WO2007065003A2

WO2007065003A2 - Laser projection display system

Info

Publication number: WO2007065003A2
Application number: PCT/US2006/046254
Authority: WO
Inventors: Dongha Kim; Jongmin Wang; James F. Shanley
Original assignee: Dongha Kim; Jongmin Wang; Shanley James F
Priority date: 2005-12-03
Filing date: 2006-12-03
Publication date: 2007-06-07
Also published as: WO2007065003A3; KR20070058266A

Abstract

A beam-shaping optical element, an illumination optical system that contains the beam-shaping optical element, and a laser projection display system that contains the illumination optical system is provided. The beam-shaping optical element is composed of a Diffraction Optical Element (DOE) lens array and a focusing lens. These components change the RGB laser beams to those having a rectangular shape and an intensity distribution made uniform regardless of the directions or locations of the entering light beams. The beam-shaping optical element makes high efficiency, ultra-compact size, and low cost of a laser projection display system possible.

Description

LASER PROJECTION DISPLAY SYSTEM

Field of The Invention

The present invention relates generally to the field of projection systems, and, more specifically, to optical systems for digital light projection systems including laser light sources.

Background Of The Invention

In addition to be a communication means, such as camera, video, TV receiver, cell phone capabilities are now developing at an amazing speed. Thus, there is presently much interest in a portable compact display. However, the built-in TFT-LCD display that presently exists has a limitation in screen size, and if one were to obtain a larger screen, there would be a portability problem.

Thus a projection system that has a portable big screen, compact display and uses a micro display panel (DLP, LCOS, HTPS, GLV, etc.) is gaining much attention. Because images in the projection system become enlarged by an optical structure, the projection system has the advantage of implementing a big screen with a small system.

However, when light efficiency is considered, not only considering a common CCFL lamp, but also an LED light source that is the next generation light source, these light sources still lack sufficient light efficiency, requiring a large size and consumption of a large amount of electricity. Thus, application to a portable display is difficult.

Therefore, a compact projection display system that uses laser light source is emerging as an alternative. Compared to an LED or CCFL light source, whose light propagates in all different directions, when a laser light source is used, the straight propagation of light is excellent. Therefore, when applied to a projection system, it has the advantage of greatly increasing light efficiency, hi addition, when applied to the light conversion (modulation) panel of a liquid crystal, such as LCOS or HTPS, it has the advantage of increasing light efficiency theoretically to 2 times higher than that of the common light sources (CCFL, LED), due to the fact that the laser light is polarized.

However, the characteristics of an oval shape and Gaussian intensity distribution of a laser light source make it difficult to apply the laser light source into a display system. That is, when the light emitted from a laser light source passes through an illumination optical system and enters into a light conversion panel, the boundary shape of the beam should be the same as the boundary shape of the panel, and the internal intensity distribution of the beam should be the same as well. If such beam- shaping is not created well, the fatal problem of a drastic increase in light loss and a drastic decrease of screen uniformity occurs.

As of now, there are two major categories in beam-shaping methods to transform the oval shape and Gaussian intensity distribution of a laser light source to a uniform intensity distribution of a rectangular shape (i.e. when the boundary shape of the panel is rectangular).

The first one is a lens design that uses traditional refractive optics. In order to make a portable display, an ultra-compact refractive lens of 1~2 mm should be used for the purpose of adjusting a laser beam that has a beam width of 0.1-0.2 mm. However, as of now, it is impossible to process an ultra-compact size lens that guarantees these functions. There is no problem, of course, when it is used as an optical system for TV in which the system size can be relatively large.

The second one is a design that uses a Diffractive Optical Element (DOE) that has optical functions as a refractive optical lens of a small size. DOE uses the wave-nature of light, and has the advantage of performing the same functions as a refractive lens does or even many more functions at a much smaller size than a refractive optical element. However, the beam-shaping DOE that is currently suggested presents the problem of having too much lower light efficiency than a refractive lens to be applied to products, but it also has a major problem. That is, because the beam-shaping DOE that is currently suggested is designed based on the correct location of the laser beam that is entering the element and the correct light distribution at that time, and if the angle of incidence or incidence location of the entering light changes, the result would be a totally different output beam. In other words, because there is almost no optical tolerance for the entering beam, when it is applied to an actual product, there will be a steep decrease in the mechanical tolerance of the product as well as in the efficiency or uniformity of the output beam. The mechanical tolerance generated during mass production of the product is generated with random distribution, which is impossible to control and consequently leads to an increase in both rejection rate and cost.

