Methods for manufacturing a micro lens

Abstract

The invention concerns methods for manufacturing micro lenses, an array of horizontally interconnected micro lenses, a micro lens and a stack of micro lenses. The method for manufacturing a micro lens (1) comprises the steps of providing a blank, in particular a polished wafer, in particular comprising glass and of forming an array (10) of horizontally interconnected micro lenses (1) by selective laser etching (SLE) of the blank. Each micro lens (1) is connected to a, preferably single, holding structure (11), by at least one interconnection (2), in particular at least one holding bar, preferably by two or three holding bars (2).

Description

[0001] Methods for manufacturing a micro lens

[0002] The invention concerns methods for manufacturing micro lenses , a method for manufacturing a system of micro lenses , an array of hori zontally interconnected micro lenses , a micro lens and a system of micro lenses .

[0003] The invention is related to the field of production of lenses from glass which need a high precision, wherein lens blanks are first formed in a polished ( glass ) wafer, preferably by means of SLE ( Selective Laser Etching) , and the invention is related to polishing lens blanks by means of a laser ( LP laser polishing) .

[0004] High precision lenses made of glass are for example needed for endoscopy . A large number of small lenses with diameters of 1 to 5 mm are used in endoscopy today . They are usually manufactured using a single-piece process . These lenses are manufactured individually from a glass block in the conventional processes of pre-grinding, lapping and polishing . The additional production steps , such as centring the individual lens and the usually double-sided coating, also require time-consuming handling steps .

[0005] In WO2019189225A1 a method for machining an aspherical lens , in particular a plano-concave lens , is shown which may comprise a pre-processing step and an etching step in which the glass substrate which has been subj ected to pre-processing is subj ected to wet etching .

[0006] The pre-processing step includes a step in which a particular position on the glass substrate is irradiated with a pulsed laser beam . A partial region inside the glass substrate is modified and a density distribution in the thickness direction is generated at least at the position irradiated with the pulsed laser beam . Chemical or physical methods may be used to form a recess having a predetermined shape of the glass substrate .

[0007] EP2683521B1 discloses a method for producing optical elements , in which the surface of a blank is processed by means of high- energy radiation to approximate to a desired surface contour, initially by coarse removal of material . After the coarse removal , the worked surface is polished with high-energy radiation, the polishing is carried out by lowering the viscosity of the surface material of the blank by using laser radiation as high-energy radiation . Laser intensities between 10 W / cm2and 1000 W / cm2are used for the polishing, and a laser beam having a beam diameter of at least 2 mm on the surface is used . The laser beam is guided over the surface in defocused mode . Extremely fine removal is carried out with a laser beam which is focused on the surface in continuous or pulsed operation of the laser and is guided over the surface with variable motion speed .

[0008] It is an obj ect of the present invention to prevent the drawbacks of the prior art and to provide methods for manufacturing a micro lens , a method for manufacturing a system of micro lens , an array of hori zontally interconnected micro lenses , a micro lens and a system of micro lenses , providing a high optical quality and reduced manufacturing costs .

[0009] The obj ect is achieved by a method for manufacturing a micro lens comprising the step of providing a blank, in particular a polished wafer, in particular comprising glass .

[0010] The polished wafer may be made of an optical glass with a low or high refractive index, such as fused silica, or glass types such as crown glasses , flint glasses , heavy flint glasses , for example, N-BK7, N-SK5, N-F2 or N-SF57 by Schott. Of course, equivalent glasses from other glass manufacturers are also possible .

[0011] The wafer may have a thickness in a range of 0.5mm to 5mm and a maximal diameter of in a range of 2cm to 25cm, in particular of 5cm to 10cm. The wafer may have the form of a circular disk, preferably with a diameter of 2 to 4 inch. Rectangular or square wafers are also suitable.

[0012] The method comprises the further step of forming an array of horizontally interconnected micro lenses preferably by selective laser etching (SLE) of the blank.

[0013] Selective laser etching (SLE) is a subtractive laser technology allowing fabrication of complex-shape 3D glass parts with micrometer precision. This technology consists of two fabrications steps: laser irradiation and subsequent chemical etching.

[0014] The combination of for example a femtosecond laser-based induced material modification and subsequent etching with potassium hydroxide, for example, allows individual parts to be produced flexibly from glass and independently of tools.

[0015] The femtosecond laser may provide a power of 5W, a wavelength of 1030nm, a pulse length of 300fs to lOps, and a repetition rate of smaller than 10MHz.

[0016] For a borosilicate glass an energy of HOOnJ, a pulse length of 5ps, a writing speed of 75mm / s and repetition rate of 105kHz may be chosen. As an example, for etching a KOH 8-9 mol / 1 may be used, at a temperature of 77 -83° C , during a processing time of 75min.

[0017] Generally, for each glass and each shape of structure and wafer size the optimum process window must be determined.

[0018] Selective laser etching allows the generation of structural surfaces without a so called "sub surface depth damage", which may affect the material to a depth in the order of some microns to tens of microns depending on the grinding or polishing means.

[0019] This has a positive effect on the subsequent polishing step and the polishing depth can be kept to a minimum and good optical quality can be achieved quickly during polishing.

[0020] Instead of the SLE process, ablation using an ultrashort pulse laser (UPLA) could also be used. This would vaporize the material and eliminate the need for a subsequent etching process. However, this process may result in somewhat lower accuracy and minor depth damage must be expected. One advantage, however, would be that this process would work for a wider range of optical glasses than SLE.

