This paper is an overview of current gyroscopes and their roles based on their applications. The considered gyroscopes include mechanical gyroscopes and optical gyroscopes at macro- and micro-scale. Particularly, gyroscope technologies commercially available, such as Mechanical Gyroscopes, silicon MEMS Gyroscopes, Ring Laser Gyroscopes (RLGs) and Fiber-Optic Gyroscopes (FOGs), are discussed. The main features of these gyroscopes and their technologies are linked to their performance.

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Redirecting the flow of light on the basis of the absorption/gain properties of optical systems is of great interest in many research fields, ranging from optical routing to optical cloaking. In this paper we investigate the control of the direction of the light propagation through loss-induced absorption in passive linear coupled optical systems. The considered optical system consists of a mode-splitting resonant cavity formed by coupling a Fabry-Perot (FP) cavity with a ring resonator. The coalescence of the asymmetric resonances, generated through mode-splitting dynamics, is the spectral result of the parity time symmetry breaking at FP resonance wavelengths. For specific values of the FP overall loss, a predominant backward propagation in the FP ring resonator occurs. In fiber optics technology, this device shows an ability to invert the sense of propagation of the light, quantified through the contrast ratio, in the order of 20 dB. This value can be obtained by externally varying the FP loss coefficient for a fixed set of the other physical parameters of the FP ring resonator. Our results can open a new way toward novel high-performance optical modulation and routing schemes.

Recently, non-Hermitian Hamiltonians have gained a lot of interest, especially in optics and electronics. In particular, the existence of real eigenvalues of non-Hermitian systems has opened a wide set of possibilities, especially, but not only, for sensing applications, exploiting the physics of exceptional points. In particular, the square root dependence of the eigenvalue splitting on different design parameters, exhibited by 2 × 2 non-Hermitian Hamiltonian matrices at the exceptional point, paved the way to the integration of high-performance sensors. The square root dependence of the eigenfrequencies on the design parameters is the reason for a theoretically infinite sensitivity in the proximity of the exceptional point. Recently, higher-order exceptional points have demonstrated the possibility of achieving the nth root dependence of the eigenfrequency splitting on perturbations. However, the exceptional sensitivity to external parameters is, at the same time, the major drawback of non-Hermitian configurations, leading to the high influence of noise. In this review, the basic principles of PT-symmetric and anti-PT-symmetric Hamiltonians will be shown, both in photonics and in electronics. The influence of noise on non-Hermitian configurations will be investigated and the newest solutions to overcome these problems will be illustrated. Finally, an overview of the newest outstanding results in sensing applications of non-Hermitian photonics and electronics will be provided.

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