Optical surface measurements of a wavelength-tuned Fizeau interferometer based on an optical power, real-time feedback and compensation system

Abstract

The wavelength-tuned Fizeau interferometer achieves the desired phase for interferograms based on the use of a phase-shifting technique. It can then use it to measure the surface and thickness of a parallel transparent object. However, phase errors occur owing to the inherent changes of the power of the tunable laser diode induced upon laser wavelength changes. To improve the measurement accuracy, we propose an optical power, real-time feedback control system, and a synchronous calibration scheme. The significance of the proposed method relies on the fact that the laser intensity variation can be detected quickly and compensated by adjusting the bias voltage. To verify the effectiveness of the proposed system, we incorporated it into the optical system of the wavelength-tuned, phase-shifting interferometer for experimentation. The control principles and the experimental validation of the proposed system are described in this letter.

Keywords

• Wavelength-tuned interferometer
• Phase error
• Real-time
• Light intensity modulation