Spatial light modulators and low-pass filtering in slit-lamp microscopes.

Abstract

The slit lamp microscope includes a microscope assembly (8) that projects an object plane (11) onto an eyepiece (18) or camera (16), and an illumination assembly (9) having a spatial light modulator (24). The illumination assembly includes a beam splitter (70) that acts as a low-pass filter to suppress the spatial frequencies of the pixels of the light modulator (24) and produce more uniform illumination. In other embodiments, actuators (90-98) may be used to deflect at least a portion of the illumination imaging optics (26) to produce a low-pass filtered image of the spatial light modulator (24).

Description

[Technical Field]

[0001] The present invention relates to a slit lamp microscope, i.e. an ophthalmic microscope adapted to illuminate a patient's eye with a slit-like or otherwise structured illumination field and to view the eye through a microscope arrangement, the structured illumination being generated using an electronically controlled spatial light modulator. [Background technology]

[0002] Conventionally, the illumination device of a slit lamp microscope includes a slit aperture and illumination imaging optics adapted to project the slit aperture into the object plane.

[0003] WO 2021144000 describes a slit lamp microscope in which the slit aperture is replaced by a high-resolution spatial light modulator. This type of slit lamp microscope illuminates the eye with a slit-shaped illumination field or another type of structured light field, making it possible to quickly and easily adapt the illumination structure to current requirements. Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to further improve the illumination quality of this type of slit lamp microscope. [Means for solving the problem]

[0005] This problem is solved by the slit lamp microscope of claim 1. The slit lamp microscope therefore comprises at least the following elements: i) Microscope device: This device projects an object plane into the eyepiece and / or camera of the slit lamp microscope. In operation, the patient's eye is placed in the object plane so that it can be viewed through the microscope device. ii) Illumination device: This device is adapted to generate a structured and adaptive illumination field in the object plane. This device includes the following elements: a) At least one light source: the light source generates the radiation to be projected into the object plane. b) Electronically controlled spatial light modulators: These modulators are adapted to spatially modulate light from a light source. They comprise an array of pixel modulators, e.g., an array of mirrors or liquid crystal light valves, which have a spatial frequency fx along a first dimension and a spatial frequency fy along a second dimension, the two dimensions extending transversely to each other, in particular perpendicularly to each other. c) Illumination and imaging optics: These optics project the pixel modulator array towards the object plane, thus generating a structured light field in the object plane. The structure (e.g., boundaries) of this light field can be defined by setting the spatial light modulator in a desired pattern.

[0006] According to the invention, the imaging optics includes a low-pass filter that attenuates at least one of the spatial frequencies fx and fy in the object plane.

[0007] In the absence of such a low-pass filter, the structure of the pixel modulator array is projected, at least to a certain extent, into the image plane. As will be explained below, this can produce a perceptible periodic modulation of light in the bright areas of the object plane at spatial frequencies corresponding to fx and fy, respectively. By including a low-pass filter, i.e., by reducing the transmission of spatial frequencies fx and / or fy into the object plane, this modulation can be reduced, thereby allowing for more homogeneous illumination in the bright areas of the illumination.

[0008] In particular, the low-pass filter attenuates the modulation transfer function T between the spatial light modulator and the object plane at spatial frequencies fx much greater than the spatial frequency fx / 10. That is, if T1 is the modulation transfer function of the illumination and imaging optical system without a low-pass filter and T2 is the modulation transfer function of the illumination and imaging optical system with a low-pass filter, then: T1(fx) / T2(fx) is at least 5 times, especially at least 10 times, greater than T1(fx / 10) / T2(fx / 10).

[0009] Advantageously, the same applies for the dimension y, ie T1(fy) / T2(fy) is at least 5 times, in particular at least 10 times, greater than T1(fy / 10) / TZ(fy / 10).

[0010] Advantageously, the low-pass filter is applied to attenuate the transmission of spatial frequencies fx and / or fy into the object plane by a factor of at least 10, in particular by a factor of at least 20, compared to the respective tenth spatial frequencies fx / 10 and fy / 10. In other words, for example for the first dimension x: If T2(fx) is the modulation transfer function of the illumination and imaging optics at spatial frequency fx, and T2(fx / 10) is the modulation transfer function of the illumination and imaging optics at spatial frequency fx / 10, then In that case, the ratio T2(fx / 10) / T2(fx) is greater than 10, especially greater than 20.

[0011] Advantageously, this type of attenuation, by a factor of at least 10, is achieved for both spatial frequencies fx and fy.

