An optical assembly

Abstract

This invention pertains to an optical assembly comprising a transparent, deformable, non-fluid optical element body positioned between two transparent substrates and an actuator system. The actuator system is configured to exert forces which vary in magnitude, direction or duration along the rim of one or both transparent substrates creating a dynamic tilt, around a virtual pivot point within the non-fluid optical element body. The optical element body, characterized by a Poisson's ratio of less than 0.499, enables precise deformation under the influence of an actuator system.

Description

[0001] AN OPTICAL ASSEMBLY

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an optical assembly or an adaptive optical systems. Specifically, the invention focuses on deformable, non-fluid optical component bodies sandwiched between transparent substrates, which can be dynamically adjusted using an actuator system.

[0004] BACKGROUND OF THE INVENTION

[0005] The evolution of optical systems has seen remarkable advancements over the past few decades, driven by the ever-growing demand for enhanced imaging capabilities, adaptive functionalities, and compact designs.

[0006] One area that has gathered significant attention is the development of deformable optical elements capable of real-time adjustments to modify optical properties. These elements play a crucial role in adaptive optics, image stabilization, and other optical systems where dynamic control over the optical path is essential. Traditionally, optical systems have relied on rigid optical components with fixed geometries to achieve desired optical performances. While these systems have served many applications well, they often face limitations when it comes to correcting optical aberrations, adapting to changing environmental conditions, or integrating into compact and mobile devices.

[0007] The need for more versatile and adaptive optical solutions has prompted the exploration and development of deformable optical elements.

[0008] Deformable optical elements introduce a paradigm shift in optical system design by allowing for dynamic adjustments of the optical elements' shape, orientation, or refractive index. These adjustments enable the correction of optical aberrations in real-time, leading to sharper and clearer imaging. Moreover, they offer the flexibility to adapt optical systems to changing conditions, such as temperature variations or mechanical disturbances, ensuring consistent performance over time. The realization of deformable optical elements hinges on the development of efficient actuation mechanisms capable of exerting precise and controllable forces on the optical elements. Over the years, various actuation mechanisms, ranging from electromagnetic to piezoelectric and electrostatic, have been explored and employed in deformable optical systems. Piezoelectric actuators, in particular, have gained traction due to their high precision, fast response times, and compatibility with miniaturized designs. These actuators convert electrical energy into mechanical motion, allowing for fine-tuned adjustments of the deformable optical elements' shape or position.

[0009] While the potential of deformable optical assemblies is vast, their development and integration into practical optical systems come with challenges. One of the primary challenges lies in designing deformable elements with suitable mechanical properties, such as stiffness, elasticity, and durability, to withstand the forces exerted by the actuation mechanisms while maintaining optical clarity and performance.

[0010] Hence, an optical assembly having an improved mechanical stability would be advantageous.

[0011] OBJECT OF THE INVENTION

[0012] It may be seen as an object of the invention to provide an optical assembly with a deformable, non-fluid optical component body capable of dynamic adjustments. The assembly aims at achieving adaptive optical functionalities through the use of an actuator system that applies variable forces to the first transparent substrate of the optical component. These dynamic adjustments lead to a dynamic tilt of the optical axis around a pivot point within the optical component body.

[0013] It is a further object of the present invention to provide an alternative to the prior art.

[0014] SUMMARY OF THE INVENTION

[0015] The above described objects and several other objects are intended to be obtained in a first aspect of the invention by providing an optical assembly comprising: a first transparent substrate and a second transparent substrate; a transparent, deformable, non-fluid optical component or element body sandwiched between the first transparent substrate and the second transparent substrate forming an optical element having an optical axis; an actuator system for applying forces to the first transparent substrate; a frame connected to the second transparent substrate and to the actuator system. The transparent, deformable, non-fluid optical element body comprises at least two opposite surfaces intersecting the optical axis and the actuator system is configured to exert forces to the first transparent substrate which vary in magnitude, direction or duration along the rim of the first transparent substrate creating a dynamic tilt of the optical axis, around a pivot point within the transparent, deformable, non-fluid optical element body, thereby rendering the at least two opposite surfaces not-parallel.

