Wavelength Division Multiplexing Access Network Research Articles

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.

Symmetric >67 Gbps OFDM-IMDD based WDM access network for mitigating Rayleigh backscattering interference noise

In this paper, we propose a symmetric >67 Gbps/λ wavelength-division-multiplexing (WDM) access network with mitigation of Rayleigh backscattering (RB) interference noise by using the orthogonal frequency division multiplexing (OFDM) modulation and intensity modulation and direct detection (IMDD) method. According to the optimal OFDM bit-loading algorithm design, the fiber chromatic dispersion and RF fading can be improved after a length fiber connection of 20 km long. Moreover, the obtained OFDM modulation rate also can meet the forward error correction (FEC) target.

High-reliable WDM access network based on alternate transmission mode featuring power optimization and network stability

A ring-based wavelength division multiplexing access network is presented in this paper. By introducing a novel alternate transmission mode, the network can optimize the optical power received by each node. By using ring topology, the central office can provide full protection in the case of both single- and double-fiber failure. It can make the number of affected RNs more predictable. And the system oscillation caused by failure can also be controlled in a stable range. By simulation, the mentioned functions are demonstrated. The simulating results show the network has good performance.

Direct Modulation of Hybrid-Integrated InP/Si Transmitters for Short and Long Reach Access Network

Recent progresses on hybrid InP/Si integration are presented for achieving high-performance tunable transmitters for cost-sensitive wavelength division multiplexing access networks. We demonstrate the generation of on-off keying non return to zero modulation format using several types of integrated directly modulated and tunable lasers. The use of the high output power hybrid silicon transmitter enables up to 28.5 dB optical budget at BER = 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> (in-band FEC assumed) under 10 Gb/s direct modulation over 25 and 50 km. Long-reach transmission over 100 km single-mode fiber is also demonstrated. Based on an enhanced modulation bandwidth hybrid laser, we successfully achieve 21.4 Gb/s direct modulation including FEC overhead on 12 wavelengths over a short-reach access link (10 km).

A Scalable Long-Reach Wavelength-Division Multiplexing Access Network Sharing Both Fiber Protection and Broadcasting Services

A novel scalable wavelength-division multiplexing access network is proposed in this article. By newly designing the remote node, this network can not only support the long-reach transmission and broadcasting services, it can also have flexible scalability and the ability of sharing fiber protection. These make this network have great resilient capability. Also, this scheme still has the characteristic of Rayleigh backscattering mitigation and shared-seeding light of upstream signals. The simulation results indicate this network has good performance.

Novel cobweb-topology WDM access network architecture featuring ultra-high reliability and easy scalability

A wavelength division multiplexing access network architecture with cobweb topology is proposed in this paper. It can be a candidate for metro access network with high reliability in the future. This architecture can provide two protection methods. The protection strategy which can maximize the protected traffic is elaborated in the context. Mathematical models of system performance such as network scale and link reliability are established and analyzed in this paper.

C+L band wavelength division multiplexing access network with distributed-controlled protection architecture

In this work, we propose and experimentally demonstrate a novel distributed-controlled protection architecture for automatic and fast network restoration in wavelength division multiplexing-passive optical network (WDM-PON). The proposed scheme can support both C and L bands. Besides, duplication of network equipments, such as optical networking unit (ONU) or optical line terminal, is not required. In this distributed-controlled system, each ONU can always keep track of the network status. Hence, this can facilitate the network manage by removing the work loads from the central office. Besides, the proposed scheme can tolerate simultaneous fiber cuts in the feeder and distributed fibers.

Tunable C- and L-band erbium-doped fiber ring lasers for performance testing of a wavelength-division multiplexing access network with injection-locked Fabry-Pérot laser diodes

A widely wavelength-tunable erbium-doped-fiber laser (T-EDFL) located at a central office is proposed for the bidirectional high-speed performance testing of wavelength-division-multiplexing access networks in which injection-locked Fabry-Perot laser diodes located at optical network units are used for upstream transmissions. The T-EDFL not only generates laser light for downstream transmission testing, but also serves as the injection source for upstream transmission testing. It has a wide tunable range of 64 nm (1540 to 1604 nm), a high output power of 2.2 dBm, and a good signal-to-noise ratio above 46 dB. For 10-Gb/s downstream and 1.25-Gb/s upstream transmissions over a 10-km single-mode fiber (SMF), power penalties at a bit error rate of 10−9 are less than 0.94 dB and 0.76 dB (1.26 dB and 1.68 dB) for downstream and upstream transmissions at C-band (at L-band) wavelengths, respectively. In the transmissions over a 25-km SMF, the penalties are 2.24 dB and 2.36 dB (3.66 dB and 4.18 dB) at C-band (at L-band) for downstream and upstream transmissions, respectively.

