This study presents the design and analysis of energy-efficient visible light communication-based downlink and uplink using a thin-film corner cube retroreflector (TCCR). The uplink establishment from the user device (UD) to base station (BS) is achieved with the retroreflection of the downlink light beams using TCCR in UD. It eliminates the requirement of active optical source in the UD that reduces the power consumption for communication from the battery-constrained devices. Additionally, the photoelectric effect-based energy harvesting from lighting sources is also incorporated in the UD. By utilising the thin-film deposition of photosensitive alkali metals Na, K, Rb, and Cs, light energy has been harvested, and the harvested energy is utilised in the UD for the uplink modulation process. It makes the real self-sustainable communication towards the battery-less execution of internet of things (IoT). The proposed system offers the downlink and uplink for the distance of 2.15 m with the data rates of 10 Gbps and 1 kbps, respectively. The maximum harvested energy from the 18 W optical source by using the 100 nm Cs-TCCR is 104.40 µJ, and it can serve the energy consumption of the uplink modulator to transmit the UD data to the BS.

The authors experimentally demonstrated the generation of mode-locked pulses from all-fibre erbium-doped fibre laser cavity by using organic material, Alq₃, as a saturable absorber (SA). The SA film was integrated into a ring fibre laser cavity to act as a mode-locker. A mode-locking operation was achieved in three different experiments with pulse width/repetition rate of 1.26 ps/3.36 MHz, 970 fs/3.36 MHz and 820 fs/4.9 MHz by using cavity length/optical coupler (OC) of 61.5 m/80:20 OC, 61.5 m /95:5 OC and 42 m/80:20 OC, respectively. All the experiments produced a soliton and a very stable mode-locking operation at central wavelength of ∼1561 nm. The experiments confirmed that organic material can readily be used as SA for a mode-locked operation in the 1.5 μm region. This demonstration might shed new insights into the potentials and techniques for developing ultrafast fibre lasers by using organic materials as SAs.

In the present paper, the bit error rate (BER) performance of hybrid power line communication (PLC) and multiple-input multiple-output (MIMO) visible light communication (VLC) system (HPMV) has been investigated using line-of-sight (LOS) and LOS plus first reflection (L-R1) signals for room size of 5 m × 5 m × 3 m (configuration A) and 7.5 m × 7.5 m × 3.5 m (configuration B). In the work, Rayleigh fading and Barry channel models have been considered for PLC and VLC channels respectively. The BER has been analysed by varying separations between LEDs as 0.2 m, 0.6m and 1m for both configurations. The results show that the BER for LOS and L-R1 signals decreases upto optimal separation of 0.6 m for configuration A. However, the result indicates that the required optimal separation for configuration B is more than configuration A. The channel frequency response of MIMO-VLC and HPMV system has been inspected and it supports the results of BER simulation. It has been found that, with increase in spatial separation between LEDs, the deep notches and attenuation in the frequency response of MIMO-VLC system decrease. The overall investigation shows that even though OFDM is resilient to frequency selective fading, an optimum separation between LEDs must be chosen according to the room size for the HPMV system.

Photo-current characteristics in close space sublimation processed multi-facetted Cadmium Telluride (CdTe) micro-granular films were studied under AM1.5, blue and green laser illuminations to assess the energy dependent charge transport characteristics. Photo-current under AM1.5 illumination (100 mW/cm²) resulted in three times more than dark current while it was observed 2.4 and 2.5 times more in case of blue and green laser illuminations, respectively. While all the three illuminations (AM1.5, blue and green lasers) were capable to generate photo-electrons in CdTe, the variation in magnitude was articulated to the effect of grain boundaries present across the charge transport pathways as evidenced from the surface morphology examined by scanning electron microscopic studies which asserted that CdTe films were micro-granular in nature separated by grain boundaries. It is elucidated in the measurements that charge carriers under the illumination of AM1.5 light, acquired energy to overcome the grain boundaries easily compared to the charge carriers produced by blue and green light sources as evidenced from the photo-current measurements.

In this study, we analyze the combined effect of TMD/Perovskite/2D Material on the performance of SPR biosensor using Kretschman configuration. In order to optimize the parameters, we compare the results of each material falls in the family of TMD/Perovskite/2D respectively and finally applied in the proposed sensor. It is observed that the combined structure based on black phosphorus, a 2D material, Barium Titanate (BaTiO₃) as a Perovskite material and Tungsten disulfide (WS₂) as a TMD material respectively shows excellent performance in terms of a performance parameter of the sensor. Incident light wavelength is fixed of 633 nm and radiative properties of a multi-layered structure are calculated by transfer Metrix method. Essential performance parameters like Figure of Merit (FOM), Sensitivity, Detection Accuracy obtained by using the standard formula given in the paper. The reported figure of merit (FoM) and sensitivity are 62.51/RIU and 370. respectively. The results obtained in this paper expect to prove a significant role in the biosensing field like DNA hybridization as well as for the application of Perovskite materials in biosensing.

