Wavelength Division Multiplexing Optical Communication Systems Research Articles

Design and Performance Analysis of Simple WDM Optical Fiber Communication System

WDM (wavelength division multiplexing) is used in this project to simultaneously send data over several channels at high speed. Single mode fiber is favored over Multimode fiber for long-distance communication. As data rate and optical fiber length grow, the quality factor falls. Dispersion effects on an 8-channel dense WDM system at a high data rate will be examined using the Optisystem 10 simulator. A dispersion compensation fiber (DCF) and an Erbium doped fiber amplifier (EDFA) are used to compensate for the dispersion and attenuation in the transmitted optical signal, respectively. Bit error rate (BER) and eye diagram analyzers were used to evaluate the optical communication system's performance.

Performance Evaluation of WDM Optical Fiber Communication System in the presence of PMD

This paper investigates for rising optical fiber transmission strength, increasing bandwidth, and decreasing communication system weakness by using wavelength division multiplexing (WDM). WDM gives today's distention speed and communication traffic. Systems using WDM faces nonlinearities, which the most intensive nonlinear attack is, four wave mixing (FWM). FWM creates and increases crosstalk between WDM channels as a result slows down and impairs the performance of the communication system. This investigation uses orthogonal frequency division multiplexing (OFDM) for evaluating execution of WDM fiber system by repairing Polarization Mode Dispersion (PMD). We took results in the case of trying PMD-Emulator and without trying PMD-Emulator in the system design. We compared the results got in both cases. Furthermore, we compared the performance of the system with the investigations done using different ways, methods, and techniques for compensating PMD and FWM appears in WDM systems. As PMD-Emulator, helps enhancing the system design performance, and OFDM gives the feature of robustness and useful execution to the system. OFDM examined by appointing interfered orthogonal signal sets, for 16 channels; with equally spaced OFDM channels. Oure results showed that the optical fiber communication system using OFDM technique gives perfect removing FWM signal crosstalk, and accurate data transmission, comparing to other techniques used in other researches. We got a decreased FWM power to -77dBm, and the BER of -0.317. Furthermore, the system quality increased with applying PMD-Emulator and OFDM. In addition, using PMD-Emulator in the system design raised the results effectiveness. The program used in the present work is optisystem-15, and the results obtained in this study coincide with the theoretical and actual results obtained by the previous studies.

Physical Layer Encryption for WDM Optical Communication Systems Using Private Chaotic Phase Scrambling

Protecting the security of optical network is a major worldwide challenge. The conventional schemes for securing communications are based on cryptography at the MAC layer and its higher layers, which are facing a great threat with the development of quantum computers. Optical encryption is a promising way for building security on the physical layer of optical communications. In this work, we propose a novel optical encryption scheme for wavelength division multiplexing (WDM) fiber-optic communication systems, by utilizing the private chaotic phase scrambling. Secure transmission of 50 Gbps signal over 50-km standard single-mode fiber is experimentally and numerically demonstrated. The results show that the WDM signal is efficiently encrypted into a noise-like signal, due to the spectral broadening effect of chaotic phase scrambling. Since the processes of encryption and decryption are totally implemented in the optical domain, the proposed scheme can encrypt the entire network traffic with low latency and high speed. Moreover, the proposed encryption scheme is compatible with the existing WDM optical networks, and only one pair of encryption and decryption devices is sufficient to encrypt all WDM channels, thus the scheme can be easily implemented at low hardware cost.

Three-channels wavelength division multiplexing based on asymmetrical coupling

In order to realize the wavelength division multiplexing (WDM) device with compact channels and high transmission, a novel three-channel WDM device based on a two-dimensional photonic crystal with a square lattice is proposed. Three parallel line defect waveguides are introduced in this structure to control the propagation of light. Elliptical and rectangular resonators are employed to carry out the selection of light wavelengths by the coupling resonant effects. The point defect cavity is placed at the end of the middle waveguide to further filter the wavelengths. We theoretically analyze the effects of the distances between the resonator and the micro-cavity and between asymmetrical resonators on the light propagation by the finite-difference time-domain (FDTD) method. Three different wavelengths (1560, 1580, and 1620nm) in the communication window range with maximum transmission over 90% are obtained. The findings may provide potential applications in filters, WDM optical communication systems and other optoelectronics devices.

Arrayed waveguide collimators for integrating free-space optics on polymeric waveguide devices.

