Patent ID: 12253744

DETAILED DESCRIPTION

According to an embodiment of the present invention the optical device comprises a second photosensitive element (or even more than two such elements), wherein the light source is configured to emit light that is affected (e.g. modulated or deflected) by said lens and impinges on the first photosensitive element and/or the second photosensitive element, wherein the second photosensitive element is designed to generate a second output signal corresponding to the intensity of the light impinging on the second photosensitive element, wherein the light source, the lens and said photosensitive elements are configured such that a change of the focal length of said lens changes the intensity distribution of the emitted light that impinges on the first photosensitive element and/or the second photosensitive element, so that each focal length of the lens is associated to a specific first output signal generated by the first photosensitive element and to a specific second output signal generated by the further second photosensitive element.

According to a preferred embodiment of the present invention, the lens of the optical device comprises a first focal length and a different second focal length (e.g. a minimal and a maximal focal length), wherein, when the lens is adjusted such that it comprises said first focal length, the peak of the intensity distribution hits the first photosensitive element, and wherein, when the lens is adjusted such that it comprises the second focal length, said peak hits the second photosensitive element.

In other words, since merely parts of the intensity distribution, i.e. merely parts of the cross section of the light beam originating from said light source, are measured/detected by the photosensitive elements, the output signals can be enhanced by designing the optics such that the peak of the intensity distribution of the reflected light is once hitting the first photosensitive element and at an e.g. another extreme tuning state the second photosensitive element.

According to a preferred embodiment of the present invention, the optical device is configured such that a change in the focal length of said lens changes the width of the intensity distribution of said emitted light that impinges on the first photosensitive element and/or the second photosensitive element. Alternatively or in addition, according to a further preferred embodiment of the present invention, the optical device is configured such that a change in the focal length of said lens changes/displaces the position of the maximum (peak) of the intensity distribution of said emitted light that impinges on the first photosensitive element and/or the second photosensitive element with respect to the first and/or second photosensitive element (see also above). Due to the fact that when the focal length of the lens is changed (e.g. by changing the curvature of the lens and/or its refractive index), the light of the light source is deflected/modulated differently by the lens and thus impinges differently on the photosensitive elements. Therefore, said output signals actually allow for determining the current focal length of the lens in principle. A calibration can be easily performed by using a further method for determining the focal length of the lens and by measuring said first and/or second output signal for the respective focal length which establishes a correspondence between the focal lengths and the respective first and/or second output signal. The output signals may be electrical currents which can be quantified using their respective strength of current.

In case several photosensitive elements (e.g. two such elements) are present, the optical device is preferably adapted to generate a further output signal X from the individual (e.g. first and second) output signals O1, O2, e.g. X=(O1−O2)/(O1+O2), wherein the focal length is preferably calibrated versus X. However a calibration versus O1and O2may also be conducted. In case only one (i.e. the first) photosensitive element is present, the focal length is calibrated versus O1. When controlling the focal length, O1(for a single first photosensitive element) is made to approach a reference value that corresponds to the individual focal length that is to be adjusted, whereas in the case of two photosensitive elements a further output signal (e.g. current) X (see above) is preferably automatically determined and made to approach a reference value that corresponds to the individual focal length that is to be adjusted.

According to an embodiment of the present invention, for controlling the focal length, the optical device may comprise a means or mechanism (e.g. an actuation means) for changing the focal length of the lens.

Further, according to a preferred embodiment of the optical device according to the invention, for controlling adjustment of the focal length of the lens to a predetermined focal length, the optical device comprises a control unit being adapted to control said (actuation) means such that the latter changes the focal length of the lens (e.g. deforms said surface/membrane of the lens or changes a refractive index of the lens in a way) so that the first and/or second output signal or a further output signal generated from the first and second output signal approaches a reference output signal, wherein said reference output signal correspond to said predetermined focal length (calibration).

According to a preferred embodiment of the optical device according to the invention, the optical device comprises a memory in which a plurality of focal lengths is stored as well as a reference output signal for each focal length. Thus, the memory contains a look-up table for looking up the reference output signal (e.g. a reference value for said further output signal or for the first and/or second output signal). For instance, in case the focal length shall be (automatically) adjusted to a certain focal length required by a user or an application, the reference output signal corresponding to said desired focal length is fetched from said table and the focal length (or curvature) of the lens is adjusted such by said (actuation) means that the current output signal (or first and/or second output signal) approaches the respective reference value. This is denoted as optical feedback in the framework of the present invention.

According to a preferred embodiment of the present invention, said optical device is a focus tunable lens device which can be used for changing the focus spot of a laser processing device, e.g. a laser marking device, wherein a processing laser is modulated by the device according to the invention before it is hitting a scanning mirror and a sample that has to be processed. Further, the optical device according to the invention can be a laser processing device or a laser marking device.

According to another preferred embodiment of the present invention, the optical device is part of a microscope (e.g. part of the objective or an ocular of the microscope) or forms such a microscope.

According to another preferred embodiment of the present invention, the optical device is part of a camera (e.g. part of the lens objective) or forms such a camera.

According to a preferred embodiment of the optical device according to the invention, the optical device further comprises a first optical element configured to reflect said light emitted by the light source before it impinges on the first and/or second photosensitive element. Further, this first optical element is preferably configured such that a main optical signal is transmitted by the first optical element, essentially without affecting said optical feedback (see also below).

