A computer implemented method for making a projection system and a projection system for projecting an irradiance distribution

Abstract

The invention provides a computer implemented method (101) for making a projection system configured for projecting a projected irradiance distribution, comprising a projection system optimization (102), comprising a variable initialization (105), and an iteration (106) comprising an optical surfaces determination (111), comprising a freeform refractive optical surfaces determination (114), a constraint verification (112), comprising determining a maximal slope of a first calculated freeform refractive optical surface and a maximal slope of a second calculated freeform refractive optical surface, comparing the maximal slope of the first calculated freeform refractive optical surface and the maximal slope of the second calculated freeform refractive optical surface to a slope threshold, a variable adaptation (107) when the maximal slope of the first and / or the second calculated freeform refractive optical surface is bigger than the slope threshold, the variable adaptation comprising assigning values to the set of decision variables

Description

[0001] A computer implemented method for making a projection system and a projection system for projecting an irradiance distribution

[0002] Technical field

[0003] The invention relates to a computer implemented method for making a projection system configured for projecting an irradiance distribution and a projection system for projecting an irradiance distribution.

[0004] Background art

[0005] Light pattern projection is the act of projecting specific patterns, images, or information onto surfaces, for decoration, signage, measurement, guidance, etc. It is known and used in multiple industries, including manufacturing, entertainment, architecture, retail, medical, surveillance and automotive.

[0006] The use of lens arrays for static or dynamic pattern projection purposes is known. Often, the known solutions make use of a patterned absorbing slide layer for generating any desired light pattern, in general a binary light pattern, with high resolution and good contrast.

[0007] A freeform surface is defined by the ISO standard 17450-1 :2011 as a surface which has no translational or rotational symmetry about the axis normal to the mean plane. A freeform refractive optical surface is a refractive optical surface with a freeform shape. The use of freeform refractive optical surfaces for light pattern generation is known, also when used in a lens array.

[0008] For example, patent publication US10764545 describes a projection system, in particular a double freeform projection system, comprising a light source, a collimating optical element, configured for collimating light from the light source into a collimated light beam, an array of neighboring optical channels, wherein all optical channels comprise a respective first freeform refractive optical surface and a respective second freeform refractive optical surface, jointly forming a respective pair of freeform refractive optical surfaces, and a respective projection optical surface. For all optical channels, the respective pair of freeform refractive optical surfaces is configured for receiving respective light from the collimated light beam, and shaping the respective light from the collimated light beam into a respective output light beam, the respective output light beam having a respective output light beam wavefront configured for generating a respective output light beam irradiance distribution on a respective output plane. For all optical channels the respective projection optical surface is configured for receiving the respective output light beam, and projecting the respective output light beam irradiance distribution onto the projection surface as a respective projection light beam irradiance distribution. The projected irradiance distribution, also called light pattern, results from a superposition of each of the optical channels’ respective projection light beam irradiance distribution. The first and second freeform refractive optical surfaces are designed to generate an irradiance distribution with minimized blurring while at the same time deflecting the light rays to converge on the projection optic according to Kohler illumination. The projection system uses the freeform optical surfaces to generate the required irradiance distribution, which is then imaged by a projection optic onto a real or virtual projection surface. This use of coupled freeform refractive optical surfaces allows to control both irradiance distribution and wavefront. In other words, the use of double freeform optical surfaces allows to generate the desired irradiance pattern from a known input irradiance distribution and input wavefront and at the same time define the direction of the output light beam.

[0009] The projection system according to US10764545 has several deficiencies. Due to the ray bending necessary to shape the planar input wavefront into a convergent output wavefront with its focal point, in particular its image plane, located on the projection optical surface, in particular the entrance pupil of the projection optic, there will generally be a large distance between the two freeform optical surfaces. This may lead to a blurred projected light pattern. In addition, the etendue of non-ideal light sources will lead to crosstalk between neighboring channels, resulting in a decrease of the overall quality of the projection, in particular a further blurring of the projected light pattern.

[0010] Another disadvantage is that a predetermined convergence of the output wavefront, in this case on the projection optic according to Kohler illumination, results in an inflexible optical surface design in order to project a predetermined pattern. The resulting surface design might have steep slopes, large slope variations and high sag height. As a result, projection performance will decrease, such as an increased blurring due to the steepness of the slopes. In addition, the surfaces, or a mold for replicating the surfaces, may not be manufacturable with one or more optical surface manufacturing or replication techniques, such as lithographic processes (laser direct writing, two photon absorption, nanoimprint lithography, ...), chip removal processes (diamond micro milling, diamond turning, ...), ablation processes (laser ablation, ...) or replication processes (injection molding, imprinting, glass molding, ...).

[0011] Disclosure of the invention

[0012] It is an aim of this invention to overcome some of the problems of the current state of the art.

[0013] This aim is achieved according to this invention with a computer implemented method for making a projection system configured for projecting a projected irradiance distribution, with a data processing apparatus comprising means for carrying out the method according to this invention for making a projection system configured for projecting a projected irradiance distribution, with a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to this invention, with a computer readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to this invention, and with a projection system for projecting a projected irradiance distribution on a projection surface made according to the computer implemented method according to this invention.

[0014] With regard to this invention, a light beam is meant to be interpreted broadly, consisting of a collection of light rays, each representing the path along which light propagates.

[0015] A wavefront of a light beam is meant to be interpreted as a surface that represents the locus of points where the phase of the light waves in the light beam is constant at a given instant in time. Each light ray is perpendicular to the wavefront.

[0016] An optical lens is meant to be interpreted as a refractive optical component from a material with a refractive index higher than the surrounding medium, with a non-negligible thickness. The imaging properties of an optical lens are described using the thin lens approximation for each optical surface of the lens. Hence each optical surface is modelled as a thin lens.

[0017] The distances and lengths are meant to be interpreted as equivalent distances and lengths in air, meaning that the distances used throughout the description of the invention take into account the refractive index of the material through which the light rays are traveling.

[0018] When a parallel bundle of rays goes through a converging optical surface, respectively a diverging optical surface, the point where they meet, respectively from which they spread out, is called the focal point of the optical surface, which is located at a distance from the optical surface, called the focal length f.

[0019] A conjugate object plane and image plane of an optical surface are interrelated by the optical surface’s focal length. The object plane is meant to be interpreted as the plane in which the object that is imaged by the optical surface is located. The image plane is meant to be interpreted as the plane on which points on the object plane are imaged. According to the thin lens approximation the conjugate image plane distance v to the center of a thin optical lens and object plane distance u to the center of a thin optical lens satisfy 1 / v ± 1 / u = 1 / f. The image to object size ratio is directly proportional to the image distance to object distance ratio, which is equal to the magnification of the lens.

[0020] A freeform optical surface creates an irradiance distribution on a plane at a certain distance from the freeform surface. The size of the irradiance distribution on the plane is determined by the vergence of the freeform optical surface, for example by the convergence of the freeform optical surface. The vergence point, for example the convergence point of the freeform optical surface is meant to be interpreted as the point where the rays going through the freeform optical surface converge to or diverge from, such that they create the irradiance distribution on the plane with the desired size, thereby creating a vergence point position, for example a convergence point position of this freeform optical surface, resulting in a light beam with a vergence angle value, for example a convergence angle value.