[0012] The low-pass filters may be based on different principles, such as imperfect imaging, temporal variation of imaging, and / or beam splitting. These techniques can be used individually or in combination.

[0013] In one embodiment, the low-pass filter is structured and adapted to generate at least two spatially offset images of the spatial light modulator at the object plane. Two or more such offset images can be used to provide low-pass filtering along at least one dimension of the pixel modulator array. To provide low-pass filtering along both dimensions x and y of the array, the filter must generate at least three images that are offset from one another along at least two different, i.e., non-collinear, directions.

[0014] Advantageously, the low pass filter generates at least four images of the spatial light modulator that are mutually offset along at least two different (ie non-collinear) directions in the object plane.

[0015] In a very simple embodiment, the low-pass filter comprises at least one beam splitter in the illumination light path after the spatial light modulator (i.e. between the spatial light modulator and the object plane), which may be adapted to generate at least two, in particular at least four, mutually offset light fields, which can then be used to generate mutually offset images in the object plane.

[0016] Additionally or alternatively, the low-pass filter may include an actuator adapted to move at least one optical element of the illumination and imaging optics between at least first and second positions to generate at least two spatially offset images in the object plane. Alternatively or additionally, the actuator may be adapted to move the spatial light modulator between at least first and second positions to generate at least two spatially offset images in the object plane. In both cases, the microscope includes a control unit adapted to cyclically operate the actuator.

[0017] Advantageously, the frequency of the periodic drive is at least 40 Hz, in particular at least 100 Hz, in order to produce for a human observer the impression of a flicker-free continuous overlap of at least two images.

[0018] In yet another embodiment, the illumination optics has a Fourier plane corresponding to the Fourier transform of the spatial light modulator, and the low-pass filter comprises a spatial filter in the Fourier plane that blocks at least the range corresponding to spatial frequencies fx and / or fy and advantageously their harmonics.

[0019] In a further embodiment, the low pass filter may be implemented by illumination imaging optics that projects an image of the spatial light modulator into an image plane that is offset from the object plane by at least 500 μm.

[0020] In another embodiment, the low pass filter may comprise a diffuser, in particular a diffractive diffuser.

[0021] The invention will be better understood and objects other than those set forth above will become apparent when the following detailed description of the invention is considered, such description referring to the accompanying drawings, in which: [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 shows one embodiment of a slit lamp microscope. [Figure 2] FIG. 2 illustrates one embodiment of the components of a lighting device. [Figure 3] FIG. 3 shows a portion of a spatial light modulator. [Figure 4] FIG. 4 shows an idealized image of a portion of the spatial light modulator of FIG. 3 at the object plane with the mirror in a first position (the dark areas represent illuminated regions). [Figure 5] FIG. 5 qualitatively shows the frequency transfer function of an illumination imaging optical system with a low-pass filter. [Figure 6] FIG. 6 shows a first embodiment of the low-pass filter. [Figure 7] FIG. 7 shows an image corresponding to that of FIG. 4 with a low pass filter in place. [Figure 8] FIG. 8 shows a Fourier filter optimized for one wavelength. [Figure 9] FIG. 9 shows Fourier filters optimized for other wavelengths. DETAILED DESCRIPTION OF THE INVENTION

[0023] Overview FIG. 1 shows one embodiment of a slit lamp microscope.

[0024] The microscope has a base 1 placed on, for example, a table, a translationally displaceable stage 2 mounted on the base 1, a first arm 3, and a second arm 4.

[0025] The stage 2 is linearly displaceable relative to the base 1 along two horizontal directions.

[0026] The arms 3 and 4 are attached to the stage 2 and rotate about a common vertical rotation axis 5 .

[0027] The device may further include a headrest 7 assembled to the base 1 for accommodating the patient's head.

[0028] Arm 3 carries a microscope device 8 and arm 4 carries an illumination device 9, a so-called "slit lamp".

[0029] The microscope assembly 8 has an optical axis 12. The assembly includes microscope optics 14, 15, such as an objective lens 14 and zoom optics 15, which project an image of the eye 10 onto a camera 16 and / or into an eyepiece 18. A beam splitter 20 or flip mirror may be provided to split the light between these components.

[0030] The illumination device 9 rotates about a pivot axis 5. The illumination device is adapted to project a structured light beam onto the examined eye 10. The illumination device includes a light source 22, a spatial light modulator 24, and illumination and imaging optics 26 including at least one lens 27.

[0031] The light source 22 may include several units that emit different wavelengths, for example in the red, green, blue, and infrared regions of the optical spectrum, which may be controlled separately to change the color of the light source 22.