In summary, there are 4 requirements that an ultra-compact laser projection display should meet: (a) compact size, (b) low electricity consumption (equaling high light efficiency), (c) low cost, and (d) high product reliability. Particularly, it is most important that the laser beam-shaping element of the configuration elements inside a laser projection display meets these four requirements. When an S-shaped laser beam is shaped using a common refractive lens, (a) compact size and (c) low cost cannot be met. And when a DOE element that has been recently suggested is used for beam- shaping, although the size can become compact and the cost can be competitive, (b) high light efficiency and especially (d) product reliability cannot be met.

This design concerns a beam-shaping optical element that meets all four of the above- mentioned requirements. It also concerns an illumination optical device structure that uses such a beam- shaping optical element. It further concerns an ultra-compact laser projection display system that uses such an illumination optical device for illumination.

These and other advantages of the present invention will become more fully apparent from the detailed description of the invention tvereinbelow.

Summary of the Invention

The present invention is directed to an illumination optical system for a laser projection display system, the illumination optical system comprising at least two laser light sources and a beam- shaping optical element. The beam-shaping optical element comprises a first DOE lens array, wherein the first DOE lens array comprises an array of DOE unit cells, and wherein the arrays are configured to correspond to the light axes of incoming light originating from the at least two laser light sources. The beam-shaping optical element also comprises a focusing lens positioned forward from the first DOE lens array. The distance between the first DOE lens array and the focusing lens is such that the focal distance of each of the DOE unit cells is forward from a location of the first DOE lens array and behind a location of the focusing lens. The beam-shaping optical element may also comprise a second DOE lens array parallel to the first DOE lens array.

Brief Description of the Drawings

For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures, wherein:

Figure 1 illustrates the basic configuration of an image projection device that uses a laser, in accordance with a preferred embodiment of the present invention.

Figure 2 illustrates the principle of the operation of a beam-shaping element, in accordance with a preferred embodiment of the present invention.

Figure 3 illustrates problems associated with a traditional beam-shaping element.

Figure 4 illustrates the principle of the operation of a beam-shaping element, in accordance with a preferred embodiment of the present invention.

Figure 5 illustrates a combination of the beam-shaping element, laser light source array and collimation optics based on the present invention.

Figure 6 illustrates a combination of the beam-shaping element, laser light source array and collimation optics based on the present invention.

Figure 7 illustrates a combination of the beam-shaping element, laser light source array and collimation optics based on the present invention.

Figure 8 illustrates a combination of the beam-shaping element, laser light source array and collimation optics based on the present invention.

Figure 9 illustrates a combination of the beam-shaping element, light conversion panel and collimation optics based on the present invention.

Figure 10 illustrates a combination of the beam-shaping element, light conversion panel and collimation optics based on the present invention.

Figure 11 illustrates a basic configuration and the principle of the operation of the beam-shaping element based on the present invention.

Figure 12 illustrates a basic configuration and the principle of the operation of the beam-shaping element based on the present invention.

Figure 13 illustrates the detailed structure of a DOE lens array in the configuration of the beam-shaping element based on the present invention. Figure 14 illustrates a front view of the detailed structure of a DOE lens array in the configuration of the beam-shaping element based on the present invention.

Figure 15 illustrates an enlarged view of the detailed structure of a single DOE unit lens cell from the DOE lens array in the configuration of the beam-shaping element based on the present invention.

Figure 16 illustrates a front view of the detailed structure of a single DOE unit lens cell from the DOE lens array in the configuration of the beam-shaping element based on the present invention.

Figure 17 illustrates the form of the phase function for designing a DOE lens array in the configuration of the beam-shaping element based on the present invention.

Figure 18 illustrates the actual lens-making method of the phase function for designing a DOE unit lens cell in the configuration of the beam-shaping element based on the present invention.

Figure 19 illustrates the actual lens-making method of the phase function for designing a DOE unit lens cell in the configuration of the beam-shaping element based on the present invention.

Figure 20 illustrates an example of a DOE unit lens cell design in the configuration of the beam-shaping element based on the present invention.

