WO2001065305A1

WO2001065305A1 - Fresnel zone plate with multiple layers of delay zones

Info

Publication number: WO2001065305A1
Application number: PCT/US2000/042621
Authority: WO
Inventors: Kan Cheng
Original assignee: Kan Cheng
Priority date: 2000-03-01
Filing date: 2000-12-06
Publication date: 2001-09-07
Also published as: AU2001245189A1

Abstract

The present Fresnel zone plate is comprised of a base plate (20), and a plurality of layers or orders (21, 22, etc.) of transparent phase delay zones arranged on the base plate. The zones of each succeeding order are narrower than those of the previous order, and are thinner to provide half the delay of the previous order. The radii of the zone boundaries are defined by the boundary formula Sj(n) = ∑(bμn)/2j-1, where j = integers representing order number, n = boundary number, b = focal length, and μ = wavelength. The innermost zone boundary is boundary number 1. The phase delays introduced by the delay zones are defined by the delay formula (0.5j+k)μ, where j = integers representing order number, k = is preferably 0 but may be any integer, and μ = wavelength. For example, with 3 orders of delay zones, the first order provides a 1/2μ delay, the second order provides a 1/4μ delay, and the third order provides an 1/8μ delay. Since each succeeding order is narrower than the previous order, a combination of 7 distinct delays are provided, from 1/8μ to 7/8μ, in 1/8μ increments. The delay increments are thus fine enough to correct most of the phase differences in the waves that passed through the zone plate to produce 97.5 % of the amplitude and 95 % of the intensity of an ideal lens. Alternative embodiments include a concave zone plate (35-37), a zone plate with linear delay zones (40-42), a reflective zone plate (80-84), and a flat prism (85-87).

Description

TITLE OF THE INVENTION

Fresnel Zone Plate with Multiple Layers of Delay Zones

APPLICANT

Kan Cheng

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. application number 09/291,725, filed 4/14/99, now abandoned.

BACKGROUND OF THE INVENTION

1. Field Of The Invention:

This invention relates generally to Fresnel zone plates.

2. Prior Art:

In Fig. 1, when a beam of light is projected through a transparent plate 10 from a point source S to a focal point P on a wall. Rays V and W passing through the outer portions of plate 10 have longer optical paths and thus greater phase delays relative to the reference center ray U. The intensity at point P is represented by a vibration curve in Fig. 2. The curve follows cosine law and spirals toward a center point Y for a net amplitude OY.

If plate 10 is replaced with an ideal lens, the intensity at the focal point is represented a vibration curve in Fig. 3. The ideal lens is able to focus the light beam into a sharp point, as well as keep the light waves in phase with each other, that is, the ideal lens is able to concentrate 100% of the light beam's energy at the focal point without any loss. Using the first 360 degrees of amplitude as an example, the ideal lens is able to correct a curve OPQSO to a straight line OP'Q'S'Y or OY. If the radius of the curve is 1, the theoretical amplitude limit of the ideal lens is OY = 2 x π = 6.28. A conventional curved lens is far from ideal because of manufacturing limitations.

In addition to curved lenses, a flat lens known as a Fresnel zone plate can focus light according to the principles of Fresnel diffraction. As shown in Fig. 4, it is comprised of a flat plate 11 with a pole O, and alternating circular transparent zones 12 and circular dark or opaque zones 13. When light from a point source S is passed through plate 1 1, it is diffracted by the edges of the dark zones to form a focal point P. Light waves that pass through pole O travel a path b to focal point P, and light waves that pass through the outer parts of the plate travel a longer path r to focal point P. Since r > b, there is a phase difference δ between the light waves as follows:

δ s = s_{n 2} ,

where λ is the wavelength of the light. Where the waves are in phase or constructive with each other, they add together to produce a wave of greater amplitude. Where the waves are out of phase or destructive with each other, i.e., offset by a half a wavelength or π (180 degrees), they cancel out each other. The light waves alternate between constructive and destructive in imaginary concentric circular zones around pole O. As shown in a vibration curve in Fig. 5, negative contribution or destructive zones represented by the dashed lines appear periodically between 180 and 360 degrees, i.e., every half wavelength. The destructive zones reduce the total amplitude of the transmitted light. When the destructive zones are darkened into dark zones 13, as shown in Fig. 4, destructive waves are blocked, and only constructive waves are passed through transparent zones 12. For a zone plate with a transparent center zone or zone 1, zones 2, 4, 6, etc. are blocked, as represented by the dashed lines in Fig. 5. The in-phase waves are combined with each other to produce a point of light of an increased amplitude OY.

