The study of light and light-based technological advancement is becoming an economic and social need in the 21st century, and hence photonics is essential to our everyday lives to provide solutions to global challenges in energy, education, agriculture, health, communication, information processing, etc. It goes without saying that photonics has now influenced a wide range of scientific and technological fields, becoming a significant and rapidly evolving area of growing multidisciplinary interest. Medical diagnostics, organic synthesis, communications, and fusion energy are just a few of the many scientific and technical uses for photonics. This can improve people’s quality of life across various industries, including advanced manufacturing, military, healthcare, and energy. Today, photonics is also widely employed in agriculture. Without sensors and cameras on tractors and drones, it would be difficult to analyze soil and crops and identify areas that need fertilizer application in precision agriculture. Photonics is also used to predict when and how to harvest crops.

Quantum key distribution (QKD) is a viable technique for safeguarding image transmission against numerous attacks. To address the limitations of existing methods in securing electronic medical records, we have explored an encryption technique using a set of real-time medical images along with existing standard images using QKD protocols including BB84 (Bennett-Brassard 1984), CASCADE (Cascading Error Correction Algorithm for Data Exchange), and differential-phase-shift (DPS) under the fiber-based (OFC) and free-space (FSO) channels. It utilizes the quantum bit-plane representation of the Real Ket (QBRK) model and a logistic chaotic system with XOR operation. The performance of the developed framework is tested via visual illustration and 11 different quantitative assessments. The average entropy of the scrambled image for the medical source image is 7.9896, which is quite near to the optimum value of 8. The UACI (Unified Averaged Changed Intensity) and the NPCR (Number of Pixels Change Rate) metrics values lie between 33.7879 to 33.9711 and 99.6014 to 99.8000 for the FSO channel. The BB84 QKD protocol achieves a QBER (Quantum Bit Error Rate) of 0.0028 for an FSO channel with DCR (Dark Count Rate), which improves to 0.0012 when DCR is ignored for a 10 km link range. In addition, we analyzed and compared the effect of OFC on system output as the quantum channel. From several experiments, it is observed that the BB84 provides better results against CASCADE and DPS. The proposed work is validated using the Optisystem 15.1 software under FSO and for OFC.

A symmetric one-dimensional photonic crystal configuration with defect layer is proposed for an optical gas sensor based device application. Here, Silicon and Si ₃ N ₄ are considered as materials of dielectric layers with zero value of extinction coefficient in the wavelength range of concern. The transmission of PC configuration is estimated using the transfer matrix approach in case of configuration with and without defect, and the infiltrated gas is treated as defect layer. On the basis of the defect mode’s wavelength, gas can be determined. In addition, quality factor and sensitivity of the device are improved due to the variation of refractive index of layer B, thickness of defect, angle of incidence and the number of unit cells on either side of defect layer. By making analysis of the effect of these parameters on the sensitivity and quality factor, interesting results have been obtained and conclusions drawn. We have also proposed and investigated a symmetric structure with defect made with a single material to improve optical sensing parameters. Further for the sake of comparison, the various gases are used to show improved sensing characteristics for respective gases, which can be used to determine gas. It is inferred that such refractive index optical sensor based on defect mode position is highly sensitive and offers precise optical sensing characteristics and possibly find applications in gas detection.