Improved analysis for SRS- and XPM-induced crosstalk in SCM-WDM transmission link in the presence of HOD

In this paper, the improved analysis for SRS- and XPM-induced crosstalk has been reported. The modified expression for XPM-induced crosstalk has been obtained and SRS- and XPM-induced crosstalks have been reported at varied walkoff parameter, modulation frequency, input optical power and transmission distance. It has been observed that there is exponent decrease in SRS-induced crosstalk with the increase in modulation frequency from 0 to 2.0 GHz. It varies with the increase in length and lie in the range of (−114 to −122.4) dB and (−115.5 to −124.4) dB at 20 and 100 km, respectively. Moreover, it increases exponentially with the increase in input optical power and lies in the range of (−121.6 to −130.6) dB at 10 mW and grows exponentially up to the range of (−114 to −122.8) dB at 60 mW optical powers at walkoff parameter of (13.6, 27.2, 54.4 and 81.6) ps/km. It has been observed that the XPM-induced crosstalk increases exponentially with the increase in transmission distance and modulation frequency for 2OD and 3OD. Furthermore, it has been found that the total SRS- and XPM-induced crosstalk rises exponentially with fluctuations with the increase in modulation frequency and transmission length in the presence of combined effect of 2OD and 3OD at varied walkoff parameters.     

Impact of 2OD and 3OD on SRS- and XPM-induced crosstalk in SCM-WDM optical transmission link

In this paper, the impact of second-order dispersion (2OD), third-order dispersion (3OD) and modulation frequency over stimulated Raman scattering (SRS)- and cross-phase modulation (XPM)-induced crosstalk in sub-carrier-multiplexed (SCM) wavelength division multiplexed (WDM) transmission link has been analyzed. It has been observed that there is significant effect of 2OD, 3OD and modulation frequency on the SRS- and XPM-induced crosstalk in a SCM-WDM transmission link. Here the results for SRS- and XPM-induced crosstalk have been reported with independent and combined higher-order dispersion. It has been observed that XPM-induced crosstalk lies between [−52.8 to −45.3] and [−94.7 to −78.6] dB in the presence of 2OD and 3OD respectively for modulation frequencies varied from 500 MHz to 2.0 GHz, while it is in the range of [−94.4 to −84] and [−128.5 to −117] dB when both SRS and XPM are taken into consideration.     

Performance evaluation of SCM-WDM communication in the presence of SRS induced crosstalk for different types of fiber

In this paper, the SRS-induced crosstalk has been evaluated in a SCM-WDM communication link at different modulation frequencies for various type of fibers. Results show that SRS-induced crosstalk dominates at low frequency. As the dispersion and effective area of fiber (A_eff) decreases, initially the crosstalk remains high and then it decreases with increase in modulation frequency. The present work shows that out of five different types of fibers, Standard Single Mode Fiber (SMF) has minimum crosstalk (−53 to −64 dB) and True Wave fiber (TW) has maximum crosstalk (−47 to −48 dB).     

Simultaneous dispersion and non-linearity compensation with mid-span optical phase conjugation and distributed Raman amplifier for a sub-carrier multiplexed optical transmission link

Optical phase conjugation (OPC) and distributed Raman amplifier (DRA) combination (OPC-DRA) is demonstrated as a potential enabling solution for simultaneous reduction of fiber non-linearities and dispersion compensation of a sub-carrier multiplexed (SCM) optical transmission link. The present work is focused on the use of OPC-DRA combination for system performance improvement in terms of composite second order distortion (CSO) and carrier to noise ratio (CNR) of the SCM link. The analysis further shows that, introduction of DRA with proper pumping scheme significantly reduce fiber non-linearity resulting in improvement of the system performance in terms of CNR, compared to the situation where only mid-way optical phase conjugation is used.     

Characterization of wavelength interleaving in radio-over-fiber systems employing WDM/SCM

A radio-over-fiber (RoF) distribution system incorporating both sub-carrier multiplexing and wavelength division multiplexing (WDM) technologies is presented. This signal is directly modulated onto three high-speed lasers. Bragg filters are employed at the receiver base station in order to both demultiplex the required optical channel, and ensure that the detected signal is single side band (in order to overcome dispersion limitations of the link). System spectral efficiency is optimised by wavelength interleaving. The channel spacing between the WDM channels is varied and the system performance for different values of channel spacing and spectral efficiencies is investigated. The results show that wavelength interleaving is a reliable technique that could be used to increase the spectral efficiency of RoF systems.     

Performance of an optical wideband WDM system considering stimulated Raman scattering,fiber attenuation and chromatic dispersion

The performance of an optical wideband wavelength division multiplexed (WDM) communication system is analyzed considering the effects of stimulated Raman scattering, fiber attenuation and chromatic dispersion. Improved models for the Raman gain and the fiber attenuation constant are proposed, which yield better and reliable performance results of the WDM system. Effect of fiber chromatic dispersion is also investigated and it is observed that dispersion can suitably be selected to overcome the limitations imposed by the stimulated Raman scattering phenomenon.     