According to a preferred embodiment of the optical device according to the invention, the optical element is a first cover element of the lens (e.g. out of a glass or plastic, or a polished metal surface when not arranged in the optical path of the main signal), wherein said first cover element and an elastically deformable membrane forming said surface of the lens delimit a volume (or container) of the lens being filled with a fluid. Here, said membrane of the lens is a thin element that is transparent (at least to the main optical signal) and elastically expandable and extends (essentially two-dimensionally) along an extension plane (the thickness of the membrane normal to its extension plane/surface is significantly smaller than the dimension of the membrane along said extension plane). The membrane can be made of at least one of the following materials: a glass, a polymer, an elastomer, a plastic or any other transparent and stretchable or flexible material. For example, the membrane may be made out of a silicone-based polymer such as poly(dimethylsiloxane) also known as PDMS or a polyester material such as PET or a biaxially-oriented polyethylene terephtalate (e.g. “Mylar”). Further, said fluid preferably is or comprises a liquid metal, a gel, a liquid, a gas, or any transparent, absorbing or reflecting material which can be deformed. For example, the fluid may be a silicone oil (e.g. Bis-Phenylpropyl Dimethicone). Additionally the fluid may include fluorinated polymers such as perfluorinated polyether (PFPE) inert fluid.

According to an embodiment of the optical device according to the invention, the curvature of the lens (e.g. curvature of said surface/membrane) is proportional to the pressure in the fluid. In order to adjust said pressure and therewith the curvature/focal length of the lens said actuation means is designed to exert a corresponding pressure on the volume (container) of the lens. For instance, the actuation means may be an electromagnetic actuator (e.g. a voice coil motor) that comprises a coil interacting with a magnet, which coil is used to exert pressure on the said volume of the lens.

Hence, the focal length of the lens is controlled by the current flowing through the coil of the actuator. The actuation means can also be formed by a stepper motor or an electrostatic actuator such as a piezo motor or an electroactive polymer actuator. The actuation means can also be designed as a reluctance actuator which exerts a reluctance force on the volume in order to change the curvature of the surface or membrane of the lens. Further, the actuation means can consist of one or multiple actuators. It is also conceivable that the actuation means is actually manually actuated (e.g. by means of a rotation that is translated into a deformation of the surface of the lens by the actuation means).

Further, according to a preferred embodiment of the optical device according to the invention, the optical device comprises a second optical element that is configured to reflect said light emitted by the light source before it impinges on the first and/or second photosensitive element (again, the second optical element is preferably configured such that said main optical signal is transmitted by the second optical element, particularly essentially without affecting the optical feedback, see also below).

According to a preferred embodiment of the optical device according to the invention, said second optical element can be a (second) cover element of the lens, too, wherein said surface or membrane of the lens is then arranged between the first and the second cover element. Preferably, said cover elements are oriented parallel with respect to each other. The second optical element can be made out of the same materials as the first optical element/cover element (see also above).

According to a preferred alternative embodiment of the optical device according to the invention, the second optical element is a partially reflective mirror that is inclined with respect to the first optical element or said lens, and is designed to reflect said light emitted by the light source towards the first and/or second photosensitive element and to transmit the main optical signal. Here, also a second cover element of the lens may be present, which second cover element is then however not configured to directly or indirectly reflect the light from the light source towards the photosensitive elements.

Further, according to an embodiment of the present invention, the optical device comprises a further light source, wherein the further light source is configured to emit light that is affected by said lens and impinges on the first photosensitive element and/or the second photosensitive element, such that each light path from said light source to one of the photosensitive elements is substantially symmetric, particularly symmetric, to a corresponding light path from the further light source to one of the photosensitive elements. Particularly, this allows the normalization of all photosensitive elements and light source efficiencies/sensitivities. For instance, in case one light source (e.g. LED) is turned on and two photosensitive elements are present, a relative signal between the two photosensitive elements (e.g. photo diodes) can be used to measure the deflection of the lens (independent of the LEDs absolute intensity). The same is true if only one photosensitive element but two light sources (e.g. LEDs) are used.

Further, according to an embodiment of the present invention, the optical device comprises at least one optical filter configured to prevent light of the first and/or second light source from exiting or re-entering the optical device and/or lens.

Further, according to an embodiment of the present invention, a consistent (e.g. linear or monotonic) feedback signal may be achieved by mechanically referencing the light source (e.g. LED) directly to an mechanical component (e.g. the lens or housing) of the optical device and connecting it through a flex cable, a wire bonding connection or molded interconnect devices to an energy source such as a current source and/or by actively aligning the light source/LED during assembly.

Further, according to an embodiment of the present invention, the optical device, particularly the lens, is configured to affect said emitted light by means of light scattering and/or refraction and/or total internal reflection, wherein particularly the optical device, particularly the lens, comprises at least one diffractive element for generating said light scattering, wherein particularly said at least one diffractive element is arranged on the membrane or comprised by the membrane of the lens of the optical device.

Further, according to an embodiment of the present invention, the optical device comprises at least one temperature sensor being in thermal contact with the first and/or second photosensitive element (30,40) (for this the sensor may be arranged in close proximity to the photosensitive elements), wherein particularly the optical device is configured to use said at least one temperature sensor for compensating a temperature-dependent sensitivity of the first and/or second photosensitive element.

Particularly, in an embodiment, the optical device is configured to compensate a temperature dependency of the first and/or second output signal (e.g. caused by a thermally induced change in the refractive index and/or a thermal expansion of one or several materials of the lens) by means of measuring the lens temperature using said at least one temperature sensor and assuming a fixed offset of the first and/or second output signal with temperature,

Further, particularly, in an embodiment, the optical device is configured to compensate a temperature dependency of the first and/or second output signal (e.g. caused by a thermally induced change in the refractive index and/or a thermal expansion of one or several materials of the lens) by characterizing the lens at more than one reference temperature, storing said characterization in a memory, and using said at least one temperature sensor within the lens as a reference.

