WDM Optical Transmission Research Articles

PPLN-Based Optical Parametric Amplification for Wideband WDM Transmission

The optical parametric amplifier (OPA) has attractive features for optical communications, such as a wideband, high gain, and fast transient response. In addition, by using idler light, which is phase-conjugated light generated in the amplification process, various kinds of optical signal processing, such as fiber-nonlinearity mitigation, wavelength conversion, and phase-sensitive amplification, can be performed. A periodically poled LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PPLN) waveguide is an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">χ</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(2)</sup> -based optical parametric amplification medium, and it makes both wideband and high-gain amplification possible. We developed a 4-port PPLN module that can combine signal light and pump light into a PPLN waveguide with low loss. In this paper, we overview the applications of OPA to WDM optical fiber transmission and explain the configurations of an OPA using 4-port PPLN modules. As applications of our PPLN-based OPA, we introduce the demonstration of wideband inline amplification exceeding 5 THz. Furthermore, we demonstrate inter-band wavelength conversion between C- and S-bands using PPLN waveguides developed for multi-band optical transmission applications.

Design and evaluation of 2.3 Tb/s (23 ch. × 100 Gb/s) multi-carrier WDM optical transmission systems

Multilevel phase modulation formats with coherent detection enable a new generation of high speed optical transport platform. We demonstrate 23 × 100 Gbps (2.3 Tb/s) WDM Optical systems employing multicarrier generation concept. Three lasers are used to generate 23 sub-carriers using multicarrier generator at transmitter section. Each sub-carrier transmits at a transmission rate of 100 Gbps using polarization division multiplexed quadrature phase shift keying (PDM-QPSK) modulation format with spacing of 25 GHz between sub carriers. The analysis is carried out for 23 × 100 Gb/s (2.3 Tb/s) PDM-QPSK WDM optical systems with ultra large area fiber (ULAF), standard single mode fiber (SSMF) and large effective area fiber (LEAF) at transmission reach from 600 to 5000 km. Coherent detection with DSP is used for all the systems at receiving end. Systems are verified with parameters like symbol error rate, error vector magnitude (EVM) and Q-factor using analytical and simulation results. Improvement of 1.66 dB to 3.21 dB and 2.08 dB to 4.63 dB is noted in Q-factor for system with ULAF in comparison with system using SSMF and LEAF respectively over 600 km to 5000 km transmission reach. EVM values are found 2.24% to 2.68% and 2.68% to 12.43% lower in system with ULAF than system with SSMF and LEAF respectively. Log of estimated symbol error is observed less for system with ULAF than systems with SSMF and LEAF fibers, respectively, at transmission distance of 5000 km. The results clearly show that WDM optical system with ULAF fiber gives better performance.

An efficient DFG induced wavelength exchanged-OPC using only two Ti:PPLN waveguides with single pump configuration

An unconventional single pump configuration of Wavelength Exchanged Optical Phase Conjugation (WE-OPC) through Difference Frequency Generation (DFG) employing two identical Ti:PPLN waveguides having same grating period and a single pump source is theoretically analyzed and simulated resulting in higher conversion efficiency of OPC.WE-OPC has been found very effective in extenuating nonlinearity and inflating spectral efficiency in optical transmission systems. The proposed WE-OPC enabled WDM optical transmission system modeled as a wavelength converter has been simulated with 10 channels offering much higher conversion efficiencies of about 3.3 dB and 3.49 dB for higher frequency band to lower frequency band and vice versa respectively.

Information Rates of Next-Generation Long-Haul Optical Fiber Systems Using Coded Modulation

A comprehensive study of the coded performance of long-haul spectrally-efficient WDM optical fiber transmission systems with different coded modulation decoding structures is presented. Achievable information rates are derived for three different square QAM formats and the optimal format is identified as a function of distance and specific decoder implementation. The four cases analyzed combine hard-decision (HD) or soft-decision (SD) decoding together with either a bit-wise or a symbol-wise demapper, the last two suitable for binary and nonbinary codes, respectively. The information rates achievable for each scheme are calculated based on the mismatched decoder principle. These quantities represent true indicators of the coded performance of the system for specific decoder implementations and when the modulation format and its input distribution are fixed. In combination with the structure of the decoder, two different receiver-side equalization strategies are also analyzed: electronic dispersion compensation and digital backpropagation. We show that, somewhat unexpectedly, schemes based on nonbinary HD codes can achieve information rates comparable to SD decoders and that, when SD is used, switching from a symbol-wise to a bit-wise decoder results in a negligible penalty. Conversely, from an information-theoretic standpoint, HD binary decoders are shown to be unsuitable for spectrally-efficient, long-haul systems.

