High-speed Passive Optical Networks Research Articles

End-to-end learning of joint noise shaping and probabilistic shaping for OAM mode division multiplexing transmission.

Intensity modulation direct detection (IM/DD) orbital angular momentum (OAM) mode division multiplexing (MDM) technology can greatly expand the capacity of a communication system, which is a promising solution for the next generation of high-speed passive optical networks (PONs). However, there are serious obstacles such as mode coupling, device nonlinear impairment, and quantization noise in an IM/DD OAM-MDM system with a low-resolution digital-to-analog converter (DAC). In this Letter, we propose a novel, to the best of our knowledge, end-to-end (E2E) learning scheme based on a double residual feature decoupling network (DRFDnet) emulator with joint probabilistic shaping (PS) and noise shaping (NS) for the OAM-MDM IM/DD transmission. Our DRFDnet emulator can accurately build a complex nonlinear model of an OAM-MDM system by separating the signal impairments into linear and nonlinear. Meanwhile, a DRFDnet-based E2E scheme for joint PS and NS is presented with the aim of compensating the signal impairment for the OAM-MDM IM/DD system. An experiment is carried out on a 200 Gbit/s PON system based on the OAM-MDM IM/DD transmission. The experimental results demonstrate that the proposed DRFDnet-based joint PS and NS scheme is a promising solution to effectively mitigate nonlinear distortions and outperforms the CGAN-based joint PS and NS scheme and traditional joint PS and NS scheme with receiver sensitivity improvements of 1.2 dBm and 2.5 dBm under hard-decision forward error correction (HD-FEC) thresholds, respectively. Our experimental results demonstrate that the proposed DRFDnet emulator-based E2E learning scheme is a viable candidate for future PON.

Investigation of OFDM-Based HS-PON Using Front-End LiFiSystem for 5G Networks

Fifth-generation (5G) technology has enabled faster communication speeds, lower latency, a broader range of coverage, and greater capacity. This research aims to introduce a bidirectional high-speed passive optical network (HS-PON) for 5G applications and services including mobile computing, cloud computing, and fiber wireless convergence. Using 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing techniques, the system transmits uplinks and downlinks with a pair of four wavelengths each. Light fidelity (LiFi) services are provided with blue light-emitting-diode-based technology. With a threshold bit error rate (BER) of 10−3, the results demonstrate reliable transportation over a 100 km fiber at −17 dBm received power and in a maximum LiFi range of 20 m. Furthermore, the system offers symmetric 4 × 50 Gbps transmission rates under the impact of fiber–LiFi channel impairments with maximum irradiance and incidence half-angles of 500. Additionally, at threshold BER, the system provides a detection surface range from 1.5 to 4 cm2. Compared to existing networks, the system also provides a high gain and low noise figure. A number of features make this system an attractive option. These include its high speed, high reach, high split ratio, low cost, easy upgradeability, pay-as-you-grow properties, high reliability, and ability to accommodate a large number of users.

Real-Time Deployment of Simplified Volterra Nonlinear Equalizer in High-Speed PON

Real-Time Deployment of Simplified Volterra Nonlinear Equalizer in High-Speed PON

Artificial Neural Network Assisted Probabilistic and Geometric Shaping for Flexible Rate High-Speed PONs

In this paper, we employ artificial neural networks (ANNs) to optimize joint probabilistic shaping (PS) and geometric shaping (GS) for a realistic 50G IM/DD passive optical network (PON) link. Apart from being able to find a generalized mutual information (GMI)-maximizing modulation for channel conditions unseen at the training phase, the compatibility of the ANN training with Monte Carlo simulation also enables us to use a more complicated channel model that more closely resembles a real PON system where fiber dispersion, bandwidth limitation and digital signal processing (DSP) are present. The forward error correction (FEC) requirement that must be satisfied in an actual implementation is imposed on the learned modulation by including a normalized GMI (NGMI) penalty term in the loss function. The proposed scheme is demonstrated with simulations. Results show that the ANN can achieve similar performance compared to a case-by-case optimization while also being capable of generalizing to a wide range of received optical power (ROP) from −30 dBm to −18 dBm and/or a broad range of fiber distance from 0 km to 20 km. About 0.1-bits/symbol GMI improvement is attained compared to uniform modulation.

