Laser image refractive index sensor based on the combination of a coreless optical fiber and a digital camera

As a laser passes through a scattering medium, the light interacts with the irregular reflections within the medium, resulting in light scattering and the formation of speckles. In this paper, an image sensor based on the combination of a coreless optical fiber and a digital camera is proposed for liquid refractive index sensing applications. The coreless fiber is used as a sensing unit, and the change in the speckle pattern is measured using the digital correlation method to detect the magnitude of the liquid’s refractive index. The experimental results indicate that the laser image sensing technique is capable of effectively distinguishing liquid samples with refractive indices ranging from 1.332 8 to 1.390 8, with a sensing sensitivity of −1.306 RIU⁻¹. Moreover, the laser image sensing technique, with its advantages of high experimental reproducibility, simple system design, remote over-control, holds great research significance and potential application in laser communication and sensor integration.