A metasurface is a layer of subwavelength‐scale nanostructures that can be used to design functional devices in ultrathin form. Various metasurface‐based optical devices – coined as flat optics devices – have been realized with distinction performances in research laboratories using electron beam lithography. To make such devices mass producible at low cost, metasurfaces over a large area have also been defined with lithography steppers and scanners, which are commonly used in semiconductor foundries. This work reviews the metasurface process platforms and functional devices fabricated using complementary metal‐oxide‐semiconductor‐compatible mass manufacturing technologies. Taking both fine critical dimension and mass production into account, the platforms developed at the Institute of Microelectronics (IME), A*STAR using advanced 12‐inch immersion lithography have been presented with details, including process flow and demonstrated optical functionalities. These developed platforms aim to drive the flat optics from lab to fab.

The demonstration of a color display metasurface on a 12-inch silicon wafer with critical dimension (CD) below 100 nm by complementary metal-oxide semiconductor (CMOS) compatible technology is reported for the first time. The 193 nm ArF deep UV immersion lithography is leveraged instead of electron beam lithography (EBL) to pattern the metasurface, which greatly improves the efficiency while keeping a high resolution. The demonstrated metasurface successfully generates the resonant modes and reflects the lights at resonance wavelengths, giving its display in red, green, and blue (RGB) colors. The wafer-level uniformities of CD and reflection characteristic of the metasurface are measured and analyzed. The experimental data show that they are well controlled in the fabrication process. The work provides a promising route towards mass production of dielectric metasurfaces.

Metalenses made of artificial sub‐wavelength nanostructures have shown the capability of light focusing and imaging with a miniaturized size. Here, we report the demonstration of mass‐producible amorphous silicon metalenses on a 12‐inch glass wafer via the complementary metal‐oxide‐semiconductor compatible process. The measured numerical aperture of the fabricated metalens is 0.496 with a focusing spot size of 1.26 μm at the wavelength of 940 nm. The metalens is applied in an imaging system to test the imaging resolution. The minimum bar of the resolution chart with a width of 2.19 μm is clearly observed. Furthermore, the same system demonstrates the imaging of a fingerprint, and proofs the concept of using metalens array to reduce the system size for future compact consumer electronics.

New methods in optogenetics^{1 – 3} and, especially, the advent of fluorescent reporters of neuronal activity, have opened many novel approaches for actuating and recording neural activity en masse, through the use of powerful free-space single-photon and multi-photon microscopy methods.^{4 – 8} However, existing approaches to functional imaging of the brain have significant limitations. Single-photon (1P) epifluorescence imaging readily lends itself to high frame-rate wide-field microscopy, but, in its simplest implementations, image contrast is hampered by out-of-focus background fluorescence, and the depth of imaging is restricted by the optical attenuation in the tissue. Confocal imaging improves the contrast by optical sectioning, and out-of-focus light is rejected using a pinhole; however, a laser beam must be scanned across each point of the tissue and this significantly slows the image acquisition rate.⁹ Multi-photon microscopy is also inherently a point or line scanning method, but because it uses infrared excitation (which provides a longer optical attenuation length⁵), the imaging depth in brain tissue can be extended to $\sim 1\mathrm{mm}$ and the focus of the light beam can be rastered in three-dimensions to achieve volumetric imaging.^{5,10 – 12}

In this paper, we report a compact wavelength-flattened directional coupler (WFDC) based chemical sensor featuring an incorporated subwavelength grating (SWG) structure for the mid-infrared (MIR). By incorporating a SWG structure into directional coupler (DC), the dispersion in DC can be engineered to allow broadband operation which is advantageous to extract spectroscopic information for MIR sensing analysis. Meanwhile, the Bragg reflection introduced by the SWG structure produces a sharp trough at the Bragg wavelength. This sharp trough is sensitive to the surrounding refractive index (RI) change caused by the existence of analytes. Therefore, high sensitivity can be achieved in a small footprint. Around fivefold enhancement in the operation bandwidth compared to conventional DC is achieved for 100% coupling efficiency in a 40 µm long WFDC experimentally. Detection of dichloromethane (CH₂Cl₂) in ethanol (C₂H₅OH) is investigated in a SWG-based WFDC sensor 136.8 µm long. Sensing performance is studied by 3D finite-difference time domain (FDTD) simulation while sensitivity is derived by computation. Both RI sensing and absorption sensing are examined. RI sensing reveals a sensitivity of −0.47% self-normalized transmitted power change per percentage of CH₂Cl₂ concentration while 0.12% change in the normalized total integrated output power is realized in the absorption sensing. As the first demonstration of the DC based sensor in the MIR, our device has the potential for tertiary mixture sensing by utilizing both changes in the real and imaginary part of RI. It can also be used as a broadband building block for MIR application such as spectroscopic sensing system.

Acousto-optic (AO) modulation technology holds significant promise for applications in microwave and optical signal processing. Thin-film scandium-doped aluminum nitride (AlScN), with excellent piezoelectric properties and a wide transparency window, is a promising candidate for achieving on-chip AO modulation with a fabrication process compatible with complementary metal-oxide-semiconductor (CMOS) technology. This study presents, to the best of our knowledge, the first demonstration of AO modulators with surface acoustic wave generation and photonic waveguides monolithically integrated on a 400-nm-thick film of AlScN on an insulator. The intramodal AO modulation is realized based on an AlScN straight waveguide, and the modulation efficiency is significantly enhanced by 12.3 dB through the extension of the AO interaction length and the utilization of bidirectional acoustic energy. The intermodal AO modulation and non-reciprocity are further demonstrated based on a multi-mode spiral waveguide, achieving a high non-reciprocal contrast (>10 dB) across an optical bandwidth of 0.48 nm. This research marks a significant stride forward, representing an advancement in the realization of microwave photonic filters, magnet-free isolators, and circulators based on the thin-film AlScN photonic platform.