[0032] Advantageously, the light source 22 comprises at least one LED and / or semiconductor laser. This type of light source is advantageous because LEDs and semiconductor lasers can be pulsed rapidly and precisely.

[0033] Illumination and imaging optics 26 project light from modulator 24 onto, for example, the front surface of eye 10 via a deflection mirror 28 mounted, for example, on arm 4. The front surface of eye 10 is assumed to be located at object plane 11, which is an optically conjugate plane of spatial light modulator 24 with respect to illumination and imaging optics 26. Note that, as explained in the "Defocusing" section below, in one embodiment, object plane 11 is not exactly in an optically conjugate plane of spatial light modulator 24.

[0034] The pivot axis 5 lies in the object plane 11 to keep the center of the image in focus while rotating one or both of the arms 3, 4.

[0035] The illumination device 9 can be arranged above or below the deflection mirror 28 .

[0036] A control unit 32 controls the components of the microscope. In particular, the control unit may include, for example, a microprocessor 34 and a memory 36. The microprocessor 34 is programmed to perform steps for controlling the microscope, and the memory 36 stores data and / or instructions for doing so.

[0037] lighting equipment 2 shows a more detailed embodiment of the illumination device 9. This illumination device is designed to project an illumination field of defined contour onto the eye 10. The illumination field may be, for example, circular, rectangular or slit-shaped. Even though the illumination device is referred to herein as a "slit lamp", the illumination field does not necessarily have to be slit-shaped; it may have any shape.

[0038] In this embodiment, the lighting device 9 comprises four individual light sources 22a-22d with different spectral emission characteristics, which together form the "light source" 22 of the lighting device. For example, the light sources may comprise an infrared light source, a red light source, a green light source, and a blue light source. Advantageously, the light sources are LEDs. In particular, each light source may be a single LED.

[0039] The light from each light source is substantially collimated using collimation optics 40a to 40d.

[0040] Three dichroic mirrors 42a, 42b, 42c are used to coaxially combine the light from the light sources 22a-22d.

[0041] The combined illumination light is passed through homogenizing optics 44, such as a fly's eye lens array as described in US Pat. No. 6,507,434.

[0042] The two cylindrical lenses 46a, 46b, the further lens 46c and the homogenizing optics 44 similarly together spread the light beam along one direction, giving it an elongated cross-section, e.g., a cross-section having a width-to-height ratio of 16:9, for example, to better match the typically available form factors of spatial light modulators.

[0043] A mirror 48 deflects the light into an assembly of two prisms 50a, 50b with a gap 52 between them.

[0044] The light beam passes through prism 50 a , gap 52 and prism 50 b and reaches spatial light modulator 24 .

[0045] In the illustrated embodiment, spatial light modulator 24 is a DMD ("Digital Micromirror Device") having a two-dimensional array of individually rotating micromirrors 60 that act as pixel modulators. Control unit 32 is adapted to control the alignment of each micromirror 60 between at least first and second positions.

[0046] When a given mirror 60 is in the first position, light from the light source 22 is reflected by the given mirror as shown by line 54, passes through the first surface 62a of the prism 50b, is completely reflected by the second surface 62b of the prism 50b (at the gap 52), and exits through the third surface 62c of the prism 50b under the direction shown by line 56.

[0047] However, when a given mirror 60 is in the second position, light from the light source is reflected by the given mirror through the first surface 62a but is not completely reflected at the second surface 62b. A portion of that light exits through surface 62b. The reflected portion leaves prism 50b through another surface, but not in direction 56, and does not pass through, for example, an aperture in illumination and imaging optics 26.

[0048] Thus, the control unit 32 can individually set each pixel (each micromirror 60) of the spatial light modulator 24 to an on state and an off state, thereby defining the contour and shape of the light field at the target 10 (shown in FIG. 2 as being located in the object plane 11 of the illumination device).

[0049] Light from the pixels of spatial light modulator 24 enters illumination and imaging optics 26, which may include one or more lenses. From there, the light can pass through a deflecting mirror 28 and reach object plane 11.

[0050] The illumination and imaging optics projects the spatial light modulator 24 onto the target 10 , ie, the target 10 is in an object plane 11 in the illumination and imaging optics 26 that is conjugate with the plane 64 of the spatial light modulator 24 .

[0051] 3 shows a subsection of 64 mirrors 60 of spatial light modulator 24 in a first position (i.e., their on position). As can be seen, mirrors 60 form a two-dimensional array extending along first and second dimensions x and y. The pixel spacing along x is dx and the spacing along y is dy. Mirrors 60 have extensions ex and ey, respectively, that are typically smaller than dx and dy, i.e., there are gaps 61 between mirrors 60 that do not reflect light.

