Optics: measuring and testing – Lens or reflective image former testing
Reexamination Certificate
2001-12-27
2004-08-03
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
Lens or reflective image former testing
Reexamination Certificate
active
06771362
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for measuring the optical parameters of phase objects. Specifically, the present invention provides a method and an apparatus that utilize the moiré effect, for determining the properties of various phase objects, particularly lenses.
BACKGROUND OF THE INVENTION
Moiré patterns are generated whenever there is overlap between two periodic structures consisting of alternating transparent and opaque regions. For example, a simple moiré pattern is observed when two sets of equally spaced straight lines are superimposed on one another such that a small angle exists between the lines of the two sets.
The art suggests a variety of technical and scientific applications based on the moiré effect, including the use of said effect for determining the optical features of lenses.
Oster et al. [Scientific American 208, p. 54-63 (1963)] and Nishijima et al. [Journal of the Optical Society of America, 54(1), p. 1-5 (1964)] disclose the use of the moiré effect for testing lenses. According to the methods described in these publications, the lens is interposed between two gratings exhibiting the moiré pattern. The presence of the lens alters the moiré pattern observed, the degree and nature of the alternation being related to the focal length of the lens.
Benton et al. [Optical Engineering, 15(4), p. 328-331, (1976)], describe an interferometer for lens testing that is based on the moiré effect. The device comprises a point source and a pair of gratings, the lens to be tested being placed in front of the first grating.
Bolognini et al. [Optica Acta., 32(4), p. 409-422(1985)] describe interferometry based on the Lau effect. According to the optical arrangements discussed in the paper, the lens under test is positioned in the space between the gratings.
U.S. Pat. No. 4,459,027 discloses a method and an apparatus for mapping an optical object, using the moiré effect. The critical characteristic of the arrangement according to U.S. Pat. No. 4,459,027 is that collimated rays pass through the lens to be tested. This is accomplished by using coherent light, which in practice is provided by a laser point source, and by introducing means for collimating said light to produce collimated rays therefrom. The object to be tested, that is, the lens, is placed in the path of said collimated rays prior to reaching two gratings capable of generating a moiré pattern. The moiré pattern observed is analyzed in order to derive the optical parameters of the lens therefrom.
It is an object of the present invention to provide an efficient optical arrangement for measuring the properties of phase objects, particularly lenses, using simple and low-cost equipment.
It is another object of the present invention to provide an optical arrangement for measuring the properties of phase objects, utilizing simple mathematical procedures.
It is yet another object of the present invention to provide an optical set-up allowing accurate and sensitive mapping of position-dependent properties of phase objects.
SUMMARY OF THE INVENTION
The inventors have found that a unique optical arrangement may be effectively used to determine the optical properties of a phase object. This optical arrangement is characterized in that gratings used to generate moiré patterns are placed between a source of diffuse light and the object to be tested. The inventors have also surprisingly found that using this novel arrangement, the optical properties of interest, such as the power of a given lens, are linearly related to certain quantities derivable from the moiré pattern, and that the proportionality coefficient of said linear relation is a constant depending on the geometrical features of said arrangement.
Thus, in one aspect, the present invention provides a method for measuring the optical parameters of a phase object, comprising recording a moiré pattern viewed through said phase object, said moiré pattern being formed by illuminating by means of a source of diffuse light, first and second gratings positioned in the space between said light source and said phase object, wherein the plane of said first grating is parallel to the plane of said second grating, and calculating the optical parameters of interest from said moiré pattern.
The term “phase object” as used herein refers to an object that neither absorbs light nor reflects it, but rather changes the phase of light or deflects it. Examples of phase objects that may be tested according to the present invention are lenses, glass plates, windshields, Perspex sheets, beamsplitters and goggles. The term “phase object”, as used herein, also embraces any medium that exhibits changes in its refractive index. Such medium may be a liquid or a crystalline solid. In a particularly preferred embodiment of the invention the phase object to be tested is a lens. The lens to be tested may be of any type, including (but not limited to): spherical lens, cylindrical lens, toric lens, progressive lens and multifocal lens.
The term “grating”, as used herein, refers to a periodic structure consisting of alternating transparent and opaque regions. Such grating may be provided in the form of a set of equally spaced straight lines, or in the form of a grid. Preferably, the first and second gratings are angularly oriented with respect to each other. According to a preferred embodiment of the invention, the first and second gratings are provided in the form of first and second grids, respectively, wherein each grid is obtained by overlapping two identical sets of equidistant parallel lines at an angle of 90°. Preferably, the periodicity of the sets of equidistant parallel lines forming the first grid is different from the periodicity of the sets of equidistant parallel lines forming the second grid.
The term “periodicity”, when used herein in relation to the gratings, refers to the length of a single period within the grating. A grating's period consists of an opaque region and the adjacent transparent region (e.g., the combined width of an opaque and adjacent transparent line). The term “periodicity”, when used herein in relation to the fringes displayed by the moiré pattern, refers to the length of a single fringe's period. One fringe period consists of a dark band and adjacent bright band observed in the moiré pattern. The term “spatial frequency”, as used herein, is proportional to the inverse of periodicity, and is given by the number of grating periods, or fringe periods, per unit of length. Preferably, the unit of length is the entire width or height of the recorded moiré pattern. The spatial frequency may be conveniently expressed by means vector quantities in the spatial frequency plane, the scalar components of said vector quantities corresponding to the number of grating's periods (or fringe periods) along the X and Y axes of said plane. These vector quantities are related to the second derivatives
∂
2
D
∂
x
2
,
∂
2
D
∂
y
2
,
∂
2
D
∂
x
∂
y
,
∂
2
D
∂
y
∂
x
of the wavefront of the beam exiting the phase object, which wavefront is designated D. The optical properties that are calculated according to the present invention depend linearly on the values of said derivatives.
According to a preferred embodiment of the invention, the gratings are illuminated by light that has been filtered, such that the light transmitted through the filter has a wavelength distribution in the form of a narrow band centered on a preselected wavelength &lgr;, and the two gratings are separated from each other by a distance d, given by d=n·p
1
p
2
/&lgr;, wherein n is an integer number (n=1, 2, 3 . . . ) and p
1
and p
2
indicate the periodicity of the first and second gratings, respectively.
According to a preferred embodiment of the invention, the recording of the moiré pattern generated between the images of the first and second gratings, said images being formed by the
Bavli Raanan
Keren Eliezer
Nixon & Vanderhye P.C.
Rotlex Ltd.
Stafira Michael P.
LandOfFree
Method and apparatus for testing and mapping phase objects does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for testing and mapping phase objects, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for testing and mapping phase objects will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3358625