Wavelength Reuse Research Articles

Simultaneous four channel wavelength conversion of 50Gbps CSRZ–DPSK signals in S and C bands using HNLF without additional pump signals

Optical wavelength conversion is expected to be an important technique for future advanced dense wavelength division multiplexing systems. It enhances wavelength routing capabilities, improves network reconfigurability and eliminating the problem associated with wavelength reuse in network. Here, simultaneous 50Gbps four channel wavelength conversion is established in S and C bands of ITU grid using four wave mixing (FWM) technique in high nonlinear fiber (HNLF) without additional pump signals. Since the four channel wavelength conversion is to be performed, the frequency spacing between the pairs of signal in S and C bands should be maintained in order to avoid the signal degradation by the effect of higher order FWM. Thereby the best frequency spacing between the pairs of signals in S and C bands is estimated to maintain good BER over the wavelength converted signals of both bands. So the selected frequency spacing between the pairs fulfills the freedom of selecting any frequency spacing within a pair of wavelengths in S and C band signals. It is also shown that CSRZ–DPSK modulated input signal enhances the BER of wavelength converted signals over the RZ–DPSK. In addition to this, uniform wavelength conversion over a wide bandwidth with a reduced length of HNLF is achieved and also the best power range is estimated to obtain good conversion efficiency.

A novel OCS millimeter-wave generation scheme with data carried only by one sideband and wavelength reuse for uplink connection

We propose a novel optical carrier suppression (OCS) millimeter-wave generation scheme with data carried only by one sideband using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system, and the transmission performance is also investigated. As the signal is transmitted along the fiber, there is no time shifting of the codes caused by chromatic dispersion. Simulation results show that the eye diagram keeps open and clear even when the optical millimeter-waves are transmitted over 110km and the power penalty is about 1.9dB after fiber transmission distance of 60km. Furthermore, due to the +1 order sideband carrying no data, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5Gbit/s data is successfully transmitted over a 40km standard single mode fiber with less than 0.8dB power penalty in the simulation. Both theoretical analysis and simulation results show that our scheme is feasible and we can obtain a simple cost-efficient configuration and good performance over long-distance transmission.

Optical millimeter-wave signal generation by frequency quadrupling using one dual-drive Mach–Zehnder modulator to overcome chromatic dispersion

We propose a novel approach to generate quadrupling-frequency optical millimeter-wave using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system. By properly adjusting the phase difference in the two modulation arms of MZM, the direct current (DC) bias, the modulation index and the gain of base-band signal, the quadrupling-frequency optical millimeter-wave with signal only carried by one second-order sideband is generated. As the signal is transmitted along the fiber, there is no time shift of the codes caused by chromatic dispersion. Theoretical analysis and simulation results show that the eye diagram keeps open and clear even when the quadrupling-frequency optical millimeter-wave are transmitted over 110km and the power penalty is about 0.45dB after fiber transmission distance of 60km. Furthermore, due to another second-order sideband carrying no signals, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5Gbit/s data is successfully transmitted over 40km standard single mode fiber with less than 0.6dB power penalty in the simulation.

Assessment of linear semiconductor amplifiers for upgrading WDM-PONs with wavelength reuse

In this work we have assessed the capacity of a linear semiconductor optical amplifier to compensate the fiber and component losses present in a wavelength division multiplexing passive optical network (WDM-PON) evolution from fiber-to-the-building (FTTB) to fiber-to-the-home access. The evaluation measurements confirm that the presence of a semiconductor optical amplifier placed at the entry of a group of optical network units that share the same wavelength channel can raise the loss budget that the link can tolerate in the fiber, compensating for the losses of a passive splitter up to a 1:16 division rate, allowing the upgrade of existing WDM-PON FTTB structures to make the fiber reach the final user's home.

A mathematical model for wavelength assignment in wavelength division multiplexing mesh networks with wavelength reuse

This letter presents a mathematical model that minimizes the number of wavelengths required for wavelength assignment in a wavelength-reusable multi-carrier-distributed (WRMD) wavelength division multiplexing mesh network. None of the source nodes in the WRMD network is equipped with laser diodes. It receives carrier wavelengths from a multi-carrier light source or reuses carrier wavelengths from other established lightpaths. The loop problem may occur in mesh topologies when a source node selects a reused carrier wavelength from a destination lightpath node, if we consider only flow conservation constraints, which are usually adopted in conventional network design. We solve the loop problem by formulating constraints that reflect the special characteristics of the WRMD network. To support the development of heuristic algorithms towards large-scale networks, our mathematical model, which can provide reference values including upper and lower bounds, is useful for benchmarks.