By putting δ = π (phase difference ^"*= half a wavelength) and a = ∞ in the above equation, the Fresnel zone plate is found to have a focal length b as follows: λ

where Si is the radius of the first boundary between the central zone and the next zone, and λ is the wavelength of the light. Accordingly, the radius s* is as follows:

The radii of the boundaries between the transparent and dark zones are chosen so that the phase difference of the waves passing through them is half a wavelength between adjacent boundaries. For the second zone, δ = 2π, and 2πbλ = πs Thus the radius s₂ of the second zone is as follows:

s₂ = V2bλ = s, J2 •

Accordingly, the radii of the boundaries are as follows:

where n = 1, 2, 3, 4 ... (consecutive positive integers).

The flat Fresnel zone plate is used as a focusing lens. It is much less expensive than a conventional optical lens with curved surfaces. However, it blocks half the incoming light. The vibration curve in Fig. 5 shows that, for its first 360 degrees of amplitude, OY = 2, so that it produces only 32% of the amplitude and 10% of the intensity of an ideal lens for which OY = 6.28.

An improved Fresnel zone plate 14 is shown in Fig. 6. It includes a transparent base plate 15, and concentric transparent rings 16 arranged on base plate 15 in place of the dark zones. Radiation slows when it is passing through a transparent substance, and resumes its original speed after leaving the transparent substance. The waves passing through only base plate 15 are slowed by the same amount. The waves passing through rings 16 and also base plate 15 have to travel through more transparent substance, so that they are slowed further relative to the waves passing through only base plate 15. Depending on its refractive index, rings 16 are made thicker than base plate 15 by a suitable amount to delay incoming destructive waves by half a wavelength (λ/2 or π), so that after the waves are passed through the zone plate, the waves in all zones are generally in phase with each other when they reach focal point P. Rings 16 are thus delay zones that introduce a half wavelength delay to the waves in the otherwise destructive zones to generally match the phase of the waves in the constructive zones.

The improved Fresnel zone plate is still far from ideal. The waves within each zone are still out of phase with each other, because the waves at the inner border of the zone have to travel a shorter distance than the waves at the outer border of the zone. The improved Fresnel zone plate in Fig. 6 has wide zones that cannot correct the phase differences within each zone to focus the light sharply. A vibration curve in Fig. 7 shows that for its first 360 degrees of amplitude, OY = 4, so that it produces only 64%> of the amplitude and 41%> of the intensity of an ideal lens for which OY = 6.28.

OBJECTS OF THE INVENTION

Accordingly, objects of the present Fresnel zone plate are: to provide a low cost lens for focusing radiation; to provide improved focus, increased amplitude, and increased intensity at low cost; to provide a low cost prism for refracting radiation; and to be relatively flat and lightweight.

Further objects of the present invention will become apparent from a consideration of the drawings and ensuing description. BRIEF SUMMARY OF THE INVENTION

The present Fresnel zone plate is comprised of a base plate, and a plurality of layers or orders of transparent phase delay zones arranged on the base plate. The zones of each succeeding order are narrower than those of the previous order, and are thinner to provide half the delay of the previous order. The radii of the zone boundaries are defined by the boundary formula S_j(n) = -J(bλn) /2 , where j = integers representing order number, n = boundary number, b = focal length, and λ = wavelength. The innermost zone boundary is boundary number 1. The phase delays introduced by the delay zones are defined by the delay formula (0.5^** + k)λ, where j = integers representing order number, k =^*** is preferably 0 but may be any integer, and λ = wavelength. For example, with 3 orders of delay zones, the first order provides a l/2λ delay, the second order provides a l/4λ delay, and the third order provides an l/8λ delay. Since each succeeding order is narrower than the previous order, a combination of 7 distinct delays are provided, from l/8λ to 7/8λ, in l/8λ increments. The delay increments are thus fine enough to correct most of the phase differences in the waves that passed through the zone plate to produce 97.5%) of the amplitude and 95% of the intensity of an ideal lens. Alternative embodiments include a concave zone plate, a zone plate with linear delay zones, a reflective zone plate, and a flat prism.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Fig. 1 is a top perspective view of a prior art lens.

Fig. 2 is a vibration curve for the lens of Fig. 1.

Fig. 3 is a vibration curve of a prior art ideal lens.

Fig. 4 is a top perspective view of a prior art Fresnel zone plate.

Fig. 5 is a vibration curve of the Fresnel zone plate of Fig. 4. Fig. 6 is a top perspective view of an improved prior art Fresnel zone plate.

Fig. 7 is a vibration curve of the improved Fresnel zone plate of Fig. 6.

Fig. 8 is a side view of the present Fresnel zone plate with two orders of delay zones.

Fig. 9 is an alternative embodiment of the zone plate of Fig. 8.

Fig. 10 is a vibration curve of the zone plates of Figs. 8 and 9.

Fig. 11 is a side view of the present Fresnel zone plate with three orders of delay zones.

Fig. 12 is an alternative embodiment of the zone plate of Fig. 1 1.

Fig. 13 is a vibration curve of the zone plates of Figs. 1 1 and 12.

Fig. 14 is another embodiment of the zone plate of Fig. 8.

