Wavelength conversion using fiber cross-phase modulation driven by two pump waves.

Wavelength conversion using all-optical phase modulation in a fiber driven by two pump waves is investigated. The operation features are analyzed using an all-optical phase modulation model with two parallel-/cross-polarized pump waves to generate a phase-preserving copy of the optical signal at an exact frequency up-/down-shifted by the two-pump detuning. The conversion efficiency is experimentally verified using a 300-m highly-nonlinear fiber. The results agree well with a theoretical prediction. The conversion bandwidth over 4 THz is achieved and error-free wavelength conversion for a 32-GBd polarization-division multiplexed 16QAM signal is demonstrated. The technique's applicability to a large-capacity wavelength-division multiplexed signals is also discussed.

1.024 Tb/s wavelength conversion in a silicon waveguide with reverse-biased p-i-n junction.

We experimentally show an all-optical wavelength conversion of 8 × 32-GBd single-polarization 16QAM signals using a silicon nano-rib waveguide. The application of reverse biasing of the p-i-n junction of the waveguide allows a conversion efficiency of -8.5 dB with a measured 3-dB optical bandwidth of about 40 nm. Using digital coherent reception, it is shown that the receiver optical signal-to-noise ratio penalty, at a bit-error ratio of 1 × 10-3, of the wavelength-converted signals over all eight channels was less than 0.6 dB with reference to their respective back-to-back signal channels.

All-optical phase-preserving multilevel amplitude regeneration.

The possibility of all-optical phase-preserving amplitude regeneration for star-8QAM is demonstrated using a modified nonlinear optical loop mirror. Experiments show a reduction in amplitude noise on both amplitude levels simultaneously, considering two different types of signal distortions: deterministic low-frequency amplitude modulation and broadband amplitude noise. Furthermore, using this amplitude regeneration, the robustness against nonlinear phase noise from fiber nonlinearity in a transmission line is increased. The scheme suppresses the conversion of amplitude noise to nonlinear phase noise. This is shown for simultaneous amplitude regeneration of the two amplitude states as well as for amplitude regeneration of the high-power states only. If the transmission is limited by nonlinear phase noise, single-level operation at the more critical higher-power state will benefit because of the wider plateau region. Numerical simulations confirm the experimental results.

Coherent UDWDM PON with joint subcarrier reception at OLT.

In this contribution, we report on the experimental investigation of an ultra-dense wavelength-division multiplexing (UDWDM) upstream link with up to 700 × 2.488 Gb/s polarization-division multiplexing differential quadrature phase-shift keying parallel upstream user channels transmitted over 80 km of standard single-mode fiber. We discuss challenges of the digital signal processing in the optical line terminal arising from the joint reception of several upstream user channels. We present solutions for resource and cost-efficient realization of the required channel separation, matched filtering, down-conversion and decimation as well as realization of the clock recovery and polarization demultiplexing for each individual channel.

Kerr nonlinearity mitigation in 5 × 28-GBd PDM 16-QAM signal transmission over a dispersion-uncompensated link with backward-pumped distributed Raman amplification.

We present experimental and numerical investigations of Kerr nonlinearity compensation in a 400-km standard single-mode fiber link with distributed Raman amplification with backward pumping. A dual-pump polarization-independent fiber-based optical parametric amplifier is used for mid-link spectral inversion of 5 × 28-GBd polarization-multiplexed 16-QAM signals. Signal quality factor (Q-factor) improvements of 1.1 dB and 0.8 dB were obtained in the cases of a single-channel and a five-channel wavelength-division multiplexing (WDM) system, respectively. The experimental results are compared to numerical simulations with good agreement. It is also shown with simulations that a maximum transmission reach of 2400 km enabled by the optical phase conjugator is possible for the WDM signal.

Analytical results on back propagation nonlinear compensator with coherent detection.

We derive analytic formulas for the improvement in effective optical signal-to-noise ratio brought by a digital nonlinear compensator for dispersion uncompensated links. By assuming Gaussian distributed nonlinear noise, we are able to take both nonlinear signal-to-signal and nonlinear signal-to-noise interactions into account. In the limit of weak nonlinear signal-to-noise interactions, we derive an upper boundary of the OSNR improvement. This upper boundary only depends on fiber parameters as well as on the total bandwidth of the considered wavelength-division multiplexing (WDM) signal and the bandwidth available for back propagation. We discuss the dependency of the upper boundary on different fiber types and also the OSNR improvement in practical system conditions. Furthermore, the analytical formulas are validated by numerical simulations.

