WDM PON Research Articles

Effects of In-Band Crosstalk in Wavelength-Locked Fabry–PÉrot Laser-Diode-Based WDM PONs

We investigated the impact of in-band crosstalk on the system's performance in wavelength-locked Fabry-Perot laser-diode (FP-LD)-based wavelength-division-multiplexed passive optical networks (WDM PONs). As expected, wavelength-locked FP-LD, which was injected by using an incoherent broadband light source, was more tolerant to in-band crosstalk than distributed-feedback (DFB) laser diode. A 1-dB power penalty in the wavelength-locked FP-LD-based PON system was observed when the crosstalk-to-signal ratio was ~-9 dB. We also compared the measured power penalties with the calculated power penalties. It has been shown that the in-band crosstalk-induced power penalty in wavelength-locked FP-LD-based WDM PON could be estimated properly by taking into account both effects of power addition and signal-crosstalk beat noise.

Effects of Reflection in RSOA-Based WDM PON Utilizing Remodulation Technique

We investigate the effects of the discrete reflection on the performances of upstream and downstream signals in the wavelength-division-multiplexed passive optical network (WDM PON) implemented in a single-fiber loopback configuration using the reflective semiconductor optical amplifiers (RSOAs). We first analyze the optical beat interference (OBI) noise caused by the discrete reflection, and clarify the relation between the reflection tolerance and the network's operating conditions such as the RSOA gain, the link loss, and the location of the reflection point, etc. The results show that the impact of the reflection can be expressed by using the effective crosstalk level. We then measured the reflection tolerance of the RSOA-based WDM PON, in which the downstream signal operating at 1.25 Gb/s is remodulated by the RSOA at the subscriber's site for the transmission of 155-Mb/s upstream signal. The reflection tolerances are measured to be in the range of -42 to - 35ndB for the downstream signals and -29 to -19ndB for the upstream signals, depending on the RSOA gain. These small reflection tolerances are caused by the fact that the reflected light is re-amplified by the RSOA. We also show that the dependence of the reflection tolerance on the RSOA gain can be explained by using the effective crosstalk level. These results are used to evaluate the impacts of the unwanted discrete reflections on the RSOA-based WDM PON.

Design and cost performance of WDM PONs for multi-wavelength users

In many research labs, WDM PON access networks are considered as the next generation optical access. WDM PONs are more adaptable to future technologies than conventional PONs due to their high transmission capacity and their optical transparency. An elementary design concept is the paradigm that defines at least one wavelength for each user. A design tool is presented to analyse all technologically feasible WDM PON architectures and the cost performance based on an optical routing device, the waveguide grating router.

10-Gb/s Operation of RSOA for WDM PON

We report on the 1O-Gb/s operation of the reflective semiconductor optical amplifier (RSOA) for the next-generation wavelength-division-multiplexed passive optical network (WDM PON). The bandwidth of the RSOA used in this experiment is merely 2.2 GHz. Nevertheless, a clear eye opening is obtained at 10 Gb/s by using the electronic equalizer processed offline. We investigate the impacts of the network's operating conditions (such as the injection power to the RSOA and the fiber length) on the performances of these equalizers. The results show that the RSOA-based WDM PON is operable at 10 Gb/s and the maximum reach can be extended to >20 km with the help of the forward error correction codes.

Enhanced Operating Range of WDM PON Implemented by Using Uncooled RSOAs

We report on the operable ranges of temperature and wavelength for a 1.25-Gb/s wavelength-division-multiplexed passive optical network (WDM PON) implemented by using uncooled reflective semiconductor optical amplifiers (RSOAs). Both the gain and modulation bandwidth of the RSOA are substantially reduced at high temperatures. As a result, it is difficult to achieve the error- free operation at temperatures above 40degC. In order to mitigate this limitation, we implement a simple bias-control circuit, in which the bias current is controlled stepwise according to the operating temperature of the RSOA. Using this circuit, we extend the operable wavelength range of the RSOA-based WDM PON to ~55 nm in the temperature range of -20degC to 60degC.

Real-time monitoring implementation in a remote-pumped WDM PON

We report on an improved configuration to monitor a passive optical network with high quality in service. This proposed system comprises fiber-Bragg gratings, a 1 × 4 optical switch, and an optical time-domain reflectometry to diagnose the broken point in real time. It could simultaneously detect multioptical network units in a WDM PON. The remote-pump integrated residual pumping reused function is implemented. Broken points in different optical paths can be detected simultaneously even when the distances to the central office are identical. The bit-error rate testing is verified with a small power penalty, making it an ideal solution for the real-time monitoring in a WDM PON.