[0021] The computer implemented method according to this invention is suitable for making a projection system for projecting a projected irradiance distribution on a projection surface. The projection surface is a real or a virtual surface. Hence, the projection system images the projected irradiance distribution on a real projection area or surface, like a screen, a wall, a road surface, a building facade. Additionally or alternatively, the projection system projects a virtual image, that can be imaged on a real surface, like the eye retina, using a further lens, like the eye lens. The projection system preferably comprises a light source, a collimating optical element, and an array of neighboring optical channels. Each channel respectively comprises multiple optical surfaces, in particular an illumination optical surface, a first freeform refractive optical surface and a second freeform refractive optical surface, jointly forming a pair of freeform refractive optical surfaces, and a projection optical surface. The light from the light source is preferably collimated by the collimating optical element onto the array of neighboring optical channels. It preferably passes the optical surfaces in the following order: illumination optical surface, the first freeform refractive optical surface, the second freeform refractive optical surface and the projection optical surface.

[0022] The computer implemented method according to this invention comprises a projection system optimization, that comprises a variable initialization and an iteration.

[0023] The variable initialization comprises assigning initial values to a set of decision variables, the set of decision variables comprising preferably at least two variables, preferably an input light beam focal point position and an output light beam convergence point position. Preferably, the input light beam focal point position is a variable affecting at least a calculated illumination optical surface and the output light beam convergence point position is a variable affecting at least a second calculated freeform refractive optical surface.

[0024] The iteration comprises an optical surfaces determination and a constraint verification.

[0025] The optical surfaces determination preferably comprises determining respective calculated optical surfaces of a modelled array of neighboring optical channels. Determining respective calculated optical surfaces of a modelled array of neighboring optical channels is based on the set of decision variables. Preferably, determining calculated optical surfaces of a modelled array of neighboring optical channels is also based on a target irradiance distribution. The target irradiance distribution is the irradiance distribution the projection system is intended to project.

[0026] Optionally, determining respective calculated optical surfaces of a modelled array of neighboring optical channels comprises determining respective calculated optical surfaces of a single modelled optical channel of a modelled array of neighboring optical channels.

[0027] More preferably, the optical surfaces determination comprises a freeform refractive optical surfaces determination. Preferably, the freeform refractive optical surfaces determination comprises determining a first calculated freeform refractive optical surface and determining a second calculated freeform refractive optical surface.

[0028] The constraint verification preferably comprises verifying constraints derived from a manufacturing method, such as one or more of: a slope threshold of a manufacturing method, a thickness threshold of a manufacturing method, a sag threshold of a manufacturing method. Optionally, the constraint verification comprises verifying constraints derived from optical properties of a projection system, such as one or more of: a convergence angle threshold of an optical surface of a projection system, a residual divergence angle of a collimated light beam of a projection system.

[0029] The constraint verification preferably comprises determining a generalized mean of the slopes of the first calculated freeform refractive optical surface and a generalized mean of the slopes of the second calculated freeform refractive optical surface and comparing the generalized mean of the slopes of the first calculated freeform refractive optical surface and the generalized mean of the slopes of the second calculated freeform refractive optical surface to a characteristic slope value.

[0030] The constraint verification more preferably comprises determining a maximal slope of the first calculated freeform refractive optical surface and a maximal slope of the second calculated freeform refractive optical surface and comparing the maximal slope of the first calculated freeform refractive optical surface and the maximal slope of the second calculated freeform refractive optical surface to a slope threshold.

[0031] The constraint verification most preferably comprises determining an RMS value of the slopes of the first calculated freeform refractive optical surface, synonym for a root mean square value of the slopes of the first calculated freeform refractive optical surface, and an RMS value of the slopes of the second calculated freeform refractive optical surface, synonym for a root mean square value of the slopes of the second calculated freeform refractive optical surface, and comparing the RMS value of the slopes of the first calculated freeform refractive optical surface and the RMS value of the slopes of the second calculated freeform refractive optical surface to a slope RMS value threshold. The iteration comprises a variable adaptation, preferably when the generalized mean of the slopes, for example the maximal slope and / or the RMS value of the slopes, of the first calculated freeform refractive optical surface and / or the generalized mean of the slopes, for example the maximal slope and / or the RMS value of the slopes, of the second calculated freeform refractive optical surface is respectively bigger than the characteristic slope value, for example the slope threshold and / or the slope RMS value threshold. The variable adaptation comprises assigning values to the set of decision variables. The variable adaptation preferably comprises a gradient descent method.

[0032] This has as an advantage that the output of the method, in particular the first calculated freeform refractive optical surface and the second calculated freeform refractive optical surface, corresponding to optical surfaces of the projection system that is being designed and manufactured, adheres to a number of constraints related to the method of manufacturing the projection system. In particular, the optical surfaces have slopes smaller than the slope threshold. This ensures that the output of the computer implemented method can be used as a design guide or as a controller file to create an optical surface according to predefined specifications. This is possible because manufacturing constraints are taken into account early in the manufacturing process, already at the design phase. An additional advantage is that it will become clear at the design phase of a projection system whether or not the projection system can be manufactured with the envisaged method of manufacturing.

[0033] The computer implemented method according to this invention optionally comprises a control file generation, comprising generating a control file for at least one lens array manufacturing machine. The control file for the at least one lens array manufacturing machine comprises the instructions to manufacture the projection system with the at least one lens array manufacturing machine, in particular to manufacture the optical surfaces of the projection system. The method of manufacturing is preferably any one of diamond turning, injection molding, and precision glass molding. Alternatively, it is another micro-lens array manufacturing method known from the state of the art. The computer implemented method according to this invention uses the calculated optical surfaces and optionally also the decision variables to derive control instructions, according to which the at least one lens array manufacturing machine can make a projection system comprising a light source, a collimating optical element, and an array of neighboring optical channels. In particular, the at least one lens array manufacturing machine can make the neighboring optical channels, each channel respectively comprising multiple optical surfaces, based on the control instructions. If the optical surfaces determination determines respective calculated optical surfaces of a single modelled optical channel of a modelled array of neighboring optical channels, the calculated optical surfaces , and optionally also the decision variables, of the single modelled optical channel of the modelled array are preferably used to derive control instructions for manufacturing all the neighboring optical channels.

[0034] The computer implemented method according to this invention optionally comprises a projection system manufacturing, comprising manufacturing a lens array master and / or a lens array. Preferably the manufacturing a lens array master and / or a lens array is done using the at least one lens array manufacturing machine, based on the control file for the at least one lens array manufacturing machine. The method of manufacturing is preferably any one of diamond turning, injection molding, and precision glass molding. Alternatively, it is another microlens array manufacturing method known from the state of the art.

[0035] This has the additional benefit that the lens array master or lens array manufactured with the computer implemented method according to this invention, is manufactured as designed. Because the design takes into account the manufacturing constraints, the lens array master or lens array will project a projected irradiance distribution that is very similar to the target irradiance distribution. As a result, the scrap rate or yield loss of the method of manufacturing can be reduced.