Figure 21 illustrates an example of simulating beam progression of the beam-shaping element based on the present invention.

Figure 22 illustrates an example of simulating beam progression of the beam-shaping element based on the present invention.

Figure 23 illustrates an example of simulating beam progression of the beam-shaping element based on the present invention.

Detailed Description of the Preferred Embodiments

It is to be understood that the figures and descriptions of the present invention may have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, other elements found in a typical projection system. Those of ordinary skill in the art will recognize that other elements may be desirable and/or required in order to implement the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. It is also to be understood that the drawings included herewith only provide diagrammatic representations of the presently preferred structures of the present invention and that structures falling within the scope of the present invention may include structures different than those shown in the drawings. Reference will now be made to the drawings wherein like structures are provided with like reference designations.

A laser projection system is generally configured as illustrated in Figure 1. First, the image signal (0) of the screen to be displayed arrives, then the image board (1) processes the received signal so that it is appropriate for the system driving method and sends it to the drivers (2-1, 2-2) that are attached to laser light source (3) and light conversion (modulation) panel (6), and the laser light source (3) that is driven by the driver (2-1) sends a laser beam of appropriate beam intensity and frequency to the collimation optics (4). The collimation optics (4) changes the laser beam it receives to parallel light and sends the latter to the beam-shaping optical system (5). The beam-shaping optical system (5) changes the beam that has a Gaussian intensity distribution of a parallel oval shape to a beam that has a uniform intensity distribution shape which is the same as the panel (6) and then sends the changed beam to the light conversion panel (6). The light conversion panel (6) is driven by the driver (2-2), and the beam converted through the light conversion panel (6) is enlarged via the projection optical system (7), and then projected to screen (8), and the system is then completed. In contrast to the projection optical system (7), the combination of collimation optics (4) and beam- shaping optical system (5) is called illumination optical system (100).

The following is the principle of the operation of the beam-shaping optical system (5) that uses DOE as illustrated in Figure 2. The light beam coming from the laser is of an oval shape (10), and the internal intensity distribution follows a Gaussian distribution (11). When the parallel (12) oval beam coming from the collimation optics (4) (not shown) enters the rectangular-shaped light conversion panel (6) (not shown), significant amount of light loss occurs and the uniformity also drastically decreases, thus the screen becomes dark and spotted. Therefore, it is necessary to change the beam shape to either rectangular or belt shape, and make its internal beam intensity distribution uniform. Such role is performed by the beam-shaping optical system (5). The parallel beam (12) that entered the beam-shaping optical system (5) is changed to a beam (13) through the beam-shaping optical system (5). At this time, the beam's shape (14) is substantially the same as that of the light conversion panel (6) and the internal beam intensity distribution (15) is made uniform.

However, the beam-shaping device (17) that has been suggested traditionally (as illustrated in Figure 3) either has an angle delta theta (16) relative to a vertical direction or when the location of the entering beam moves (18), the shape (20) of output beam (19) changes greatly from the desired shape (such as a rectangular shape) and so does the internal beam intensity distribution (21). This is because each pixel of the beam-shaping device is differently and delicately designed so that each pixel can cause a diffraction correctly corresponding to the distribution of entering beam. When the angle of incidence or incidence location of the beam changes, the result is a shape (20) and/or distribution (21) that is completely different from the intended beam-shaping shape (14) and/or distribution (15).

The beam-shaping optical device (5) of this design (Figure 4) obtains the desired shape (14) and intensity distribution (15) of the output beam (13) regardless whether the entering beam has a random angle theta (16) vertically or the entering beam's location moves (18). This is possible because the DOE of this design is formed with a repetitive array of unit cells that have the same structure, and each unit (lens) cell takes the same optical function. However, because the existing beam-shaping DOE does not have the repetitiveness of such unit cells and each pixel has different optical function, when the angle of incidence or incidence location of an entering beam changes, the DOE will have an output beam shape of a different pattern and intensity distribution, which leads to an unfavorable optical tolerance. A detailed structure and operation principle of DOE (5) of this design will be introduced in a more detailed manner below.

