Theoretical analysis of sensitivity-tunable total-internal-reflection heterodyne interferometer

Theory and analysis of phase sensitivity-tunable optical sensor based on total internal reflection

The studies conducted on light emitting diode plant factories have mostly adopted hydroponics for convenient nutrient management and pest and disease prevention. In particular, in nutrient management, liquid electrolytes can be measured to determine the aqueous nutrient concentrations and absorption rates as well as electrical conductivity (EC) and pH variations. Precisely controlling the aqueous nutrient contents is crucial to large-scale healthy plant production. However, in most of the current conductivity measurements, electrodes are adopted for determining the nutrient additive concentrations. This approach can be problematic in some cases, such as low electrode sensitivity, which results in nutrient overdose, specifically in nonconductive additives, and hinders plant growth. Therefore, this paper proposes an optical method for measuring the aqueous nutrient contents. In this method, the high sensitivity of common-path heterodyne interferometry is incorporated into aqueous measurements to prevent errors caused by interfering impurities on the electrodes and improve measurement and analytical accuracy. The sensitivity of the sensor used in EC measurements can reach 2300°/mS $\cdot $ cm $^{-1}$ . The method has some merits, e.g., a simple optical setup, high stability etc., high measurement accuracy, high resolution, rapid measurement, and easy operation. In addition, its feasibility is demonstrated.

Application of Total Internal Reflection and Heterodyne Interferometry in Electrical Conductivity Measurements

A phase geographical map for determining a right-angle prism is presented. The proposed method is based on total-internal-reflection effects and chromatic dispersion. Under the total-internal-reflection condition, the phase difference between the S and P polarizations, as a function of the wavelength and refractive index, can be extracted and measured using heterodyne interferometry. Various wavelengths correspond to various refractive index values. The proposed map is convenient in ensuring the prism material using a specific V number. The method has the following merits: high stability, ease of operation, and rapid measurement.

https://ir.nctu.edu.tw:443/bitstream/11536/11781/1/000240355100019.pdf

Springfield Chang

Papers

Phase geographical map for determining the material type of a right-angle prism