Volume 46, Issue 3

Four wave mixing (FWM) in wavelength division multiplexed (WDM) systems is prominent performance degrading nonlinearity and limits the total capacity of the system. FWM is explored in different fiber optical amplifiers such as erbium-doped fiber amplifier (EDFA), Raman fiber amplifier (RFA), and also in semiconductor optical amplifier (SOA). Reported studies in HOFA revealed that nonlinear effects in these amplifiers are low; however, in present study, in this research article WDM-HOFA system has been simulated and studied FWM in detail at different HOFA parameters such as input power, length, core radius, doping radius, numerical aperture (NA), Ho ion density, and effects of co- and counter-pumping. Gain and noise figure (NF) are also investigated at aforementioned parameters, and performance is evaluated in terms of optical signal to noise ratio (OSNR) at 2,030 nm wavelength window. It is observed that least FWM obtained at 3 m Ho fiber length, 2 µm core radius and doping radius, 15.6 × 10 23  m −3 Ho ion doping, 0.1 NA, −10 dB input power, 0.8 GHz channel spacing, and 4 WDM channels. However, better gain and NF comes at different values of these parameters, and as a result, there is trade-off between FWM and gain, NF.

Current developments in wireless communications accentuate the exigency of high gain, low noise figure (NF) and minimum gain fluctuations (GF) based optical amplifier in 1.9–2.15 μm eye safe wavelength band. Hybrid thulium (Tm) doped fiber amplifier (TDFA) and holmium (Ho) doped fiber amplifier (HDFA) are the perfect candidates to extend the bandwidth towards 2 μm long wavelengths. In this work, amplifier spontaneous emission (ASE) re-injected double clad TDFA-HDFA hybrid amplifier using Fiber bragg gratings (FBGs) is presented for the amplification of 64 wavelength division multiplexed (WDM) channels covering 63 nm wavelength window. Further, performance of proposed amplifier with and without ASE reinjection is evaluated in terms of Gain, NF, GF and optical signal to noise ratio (OSNR). Effects of single and double clad on the Gain are studied and optimization of Tm and Ho doped fiber length, pump powers, and input power has also been accomplished. The GF as low as ±1.44 dB, Gain >28 dB, NF < 5.08 dB, output power 4.2 W are achieved in ASE re-injected configuration using 785 nm pump at 55 dBm in TDFA and 1,900 nm pump at 20 dBm in HDFA. It is noticed that double clad and ASE reinjection in TDFA and HDFA offer better GF.

This paper has clarified the performance parameters estimation of high speed silicon/germanium/InGaAsP avalanche photodiodes wide bandwidth capability in ultrahigh speed optical communication system. The basic structure configuration of avalanche photodiode is clarified. The basic depletion region configuration schematic view is demonstrated. As well as the maximum electric field is indicated for impact ionization through avalanche photodiode in the presence of load. Various avalanche photo-detectors multiplication factor is clarified versus reverse bias voltage at room temperature. Different avalanche photo-detectors dark current is measured against avalanche photo-detectors volume at room temperature. Various avalanche photo-detectors effective doping concentration is demonstrated against ambient temperature variations. Si/Ge/InGaAsP avalanche photo-detectors excess noise factor is demonstrated versus the ionization ratio at room temperature ( T  = 300 K) and different ambient temperature ( T  = 350 K and T  = 400 K). Various avalanche photo-detectors excess noise factor is measured clearly versus the multiplication factor at room temperature. Si/Ge/InGaAsP avalanche photo-detectors excess noise factor is demonstrated versus reverse bias voltage at room temperature. Si/Ge/InGaAsP avalanche photo-detectors noise equivalent power is clarified versus multiplication factor at room temperature. Various avalanche photo-detectors noise equivalent power is studied versus temperature variations. Si/Ge/InGaAsP avalanche photo-detectors sensitivity is measured in relation to the temperature variations. Different avalanche photo-detectors sensitivity is demonstrated in relation to reverse bias voltage variations at room temperature.