Real-time validation of downstream 50G/25G and 50G/100G flexible rate PON based on Miller encoding, NRZ, and PAM4 modulation

Experimental demonstration is given of a real-time flexible downstream 50 Gb/s passive optical network (PON) mixed with 25 Gb/s or 100 Gb/s signals. 25 Gb/s transmission is enabled by using 25 Gb/s Miller encoding. For back-to-back a lower sensitivity for 25 Gb/s Miller of ∼2.2dB is found relative to 50 Gb/s non-return-to-zero (NRZ). An extended reach of 40 km and up to ∼5dB optical power budget improvement after worst-case 20 km standard single-mode fiber over 50 Gb/s NRZ was shown for 25 Gb/s Miller. It was also shown that optical network units (ONUs) that have 9 dB additional optical received power because they experience a lower optical loss can receive 100 Gb/s four-level pulse amplitude modulation (PAM4) instead of NRZ in a flexible rate PON, which will double the bit-rate to these ONUs. 50 Gb/s NRZ transmission under mixed modulation (50% NRZ and 50% Miller or 50% PAM4) can operate with very low penalty. A power penalty of <0.4dB was found for 50 Gb/s NRZ after worst-case total dispersion (as specified in ITU-T G.9804) when mixed with 25 Gb/s Miller or 100 Gb/s PAM4. For back-to-back there was a smaller penalty of <0.2dB for 50 Gb/s NRZ under mixed modulation. The 25 Gb/s Miller signal spectrum is similar to 50 Gb/s NRZ and 100 Gb/s PAM4, which enables good performance of the real-time clock and data recovery with an integrated adaptive feed-forward-equalizer based equalizer under mixed signal modulation. The increased optical power budget enabled by the 25 Gb/s Miller encoding effectively improves power margins of the high-speed PON and will enable reliable transmission for ONUs deployed with out-of-spec (higher) loss and/or (larger) fiber reach. The additional margin provided by 25 Gb/s Miller encoding will also enable a safe-mode for ONUs that experience out-of-spec scenarios because of faults in the PON fiber network.

Demonstration of 200 Gb/s/λ PON in O-Band With High-Bandwidth TFLN Modulator

As the broadband applications continue rising, the solutions of high-speed passive optical network (PON) with large power budget are highly desired. Direct detection scheme combined with digital signal procession (DSP) has been considered as a promising candidate due to its low cost, low power consumption and simple architecture. In this paper, we experimentally demonstrate 200 Gb/s/λ and 240 Gb/s/λ time division multiplexed passive optical network (TDM-PON) downstream transmissions based on four-level pulsed amplitude (PAM-4) modulation with direct detection in O-band. A high bandwidth thin film lithium niobate modulator is adopted to generate high Baudrate optical signal at the optical line terminal (OLT) side. A pre-amplified semiconductor optical amplifier SOA is employed at the optical network unit (ONU) side to improve the power budget. Several DSP algorithms are studied to compensate the linear and nonlinear distortions. We also propose a simplified Volterra nonlinear equalizer (S-VNLE) to reduce the computational complexity. Considering the soft-decision FEC (SD-FEC) threshold (1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> ), over 29 dB and 28 dB power budgets are achieved respectively for 200 Gb/s/λ and 240 Gb/s/λ PON system after 20 km standard single mode fiber (SSMF) based on our proposed S-VNLE.

