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Photonic crystal fibers (PCFs) which can transmit orbital angular momentum (OAM) modes are attractive to optical communication due to the large capacity and flexible structure. Herein, a method is proposed to optimize a simple fiber structure by changing the thickness of the annular area. The changes in the effective index, effective index difference, dispersion, effective mode area, nonlinear coefficient, numerical aperture, mode purity, and walk-off length in the thickness range of 2.0 μm to 2.5 μm are determined, compared, and analyzed systematically. The distance between the square air holes and central air hole is the better parameter to optimize the dispersion, effective mode area, and nonlinear coefficient, whereas the radius of the central air hole is more suitable for optimizing the NA, OAM purity and walk-off length. The optimization method and results have great value pertaining to the design and improvement of PCFs for transmission of OAM modes.

The simulation and investigation of a 32×10 Gb/s WDM all–optical bidirectional hybrid communication system for outdoor applications is presented in this article via multidisciplinary softwares. In order to track the system condition, a strain sensor based on fiber Bragg grating (FBG) is integrated in–line with the fiber optic link (FO–link). Then, a free space optical link (FSO–link) with 4–channel is simulated to act backup or rescue to the FO–link in the event of disaster or bombing. The FO–link is working well until the strain reach to 180 µε, after that the FO–link has degraded. Therefore, an optical switch is incorporated in between these systems (FO–link & FSO–link) to turn–on the FSO–link which act as a backup system to FO–link and maintains the continuity of the data transmission. According to the hybrid link results, there is an efficient enhancement in the Q–factor as compared with the FO–link even when there is heavy rain.

During the course of a typical deep space mission like Mars Earth mission, there exist a wide range of operating points due to the different changes in geometry that consequently cause different Link Budgets in terms of received signal and noise power. These changes include: Distance Range, Sun-Earth-Planet Angle, Zenith Angle and Atmospheric conditions. The different operating points with different losses (background noise, pointing losses and atmospheric losses) lead to different capacities and data rates over the course of a typical Deep Space mission. Consequently, different engineering parameters are adjusted and optimized to combat some of these varying losses in order to get an acceptable data rate and bit error probabilities. This provides a good basis to undertake analysis and simulations of the various operating conditions that occur with the varying spatial orbital time periods on the resulting received signal power level, noise power level, capacity, data rates and bit error probabilities. This paper details results of simulations done in a typical Deep Space Optical Communication link operation.

This paper offers to analyze the performance and mitigation strategy for multi-user interference (MUI) based line-of-sight (LOS) infrared (IR) communication system in free space optics (FSO). The model is predicated upon the modulation scheme of code shift keying (CSK) in comparison with the conventional on off keying technique (OOK) for the outdoor environment. To interpret the analytical study, in addition to CSK, 20 μm is guaranteed as an operating wavelength for far infrared (FIR) communication purpose. With a power allocation of 1–10 mW, a maximum data rate of greater than $$10^6$$ bps is achieved and the results are obtained in 1000 m distance. The results indicate that the device output is very responsive to the channel model preference. During the case of atmospheric instability, the comparatively unused FIR spectrum has been found to be ideal for external optical communications. The outcomes are illustrated with the consequences on the system due to intrusions and disruption with the FSO waveforms with increasing numbers of users and the performances of signal to noise ratio as well as bit error rate are improved in the turbulence FSO environment.

We present the graphene-based TM/TE independent ring modulator with large resonance tunability and modulation bandwidth. By adjusting the external voltage from different directions, the graphene-based ring modulator can operate either on TM or TE mode. Through the performance analysis and optimization, the proposed optical ring modulator exhibits a large resonance tunability over 5.8 nm/V and a broadband operation wavelength spectrum from 1.3 $${\mu }$$ m to 2 $$\mu $$ m, the large extinction ratio of 20.8 dB and 24 dB can be achieved for TM and TE modulator, respectively. Besides, this device exhibits a large 3 dB electro-optic bandwidth which is rarely seen in conventional ring modulators, and all these features would make the proposed graphene ring modulator find great potential use in future optical communications.

Orthogonal frequency division multiplexing (OFDM) of the optical communication system is a known approach for light fidelity and the screen-to-a-camera (S2C) communication system is an innovative implementation for optical camera communication (OCC). In This paper, two dimensional (2D) asymmetrically clipping optical (ACO) OFDM for the S2C model can be obtained which develops a single screen display, consisting of several cells, for a data rate of up to 100 kb/s. This paper contains an innovative system design focused on validation of implementation and theoretical study. The source distribution of the ACO OFDM system has been implemented using LAB VIEW software. The performance of the suggested model was verified through numerical assessment techniques, as it was checked that within the transmission distance of 4.5 m and the field of view of 30 $$^\circ$$ overall bit error rate (BER) of 10−6 and signal to noise ratio (SNR) 18 dB is achieved. Under the existing IEEE 802.15.7 m standard, the overall results of the S2C OFDM system are being evaluated by comparing them to the 2D OFDM OCC system to illustrate the efficiency of the proposed scheme.

