Characterizations of displaying magnetic-fluid microelectromechanical light modulator with laser speckle technique

Abstract

The change of the thickness of magnetic fluid which modulates light intensity is the display principle of magnetic-fluid microelectromechanical light modulator which has two display states - light state and dark state. As a kind of non-contacting, non-destructive, and real-time testing method, laser speckle technique can be used to character the display process of magnetic-fluid microelectromechanical light modulator. In this paper, during displaying the magnetic-fluid microelectromechanical light modulator, a collimated laser beam is illuminated on it. Meanwhile, a charge-couple device (CCD) camera capable of 480*640 square pixels is used to real-timely record speckle patterns which can be used to character the state of the magnetic-fluid microelectromechanical light modulator, and the time interval of adjacent speckle patterns is 20 ms which is chosen depending on the transition speed the device changes from a dark state to a light state. 160 frames adjacent speckle patterns are chosen to be analyzed. The 80th, 160th, 320th (the middle columns), 480th, and the 640th columns are taken out separately from the chosen speckle patterns to obtain five THSP (Time History speckle pattern) images 480*160 pixels. Based on these five THSP images, the relationship between the change of light intensity and the change of time is got. Change of light intensity with time shows that: the change of light intensity of speckle patterns has a good agreement with the display state of magnetic-fluid microelectromechanical light modulator. laser speckle pattern technique is an efficient way to be applied to real-time test and character modulator. In one word, as for microelectromechanical system (MEMS) test, the laser speckle pattern technique will be a non-contact, real-time, and non-destructive optical method which have a rapid developing speed and a wide application in the future. © 2009 SPIE.