[0036] Optionally, the constraint verification further comprises determining at least one of an input light beam convergence angle value, an intermediate light beam convergence angle value and an output light beam convergence angle value. It respectively comprises at least one of comparing a magnitude of the input light beam convergence angle value to a collimated light beam residual divergence angle magnitude, comparing a magnitude of the intermediate light beam convergence angle value to the collimated light beam residual divergence angle magnitude and comparing a magnitude of the output light beam convergence angle value to the collimated light beam residual divergence angle magnitude. The projection system optimization further comprises the variable adaptation when at least one of the magnitude of the input light beam convergence angle value, the magnitude of the intermediate light beam convergence angle value and the magnitude of the output light beam convergence angle value is smaller than the collimated light beam residual divergence angle magnitude. For example the constraint verification further comprises determining an input light beam convergence angle value and an output light beam convergence angle value, comparing a magnitude of the input light beam convergence angle value and a magnitude of the output light beam convergence angle value to the collimated light beam residual divergence angle magnitude, the projection system optimization further comprises the variable adaptation when the magnitude of the input light beam convergence angle value and / or the magnitude of the output light beam convergence angle value are smaller than the collimated light beam residual divergence angle magnitude. For example the constraint verification further comprises determining an input light beam convergence angle value, an intermediate light beam convergence angle value and an output light beam convergence angle value, comparing a magnitude of the input light beam convergence angle value, a magnitude of an intermediate light beam convergence angle value and a magnitude of the output light beam convergence angle value to the collimated light beam residual divergence angle magnitude, the projection system optimization further comprises the variable adaptation when at least one of the magnitude of the input light beam convergence angle value, the magnitude of the intermediate light beam convergence angle value and the magnitude of the output light beam convergence angle value is smaller than the collimated light beam residual divergence angle magnitude.

[0037] This has the additional advantage that the projection system resulting from the computer implemented method reduces crosstalk between the neighboring channels. As a result, the overall quality of the projected irradiance distribution increases.

[0038] The set of decision variables optionally further comprises at least one, preferably two, of an intermediate light beam irradiance distribution size target, an intermediate plane position and an output plane position, for example the intermediate light beam irradiance distribution size target and the output plane position, or for example the intermediate plane position and the output plane position. The intermediate light beam irradiance distribution size target can comprise an intermediate light beam irradiance distribution height target and / or an intermediate light beam irradiance distribution width target. Preferably, the intermediate light beam irradiance distribution size target and the intermediate plane position are variables affecting at least a first calculated freeform refractive optical surface and the output plane position is a variable affecting at least a second calculated freeform refractive optical surface.

[0039] An advantage of including these variables in the set of decision variables is that it allows to trade off optical imaging systems’ figures of merit, such as irradiance distribution blur and irradiance distribution distortion, with manufacturing method related criteria such as a maximal optical surface slope, an optical surface slope variation, an optical surface sag height. In particular, it allows to not only optimize the respective calculated optical surfaces of a modelled array of neighboring optical channels with regard to the manufacturing method related criteria, but also worsen the respective calculated optical surfaces of a modelled array of neighboring optical channels with regard to the manufacturing method related criteria in the interest of optical imaging systems’ figures of merit.

[0040] The freeform refractive optical surfaces determination optionally comprises using a direct design method and / or using a numerical optimization method. A direct design method comprises determining a ray mapping and subsequently calculating the calculated freeform refractive optical surfaces. Direct design methods available in the state of the art comprise calculating Cartesian ovals, solving of the Levi-Civita problem that generalizes the use of Cartesian ovals to non-spherical wavefronts, executing the 3D Simultaneous Multiple Surfaces method, or solving Monge-Ampere equation problems. A numerical optimization method comprises obtaining coefficients for each component in a freeform optical system, these components being Zernike, Forbes, splines and radial basis functions describing the calculated freeform refractive optical surfaces by minimizing a performance-based merit function, for example using iterative numerical optimization techniques. It comprises one or more of steepest descent, damped least squares, multi-start, simulated annealing, genetic algorithm, global synthesis, escape function and neural network numerical optimization techniques known from the state of the art. The freeform refractive optical surfaces determination preferably comprises a 3D Simultaneous Multiple Surfaces method and a numerical optimization method. More preferably it comprises a 3D Simultaneous Multiple Surfaces method, followed by a numerical optimization method. The numerical optimization method uses basic optical surface geometries obtained from the 3D Simultaneous Multiple Surfaces method for both calculated freeform refractive optical surfaces.

[0041] An advantage of including both a 3D Simultaneous Multiple Surfaces Method and a numerical optimization method in the computer implemented method according to this invention is that the 3D Simultaneous Multiple Surfaces Method limits a search space of the numerical optimization method and avoids ending up in local minima of the performance-based merit function, helping to attain better results in a lower time.

[0042] The optical surfaces determination optionally comprises a projection optical surface determination, comprising determining a calculated projection optical surface. The calculated optical surfaces comprise the calculated projection optical surface. The calculated projection optical surface is designed according to optical imaging systems’ figures of merit such as a RMS spot radius target, synonym for root mean square spot radius target, preferably as small as possible, a Strehl ratio target, preferably greater than 0.7, more preferably 0.8, most preferably greater than 0.8, and a distortion target, preferably smaller than 25%, more preferably 15%, most preferably smaller than 15%.

[0043] It is an advantage of the computer implemented invention with the projection optical surface determination that the projection system optimization has more degrees of freedom. As a result, the computer implemented method is more flexible to determine a projection system that better satisfies any manufacturing or optical constraints, resulting in a projection system with increased quality of the projected irradiance distribution.

[0044] Optionally, the projection system optimization further comprises a projection optical surface focusing. The projection optical surface focusing comprises a raytracing simulation of at least one modelled optical channel of the modelled array of neighboring optical channels, yielding a calculated projection light beam irradiance distribution, while iterating over potential focus positions of the calculated projection optical surface of the at least one modelled optical channel, slightly moving an object plane of the calculated projection optical surface, the object plane being one of the conjugate planes of the calculated projection optical surface. Iterating over potential focus positions can be done by changing a distance between the respective second calculated freeform refractive optical surface and the respective calculated projection optical surface of the at least one modelled optical channel. For each potential focus position, a blur percentage of the calculated projection light beam irradiance distribution is determined. The focus position with the smallest blur percentage is maintained. Preferably, the blur percentage is determined using Otsu’s method, preferably followed by characterizing a blurring value per segment of the calculated projection light beam irradiance distribution as high- and low-blur, for example by a gradient magnitude calculation, and taking the ratio between the number of high-blur segments and the number of low-blur segments. Optionally, for each potential focus position, a distortion measure of the calculated projection light beam irradiance distribution is determined, and the focus position with an optimal tradeoff between blur percentage and distortion measure is maintained. Preferably, the distortion measure is determined using a quantitative distortion characterizing method. Optionally, a distortion measure can be determined by reading information from an information carrier.

[0045] This has as an advantage that irradiance distribution smearing effects, such as blurring and / or distortion are minimized, leading to an improved performance of the projection system made by the computer implemented method according to this invention.

