NRZ Transmission Research Articles

High-performance single-frequency fibre Fabry-Perot laser (FFPL) with self-injection locking

The characteristics are presented of a 5 mm long Er3+:Yb3+ fibre Fabry-Perot laser (FFPL) with self-injection locking by a fibre Bragg grating (FBG), and its high performance is demonstrated in a 10 Gbit/s NRZ transmission system. The laser produces a single frequency and single polarisation output, has a high output power exceeding 13 mW, a narrow linewidth of ~100 kHz, and low relative intensity noise (RIN) below –120 dB/HZ. A 10 Gbit/s NRZ transmission test demonstrates that the FFPL is useful as a signal source for optical fibre communications.

Marked increase in power margin through the use of dispersion-allocated soliton and evaluation of transmission characteristics using Q map: Comparison between D-A soliton, NRZ pulse, and RZ pulse at zero GVD

When fiber routes for optical soliton transmissions are dispersion allocated, higher order solitons cannot be formed even at power levels reaching the higher-order soliton power determined by the average dispersion, since the group velocity dispersion (GVD) in the individual fiber is large and the phase matching necessary to form higher-order solitons cannot be obtained. Therefore, solitons with intensity higher than that of N = 1 can still be propagated with a simple and clean pulse waveform without splitting. In this paper, it is first shown that the power margin of the dispersion-allocated (D-A) soliton is 6–9.5 dB larger than that of the soliton with a uniform GVD. Next, a new method (Q map method) for the evaluation of optical transmission systems using the Q value is described, which indicates the signal-to-noise ratio of the received eye pattern. By using this method, the power margins and dispersion tolerances of the soliton, NRZ, and zero-dispersion RZ pulse transmissions are discussed and it is found that the D-A soliton transmission has the highest power margin. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(12): 17–27, 1997

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.

DFB lasers with integrated electroabsorption modulator

The design, fabrication and testing of 1550 nm DFB lasers with monolithically integrated electroabsorption modulators are reported. System performance of butterfly-packaged devices in 10 Gbit/s NRZ transmission over standard single mode fibre (SMF) with 17 ps/nm/km dispersion is included. Among the results are l0 Gbit/s transmission without the aid of optical amplifiers up to the theoretical limit of 50 km and up to 150 km using one optical booster amplifier.

Penalty-free 10 Gb/s NRZ transmission over 100 km of standard fiber at 1.55 μm with a blue-chirp modulator integrated DFB laser

We present transmission beyond the dispersion limit with a blue-chirp modulator integrated DFB laser for the first time. By suppressing the hole pile-up in the modulator, stable modulation characteristics were realized in negative /spl alpha/ regime. Blue-chirp operation was clearly observed by time-resolved dynamic chirp measurement. Penalty-free 10 Gb/s transmission over 100 km of standard fiber at 1.55 /spl mu/m was demonstrated with the device. This modulator integrated DFB laser is promising for use as a high-power blue-chirp transmitter in multigigabit transmission systems.

Influence of fiber four-wave mixing in multichannel return-to-zero (RZ) signal transmissions

The influence of fiber four-wave mixing (FWM) is theoretically discussed for multichannel RZ (return-to-zero) transmissions. The probability of FWM light generation is taken into account as well as the receiver sensitivity. The result shows that the repeater gain in RZ transmissions is larger than that in NRZ transmissions.

Electrooptic polarization scramblers for optically amplified long-haul transmission systems

To combat polarization hole burning in erbium-doped fiber amplifiers, we modulate the input polarization state to a 8800-km long 5.33-Gb/s NRZ transmission system at rates between 10 kHz and 10 GHz using integrated-optic polarization scramblers in lithium niobate. At modulation frequencies of 40 kHz and 10.66 GHz, we observe improvements in the signal-to-noise ratio of the received electrical signal of 4 and 5 dB, respectively. >

Gain-switching of dbr laser monolithically integrated with electroabsorption modulator for RZ transmission

A photonic integrated transmitter for RZ transmission provides 50 ps optical pulses on-off modulated at a bit rate of 3Gbit/s. BER performance is measured in a back-to-back transmission experiment and compared to NRZ transmission using the same photonic circuit with the laser operated CW. A 2.8 dB improvement in receiver sensitivity is obtained for the RZ case.