Connection anonymity analysis in coded-WDM PONs

A coded wavelength division multiplexing passive optical network (WDM PON) is presented for fiber to the home (FTTH) systems to protect against eavesdropping. The proposed scheme applies spectral amplitude coding (SAC) with a unipolar maximal-length sequence (M-sequence) code matrix to generate a specific signature address (coding) and to retrieve its matching address codeword (decoding) by exploiting the cyclic properties inherent in array waveguide grating (AWG) routers. In addition to ensuring the confidentiality of user data, the proposed coded-WDM scheme is also a suitable candidate for the physical layer with connection anonymity. Under the assumption that the eavesdropper applies a photo-detection strategy, it is shown that the coded WDM PON outperforms the conventional TDM PON and WDM PON schemes in terms of a higher degree of connection anonymity. Additionally, the proposed scheme allows the system operator to partition the optical network units (ONUs) into appropriate groups so as to achieve a better degree of anonymity.

Performance analysis of a FTTH link utilizing asymmetric data transmission

A WDM–PON recycling incoming light to transmit upstream data has been analyzed. Effect of Rayleigh scattering, uneven energy distribution and noise accumulation are evaluated to achieve 80 km bidirectional communication with <64× asymmetry factor.

A Challenge to Access/Backbone Integrated Network

An integration of the access/backbone network is expected to become indispensable in the future. We analyze the current and future optical networks and we describe the promising technologies. GMPLS architecture in backbone networks and WDM PON architecture in access networks will play the most important roles. We overview recent studies on the access/backbone integrated network to achieve guaranteed QoS. We also describe the developed system architecture as a milestone toward the access/backbone integrated network.

STARGATE: the next evolutionary step toward unleashing the potential of WDM EPONs [Topics in Optical Communications

WDM EPONs are rapidly becoming mature. In this article we briefly review the state of the art of cost reduction, colorless ONUs, and WDM PONs. We then lift the veil of future WDM EPONs, and elaborate on evolutionary cost-effective upgrades of WDM EPONs and their all-optical WDM integration with Ethernet-based metropolitan area networks to provide transparent connections at the wavelength and sub-wavelength granularity on demand between ONUs residing in different WDM EPONs.

High-speed WDM-PON using CW injection-locked Fabry-Pérot laser diodes

We propose a new WDM-PON architecture using Fabry-Pérot laser diodes (FP-LDs) that are injection-locked by continuous wave (CW) seed light. The modulation characteristics of the CW light injection-locked FP-LD are first investigated. Both uplink and downlink transmissions at 10 Gb/s are experimentally demonstrated using the proposed CW injection-locked FP-LDs. It is shown that up to 16 laser cavity modes can be selectively injection-locked with side mode suppression ratio larger than 30dB. The effects of the location of FP-LD cavity modes, transmission distance, and injection wavelength detuning on the overall transmission performance are investigated. The possibility of eliminating polarization dependence of the proposed CW injection scheme is also experimentally demonstrated by properly configuring a depolarizer. The deployment cost for the proposed WDM PON is potentially low from the fact that the CW laser sources located at the central office can be shared by many WDM-PONs and low-cost FP-LDs are used as light sources for data rates as high as 10 Gb/s.

Enhanced performance of RSOA-based WDM PON by using Manchester coding

Feature Issue on Passive Optical Network Architectures and TechnologiesWe propose and demonstrate that the power budget and scalability of the wavelength-division-multiplexed passive optical network (WDM PON) implemented by using reflective semiconductor optical amplifiers (RSOAs) can be significantly improved by modulating the downstream signals in Manchester format instead of the conventional non-return-to-zero format. As an example, we experimentally show that the maximum transmission distance of the RSOA-based WDM PON can be increased by a factor of 2 by using the Manchester-encoded downstream signals.

Optical reflectometry based on correlation detection and its application to the in-service monitoring of WDM passive optical network

We propose and demonstrate a novel technique for measuring the distribution of the reflectivity along an optical fiber transmission line. Unlike the conventional optical time-domain reflectometer (OTDR), the proposed technique utilizes the data-modulated transmitter itself instead of the optical short-pulse source, and monitors the distribution of the back-reflected light by calculating the cross-correlation of the transmitted and back-reflected signals. In this paper, we describe the operating principle of the proposed technique and discuss its potential limitation on the dynamic range. We also show that this limitation can be mitigated by using the discrete-component elimination algorithm. In addition, we experimentally demonstrate that the proposed technique can be used for the in-service monitoring of the transmission fibers in a wavelength-division multiplexed passive optical network (WDM PON).

