Diffusing imager and associated methods

A diffusing function and a lens function are provided on a single surface. Such a structure may be formed from a computer generated hologram including free form regions having a phase shift associated therewith, i.e., the computer generated hologram being shifted within the free form regions by the phase shift relative to the computer generated hologram outside the free form regions. When the computer generated hologram includes zero and .pi. regions, the zero and .pi. regions may be transposed within the free form regions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to an optical element having a single 
surface which both diffuses light and has optical power. 
2. Description of Related Art 
Diode lasers, LEDs and other light sources produce beams having a 
nonuniform power distribution. This non-uniformity is often detrimental to 
performance of a system. It is difficult to achieve uniform power 
distribution using a conventional lens system. Elements which could be 
used to re-map the power distribution to one having uniform illumination 
are desirable for many applications. 
It is advantageous to use a diffractive diffuser as shown in FIG. 1, to 
provide the desired uniform illumination. The diffractive diffuser in FIG. 
1 is discussed in detail in U.S. application Ser. No. 08/770,524 entitled 
"Beam Homogenizer" filed Dec. 20, 1996, which is hereby incorporated by 
reference in its entirety. In FIG. 1, an incident optical beam 14, 
preferably a collimated beam, illuminates a diffractive diffusing element 
10. The diffractive diffusing element is preferably a computer-generated 
hologram having irregularly patterned, free-form fringes of diffractive 
gratings 12. The diffractive fringes 12 of the preferred embodiment are 
made up of plateaus 16, shown as white areas and presenting a phase shift 
of zero at the design wavelength to the input beam 14, and vias or valleys 
18, shown as black areas and presenting a phase shift of .pi. at the 
design wavelength to the input beam. Such a homogenizer eliminates 
undesired intensity variations encountered when using a homogenizer having 
regularly shaped, regularly patterned facets. 
The diffractive diffuser 10 transmits transmittal beams 11a, 11b, 11c 
having a preselected angular spread which provides a beam having uniform 
illumination at a target 20 in an output plane 22. The output plane 22 
represents an area in space rather than any particular element. It would 
be possible to place another optical element or any device which would 
make use of the output beam downstream. Any area of sufficient size, i.e., 
to insure that the full range of line widths present in the pattern, at 
any position on the diffuser 10 will provide this angular spread to the 
input beam 14. Each area of sufficient size is nominally uncorrelated to 
another area of similar size. The choice of angular spread depends upon 
the application for which the homogenizer is used and the desired output 
beam. 
Often, it is desirable to deflect or focus an image, as well as to diffuse 
it. However, due to space considerations for some applications, it is not 
convenient to insert an additional optical element for providing diffuse 
illumination. Further, there is an additional expense associated with 
making an additional element. 
SUMMARY OF THE INVENTION 
The present invention is therefore directed to an optical element, and 
associated systems and methods, which substantially overcomes one or more 
of the problems due to the limitations and disadvantages of the related 
art. 
It is therefore an object of the present invention to provide a diffractive 
diffusing optical element in a single surface which can map non-uniform 
illumination into more uniform illumination and perform additional optical 
functions on the input light. The integration of both diffusing and other 
optical functioning on a single surface provides advantages such as space 
savings and does not increase the cost over making a diffractive 
performing only the other optical functions, since no additional surface 
needs to be made. The surface incorporating the diffusing function is 
created during the design phase and the resulting element costs the same 
to manufacture as an optical element without the diffusing function 
incorporated therein. 
At least one of these and other objects may be realized by providing an 
optical element including a computer generated hologram for performing at 
least one lens function and at least one diffusing function, the computer 
generated hologram including free form regions having a phase shift 
associated therewith, the computer generated hologram being shifted within 
the free form regions by the phase shift relative to the computer 
generated hologram outside the free form regions, the computer generated 
hologram being on a first surface of the optical element. 
The computer generated hologram outside the free form regions may include 
zero regions and .pi. regions, the zero regions and .pi. regions being 
transposed within the free form regions. The at least one lens function 
may include at least one of focusing and deflecting. The optical element 
may further include features provided on a second surface of the optical 
element opposite the first surface and aligned with the computer generated 
holograms. The features may also perform the at least one lens function. 