In this research paper, high-speed Free-space optical connectivity is explored for the longdistance of data transfer in various weather conditions. The system evaluates information transmission with the data rate of 2.5 Gbps up to a distance of 5 km. A high-speed SS-based free-space optical communication system is incorporated. It has been investigated by changing the WDM spectrum of Highly Non Linear Fiber by the Kerr effect of nonlinearity. The de-multiplexer provides 4 data-carrying channels with the capacity of 2.5 Gbps that are modulated using various modulation techniques. Furthermore, the efficiency of the system is evaluated by varying various parameters of the system including beam divergence angle, receiver/ transmitter antenna diameter, etc. The use of spectrum slicing offers an opportunity for a high data rate, broader bandwidth communication.

Due to atmospheric turbulence, the wavefront phase and the light intensity distribution would change, and the information carried by beams may be damaged or even lost. Hence, using the non-Kolmogorov spectrum and the generalized Huygens-Fresnel principle, the propagation characteristics of circular-linear edge dislocation beams are studied in this paper. The results show that the light intensity distribution of the beams eventually evolves into the light intensity distribution of Gaussian-like beams. Circular edge dislocation and linear edge dislocation evolve into two pairs of optical vortices. When the beams propagate far enough, two pairs of optical vortices will annihilate. With the decrease of the inner scale of turbulence and the general exponent, and the increase of the general structure constant, the evolution of the beams will be accelerated. The effect of the outer scale of turbulence on the evolution can be negligible. The results obtained provide theoretical guidance for optical communications and spatial modulation of optical fields.

The last decade has witnessed significant growth of optical communication systems due to low attenuation offered for longer distances with high capacities. Optical wireless communication such as Free space Optical (FSO) systems provide license free secure transmission with lower deployment cost to make it attractive solution for providing communication services in remote areas. However atmospheric turbulences can become major challenges for deploying the FSO systems as it affects its performance. In this work, we propose a 320 Gbps, 32 channel’s hybrid fiber + FSO system using cost efficient On OFF Key modulation by incorporating hybrid dense wavelength division multiplexing scheme. Each channel carries 10 Gbps data segregated by 100 GHz channel spacing. Also, the effect of variant climatic turbulence analyzed for non-return to zero and Return to zero system considering clear sky, light fog, moderate fog and dense fog conditions.

In this paper, we present a proposal for compact photonic wavelength filtering and 3-dB wavelength splitting device based on nanoplasmonic metal-insulator-metal structure. The working performance of the device has been accurately simulated using the temporal coupled-mode theory. We use a numerical simulation method of eigenmode expansion propagation for the overall design process. We show that the transmission efficiency of the drop filter can be significantly enhanced by applying specifically optimization of nanostub waveguide. The proposed structure has potential applications in highly efficient ultra-compact integration circuits as well as in optical communication systems at nanoscale.

In this paper, a polarization filter based on hybrid silver-graphene coated pentagonal Photonic Crystal Fiber (PCF) is proposed. The finite element method is used to analyse the confinement loss characteristics of the proposed PCF. The proposed PCF based filter selects the desired X-polarization mode with a low confinement loss of 0.12 dB/cm and 0.59 dB/cm and rejects the unwanted Y-polarization mode with a very high confinement loss of 361.26 dB/cm and 1508.37 dB/cm at the mostly used wavelengths of 1.31 μm and 1.55 μm for optical communication. The proposed PCF with a length of 300 μm achieves the cross-talk of 216.68 dB and 904.67 dB at 1.31 μm and 1.55 μm. It also accomplishes a broad spectral width of 816 nm with the cross-talk value greater than 20 dB. The influence of the structural parameters of the proposed PCF is studied. The fabrication feasibility of the proposed PCF is also investigated. The proposed PCF based polarization filter will be an inevitable candidate for the integrated optical system.

All-optical logic gates have extraordinary application in ultra-high-speed Boolean operation and logical computation. All-optical logic gates like XOR, OR, and NOT using metal–insulator–metal waveguides are proposed here and designed under the footprint of 13 $${\upmu}{\text{m}}^{2}$$ which is smaller than the previously reported work. The device's analysis is performed using the finite-difference time-domain method (FDTD), and results have been verified using MATLAB simulation. The performance parameter, extinction ratio for the proposed device, is computed and obtained 27.80 dB. The suggested logic gates can also be used as major components in optical communication, which leads to the development of a new way for the design of plasmonic integrated circuits.

