160 Gbps S-band WDM transmission system over 1400 km using ITUT-652a and ITUT-655 fibers with low dispersion accumulation

Dispersion accumulation with the distance effects optical WDM system's performance severely. For every modulation format used there is a limit on maximum transmission distance due to dispersion accumulation. So dispersion compensation is required. But dispersion compensation can be avoided to a large extent by alternatively using different fiber standards. In this paper it has been proposed that the dispersion accumulation can be reduced to a large extent by alternatively transmitting in S-band and using fiber standards ITUT-652a and ITUT-655. To validate the claim, performance of a 16 channel 10 Gbps WDM system with the proposed method has been analyzed in terms of BER and Q-factor. And it has been observed that with the proposed scheme without any dispersion compensation the system performs well up to 1400 km.     

Boost up of four wave mixing signal in semiconductor optical amplifier for 40 Gb/s optical frequency conversion

The 40 Gb/s optical frequency converter for non-return to zero differential phase shift keying (NRZ-DPSK) signal by using four wave mixing in semiconductor optical amplifier (SOA) have achieved sucessfully. The optimized signal-to-pump ratio for NRZ-DPSK by using optimized SOA structure with enhanced FWM effect is also evaluated. The optimum signal-to-pump ratio is 12 dB and 10 dB with Q factor penalty of 0.685 dB and 0.663 dB. The dependence of four wave mixing efficiency and converted signal power on signal input power is studied and it is evaluated that four wave mixing efficiency decreases with increase in the input power. The impact of pump power, signal-to-pump ratio, and SOA parameters with Q factor penalty for 40 Gb/s has been illustrated. It has shown that converted signal power increases up to the saturation power of semiconductor optical amplifier, then decreases. It is observed that for the optimum pump power, OSNR of converted signal varies little with signal input power.     

On WDM RoF–EPON link using OSSB transmission with and without DCF + FBG

A system is presented which uses optical SSB transmission on WDM RoF–EPON link to compensate dispersion and FWM with DCF and FBG. Performance of the system is improved by 8.91% with the use of DCF and FBG for equal spacing between the channels and it is further increased by 9.51% by keeping unequal spacing between the channels. Results are compared for equal and unequal spacing with and without DCF and FBG. BER, Q factor and eye diagrams have been analyzed for evaluating the performance of the system.     

400 Gbps WDM transmission over short range with discrete multi-tone

We simulate 400 Gbps WDM transmission system with DMT modulation. The system reaches 5 km SSMF with 100 Gbps per wavelength when the BER is 1e−3. From our analyses, we can see that DMT can be a promising solution for high capacity optical transmission system over short distance.     

Design of adaptive dispersion compensation and demodulation system for 40 Gbps RZ-DQPSK optical fiber communication receivers

An adaptive terminal dispersion compensation and demodulation scheme based on dual-feedback strategy for 40 Gbps return-to-zero differential quaternary phase shift keying (RZ-DQPSK) fiber communication receivers is proposed to achieve high reliability receiving performances. In the receiving system introduced in this paper we utilize both the balanced receiver feedback and framer error rate to achieve accurate RZ-DQPSK optical signal demodulation and adaptive dispersion compensation. Compared to traditional RZ-DQPSK receivers, the proposed design combines the chromatic dispersion (CD) compensation and Mach-Zehnder interferometer (MZI) adjusting and automatically estimates the dispersion compensation parameters without human intervention. And another improvement is introducing the framer error rate as feedback quantity to ensure the accuracy of CD and MZI adjusting. Finally, we present the performance of the designed receiver by showing the simulations and experiment results in actual telecommunication engineering projects.     

An 8 × 10 Gbps parallel single-chip light-to-logic converter

An 8 × 10 Gbps direct light-to-logic converter for hybrid mounted Ge photodiodes is presented. The receiver is realized in standard 0.35 μm SiGe BiCMOS technology and the Ge photodetector is directly mounted on the top of the CMOS wafer. Each of the 8 channels includes a transimpedance amplifier, limiting amplifier stages and a 50 Ω CML output driver. The overall transimpedance is 275 kΩ and at a data rate of 10 Gpbs a sensitivity of − 23.1 dBm (BER = 10⁻⁹) is reached.     

