Passive Optical Network Applications Research Articles

Multi-Tone Optical Source Generation for Applications in Next-Generation Passive Optical Networks using Photonic Structures

This study presents the design and simulation of an integrated multi-carrier optical source with a 227 GHz bandwidth for passive optical network (PON) applications. The optical comb generation attained using a photonic structure known as a micro-ring resonator fabricated in silicon nitride (Si3N4) facilitates cost reduction when produced on a large scale. Additionally, the generated optical comb accomplishes non-uniform tones in terms of the optical signal-to-noise ratio (OSNR), which allows for the dynamic assignment of carriers to retainable customers as a function of the data rate and transmission distance requirements. The design and simulation demonstrate the generation of frequency combs with optical carriers in a range of 5-40 tones, an OSNR range of 20-80 dB, and a free spectral range (FSR) of 50-3 610 GHz. To achieve these features, a geometric design of the device is proposed, and its response to variations of input laser parameters is described. In summary, the device uses two optical micro-resonators with radii of 100 and 450 µm and controls the power and the tuning of laser parameters. The proposed method allows generating a deterministic and reliable path to the frequency combs. Finally, the characteristics of the obtained combs are tested to determine their potential use in PON transmissions.

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&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&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&XGM technique.

Phase Carrier approach based on Optical Code Division Multiple Access Networks

A technique for optical code-division multiple-access (OCDMA) spectral amplitude coding is proposed and analyzed. The proposed approach is based on combining both OCDMA systems over a phase carrier. Compared with conventional OCDMA systems, this approach exhibits numerous advantages such as simplicity in the system design and cost efficiency. The phase shift based on phase modulation is adopted in the proposed system, and the orthogonal function based on the random diagonal code is applied. The proposed scheme is considered cost-effective because only one laser source is used; which minimizes interference for access network passive optical network applications and improves the system performance of bit-error rate (BER 10-12).

Investigation of transmission properties of a practical double exponential pulse for communication and sensing application

In this paper, a simple generation technique and the propagation characteristics, of a practically possible double exponential pulse are proposed and numerically analyzed. Solutions of non-linear Schrödinger's equation (NLSE) has mostly been used to analyze the same in comparison with Gaussian ultrashort pulses, for various classes of optical fibers. The Double exponential pulses have shown a bandwidth-efficiency ~ 23% over Gaussian pulses, making it suitable for time-and-wavelength-division-multiplexed passive optical networks (TWDM-PON) applications in optical communication, as recommended by ITU-T G-989. Non-linear behavior of the pulse was also investigated for super-continuum (SC) generation. Super-continuum generated by Double exponential pulses was found to have ~12% higher Spectral Broadening factor compared to Gaussian pulse. Overall, the proposed double exponential pulse, generated by the proposed method, potentially displays comparable, and sometimes better sensing and communication properties, compared to the Gaussian pulses.

All-optical frequency encoded dibit-based parity generator using reflective semiconductor optical amplifier with simulative verification

High-speed signal computation and communication are an essential part of modern communication that increases optical necessity. Therefore, researchers developed different types of digital devices in the all-optical domain. Due to the versatile gain medium of reflective semiconductor optical amplifiers (RSOAs), it has various important applications in passive optical networks. In comparison with semiconductor optical amplifier (SOA), RSOAs exhibit better gain performance because of their double pass property. Therefore, RSOA shows better switching properties. In this communication, co-propagation scheme of RSOA is used to design and analyze a frequency encoded dibit-based parity generator. Taking the advantages of RSOA like high switching speed, low noise, high gain, and low power consumption, the proposed design achieves these qualities. This design simulated in MATLAB and simulated outputs accurately verify the truth table.