Array-type optical devices are important for wavelength-division multiplexing optical communication system to achieve small footprint, mass production, and reliability. For fabricating transmitter module in an array configuration, it is difficult to achieve a passive alignment of isolator, collimating lens, and laser diode. To facilitate array isolator integration, a waveguide collimator is proposed in this work by using a low-contrast, large-core polymer waveguide. The diffraction of a guided mode propagating through a free-space region is suppressed by enlarging the guided mode. The fiber coupling loss due to the enlarged mode was overcome by incorporating an adiabatic taper structure. The excess loss of waveguide collimator including the loss through a 400-μm free-propagation region was less than 1.0 dB.

Low-crosstalk high-density polymeric integrated optics incorporating self-assembled scattering monolayer.

Highly integrated optical components are strongly demanded because they enable wavelength-division multiplexing optical communication systems to achieve smaller footprints, lower power consumption, and enhanced reliability. Variable optical attenuator (VOA) arrays are often used with optical switches in cascaded form for reconfigurable optical add-drop multiplexer systems. Although VOAs and optical switches based on polymer waveguide technology are commercially available, it is still not viable to integrate these two array devices on a single chip because of significant interchannel crosstalk. In this work, we resolved the issue of crosstalk and integrated the arrays of optical switch and VOA on a single chip by incorporating a self-assembled scattering monolayer (SASM). The SASM was effective for scattering the planar guided mode; consequently, the crosstalk into an adjacent channel was significantly reduced, to less than -35 dB.

DPSK Modulated (Tbit/s) Transmission Incorporating Dispersion-compensated Hybrid Amplifier

The simulative implementation of differential phase shift keying (DPSK) modulated data transmission incorporating single-pump highly efficient dispersion compensated Raman/EDFA hybrid amplifier is demonstrated. The simulative results are discussed to compare two different types of configurations of dispersion compensated 16-channel wavelength division multiplexing (WDM) system to achieve transmission of Tbit/s data. In pre-compensation technique, dispersion compensated fiber (DCF) is used prior to fiber Raman amplifier (FRA) (Type I) and in post-compensation technique; the DCF is used after FRA (Type II) in a WDM optical communication system. The pumped dispersion shifted fiber (DSF) is in use to act as FRA amplifier. The performance characteristics such as Q factor, BER and eye closure penalty are premeditated to realize the ultra high speed WDM systems by employing DCF based FRA together with DPSK modulation. From simulated results, it is recommended to implement Type I over Type II to realize the feasibility of such high speed WDM systems.

Impact of Crosstalk on Indoor WDM Optical Wireless Communication Systems

In this paper, we investigate the impact of optical crosstalk on our recently proposed indoor gigabit optical wireless (OW) communication system incorporating wavelength division multiplexing (WDM). A theoretical model that allows this impact to be assessed has been proposed. The analytical results are validated via experiments. We show that the power penalty due to crosstalk in our proposed indoor WDM OW system is lower compared to that in the conventional optical fiber communication systems. In addition, it is found that the power penalty due to crosstalk is lower for the higher speed system since the receiver preamplifier-induced noise dominates the noise process. Finally, the maximum error-free beam footprint for different levels of optical crosstalk has been investigated. The results show that, for the 10- and 12.5-Gb/s systems, the maximum error-free beam footprint is only reduced by <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 5 cm, even with comparatively strong crosstalk.

FWM minimization in WDM optical communication systems using the asymmetrical dispersion-managed fibers

Four wave mixing (FWM) induced power penalty is investigated theoretically for asymmetrical dispersion-managed fibers in wavelength division multiplexing (WDM) systems. The power penalty in these fibers is analyzed for various values of channel spacing, maximum dispersion and number of sections in different channels. Using numerical simulations, it is illustrated that the FWM induced power penalty is minimized for the case of two fiber sections with unequally special lengths and symmetrical dispersion values.

