Wavelength Reuse Research Articles

All-optical wavelength reuse for meter reading application using EDFA saturation and DFB laser

The experiment utilizes the all-optical wavelength reuse for the realization of a cheaper meter reading approach. We demonstrate the all- optical wavelength reuse approach while exploiting a holding beam and the gain saturation of the erbium doped fiber amplifier (EDFA). A 10 Gb/s data is used to modulate a distributed feedback laser (DFB) and is transmitted downstream over 50 km. The saturated EDFA lowered the downstream data’s extinction ratio (ER) from 9.678 dB to 0.701 dB which is significant for both wavelength reuse and data rewrite for upstream transmission of meter reading as it facilitates the direct reuse of the downstream carrier without the addition of another electrical eraser for meter reading application. The variation of ER and the corresponding Peak to Peak power with EDFA input power for a 1550 nm 10 Gb/s DFB laser was demonstrated by Changing the bias current while maintaining the modulation voltage at 0.5 V allowed the input power into the EDFA to be adjusted from −7.278 dBm to 1.079 dBm. The performance analysis for upstream and downstream transmission was done and the receiver sensitivities determined at BER 10−9. The various eye diagrams were also analyzed for back-to-back (B2B) and 50 km upstream link and downstream link transmissions. This work is crucial for offering an all-optical wavelength reuse option for electrical meter reading application. In addition, the technique is all-optical and can therefore be able to support ultrafast systems with higher formats of modulation while ensuring efficiency in power.

A full-duplex 5G mobile fronthaul based on analog RoF-WDM-PON supporting flexible frequency-band switching with colorless and simple RRH

In this paper, a full-duplex analog radio over fiber scheme based on wavelength division multiplexing passive optical network (A-RoF-WDM-PON) is proposed for the 5G mobile fronthaul (MFH). For the downlink, a flexible switching of the frequency-band covering sub-6G and millimeter wave (MMW) is enabled by the combination of a polarization controller and a polarizer. The colorless and simple remote radio head (RRH) is realized by the wavelength reuse and phase modulation of the upstream (US) signal. For the uplink, the high-frequency US signal can be photonic down-converted to an immediate frequency (IF) with the assistance of the 2nd order harmonic of the electrical local oscillator (ELO) and the coherent detection is employed to improve the receiver sensitivity. The proposed scheme is experimentally demonstrated by the transmission of a 100-Msym/s 16-QAM downstream (DS) signal over 25 km single-mode fiber (SMF) and a 100-Msym/s 16-QAM US signal over 10 km SMF. The experimental results show that the error vector amplitudes (EVMs) for downlink at frequency bands of 3.5 GHz, 12.5 GHz and 21.5 GHz are 6.30%, 5.90% and 7.15% respectively. The EVM of US signal at 19 GHz is 7.64%. The EVM performance versus the received optical power for both up- and down-link are also measured. Additionally, a dual-wavelength multiplexing transmission is carried out, the measured EVMs in one wavelength channel are 7.65%, 7.63%, 11.33% and 8.47%, and the EVMs for the other wavelength channel are 8.09%, 7.74%, 11.45% and 8.42%, which meets the standard of the Third Generation Partnership Program (3GPP).

Performance Enhancement of Indoor Cellular Visible Light Communication through Cell Size and Wavelength Reuse Pattern