Design of L-Band Multiwavelength Laser for TDM/WDM PON Application

This paper presents on the design of L-Band Multiwavelength laser for Hybrid Time Division Multiplexing/ Wavelength Division Multiplexing (TDM/WDM) Passive Optical Network (PON) application. In this design, an L-band Mulltiwavelength Laser is designed as the downstream signals for TDM/WDM PON. The downstream signals ranging from 1569.865 nm to 1581.973 nm with 100GHz spacing. The multiwavelength laser is designed using OptiSystem software and it is integrated into a TDM/WDM PON that is also designed using OptiSystem simulation software. By adapting multiwavelength fiber laser into a TDM/WDM network, a simple and low-cost downstream signal is proposed. From the simulation design, it is found that the proposed design is suitable to be used in TDM/WDM PON for up to 64 Optical Network Units (ONUs).

Experimental investigation of VCSEL-based optical heterodyning with PAM 4 and envelop detection for 5G fronthaul systems

Vertical cavity surface-emitting lasers (VCSELs) are power-efficient optical sources for application in passive optical networks. Despite these sources having the potential of generating coherent high-frequency radio frequency signal, their application for high-order amplitude modulation formats is yet to be demonstrated experimentally. In this work, for the first time, we experimentally demonstrate a four-level pulse amplitude modulation (4-PAM) format on a photonically generated RF carrier signal using optical heterodyning of two independent VCSELs. Two low-power VCSELs were combined at an optical coupler and allowed to beat a PIN photodiode to generate a 10-GHz RF carrier. In the first demonstration, an 8.5 Gbps data signal was modulated on the photonically generated 10 GHz RF carrier. In the second demonstration, a 17-Gbps PAM-4 data signal was externally modulated onto the same VCSEL carrier, ultimately doubling the network bit rate. A simple digital signal processing (DSP) receiver was used as an alternative to costly receiver hardware to decode the transmitted PAM-4 data signal. A 24-km fiber transmission penalty of 7-dB was recorded when PAM-4 signal was photonically generated and transmitted. The penalty introduced by moving from binary transmission to PM-4 transmission was recorded to be 3-dB.

Experimental Study on 25 Gbps C-Band PON over up to 25 km SMF Using a 10G-Class DML + APD IM-DD System

In this paper we present an experimental analysis of several modulation formats (pulse amplitude modulation (PAM-2), quaternary pulse amplitude modulation (PAM-4) and electrical duobinary (EDB)) for passive optical network (PON) applications at 25 Gbps bit rate in a C-band 10G-class directly modulated lasers (DML) and avalanche photodiode (APD) intensity modulation and direct detection (IM-DD) system over a single mode fiber (SMF) of up to 25 km, optimizing DML operations and demonstrating that PAM-2 is a promising choice. We also theoretically and experimentally analyzed the channel frequency response of DML and SMF affected by DML chirp and SMF chromatic dispersion.

Low-complexity blind polarization demultiplexing and frequency domain equalization for coherent passive optical network systems

Algorithmic and architectural options and trade-offs between performance and complexity/power dissipation are necessary to consider in the transfer of coherent technology from long-haul transmission to short-reach application. An adaptive equalization algorithm cascading polarization demultiplexing and frequency domain equalization is proposed to target passive optical network applications that feature extremely low computational complexity. Three coordinate rotation digital computer-based vector rotators are introduced to realize polarization demultiplexing without performing multiplications. A simplified gradient descent algorithm is proposed to search and trace the state of polarization. A nonbutterfly adaptive equalizer in the frequency domain for each polarization is designed to handle link chromatic dispersion and the imperfection of the transceiver frequency response. The performance of the proposed equalization scheme is experimentally verified by a 32-GBaud dual-polarization Nyquist quadrature phase-shift keying system over 20-km standard single-mode fiber transmission. With the proposed method, the number of hardened multipliers for field-programmable gate array realization is reduced by ∼85 % compared with a conventional 2 × 2 multiple-input multiple-output finite impulse response filter with the same receiver sensitivity.