[0016] The pivot point may also be referred to as a virtual pivot point.

[0017] Generally a pivot point is a fixed point within a system where motion or rotation occurs by means of an element, such as a hinge.

[0018] A virtual pivot point refers to a theoretical point, even though there may not be a physical element acting as a pivot point, i.e., the pivot point is created by and within the transparent, deformable, non-fluid optical element body

[0019] In the context of the optical assembly described the reference to a virtual pivot point suggests that although there may not be a physical pivot element within the deformable optical element body, the dynamic tilting of the optical axis creates an effect similar to rotation around a fixed point. This virtual pivot point allows for precise control and manipulation of the optical element's optical properties, enabling adjustments to be made as if there were a physical pivot present.

[0020] This arrangement achieves a dynamic adjustment of the optical element 's shape and orientation. By applying variable forces to the flexible membrane surrounding the optical element, the optical axis can be tilted. This alteration in the optical element 's orientation causes its surfaces to become not parallel

[0021] In the context described, the system can dynamically adjust the orientation of the optical element surfaces in response to motion or vibrations, and thus compensate for unwanted movements, achieving optical image stabilization (OIS) along with other functionalities.

[0022] In some embodiments, the actuator system comprises at least one actuator, such as two or more individually addressable actuators, adapted to apply forces to the first transparent substrate in a direction along said optical axis, such as in a direction at least substantially along the optical axis.

[0023] The actuator has the function of shaping the transparent substrate into a desired shape. The transparent substrate is bent into the desired shape due to the pattern and disposition of the actuator system located on its top surface and by the magnitude of respective applied voltages. The shaping of the transparent substrate indirectly changes the shape of the abutted transparent, deformable, non-fluid optical element body.

[0024] The actuator system is configured to apply forces to the first and / or to the second transparent substrate.

[0025] In some other embodiments, the actuator system is arranged for displacing at least a part of, such as all of, the first transparent substrate with respect to the frame.

[0026] In some further embodiments, each of the two or more individually addressable actuators involves a cantilever with a first end connected to the frame and a second end adapted to engage the first transparent substrate to apply the force. Each cantilever comprises at least one layer of piezoelectric material and addressing the two or more individually addressable actuators involves applying a voltage over the piezoelectric material.

[0027] In some other embodiments, the piezoelectric materials are ferroelectric materials

[0028] Ferroelectrics with a huge coercive field materials are a subset of piezoelectric materials in that they also possess a spontaneous polarization, i.e. which remains without applied field in the unit cell, which can be reoriented by application of an electric field.

[0029] Ferroelectric materials with a huge coercive field exhibit spontaneous electric polarization that can be controlled and reversed by applying an external electric field, allowing for highly accurate and responsive actuation.

[0030] The presence of one or more layers of ferroelectric materials may provide better mechanical strength and durability under repeated actuation cycles. This makes the optical assembly with higher tunable range and more reliable over time, reducing the likelihood of performance degradation. For example, the actuator system may comprise at least two layers of ferroelectric materials.

[0031] Incorporating at least two layers of such ferroelectric materials can amplify the force generated by the actuator system. This is particularly beneficial for applications requiring significant mechanical movement or higher force output to achieve the desired optical adjustments.

[0032] Furthermore, multiple layers of ferroelectric materials can offer better control over the actuation process. The layered structure allows for more refined manipulation of the electric fields applied, resulting in smoother and more stable adjustments of the optical component.

[0033] In some embodiments, the actuator system comprises AIScN.

[0034] AIScN may produce mechanical displacements or forces in response to an applied electric field, enhancing the actuation performance of the optical assembly.

[0035] AIScN also exhibits excellent thermal stability, maintaining its piezoelectric properties over a wide temperature range. This ensures reliable performance in various environmental conditions, making it suitable for applications in harsh or fluctuating environments.

[0036] Furthermore, AIScN has low dielectric loss, which means it can operate efficiently with minimal energy dissipation. This is particularly important for battery-powered or energy-sensitive applications, as it helps extend the operational lifespan of the device.

