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In this paper, a novel architecture of bidirectional underwater wireless optical communication (UWOC) system has been proposed to interconnect stationary and moving underwater sensor nodes for diverse applications. To achieve the bidirectional communication, wavelength division multiplexing (WDM) and remodulation approach have been used in this work. The proposed bidirectional UWOC system works at 40 Gbps data rate for both downlink (stationary node to moving node) and uplink (moving node to stationary node). Two distinct wavelengths of 532 nm and 531 nm have been used for uplink and downlink, the main attraction of the proposed architecture is that both the laser sources are placed at the stationary node. The moving node do not have any laser source and it remodulates the signal for sending data back to the stationary node. Because of this, the moving node contains lesser components which results in cost effectiveness, low power requirement and light weight. The proposed system successfully transmits the bidirectional information at a link range of 40 m under pure sea conditions in the presence of distinctive air bubble populations. The observed bit error rate (BER) values are 1.89 × 10− 13 and 1.19 × 10− 04 for the downlink and uplink respectively at a link range of 40 m, these BER values are under the acceptable forward error correction (FEC = 2 × 10− 3) limit. The proposed bidirectional UWOC system is beneficial for the development of a high-speed last-mile underwater solution. [ABSTRACT FROM AUTHOR]

The next generation passive optical network stage 2 (NG-PON2) is a broadcast network in which a large number of optical network units (ONUs) can be served using various network topologies. In this paper, a purely passive remote node (RN) design based on fiber bragg grating (FBG) is presented for the bus topology of a high split NG-PON2 system. The performance of the proposed node has been analysed for a symmetric 80 Gbps NG-PON2 system serving 1024 ONUs in terms of bit error rate (BER) and optical signal to noise ratio (OSNR). The working of the proposed node has been explained with the optical frequency spectrums for downstream and upstream signals. The observed OSNR levels for the ONUs operating at the 1st RN is 84.8743 dB which decreases to 75.7973 dB for the ONUs connected to the 8th RN. The BER level < 10–9 for both upstream and downstream confirms the correct working of the proposed node in the NG-PON2 system. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated wavelength division multiplexed (WDM) hybrid (ring-tree-star) topology. Eight optical add/drop multiplexers (OADMs) are used to make ring structure. The single mode fiber and dispersion compensating fiber and semiconductor optical amplifier (SOA) are employed between each OADM to achieve a maximum. To increase the number of users each OADM node of ring network is connected to star and tree network topology which can accommodate more than 2048 users. Various system parameters (for different channel spacing, different input power signal, different data rates and the fiber length) are varied to investigate the system performance in the term of BER and Q factor. [ABSTRACT FROM AUTHOR]

A simple genetic algorithm is implemented to perform multi parameter optimization of Raman Fiber Amplifier for 100 channel S band dense wavelength division multiplexed system at 25 GHz interval. A cost effective system using single Raman pump is investigated aiming at maximum average gain. The single counter propagating pump is optimized to frequency of 211.528 THz and 652.93 mW power level with optimum Raman fiber length of 44.064 Km. There is evidence to show that the optimum solution presents a small gain variation (less than 3 dB) over an effective bandwidth covering 197–199.475 THz. The optimized configuration enabled an adequate system performance in terms of acceptable Q -factor (19.52 dB) and BER (1.46 × 10 −21 ). [ABSTRACT FROM AUTHOR]

For the first time, a novel flat-gain optical amplifier is proposed using a hybrid configuration with an Er-Yb co-doped waveguide amplifier (EYDWA) and a semiconductor optical amplifier (SOA) for 100 × 10-Gb/s dense wavelength division multiplexed system at 0.2 nm interval. With an EYDWA-SOA hybrid amplifier, a flat gain of is obtained across the effective bandwidth with a gain variation of the order of 0.75 dB without using any gain clamping techniques. It is observed that when the proposed hybrid amplifier is used as a booster for hybrid distributed Raman amplifier and erbium doped fiber amplifier, the gain variation is reduced from 2.01 to ~ 1.15 dB efficiently with acceptable bit error rate. [ABSTRACT FROM PUBLISHER]

We present a simple genetic algorithm implemented to perform multiparameter optimization of a Raman fiber amplifier for a 100-channel L-band dense wavelength division multiplexed system at a 25-GHz interval. The system is investigated for various cases with fixed pump frequency leading to 202.2-THz pump as the best choice with average gain above 19.5 dB. There is evidence to show that a single counterpropagating pump optimized to 588.2-mW power level and optimum Raman fiber length of 38.8 km presents a small gain variation (<2 dB) over an effective bandwidth covering 187 to 189.475 THz. The optimized configuration enabled an adequate system performance in terms of acceptable Q-factor (17 dB) and bit error rate (5.60 x 10-13). [ABSTRACT FROM AUTHOR]

Abstract: In this paper, four modulation formats including nonreturn-to-zero (NRZ), nonreturn-to-zero raised cosine (NRZ-RC), return-to-zero (RZ), return-to-zero raised cosine (RZ-RC) DWDM system with different hybrid optical amplifiers are introduced. We show that NRZ-DPSK and RZ-DPSK degrade the performance when Raman amplifier is considered. The obtained results reported that RZ and RZ-RC DWDM system with Raman-EDFA provide better results and cover 1512 and 1260km of transmission distance, respectively, with acceptable quality factor (>15dB) and bit error rate (<10−9). Further, it is also confirmed that using the hybrid optical amplifiers is a best alternative to increase the span distance. [Copyright &y& Elsevier]