The millimetre (mm) waves from 30 to 300 GHz have evolved as the possible carrier for high speed fifth generation services. But however, limited bandwidth of mm waves is one of the major challenges for broadband service operator. Radio over free space (Ro-FSO) may be possible solution to transport high speed mm waves by integrating the wireless system with optical communication systems. In this work, a high speed Ro-FSO link which can support the transmission of four independent high speed channels, each one carrying 20 Gbps data up-converted to 40 GHz mm wave is designed. The spectral efficiency of proposed Ro-FSO link is improved by incorporating mode division multiplexing of linear polarized (LP) mode 00 and 01 and wavelength division multiplexing scheme with the channel spacing of 1 nm. The reported result shows the successful transmission of all the channels with the required signal to noise and received power.

ROADM technology has reformed optical networking and an intimate part of recent optical communication offering enormous bandwidth for data conveyance at least expense. In this paper, reconfigurability in the dense wavelength division multiplexing system is analyzed with the placement of digital switches by varying the bit rate from 10 to 40 Gbps by adding and dropping certain wavelengths. The performance of the dense wavelength division multiplexing system is characterized in terms of the quality factor, bit error rate and optical signal to noise ratio. It is observed that the signal can be communicated over a distance of 780 km with 16 channels, 420 km with 32 channels and 300 km with 64 channels having a low input power of −10 dBm with an acceptable bit error rate and quality factor. Furthermore, the performance of the system is calculated by varying the number of fiber spans with input power of −10 dBm with a bit rate of 40 Gbps. This structural design permits for remote traffic provisioning at the wavelength level in network node, operation cost reduction, better consumption of communication bandwidth, simplification of network design and implementation.

In this paper, a simulation was proposed to study underwater visible light communication (UVLC) system using a multiple input–single output (MISO) technique with different modulation schemes under coastal water. MISO technique has enhanced the distance link with high speed data rate compared with the traditional technique of single input–single output (SISO), MISO technique was also employed to examine the performance of BER and data rate under different Jerlov types of coastal water. Various impairments such as distance link, pathloss, channel loss and the attenuation of coastal water were introduced into the transmission of the optical signal to assess the reliability of the MISO technique. The simulation analysis shows the proposed technique can outperform the SISO technique in terms of BER and Q. factor. Moreover, the Q. factor of up to 16 dB and 10−10 BER under J9C of coastal water by using (4Tx/1Rx) technique. The radiation angle of LED and the attenuation coefficient of coastal water were restricted for achieving longer distances link. The system accomplished a distance link about 2.9 and 13.5 m for coastal water types J9C and JIC respectively. The 32-PPM is a suitable modulation for obtaining a best distance link for LoS and NLoS scenarios.

Miniaturized and broadband polarization-dependent filters with high crosstalk values are extremely desirable for practical applications in the fields of optical communications and sensing. A miniaturized photonic crystal fiber (PCF) with highly broadband polarization filtering properties is proposed in this paper. Two relatively large air holes coated with a gold film on opposite sides of the liquid crystal-filled offset core are introduced in this PCF structure to produce highly broadband polarization-dependent filtering transmissions. The impacts of the filtering properties with variable structural parameters have been studied based on the finite element method. By altering the gold film thickness (t) to be 18.7 nm and 13.8 nm, the proposed broadband polarization filter offers high resonance peaks of 2041.79 dB/cm and 2342.88 dB/cm for y-polarized mode at the wavelengths of 1.31 μm and 1.55 μm, while the corresponding loss for x-polarized one is 0.10 dB/cm and 0.83 dB/cm, respectively. Moreover, the crosstalk of the 100-μm-long PCF polarization filter with t = 18.7 nm and t = 13.8 nm is up to 177.34 dB and 203.43 dB at 1.31 μm and 1.55 μm, respectively. As the fiber length is 100 μm, the bandwidth with the crosstalk less than − 20 dB can be up to 1200 nm, from 1.2 to 2.4 μm. In addition, the proposed broadband and miniaturized PCF filter is not sensitive to the temperature variation and exhibits stable filtering characteristics with the ± 1% fabrication tolerances.