Further, particularly, in an embodiment, the optical device further comprises a heating means that is configured to stabilize the temperature of the lens in order to reduce temperature-induced changes of optical properties of the lens such as its focal length, wherein particularly the temperature is stabilized at the same temperature for which it has been characterized or designed.

Further, regarding sensing of the temperature of the lens, an aspect of the present invention relates to controlling the temperature of the lens of an optical device according to the invention by driving the lens in a constant power regime to stabilize its temperature at the same temperature for which it has been characterized or designed.

According to a preferred embodiment of the optical device according to the invention, the lens is further designed to focus or diverge a main optical signal transmitted through the lens along an optical axis of the lens, wherein the light source, said photosensitive elements and particularly said first and/or second optical element are arranged such with respect to the lens that said main optical signal does not affect said first and/or second output signal (or said further output signal), i.e., is not coupled into the optical path of said light from said light source).

Further, according to a preferred embodiment of the optical device according to the invention, the optical device is designed to measure a background noise generated by the first and/or by the second photosensitive element, when the light source is turned off, and to subtract said background noise measured by the first photosensitive element from the first output signal and/or said background noise measured by the second photosensitive element from the second output signal.

Alternatively or in addition, for reducing (such) external noise in the first and/or second output signal (or in the further output signal), the optical device is configured such that the light source emits modulated light (the optical device may comprise a modulator interacting with the light source such that the light emitted from the light source is modulated, wherein the modulation frequency is larger than the frequencies of the fluctuations/adjustments of the shape/curvature of the surface or membrane of the lens. In order to remove said unwanted noise, the device is preferably adapted to demodulate the output signal(s) and to band-pass filter or low-pass filter the output signal(s) which finally removes said noise.

Further, according to an embodiment of the present invention, the optical device is a contact lens that is configured to be placed directly on the surface of an eye of a user or an optical device to be worn in front of an eye (e.g. a pair of glasses or a single eye glass or a virtual display) or an intraocular lens.

Further, according to an embodiment of the present invention, said optical device comprises at least one light source, at least one photosensitive element and a membrane lens (a lens comprising a deformable membrane and a fluid), a liquid crystal, an electro-wetting based or another focus adjustable lens.

Further, according to an embodiment of the present invention, the light source, the lens and the first photosensitive element are further configured such that emitted light is reflected by the lens of the eye of the user before impinging on the first photosensitive element, so that the intensity distribution of the emitted light that impinges on the first photosensitive element changes when said user deforms the lens of his eye (e.g. when focusing) or changes the position of the eye with respect to the glasses or the contact lens on the surface of the eye (e.g. in a radial direction) which may be conducted by the user by looking at an object (e.g. his hand) close by or by looking down.

Further, the problem underlying the present invention is solved by a method for adjusting the focal length of a lens, particularly using an optical device according to the invention, particularly a contact lens, an optical device to be worn in front of an eye of a user (e.g. glasses) or even an intraocular lens.

The method according to the invention comprises the steps of: emitting light by means of a light source (e.g. an LED or laser) such that said light is affected (e.g. deflected or modulated) by said lens (e.g. by a surface/membrane of said lens) and merely a part of said light (i.e. a portion of the intensity distribution of said light) impinges on at least a first photosensitive element, which part (or portion) depends on the focal length of the lens (see also above) or on the form of the lens of the eye of the user wearing the optical device (e.g. a contact lens or glasses) or on the position of the contact lens on a surface of the eye of the user or on the position of the eye with respect to the optical device/glasses, wherein the first photosensitive element generates a first output signal when said part of said light impinges on the first photosensitive element, wherein said first output signal corresponds to the intensity of said part of the light impinging on the first photosensitive element, and preferably automatically adjusting the focal length to a desired or predetermined focal length using the first output signal as a control signal (e.g. for triggering an actuator that adjusts the focal length to the desired focal length) such that said first output signal (or a further output signal determined with help of the first output signal) approaches a reference output signal that is associated to said predetermined focal length.

Preferably, at least a further (second) photosensitive element is used, and the following steps are then performed: emitting light by means of a light source such that said light is affected (e.g. deflected or modulated) by the lens (e.g. by a surface/membrane of said lens) and impinges on a first and/or a second photosensitive element, wherein the first photosensitive element generates a first output signal when (merely) a part of the light impinges on the first photosensitive element, wherein said first output signal corresponds to the intensity of the part of light impinging on the first photosensitive element, and wherein the second photosensitive element generates a second output signal when (merely) another part of said light impinges on the second photosensitive element, wherein said second output signal corresponds to the intensity of the part of the light impinging on the second photosensitive element; and adjusting the focal length to a predetermined focal length (e.g. by adjusting the curvature of a deformable surface/membrane of the lens or a refractive index of the lens) such that said first and/or second output signal or a further output signal generated from the first and second output signal (see e.g. further output signal X above) approaches a reference output signal, wherein said reference output signal corresponds to said predetermined focal length.

Preferably, a plurality of reference output signals (see also above) are pre-stored in a look-up table which assigns to each focal length of a plurality of focal lengths a corresponding reference output signal (see e.g. also above), which reference output signal is preferably determined by means of a calibration procedure where the respective focal length is determined using a further method which then yields the correspondence between the respective focal length and the first and/or second output signal or said further output signal, which signals are to be expected when the respective focal length is set.

Further, according to a preferred embodiment of the method according to the invention, a background noise generated by the first and by the second photosensitive element is measured when the light source does not emit light, wherein said background noise measured by the first photosensitive element is subtracted from the first output signal, and/or wherein said background noise measured by the second photosensitive element is subtracted from the second output signal.