[0037] The use of AIScN in the actuator system of an optical assembly provides significant advantages in terms of piezoelectric performance, environmental safety, thermal stability, mechanical durability, and manufacturing compatibility.

[0038] In some other embodiments, the first transparent substrate is connected to the frame via, such as exclusively via, the actuator system.

[0039] The word exclusively means that the first transparent substrate is connected to the frame solely through the actuator system, without any additional connections or support structures. This exclusive connection allows the actuator system to fully control the movement and adjustments of the first transparent substrate, ensuring precise and dynamic manipulation of the optical element 's optical properties.

[0040] In some embodiments, the second end is in sliding contact with the first transparent substrate, thereby allowing for adjustments of the location of surface contact upon dynamic tilt.

[0041] The optical assembly incorporates a sliding contact arrangement between the actuator system and the first transparent substrate, i.e. the interface between the actuator system and the first transparent substrate comprises a sliding contact, eliminating the need for adhesives. This design facilitates dynamic tilting by allowing precise adjustments in the contact point or surface interface. The absence of adhesive enhances the system's reliability and durability, as there is no risk of adhesive degradation over time. Moreover, the sliding contact ensures smoother, more accurate actuator movements, leading to better control over the optical axis tilt. This precision improves the overall performance of the optical element, enabling finer adjustments and enhancing adaptive optical functionalities such as focus and image stabilization.

[0042] The presence of the sliding contact allows for relative movement without generating pulling forces, thereby maintaining the integrity and functionality of the optical assembly.

[0043] Sliding contact may also be referred to as pseudo sliding contact enabling the correct degree of freedom of motion, with low friction contact between the actuator displacement element and the first or second transparent substrate.

[0044] In some embodiments of the optical assembly, the at least two opposite surfaces of the optical element are not parallel when the actuator system is not activated, such as in a Zero Volt state. This Zero Volt state, also referred to as the "default," "inherent," or "zero Volt" state of the optical element, represents the natural configuration of the optical element without any external forces applied by the actuator system, thereby setting said first transparent substrate at a default tilt angle.

[0045] In other words, the actuator system is configured to apply a preload condition as part of the assembly, wherein the preload condition biases the first transparent substrate towards a default tilt angle. The actuator system may operate bidirectionally, moving up to reduce the tilt angle and potentially flattening the lens, and moving down to increase the tilt angle.

[0046] In some further embodiments, the first transparent substrate comprises one or more stiffeners, on its circumferential section distributing strain and non- symmetrical deformations around the optical axis resulting from the exerted forces over larger areas of the first transparent substrate under operation.

[0047] In this optical assembly context, the first transparent substrate is reinforced with one or more stiffeners along its circumferential section. These stiffeners, possibly in the form of ring-shaped structures, serve to distribute strain and non- symmetrical deformations around the optical axis caused by the exerted forces. By spreading the load over larger areas of the substrate during operation, these stiffeners enhance the structural integrity of the optical element assembly and help maintain optical alignment and stability under dynamic conditions.

[0048] In some embodiments, the first transparent substrate may be a first bendable transparent membrane and the second transparent substrate may be a second bendable transparent membrane.

[0049] In some embodiments, the transparent, deformable, non-fluid optical element body has: an elastic modulus larger than 300 Pa; a refractive index above 1.35 ; and comprises a polymer network of cross-linked or partly cross-linked polymers and a miscible oil or combination of oils.

[0050] The polymer network of cross-linked or partly cross-linked polymers and a miscible oil or combination of oils used within the transparent, deformable, nonfluid optical element body allows for the creation of a pivot point.

[0051] The pivot point, or virtual pivot point, is generally a fixed point within a system where motion or rotation occurs by means of an element, such as a hinge.

[0052] The polymer network of cross-linked or partly cross-linked polymers and a miscible oil or combination of oils of the invention allows for the creation of a virtual pivot point acting as a pivot point even though there may not be a mechanical pivot element.

