Three-spherical-mirror test for radius of curvature measurement using a Fabry-Pérot cavity

Laser transverse dual differential confocal radius measurement with high efficiency and high precision

To meet the need for rapid, high-precision, and non-contact measurement of the radius of curvature (ROC) for large quantities of spherical optics, a radius measurement method based on transverse dual differential confocal (TDDC) detection is proposed in this study. First, a template S₀ with a known ROC, R₀, is axially scanned on its confocal position to obtain the fitted linear function lTDDC(z) using TDDC. Second, the template S₀ is replaced by Sn, which is one of the test sample in large quantities, then the single point TDDC intensity ITDDC(Δzn) is captured without scan, which will be applied to obtain the defocus Δzn according to the linear function lTDDC(z). Finally, the ROC Rn under test is calculated using Δzn and R₀. Simulation and experiments show that the measurement accuracy can achieve 8.0 ppm, and the measurement efficiency is 60 times higher than that of the traditional differential confocal scanning measurement. Measurement based on TDDC only requires scanning once and replacing Sn N times to realize the fast, high-precision, non-contact ROC detection of N pieces of spherical optics, which enables the high-efficiency and high-precision measurement of large quantities of spherical optics.

Diamond Structures for Tuning of the Finesse Coefficient of Photonic Devices

Finesse coefficient is one of the most important parameters describing the properties of a resonant cavity. In this research, a mathematical investigation of the application of diamond structures in a fiber-optic Fabry–Perot measurement head to assess their impact on the finesse coefficient is proposed. We present modeled transmission functions of cavities utilizing a nitrogen-doped diamond, a boron-doped diamond, nanocrystalline diamond sheet and a silver mirror. The diamond structures were deposited using a microwave plasma-assisted chemical vapor deposition system. A SEM investigation of surface morphology was conducted. The modeling took into consideration the fiber-optic Fabry–Perot setup working in a reflective mode, with an external cavity and a light source of 1550 nm. A comparison of the mathematical investigation and experimental results is presented.