The beam-shaping illumination optical system (5) of this design can be used along with various laser light source (3) arrays and various collimation optics (4) both of which are not illustrated in Figures 5-8. In the first example (Figure 5), from laser light sources of three colors—red, green, blue (31, 32, 33), a laser beams with Gaussian beam distributions (22, 23, 24) and beam shapes of oval pattern (25, 26, 27) enter the optical system in a direction that is parallel to the light axes (28, 29, 30). Each laser beam that radiates at a certain angle is changed to a parallel light by the collimation lens arrays (34, 35, 36), enters the beam-shaping optical system (5) of this design with a certain angle corresponding to light axes caused by light- path-changing optical elements (37, 38, 39) that changes the advance direction of the beam. A diffractive element or refractive lens such as a grating can be used as an element that changes the beam direction. An important point here is that even though three lights enter the optical system at random angles (40, 41, 42) corresponding to the light axes, when the beam- shaping optical system (5) of this design is used, all the progression paths will be changed to a direction that is parallel (43) to the light axes. At the moment, the output beam will have the panel shape (44) with an intensity distribution (45) made uniform without any distortion. For more than 3 laser light sources (or even 2 laser light sources), a uniform output can also be created with the same method. Unlike the first example (Figure 5), the second example (Figure 6) is an example that, by giving certain angles (31, 32, 33) to red, green and blue laser light sources, the need to use light-path-changing optical elements (37, 38, 38) that change the beam direction is eliminated. Because the beam-shaping optical system (5) of this design has a very large optical tolerance for angles of the entering beam, a precise angle of incidence control for the entering beam is not required, thus the system configuration as shown in the second example is possible.

The third example (Figure 7) is an example that uses dichroic mirrors (46, 47, 48) for combining red, green and blue beams. When the beam-shaping optical element (5) of this design is used, it is possible to combine colors simultaneously with beam-shaping without using any special dichroic mirror, but when there is a mechanical limitation in the form factor of laser light source and system, using the third example will be helpful to optimize the system size. The fourth example (Figure 8) illustrates where an X-CUBE (50) is used for color combining. In this case, it is also possible to have color combining and beam-shaping simultaneously when the beam-shaping optical system (5) of this design is used. When a mechanical limitation that corresponds to the form factor of laser light source and system usage occurs, this method may also be favorable in optimizing the entire system configuration. In any case, the illumination optical system (5) of this design performs the beam-shaping function (44, 45) of high mass production capability that is not affected by the mechanical tolerance of the system.

The laser light source arrays (3) and collimation optical system (4), that are preferably used with the beam-shaping optical system (5), have been discussed above. The following figures show various form factors of light conversion panel (6) and projection optical system (7) that are preferably used with the beam-shaping optical system (5) of the present invention. The first example (Figure 9) is an example that uses a reflective liquid crystal light conversion panel (52). The panel-shaped and uniform beam, that is coming from the beam-shaping optical device (5), passes through the Polarization Beam Splitter (PBS) (51) and enters the reflective liquid crystal light conversion panel (52). PBS (51) is an optical device that plays a role of either reflecting polarized light that is needed or allowing it to pass through, and when a laser beam is used as light source, because all the light can pass through due the polarized nature of the laser beam, it is possible to obtain a light efficiency that is higher than that of existing light sources (CCFL₅ LED₅ UHP lamp).

In the first example, the reflective liquid crystal light conversion panel (52) can be replaced with a reflective micro electro-mechanical system (MEMS) light conversion device and used with an appropriate reflective optical system. The second example (Figure 10) illustrates using a projecting liquid crystal light conversion panel (54). This is the simplest optical structure. Light that passed through the beam-shaping optical device (5) of the present invention enters the projecting liquid crystal light conversion panel (54) along the light axis without changing the direction of progression of the light. Light is converted to the desired image, and then enlarged and projected to the screen via the projection optical system (53). In the second example, the projecting light conversion liquid crystal panel (52) can be replaced by, for example, a projecting DMD light conversion panel.

^■ As described so far, the beam-shaping illumination optical device (5) of the present invention is used along with the laser light source array (3), collimation optics (4) (Figures 1, 5, 6, 7, and 8), light conversion device (6) and projection optical system (7) (Figures 1, 9, and 10) that are preferably used in this design. Not only can it be applied to Field Sequential Color (FSC) actuation in which red, green and blue lasers are actuated consecutively according to time, but also to a 3 -panel process in which red, green and blue (lasers) are actuated individually so that each beam can be shaped individually.