[0053] In the context of the invention the presence of a pivot point created by the properties of the polymer network of cross-linked or partly cross-linked polymers and a miscible oil or combination of oils of the invention suggests that although there may not be a physical pivot element within the deformable optical element body, the dynamic tilting of the optical axis creates an effect similar to rotation around a fixed point. This virtual pivot point allows for precise control and manipulation of the optical element's optical properties, enabling adjustments to be made as if there were a physical pivot present.

[0054] The invention prioritizes achieving mechanical stability within the optical element, crucial for optical performance. By tailoring the chemical structure of the polymer network, desired mechanical stability is ensured once cured. Maintaining an optimal balance of mechanical properties is essential. Excessive stiffness in the optical element body can restrict the degree of bending achievable by the actuator, compromising focus shifting. Conversely, overly soft materials might hinder actuation strength. The solution of the invention lies in a deformable, yet non-fluid optical element body, combining resistance to deformation with elastic behaviour. This balance optimizes actuation efficiency, reducing power consumption and production costs.

[0055] In some embodiments, the at least one deformable optical element body has a shear modulus of less than 100 KPa.

[0056] This value of shear modulus ensures retaining the ability to return to its original shape after deformation induced by external stimuli. This requirement arises from the necessity for the optical element to maintain adjustability for focus changes without undergoing permanent deformation. The shear modulus, denoted as G, reflects the material's tendency to deform when subjected to shear forces. For polymers used in adjustable optical element applications, a shear modulus below 100 kPa is deemed essential, with values even lower, such as 50 kPa or 10 kPa, being highly desirable.

[0057] Moreover, for the deformable optical element body to withstand gravitational forces during the device's working life, an elastic modulus exceeding 300 Pa is required. This threshold prevents deformation due to gravitational effects during normal operation of the optical device. The relationship between the elastic modulus (E), shear modulus (G), and Poisson's ratio (v) further dictates the preferred range of shear modulus between 100 Pa and 100 kPa, corresponding to an elastic modulus range of 300 Pa to 300 kPa.

[0058] Balancing stiffness and adjustability is crucial; excessive stiffness risks structural collapse, while excessive softness compromises the optical element's adjustability. While variations in polymer chain structure can reduce stiffness, they may also affect the material's time-dependent viscoelastic properties. Therefore, in some embodiments, ensuring a shear modulus below 100 kPa maintains both structural integrity and adjustability, fulfilling the optical assembly's functional requirements seamlessly.

[0059] In some embodiments, the difference in refractive index ratio between said transparent polymer network of cross- 1 inked or partly cross-linked polymers and the oil or combination of oils is between 0.01 and 0.30.

[0060] In some embodiments, the non-fluid optical element body further has an absorbance in the visible range lower than 10% per millimeter thickness of the transparent, deformable, non-fluid optical element body.

[0061] The optimization of the polymer and oil composition having the desired refractive index is crucial to achieve the desired performances.

[0062] In some further embodiments, the polymer network of cross-linked or partly cross-linked polymers is a polymer network of cross-linked or partly cross-linked polysiloxanes and wherein the oil or combination of oils have a molecular weight lower than 1000 g / mol.

[0063] In some embodiments, the amount of the oil or combination of oils is in a range between 0.1 to 90 % vol / vol of said transparent polymer network of cross-linked or partly cross-linked polymers. In some other embodiment, the transparent, deformable, non-fluid optical element body is configured to have a pre-determined mechanical property fitting a frequency domain of actuation of the actuator system, such as between 5 Hz to 3000 Hz, such as between 5 Hz and 2000 Hz.

[0064] The chosen frequency range ensures that the optical element body can respond dynamically to the actuation forces without exhibiting resonance or instability. This is crucial for maintaining precise control over the optical element shape and optical axis orientation, which is essential for high-performance optical systems.

[0065] Many practical applications, such as autofocus camera systems and adaptive optics, require rapid and stable adjustments. Frequencies between 5 Hz and 3000 Hz cover the operational spectrum needed for these applications, allowing for quick focus changes and stabilization.

[0066] The mechanical properties of the optical element body, including its elastic and shear moduli, must be compatible with this frequency range. Materials that can perform well under these conditions ensure that the optical element body will not degrade or fail during operation, providing long-term reliability.