FiWi network planning for WiFi enabled gram panchayats of India: A frame work using component placement optimization

Fiber Wireless (FiWi) access network consists of high speed passive optical network (PON) at back end and wireless mesh network at front end. It is emerging as the most prominent access network due to its inherent feature. It may provide fast Internet services at minimum possible cost. Many of the villages of the India are still not connected with high speed network hence the present paper provides FiWi network planning for creating the Wireless Fidelity (WiFi) enabled villages (Gram Panchayats) of India. The main aim of the paper is to deploy the cost effective FiWi network to provide the faster internet services at reasonable prices to the users of the gram panchayat (GP) in India. The area of the GP and the user’s location in particular GP is taken as input for network planning. The proposed planning provides the optimized position of wireless routers and Optical Network Units (ONUs) in terms of latitude and longitude. For optimizing position of wireless router and ONUs, we propose to use customized Slime Mould algorithm (SMA). We considered four gram panchayats of Indore region of India to make them WiFi enabled using FiWi access network. The customized SMA algorithm provides the best possible position and number of wireless routers and ONUs to connect all the users of gram panchayat. Beside, the total fiber length from the Optical Line Terminal (OLT) to all the ONUs and total cost estimation is also given to create the complete network.

High-speed passive optical networks performance signature in downstream direction based on the engagement of both nonlinear cross-phase modulation (XPM) and cross-gain modulation (XGM) techniques

Abstract This work clarified the engagement of both nonlinear XPM/XGM in conventional band applications with the wide band traveling semiconductor optical amplifiers (WBTWSOAs) for passive optical network applications in downstream directions. The max. Q, total output power versus up/down wavelength conversion by using cascaded XPM with XGM at 10 Gbps are simulated. Besides, the max. Q Factor, conversion efficiency, and total optical power (TOP) variations are clarified in relation to bit rate variations for cascaded CPM&amp;XGM and CPM, XGM stages. Moreover, the enhancement percentage ratio (EPR) in Q factor and TOP are analyzed and demonstrated versus bit rate variations for cascaded CPM&amp;XGM stage over both CPM stage and XGM stage. The study emphasized the network reach can be extended to 80 km with available maximum data rates up to 250 Gb/s with power budget of 28.65 dB based on the cascaded CPM&amp;XGM technique.

Performance and Complexity Analysis of Conventional and Deep Learning Equalizers for the High-Speed IMDD PON

To accommodate the exponential growth of network services in the five-generation (5G) and beyond wireless system, 50 Gb/s/λ passive optical network (PON) is developed for mobile xhaul applications. Intensity modulation and direct detection (IMDD) technology together with digital signal procession (DSP) is being considered as the promising solution for 50 Gb/s/λ PON due to its low cost, low power consumption, and compact footprint. Different DSP algorithms with varied structures are proposed for linear and nonlinear impairments compensation in the high-speed PON, while the performance and complexity analysis of these algorithms is still missing. To find the most efficient equalizers, in this paper, four conventional equalizers, including feed-forward equalizer, decision feedback equalizer (DFE), Volterra equalizer (Vol) and Volterra DFE equalizer (Vol-DFE), together with two deep learning equalizers namely fully-connected neural network, and long short-term memory equalizer are experimentally compared in a 10G optics based 50G-PON system in terms of the equalization performance, computation complexity, optimization difficulty, and generalization ability. After the evaluation of our proposed fair comparison algorithm, we consider Vol-DFE is the most efficient one considering both performance and complexity. Attributes to the strong and efficient equalization capability of Vol-DFE, C-band 50 Gb/s PAM-4 signal transmission can be supported in a 10G optics based IMDD system with a 3 dB bandwidth of 6.11 GHz, and a power budget up to 38 dB can be achieved.

Fixed-Point Analysis and FPGA Implementation of Deep Neural Network Based Equalizers for High-Speed PON

Adeep neural network based equalizer is proposed to mitigate the intersymbol interference observed in next generation high speed passive optical network (PON) links. The DNN based equalizer is shown to outperform the best known conventional equalizer, the maximum likelihood sequence estimator (MLSE) both in back-back and through fiber experiments. To reduce the hardware complexity of DNN based equalizer for PON systems, we investigate the use of embedded parallelization within a DNN structure having multiple symbol outputs from one DNN. We further investigate using a classification output stage with cross entropy cost to perform joint decision on multiple symbol outputs and demonstrated that the sensitivity gain of such scheme over regression output. To understand the complexity of hardware implementation, the fixed-point DNN based equalizers are developed and implemented in FPGA. The impact of fixed-point resolution on the receiver sensitivity and hardware resource utilization in FPGA implementation is analyzed and reported in detail. We show that a reduction of over 40% in LUTs (look up table) utilization is possible by reducing the DNN's weight resolution from 8-bit to 4-bit while incurring a small penalty in receiver sensitivity.

