Metasurfaces have gained growing interest in recent years due to their simplicity in manufacturing and lower insertion losses. Meanwhile, they can provide unprecedented control over the spatial distribution of transmitted and reflected optical fields in a compact form. The metasurfaces are a kind of planar array of resonant subwavelength components that, depending on the intended optical wavefronts to be sculpted, can be strictly periodic or quasi-periodic, or even aperiodic. For instance, gradient metasurfaces, a subtype of metasurfaces, are designed to exhibit spatially changing optical responses, which result in spatially varying amplitudes of scattered fields and the associated polarization of these fields. This paper starts off by presenting concepts of anomalous reflection and refraction, followed by a brief discussion on the Pancharatanm–Berry Phase (PB) and Huygens’ metasurfaces. As an introduction to wavefront manipulation, we next present their key applications. These include planar metalens, cascaded meta-systems, tunable metasurfaces, spectrometer retroreflectors, vortex beams, and holography. The review concludes with a summary, preceded by a perspective outlining our expectations for potential future research work and applications.

As a flexible and compact nanophotonic device, the metasurface exhibits excellent potential in holographic display and optical information encryption. However, most metasurfaces are passive devices due to the limitations of fixed material properties and structural components. Magneto-optical metasurface is a hybrid device that integrates tunable functional material with elaborately designed nanostructures. It can realize dynamic modulation of the properties of light since the permittivity tensor for the magneto-optical material can be changed by applying an external magnetic field. Here, we propose a tunable metasurface composing metallic nanohole arrays with a bismuth-substituted yttrium iron garnet interleave layer and a metallic film underlayer placed on a glass substrate. The magneto-optical metasurface can achieve dynamic switchable holographic display in different polarization channels via magnetic field control based on the optical rotation of magnetic material and the complex amplitude modulation of the elaborately designed nanoholes. This feature provides a novel approach for the construction of an active tunable metasurface, which can improve the information storage capacity and security of the device. This concept is expected to be applied to various dynamic modulation fields, such as magnetically tunable lens, beam shaping, and optical information encryption.

In this work, the spectral properties of distributed Bragg reflector-based photonic crystal (DBR-PhC) structures were studied for the near-infrared (NIR) range. Different structural properties were varied to study their effect on the quality of the stopband and the appearance of the resonant dips in the reflection spectra of the DBR-PhC structure. The investigated structural features included the depth of PhC holes, hole radius, and number of PhC elements in the DBR structure. The 11-layered DBR structure was designed with a 2.4/1.4 refractive index contrast of alternating layers. The study aimed to achieve optical filtering properties in the DBR-PhC structure, to simplify the structural complexity of Fabry-Pérot filters by eliminating the FP cavity and upper-DBR mirror. The proposed DBR-PhC device can be used in different optical filtering and sensing applications.

In this paper a perfect absorber with a photonic crystal cavity (PhC-cavity) is numerically investigated for carbon dioxide (CO₂) gas sensing application. Metallic structures in the form of silver are introduced for harnessing plasmonic effects to achieve perfect absorption. The sensor comprises a PhC-cavity, silver (Ag) stripes, and a host functional material—Polyhexamethylene biguanide polymer—deposited on the surface of the sensor. The PhC-cavity is implemented within the middle of the cell, helping to penetrate the EM waves into the sublayers of the structure. Therefore, corresponding to the concentration of the CO₂ gas, as it increases, the refractive index of the host material decreases, causing a blue shift in the resonant wavelength and vice versa of the device. The sensor is used for the detection of 0–524 parts per million (ppm) concentration of the CO₂ gas, with a maximum sensitivity of 17.32 pm (pico meter)/ppm achieved for a concentration of 366 ppm with a figure of merit (FOM) of 2.9 RIU⁻¹. The four-layer device presents a straightforward and compact design that can be adopted in various sensing applications by using suitable host functional materials.

In this paper, we present a new approach to design photonic crystal based optical filters using machine learning based mathematical model. The presented optical filter device finds its application in near infrared spectral range. The design and spectral response of the filter can be predicted using the proposed mathematical model which can considerably reduce simulation time and efforts. The numerical simulation of the optical filter device along with its spectral results and mathematical modeling are described.

This work investigates a Fano filter design based on a nano-hole array, patterned in fused silica using high-energy ultrafast femtosecond laser pulses. After carefully observing the experimental results, the structural profile of the nano-holes is numerically modeled in a 3D finite-difference time-domain-based software platform. The metasurface design consists of conical shaped air holes structured in the substrate, and a later deposited waveguide layer which leaves craters on the surface as the material fills inside the nano-holes. The spectral properties of the device are studied against variations in the structural parameters, such as the depth of the nano-holes, its surface diameter, and the depth of the craters on the surface of the waveguide. The proposed Fano filter device is designed to operate in the near-infrared (NIR) wavelength range around a telecommunication window of 1550 nm. Multiple narrowband resonances are observed with a linewidth in the range of 1.4 to 24.2 nm and a quality factor of 66.51 to 1090.12. The device shows good spectral tunability over a wide range from 1380 to 1650 nm comprising multiple narrowband resonances and variations in the structural parameters. Since the device can be implemented using a cost-effective and rapid fabrication method, it can be proposed for use in various optical filtering and sensing applications.