Multi-mode illumination module and related method

Abstract

The illumination module for emitting light (5) can operate in at least two different modes, wherein in each of the modes, the emitted light (5) has a different light distribution. The module has a mode selector (10) for selecting the mode in which the module operates, and it has an optical arrangement. The arrangement includes—a microlens array (LL1) with a multitude of transmissive or reflective microlenses (2) which are regularly arranged at a lens pitch P (P1);—an illuminating unit for illuminating the microlens array (LL1). The illuminating unit includes a first array of light sources (S1) operable to emit light of a first wavelength L1 each and having an aperture each. The apertures are located in a common emission plane which is located at a distance D (D1) from the microlens array (LL1). In a first one of the modes, for the lens pitch P, the distance D and the wavelength L1 applies P2=2.Math.L1.Math.D/N wherein N is an integer with N≥1.

Claims

1. An illumination module, the module being operable in at least two different modes, the module comprising: a microlens array comprising a multitude of transmissive or reflective microlenses which are regularly arranged at a lens pitch P; an illuminating unit for illuminating the microlens array; and a mode selector for selecting in which one of the modes the module operates; the illuminating unit comprising a first array of light sources operable to emit light of a first wavelength L1 each and having an aperture each, wherein the apertures are located in a common emission plane which is located at a distance D from the microlens array, wherein in a first one of the modes,
P.sup.2=2.Math.L1.Math.D/N and wherein N is an integer with N≥1.

2. The module according to claim 1, wherein the mode selector comprises an actuator for changing a relative orientation in space of the microlens array with respect to the illuminating unit.

3. The module according to claim 1, wherein the mode selector comprises an actuator for changing the distance D.

4. The module according to claim 1, wherein the mode selector comprises an actuator for changing a rotational orientation about an axis perpendicular to the common emission plane of the microlens array with respect to first array of light sources.

5. The module according to claim 1, wherein the illuminating unit comprises a second array of light sources operable to emit light each and having an aperture each, and wherein the mode selector comprises a control unit for controlling a ratio of an intensity of light emitted from the first array of light sources and an intensity of light emitted from the second array of light sources.

6. The module according to claim 5, wherein the control unit is operable to have the light sources of the first array switched on and to have the light sources of the second array switched off in the first one of the modes, and to have the light sources of the second array switched on in a second one of the modes.

7. The module according to claim 5, wherein the light sources of the second array are operable to emit light of a second wavelength L2 each, wherein the second wavelength L2 is different from the first wavelengh L1.

8. The module according to claim 5, wherein the light emitters of the first array of light sources are regularly arranged at a light source pitch Q1, wherein P=Q1, and wherein an axis along which the microlenses are arranged at the pitch P is aligned parallel to an axis along which the light sources of the first array are arranged at the pitch Q1, and wherein the light emitters of the second array of light sources are irregularly arranged; or at least one of regularly arranged at a light source pitch Q2, wherein P≠Q2; regularly arranged at a light source pitch Q2, wherein an axis along which the microlenses are arranged at the pitch P is aligned at an angle with respect to an axis along which the light sources of the second array are arranged at the pitch Q2.

9. The module according to claim 5, wherein the second array of light sources is arranged aside the first array of light sources.

10. The module according to claim 5, wherein the first and the second arrays of light sources are mutually superimposed arrays of light sources.

11. The module according to claim 1, wherein in each of the modes, the emitted light has a different light distribution, and wherein the light distribution in a second one of the modes is more diffuse than the light distribution in the first one of the modes.

12. An apparatus for optically determining distances, the apparatus comprising an illumination module according to claim 1 and an image sensor for detecting light reflected from a scene illuminated by light emitted from the illumination module.

13. An illumination module, the module being operable in at least two different modes, the module comprising: a microlens array comprising a multitude of transmissive or reflective microlenses which are regularly arranged at a lens pitch P; an illuminating unit for illuminating the microlens array; and means for selecting in which one of the modes the module operates; the illuminating unit comprising a first array of light sources operable to emit light of a first wavelength L1 each and having an aperture each, wherein the apertures are located in a common emission plane which is located at a distance D from the microlens array, wherein in a first one of the modes,
P.sup.2=2.Math.L1.Math.D/N and wherein N is an integer with N≥1.