In addition, or as an alternative, for reducing external noise in the first and/or second output signal (or in said further output signal), said emitted light may be emitted as modulated light, wherein the generated first and/or second output signal (or the further output signal) are then correspondingly demodulated and filtered by a band pass filter or low pass filter so as to filter out external noise in the first and second output signal (see also above).

According to a further aspect of the present invention, a contact lens for vision correction is disclosed, wherein the contact lens is configured to be placed directly on the surface of an eye of a user (e.g. person wearing the contact lens), wherein the contact lens comprises: a lens that is configured to be controlled so as to adjust the focal length of the contact lens, and wherein the contact lens further comprises at least one light source for emitting light (preferably an LED emitting preferably IR light) and at least one photosensitive element (preferably a photo diode) for detecting light emitted by the light source and for providing an output signal depending on the intensity distribution of the emitted light that impinges onto the photosensitive element, wherein said light source and said photosensitive element are configured such that light emitted by the light source is reflected by the lens of the eye of the user or the retina of the user before impinging onto said photosensitive element, when the contact lens is placed on the surface of the eye of the user as intended.

Further, according to a preferred embodiment of the contact lens, the light source and the photosensitive element are further configured such that the intensity distribution of the emitted light that impinges on the photosensitive element changes when the form of the lens of said eye of the user is changed and/or when the position of the contact lens on the surface of the eye changes (e.g. in a radial displacement), so that said output signal changes as well.

Further, according to a preferred embodiment of the contact lens according to the invention, the contact lens comprises a mechanism (e.g. deformation or refractive index change) so as to adjust the focal length of the contact lens, and a control unit for controlling said mechanism, wherein the control unit is configured to control said mechanism using said output signal (e.g. as a feedback signal or as a control signal for activating and/or deactivating said focus adjustment mechanism).

Preferably, the lens of the contact lens is formed by a (at least partially) transparent container comprising a transparent and elastically expandable membrane wherein the container is filled with a transparent fluid, so that light can pass through the contact lens via said the membrane and said fluid. Alternatively, the lens of the contact lens is formed of an liquid crystal lens.

Further, the membrane preferably comprises a curvature-adjustable area comprising a curvature that can be adjusted by means of said mechanism in order to adjust the focal length of the lens/contact lens.

According to a further aspect of the present invention, an optical device (e.g. glasses) for vision correction or virtual or augmented reality disclosed, wherein the optical device is configured to be placed or worn in front of an eye of a user, e.g. on a nose of a user (e.g. person wearing the optical device in form of glasses), wherein the optical device comprises: at least one lens that is configured to be controlled so as to adjust the focal length of the at least one lens or optical device, and wherein the optical device further comprises at least one light source for emitting light (preferably an LED emitting preferably IR light) and at least one photosensitive element (preferably a photo diode) for detecting light emitted by the light source and for providing an output signal depending on the intensity distribution of the emitted light that impinges onto the photosensitive element, wherein said light source and said photosensitive element are configured such that light emitted by the light source is reflected by the lens of the eye of the user or the retina of the eye of the user (in front of which eye said lens is arranged) before impinging onto said photosensitive element, when the glasses are worn by the user.

Further, according to a preferred embodiment of the optical device (e.g. glasses), the light source and the photosensitive element are further configured such that the intensity distribution of the emitted light that impinges on the photosensitive element changes when the form of the lens of said eye of the user is changed and/or when the position of the eye changes (e.g. looking inwards or downwards), so that said output signal changes as well.

Further, according to a preferred embodiment of the glasses according to the invention, the glasses comprise a mechanism (e.g. deformation or refractive index change) so as to adjust the focal length of the glasses, and a control unit for controlling said mechanism, wherein the control unit is configured to control said mechanism using said output signal (e.g. as a feedback signal or as a control signal for activating and/or deactivating said focus adjustment mechanism).

Further, in an embodiment, the optical device may provide vision correction for the one eye only and may thus only comprise said one lens. In another embodiment, said optical device provides vision correction for both eyes and may comprise a lens for one eye and a further lens for the other eye. Each lens is then arranged in front of the associated eye.

The further lens may also be focus adjustable and may be configured as described above. The focal length of the further lens may also be adjusted by the above-described means (e.g. simultaneously to the focal length of said lens). It is also conceivable that the focal length of each lens can be independently adjusted (e.g. each lens comprises the means for adjusting the focal length described above).

Preferably, the lens of the optical device (e.g. glasses) is formed by a (at least partially) transparent container comprising a transparent and elastically expandable membrane wherein the container is filled with a transparent fluid, so that light can pass through the glass via said the membrane and said fluid. Alternatively, the lens of the glass is formed of a liquid crystal lens.

Further, the membrane preferably comprises a curvature-adjustable area comprising a curvature that can be adjusted by means of said mechanism in order to adjust the focal length of the lens/glass.

By modulating the light source(s), which may be done in all embodiments of the present invention, the power consumption of the system can be strongly reduced.

FIGS.1and2show a schematical illustration of an optical device1according to the invention. Particularly, the optical device1is designed to focus or diverge a main optical signal (e.g. a light beam such as a laser light beam)100. For this, the optical device1comprises a focus tuneable lens10that has a deformable surface10aso that the surface10acan assume a plurality of different curvatures each corresponding to a different focal length f of the lens10as shown on the left hand side ofFIG.1.