Multi-PON access network using a coarse AWG for smooth migration from TDM to WDM PON

An interoperable access network architecture based on a coarse array waveguide grating (AWG) is described, displaying dynamic wavelength assignment to manage the network load across multiple PONs. The multi-PON architecture utilizes coarse Gaussian channels of an AWG to facilitate scalability and smooth migration path between TDM and WDM PONs. Network simulations of a cross-operational protocol platform confirmed successful routing of individual PON clusters through 7 nm-wide passband windows of the AWG. Furthermore, polarization-dependent wavelength shift and phase errors of the device proved not to impose restrain on the routing performance. Optical transmission tests at 2.5 Gbit/s for distances up to 20 km are demonstrated.

Reduction of polarization-induced performance degradation in WDM PON utilizing MQW-SLD-based broadband source

We report on the reduction of polarization-induced performance degradation in WDM PON utilizing MQW-SLD-based ASE source for injection locking to FPLD. The results show that, to suppress the polarization-induced Q penalty sufficiently less than 0.5 dB, the MQW-SLD output should be depolarized within the locking range of the wavelength-locked FPLD.

Analysis of narrow-FSK downstream modulation in colourless WDM PONs

The performance of a colourless WDM PON architecture based on frequency-shift keying (FSK) by direct modulation of a DFB laser diode for the downstream and intensity modulation by means of a reflective semiconductor optical amplifier for the upstream channel is assessed. The operation of the architecture is demonstrated, showing excellent performance for distances up to 25 km.

Analysis of maximum reach in WDM PON architecture based on distributed Raman amplification and pump recycling technique

We analyze the performance of bidirectional WDM PON architecture which utilizes distributed Raman amplification and pump recycling technique. The maximum reach at data rates of 622 Mb/s and 1.25 Gb/s in the proposed WDM PON architecture is calculated by taking into account the effects of power budget, chromatic dispersion of transmission fiber, and Raman amplification-induced noises with a given amount of Raman pump power. From the result, the maximum reach for 622 Mb/s and 1.25 Gb/s signal transmission is calculated to be 65 km and 60 km with a Raman pump power of 700 mW, respectively. We also find that the calculated results agree well with the experimental results which were reported previously.

Forward error correction in WDM PON using spectrum slicing

This paper presents experimental results of the introduction of FEC (forward error correction) in optical access network architectures operating at 625 Mb/s. We have first tested a Reed Solomon code on a point to point architecture to confirm the theoretical 3 dB gain in link budget. The innovative architecture is a wavelength division multiplexed passive optical network (WDM PON) using spectrum slicing and a reflective semiconductor optical amplifier (RSOA) to generate upstream signals. Optical carrier supply by spectrum slicing and modulation and amplification by RSOA is a way of reducing costs in WDM PON but it gives a noisy transmission due to excess intensity noise of broadband sources, Amplified Spontaneous emission of the SOA and beat noise at detection. In this case, adding FEC has more effect and it results in an increased link budget of 5.5 dB. FEC are a simple and efficient solution to compensate for penalties introduced by low cost components in innovative architectures like WDM PON.

Traffic shaping at the edge node in synchronous optical packet-switched networks

We propose and demonstrate simple architectures with self-protection capability for the wavelength-division-multiplexed passive optical network (WDM PON). By utilizing two different wavelength bands for the neighboring WDM PONs, the proposed networks can recover the disrupted signals through the fiber links of the neighboring WDM PON. The protection time was measured to be less than 9 ms, and the power penalty caused by the protection process was negligible.

Broadband, high power, erbium fibre ASE-based CW supercontinuum source for spectrum-sliced WDM PON applications

A simple scheme for the implementation of an erbium fibre ASE-based ultra-broadband source with a high power spectral density, which is based on the CW supercontinuum generation technique, is experimentally demonstrated. A ∼130 nm broadband incoherent light with 500 mW output power is presented. The broadband source is shown to be suitable for spectrum sliced WDM PON applications through a short reach transmission experiment. Error-free transmission of spectrum sliced signals over a 25 km SMF link is achieved.