Volume 43, Issue 1

Thulium-doped fiber amplifiers (TDFAs) can provide high power optical amplification in the wavelength range of 1,460–1,545 nm (S and near-C bands). They can be employed for dense wavelength division multiplexing (DWDM) in optical fiber communication over a broad range, unlike the Erbium-doped fiber amplifiers (EDFAs), which are active in the C-band only in the conventional “erbium window.” Line service surveillance and management of digital optical information in DWDM TDFA networks can be done by low-frequency amplitude modulation (~100 kHz) of TDFA pump and communication signal, termed as overmodulation. Governing equations for overmodulation gain dynamics in TDFAs using the Bononi and Rusch (1998) model was first derived in a companion paper (2017). The research provides a methodical test bed analysis using MatLab Simulink model with a different outlook in the respective field. The transfer functions for signal-to-signal and signal-to-amplified spontaneous emission were implemented to develop a simulator. An undesirable 30 % increment in the output modulation index at 8 dBm and 1,490 nm were obtained by simulating overmodulation sensitivity at different levels of mean input signal power and signal wavelength respectively at corner frequency. The optimum operating wavelength for TDFAs obtained was 1,490 nm.

All optical logic gates are the key elements of contemporary optical computing unit. For that non-linear attribute of reflective semiconductor optical amplifier (RSOA) is exploited to configure optical logic gates. Accordingly, in the manuscript all optical OR/NOR/Buffer binary logic network for the nonreturn to zero format has been designed. Its operation at 100 Gbps data rate has been successfully realized. For the applied data inputs in nonreturn to zero patterns, their corresponding output waveforms for the stated logic action have been verified. Numerical investigations for the imperative design constraints as data rate, injected power and imperative elements of the semiconductor optical amplifiers (SOAs) pump current, carrier density, active length, confine factor, laser power has been appropriately executed with optimum performance. It has depicted good extinction ratio (>10 dB) performance with confine factor more than 0.2 and higher carrier density of amplifier. Further, it also accomplished, that for the OR, buffer logic execution with lower power of pump laser and for the NOR logic execution higher power laser pump source is required. The proposed design could fulfill need for the impending higher data rate composite optical computing units.

Optical NAND gate is a universal gate which can be used for implementing different kinds of combinational circuits without using other gates. Due to significance of optical NAND gates in the optical communications, in this paper we proposed a novel structure for designing an all optical NAND gate based on photonic crystal structures. The proposed structure was designed using threshold switching mechanism which can be implemented using nonlinear ring resonators. In the proposed structure delay time is about 2.3 ps.

In this paper, sixteen 50 GHz spaced orthogonal frequency division multiplexing channels at 10 Gbps has been investigated with reconfigurable optical add drop multiplexer based on digital optical switch. The effects of fiber link length and input optical signal power on bit error rate, quality factor, output signal power, optical signal to noise ratio at the receiving side are observed. It is observed that maximal transmission distance of 2,100 km is achieved with an input optical power of −8 dBm.

In this report, mode conversion based on the lateral misalignment between two similar multi-ring core fibers (M-RCFs) is proposed. The conversion was achieved by varying the lateral height (y) and the distance (x) that separates the two M-RCFs. Based on the achieved coupled power of 94%, this technique may find application as a conversion device during multiplexing in mode-division multiplexed systems (MDM).

The impact of major nonlinearities in optical fiber such as SRR (Stimulated Raman Scattering) and Four Wave Maxing (FWM) in cascaded amplifier Dense Wavelength Division Multiplexing optical long reach and high speed data rate transmission scheme have been investigated at different data rates. Pulse walk off effect is considered for the purpose of calculating Stimulated Raman Scattering (SRS) nonlinear factor. Examination has been accomplished to assess signal to noise ratio thinking about the consolidated impact of SRS and FWM within the sight of amplified spontaneous emission noise to achieve minutest noise at altered data rates.

In this paper, a photonic structure for reservoir computing is presented. A new approach for photonic reservoir computing is proposed using a network of SOAs arranged in a waterfall topology and coupled by semi-transparent mirrors. The proposed method is then simulated in OptiSystem software. As this software is hardware framework-based, the simulation result is one step closer to fabrication than the previous works. A series of noisy and noise-free time-series signals are employed to evaluate the performance of the proposed method. The used time-series signals contain random sequence of both square and triangular wave forms. The results of this simulation show 92.14% recognition of a noise-free signal and 79.32% of a 60 dB noisy signal. The parameters of the simulated photonic reservoir network are also optimized to achieve higher accuracy in this time-series classification.

The hybrid optical code-division multiple-access over wavelength-division multiplexing (OCDMA/WDM) scheme has attractive features of supporting system reach, multi Gbps data rates, security, and robustness for optical communication networks. This paper presents the performance of such scheme under DPSK and QPSK modulation formats using spectral direct detection technique. The modified double weight (MDW) code is used as spectral amplitude coding which also acts as a signature address code for the OCDMA system. The MDW code has the advantage of reducing the multiple access interference (MAI) and enhancing the security of the proposed hybrid system. The study focuses on the comparison between the two advanced modulation techniques (DPSK, QPSK) using spectral direct detection. Simulation results show bit-error-rate (BER) ≤10 –09 for up to 25 km distance at the bit rate of 1 Gbps for optical communication networks.

