Point-of-use refractometer using self-mixing optical feedback interferometry with predictive measurement for flowmetry applications
摘要
The refractive index is a critical parameter in conducting cellular-level operations in microscale fluidic devices. Higher diffusion rate and use of minuscule samples make these devices an evident choice for point-of-use applications. The main challenge in realizing these devices is maintaining their form factor at a low cost. To address this issue, SM-OFI is being widely explored to design microfluidic flowmetry devices for refractive index measurement due to its portability and less expensive structure. However, measuring the dynamic refractive index of the different concentrated samples is still a limitation for SM-OFI. In this paper, the authors present an Auto-Regressive Least Mean Squares (AR-LMS) signal processing algorithm to measure the refractive index of a sample using SM-OFI. The proposed method takes advantage of the AR-LMS algorithm’s predictive capabilities to analyze the interferometric signal. The method was validated using a 650 nm VCSEL on samples with different refractive indices, flowing through a Perspex tube under a controlled flow rate. The samples were prepared using distilled water, benzyl chloride, and methylene iodide for static refractive index, and aqueous NaCl samples for dynamic refractive index. To test the method’s efficiency, a comprehensive statistical study has been conducted. The study confirmed the robustness of the measurement scheme with standard errors of 2.14 × 10–3, 1.99 × 10–3, and 1.79 × 10–3 for distilled water, benzyl chloride, and methylene iodide, respectively. Whereas for linearly incremented refractive index, the proposed measurement scheme showcased an R2 value of 0.9995 and a standard error of 0.0022 with a resolution of 0.0152.