The features may include a Fresnel lens. The phase shift may be .pi.. 
At least one of the above and other objects may be realized by providing a 
method of making a diffractive diffusing lens, including generating a 
computer hologram pattern in accordance with a desired lens function and a 
diffusing function, the computer hologram including a plurality of free 
form regions having a phase shift associated therewith, within the free 
form regions, the computer hologram is shifted by the phase shift relative 
to the computer hologram outside the free form regions, and manufacturing 
the diffractive diffusing lens in accordance with the computer hologram 
pattern. 
The manufacturing may include photolithographic processing. The 
manufacturing includes injection molding. The generating may include 
transposing the computer hologram within the free form regions. 
At least one of the above and other objects may be realized by providing an 
optical system including a light source, transmit optics for delivering 
light from the light source to a target, and return optics for receiving 
light from the target, wherein at least one of the transmit optics and the 
return optics includes a diffractive diffusing lens providing diffusion 
and at least one lens function on a single surface. 
The transmit optics and return optics may be integrated on a single 
substrate. The diffractive diffusing lens may include a computer generated 
hologram for performing at least one lens function and at least one 
diffusing function, the computer generated hologram including free form 
regions having a phase shift associated therewith, the computer generated 
hologram being shifted within the free form regions by the phase shift 
relative to the computer generated hologram outside the free form regions, 
the computer generated hologram being formed on the single surface. The 
transmit optics may include the diffractive diffusing lens. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
While the present invention is described herein with reference to 
illustrative embodiments for particular applications, it should be 
understood that the present invention is not limited thereto. Those having 
ordinary skill in the art and access to the teachings provided herein will 
recognize additional modifications, applications, and embodiments within 
the scope thereof and additional fields in which the invention would be of 
significant utility without undue experimentation. As used herein, the 
term "lens function" means a function having optical power. 
FIG. 2 illustrates a configuration incorporating the optics of the present 
invention. A light source 28, preferably a light emitting diode, emits 
light toward a transmit optical apparatus 30. The transmit optical 
apparatus 30 delivers light to a target 34. Light reflected by the target 
34 is delivered to a detector 38 via a return optical apparatus 36. 
Preferably, the optical apparatuses 30, 36 are integrated on a common 
substrate 40, and the light source 28 and the detector 38 are integrated 
on a common substrate 42. As can be seen in the configuration of FIG. 2, 
the transmit optical apparatus 30 focuses the light from the light source 
28 onto the target 34. 
Further details of the optics are shown in FIGS. 3A and 3B. The top view in 
FIG. 3A illustrates the integration of the optical apparatuses 30, 36 onto 
a single substrate 40. As shown in the side view of FIG. 3B, the return 
optical apparatus 36 includes a diffractive element 44 on a first surface 
and a refractive element 45 on a second surface. 
As can also be seen in the side view of FIG. 3B, the transmit optical 
apparatus 30 includes a diffractive element 46 on a first surface thereof 
and a Fresnel element 47 on a second surface thereof. Both of these 
elements 46, 47 are needed in the transmit path due to the large 
deflection angle required in the configuration shown in FIG. 2. Without 
the use of the diffractive element 46, total internal reflection greatly 
limits the amount of power that can be directed onto a target. If only the 
diffractive element 46 is used, the large deflection angle required will 
result in greatly reduced diffraction efficiency. 
A diffusing element is also incorporated into the diffractive element 46 on 
the first surface. Thus, the diffractive element 46 serves three 
functions. It will provide approximately half of the required deflection 
angle. It will aid in focusing light onto the target. It will diffuse and 
homogenize the light to a more uniform intensity distribution in the 
illumination region of the target. 
A binary mask 48a for making a diffractive for performing a lens function 
is shown in FIG. 4A. Hatched regions 52 present a phase shift of zero and 
white regions 54 present a phase shift of .pi. to the design wavelength. 
These regions or fringes respectively correspond to plateaus and vias on 
the surface itself. In the design shown in FIG. 4A, adjacent hatched or 0 
regions and white or .pi. regions have the approximately the same width. 