Abstract: In this paper, we investigate pre-, post-, symmetrical dispersion and power compensation in parallel for 96 channels×10Gbps non-return to zero DWDM system using pumped dispersion compensating fiber (PDCF) and pumped single mode fiber (PSMF). The results of three compensation methods have been compared in the term of bit error rate, eye closure penalty and Quality factor and it is found that both post-, and symmetrical compensation methods are provide better results for short haul communication but for long haul communication post-compensation method is the best alternative among other. The impact of bit error rate and eye closure penalty is also observed for large transmission distances and cover 420km using post-compensation method with acceptable bit error rate (2.3×10−10) and eye closure (1.73dB). [Copyright &y& Elsevier]

Fractional domain optimum combining (OC) using fractional Fourier transform has been considered in this article. It has already been established that in an interference-dominated environment, OC is the best among all the diversity techniques used for single-input multiple-output systems. This technique is based on the principle of maximising the signal-to-interference plus noise ratio at the output of the combiner. In this article, a new combiner, which calculates the weights in fractional domain, has been proposed to further enhance the performance of OC in terms of bit error rate (BER). Fractional domain combining gives better signal-to-noise ratio (SNR) at the output of the combiner as compared to time- or frequency-domain combiner due to complete removal of noise. For two receive antennas, the proposed combiner gives an SNR improvement of 7.2 and 2.4 dB as compared to time- and frequency-domain combiners, at a BER of 10−2. It has been concluded that the proposed technique clearly outperforms the existing technique. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, we investigated the post-, pre- and symmetrical power compensation methods for a different position of hybrid optical amplifier RAMAN–EDFA in fiber link. The effect of increase in signal input power for three power compensation methods is compared in terms of bit error rate, eye closure penalty and output received power. It is found that the post power compensation method is superior to pre- and symmetrical power compensation methods. Further, the effect of variation in length of the standard single mode fiber and dispersion-compensated fiber for three power compensation configurations has also been observed. We observed that RAMAN–EDFA as post power compensation method provides least bit error rate (10−40) and high output power (12dBm) at −15dBm signal input power at fiber link. [Copyright &y& Elsevier]

This article proposes various combinations of optical amplifiers for a dense wavelength division multiplexed system and investigates the impact of reduced channel spacing at high bit rates in terms of quality factor, bit error rate, eye closure, and output power. It is reported that the hybrid optical amplifier (Raman–erbium-doped fiber amplifier [EDFA]) provides better results with a maximum covered single span distance (220 km) at channel spacing of 6.25 GHz. The maximum acceptable bit rate for the 12.5-GHz channel spacing dense wavelength division multiplexed system is also investigated, and the recommendation is provided that for the Raman–EDFA, Raman–EDFA–Raman, EDFA–Raman–EDFA, and EDFA–semiconductor optical amplifier–EDFA, the operating bit rate should not be greater than 20, 16, 19, and 20 Gbps, respectively. [ABSTRACT FROM AUTHOR]

The performance of DWDM ring network topology is investigated with 13 × 15 Gbps channels without using dispersion compensating fiber among the 3 channels are added and droped using OADM, respectively. Each OADM node having 70 km distance between each other. This ring network topology is evaluated by considering the signal quality factor and BER for different input power at all nodes. Further, this ring network topology is also investigated for different data rate at all nodes. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the performance of optical/hybrid optical amplifier for 64×10Gbps dense wavelength division multiplexed system has been compared. It is observed that hybrid optical amplifier (RAMAN–EDFA) provides better results as compared to conventional amplifiers. The impact of modulation formats (NRZ, RZ and DPSK) on hybrid optical amplifier has been further investigated and it is found that 64×10, RZ is more adversely affected by nonlinearities, where as NRZ and DPSK is more affected by dispersion. [Copyright &y& Elsevier]

• A novel remote node design has been presented with fiber fault protection for ring topology NG-PON2. • The presented NG-PON2 architecture is based on single fiber ring topology. • The proposed remote nodes are able to communicate in both clockwise and anticlockwise directions. • In case of fiber fault the remote nodes can change the direction of communication and service disruption can be avoided. The service disruptions in passive optical networks (PONs) due to fiber or node failure is an important issue. In the conventional star topology time and wavelength division multiplexing (TWDM) based next generation passive optical network stage 2 (NG-PON2), there is no provision to restore the service if the fiber between remote node (RN) and optical network unit (ONU) fails. In this paper, we proposed a novel entirely passive node design for ring based NG-PON2 which provides fiber fault protection against any fiber break between RNs. The working of the proposed node is verified by simulating normal conditions and fault conditions. It is observed that in the case of fiber failure, the affected ONUs can still communicate with the optical line terminal (OLT). The performance of the system has been analyzed in terms of bit error rate (BER), and the BER <10−9 confirms the correct working of the system. [ABSTRACT FROM AUTHOR]