Here, the authors propose a new approach for realising wideband and polarisation-independent antireflection coating, based on a metamaterial composed of a subwavelength array of metallic pillars with a square cross-section. The effective impedance of the array can be duly adjusted by the size and distance of the pillars. As such, the authors design the effective impedance of the antireflection coating to be the geometrical mean of the impedance of upper and lower media and choose its height to be quarter of operating wavelength. Doing so, the reflection vanishes at the desired frequency and fractional bandwidth of 56% is achieved with a criterion of 10% reflectance (the refractive index of the substrate is assumed to be 4). Importantly, the proposed structure is symmetric in both directions. Thus, in contrast to prior arts, it is not sensitive to the polarisation of the incident wave at normal incidence. In addition to that, it is designed based on a multilayer Chebyshev matching transformer of transmission line theory, which potentially increases the bandwidth of the antireflection up to 107%, albeit at the expense of pass-band ripples. This structure can be used from very low frequencies up to the infrared regime by appropriate scaling.

This work examined the possibility of overcoming narrow band optical absorption of organic dyes in the range of 350–700 nm via surface plasmon effect mediated by RF-sputtered tungsten (W) thin film on mesoporous TiO₂ for dye-sensitised solar cells (DSSCs) application. The UV–visible spectroscopic measurement showed optical absorption of W-film in the spectral range of 350–700 nm with a dominant characteristic feature in the range of 350–550 nm. W-thin film-coated TiO₂ was used as an electron acceptor in DSSCs and observed ∼28% enhancement in short circuit current density compared to that of in a pristine TiO₂-based DSSC which did not use W-thin film on TiO₂. It is attributed to the local field-induced enhancement in optical absorption which resulted in improved exciton generation and effective charge transport in DSSCs enabled by W-thin film coating onto mesoporous TiO₂.

This study experimentally demonstrates a Q-switched fibre laser using a new tungsten tri-oxide (WO₃)-based saturable absorber (SA). Using the drop and casting approach, we managed to prepare a thin film that contained WO₃ powders in polyvinyl alcohol. A small bit of the film was used to form an SA which was placed in a ytterbium-doped fibre laser cavity to generate a Q-switched laser. The laser, operating at 1063.78 nm, was realised at the threshold pump power of 85 mW with a repetition rate of 23.87 kHz and a pulse width of 5.56 μs. At the pump power of 147 mW, the laser produced the maximum pulse energy of 625 nJ, signal-to-noise ratio of 59 dB, the repetition rate of 39.79 kHz and pulse width of 2.37 μs. To the best of our knowledge, this is the first demonstration of using WO₃ SA to generate the pulse laser in the 1 μm region.

A new device architecture of an all-optical logic inverter (AOLI) has been proposed in this study. The AOLI functions based on stimulated Raman scattering (SRS) in silicon nanocrystal embedded slotted photonic crystal waveguide (SPCW). The operating power and footprint size of the proposed device have significantly been scaled down to ∼1.5 mW and , respectively, by combining the benefits of giant SRS gain of silicon nanocrystal and ultra-high spatio-temporal confinement of the SPCW. Cascadability of the proposed AOLI has been investigated using the maximum product criterion of the noise margin. The successful operation of the AOLI has been demonstrated for the repetition rate of the pulses as high as 100 Gbps. Finally, tolerance of performance of the design under different types of fabrication imperfections has also been calculated to establish its sustainability in a practical scenario.

A small portion of an optical fibre clad was removed and coated with methylamine hydroiodide by a slurry deposition process to develop an evanescent wave optical fibre ammonia sensor. The experiment was performed for a few volatile organic compounds in order to understand the selectivity and sensitivity. Prior to the gas sensing measurement, the methylamine hydroiodide sample was characterised using X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray spectroscopy, Fourier transform infrared, Raman, diffuse reflectance and UV–Vis spectroscopy. In order to understand the sensor response, the samples were independently exposed to acetone, ammonia, ethanol and methanol gases and then analysed using the XRD technique. This analysis reveals that the structural variation is observed because of the ammonia exposure as compared to other gases. It has initiated to fabricate a clad-modified optical fibre ammonia sensor that exhibits ∼28% of the sensitivity. These experimental results are discussed in detail.