High-speed PON downstream transmission based on pre-configured KK scheme with CD pre-compensation and direct detection

In this paper, the pre-configured Kramers–Kronig (Pre-KK) scheme combined with the chromatic dispersion pre-compensation (CDPC) has been proposed and studied to reduce the complexity of DSP and hardware implementation at the optical network unit (ONU) side for passive optical network (PON), avoiding the use of KK receiver. For further analysis and verification, 100 Gb/s/λ PON downstream transmissions with 4-level pulse amplitude modulation (PAM-4) signal based on the Pre-KK scheme and KK receiver have been implemented and compared on a unified optical system platform. The results show that the Pre-KK requires 1-bit resolution lower than KK receiver for ADC, and achieves a power budget of 29 dB after 20 km fiber transmission at the strong FEC threshold of 1 × 10−2. By increasing the launch power, the maximum power budget of 33.2 dB can be achieved due to the fiber nonlinearity. The effectiveness of CDPC in Pre-KK scheme has also been investigated and demonstrated over 20 and 50 km transmission. Besides, the computational complexities of two schemes are analyzed and discussed in detail. Hence, the Pre-KK scheme joint with CDPC can be a promising solution for the high-speed PON downstream transmission.

Simplified SVM Equalization Algorithm Based on Single Hyperplane Training Enabled 50Gb/s PAM-4/8 With 10-G Optics in NG-PON System

In this paper, we firstly present a novel equalizer only with a single support vector machine (SVM) training hyperplane to compensate the distortion of multi-class PAM-M signals in low-cost limited-bandwidth next generation passive optical network (NG-PON) system. For this scheme, only single SVM-based hyperplane is trained, and then it is extracted and used to realize the multi-classification task of PAM-M by adjusting the corresponding offset, which would greatly reduce the complexity of equalization algorithm and enhance its application in future high-speed PON system. Moreover, the 50-Gb/s PAM-4/8 per wavelength transmission experiment with 10-G optics in 20km standard single mode fiber (SSMF) PON system are set up and utilized to manifest the feasibility and effectiveness of our scheme. The results show that, compared with the common SVM scheme with multi-classification hyperplane training, our method can reduce M-1 times computational complexity caused by hyperplane training for multiple-level pulse amplitude modulation (PAM-M) signals. Except this, the propose scheme can also maintain almost the same bit error ratio (BER) performance as the common SVM classifier with multi-hyperplane case.

Inter-ONU-communication for future PON based on PAM4 physical-layer network coding

A physical-layer network coding (PNC) based inter-ONU-communication (IOC) scheme is proposed for next generation high-speed PONs which apply four-level pulse amplitude modulation (PAM4). A 25 Gb/s full-duplex and private communication is demonstrated.

IM/DD probabilistically shaped 64-QAM OFDM-PON transmission assisted by selective-mapping and flexible systematic polar code

Intensity-modulation direct-detection (IM/DD) orthogonal frequency division multiplexing (OFDM) has advantages of low cost and simple structure, which is a promising candidate for next-generation high-speed passive optical networks. In this work, we propose and experimentally demonstrate a look-up-table-based probabilistic shaping scheme assisted by selective-mapping (SLM) and flexible systematic polar code (SPC) to improve the performance of IM/DD 64-QAM OFDM transmission system. Meanwhile, we experimentally compare the performance between the proposed scheme and the joint constant composition distribution matching (CCDM) and low-density parity-check (LDPC). Here, abundant phase sequences in the SLM are generated by chaotic sequence to suppress peak-to-average power ratio (PAPR). The pre-set bits of SPC are utilized for the additional information of probabilistic shaping to reduce the redundancy and the cyclic redundancy check (CRC) aided successive cancellation list (CA-SCL) decoder is used for decoding. Joint probabilistic shaping and PAPR suppression have contributed 4.6-dB and 3-dB bit error ratio performance improvements for the IM/DD 64-QAM OFDM transmission system in the pre and post forward error correction (FEC), respectively.