InP-Based Polarization-Insensitive Planar Waveguide Concave Grating Demultiplexer with Flattened Spectral Response

ABSTRACT ⎯ InP-based planar waveguide 48-channel concave grating demultiplexers with a channel spacing of 0.8 nm (100 GHz) are described and demonstrated. Polarization insensitivity and flattened spectral response are successfully achieved by the introduction of a polarization compensator and a two-focus grating, respectively. The fabricated device shows a polarization-dependent wavelength shift of less than 20 pm and a -3 dB spectral width of about 0.55 nm (68.75 GHz) over all channels. Keywords ⎯ Planar waveguides, demultiplexer, concave grating, polarization, wavelength division multiplexing. Planar waveguide grating devices have been widely used for wavelength (de)multiplexing, switching, and optical add-drop applications in dense wavelength-division multiplexing optical communication systems. Among the various types of devices to implement a demultiplexer (demux) [1]-[4], the InP-based planar waveguide concave grating (CG) has shown great potential due to its compactness [2] and monolithic integration with laser diodes (LDs), photodetectors (PDs) [3], and semiconductor optical amplifiers [4]. However, compared to silica- or polymer-based CGs, it is difficult to achieve desirable performance in such areas as high channel-spacing accuracy, low polarization dependence, and flat-top spectral response over all channels due to its high refractive index dispersion,

Gain Flattening Approach to Physical EDFA for 16 × 40 Gb/s NRZ-DPSK WDM Optical Communication Systems

We are using different approaches to gain flattening in EDFAs without using additional components; i.e., gain flattening filter, dispersion shift fiber, periodic gratings, etc. By using gain flatten approach 3, it is possible to achieve the transmission of sixteen channels at 40 Gb/s wavelength division multiplexing (WDM) over a transmission distance of 490 km by single-mode fiber and dispersion-compensating fiber at a span of 70 km with channel spacing of 200 GHz. We observed the bit error rate less than 10-9 and power of received signal more than -5 dBm with NRZ-DPSK format.

Planar reflection grating wavelength filters in silicon

The design, fabrication, and performance of reflection-type multiplexers and demultiplexers in the silicon-on-insulator material system is discussed. These devices provide a more compact alternative to arrayed waveguide grating filters in planar technologies. Their suitability for application to both dense wavelength-division multiplexing and coarse wavelength-division multiplexing optical communication systems is considered.

Semiconductor Raman amplifier for terahertz bandwidth optical communication

Semiconductor Raman amplifiers are useful for frequency selection in terahertz bandwidth and wavelength division multiplexing (WDM) systems with terabit capacity, as well as direct terabit optical communication systems. We have developed GaP-AlGaP Raman waveguides with micrometer-size cross sections. We have reduced residual optical loss of the waveguide by improvement of the fabrication process and realized a low-loss waveguide that is 10-mm long, which has a continuous wave (CW) Raman gain of 3.7 dB. Also, the time-gated amplification with 80-ps pulse pumping is performed and 20-dB gain is obtained. These performances are very suitable for light frequency selection in terahertz bandwidth and WDM optical communication systems.

Gas source MBE growth of TlInGaAs/InP DH structures for the application to WDM optical fiber communication systems

TlInGaAs/InP double heterostructures (DHs) were grown on (1 0 0) InP substrates by gas source MBE. The photoluminescence (PL) peak energy and its variation with temperature decreased with increasing Tl composition. For the DH with a Tl composition of 13%, the PL peak energy varied only slightly with temperature (−0.03 meV/K). This value corresponds to a wavelength variation of 0.04 nm/K and is much smaller than that of the lasing wavelength of InGaAsP/InP distributed feedback laser diodes (0.1 nm/K). The TlInGaAs/InP light emitting diodes were also fabricated and the similar small temperature variation for the electroluminescence peak energy was observed. The results are a great first step to realize the laser diodes with temperature insensitive lasing wavelength characteristics, which are important in the wavelength division multiplexing (WDM) optical fiber communication systems.

Tunable add/drop optical filter providing arbitrary channel arrangements

A novel add/drop optical filter providing arbitrary channel arrangements between two input wavelength division multiplexing (WDM) signals and two output WDM signals is presented. This device can have useful applications in WDM optical communication systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Signal light amplification by stimulated Raman scattering in an N-channel WDM optical fiber communication system

The use of forward and backward Raman amplification in an N-channel wavelength-division-multiplexing (WDM) optical-fiber communication system is analyzed. Analytical expressions for the signals, the pumps, and the amplified spontaneous scattered power (ASSP) are presented. The crosstalk among the signal channels is analyzed in terms of system parameters. It is found that the crosstalk is negligible while low pump power is used and becomes significant if high pump power is used. The signal-to-ASSP ratio can be improved by increasing pump power; however, the improvement is small when pump power is already high. A 300-km repeater spacing with more than 20-dB signal-to-ASSP ratio is calculated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>