This paper presents the performance analysis of different schemes for generating linearized photonic signal by varying phase shifter arrangements of a dual-drive dual parallel Mach–Zehnder modulator (DD-DPMZM). The RF signals at the electrodes of sub-modulators of DD-DPMZM are fed using different phase angles to generate optically modulated signals in the output. The proposed system consists of a DD-DPMZM and phase shifters. Spurious free dynamic range (SFDR) is evaluated for different configurations of sub modulators in upper and lower arm of DD-DPMZM. SFDR of 135.6 dB Hz 4/5 is obtained for quadrature and optical carrier suppression modulation in upper and lower submodulators by suppressing third order intermodulation distortion completely. It is found to be high performance configuration for dual parallel Mach–Zehnder modulator based linear microwave photonic link.

Studying high-performance photonic crystal fibers (PCF) is of significant scientific importance for terahertz (THz) waveguide systems. This study introduces a novel PCF design with a core composed of the smallest sub-wavelength units resembling a slotted structure, aiming to achieve high birefringence and low loss. The optical properties of the proposed PCF are analyzed through simulations, yielding impressive results. The PCF exhibits an ultra-high birefringence of 0.07848, a minimum limiting loss of 10 −17  dB/cm, and an effective material loss as low as 0.04251 cm −1 . Moreover, it demonstrates near-zero flat dispersion of −0.012 ± 0.074 ps/THz/cm over a broad frequency range of 1.2–2.2 THz. This fiber stands out by not only providing high birefringence but also by striking an optimal balance among birefringence, transmission loss, and dispersion for THz waveguides. The implications of this work are profound for the development of THz communication systems, THz polarization-maintaining transmission, and sensing applications. Furthermore, it established an important benchmark for the design of THz-PCFs that prioritize high birefringence, low loss, and near-zero flat dispersion, offering an essential reference for future research and development in this field.

This paper has clarified comparative analysis of high index core micro structured optical fibers (HIMSOF) and hollow core band gap fibers (HCBGF) performance efficiency in the fiber communication system. Total fiber dispersion is clarified versus distance between holes in µm at the employment of 850 nm, 1,300 nm and 1,550 nm wavelength transmission. Besides, the total fiber dispersion is also demonstrated against the hole diameter in µm at the employment of 850 nm, 1,300 nm and 1,550 nm wavelength transmission. The total fiber confinement loss is studied and illustrated against the distance between holes in µm at the employment of various wavelength band transmission. Total fiber losses are demonstrated in relation to the distance between holes in µm at the employment of 850 nm, 1,300 nm and 1,550 nm wavelength transmission.

This paper has illustrated the management of lateral misalignment loss and total insertion loss with beam waist control in high contrast single mode coupling fibers. The beam waist variations are clarified versus the fiber coupler wavelength and coupling length variations for the silica glass/fluoride glass fiber coupler with the optimum incident beam angle of 60°. Besides, the coupling loss is demonstrated against the fiber coupler wavelength and coupling length variations for the silica glass/fluoride glass fiber coupler with the optimum incident beam angle of 60°. The optimum beam waist and optimum coupling loss are deeply studied against the fiber coupler core radius variations for the silica/fluoride glass fiber coupler with the optimum incident beam angle of 60° and wavelength of 1,550 nm.

In this paper, a dispersion compensation technique for an ultra-long haul optical network utilizing a chirped fiber Bragg grating (CFBG) is presented. A high bit-rate signal of 40 Gbps is inputted into each channel. The CFBG, employed for dispersion compensation, is positioned after demultiplexing, enabling effortless network upgrades. The grating parameters of the implemented CFBG are mathematically analyzed and optimized to counteract net dispersion of over 3153 ps/nm across the channel. The design is verified using the OptiSystem software, resulting in a successful transmission up to 240 km with an average Q-factor of 8.09, utilizing an amplification gain of 49.5 dB. Additionally, the achieved optical signal-to-noise ratio (OSNR) level using the symmetrical amplification technique surpasses the acceptable value, with an average bit error rate of 10 −16 .