[0046] Optionally, the projection system optimization further comprises projection optical surface positioning, comprising positioning the calculated projection optical surfaces in the modelled array of neighboring optical channels, such that the similar, preferably the same irradiance patterns projected by calculated projection optical surfaces of various modelled optical channels in the modelled array of neighboring optical channels are superimposed on the same location on a modelled projection surface.

[0047] The projection system optimization preferably further comprises a system evaluation. The system evaluation comprises determining a calculated projected irradiance distribution, comparing the calculated projected irradiance distribution to the target irradiance distribution, determining a calculated projected irradiance distribution accuracy, and comparing the calculated projected irradiance distribution accuracy with an irradiance distribution accuracy threshold. The system optimization preferably further comprises the variable adaptation when the calculated projected irradiance distribution accuracy is lower than the irradiance distribution accuracy threshold. Determining a calculated projected irradiance distribution preferably comprises a raytracing simulation.

[0048] Determining a calculated projected irradiance distribution accuracy preferably comprises one or more of: a comparison with the target irradiance distribution, determining a blur percentage of the calculated projected irradiance distribution, determining a distortion measure and executing a manufacturing sensitivity analysis, configured for determining how small errors in the projection system manufacturing would impact the irradiance distribution accuracy. Optionally, determining a distortion measure comprises reading information from an information carrier.

[0049] Preferably, the computer implemented method according to this invention performs the comprising steps in the following order: projection system optimization, control file generation, projection system manufacturing. Preferably, the projection system optimization performs the comprising steps in the following order: variable initialization, iteration, projection optical surface focusing, system evaluation. The iteration is repeated when the variable adaptation is performed. Preferably, the iteration performs the comprising steps in the following order: optical surfaces determination, constraint verification, variable adaptation. Preferably, the optical surfaces determination performs the comprising steps in the following order: projection optical surface determination, freeform refractive optical surfaces determination. Preferably, the constraint verification performs the comprising steps in the following order: determining an input light beam convergence angle value, an intermediate light beam convergence angle value and an output light beam convergence angle value, comparing a magnitude of the input light beam convergence angle value to a collimated light beam residual divergence angle magnitude, comparing a magnitude of the intermediate light beam convergence angle value to the collimated light beam residual divergence angle magnitude and comparing a magnitude of the output light beam convergence angle value to the collimated light beam residual divergence angle magnitude, determining a generalized mean of the slopes of a first calculated freeform refractive optical surface and a generalized mean of the slopes of a second calculated freeform refractive optical surface, comparing the generalized mean of the slopes of the first calculated freeform refractive optical surface and the generalized mean of the slopes of the second calculated freeform refractive optical surface to a characteristic slope value. Preferably, the system evaluation performs the comprising steps in the following order: determining a calculated projected irradiance distribution, comparing the calculated projected irradiance distribution to a target irradiance distribution, determining a calculated projected irradiance distribution accuracy, comparing the calculated projected irradiance distribution accuracy with an irradiance distribution accuracy threshold. If one or more of the optional steps of the computer implemented method or of the comprising steps of the computer implemented method are not performed, the order of the performed steps remains unchanged. If additional steps are performed, the relative order of the steps mentioned above remains unchanged.

[0050] The projection system according to this invention, made according to the computer implemented method according to this invention, comprises a light source, a collimating optical element, and an array of neighboring optical channels.

[0051] The light source is a known light source from the state of the art, for example a light source configured to emit light, which may be divergent or collimated light, incoherent or coherent, or partially coherent, light, monochromatic, polychromatic or white light, i.e. light having a certain spectral distribution. The light source is for example a real, non-ideal, spatially extended light source comprising LEDs, VCSELs and / or other light emitters.

[0052] The collimating optical element is configured for collimating light from the light source into a collimated light beam. Preferably, the collimating optical element is a collimating refractive optical element, such as a collimating lens. Alternatively, the collimating optical element is a collimating reflective optical element, such as a collimating mirror or any other optical collimator known from the state of art.

[0053] The collimated light beam has a residual divergence angle. In embodiments, the residual divergence angle is greater than 0° due to the spatial extension of the light source, non-ideal collimation optics and diffraction. Preferably, the residual divergence is smaller than 2°.

[0054] At least one optical channel of the array of neighboring optical channels comprises, preferably all optical channels of the array of neighboring optical channels comprise a respective first freeform refractive optical surface and a respective second freeform refractive optical surface, jointly forming a respective pair of freeform refractive optical surfaces, and a respective projection optical surface.

[0055] For the at least one optical channel, preferably all optical channels, the respective pair of freeform refractive optical surfaces is configured for receiving respective light from the collimated light beam, and for shaping the respective light from the collimated light beam into a respective output light beam, the respective output light beam having a respective output light beam wavefront configured for generating a respective output light beam irradiance distribution on a respective output plane, the respective output plane being one of the respective conjugate planes, in particular the respective image plane, of the respective second freeform refractive optical surface.

[0056] For the at least one optical channel, preferably all optical channels, the respective projection optical surface is configured for receiving the respective output light beam, and for projecting the respective output light beam irradiance distribution onto the projection surface as a respective projection light beam irradiance distribution.

[0057] The projected irradiance distribution results from a superposition of each of the optical channels’ respective projection light beam irradiance distributions.

[0058] The at least one optical channel of the array of neighboring optical channels further comprises, preferably all optical channels of the array of neighboring optical channels further comprise a respective illumination optical surface.

[0059] For the at least one optical channel, preferably all optical channels, the respective illumination optical surface is configured for receiving respective light from the collimated light beam, and for shaping the respective light from the collimated light beam into a respective input light beam having a respective input light beam wavefront with a respective input light beam convergence angle configured for compensating for the residual divergence angle. Preferably, the respective input light beam wavefront is determined by the input light beam focal point position, of the set of decision variables of the computer implemented method according to this invention.

[0060] For the at least one optical channel, preferably all optical channels, the respective first freeform refractive optical surface is configured for receiving the respective input light beam, and for shaping the respective input light beam into a respective intermediate light beam having a respective intermediate light beam wavefront with a respective intermediate light beam convergence angle configured for compensating for the residual divergence angle.

[0061] For the at least one optical channel, preferably all optical channels, the respective second freeform refractive optical surface is configured for receiving the respective intermediate light beam, and for shaping the respective intermediate light beam into the respective output light beam wherein the respective output light beam wavefront further has a respective output light beam convergence angle configured for compensating for the residual divergence angle. Preferably, the respective output light beam wavefront is determined by the output light beam convergence point position, of the set of decision variables of the computer implemented method according to this invention.

[0062] For the at least one optical channel, preferably all optical channels, the receiving respective light from the collimated light beam by the respective pair of freeform refractive optical surfaces comprises receiving the respective input light beam by the respective first freeform refractive optical surface and receiving the respective intermediate light beam by the respective second freeform refractive optical surface, and the shaping the respective light from the collimated light beam into the respective output light beam by the respective pair of freeform refractive optical surfaces comprises shaping the respective input light beam into the respective intermediate light beam by the respective first freeform refractive optical surface and shaping the respective intermediate light beam into the respective output light beam by the respective second freeform refractive optical surface.

