22-channel detuning capacity of a 2.5Gbit/s directly modulated FPLD based ONU under side-mode
injection-locking for DWDM-PON is demonstrated with SMSR >35dB, Q-factor 6.8-9.2, locking range of 24nm, power
penalty of -0.7dB, and BER of 10-10 at -17dBm. The demonstrated side-mode injection-locked FPLD is a potential
candidate to achieve the cost effective and high capability 2.5Gbit/s DWDM-PON systems. The maximum usable ONU
channels of the side-mode injection-locking FPLD are 22, corresponding to a wavelength locking range of 24 nm.
Direct modulation of the upstream channels was successfully obtained and shows high quality eye diagram at ONU
transmission.
With the overwhelming success of Ethernet technology in local access networks (LANs), owing to its ease of management and its much lower line rate cost, there has been a continuous effort in migrating Ethernet technology into metro-area networks (MANs) and wide-area networks (WANs). However, current Ethernet technology has to overcome the scalability and reliability deficiencies in order to be recognized as a viable MAN/WAN technology. Recently these concerns are being addressed under the framework of Generalized-MPLS (GMPLS) and its traffic-engineering (TE) intelligence. In this paper we propose an optical Ethernet solution viable for MAN/WAN based on the concept of a reconfigurable Ethernet node, integrating reconfigurable optical cross-connects (OXCs) with traditional Ethernet switches. We subsequently proposed a dynamic TE scheme that utilizes both the simplicity of all-optical switching and the flexibility of optical-electrical-optical (OEO) traffic grooming realized by the proposed optical Ethernet node. We showed through simulations that with our proposed TE scheme, the number of OEO transceivers needed by such an optical Ethernet node is only about 20% of a fully-populated one in the extreme case (very high load) and about only 10% in normal load conditions, without degrading the performance. This actually implies a tremendous cost saving on Ethernet OEO transceivers, and on the other hand indicates that a highly efficient and scalable MAN/WAN Ethernet network system could be well achieved by using Ethernet switches of only modest switching capacity (as legacy Ethernet switches have) along with reconfigurable OXCs. To demonstrate and test our proposed ideas we have built a GMPLS testbed using MEMS-based optical cross-bar switches and legacy Gigabit Ethernet switches. The testbed consists of three core nodes and six edge nodes. Performance experiments have been conducted on the testbed as well.
Measured and simulated power penalties were compared for 10Gbit/s NRZ loop experiments for cascaded AWG filters with 50GHz and 100GHz channel spacings. The results show that spectral flatness of cascaded filters can strongly influence the performance of high-speed systems with small channel spacing.
In this paper, we analyzed the system power penalty induced by the coherent crosstalk components as the dominant crosstalk channel in WDM-OXC, and present a simple expression, which can be readily calculated by popular software. We also present an expression of the power penalty when both incoherent and coherent crosstalks are presented. The simulation results show that by introducing a bit pattern mismatch method in a WDM-OXC, the extra penalty caused by the coherent crosstalk can be distinctively suppressed.
In this paper, the design and applications of Large Scale Integrated (LSI) Planar Lightwave Circuits (PLCs) for WDM systems are discussed. The general design issues of PLCs', such as size, loss and crosstalk are addressed. A 32-wavelength optical add/drop multiplexer (OADM) with 4 pairs of fully addressable add/drop ports is presented as an example application for LSI-PLCs.
Reconfigurable optical network, the way of the future, can encounter serious packet loss problem during optical level reconfiguration. This paper presents a novel buffering scheme for GMPLS optical networks that minimizes packet loss during reconfiguration of optical nodes, consisting of both a reconfigurable optical cross-connects (OXCs), or an optical add-drop multiplexers (OADMs), and a packet-capable layer-two switch [1]. In this scheme, buffering takes place whenever an optical path is altered due to either a node reconfiguration or protection/restoration. Packets are buffered in a distributed manner starting from the first O/E/O-capable node before the reconfigured optical node all the way to the ingress node, if needed. In the worst-case scenario, where the path is all-optical or buffers are full along the path, all incoming packets are buffered at the ingress node, or the edge router. Buffering is carried out at layer two so that the interruption of service is kept at a minimum (less than 50ms, if possible). Furthermore, if buffers are overflowed, packets dropping will be carried out in accordance with the QoS levels, which further ensure that QoS of the network is maintained. It is shown by both analysis and simulation methods that this scheme performs quite well on either a general local area network, such as the UMBC WDM optical testbed, or the MCI backbone network. It is also cost-effective in that, even at the worst-case scenario, the required buffer is quite small.