Fig. 15 is an alternative embodiment of the zone plate of Fig. 14.

Fig. 16 is another embodiment of the zone plate which acts as a concave lens.

Fig. 17 is an alternative embodiment of the zone plate of Fig. 16.

Fig. 18 is another embodiment of the zone plate with linear zones.

Fig. 19 is another embodiment of the zone plate arranged for focusing full color light.

Fig. 20 is an alternative embodiment of a color filter of Fig. 19.

Fig. 21 is a side view of the zone plate of Fig. 19.

Fig. 22 is an alternative arrangement of the delay zones of Fig. 21. Fig. 23 is a red light vibration curve of the zone plate of Fig. 22.

Fig. 24 is a blue light vibration curve of the zone plate of Fig. 22.

Fig. 25 is another embodiment of the zone plate combined with a mirror.

Fig. 26 is another embodiment of the zone plate arranged as a prism.

DETAILED DESCRIPTION OF THE INVENTION

Figs. 8-10:

A first embodiment of the present Fresnel zone plate is arranged to function as a convex lens, and is shown in a side view in Fig. 8. It is preferably round, but it may be in other shapes. Half the plate is shown. The other half is symmetrical about the centerline or axis on the left. It is comprised of a transparent base plate 20, a first layer or order of transparent annular delay zones 21 arranged on one side of base plate 20, and a second layer or order of delay zones 22 arranged on an opposite side of base plate 20. The delay zones in each order are alternated with gaps.

The zone plate is made of any suitable material which is transparent to the type of radiation for which it is used. All radiation slows when passing through a transparent material, and resumes its original speed after exiting the material. The delay zones delay the waves passing through them relative to the waves passing only through the base plate, so that all the waves are generally in phase with each other after passing through the zone plate for improving amplitude and intensity at the focal point.

The boundaries of the delay zones have radii or perpendicular distances S_j(n), where j = integers 1, 2, 3, 4, etc. representing the order number, and n = boundary number. The terms "radius" or "radii" herein encompass the distance from the center of the plate to a zone boundary of any shape, even if it is not round. The first delay zone of each order is preferably within the first boundary, which has a radius S_j(l) as follows:

where j = integers representing order number, b = focal length, and λ = wavelength. The radii S_j(n) of the other boundaries are equal to the square roots of consecutive positive integers multiplied by the radius of the first boundary s* . The formula is as follows:

where n = boundary number, e.g., 1, 2, 3 ... (consecutive positive integers). The general formal for the radii of all zone boundaries is as follows:

_c , bλn

where j = integers representing order number, n = boundary number, b = focal length, and λ = wavelength. The delay zones of each order are all about the same thickness, and have parallel opposite faces. The delay zones of each order have a generally identical thickness selected to provide a predetermined phase delay in the waves. Each succeeding order has narrower zones than the previous order, and is thinner to provide half the delay of the previous order.

The delays introduced by respective orders of delay zones are defined by the delay formula as follows:

(0.5^J + k)λ,

where j = integers representing order number, k = is preferably 0 but may be any integer, and λ = wavelength. An alternative arrangement of a two order plate is shown in Fig. 9. First order delay zones 21 and second order delay zones 22 are on the same side of base plate 20. The radii and delays of all the zones follow the same formulas described in conjunction with Fig. 8. First order zones 21 and second order zones 22 are shown as distinct elements in Fig. 9 for clarity, but they may be made without any delineation between them.

For either embodiment in Fig. 8 or Fig. 9, first order delay zones 21 provide a l/2λ delay, and second order delay zones 22 provide a l/4λ delay. Since second order delay zones 22 are narrower than first order delay zones 21, a combination of 3 distinct delays are provided: 3/4λ, l/2λ, and l/4λ in a repeating, descending sequence in an outward direction. The delay increments are finer than prior art Fresnel zone plates for correcting more of the phase differences in the waves that pass through the zone plate. The resulting vibration curve is shown in Fig. 10. As an example, the first 360 degrees of amplitude is corrected from OPQSO to OP'Q'S'Y, and OY = 5.656. Since an ideal lens has OY = 6.28, a two order zone plate produces 90.1% of the amplitude and 81.2% of the intensity of the ideal lens.

The zone plate can be of any diameter and have any number of zones as long as the boundaries are properly proportioned. The zone plate may be made of any suitable material which is transparent to a selected range of electromagnetic radiation, including gamma rays, x-rays, ultraviolet rays, visible light, infrared waves, microwaves, and radio waves. E.g., an acrylic plate is transparent to visible light, whereas a wood plate is transparent to x-rays.

For full color applications, RGB color filters can be respectively used with or added to three separate zone plates. The output from the zone plates are combined into a full color image using any suitable technique known in the art.

