Contents lists available at ScienceDirect Optik journal homepage: www.elsevier.com/locate/ijleo Realization of a highly sensitive multimode interference effect- based fiber-optic temperature sensor by radiating with a Vortex beam Arijit Datta a, *, Ardhendu Saha b a Department of Electrical & Electronics Engineering, CMR Institute of Technology, Bengaluru, Karnataka, 560037, India b Department of Electrical Engineering, National Institute of Technology, Agartala, Barjala, Jirania, Tripura, (West), 799046, Tripura, India ARTICLE INFO Keywords: Fiber optic sensors Vortex beam Multimode interference Fiber optic applications Temperature sensor High sensitivity ABSTRACT In this research, an ultra-high sensitive multimode interference-based fiber-optic temperature sensor is unveiled by radiating with a Vortex beam. The efficient excitation of several high-order modes within the waveguide structure has been affirmed by using the classical wave-optic model. By exploiting the advantages of Vortex beam, the difference in transmitted output power is de- termined for various surrounding temperatures, ranging from 28 °C–100 °C. To corroborate our theoretical study, an Eigenmode expansion solver (EME) propagation analysis has been carried out in commercially offered Mode solution software (Lumerical Inc.) to investigate the propa- gation characteristics of Vortex beam inside the waveguide structure. Our simulation outcome reflects a maximal temperature sensitivity of 0.14 dB/°C with a commendable sensing resolution of ∼0.07 °C. When compared to the conventional Gaussian beam-based sensor, such sensitivity of the proposed temperature sensor was found to be enhanced by a factor of about 3.5. Finally, we presented the systematic study describing the impact of fiber radius, order of Vortex beam, and waist size of input field on the sensor response. On account of such superior sensing per- formance, the proposed idea expedites new possibilities in any sort of physical, chemical or biological sensing needs. 1. Introduction Over the years, the multimode interference (MMI) effect has been the key interest of researchers due to several advantageous properties like compactness and light weight, highly sensitive, cost-effectiveness, resistance to electromagnetic interference, high response time, easiness in multiplexing and so on [1–3]. In the year of 1979, Layton et al. first demonstrated the MMI as a sensing tool to detect acoustic wave in a multimode fiber where the variation in phase shift was measured involving two interfering waveguide modes [4]. In 1995, Soldano et al. suggested the concept of multimode interference in integrated optical devices by using the self- imaging principle [5]. Later, Mohammed et al. first conceptualized a new fiber-based wavelength-tunable condensing lens by ex- ploiting multimode interference and self-imaging principle [6]. In [7], Wang et al. demonstrated the concept of multimode inter- ference as a refractometer where a refractive index sensing resolution of 5.4 × 10 -5 RIU (refractive index unit) and 3.3 × 10 -5 RIU was realized over the refractive index range of 1.33–1.45 and 1.38–1.45, respectively. In 2008, Q. Wang and co-workers provided a rigorous and detailed theoretical outline for a Single-mode-Multimode–Single-mode (SMS) fiber structure by using guided-mode https://doi.org/10.1016/j.ijleo.2020.165006 Received 21 April 2020; Received in revised form 15 May 2020; Accepted 22 May 2020 ⁎ Corresponding author. E-mail address: arijit.datta048@gmail.com (A. Datta). Optik - International Journal for Light and Electron Optics 218 (2020) 165006 0030-4026/ © 2020 Elsevier GmbH. All rights reserved. T