Bidirectional Wavelength Division Multiplexing Research Articles

Bidirectional WDM Multi-Nodes Analog Radio-Over-Fiber Mobile Fronthaul Link Enhanced by Photonic Integrated Devices

A bidirectional wavelength division multiplexing (WDM) analog radio-over-fiber (A-RoF) mobile fronthaul (MFH) link is enhanced using photonic integrated devices. Two key photonic integrated devices are combined in the A-RoF link: an 8-channel InP directly modulated laser (DML) transmitter and a 32×100-GHz silicon array waveguide grating (AWG). The DML transmitter has 8 parallel monolithically integrated distributed feedback lasers, enabling cooperative and reconfigurable downlink analog transmission. Moreover, the 32×100-GHz AWG is featured by low insertion loss (<4.5-dB) and low crosstalk (<−20.4-dB), to achieve a high-density WDM system. In the distributed field experiments, we have successfully demonstrated a bidirectional A-RoF MFH over 10-km standard single mode fiber, providing an 8×5-Gbit/s 4-quadrature amplitude modulation (QAM) orthogonal frequency division modulation (OFDM) downlink transmission and a 3×12-Gbit/s 16-QAM uplink transmission.

Multiple-Node Time Synchronization Over Hybrid Star and Bus Fiber Network Without Requiring Link Calibration

In this article, a multiple-node fiber-optic time synchronization scheme is proposed over a hybrid star and bus-shaped optical fiber network based on the bidirectional wavelength division multiplexing (BWDM) transmission. Time signals can be obtained at arbitrary access and remote nodes, which are accurately synchronized with the one at the local node by compensating for the transmission delay of corresponding fiber link. By utilizing the optimized wavelengths configuration, in addition to eliminating the impact of single Rayleigh backscattering of the optical fiber, the effect of bidirectional wavelengths asymmetry on the accuracy of time synchronization is also effectively suppressed. Therefore, link calibrations are not required in the proposed scheme. Experimentally, a multiple-node time synchronization system is demonstrated over a hybrid star and bus fiber network with three branches. The results show that the stabilities in terms of time deviation (TDEV) of less than 30 ps at 1 s and 5 ps at 10000 s can be obtained for all of the access and remote nodes, and the clock difference of less than 25 ps can be achieved.

Research on Rayleigh Scattering and Brillouin Scattering of Bidirectional Wavelength Division Multiplexing System

In order to study the influence of Rayleigh and Brillouin scattering on the performance of bidirectional Wavelength Division Multiplexing (WDM) system. On the VPI simulation platform, a two-way WDM simulation system was built. Rayleigh scattering and Brillouin scattering were generated by setting the parameters of the optical fiber module and system parameters such as Brillouin Scattering, Rayleigh scattering, Rayleigh Distortion, and Rayleigh Distortions. Then, the frequency spectrum of the received signal and the bit error rate were observed and analysed. Experimental results show that Rayleigh and Brillouin scattering will cause the performance of the two-way WDM system to degrade. By separating the back propagation channel, the impact of these two effects on the performance of the two-way WDM system can be reduced.

Bidirectional optical amplifier for time transfer using bidirectional WDM transmission

In this letter, we propose a bidirectional optical amplification scheme for fiber-optic time transfer based on bidirectional wavelength-division multiplexing (WDM) transmission. The proposed scheme employs single unidirectional erbiumdoped fiber amplifier (Uni-EDFA) for commercial optical networks to implement bidirectional optical amplification. Since including isolators, the effect of backscattering due to the accumulated amplification can be efficiently suppressed by the proposed amplifier. The proposed scheme is validated over different length fiber links in laboratory. Experimental results show that the proposed amplifier can support fiber-optic time transfer over several thousands of kilometers with an additional bidirectional delay difference fluctuation at picosecond magnitude.

Silicon-based hybrid demultiplexer for wavelength- and mode-division multiplexing.

