Iet Optoelectronics最新文献

Compared with electrons, photons have the potential to realise ultra-high speed operations because of its unique high speed and high parallelism. In recent years, there have been many researches on neural networks using optical hardware. The Mach–Zehnder interferometer (MZI) and micro-ring resonator (MRR) are commonly used as optical devices to realise linear operation units in optical neural networks (ONN). MZI has the advantages of simple fabrication, high sensitivity, and easy integration, which has attracted the attention of researchers. We summarise the implementation methods of ONN matrix multiplication based on MZI, the implementation methods of non-linear activation, and the on-chip training methods. We first summarise the researches on matrix multiplication of ONN based on MZI. Three kinds of MZI grid decomposition methods, Fast Fourier Transform (FFT) grid structures, and the corresponding derivation processes are introduced, respectively. Then, several experimental implementations of ONN based on MZI are summarised, and the characteristics of optical processors fabricated in these references are analysed. Finally, the realisation methods of non-linear activation and on-chip training of silicon ONN are introduced, respectively.

Effects of the deposition time and voltage on the characteristics of gold nanoparticles (NPs) thin films, prepared by the electrophoretic deposition (EPD) method on the silver substrate, were investigated experimentally. Au NPs were synthesised using the pulsed laser ablation method in distilled water. The suspended solution of the gold NPs was used as the electrolyte of EPD. An irradiation was carried out by the fundamental wavelength of a Q-switched NdYAG laser at 1064 nm and 7 ns pulse width. The electrophoretic deposition apparatus consisted of two 2 × 2 cm pieces of silver plates as the electrodes. They were immersed in parallel with a 7 mm gap in the gold NP suspension. Five samples of gold NP thin films were prepared at different deposition times and applied voltages. Results show that the roughness, thickness and surface quality of EPD prepared thin films can be strongly controlled by the deposition time and applied voltage. The thickness of deposited films was dependent on the voltage of deposition in which their roughness was increased with increasing the deposition time. Furthermore, the reflection of deposited films was affected by the surface roughness.

This study presents an investigation on the performance of the sensitivity of a dual spider-shaped surface plasmon resonance (SPR)-based photonic crystal fibre (PCF) refractive index sensor having unique design specifications. To evaluate the fibre guiding properties, Finite Element Method is used for utilising the monetarily accessible COMSOL Multiphysics version 5.3a. A gold layer has been used as the plasmonic material surrounding the fibre to ensure chemical stability, and a single fine coating of TiO₂ supported the improvement of gold attachment with the fibre. The structural air holes' design arrangement inside the PCF gives an enhanced sensitivity performance. The proposed PCF-SPR gives extremely reduced confinement losses. Numerous precise investigations on the fibre parameters show the highest amplitude sensitivity of 4233 RIU⁻¹ in detecting the scope of the refractive index (RI) 1.32–1.41. 2.36 × 10⁻⁶ and 1.18 × 10⁻⁵ and are achieved as amplitude resolution and wavelength resolution, respectively. The highest confinement loss found for this sensor is recorded to be 6.22 dB/cm. The RI sensor can lead to the exact identification of organic chemicals and biological analytes for the proposed design specifications, providing good sensitivity with significantly reduced confinement loss.

Microwave photonic filters have been regarded as an alternative to traditional radio-frequency filters because of their wide bandwidth and large tunability. Integrated microwave photonic filters can integrate all necessary components into a single chip and are highly demanded for future radio-frequency applications. Here, a highly integrated frequency-tunable microwave photonic bandpass filter based on a silicon platform is proposed and demonstrated. The integrated filter consists of a phase modulator, four cascaded microring resonators and a photodetector. The frequency-tunable range of the integrated filter is from 6.1 to 35.9 GHz, and the reconfigurable bandwidth is from 0.22 to 0.54 GHz. A large spurious free dynamic range of 102.1 dB Hz^2/3 is obtained. This highly integrated approach holds great promise for miniaturised, flexible, and high-performance microwave signal processing in modern radar and communication systems.

The mean photon energy of a light-emitting diode (LED) as recently defined in the IEC standard is theoretically examined. It is pointed out that defining the mean photon energy as an arithmetic mean of photon energies in the emission spectrum is crucial in decomposing the power efficiency of an LED into the voltage efficiency and the external quantum efficiency (EQE). The mean photon energy thus defined and the photon energy calculated from the more convenient peak wavelength in the spectrum are then evaluated and compared for blue and red LED samples. The EQEs of the blue and red LEDs are subsequently obtained, demonstrating that the EQE values from the peak photon energy have small errors within 0.5%p of the true EQE values. The current work presents useful criteria in substituting the EQE value calculated from the peak wavelength for the true EQE value using the mean photon energy for both the blue and red LEDs.

Brillouin optical time-domain reflectometry (BOTDR) is a branch of distributed fibre-optic sensors, and it can measure the strain and the temperature information, localised by the return time of the probe pulse, along the fibre based on the spontaneous Brillouin scattering process. Parameters of the BOTDR system, including the spatial resolution, the signal-to-noise ratio, the measurement speed, and the sensing range, have a mutually restrictive relationship. In order to improve the performance of the BOTDR system, researchers have focussed on improving the design of the probe pulse, for example, transforming the shape, the sequence, and the spectral properties of the pulse. This study summarises the recent progress in the design of detection pulses in BOTDR systems, and comprehensively demonstrates the improvement effects of various pulse modulation formats on the system performance.

For a serial relaying underwater wireless optical communication (UWOC) system with ON-OFF keying modulation, we theoretically evaluate the optimal power allocation techniques in order to minimise the end-to-end bit error rate (BER), subject to transmission power constraints. At first, we evaluate the end-to-end BER with respect to all degrading effects of the UWOC channel, namely scattering, absorption, and turbulence-induced fading and then develop a closed-form BER expression as a function of transceiver parameters and water type. The optimal power allocation methods are obtained using the perfect channel state information available at the receiver (CSIR) and transmitter (CSIT) for both detect-and-forward (DF) and amplify-and-forward (AF) serial relaying systems. For each relaying method, we consider a dual-hop UWOC system and determine optimal power allocation to minimise the BER. Afterwards, the optimal power allocation in a multi-hop system is obtained to minimise the end-to-end BER. Compared to the equal power allocation, our results illustrate that UWOC relaying systems with optimal power allocation can significantly improve the end-to-end BER and expand the communication link. For instance, the proposed power allocation method for the DF and AF relay node in a 60 m single relay system improves the system performance at the BER of 10⁻⁵ by 2.5 and 1.8 dB compared to the equal power allocation, respectively.