[0063] For the at least one optical channel, preferably all optical channels, slopes, preferably the slopes, more preferably substantially all the slopes, most preferably all the slopes of the respective first freeform refractive optical surface are smaller than a slope constraint and slopes, preferably the slopes, more preferably substantially all the slopes, most preferably all the slopes of the respective second freeform refractive optical surface are smaller than the slope constraint. Preferably the slope constraint is 40°, more preferably 30°, and most preferably 20°. The respective input light beam convergence angle and respective output light beam convergence angle are jointly configured for ensuring that slopes of the respective freeform refractive optical surfaces are smaller than the slope constraint.

[0064] Preferably, for the at least one optical channel, preferably all optical channels, the RMS value of the slopes of the respective first freeform refractive optical surface, synonym for the root mean square value of the slopes of the respective first freeform refractive optical surface, is smaller than a slope RMS value constraint and the RMS value of the slopes of the respective second freeform refractive optical surface, synonym for root mean square value of the slopes of the respective second freeform refractive optical surface, is smaller than the slope RMS value constraint. Preferably the slope RMS value constraint is 40°, more preferably 30°, and most preferably 20°. The respective input light beam convergence angle and respective output light beam convergence angle are jointly configured for ensuring that the RMS value of the slopes of the respective freeform refractive optical surfaces are smaller than the slope RMS value constraint.

[0065] It is an advantage of the projection system according to this invention that the slope constraint or the slope RMS value constraint can be related to a specific optical surface manufacturing technique, so that the surfaces are manufacturable with one of more optical surface manufacturing techniques, such as lithographic processes (laser direct writing, two photon absorption, nanoimprint lithography, ...), chip removal processes (diamond micro milling, diamond turning, ...) or ablation processes (laser ablation, ...), in particular with a diamond turning process, for example using a chuck as described in EP3344411. It is a further advantage that the slope constraint or the slope RMS value constraint can be related to a specific optical surface replication technique, such that a mold for replicating the surfaces is manufacturable and usable in a subsequent replication process to create lenses, such as injection molding, imprinting, glass molding, ... .

[0066] Optionally, for the at least one optical channel, preferably all optical channels, the respective output light beam wavefront is determined by the output plane position, of the set of decision variables of the computer implemented method according to this invention.

[0067] Optionally, for the at least one optical channel, preferably all optical channels, the respective intermediate light beam wavefront is determined by the intermediate light beam irradiance distribution size target, of the set of decision variables of the computer implemented method according to this invention.

[0068] Optionally, the projection system further comprises for the at least one optical channel, preferably all optical channels, a respective input light beam focal point, determined by the respective input light beam convergence angle, a respective intermediate light beam convergence point, determined by the respective intermediate light beam convergence angle, a respective output light beam convergence point, determined by the respective output light beam convergence angle, a respective first distance between the respective illumination optical surface and the respective first freeform refractive optical surface, a respective second distance between the respective first freeform refractive optical surface and the respective second freeform refractive optical surface, a respective third distance between the respective second freeform refractive optical surface and the respective projection optical surface, a respective fourth distance between the respective illumination optical surface and the respective input light beam focal point, a respective fifth distance between the respective first freeform refractive optical surface and the respective intermediate light beam convergence point, and a respective sixth distance between the respective second freeform refractive optical surface and the respective output light beam convergence point. The respective first distance is smaller than the respective fourth distance, the respective second distance is smaller than the respective fifth distance, and the respective third distance is smaller than the respective sixth distance.

[0069] It is a further advantage of the projection system according to this invention for projecting a projected irradiance distribution having distances with the specified relationship, that the slopes will be smaller than another projection system for projecting the projected irradiance distribution having distances without the specified relationship.

[0070] Optionally, for the at least one optical channel, preferably all optical channels, the respective intermediate light beam wavefront is configured for generating a respective intermediate light beam irradiance distribution on a respective intermediate plane, the respective intermediate light beam irradiance distribution having a respective intermediate light beam irradiance distribution size configured for enabling diffraction limited imaging for ideally the entire field height, and satisfying other field dependent imaging systems’ figures of merit, for example blur or distortion, by the respective projection optical surface. For example, the respective intermediate light beam irradiance distribution size is further configured for minimizing blur of the intermediate light beam irradiance distribution. The respective intermediate plane is one of the conjugate planes, in particular the image plane, of the respective first freeform refractive optical surface. Preferably, it is located at the respective second freeform refractive optical surface. It is a further advantage of the projection system configured for enabling diffraction limited imaging that optical aberrations in the optical channels are reduced. As a result, the quality of the resulting projected irradiance distribution is increased.

[0071] Optionally, the array of neighboring optical channels comprises channels whose respective illumination optical surfaces are substantially identical, preferably identical, whose respective first freeform refractive optical surfaces are substantially identical, preferably identical, whose respective second freeform refractive optical surfaces are substantially identical, preferably identical, and whose respective projection optical surfaces are substantially identical, preferably identical.

[0072] This can be achieved by including determining respective calculated optical surfaces of a single optical channel of a modelled array of neighboring optical channels in the computer implemented method according to this invention and manufacturing each channel according to the respective calculated optical surfaces of the single optical channel.

[0073] Known features from the state of the art can be added to the projection system according to this invention, such as a plurality of light sources having a different wavelength or a plurality of color filters having a different color, each element of the plurality associated with a subset of optical channels, such as a plurality of independently controllable light sources, controllable regarding intensity and optionally regarding color, each light source of the plurality associated with a subset of optical channels, such as additional optical surfaces located behind the array of optical channels in order to redirect the irradiance distributions of different subsets of optical channels to different directions, etc.

[0074] Brief description of the drawings

[0075] The invention will be further elucidated by means of the following description and the appended figures.

[0076] Figure 1 shows a computer implemented method for making a projection system configured for projecting a projected irradiance distribution according to the invention.

[0077] Figure 2 shows a projection system according to the invention. Figure 3 shows a schematic illustration of one optical channel of a projection system according to the invention.

[0078] Figure 4 shows a schematic illustration of one optical channel of a projection system according to the invention with the different distances between focal points, convergence points and optical surfaces.

[0079] Modes for carrying out the invention

[0080] The invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the invention.

[0081] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein.

[0082] Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the invention described herein can operate in other orientations than described or illustrated herein.

[0083] The term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the invention, the only relevant components of the device are A and B.

[0084] Fig. 1 shows a computer implemented method for making a projection system configured for projecting a projected irradiance distribution according to the invention. The output of the method is a projection system that comprises a light source, a collimating optical element, and an array of neighboring optical channels. Each channel respectively comprises multiple optical surfaces, in particular an illumination optical surface, a first freeform refractive optical surface and a second freeform refractive optical surface, jointly forming a pair of freeform refractive optical surfaces, and a projection optical surface.

[0085] The computer implemented method 101 shown in Fig. 1 comprises a projection system optimization 102, a control file generation 103, and a projection system manufacturing 104. The projection system optimization 102 precedes the control file generation 103. The control file generation 103 precedes the projection system manufacturing 104. In other embodiments, the control file generation 103 and / or the projection system manufacturing 104 are not present.