Fiber-wireless (FiWi) networks have begun to be fully integrated into contemporary optical access network systems as a result of utilizing the combined advantages of wired and wireless techniques. Passive optical networks (PON) are heavy energy consumers and one of the main contributors to greenhouse gas emissions (GHG) that are a result of climate change. These systems also present economic challenges. In this work, three different FiWi systems are presented such as (i) even/odd active transmitters with only free space optical (FSO) based optical network units (ONUs)/with dual channel option such as distribution fiber (DF)/FSO supported ONUs, (ii) a novel resource allocation on demand (RAoD) incorporated bidirectional FiWi system supporting DF/FSO based ONUs and four wave mixing (FWM) generated upstream wavelengths and (iii) transmitter diversity enabled 5G supported FiWi system supporting bidirectional communication. It is observed that the energy efficiency of 26.04 % is obtained in even/odd active transmitter and only FSO supported ONUs and under the harsh weather conditions, by adopting DF channel instead of FSO, 30 % energy efficiency further added. However, in novel RAoD technique, energy efficiencies for optical distribution networks (ODN 1 ), ODN 2 , ODN 3 , and ODN 4 are 48.52 %, 46.4 %, 36.96 %, and 44.31 %. Further, DF option in channel selection improve 30 % more energy saving. In performance enhanced transmitter diversity employed system, at 60 km reduction in bit error rate (BER) are 25 % for ODN 1 , 5.88 % for ODN 2 , 20 % for ODN 3 , and 12.5 % for ODN 3 .

The paper discusses an optical frequency comb source (OMCG)-enabled hybrid single mode fiber (SMF) and free space optical (FSO) communication system (fiber-wireless) delivering a total capacity of 96 Gbps by incorporating polarization division multiplexing (PDM) in passive optical network (PON) architecture. For the accomplishment of PDM, three diverse states of polarization (SOPs) are explored such as 00, 450, and 900. Performance investigation of proposed system is conducted for assessing Q factor and BER by exploring the different modulation formats in proposed system such as modified duo-binary return to zero (MDRZ), return to zero (RZ), compressed spectrum RZ (CSRZ), and non-RZ (NRZ). Results revealed that presented design can cover 30 km SMF + 3.4 km FSO range by incorporating MDRZ due to its spectral efficient and dispersion tolerant properties.

Fi-Wi networks, emblematic of the convergence between optical fibers and wireless access, stand resolutely at the vanguard of the transformative redefinition of communication paradigms. As advanced communication networks persistently redefine the contours of connectivity, characterized by their unparalleled speed, minimal latency, and augmented capacity, the exigency for innovative approaches undergoes heightened intensification. The crux of this study pivots upon the methodical application of multiplexing techniques, notably wavelength division multiplexing (WDM), optical code division multiplexing (OCDMA), and optical time division multiplexing (OTDM), each deployed with precision to elevate the nuanced performance of the Fi-Wi network. The multifaceted optimization of these techniques not only imparts an impetus to data transfer rates, mitigates latency, and augments spectral efficiency but concurrently instigates the realm of wireless connectivity. The research undertakes a technical exploration of the deployed multiplexing strategies, delineating their idiosyncratic advantages. A discerning comparative analysis vis-a-vis the hybrid (Fi-Wi)-single model, precisely serving as the baseline, unequivocally delineates the superior performance of the proposed methods across metrics of Q-factor, eye height, and logarithmic bit error rate-Q factor.

The explosive growth of worldwide mobile data traffic seeks innovations in communication technology to cater to the mounting need for rapid connectivity, high-capacity connections. The mainstreaming of 5G technologies for communication is a dramatic step towards meeting the aforementioned goals, with the ability for reshaping IoT (Internet of things), D2D (device-to-Device) communications, and the smart grids. This work conveys an in-depth study of the fundamental innovations that underlie 5G, including full-duplex distribution, huge multiple-input-multiple-output, ultra-dense connections, the phenomenon of beamforming and millimeter-wave approaches. A special emphasis is focused on the integration of photonic technologies, or microwave photonics, which serves as a critical multidisciplinary study topic. Optical fibers, with their tremendous bandwidth and capacity, have been determined as the best medium for backhaul and fronthaul amenities, outpacing conventional copper cables to accommodate tiny cells and next-generation networks. The synergy between optical and wireless access technologies is analyzed with the emphasis on the central role of wavelength-division multiplexing (WDM) for improving network efficiency and speed. The investigation additionally explores the possibility of intelligent signal processing methods combined with WDM to optimize photonic network communications. The mingling of these technologies anticipates producing unrivaled levels of performance, rupturing the path for an additional intelligent, interconnected era.

