Temporal dithering using optical element

Abstract

The invention relates to a method of operating an interferometric optical element, the optical element comprising a cover supported by a support, and a means. A spatial arrangement of the cover as seen in a cross section of the cover defines a cover contour profile, the means is arranged to move the cover from a first cover contour profile to a further cover contour profile which is different from the first cover contour profile. Wherein the optical element further comprises a substrate on a side of the support opposite the cover, a cavity being defined between the cover and the substrate, with a cavity height defined as a distance from the substrate to the cover. The method comprises alternating between two different cover contour profiles to achieve a perceived optical behaviour that corresponds to a received desired optical characteristic for the optical element.

Description

[0001] TEMPORAL DITHERING USING OPTICAL ELEMENT

[0002] The current application relates to a method of operating an optical element, the optical element comprising a cover having a first surface and a second surface, a support, and a means. The cover is orientated with the first surface directed towards the support, a part of the first surface is attached to the support, a spatial arrangement of the cover as seen in a cross section of the cover defines a cover contour profile, and the means is arranged to move the cover from a first cover contour profile to a further cover contour profile which is different from the first cover contour profile. The optical element further comprises a substrate on a side of the support opposite the cover, a cavity being defined between the cover and the substrate, with a cavity height defined as a distance from the substrate to the cover.

[0003] An optical element is known from e.g. WO 2021 / 032752 Al and WO 2018 / 228671 Al. This document discloses optical devices of specific interest. The working principle is that when a cover is provided that has some desired optical behaviour, e.g. reflecting light, transmitting only some light, etc. the interaction of incident light can be changed by changing the cover contour profile. To facilitate the cover changing shape to facilitate changing the optical behaviour of the optical device, the cover is made relatively thin, in terms of WO 2021 / 032752 Al 2-dimensional. As an example, a single graphene layer cover is presented, with a coating on top to obtain desirable optical characteristic. Since the optical device is very small, they can be used to act like a pixel in a larger collection of similar devices. Control of scattering, reflection and / or interference behaviour can be used to turn a pixel on or off and / or vary its colour. This way, images can be generated and / or manipulated.

[0004] Several principles of operation are available with such optical devices. A first operational principle is shown in figures 1A - 1C, which correspond to figures 9 - 11 of WO 2021 / 032752 Al. These figures show respectively an optical device with a flat cover, a convex cover, and a concave cover. Light incident on the flat cover (fig. 1A) is reflected as if hitting a smooth and straight surface, i.e. parallel incident rays remain parallel after reflection. As such, specular reflection takes place at the cover. In the convex and concave positions of the cover, parallel incident rays are no longer parallel after reflection, thus causing diffuse reflection. By changing the shape of the cover, it is thus possible to alternate between specular and diffuse reflection. To suit this first operational principle, the cover is sufficiently reflective towards the incident light. In this example, the light is incident on the second surface, which may also be called the outside of the optical device.

[0005] Figures 2A - 2C, which correspond to figures 12 - 14 of WO 2021 / 032752 Al, show a second operational principle. Reference is first made to the substrate which spans the support on an opposite side of the cover, in order to define a cavity between the cover and the substrate. The substrate is partly reflective and partly transmissive. The cover is relatively reflecting. Light incident on the substrate is thus partly transmitted and partly reflected. The transmitted light reflects on the first surface of the cover, i.e. coming from the inside, and is transmitted back through the substrate, where it interferes with the light reflected by the substrate. Depending on the wavelength of the light and the distance between the cover and the substrate, the interaction can be constructive or destructive. Since that distance changes when the cover changes shape, the interferometric characteristics of the optical device can be changed.

[0006] Figures 6 and 7 show even other ways of using the changing cover contour profile. In the case of figure 6, an optical element is shown with a substrate 106 that is relatively reflective. The cover 101 in this case is relatively absorbing. Nevertheless, of an incoming light beam 601, at least some light may be transmitted towards the substrate 106 as transmitted light beam 603. This reflects back via the substrate 106 as reflected light 604. Due to interference of the transmitted light beam 603 and the reflected light 604, a pattern of nodes and antinodes is present. The cover 101 can then be moved, e.g. by changing its cover contour profile or its position with respect to the support, to place the cover at an antinode for absorbing the light, or at a node for not or absorbing less the light. Accordingly, the exiting light 605 can be present in less or more intensity by controlling the cover. This principle is called interferometric absorption.

