Active waveband selective switches for the telecommunication wavebands are fabricated and demonstrated. This type of active waveband selective switch is composed of a guided-mode resonance filter, a twisted nematic liquid crystal (TN-LC) layer, and a linear polariser. In voltage-off status, a fabricated active waveband selective switch with grating period of 893.86 nm exhibits high resonance peak with wavelength around 1311.2 nm. In voltage-on status, this switch exhibits a high resonance peak with wavelength around 1551.3 nm. The measured reflection peaks of another active waveband selective switch with grating period of 872.84 nm are located at 1309.1 and 1549.4 nm in voltage-on status and voltage-off status, respectively. Thus, light waveband can be tuned between O-band and C-band by electrically driving the TN-LC layer of this type of active waveband selective switch in real time.

The authors experimentally demonstrate that the spectral flatness of chaotic light from an external-cavity feedback semiconductor laser is significantly improved using a fibre Bragg grating. The effects of detuning between the Bragg frequency and chaotic frequency on the bandwidth and spectral flatness are both investigated. The flatness of the power spectrum is enhanced to ±1.4 dB whilst maintaining the spectral bandwidth at around 8 GHz. The experimental results are in accordance with theoretical predictions which also have shown that the spectral flatness decreases initially then increases with increasing the 3 dB bandwidth of grating. A flattened spectrum with a low-pass energy distribution increases the utilisation efficiency of chaotic light in chaotic radar and reflectometry.

The sensitivity is an important performance for a polarisation maintaining fibre (PMF) loop mirror (PM-FLM) sensor based on voltage demodulation. This paper investigates the method of improving the strain sensitivity of a PM-FLM based on voltage demodulation, including the demodulation principle, the derivation of the output light power equation, and experimentally studies on the strain sensitivity of a PM-FLM with different narrow-band input light source. The results show that the PM-FLM using a high-power light source as input has a high strain sensitivity but a small linear range of strain measurement, and the PM-FLM using a low-power light source as input has a low strain sensitivity but a large linear range of strain measurement. Hence, a high-power narrow-band light source as input can be chosen to improve the strain sensitivity, and the authors can also reduce the input light source power to enlarge the linear range of strain measurement.

Copper ions are incorporated into the PbS quantum dots as dopants via a chemical method and an ion irradiation method. For irradiating the samples, a 100 MeV copper swift heavy ion beam is used with three different doses of 1 × 10¹¹, 3 × 10¹¹, and 1 × 10¹² ions/cm². The doped and irradiated samples are characterised by different techniques and introduced as a sensitising layer in a solar cell. The current density–voltage characteristics of the solar cells are studied under white light illumination conditions and the solar cell parameters such as J _sc, V _oc, fill factor, and efficiency are obtained. Efficiency as high as 4.78% is obtained for irradiated quantum dots, which is significantly higher than that of pristine and doped quantum dot solar cells. However, at higher ion dosage, the solar cell efficiency degrades due to unwanted particle agglomeration in quantum dots.

An enhanced compact sensitivity of glucose sensor in the presence of human blood using tricore photonic crystal fibre is numerically proposed where one hollow channel filled by analyte acts as liquid core and remain two cores considering the silica substrate. The uniqueness of this structure is single material substrate and capable of tuning its sensitivity with minimum variation of glucose concentration (g/l) to detect the low level presence of glucose in the human blood. The transmission spectrum shows the maximum wavelength shift for x-polarisation at 470 nm, and 440 nm for y-polarisation to the response of refractive index of glucose resulting enhanced average sensitivity of 23,267.33 nm/RIU achieved at 470 nm of wavelength shift. The entire analysis and its mechanism of the proposed structure are applied with help of finite-element method.

The technology of visible light communication (VLC) is regarded as an appealing technique for upcoming wireless indoor multimedia communications. Considering the broadcast aspect of visible light propagation, the visible light interface is exposed and approachable to both licensed and unlicensed parties settled within the illuminated region. In this study, the authors present a chaos-based physical-layer encryption method for orthogonal frequency division multiplexing (OFDM)-based VLC schemes with the ability to counter known-plaintext attacks (KPAs) and chosen-plaintext attacks (CPAs). A logistic map is utilised for the chaos mapping. The presented method produces dynamic ciphertexts by employing the random quality of the chaotic keys and input data. It uses a multiple-fold encryption protocol which implements chaotic scrambling of the subcarrier distribution in time and frequency domains, as well as chaotic polarity inversion of subcarriers. To generate the secret key, a chaotic key creation approach is introduced by including the position-sensitive and real-valued channel state information of the VLC channel. The presented method provides supreme confidentiality for the OFDM-based VLC schemes to counter KPAs, CPAs, brute-force attacks, and statistical attacks. The secrecy capacity of the presented method is improved by applying a pre-equalisation technique at the transmitter instead of the receiver.

The authors theoretically propose a design for electrically tuning a metasurface based on piezoelectric actuation. The design comprises 2D gap-plasmon elements arranged periodically on a piezoelectric substrate which controls the period between them. The technique is numerically studied for a metasurface that anomalously reflects an incident p-polarised wave by 30° at the optical communication wavelength, 1550 nm. The dynamic behaviour of the system is investigated for two main applications; (a) steering the reflection angle and (b) retrieving the reflection angle for an incident wave of a shifted wavelength. It is demonstrated that a reflected beam can cover an angle of ∼3° upon a strain of <3.3%. It is also shown that at the same strain value, the reflection angle is retrieved for a wavelength error of ±50 nm. These results suggest a potential to design large-bandwidth, reconfigurable metasurfaces that are integrable with planar opto-electromechanical devices.

Using a two-dimensional photonic crystal lattice, a compact and simple structure has been introduced in the present study to construct an all-optical half adder. The designed structure operates under the interference effect. The phase difference has been created in different states by putting the point defects and the difference in the length of the input waveguides. To do analyses, the finite-difference time-domain method and the plane wave expansion have been used. The advantages of this design include the small dimensions, high possibility of construction, compatibility with the silicon-based technology, and equality of the output power in the logic states 0 and 1. The contrast ratio calculated for the port Sum and the port Carry has been equal to 9.3 and 8.22 dB. The response time has been equal to 0.22 ps, generating the data transfer rate of 4.55 Tbps.

A detailed study of the performance analysis of a low-cost PIN/heterojunction bipolar transistor (HBT) opto-electronic integated circuit (OEIC) is described. Measured and of 54 and 57 GHz for 10 × 10 µm² HBTs were achieved for such a large emitter size. The base and collector regions of the transistor were utilised to form a PIN photodiode which has a dc responsivity and quantum efficiency of 0.5 A/W and 0.45, respectively, without antireflection coating at a wavelength of 1.55 µm. For both active devices, a model was realised taking all parasitic and physical-based impacts into account, for example, equivalent circuit of the pads surrounding the devices and transit delay time across the collector depletion region. The simulation results of the discrete passive and active elements showed good agreement with experimental measurements. The OEIC module was implemented in Keysight-advanced design system software with a three-stage preamplifier which has a transimpedance gain of 40 dB Ω and a −3 dB bandwidth of 18 GHz. This corresponds to a transimpedance-gain product of 1.8 THz. A series peaking inductor technique was used in the design, contributing to an enhancement in the opto-electrical bandwidth of >60%. The optical/electrical response offers a bandwidth of ∼15 GHz, adequate for up to 20 Gb/s data rate operation.