The emerging technology of visible light communication (VLC) has become a promising solution for the requirements of wide-bandwidth, high-speed, and infinite-capacity wireless communication networks. A novel design of high-performance multi-user indoor visible light communication (VLC) based on hexagonal-cell arrangement is introduced in the present paper. The wavelength division multiple access (WDMA) is used to enable multiple users to communicate through the network of access point (APs) by assigning a unique wavelength division channel (WDC) to each user. A wavelength reuse scheme is utilized to increase the maximum number of users in the system and to enhance the VLC system capacity. The on–off keying (OOK) is used as the modulation technique for light signaling. The intercell interference (ICI) caused by the wavelength reuse is evaluated and its dependence on the cell radius and the wavelength reuse pattern size is numerically investigated. Both the received power density and the ICI at the location of the moving user are evaluated and the resulting signal-to-ICI ratio (SICIR) is calculated at every point over the indoor area. The VLC system capacity is evaluated and its dependence on the design parameters including the cell radius, the size of the wavelength reuse pattern, and the user data rate is numerically investigated. A design procedure is proposed to minimize the bit-error rate (BER) resulting from the ICI and to maximize the system capacity and the maximum allowable number of users in the system by selecting the optimal radius of the hexagonal cells and the most appropriate size of the frequency reuse pattern. The effect of the data rate per user on the system capacity is numerically investigated. It is shown that a SICR of greater than 21 dB and BER of less than 1 × 10−15 is achieved. Also, a system capacity of more than 4 bps/Hz is achieved by the application of the proposed VLC design optimization procedure.

Universal wavelength reuse mechanism for optical networks-on-chip based on a cooperative game

Optical networks-on-chip (ONoCs) based on wavelength division multiplexing (WDM) technology have lower end-to-end (ETE) delay, larger bandwidth, and higher throughput than NoCs. However, the utilization and parallelism of individual wavelengths are essential since WDM technology would require more optical devices to be integrated with ONoCs, leading to higher on-chip overhead. In this paper, we propose an optimal model of communication node cooperation based on game theory, in which the loss of the optical signal on the transmission path for a specific optical receiver sensitivity establishes the payoff function of each participant. In this cooperative game model, the communication nodes are regarded as the participants of the cooperative game. By analyzing the principle of optical router port occupation, the coordinate-based coalition assignment algorithm is proposed to implement fast construction of coalitions and reach the Nash equilibrium of the cooperative game. In Nash equilibrium, the utilization and parallelism of individual wavelengths are higher, and the network’s performance is optimized and improved. Cooperative-game-based ONoCs have more significant throughput and lower ETE delay. The optical signal loss and minimum output power of the optical transmitter can be further reduced at a given optical receiver sensitivity. By applying the cooperative game to ONoCs, the network’s optimization effect becomes more evident as the network scale increases and the number of communication nodes grows.

Demonstration of High Capacity Bidirectional A-RoF System Using Wavelength Reuse and Frequency Multiplexing

We demonstrate a practical wavelength reuse bidirectional analog radio-over-fiber (A-RoF) system served by a single distributed feedback (DFB) laser. Frequency interleaving of downlink and uplink signals is proposed to ameliorate the spectral efficiency and mitigate the interference raised by the bidirectional transmission. Pre-emphasis is exploited to counteract the performance impairment brought about by the interaction between laser chirp and fiber chromatic dispersion. Through employing 64-QAM modulated 16 bands and 16-QAM modulated 12 bands filtered orthogonal frequency division multiplexing (f-OFDM) signals with 200 MHz bandwidth, asymmetric transmission with superior flexibility over 25 km fiber is attained, with an aggregate capacity of 20 Gb/s for downlink and 10 Gb/s for uplink. The mutual interference between the downlink and uplink is explored by overlapping the downlink and uplink signal spectra to varying degrees. Using the optimum frequency configuration, system performance is evaluated in terms of EVM and phase noise. To further investigate the effects caused by the Rayleigh backscattering and the stimulated Brillouin scattering (SBS), simulations are conducted on the proposed architecture, validating the conclusion from the experiment that the bidirectional transmission is primarily limited by the Rayleigh backscattering than the stimulated Brillouin scattering.