Investigation of optimum pulse shape for 112 Gbps DP-DQPSK in DWDM transmission

This paper reports the simulative analyses to investigate the impact of different pulse shapes on DP-DQPSK modulation for high-spectral efficient DWDM transmission at 112 Gbps per channel. In the simulation model we have considered three different pulse shapes viz. NRZ, 50% duty cycle RZ (RZ50) and 67% duty cycle RZ (RZ67) in symbol-aligned and symbol-interleaved format. The analysis has been carried out for various linear and nonlinear system impairments where the pulse is subjected to degradation under the influence of amplified spontaneous emission (ASE) noise, group velocity dispersion (GVD), cross-phase modulation (XPM) and polarization mode dispersion (PMD) and thus, limiting the system performance. Results show that the RZ50 pulse shape for DP-DQPSK with symbol interleaving shows the maximum tolerance for the various system degradations in long haul DWDM transmission. Even the system based on the NRZ pulse shape can gain significant improvement from the symbol-interleaving.     

Performance analysis of NRZ, RZ, CRZ and CSRZ data formats in 10 Gb/s optical soliton transmission link under the impact of chirp and TOD

This paper presents the performance analysis of non-return-to-zero (NRZ), return-to-zero (RZ), chirped return-to-zero (CRZ) and carrier suppressed return-to-zero (CSRZ) data formats in optical soliton transmission link under the impact of chirp and third-order dispersion (TOD). The performance of these data formats has been analyzed on the basis of certain performance metrics, viz, bit error rate (BER), Q² (dB), OSNR, eye opening, etc. It has been reported here that the performance of CRZ and CSRZ modulation format is better as compared to NRZ and RZ in a soliton transmission link. Further, CSRZ modulation format has been found to deliver optimum performance on the basis of performance evaluation metrics reported in this paper. In case of NRZ and CSRZ, comparatively narrow power spectrum has been observed. Best eye opening, highest value of Q² (dB) of 18 dB and lowest value of BER of the order of 10⁻¹⁶ has been reported in case of CSRZ among the considered data formats. The results have been obtained by varying noise figure from 3.0 to 9.0. No considerable effect of noise was observed. It was observed that at very narrow and ultra short pulse width, OSNR value suffers heavily and reduced to even negative values in dB, thus inducing a high degree of OSNR power penalty. The results were obtained by varying chirp factor from −0.6 to +0.6. Negative chirp resulted in improved OSNR as compared to positive chirp. RZ data format yielded a broader optical spectrum, comparatively low spectral efficiency and poor OSNR thus it was found that RZ format is not suitable for optical soliton transmission under the impact of chirp and TOD.     

The analysis of the error statistics in a 5 × 40 Gbit/s fibre link with hybrid amplification

We quantify the error statistics and patterning effects in a 5 × 40 Gbit/s WDM RZ-OOK SMF/DCF fibre link using hybrid Raman/EDFA amplification. By extensive use of a numerical model, we determine how the error statistics change with the transmission distance. This knowledge is used as a basis for a constrained coding technique in order to improve the transmission error rate. We propose an adaptive constrained code for mitigation of the patterning effects and demonstrate that this approach can substantially reduce the bit error rate (BER) even for very large values of the channel BER (BER > 10^− 1). The proposed technique can be used in combination with forward error correction schemes (FEC) to extend the range of channel BERs that an FEC scheme is effective over.     

Impact of polarization mode dispersion on the performance of optical CDMA transmission system

The impact of fiber polarization mode dispersion (PMD) on the bit error rate (BER) performance of a direct sequence optical code-division multiple-access system is analyzed by the split-step Fourier method based on the coupled nonlinear Schrödinger equation, the three-dimensional Poincare sphere theory and the Jones matrix method. When the incident pulse's width is bigness than the chip duration, which causes spreading and overlapping of chips and degrades system performance due to increased interchip interference and reduced received optical power conduce cannot decoding or error decoding. When the incident pulse's width is less than the chip duration, good encoding/decoding performance can be achieved.     