Said surface10amay be formed by an elastically deformable membrane11of the lens10that is transparent for the main optical signal100. The membrane11is arranged in a housing2of the optical device1/lens10and faces (in the direction of the optical axis A) a first optical element80in the form of a (transparent) cover element80, wherein the membrane11(which can be designed as described above) and said cover element80delimit a volume V of the lens10that is filled with a fluid F (which can be designed as described above).

In case a pressure is exerted on said volume, e.g. by means of an actuation means20, the pressure of the fluid F increases due to the essentially constant volume V of the fluid F causing the membrane11to expand and said curvature of the membrane11/surface10ato increase. Likewise when the pressure on said volume V is decreased, the pressure of the fluid F decreases causing the membrane11/surface10ato contract and said curvature of the first membrane to decrease, as is shown on the right hand side ofFIG.1. Here, increasing curvature means that the membrane11/surface10adevelops a more pronounced convex bulge, or that the membrane11/surface10achanges from a concave or a flat state to a convex one. Likewise, a decreasing curvature means that the membrane11/surface10achanges from a pronounced convex state to a less pronounced convex state or even to a flat or concave state, or changes from a flat or concave state to an even more pronounced concave state.

Hence, the curvature of the membrane11/surface10aof the lens10can be adjusted by means of the actuation means20and therewith the focal length f of the lens10.

As shown inFIG.1, the optical device1further comprises a second (transparent) optical element90being formed as a cover element90as well which runs parallel to the first optical element so that the membrane11/surface10ais arranged between these two optical elements80,90.

Further, for measuring and/or controlling said focal length f of the lens10, the optical device1further comprises a light source50(e.g. such as an LED), wherein said light source50is arranged e.g. on an inner side of a lateral circumferential wall of the housing2of the lens10and is configured to emit light51such that said light51is reflected by the second optical element towards the surface10aof the lens10, is then deflected by the lens10towards the first optical element80, is then reflected back towards the surface10aof the lens10, deflected by the lens10, and finally reflected by the second optical element90onto a—depending on the actual curvature of the surface10a—first and/or a second photosensitive element30,40, e.g. in the form of photo diodes30,40that are arranged adjacent/close to each other on said inner side of the circumferential wall, too (e.g. facing the light source50).

Preferably, the first photo diode30is designed to generate a first output signal O1(e.g. in the form of an electrical current) corresponding to the intensity of the light51impinging on the first photo diode30, and the second photo diode40is designed to generate a second output signal O2corresponding to the intensity of the light51impinging on the second photo diode40.

As shown inFIGS.2and5such a configuration of photosensitive elements30,40allows to determine the focal length f of the lens10, since each curvature of the surface10aor membrane11generates a specific first and second output signal O1, O2so that the curvatures/focal lengths f can be distinguished. In other words (cf.FIG.5) the light51(feedback signal) impinges differently on the two photo diodes30,40depending on the curvature of the surface10aor membrane11of the lens10. However, the present invention also works with a single photosensitive element (e.g. photo diode etc.)30. Preferably, two such elements (e.g. photo diodes)30,40are used to account e.g. for any possible variation of the (LED) signal of the light source50. In other words, to prevent any aging effects. When two photosensitive elements are present a further output signal X is preferably generated from the first and the second output signal O1, O2, which is X=(O1−O2)/(O1+O2).

Due to the configuration of the optical device1, the intensity distribution of the light51of the light source50which is shown inFIG.2for different focal lengths f of the lens10not only changes its widths when the focal length is changed, but also the position of the peak P of the distribution51is shifted when the focal length is changed. Since the photosensitive elements30,40are generally configured such in all embodiments of the present invention that they detect only a part of the intensity distribution of the light51from the light source50, the intensity of the detected light51changes significantly with changing focal length of the lens10. While the changing width of the distribution alone allows for identifying different focal lengths of the lens10, the feature that the optical device1can be configured such that the peak P of the (reflected) light51impinging on the respective element30,40is shifting, further enhances the signal difference. These features of the present invention are also illustrated inFIG.5, which shows a main optical signal100that is focused or diverged by the lens10, but does clearly not interfere with the light51from the light source50(feedback signal). In the left-hand panel ofFIG.5a different focal length of the lens10is adjusted compared to the right-hand panel ofFIG.5. Correspondingly, the photo sensitive elements (e.g. photo diodes)30,40are hit differently from the signal51in these two panels.

Further, as can also be inferred fromFIG.5, said light source50, said photosensitive elements30,40and particularly said first and/or second optical element80,90are arranged such with respect to each other that the main optical signal (main laser)100does not impinge on the photo diodes30,40, i.e. does not affect said first and second output signal O1, O2.

Now, for controlling the focal length f of the lens10, so that the latter can be automatically adjusted to a predetermined focal length, the optical device1comprises a control unit60as shown inFIG.1which is adapted to control said actuation means20such that the latter deforms said surface10aof the lens10in a way that said first and/or second output signal O1, O2approaches a reference output signal, wherein preferably said surface10aof the lens10is deformed in a way that said further output signal X approaches a reference output signal. These reference output signals are calibrated, i.e., correspond to the respective predetermined focal length f that is to be adjusted.

Preferably, the optical device1comprises a memory70in which a plurality of focal lengths as well as plurality of corresponding reference output signals are stored, wherein a reference output signal is assigned to each focal length.

The correspondence between the first and/or second output signals O1, O2or said further output signal X on one side and the focal lengths on the other side can be established by using another method for determining the focal length of the lens10(e.g. a Shack-Hartmann sensor). Then the individual focal length can be adjusted and the corresponding first and second output signal O1, O2or further output signal X are measured and later stored e.g. in said look-up table in memory70.