14. An illumination module, the module being operable in at least two different modes, the module comprising: a microlens array comprising a multitude of transmissive or reflective microlenses which are regularly arranged at a lens pitch P; an illuminating unit for illuminating the microlens array; and a mode selector for selecting in which one of the modes the module operate; the illuminating unit comprising one or more light sources operable to emit light of a first wavelength L1 each and having an aperture each, wherein for each of the one or more light sources, an optical path length for light emitted from the respective light source from the respective aperture to the microlens array amounts to one and the same distance D, wherein in a first one of the modes,
P.sup.2=2.Math.L1.Math.D/N and wherein N is an integer with N≥1.

15. The module according to claim 14, wherein the light emitted from each of the one or more light sources propagates from the respective aperture to the microlens array along a light path, wherein at least a portion of the light path is running through a material having a refractive index different from 1.

16. The module according to claim 14, wherein the module comprises at least one reflective element, and wherein the light emitted from each of the one or more light sources propagates from the respective aperture to the microlens array along a light path along which it is reflected at least once by the at least one reflective element.

17. The module according to claim 14, wherein the one or more light sources comprise an array of light sources.

18. The module according to claim 14, wherein in the first mode, each of the one or more light sources is arranged to illuminate a respective subset of the multitude of microlenses, and each of the subsets includes a plurality of neighboring microlenses, such that light from each particular one of the one or more light sources passes through different ones of the microlenses in the respective subset so as to produce an interference pattern.

Description

(1) Below, the invention is described in more detail by means of examples and the included drawings. The figures show schematically:

(2) FIG. 1 an illustration of an illumination module, in a side view;

(3) FIG. 2 an illustration of a pattern created by the light emitted from the illumination module of FIG. 1 in a first mode of operation;

(4) FIG. 2A a strongly schematized illustration of an intensity distribution along a line in the pattern of FIG. 2;

(5) FIG. 2B a strongly schematized illustration of an intensity distribution along a line in a pattern similar to the one of FIG. 2, but in a second mode of operation;

(6) FIG. 3 a graph illustrating contrast in patterns obtained for different numbers N1;

(7) FIG. 4 an illustration of an illumination module, to scale, in a side view;

(8) FIG. 5A an illustration of an illumination module including an actuator for changing a distance between MLA and LSA, in a first mode, in a side view;

(9) FIG. 5B an illustration of the illumination module of FIG. 5A, in a second mode, in a side view;

(10) FIG. 6A an illustration of an illumination module including an actuator for (laterally) rotating MLA vs. LSA, in a first mode, in a top view;

(11) FIG. 6B an illustration of the illumination module of FIG. 6A, in a second mode, in a top view;

(12) FIG. 7A an illustration in a top view of a detail of an illumination module including two arrays of light sources in which the light sources are differently arranged, wherein the arrays are aside each other;

(13) FIG. 7B an illustration in a top view of a detail of an illumination module including two arrays of light sources in which the light sources are differently arranged, wherein the arrays are overlapping each other;

(14) FIG. 8A an illustration in a top view of a detail of an illumination module including two arrays of light sources emitting light of different wavelengths, wherein the arrays are aside each other;

(15) FIG. 8B an illustration in a top view of a detail of an illumination module including two arrays of light sources emitting light of different wavelengths, wherein the arrays are overlapping each other;

(16) FIG. 9 an illustration of an illumination module with two arrays of light sources and with an additional optical component, in a side view;

(17) FIG. 10 an illustration of an apparatus for optically determining distances, in a side view.

(18) The described embodiments are meant as examples or for clarifying the invention and shall not limit the invention.

(19) FIG. 1 shows a schematic illustration of an illumination module for emitting light 5, in a side view. At the same time, FIG. 1 shows a schematic illustration of an optical arrangement for producing light 5. Light 5 can be structured light.