The Ro-FSO system was designed using Opti System software (version 20), and its efficiency is evaluated in this study using two distinct digital modulators (PSK and DPSK). The proposed system consists of four transmission channels, each with its own wavelength (193.1, 193.2, 193.3, and 193.4 THz). The system was utilized to transmit data at three different rates (10, 20, and 40 Gbit/s) under four different levels of dust attenuation. Because of the large quantity of data retrieved, only results from two specific wavelengths (193.1 and 193.4 THz) were disclosed, as they exhibited the highest Q -factor and lowest bit error rate (BER). The study observed that the (DPSK) modulator surpassed the (PSK) modulator in multiple attenuation scenarios and had superior performance when transmitting data at speeds of 10 and 40 Gb/s. The wavelength of 193.4 THz performed optimally with both modulators in terms of wavelengths.

This study proposes a hybrid approach combining Energy Detection (ED) and Matched Filter (MF) spectrum sensing techniques to enhance power spectrum density (PSD) in optical Nonorthogonal Multiple Access (NOMA) systems. Optical NOMA has emerged as a key technology for boosting spectral efficiency in optical communication networks. However, optimizing PSD remains a critical challenge due to various factors including signal detection and noise interference. The hybrid ED–MF spectrum sensing method aims to address these challenges by leveraging the strengths of both techniques. Energy Detection (ED) offers simplicity and robustness in detecting primary users, making it suitable for initial spectrum sensing in cognitive radio networks. Matched Filter (MF) spectrum sensing, on the other hand, provides superior signal detection and noise rejection capabilities, particularly in low signal-to-noise ratio (SNR) environments. By integrating these two techniques, we aim to achieve improved sensitivity and accuracy in spectrum sensing, thus enhancing spectral efficiency and system performance in optical NOMA networks. The effectiveness of the proposed hybrid approach is evaluated through theoretical analysis and simulation experiments. Results demonstrate significant enhancements in spectral efficiency and system reliability compared to conventional spectrum sensing methods, highlighting the potential of the hybrid ED–MF approach for enhancing PSD in optical NOMA systems. This research contributes to advancing the design and optimization of optical communication systems for future high-capacity and high-speed data transmission applications. The PSD values −920 are obtained and it confirmed that the proposed algorithm outperforms the standard algorithms.

In this paper, we have reported radio over fiber system with 30-tuple millimeter-wave generation using dual parallel Mach–Zehnder modulator and semiconductor optical amplifier. The optimum choice of Mach–Zehnder modulator parameters has resulted into generation of signal lightwave and pump signal with frequency separation of 10 f RF . Four wave mixing effect in semiconductor optical amplifier results into 30-tuple millimeter-wave signal. The proposed scheme is applicable to radio over fiber system with multiple base stations. The multiple number of frequencies such as 50 GHZ, 100 GHz, and 150 GHz have been generated using 5 GHz radio frequency only. NRZ data at 2.5 Gbps was modulated and successfully transmitted via optical fiber. The impact of injection current on the sideband ratio and BER is investigated. The proposed scheme confirms quality reception of demodulated signal at a transmission distance of 20 km.

From the concepts of the dispersion-folded digital backward propagation (DBP) and optical phase conjugation (OPC), a hybrid optical-electronic nonlinearity-compensation scheme is proposed to enhance the system performance of the dispersion-managed transmission. The computational complexity of the proposed scheme, compared with that of the conventional DBP method, is reduced significantly while the performance penalty is negligible. The compensation efficiency of the proposed scheme has been validated in a 5 (and 9)-channel PM-16QAM system at 256 Gbit/s.

This paper demonstrated the high speed operation efficiency of doped light sources with the silica-doped fiber channel for extended optical fiber system reach. The output power and required bias voltage are clarified of AlIn ( x ) Ga ( y ) As light source versus injection current variations and indium, gallium dopants concentration variations at room temperature and 1.55 μm wavelength. The output power and required bias voltage are studied of PAl ( z ) Ge ( h ) Sb light source versus injection current variations and aluminum, germanium dopants concentration variations at room temperature and 1.55 μm wavelength. Required resonance frequency is measured for AlIn ( x ) Ga ( y ) As light source versus injection current variations and indium, gallium dopants concentration variations at room temperature and 1.55 μm wavelength. Required resonance frequency is demonstrated for PAl ( z ) Ge ( h ) Sb light source versus injection current variations and aluminum, germanium dopants concentration variations at room temperature and 1.55 μm wavelength.