A Cost-Effective Full-Duplex Radio-over-Fiber System Based on Frequency Octupling and Wavelength Reuse

The article proposes a novel scheme for full-duplex radio-over-fiber transmissions with frequency-octupling millimeter-wave and wavelength reuse. In this scheme, the base station is simplified greatly as there is no laser, and the uplink millimeter-wave signal is down-converted to a low frequency using a 60-GHz local oscillator, which is optically obtained from the downlink signal. The scheme can utilize optical power efficiently, and thus, a cost-effective radio-over-fiber system is achieved. Transmission performance for both down- and uplink data are theoretically analyzed and investigated by simulation; results show that the performance of the system is not sensitive to fiber dispersion.

Wavelength reuse for uplink on dense wave-division multiplexing single-fiber ring for radio over fiber broadband systems with downlink signal generation in optical domain

We have presented a single-fiber dense wave-division multiplexing (DWDM) ring scheme with wavelength reuse for uplink and optical signal generation for downlink. Instead of using a new laser for uplink, the wavelength already used for wavelength beating to generate the downlink signal in optical domain is reused for uplink. Algorithms for power optimization using Erbium-doped fiber amplifier, wavelength routing, and wavelength assignment are developed and simulated. The DWDM-radio over fiber scheme reusing the wavelength can support the data rate in the range of 1 Gbps. Fifteen remote antenna units (RAUs) are simulated in this scheme; however, these can be increased by adding more wavelengths. The proposed scheme simplifies the architecture or RAUs, decreases the overall cost while enhancing the bandwidth and operational flexibility of radio over fiber systems.

Colorless ONU With All-Optical Clock Recovery for Full-Duplex Dense WDM PONs

We propose a colorless optical network unit (ONU) comprised of a Fabry-Pérot filter (FPF) and a semiconductor optical amplifier (SOA) for all-optical clock recovery of the downstream signal, followed by a Mach-Zehnder modulator (MZM) as the upstream modulator. The all-optical clock recovery performs data erasure allowing for efficient wavelength reuse of the downstream signal for upstream remodulation. Operation at a full-duplex 10-Gb/s symmetrical data rate and 20-dB loss budget is demonstrated over fiber spans of 50 km.

The effect of AWG-filtering on a bidirectional WDM-PON link with spectrum-sliced signals and wavelength-reused signals

The AWG-filtering effect was investigated on a bidirectional 100-GHz-channel-spacing WDM-PON link using spectrum-sliced and RSOA-amplified light sources for downstream signals and a wavelength reuse technique for upstream signals. Three different AWGs including Gaussian, trapezoidal, and rectangular filtering types were applied and their signal performance was compared for link transmission. The performance influence to both directional signals was analyzed and optimized according to an extinction ratio of a downstream signal. It was found that there was an optimal pass bandwidth of AWG for achieving balance between relative intensity noise decrement and cross phase modulation noise increment as the bandwidth got wider.

Photorefractivity of zirconium-doped lithium niobate crystals

Polarization-independent all-optical wavelength converters (AOWCs) enable dynamic signal routing, wavelength reuse, path protection, and restoration.1 These features will be of utmost importance in future generation, high bit-rate optical communication networks. An efficient AWOC—operating on a 100Gb/s phase-modulated polarization-multiplexed signal at 1550nm—was recently realized by exploiting the cascade of two nonlinear optical processes in a lithium niobate (LN) waveguide.2 This cascading technique for wavelength conversion is only effective if the LN crystals are prepared with alternating up and down domains (i.e., periodical poling) of appropriate periodicity. Currently, LN crystals offer the best performance in nonlinear devices, but their applicability is limited by the photorefractive effect, which is a change of refractive index under strong illumination. The standard growth process of LN produces lithium-deficient (i.e., congruent) crystals. The presence of defects in the congruent crystals gives rise to photorefractivity, which is detrimental to the efficiency of nonlinear interactions. To avoid this, one can operate the LN-based wavelength converters at temperatures above 100iC.2 Since this is impossible for most in-field applications, crystals with negligible photorefractivity must be developed. Here, we explore the use of zirconium-doped congruent LN crystals (Zr:LN) for AOWC and other optical devices.3 Photorefractivity can be reduced by employing stoichiometric LN or magnesium ion (Mg2C)-doped LN.4 However, neither approach is fully satisfactory because it is often difficult to grow large crystals of high optical quality. Also, there are Figure 1. Birefringence variation (i n) induced on lithium niobate crystals, as a function of the zirconium (Zr) dioxide doping concentration, at pump-beam intensities of 300 ( ), 600 (N), 900 ( ), and 1200 ( ) W/cm2.

