WDM optical components using PLCs

We experimentally and theoretically investigate GeSi-based photonics for future on-chip optical interconnect on bulk Silicon substrates with dense wavelength division multiplexing (WDM) system. We experimentally show that Ge-rich Si_1-xGe_x can be used as both a passive low loss waveguide and a substrate to facilitate low-temperature epitaxial growth of Ge-based active devices working at low optical loss wavelength of Ge-rich Si_1-xGe_x waveguides. We also theoretically discussed the possibilities to realize a compact passive component based on Ge-rich Si_1-xGe_x material system on bulk Si wafer. From simulation the system based on Ge-rich Si_1-xGe_x waveguide and the Si_1-yGe_y (y < x) lower cladding layer is good enough to ensure compactness of important on-chip photonic components including passive waveguide and GeSi-based array waveguide grating (AWG). The small refractive index contrast between Ge-rich Si_1-xGe_x waveguide and the Si_1-yGe_y lower cladding layer potentially avoid the polarization dependent loss and detrimental fabrication tolerance of WDM system. Our studies show that GeSi-based photonics could uniquely provide both passive and active functionalities for dense WDM system.

Recently, photonic networks based on wavelength division multiplexing (WDM) systems have developed considerably in response to the explosive growth of the Internet. Devices with novel functions are required for photonic networks, and planar lightwave circuits (PLCs) are being considered to meet this need. This paper reports recent progress on PLC- type devices with advanced functions developed for the photonic networks. We describe fabrication techniques and device applications for silica and silicone polymer based PLC technologies.

Along with the emergence and maturity of 100Gbit/s technologies, numbers of trial and commercial 100Gbit/s Wavelength Division Multiplexing (WDM) systems have been established worldwide. The research-oriented lab tests of 100Gbit/s WDM systems were done by China Unicom in 2012. The 100Gbit/s technologies of polarization multiplex-quadrature phase shift keying with coherent detection from multiple vendors have been studied. There are some further issues to be specified before the commercial application of 100Gbit/s WDM system is implemented in large scale in backbone network, including optical performance parameters, optical performance monitoring of 100Gbit/s system, protection mechanism, selection of client interface and comprehensive Operation, Administration and Maintenance (OAM).

The authors have studied the possibilities to obtain the maximum spectral efficiency for a combined wavelength division multiplexing (WDM) system by minimizing the channel spacing. The fiber optic transmission systems under study can be considered in the context of next generation optical networks and is offered as a model for designing the future backbone networks. In the case of different telecom operators' optical networks merging, in the nearest future the necessity may arise to transmit variously modulated optical signals over a single optical fiber (even with different per channel bitrates). In this paper the authors show an optimal combined WDM system configuration that provides the least bit-error-rate values for the signals detected in system's channels. It is found that the minimal channel spacing for differently modulated optical signals in the investigated mixed data rates WDM system is 75 GHz if these signals are transmitted with 10 Gbit/s and 40 Gbit/s per channel bitrates. It is revealed that such a system's average spectral efficiency depends also on a combined system's configuration in the case of channel separation with equal frequency intervals.

With rapidly increasing demand for communication channels, wavelength division multiplexing (WDM) system are being deployed to expand the capacity. WDM systems require devices for the manipulation of multi-wavelength channels. Among these devices, the integrated acousto-optic tunable filter (AOTF) is rapidly gaining importance in the field of WDM communication systems because it has the combined features of rapid switching time, broad tuning range and parallel processing capability. The technology of hybrid unidirectional and focused transducer was adopted for the design of the AOTF. The AOTF consisted of a single-mode optical waveguide placed along the SAW propagation direction. Extensive researches areas, which were in optical add-drop multiplexers (OADM), gain equalization and optical switches, have been done.

Performance of Wavelength Division Multiplexing (WDM) System is analyzed using Dispersion Compensating Fiber. In this work, Optimized link of 8-channel WDM (Wavelength Division Multiplexing) system using OptiSystem is designed. Comparison of the link performance is investigated at different wavelength i.e. 980nm, 1300nm and 1550nm. The better Performance of the WDM link can be achieved at wavelength of 1550nm as compared to 1300 and 980nm using dispersion compensating fiber along with single mode fiber for link length of 105 km operating at data rate of 3Gb\s with 8-channel of WDM System. The BER, Q-factor and eye diagram have been used for evaluating the performance of the system.