Single-Carrier, Single-λ Full-Duplex Analog Radio Feed Over a Single-Port RRH Transceiver

The densification of radio access and the massive deployment of radio heads calls for efficient optical fronthaul technologies. The adoption of analogue radio-over-fiber schemes promises greatly simplified equipment that can be distributed at the antenna sites for the purpose of radio signal conditioning and electro-optic conversion. Towards this direction, we propose and experimentally evaluate a full-duplex interface at the intersection between the optical and the radio frequency layer, aiming at bidirectional radio signal transmission over a single wavelength (1577 nm) and a single carrier frequency (5.375 GHz). Analogue coherent optical reception is performed through an electro-absorption modulated laser, which is employed as multi-functional element that accomplishes wavelength re-use for full-duplex radio-over-fiber transmission. The directional split is shifted to the electrical domain through adoption of a crosstalk-cancelling circulation stage, ensuring compatibility with a high dynamic power range for the simultaneous transmission and reception of up- and downlink radio signals, respectively, without the need for further duplexing methods subject to frequency translation or time slotting. We prove that margins of >2% in terms of error vector magnitude can be accomplished for an unpaired spectral configuration, where down- and uplink radio signals share the same spectrum in the optical and electrical domains.

A Bidirectional WDM-PON Free Space Optical (FSO) System for Fronthaul 5 G C-RAN Networks

High-speed cellular technologies require low-latency and high-capacity optical networks. The Centralized Radio Access Network (C-RAN) architecture offers a cost-effective solution for mobile network deployment. To maximize flexibility and minimize deployment costs of fronthaul networks, we propose a hybrid bidirectional fronthaul C-RAN topology based on Wavelength Division Multiplexing (WDM) passive optical networks (PONs) and free space optical communication (FSO). The wavelength reuse scheme utilized here relies on reflective semiconductor optical amplifiers (RSOAs) to reduce cost and increase capacity. The system was demonstrated for 20 Gbps 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> quadrature amplitude modulation (16-QAM) intensity-modulated orthogonal frequency-division multiplexing (OFDM) downstream signals and 5 Gbps On-off keying (OOK) upstream signals, respectively. A Gamma-Gamma channel model is used to demonstrate optical signal transmission over an FSO link. The bit error rate (BER) results indicate that the hybrid WDM-PON-FSO based fronthaul architecture could achieve 320 Gbps over 20 km of single-mode fiber (SMF) and 700 m free space transmission.

SOA Assisted Wavelength Reusing for 25G Colorless PON With Low-Cost 10G EAM

This paper demonstrates a C-band 25G colorless passive optical network (PON) based on semiconductor optical amplifier (SOA) and 10G electro-absorption modulator (EAM). The experimental results show that the SOA in the optical network unit (ONU) can erase the downlink signal by taking advantage of the gain saturation feature, realizing the reuse of downstream wavelength. Meanwhile, the SOA gain can compensate for the EAM loss by optimizing the current and injection power. Apart from this, equalization algorithms at the optical line terminal are investigated for linear and nonlinear impairments compensation. Besides, the system robustness to the ASE and the maximum transmission speed are also evaluated. Finally, the system capacity can reach up to 25 Gbps with NRZ format at a bit-error ratio threshold of 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> , proving that this system is a promising technology for future high-speed colorless 2 × 25G or 4 × 25G Wavelength division Multiplexing (WDM) PON system.

Bidirectional colorless WDM-PON RoF system with large spurious free dynamic range

A bidirectional colorless wavelength-division-multiplexed passive optical network radio over fiber system with a large spurious-free dynamic range (SFDR) is proposed. By separating the unmodulated optical carrier from the polarization multiplexed optical signal in the optical network unit, upstream wavelength reuse is realized. By adjusting the angle and phase difference between the orthogonal optical polarization modes, third-order intermodulation distortion (IMD3) suppression of the downstream link is realized. The periodic power fading caused by dispersion in the system is solved through single sideband modulation. Experiments have verified the wavelength reuse effect of the upstream link. Compared with the traditional link based on a Mach–Zehnder modulator, the periodic power fading of the system is suppressed under different radio frequencies (RFs) and fiber lengths. The IMD3 of the downstream link is suppressed, and the SFDR is improved by more than 17 dB. Also, the proposed system is tested with a 16 quadrature amplitude modulation RF signal in the experiment, where a good adjacent channel power ratio and error vector magnitude of the system are obtained.