25-Gb/s Laser Modulated EML With High Output Power

Using a conventional electro-absorption modulated laser (EML) device, with a dual-drive scheme, we show increased output power before modulator saturation effects degrade the signal quality. Both the laser and modulator section of the EML are driven simultaneously to generate a 25 Gb/s intensity modulated optical signal. With this dual-drive scheme we achieved a modulated output power of +7 dBm while maintaining a high extinction ratio (≥ 9 dB) and sufficient mask margin. Since the operating wavelength was 1301 nm, the optical path penalty was negligible after a 20 km fiber link. Compared with a conventional EML, in which the laser is continuously on and only the EAM is driven, we improved the mean modulated output power by 3.2 dB. With the proposed driving scheme, conventional simple and low-cost EMLs could be used to meet the requirements of high loss budget links such as those in passive optical network applications.

Numerical simulations of an all-optical parity generator and checker utilizing a reflective semiconductor optical amplifier at 200 Gbps

Reflective semiconductor optical amplifiers (RSOAs) are versatile gain media that find applications in passive optical networks. Due to their double-pass characteristics, they show better gain compared with ordinary semiconductor optical amplifiers, resulting in better switching performance. In this work, the RSOA-based gain dynamics is utilized to design and analyze a parity checker and generator using soliton pulses. The results of MATLAB simulations at a rate of 200 Gbps show the practical feasibility of such gates. The effect of the amplified spontaneous emission noise on the performance of the logic gate is also investigated.

An optimized architecture to reduce the impact of fiber strands in spectral/spatial optical code division multiple access passive optical networks (OCDMA-PON)

Abstract Exploitation of the spectral/spatial two dimensional optical code division multiple access (2D-OCDMA) systems in passive optical networks (PONs) is not explored extensively due to the fact spatial encoding requires deployment of multiple star couplers in the topology where each coupler is connected to different ends of either transmitter or receiver nodes. As a result, this scheme is not suitable for PON applications because it requires a significant increase in the amount of fiber deployment within the network along with the complexity of implementation to deploy the required star couplers. To deploy spectral/spatial OCDMA systems at PON and reduce the impact of fiber strands, this work proposes and investigates an optimized architecture of 2D-OCDMA for PONs based on enhanced multi-diagonal (EMD) code. Spectral/spatial encoding technique is used to develop 2D-EMD coding algorithm from the existing 1D-EMD scheme. This operation elevates orthogonality between the adjacent codes and supports high capacity through superior noise mitigation at the receiving end. A complete system architecture is developed and implemented in an excessively used software for optical networks implementation and analysis called Optisystem, for analysis under different performance parameters of PON. It is observed that the proposed system provides better performance in terms of transmission capacity, and cardinality, in comparison with existing 1D-EMD code and other 2D-OCDMA counterparts. Analysis shows that for an agreeable BER of 10 - 9 the proposed system can support 192 subscribers each communicating at 2 Gbps of data over 25 km single mode fiber. In terms of capital expenditure (CAPEX), four times cost saving per user is achieved for proposed architecture (PA) over conventional architecture (CA) for nearly similar performance.

An efficient adaptive equalization architecture for high-speed coherent PON systems

Algorithmic and architectural options and tradeoffs between performance and complexity/power dissipation are imperative to be considered in the transfer of coherent technology from long-haul transmission to passive optical network (PON) application. In this work, a novel low-complexity equalization architecture cascaded two frequency domain equalizers (FDEQs) and one 1-tap 2 × 2 butterfly equalizer is proposed targeting PON applications. FDEQ is designed to handle link chromatic dispersion (CD) and the imperfection of transceiver frequency response. The 1-tap 2 × 2 butterfly equalizer is introduced to realize polarization demultiplexing. A simplified FDEQ tap coefficient calculation method is designed. The performance of the proposed equalization architecture is experimentally verified by a 32-GBaud dual-polarization (DP) Nyquist-QPSK system over 20-km standard single-mode fiber (SSMF) transmission. With the proposed method, the number of hardened multipliers for field-programmable gate array (FPGA) realization is reduced by ∼90% compared with conventional 2 × 2 butterfly equalizer, at the expense of 0.5 dB receiver sensitivity.