[0021] Within this context an "array of horizontally interconnected micro lenses" means an arrangement of at least two, more preferably up to 100, single micro lenses, preferably of the same type. The number of micro lenses on a wafer depends on the diameters of the micro lenses and the diameter of the wafer.

[0022] The micro lenses may have a maximal thickness in a range of 0.2mm to 4.5mm and a maximal diameter of up to 10mm, preferably a maximal diameter in a range of 1mm to 9mm. The micro lenses may be arranged in an ordered way, in particular in a regular two-dimensional , for example hexagonal , pattern .

[0023] Each micro lens is connected to a, preferably single , holding structure by at least one interconnection, in particular at least one holding bar, preferably by two or three holding bars .

[0024] The holding structure and the interconnections also result from the SLE process or the UPLA process and are also formed from the blank during the process of forming the micro lenses .

[0025] Especially the SLE process allows to generate slim interconnections , which do not widely af fect the shape of the perimeter of the micro lens , and which may easily be disconnected .

[0026] The holding structure may be a single structure or may consist of several parts which may be held together by the micro lenses and / or the interconnections .

[0027] When forming the array of hori zontally interconnected micro lenses there may arise a gap between the micro lenses and the holding structure . The interconnections may bridge this gap . The interconnections preferably have a maximal thickness which is smaller than the maximal thickness of the micro lenses . Preferably, the interconnections are formed by holding bars whose length is greater than the thickness .

[0028] The thickness of the interconnections may be in a range of 0 . 05mm to 0 . 2mm, the length in a range of 0 . 1mm to 0 . 5mm .

[0029] Each micro lens has an optical surface on at least one side . The micro lenses may have an optical surface on both sides .

[0030] Within this context the "optical surface" is the part of the surface of a micro lens which defines the clear aperture , that is the dimensional area of an optical component over which the speci fications for optical imaging performance by refraction must be met .

[0031] The forms and the distance of the two optical surfaces of each micro lens in combination provide a speci fic imaging characteristic by refraction, such as collimation .

[0032] The micro lenses may be plano-concave lenses , piano , convex lenses , bi-convex lenses , bi-concave lenses , convex-concave lenses and / or may have spherical and / or aspherical and / or freeform optical surfaces .

[0033] The SLE process and the UPLA process also allows for generation of free- form surfaces , such as for example aspherical or rotationally non-symmetric surfaces , without any additional ef fort .

[0034] An optical axis , which may be considered as the imaginary axis that passes through the centre of the refractive surface perpendicular to the surface , may be defined for, in particular rotationally symmetric, optical imaging surfaces of any type , also for aspherical lenses .

[0035] The micro lenses preferably have a cylindrical sheath which is parallel to the optical axis .

[0036] The micro lenses may have a cylindrical sheath having a basically circular base . However, other geometries are also conceivable , such as an ellipse , a square or a hexagon . Preferably, the array of hori zontally interconnected micro lenses is formed such that the optical axis of each micro lens crosses a predefined position with respect to the perimeter of the micro lens . For example , the optical axis lies at the centre of the preferentially round circumference in case of rotation- ally symmetric micro-lenses .

[0037] Preferably, the optical axes of opposing optical surfaces of the same micro lens coincide and may be centered with respect to an outer perimeter of the micro lens .

[0038] Usually, for forming a stack of micro lenses , the micro lenses have to be aligned under optical control and subsequently the lens mount is machined to a fit dimension referenced to the optical axis .

[0039] As according to the method of this invention the optical axis and the perimeter of the micro lenses have a defined relation, micro lenses may easily be stacked to form a lens system without the necessity of alignment under optical control and subsequent grinding for centering .

[0040] Due to the slim interconnections the cylindrical sheath of a separated micro lens is not af fected by the cut interconnection and the sheath may be used as a reference surface for stacking .

[0041] The cylindrical sheath of each micro lens may comprise at least one recess parallel to the optical axis and preferably extending along the complete thickness of the micro lens . This recess may give place for interconnections and / or may be used for an alignment of micro lenses during a subsequent stacking step . On at least one side the optical surface for optical imaging of each micro lens , preferably a central part of each micro lens , is surrounded by an edge section .

[0042] The edge section may be part of the micro lens which surrounds the optical surface , in particular a concave optical surface of a micro lens may be surrounded by an edge section . The edge section may at least partly remain unpolished during a subsequent polishing step .

[0043] The edge section may also be arranged on the holding structure .

[0044] The edge section, preferably surrounding a convex optical surface , of each micro lens may be chamfered or flat .

[0045] During a subsequent polishing step a flat or chamfered edge section provides a polishing laser to reach the complete surface of the optical surface without destroying the outer regions of the optical surface .

[0046] I f a steep edge surrounds the optical surface , during polishing this steep edge may be molten up and may af fect the outer regions of the optical surface .

[0047] A flat edge region of a micro lens may provide for a stop surface with respect to an adj acent contact surface of a neighbouring micro lens or a spacer element in a system of stacked micro lenses .

[0048] Each micro lens may comprise at least one concave optical surface and / or at least one convex optical surface . In particular, the manufacturing of concave surfaces is more costly and time consuming using conventional methods than using the present invention .

[0049] Preferably the micro lenses are formed to have imaging properties suitable for endoscopic imaging .

[0050] At least a part of the at least one interconnection may be arranged within the outer perimeter of each micro lens .

[0051] Within this context the "outer perimeter" is an envelope of the perimeter of the axial proj ection of the sheath of the micro lens , which eventually encompasses recesses having an extension parallel to the optical axis .

[0052] For example , each micro lens may have a cylindrical sheath with a circular base , having recesses giving space for at least parts of the interconnections . In this case the outer perimeter would have a circular shape . Analogously, the micro lens may have a cylindrical sheath with a di f ferent base shape .