[0067] Overall, configuring the optical element body to match the frequency domain of 5 Hz to 3000 Hz allows for optimal performance in various optical applications, balancing dynamic responsiveness, mechanical stability, and energy efficiency.

[0068] In some further embodiments, the transparent, deformable, non-fluid optical element body has a Poisson's ratio smaller than 0.499.

[0069] The Poisson's ratio (v) is a measure of the material's tendency to expand in directions perpendicular to the direction of compression or contraction when subjected to mechanical forces. It is defined as the negative ratio of transverse to axial strain.

[0070] The Poisson's ratio (v) is a dimensionless constant given by:

[0071] Where: e transverseisthe transverse strain (perpendicular to the applied force).eaxialisthe axial strain (in the direction of the applied force).

[0072] In practical terms, if a material is compressed along one axis, it will tend to expand along the perpendicular axes, and the Poisson's ratio quantifies this behaviour.

[0073] For the transparent, deformable, non-fluid optical element body, the Poisson's ratio provides insights into how the optical element material deforms under the influence of the actuator system, i.e. the mechanical behaviour of the deformable optical element body.

[0074] According to the invention, the optical element body is designed to operate within a specific frequency range, and its Poisson's ratio is tailored to enhance its deformability or other mechanical properties relevant to its function within the actuator system.

[0075] In the optical assembly described, the Poisson's ratio of the deformable optical element body impacts the way the optical element body deforms under actuation, thus will affect the dynamic tilt and the overall optical performance.

[0076] Choosing the optimal Poisson's ratio helps ensure the optical element deforms in a controlled manner that optimizes optical clarity and functionality.

[0077] Furthermore a optical element body with an appropriate Poisson's ratio will maintain structural integrity while allowing the necessary dynamic adjustments, preventing unwanted distortions that could degrade optical performance.

[0078] Moreover, the ability of the optical element body to adapt to changes, such as varying the focal length or correcting optical aberrations, is influenced by how it deforms under mechanical forces. The Poisson's ratio plays a crucial role in determining the responsiveness and precision of these adjustments.

[0079] By selecting a optical element body with a suitable Poisson's ratio, the design can achieve the desired balance between flexibility and stability, ensuring the optical element body performs optimally under the actuator system's dynamic forces. In search for optimal Poisson's ratio values, the inventors observed that the transparent, deformable, non-fluid optical element body of the invention with Poisson's ratio smaller than 0.499 provide optimal performances.

[0080] The tilt angle achievable by the actuator system is highly dependent on the Poisson's ratio, with a noticeable impact when using a polymer with a Young's modulus of around 10 kPa. By carefully measuring and adjusting both the Poisson's ratio and Young's modulus, the optical assembly can be optimized for superior dynamic tilt and optical performance. The first and other aspects or embodiments of the present invention may each be combined with any of the other aspects and embodiments. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0081] BRIEF DESCRIPTION OF THE FIGURES

[0082] The optical assembly according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0083] Figure 1 shows the optical assembly according to some embodiments of the invention.

[0084] Figures 2a and 2b show the optical assembly of figure 1 when a force is applied to the first transparent substrate according to some embodiments of the invention. Figure 3 shows the optical assembly according to some embodiments of the invention of figure 1 when a force is applied to the first transparent substrate according to some embodiments of the invention.

[0085] Figure 4 is a plot showing Poisson's ratio value vs tilt angle as a function of ferees applied.

[0086] DETAILED DESCRIPTION OF EMBODIMENTS

[0087] Figure 1 shows an optical assembly 7 comprising a first transparent substrate 1 and a second transparent substrate 2 and a non-fluid optical element body 3 sandwiched in between the two substrates.

[0088] The actuator system 4 is configured to apply forces to the substrate 1.

[0089] A frame (not shown) is connected to the second substrate 2 and to the actuator system 4.

[0090] As shown in figure 1, the actuator system 4 may be designed to introduce a preload force, which predisposes the first transparent substrate 1 towards an initial tilt angle.

[0091] As show in figure 2a when the actuator system 4 moves down 6, a dynamic tilt of the optical axis is created around a pivot point 5 within the non-fluid optical element body 3, thereby rendering the two opposite surfaces of 1 and 2 not- parallel.