The crosstalk performance of an arrayed-waveguide grating (AWG) multi-/demultiplexer is
primarily caused by random optical phase errors introduced in the arrayed-waveguides. Since the layout of
waveguides on a wafer is patterned by photomask through photolithography process, the resolution of a
photomask has a direct influence on the phase errors of an AWG. This paper presents a theoretical analysis
on the phase error caused by photomask resolution along with other basic design parameters. Both
calculation and measurement results show that a high-resolution photomask (better than 25 nm) is a critical
requirement to produce low-crosstalk (less than -30 dB) AWG demultiplexers. We also investigated the
non-ideal power distribution in the array waveguides since it contributes considerable phase errors when
material impurity is not well controlled during wafer fabrication. Basic criteria of power profile truncation,
number of grating waveguides, and material index variation are summarized in this paper as well.
A wavelength-shift-keying (WSK) proof-of-concept experiment was demonstrated by using tunable
laser and wavelength discriminator with both 2-level and 3-level modulations. Basic applications of this
new technology have been discussed. The WSK could potentially be a high-speed and flexible
transmission technology for future optical networks.
In a dynamic WDM-OXC, due to the various available paths for an incoming signal, there exits a special kind of samewavelength
crosstalk, termed same-source crosstalk. Its impact on the system is more severe than that of other kinds of
crosstalk under the worst case. This paper also points out that, by introducing light path differences between different
channel, one can distinctly reduce the impact of the same-source crosstalk with simple and minimum hardware cost.
This paper reviews performance of hybrid and monolithically integrated WDM transmitter arrays based on directly modulated 2.5Gbps lasers, with a focus on the wavelength accuracy and stability under normal operating conditions. We also consider power stability, chromatic dispersion penalties, and the channel cross-talk. Large numbers of four-wavelength devices were obtained and evaluated under a program designed to provide university-based system researchers with advanced WDM components We show that multi-wavelength laser arrays capable of high-performance out-of-the-box operation can be now produced for research-type WDM systems.
Recent explosive growth of Internet traffic greatly accelerates the needs of telecommunication and networking bandwidth. To satisfy this rapid increase in demand of bandwidth, WDM is the technology of choice. To implement an advanced WDM system, there are needs of various high performance and high complexity photonic devices: multiple wavelength laser arrays, wavelength multiplexer and/or demultiplexer, wavelength router/switches, wavelength add-drop switch, etc. Spectrometer on a chip (SOC) is one of the key enabling technologies to meet those needs. In this paper we review the advancement of planar waveguide WDM technology—from SOC components to integrated SOC WDM systems.
This paper describes the development and testing of a 4 channel, 10 Gbps/channel WDM module. This model incorporates four DFB lasers whose wavelengths are spaced 1.6 nm apart within the 1550 nm fiber window. A driver circuit have been developed based on a commercially-available monolithic amplifier which provides high-speed operation at low cost. The performance of the module was measured at 10 Gbps and 2.5 Gbps. Time-domain performance and crosstalk results are presented.
Wavelength Division Multiplexing (WDM) has become the technology of choice for meeting the rapid increase in demand for bandwidth and capacity in telecommunication and computer networking systems. One of the key enabling technologies for WDM systems is multiwavelength filters. The spectrometer on a chip (SOC) is an integrated optics approach to the implementation of a high performance multiwavelength filter. This paper provides an overview of the design, processing, and testing issues for two types of SOCs: etched grating and phased-array waveguide grating. Both types of devices are used in various WDM components. In addition to wavelength multiplexers/demultiplexers, other integrated WDM photonic devices which utilize SOCs for their wavelength filtering functions will also be discussed.
We report on low-loss, alignment-tolerant coupling between a single quantum well GaAs/AlGaAs laser and a cleaved single mode fiber. The laser has been fabricated using conventional growth and processing techniques. The mode size in the transverse direction is expanded by using a diluted waveguide structure to better match the fiber mode size. The diluted waveguide was realized by reducing the Al mole fraction between the core and the cladding, thus providing weak confinement. Very small far field divergence angles (15 degree(s) (transverse) and 4.5 degree(s) (lateral)) were measured from this device, indicative of the expanded mode. A butt coupling efficiency of 70% was achieved against a theoretically possible 78%. In addition, large misalignment tolerances for a 1 dB excess loss of +/- 2 micrometers in the lateral and +/- 1.5 micrometers in the transverse directions, were measured. The To of the device was found to be 112 K, showing that the carrier leakage is not significant despite the diluted nature of the waveguide.
The coming of age of wavelength-division-multiplexed (WDM) laser arrays is bringing new challenges in the testing of semiconductor lasers. Because of stringent requirements on the laser linewidths and their frequency stability and because of electrical, optical, and thermal crosstalk problems, a new methodology is required for evaluating the performance of WDM laser arrays. This paper describes techniques that will be used to test WDM laser arrays both cw and under pulsed conditions. The laser arrays for these studies will be procured under a new program called `The WDM Alliance' sponsored by BMDO/AFOSR. Preliminary data on monolithic WDM laser arrays are also presented in this paper.
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