If only two levels are desired in the diffractive diffusing lens, then the 
lens will look like this mask 48. The annular fringes required to create a 
diffractive for performing the lens functions may be computer generated in 
a conventional manner. 
A binary mask 48b for making a diffractive diffuser is shown FIG. 4B. An 
example of a diffractive diffuser that would be made from such a mask is 
shown in FIG. 1. The hatched regions 53 present a phase shift of .pi. and 
the white regions 55 present a phase shift of zero to the design 
wavelength. These regions or fringes respectively correspond to vias and 
plateaus on the surface itself. If only two levels are desired in the 
diffractive diffuser, then the lens will look like this mask 48b. Such a 
diffuser may be designed as set forth in U.S. application Ser. No. 
08/770,524. Generally, these regions may be described as free form 
regions. The use of free form regions to provide the diffusing function 
eliminates undesired intensity variations due to sharp edges between the 
.pi. and 0 regions. 
A binary mask 48c for making a diffractive element 46 incorporating lens 
functions, such as deflection and focusing, as well as the diffusing 
function is shown in FIG. 4C. In accordance with the present invention, 
the diffusing imager may be created by adding the phases of the two 
functions forming the masks shown in FIGS. 4A and 4B. Such an addition 
results in shifting the base lens function pattern 54 within the .pi. 
regions 53, creating shifted regions 56, to form a diffractive diffusing 
lens on a single surface. In the zero regions 55 of the diffusing mask 
48b, the lens function pattern 54 is unaffected. In the specific example 
of a portion of a mask 48c shown in FIG. 4c, the 0 regions 52 and the .pi. 
regions 50 within the diffuser .pi. regions 53 are shifted in the 
resultant shifted regions 56 sufficiently so that they appear transposed 
from those in the lens function region 54. 
The shifting resulting from the incorporation of the diffusing function 
will result in a slight loss of power from the base lens function, i.e., 
the point will be slightly blurred. The blur is due to the fact that while 
a lens maps to a point, the diffuser maps to a region, as described above 
in connection with FIG. 1. The amount of blur will depend on the design of 
the diffuser. In order to achieve the diffusing function preferably 
between approximately 5% and 50% of the surface is encompassed by the 
shifted regions. 
The mask 48c may be used in accordance with U.S. Pat. No. 4,895,790, the 
entirety of which is hereby incorporated by reference, to create optical 
elements having plateaus and vias using binary masks. Further, U.S. Pat. 
No. 5,202,775, which is hereby incorporated by reference in its entirety, 
discloses a method of fabricating holograms using photolithography and 
U.S. application Ser. No. 08/381,169, which is hereby incorporated by 
reference in its entirety, discloses a method of fabricating diffractive 
elements using injection molding. The mask may thus be used with a variety 
of methods to form the diffractive diffusing lens in accordance with the 
present invention. 
An actual diffractive diffusing lens in accordance with the present 
invention is shown in FIG. 5. The element 58 shown in FIG. 5 can be made 
using two or three masks, depending on the technique used, and has four 
levels or regions, the white or .pi. region 50, presenting a phase shift 
of .pi., the large dot region 57 presenting a phase shift of .pi./2, the 
black or 0 regions 52, and the small dot region 59 presenting a phase 
shift of 3 .pi./2. All of the noted phase shifts are at the design 
wavelength. The .pi./2 and 3 .pi./2 regions will actually appear as gray 
regions, but the dots were used to facilitate visibility. As with the mask 
48c, the element 58 has lens function or original regions 54 and shifted 
regions 56, in which the base lens function pattern is shifted to provide 
the diffusing function. In the example shown in FIG. 5, the shifting in 
the free form regions 56 is two levels from the original regions 54. 
Each mask used to create the element 58 does not have to have the diffusing 
function incorporated therein. The element 58 shown in FIG. 5 only had one 
mask with the diffusing function incorporated with the base lens function, 
i.e., mask 48c shown in FIG. 4. The other masks were for forming only the 
base lens function. Preferably, if only one mask has the diffusing 
function incorporated, it is the mask for the primary or biggest etch. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.