Direct Detection Passive Optical Network Research Articles

Low-Complexity Recurrent Neural Network Based Equalizer With Embedded Parallelization for 100-Gbit/s/λ PON

To meet the demand of emerging applications, such as fixed-mobile convergence for the fifth generation of mobile networks and beyond, a 100-Gbit/s/λ access network becomes the next priority for the passive optical network roadmap. We experimentally demonstrate the transmission of 100-Gbit/s/λ intensity modulation and direct detection passive optical network based on four-level pulsed amplitude modulation in the O-band by using 25G-class optics. To mitigate the severe distortions caused by inter-symbol interference and fiber nonlinearity, a low-complexity recurrent neural network based equalizer with parallel outputs is proposed. Experimental results show that the proposed recurrent neural network equalizer can consistently outperform fully-connected neural network with the same input/output size and number of training parameters. The neural network equalizer's sensitivity against quantization is also evaluated. To further understand the complexity and actual hardware resource consumption of the parallel-output equalizers, we implement an 8bits-integer-quantized neural network model using FPGA, with the benefits and challenges validated and discussed.

Multi-electrode quantum-dot semiconductor optical amplifier as an intensity modulator of signals in optical communication systems

In this paper, we are going to exhibit the system performance using the single, double and three-electrode quantum-dot semiconductor optical amplifier as an intensity modulator (3E-QD-SOA-IM) of the adaptively modulated optical orthogonal frequency division multiplexing (AMOOFDM) signals in the intensity-modulation direct-detection passive optical network (IMDD-PON) systems. Moreover, to compare the bit-rate versus transmission distance of the proposed fiber link model when using both configurations multi-electrode semiconductor optical amplifier intensity-modulator (ME-SOA-IM) and multi-electrode quantum-dot semiconductor optical amplifier intensity-modulator (ME-QD-SOA-IM), to study the improvement of the transmission capacity, distance reach and power efficiency when applying the proposed configurations for optical access networks for distances ranging from 20 km up to 120 km. The three-electrode configuration solved the nonlinearity of the two-electrode configuration and offered a considerably wider range of optimum operating conditions to achieve up to 35 Gbps. Furthermore, the 3E-QD-SOA-IM showed a better performance over the 3E-SOA-IM over all the 120 km, and a 5 Gbps enhancement in the bitrate with a 20 dB less optical input power at 20 km.

Demonstration of 2 × ONU 80 Gbps direct detection colorless polarization division multiplexing frequency division multiplexing passive optical network uplink transmission

In this study, we propose and experimentally demonstrate a simple direct detection passive optical network (PON) uplink transmission scheme based on frequency division multiplexing and polarization division multiplexing. Two optical network units (ONUs) are assigned to two different frequency bands at two different orthogonal polarization directions. At the optical line terminal, both ONU signals can be simultaneously detected by a single photodiode without utilizing any polarization control, polarization selection, or complicated polarization demultiplexing algorithms. As a proof-of-concept, the 2×ONU 80 Gbps 32-ary quadrature amplitude modulation Nyquist single carrier signals are successfully transmitted over 2 km standard single mode fiber or 20 km large effective area fiber with the assistance of frequency domain equalization and decision-directed least-mean-square. The measured bit error rate can be below the 7% pre-forward error correction threshold of 3.8×10−3. Meanwhile, this scheme is compatible with the widely used wavelength-division multiplexed PON, which shows the promising potential and feasibility of this proposal.

Low‐cost OFDM Direct Detection Passive Optical Network

ABSTRACTIn this article, operation of a low‐cost orthogonal frequency division multiplexing–based passive optical network is presented. At the optical network units, the received signal is downconverted and filtered in analog domain, which enables use of analog to digital converters of low sampling rates. The conception is verified experimentally. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2504–2507, 2013

Compensation of directly modulated distributed feedback laser frequency chirps in optical orthogonal frequency division multiplexing intensity-modulation and direct-detection passive optical network systems

A simple and effective technique capable of compensating frequency chirps associated with directly modulated distributed feedback (DFB) lasers (DMLs) is proposed, which utilises an electrical analogue circuit (EAC) and an optical phase modulator. The EAC produces a phase signal mimicking the original phase of the DML-modulated optical signal, and the optical phase modulator driven by the phase signal compensates for the DML frequency chirp in the optical domain. In optical orthogonal frequency division multiplexing (OOFDM) passive optical network (PON) systems utilising DMLs and intensity-modulation and direct-detection (IMDD), the proposed technique can almost completely alleviate the DML frequency chirp effect. In particular, compared to uncompensated conventional DML-based OOFDM IMDD PON systems, the proposed technique can not only improve the transmission capacity by approximately 25% over a wide transmission distance range but also considerably enhance the system performance robustness to variations in DML operating conditions. In addition, optimum EAC design parameters are also identified, based on which the present technique offers system operating condition-independent transmission performance.