Figs. 11 -13:

Another embodiment of the zone plate is shown in Fig. 1 1 with first order delay zones 25 arranged on one side of a first base plate 26, second order delay zones 27 arranged on an opposite side of base plate 26, and third order delay zones 28 arranged on one side of a second base plate 29. Although the orders are comprised of a series of diminishing delays, they may be arranged in any sequence, e.g., the second order may be on a different plate than the first order, and the third order may be on the same plate as the first order, etc. The radii and delays of all the zones follow the same formulas described in conjunction with Fig. 8.

An alternative arrangement of the three order plate is shown in Fig. 12. All the delay zones are on the same side of base plate 26. The radii and delays of all the zones follow the same formulas described in conjunction with Fig. 8. The different order delay zones are shown as distinct elements in Fig. 12 for clarity, but they may be made without any delineation between them.

For either embodiment in Fig. 1 1 or Fig. 12, first order delay zones 25 provide a l/2λ delay, second order delay zones 27 provide a l/4λ delay, and third order delay zones 28 provide a l/8λ delay. Since the zones of each succeeding order are narrower than those of the previous order, a combination of 7 distinct delays are provided, from l/8λ to 7/8λ, in l/8λ increments. The delay increments are thus fine enough to correct most of the phase differences in the waves that pass through the zone plate. The resulting vibration curve is shown in Fig. 13. As an example, the first 360 degrees of amplitude is corrected from OPQSO to OP'Q'S'Y, and OY = 6.123. Since an ideal lens has OY = 6.28, a three order zone plate produces 97.5% of the amplitude and 95%> of the intensity of the ideal lens. Additional orders of delay zones may be provided for providing performance even closer to the ideal lens. If necessitated by manufacturing limitations, fewer orders of delay zones may be provided toward the periphery than nearer the center of the zone plate.

Figs. 14-15:

Another alternative embodiment is shown in Fig. 14. First order delay zones 30 are arranged on one side of a base plate 31, and second order delay zones 32 are arranged on the opposite side of base plate 31. However, first order delay zones 30 are reversed with respect to those in Fig. 8, that is, first order delay zones 30 start between the first and second boundaries s*(l) and s*(2) instead of within the first boundary as in Fig. 8. Second order delay zones 32 start within the first boundary s₂(l) just as in Fig. 8. The delay zones are arranged to order the effective phase delays in a repeating, descending sequence, such as l/4λ, Oλ, 3/4λ, l/2λ, l/4λ, Oλ, and so on in an outward direction.

All the orders of delay zones can be alternatively arranged on the same side of base plate 31, as shown in Fig. 15. The delay zones are shown as distinct elements in Fig. 15 for clarity, but they may be made without any delineation between them. Additional orders of delay zones may be provided, wherein the delay zones of any order may start within the first boundary, or between the first and second boundaries, independently of the starting point of the other orders.

Figs. 16-17:

Another alternative embodiment shown in Fig. 16 is arranged to function as a concave lens. First order delay zones 35 are arranged on one side of a base plate 36, and second order delay zones 37 are arranged on the opposite side of base plate 36. However, the delay zones are reversed with respect to those in Fig. 8, that is, the first delay zone in each order is between the first and second boundaries, so that the effective delays are repetitively arranged in an ascending sequence, such as Oλ, l/4λ, l/2λ, 3/4λ, 0, l/4λ, l/2λ, and so on in an outward direction. All the orders of delay zones can be alternatively arranged on the same side of base plate 36, as shown in Fig. 17. The delay zones are shown as distinct elements in Fig. 17 for clarity, but they may be made without any delineation between them.

Fig. 18:

Another embodiment of the zone plate is shown in Fig. 18. It is comprised of linear first order delay zones 41 arranged on one side of a base plate 40, and linear second order delay zones 42 arranged on the opposite side of base plate 40. The distances between the zone boundaries to the center of the plate are according to the radius formula described in conjunction with Fig. 8. Accordingly, the terms radius or radii also apply to linear delay zones. Alternatively, all the orders of delay zones may be provided on the same side of base plate 40 (not shown). The first delay zone of each order may be within the first boundary as shown, or between the first and second boundaries, such as described in conjunction with Figs. 14 and 15.

Figs. 19-24:

Although separate RGB color filters can be used with three separate zone plates for focusing full color visible light, another embodiment is shown in Fig. 19 for focusing full color visible light with a single zone plate.

It is comprised of a color filter 45 axially aligned with a zone plate 46. Color filter 45 may be separate from zone plate 46, or it may be attached to zone plate 46. Color filter 45 may also be integrated with zone plate 46 as a single unit, for example, zone plate 46 may be made of a translucent color material. They may be round, square, or other shapes. Color filter 45 may be on either side of zone plate 46. Further, zone plate 46 may include delay zones on a single plate or a plurality of plates.

Color filter 45 is divided into red segments 47, green segments 48, and blue segments 49 which are duplicated many times throughout the filter. Color filter 45 is preferably divided into many small and even segments for even and unidirectional color blending. The color segments are shown in a radial arrangement in Fig. 19. Other arrangements are possible, such as the one shown in Fig. 20 in which red segments 50, green segments 51, and blue segments 52 have radial and annular divisions.