Backscattering Interferences in WDM Optical Transmission System

Wavelength division multiplexed-passive optical networks (WDM-PONs) are attractive solutions for future broad band access networks. However, WDM can be relatively expensive to implement owing to the cost of the specified wavelength sources. The reflective structure is a common solution to solve this problem. There is a Reflective Semiconductor Optical Amplifier (RSOA) at the Optical Network Unit (ONU) in reflective structure. Bidirectional transmission over a single fiber is applied in WDM transmission system, as it uses a single source at the Center Office side and reduces the requirement number of the fiber and cost, but also injects the Rayleigh backscatterings. A RSOA and the other reflective components in Optical Distribute Network (ODN) generate reflection. These two interferences are critical noise on the single fiber transmission system. In this paper, we have studied the influences of the reflections and Rayleigh backscattering interferences by theoretically analysis and experiment.

XPM-induced crosstalk with variety of fiber in SCM–WDM optical transmission link

In this paper, XPM-induced crosstalk has been evaluated in a SCM–WDM communication link at different modulation frequencies, transmission lengths and optical powers for variety of fiber. Results show that XPM-induced crosstalk dominates at high frequency. As the dispersion and effective area of fiber (Aeff) decrease, crosstalk increases with increase in modulation frequencies, transmission lengths and optical powers. The present work shows that out of five different types of fiber, Standard Single Mode Fiber (SMF) has minimum crosstalk (−78 to −38)dB, (−55 to −33)dB and (−46 to −34)dB at modulation frequencies, transmission lengths and optical powers. Dispersion compensation fiber (DCF) has maximum crosstalk (−60 to −12)dB, (−37 to −12)dB and (−27 to −12)dB at modulation frequencies, transmission lengths and optical powers.

Improved XPM-induced crosstalk with higher order dispersion in SCM–WDM optical transmission link

In this paper, the XPM-induced crosstalk has been evaluated with higher order dispersion in SCM–WDM optical transmission link at different modulation frequencies, transmission lengths and optical powers. It has been observed that there is exponent increase in XPM-induced crosstalk with the increase in modulation frequencies, transmission lengths and optical powers, respectively. The impact of 3OD, 4OD and 5OD is small as compared to 2OD but still contributes when the combined terms are considered. The combined effect of second, third, fourth and fifth-order dispersion parameters, the induced crosstalk introduced by XPM little increase.

XPM-induced crosstalk with combined effect of 2OD and 3OD in SCM–WDM optical transmission link

In this paper, the XPM-induced crosstalk has been evaluated with combined effect of second order Dispersion (2OD) and third order Dispersion (3OD) in SCM–WDM optical transmission link for varied dispersion parameters in different modulation frequencies and transmission lengths. It has been observed that there is significant effect of 2OD and 3OD on the XPM-induced crosstalk in a SCM–WDM transmission link. It has been observed that XPM-induced crosstalk lies between (−54 to −30) to (−42 to −18) dB and (−54 to −28) to (−38 to 16) dB in the presence of combined effect of 2OD and 3OD respectively for dispersion varied from 5ps/nm/km to 20ps/nm/km. Hence it observed that there is exponent increase in XPM-induced crosstalk with the increase in different modulation frequencies and transmission lengths and as dispersion increases, XPM-induced crosstalk also increases.

XPM-induced crosstalk with higher order dispersion in SCM–WDM optical transmission link

In this paper, the XPM-induced crosstalk has been evaluated with higher order dispersion in SCM–WDM optical transmission link at different modulation frequencies. It has been observed that there is exponent increase in XPM-induced crosstalk with the increase in modulation frequency from 0 to 3GHz. The impact of 3OD, 4OD and 5OD is small as compared to 2OD but still contributes when the combined terms are considered. The combined effect of second, third, fourth and fifth-order dispersion parameters is that the induced crosstalk introduced by XPM increases.

Realization of Combined Chromatic Dispersion Compensation Methods in High Speed WDM Optical Transmission Systems

Chromatic dispersion (CD) has a significant impact on a quality of transmitted optical signal in high-speed fiber optic communication systems with data rates up to 10 Gbit/s, and as a result CD limits the maximum length of transmission distance. In order to operate fiber optic communication system with a sufficiently low bit error ratio (BER) and minimize the performance degradation caused by pulse distortion and broadening, dispersion compensation is needed. In this work using OptSim simulation software we realize an experimental high-speed WDM fiber optic communication system model with a new combined dispersion compensation mechanism where a conventional dispersion-compensating fiber (DCF), fiber Bragg grating (FBG) or optical phase conjugator (OPC) are used together. The best results were obtained by using FBG-OPC dispersion compensation scheme which showed the lowest BER value. Basis of the results we recommend avoiding the use of DCF for CD compensation where it is possible and use FBG instead. Ill. 15, bibl. 9 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.116.10.875

Realization of Combined Chromatic Dispersion Compensation Methods in High Speed WDM Optical Transmission Systems