Coherent 16-QAM bidirectional fiber-wireless hybrid access network with optimal use of the optical local oscillator signal

This work reports on the optimal use of an optical local oscillator signal from a gain-switched vertical cavity surface emitting laser (VCSEL) optical frequency comb (OFC) in wavelength division multiplexed (WDM) fixed-wireless access networks. The system was tested for its ability to transmit full-duplex error-free data signals to and from a fixed/wireless user. The idea of wavelength reuse was used for the first time to our knowledge, for simultaneous upstream, downstream, and photonic up-conversion to high-frequency RF carrier. Two optical carrier signals were filtered from the generated OFC. One of the two optical carriers was modulated with 16-QAM 28-Gbps data signal. The second optical carrier was amplitude-modulated with an 8.5-Gbps on-off keying (OOK) data signal. These two modulated optical carriers were multiplexed and transmitted over 24 km of standard single mode fiber (SSMF). At the remote site, the second optical carrier carrying the 8.5-Gbps data was selected, demodulated, and recovered. The recovered optical wavelength was used both for photonic up-conversion and for upstream data transmission. Error-free performance was obtained for both downstream, upstream, and wireless data transmission. The wireless carrier obtained after photonic up-conversion using the recovered wavelength was transmitted over a 4-m wireless distance. An EVM of 7% was obtained for the 16-QAM signal. These results are attractive as they demonstrate and motivate the possibility of using gain-switched VCSELs as OFC sources in future fixed-wireless WDM access networks. Wavelength reuse improves the spectral efficiency in the optical and RF domain. The use of VCSELs results in power-efficient access networks.

Intracavity interrogation of an array of fiber Bragg gratings.

In this work, we explore the interrogation of an array of fiber Bragg gratings as part of a laser cavity. A semiconductor optical amplifier in a sigma-shaped fiber cavity provides gain and is gated periodically at a rate that matches the roundtrip time associated with each grating of the array. The interrogator exhibits clear laser properties such as a threshold and linewidth narrowing. Besides improving the signal-to-noise ratio and enabling the re-use of wavelengths, it is found that this interrogation scheme enables monitoring of weak gratings spaced by less than 1 cm. Intracavity grating interrogation studied here is found to be a simple and powerful way to increase the number of sensor points for industrial applications.

A full duplex ultrawideband over free‐space optics architecture based on polarization multiplexing and wavelength reuse

AbstractThis article demonstrates the integration of fiber optics with free space optics for the transmission of ultrawideband signals at a data rate of 2 Gbps. The fiber‐based components enable all‐optical generation of ultrawideband signals. The free space optical link allows bandwidth flexibility along with reduced installation costs. The proposed architecture employs polarization multiplexing and carrier reuse in order to make the radio access units simple and cost‐efficient. The free space optical link is modeled using the log‐normal (LN) channel model. Bit‐error‐rate (BER) measurements demonstrate that the proposed link is suitable for the transmission of high throughput ultrawideband signals.

Full-duplex WDM-RoF system based on OFC with dual frequency microwave signal generation and wavelength reuse