System degradation due to phase error induced crosstalk in WDM optical networks employing arrayed waveguide grating multi/demultiplexer

The phase error induced crosstalk within arrayed waveguide gratings (AWG) have been investigated theoretically as well as simulation. For WDM system, a crosstalk level of −21.9 dB causes a power penalty of 1 dB for 64 channels and less than 0.5 dB for 16 channels and 32 channels, respectively. For crosstalk level of −30 dB and below, the power penalty is negligible. Crosstalk due to phase error also causes higher power penalty at higher bit rate. Bit rate of 10, 20 and 40 Gbits/s causes power penalty of 1 dB with crosstalk level of −41.5, −46.25 and −49 dB, respectively.     

Amplification of 12 × 10 Gb/s WDM signals with negligible FWM crosstalk in a double-pumped fiber optical parametric amplifier

We report on the amplification of 12 × 10 Gb/s wavelength-division-multiplexed signals by a double-pumped fiber optic parametric amplifier (2P-FOPA). A gain of 10 dB is obtained using a 4.3 km-long conventional dispersion shifted fiber (DSF) as nonlinear medium. Our spectra show negligible generation of spurious FWM products, and we attribute this to the small variations of the zero-dispersion wavelength of the DSF. The 2P-FOPA performance is assessed through Q-factor measurements, and we show that for output powers per channel ranging from −15 to 3 dBm the power penalty is less than 0.5 dB.     

Colorless gigabit WDM-PON link using injection locking and electro-absorption transceiver

In this paper, a novel colorless wavelength division multiplexing-passive optical network (WDM-PON) system using injection locking and electro-absorption transceiver (EAT) is proposed and demonstrated experimentally. This system has advantages, high data transmission, small downlink signal effect to uplink signal and less polarization sensitivity, compared to the system using reflective semiconductor optical amplifier (RSOA). Downlink signal modulates the right side carrier of the double side band signal by using injection locking. EAT functions as both photo detector in downlink signal and modulator for uplink signal, simultaneously. A possible cross absorption modulation effect from the EAT is analyzed experimentally. Bidirectional transmission of 1.25 Gbps and 622 Mbps for downlink and uplink, respectively, were verified through 23 km standard single mode fiber (SSMF).     

An optical power-equalized amplifier with a wide dynamic range

An optical power equalization amplifier with a wide dynamic range is proposed and demonstrated with no electronic control. It shows constant and equalized outputs when a power difference between input channels and a total input power are changed. It has more than a 15 dB dynamic range for input signals between −30 dBm and −5 dBm. The structure of this amplifier can be more promising when it is applied to a planar waveguide device.     

Four-wave mixing analysis in WDM optical communication systems with higher-order dispersion

Four-wave mixing (FWM) is one of the major limiting factors in WDM optical fiber communication systems. In this paper, we analyze the individual and combined effect of second-, third-, fourth- and fifth-order dispersion parameters on FWM at different input channel powers and core effective areas, which have not been calculated earlier. FWM power versus channel power graphs for individual and combined effects of dispersion parameters have been presented, and it has been observed that FWM reduces for combined effect of dispersion parameter.     

Wavelength assignment for all-to-all broadcast in bidirectional WDM optical ring with limited drops

All-to-all broadcast is to disseminate a unique message from each node to every other node in a network. This problem is significant in the context of control plane design as it relates to status information dissemination. In this paper, a wavelength assignment method to reduce the number of wavelengths is proposed to establish all-to-all broadcast in a bidirectional WDM ring network. The network model is an all-optical network, in which a message from source node can be dropped (or split) only at a limited number of destination nodes along a light path due to power loss of dropping optical signals. An expression for the upper bound on the number of wavelengths required to support all-to-all broadcast is derived for certain cases of WDM ring while for other cases, an attractive algorithm is given to identify the lengths of connection sets that can be grouped together with suitable wavelength assignment strategies. Numerical results are computed to show that the results obtained are close to the lower bound.     

The cost benefits of multi-layer architecture with multi-granularity switching in optical networks

The benefits of using multi-granularity switching to reduce the number of ports, including both electronic and optical ports, have been investigated. A novel multi-layer ring architecture with multiple switches is proposed and two general equations to count the number of ports are derived. Comparisons are made between the multi-layer multi-granularity switching (MM-XC) architecture and the reported architectures: multi-switching (M-XC) and single switching (S-XC) architectures. The results show that the M-XC or S-XC architectures can be deduced from the MM-XC architecture and the latter architecture can achieve more considerable savings of the port count compared to the former.     