[0053] The outer perimeter coincides for the most part with the perimeter of the axial proj ection of the sheath of the micro lens .

[0054] When the micro lenses are separated from the holding structure the interconnections have to be broken . The breaking point may be chosen to lie within the outer perimeter, as at least parts of the interconnections are arranged within the outer perimeter . Thus , the , preferably regular, outer perimeter defines the main outer contour of the micro lens and the maximal diameter .

[0055] The method may comprise the further step of polishing and / or coating the micro lens . Preferably the further step is performed before the micro lenses are separated from the holding structure .

[0056] Forming an array of hori zontally interconnected micro lenses has the advantage that the handling of the micro lenses for subsequent manufacturing steps like polishing and / coating is facilitated . As long as the micro lenses are connected to each other all micro lenses of the array can be stored and trans ferred in a safe way and all micro lenses of the array can be supplied for a subsequent manufacturing process in one step, which simpli fies the process .

[0057] This process allows for a very cost-ef fective production .

[0058] Preferably an aperture is used during polishing and / or coating .

[0059] The aperture may be arranged on one side of the array or respective apertures are arranged on both side of the array .

[0060] The aperture may expose only a part of each micro lens . Preferably only the optical surface is exposed for polishing and / or coating . An edge section of each micro lens may remain unpolished and / or uncoated . Alternatively, a part of or the complete edge section may be polished and / or coated, preferably to ensure that the complete optical surface is homogenously polished and / or coated .

[0061] The aperture allows a sharp-edged coating of the single micro lenses .

[0062] A dielectric anti-reflective (AR) coating may be applied, for example using ion-based electron beam evaporation ( PVD) , ion beam sputtering ( IBS ) or plasma sputtering (APS ) . Typically, each side of the wafer usually is be coated individually, i . e . two runs are required . Said techniques may have angle-dependent application rates which may be disadvantage for micro lenses having large di f ferences in height .

[0063] ALD (Atomic Layer Deposition) allows to coat both sides simultaneously . With this technique a uni form layer may be applied .

[0064] Even for highly curved optical surfaces , the layer has the same thickness over the entire optical surface to guarantee a uni form and function over the entire area .

[0065] Preferably the method comprises the further step of separating the micro lenses by disconnecting all interconnections of each micro lenses respectively, in particular by laser cutting with for example an ultrashort pulse laser (USP laser ) .

[0066] The obj ect is also achieved by a method for manufacturing a micro lens , in particular as described above , comprising the step of providing a blank, preferably comprising glass . In a further step an array of hori zontally interconnected micro lenses is formed by selective laser etching from the blank . According to this aspect of the invention both side of the array are coated simultaneously, preferably using atomic layer deposition . Preferably, the micro lenses are polished before coating, in particular as described below .

[0067] Preferably, the micro lenses are separated, such that parts of the interconnections resting at the lenses do not extend beyond the outer perimeter .

[0068] The outer perimeter of the micro lens may define a mounting face , which is not af fected by remainders of the interconnections . The separated micro lenses may be stacked in a tube having a recess with a circumference corresponding to the outer perimeter without the necessity of removing the remainders of the interconnections in a separate manufacturing step .

[0069] The obj ect is also achieved by a method for manufacturing a micro lens , in particular as described above , comprising the step of providing a blank, preferably comprising glass .

[0070] In a further step an array of hori zontally interconnected micro lenses is formed by selective laser etching from the blank .

[0071] During the same step at least one aperture array on at least one side of the array is formed by selective laser etching from the same blank, forming an integrated aperture array .

[0072] An integrated aperture array provides for a high precision, as the aperture array does not have to be moved with respect to the micro lenses for alignment .

[0073] The aperture array comprises , preferably hori zontally interconnected, apertures having openings . Each aperture is aligned with a respective micro lens .

[0074] Preferably, the number of apertures corresponds to the number of micro lens .

[0075] Preferably, the form and / or the area of the opening of each aperture corresponds to the form and / or the area of the surface , in particular to the optical surface , of a respective micro lens . An aperture may cover an edge section or a part of an edge section of a respective micro lens .

[0076] The aperture array may comprise at least one aperture holding connection, preferably two or three aperture holding connections , preferably for each aperture .

[0077] The aperture holding connections may provide for interconnecting the apertures and / or for fixing the aperture array to the array of hori zontally interconnected micro lenses , in particular to the holding structure .

[0078] The aperture array and / or the holding structure of the array of hori zontally interconnected micro lenses may comprise fluid channels allowing the etching bath reaching further regions with weakened material .

[0079] The method may comprise the further step of polishing of and / or coating each micro lens , in particular at least a central part comprising an optical surface of each micro lens .

[0080] Typically, the wafer comprising the array of hori zontally interconnected micro lenses and comprising the aperture array is exposed to polishing and / or coating . The whole surface of the wafer may be coated . Parts covered by the aperture array remain unpolished and / or uncoated .

[0081] Preferably, in a first step a first side of the wafer is exposed to polishing and / or coating and subsequently the second side is exposed to polishing and / or coating . Alternatively, both sides can be treated at the same time . For example , the micro lenses may be polished in one side in a first step, and on the second side in a second step . Subsequently the first side of the wafer is coated and then the second side of the wafer may be coated, for example using PVD .

[0082] Alternatively, after polishing the first and the second side of the micro lenses , the first and the second side of the wafer may be coated simultaneously, for example using ALD .