[0086] The output of the projection system optimization 102 is a set of design values, comprising a calculated illumination optical surface, a first calculated freeform refractive optical surface, a second calculated freeform refractive optical surface and a calculated projection optical surface. These are called calculated optical surfaces. The set of design values comprise calculated optical surfaces for all channels of a modelled array of neighboring optical channels, called the respective optical surfaces of the modelled array of neighboring optical channels.

[0087] The projection system optimization 102 comprises a variable initialization 105, an iteration 106, a variable adaptation 107, a projection optical surface focusing 108, a projection optical surface positioning 109, and a system evaluation 110. The variable initialization 105 precedes the iteration 106. The iteration 106 comprises the variable adaptation 107. The iteration 106 precedes the projection optical surface focusing 108. The projection optical surface focusing 108 precedes the projection optical surface positioning 109. The projection optical surface positioning 109 precedes the system evaluation 110. In other embodiments, one or more of the projection optical surface focusing 108, the projection optical surface positioning 109 and the system evaluation 110 are not present.

[0088] The variable initialization 105 comprises assigning initial values to a set of decision variables, the set of decision variables comprising multiple variables, in particular an input light beam focal point position, an output light beam convergence point position, an intermediate light beam irradiance distribution size target, and an output plane position. The input light beam focal point position is a variable affecting at least the calculated illumination optical surface, the output light beam convergence point position is a variable affecting at least the second calculated freeform refractive optical surface, the intermediate light beam irradiance distribution size target is a variable affecting at least the first calculated freeform refractive optical surface and the output plane position is a variable affecting at least the second calculated freeform refractive optical surface.

[0089] The iteration 106 comprises an optical surfaces determination 111 and a constraint verification 112. The optical surfaces determination 111 precedes the constraint verification 112. The constraint verification 112 precedes the variable adaptation 107.

[0090] The optical surfaces determination 111 comprises determining the respective calculated optical surfaces of the modelled array of neighboring optical channels. Determining the respective calculated optical surfaces of the modelled array of neighboring optical channels comprises determining respective calculated optical surfaces of a single modelled optical channel of the modelled array of neighboring optical channels and replicating the resulting design values for all channels of the modelled array of neighboring optical channels. Determining the respective calculated optical surfaces of the modelled array of neighboring optical channels is based on the set of decision variables. Determining the respective calculated optical surfaces of the modelled array of neighboring optical channels is also based on a target irradiance distribution. The target irradiance distribution is the irradiance distribution the projection system 201 is intended to project.

[0091] The optical surfaces determination 111 , comprises a projection optical surface determination 113 and a freeform refractive optical surfaces determination 114. The optical surfaces determination 111 in particular comprises determining the respective calculated optical surfaces of a single modelled optical channel. The projection optical surface determination 113 precedes the freeform refractive optical surfaces determination 114. In other embodiments, the projection optical surface determination 113 is not present.

[0092] The projection optical surface determination 113 comprises determining the calculated projection optical surface. The calculated projection optical surface is designed according to optical imaging systems’ figures of merit, in particular with a RMS spot radius target, synonym for root mean square spot radius target that is as small as possible, in particular the size of the Airy disk of a perfect optical system with the same diameter as the calculated projection optical surface, a Strehl ratio target of 0.8, and a distortion target of 15%.

[0093] The freeform refractive optical surfaces determination 114 comprises determining the first calculated freeform refractive optical surface of the single modelled optical channel of the modelled array of neighboring optical channels and determining the second calculated freeform refractive optical surface of the single modelled optical channel of the modelled array of neighboring optical channels. The freeform refractive optical surfaces determination 114 comprises using a direct design method and a numerical optimization method. In particular, it comprises a 3D Simultaneous Multiple Surfaces method as direct design method, followed by a numerical optimization method optimizing the set of design variables using a gradient descent algorithm. In other embodiments, other direct design methods known from the state of the art and / or other numerical optimization methods known from the state of the art are used.

[0094] The constraint verification 112 comprises verifying constraints derived from a manufacturing method used during projection system manufacturing 104, such as a slope threshold of the manufacturing method, and comprises verifying constraints derived from optical properties of a projection system 201 , in particular a convergence angle threshold of an optical surface of a projection system 201 , and a residual divergence angle a of a collimated light beam 301 of a projection system 201. The constraint verification 112 comprises determining an RMS value of the slopes of the first calculated freeform refractive optical surface and an RMS value of the slopes of the second calculated freeform refractive optical surface and comparing the RMS value of the slopes of the first calculated freeform refractive optical surface and the RMS value of the slopes of the second calculated freeform refractive optical surface to a slope RMS value threshold. The constraint verification 112 further comprises determining an input light beam convergence angle value, an intermediate light beam convergence angle value and an output light beam convergence angle value, comparing a magnitude of the input light beam convergence angle value, a magnitude of the intermediate light beam convergence angle value and a magnitude of the output light beam convergence angle value to a collimated light beam residual divergence angle magnitude. The variable adaptation 107 preferably comprises a gradient descent method. The iteration 106 is repeated when the variable adaptation 107 is performed.

[0095] The projection optical surface focusing 108 comprises a raytracing simulation of one modelled optical channel of the modelled array of neighboring optical channels, yielding a calculated projection light beam irradiance distribution, while iterating over potential focus positions of the calculated projection optical surface of the at least one modelled optical channel, slightly moving an object plane of the calculated projection optical surface, the object plane being one of the conjugate planes of the calculated projection optical surface. Iterating over potential focus positions of the calculated projection optical surface of the at least one modelled optical channel comprises changing a distance between the respective second calculated freeform refractive optical surface and the respective calculated projection optical surface of the at least one modelled optical channel. For each potential focus position, a blur percentage of the calculated projection light beam irradiance distribution is determined, using Otsu’s method, followed by characterizing a blurring value per segment of the calculated projection light beam irradiance distribution as high- and low-blur, in particular by a gradient magnitude calculation, and taking the ratio between the number of high-blur segments and the number of low-blur segments. A distortion measure of the calculated projection light beam irradiance distribution is determined, and the focus position with an optimal trade-off between blur percentage and distortion measure is maintained. In other embodiments, only the blur percentage of the calculated projection light beam irradiance distribution is determined and the focus position with the smallest blur percentage is maintained.

[0096] The projection optical surface positioning 109, comprising positioning the calculated projection optical surfaces in the modelled array of neighboring optical channels, such that the irradiance patterns projected by calculated projection optical surfaces of various modelled optical channels in the modelled array of neighboring optical channels are superimposed on the same location on a modelled projection surface.

[0097] The system evaluation 110 comprises determining a calculated projected irradiance distribution with a raytracing simulation, comparing the calculated projected irradiance distribution to the target irradiance distribution, determining a calculated projected irradiance distribution accuracy, and comparing the calculated projected irradiance distribution accuracy with an irradiance distribution accuracy threshold. The system optimization preferably further comprises the variable adaptation 107 when the calculated projected irradiance distribution accuracy is lower than the irradiance distribution accuracy threshold, restarting the iteration 106 after the variable adaptation 107.

[0098] Determining a calculated projected irradiance distribution accuracy comprises a comparison with the target irradiance distribution, determining a blur percentage of the calculated projected irradiance distribution, determining a distortion measure and executing a manufacturing sensitivity analysis, configured for determining how small errors in the projection system manufacturing 104 would impact the irradiance distribution accuracy.