Development of an OADM to reduce the incoherent crosstalk in WDM system

We begin reasons why high system availability is important. Furthermore, the basic terms are introduced pertaining to the availability with particular review of the parallel structure. Then the availability of different wavelength division multiplexing (WDM) systems is analysed: point to point, chain and ring with 1+1 protection of the wavelength channel, plus the influence of availability of nodes and links on the total system availability. The data on failure intensity and mean time to repair of certain components were taken from various literature sources. We assumed in the analysis a WDM system with 16 wavelengths and 2.5 Gbit/s capacity per wavelength channel. Finally, results of calculation and comparisons of availability of different WDM systems and proposals for improvement of their availability are presented.

Silica-based planar lightwave circuit (PLC) devices are starting to be introduced into commercial optical communication systems. PLC devices such as optical splitters, wavelength-insensitive coupler (WINC) arrays, and hybrid- integrated wavelength-division-multiplexing (WDM) transceivers are used to construct cost effective optical access systems. In trunk lines, on the other hand, arrayed-waveguide gratings (AWG) are employed for dense WDM systems to increase the transmission capacity. This paper reviews the current status and recent progress on these practical PLC devices.

This paper describes the performance improvement of 10-Gb/s four-channel WDM dispersion-supported transmission systems by using broadened passband arrayed-waveguide grating demultiplexers. Multimode interference couplers are assumed to be used to broaden the passaband of these demultiplexers. Performance Improvement of 40-Gb/s Capacity Four-Channel WDM Dispersion-Supported Transmission by Using Broadened Passband Arrayed-waveguide Grating Demultiplexers Mario M. Freire Department of Mathematics and Computer Science, University of Beira Interior Rua Marques d'Avila e Bolama, P-6200 Covilha, Portugal Telephone: +351 75 3101700, Fax: +351 75 26198, E-mail: mfreire@ alpha.ubi.pt Henrique J. A. da Silva Department of Electrical Engineering, Pole II of University of Coimbra Pinhal de Marrocos, P-3030 Coimbra, Portugal Telephone: +351 39 7006248, Fax: +351 39 7006247, E-mail: hjas@ci.uc.pt Summary Integrated N×N wavelength multiplexers based on arrayed-waveguide gratings (AWG) are being developed for wavelength division multiplexing (WDM) systems and networks, since they can offer four basic functions: multiplexing, demultiplexing, add/drop multiplexing, and N×N full-interconnection [1]. The use of this technology for demultiplexing in high density WDM systems may impose very stringent requirements on the alignment of signal wavelengths and demultiplexers due to their peaked (Gaussian-like) spectral passband. However, the passband of these demultiplexers may be broadened by the use of multimode interference couplers (MMI), as proposed and demonstrated in [2]. In this paper, we describe the performance improvement due to the use of broadened passband AWG demultiplexers in 40-Gb/s capacity four-channel WDM dispersion-supported transmission (DST) systems with 0.5 nm channel spacing. The block diagram of the simulated 10-Gb/s four-channel WDM-DST system is shown in Fig. 1. The system model is broadly similar to the one reported in [3] and includes a rate equation model for quantum-well lasers, and the frequency responses of a PIN photodiode and of a standard singlemode fiber (SMF) with chromatic dispersion of 17 ps/(nm.km) at 1532 nm. The frequency response of the AWG filter is assumed to be Gaussian and the frequency response of the broadened passband AWG filter is modeled by the double Gaussian approximation [2] with r = 2 , which is the ratio between the peak separation and the FWHM of each simple Gaussian profile. The optical amplifiers (EDFAs) have been considered as linear with a noise figure of 6 dB and an equivalent noise bandwidth of 1 THz. A RC lowpass filter was used to provide the 3-dB bandwidth required by the DST method [4]. The receiver sensitivity was estimated taking into account the signal-ASE and ASE-ASE beat noises, the thermal and shot noises, as well as the contribution due to frequency-to-intensity conversion of laser phase noise after propagation via dispersive fibers [5]. Fig. 2 shows the receiver sensitivity for channel 2 versus fiber length for single-channel DST, without optical filters, and for four-channel WDM-DST using an arrayed-waveguide grating demultiplexer with (BP-AWG) and without (AWG) broadened passband. For comparison purposes, the receiver sensitivity of four-channel WDM-DST using a three-mirror Fabry-Perot demultiplexer (TMF) is also shown. For distances larger than 80 km, the performance of four-channel WDM-DST systems using three-mirror Fabry-Perot demultiplexers is close to the performance of single-channel DST systems without optical filters. Compared with the performance of single-channel DST without optical filters, the use of conventional arrayed-waveguide grating filters as demultiplexers in four-channel WDMDST degrades the system performance at least 0.6 dB for link lengths larger than 11 km. However, the use of broadened passband AWG demultiplexers instead of the conventional AWG demultiplexers improves the performance of the four-channel WDM-DST system at least 1.5 dB, for link lengths larger than 11 km (see Fig. 2). Detailed BER characteristics for channel 2 are displayed in Fig. 3 for four-channel WDM-DST via 204 and 253 km SMF. For the 204 km transmission simulation, sensitivities of -23.886, -23.169 and -24.827 dBm have been estimated for TMF, AWG and BP-AWG demultiplexers, respectively. The BER curves for 253 km clearly indicate an error floor due to laser phase noise. In conclusion, the use of broadened passband AWG demultiplexers improves the performance of four-channel WDM-DST systems with 0.5 nm channel spacing, while conventional AWG demultiplexers are less suitable to operate at this channel spacing.