[0007] Figure 7 shows the principle of interferometric reflection, similar to fig. 2, but with light 601 incident the cover. In this case, light is partially transmitted through the cover 101, and reflected at the substrate 604, which forthat purpose is reflective. The cover 101 reflects some light 605, but also transmits some light 603. After reflecting 604 from the substrate 106, light passing through the cover 101 again interferes with the reflected light 605. By controlling the position or cover contour profile of the cover 101, control is possible of wavelengths of light that do or do not interfere constructively.

[0008] In both cases, light transmitted through the cover may actually be refracted. However, since the figures show a specific example of light incident normal to the cover, the wording transmitting was used. The invention can however be applied, depending on the use-case, to nonnormal light also. These principles have been described only briefly herein, as the operational principles involved are in themselves known, and have been applied e.g. in WO 2018 / 228671 Al (see figures 1 and 2).

[0009] These principles thus show that by varying the reflectance and / or transmittance and / or absorbance of the cover and the substrate, and the direction at which light is incident (from outside or inside the optical device), it is possible to cause the cover to create a certain interaction with the light, optionally in cooperation with the substrate. The interaction changes when the cover shape changes, i.e. when the cover contour profile changes. WO 2021 / 032752 Al mentions use of its optical element in a display. However, there remains a challenge when it comes to improving the resulting display, specifically, in the colours or other characteristics it can produce. It is therefore an object of the invention to make better, specifically more versatile, use of the optical element.

[0010] The object is achieved by the method according to the preamble, wherein the method comprises the steps of: i) receiving a desired optical characteristic for the optical element; ii) calculating a cover contour profile and a further cover contour profile that, when assumed altematingly, result in the desired optical characteristic; and iii) controlling the means to alternate the cover from the first cover contour profile to the further cover contour profile repeatedly.

[0011] This process, which from hereon will be referred to as temporal dithering, allows the optical element to switch relatively quickly between two “settings” corresponding to the first and further cover contour profile. Each setting has its own visual characteristic, or otherwise optical behaviour. As an example, although the invention is not limited thereto, each setting may correspond to a colour which the optical element reflects for a user to see. The process of temporal dithering entails switching between the two settings quickly enough for a user to see not two distinct settings, but rather a sort of average. This can be used to display colours which might not be able to be displayed separately by the optical element, such as when the colour consists of multiple wavelengths. Alternatively or additionally, intensities of displayed or reflected radiation may be achieved that could not be achieved without dithering.

[0012] At this point it is noted the invention is not strictly limited to visual light. The concept of temporal dithering can be used also in other wavelength ranges, in which the concept of colour is not defined. Nevertheless, switching between the cover contour profiles is in this case still advantageous to expand the total space of behaviours that can be achieved using the optical element, which may make the element particularly versatile.

[0013] Step ii) may comprise calculating a desired ratio between respective residence times for the first cover contour profile and the second cover contour profile suitable for resulting in the desired optical characteristic, and step iii) can comprise controlling the means so that the cover exhibits the first cover contour profile during a first residence time and exhibits the further cover contour profile during a further residence time, wherein a ratio between the first and the further residence time corresponds to the desired ratio.

[0014] When dithering with sufficiently high frequency, the ratio of residence times defines the perceived output for a user.

[0015] It may be especially advantageous if the desired optical characteristic is defined as a set of values, preferably less than five values, such as four values, preferably three values or alternatively two values or one value. This way, it can be possible to quickly implement existing colour spaces. In the case of a single value, this could for example be a direct input of the actual wavelength.

[0016] It is noted that the cover can be understood as having a single tunable parameter, i.e. its height above the substrate. Accordingly, it would be impossible to account for all three variables in customary colour spaces, which usually have three or four parameters. However, by temporal dithering, a new tunable parameter is introduced by combining cover contour profdes, so that the resulting perceived behaviour represents at least more closely a full desired colour space.

[0017] The set of values could for example reflect intensities of different colours, such as Red, Green and Blue (RGB), or the set of values could reflect parameters of a colour space such as HSV, NCS, RGB, such as sRGB or Adobe RGB, or CMYK. Colour spaces such as these are used widely, both in industrial products as well as products aimed at the consumer market. By allowing input in these colour spaces, the resulting optical element can be used relatively easily with existing image sources.

[0018] On the other hand, the set of values could reflect optical properties of a single colour. As an example, the set of values could represent a point along a grayscale. Thus, for a predefined colour scale, the desired optical characteristic could be an intensity. A plurality of optical elements could then together form a grayscale image, produced through grayscale dithering.