FIGS.3and4show a further embodiment of an optical device1according to the invention, wherein the lens10is configured as shown inFIG.1and has a first optical element80in the form of a first cover element80, a second cover element81(corresponding to cover element90inFIG.1) as well as a second optical element90which is an optical window (for light51) that is inclined with respect to the lens10and the transparent cover elements80,81and which is partly transmissive for the main optical signal100extending along the optical axis through the lens10, wherein light of the main optical signal100that is reflected by the second optical element90is collected in a laser dump120for absorbing said reflected light. The first cover glass80and the second optical element90are transparent for the main optical signal100and reflective for the signal light51. Cover glass81is transparent for both optical signals and can also be omitted. It is to be noted thatFIGS.3and4both show two different states of the membrane11.

Now, in contrast to the embodiment shown inFIG.1, the light source (e.g. LED)50is arranged such that light51generated by light source50is reflected by the second optical element90towards the lens10, enters the second cover element81and lens10, is reflected on the first cover element80towards the second optical element90, and is then reflected onto the first and/or second photosensitive element (e.g. photo diode)30,40depending on the focal length f or curvature of the membrane11/surface10a(cf.FIG.4dashed line).

Here, the two photosensitive elements30,40are integrated into a printed circuit boards that also comprise an interface to the control unit60and particularly memory70as shown inFIG.1.

FIG.6(showing also two different states of the membrane11) shows a modification of the embodiment shown inFIG.4, where now in contrast toFIG.4the light source50is integrated onto the printed circuit board, too, and is thus arranged adjacent said photosensitive elements30,40. In both embodiments (FIGS.3,4andFIG.6), the printed circuit board is arranged on a lateral inner side of the housing2of the lens10that extends parallel to the optical axis A. Furthermore, the printed circuit board also has connections for the lens10and the light source50.

In conjunction withFIG.6,FIG.7shows a preferred reflectance of the first optical element80(first cover element) with respect to the impinging light51of the light source50. According thereto, the reflectance is preferably essentially 100% for light51having a wavelength in the range from 750 nm to 900 nm, which wavelengths are preferably used for the light51of light source50. Further, as shown inFIG.9, a preferred reflectance of the second optical element90for light in the range from 750 nm to 950 nm is again very high (nearly 100%), so that a good reflection of light51can be assured. Further, the cover element83covering the photo diodes30,40of the embodiment shown inFIG.6preferably has a very good transmittance as shown inFIG.8, so that the light51actually reaches said photosensitive elements30,40with certainty. Furthermore, it has close to 100% reflectance for typical wavelengths of the main optical signal in particular 532 nm and 1064 nm.FIG.10shows a further embodiment of an optical device1according to the invention, which is essentially configured as shown inFIG.1, i.e., comprises a lens10having a first and a second optical element80,90in the form of transparent cover elements80,90, wherein the deformable membrane11defining surface10ais arranged between said two cover elements80,90. The housing2of the lens10/optical device1comprises a circumferential wall201surrounding the membrane11, wherein a first annular member202is connected to said wall201, which first annular member202holds the (circular) first optical element80, as well as a second annular member204which holds the second optical element90. Further, said first annular member202comprises a circumferential edge region203to which said membrane11is fastened. Likewise, the second annular member204comprises a circumferential edge region205. By pushing (e.g. by means of an actuation means20) on an outer membrane part12that is not optically active, the fluid F is pushed from the outer region into the central fluid volume section and the lens10becomes more convex (or less convex when the pressure is decreased). This allows one to adjust the focal length f of the lens10.

As shown inFIG.10, the photosensitive elements30,40as well as the light source50are arranged on the same side of the membrane11/surface10a, namely on the second annular member204, so that the light51is reflected as described with respect toFIG.1, wherein particularly the two photosensitive elements30,40are arranged adjacent to each other in a circumferential direction of the second annular member204, wherein they face the light source50which is arranged on the other side or the second annular member204.

Further, the optical device1may comprises at least one optical filter54configured to prevent light of the first light source50(particularly also of a further light source52when present) from exiting or re-entering the optical device1and/or lens10. Particularly, the second optical element90may be provided with such a filter54. Such filters may also be used in the other embodiments described herein.FIG.11shows a modification of the embodiment shown inFIG.10, wherein the photosensitive elements30,40and the light source50are arranged such that the light51is merely reflected by the first optical element80(and deflected by the lens10) when travelling to the photosensitive elements30,40. Particularly, the photosensitive elements30,40are now arranged adjacent to each other in the direction of the optical axis running perpendicular to the first and second optical element80,90. Also in this embodiment, the light source50and photosensitive elements30,40are on the side of the tunable lens10which has no fluid F, making the assembly process simpler. Furthermore, the light51crosses the membrane11/surface10atwice, resulting in a stronger optical effect and therefore stronger feedback signal.

FIGS.12and13shows a modification of the embodiment shown inFIG.10, wherein the photosensitive elements30,40and the light source50are arranged such that the light51is merely deflected by the lens10when travelling to the photosensitive elements30,40. For this, in contrast toFIG.11, the light source50is now arranged on the other side of the membrane11with respect to the photosensitive elements30,40which are arranged as described with respect toFIG.11.

Further, inFIGS.12and13the lens10may be configured to affect said emitted light51by means of light scattering and/or refraction, wherein particularly the optical device1, particularly the lens10, may comprises at least one diffractive element for generating said light scattering, wherein particularly said at least one diffractive element55is arranged on the membrane11or comprised by the membrane11. Such elements55may also be used in other embodiments.