For wavelength division multiplexing (WDM) systems, excessive linear and nonlinear noise will seriously decrease the quality of optical signals, and the effective joint monitoring scheme can prevent the degradation of system performance due to noise accumulation. In this paper, we propose a probability information assisted knowledge distillation (PIAKD) scheme that achieves intelligent joint monitoring for linear signal-to-noise ratio (SNRL) and nonlinear signal-to-noise ratio (SNRNL) in WDM systems. Under the condition of multi-task regression, outputs are independent and continuous, PIAKD addresses the longstanding challenge that the student model fails to effectively learn knowledge from the teacher model by introducing probability information into the loss function. The effectiveness of the scheme is verified by WDM simulation and experiment system which has a symbol rate of 28 GBaud per channel. The simulation results demonstrate that the overall mean absolute error (MAE) for jointing SNRL and SNRNL monitoring of the student model after PIAKD is reduced by 0.08 dB and 0.09 dB, corresponding to 32% and 34% error reductions respectively. Furthermore, when compared with the KD scheme without probability information, our scheme also reduces the overall MAE of SNRL and SNRNL by 16% and 11%, respectively. The results of the experiment reveal that the estimated MAE could be reduced by 0.13 dB and 0.16 dB, respectively, corresponding to error reductions of 17% and 18%. Moreover, the floating-point operations (FLOPs) and parameters (Params) of the student model is only 3.30 M and 0.0015 M, respectively, which is both significantly lower than the complexity of existing joint monitoring schemes for SNRL and SNRNL.

In this paper we describe a new family of teaching packages designed to offer a practical introduction for graduate students of Science and Engineering to the topic of wavelength division multiplexing (WDM) in fibre optics.The teaching packages described here provide students with the background theory before embarking on a series of practical experiments to demonstrate the operation and characterisation of WDM components and systems.The packages are designed in a modular format to allow the user to develop from the fundamentals of fibre optical components through to the concepts of WDM and dense WDM (DWDM) systems and onto advanced topics covering aspects of Bragg gratings.This paper examines the educational objectives, background theory, and typical results for these educational packages.

Crosstalk due to four-wave mixing (FWM) is increasing sharply when lightwave channel is upgrading in wavelength division multiplexing (WDM) fiber-optical communication systems. A technique, designed the channel wavelength allocation to reduce the crosstalks due to FWM, is submitted, when multi-channel is extended easily from 3-channel to 22-channel in WDM system. The result of simulation is presented. It is shown that suitable unequally channel separations can be found for which no FWM product term is superimposed on any of the transmitted channels, and the bandwidth expansion factor is not always increasing, and the span between the FWM crosstalks and channel wavelengths are not always decreasing, when increasing WDM system channels.

Optical dense wavelength division multiplexing (WDM) systems have been investigated in order to enlarge transmission capacity and improve network flexibility. Arrayed-waveguide grating (AWG) multiplexers are key components in such systems because they can process plural wavelengths simultaneously. This paper reviews recent work on AWGs based on silica-based planar lightwave circuits and their applications to dense-WDM systems. An AWG consists of plural input/output waveguides, two focal slab waveguides and a waveguide array. Applications investigated include optical add/drop multiplexers, wavelength routers and multi-channel light sources.

Planar lightwave circuits (PLCs) are waveguide devices that integrate fiber-matched optical waveguides on Silicon or glass substrate to provide an efficient means of interaction for the guided-wave optical signals. The most prominent feature of the silica waveguides is their simple and well defined waveguide structures. This allows us to fabricate multi-beam or multi-stage interference devices such as arrayed-waveguide gratings and lattice-form programmable dispersion equalizers. PLCs provide various important and functional devices for optical wavelength division multiplexing (WDM), time division multiplexing (TDM) systems and subscriber networks. This paper reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating multiplexers, optical add/drop multiplexers, programmable dispersion equalizers and hybrid optoelectronics integration technologies.