Optics-Simplified DSP for 50 Gb/s PON Downstream Transmission using 10 Gb/s Optical Devices

Directly-modulated laser (DML) is widely employed in intensity modulation and direct detection (IMDD) system due to its low cost and high output power. However, the corresponding frequency chirp is regarded as one of the main disadvantages for its application in passive optical networks (PONs). In this paper, we theoretically analyze the frequency response evolution of DML based system under different chirp and dispersion conditions, proving that the system bandwidth can be improved by interactions between negative dispersion and DML chirp. Based on this concept, we experimentally demonstrated downstream 50 Gb/s PAM4 signal transmission over 20 km single-mode fiber (SMF) access based on the 10 Gb/s DML operating at 1310 nm and avalanche photodiode (APD). A dispersion-shifted fiber (DSF) providing −150 ps/nm dispersion at 1310 nm in the optical line terminal (OLT) is used to pre-equalize the frequency response of bandwidth-limited directly modulated signals in the optical domain. Thanks to our proposed dispersion-supported equalization (DSE) technique, the system bandwidth can be improved by 5 GHz. Feed-forward equalization (FFE), decision feedback equalization (DFE) and Volterra filter are employed to evaluate the signal performance improvement, respectively. By evaluating the receiver sensitivity, the DSE combined with FFE scheme shows 2 dB improvement than the complex Volterra algorithm, indicating its potential to reduce the complexity of digital signal processing (DSP) and therefore a lower cost and power consumption in PON.

400-Gbit/s DP-16-QAM Transmission Over 40-km Unamplified SSMF With Low-Cost PON Lasers

We successfully demonstrate 400 Gbit/s transmission at 1577 nm over an unamplified 40 km standard single-mode fiber (SSMF) link with 11-dB loss target. Commercially available high-bandwidth coherent driver modulator (HB-CDM) and high-bandwidth micro integrated coherent receiver (HB- $\mu $ ICR), designed for $C$ -band are used in combination with two TO-can packaged and thermally tuned low-cost $L$ -band laser sources. With the aid of a memory-less one sample/symbol nonlinear offline digital-signal processing (DSP) correcting for the nonlinear transfer curve of the driver and modulator we can maximize the transmitter optical power, which is critical for unamplified fiber applications. In addition, multistage carrier recovery enables stable performance also with the large phase noise of the used coherent laser source, originally part of an electro-absorption modulated laser module (EML) and designed for extremely price-sensitive passive optical network (PON) applications.

A Numerical Solution for Broadband PLC Splitter with Variable Splitting Ratio Based on Asymmetric Three Waveguide Structures

A numerical solution for the broadband planar-lightwave-circuit (PLC) splitter with a variable splitting ratio based on asymmetric three waveguides weighted by the Blackman weighting function is designed for passive optical network applications with wavelengths between 1.53 and 1.57 µm. The performance of the proposed splitter is verified using the beam propagation method (BPM). It was found that a polynomial function of the splitting ratios accompanying a geometrical shift can be derived from the proposed splitter. The splitting ratio can be changed from 50:50 to 90:10 with this geometrical shift. The excess loss, crosstalk, polarization dependent loss, and splitting ratio variations against wavelength of the proposed splitter with wavelengths between 1.53 and 1.57 µm are better than 0.139 dB, −22.75 dB, 0.006 dB, and 0.335%, respectively. Obviously, the proposed splitter with variable splitting ratio retains the advantages of the symmetric design, such as low excess loss, low crosstalk, polarization insensitivity, broadband, and wavelength insensitivity.