For the particular arrangement of color filter 45 shown in Fig. 19, zone plate 46 is divided into zone segments 53-55 respectively aligned with red, green, and blue segments 47-49. The radii of the zone boundaries in each zone segment follow the radii formula already described in conjunction with Fig. 8. As shown in Fig. 19, the zone boundaries are different between zone segments 53-55 because of the difference in wavelengths between red, green, and blue light. Among visible light, red light has the longest wavelength, green light has an intermediate wavelength, and blue light as the shortest wavelength. Therefore, the boundaries range from the widest for zone segment 53 for red light to the narrowest for zone segment 55 for blue light.

Since the thickness of a delay zone is proportional to the wavelength of the light, the different delay zones on the zone plate segments are of different thickness for providing suitable delays. A l/2λ delay zone for longer wavelength red light must be thicker than a l/2λ delay zone for shorter wavelength green light. As shown in Fig. 21, if delay zones of only a single thickness are provided on each side of a base plate, first order delay zones comprising l/2λ red delay zones 60, l/2λ green delay zones 61, and l/2λ blue delay zones 62 must be arranged on different sides of base plates 63 and 64; second order delay zones comprising l/4λ red delay zones 65, l/4λ green delay zones 66, and l/4λ blue delay zones 67 must be arranged on different sides of base plates 64 and 68. The orders may be arranged on different base plates than in the example shown. Additional orders of delay zones may be provided on additional base plates.

Alternatively, the delay zones for different colors but of the same order may be arranged on the same side of a base plate 70, as shown in Fig. 22. For example, first order delay zones comprising l/2λ red delay zones 71, l/2λ green delay zones 72, and l/2λ blue delay zones 73 are arranged on the same side of base plate 70; and second order delay zones comprising l/4λ red delay zones 74, l/4λ green delay zones 75, and l/4λ blue delay zones 76 are all arranged on the opposite side of base plate 70. The delay zones on each side of base plate 70 may be of the same thickness for simplicity. The thickness may be chosen for providing an accurate delay for a selected color. As an example, when the delay zones are of the correct thickness for green light, they are of the wrong thickness for red light and blue light. Amplitude losses for red light and blue light are respectively shown as out-of-phase vibrations curves in Figs. 23 and 24. Since green light is between red light and blue light in wavelength, the amplitude loss is minimal when the delay zones are sized for green light. The amplitude loss can be equalized by the color filter. Fig. 25:

Another alternative embodiment is comprised of zone plates 80 and 81, and a mirror 82 positioned on one side of zone plate 80. Mirror 82 may be attached to zone plate 80 as shown, or it may be separated from it. Since light passing through zone plates 80 and 81 is reflected by mirror 82 to pass through them a second time, delay zones 83 and 84 are half as thick as those of non-reflective zone plates to provide the same phase delay. For example, a l/2λ delay is provided by a l/4λ thick delay zone, a l/4λ delay is provided by a l/8λ thick delay zone, etc. The delay formula is as follows:

0.5(0.5^J + k)λ,

where j ^*= integers representing order number, k = is preferably 0 but may be any integer, and λ = wavelength.

Fig. 26:

Another alternative embodiment shown in Fig. 26 is arranged as a prism for diffracting light. A two order prism is shown as an example, but additional orders may be provided. Linear first order delay zones 85 are arranged on one side of a base plate 86, and linear second order delay zones 87 are arranged on an opposite side of base plate 86. Alternatively, both orders may be arranged on the same side of the base plate. Unlike previous embodiments which function as lenses to focus light, the prism is not symmetrical about an axis or centerline. The spatial relationship between the different orders of delay zones is as shown throughout the prism. The delay formula is as follows:

(0.5^J + k)λ,

where j ^*= integers representing order number, k = is preferably 0 but may be any integer, and λ = wavelength. The formula for the diffraction angle θ is as follows: λ λ sinθ = — = d 2^Js,

where λ = wavelength, j = integers representing order number, s = width of a single delay zone, and d = total width of all delay zones for one full period and is fixed for a selected diffraction angle and wavelength, d is also defined as follows:

d = 2^Js.

The width s_} of a single delay zone of each order is as follows:

λ

^J sin θ2^J

where j = integers representing order number, θ = desired diffraction angle, and λ = wavelength.

Fig. 27:

Another alternative embodiment shown in Fig. 27 is arranged as a reflective prism for reflecting and diffracting light. A two order prism is shown as an example, but additional orders may be provided. Linear first order delay zones 90 are arranged on one side of a first base plate 91, and linear second order delay zones 92 are arranged on an opposite side of base plate 91. A mirror 93 is arranged on a second base plate 94 for reflecting light. Alternatively, all the orders of delay zones may be arranged on one side of first base plate 91, and mirror 93 may be arranged on the other side of first base plate 91.