[0083] The method may comprise the further step of separating the apertures , in particular separating the aperture array from the array of hori zontally interconnected micro lenses , preferably after polishing and / or coating .

[0084] The aperture array may be separated from the array of hori zontally interconnected micro lenses , in particular by separating the apertures from each other and / or from an aperture holding structure and releasing them from the array of hori zontally interconnected micro lenses .

[0085] Micro lenses and respective apertures may be singulari zed, and the apertures may be removed thereafter .

[0086] The method may comprise the further step of separating each micro lens , preferably after polishing and / or coating and / or separating the apertures .

[0087] The polishing of glass lenses using a C02 laser is well known .

[0088] The laser beam is moved over the surface to be polished . This is usually done with a scanner . The surface is scanned with the laser beam in a pattern, for example in a meandering pattern . The energy applied melts the surface and smoothes it . However, this process has the disadvantage with relatively slow rasters that a wavy, i . e . optically deformed surface remains after cooling due to heat di f fusion into the depth of the melt and the scanning movement . Optimi zing this slow process is very time-consuming and finding a stable process window in which the deformation on the surface is still acceptable for the optical function is complex and di f ficult .

[0089] The obj ect is also achieved by a method for manufacturing a micro lens , in particular as described above , comprising the step of providing a blank, the blank preferably comprising glass .

[0090] In a further step an array of interconnected micro lenses is formed from the blank, preferably by selective laser etching . Preferably the array of interconnected micro lenses has a Sq (Root Mean Square Height ) surface roughness of 500 - l O O Onm .

[0091] Roughness may be defined according to ISO 10110- 8 .

[0092] In a further step the micro lenses arranged in the array are polished by, preferably successively, exposing each micro lens arranged in the array to a laser beam having a diameter larger than the maximal diameter of the micro lens or at least larger than the maximal diameter of an optical surface of the micro lens . As the whole surface of at least the optical surface of the micro lens is within the laser beam, and thus has not to be scanned, the method step is called "one shot polishing" . During the one shot polishing the whole surface is exposed to melting process induced by the laser beam at the same time . Thus , no scanning pattern will arise .

[0093] A laser device may be provided which emits a laser beam to scan the array of interconnected micro lenses , such that one micro lens after the other is polished . Alternatively, especially for small micro lenses , a laser beam may be provided, having a beam diameter including several adj acent micro lenses to polish more than one micro lens simultaneously . Alternatively, a laser device may be provided which emits a plurality of laser beams to polish a number of micro lenses simultaneously .

[0094] For one-shot polishing a C02 laser may be used having a power of up to 500W . Pulses may be generated by an Acoustic Optic Modulator (AOM) . The laser may comprise a scanner with a focusing optics . The laser may comprise a retractable di f fractive optical element ( DOE ) for generating a top hat profile and for changing between a Gaussian and a top hat profile .

[0095] Especially for small lenses in the 1-3 mm diameter range , scanning the laser beam over the lens surface can be dispensed as long as the " fluence" ( energy delivered per surface ) is suf ficiently high and the pulse duration is shorter than a thermal relaxation time . This is ful filled, i f the diameter of the laser beam is larger than the lens diameter .

[0096] One-shot polishing can be provided by a stationary laser beam for short-term melting of the lens surface , which has a larger beam diameter than the diameter of the individual lens .

[0097] As lenses arranged in an array shall be polished, a scanner still may be used . However, this only positions the laser beam on the lens to be polished within the wafer .

[0098] The obj ect is also achieved by a method for manufacturing a micro lens , in particular as described above , comprising the step of providing a blank, preferably comprising glass .

[0099] In a further step an array of interconnected micro lenses is formed from the blank, preferably by selective laser etching . Preferably the array of interconnected micro lenses has a Sq (Root Mean Square Height ) surface roughness of 500 - l O O Onm .

[0100] In a further step each micro lens arranged in the array is polished by, preferably successively, scanning each micro lens arranged in the array or at least scanning the optical surface of each micro lens arranged in the array with a laser beam, wherein the interaction time of each laser spot is smaller than 0 . 1ms , preferably smaller than 0 . 01ms , and the maximal diameter of the laser spot is less than 1 / n of the diameter of the micro lens , wherein n is a number from 10 to 100 .

[0101] The laser spot is the area on the surface of the micro lens illuminated by the laser beam .

[0102] As the laser spot is small and fast , this polishing step is called " fast scan polishing" . During the fast scan polishing the surface of the respective micro lens is exposed to a melting process induced by the laser beam during only a very short time . Thus , there is no time for reshaping the surface and hence no scanning pattern will arise .

[0103] For fast scan polishing a laser similar to the laser described above for one-shot polishing may be used, which laser is able to generate very short pulses ( in the microseconds-range ) . The laser may have a scanning or rotating unit which provides for a high traversing speed, as for example shown in EP3421170B1 .

[0104] A laser device may be provided which emits a laser beam to scan the array of interconnected micro lenses , such that one micro lens after the other is polished . Alternatively, a laser device may be provided which emits a plurality of laser beams to polish a number of micro lenses simultaneously, preferably but not only for the one-shot polishing .

[0105] Physically, it is advantageous to limit the thermal interaction process of melting to a very thin, quasi two-dimensional layer on the glass surface and thus benefit from the surface tension as a smoothing function and, on the other hand, not allow any deformation due to the reduced two-dimensional dynamics on the surface . On the one hand, this is already ensured by the very short absorption depth in glass of approx . 1 / 100 mm at the CO2 laser wavelength . On the other hand, the exposure time must also be reduced to such an extent that the melting process does not penetrate into the depth by di f fusion, typically in the order of 1 / 100 ms .