Now the detailed structure and principle of the beam-shaping device (5) of the present invention will be discussed with respect to Figures 11 and 12. A beam-shaping illumination optical system (5) is mainly composed of a 1^st DOE lens array (55), 2^nd DOE lens array (56) and a focusing lens (57).

The laser beam that enters the DOE lens array parallel via the collimation optics (4) is divided to surface areas (58, 59, 60, 61, 62) corresponding to internal DOE unit cells, and the 1^st DOE lens array (55) plays the role that makes the entering beam to each surface area such that a focus can be produced on the 2^nd DOE lens array (56). Figure 11 shows an example in which the entering laser beam is divided into 5 surface areas (portions) (58, 59, 60, 61, 62) and produces a focus on the 2^nd DOE lens array (56). The flux of each beam that enters the five surface areas is different due to the Gaussian distribution characteristic of the laser beam. That is, the flux in the central area (60) is the largest, and areas toward both ends (58, 62) have a lower flux. Beams (63, 64, 65, 66, 67) that produce focuses on the 2^nd DOE lens array (56) through being divided to areas that have different fluxes (58, 59, 60, 61, 62) by the 1^st DOE lens array (55) radiate while having the same directional distribution regardless of initial angle of incidence and location where the focus is produced. Beams of each area then pass through focusing lens (57) and produce an image on the same location (68, 69, 70). Based on this principle, five beams with different fluxes (58, 59, 60, 61, 62) produce images on the same location (68, 69, 70) and the intensity of light distribution of each beam is combined and mixed together, so that the final output beam will have a uniform beam intensity distribution (15). Figure 11 shows the structure in which one DOE unit cell, i.e. a DOE unit lens is repeated 4 times in the vertical direction. That is, the vertical DOE lens array is configured with five DOE unit cells. As the number of repeated DOE unit cells increases inside the entering beam size, because the light distribution change of the entering beam inside one area becomes smaller, the uniformity of the intensity distribution of the output beam becomes better.

The number of DOE unit cells inside the optimized DOE lens arrays (55, 56) may vary depending on the intensity distribution of the entering laser beam and the uniformity goal of the output beam. That is, when the inclination of the intensity distribution function of the entering laser beam is severe, more DOE unit cells are needed to obtain the same degree of uniformity.

As mentioned earlier, the beam-shaping optical system (5) in this design is different from the beam-shaping DOE device of traditional designs. With a laser beam that has an inclined angle of incidence, it works without any problems while having the same functions (Figure 12). The beam with inclined incidence also passes through the 1^st DOE lens array (55) and is divided into five portions (58, 59, 60, 61, and 62), each portion producing a focus on the 2^nd DOE lens array (56). In the case of an inclined beam, the focus is produced in portions (63, 64, 65, 66, and 67) that are different from those in the case of beams parallel to light axis (Figure 11). However, when passing through the 2^nd DOE lens array (56), the inclined beam changes to a beam that radiates with the same directional distribution, and it passes through the focusing lens (57), it produces an image on the portions (68, 69, 70) similar to the beam parallel to the light axis does. Therefore, the intensity of five beams that have different flux values is combined at the same portions (68, 69, 70) so that an output beam with a uniform intensity distribution (15) can be obtained. This is the principle that explains how this design can produce an output beam with a uniform intensity distribution (15) even from beams that are incident at different angles. Although the discussions so far dealt with only one dimension (for example, along the y axis), since the same principle can be applied to the x axis, the same principle works in two dimensions also. Therefore, not only can an output beam with a uniform intensity distribution be obtained with the aid of the above-mentioned principles of operation, but also an output beam with the shape of desired panel shape can be obtained when the principle is expanded to two dimensions.

A simplified structure of the 1^st DOE lens array (55) is shown in Figures 13, 14. The examples in the figures show the pattern of a 5 x 5 DOE lens array (55), which means that the DOE lens array is composed of 25 DOE unit cells (71) as illustrated in Figures 15 and 16. Although basically the same structure as the 1^st DOE lens array (55), the DOE unit cells (71) that comprise the 2^nd DOE lens array (56) preferably use those from the 1^st DOE lens array. However, the designs for the DOE unit cells that complete the 2^nd DOE lens array may utilize another phase function (Figure 17) to increase quality of the screen.