This work has clarified the relative intensity noise management and thermal/shot noise control for high speed ultra high bandwidth fiber reach transmission performance. Total link losses variations are clarified against ambient temperature and relative refractive index difference variations at 1,550 nm wavelength, 20 km fiber link length, and 45 % fluoride dopant ratio inside the fiber material cable. Besides the total link losses variations are demonstrated versus fiber link length and relative refractive index difference variations at 1,550 nm wavelength, room temperature, and 45 % fluoride dopant ratio inside the fiber material cable. Required optical signal per noise ratio (OSNR), electronic signal to noise ratio (SNR), and optimum gain variations are measured and analyzed versus the fiber link length and relative refractive index difference variations at 1,550 nm wavelength, room temperature, and 45 % fluoride dopant ratio inside the fiber material cable.

Optical communication systems provide high data rates to fulfil users’ demands. In addition, the modulation format is essential to the system’s transmission quality and spectral efficiency. Furthermore, the effects of chromatic dispersion, which impair the performance and quality of transmitted signals, are mitigated using dispersion compensation techniques. In optical communication systems, dispersion compensation techniques are essential for preserving signal quality, increasing transmission distances, improving system performance, and offering network designers flexibility. These methods seek to improve signal quality and enable transmission at longer distances by reducing or eliminating the distortion brought on by dispersion. This paper uses a symmetrical compensation technique to analyze the performance of the CSRZ modulation format-based optical communication system. The research is conducted within a communication range of 150–350 km. The system is evaluated in terms of input power, filter order, and filter depth. The results indicate that the proposed system performed better at an input power of 4 dBm using a third-order filter and 60 dB filter depth.

One well-known demerit of orthogonal frequency division multiplexing (OFDM) is its high peak-to-average power ratio (PAPR) which limits the efficiency of high-power amplifier (HPA) and also destroys its bit error rate (BER) performance. Hence, a method based on grouping of discrete sine transform (DST) precoder and iterative clipping and filtering (ICF) is proposed to reduce PAPR in this article. The DST precoder reduces PAPR to certain level by changing phase of the signal. Moreover, the ICF technique is also implemented in DST based-OFDM signal for additional minimization of PAPR. Therefore, the proposed method (DST-ICF) preserves BER performance also from other existing methods. At complementary cumulative distribution function (CCDF) = 10 −3 , the simulation results indicate the proposed technique that minimizes PAPR with iteration values ( I  = 1, I  = 2, and I  = 3) to 6.37 dB, 5.29 dB, and 4.81 dB respectively. Moreover, at same BER, the E b / N 0 of proposed technique with iteration value ( I  = 3) is achieved by 9.75 dB for quadrature phase shift keying (QPSK).

Diversity and combining is one of the robust techniques to mitigate multi-path fading in RF links and turbulence-induced scintillation in FSO links. This article evaluates the effect of different diversity and combining techniques on outage and BER performance of decode and forward RF-FSO link. We have utilized diversity and combining techniques over source to relay RF link and/or relay to destination FSO link. The selection combining, transmit antenna selection, maximal ratio combining, and maximum ratio transmission schemes are considered. The Monte-Carlo simulation results of outage probability and bit error rate are compared by considering different parameters affecting link quality like the strength of atmospheric turbulence, pointing error, FSO link detection scheme, RF link fading strength, diversity order, etc. It is found that configurations like SIMO-SISO, MISO-SISO, SISO-SIMO, and SISO-MISO, where diversity is applied in either source to relay link or relay to destination link, are improving the overall link performance provided that diversity is applied at the link experiencing stronger fading compared to another link. The link configurations SIMO-MISO or MISO-SIMO also improve the link performance and it can achieve BER of 10 −5 at less than 15 dB SNR in favourable link conditions.