Vertical cavity surface emitting laser based hybrid fiber-free space optic link for passive optical network applications

In this work, a hybrid architecture employing Vertical Cavity Surface Emitting Laser (VCSEL) based Single Mode Fiber (SMF) link followed by Free Space Optic (FSO) transmission, is investigated. The VCSEL is biased below threshold to generate short optical pulses, which is coded in NRZ format. After the 20 km SMF link, a splitter divides the received power into two branches. One portion is coupled to a PIN photodiode for receiver operation, whereas the remaining power is coupled to a lens for free space transmission. The VCSEL-SMF-FSO link is simulated and performance measures are computed and verified with link budget calculation. The maximum FSO link distances under different weather conditions and coupling ratio were found. For BER ≤10−12, under clear weather, the maximum attainable FSO link lengths for 1.25, 2.5, 5 and 10 Gbps data rates are found to be 0.205 km, 0.16 km, 0.14 km and 0.11 km respectively. The same procedure when extended to snowy conditions, yield FSO link length of 155 m, 125 m, 110 m and 90 m for 1.25, 2.5, 5 and 10 Gbps data rates under similar BER performance. The impact of fractional power coupled to FSO link was analyzed for 5 Gbps by varying the splitting ratio from 80:20 to 86:14. The optimum ratio up to which both SMF and the cascaded link system meet the required BER for Gigabit PON application is also determined.

A 25 Gb/s All-Digital Clock and Data Recovery Circuit for Burst-Mode Applications in PONs

The upcoming 100 Gb/s links in the next-generation ethernet passive optical networks will be based on four channels of 25 Gb/s. The corresponding transceivers in these optical links require a high-speed clock and data recovery circuit to extract a synchronous clock and recover the received data. To achieve a sufficiently fast settling time for 25 Gb/s burst mode upstream applications in passive optical networks (PONs), we introduce an architecture of the first 25 Gb/s all-digital clock and data recovery circuit (AD-CDR). Thanks to the implementation of a digital loop filter, our AD-CDR avoids the need of a system clock or a start-of-burst signal. This circuit is implemented in a 40-nm CMOS process and has a very compact active chip area of only 0.050 mm $^2$ . Furthermore, the performance of the burst-mode operation of our AD-CDR in an optical setup is measured and reported, resulting in a burst-mode lock time of 37.5 ns and consuming only 46 mW.

Multiple Fiber Fault Location With Low-Frequency Sub-Carrier Tone Sweep

We present a monitoring technique that can be directly integrated in the sub-carrier multiplexing (SCM) transceiver for PtP and wavelength division multiplexing and sub-carrier multiplexing passive optical networks applications. The technique is based on the detection of the backscattered signal from a baseband tone (100 Hz to 100 kHz) and interpretation with the least absolute shrinkage and selection operator (LASSO) operator, a signal processing technique which identifies the fault positions based on the mathematical model of the received signal. The proposed single-ended fiber probing method enables the location of multiple faults with no a-priori knowledge of the fiber, and offers low-cost in-service operation with negligible impact on data transmission, few meters spatial resolution, and limited dynamic range. Due to all its advantages, but also considering its reach limitation, the SincLASSO method features as an ideal monitoring candidate for short reach sub-carrier multiplexed optical fiber networks, such as the ones intended for analog mobile Fronthaul based on fiber and fiber-extended copper lines.

Demonstration of Real-Time Burst-Mode Digital Coherent Reception With Wide Dynamic Range in DSP-Based PON Upstream

This paper proposes a real-time burst-mode coherent receiver (BMCR) that enables wide dynamic range reception for future passive optical network (PON) applications, wherein two key burst-mode components are implemented; an automatic gain controlled semiconductor optical amplifier (AGC-SOA) for optical power equalization and a real-time digital signal processor (DSP) with a frame detection (FD) function. The AGC-SOA greatly increases the receiver dynamic range by reducing the impact of quantization errors in the analogue-to-digital conversion used for DSP-based signal demodulation while the FD function detects burst frame arrivals for frame-by-frame optimization of tap weights of an adaptive filter in the DSP. Successful real-time reception of 20 Gb/s single polarization quadrature phase shift keying burst signals with wide dynamic range of 22.0 dB is experimentally demonstrated. New system configurations of the DSP-based coherent PONs using the BMCR and wavelength plans assigned to the new systems are also proposed to offer a smooth migration from existing PONs.