[0019] In one embodiment of the invention, in step ii), the calculation is further based on an intensity of light incident the optical element.

[0020] Via temporal dithering, the optical element can be used to account for different sources and / or source strengths and / or sources of different spectral distributions and / or sources of light of different states. Accordingly, it is advantageous if the calculation is based in part on the intensity of light incident the optical element to facilitate said accounting. As an example, when the desired output is a relatively intense colour, e.g. a monochromatic colour, the method could include switching between a first cover contour profile which results in a high intensity output, and a further cover contour profile which results in a low intensity output. When the incident radiation is relatively strong (that is to say too strong), the residence time of the further cover contour profile may be lengthened as compared to the residence time of the first cover contour profile, in comparison with a situation in which the incident radiation is relatively weak, so that a desired intensity output is still achieved. The ratio of residence times can be changed in the other direction for relatively weak incident radiation.

[0021] Moreover, it is advantageous if the calculation is additionally or alternatively based at least in part on a spectral distribution of light incident the optical element. As an example, when the desired output is certain spectral distribution comprising e.g. a combination of two colours, the method could include switching between a first cover contour profile which results in a certain intensity output of a first colour of the two colours of said certain spectral distribution, and a further cover contour profile which results in another intensity output of a second colour of said spectral distribution. The ratio of residence times defines the desired output in colour and intensity, i.e. defines the spectral distribution that is output on average. When the incident radiation contains radiation of the first colour that is relatively strong (that is to say too strong), the residence time of the further cover contour profile may be lengthened as compared to the residence time of the first cover contour profile, in comparison with a situation in which the incident radiation contains radiation of the first colour that is relatively weak, so that a desired intensity output for that colour is still achieved. The ratio of residence times can be changed in the other direction for incident radiation that is relatively weak for the first colour.

[0022] In another embodiment of the invention a third cover contour profile is calculated and alternated with the first cover contour profile and further cover contour profile.

[0023] This results in dithering using three distinct cover contour profiles, which allows even more optical behaviours, and thus makes the optical element more versatile.

[0024] It is especially advantageous for the method if in step iii) the alternating is performed at a pixel framerate, and steps i) - ii) are performed at a display framerate, which is different from the pixel framerate. The display framerate herein effectively translates to the framerate of the optical element.

[0025] When a display is considered, pixels in the display are updated at a - usually fixed - pixel switching frequency, which by combining all pixels in a display results in a framerate of e.g. 30 Hz, 60Hz or some other number. Sometimes the framerate is not fixed but variable. Nevertheless, the framerate is sufficiently high so that a user perceives the rapidly changing pixels as a moving image. According to the invention, the pixel framerate is chosen sufficiently higher than the framerate, which herein is called the display framerate. Accordingly, it is possible to - withing a single frame - still use temporal dithering to achieve desired behaviour.

[0026] It is advantageous for the pixel framerate to be at least 100 Hz, preferably at least 1 kHz, more preferably at least 1 MHz, more preferably at least 1 GHz. At these frequencies, a human is not likely or even unable to perceive the separate cover contour profiles, but rather sees the dithered end result. A sufficiently high frequency may also eliminate or reduce headaches or other discomfort caused in some users when temporal dithering using prior art pixels at a slower rate.

[0027] As explained above, it can be of importance for the pixel framerate to be larger than the display framerate, preferably at least two times larger, more preferably at least 10 times larger, most preferably at least 20 times larger.

[0028] The invention also relates to an optical modulator, which may be a display or a spatial light modulator, comprising a plurality of optical elements and a controller, the controller being configured to perform, for each of the optical elements, the method of any of the preceding claims. The optical elements may be those described in the method hereabove.

[0029] It is advantageous if the optical modulator further comprises a light source, providing light to be modulated before being output. The optical modulator can therefore become a stand-alone device, independent from external light input.

[0030] In one version of the optical modulator, the controller is further configured to control the light source based on the desired characteristic received for each optical element. Accordingly, the light source can be made to produce sufficient light for modulation in one place (for one optical element), but can e.g. be reduced in intensity in another place, so as to allow displaying darker parts of an image.

[0031] It is of course also possible to make the light source dither, i.e. to switch between intensities, so as to achieve an intermediate perceived intensity. Similarly, color sequential imaging can be applied at the light source in combination with the method or optical element described herein.

[0032] The optical element described herein can be of any suitable type, and provide optical behaviour based on any number of suitable principles.