In high-mobility operating scenarios orthogonal frequency division multiplexing (OFDM) system lacks its optimality, intercarrier interference (ICI) occurs and the Doppler shifts deteriorate the orthogonality of the subcarriers. However, this problem can be overcome by utilizing complicated equalizers at the receiver. Discrete cosine transform (DCT) and discrete Hartley transform (DHT) have been used instead of discrete Fourier transform (DFT) in the standard OFDM system. The performance results achieved enhancement over dispersive selective channels that cannot be accomplished with a standard OFDM system, even with utilizing complex equalizers. In this paper, the performance of the DCT-based OFDM system and DHT-based OFDM system is compared and analyzed with respect to DFT-based OFDM system performance over doubly dispersive fading channel at various Doppler shifts, the block diagrams of the proposed systems are provided to simplify the theoretical analysis by making it easier to follow. Simulation results emphasized that the performance of DCT and DHT-based OFDM systems under doubly dispersive fading conditions scenario outperforms DFT-based OFDM system of order 3 dB energy per bit to noise power spectral density ratio (E b /N 0 ).

In this paper, the performance analysis of the WDM (wavelength division multiplexing) system on the optical fiber transmission link is proposed. High data transmission is possible by implementing a WDM optical communication system using different modulation formats. Firstly, the WDM optical communication system is designed on an Optiwave simulation tool and distortion in the optical fiber by “eye pattern analysis” is analyzed. Secondly, the optical SNR of the proposed WDM optical communication system is studied. Further, the bit-error rate (BER) plot is studied and optimization techniques are applied to enhance the proposed system for long-haul communication. Furthermore, the BER plots are analyzed by varying the length of the fiber and applying different coding techniques like NRZ (non-return zero), RZ (return to zero), QAM (quadrature amplitude modulation) etc. using the Optiwave simulation tool. The results obtained in the Optiwave simulation tool are validated by theoretical implementation in the MATLAB tool.

This study presents the analysis of a designed Ro-FSO system by Opti System v.20. The system analysis depends on transferring three values of data (10, 20, and 40 Gb/s) using two digital modulators (PSK and DPSK). Two scintillation systems (L-N and G-G) are applied for transmitting a signal through free space; this signal is subject to four values of atmospheric turbulence. The research showed that the (L-N) scintillation model can send data at rates of 10, 20, or 40 Gb/s, irrespective of what kind of digital modulator is used. For data rates of 10 and 20 Gb/s, the suggested system could transmit it over a maximum link distance of up to 2 km under different turbulence intensities. For 40 Gb/s of data rate, the maximum link distances decline to 1.75 km at the same amount of turbulence conditions. When the scintillation system (G-G) is applied as a turbulence link, the system is able to transmit the signal well for a maximum link distance not exceeding 0.75 km.

Due to its great spectral efficiency and resistance to multi-path fading, OFDM, or orthogonal frequency division multiplexing, is commonly utilized in optical communication systems. However, because of nonlinear distortions in optical components, OFDM signals are prone to a high peak-to-average power ratio (PAPR), which can severely impair bit error rate (BER) performance. This paper introduces a companding scheme to address high PAPR in optical OFDM systems and improve BER performance. The proposed scheme uses a nonlinear transformation to compress signal peaks and expand valleys, effectively reducing PAPR. Specifically, we investigate the µ-law companding technique, known for its simplicity and effectiveness in handling the active range of OFDM signals in optical communication. The companded signals are transmitted through an optical link and demodulated at the receiver. Simulation results show that the µ-law companding technique substantially reduces PAPR, leading to a significant improvement in BER performance. The companding process maintains signal integrity and spectral efficiency with minimal computational complexity and implementation cost. By mitigating nonlinearities introduced by optical components, this companding scheme enhances the overall reliability and efficiency of the optical OFDM system. An SNR gain of 2 dB–3 dB was achieved at a BER of 10 −3 .

This paper clarified the high thermal stability and high-performance efficiency capability of silicon light sources–based rate equation models in the optical fiber transmission systems. The laser diode and light emitting diode output power variations are measured with input injection current under various ambient temperature effects. The light source differential quantum efficiency is demonstrated for both LED and laser diode with different injection input current and various temperature variations. The LED/laser diode light source external efficiency is clarified with different injection input current and various temperature variations. The LED/laser diode light source total efficiency is measured with different injection input current and various temperature variations. As well as the laser diode and light emitting diode, threshold current variations are demonstrated clearly with input injection current under room temperature and various spectral thermal effects. The laser diode and light emitting diode power dissipation variations are measured with input injection current under room temperature and various spectral thermal effects.