파장분할 다중화 수동광 네트워크에서 적용된 반사형 반도체 증폭기 기반의 광역선폭 광원의 광필터 특성 의존성

The AWG-filtering effect was investigated on a bidirectional 100-GHz-channel-spacing WDM-PON link using spectrum-sliced and RSOA-amplified light sources for downstream signals and a wavelength reuse technique for upstream signals. Signal performances of three different filtering AWGs, including Gaussian, trapezoidal, and rectangular types, were compared on link transmission with fiber nonlinear effects. As an extinction ratio of a downstream signal varied, the effect for both directional signals was analyzed and optimized. It was found that there was an optimal pass bandwidth of an AWG for the balance between relative intensity noise decrement and cross phase modulation noise increment as the bandwidth got wider.

Performance enhancement scheme for RSOA-based WDM-PONS by using a single Fabry-Perot etalon

A scheme for simultaneous extinction ratio enhancement, optical frequency stabilization, and wavelength reuse is proposed for reflective semiconductor optical amplifier-based wavelength-division-multiplexed passive optical networks to stabilize the optical channel frequency and enhance bidirectional transmission.This is achieved by simply employing a single Fabry-Perot etalon at the optical line terminal rather than having one at each optical network unit. Compared with the remodulation scheme that uses a 10-Gb/s optical signal with a 3-dB extinction ratio as a downstream optical signal and a seed light, our scheme shows improvements in power penalties greater than 1.8 dB and 1.4 dB for 10-Gb/s downstream and 1.25-Gb/s upstream signals, respectively, after transmission of 25 km at a bit-error-rate = 10−9. Moreover, a power penalty of only 0.5-dB is observed in comparison to the two 1.25-Gb/s upstream bit-error-rate results based on using a continuous-wave seed light and a data-erased seed light. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26178

Switch Architecture with Wavelength Conversion in Optical Networks

In this paper, we analyze the optical network with wavelength conversion, and discuss the architecture of network with wavelength converter in its node. The optical cross connects technology for wavelength division multiplexing (WDM) is rapidly developing. Wavelength conversion is one of the key techniques for switch WDM optical networks. The wavelength conversion technology can achieve wavelength reuse, decrease wavelength competition, enhance network flexibility and scalability, and simplify network structure and management. The results show that If these cross-connectors feature integrated with wavelength conversion, network will be better able to play the full potential of WDM optical networks.

A Torus-Based 4-Way Fault-Tolerant Backbone Network Architecture for Avionic WDM LANs

In this paper, we leverage the torus topology to design a wavelength division multiplexing (WDM) backbone network for operation in hazardous avionic environments. The proposed WDM local area network offers efficient data delivery and fast fault recovery via establishing four non-overlapping lightpaths for any source-destination pair. First, we describe a torus-based architecture and propose an efficient non-overlapping lightpath setup algorithm: FOLD (Four-way Optimal Disjoint Routing). The algorithm is proved to achieve optimal link utilization. Second, based on the proposed lightpath setup algorithm, a wavelength allocation and reuse (WAR) scheme enforcing wavelength continuity is proposed to minimize the wavelength utilization for all-to-all communication. An analytical calculation on wavelength utilization shows that the proposed WAR performs very close to an ideal wavelength assignment scheme without wavelength continuity being enforced. Lastly, the probabilistic and capacity analysis demonstrates vast reliability improvement via applying the proposed network architecture in terms of network-failure-induced impact on connection reliability and network capacity degradation.

Wavelength Assignment in Multi-Carrier Distributed Optical Ring Networks With Wavelength Reuse

This paper investigates the problem of wavelength assignment in wavelength reusable multi-carrier distributed (WRMD) wavelength-division-multiplexing (WDM) ring networks. In conventional WDM ring networks, each edge node (EN) has its own light sources, and optical channels, called lightpaths, are established by using optical carriers generated from laser diodes (LDs) at the source EN. However, such networks will suffer from the need for complicated wavelength management (e.g., monitoring LDs, avoiding wavelength collision) in the future since each EN requires a large number of LDs to deal with the exponential increase in traffic. On the other hand, a WRMD ring network overcomes this problem. In this network, lightpaths between source and destination ENs are established by using carriers generated from a centralized multi-carrier light source. Moreover, the carrier regeneration technique is applied for the purpose of reducing the number of wavelengths used for lightpath establishment. Although optical carrier regeneration reduces the number of wavelengths, the quality of the regenerated carrier is slightly degraded after carrier regeneration. Therefore, in the WRMD network, the allowable number of carrier regenerations per wavelength must be limited in order to avoid communication error. This paper formulates the wavelength assignment problem, minimizing the number of wavelengths needed to establish all requested lightpaths, as the vertex coloring problem, and then an integer linear programming (ILP) solution is provided. Since ILP problems are non-deterministic polynomial-time- (NP-) complete, a heuristic algorithm is developed. Numerical results indicate that our developed algorithm performs well in our test cases. It is observed that one and two carrier regenerations per wavelength reduce the number of wavelengths for lightpath establishment by approximately 50% and 60%, respectively, compared to that without carrier regeneration. The results also show that regenerating carriers more than two times per wavelength has little effect on the required number of wavelengths regardless of the number of ENs.