A silicon-based hybrid demultiplexer for wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM) is proposed and demonstrated by integrating an M-channel-mode demultiplexer and N-channel WDM filters based on microring resonators (MRRs) with box-like responses. For the mode demultiplexer, the 2k-th output port is connected with the (2k+1)-th output port through the bus waveguide for the k-th MRR array, so that each MRR-based optical filter works bi-directionally and provides two drop ports. As an example, a 32-channel hybrid MDM-WDM demultiplexer is realized by integrating a 4-channel mode demultiplexer based on dual-core adiabatic tapers and two bi-directional MRR-based WDM filters with eight wavelength-channels. For the fabricated hybrid demultiplexer, the excess loss is 0.5-5dB, the intermode cross talk is -16.5 to -23.5 dB, and the cross talks between the adjacent and nonadjacent wavelength channels are about -25 dB and -35 dB, respectively.

Spectral Efficiencies of Channel-Interleaved Bidirectional and Unidirectional Ultradense WDM for Metro Applications

We measure spectral efficiencies of ultra-dense (UD) wavelength-division multiplexing (WDM) channels for metro applications. We change the channel spacing in 500-MHz step using a beat-frequency-locking method. Applying both a polarization control (PC) and a forward-error correction (FEC), we achieve spectral efficiencies as high as 1.54 and 0.91 b/s/Hz in back-to-back operations for channel-interleaved (CI) bidirectional and unidirectional UD-WDM, respectively. If we use the PC and the FEC separately for the CI-bidirectional UD-WDM, the PC enhances the spectral efficiency over the FEC by 4.6%-21.2% as the transmission distance is increased.

A Bidirectional WDM Transport System Based on RSOAs and Optoelectronic Feedback Technique

Abstract-A bidirectional wavelength-division-multiplexing (WDM) transport system base on two reflective semiconductor optical amplifiers (RSOAs) and optoelectronic feedback technique is proposed and experimentally demonstrated. One RSOA is employed as a broadband light source and another RSOA in combination with optoelectronic feedback technique is used as wavelengths reuse and data signal remodulation scheme. System architecture is further simplified by using only one RSOA at the optical node, and system performance is further improved by optoelectronic feedback technique. Impressive performances of bit error rate (BER) (<;10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> ) were achieved for both 2.5 Gbps down-link and 1.25 Gbps up-link transmissions.

Multicast Capacity of Packet-Switched Ring WDM Networks

Packet-switched unidirectional and bidirectional ring wavelength division multiplexing (WDM) networks with destination stripping provide an increased capacity due to spatial wavelength reuse. Besides unicast traffic, future destination stripping ring WDM networks also need to support multicast traffic efficiently. This article examines the largest achievable transmitter throughput, receiver throughput, and multicast throughput of both unidirectional and bidirectional ring WDM networks with destination stripping. A probabilistic analysis evaluates both the nominal capacity, which is based on the mean hop distances traveled by the multicast packet copies, and the effective capacity, which is based on the ring segment with the highest utilization probability, for each of the three throughput metrics. The developed analytical methodology accommodates not only multicast traffic with arbitrary multicast fanout but also unicast and broadcast traffic. Numerical investigations compare the nominal transmission, receiver, and multicast capacities with the effective transmission, receiver, and multicast capacities and examine the impact of number of ring nodes and multicast fanout on the effective transmission, reception, and multicast capacity of both types of ring networks for different unicast, multicast, and broadcast traffic scenarios and different mixes of unicast and multicast traffic. The presented analytical methodology enables the evaluation and comparison of future multicast-capable medium access control (MAC) protocols for unidirectional and bidirectional ring WDM networks in terms of transmitter, receiver, and multicast throughput efficiency.