Spectral filtering of multiple directly modulated channels for WDM access networks by using an FP etalon

Spectral and waveform reshaping schemes can enhance the transmission distance of fiber links that use directly modulated lasers as transmitters. We prove the feasibility of using a simple Fabry-Perot (FP) etalon as the spectral reshaper for applications in wavelength division multiplexing (WDM) access networks. The transient chirp and adiabatic chirp of a directly modulated laser are analyzed in detail by using the time-resolved chirp measurement. The effects of the original extinction ratio and the adiabatic chirp on the spectral reshaping are clarified to obtain the optimal operation conditions. It is shown that placing a single-cavity FP etalon filter after multiple 10 Gbits/s directly modulated lasers can extend their transmission distances from 50 km in the 1.55 μm wavelength window. Due to the limited filtering capability of the etalon, the choice of the original extinction ratio and finesse of the etalon is discussed in detail from the experiments and simulation.

Gain transient control for wavelength division multiplexed access networks using semiconductor optical amplifiers

Gain transients can severely hamper the upstream network performance in wavelength division multiplexed (WDM) access networks featuring erbium doped fiber amplifiers (EDFAs) or Raman amplification. We experimentally demonstrate for the first time using 10 Gb/s fiber transmission bit error rate measurements how a near-saturated semiconductor optical amplifier (SOA) can be used to control these gain transients. An SOA is shown to reduce the penalty of transients originating in an EDFA from 2.3 dB to 0.2 dB for 10 Gb/s transmission over standard single mode fiber using a 2 31–1 PRBS pattern. The results suggest that a single SOA integrated within a WDM receiver at the metro node could offer a convenient all-optical solution for upstream transient control in WDM access networks.

Precise frequency stabilisation by dithering bias current of directly modulated laser-diodes

A frequency monitoring/stabilisation technique for dense wavelength division multiplexing access networks is proposed. To achieve more precise frequency stabilisation, the bias current used to drive each directly modulated LD is dithered. The key techniques are adding an offset bias to the detected error signal and offsetting the centre frequency of the arrayed waveguide grating port against the grid frequency to achieve effective frequency stabilisation. Experiments show that the relative frequency deviation of ±30 GHz can be suppressed to less than ±1 GHz without any BER degradation.

A centralized-light-source WDM access network utilizing inverse-RZ downstream signal with upstream data remodulation

We propose and demonstrate employing inverse-return-to-zero (IRZ) downstream signal format to facilitate upstream data remodulation in a wavelength division multiplexing (WDM) passive optical network (PON) architecture with centralized light sources. The finite optical power in each downstream IRZ bit can be simply remodulated by the upstream data at the optical network unit. This can make each downstream and upstream pair share a single light source and such light reuse can be easily realized. An experiment on 10-Gb/s downstream IRZ signal generation, 2.5-Gb/s upstream signal remodulation, and two-way transmission is successfully demonstrated. The downstream/upstream signal performance in such a PON has also been analyzed, which is useful for system design.

Tunable external cavity laser based on polymer waveguide platform for WDM access network

We developed a wide-range wavelength tunable external cavity lasers based on a polymer waveguide platform for use in wavelength-division-multiplexing (WDM) access networks as a low-cost light source. The lasing wavelength is tuned over 13 nm by thermally changing the reflection spectrum of the polymer waveguide Bragg grating with a heater. With the sidemode suppression ratio higher than 30 dB, it can support 16 WDM channels spaced by 100 GHz. The directly modulated 1.25-Gb/s data streams were successfully transmitted over the single-mode optical fiber link of 20 km.

An optical network unit for WDM access networks with downstream DPSK and upstream remodulated OOK data using injection-locked FP laser

We investigate the use of optical differential phase-shift keying (DPSK) as the downstream modulation format in a low-cost upstream data remodulation scheme for a wavelength-division multiplexing (WDM)-based passive optical network. A 2.5-Gb/s upstream data transmitter is realized by directly modulating a Fabry-Perot (FP) laser, injection-locked with a 10-Gb/s downstream optical DPSK signal. A simple polarization-offset technique is proposed to largely minimize the induced power penalty.

Upstream traffic transmitter using injection-locked Fabry-Perot laser diode as modulator for WDM access networks

An upstream-traffic transmitter based on a Fabry-Perot laser diode (FP-LD) as modulator is proposed and demonstrated for wavelength division multiplexed (WDM) access networks. By injection-locking the FP-LD with the downstream wavelength at the optical network unit (ONU), the original downstream data can be largely suppressed while the upstream data can be transmitted on the same injection-locked wavelength by simultaneously directly-modulating the FP-LD.

Scalable WDM access network architecture based on photonic slot routing

This paper introduces an approach to solving the fundamental scalability problem of all-optical packet switching wavelength-division multiplexing (WDM) access networks. Current optical networks cannot be scaled by simply adding nodes to existing systems due to the accumulation of insertion losses and/or the limited number of wavelengths. Scalability through bridging requires, on the other hand, the capability to switch packets among adjacent subnetworks on a wavelength basis. Such a solution is, however, not possible due to the unavailability of fast-switching wavelength sensitive devices. In this paper, we propose a scalable WDM access network architecture based on a recently proposed optical switching approach, termed photonic slot routing. According to this approach, entire slots, each carrying multiple packets (one on each wavelength) are "transparently" routed through the network as single units so that wavelength sensitive data flows can be handled using fast-switching wavelength nonsensitive devices based on proven technologies. The paper shows that the photonic slot routing technique can be successfully used to achieve statistical multiplexing of the optical bandwidth in the access network, thus providing a cost-effective solution to today's increasing bandwidth demand for data transmissions.