(20) The module (and the optical arrangement) includes a microlens array LL1 (MLA LL1) including a multitude of microlenses 2 which are regularly arranged at a pitch P1. In the illustrated example, the microlenses 2 are congeneric microlenses. The module also includes an illuminating unit by means of which MLA LL1 is illuminated. The illuminating unit comprises array S1 of light sources (LSA S1). LSA S1 includes a multitude of light sources 1 which are regularly arranged at a pitch Q1. In the illustrated example, the light sources 1 are congeneric light sources. The light emitted from the light sources 1 can travel on a light path to the MLA LL1 which is free of any intervening surface having optical power.

(21) The module also includes a mode selector 10 by means of which it can be selected in which one of two or more modes of operation the module operates, wherein a light intensity distribution of the emitted light 5 is different in different modes.

(22) In the illustrated case of FIG. 1 and also in other Figures, the microlenses 2 are transparent refractive semi-concave microlenses. However, the microlenses 2 may alternatively be concave microlenses or convex microlenses or semi-convex microlenses. And they may furthermore alternatively be diffractive microlenses or diffractive-and-refractive microlenses, the latter also being referred to as hybrid microlenses. And the microlenses 2 may also be reflective microlenses. In the latter case, the structured surface of the microlens reflects light impinging on it.

(23) In the illustrated case of FIG. 1 and also in other Figures, only a small number of microlenses 2 is illustrated. However, in practice many more microlenses may be provided, and the same holds also for the relatively small number of illustrated light sources drawn.

(24) LSA S1 can be, e.g., an array of VCSELs, such that each of the light sources 1 is a VCSEL.

(25) Light sources 1 emit light of a wavelength L1 (not indicated in the Figures) into an emission cone each, as indicated in FIG. 1, wherein the cones may have a circular cross-section but do not need to have a circular cross-section. Opening angles of the cones are typically between 2° and 120° or rather between 5° and 25°, e.g., about 10°. The emission cones are not free from overlap, as can be seen in FIG. 1 (dashed lines). The emission cones overlap, typically at least for immediately adjacent light sources 1, and optionally rather, each microlens 2 is illuminated by at least 6 light sources 1.

(26) Light sources 1 may, e.g., emit infrared light.

(27) Each light source 1 illuminates several ones of the microlenses 2. E.g., a subset of at least two, e.g., of four or more such as of at least 20 microlenses 2 is illuminated by each of the light sources 1.

(28) This way, interference between light emitted from a specific light source 1 but having passed through different ones of the microlenses 2 can interfer so as to produce an interference pattern. Light emitted from another one of the light sources 1 produces, in the same way, the same interference pattern, such that, in the far field, e.g., beyond 2 cm or beyond 5 cm after having interacted with MLA LL1, all the interference patterns superimpose. This way, the emitted light 5 produces a high-intensity interference pattern which can be used to illuminate a scene or be caught on a screen.

(29) Manufacture of an module of the described kind is simplified by the fact that no precision lateral alignment of MLA LL1 and LSA S1 is necessary for producing high-contrast illumination patterns. The x-y-tolerance (shifts in a plane parallel to the MLA plane/emission plane) is very high; z tolerances (relating to the distance between the MLA and the illuminating unit) are not very delicate; and also rotational alignment requirements are not very high.

(30) A distance between LSA S1 (and, more particularly the light sources 1 and their respective apertures, respectively) and MLA LL1 (and, more particularly the microlenses 2) is referred to as D1 (at least on the first mode of operation).

(31) FIG. 2 is a schematic illustration of a pattern 8 created by light 5 produced by the module of FIG. 1, e.g., in the first mode. The pattern 8 is recorded in the far-field. The dark spots indicate locations of high light intensity, whereas white area indicates regions of low light intensity.

(32) It turned out that for specific selections of pitches P1, wavelengths L1 and distances D1, a contrast present in such a pattern is particularly high, whereas for other distances, only much lower contrast is present in a created pattern.

(33) A formula in which the decisive magnitudes P1, L1 and D1 are interconnected so as to obtain triplets P1, L1, D1 for which particularly sharp contrast in patterns 8 is obtained reads as follows:
(P1).sup.2=2*(L1)*(D1)/(N1).

