The next-generation passive optical networks (NG-PONs) are expected to offer very high data rate to large number of users. Long-reach passive optical network (LR-PON) is considered to be one of the most promising solutions for NG-PONs. Since providing full protection (i.e., 100 % reliability) to each user in LR-PON is complex and cost-prohibitive, we propose in this study a novel heuristic scheme against single shared-risk link group (SRLG) failure to ensure certain degree of reliability (as determined by the network operator) to the users. In the proposed scheme (referred to as clustering-based multi-hop protection or CMHP scheme), we allocate residual capacity of backup optical network units (ONUs) among the ONUs that require protection by using bypass-based multi-hop traffic transmission strategy through backup fibers. CMHP scheme reduces the total length of backup fibers to be deployed between the ONUs (that require protection) and the respective backup ONUs through sharing of the backup fibers. In this study, we evaluate the total required length of backup fiber for a given network setting and different reliability requirements (viz. 75, 85 and 95 %). With the help of exhaustive simulations, we show that CMHP scheme significantly reduces the total length of backup fiber with reference to existing scheme to protect against single SRLG failure. We also explore a heuristic scheme referred to as clustering-based multi-hop protection with consideration of street layout (i.e., CMHP-SL) to implement CMHP scheme in practical scenario with due consideration of the street layout. CMHP-SL scheme provides protection to ONUs following a cost-efficient approach based on the existing fiber infrastructure in the distribution section.

In recent years, p-cycles have been widely investigated for survivability of WDM networks. They provide fast recovery speed such as ring and capacity efficiency as mesh survivability schemes. However, restoration paths are very long, which causes excessive latency and intolerable physical impairments. On the other hand, nowadays, a wide set of applications require an optical path with almost no delay. The existing approaches, namely loopbacks removal and inter-cycle switching, provide a significant reduction in the restored path, but even then a number of restored paths remain many times longer than the working path lengths. In this paper, we propose a network partitioning-based approach to control the length of each restored path as per delay sustainability of time critical applications. The basic idea of the work is to partition the network into domains and construct the p-cycles for each domain independently. The domain wise construction of p-cycles restricts their length, which consequently reduces the length of restored paths. Here, we introduce a new concept where the selected border nodes are overlapped among adjacent domains to cover inter-domain spans of the network as a domain span in order to ensure their survivability through domain p-cycles. Simulation results show that the proposed solution is good enough to control the restored path length with small augmentation in redundancy of spare capacity as compared to optimal design of p-cycles. More importantly, it enhances the dual failure restorability significantly.

We present an approximate analytical method to evaluate the performance measurements in optical orthogonal frequency-division multiplexing networks. Our approach divides the network into layers, and the equivalent path technique is used to model each path as an equivalent single-link system. The analysis of the performance measurements for an equivalent single-link system is based on a superposition concept using the Kaufman/Delbrouck recursion model. We assume static routing with a first-fit spectrum allocation. The simulation results indicating the accuracy of our method are presented.

We propose a family of one-dimensional subtracted square codes in the spectral amplitude coding optical code division multiple access system. The proposed codes perform the subtraction and multiplication operations to give one-to-one mappings function, which produces the code sequences of 1-D subtracted square codes. The proposed structure uses one optical line terminal to produce all of the transmitters. This proposed system overcomes the interference from other simultaneous users, known as multiuser interference, and the cross-correlations suppress the phase-induced intensity noise. In numerical simulations using the proposed 1-D subtracted square codes, we show that 83 simultaneous users can be supported at a bit error rate of \(10^{-9}\). This number of simultaneous users in the proposed system using the 1-D subtracted square codes is superior to that in the other systems using the 1-D M sequence codes, 1-D RSQC codes, and 1-D ESP codes. The proposed system using the 1-D subtracted square codes achieves a data transmission rate of 3.2 Gbps.

In order to improve the performance of the $$\hbox {Pr}^{3+}$$Pr3+-doped fiber laser, the optimum fiber length and reflectivity of mirrors, the maximum output power, the lasing threshold, and the slope efficiency are needed to be estimated. In this work, a $$\hbox {Pr}^{3+}$$Pr3+-doped fiber laser is considered with fiber Bragg gratings (FBG) as reflectors and an injected pump power in one side. To do so, the rate and power propagation equations of the $$\hbox {Pr}^{3+}$$Pr3+-doped fiber laser are solved numerically by finite difference method and the boundary conditions are obtained by shooting method in an iterative process. The effect of some structural parameters such as the laser background loss, the pump power, the $$\hbox {Pr}^{3+}$$Pr3+ dopant concentration, and the reflectivity coefficient of FBG2 on the performance of laser is studied, and the optimum values for fiber length and reflectivity of FBG2 are obtained.