Implementation of Multi-Wavelength Source for DWDM-PON Fiber Optical Transmission Systems

Abstract Four-wave mixing (FWM) is one of the well-known nonlinear optical effects (NOE), and it is considered as an adverse impact in fibre optical communication lines. This nonlinear optical effect as a productive one can be used in fibre optical communication systems for various optical processing functions, like wavelength conversion, high-speed time-division multiplexing (TDM), pulse compression, fibre optical parametric amplifiers (FOPA), etc. In most of the fibre optical communication systems, each data transmission channel requires one light source (e.g., laser) as a carrier, which can make these transmission systems expensive. For example, to provide operation of 4-channel dense wavelength-division-multiplexed (DWDM) system four separate lasers at specific operation wavelengths are needed. On the contrary, through the FWM effect, which can be obtained in highly nonlinear optical fibre (HNLF) by using two high-power pump lasers, the generation of new multiple carriers forming the laser array or a multi-wavelength source is possible. Accordingly, within the present research, we investigate the latter approach for FWM light source implementation in DWDM passive optical networks (DWDM-PONs). We analyse up to 16-channel 50 GHz spaced DWDM-PON system with a bitrate of up to 10 Gbit/s per channel, constructed on the basis of two high-power continuous wave (CW) pump lasers. We evaluate the system performance against the number of its channels by changing it from 4 to 16 and in each case find the most optimal HNLF fibre length (for a 4-channel system it is 0.9 km; for an 8-channel system – 1.39 km; and for a 16-channel system – 1.05 km) and laser pump powers (for a 4-channel system it is 20 dBm; for an 8-channel system – 24.1 dBm; and for a 16-channel system – 26.3 dBm). These optimal parameters were found in order to get the highest system performance, respectively, the lowest BER (threshold BER≤10−10), and minimal power fluctuations among FWM generated carriers. The obtained results show that the proposed transmission system can be a promising solution for next-generation high-speed PONs.

Photonic Integrated Circuits for NGPON2 ONU Transceivers (Invited)

The development of photonic integrated circuits (PIC) for access network applications, such as passive optical networks (PON), constitutes a very attractive ecosystem due to PON’s potential mass market. The implementation of PIC solutions in this context is expected to facilitate the possibility of increasing the complexity and functionalities of devices at a potentially lower cost. We present a review addressing the prominent access network market requirements and the main restrictions stemming from its specific field of application. Higher focus is given to PON devices for the optical network unit (ONU) and the implications of designing a device ready for market by discussing its various perspectives in terms of technology and cost. The discussed PIC solutions/approaches in this paper are mainly based on indium phosphide (InP) technology, due to its monolithic integration capabilities. A comprehensive set of guidelines considering the current technology limitations, benefits, and processes are presented. Additionally, key current approaches and efforts are analyzed for PON next generations, such as next-generation PON 2 (NGPON2) and high-speed PON (HSP).

Comparative investigation on 10G-class and 25G-class receivers for O-band DML-based 25/50 Gbps TDM-PON

Abstract Reliable and cost-efficient transceivers are desired for next generation high-speed passive optical network (PON). In this paper, we experimentally demonstrate 25/50 Gbps transmissions based on an O-band directly modulated laser (DML), and the receiver-side solutions are investigated in detail to realize a low-cost high-speed PON system. Specifically, a comprehensive comparison of two commercially available receiver candidates is presented, which are the 10G-class receiver and the 25G-class receiver. Three typical transmission cases for next generation PON systems based on these two receivers are demonstrated, and the system bandwidth limitation induced signal distortions in corresponding cases are compensated by equalization-based digital signal processing (DSP). System performances and the DSP-induced implementation complexity of the two receivers are comprehensively analyzed and compared. Results indicate that, for the 25 Gb/s transmission, the 25G-class receiver without any DSP is more favorable than the 10G-class one with post-equalization, and a power budget of 25.4 dB is achieved without amplification for non-return-to-zero on-off keying (NRZ-OOK) signal. While for the 50 Gb/s case, the two receivers manifest similar performances and DSP-induced hardware complexities, making both feasible solutions for real deployments, and after 20 km fiber transmission, an optimum power budget of 20.3 dB is achieved for the 4-level pulse amplitude modulation (PAM4) system.