In this paper, a cascaded fiber Bragg grating (FBG) system is proposed to reduce the dispersion in the optical signal in single mode optical fibers. This consequently enhances the system performance, which is evaluated by the bit error rate (BER) and quality factor (Q-factor). The proposed model consists of four uniform cascaded FBGs connected at the transmitter to get narrow linewidth, Δλ, of the optical signal, which is a major cause of the delay. The Optisystem7 is used to simulate the proposed model in a WDM system with and without the model for distance 200 km. The system parameters are investigated showing an enhanced performance with 12%, including eye diagram, Q-factor and BER. A 10−6–10−10 BER is achieved with a quality factor in the range 7–14, including the effects of fiber length, input power and FBG length.

In this paper, a novel design, photonic crystal fiber (PCF) has been reported to support more orbital angular momentum (OAM) modes for the first time. The cladding region formed by employing the three-layer chain shaped air cavities. The OAM properties and parameters are calculated by optimizing the design of the PCF. The simulation results can support 26 OAM modes with a wider bandwidth (750 nm). The confinement loss of the most OAM modes is below average 10−7 dB/m and the nonlinear coefficient is less than 4 W−1/km. Some OAM modes with comparatively flat dispersion variation (such as 3.8684 ps/km-nm) for HE2,1 are noticed from the design. Moreover, fundamental optical characteristics have been rigorously computed by utilizing the finite element method. Now, it can be anticipated that, these excellent optical characteristics confirm the introduced design as a prominent candidate for the OAM transmission and other relevant areas of optical communications.

We propose a feasible temporal filtering (or spectrum weighting) system to implement optical differentiation with arbitrarily-tunable order. Differentiation order is tuned by programming the temporal weighting mask (TWM) as power function of different exponents, not limited by the structure of the system. Assembly of the system is feasible, since the active parts are implemented by electro-optic elements and some key elements are reused between sub-systems involved in the scheme. Tuning of the system is simple, since electronically pre-stored TWMs are easy to switch among each other. The order-tunable functionality is verified by numerically testing the differentiation cases of normalized input pulse duration ranging from 0.1 to 0.4, and of differentiation order tuned from 1 to 10. Good accuracy is achieved, and measured by root mean square error lower than 0.1. Feasibilities of the system are also verified in terms of accuracy maintaining and distortion avoiding. Compared with existing methods, apart from the arbitrary order-tunable capacity and good accuracy, our proposed optical differentiator also possesses properties of good compactness and constant complexity. The proposed differentiator has unique applications on multi-peak waveform generation for optical communications and photonics-aided Radars with enhanced agility and feasibility.

In this work, a configuration of nano plasmonic switch is proposed and investigated. The structure is comprised of the combination of split square ring and straight waveguides. Simulations are done based on Finite-Difference-Time Domain method. The structure is based on metal-insulator-metal configuration. Split square ring and straight waveguides are consisted of air, which are situated in a silver background. The proposed switch can confine light to sub-wavelength dimensions (on the order of nano meter); therefore it can be used in highly integrated optical circuits. The split square ring structure can operate both directly or reversely based on the split position. The transmitted powers in different cases of split square switch are acceptable and higher than 0.6. Therefore, the proposed switch is an appropriate candidate for highly integrated optical communication systems.

Waveguide-coupled Ge/Si separate absorption, charge and multiplication avalanche photodiodes (SACM APDs) have shown significant potential as high-sensitivity, low-noise, and high-speed photo-detection for optical communications. Here we present a nanoscale single-mode waveguide-integrated vertical Ge absorption, lateral Si charge and single multiplication configuration for a waveguide Ge/Si SACM APD. This device can achieve 90% absorption at 1550 nm wavelengths with a 10 μm-long Ge layer. The device exhibits a seven times reduction in device length compared to conventional waveguide structures and a 29% increase compared to multi-mode interference coupling. Meanwhile, a 3-dB bandwidth can achieve 47 GHz, which is five times higher than the conventional vertical Ge absorption, lateral Si charge and multiplication devices.

In this paper, a simulation analysis of 40 Gb/s wavelength division multiplexing system of 32 channels is implemented through RZ modulation format by using a different hybrid fiber amplifier (HFA) configurations, namely, serial HFA, parallel HFA, and combined serial–parallel hybrid fiber amplifier (CSP-HFA). The performance of the proposed amplifiers is compared in terms of average gain level, average noise figure, flat gain bandwidth. In addition, quality factor, bit error rate, and eye diagram for the demonstrated 32 channel × 40 Gb/s wavelength division multiplexing optical communication system utilizing different configurations of the hybrid fiber amplifier is compared. The CSP-HFA shows better performance than serial and parallel hybrid amplifiers in terms of wider flat gain bandwidth, higher quality factor, lower bit error rate, and wider and clearer eye opening. Furthermore, CSP-HFA exhibits a flat gain bandwidth of 65 nm with an acceptable average gain of 16 dB and average noise figure of 7 dB.

