Gyroscopes are inertial sensors whose field of application is rapidly expanding. The growing interest in autonomous systems, CubeSats as well as their constellations, and unmanned vehicles is stimulating a strong interest in miniaturized gyroscopes for integration in inertial units with a volume smaller than 100 cm ³ . Some of these applications require gyroscopes that are highly immune to disturbances, especially vibrations, mechanical shocks, and radiation. In these application contexts, the use of microelectromechanical gyroscopes is often avoided in favor of sensors without moving parts, such as optical gyroscopes based on the Sagnac effect. The technology of interferometric optical gyroscopes is currently considered to be potentially capable of enabling the development of highly innovative angular velocity sensors, which are simultaneously inertial grade and miniaturized. This paper critically examines the scientific and R&D activity aimed at miniaturization of interferometric optical gyroscopes, focusing on recent results, perspectives, and physical limitations. Interferometric optical gyroscopes with dimensions similar to those of microelectromechanical gyroscopes and better performance than the latter in terms of immunity to disturbances have not yet been demonstrated, but this paper shows how this goal could be realistically achieved in the medium term through the use of integrated microphotonics. This paper compares the technology being analyzed with the competitive technologies, highlighting their strengths and limitations.

We demonstrate a cascaded Mach-Zehnder interferometer (MZI) based coarse wavelength division multiplexing (CWDM) (de)multiplexer on silicon-on-insulator with its spectral responses well aligned to the defined wavelength grids and are highly tolerant to the manufacturing linewidth variability. This was achieved by optimizing the waveguide widths and lengths of two arms in every MZI. As-realized CWDM (de)multiplexer exhibits a spectral shift of 0.487 nm, an insertion loss of less than 2.1 dB, and a channel crosstalk of lower than -20 dB consistently over the entire 8-inch wafer, while reference devices fabricated on the same chips suffer from serious spectral shift of 15.4 nm to the shorter wavelength and higher insertion loss/channel crosstalk. The proposed MZI design concept can be applied to all MZI-based photonic devices and related photonic integrated circuits, so this work validates a promising design path towards practical WDM applications on silicon-on-insulator.

Demand for rapid and massive-scale exfoliation of bulky graphite remains high in graphene commercialization and property manipulation. We report a procedure utilizing “preformed acidic oxidizing medium (PAOM)” as a modified version of the Hummers’ method for fast and reliable synthesis of graphene oxide. Pre-mixing of KMnO₄ and concentrated H₂SO₄ prior to the addition of graphite flakes enables the formation of effectively and efficiently oxidized graphene oxide (EEGO) featured by its high yields and suspension homogeneity. PAOM expedites diffusion of the Mn-oxidants into the graphite galleries, resulting in the rapid graphite oxidation, capable of oxidizing bulky graphite flakes (~0.8 mm in diameter) that can not be realized by the Hummers’ method. In the scale-up tests, ten-time amount of graphite can be completely exfoliated by PAOM without need of extended reaction time. The remarkable suspension homogeneity of EEGO can be exploited to deposit ultra-flat coating for wafer-scale nanopatterning. We successfully fabricated GO optical gratings with well-defined periodicity (300 nm) and uniform thickness (variation <7 nm). The combination of the facile and potent PAOM approach with the wafer-scale patterning technique may realize the goal for massive throughput graphene nanoelectronics.

Interferometric fiber optic gyroscope (IFOG) is advantageous for inertial navigation due to its high reliability as a solid-state technology with no moving parts. The size, weight, power, and cost of IFOG can be improved by employing photonic integration technology. Here, by leveraging the foundry-enabled silicon photonics platform, we demonstrate a silicon multi-function integrated optical circuit (Si-MIOC) with a fingertip size that can easily interfaces with light source and fiber coil to perform a tactical-grade gyroscope (0.1 °/hr bias instability). This achievement comes from the pros of high-index-contrast silicon waveguide that enables high polarization extinction ratio of > 60 dB and high electro-optic efficiency in silicon phase modulator, while the cons of the signature lead to non-negligible optical back-reflection at silicon/fiber interfaces and generate spurious bias voltage offset at the gyroscope outputs. Nevertheless, the results of earth rotation measurement and Allan deviation analysis confirmed that Si-MIOC based IFOG is a promising angular sensor and can be utilized to construct a compact and low-cost inertial measurement unit.

This work proposes a tunable reflective guided-mode resonant (GMR) filter that incorporates a 90° twisted nematic liquid crystal (TNLC). The GMR grating acts as an optical resonator that reflects strongly at the resonance wavelength and as an alignment layer for LC. The 90° TNLC functions as an achromic polarization rotator that alters the polarization of incident light. The resonance wavelength and reflectance of such a filter can be controlled by setting the angle of incidence and driving the 90° TNLC, respectively. The designed filter exhibits a very large spectral shift in resonance wavelength from 710 to 430 nm, which covers the entire visible spectrum. The transmittance can be tuned to within 10 V at various resonance wavelengths. The hybrid GMR - LC filter is compact, has a simple design, and is easy to fabricated. It can therefore be used in practical applications.

Uniform periodic structure formation over a large sample area has been challenging in laser interference lithography (LIL) mainly due to the Gaussian intensity distribution inherent to a laser beam. In this work, refractive beam shaping devices are applied in a Lloyd's interferometer to create a flat-top light field (2.8% intensity variation over an area of 20 × 20 cm2) for wafer-scale nanopatterning. Around 10−2 variation in fill factors are obtained for all the reported one dimensional and two dimensional periodic structures across a 2-in. wafer, which is 1 order of magnitude lower than the values obtained for the samples exposed to a Gaussian light field. The proposed LIL system also allows gradual light field transitions from the Gaussian, super-Gaussian, and flat-top to the inverse-Gaussian by simply adjusting the spot size of the laser incident to the beam shaper. The authors believe that the proposed LIL system can be applied for a variety of applications that benefit from the nature of periodic nanostructures.