FIG.16shows a schematical view of a further embodiment of the optical device1according to the invention, where the light source50and the first and second photosensitive element (e.g. photo diodes)30,40are arranged outside the housing2of the lens10, which is configured in principle as shown inFIG.1. Here, the light source50and the photo diodes30,40are arranged on the side of the first optical element80(e.g. cover glass) on which side also the photosensitive elements30,40are arranged, namely adjacent to each other in a plane running parallel to the cover glass80, wherein the first photosensitive element30is arranged above the second photosensitive element40so that the second photosensitive element40is arranged between the first one30and the optical axis. The membrane11of the lens10is arranged between the first and the second cover glass80,90(the fluid F is arranged between the first cover glass80and the membrane11), wherein the second optical element (second cover glass)90is reflective for the light51. In order to reflect the light51from the light source50finally back onto the photosensitive elements30,40a mirror88is present that extends parallel to the plane of the cover glass on said side of the cover glass80where also the elements30,40and the light source50are arranged.

InFIG.16the afore-described configuration is shown for three different focal lengths of the lens10. The respective panels in the lower row show the corresponding intensity distribution of the light51that impinges onto the elements30,40.

Further, as shown inFIG.14, for reduction of external noise (which can be conducted in all embodiments), the light51generated by the light source50is modulated by means of a modulator300, so that the intensity Slof the light51takes e.g. the form
Sl=Vl·sin(ω·t)
where ω is the modulation frequency. The adaptive optics, i.e., lens10modifies said intensity as follows when adjusting the curvature:
So=f(x)·Vl·sin(ω·t)
wherein external noise f(y) is added to this signal which then reads:
Sd=f(x)·Vl·sin(ω·t)+f(y)

This intensity is detected by the photosensitive means30,40.

In order to remove the noise f(y), a demodulator301is configured to demodulate this signal by multiplying the function sin(ω·t) to the detected intensity Sdyielding
Sde=f(x)·Vl·sin(ω·t)·sin(ω·t)+f(y)·sin(ω·t)
which corresponds to
Sde=(1/2)·f(x)·f(x)·V1−f(x)·Vl·(1/2)·cos(2·ω·t)+f(y)·sin(ω·t)

Now, the parts varying with frequency 2·ω and ω can be filtered out by means of a corresponding band-pass or low-pass filter110. So that the clean output signal
Ss=(1/2)·f(x)·V1
remains.

Finally,FIG.15shows possible applications of the optical device1according to the invention in laser light processing systems. In this regard,FIG.15shows an optical system1in form of a laser marking equipment1that is designed to focus a laser light beam100generated by a laser400of the device1onto a three-dimensional surface of an object404. For this, the generated laser light beam100is send through an optional beam expander401for widening the diameter of the laser light beam100(e.g. to a diameter of 5 mm). Now, in order to converge/focus the laser light beam100, a lens10according to the invention as described herein having an adjustable focus f (e.g. in the range from +400 mm to −600 mm) can be positioned in the optical path either in front of the beam expander401, in the beam expander401, or after the beam expander (in front of a mirror means402for deflecting the laser light beam100onto the surface of said object404). After focusing/converging the laser light beam100by means of the lens10, the laser light beam100is deflected by a mirror means402towards an F-Theta lens403and then focused on the surface of said object404. Due to the mirror means402and the focus adjustable lens10, the laser light beam100can be focused in three dimensions x, y, z as illustrated inFIG.15. The mirror means402(e.g. mirrors mounted onto x-y Galvo-scanners) can be a single mirror that can be pivoted (in two dimensions) about two independent axes or can be comprised of two mirrors which are each pivotable about an axis, the two axes being orthogonal with respect to each other. In such an optical system1, the F-theta lens can also be omitted or additional lenses can be added to the light path of the laser light beam100to achieve e.g. small spot sizes.

Further,FIG.17shows a configuration using two light sources50,52(e.g. LED) and two photosensitive elements (30,40). This configuration may be used in conjunction with all embodiments described herein. Particularly, here, each light path T11, T12from the light source50to one of the photosensitive elements30,40is symmetric to a corresponding light path T21, T22from the further light source52to one of the photosensitive elements30,40. Advantageously, this allows for the normalization of all photosensitive elements30,40and light source efficiencies/sensitivities.

Further,FIG.18shows a further embodiment of an optical device1according to the invention, which comprises a lens10having a first and a second optical element80,90in the form of transparent cover elements80,90, wherein the deformable membrane11defining surface10ais arranged between said two cover elements80,90. Further, the optical element1comprises a housing2that has a circumferential wall201surrounding the membrane11, wherein a first annular member202is connected to said wall201, which first annular member202holds the (circular) first optical element80, as well as a second annular member204which holds the second optical element90. Further, said first annular member202comprises a circumferential edge region203to which said membrane11is fastened.

Furthermore, as indicated inFIGS.17and18, the optical device1may comprises at least one temperature sensor56(or several such sensors56for each photosensitive element (e.g. photo diode)30,40being in thermal contact with the first and/or second photosensitive element30,40, wherein particularly the optical device1is configured to use said at least one temperature sensor56for compensating a temperature-dependent sensitivity of the first and/or second photosensitive element30,40. These kind of temperature sensors56and compensation means may also be present in the other embodiments.

By pushing (e.g. by means of an actuation means20) on an outer membrane part12that is not optically active, the fluid F is pushed from the outer region into the central fluid volume section and the lens10(namely inner part of membrane11) becomes more convex (or less convex when the pressure is decreased). This allows one to adjust the focal length f of the lens10.

As shown inFIG.18, the photosensitive elements30,40are arranged outside the lens10while the light source50irradiates the photosensitive elements30,40through the membrane11such that the emitted light51is reflected on the second cover element90before impinging on the elements30,40.