(34) Therein, N1 designates an integer which is at least 1. I.e. for N1=1 or 2 or 3 or 4, . . . , triplets P1, L1, D1 can be selected which fulfill the above equation, and thus, the parameters for an illumination module for high-contrast pattern generation are determined.

(35) In the first mode of operation, the module operates to fulfill the equation and thus to produce a high-contrast light distribution and thus a high-contrast light pattern.

(36) In the second mode of operation, another light distribution is produced which can fulfill the above equation, too, or, alternative, not fulfill the equation.

(37) For example, the emitted light 5 exhibits a higher contrast and/or is less diffuse than the light distribution of the light 5 emitted in the second mode.

(38) FIGS. 2A and 2B very schematically illustrate an intensity distribution along a line each, wherein the intensity is on the y-axis, and a space coordinate runs along the x-axis.

(39) FIG. 2A very schematically illustrates an intensity distribution along a line of the pattern illustrated in FIG. 2, the line running through intensity maxima of the light pattern of FIG. 2. During operation in the first mode, in this case, the above equation is fulfilled, P1=Q1 applies, the LSA S1 is aligned parallel to the MLA LL1 (i.e. the plane defined by MLA LL1 is aligned parallel to the plane defined by LSA S1), and LSA S1 and the MLA LL1 are also laterally aligned parallel to each other, i.e. both pitches P1 and Q1 are distances of microlenses and of light sources, respectively, positioned along lines which are parallel to each other. The contrast of the produced light pattern is high (pronounced intensity maxima on low background).

(40) In the second mode, an intensity distribution along a line of a pattern analogous to the one illustrated in FIG. 2 can look like illustrated in FIG. 2B. Disrupting the above equation and/or using a different arrangement of light sources 1 can lead to (pronouncedly) less contrast.

(41) Some ways of accomplishing that the illumination module can emit, in the at least two modes, at least two different light distributions will be discussed further below.

(42) FIG. 3 shows a graph illustrating contrast in patterns 8 from emitted light 5, obtained for different numbers N1, wherein in the graph of FIG. 3, N1 is a continuous positive number, assigned to the horizontal axis. Along the vertical axis, a magnitude indicative of the contrast obtained in a light pattern 8 is indicated.

(43) As is obvious from FIG. 3 (cf. the small arrows), particularly high contrast is present if N1 is an integer. N1=2 promises highest contrast, and in the case of N1 being 1 or 3 or 4, also very high contrast patterns can be obtained. For higher integers N1, still a high contrast is obtained, which is clearly higher than contrast for non-integer numbers in between. However, illumination patterns may also be produced for non-integer factors instead of integer N, e.g., for 0.5 or 1.5.

(44) If P1 and L1 are given (fixed), N1=1 results in a small value for D1 such that the optical arrangement and thus also the illumination module can be rather shallow, i.e. small in the direction of light emission. Cf. the equation above.

(45) As can be inferred from FIG. 3 and the equation depicted above, a gradual variation of the distance D1 starting at one of the peaks (with an integer N1, and with the equation fulfilled) can result in a gradually decreasing contrast in the emitted light distribution. And similarly can a gradual variation of the wavelength L1 starting at one of the peaks (with an integer N1 and the equation fulfilled) result in a gradually decreasing contrast in the emitted light distribution.

(46) FIG. 4 is an illustration to scale and in a side view, of an illuminating unit. FIG. 4 illustrates, e.g., the case of P1=Q1=50 μm for N1=2 and L1=833 nm. The far-field in which the pattern 8 can be observed and recorded is much too far away to be illustrated in FIG. 4.

(47) LSA S1 does not have to, but may be a regular array. And it turned out that particularly high contrast patterns can be obtained when MLA LL1 and LSA S1 are mutually parallel arrays of the same geometry, wherein P1=Q1 applies. And still very high contrast patterns can be achieved if P1/Q1 amounts to 2 or 3 or 4 or to 3/2 or 4/3 or 5/2 or 5/4 or if Q1/P1 amounts to 2 or 3 or 4 or to 3/2 or 4/3 or 5/2 or 5/4. In fact, for p1P1=q1Q1 (with p1≥1 and q1≥1, p1 and q1 designating integers), illumination patterns can be produced which have an increased complexity, in particular illumination patterns which have a larger unit cell, and wherein the larger unit cell is repeated with a larger periodicity—than compared to the case P1=Q1.