Transmission performance of 20 × 10 Gb/s WDM signals using cascaded optimized SOAs with OOK and DPSK modulation formats

We investigated 20 channels at 10 Gb/s wavelength division multiplexing (WDM) transmission over 1190 km single mode fiber and dispersion compensating fiber using cascaded inline semiconductor optical amplifier at a span of 70 km for RZ-DPSK (return zero differential phase-shift keying) modulation format by using same channel spacing, i.e. 100 GHz. We show for RZ-OOK (return zero on-off keying) format a transmission distance of up to 1050 km with Q factor more than 15 dB, without any power drops. We developed the SOA model for inline amplifier having minimum cross-talks and ASE (amplified spontaneous emission) noise power with sufficient gain. At optimal bias current of 400 mA, a high constant gain of 36.5 dB is obtained up to a saturation power of 21.36 mW. So reduction of cross-talk and distortion is possible by decreasing the bias current at appropriate amplification factor.The DPSK modulation format has less cross-talk as compared to OOK format for nonlinearities and saturation case. The impact of optical power received and Q factor at different distance for both RZ-OOK and RZ-DPSK modulation format has been illustrated. We have shown the optical spectrum and clear Eye diagram at the transmission distance of 1190 km in RZ-DPSK system and 1050 km in RZ-OOK systems.The bit error rate (BER) for all channels observed is less than 10⁻¹⁰ up to gain saturation for both DPSK and OOK systems. Finally, we investigated that the transmission distance decreases with a decrease in channel spacing of up to 20 GHz.     

Transmission of 4× 40/10 Gbps in a WDM-PON using NRZ-DQPSK/ASK modulation

In this paper we demonstrate the feasibility to deploy a wavelength division multiplexing passive optical network (WDM-PON) of a 30 km standard single-mode fiber (SSMF-28) carrying 160 Gbps data in downstream and 40 Gbps through the uplink. The developed method is based on the comparison between two WDM-PON systems of 4 channels with the same characteristics, using two different formats of modulation in OLTs. The first system uses the NRZ-ASK in the downlink direction, while the second uses the NRZ-DQPSK.     

Comparative investigation and suitability of various data formats for 10 Gb/s optical soliton transmission links at different chirps

This paper presents the comparative investigation and suitability of various data formats for optical soliton transmission links at 10 Gb/s for different chirps (−0.7 to 0.7). Here the investigations focused on data formats: NRZ, RZ soliton, RZ raised cosine and RZ super Gaussian. The comparative results and suitability of data formats is based on various performance measures such as Q-factor, eye opening, BER and jitter. It has been indicated that RZ super Gaussian yields the highest value of Q (34.08 dB), good eye opening and lowest BER.     

10 Gbps optical soliton transmission link using in-line SOA on standard SMF at 1.3 μm

In this paper, 10 Gbps optical soliton transmission link using in-line semiconductor optical amplifiers (SOAs) for already installed standard single mode fibers (SMF) at 1.3 μm wavelength has been reported. The pattern effect and the impact of chirp on pulse propagation after amplification have been investigated. The observations are based on modeling and simulation optical soliton transmission link. Optical soliton pulse transmission over distances of the order of several hundreds of kilometers has been shown with and without initial chirp.     

Optimizing 10 Gbps optical communication system with duty cycle selection of return to zero pulse

We have investigated the return-to-zero (RZ) pulse duty cycle for single-channel Standard Single mode fiber (SSMF), Non Zero Dispersion shifted fibers (normal NZDSF and anomalous NZDSF fiber) for 10 Gbps optical fiber communication system. We give a comprehensive look on the behavior of variable duty cycle optical RZ pulse indicating that lowest bit error rate for duty cycle 0.8 among the duty cycle values 0.2, 0.4, 0.6 and 0.8 investigated for the case of SSMF. The single repeaterless mode fiber length is increased from existing 55 km at duty cycle 0.2 to fiber length 85 km by keeping duty cycle at 0.8. The result is also emphasized through the 10 dB Q value improvement and corresponding improvement in average eye opening diagram. The normal NZDSF show similar improvement but at greater fiber length, it offers BER 10⁻⁹ at length 110 km with duty cycle 0.2. NZDSF operating length can further be increased to length 160 km by keeping duty cycle 0.8. The corresponding 8 dB Q value improvement and Average eye opening improvement also supports the result through its graphical variation. Thirdly Anomalous NZDSF for same optical communication system showed that 0.2 duty cycle value give operational length of 130 km which could be extended to 160 km if 0.8 duty cycle is kept. The corresponding 8 dB Q value improvement, average eye-opening improvement endorsed the fact in the graphs.     

