Zoran Vujicic

Ultra High Capacity Self-Homodyne PON With Simplified ONU and Burst-Mode Upstream

In this letter, we demonstrate a proof of concept fully loaded bidirectional ultrahigh capacity coherent passive optical network (2 × 1008 × 8.3 Gb/s). This was achieved using partial spectrum overlap, Nyquist shaping, digital frequency shifting, self-homodyne detection, and pilot tone remodulation. Upstream burst mode operation is also demonstrated.

Coherent Access: A Review

In this paper, we will address the benefits of the coherent detection in future optical access networks. The scarcity of the optical spectrum, the required flexibility, and constant evolution of requirements highlight the effectiveness of coherent techniques toward the future passive optical networks (PON). A set of architectures for coherent optical access networks will be presented and the key attributes of each scenario will be investigated. In addition, as a basis to decrease the cost of the local oscillator (LO) at customer side, we experimentally investigate the possibility of using a low-cost laser as LO with real-time detection of a Nyquist-shaped differential quadrature phase-shift keying (DQPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array. Moreover, we experimentally derive a set of optimized parameters and their impact on the network operation for coherent ultradense wavelength-division multiplexing (UDWDM) systems. The balance between the number of channels, power budget, and dynamic power range will be evaluated. Furthermore, we demonstrate a reconfigurable real-time receiver DSP for future flexible UDWDM-PON systems applying the DQPSK and D8PSK modulation formats. By reviewing some of the motivations for this technology, such as flexibility, spectral efficiency, as well as compatibility with software-defined networking, we show that this technology is approaching the required maturity.

Self-Homodyne Detection-Based Fully Coherent Reflective PON Using RSOA and Simplified DSP

We investigate the power budget of a fully coherent reflective passive optical network, based on self-coherent upstream (US) and self-homodyne downstream (DS) detection schemes. We consider, for US, both binary phase-shift keyed (BPSK) and quadrature phase-shift keyed (QPSK) at 1 GBd generated by direct modulation of a low-cost reflective semiconductor optical amplifier having 1-GHz electrical bandwidth and using simplified digital signal processing (DSP). We find that the penalty of increasing the order of US modulation format from BPSK to QPSK for higher capacity can be reduced to 1 dB by means of DS digital spectral shifting and US static postequalization.

Efficient Dynamic Modeling of the Reflective Semiconductor Optical Amplifier

Reflective semiconductor optical amplifier (RSOA) is considered a strong candidate to play an important role in realizing the next generation wavelength division multiplexing passive optical network, based on the wavelength reuse concept. Therefore, an accurate and efficient modeling of RSOA is of significant importance. We present a time-domain wideband model for simulation of spatial and temporal distribution of photons and carriers in a bulk RSOA. We provide a novel approach for efficient amplified spontaneous emission modeling, considering a tradeoff between the accuracy and the computational efficiency. The multiobjective genetic algorithm is utilized for parameter extraction. Experimental validation has been performed for continuous wave input, nonreturn to zero (NRZ) on-off keying, and quadrature phase-shift keying (QPSK) signaling pulses up to 40 Gb/s of bit rate, in both amplification and remodulation regimes. We further present systematic performance evaluation under remodulation scenario. Saturation, noise, chirp, and signal broadening are successfully predicted, while reducing the computational time compared to other wideband models.

Fully Coherent Self- Homodyne Bi-directional Enhanced Performance PON

We present a coherent-PON employing partial overlap of downstream/upstream Nyquist spectra, allowing bi-directional operation and enhanced spectral efficiency (2×120Gb/s@50GHz). Additionally, frequency shifting of Nyquist bands from the carrier allowed reduced RBS and dynamic SRS.

Demonstration of Wavelength-Shared Coherent PON Using RSOA and Simplified DSP

We investigate the role of a reflective semiconductor optical amplifier (RSOA) in a fully coherent wavelength-shared passive optical network architecture, based on self-coherent upstream (US) and self-homodyne downstream (DS) detection schemes. We present a proof of concept experimental study, demonstrating 32-dB loss budget over a 30-km fiber link, operating at 9.4-Gb/s DS and 750-Mb/s US effective rates with 7% forward error correction and 8b/10b US overheads, respectively. This was achieved using simplified digital signal processing and a low-cost, off-the-shelf RSOA with 18-dB gain and 1-GHz modulation bandwidth.

Spectrally efficient enhanced-performance bidirectional coherent PON with laserless 10 Gb/s ONU [invited]

We present and experimentally characterize a spectrally efficient, bidirectional, ultradense wavelength-division multiplexing passive optical network (PON) (2 × 120 Gb/s at 50 GHz) over 30 km standard single-mode fiber. This is achieved using a 4 GHz grid with partial spectrum overlapping, Nyquist-shaped 16-ary quadrature amplitude modulation, and digital frequency shifting. This scheme is based on a laserless, self-homodyne PON with centralized wavelength control. We achieve reduced impact of the Rayleigh back-scattering effect due to Nyquist-pulse shaping and frequency upshifting. Self-homodyne detection relaxes the laser linewidth requirement and digital signal processing complexity at the optical network unit. To demonstrate the extra benefit of the proposed PON system, we also experimentally and theoretically evaluate the impact of nonlinear Raman crosstalk in video overlay. Compared to a baseband Nyquist signal and baud rate non-return-to-zero equivalent, the proposed system improves the carrier-to-Raman crosstalk ratio of video overlay by 4 and 6 dB, respectively.

Free space optics hybrid PTMP advanced modulation bidirectional PON

We experimentally demonstrate a 12×10Gb/s bi-directional hybrid SSMF and FSO PHY PON recurring to 6.25 GHz grid, Nyquist shaping and frequency-shifting. Performance is evaluated over a 30.5 dB ODN with Hybrid splitting and coexistence with TWDM-PON.

Multiple system configuration for next generation optical access networks with real-time Nyquist UDWDM-PON

We experimentally characterize 2.5-Gb/s bidirectional UDWDM based on Nyquist shaped QPSK with DSP in real-time. A 41 dB ODN is achieved over 80-km SSMF. Additionally, the required guard-bands for a coexisting scenario with TWDM and video overlay are evaluated.

SBS induced four-wave mixing in ultra dense WDM systems

We experimentally investigated the efficiency of the Brillouin induced FWM process, using two types of fibers. Even with the pump power levels above the SBS threshold, the power of the FWM signal was found to saturate at low power, inducing low crosstalk in bidirectional WDM transmission.