The delay formula is as follows:

0.5(0.5^J + k)λ, where j = integers representing order number, k = is preferably 0 but may be any integer, and λ = wavelength. The formula for the diffraction angle θ and the widths d and s are the same as those already described in conjunction with Fig. 26.

SUMMARY AND SCOPE

Accordingly, a Fresnel zone plate with multiple layers of delay zones is provided. It functions as a low cost lens for focusing radiation. It provides improved focus, increased amplitude, and increased intensity at low cost. It provides a low cost prism for refracting radiation. It is also relatively flat and lightweight.

Although the above description is specific, it should not be considered as a limitation on the scope of the invention, but only as an example of the preferred embodiment. Many variations are possible within the teachings of the invention. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents, not by the examples given.

Claims

CLAIMSI claim:

1. A zone plate for correcting phase differences in a beam of electromagnetic radiation, comprising: a transparent base plate; and a plurality of orders of transparent delay zones arranged on said base plate; wherein said delay zones in different ones of said orders are of different thickness to introduce different phase delays to different parts of said beam of electromagnetic radiation; wherein all of said delay zones have outer surfaces which are generally parallel to each other and to said base plate; wherein said outer surfaces of said delay zones of different orders are on different planes; and wherein said delay zones in each of said orders are spaced apart from each other and bound by respective zone boundaries.

2. The zone plate of claim 1, wherein all of said delay zones are generally symmetrical about an interior portion of said base plate; wherein a radius S_j(n) of each of said zone boundaries is defined as follows:

^■*»> ^*- •

where j = integers representing order number, n = boundary number, b = focal length, and λ = wavelength; wherein said delay zones in each of said orders have a predetermined thickness to provide a phase delay which is defined as follows:

(0.5^J + k)λ,

where j = integers representing order number, k = any integer, and λ = wavelength; wherein said plurality of orders of said delay zones are adapted to correct phase differences in finer increments than a single order prior art zone plate for improved amplitude and intensity.

3. The zone plate of claim 1, wherein said delay zones comprise annular zones concentric about a central point.

4. The zone plate of claim 1 , wherein said delay zones comprise generally linear zones symmetrical about a central point.

5. The zone plate of claim 1 , wherein said delay zones in each of said orders are arranged to provide said different phase delays in a repeating and descending order in an outward direction from an interior portion of said base plate, thereby said zone plate is adapted to function as a convex lens.

6. The zone plate of claim 1, wherein said delay zones in each of said orders are arranged to provide said different phase delays in a repeating and ascending order in an outward direction from an interior portion of said base plate, thereby said zone plate is adapted to function as a concave lens.

7. The zone plate of claim 1, wherein a first order of said delay zones generally provides a l/2λ phase delay, and subsequent orders of said delay zones each generally provides half as much delay as a previous one of said delay zones.

8. The zone plate of claim 1, wherein fewer orders of said delay zones are provided toward a periphery of said base plate than toward a center of said base plate for easier manufacturing.

9. The zone plate of claim 1 , wherein a first order of said delay zones starts between first and second ones of said zone boundaries.

10. The zone plate of claim 1, further including a color filter generally axially aligned with said base plate; wherein said color filter comprises a plurality of groups of color segments; and wherein each of said groups comprises a red segment, a green segment, and a blue segment.

11. The zone plate of claim 1 , further including a color filter generally axially aligned with said base plate; wherein said color filter comprises a plurality of groups of color segments; wherein each of said groups comprises a red segment, a green segment, and a blue segment; and wherein said groups are arranged between radial divisions radiating from an interior portion of said base plate.

12. The zone plate of claim 1, further including a color filter generally axially aligned with said base plate; wherein said color filter comprises a plurality of groups of color segments; wherein each of said groups comprises a red segment, a green segment, and a blue segment; and wherein said groups are arranged between radial and annular divisions respectively radiating from and coaxial with an interior portion of said base plate.

13. The zone plate of claim 1, further including a color filter generally axially aligned with said base plate; wherein said color filter comprises a plurality of groups of color segments, each of said groups comprising a red segment, a green segment, and a blue segment; wherein said delay zones in each of said orders are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; wherein radii of said zone boundaries in each of said zone segments are sized for a predetermined wavelength of a corresponding color light; and wherein said zone boundaries in said zone segments for red light are widest, said zone boundaries in said zone segments for green light are narrower, and said zone boundaries in said zone segments for blue light are narrowest.

14. The zone plate of claim 1, further including a color filter generally axially aligned with said base plate; wherein said color filter comprises a plurality of groups of color segments, each of said groups comprising a red segment, a green segment, and a blue segment; wherein said delay zones in each of said orders are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; wherein said zone segments corresponding to different ones of said color segments are of different thickness for providing corresponding phase delays for different color light; wherein said zone segments for red light are thickest, said zone segments for green light are thinner, and said zone segments for blue light are thinnest.