Abstract A novel full-duplex wavelength division multiplexing radio-over-fiber (WDM-RoF) system based on optical frequency comb (OFC), which can generate dual frequency microwave signal simultaneously and realize wavelength reuse for uplink transmission, is proposed. In this proposal, OFC, which serves as the optical carriers of the WDM-RoF network, is performed by cascading two electro-absorption modulators (EAMs) and a frequency modulator (FM). The optical carriers are modulated by the radio frequency (RF) signal in LiNbO3 Mach-Zehnder modulator (LN-MZM) to produce multiple optical single sidebands (OSSB). The multiple OSSB signals are divided into multiple individual channels by AWG, and each channel contains two optical carriers and two corresponding +1 order sidebands. The first optical carrier of each channel is reflected by fiber bragg grating (FBG) and reused to provide the optical source for the uplink transmission in the base station (BS), which simplify the configuration of base station. Dual-frequency microwave signals are generated in the downlink by beating the remaining second optical carrier and two +1 order sidebands. In the simulation, 6 WDM channels each carrying 2.5 Gb/s downlink data have been up-converted to 15 GHz and 25 GHz microwave signals simultaneously, and 6 WDM channels each carrying 2.5 Gb/s uplink baseband data are sent to the central station. Both downlink and uplink transmission with less than 1 dB power penalty on average after 20 km SMF transmission. This full-duplex WDM-RoF system shows high spectral-efficiency, large communication capacity, simple cost-efficient configuration and good performance over long distance transmission.

Improved self-seeding and carrier remodulation performance for WDM-PON by means of double RSOA erasure

In this work, we investigated a novel wavelength division multiplexing passive optical network (WDM-PON) configuration, based on cascaded reflective semiconductor optical amplifiers (RSOA) data erasure for combined self-seeding and wavelength reuse. Improved performance is achieved by enhanced erasure efficiency using a self-seeded double-RSOA cavity at the optical line terminal (OLT) and cascaded RSOAs at the optical network terminal (ONT). To carry out the study, our experimental results for our earlier combined topology layout operating at a symmetric transmission were used to validate the simulation framework for the proposed double-RSOA erasure configuration. Using our original single-cavity self-seeding WDM-PON architecture as a benchmark, downstream extinction ratio (ERD) margins of 6.5 dB and 9.0 dB are obtained, for generating self-seeded downstream signals and upstream remodulation, respectively. Also, bidirectional transmission of 1.25 Gb/s over links reach up to 45 km is achieved by the double-RSOA cavity, surpassing in 25 km our original combined topology. The results indicated that our proposition effectively addresses a fundamental trade-off for WDM-PONs based on the wavelength reuse and/or self-seeding techniques. Specifically, the double erasure procedure allows the use of relatively high levels of ERD, thereby providing improved bit error rate (BER) at the ONT, while assuring high-quality generation of the self-seeding carrier and loopback operation.

Ultra-fast optical switch with reconfigurable wavelength reuse functionality for dynamic flexible spectrum networks

ABSTRACTCurrent optical interconnects are dominated by electrical wavelength converter module technologies which are not only power consuming but also bandwidth limited. We experimentally demonstrate a technique to maximize network robustness, flexibility and efficiency through combined adoption of energy-efficient VCSELs, distributed forward Raman, all-optical wavelength conversion and reuse. The precise wavelength selectivity of a fibre Bragg grating (FBG) is exploited to realize all-optical wavelength switch at 10 Gbps directly modulated 1549.60 nm VCSEL channel. The 6.2 dB flat gain of a forward Raman amplifier is exploited to achieve a 25.25 km downstream transmission of the switched channel incurring a 1.23 dB transmission penalty. Gain saturation of an Erbium-doped fibre amplifier (EDFA) is incorporated to achieve real-time all-optical data erase/rewrite. The 1549.62 nm VCSEL channel is further reused for upstream transmission of 8.5 Gbps data incurring a maximum penalty of 0.83 dB. Our concept is key for adoption in dynamic wavelength routing for spectral utilization in optical interconnect.

OPTUNS: Optical intra-data center network architecture and prototype testbed for a 5G edge cloud [Invited