Optimization of Band-Limited DSP-Aided 25 and 50 Gb/s PON Using 10G-Class DML and APD

The increasing demand for network capacity is driving the development of next-generation high-speed Passive Optical Networks (PON) supporting 25 and 50 Gbps. One solution to reduce transceiver cost is reusing the 10G-class optical transmitter (including Directly Modulated Lasers, DML, in O-band) and receiver components in combination with Digital Signal Processing (DSP) techniques to compensate for bandwidth limitations. In this article, by means of both a set of laboratory experiments and a metropolitan field demonstrator, we discuss practical PON solutions at 25 and 50 Gbps per wavelength and per direction. In terms of modulation formats, we compare 2-level pulse amplitude modulation (PAM-2), 4-level PAM (PAM-4), and electrical duobinary (EDB) modulation formats, with feed-forward (FFE) and decision-feedback (DFE) adaptive equalizer at the receiver side. The novelty of our article is manifold. First, we present an optimization in terms of optical receiver band requirements for the 50 Gbps transmission. We show, by means of experimental measurements and numerical simulations, the minimum required bandwidth for DML laser and APD receiver (with appropriate DSP techniques) to realize next generation 25 and 50 Gbps PON transceivers. Second, we discuss also the upstream point of view, with a specific focus on DSP, and in particular, we propose an experimental solution based on a burst mode receiver with memory-aided DSP technique, together with a novel DSP approach to overcome the typical AC coupling distortion due to the burst mode scenario. Finally, we show a coexistence experiment between XGS-PON and 25 Gbps PON on an installed metropolitan field trial.

High Speed Passive Optical Network Based Elastic Optical Communication System

Abstract For addressing needs of modern day communication needs, new type of networks are required to be evolved to cater the demand of high data rates. Use of survivable elastic-optical-network (EON) with existing passive-optical-networks (PON) may provide the solution for this. The present work focus on employing EON–PON based wave-length-division multiplexing enabled communication system comprises of 2×5 Gbps for downlink and 2×1 Gbps for uplink over a single-mode-fibre of length 100 km. The results are the evaluated via bit-error-rate analyser, q factor and eye diagrams.

Demonstration of a 120° hybrid based simplified coherent receiver on SOI for high speed PON applications.

We demonstrate the first simplified coherent receiver using a 120° hybrid on silicon-on-insulator (SOI) for high speed PON applications. This coherent receiver integrates an inverse taper edge coupler for the received signal, a vertical grating coupler for the local oscillator input, a polarization splitter and rotator (PSR), a 120° hybrid based on a 3×3 multimode interference (MMI) coupler, and three germanium photodetectors. We achieved 25 Gbit/s two-level pulse amplitude modulation (PAM-2) transmission over 30 km standard single mode fiber (SMF) in the C-band without any digital signal processing (DSP) (e.g., pre-emphasis, pulse shaping, equalization, nonlinearity compensation) and dispersion compensation (e.g., optical or digital) either at the transmitter or at the receiver. The requirements for frequency and phase locking of the local oscillator (LO) were avoided due to the use of intensity modulated signals. Receiver sensitivities of -23.70 dBm, -20.30 dBm, and -15.10 dBm are achieved at a bit error rate (BER) below the hard-decision forward error correction (HD-FEC) threshold (i.e., 3.8 × 10-3) in back-to-back (B2B), after 21 km and 30 km, respectively. We also demonstrate 25 Gbit/s PAM-4 transmission achieving receiver sensitivities of -15.30 dBm, -13.90 dBm, and -9.50 dBm below the HD-FEC threshold in B2B, after 10.5 km and 21 km, respectively.