Iet Optoelectronics最新文献

Visible light communication (VLC) has emerged as a good accompaniment to radio-frequency (RF) technologies by deploying multicarrier schemes such as orthogonal frequency division multiplexing (OFDM). However, the coherent summation of carriers in the OFDM system leads to a high peak-to-average-power ratio (PAPR), causing non-linear clipping distortion at the transmitting light-emitting diode. This intricacy becomes a potential barrier for intensity modulation and limits the VLC systems' bandwidth. In the literature, non-distorting PAPR lowering approaches, such as the selective mapping (SLM) approach, have been confirmed as the most effective strategy for reducing ineludible high PAPR in optical OFDM systems among all other available techniques. Besides its astounding performance, the computational complexity also becomes a major complication in SLM due to the generation of multiple candidates. This paper proposes a computational complexity minimisation approach using inherit system properties in the SLM-based PAPR suppression method for VLC systems, where the phase sequence vectors are considered periodic. The alternative direct current-biased optical orthogonal frequency division multiplexing candidates for the single frequency-domain data block are generated with the periodic phase rotation vector. The evaluation of the complexity analysis and the simulation results shows that the mitigation of computational complexity surpasses the standard SLM technique.

A scheme for multi-band frequency generation is proposed and experimentally demonstrated using a dual-parallel Mach–Zehnder modulator (DPMZM)-based optoelectronic oscillator (OEO). The principle of this generator is theoretically described in detail. It is found that multiple frequencies with a small power variation can be produced by setting the three working points and the modulation depth of the DPMZM. In the proving experiment, an 8-GHz fundamental oscillation with a side mode suppression ratio of 44 dB is generated. The phase noise is measured to be −96.8 dBc/Hz @ 10 KHz offset with a 100-m and 1-Km optical fibre used in the two oscillation loops. When the oscillating signal is applied to drive the two sub-modulators in the DPMZM, doubled and tripled frequencies are produced at the same time, and the phase noises of the two frequencies are also measured to be −90.2 dBc/Hz and −85.9 dBc/Hz @10 KHz, respectively.

All-optical likelihood calculation has the potential to improve the performance of operating speed and power consumption in future communication systems. The author previously proposed a novel scheme of likelihood calculation, which is capable of applying multi-value modulation. However, these studies have a limitation that requires higher integration into an actual system. In this study, an optical device of likelihood calculation for a 4-bit quadrature phase-shift keying (QPSK) modulated signal (i.e. two sequential QPSK symbols) is demonstrated. The integrated device consists of two delayed interferometers with silicon waveguide. The device is designed according to the types of 4-bit code string as follows (00 00), (00 11), (11 00), and (11 11), and the output light waveform from the device is observed by an oscilloscope for a plurality of 4-bit QPSK signals. The light intensity obtained from the device accurately corresponds to the Hamming distance between the code string and the input signal. The results indicate that the proposed scheme correctly calculates a likelihood for a 4-bit QPSK signal at 10 Gbaud.

The microring modulator (MRM) is a small-size and low-power component, which is the potential for the next-generation optical interconnection. By the theoretical analysis, increasing the electrical bandwidth, which is relevant to the cross section and the doping concentration of the doping region, is a better way to increase electro-optical (EO) bandwidth. Therefore, a new doping profile of the PN depletion region with 4 doping concentration levels is introduced considering the electrical bandwidth. Based on the new doping profile, the MRM with the 160 μm length and the 0.33 and 0.2 μm coupling space are determined considering the trade-off between the EO bandwidth, quality factor (Q), extinction ratio, area of MRM, and power consumption. Moreover, the MRM is characterised and is applied in a wavelength division multiplexing transmitter. By the measurement, the transmitter with the designed MRM could transmit PAM4 signal at 52 Gbps rate, which indicates the MRM could be potential for the 50 Gbps/ch optical interconnection.

In this paper, we present a GST-based wideband plasmonic switch. With the excitation of localised surface plasmons and concentration of electric field in the structure, a near-perfect and wideband absorption is achieved. The switch consists of a GST layer, which acts as a Fabry–Perot cavity. Increasing the temperature and changing the state of GST lead to a high difference between the absorption spectra in amorphous and crystalline states in a wide range of wavelength. Therefore, the switch has a high extinction ratio of 13.71 dB at the wavelength of 1343 nm. Also, the response time of the switch is obtained as 46 fs. The structure has near-perfect absorption up to the incident angle of about 20°. Moreover, due to the symmetry of structure, the absorption spectrum is independent of polarisation. To show the validity of simulation results, the analytical method of equivalent circuit model is presented. The proposed polarisation-insensitive switch with high extinction ratio, fast response time and wide bandwidth can be used in photodetectors, plasmonic modulators and logic gates.