15. The zone plate of claim 1, further including a color filter generally axially aligned with said base plate; wherein said color filter comprises a plurality of groups of color segments, each of said groups comprising a red segment, a green segment, and a blue segment; wherein said delay zones in each of said orders are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; wherein all of said zone segments have a single predetermined thickness for providing a generally correct phase delay for a predetermined color light.

16. The zone plate of claim 1, further including a mirror positioned a side of said base plate; wherein said delay zones in each of said orders have a predetermined thickness to provide one of said phase delays which is defined as follows:

0.5(0.5^J + k)λ,

where j = integers representing order number, k = any integer, and λ = wavelength.

17. The zone plate of claim 1, wherein said zone plate is adapted to function as a prism; wherein said delay zones in each of said orders comprise generally linear zones of generally a predetermined thickness to provide one of said phase delays which is defined as follows:

(0.5^J + k)λ,

where j = integers representing order number, k = any integer, and λ = wavelength; wherein said delay zone are arranged to provide a diffraction angle θ defined as follows:

λ λ sinθ

2^Js

where λ = wavelength, j = integers representing order number, s = width of each of said delay zones in each of said orders, and d = total width of all delay zones for one full period and is fixed for a selected diffraction angle and wavelength; wherein d is also defined as follows:

d = 2^Js.

where width s_} of each of said delay zones in each of said orders is defined as follows:

λ ^sι ⁼ >

^J sin θ2^J

18. The zone plate of claim 1, further including a mirror arranged a side of said base plate, so that said zone plate is adapted to function as a reflective prism; wherein all of said delay zones in each of said orders comprise generally linear zones of generally a single predetermined thickness to provide a phase delay which is defined as follows:

0.5(0.5^j + k)λ,

λ λ sinθ = — =^*

2's.

d = 2^J _Sj ;

where width s, of each of said delay zones in each of said orders is defined as follows:

λ s, =-

^J sin θ2^J '

19. A zone plate for correcting phase differences in a beam of electromagnetic radiation, comprising: one or more transparent base plates with a plurality of axially aligned sides; and a plurality of orders of transparent delay zones arranged on said base plates; wherein said delay zones in different ones of said orders are of different thickness to introduce different phase delays to different parts of said beam of electromagnetic radiation; wherein all of said delays zones have outer surfaces which are generally parallel to each other and to said base plates; wherein said delay zones in each of said orders are spaced apart from each other and bound by respective zone boundaries; wherein no more than one of said orders of said delay zones is arranged on each of said sides of said base plates for easier manufacturing; wherein each succeeding order of said delay zones is arranged to provide about half as much delay as a previous order of said delay zones; and wherein said plurality of orders of said delay zones are adapted to correct said phase differences in finer increments than a single order prior art zone plate for improved amplitude and intensity.

20. The zone plate of claim 19, wherein said delay zones comprise annular zones concentric about a central point.

21. The zone plate of claim 19, wherein said delay zones comprise generally linear zones symmetrical about a central point.

22. The zone plate of claim 19, wherein said delay zones in each of said orders are arranged to provide said different phase delays in a repeating and descending order in an outward direction from an interior portion of said one or more transparent base plates, thereby said zone plate is adapted to function as a convex lens.

23. The zone plate of claim 19, wherein said delay zones in each of said orders are arranged to provide said different phase delays in a repeating and ascending order in an outward direction from an interior portion of said one or more transparent base plates, thereby said zone plate is adapted to function as a concave lens.

24. The zone plate of claim 19, wherein a first order of said delay zones generally provides a l/2λ phase delay, and subsequent orders of said delay zones each generally provides half as much delay as a previous one of said delay zones.

25. The zone plate of claim 19, wherein fewer orders of said delay zones are provided toward a periphery of said one or more transparent base plates than toward a center of said one or more transparent base plates for easier manufacturing.

26. The zone plate of claim 19, wherein a first order of said delay zones starts between first and second ones of said zone boundaries.

27. The zone plate of claim 19, further including a color filter generally axially aligned with said one or more transparent base plates; wherein said color filter comprises a plurality of groups of color segments; and wherein each of said groups comprises a red segment, a green segment, and a blue segment.

28. The zone plate of claim 19, further including a color filter generally axially aligned with said one or more transparent base plates; wherein said color filter comprises a plurality of groups of color segments; wherein each of said groups comprises a red segment, a green segment, and a blue segment; and wherein said groups are arranged between radial divisions radiating from an interior portion of said one or more transparent base plates.

29. The zone plate of claim 19, further including a color filter generally axially aligned with said one or more transparent base plates; wherein said color filter comprises a plurality of groups of color segments; wherein each of said groups comprises a red segment, a green segment, and a blue segment; and wherein said groups are arranged between radial and annular divisions respectively radiating from and coaxial with an interior portion of said one or more transparent base plates.