[0033] As an example, the optical device can operate by reflecting light using the cover. For that purpose, it is possible the cover has a relatively large reflectance as compared to its transmittance. As an example, the value of transmittance divided by reflectance would be not more than 0.5, preferably not more than 0.25, more preferably not more than 0.1, most preferably not more than 0.01.

[0034] The transmittance, reflectance and absorbance defined herein may be measured at a wavelength X which varies from 10 nm to 3000 pm. In one aspect, most preferably 380 to 740 nm. In another aspect, more preferably from 10 nm to 200 nm, most preferably from 13 nm to 193 nm. In another aspect, more preferably from 700 nm to 2000 nm, most preferably from 850 nm to 1550 nm. In another aspect, more preferably from 30 000 nm to 3 000 000 nm.

[0035] Of course, absorption may also be considered. As an example, the optical device can operate by absorbing light using the cover. For that purpose, it is possible the cover has a relatively large absorbance as compared to its reflectance. As an example, the value of reflectance divided by absorbance would be not more than 0.5, preferably not more than 0.25, more preferably not more than 0.1, most preferably not more than 0.01.

[0036] The absorbance and reflectance defined above may be measured at a wavelength X which varies from 10 nm to 3000 pm. In one aspect, most preferably 380 to 740 nm. In another aspect, more preferably from 10 nm to 200 nm, most preferably from 13 nm to 193 nm. In another aspect, more preferably from 700 nm to 2000 nm, most preferably from 850 nm to 1550 nm. In another aspect, more preferably from 30 000 nm to 3 000 000 nm.

[0037] The optical element may be configured for reflecting light incident on the second surface. In that case, the transmittance and reflectance may be measured for light incident the second surface.

[0038] Alternatively, the optical element may be configured for reflecting light incident on the first surface, in that case, the transmittance and reflectance may be measured for light incident the first surface.

[0039] Besides using the cover for reflection only or mainly, it is also possible to employ reflective interference, taking place mainly between a reflected light beam at the substrate (or cover) and a refracted light beam through the substrate (or the cover) that the cover (or substrate) reflects, or absorbing interference, taking place mainly between a reflected light bean with the incident light beam at the substrate (or cover) and its absorption at the cover (or substrate). An optical element configured for this purpose is called an interferometric optical device. The absorbance of the cover may accordingly also be relevant, as explained above.

[0040] The interference may take place for light incident the second surface, or for light incident the first surface. In the latter case, a substrate is needed below the cover, as is described further below. The substrate is configured for transmitting a part of the light and reflecting a part of the light. The transmitted light is then reflected on the cover, and transmitted back out through the surface. The egressing light interferes (constructively or destructively) with the directly reflected light. Depending on the position of the cover with respect to the substrate, it is possible to change the interference-based behaviour of the optical element.

[0041] Depending on the desired optical behaviour, it is of course possible to use a cover with different ratios of reflectance, transmittance and absorbance, optionally in combination with e.g. a reflective, transmissive or absorbing substrate, the terms reflective, transmissive or absorbing being defined using the same ranges for these respective quantities, and / or the same ratio’s between them as is defined for the cover. In general, the optical properties for the substrate are chosen complimentary to the optical properties of the cover, defined using similar characteristics. The invention is not limited to any such combination, rather to improving movement of the cover using temporal dithering.

[0042] Of course, the substrate need not be square or rectangular. The substrate’s shape in general is not important, it is even possible for a single substrate to span multiple optical elements. More relevant may be the shape defined within the support, as this defines the shape of the optical element in plan view. It is possible this shape is square or rectangular, to create a pixel-like element, but circular optical elements are also envisaged. The invention may however be applied to optical elements of all shapes. This is true for all embodiments described herein, whether they do or do not have a substrate.

[0043] It is noted that for some shapes of optical elements, the substrate is rigid and planar, while for others it is possible for it to be flexible and / or curved. In such cases, the spacer and cover are adapted to the substrate, in such a way that the second surface of the cover is approximately parallel to the substrate.

[0044] In this case, the cover is preferably reflective, for instance as expressed in the ratio above. The substrate is not as reflective, for example having a ratio of transmittance divided by reflectance of more than 0.5, more than 0.75, more than 0.9 or even more than 0.99, or even more than 1, preferably for light incident from a surface of the substrate facing away from cover.