A diffractive optical element design can be done with different methods according to the sizes of d and h (Figure 18) that are the representative sizes of the diffractive element. Here, d is the value related to the grating interval corresponding to the y axis of the diffractive element, and h is the value related to the thickness corresponding to the z axis of the diffractive element. Where λ is the wavelength of the incidence beam, if d, h <0.5 λ, it is possible to design the DOE element with continuous medium approximation where the refractive index continuously changes along the z axis. That is, because the wavelength is sufficiently large compared to the typical sizes of DOE elements, the light only identifies the DOE element as an element that continuously changes along the direction of z axis. If d, h > 3~4 λ, it is possible to design the DOE element without having a thickness but simply by approximating it to a phase plate where the phase changes corresponding to the x or y axis. This is called the complex-amplitude approximation method. That is, because the wavelength of the light is sufficiently large compared to the size of the DOE element, from the light's stand point, the DOE element is not perceived as having a detailed curvature, it is simply perceived as a phase plate that does not have any thickness.

There is no special approximation method in the intermediate area of 0.5 λ < d, h < 3~4 λ, so that the rigorous diffraction theory, which is a method that solves Maxwell's equation at the interface, should be used. In the rigorous diffraction theory, the light satisfies Maxwell's equation even at the curvature of the DOE element, i.e. the interface, so that the theory can be used in the entire area regardless of the size relationship between d, h and wavelength. The DOE element of this design meets the d, h > 3~4 λ requirement, so that the DOE element is designed using the complex-amplitude approximation method. If the complex-amplitude approximation method is used (i.e. if the DOE element is viewed as a simple phase plate that does not have any curvature - of course only the modeling can be done so because the actual DOE element that is manufactured does have curvature or cascade shape), there are mainly two DOE design methods.

The first method is called Computer Generated Hologram (CGH, also called

"Numerical Type DOE"). The foundation of this method is the wavefront of light concept. It determines the wavefront of the output beam that has the desired shape and intensity distribution and correctly predicts the wavefront of the entering beam to design a wavefront conversion phase place that creates the desired output beam. In CGH, there are also two main methods — the direct design method and inverse design method. The direct design method is a method that directly carries out optimization until the merit function of the parameters of the DOE element (such as phase delay of each pixel, complex- amplitude transmittance) is met. The direct search technique, simulated annealing, and genetic algorithm are some of direct design methods. The inverse design method is a method that optimizes the requirements of the output beam, and then finds parameters of the DOE at that time. The famous Iterative Fourier Transform Algorithm (IFTA) is an example of this method.

The second method is a design method based on a phase function that is called Kinoform (this method is also called "Analytic Type DOE"). It is a method using refractive optics as the basis and changes the phase function (Figure 17) that is obtained to perform certain optical function on a DOE element that plays the role of a thin phase plate. The first method (CGH) is a method that changes the wavefront to a desired shape, so it is good for the DOE design to obtain a desired pattern at a far field. For example, it is appropriate to be used in a beam splitter (where a single laser beam is divided into several beams, then the latter are directed to the desired locations), beam-shaping (where a round/oval laser beam is changed to the desired shape), a Holographic Optical Element (HOE) (where a business logo or a complicated shape needs to be obtained). However, it is hard to apply focusing optics at a near field because the design accuracy decreases in the Fresnel region (which is not a far field), and the output beam shape becomes distorted easily by the shape change of the entering beam. Therefore, in this preferred design, the complex-amplitude approximation method is used to design the phase plate, and the phase function called Kinoform is also used.

A phase function is utilized that is the most basic equation (0) to design one DOE unit cell (71) in the DOE lens arrays (55, 56). This phase function is the most basic shape of a lens that produces a focus. It does not matter if a slightly modified phase function is used to correct color aberration, spherical aberration, etc.

where φ is the phase delay, K is the direction vector, p is the root (x^ + y2)₃ f is the focal distance, and in this design, it means the distance between the 1^st DOE lens array (55) the 2^nd DOE lens array (56).

Fig. 18 clearly shows how to change the phase function obtained from the equation to an actual DOE unit cell. That is, the phase function is cut with an interval of n π (phase difference) along the z axis, and then projected to an actual lens plane. This does not mean that the shape of the phase function is projected to the lens plane as it is. That is, if n = 2 (when the phase function is cut at an interval of 2 π), the curvature h(r) of the lens is determined in correspondence to the phase function φ(r) as equation (1) . h(r) = [λ/(n(λ) -l)] * [Φ(r)/2π] (i)

2nπ < φ(r) < 2(n + l)π, n = 0, 1, 2....