[0052] Assuming all mirrors 60 of the modulator section of Figure 3 are in their first position, the illumination pattern in object plane 11 produced by these mirrors would appear as shown in Figure 4, assuming substantially perfect imaging of the illumination imaging optics (Note: the dark areas in Figure 4 represent illuminated portions in object plane 11).

[0053] As can be seen, an array of illumination areas 66 extending along directions x' and y' is created, the array having a spacing dx' along direction x' and a spacing dy' along direction y'.

[0054] Between the illuminated areas 66 there are unilluminated areas 68 corresponding to the gaps 61 between the mirrors 60. The illumination is therefore inhomogeneous.

[0055] This inhomogeneous pattern in the bright areas of object plane 11 can become apparent when viewing eye 10 at high magnification using microscope apparatus 8. This is particularly true for examinations that rely on specular reflection of light on the eye, such as when viewing the anterior or posterior surface of the cornea to examine the endothelium, or when viewing the anterior or posterior aspects of the lens. Inhomogeneous illumination is also particularly evident when recording cross-sections of the eye with narrow slit illumination.

[0056] Although artifacts due to inhomogeneous illumination can be removed from camera images using image processing, such processing can be difficult, especially when the illumination structure interferes with the camera's pixel structure, and is impossible when viewing the microscope image directly through the eyepiece. Likewise, any such processing would potentially reduce the resolution of the microscope device 8.

[0057] Low-Pass Filter To reduce artifacts due to inhomogeneous illumination, the illuminator is equipped with a low-pass filter, such as a beam splitter or other means, as described in the following section.

[0058] That is, the purpose of this low-pass filter is to suppress (i.e., attenuate) spatial frequencies fx=1 / dx and / or fy=1 / dy along x and y when imaging the spatial light modulator 24 into the object plane 11.

[0059] In the coordinate system of the object plane 11, the spatial frequencies fx and fy of the light modulator correspond to the spatial frequencies fx'=1 / dx' and fy'=1 / dy'.

[0060] In the following, we define T as the modulation transfer function of the illumination and imaging optics 26, which is a function of the spatial frequency f at the spatial light modulator 24 (see https: / / en.wikipedia.org / wiki / Optical_transfer_function), where f is the spatial frequency in the x and y dimensions (note: for simplicity, we assume that both dimensions x and y have the same modulation transfer function T; if this is not the case, Tx(f) and Ty(f) can be used).

[0061] 5 shows the modulation transfer function T1(f) of the illumination and imaging optics 26 without the low-pass filter. As can be seen, although T1 is attenuated for higher frequencies, there is at least one residual modulation transfer at frequency fx.

[0062] 5 further shows the modulation transfer function T2(f) of the illumination and imaging optics 26 when the low-pass filter is present. As can be seen, the low-pass filter produces a strong attenuation at fx, but a much smaller attenuation at lower spatial frequencies, such as fx / 10. Thus, for a given brightness of the illuminated area of ​​the target in the object plane, illumination inhomogeneities at fx are suppressed.

[0063] As mentioned above, advantageously, the attenuation of the modulation transfer function at fx / 10 is at least 5 times, in particular at least 10 times, smaller than at fx, i.e. T1(fx) / T2(fx) is at least 5 times, in particular at least 10 times, larger than T1(fx / 10) / T2(fx / 10).

[0064] Advantageously, the same applies to fy.

[0065] 5, the modulation transfer function T2(f) with a low-pass filter should be significantly smaller at fx than at lower frequencies such as fx / 10, so that illumination inhomogeneities at fx are barely visible. Therefore, as mentioned above, the ratio T2(fx / 10) / T2(fx) is advantageously greater than 10, in particular greater than 20. The same advantageously applies to fy.

[0066] 5 shows a further variation of the modulation transfer function T2'(f) in the presence of a low-pass filter. In this variation, the modulation transfer function T2'(f) has a minimum at fx and then rises again to a higher frequency, e.g., 1.5 fx, thereby improving the imaging quality for high-frequency components of the illumination pattern that are not caused by the repetitive structure of the spatial light modulator. However, T2'(f) should advantageously decrease again toward the second harmonic frequency 2 fx.

[0067] Thus, more generally, the modulation transfer function T2(fx) at frequency fx is advantageously at least one half that of the modulation transfer function at T2(1.5·fx) at frequency 1.5fx, i.e., T2(fx) < T2(1.5·fx) / 2. In particular, T2(1.5·fx) at frequency 1.5·fx is advantageously at least twice that of T2(2·fx) at frequency 2·fx, i.e., T2(2·fx) < T2(1.5·fx) / 2.