[0106] Especially for larger areas , a fast scan process with focused power can be used, whereby the fast scan limits the heat interaction on the surface in the focus zone . With this method, suitable optical methods have to be used to ensure ef ficient coverage of the surface during the scanning movement . This can be conceptually brought into acceptable process windows by the optical high speed rotation as disclosed for example in EP3421170B1 .

[0107] The parameters during one shot polishing and / or fast scan polishing are selected in such a way that only a thin surface layer in the micron range is brought into the liquid state . This ensures that the optical surface retains its shape . Only the glass surface is melted . No ablation occurs with a very short dwell time , in particular on small surfaces up to a maximum diameter of 3mm diameter . Instead of laser polishing, plasma etching or ion etching could also be used for micro lens formed by SLE . However, these processes are less economical .

[0108] A first side of the wafer may be exposed to one shot polishing and / or fast scan polishing first and subsequently the second side may be exposed to one shot polishing and / or fast scan polishing . Alternatively, both sides can be treated at the same time .

[0109] Preferably, during one shot polishing and / or during fast scan polishing the array of interconnected micro lenses is covered by an aperture array comprising apertures having an opening, each aperture being aligned with a respective micro lens .

[0110] Preferably, the number of apertures corresponds to the number of micro lenses . Preferably, the form and / or the area of the opening of each aperture corresponds to the form and / or the area of the surface , in particular to the optical surface , of a respective micro lens .

[0111] Preferably, the aperture array is an integrated aperture array . Alternatively, a separate aperture array, for example made of a metal , sapphire or a glass with a matt surface , may be provided . A separate aperture array may be used several times for manufacturing several arrays of interconnected micro lenses , whereas an integrated aperture array usually is destroyed after use and cannot be used again .

[0112] The profile of the laser beam for one shot polishing or for fast scan polishing may be gaussian or top hat like . With a gaussian profile no sharply defined polished area is achieved .

[0113] A top hat profile results in better heat distribution over the surface to be polished . However, even a top hat profile does not achieve a sharp boundary on the outer diameter of the beam and also for a top hat profile no sharp boundary can be achieved at the transition from the polished to the unpolished zone .

[0114] However, a sharp-edged, polished surface can be achieved with an aperture . Another advantage of the aperture is that rough surfaces can be reali zed on a lens . This is often required optically for meniscus lenses , for example .

[0115] Instead of a gaussian or top hat profile , a beam profile optimi zed for the lens shape could be used . A di f fractive optical element ( DOE ) could be used to create a super gaussian profile and / or a profile individually structured for a speci fic lens shape , for example a sombrero form profile .

[0116] Each micro lens or at least an optical surface of each micro lens on at least one side may be polished by one shot polishing and / or by fast scan polishing to a roughness of smaller than l Onm, preferably smaller than 5nm, more preferably smaller than 2nm .

[0117] The obj ect is also achieved by an array of hori zontally interconnected micro lenses , preferably fabricated by a method as described above , wherein each micro lens is connected to a, preferably single , holding structure , by at least one interconnection, preferably by two or three interconnections . The micro lenses may be separated as micro lens blanks which may be further processed . Alternatively, for subsequent process steps , the micro lens blanks keep connected as an array and the whole array is subj ected to further processing, such as polishing, coating and / or stacking .

[0118] The obj ect is also achieved by an array of hori zontally interconnected micro lenses , preferably as described above and preferably fabricated by a method as described above , wherein the array of interconnected micro lenses is connected to at least one integrated aperture array comprising apertures having an opening, wherein each aperture is aligned with a respective micro lens .

[0119] Preferably, the number of apertures corresponds to the number of micro lenses . Preferably, the form and / or the area of the opening of each aperture corresponds to the form and / or the area of the surface , in particular to the optical surface , of a respective micro lens .

[0120] The at least one integrated aperture array may be arranged on one side of the array of interconnected micro lenses or at least one integrated aperture array may be arranged on both sides of the array of interconnected micro lenses .

[0121] The obj ect is also achieved by a micro lens fabricated from glass , fabricated by a method as described above , wherein the micro lens has been separated from a holding structure by disconnecting all interconnections , in particular by laser cutting .

[0122] The micro lens may have a cylindrical sheath which is parallel to the optical axis , wherein a recess may be arranged parallel to the optical axis . Remainders of the interconnections may be arranged within the recess , that do preferably not extend beyond the outer perimeter .

[0123] The obj ect is also achieved by a method for manufacturing a system of at least two stacked micro lenses comprising the steps of providing at least two arrays of hori zontally interconnected micro lenses as described above , wherein preferably each array of hori zontally interconnected micro lenses is manufactured by one of the methods as described above .

[0124] The arrays of hori zontally interconnected micro lenses are arranged in a stack with a predefined distance to each other .

[0125] The arrays of hori zontally interconnected micro lenses are connected, such that each micro lens of each array is connected to corresponding micro lenses of neighbouring arrays of hori zontally interconnected micro lenses , and such that stacks of micro lenses are formed . Each array of hori zontally interconnected micro lenses comprises micro lenses with optical surfaces , which may be polished and / or coated .

[0126] Micro lenses of a respective stack may be fixed directly together or via a spacer element . Elements may be bonded to each other, for example by use of a laser or by cementing with an adhesive . The spacer elements may be provided by an array of spacer elements which is arranged between to arrays of hori zontally interconnected micro lenses .

[0127] Subsequently the stacks of micro lenses are separated by disconnecting the interconnections , for example by laser cutting .