On the multicast capacity of unidirectional and bidirectional packet-switched WDM ring networks

In this paper we examine the relationship between the effective capacity (stability limit) of unidirectional and bidirectional packet-switched wavelength division multiplexing (WDM) ring networks for multicast traffic. We consider both bidirectional rings with one packet copy transmission per wavelength channel and two packet copy transmissions. We first prove bounds for the ratio of the multicast capacity of the bidirectional ring to the multicast capacity of the unidirectional ring. Specifically, we show that this ratio is at least two for two copy transmission in the bidirectional ring, and at most two for one copy transmission. We derive closed form expressions of the multicast capacity ratios for networks with a large number of nodes and from these expressions show that the ratios tend to two for a large number of multicast destinations. We demonstrate that for the bidirectional ring with two copy transmission the ratio becomes as large as 2.276. We also find that in the bidirectional ring, the capacity gain with two copy transmission over one copy transmission reaches 30.4%

Bidirectional WDM Transmission Technique Utilizing Two Identical Sets of Wavelengths for Both Directions Over a Single Fiber

In-band crosstalk due to Rayleigh backscattering (RB) can be avoided in bidirectional wavelength-division multiplexed (WDM) transmission systems when using two identical sets of wavelengths in opposite directions over a single fiber. We describe this by using such sets in a disjoint manner and eliminating the RB crosstalk with the help of simple optical edge filters instead of the WDM comb filters previously employed in interleaved bidirectional systems. We also provide a practical application example and describe the power penalty due to the interferometric RB crosstalk, taking into account recent polarized optical noise research because RB light is partially polarized. Numerical results for externally modulated intensity-modulation/direct-detection (IM/DD) optical systems show that the power penalty can be kept less than 0.5 dB with moderate edge filters, even for more than several tens of optically amplified repeater segments

Employing injection-locked Fabry–Perot laser diodes to improve bidirectional WDM–PON performances

We proposed and demonstrated a bidirectional wavelength-division-multiplexing (WDM)–passive optical network (PON) employing injection-locked Fabry–Perot laser diodes (FP LDs) at both transmitting sites, and adaptive filters at both receiving sites. Injection-locked FP LDs, a particularly inexpensive option, are used to replace the conventional distributed feedback (DFB) LDs in WDM–PON. Adaptive filters are attractive because they can track the variations and compensate the nonlinear distortions. Transmission performance over 20km of a standard single-mode fiber (SMF) was investigated. Improved performance of bit error rate (BER), better and clear eye diagram were achieved in our proposed WDM–PON.

HDTV/Gigabit Ethernet over bidirectional WDM–PON based on injection-locked Fabry–Perot laser diodes

Bidirectional high definition television (HDTV)/Gigabit Ethernet over wavelength-division-multiplexing (WDM)-passive optical network (PON) based on injection-locked Fabry–Perot laser diodes (FP LDs) as transmitters were proposed and demonstrated. Injection-locked FP LDs, a particularly inexpensive option, are used to replace conventional distributed feedback (DFB) LDs. Services with 77 HDTV channels and 1 Gigabit Ethernet channel connection were successfully demonstrated over 40km single-mode fiber (SMF) transport. Good performance of bit error rate (BER) and clear eye diagram were achieved in our proposed bidirectional WDM–PON.

Fiber link loss monitoring scheme in bidirectional WDM transmission using ASE-injected FP-LD

We propose and demonstrate a novel fiber link loss monitoring method for a wavelength-division-multiplexed (WDM) passive optical network. This method is based on the optical signal comparison between a reference amplified spontaneous emission signal and its reflection from an optical reflector. Therefore, we can calculate the link loss exactly and also measure the characteristics of upstream optical signals without suspending the in-service channels. Since this scheme does not use narrow-band wavelength-dependent components such as fiber Bragg gratings, it is cost-effective in implementation and maintenance within a real optical network. We experimentally demonstrate that the link quality of upstream signals as well as fiber link faults on all WDM channels can be monitored in real time

Estimation of performance degradation of bidirectional WDM transmission systems due to Rayleigh backscattering and ASE noises using numerical and analytical models

We develop a numerical model for the transmission performance of bidirectional wavelength-division-multiplexed (WDM) transmissions. Using the numerical model, wavelength-interleaved 10-Gb/s bidirectional WDM systems are analyzed by considering the impairment of the system performance due to Rayleigh backscattering (RB). We also calculate the power penalty and the crosstalk due to RB from the analytical model, and then compare to the results obtained from the numerical model. The analytical model can provide similar results obtained from the numerical model. Both the numerical and analytical models suggest that the total isolation of filters must be more than 19.5 dB for 320-km transmission while keeping the power penalty of less than 2 dB.

