F. Wust

5.94-Tb/s 1.49-b/s/Hz (40/spl times/2/spl times/2/spl times/40 Gb/s) RZ-DQPSK polarization-division multiplex C-band transmission over 324 km

The combination of return-to-zero differential quadrature phase-shift keying with polarization-division multiplex, a 16-ary modulation scheme, allows for ultimate spectral efficiency. We raise C-band fiber capacity with phase-shift keying transmission beyond previously reported figures, achieving forward-error correction limit performance over four fiber spans.

Crosstalk detection schemes for polarization division multiplex transmission

Polarization division multiplex (PolDM) is a bandwidth-efficient and sensitive modulation format suitable for upgrading bandwidth-limited trunk lines. We show how control signals for polarization demultiplex can be obtained efficiently. For interleaved return-to-zero (RZ) signals, incoherent crosstalk has to be detected and minimized. In other cases, in particular for non-return-to-zero (NRZ) signals, coherent crosstalk senses penalties much better and should be detected instead. NRZ transmission experiments with either scheme are presented at a data rate of 2/spl times/10 Gb/s, with endless polarization tracking. Polarization mode dispersion (PMD) tolerance is also assessed.

Polarization mode dispersion detected by arrival time measurement of polarization-scrambled light

Polarization mode dispersion (PMD) limits optical fiber capacity. PMD compensators usually minimize the associated eye closure. This measure scales with the square of the differential group delay (DGD) and makes it difficult to detect low DGDs. However, light with a low-speed polarization modulation suffers arrival time variations, in the presence of PMD, that are proportional to the DGD. These are detected by integrating the voltage-controlled oscillator (VCO) input signal of the clock recovery phase-locked loop (PLL). This novel method has been demonstrated for 40 Gb/s nonreturn-to-zero (NRZ) and for 2/spl times/40 Gb/s return-to-zero (RZ) polarization division multiplex transmission. PMD detection sensitivities range between 2 ps and 84 fs.

Novel nonmagnetic 30-dB traveling-wave single-sideband optical isolator integrated in III/V material

Various attempts have been made to fabricate waveguide-type isolators in III/V material by implanting magnetic materials, but none of them has so far resulted in a commercial product. Here, we report for first time on an integrated optical isolator implemented in III/V material. It consists of a single-sideband electrooptic modulator where traveling electrical waves make the transmission direction-dependent. Isolation is 30 dB, excess insertion loss is 8 dB. Residual rms ripple is 7% for peak-to-peak RF driving amplitudes of 3.5 V at 4.0 GHz. The estimated transmission penalty for 40 Gb/s return-to-zero differential phase shift keying (RZ-DPSK) signals is 0.2 dB (0 dB measured).

Standard (NRZ 1 x 40 Gb/s, 210 km) and polarization multiplex (CS-RZ, 2 x 40 Gb/s, 212 km) transmissions with PMD compensation

A single-waveplate polarization scrambler at the transmitter (TX) generates pulse arrival time fluctuations in the presence of polarization-mode dispersion. These were detected with a 680-fs sensitivity in the receiver clock recovery phase-locked loop, thereby enabling a polarization-mode dispersion (PMD) compensated 210-km nonreturn-to-zero transmission. For polarization division multiplex, polarizations were scrambled by an interchannel phase modulation which enabled PMD-compensated CS-RZ 212-km transmission.

Polarization mode dispersion tolerance of bandwidth-efficient multilevel modulation schemes

We have identified polarization division multiplex to be advantageous for capacity doubling of fiber spans with a given amplification bandwidth, due to its superior sensitivity, good polarization mode dispersion tolerance and terminal equipment simplicity.

Signed online chromatic-dispersion monitoring by synchronous detection of FM-induced arrival-time modulations in the clock-recovery phase-locked loop

Feature Issue on Optical Performance Monitoring (OPM). Chromatic dispersion (CD) in optical single-mode fibers, i.e., the wavelength dependence of the propagation delay, distorts pulses and is a big problem in 10- and 40-Gbit/s transmission systems. Adjustable drop-in CD compensators require an online CD detection. For this purpose, we modulate the optical power of the laser in a 40-Gbit/s transmitter by 1.2% (rms) at a frequency of 5 MHz. In the presence of CD, the associated periodic optical frequency variation modulates the signal arrival time, which is measured by synchronous (lock-in) detection of an error signal in the clock recovery of the receiver. CD as large as -268 to +350 ps/nm is detected including its sign, more than by any comparable technique. The uncertainty of measured arrival-time modulations can be as low as 100 attoseconds. Moreover, no extra optics or high-frequency electronics are needed, which makes this method extremely cheap to implement. Results are given for nonreturn to zero and carrier-suppressed return to zero (CSRZ), intensity modulation, and differential phase-shift keying.

PMD compensation in a 2/spl times/40 Gbit/s, 212 km, CS-RZ polarization multiplexed transmission experiment

Endless polarization control is combined with PMD (polarization-mode dispersion) compensation in a polarization division multiplexing experiment. Interchannel phase modulation allows the detection of interference and pulse arrival time variations caused by polarization mismatch and PMD, respectively.

1.6-Tb/s (40/spl times/40 Gb/s) transmission over 44,...,94 km of SSMF with adaptive chromatic dispersion compensation

Full-band 1.6-Tb/s adaptive chromatic dispersion compensation is demonstrated for the first time. A multichannel tunable dispersion compensator is automatically controlled by arrival time detection on one out of 40 wavelength-division-multiplexed transmitted channels.

Electrical slope steepness difference indicates higher-order PMD at 40 Gbit/s

Polarization scrambling combined with arrival time detection is used to detect 1st-order PMD. The measured difference between rising/falling detected signal slope steepnesses indicates residual higher-order PMD more sensitively than any other electrical scheme. PMD is also compensated.