Special section editors Shanti Bhattacharya, Akshay Naik, and Siddharth Tallur introduce the Special Section on MOEMS and Nanophotonics in India.

Shaping light to meet the needs of diverse optical applications is of utmost importance. Beam shaping allows one to alter the properties of light, enabling more complex behavior not possible with standard beams, such as Gaussian beams. Such beams have been generated using diffractive optics and more recently, meta-optics. For the latter, standard fabrication processes using electron beam lithography with the popular polymethyl methacrylate resist exist. However, there are several challenges due to the sub-wavelength features. We propose an alternate fabrication approach using a highly sensitive resist called mr-EBL resist. We show how the use of this resist reduces the patterning time, as well as the number of process steps. The process is explained with a case study on the fabrication of a meta-optical element that generates a modified Bessel beam with special properties.

We review the design and demonstration of distributed Bragg reflector (DBR)-based resonance filters developed at CoE-CPPICS, IIT Madras, with the in-house complementary metal oxide semiconductor (CMOS)-compatible silicon photonics technology platform. The proposed devices include two types of band-pass filter design approaches, i.e., the higher-order DBR coupled cavity filter and apodized DBR cavity filter with ultra-broad stopband for guided Fabry–Pérot resonance in a silicon-on-insulator rib waveguide structure. The device design parameters are optimized through semi-analytical simulation methods for a low insertion loss singly resonant transmission peak at a desired wavelength. Fourth- and fifth-order passive resonant filters are designed and demonstrated with nearly lossless, flat-top response (ripple <1 dB) with large out-of-band rejection (>40 dB), and a maximum shape factor of 0.9 without any active tuning. With optimized apodization parameters for the DBR cavity, a device of length as low as ∼35μm exhibits a large rejection band of ∼60 nm and an extinction of ∼40 dB at the resonant wavelength peak at λr∼1550 nm (FWHM ∼80 pm, IL ∼2 dB). The demonstrated devices are potential candidates for many integrated photonic applications such as microwave filters, modulators, add-drop multiplexers, sensors, and broadband noise suppression.

Four-wave mixing (FWM) in silicon photonics offers promising applications in optical signal processing, wavelength conversion, and quantum photonics, necessitating a comprehensive understanding of its underlying physics and limitations. Stimulated four-wave mixing in silicon photonic wire waveguides has been investigated theoretically by considering two-photon absorption, free carrier absorption, and free carrier dispersion, etc., operating near λ∼1550 nm. It has been shown that these effects severely degrade the performance when operating at higher pump power levels. We present exact numerical calculations of idler wavelength conversion efficiency and bandwidth taking into account the abovementioned nonlinearities, to show the effects of various parameters within the waveguide structure. We extended to investigate silicon photonic microring resonators in terms of the four-wave mixing performance of high-Q-value microring resonators, which are very promising as photon sources (spontaneous four-wave mixing) for large-scale quantum photonic circuits. Our analysis illustrates the limitations of analytical models in describing FWM in ring resonator behavior at a moderate input power level, necessitating a rigorous numerical approach. Experimentally, we demonstrate stimulated FWM (1525 nm≤λp≤1575 nm) in a silicon photonic wire with a cross-section of 500 nm×220 nm and with a small waveguide length of 2 mm. The idler-to-signal conversion efficiency of about −35 dB has been measured for an approximate launched pump power of 30 mW. The conversion efficiency is improved further in the microring resonator as predicted by the simulation results.

We demonstrate the use of cost-effective tapered telecommunication fiber in refractive index-based sensing when operated in the visible range of wavelength. To fabricate the tapered fiber, a two-step chemical-etching method is adopted. The two-step etching method is quintessential in overcoming issues such as the uncontrollable etching of Ge-doped silica fibers by hydrofluoric acid. The work details the optimization of the etching process. The tapered fiber is then chemically treated to immobilize gold nanoparticles on it. Finally, the performance of the proposed Au-immobilized tapered fiber sensor probe is studied when excited with visible light. Different concentrations of sucrose are used to detect the refractive index sensitivity. Performance parameters such as sensitivity, full-width half maximum, the figure of merit, and quality factor are determined for the sensor probe.