Higher spectral efficiency and data rate per channel are the most cost-effective approaches to meet the exponential demand of data traffic in optical fiber network communication system. In this paper, diverse modulation formats are analyzed for Dense Wavelength Division Multiplexed system at 100 Gbps * 16=1600 Gbps data rates. The performance analysis of proffered system for Non-Return to Zero, Return to Zero, Carrier- Suppressed Return to Zero and Duo binary RZ with duty cycle 0.5 to 0.7 ranges like modulation formats are considered to find optimum modulation format for a 100 Gbps bit rate per channel optical fiber transmission network system. The simulations are analyzed for different values of input power, length of fiber, nonlinear refractive index, nonlinear dispersion and nonlinear effective area for all above mentioned modulation formats with spacing 100 to 250 GHz. to evaluate the effect of modulation format Fiber Bragg Gratting, optical fiber amplifier and Dispersion Compensation Fiber dispersion compensation techniques are enacted on this proposed optical network system.

In this article, we focus on the optimization of lightpath routing in an online Space Division Multiplexing-based Elastic Optical Network (SDM-b-EON) which is protected by the dedicated route protection (DRP) strategy. In view of the aforementioned, the Online Protection and Routing Algorithm with Regeneration (OPaRAwR) method is proposed which (i) protects the lightpaths through DRP, (ii) accounts for the presence of transceivers in the network, and (iii) ensures the routing of translucent lightpaths through the spectral super-channels over the spatial modes links. In regard to regeneration, we investigate two scenarios which differ in their regeneration variability level in addition to the adjustment of modulation formats (MFs) as per the transmission route characteristics. Extensive simulation experiments are conducted considering realistic transmission reach values and two realistic network topologies. The obtained simulation results demonstrate that the proposed OPaRAwR method significantly outperforms various reference techniques in terms of bandwidth blocking probability (BwBP). In addition, the results also show that significant benefits can be obtained in regard to the utilization of resources (spectrum and transceivers) with much lesser BwBP when the regeneration is conducted with complete flexibility and MF conversion is also permitted at every node of the SDM-b-EON.

Optical label switching is proposed for providing fast all-optical switching, covering all granularities transfer and assuring quality of service support. However, the important issue is improving optical resource and providing a steadiness between satisfying traffic demands and reducing resource utilization. This paper proposes a novel multicast approach which enables grooming using an upgraded core node architecture that switches suitably unicast and multicast connections. The proposed node architecture manages appropriately all optical resource including a fiber delay line and wavelength bandwidth, as well as traffic requirements. A new label framework is introduced to assure the required information exchange for handling suitably real-time traffic constraints and optical resource status. Moreover, innovative signaling and switching schemes are introduced to perform suitably lightpath and traffic constraints supervision. Theoretical model and simulation experiments are conducted for validating the proposed scheme and evaluating its performances and effectiveness. Finally, the proposal guarantees traffic requirements and reduces resource usage while improving resource availability.

Dense Wavelength-Division Multiplexing (DWDM) optical networks meet ever-increasing bandwidth demand of internet applications. Network failure results in massive information loss particularly in networks carrying a huge volume of data. Survivability techniques ensure uninterrupted network functioning even in case of failure. Research in the domain of DWDM network survivability has contributed toward the development of protection and restoration techniques to provide resilience in optical networks. In this paper, basic concept of protection and restoration in optical networks has been introduced followed by review and analysis of existing routing and survivability techniques. It is observed that a trade-off among network performance parameters exists for any survivability scheme. A novel scheme, Dynamic Hybrid Technique based on Failure Location and Traffic Priority (DHbLP) adaptable to Quality of Service (QoS) demands, has been proposed. DHbLP is tested for one of the possible failure scenarios in the standard National Science Foundation NETwork (NSFNET) and it is observed that this technique improves network performance in terms of throughput and blocking probability.

Spectral amplitude coding optical code division multiple access (SACOCDMA) is a multiplexing technique, which provides faster speed, efficiency, security and unlimited bandwidth. It is widely preferred because of its ability to eliminate multiple access interference (MAI). Free space optics (FSO) provides a wireless link to transmit data securely at higher rates for last mile access. In this work, a 100 Gb/s hybrid FSO-SACOCDMA is designed using direct detection. The performance of FSO using SACOCDMA utilizing NZCC (New Zero Cross Correlation) code is evaluated under different weather conditions (clear weather, haze and fog) for ten users where each user carries 10 Gb/s. The results indicate that in clear weather FSO distance can be extended up to 13 km. Moreover, after using preamplifier in clear weather, FSO enhances the maximum distance to 35 km with acceptable signal to noise ratio and bit error rate. Using an amplifier in the link not only makes the quality of the signal better but it also increases the communication range.

