Special issue “optical communications, sensing, and laser applications”

This Special Issue highlights topics relating to recent research advances in optical communications, optical sensing and laser applications, emphasising fibre-optic communication systems/sub-systems; optical signal processing; optical fibre sensors and devices; and various applications of silicon photonics, modulators, and optoelectronic integration circuits. It brings together contributions by outstanding international leaders, researchers, scientists, and engineers from a broad range of interdisciplinary fields to present their work in the science, technology, and applications of optical communications, optical sensing, and related laser techniques.

In this Special Issue, we have accepted five papers, which can be clustered into two main categories, namely optical communications and optical sensing. The papers falling into the first category exhibit novelties in optical switches and modulators. The papers in this category are from Zhentian Shan et al. and Yue Wu et al. The second category of papers offers direct solutions to optical sensing with applications to environmental and biomedical monitoring. These papers are from Mupeng Li et al., Majid Mafi et al., and Ying Zhang et al. A brief presentation of each paper in this special issue is as follows:

Zhentian Shan et al. report a 1*48 large-scale multi-mode fibre optical switch driven by a stepper motor. The insertion loss is <1.42 dB, which can be further reduced to 1.02 dB after optimisation. With the employment of a corner cube prism in the optics, the device is characterised by good repeatability of <±0.01 dB. The device has a fast response of <8 ms.

Yue Wu et al. present a new doping profile of the PN depletion region with four doping concentration levels for Microring modulator (MRM) considering the electrical bandwidth. By increasing the electrical bandwidth, the electro-optical (EO) bandwidth is increased. The MRM is characterised and is applied in a WDM 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.

Mupeng Li et al. give a review on Brillouin optical time-domain reflectometry (BOTDR), which is a branch of distributed fibre-optic sensing, and can measure the strain and temperature information. This paper 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.

Majid Mafi et al. investigate 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. 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. This structure detects the differences between refractive index analytes with a high-quality factor and a high and stable output transmittance spectrum.

Ying Zhang et al. introduce a sub-ppm-level SO₂F₂ and SOF₂ gas sensor based on photoacoustic spectroscopy (PAS). They design and fabricate a steel resonant photoacoustic cell with a resonant frequency of 1750 Hz. The proposed sensor has performed with favourable linearity within the dynamic range and reached the minimum detection limit of 0.22 ppm for SO₂F₂ and 0.28 ppm for SOF₂. It indicates great potential for monitoring the decomposition process of SF₆ in Gas-Insulated Switchgear.

All of the papers selected for this Special Issue show that the field of optical communications and sensing is steadily moving forward. This Special Issue focuses on the state-of-the-art of optical communications, optical sensing, and related laser techniques, covering recent technological developments in new principles, systems, and the emerging applications.