Timing jitter dependence on data format for ideal dispersion compensated 10 Gbps optical communication systems

Simulations for data formats Return to Zero (RZ), Non-Return to Zero (NRZ), RZ-Soliton, Duobinary and their subcategories have been done with and without ideal dispersion compensation for optical communication systems. The results show that, in general, dispersion compensation improves timing jitter. RZ-Rectangular pulses show the smallest value of jitter without compensation. It has been observed that the RZ-Raised Cosine, and Soliton, give minimum jitter after ideal compensation. It has been reported that the BER performance of optical communication system using Duobinary data format is 10⁻⁸ and 10⁻³⁷ before and after dispersion compensation, respectively. Further the comparative study shows that the timing jitter is the lowest in case of RZ-Soliton (0.0127 ns) after dispersion compensation and 0.0135 ns for RZ-Rectangular data format before dispersion compensation.     

170 Mb/s multilevel transmission over 115 m standard step-index plastic optical fiber using an integrated optical receiver

An optical receiver having a high linearity is used for multilevel communication over standard step plastic optical fiber. A large-diameter photodiode with an antireflection coating optimized for red light was integrated. These features enable the used optical receiver to be a promising plastic optical fiber receiver. An error free (< 10⁻⁸) 170 Mb/s data rate over 115 m standard PMMA step-index plastic optical fiber is achieved with four-level and eight-level pulse amplitude modulation.     

Simulative analysis of co-existing 2.5 G/10 G asymmetric XG-PON system using RZ and NRZ data formats

In this paper, a fiber optic communication system has been employed using co-existing 10 G/2.5 G asymmetric gigabit passive optical network (XG-PON) architecture. In this system, bidirectional optical fiber has been used for upstream and downstream data transmission. The system performance has been investigated for non-return-to-zero (NRZ) and return-to-zero (RZ) data formats operating at varying bit rates by varying the length of the fiber for analyzing the feasibility of this co-existence. The results have been compared for NRZ and RZ formats for upstream and downstream data in terms of Q value and eye opening. It is observed that RZ modulation format is superior as compared to conventional NRZ format and the faithful transmission of signal has been carried up to 90 km at 1577 nm for downstream and 140 km at 1270 nm for upstream.     

Patterning effects in a WDM RZ-DBPSK SMF/DCF optical transmission at 40 Gbit/s channel rate

Through extensive direct modelling we quantify the error statistics and patterning effects in a WDM RZ-DBPSK SMF/DCF fibre link using hybrid Raman/ EDFA amplification at 40 Gbit/s channel rate. We examine the BER improvement through skewed channel pre-coding reducing the frequency of appearance of the triplets 101 and 010 in a long data stream.     

Impact of optical modulation formats on SPM-limited fiber transmission in 10 and 40 Gb/s optimum dispersion-managed lightwave systems

In this paper, 10 and 40 Gb/s optical systems have been investigated for nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CSRZ) and RZ-differential phase-shift-keying (RZ-DPSK) data formats. For the range of the optical signal power from −5 to 15 dBm, a maximum self-phase modulation (SPM)-limited transmission distance L_SPM is determined with eye-opening penalty (EOP) >1 dB .The observations are based on the modeling and numerical simulation of optimum dispersion-managed transmission link. Transmission over distances of the order of several hundreds of kilometers has been shown with and without amplified spontaneous emission (ASE) noise of the in-line erbium-doped fiber amplifiers (EDFAs).