(48) MLA LL1 and/or LSA S1 may be one-dimensional (i.e. linear) arrays, but for many applications, MLA L1 and/or LSA S1 are two-dimensional (i.e. aerial) arrays.

(49) FIGS. 5A and 5B are illustrations (in a side view) of an illumination module including an actuator for changing a distance between MLA LL1 and and LSA S1, which can constitute a mode selector 10 or can be included in a mode selector 10. The actuator can include, e.g., a piezoelectric element or a coil for accomplishing a change of said distance from a value D1 in the first mode (cf. FIG. 5A) to a value D2 in the second mode (cf. FIG. 5B) and, optionally, also back to D1, e.g., repeatedly.

(50) For example, in the first mode, the above-mentioned equation can be fulfilled, resulting in a high-contrast pattern, while in the second mode, the equation (with D1 replaced by D2) is not fulfilled, .i.e. there exists no integer N1 such that the equation would apply; and thus, the light emitted from the illumination module can have a lower contrast.

(51) FIGS. 6A and 6B are illustrations (in a top view) of an illumination module including an actuator for changing a rotational orientation of MLA LL1 versus LSA S1 about a vertical axis, i.e. about an axis perpendicular to the common emission plane from which the light sources emit light. In FIGS. 6A, 6B, the microlenses are symbolized by large open circles, and the light sources are symbolized by small black circles.

(52) The actuator can constitute a mode selector 10 or can be included in a mode selector 10. The actuator can include, e.g., a piezoelectric element or a coil for accomplishing a rotation of MLA LL1 versus LSA S1 such that the relative rotational orientation of MLA LL1 and LSA S1 is changed by the mode selector when switching from the first mode to the second mode and vice versa. Like in all other embodiments, too, also here the mode selector can be operable to repeatedly, e.g., periodically, change between different modes such as between the first and the second mode, wherein also a third mode and still further modes can be arranged for.

(53) For example, in the first mode, MLA LL1 and LSA S1 can have a laterally parallel mutual arrangement (like shown in FIG. 6A), whereas in the second mode, MLA LL1 and LSA S1 can have a laterally angled mutual arrangement (like shown in FIG. 6B).

(54) It is possible therein that in both modes, the first mode and the second mode, the above-mentioned equation is fulfilled. However, in an alternative, the equation is fulfilled in the first, but not in the second mode.

(55) The arrangement in the first mode (FIG. 6A) can result in a high-contrast pattern, while in the second mode (FIG. 6B), the emitted light can be more diffuse having less contrast and/or can produce a more complex pattern.

(56) FIGS. 7A and 7B are an illustration in a top view each of a detail of an illumination module including two arrays of light sources S1, S2 in which the light sources are differently arranged. In array S1 of light sources, the light sources (symbolized by small black circles) are periodically arranged, even two-dimensionally periodically, the light sources being located in a square grid. In array S2 of light sources, the light sources (symbolized by small open squares) are not periodically arranged (and neither regularly arranged), but, e.g., randomly distributed, as illustrated. The light sources of both arrays S1, S2 are arranged such that they can illuminate the microlens array (not illustrated, but similar as in FIGS. 1 and 4).

(57) In FIG. 7A, the arrays are aside each other. In FIG. 7B, however, the arrays are overlapping each other, such that the light sources of the first array S1 and the light sources of the second array S2 are interspersed or interlacing. This can also be considered as mutually superimposed arrays of light sources.

(58) In both cases (FIG. 7A and FIG. 7B), the mode selector 10 is operated such that in the first mode, the microlens array is illuminated by LSA S1 only and that in the second mode, the microlens array is illuminated by LSA S2 only, wherein it is also possible that in the second mode, the microlens array is illuminated by both microlens arrays S1 and S2. Instead of merely switching on and of light sources, mode selector 10 could control the emitted light intensities in a graded way.

(59) In the first and optionally also in the second mode, the equation described above can be fulfilled.