[0128] The obj ect is also achieved by a system of at least two stacked micro lenses fabricated from glass by a method as described above , wherein each micro lens has been separated from a holding structure by disconnecting all interconnections , in particular by laser cutting .

[0129] Preferably, the at least two stacked micro lenses are bonded together, either directly or indirectly for example via a spacer element .

[0130] Preferably, the system of at least two stacked micro lenses is cut from a stack of arrays of hori zontally interconnected micro lenses .

[0131] In the following, the invention is further explained in embodi- ments by means of figures , wherein functionally similar parts have the same reference number .

[0132] Figure 1 shows first example of an array of hori zontally interconnected micro lenses in a perspective view;

[0133] Figure 2 shows one micro lens of an array according to figure 1 in a top view;

[0134] Figure 3 shows a second example of an array of hori zontally interconnected micro lenses with in integrated aperture array in a perspective view in tow perspective views ;

[0135] Figure 4 shows a micro lens with an integrated aperture in a first perspective view;

[0136] Figure 5 shows the micro lens of figure 4 in a second perspective view;

[0137] Figure 6 shows a further example of an array of a micro lenses in a perspective view;

[0138] Figure 7 shows an individual micro lens 1 as shown in fig- ure 6 in a perspective view and in a top view; Figure 8 shows an individual micro lens 1 as shown in figure 6 and a detailed view;

[0139] Figure 9 shows a first example of a micro lens in a cross sectional side view;

[0140] Figure 10 shows a second example of a micro lens in a cross sectional side view;

[0141] Figure 11 shows a third example of a micro lens in a cross sectional side view;

[0142] Figure 12 shows a first example of a stack of arrays of micro lenses in a perspective view;

[0143] Figure 13 shows a detailed view of figure 12 .

[0144] Figure 1 shows an array 10 of micro lenses 1 in a perspective view . The micro lenses 1 have been produced from a polished wafer but are still connected to a holding structure .

[0145] Figure 2 shows one micro lens 1 of an array 10 according to figure 1 in a top view . The micro lens 1 is connected to the holding structure 11 via two interconnections 2 .

[0146] A part of each interconnection 2 is arranged within the circular outer perimeter 8 of the micro lens 1 .

[0147] The micro lens comprises a concave optical surface 3 surrounded by an edge section 4 .

[0148] Figure 3 shows an array 10 of micro lenses 1 with an integrated aperture array 20 in perspective views on a first side 5a and on a second side 5b . The aperture array 20 covering the second side 5b of the array 10 of micro lenses 1 comprises apertures 21 having openings 20 which provide access to the micro lenses 1 on the second side 5b during a polishing and / or coating step . On the first side 5a the lenses 1 may have a flat surface . During coating the whole surface of the wafer is processed .

[0149] Figure 4 shows a micro lens 1 with an integrated aperture 21 on the second side 5b in a first perspective view . On the first side 5a the , in this case convex, optical surface 7 is formed over the entire surface of the micro lens 1 .

[0150] The optical surface 7 is surrounded by a flat edge section 4 which is formed in the holding structure 11 . The flat edge section 4 provides for an equal quality over the whole optical surface 7 during a polishing step as all areas of the surface may receive the same energy density and the rim area will not melt up more than the central area . The laser beam is not disturbed by a steep edge and melting material from a steep edge does not af fect the rim area of the optical surface 7 .

[0151] The micro lens 1 is connected to the holding structure 11 by interconnections 2 , in this case holding bars 2 . The holding bares 2 bridge a gap 9 between the holding structure 11 and the micro lens 1 .

[0152] Figure 5 shows the micro lens 1 with the integrated aperture 21 according to figure 4 in a second perspective view . In the second side 5b the micro lens 1 comprises a central part 3 with a concave optical surface 7 which is surrounded by a flat edge section 4 .

[0153] The aperture 21 comprises an opening 22 exposing only the central part 3 of the micro lens 1 . The edge section 4 remains unpolished and / or uncoated, as long as the edge section 4 is covered by the aperture 22 during a polishing and / or coating step . The apertures 22 are connected to the holding structure 11 by aperture holding connections 23 .

[0154] The micro lens 1 may be separated by cutting the interconnections 2 and by releasing the apertures 21 , which may be released by cutting the aperture holding connections 23 .

[0155] Figure 6shows a further example of an array 10 of micro lenses 1 in a perspective view . Similar to the example in figure 1 , the micro lenses 1 are embedded in a holding structure 11 .

[0156] Each micro lens 1 comprises on one side a central part 3 having a concave optical surface 7 being surrounded by a flat edge section 4 .

[0157] Figure 7 shows an individual micro lens 1 as shown in figure 6 in a perspective view and in a top view .

[0158] The optical axis 12 of the optical surface 7 crosses a predefined position with respect to the circular outer perimeter 8 of the micro lens 1 , namely the optical axis 12 crosses the centre 15 of the micro lens 1 .

[0159] The micro lens 1 comprises a cylindrical sheath 13 parallel to the optical axis 12 which is shaped to have recesses 14 in which the interconnections 2 meet the micro lens 1 .

[0160] The cylindrical sheath 13 further comprises alignment surfaces 16 , which might also be regarded as recesses of the sheath 13 with respect to a circular base corresponding to the outer perimeter 8 of the micro lens 1 . The alignment surface 16 may form an abutment face when di f ferent micro lenses 1 having the same shape of their sheath 13 and the same location of the optical axis 12 are stacked . All stacked micro lenses 1 may have the same orientation with respect to a rotation around the optical axis .

[0161] Figure 8 shows an individual micro lens 1 as shown in figure 6 and a detailed view .

