Interferometric Navigation with Quadrature Optical Bias
Publication Date: 2007-Jan-31
The IP.com Prior Art Database
A simple, low cost technique is described for biasing an interferometer in quadrature, which is particularly applicable to navigation applications involving semiconductor laser sources and low cost optics, as in a computer mouse.
Interferometric Navigation with
Quadrature Optical Bias
David Dolfi, Michael Tan, and Michael Brosnan, Avago Technologies
Abstract: A simple, low cost technique is described for biasing an interferometer in quadrature, which is particularly applicable to navigation applications involving semiconductor laser sources and low cost optics, as in a computer mouse.
The biasing technique we describe in this paper is relevant to the use of interferometric techniques for optical navigation on a surface, in particular when the surface is very smooth, as would be the case for a glass table top. Such techniques  have employed two beam interferometers, in particular of the shearing variety, or order to crate an interference pattern from features on the surface which are navigable. Figure 1 below shows a shearing plate interferometer, in which the fromt and rear surfaces sulloy the two beams which interfere to give a pattern in their overlap region which is related to the shape and texture of the surface at the left of the figure from which the light is reflected, and which can be used to navigate over the surface.
Figure 2 shows a similar arrangement in which a Michaelson interferometer configuration is used. Here, one beam is provided by the surface while the other is provided by a fixed mirror. Again, the interference pattern is related to the shape and texture of the surface. There are other interferometer geometries (for example, Mach-Zehnder) which will give similar results.
In all such two beam systems, the received optical power Pr at any point in the field of view has a sinusoidal transmission characteristic with respect to the optical phase difference f of the two beams, of the form shown below in Figure 3.
The sensitivity of the interferometer to small changes in phase (in this application, to small changes in the surface features) is greatly enhanced if the interferometer can bge made to operate at the steep part of the slope of Fig 3, the so-called quadrature biasing condition. This can be most straightforwardly accomplished by adjusting the relative path length difference of the two beams at some reference point in the field of view. In the case of the shearing interferometer, this would be accomplished by contr...