[21a-C304-1~9] 4.2 Photonics Devices, Photonic Integrated Circuit and Silicon Photonics

▲ [21a-C304-7] Oscillating optical fiber speckle patterns

〇Eric Fujiwara¹, Carlos Suzuki¹ (1.UNICAMP)

Keywords:Optical fiber speckle, Optical fiber sensor, Instrumentation

Multimode optical fibers excited by coherent light produce speckle patterns (specklegrams) due to the interference between several modes. The specklegrams carry detailed information about the fiber state, enabling applications in imaging and sensing. However, reflection-type setups generate a peculiar pattern that cycles around well-defined states. This work investigates such a phenomenon by modeling the system as an extrinsic multimode Fabry-Perót interferometer. Changes in cavity parameters (length, refractive index, and light wavelength) yield a phase shift that modulates every fiber mode, causing the oscillatory specklegram behavior. Conversely, disturbances in the fiber probe (due to bending, for example) modify the speckle pattern systematically, affecting both DC and AC components of the correlation curve. Under controlled conditions, one may use this setup as a straightforward physical/chemical sensor or spectrum analyzer, avoiding expensive optical instrumentation.