In this paper authors have studied the error performance of an ISI compensating modulation technique called phase sampled RZ-GMSK. The numerical results are derived suitably for optical wireless back-haul networks under log-normal turbulence fading. It is seen that the proposed modulation technique outperforms other techniques at higher turbulence and for high speed data transmission.

In an incoherent optical code division multiple access (OCDMA) system using amplitude spectral coding (SAC), which exceeds 1.5 Gbps, it is difficult or impossible to make a transmission with a bit error rate better than 10 –9 . For this, it is necessary to associate an error correction code (ECC) to the SAC-OCDMA system. In this paper, we proposed an architecture of a two-dimensional SAC-OCDMA system (spectral (w) and spatial (s)) using multi-diagonal code (MD) as spreading code and low-density parity check code (LDPC) as ECC. According to the properties of the MD code and the proposed architecture, the phase induced intensity noise is eliminated, which has improved the performance of the system. The theoretically results shows that LDPC/2D-SAC-OCDMA allowing more than 40 users to be multiplexed compared to a non-coded 2D SAC-OCDMA system. This combination allowed us to increase the cardinality of the LDPC/SAC-OCDMA (W/S) system without using an optical hard limiter.

This work aims to investigate the integrated ultra-dense wavelength division multiplexing (UDWDM) and polarization division multiplexing (PDM) schemes incorporated in the free space optic (FSO) communication system. Erbium-doped fiber amplifiers (EDFAs) are used as post and pre-amplifiers in the proposed UDWDM–PDM–FSO system to boost the transmission power for increasing the distance. Thirty-two channels are transported over the FSO link to realize the total data transmission of 160 and 320 Gbps with 0.08 and 0.1 nm channel spacing, respectively. Results are also reported with non-return to zero modulation schemes. The performance of the proposed UDWDM–PDM–FSO transmission system is measured in terms of bit error rate (BER) and eye diagrams. The transmission distances are 100 and 87 km under clear weather and have acceptable BERs with 0.08 and 0.1 nm channel spacing, respectively. The weather conditions may worsen due to the increase in atmospheric turbulence. Hence, the transmission distances decrease to 3.93 and 2.6 km for heavy rain weather conditions. The UDWDM–PDM–FSO communication system exhibits an excellent performance due to the use of EDFAs with high achievable maximum distance and good and acceptable BER performance. The UDWDM–PDM–FSO communication system considerably enhances the transmission distance compared with the UDWDM–FSO communication system.

In this paper, the bit error rate (BER) performance of Duobinary (DB) is compared with carrier-suppressed return-to-zero (CSRZ) based polarization interleaving (PI) schemes for high-speed transmission system. The system is integrated with wavelength-division multiplexing (WDM) scheme and PI scheme for free space optical communications (FSO). The simulation results show that DB offers betters BER performance compared to CSRZ in high-speed WDM-FSO-PI system.

Free space optical (FSO) communication has fascinated a lot of attention for a variety of applications in telecommunication area. It is dream of every researcher and telecommunication society to make it a real alternative solution for the last mile problem, to replace fiber optics. FSO is much favored because of its low maintenance cost and deployment time. Pointing error is one of the main challenges in FSO communication system which affects its performance especially at high data links that leads to significant performance degradation. In this paper, the impact of pointing error for multi-beam Hybrid Wavelength Division Multiplexing (HWDM) FSO system is investigated. Then the effect of link distance and Bit Error Rate (BER) are estimated by accounting the pointing error and atmospheric attenuation. The effect of change of link distance is examined while changing the number of beams between the transmitter and receiver as well. In this attempt, the HWDM system is considered by combining eight Dense Wavelength Division Multiplexing (DWDM) channels and four Coarse Wavelength Division Multiplexing (CWDM) channels. In addition, the influences of BER and receiver sensitivity are analyzed for the proposed system by incorporating Erbium Doped Fiber Amplifier (EDFA) at the receiver end. The data rate 2.5 Gbps is considered for both CWDM and DWDM channels for investigation.

Optical wireless is the alternative approach to complete the deployment of optical cable networks in case of failure in implementation. In optical wave the attenuation due to atmospheric turbulence conditions causes a performance degradation of a free space optical (FSO) system. Thus, it will lead to the deterioration of the signal power in the optical cable. To overcome these challenges, multi-channel FSO transmitter and erbium doped fiber in optical link was adopted with high transmission power. In this paper, a hybrid FSO/fiber optic (FSO/FO) link is simulated and investigated under different weather conditions. The proposed hybrid link is evaluated in terms of BER and Q-factor. The proposed system shows a closely performance as compared with the conventional FSO for whole investigation range from 200 m to 2000 m. While the communication distance with the hybrid link is increased by 40 km as compared to conventional FSO. The results show good agreement with Kim model, especially at high input power of 160 mW.