Highly efficient CW parametric conversion at 1550 nm in SOI waveguides by reverse biased p-i-n junction.

In this paper we present four-wave mixing (FWM) based parametric conversion experiments in p-i-n diode assisted silicon-on-insulator (SOI) nano-rib waveguides using continuous-wave (CW) light around 1550 nm wavelength. Using a reverse biased p-i-n waveguide diode we observe an increase of the wavelength conversion efficiency of more than 4.5 dB compared to low loss nano-rib waveguides without p-i-n junction, achieving a peak efficiency of -1 dB. Conversion efficiency improves also by more than 7 dB compared to previously reported experiments deploying 1.5 µm SOI waveguides with p-i-n structure. To the best of our knowledge, the observed peak conversion efficiency of -1dB is the highest CW efficiency in SOI reported so far.

Experimental Investigation of 126-Gb/s 6PolSK-QPSK signals.

We experimentally generate 28-GBd 6-ary polarization-shift keying quadrature phase-shift keying (6PolSK-QPSK) signals by utilizing a high-speed 4-channel digital-to-analog converter and an integrated dual-polarization I/Q modulator. In WDM transmission experiments over up to 4800 km standard single-mode fiber, we compare the performance of 126-Gb/s 6PolSK-QPSK and 112-Gb/s polarization-division multiplexing (PDM) QPSK signals. Furthermore, we discuss the implications of applying an inner Reed-Solomon RS(511,455) forward error correction code in order to correct burst errors due to the anti-Gray mapping of 6PolSK-QPSK.

Experimental demonstration of a format-flexible single-carrier coherent receiver using data-aided digital signal processing.

We experimentally demonstrate the use of data-aided digital signal processing for format-flexible coherent reception of different 28-GBd PDM and 4D modulated signals in WDM transmission experiments over up to 7680 km SSMF by using the same resource-efficient digital signal processing algorithms for the equalization of all formats. Stable and regular performance in the nonlinear transmission regime is confirmed.

40 Gb/s wavelength conversion via four-wave mixing in a quantum-dot semiconductor optical amplifier.

The static and dynamic characteristics of degenerate four-wave mixing in a quantum dot semiconductor optical amplifier are investigated. A high chip conversion efficiency of 1.5 dB at 0.3 nm detuning, a low (< 5 dB) asymmetry of up and down conversion and a spectral conversion range of 15 nm with an optical signal-to-noise ratio above 20 dB is observed. The comparison of pumping near the gain peak and at the edge of the gain spectrum reveals the optical signal-to-noise ratio as the crucial parameter for error-free wavelength conversion. Small-signal bandwidths well beyond 40 GHz and 40 Gb/s error-free 5 nm wavelength down conversion with penalties below 1 dB are presented. Due to the optical signal-to-noise ratio limitation, wavelength up conversion is error-free at a pump wavelength of 1311 nm with a penalty of 2.5 dB, whereas an error floor is observed for pumping at 1291 nm. A dual pump configuration is demonstrated, to extend the wavelength conversion range enabling 15.4 nm error-free wavelength up conversion with 3.5 dB penalty caused by the additional saturation of the second pump. This is the first time that 40 Gb/s error-free wavelength conversion via four-wave mixing in quantum-dot semiconductor optical amplifiers is presented.

Multi-stage optical FDM of 12-channel 10-Gb/s data with 20-GHz exact channel spacing using fiber cross-phase modulation with optical subcarrier signals.

A sequential optical frequency-division multiplexing technique using cross-phase modulation in fibers with exactly frequency-controlled optical subcarrier signals is proposed and demonstrated. 12 channels of 10-Gb/s ASK/DPSK signals with 20-GHz exact channel spacing are successfully multiplexed all-optically at 12 stages with 1-km intervals.

Experimental investigation of 84-Gb/s and 112-Gb/s polarization-switched quadrature phase-shift keying signals.