Further,FIGS.19to22show cross sectional views of an aspect and embodiment of the present invention, wherein here, the optical device forms a contact lens1that is configured to be placed directly onto a surface300aof an eye301of a user, namely on top of the pupil of the eye300. The contact lens1comprises at least a lens10that is configured to be modified so as to adjust the focal length of the contact lens.

Further, the contact lens1comprises a light source50for emitting light51(particularly IR light so that the eye is not disturbed) and a photosensitive element30, which may be a photo diode, for detecting emitted light51from source50and for providing an output signal depending on the intensity of the emitted light51that impinges onto the photosensitive element30.

According to the invention, said light source50and said photosensitive element30are arranged such on the contact lens1that light emitted51by the light source50is reflected by the lens301of the eye300of the user before impinging onto said photosensitive element30, when the contact lens is properly worn by the user.

Preferably, the light source50and the photosensitive element30are further configured such that the intensity distribution of the emitted light51that impinges on the photosensitive element30changes when the form of the lens301of said eye300of the user is changed and/or when the position of the contact lens1on the surface300aof the eye300is changed (i.e. due to a radial displacement of the contact lens1so that the contact lens is off center in a radial direction), so that said output signal changes as well.

Such arrangement of the source50and element30can e.g. be found by simulating the emitted light as shown inFIGS.19to22.

Further, the contact lens1preferably comprises a mechanism303for adjusting the focal length of the lens10, and a control unit304for controlling said mechanism303, wherein the control unit is configured to control said mechanism303using said output signal.

In detail,FIG.19shows the situation of an accommodation of the eye300to 0 D (diopter), wherein the output signal of the photosensitive element corresponds to a light intensity of 0.68% of the source intensity (i.e. intensity of light51emitted by light source50).

Further, inFIG.20, the accommodation of the eye300is 2D, wherein the output signal of the photosensitive element corresponds to a light intensity of 0.63% of the source intensity.

Finally,FIG.21corresponds to an accommodation of the eye300of 0 D wherein now the contact lens has been shifted radially on the surface300aof the eye300by an amount of 0.5 mm, which can be achieved by the user by focusing an object nearby. The contact lens can for example be designed such that the lens moves when the users looks down or towards the nose. Here, the output signal corresponds to a light intensity of 0.39% of the source intensity.

Thus, the output signal from the photosensitive element30can be advantageously used to control the contact lens1, particularly the focal length of the contact lens1.

As a comparison,FIG.22shows all light rays extending from the source50.

FIGS.23to25also show the optical device1in the form of a contact lens that is arranged on a surface300aof an eye300of the user (e.g. a person wearing the contact lens1), wherein this time, the light source50and the photosensitive element30are configured such that the light51emitted by the light source50passes the lens301of the eye300on which the contact lens1is placed is particularly deflected by said lens301and is then reflected on the retina300bof said eye and travels back via the lens301(where the light51is particularly deflected again) to the photosensitive element30.

Here,FIG.23shows the situation where emitted light51reflected on the retina300bhits the photosensitive element30, while inFIG.24less emitted light51impinges on the photosensitive element30due to the fact that the lens301is deformed (e.g. by focusing it) by the user of the contact lens1. Further, less light51on the photosensitive element can also be achieved by displacing the position of the contact lens on the surface300aof the eye300which is shown inFIG.25. Such a movement can be achieved by the user as described above. Thus, also in case the emitted light is guided via the retina300b, the output signal of the photosensitive element30can be used to control the contact lens1as described above.

Further,FIGS.26to28show cross sectional views of an aspect and embodiment of the present invention, wherein here, the optical device1is designed to worn in front of an eye300of a user, e.g. forms glasses1, that are e.g. configured to be placed on a nose of a user. The optical device1comprises at least a lens10that is configured to be modified so as to adjust the focal length of the optical device (e.g. glasses).

Further, the optical device1comprises a light source50for emitting light51(particularly IR light so that the eye is not disturbed) and a photosensitive element30, which may be a photo diode, for detecting emitted light51from source50and for providing an output signal depending on the intensity of the emitted light51that impinges onto the photosensitive element30.

According to the invention, said light source50and said photosensitive element30are arranged such on the frame of the optical device1or glasses1or on the glasses1that light emitted51by the light source50is reflected by the eye300and in particular the lens301of the eye300, the cornea300cor the retina300bof the user before impinging onto said photosensitive element30, when the optical device1(e.g. glasses) is properly worn by the user.

Preferably, the light source50and the photosensitive element30are further configured such that the intensity distribution of the emitted light51that impinges on the photosensitive element30changes when the form of the lens301of said eye300of the user is changed and/or when the position of the eye300of the user changes with respect to the optical device1(i.e. due to a looking downwards or inwards), so that said output signal changes as well.

Such arrangement of the source50and element30can e.g. be found by simulating the emitted light as shown inFIGS.26to28.

Further, the optical device (e.g. glasses)1preferably comprises a mechanism303for adjusting the focal length of the lens10, and a control unit304for controlling said mechanism303, wherein the control unit304is configured to control said mechanism303using said output signal.

In detail,FIG.26shows the situation of an accommodation of the eye300to 0 D (diopter).

Further, inFIG.27, the accommodation of the eye300is 2D.

Finally,FIG.28corresponds to an accommodation of the eye300of 0 D wherein now the eye ball has rotated with respect to the optical device1or the respective eye glass.

Thus, the output signal from the photosensitive element30can be advantageously used to control the optical device or glasses1, particularly the focal length of the optical device or glasses1.