In this work, all-optical polarisation state modulation using a tungsten disulfide (WS₂) coated side-polished fibre (SPF) as modulator is experimentally demonstrated. A bulk layer WS₂ is exfoliated into a few-layer WS₂ thin film using liquid phase exfoliation technique. The few-layer WS₂ film is then coated onto a SPF to serve as an optical polarisation state modulator based on the thermo-optic effect. The rotation of the polarised signal light is controlled using a pump laser. Throughout the pump power range of 514.5 mW, the polarisation state of the polarised signal light has rotated ∼70°, with a minor ellipticity fluctuation of <6°. The proposed experiment is carried out on the basis of the photon-modulate-photon principle and achieved all-optical modulation in a fibre laser system.

In this paper, we proposed a new method to realize the rotational freedom of thin-film solar cells. In this method, an array of reconfigurable nano-patches fed by a plasmonic waveguide is integrated inside the solar cell to receive and trap light in the active layer. The reconfigurable nano-antenna is designed to achieve beam steering by bias voltage in the direction of sunlight during the day using 4-Dimethyl-Amino-N-methyl-4-Stilbazolium Tosylate as an active electro-optic material integrated into the plasmonic waveguide. The proposed solar cell is investigated using the finite-difference frequency-domain method and the drift-diffusion equations of COMSOL Multiphysics software at different wavelengths of light and a wide range of angles of incidence for transverse magnetic (TM) and transverse electric (TE) polarizations. The numerical results show increase in the absorption in large wavelengths of sunlight for the thin-film solar cell with nano-antenna, resulting in a short circuit current enhancement of 1.48 and 1.45 for TE and TM polarisations, respectively. Also, another advantage of the proposed reconfigurable structure is maintaining the performance in different angles of incidence, which may open up a new opportunity in solar energy harvesting.

With the rapid development of digital ecosystems, such as mobile applications towards goods/monetary transactions, a new paradigm of data transfer arises, which requires fast and reliable algorithms to generate random numbers. The statistical nature of speckle-based imaging creates an opportunity for these generators to arise as random number generators given the unpredictability and irreproducibility of such patterns. Hence, it is shown that the establishment of an experimental system is able to produce unique speckle patterns for remote cryptographic key storage and distribution, with a potential key rate generation of Gbs.

A hexagonal outlined porous cladding with vacant core photonic crystal fibre (HOPC-VC-PCF) sensor using Zeonex has been presented, which can detect cyanides at the THz regime. Cyanides are incredibly lethal chemicals to humans as they can rapidly cause impairment or even death; such harmful substances must be identified precisely. The proposed model has been analysed at a broad spectrum of THz regimes for three different analytes, and the numerical investigation is performed using the Finite element method (FEM). Simulation results exhibit that at optimum design parameters, extremely high sensitivity of 99.75%, negligible confinement loss of 0.5 × 10⁻¹³ cm⁻¹, extremely low and flat dispersion of 0.12 ps THz/cm, and other excellent features were obtained. The performance analysis and the design methodology have been depicted in detail. Due to the simplistic design, fabrication of the model is easily achievable by current technology. The remarkable sensing capabilities will not only make it suited in chemicals analysis but also will play vital roles in other applications as well.

This paper investigates a high-quality and multi-purposed biosensor with maximum stable output transmittance numerically by using the inverse design method. The proposed biosensor utilises particle swarm optimisation for inverse design which will be a helpful way of designing different kinds of precise sensors in the future. In this research, some parameters are introduced to the optimiser to find the best cavity parameters for developing a high-quality sensor to sense different targets. Many previous studies were on single-goal biosensors, or their quality factor and output spectrum were very low. The proposed sensor can sense different parts of blood components, the amount of glucose in the urine, and tear's glucose for the first time just in one device to the best of our knowledge. Compared to previous works, this structure detects the differences between refractive indexes analytes with a high-quality factor and a high and stable output transmittance spectrum. This structure contains two-dimensional photonic crystal microresonators to provide resonance frequencies in the photonic bandgap. The device works on a window of 1.55 μm with a quality factor equal to 24,000, the sensitivity is 500 nm/RIU (refractive index unit), and the resolution is equal to 4 × 10⁻⁵. In this paper, the scaling method, particle swarm optimisation, two-dimensional finite-difference dime domain, and Plane-Wave Expansion methods are utilised.