[0162] The micro lens 1 has been separated from the holding structure 11 . The interconnections 2 have been cut , such that the remnants 17 of the interconnections 2 , which remain on the micro lens 1 are arranged within the outer perimeter 8 of the micro lens 1 .

[0163] Figure 9 shows a first example of a micro lens 1 in a cross-sectional side view . The micro lens 1 has optical surfaces 7 on both sides 5a, 5b .

[0164] On a first side 5a the micro lens 1 comprises a convex optical surface 6a and on the second side 5b a concave optical surface 6b .

[0165] In this example the convex optical surface 6a is surrounded by a steep edge . When the convex optical surface 6a is laser polished there is the risk, that the steep edge melts up in an undefined way . The outer area of convex optical surface 6a may be af fected by this undefined melting . This would have a negative impact on shape retention .

[0166] To avoid this , the optical surface may be surrounded by a chamfered of flat edge section 4 as shown in figures 10 and 11 . The transition from the convex optical surface 6a to the surrounding holding structure has to be selected in such a way that the flank of the convex optical surface 6a is not melted .

[0167] Any profiles of edge sections 4 can be easily be reali zed by SLE or by UPLA.

[0168] Figure 10 shows a second example of a micro lens in a cross-sectional side view . The micro lens 1 has optical surfaces 7 on both sides 5a, 5b . On a first side 5a the micro lens 1 comprises a convex optical surface 6a and on the second side 5b a concave optical surface 6b .

[0169] In this example the convex optical surface 6a is surrounded by a chamfered edge section 4 .

[0170] Figure 11 shows a third example of a micro lens in a cross-sectional side view . The micro lens 1 has optical surfaces 7 on both sides 5a, 5b similar to the micro lenses 1 in figures 9 and 10 .

[0171] In this example the convex optical surface 6a is surrounded by a flat edge section 4 . The edge section 4 may be part of the micro lens 1 having a maximal diameter DI .

[0172] When laser polishing the micro lens 1 with a one-shot polishing step the laser spot at least has a diameter larger than the maximal diameter D2 of the optical surface 7 .

[0173] Figure 12 shows a first example of a stack 30 of two arrays 10 of micro lenses 1 in a perspective view .

[0174] The arrays 10 each comprise micro lenses 1 of a di f ferent type . In this example the micro lenses 1 of both arrays 10 are connected to the holding structure 11 by two interconnections 2 .

[0175] The arrays 10 may be aligned under optical control of two stacks of two corresponding micro lenses 1 . Alternatively or additionally, the arrays 10 may comprise positioning marks 18 which may also be formed during the SLE process or during an UPLA process and which have a defined position with respect to the micro lenses 1 .

[0176] Figure 13 shows a detailed views of figure 12 in a side view and in a perspective view .

[0177] For forming a stack 40 of micro lenses 1 in a first step arrays 10 ( see figures 1 , 3 or 6 ) of hori zontally interconnected micro lenses 1 are formed . The surfaces of the arrays 10 are then processed to form finished optical surfaces 7 , by polishing and / or coating .

[0178] Subsequently the arrays 10 are aligned, for example with the help of positioning marks 18 , such that the optical axes 12 of stacked micro lenses 1 form a common optical axis 12 .

[0179] In this example , the arrays 10 are aligned such that the interconnections 2 of an array 10 extend in a direction dl perpendicular to the extension direction d2 of the interconnections 2 of a neighbouring array 10 .

[0180] The arrays 10 may then be bonded together, for example in a conventional way by cementing with UV adhesive or by laser bonding .

[0181] Finally, the stacks 40 of micro lenses may be separated by disconnecting the interconnections 2 for example by laser cutting . As the optical axis 12 of each micro lens 1 has a predetermined position with respect to the micro lens and therefor to the array 10 axes of corresponding micro lenses 1 are automatically aligned when the arrays 10 are stacked . A separate step of aligning micro lenses under optical control is not any more necessary .

Claims

Claims1. Method for manufacturing a micro lens (1) comprising the following steps- providing a blank, in particular a polished wafer, in particular comprising glass,- forming an array (10) of horizontally interconnected micro lenses (1) , preferably by selective laser etching of the blank, wherein each micro lens (1) is connected to a, preferably single, holding structure (11) , by at least one interconnection (2) , in particular at least one holding bar, preferably by two or three holding bars (2) .

2. Method according to claim 1, wherein the optical axis (12) of each micro lens (1) crosses a predefined position with respect to the outer perimeter (8) of the micro lens (1) , preferably the optical axis (12) crosses the centre of the micro lens ( 1 ) .

3. Method according to claim 1 or 2, wherein on at least one side an optical surface (7) for optical imaging of each micro lens (1) , preferably a central part of each micro lens, is surrounded by an edge section (4)4. Method according to claim 3, wherein the edge section (4) , preferably surrounding a convex optical surface (6a) , of each micro lens (1) is chamfered or flat, preferably on at least one side (5a)5. Method according to at least one of the preceding claims, wherein each micro lens (1) comprises at least one concaveoptical surface (6b) and / or at least one convex optical surface ( a) .

6. Method according to at least one of the preceding claims, wherein at least a part of the at least one interconnection (2) is arranged within the outer perimeter (8) of each micro lens ( 1 ) .

7. Method according to at least one of the preceding claims, comprising the further step of polishing and / or coating the micro lenses (1) , preferably using an aperture (21) during polishing and / or coating, the aperture (21) preferably exposing only a part of each lens (1) , more preferably exposing only the optical surface (7) of each micro lens (1) .