30. The zone plate of claim 19, further including a color filter generally axially aligned with said one or more transparent base plates; wherein said color filter comprises a plurality of groups of color segments, each of said groups comprising a red segment, a green segment, and a blue segment; wherein said delay zones in each of said orders are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; wherein radii of said zone boundaries in each of said zone segments are sized for a predetermined wavelength of a corresponding color light; and wherein said zone boundaries in said zone segments for red light are widest, said zone boundaries in said zone segments for green light are narrower, and said zone boundaries in said zone segments for blue light are narrowest.

31. The zone plate of claim 19, further including a color filter generally axially aligned with said one or more transparent base plates; wherein said color filter comprises a plurality of groups of color segments, each of said groups comprising a red segment, a green segment, and a blue segment; wherein said delay zones in each of said orders are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; wherein said zone segments corresponding to different ones of said color segments are of different thickness for providing corresponding phase delays for different color light; wherein said zone segments for red light are thickest, said zone segments for green light are thinner, and said zone segments for blue light are thinnest.

32. The zone plate of claim 19, further including a color filter generally axially aligned with said one or more transparent base plates; wherein said color filter comprises a plurality of groups of color segments, each of said groups comprising a red segment, a green segment, and a blue segment; wherein said delay zones in each of said orders are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; wherein all of said zone segments have a single predetermined thickness for providing a generally correct phase delay for a predetermined color light.

33. The zone plate of claim 19, further including a mirror positioned on one of said sides of said one or more transparent base plates; wherein said delay zones in each of said orders have a predetermined thickness to provide one of said phase delays which is defined as follows:

0.5(0.5^j + k)λ,

34. The zone plate of claim 19, wherein said zone plate is adapted to function as a prism; wherein said delay zones in each of said orders comprise generally linear zones of generally a predetermined thickness to provide one of said phase delays which is defined as follows:

(0.5^J + k)λ,

λ λ sinθ = — = d 2^Js. where λ = wavelength, j = integers representing order number, s = width of each of said delay zones in each of said orders, and d = total width of all delay zones for one full period and is fixed for a selected diffraction angle and wavelength; wherein d is also defined as follows:

d = 2^Js,

λ

^Sj sin θ2^J

35. The zone plate of claim 19, further including a mirror arranged on one of said sides of said one or more transparent base plates, so that said zone plate is adapted to function as a reflective prism; wherein all of said delay zones in each of said orders comprise generally linear zones of generally a single predetermined thickness to provide a phase delay which is defined as follows:

0.5(0.5^J + k)λ,

where j = integers representing order number, k - any integer, and λ = wavelength; wherein said delay zone are arranged to provide a diffraction angle θ defined as follows:

sinθ = — = ^■ d 2^J _Sj where λ = wavelength, j = integers representing order number, s = width of each of said delay zones in each of said orders, and d = total width of all delay zones for one full period and is fixed for a selected diffraction angle and wavelength; wherein d is also defined as follows:

d = 2^Js.

where width S_j of each of said delay zones in each of said orders is defined as follows:

λ s, = ,

^J sin θ2^J

36. A zone plate for correcting phase differences in a beam of electromagnetic radiation, comprising: a transparent base plate; and a plurality of transparent delay zones arranged on said base plate; and a color filter generally axially aligned with said base plate; wherein said delay zones are of a predetermined thickness to introduce a predetermined phase delay to selected parts of said beam of electromagnetic radiation; wherein said delay zones are spaced apart from each other and bound by respective zone boundaries; wherein said color filter comprises a plurality of groups of color segments; and wherein each of said groups comprises a red segment, a green segment, and a blue segment.

37. The zone plate of claim 36, wherein said groups of color segments are arranged between radial divisions radiating from an interior portion of said base plate.

38. The zone plate of claim 36, wherein said groups of color segments are arranged between radial and annular divisions respectively radiating from and coaxial with an interior portion of said base plate.

39. The zone plate of claim 36, wherein said delay zones are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; wherein radii of said zone boundaries in each of said zone segments are sized for a predetermined wavelength of a corresponding color light; and wherein said zone boundaries in said zone segments for red light are widest, said zone boundaries in said zone segments for green light are narrower, and said zone boundaries in said zone segments for blue light are narrowest.

40. The zone plate of claim 36, wherein said delay zones in each of said orders are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; wherein said zone segments corresponding to different ones of said color segments are of different thickness for providing corresponding phase delays for different color light; and wherein said zone segments for red light are thickest, said zone segments for green light are thinner, and said zone segments for blue light are thinnest.

41. The zone plate of claim 36, wherein said delay zones in each of said orders are divided into a plurality of zone segments respectively aligned with said red segment, said green segment, and said blue segment; and wherein all of said zone segments have a single predetermined thickness for providing a generally correct phase delay for a predetermined color light.