Three- and four-port circulators based on resonators in 2D photonic crystals with square unit cell possessing a low symmetry are investigated. The three-ports are described by only one specific element named antiplane of symmetry. On the other hand, the four-port circulators formed by cascading these two three-ports can have one of the two symmetries. One of them is described by the antiplane of symmetry, and the other symmetry corresponds to a twofold rotational axis. The theoretical part of our paper concerns scattering matrix analysis of the devices with different symmetries and also the operation of the four-port circulator as a single-pole triple-throw switch. Finally, the calculated frequency responses of two circulators are presented.

In this paper, we investigate the impact of the transmitter finite extinction ratio and the receiver carrier recovery phase offset on the error performance of two optically preamplified hybrid M-ary pulse position modulation (PPM) systems with coherent detection. The first system, referred to as PB-mPPM, combines polarization division multiplexing (PDM) with binary phase-shift keying and M-ary PPM, and the other system, referred to as PQ-mPPM, combines PDM with quadrature phase-shift keying and M-ary PPM. We provide new expressions for the probability of bit error for PB-mPPM and PQ-mPPM under finite extinction ratios and phase offset. The extinction ratio study indicates that the coherent systems PB-mPPM and PQ-mPPM outperform the direct-detection ones. It also shows that at $$P_b=10^{-9}$$Pb=10-9 PB-mPPM has a slight advantage over PQ-mPPM. For example, for a symbol size $$M=16$$M=16 and extinction ratio $$r=30$$r=30 dB, PB-mPPM requires 0.6 dB less SNR per bit than PQ-mPPM to achieve $$P_b=10^{-9}$$Pb=10-9. This investigation demonstrates that PB-mPPM is less complex and less sensitive to the variations of the offset angle $$\theta $$? than PQ-mPPM. For instance, for $$M=16$$M=16, $$r=30$$r=30 dB, and $$\theta =10^{\circ }$$?=10? PB-mPPM requires 1.6 dB less than PQ-mPPM to achieve $$P_b=10^{-9}$$Pb=10-9. However, PB-mPPM enhanced robustness to phase offset comes at the expense of a reduced bandwidth efficiency when compared to PQ-mPPM. For example, for $$M=2$$M=2 its bandwidth efficiency is 60 % that of PQ-mPPM and $$\approx 86\,\%$$?86% for $$M=1024$$M=1024. For these reasons, PB-mPPM can be considered a reasonable design trade-off for M-ary PPM systems.

In this paper, the performance improvement of a free space optical communication system with multi-hop and beam optimization has been studied. Novel closed-form expressions for the end-to-end avera...

Quality factor and refractive sensitivity are significant parameters in designing optical devices such as filters, demultiplexers, switches and sensors. In this paper, we proposed a novel structure for photonic crystal ring resonator with octagon-shaped core. The transmission efficiency of the proposed ring resonator at \(\lambda =1551\,\hbox {nm}\) is about 99.6 % with bandwidth and quality factor values equal to 0.3 nm and 5170. The proposed structure is very sensitive upon the variation of refractive index of total structure and core part of the resonator, such that the refractive index sensitivity to the refractive index of total structure and the resonant ring core is \(\Delta \lambda /\Delta \lambda =3.1\,\hbox {nm}\,/\,0.01\) and \(\Delta \lambda /\Delta \hbox {n}=2.9\,\hbox {nm}\,/\,0.01\), respectively.

We present some optical signal processing methods for optical time-division multiplexing, based on electro-optic modulators. Dual-parallel Mach–Zehnder modulator and time-lens-based signal processing for optical frequency comb generation, optical Nyquist pulse generation and time-domain demultiplexing are realized. Multifunctional optoelectronic oscillators which are capable of performing simultaneous electrical clock recovery, optical clock recovery and demultiplexing are demonstrated with modulators embedded as the key components.