Noise reduction techniques, fractional bi-spectrum and fractional cross-correlation, and applications

Abstract

A measurement method and system include illuminating an object to be measured with light at two different wavelengths and an incident angle; capturing an image of the object; detecting a frequency of an interference pattern from the image using Fractional Bi-Spectrum Analysis; and calculating a thickness of the object based on the Fractional Bi-Spectrum Analysis. The thickness is calculated based on a relationship between the thickness and the frequency of the interference pattern. The Fractional Bi-Spectrum Analysis is performed on a linear medium with the two different wavelengths being known.

Description

FIELD OF THE DISCLOSURE[0001]The present invention relates to the field of noise reduction. More specifically, the invention relates to noise reduction, optical measurements, and interferometry.BACKGROUND OF THE DISCLOSURE[0002]Laser interferometry has tremendous applications in several fields including manufacturing and biology. One of the serious limitations of this technique is the inherent speckle noise in laser interferometry of rough surfaces. Waves reflected or transmitted by rough surfaces result in unclear interference pattern. Therefore speckle noise reduction is an important step in laser interferometry of the rough surfaces. Many methods have been proposed over the years to compensate the speckle noise in laser interferometric based technologies such as optical coherent tomography, synthetic aperture radar (SAR), ultrasound, etc. One proposed technique to suppress the speckle noise is moving the aperture of the camera. This technique averages the speckle pattern and redu...

AI Technical Summary

Benefits of technology

The patent describes a method and system for measuring the thickness of an object by illuminating it with light of two different wavelengths and capturing an image. The interference pattern of the light is detected using a special analysis method, which calculates the thickness of the object based on the frequency of the interference pattern. This method is useful for measuring the thickness of objects that have a linear structure.

Problems solved by technology

Conventionally, there are several techniques to calculate the phase and magnitude of a signal from its computed bi-spectrum, although all of these techniques require huge amount of computation and are very time consuming.

Physically, in order to have a non-zero value for the bi-spectrum, the medium needs to possess a property to produce a frequency component at f1+f2, therefore for linear medium this techniques is not applicable and bi-spectrum does not contain any useful information of the signal.

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