[0099] The control file generation 103, comprises generating a control file for at least one lens array manufacturing machine. The control file for the at least one lens array manufacturing machine comprises the instructions to manufacture the projection system 201 with the at least one lens array manufacturing machine, in particular to manufacture the optical surfaces of the projection system 201. The control file generation 103 uses the set of design values, in particular the calculated optical surfaces to derive control instructions, according to which the at least one lens array manufacturing machine can make a projection system 201.

[0100] The projection system manufacturing 104 comprises manufacturing a lens array master and / or a lens array with the at least one lens array manufacturing machine. The projection system manufacturing 104 for example comprises the manufacturing of a lens array master by a diamond turning process and replicating at least one lens array using an injection molding process.

[0101] Figs. 2, 3, and 4 show a projection system, or one optical channel thereof, according to the invention, made according to the computer implemented method according to this invention. In particular, Fig. 2 shows a projection system according to the invention, Fig. 3 shows a schematic illustration of one optical channel of a projection system according to the invention, and Fig. 4 shows a schematic illustration, in particular a thin lens representation, of one optical channel of a projection system according to the invention with the different distances between focal points, convergence points and optical surfaces. The projection system 201 for projecting a projected irradiance distribution on a projection surface 404 comprises a light source 202, a collimating optical element 203, and an array of neighboring optical channels 204.

[0102] The light source 202 is a real, non-ideal, spatially extended light source 202 comprising LEDs. The collimating optical element 203 is a collimating refractive optical element, in particular a collimating lens, configured for collimating light from the light source 202 into a collimated light beam 301. The collimated light beam 301 has a residual divergence angle a.

[0103] At least one, in particular all optical channels 205 of the array of neighboring optical channels 204 comprise a respective illumination optical surface 206, a respective first freeform refractive optical surface 207 and a respective second freeform refractive optical surface 208, jointly forming a respective pair of freeform refractive optical surfaces 209, and a respective projection optical surface 210. Below, these surfaces are described for a single optical channel 205. The description holds for all optical channels 205 in the array of neighboring optical channels 204.

[0104] The respective illumination optical surface 206 is configured for receiving respective light from the collimated light beam 301 , and for shaping the respective light from the collimated light beam 301 into a respective input light beam 302 having a respective input light beam wavefront with a respective input light beam convergence angle p configured for compensating for the residual divergence angle a.

[0105] The respective pair of freeform refractive optical surfaces 209 is configured for receiving respective light from the collimated light beam 301 , and for shaping the respective light from the collimated light beam 301 into a respective output light beam 401 , the respective output light beam 401 having a respective output light beam wavefront configured for generating a respective output light beam irradiance distribution on a respective output plane 402, the respective output plane 402 being one of the conjugate planes, in particular the image plane, of the respective second freeform refractive optical surface 208.

[0106] The respective first freeform refractive optical surface 207 is configured for receiving the respective input light beam 302, and for shaping the respective input light beam 302 into a respective intermediate light beam 403 having a respective intermediate light beam wavefront with a respective intermediate light beam convergence angle configured for compensating for the residual divergence angle a. The respective intermediate light beam wavefront is configured for generating a respective intermediate light beam irradiance distribution on a respective intermediate plane 414, the respective intermediate light beam irradiance distribution having a respective intermediate light beam irradiance distribution size configured for enabling diffraction limited imaging for ideally the entire field height, and satisfying other field dependent imaging systems’ figures of merit, for example blur or distortion, by the respective projection optical surface 210. The respective intermediate plane 414 is one of the conjugate planes, in particular the image plane, of the respective first freeform refractive optical surface 207. It is located at the respective second freeform refractive optical surface 208.

[0107] The respective second freeform refractive optical surface 208 is configured for receiving the respective intermediate light beam 403, and for shaping the respective intermediate light beam 403 into the respective output light beam 401 wherein the respective output light beam wavefront further has a respective output light beam convergence angle configured for compensating for the residual divergence angle a.

[0108] The receiving respective light from the collimated light beam 301 by the respective pair of freeform refractive optical surfaces 209 comprises receiving the respective input light beam 302 by the respective first freeform refractive optical surface 207 and receiving the respective intermediate light beam 403 by the respective second freeform refractive optical surface 208, and the shaping the respective light from the collimated light beam 301 into the respective output light beam 401 by the respective pair of freeform refractive optical surfaces 209 comprises shaping the respective input light beam 302 into the respective intermediate light beam 403 by the respective first freeform refractive optical surface 207 and shaping the respective intermediate light beam 403 into the respective output light beam 401 by the respective second freeform refractive optical surface 208.

[0109] The respective input light beam convergence angle p, respective intermediate light beam convergence angle and respective output light beam convergence angle are jointly configured for ensuring that the RMS value of the slopes of the respective freeform refractive optical surfaces are smaller than a slope RMS value constraint. The RMS value of the slopes of the respective first freeform refractive optical surface 207 is smaller than the slope RMS value constraint and the RMS value of the slopes of the respective second freeform refractive optical surface 208 is smaller than the slope RMS value constraint. The slope RMS value constraint is 20°.

[0110] The respective projection optical surface 210 is configured for receiving the respective output light beam 401 , and for projecting the respective output light beam irradiance distribution onto the projection surface 404 as a respective projection light beam irradiance distribution 211. The projected irradiance distribution results from a superposition of each of the optical channels’ respective projection light beam irradiance distributions 211.

[0111] The projection system 201 further comprises for the at least one optical channel 205, in particular for all optical channels 205, a respective input light beam focal point 405, determined by the respective input light beam convergence angle P, a respective intermediate light beam convergence point 406, determined by the respective intermediate light beam convergence angle, a respective output light beam convergence point 407, determined by the respective output light beam convergence angle, a respective first distance 408 between the respective illumination optical surface 206 and the respective first freeform refractive optical surface 207, a respective second distance 409 between the respective first freeform refractive optical surface 207 and the respective second freeform refractive optical surface 208, a respective third distance 410 between the respective second freeform refractive optical surface 208 and the respective projection optical surface 210, a respective fourth distance 411 between the respective illumination optical surface 206 and the respective input light beam focal point 405, a respective fifth distance 412 between the respective first freeform refractive optical surface 207 and the respective intermediate light beam convergence point 406, and a respective sixth distance 413 between the respective second freeform refractive optical surface 208 and the respective output light beam convergence point 407. The respective first distance 408 is smaller than the respective fourth distance 411 , the respective second distance 409 is smaller than the respective fifth distance 412, and the respective third distance 410 is smaller than the respective sixth distance 413. The array of neighboring optical channels 204 comprises channels whose respective illumination optical surfaces are identical, whose respective first freeform refractive optical surfaces are identical, whose respective second freeform refractive optical surfaces are identical, and whose respective projection optical surfaces are identical.

