In this paper, a novel multi-hop hybrid Free Space Optical (FSO)/RF link is presented; it is made up of two main parts. The first part establishes the connection between the mobile user and source base station, and the second part establishes the connection between the source and the destination base stations. In the first part, a mobile user wants to connect to the source base station via a long range link; therefore, a fixed gain amplify and forward relay with multiple receive antennas is used for communication establishment. In the second part, the source and the destination base stations are connected via a multi-hop hybrid parallel FSO/RF link with demodulate and forward relaying. Considering the FSO link in Gamma-Gamma atmospheric turbulence with the effect of pointing error in moderate to strong regime and the Negative Exponential atmospheric turbulence in saturate regime, and the RF link in Rayleigh fading, new closed form exact and asymptotic expressions are derived for the Outage Probability and Bit Error Rate of the proposed structure.

In this work, the influence of quantum dot (QD) position on the performance of solar cells was studied. The presence of QDs within the base regions leads to improved open circuit voltage (V _oc) from 0.73 to 0.90 V. Despite a slight reduction in short-circuit current (J _sc) due to carrier collection loss, the enhancement of the V _oc of QDSCs with QDs in base region is significant enough to ensure that power conversion efficiencies (η) are higher than the reference quantum dot solar cell (QDSC) of which QDs are embedded in the intrinsic region. Moreover, sample with QDs in deep base region achieved the highest η of 9.75%, an increase of 29% with regard to the reference quantum dot solar cell.

The transmission of 5 × 4.224 Tb/s Nyquist superchannels over 2688 km distance has been demonstrated using trench-assisted multicore fibre (TA-MCF) at different spans for the first time at reduced channel spacing. The channel spacing has been efficiently reduced from 32 GHz (before modulation) to 25 GHz (after modulation) using Nyquist superchannels with hybrid modulation to transmit 15 subcarriers in one superchannel without any distortion. Five Nyquist superchannels, each using 15 × 35.2 Gbaud PM-16QAM subcarriers (4.224 Tb/s), are transmitted over seven cores of TA-MCF with low crosstalk over the same distance. Further, by utilising the core-to-core rotation scheme, the inter-core crosstalk from the neighbouring cores has been reduced after WDM/SDM transmission.

This study introduces an analytical approach to compromise between the figures of merit of a microwave photonic link (MWPL) and accordingly to design its corresponding matching networks using a graphical tool such as the Smith chart. In particular, the concept of constant gain and noise figure circles in the Smith chart is introduced in the field of microwave photonics. An analytical approach is used and expressions for circles of constant gain and noise figure are derived for unconditionally stable MWPLs. Then a procedure for designing high-gain low-noise MWPLs in the Smith chart is presented which involves trade-offs between gain and noise figure. Since the presented systematic approach is similar to the one used in high-gain low-noise amplifier design, using this approach to designing the intrinsic link leads to a consistency in the whole design procedure.

A cylindrical vector beam (CVB)-pulsed fibre laser with compact linear-cavity configuration has been demonstrated, using a two-mode fibre (TMF) Bragg grating (TM-FBG) for mode discrimination and a semiconductor saturable absorber mirror (SESAM) for passive mode-locking. As a result, mode-locked CVB pulses with fundamental repetition rate of 10.295 MHz have been obtained. Besides, with increased pump power harmonic, mode-locked CVB pulses have been achieved, for the first time.

Here, the design of a wideband absorber operating at terahertz frequencies is presented. The design is based on an analytical circuit model of graphene arrays of rectangular patches obtained from the presented circuit model of graphene arrays of disks. A recently proposed method is generalised for the design of wideband absorbers at higher frequencies. The bandwidth is increased by correct tuning of the input impedance for a structure composed of two layers of graphene arrays and a metal-backed dielectric layer. Using two-layer graphene arrays, the authors decrease the slope of the imaginary part of the input impedance to increase the bandwidth. The designed absorber works at a frequency of 4THz and has a higher bandwidth of about 30% with respect to the predicted bandwidth by the recently proposed method. The structure is analysed by a transmission-line formulation method. Consequently, it is demonstrated that the 90% -absorption bandwidth can be increased up to 80% of the central frequency.

Here to determine the thermal stability of buffered layer organic solar cell (BL-OSC), the effect of post anneal treatment has been studied. To investigate the effect of post annealing, the organic solar cells (OSCs) are annealed at the 120°C for different time duration. It has been observed that the BL-OSC structure exhibits the better thermal stability. Further, as the authors vary the post-annealing time duration from 0 min to 20 min, the power conversion efficiency (PCE) in the case BL-OSC drops by ∼20%, whereas in conventional OSC, the PCE drops by ∼35%. This annealing dependent study shows that, in conventional OSC structure an increase in phase segregation between donor and acceptor molecules reduces exciton dissociation and charge separation, this leads to sharp increase in series resistance and significant reduction in fill factor of the device. Whereas in the case of BL-OSS, there is a minimum reduction in the fill factor, which also determines the superior carrier collection and low recombination on the elevated annealing conditions. Further, the experimental results show that, in comparison with the conventional OSC structure, inserting the pure P3HT interlayer between PEDOT:PSS (hole transport layer) and P3HT:PCBM (photoactive layer) improves the PCE of the device by 34%.

A passively Q-switched erbium-doped fibre laser was demonstrated by using tris-(8-hydroxyquinoline)aluminium (Alq₃) organic material as a passive saturable absorber (SA). The SA was fabricated by a drop casting technique at room temperature and incorporated into a laser cavity by inserting it between two optical fibre ferrules. The Q-switched fibre laser operates at a centre wavelength of 1559 nm with a full-width half maximum of 1 nm. The generated pulse train is stable and has a pulse width decreased from 6.65 to 1.2 µs and the pulse repetition rate increased from 31.65 to 144.5 kHz as the pump power increased from 20 to 122 mW. The maximum pulse energy obtained is 63.89 nJ. This work indicates that the Alq₃ as SA has a great potential to be utilised for pulsed laser generation. To the best of the authors' knowledge, this is the first time an organic material is utilised as a SA device for generating a stable Q-switched laser pulse.

Here, the authors have optimised electron-blocking layer (EBL) with step graded design for a laser diode (LD) with an emission wavelength of 450 nm. Step graded EBL contain layers of varying compositions from In_0.04Ga_0.96N to Al_0.2Ga_0.8N with the total thickness of 30 nm. The electron leakage has reduced from ∼2272 to ∼6.6 A cm^−2, while hole transportation has improved by 2.185at 10 kA cm⁻² injected current density.The light output power per facet of reference LD is 146.8 mW, which the authors have enhanced to 247.7 mW in authors’ step-graded EBL structure. The slope efficiency has increased by ∼61.9%.Also, the EBL energybarrier hasincreased by 324.2 meV, while the hole transportation barrierhas reduced by 77.1 meV. The reduction in hole transportation barrier and increase in EBL barrier plays the vital role in the improved performance of LDs. The built-in potential affects the EBL band bending. Electric fields due to polarisation, ionised impurity charge distribution, and externally applied bias are investigated. It is observed that the step graded EBL structurereduces the built-in potential at the EBL interface, thus, resulting in reduced band bending as compared to reference laser structure.