[0068] Such frequency synchronization of the modulation transfer function is most successfully achieved using Fourier filtering techniques, as will be explained below.

[0069] There are various ways to implement such low-pass filtering, some of which are described in the following section.

[0070] Beam splitter A first embodiment of the low-pass filter is shown in FIG. 6. In this embodiment, the low-pass filter includes a beam splitter 70. This low-pass filter is disposed in the path of the illumination light after the spatial light modulator 24 and before the object plane 11, and is arranged to generate at least two, particularly at least four, mutually offset light fields.

[0071] In the illustrated embodiment, the beam splitter 70 includes a first birefringent plate 72, a quarter-wave retardation plate 74, and a second birefringent plate 76, and the quarter-wave retardation plate 74 is disposed between the birefringent plates 72, 76.

[0072] The first birefringent plate 72 has an optical axis disposed advantageously at 45° with respect to its input surface for splitting the incident light 78a into two light fields 78b, 78c of equal intensity (here, it is assumed that the incident light 78a is unpolarized. If it is partially or fully polarized, one or more polarizers and / or wavelength retardation plates may be used to adapt the polarization so that the light fields 78b, 78c have the same intensity, as is known to those skilled in the art).

[0073] Since the light fields 78b, 78c after the first birefringent plate 72 are linearly polarized, a quarter wave retarder 74 is used to convert their polarization to circular polarization.

[0074] The light fields 78b, 78c then enter the second birefringent plate 76. Again, the second birefringent plate 76 has its optical axis arranged at 45° with respect to its input surface to once again split the incident light fields 78b, 78c. The second birefringent plate 76 is oriented differently from the first birefringent plate 72 to produce a split in a different direction. Thus, at the output side of the beam splitter 70, the incident light 78a has been split into four mutually offset light fields 80a, 80b, 80c, and 80d.

[0075] Advantageously, the four light fields 80a to 80d are offset from one another along rectangular directions rx, ry corresponding to the dimension x.

[0076] The offset between the optical fields along rx and ry is approximately half the spacing dx and dy of mirror 80, respectively, for reasons explained below.

[0077] Beam splitter 70 may be arranged adjacent to prism 50b, in particular adjacent to first surface 62a or third surface 62c. Advantageously, this beam splitter is assembled to one of these surfaces, in particular glued thereto. Placing a transparent filler (e.g., adhesive) between prism 50b and beam splitter 70 to prevent an air gap between the two components is highly advantageous, as it reduces the number of surfaces that the light must traverse.

[0078] In the embodiment of FIG. 2, beam splitter 70 is shown disposed on third surface 62c, with a transparent filler 71 between the two components.

[0079] Beam splitter 70, as mentioned, functions as a low-pass filter. In particular, if not placed too close to lens 27, the beam splitter essentially splits the image of spatial light modulator 24 in object plane 11 (as shown without the beam splitter in FIG. 4) into spatially offset images as illustrated in FIG.

[0080] To illustrate these four images, FIG. 7 shows a single mirror 60 in each of these four images outlined with different dashed lines as reference numerals 82a-82d.

[0081] As can be seen by comparing Figures 4 and 7, the illumination pattern in Figure 7 is more homogeneous than that in Figure 4, i.e. the mirror structure is less obvious, thus producing a better quality image.

[0082] The image offset along the direction x' is mx', and the offset along the direction y' is my'. The offset must be within a range that "blurs" the non-illuminated area 68 in FIG. 4. Therefore, advantageously, mx'=dx' / 2 and my'=dy' / 2. However, the offsets may deviate from these figures if the gap between the mirrors 60 is not too large. Along x', the offset mx' is advantageously between 0.2·dx'=0.2 / fx' and 0.8·dx'=0.8 / fx'. Similarly, along y', the offset my' is advantageously between 0.2·dy'=0.2 / fy' and 0.8·dy'=0.8 / fy'. Advantageously, mx' is between 0.4 / fx' and 0.6 / fx', and my' is between 0.4 / fy' and 0.6 / fy'.

[0083] A beam splitter based on a birefringent plate is described, for example, in Dimensioning of Optical Birefringent Anti-Alias ​​Filters for Digital Cameras, Proc. of 2010 IEEE 17 thIt has also become known for a completely different application, namely as an anti-aliasing filter disposed on a camera chip, as described by Schoberl et al. in International Conference on Image Processing, September 26-29, Hong Kong. This document mentions stacks of M=2, M=3, M=4, and even more mutually rotated birefringent plates, which can be used in this context as well.