[0045] The opposite direction is also possible, where the cover transmits and reflects light, and the substrate reflects the transmitted light. In this case, the cover would be relatively transmissive, for example having a ratio of transmittance divided by reflectance of more than 1, for light incident the second surface, so that it is relatively transmissive. Said ratio could for instance be between 1 and 3, such as between 1.5 and 2.5, such as around 2. The absorbance could in this case be relatively high. The substrate would preferably be reflective for light incident a surface of the substrate facing the cover. The reflectance could be defined by a ratio of transmittance divided by reflectance of not more than 0.5, preferably not more than 0.25, more preferably not more than 0.1, most preferably not more than 0.01.

[0046] Unless stated otherwise, transmittance and reflectance are measured for light normal to the surface of the cover.

[0047] In case a cover is used that is relatively reflective, a value of absorbance divided by reflectance of the cover can be less than 0.5, preferably not more than 0.25, more preferably not more than 0.1, most preferably not more than 0.01, for light incident the first and / or second surface, depending on the desired optical behaviour.

[0048] It is noted that in all cases, the position and shape of the cover influences how the optical device interacts with incident light. Other operational principles which rely on the change of the cover position and shape can however also be applied, and the current invention is thus not limited to either reflective or interferometric operational principles. In any case, the invention is not limited solely to a cover with a changing shape or a changing cover. In terms of claim 1, this can be realized by defining the spatial arrangement of the cover with respect to the support. After all, a cover that has not changed in shape but is at a different position with respect to the support, still has a different spatial arrangement as seen in cross section of the cover with respect to the support. As such, depending on the use, changing the position of the cover (without changing its shape) or changing the shape of the cover, thereby changing partially its position, could be used interchangeably. The cover may comprise a 2-dimensional portion. The 2-dimensional portion may be an extreme membrane. For the purpose of the invention in general however, it is sufficient if the 2- dimensional portion is sufficiently thin to be deformed and / or moved using the applicable means. In general, it is not necessary, however possible, that the 2-dimensional portion has favourable optical properties in and of itself. Instead, it is possible to provide the desired optical properties using additional material, such as an additional layer or an amorphous portion of the cover, which could be or could comprise a metal or an additive. In that regard, reference is made to WO 2021 / 032752 Al which explains multiple configurations of the cover. The skilled person is readily able to vary e.g. the thickness and material of the additional material to arrive at desired optical properties for the cover. In that regard, it is noted the 2-dimensional portion may function as a carrier, whereas the additional material provides desired optical properties.

[0049] The 2-dimensional portion may be as defined in embodiment [39a] of WO 2021 / 032752 Al. Accordingly, the 2-dimensional portion may be one or more of the following: a. One or more selected from the group consisting of: C, BN, P, MoS2, MoSe2, MoTe2, WS2, WSe2, WTe2, NbS2, NbSe2, NbTe2, TaS2, TaSe2, TaTe2, TiSe2, VSe2, CrS2, CrSe2, B, Ge, Si, Si2BN, Sn, Pb, P, Sb, Bi. The preferred C in this context is one or more selected from the group consisting of: graphene, one or more graphitic layers and graphyne; preferably graphene. The preferred BN in this context is h-BN. The preferred P in this context is black phosphorus or phosphorene. The preferred B in this context is borophene. The preferred Ge in this context is germanene. The preferred Si in this context is silicene. The preferred Sn in this context is stanene. The preferred Pb in this context is plumbene. The preferred Sb in this context is antimonene. The preferred Bi in this context is bismuthine; b. One or more transition metal chalcogenides, each being a transition metal chalcogenide not listed in a.; c. One or more oxides, each being an oxide of a species listed in a. or b.; d. One or more atomic intercalated variants, each being an atomic intercalated variant of a species listed in a. or b.; e. One or more physically, chemically, mechanically and / or electromagnetically functionalised derivatives, each being a chemically functionalised derivative of a species listed in a. or b.. A preferred physical functionalisation is perforation or atomic barrage treatment. A preferred mechanical functionalisation is stretching or stressing. A preferred electromagnetic functionalisation is application of a voltage.

[0050] In one aspect of this embodiment, the 2-dimensional portion is a combination selected from the group consisting of: a., b., c., d., e., a.+b., a.+c., a.+d., a.+e., b.+c., b.+d., b.+e., c.+d., c.+e., d.+e., a.+b.+c., a.+b.+d., a.+b.+e., a.+c.+d., a.+c.+e., a.+d.+e., b.+c.+d., b.+c.+e., b.+d.+e., c.+d.+e., b.+c.+d.+e., a.+c.+d.+e., a.+b.+d.+e., a.+b.+c.+e., a.+b.+c.+d. and a.+b.+c.+d.+e.. Specifically, the 2-dimensional portion may comprise or be graphene or boron nitride or both. A preferred boron nitride is hexagonal boron nitride. Graphene is preferably chemical vapour deposited. Boron nitride is preferably chemical vapour deposited. In one aspect of this embodiment, the 2-dimensional portion comprises graphene, preferably is graphene. In one aspect of this embodiment, the 2-dimensional portion comprises boron nitride, preferably is boron nitride.