(60) The wavelength of the light emitted by the first array S1 can be identical with or, alternatively, be different from the wavelength of the light emitted by the second array S2.

(61) The emission plane of the first array S1 can be identical with or, alternatively, be different from the emission plane of the second array S2.

(62) FIGS. 8A and 8B are an illustration in a top view each of a detail of an illumination module including two arrays of light sources S1, S2, wherein a wavelength of the light emitted by the light sources of LSA S1 is different from a wavelength of the light emitted by the light sources of LSA S2.

(63) The light sources of both arrays S1, S2 are arranged such that they can illuminate the microlens array (not illustrated, but similar as in FIGS. 1 and 4). However, in array S1 of light sources, the light sources (symbolized by small black circles) emit light at a wavelength which is not emitted by light sources of array S2 (symbolized by open circles).

(64) In one of the arrays or in both arrays S1, S2, the respective light sources can be periodically arranged, even two-dimensionally periodically, the light sources being located, e.g, on a square grid, as illustrated in FIGS. 8A, 8B

(65) In FIG. 8A, the arrays S1, S2 are aside each other. In FIG. 8B, however, the arrays are overlapping each other, such that the light sources of the first array S1 and the light sources of the second array S2 are interspersed or interlacing. This can also be considered as mutually superimposed arrays of light sources.

(66) In both cases (FIG. 8A and FIG. 8B), the mode selector 10 is operated such that in the first mode, the microlens array is illuminated by LSA S1 only and that in the second mode, the microlens array is illuminated by LSA S2 only, wherein it is also possible that in the second mode, the microlens array is illuminated by both microlens arrays S1 and S2. Instead of merely switching on and of light sources, mode selector 10 could control the emitted light intensities in a graded way.

(67) In the first and optionally also in the second mode, the equation described above can be fulfilled.

(68) The emission plane of the first array S1 can be identical with or, alternatively, be different from the emission plane of the second array S2.

(69) In array S1 of light sources, the light sources can be (as illustrated in FIGS. 8A, 8B) periodically arranged, even two-dimensionally periodically, the light sources being located in a square grid. In array S2 of light sources, the light sources can be arranged like in array S1 (as illustrated in FIGS. 8A, 8B), but it can also be provided that the light sources in one or both of arrays S1, S2 are arranged in a different way.

(70) FIG. 9 is an illustration of an illumination module with two arrays S1, S2 of light sources and with an optional additional optical component 3, in a side view. The additional component can be, e.g., a prism array including a plurality of prisms 4.

(71) Light from the MLA L1 is redirected by the additional optical component 3.

(72) The microlens array MLA LL1 is arranged between the illuminating unit and the additional optical component and thus between the LSAs S1, S2 and the additional optical component.

(73) FIG. 9 can be, e.g., a side view of an illuminating unit of which FIG. 8A illustrates a detail.

(74) FIG. 10 is an illustration of an apparatus 200 for optically determining distances, in a side view and strongly schematized. The apparatus 200 can be used for optical ranging based on illuminating objects in a scene such as objects 50a, 50b and evaluating the reflected light in order to determine distances.

(75) Apparatus 200 includes an illumination module 20 which can be an illumination module as described herein before, and a light sensor 30 for detecting light emitted from the illumination module and reflected from objects in the illuminated scene. Sensor 30 can be an image sensor. Apparatus 200 can furthermore include a controller 50 for controlling and/or reading out the sensor 30, and/or for controlling the illumination module 20, and/or controller can be used for determining distances based on the data obtained by sensor 30. Apparatus 200 can optionally includes an optical system 40 such as one or more lenses.

(76) Light emitted from the illumination module 20 in the first mode of operating module 20 is referened 5A, wherein in FIG. 10, only one exemplary ray is drawn; and light emitted from the illumination module 20 in the second mode of operating module 20 is referenced 5B, wherein in FIG. 10, only one exemplary ray is drawn.

(77) The above-explained operation of the the illumination module 20 in at least two different modes in which light of different light distributions is emitted can facilitate covering a larger range of distances determinable by the apparatus 200 and/or can facilitate to covering a wider range of textures of objects 50a, 50b.

(78) Other implementations are within the scope of the claims.