[0084] More generally, therefore, the beam splitter 70 advantageously includes at least two differently oriented birefringent plates 72, 76 and a quarter wave retarder 74 disposed between each of the two birefringent plates 72, 76.

[0085] Instead of using a birefringent beam splitter, the technique may use other types of beam splitters that generate two or more mutually offset light fields. For example, semi-transparent mirrors can be used to split the light, and the resulting light fields can be redirected and directed by mirrors so that they are parallel and offset as desired.

[0086] Actuator In another type of embodiment, the low pass filter may include one or more actuators.

[0087] 2 as being disposed on the deflection mirror 28 of the illumination and imaging optics 26. The actuator 90, which may include, for example, one or more piezoelectric elements, is adapted to change the tilt angle of the deflection mirror 28 and thus offset the image of the spatial light modulator 24 in the object plane 11.

[0088] Advantageously, the actuator 90 is adapted to tilt the deflecting mirror 28 about two transverse axes to produce images that are offset along both the directions x' and y' in the object plane 11.

[0089] The actuator 90 is operated periodically by the control unit 32 to rapidly move the image. If such movement is fast enough, for example with a frequency of at least 40 Hz, advantageously at least 100 Hz, several spatially offset images will be generated on the object plane 11 for a human observer, which will again blur the unilluminated areas 68 of Figure 4, thereby producing a more homogeneous illumination.

[0090] Instead of (or in addition to) moving the deflection mirror 28, the actuator may move other parts of the illumination and imaging optics 26. For example, Figure 2 shows another actuator 92 adapted to periodically move the lens 27, and another actuator with reference numeral 94 adapted to move the prism assemblies 50a, 50b or parts thereof.

[0091] As a further variation, an actuator 96 may be provided to move the spatial light modulator 24 along the directions x and / or y.

[0092] In yet another embodiment as illustrated in FIG. 1, an actuator 98 may be provided to move all of the lighting devices 9 .

[0093] To assess whether a given actuator-based device is a low-pass filter within the meaning of the present invention, the image of the spatial light modulator 24 at the object plane 11 is preferably averaged over a period of time to obtain a "subjective image," i.e., the image as perceived by a human observer. Such averaging occurs while the actuator is periodically operated. The averaging preferably covers a period of at least 2.5 ms (corresponding to 40 Hz), in particular at least 5 ms (corresponding to 20 Hz). Low-pass filtering is then detected by testing whether specific frequencies fx' and / or fy' in the subjective image are suppressed, for example, by a factor of at least two, in particular by a factor of at least five, as described above.

[0094] Fourier filtering In yet another embodiment, filter 100 is placed in the back focal plane (Fourier plane) 102 of lens 27 (see FIG. 2). This plane holds the Fourier transform of the image of spatial light modulator 24. Filter 100 is applied to suppress Fourier components corresponding to spatial frequencies fx and fy and advantageously their higher harmonics.

[0095] For narrowband illumination, the filter 100 may consist, for example, of a simple aperture that blocks spatial frequencies above a given threshold, say 0.8fx and 0.8fy.

[0096] If it is desired to block only fx and fy and their harmonics, as illustrated by modulation transfer function T2' in Figure 5, filter 100 may be calculated, for example, from the Fourier transform of the pattern produced by the spatial light modulator (i.e., the pattern shown in Figure 4). Such a filter 100 is shown in Figure 8, where dark areas indicate areas that block light.

[0097] As known to those skilled in the art, the Fourier transform in the back focal plane 102 scales with the wavelength of light. Thus, if the light source 22 is a broadband light source, the filter 100 may include, for example, several stacked color filters attributed to different wavelengths, each color filter blocking spatial frequency components fx, fy (and their harmonics) in a wavelength range centered around its attributed wavelength.

[0098] As shown in the embodiment of FIG. 2, various wavelengths λ i If there are several individual light sources 22a-22d centered around the wavelength λ i, and includes several wavelength-selective filters that block spatial frequencies fk and their harmonics. For example, Figure 9 shows the same filters as Figure 8 but scaled to approximately twice the wavelength. For example, the filter in Figure 9 will be absorbing (in the dark areas) at a first (longer) wavelength λ1 (but not absorbing or much less at λ2), and the filter in Figure 8 will be absorbing (in the dark areas) at a second (shorter) wavelength λ2 (but not absorbing or much less at λ1).