Therefore, it becomes the maximum h value which is h(max) = λ/(n(λ) -1). The DOE unit cell (Figure 18) implemented using such method is generally called Kinoform. The production of DOE unit cell is possible by using the diamond turning method and reproducing the curvature of h(r) as it is. Theoretically, the efficiency will be 100% in this case, but because manufacturing is difficult when the interval d is narrow, a semiconductor lithography method may be used for the manufacture of a DOE unit cell by approximating the continuous curvature to several cascades as in Figure 19. In this case, the efficiency of the DOE lens is determined by cascade numbers, and although the efficiency is generally different according to the shape of the phase function, when the DOE lens is manufactured for 6-8 levels, a high efficiency of more than 80% may be obtained.

Regarding the methods of actually incorporating the phase function to the DOE lens, in addition to the methods described above, there is a geometrical method that approximates the phase function to dg(x) in which the grating interval changes continuously. That is, the following approximation equation (2) can be established with dense interval grating. (dφ(x₁)/dx) * dg(x) = 2π (2)

This means when the inclination change of the phase function is small at any location x, after it is moved as much as the grating interval dg, the phase change will be 2π. Therefore, the grating interval that changes in equation (2) can be represented by the following equation (3). dg(x) = 2 π/|d φ(x)/d x | (3)

This exemplary model has the advantage of being relatively convenient to manufacture because it only requires figure grating lines while simply changing the interval without creating special curvature such as h(r) or approximating multilevels to create a cascade structure. However, to realize this model, the phase function change along the x axis must be very small, so that the dg value has to be extremely small for an accurate approximation. For example, when considering the phase function (equation (4)) of a DOE unit cell that has common radial symmetry, we have φ(x) = k[f-(f² + xY^/2] (4)

f: focal distance

dg(x) that is calculated by equation (3) can be represented by the following equation

(5). dg(x) = λ[l + (f/x)²]^1/2 (5)

As seen in equation (5), dg becomes on the order of ~ λ, the complex-amplitude size approximation that can be realized at d > 3~4 λ does not fit, and calculation through the phase function has a conflict of its own, so there is difficulty hi using it for an accurate modeling. Therefore, in this design, when the decided phase function is made for the DOE element, instead of the method of approximating with grating, the former method of projecting (i.e. the phase function) as it is to an actual lens plane is used to increase design precision.

A 5 x 5 DOE lens array with each DOE unit cell size of 3.2 mm x 2.4 mm is designed and an actual simulation is conducted using the method presented in this design. Figure 20 illustrates the phase function (73) used in the actual DOE unit cell design and the actual lens shape (74) projected to the lens plane. Figure 21 illustrates the result of a two-dimensional simulation using the DOE unit cell designed as such. The laser beam becomes divided for entrance into 5 DOE unit lenses thereby correctly producing the phase at the same location on the panel (6). Figure 22 illustrates the result of a three-dimensional simulation. After the oval shaped laser beam passes through the beam-shaping device of the present invention, the beam is transformed into a rectangular shape that is exactly or substantially the same as the panel shape. Figure 23 shows the light distribution of the beam entering the panel plane after it passes through the beam-shaping device of the present invention. The shape is exactly or substantially a rectangular shape, and one can see that the intensity distribution of the beam is veiy good as the uniformity reaches 90%. According to the beam-shaping device of the present invention, the illumination optical system that contains the beam-shaping device, and the laser projection display system that contains the illumination optical system, a laser projection display system of ultra-compact size, high efficiency, and low cost is possible.

With the simplification of beam composition structure and the use of DOE lenses, making an ultra-compact size device, which was not possible in the past, is now possible. High efficiency is also achievable due the beam-shaping that corresponds to the shape of the light conversion panel. Further, because of an optical structure that works regardless of the location or angle of the entering beam, the rejection rate of the product decreases, which makes low cost possible.

In any of the embodiments described above, the DOEs may be comprised of, for example, glass or plastic.