In optical fibre communication system, improved modulation schemes have been proposed to increase capability and high bit rate transmission. One such technique is optical duobinary modulation, which can able to broadcast high-speed optical signals over bandwidth-limited channels. The conventional modulation schemes employ the non-return-to-zero modulation and return-to-zero modulation technique. These schemes decrease spectrum width and increase the dispersion tolerance. However, the effect of inter-symbol inference presents between the pulses. These techniques give a reduced performance for high bit rate transmissions and transmission over long distances. Hence in this work, the implementation of duobinary modulation improves the performance of optical communication along with the provision of enhanced security through bio-inspired chaos masking scheme. The bio-inspired chaos-masking scheme generates the security key using the spider security pattern generator to provide improved security. The parameters of the proposed technique are analysed for different transmission rates and the performance improvement is validated.

Non-linearities introduced by power amplifiers in communication systems have been a subject of interest for industry and academia for a long time. On one hand, the search for increased range intrinsically incites operators to boost input power. On the other hand, this leads to stronger non-linear phenomena in amplifiers, which in turn increase the bit error rate. The situation led to the emergence of digital predistortion algorithms that compensate for the power amplifier's non-linearities and improve the overall performance of the link. A rich corpus of literature exists on this topic but it mainly addresses wireless microwave networks. The case of digital predistortion specifically tailored for optical communications is much less explored. This study focuses on predistortion via filter-lookup-tables and tackles the issue of non-uniform spacing. The work is mainly aimed at coherent optical-orthogonal frequency-division multiplexing systems including low-cost semiconductor optical amplifiers.

Evolution and accessibility of smart-phones have led to a huge demand in network bandwidth. The ubiquitous use of smart-phones in high-speed trains poses a unique challenge in delivering high-speed internet service on board. This challenge can be overcome by employing free-space optics, an alternative to radio-frequency technology. Previous coverage models for ground–train communications employed single laser systems with a larger divergence angle to cover a larger distance. Larger divergence angles lead to larger geometric losses, which may result in a non-reliable communication link. This study proposes a sectorised multi-beam coverage model with a smaller divergence angle to reduce the impact of geometric losses in the system. This study also proposes two receiver (Rx) architectures for Rxs deployed on the train. Along with geometric losses, the atmospheric attenuation is taken into consideration for the FSO link. The performance of the ground–train communications system in terms of bit-error-rate is evaluated under weak turbulence conditions via numerical simulation.

A novel liquid-core photonic crystal fibre (LC-PCF) based on the Zeonex substrate has been proposed for sensing the varying concentration of kerosene in petrol and diesel fuels in terahertz frequencies. Fuel sample infiltration is achieved by designing a single hexagon in the porous core region. The LC-PCF has been numerically studied using a finite element method. By filling the core hexagon with different petrol–kerosene and diesel–kerosene concentrations, sensitivity and transmission profiles of the proposed LC-PCF have been examined. The impact of different design parameters of the fibre on its performance has been analysed, allowing the optimum design parameter set to be selected for further analysis. The proposed fibre shows relative sensitivities above 96% and effective material losses in the order of 10⁻³. With negligible confinement losses, the proposed fibre demonstrates near-zero ultra-flattened group velocity dispersion profiles within 1–1.6 THz. It is envisaged that the proposed fibre may be fabricated easily due to its simple design, and thus, serving as a significant step towards understanding THz pulse interaction with liquid petrochemical products.

Rich scattering of ultraviolet signals enables the non-line-of-sight outdoor wireless connectivity and eliminates the line-of-sight requirement of free-space optical links. Besides scattering losses, ultraviolet signals also suffer from the atmospheric turbulence-induced fading. One of the strong fading mitigation techniques is the spatial diversity, which has been extensively studied in the context of wireless radio frequency and infrared networks. In this study, spatial diversity techniques for non-line-of-sight ultraviolet communication links are considered. In particular, multiple-input-single-output (MISO), single-input-multiple-output (SIMO), and multiple-input-multiple-output (MIMO) non-line-of-sight ultraviolet communication systems are derived. The BER performance of the single-input-single-output (SISO) link is also derived as a benchmark. The accuracy of the derivations is confirmed through Monte Carlo simulations. The results demonstrate the significant performance improvements in spatial diversity schemes over SISO counterparts. The authors further investigate the effect of spatial correlation on the performance of non-line-of-sight ultraviolet links with spatial diversity. They demonstrate that the spatial correlation degrades the performance significantly, and efficient separation between apertures is crucial to achieve the maximum diversity gain.