Polarization splitters are beneficial in the field of passive optical devices which are principally used in the coherent optical communication systems. An ideal polarization splitter must possess an efficient coupling with significant optical bandwidth. Hence, we proposed a novel metal-filled polarization splitter based on twin-core sunflower-type photonic quasicrystal fiber (PQF). The characteristics of the proposed splitter such as coupling length, extinction ratio, and available optical bandwidth were investigated by using the commercially available software, COMSOL Multiphysics. These aforementioned characteristics were determined by optimizing the geometrical parameters of proposed PQF—first by using gold-filled PQF (AuPQF). With optimized geometrical parameters, the splitter achieved an ultra-short coupling length of 132 µm and an ultra-broad bandwidth of 301 nm (wavelength range 1.36–1.68 µm) with an extinction ratio below than − 20 dB which comprised E + S+C + L+U band. Secondly, a comparative study to use silver- and copper-filled PQF (AgPQF and CuPQF) was explored. Both AgPQF and CuPQF retained a short length with adequate bandwidth and a significant extinction ratio below than − 20 dB. The AgPQF has a coupling length of 137 µm with a bandwidth of 136 nm which operated at 1.44 µm wavelength, while CuPQF with 134 µm lengths with a bandwidth of 149 nm and operated at 1.50 µm wavelengths.

In this paper, compact all-optical XOR and XNOR gates based on different configurations of metal–insulator–metal plasmonic ring resonators (PRRs) have been proposed. Square and octagon-shaped rings have been used in this case. The logic gates have been simulated using the two-dimensional finite-difference time-domain numerical method, with a conventional perfectly matched layer as the absorbing boundary condition of the area under simulation. The phenomenon of Fano resonance is employed by the proposed gates to excite ON/OFF states. As a result, a large value of contrast ratio (C.R.) is obtained. The results show that the values of C.R. of XNOR and XOR gates for square-shaped PRR are 22.66 and 22.9 dB, respectively and the values of C.R. of XNOR and XOR gates for octagon-shaped PRR are 23.01 and 23.52 dB, respectively. Also, it is shown that the octagon-shaped gates have higher transmission ratios than other proposed configurations. The proposed optical logic gates can be used as key components in optical communications and for designing compact plasmonic devices.

An ultra-short and broadband polarization splitter based on PCF and metal surface plasmons resonance is proposed by designing a new structure and filling gold wire into certain air holes. The introducing of gold wire aims to couple with the basic modes. Then high birefringence is obtained to improve the splitter’s performances including length, bandwidth and maximal extinction ratio. The numerical results demonstrate that the splitter can be the shortest length of 100 μm (to our knowledge) and the broad bandwidth is 470 nm simultaneously. And when the splitter’s length is set as 104 μm, the widest bandwidth reaches the maximum 575 nm (to our knowledge) which covers almost all the E, S, C, L, and U communication band. In addition, the structure is relatively simple, so it is easy to fabricate using available methods. These properties will help designing splitter in the optical communication and sensing system.

In this paper, we discuss the basic characteristics of the SOI based micro-ring resonator, and understand the influence of the high refractive index difference and the small size on the spectral characteristics of the ring resonator. The novelty and importance of the spectral response selectivity of ring resonators is driven by the grating couple technique. This advantage is the periodic variation of the refractive index in the coupled grating, which will result in the coupling of the conduction wave modes. By means of measurement and simulation, observe the changes and trends of the spectrum in steady state and transient state, and finally analyze the performance of the ring resonator in the application of signal processing. It achieves polarization-independent grating couplers with high efficiency, wide bandwidth and low polarization-dependent loss at around the 1560 nm optical communication band. Drop end set laser wavelength correction 1591.9 nm.

A highly birefringent elliptic porous-core photonic crystal fiber with kagome lattice cladding has been presented for terahertz (THz) wave transmission. The slotted airholes inside the elliptic core effectively disrupt the symmetry of the porous-core which offers extremely high modal birefringence whereas the kagome cladding structure results in significantly low effective material loss (EML). The birefringence of the proposed structure is $$9.73\times 10^{-2}$$ and the EML is $$0.056\,{\hbox {cm}}^{-1}$$ for y-polarized mode at an operating frequency of 1 THz. The suggested structure also provides very flat dispersion over a bandwidth of 300 GHz. It is highly expected that this elliptic core waveguide would be remarkably useful in numerous polarization maintaining THz applications.