[0099] More generally, therefore, the filter 100 advantageously filters several different wavelengths λ i for the spatial frequency fk and advantageously for suppressing its harmonics, the filters being of different wavelengths λ i Advantageously, in this case, the illumination device 9 includes a light blocking structure whose size is scaled at a wavelength λ i The present invention includes several light sources with different emission spectra, with emission maxima at

[0100] Defocusing In another embodiment, the low pass filter may be implemented by intentionally defocusing the illumination imaging optics 26. For example, lens 27 may be dimensioned to project the image of the spatial light modulator not towards object plane 11, but towards image plane 104 (as illustrated in FIG. 2) that is offset from object plane 11 by an offset r of at least 500 μm.

[0101] As mentioned above, the illumination device 9 rotates about a vertical rotation axis 5, which lies in the object plane 11. Such defocusing therefore implies that the image of the spatial light modulator 24 will be in front of or behind the rotation axis 5.

[0102] 2, object plane 11 is best disposed between microscope arrangement 8 and image plane 104, i.e., image plane 104 is located behind object plane 11 as viewed from microscope arrangement 8. This is advantageous because if microscope arrangement 8 is adjusted so that the user focuses their eyes at infinity in order to clearly see objects in object plane 11 (as is common), it will be more difficult for the user to focus on image plane 104, i.e., the user will be less likely to "accidentally" focus on image plane 104.

[0103] In another embodiment, such defocusing may be implemented by introducing spherical aberration into lens 27 or other components of imaging optics 26 .

[0104] Spherical aberration, as well as higher-order spherical aberrations, are aberrations (e.g., defocus) that are independent of the position and rotation of the illumination field and can be used to intentionally and uniformly blur the image of the spatial light modulator across the entire object plane to form a low-pass filter. In a similar manner, other aberrations, such as astigmatism, act as low-pass filters. Advantageously, a combination of classical higher-order aberrations can be used to generate the desired low-pass filter.

[0105] Diffuser In yet another embodiment, a diffuser 106 disposed between the spatial light modulator 24 and the object plane 11 may be used as a low-pass filter. Such a diffuser may be disposed, for example, on the first surface 62a or the third surface 62c of the prism 50b, similar to the beam splitter 70. Alternatively, it may be disposed, for example, in the Fourier plane.

[0106] Advantageously, the diffuser 106 is a diffractive diffuser, ie a diffuser that uses diffraction to diffuse light.

[0107] Note In the above embodiments, the low-pass filters are applied to suppress spatial frequencies fx and fy along x and y. Alternatively, the low-pass filters may also be designed to suppress only one of these spatial frequencies, particularly if the illumination system is designed in such a way that one of the corresponding frequencies fx' and fy' is much larger than the other at the object plane 11. In that case, only the smaller frequency may need to be suppressed, since the larger frequency may be beyond the resolution of the microscope system 8.

[0108] The various embodiments of the low pass filters described above may be combined with a beam splitter in one direction x and an actuator in the other direction y.

[0109] In the above-described embodiments, the light source and the spatial light modulator are separate elements. Alternatively, they may also be formed by a single device having an array of light sources, where each light source defines the illumination within one pixel.

[0110] While presently preferred embodiments of the present invention have been illustrated and described, it is to be clearly understood that the invention is not limited thereto and may be embodied and practiced in various other forms within the scope of the following claims.

Claims

1. i) a microscope device (8) that projects an object plane (11) into at least one of an eyepiece (18) and a camera (16); ii) an illumination device (9) comprising: a) at least one light source (22); b) an electronically controlled spatial light modulator (24) including an array of pixel modulators extending along first and second dimensions (x, y), said pixel modulators having spatial frequencies fx and fy along said first and second dimensions (x, y); and c) illumination and imaging optics (26) for projecting said array towards said object plane (11); The illumination device (9) includes a low-pass filter (70, 90-100, 106) that attenuates at least one of the spatial frequencies fx and fy in the object plane (11).

2. T1 is the modulation transfer function of the illumination and imaging optical system (26) without a low-pass filter (70, 90-100, 106) between the spatial light modulator (24) and the object plane (11), T2 is the modulation transfer function of the illumination and imaging optical system (26) with the low-pass filter (70, 90-100, 106) between the spatial light modulator (24) and the object plane (11), and T1(fx) / T2(fx) is at least 5 times, in particular at least 10 times, greater than T1(fx / 10) / T2(fx / 10); 2. The microscope according to claim 1, wherein in particular T1(fy) / T2(fy) is likewise at least 5 times, in particular at least 10 times, greater than T1(fy / 10) / T2(fy / 10).