Remotely Pumped Long-Reach Hybrid PON With Wavelength Reuse in RSOA-Based ONUs

Symmetrical full-duplex transmission in a Passive Optical Network (PON) is demonstrated over a 100 km dual-fiber ring with 1:16 split trees. The customer premises equipment is based on a Reflective Semiconductor Optical Amplifier (RSOA), which reuses the wavelength of the intensity modulated downstream signal for upstream data transmission. A commercial RSOA was used together with optical offset filtering at the upstream receiver to operate at data rates of 5 and 10 Gb/s. Margins of >; 8 dB are left at a data rate of 5 Gb/s, proving that the utilized downstream suppression scheme and therefore the intensity modulation format for both, down- and upstream, is suitable for its application in long-reach hybrid access networks. The signal degradation along the PON and the transmitted pump that features means of remote amplification in its conjunction points between the metro ring and the local trees are discussed and further possibilities for an improvement of the transmission performance are proposed.

Bidirectional 60-GHz RoF System With Multi-Gb/s $M$-QAM OFDM Single-Sideband Modulation Based on Injection-Locked Lasers

We have experimentally demonstrated a 60-GHz bidirectional radio-over-fiber system with single-sideband (SSB) modulation of orthogonal frequency-division-multiplexing (OFDM) signals for the downlink and wavelength reuse for the uplink. A two-carrier-injected distributed-feedback laser is used to realize the OFDM signals' SSB modulation in the central office for the downlink. In the uplink, the weakly modulated one of the two downlink carriers is filtered out for wavelength reuse. Transmission of 4.3-Gb/s 16-quadrature-amplitude-modulation (QAM) or 3.2-Gb/s 64-QAM OFDM signals on the 60-GHz carrier for the downlink and the 2.5-Gb/s nonreturn-to-zero signal for the uplink are both successfully demonstrated over 56-km standard single-mode fiber without chromatic dispersion compensation.

Simulation and Comparison of Advanced Modulation Formats for Wavelength Reuse in High-SpeedWDM-PON System

In recent years, the innovation in devices and schemes of physical layer plays an important role in promoting the development of WDM-PON (Wavelength Division MultiplexingPassive Optical Network).Among the key technologies adopted in the WDM-PON system, advanced modulation formats at downstream and remodulations at upstream attract the most attention. DPSK (Differential Phase Shift Keying Modulation), FSK(Frequency-Shift Keying), IRZ(Inverted Return-to-Zero) and Manchester are four of the most common formats and each of them was studied before, but, however, nobody compared and analyzed them together.So, we will do the job by numeralsimulation in this paper. During our simulation, the 40-Gbit/s FSK is generated through the demodulation of two DPSK signals and 40-Gbit/s Manchester signal bases of employing a delay interferometer (DI) and an optical delay line as format conversion device to convert RZ-DPSK(Return to Zero-Differential Phase Shift Keying Modulation) coding to Manchester coding, both of the two format generation schemes are novel.Meanwhile,this paper emphasizes the input optical power and dispersion tolerance, which both related to the sensitivity of the system. Analyze the sensitivity with DPSK, FSK, IRZ and Manchester, and then compare the four advanced modulation formats.

Employing inverse return-to-zero and Manchester formats for uplink wavelength reuse in RoF systems

The inverse return-zero (IRZ) modulation format and Manchester format were investigated as wavelength reusing schemes in the RoF downlink systems. Since both of the modulation formats featured power remaining in the bit slot regardless of the bit value, the downlink optical carrier can be reused as the uplink light source. The performances of two formats were analyzed in the symmetrical and asymmetrical duplex RoF system. It was found that IRZ is more suitable for symmetrical system, and the duty cycle of IRZ pulse is the critical factor on the asymmetrical RoF system performance. However the Manchester format demonstrated the large system tolerance on asymmetrical duplex RoF system with the receiver sensitivity degradation within 1 dB.

A Novel Wavelength Re-Use WDM Passive Optical Network Architecture with Broadcasting Service

A novel wavelength re-using architecture with the capability to support broadcasting service has been proposed, which employs a 2N wavelengths to support 2N optical network units (ONUs) for the downstream, upstream signals and broadcasting service. The proposed architecture can significantly improve the wavelength utilization ratio. Compared with other wavelength re-use schemes based on the light-loop and re-modulation using reflective semiconductor optical amplifier (RSOA), the proposed network has a good cross-talk resistance. The maximum transmission distance without amplification is 60 km when the receiver sensitivity is -30 dBm.