In particular, when used along with a liquid crystal light conversion panel, due to the characteristic of polarization of laser light, the light efficiency can be increased far more than in existing projection systems. It should be noted that the beam-shaping device of the present invention can also be used with other types of light conversion panels, such as, for example, DMD and GLV, such utilization is to be considered within the scope of the present invention.

The contemplated modifications and variations specifically mentioned above are considered to be within the spirit and scope of the present invention.

Those of ordinary skill in the art will recognize that various modifications and variations may be made to the embodiments described above without departing from the spirit and scope of the present invention. For example, other colored lasers may be employed for the lasers instead of the red, green, or blue lasers mentioned in the above embodiments. It is therefore to be understood that the present invention is not limited to the particular embodiments disclosed above, but it is intended to cover such modifications and variations as defined by the following claims.

Claims

006/046254What is claimed is:

1. An illumination optical system for a laser projection display system, the illumination optical system comprising: at least two laser light sources; and a beam-shaping optical element, wherein the beam-shaping optical element comprises: a first DOE lens array, wherein the first DOE lens array comprises an array of DOE unit cells, and wherein the arrays are configured to correspond to the light axes of incoming light originating from the at least two laser light sources; and a focusing lens positioned forward from the first DOE lens array; wherein the distance between the first DOE lens array and the focusing lens is such that the focal distance of each of the DOE unit cells is forward from a location of the first DOE lens array and behind a location of the focusing lens.

2. An illumination optical system for a laser projection display system, the illumination optical system comprising: at least two laser light sources; and a beam-shaping optical element, wherein the beam-shaping optical element comprises: a first DOE lens array; a second DOE lens array positioned forward from the first DOE lens array, wherein the first DOE lens array is substantially parallel to the second DOE lens array, wherein the first DOE lens array and the second DOE lens array each comprise an array of DOE unit cells, and wherein the arrays are configured to correspond to the light axes of incoming light originating from the at least two laser light sources; and a focusing lens positioned forward from the second DOE lens array; wherein the focal distance of each of the DOE unit cells within the first DOE lens array is forward from a location of the first DOE lens array and behind a location of the focusing lens.

3. The illumination optical system of claim 1 further comprising a collimating lens associated with each of the laser light sources, wherein each collimating lens receives light from a corresponding one of the laser light sources to thereby form a collimated light beam, and wherein the collimating lenses are positioned behind the first DOE lens array.

4. The illumination optical system of claim 2 further comprising a collimating lens associated with each of the laser light sources, wherein each collimating lens receives light from a corresponding one of the laser light sources to thereby form a collimated light beam, and wherein the collimating lenses are positioned behind the first DOE lens array..

5. The illumination optical system of claim 3, wherein the first DOE lens array receives light directly from the collimating lenses.

6. The illumination optical system of claim 4, wherein the first DOE lens array receives light directly from the collimating lenses.

7. The illumination optical system of claim 3, wherein the first DOE lens array receives light from the collimating lenses via a corresponding light-path changing optical element which redirects each collimated light beam toward the first DOE lens array.

8. The illumination optical system of claim 4, wherein the first DOE lens array receives light from the collimating lenses via a corresponding light-path changing optical element which redirects each collimated light beam toward the first DOE lens array.

9. The illumination optical system of claim 7, wherein each light-path changing optical element is diffractive or refractive.

10. The illumination optical system of claim 8, wherein each light-path changing optical element is diffractive or refractive.

11. The illumination optical system of claim 7, wherein light emitted from each light-path changing optical element enters the same plane on the first DOE lens array.

12. The illumination optical system of claim 8, wherein light emitted from each light-path changing optical element enters the same plane on the first DOE lens array.

13. The illumination optical system of claim 1, wherein the at least two laser light sources comprise red, green, and blue lasers.

14. The illumination optical system of claim 2, wherein the at least two laser light sources comprise red, green, and blue lasers.

15. The illumination optical system of claim 3, wherein each of the at least two laser light sources are separated from each of the corresponding collimating lenses in an amount substantially equal to a focal distance of the corresponding collimating lens.

16. The illumination optical system of claim 4, wherein each of the at least two laser light sources are separated from each of the corresponding collimating lenses in an amount substantially equal to a focal distance of the corresponding collimating lens.

17. The illumination optical system of claim 1, wherein the first DOE lens array is comprised of glass.

18. The illumination optical system of claim 1, wherein the first DOE lens array is comprised of plastic.