We experimentally investigate 28-GBd (84-Gb/s) and 37.3-GBd (112-Gb/s) polarization-switched quadrature phase-shift keying (PS-QPSK) signals. In single-channel transmission experiments over up to 12500 km ultra large effective area fiber, we compare their performance to that of polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK) signals at the same bit rates. The experimental results show that PS-QPSK not only benefits from its better sensitivity but also offers an increased tolerance to intra-channel nonlinearities.

Comparison of 8 × 112 Gb/s PS-QPSK and PDM-QPSK signals over transoceanic distances.

We experimentally investigate polarization-switched quadrature phase-shift keying (PS-QPSK) with a symbol rate of 37.3 GBd corresponding to a bit rate of 112 Gb/s. In a wavelength-division multiplexing (WDM) experiment with 50 GHz channel spacing, the transmission performance of PS-QPSK is compared to that of polarization-division multiplexed QPSK (PDM-QPSK) over an EDFA amplified ultra-large-effective-area fiber link. For a bit-error ratio (BER) of 3.8 × 10(-3), the achieved transmission distance is 11000 km for PS-QSPK and 10000 km for PDM-QPSK.

Polarization multiplexed 16QAM transmission employing modified digital back-propagation.

We experimentally demonstrate performance enhancements enabled by weighted digital back propagation method for 28 Gbaud PM-16QAM transmission systems, over a 250 km ultra-large area fibre, using only one back-propagation step for the entire link, enabling up to 3 dB improvement in power tolerance with respect to linear compensation only. We observe that this is roughly the same improvement that can be obtained with the conventional, computationally heavy, non-weighted digital back propagation compensation with one step per span. As a further benchmark, we analyze performance improvement as a function of number of steps, and show that the performance improvement saturates at approximately 20 steps per span, at which a 5 dB improvement in power tolerance is obtained with respect to linear compensation only. Furthermore, we show that coarse-step self-phase modulation compensation is inefficient in wavelength division multiplexed transmission.

80 Gb/s wavelength conversion using a quantum-dot semiconductor optical amplifier and optical filtering.

Wavelength conversion of 40 Gb/s and 80 Gb/s return-to-zero on-off-keying signals using a quantum-dot semiconductor optical amplifier in combination with a delay interferometer as subsequent filter is demonstrated. The performance of the 80 Gb/s wavelength converter measured in terms of the bit-error ratio demonstrated here is the highest reported up to now for quantum-dot semiconductor optical amplifiers. The typical fast gain dynamics manifests itself in open eye diagrams of the converted signal. The slow phase dynamics of the carrier reservoir however induces severe patterning and requires compensation. Adaptation of the free-spectral range of the delay interferometer is necessary in order to mitigate these phase effects and to achieve error-free wavelength conversion.

Dual-quadrature coherent receiver for 100G Ethernet applications based on polymer planar lightwave circuit.

A dual-quadrature coherent receiver based on a polymer planar lightwave circuit (PLC) is presented. This receiver comprises two separate optical 90°-hybrid chips made of polymer waveguides and hybridly integrated with InGaAs/InP photodiode (PD) arrays. The packaged receiver was successfully operated in 112 Gbit/s dual-polarization quadrature phase-shift keying (QPSK) transmission experiments. In back-to-back configuration the OSNR requirement for a BER value of 10(-3) was 15.1 dB which has to be compared to a theoretical limit of 13.8 dB.

110 km transmission of 160 Gbit/s RZ-DQPSK signals by midspan polarization-insensitive optical phase conjugation in a Ti:PPLN waveguide.

We demonstrate 160 Gbit/s return-to-zero (RZ) differential quarternary phase-shift keying (DQPSK) signal transmission over a 110 km single-mode fiber by taking advantage of mid-span optical phase conjugation (OPC). The technique is based on nonlinear wavelength conversion by cascaded second harmonic and difference frequency generation in a Ti:PPLN waveguide. Error-free operation with a negligible optical signal-to-noise ratio penalty for the signal after the OPC transmission without and with polarization scrambling was achieved. The results also show the polarization insensitivity of the OPC system using a polarization diversity scheme.