Automatic gain-controlled bidirectional add-drop amplifier for dynamically reconfigurable bidirectional WDM networks

An automatic gain-controlled bidirectional add-drop amplifier (BADA) has been realized by incorporating pump-controlled bidirectional and unidirectional EDFAs. By using the BADAs, we demonstrate a dynamically reconfigurable bidirectional wavelength division multiplexed (WDM) ring network. The BADA enables dynamic add-drops of wavelength-interleaved bidirectional signals and protects surviving signals against the impairments induced by dynamic network reconfigurations.

A performance and implementation comparison of bidirectional and dual bus 2-D WDM multiple-plane optical interconnections with row-column multihop network structures

Bidirectional and dual bus wavelength division multiplexing (WDM) two-dimensional (2-D) multiple-plane optical interconnections with row-column multihop network structures using vertical-cavity surface-emitting lasers (VCSELs) and wavelength-selective detectors are analyzed and compared in terms of the expected number of hops (switching delay) and practical implementation considerations. The bidirectional WDM optical interconnection significantly reduces the necessary implementation hardware while maintaining the performance very closely compared to the dual bus architecture. Both WDM structures show significant performance improvements even when only three to five wavelengths are used. Also, the multihop efficiency is analyzed with the consideration of both electrical hops and optical hops.

16 x 10 Gb/s WDM bidirectional gating in a semiconductor optical amplifier for optical cross connects exploiting network connection symmetry

In order to further reduce the number of gating elements in space switches, the performance of 10 Gb/s wavelength division multiplexing (WDM) bidirectional semiconductor optical amplifier (SOA) gating is investigated, We demonstrate for the first time that a conventional SOA can be used for bidirectional WDM gating operation at 10 Gb/s by the use of holding light injection.

2.5 Gb/s x 16-channel bidirectional WDM transmission system using bidirectional erbium-doped fiber amplifier based on spectrally interleaved synchronized etalon filters

The implemented a bidirectional erbium-doped fiber amplifier using two spectrally interleaved synchronized etalon filters. This amplifier was used to demonstrate 2.5 Gb/s/spl times/16 channel bidirectional wavelength-division-multiplexed (WDM) transmission over 160-km-long single mode fiber. No power penalty was observed in receiver sensitivity caused by relative intensity noise. In addition, we measured the performance of the concatenated amplifiers using a recirculating loop. The results show that it would be possible to use the proposed amplifier for the transmission of bidirectional WDM signals over seven amplifier spans (/spl sim/560 km) with a span loss of 20 dB.

Accurate time/frequency transfer method using bidirectional WDM transmission

An accurate time transfer method is proposed using bidirectional wavelength division multiplexing (WDM) signal transmission along a single optical fiber. This method will be used in digital telecommunication networks to yield a time synchronization accuracy of better than 1 ns for long transmission lines over several tens of kilometers. The method can accurately measure the difference in delay between two wavelength signals caused by the chromatic dispersion in the fiber for conventional simple bidirectional dual-wavelength frequency transfer methods. We describe the characteristics of this difference in delay and show that the accuracy of the delay measurement can be obtained below 0.1 ns by transmitting 156-Mb/s time reference signals of 1.31 and 1.55 /spl mu/m along a 50-km fiber using the proposed method. Subnanosecond delay measurement using the simple bidirectional dual-wavelength transmission along a 100-km fiber with a wavelength spacing of 1 nm in the 1.55-/spl mu/m range is also shown.

Eight-channel bidirectional WDM add/drop multiplexer

The authors propose and demonstrate an eight-channel reconfigurable bidirectional wavelength division multiplexed (WDM) add-drop multiplexer in which all channels can be added/dropped independently in either direction. The performance of the bidirectional WDM add/drop multiplexer is experimentally studied for a data rate of 10 Gbit/s per channel, providing an overall capacity of 80 Gbit/s. It is found that the performance of the add/drop multiplexer is not degraded by a backward propagating signal.