Claims

Claims1. A computer implemented method (101) for making a projection system configured for projecting a projected irradiance distribution, comprising - a projection system optimization (102), comprising a variable initialization (105), comprising assigning initial values to a set of decision variables, the set of decision variables comprising an input light beam focal point position, an output light beam convergence point position, and an iteration (106) comprising an optical surfaces determination (111), comprising a freeform refractive optical surfaces determination (114), a constraint verification (112), comprising determining a generalized mean, preferably a root mean square value, of the slopes of a first calculated freeform refractive optical surface and a generalized mean, preferably a root mean square value, of the slopes of a second calculated freeform refractive optical surface, comparing the generalized mean, preferably the root mean square value, of the slopes of the first calculated freeform refractive optical surface and the generalized mean, preferably the root mean square value, of the slopes of the second calculated freeform refractive optical surface to a characteristic slope value, preferably a slope RMS value threshold, a variable adaptation (107) when the generalized mean, preferably the root mean square value, of the slopes of the first calculated freeform refractive optical surface is bigger than the characteristic slope value, preferably the slope RMS value threshold, and / or the generalized mean, preferably the root mean square value, of the slopes of the second calculated freeform refractive optical surface is bigger than the characteristic slope value, preferably slope RMS value threshold, the variable adaptation comprising assigning values to the set of decision variables, preferably using a gradient descent method.

2. A computer implemented method according to claim 1 , further comprising a control file generation (103), comprising generating a control file for a lens array manufacturing machine.

3. A computer implemented method according to any of the claims 1 to 2, further comprising a projection system manufacturing (104), comprising manufacturing a lens array master and / or a lens array.

4. A computer implemented method according to any of the claims 1 to 3, wherein- the constraint verification further comprises determining an input light beam convergence angle value and an output light beam convergence angle value, comparing a magnitude of the input light beam convergence angle value and a magnitude of the output light beam convergence angle value to a collimated light beam residual divergence angle magnitude,- the iteration further comprises the variable adaptation when the magnitude of the input light beam convergence angle value and / or the magnitude of the output light beam convergence angle value are smaller than the collimated light beam residual divergence angle magnitude.

5. A computer implemented method according to any of the claims 1 to 4,- wherein the set of decision variables further comprises an intermediate light beam irradiance distribution size target, and an output plane position- or wherein the set of decision variable further comprises an intermediate plane position, and an output plane position.

6. A computer implemented method according to any of the claims 1 to 5, wherein the freeform refractive optical surfaces determination, comprises using a direct design method and / or using a numerical optimization method, preferably using a 3D Simultaneous Multiple Surfaces method and a numerical optimization method.

7. A computer implemented method according to any of the claims 1 to 6, wherein the optical surfaces determination comprises a projection optical surface determination (113).

8. A computer implemented method according to any of the claims 1 to 7, wherein the projection system optimization further comprises a projection optical surface focusing (108).

9. A data processing apparatus comprising means for carrying out the method of any of the claims 1 to 8.

10. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any of the claims 1 to 8.

11. A computer readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method of any of the claims 1 to 8.

12. A projection system (201) for projecting a projected irradiance distribution on a projection surface (404) made according to the method of any of the claims 1 to 8, comprising- a light source (202),- a collimating optical element (203), configured for collimating light from the light source into a collimated light beam (301), the collimated light beam having a residual divergence angle (a),- an array of neighboring optical channels (204), wherein- at least one optical channel (205) of the array of neighboring optical channels comprises a respective first freeform refractive optical surface (207) and a respective second freeform refractive optical surface (208), jointly forming a respective pair of freeform refractive optical surfaces (209), and a respective projection optical surface (210),- for the at least one optical channel- the respective pair of freeform refractive optical surfaces is configured for receiving respective light from the collimated light beam, and shaping the respective light from the collimated light beam into a respective output light beam (401), the respective output light beam having a respective output light beam wavefront configured forgenerating a respective output light beam irradiance distribution on a respective output plane (402),- the respective projection optical surface is configured for receiving the respective output light beam, and projecting the respective output light beam irradiance distribution onto the projection surface as a respective projection light beam irradiance distribution (211),- the projected irradiance distribution results from a superposition of each of the optical channels’ respective projection light beam irradiance distributions, characterized in that- the at least one optical channel further comprises a respective illumination optical surface (206), and- for the at least one optical channel- the respective illumination optical surface is configured for receiving respective light from the collimated light beam, and shaping the respective light from the collimated light beam into a respective input light beam (302) having a respective input light beam wavefront with a respective input light beam convergence angle configured for compensating for the residual divergence angle,- the respective first freeform refractive optical surface is configured for receiving the respective input light beam, and shaping the respective input light beam into a respective intermediate light beam (403) having a respective intermediate light beam wavefront with a respective intermediate light beam convergence angle configured for compensating for the residual divergence angle,- the respective second freeform refractive optical surface is configured for receiving the respective intermediate light beam, and shaping the respective intermediate light beam into the respective output light beam wherein the respective output light beam wavefront further has a respective output light beam convergenceangle configured for compensating for the residual divergence angle,- the receiving respective light from the collimated light beam by the respective pair of freeform refractive optical surfaces comprises receiving the respective input light beam by the respective first freeform refractive optical surface and receiving the respective intermediate light beam by the respective second freeform refractive optical surface,- the shaping the respective light from the collimated light beam into the respective output light beam by the respective pair of freeform refractive optical surfaces comprises shaping the respective input light beam into the respective intermediate light beam by the respective first freeform refractive optical surface and shaping the respective intermediate light beam into the respective output light beam by the respective second freeform refractive optical surface,- the root mean square value of the slopes of the respective first freeform refractive optical surface is smaller than a slope RMS value constraint and the root mean square value of the slopes of the respective second freeform refractive optical surface is smaller than the slope RMS value constraint.

13. The projection system according to claim 12, wherein the slope RMS value constraint is 40°, more preferably 30°, and most preferably 20°.

14. The projection system according to any of the claims 12 and 13, further comprising for each optical channel- a respective input light beam focal point (405), determined by the respective input light beam convergence angle,- a respective intermediate light beam convergence point (406), determined by the respective intermediate light beam convergence angle,- a respective output light beam convergence point (407), determined by the respective output light beam convergence angle,- a respective first distance (408) between the respective illumination optical surface and the respective first freeform refractive optical surface,- a respective second distance (409) between the respective first freeform refractive optical surface and the respective second freeform refractive optical surface,- a respective third distance (410) between the respective second freeform refractive optical surface and the respective projection optical surface,- a respective fourth distance (411) between the respective illumination optical surface and the respective input light beam focal point,- a respective fifth distance (412) between the respective first freeform refractive optical surface and the respective intermediate light beam convergence point, and- a respective sixth distance (413) between the respective second freeform refractive optical surface and the respective output light beam convergence point, wherein- the respective first distance is smaller than the respective fourth distance,- the respective second distance is smaller than the respective fifth distance, and- the respective third distance is smaller than the respective sixth distance.

15. The projection system according to any of the claims 12 to 14, wherein for the at least one optical channel the respective intermediate light beam wavefront is configured for generating a respective intermediate light beam irradiance distribution on a respective intermediate plane (414), the respective intermediate light beam irradiance distribution having a respective intermediate light beam irradiance distribution size configured for enabling diffraction limited imaging by the respective projection optical surface.

Images