[0092] Figure 2b shows the condition in which the actuator system 4 moves up 10 and a dynamic tilt of the optical axis is created around a pivot point 5 within the non- fluid optical element body 3, thereby reducing the tilt, which eventually may become flat as shown.

[0093] Figure 3 shows displacement data 8 of the first surface upon application of ferees. Figure 4 is a plot 9 showing the Poisson's ratio value vs tilt angle as a function of forces applied.

[0094] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

CLAIMS1. An optical assembly comprising:- a first transparent substrate and a second transparent substrate; a transparent, deformable, non-fluid optical element body sandwiched between said first transparent substrate and said second transparent substrate forming an optical component having an optical axis; wherein said transparent, deformable, non-fluid optical element body has an elastic modulus larger than 300 Pa, a refractive index above 1.35 and comprises a polymer network of cross-linked or partly cross-linked polymers and a miscible oil or combination of oils.- an actuator system for applying forces to said first transparent substrate; wherein said transparent, deformable, non-fluid optical element body comprises at least two opposite surfaces intersecting said optical axis; wherein said actuator system is configured to exert forces to said first transparent substrate which vary in magnitude, direction or duration along the rim of the first transparent substrate creating a dynamic tilt of said optical axis, around a pivot point within said transparent, deformable, non-fluid optical element body, thereby rendering said at least two opposite surfaces not-parallel.

2. An optical assembly according to claim 1, further comprising a frame connected to said second transparent substrate and to said actuator system.

3. An optical assembly according to any of the preceding claims 1-2, wherein said actuator system comprises at least one actuator adapted to apply forces to said first transparent substrate in a direction along said optical axis.

4. An optical assembly according to any of the preceding claims 2-3, wherein said actuator system is arranged for displacing at least a part of, such as all of, said first transparent substrate with respect to said frame.

5. An optical assembly according to any of the preceding claims 2-4, wherein said actuator system comprises two or more individually addressable, wherein each of said two or more individually addressable actuators involves a cantilever with a first end connected to said frame and a second end adapted to engage said first transparent substrate to apply said force, and wherein each cantilever comprisesa layer of piezoelectric material and addressing of said two or more individually addressable actuators involves applying a voltage over said piezoelectric material.

6. An optical assembly according to any of the preceding claims 2-5, wherein said first transparent substrate is connected to said frame via, such as exclusively via, said actuator system.

7. An optical assembly according to any of the preceding claims 1-6, wherein said second end is in sliding contact with said first transparent substrate, thereby allowing for adjustments of the location of surface contact upon dynamic tilt.

8. An optical assembly according to any of the preceding claims 1-7, wherein said at least two opposite surfaces are not parallel when said actuator system is not activated, such as in a Zero Volt state.

9. An optical assembly according to any of the preceding claims 1-8, wherein said actuator system is configured to apply a preload condition, thereby setting said first transparent substrate at a default tilt angle.

10. An optical assembly according to any of the preceding claims 1-9, wherein said first transparent substrate comprises one or more stiffeners, on its circumferential section distributing strain and non-symmetrical deformations around the optical axis resulting from said exerted forces over larger areas of said first transparent substrate under operation.

11. An optical assembly according to any of the preceding claims 1-10, wherein said polymer network of cross-linked or partly cross-linked polymers is a polymer network of cross-linked or partly cross-linked polysiloxanes and wherein said oil or combination of oils have a molecular weight lower than 1000 g / mol.

12. An optical assembly according to any of the preceding claims 1-11, wherein said at least one deformable optical element body has a shear modulus of less than 100 KPa.

13. An optical assembly according to any of the preceding claims 1-12, wherein said transparent, deformable, non-fluid optical element body is configured to have a pre-determined mechanical properties fitting a frequency domain of actuation of said actuator system, such as between 5 Hz to 3000 Hz.

14. An optical assembly according to any of the preceding claims 1-13, wherein said transparent, deformable, non-fluid optical element body has a Poisson's ratio smaller than 0.499.

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