-9 was -2.0 dBm. The addition of an optical preamplifier required a more sensitive receiver to avoid saturation-induced distortion in the preamplifier. This was accomplished by reducing the 2-Gb/s word length to 24 b, thereby lowering the intersymbol interference penalty and effectively increasing the receiver sensitivity. Under these conditions, the optical preamplifier receiver sensitivity was -19 dBm, and a 64.5-km transmission was demonstrated     

1064 nm, 565 Mbits/s PSK transmission experiment with homodyne receiver using synchronisation bits

An optical 565 Mbit/s transmission system at 1064 with phase shift keying and homodyne detection using a new carrier recovery technique is presented. The phase error signal in the receiver is obtained by means of synchronisation bits. This method combines the advantages of the Costas loop with the simplicity of the pilot carrier technique.<>     

10 Gbit/s transmission over 69 km of non-dispersion-shifted singlemode fibre with CPFSK direct modulation of 1.55 mu m BH DFB laser

With low chirp direct modulation of a commercially available lambda =1.55 mu m BH DFB laser module at 10 Gbit/s, a transmission experiment over 69 km of non-dispersion-shifted singlemode fibre was successfully performed. The scheme is based on optical FM by modulation of the injection current with subsequent conversion into intensity modulation by means of a fibre Mach-Zehnder interferometer.<>