Chromatic dispersion (CD) has a significant impact on a quality of transmitted optical signal in high-speed fiber optic communication systems with data rates up to 10 Gbit/s, and as a result CD limits the maximum length of transmission distance. In order to operate fiber optic communication system with a sufficiently low bit error ratio (BER) and minimize the performance degradation caused by pulse distortion and broadening, dispersion compensation is needed. In this work using OptSim simulation software we realize an experimental high-speed WDM fiber optic communication system model with a new combined dispersion compensation mechanism where a conventional dispersion-compensating fiber (DCF), fiber Bragg grating (FBG) or optical phase conjugator (OPC) are used together. The best results were obtained by using FBG-OPC dispersion compensation scheme which showed the lowest BER value. Basis of the results we recommend avoiding the use of DCF for CD compensation where it is possible and use FBG instead. Ill. 15, bibl. 9 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.113.7.622

Efficient compensation of inter-channel nonlinear effects via digital backward propagation in WDM optical transmission

An advanced split-step method is employed for the digital backward-propagation (DBP) method using the coupled nonlinear Schrodinger equations for the compensation of inter-channel nonlinearities. Compared to the conventional DBP, cross-phase modulation (XPM) can be efficiently compensated by including the effect of the inter-channel walk-off in the nonlinear step of the split-step method (SSM). While self-phase modulation (SPM) compensation is inefficient in WDM systems, XPM compensation is able to increase the transmission reach by a factor of 2.5 for 16-QAM-modulated signals. The advanced SSM significantly relaxes the step size requirements resulting in a factor of 4 reduction in computational load.

Unveiling nonlinear effects in dense coherent optical WDM systems with Volterra series

In this paper, the effect of fiber nonlinear effects on coherent optical WDM systems is investigated through numerical simulations. The analysis of the most relevant fiber nonlinear effects is made recurring to the Volterra series transfer function method, which allows us to quantify its impact on the transmission of multi-level modulated signals employing digital coherent receiver. The performance transmission is evaluated using vector analysis of the received signal's constellation where firstly we validate against split-step simulations that VSTF is suitable for optimizing coherent optical WDM transmission; then we evaluate the different contributions of the fiber nonlinear distortions imposed on the coherent optical QPSK, 8PSK and 16QAM channels by co-propagating lower data rate intensity modulated channels.

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 of a Chirped Bragg Grating Based First Order PMD Compensator in WDM Optical Transmission System

Performance of a Chirped Bragg Grating Based First Order PMD Compensator in WDM Optical Transmission System

Simulative analysis of pre- and post-compensation using CRZ format in WDM optical transmission link

This paper reports the effects of pre- and post-compensation using CRZ modulation format in long-haul WDM optical transmission link using wavelengths in three bandwidths viz. 1537.4; 1550; 1562.6 nm at per channel bit rates of 10 Gbit/s. It has been investigated here that optimization of dispersion map results in improved management of nonlinear effects in long-haul light wave systems operating in the quasi-linear regime. In addition, pre- and post-dispersion compensation was applied at the transmitter and receiver depending on the signal wavelength, which resulted in improvement of performance metrics viz. Q 2 (dB), BER and OSNR over longer transmission distances. It is reported here that optimum values of Q 2 dB of 17.1 dB, BER of 8.4933e −015 and OSNR of 30.1 dB are obtained at 1550 nm at a transmission distance of 7360 km with pre- and post-compensation using CRZ modulation format.

An ASE Reduction Filter Using Cascaded Optical Fiber Grating Couplers in EDFA Repeater

A new configuration for an ASE reduction filter in EDFA repeaters for WDM optical transmission systems using optical fiber grating couplers (FGCs) was proposed and first demonstrated. The filtering characteristics of the proposed filter for amplified single wavelength signal and 2-channel WDM signals using EDFA were identified. It was found that the filter was effective to improve SNR in optical domain by reducing ASE noise. The required FGC characteristics for the filter were theoretically predicted under the condition that the total filter loss did not exceed 3 dB. More than 70% of drop efficiency was required in each FGC for the application of the proposed filter to an 8-channel WDM system using EDFA repeaters.

Fabrication of high quality UV-written fiber bragg gratings

In conclusion, we have reported that 98.5 % peak power reflectivity fiber Bragg gratings were fabricated in the core of B/Ge co-doped optical fiber using 248 nm KrF excimer laser pulses to irradiate a phase mask. The fiber gratings fabricated by the method described above have negligible sideband and good wavelength selectivity. They can find applications in WDM optical fiber transmission systems, fiber grating external cavity semiconductor lasers, and rearearth-doped fiber lasers. But more efforts are needed to further improve the transmission spectra of the gratings, because the ripple in the short wavelength side is harmful to their use in WDM systems.

ＨＤＴＶ波長多重光伝送システム

ＨＤＴＶ波長多重光伝送システム

459 km, 2.4 Gbit/s four wavelength multiplexing optical fibre transmission experiment using six Er-doped fibre amplifiers

A 2.4 Gbit/s, four WDM optical fibre transmission experiment over 459 km using six Er-doped fibre amplifiers in the 1.55 mu m wavelength region is presented. The results confirm the possibility of WDM multiple optical amplifier repeater transmission systems. >