Experimental realization of a novel dispersion- compensating optical fiber amplifier for simultaneous compensation of positive dispersion and losses

Erbium-doped dispersion-compensating optical fiber (EDCF) has been theoretically simulated and experimentally fabricated using Modified Chemical Vapor Deposition (MCVD) for optimum operation at 5.0km. It is optimized for both gain as well as negative dispersion. The erbium has been doped into the cladding region while the core of the optical fiber is chosen to be narrow so as to have a high negative dispersion. Measured gain of 3.1 dB at 200 m using 100 mW pumping power (980 nm wavelength) at 1550 nm has been obtained and the gain of 32 dB at 5.0 km using same pumping scheme has been predicted. The chromatic dispersion of this EDCF has been also measured to be –43.5 ps/km-nm at 1550 nm and thus, providing the dispersion of –217.5 ps/nm at 5 km. The bend-induced losses are found to be negligible. We are the first to report the experimental realization of EDCF.     

Performance limitations of an optical heterodyne CPFSK transmission system due to self-phase modulation

A detailed theoretical analysis is presented to evaluate the combined influence of self-phase modulation (SPM) and group velocity dispersion (GVD) of optical fiber on the bit error rate (BER) performance of a heterodyne optical CPFSK system. The power penalty suffered by the system due to the combined influence of GVD and SPM is evaluated from the BER performance results. It is found that the penalty due to SPM at a BER of 10⁻⁹ is significant when the input power exceeds 7 dBm. Further, the CPFSK system with modulation index of 0.5 is less sensitive to the effects of GVD and SPM compared to the system with a modulation index of 1. The theoretical results are in conformity with the experimental results reported earlier.     

Effects of polarization mode dispersion on cross-phase modulation in a WDM optical transmission system

The cross-phase modulation (XPM) changes the state-of-polarization (SOP) of various channels and leads to amplitude modulation of the propagating waves in a WDM system. Due to the presence of polarization mode dispersion (PMD), the angles between the SOP of the channels change randomly and cause the modulation amplitude fluctuation random in the perturbed channel. We analytically derive the dynamic equation of the perturbed channel, determine the combined probability density function of the random angle between the SOP of pumps and probe channel and evaluate the effects of PMD on XPM for a 4-channel IM-DD WDM system in terms of BER at bit rate of 10 Gb/s per channel. We also simulate the impact PMD on XPM for a 4-channel WDM system in terms of eye diagram and found that eye opening penalty is 1.85 dB higher when the fiber PMD coefficient increases from 0.5 to 1.5 ps/√km.     

Performance comparison of wavelet packet transform based and conventional coherent optical OFDM transmission system

In this work, the performance of WPT-COOFDM system is investigated and compared to that of FFT-COOFDM system over a fiber link. Simulation results show that the longer length of wavelet filters achieve a better performance, whereas the complexity is higher. For different wavelet mother functions employed in WPT-COOFDM systems, the chromatic dispersion robust of John64E wavelet outperforms that of other wavelets, and which could be a viable alternative for coherent optical OFDM to be considered in short distance transmissions. The simulation results also show that most of the developed wavelet mother functions mainly for image processing are not suitable for COOFDM transmission for its sensitivity to chromatic dispersion.     

Improved analysis of dispersion compensation using differential time delay for high-speed long-span optical link

Abstract

A dispersion-compensation technique using differential time delay has been analyzed for a high bit rate dispersive limited system using higher order dispersion terms. The technique is based on splitting the power spectrum into upper and lower parts, corresponding to the two modulation sidebands, and delaying one of these with respect to the other. RMS, phase deviation, dimension free chirp parameter, and figure of merit have been evaluated due to higher order dispersion terms for ideal and realistic optical communication systems. It has been shown that the transmission distance could be enhanced to fourfold, sixfold, and eightfold when the compensation has been performed using second-, third-, and fourth-order dispersion (20D, 30D, and 40D) terms.     

Improved analysis of dispersion compensation using differential time delay for high-speed long-span optical link

A dispersion-compensation technique using differential time delay has been analyzed for a high bit rate dispersive limited system using higher order dispersion terms. The technique is based on splitting the power spectrum into upper and lower parts, corresponding to the two modulation sidebands, and delaying one of these with respect to the other. RMS, phase deviation, dimension free chirp parameter, and figure of merit have been evaluated due to higher order dispersion terms for ideal and realistic optical communication systems. It has been shown that the transmission distance could be enhanced to fourfold, sixfold, and eightfold when the compensation has been performed using second-, third-, and fourth-order dispersion (20D, 30D, and 40D) terms.     

The effects of different dispersion compensation ratios on nonlinear single channel and WDM systems

The effects of the compensation ratio with dispersion post-compensation on nonlinear single channel and WDM systems with 10 Gb/s per channel are numerically investigated. When the transmission signal per channel is 10 Gb/s RZ pulse and the amplifier span is 50 km, proper undercompensation can enhance the performance of the nonlinear single channel system and the nonlinear WDM system. But the enhanced distance of the nonlinear WDM system is not as obvious as that of the single channel system, because the cross-phase-modulation effect plays an important role in the nonlinear WDM system.