A Thickness Measurement Method for Biological Samples using Lensed-Fiber Sensors

We present a simple fiber-optic confocal method for high-precision thickness measurement of optically transparent and non-transparent objects that require noncontact measurement. The method is based on measurement of confocal back-reflection responses from the opposite surfaces of objects, which imposes inessential limitations on the shape, thickness, and transparency of testing objects. A novel reference comparison method to eliminate additional errors existing commonly in confocal microscope designs is adapted. The measurement error highly depends on the axial response of confocal microscope, and was measured to be 5.0 mu m using a single-mode optical fiber construction, 60x objective lenses, and a 658-nm-wavelength laser source. We demonstrate the method using lensed-fiber sensors, which reduces the size of the experimental setup so that the method can be utilized for smaller samples at in-vivo situation. We demonstrate the proof-of-concept measurement using biological samples.