Tarek Rahman

Achieving achromaticity across the visible light spectrum is crucial for metalenses in imaging systems. Single-layer metalenses struggle with weak focusing power or small aperture sizes due to inadequate group delay control. Multilayer metalenses offer some improvement but come with increased design and fabrication complexity. Here, we demonstrate a strategy using meta-atoms with material layers engineered for matching dispersion, allowing large and fine adjustments of group delay. Our design substantially broadens the group delay range, allowing us to experimentally demonstrate several polarization-independent metalenses operating across the entire visible spectrum (400-700 nm). We design, fabricate, and characterize achromatic metalenses with aperture diameters of 16 μm, 66 μm, 200 μm, and 400 μm, and numerical apertures of 0.27, 0.11, 0.04, and 0.02, respectively. Among them, the 400-μm diameter, 0.02-numerical-aperture metalens is used to demonstrate full-color imaging capabilities. Our results exhibit diffraction-limited performance, high efficiency, and accurate full-color image reproduction.

Light fields carry a wealth of information, including intensity, spectrum, and polarization. However, standard cameras capture only the intensity, disregarding other valuable information. While hyperspectral and polarimetric imaging systems capture spectral and polarization information, respectively, in addition to intensity, they are often bulky, slow, and costly. Here, we have developed an encoding metasurface paired with a neural network enabling a normal camera to acquire hyperspectro-polarimetric images from a single snapshot. Our experimental results demonstrate that this metasurface-enhanced camera can accurately resolve full-Stokes polarization across a broad spectral range (700 to 1150 nanometer) from a single snapshot, achieving a spectral sensitivity as high as 0.23 nanometer. In addition, our system captures full-Stokes hyperspectro-polarimetric video in real time at a rate of 28 frames per second, primarily limited by the camera’s readout rate. Our encoding metasurface offers a compact, fast, and cost-effective solution for multidimensional imaging that effectively uses information within light fields.

The metasurfaces have shown great potential for miniaturizing conventional optics while offering extended flexibility. Recently, there has been considerable interest in using algorithms to generate meta‐atom shapes for these metasurfaces, as they offer vast design freedom and not biased by the human intuition. However, these complex designs significantly increase the difficulty of fabrication. To address this, we introduce a design process that rigorously enforces the fabricability of both the material‐filled (fill) and empty (void) regions in a metasurface design. This process takes into account specific constraints regarding the minimum feature size for each region. Additionally, it corrects any violations of these constraints across the entire device, ensuring only minimal impact on performance. Our method provides a practical way to create metasurface designs that are easy to fabricate, even with complex shapes, hence improving the overall production yield of these advanced meta‐optical components.

We present a compact polarization splitter on a dual hollow-core antiresonant fiber with broad bandwidth covering two well-known communication wavelengths of 1.31 μm and 1.55 μm. It can achieve excellent polarization splitting performances in a simpler optimized single-layer geometry compared to the related splitters and for the first time, simultaneously offers a very short splitter length of 21.52 mm and a broad bandwidth of 340 nm by maintaining an extinction ratio higher than 20 dB. It also achieves the highest extinction ratio of 140 dB at 1.55 μm and maintains a standard single mode performance. Therefore, the proposed splitter has the potentiality to be a promising candidate for the integrated optical devices in communication systems.

We demonstrate the direct generation of focused transverse spin of light with a metasurface fully controlling the vectorial properties of the transmitted light field through sub-wavelength pixelized manipulation of phase, polarization, and amplitude independently.

We experimentally demonstrate photonic integrated visible full-color meta-holograms based on guided wave-driven metasurfaces with complete phase-and-amplitude control capability. Our lightweight and compact meta-holograms can be potentially used for virtual/augmented/mixed reality near-eye displays.

A photonic crystal fiber based highly sensitive sensing mechanism is proposed, in the terahertz frequency band, able to detect a wide range of analytes, such as toxic or non-toxic chemicals and illicit drugs. The proper optimization of the PCF structure increases the light-matter interaction in the core, which results in a high relative sensitivity of about 94.0% with negligible confinement loss at the optimum frequency. Few liquids, chemicals, and drugs are considered to justify the sensing mechanism: a relative sensitivity of 99.60% can be achieved for the maximum porosity of core while ketamine was the analyte. Other fiber properties are also analyzed to check the feasibility of the proposed fiber with standard fiber and have obtained good performance. Therefore, the sensor may find applications to sense a wide range of analytes, non-toxic and toxic chemicals, as well as illicit drugs for example, in the THz region.