3. 3. The microscope according to claim 1, wherein T2(fx / 10) / T2(fx) is greater than 10, in particular greater than 20, where T2 is a modulation transfer function of the illumination and imaging optical system (26) having the low-pass filter (70, 90-100, 106) between the spatial light modulator (24) and the object plane (11).

4. 4. The microscope according to claim 3, wherein T2(fx)<T2(1.5*fx) / 2, in particular T2(2*fx)<T2(1.5*fx) / 2.

5. 5. The microscope of claim 1, wherein the low-pass filters are adapted to generate at least two spatially offset images of the spatial light modulator at the object plane.

6. 6. The microscope of claim 5, wherein at the object plane (11), the image (82a-82d) of the spatial light modulator (24) has an offset mx' along the imaged first dimension between 0.2 / fx' and 0.8 / fx', in particular between 0.4 / fx' and 0.6 / fx', where fx' and fy' are the spatial frequencies of the array within the image at the image plane.

7. 7. The microscope of claim 5, wherein the low-pass filters are adapted to generate at least four spatially offset images of the spatial light modulator at the object plane.

8. 8. The microscope of claim 1, wherein the low-pass filter (70, 90-100, 106) comprises at least one beam splitter (70) after the spatial light modulator (24), the beam splitter (70) being adapted to generate at least two mutually offset light fields (80a-80d).

9. 9. The microscope of claim 8, wherein the beam splitter (70) is adapted to generate at least four mutually offset light fields (80a-80d).

10. 10. The microscope of claim 9, wherein the beam splitter (70) includes at least two birefringent plates (72, 76) of different orientations and a quarter-wave retarder (74) disposed between each of the two birefringent plates (72, 76).

11. The lighting device (9) an array of individually rotating mirrors (60), each mirror (60) having a first and a second position; a prism (50b) having first, second and third surfaces (62a, 62b, 62c), such that for a given mirror (60) in the first position, the light from the light source (22) is reflected by the given mirror (60), passes through the first surface (62a), is completely reflected at the second surface (62b), and exits through the third surface (62c), while for a given mirror (60) in the second position, the light from the light source (22) is reflected by the given mirror (60), passes through the second surface (62e), and is not completely reflected at the second surface (62b); 11. The microscope of claim 9, wherein the beam splitter (70) is disposed adjacent to the prism (50b).

12. 12. The microscope according to claim 11, wherein the beam splitter (70) is arranged on the first or third surface (62a, 62c), in particular on the third surface (62c).

13. 13. The microscope of claim 12, wherein the beam splitter (70) is coupled to the first or third surface (62a, 62c) via a transparent filler (71).

14. the low-pass filter (70, 90-100, 106) includes an actuator (90-100) adapted to move at least one optical element of the illumination and imaging optical system (26) and / or the spatial light modulator (24) between at least first and second positions to generate at least two spatially offset images (82a-82d) at the object plane (11); The microscope according to any one of the preceding claims, comprising a control unit (32) adapted to periodically operate said actuators (90-100).

15. 15. The microscope of claim 14, wherein the illumination and imaging optical system (26) includes at least one deflection mirror (28) that deflects light from the spatial light modulator (24) toward the object plane (11), and the actuator (90) is adapted to change the tilt angle of at least one of the deflection mirrors (28).

16. 16. A microscope according to any one of claims 1 to 15, wherein the illumination optical system has a Fourier plane (102) that holds the Fourier transform of the spatial light modulator (24), and the low-pass filter (100) suppresses the Fourier components of the image of the spatial light modulator (24) in the Fourier plane (102).

17. The low-pass filter (100) is configured to filter at several different wavelengths λ ｉ and several wavelength-selective filters which suppress said spatial frequencies fk and advantageously its harmonics for said different wavelengths λ ｉ 17. The microscope of claim 16, including a blocking structure scaled by

18. The illumination device (9) emits light of wavelength λ ｉ 18. The microscope according to claim 17, comprising several light sources (22a-22d) with different emission spectra, the emission of which is maximized at .

19. The illumination device (9) rotates around a rotation axis (5) lying in the object plane (11), A microscope according to any one of claims 1 to 18, wherein the low-pass filter (70, 90-100, 106) is implemented by the illumination and imaging optical system (26) that projects the image of the spatial light modulator (24) into an image plane (104) offset from the object plane by at least 500 μm.

20. 20. The microscope according to claim 19, wherein the object plane (11) is located between the microscope device (8) and the image plane (104).

21. The microscope according to any one of claims 1 to 20, wherein the low-pass filter (70, 90-100, 106) comprises a diffuser (106), in particular a diffractive diffuser.

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