An edge data center (EDC) network infrastructure is required to flexibly deliver massive bandwidth and ultralow latency for a 5G edge cloud. Existing electrical-switching-based infrastructure, however, has been shown incapable of meeting such requirements. In this paper, we present an EDC network architecture and prototype testbed, referred to as the intelligence-defined optical tunnel network system (OPTUNS). OPTUNS consists of a set of optical switching subsystems that operate collectively to facilitate packet transport through logical wavelength-based optical tunnels. These optical tunnels are governed by a software-defined-networking-based intelligent tunnel control system, in a proactive manner. As such, optical tunnels are always made available whenever needed. In essence, OPTUNS boasts several crucial features, including high scalability, massive wavelength reuse (yielding high bandwidth), proactive optical tunnel control (yielding ultralow latency), and fault tolerance. We have built an OPTUNS testbed, including 30 optical switching subsystem prototypes, that interconnect a total of 25 racks (400 servers). Benchmarking results show that OPTUNS achieves 82.6% power saving compared with electrical spine-leaf networks. Further, our NetPipe-based experimental results show that OPTUNS invariably achieves mean and p99 end-to-end latencies of less than 17 µs, regardless of traffic load and locality.

Optimal and Computationally Efficient Priority-Based Routing and Wavelength Allocation Strategy Supporting Qos for High-Speed Transport Networks

One of major optical network problem is to route and to assign the wavelength efficiently because of its wavelength reuse characteristics and information transparency. By utilizing the trade-off scheme between the blocking probability and setup time of the requested route, priority-based RWA (PRWA) approaches has been studied for WDM networks by introducing a priority criterion which depends on calculation of hop counts and volume of the traffic. The simulation result shows that PRWA technique reduces both the blocking probability (approx. 20%) as compare with non-priority based RWA scheme and the average end to end delay near about (10 msec.) as compare with Adaptive routing (AR) at various traffic load conditions. This approach also results in cost-effectiveness as well as reduction in the complexity of the network in comparison to earlier reported techniques

VCSEL wavelength reuse for intrinsically bidirectional data traffics in next generation GPONs

VCSEL wavelength reuse for intrinsically bidirectional data traffics in next generation GPONs

Real-time wavelength reuse based on Bragg trans-reflection for dynamic reference frequency and data transfer in Datacom

ABSTRACTWe experimentally demonstrate the first VCSEL-based all-optical wavelength reuse technique with reconfigurable fibre Bragg grating add and drop multiplexer. EDFA gain saturation and Bragg trans-reflection effect on a single FBG are respectively, adopted for full-duplex reference frequency and data transfer. A 1550 nm energy-efficient VCSEL is modulated with 1.7 GHz clock signal and transferred downstream over 26.6 km fibre OLT attain a phase noise stability of −54.01 dBc/Hz at 10 kHz offset frequency. A saturated EDFA is exploited to optically reduce the peak-to-peak voltage of the incoming downstream RF, allowing for wavelength reuse with 10 Gbps upstream data. A 1.57 dB transmission penalty is incurred over the transmission fibre. An all-passive OADM is developed exploiting Bragg trans-reflection at 1549.45 nm. The reflected wavelength is routed over another 24.7 km fibre network attaining an extinction ratio of 6.1 dB and a SNR of 5.8 dB. This work provides an all-optical technique for routing and spectral management in flexible networks.

All-optical wavelength reuse with simultaneous upstream data and PPS timing signal transfer for flexible optical access networks

All-optical wavelength reuse is a viable approach for realization of low cost colourless ONUs. We experimentally demonstrate a novel all-optical wavelength reuse technique with simultaneous upstream data and pulse-per-second signal transfer, exploiting EDFA gain saturation with a holding beam. A DFB laser is modulated with 8.5 Gbps data and transmitted downstream over 24.7 km fibre. A saturated EDFA located at the ONU is adopted to reduce the extinction ratio of the downstream data from 6.2 dB to 839.1 mdB. This allows for data rewrite and wavelength reuse for upstream transmission. Receiver sensitivities of −20.19 dBm and −19.60 dBm are achieved at back-to-back analysis and 24.7 km downstream link respectively. A holding beam is further exploited to attain simultaneous carrier reuse and PPS clock upstream transfer. PPS jitter stability of 1.01 × 10-08 ns and 6.64 × 10-08 ns are attained respectively. This work offers a convenient all-optical wavelength reuse solutions for optical access networks.