8. Method for manufacturing a micro lens, in particular according to at least one of the preceding claims, comprising the steps of- providing a blank, preferably comprising glass, forming an array (10) of horizontally interconnected micro lenses (1) by selective laser etching from the blank,- preferably polishing each micro lens,- coating both side of the array simultaneously, preferably using atomic layer deposition.

9. Method according to at least one of the preceding claims, comprising the further step of separating the micro lenses (1) by disconnecting all interconnections (2) of each micro lens (1) respectively, in particular by laser cutting, preferably such that parts of the interconnections (2)resting at the lens (1) do not extend beyond the outer pe- rimeter ( 8 ) .

10. Method for manufacturing a micro lens, in particular according to at least one of the preceding claims, comprising the steps of- providing a blank, preferably comprising glass, forming an array (10) of horizontally interconnected micro lenses (1) by selective laser etching from the blank,- and forming at least one aperture array (21) on at least one side (5b) of the array (10) by selective laser etching from the same blank, comprising, preferably horizontally interconnected, apertures (20) having openings (22) , each aperture (20) being aligned with a respective micro lens ( 1 ) .

11. Method for manufacturing micro lens according to claim 10, wherein the aperture array (20) comprises at least one aperture holding connection (23) , preferably two or three aperture holding connections (23) , preferably for each aperture (21) .

12. Method for manufacturing micro lens according to claim 10 or 11, comprising at least one of the steps of- Polishing each micro lens (1) , in particular polishing at least a central part comprising an optical surface (7) of each micro lens (1) ;- Coating each micro lens (1) , in particular coating at least a central part comprising an optical surface (7) of each micro lens (1) ;- separating the apertures, in particular separating the aperture array from the lens array, preferably after polishing and / or coating.

13. Method for manufacturing micro lens according to one of claims 10 to 12, comprising the step of separating each micro lens ( 1 ) .

14. Method for manufacturing a micro lens, in particular according to at least one of the preceding claims, comprising the steps of- providing a blank, preferably comprising glass, forming an array (10) of interconnected micro lenses (1) from the blank, preferably by selective laser etching (SLE) , the blank preferably having a surface roughness of 500 - lOOOnm,- polishing the micro lenses (1) arranged in the array (10) by, preferably successively, exposing each micro lens (1) arranged in the array (10) to a laser beam having a diameter larger than the maximal diameter (DI) of the micro lens (1) or at least larger than the maximal diameter (D2) of an optical surface (7) of the micro lens.

15. Method for manufacturing a micro lens, in particular according to at least one of the preceding claims 1-13, comprising the steps of- providing a blank, preferably comprising glass, forming an array (10) of interconnected micro lenses (1) from the blank, preferably by selective laser etching (SLE) , the blank preferably having a surface roughness of 500 - lOOOnm,- polishing each micro lens (1) arranged in the array (10) , by, preferably successively, scanning each micro lens (1) arranged in the array (10) or at least scanning an optical surface (7) of each micro lens (1) arranged in the array (10) with a laser beam, wherein the interactiontime of each laser spot is smaller than 0.1ms and the maximal diameter of the laser spot is less than 1 / n of the diameter of the micro lens, wherein n is a number from 10 to 100.

16. Method for manufacturing a micro lens (1) according to claim 14 or 15, wherein during polishing the array (10) of interconnected micro lenses is covered by an aperture array (20) comprising apertures (21) having an opening (22) , each aperture (21) being aligned with a respective micro lens (1) , wherein the aperture array (20) preferably is an integrated aperture array (20) .

17. Method according to claim one of claims 14-16, wherein a profile of the laser beam is gaussian, top hat like, super gaussian or individually structured.

18. Method according to one of the previous claims, wherein each micro lens (1) or at least an optical surface (7) of each micro lens (1) on at least one side (5a, 5b) is polished to a roughness of smaller than lOnm, preferably smaller than 5nm, more preferably smaller than 2nm.

19. Array (10) of horizontally interconnected micro lenses (1) , preferably fabricated by a method according to one of claims 1-8, 10-12 or 14-18, wherein each micro lens (1) is connected to a, preferably single, holding structure (11) , by at least one interconnection (2) , preferably by two or three interconnections (2) .

20. Array (10) of horizontally interconnected micro lenses (1) , preferably according to claim 19, preferably fabricated by a method according to one of claims 1-8, 10-12 or 14-18,wherein the array (10) of interconnected micro lens (1) is connected to at least one integrated aperture array (20) comprising apertures (21) having an opening (22) , wherein each aperture (21) is aligned with a respective micro lens (1) •21. Micro lens (1) fabricated from glass, fabricated by a method according to one of claims 1-18, wherein the micro lens (1) has been separated from a holding structure (11) by disconnecting all interconnections (2) , in particular by laser cutting.

22. Method for manufacturing a system of at least two stacked micro lens comprising the steps of- providing at least two arrays (10) of horizontally interconnected micro lenses (1) according to claim 19;- arranging the arrays (10) of horizontally interconnected micro lenses (1) in a stack (30) with a predefined distance to each other,- connecting the arrays (10) of horizontally interconnected micro lenses (1) , such that each micro lens (1) of each array (10) is connected to a corresponding micro lens (1) of at least one neighbouring array (10) of horizontally interconnected micro lenses (1) , and such that stacks (40) of micro lenses (1) are formed,- separating the stacks (40) of micro lenses (1) by disconnecting the interconnections (2) .

23. System of at least two stacked micro lenses (1) fabricated from glass by a method according to one of claims 1-18 or 22, wherein each micro lens (1) has been separated from a holding structure (11) by disconnecting all interconnec- tions (2) , in particular by laser cutting.

Images