[0051] As mentioned earlier, the thickness of the 2-dimensional portion is relatively small. For instance, 1 mm or less, preferably 10 pm or less, more preferably 1000 nm or less, more preferably 100 nm or less, more preferably 50 nm or less. In one aspect of this embodiment, more preferably 10 nm or less, more preferably 5 nm or less, most preferably 1 nm or less.

[0052] A minimum thickness may be defined as 25 pm or more, preferably 69 pm or more, more preferably 100 pm or more. In one aspect of this embodiment, the thickness is 1 nm or more, preferably 3 nm or more, more preferably 5 nm or more, more preferably still 10 nm or more. In another aspect of this embodiment, the thickness is 15 nm or more, preferably 20 nm or more, more preferably 30 nm or more.

[0053] Accordingly, the 2-dimensional portion may be relatively light per unit area, such as 24 kg / m2or less, preferably 2.4- 101kg / m2or less, more preferably 2.4- 102kg / m2or less, more preferably 2.4- 103kg / m2or less, most preferably 1.2- 103kg / m2or less. A lower limit on the same weight per unit area is 1.7- 109kg / m2or more, preferably 3.4-108kg / m2or more, more preferably 1.8 • 107kg / m2or more . In one aspect of this embodiment, the mean density is 5 • 107kg / m2or more, preferably 1.5- 106kg / m2or more, more preferably 5.4-106kg / m2or more, more preferably 5.7- 105kg / m2or more.

[0054] Various operational principles for the means are available, and have been identified throughout the previous paragraphs. It is noted that some operational principles may allow exerting a force on the cover only in one direction, whereas for others the same means can be used to exert forces in opposing or even various directions on the cover. In case the operational principle only allows forces in a single direction, further means, which may be identical, may be applied on the opposite side of the cover, e.g. in a mirrored position with respect to the previously mentioned means, so that collectively control can be exerted in both or more directions.

[0055] While above an optical element has been described that has means configured to affect the cover, the inverse is also possible and envisaged. Accordingly, the means may alternatively or additionally be arranged to provide an output that is representative of the cover changing from the first cover contour profile to the further cover contour profile.

[0056] In this manner, the optical element can be used as a sensor responsive to any phenomenon, not necessarily optical, that changes the cover shape. For instance, incident radiation, pressure, sound waves, an electrical charge, temperature, etc. could all be sensed using suitable means. As an example, an electrode could be used to sense a changing electrical charge, e.g. changing in response to a charged cover moving. If a predetermined and externally applied electrical charge is applied to the cover, the electrodes could be used to measure deformation of the cover by capacitive means, for instance as a result of incoming radiation or pressure. An electrode or other type of sensing means would be necessary to measure the changing electric field as the charged cover moves.

[0057] In these circumstances, the element described herein need not be described as an optical element per se.

[0058] In particular, the means and / or further means may each, independent from one another, comprise any one or more of:

[0059] - an optical actuator, such as an optical tweezer or photonic circuitry;

[0060] - a means for applying or changing radiation incident on the cover, such as a radiation source.

[0061] - a means for influencing a gas pressure acting on the cover;

[0062] - a speaker or any other sound emitter;

[0063] - a thermal actuator, operating via thermal expansion; and

[0064] - an electromagnetic and / or superconducting actuator, for instance operating based on tunneling or field emission.

[0065] At this time, it is noted that regardless of the actuation method used, given a sufficiently small system, any one actuation method will often have some corresponding co-phenomenon in another domain as well. As such, at nano-scale, the actuation method and corresponding cophenomena usually pair up. Examples of such pairs, which may be used in the currently described invention as a non-exclusive list of examples, are:

[0066] Thermo-electrical and electro-thermal actuation;

[0067] Thermo-optical and opto-thermal actuation;

[0068] Thermo-magnetic and magneto-thermal actuation;

[0069] Opto-electrical and electro-optic actuation; and Magneto-optic and opto-magnetic actuation.

[0070] At the same time, quantum and superconducting effects may also play a role. Accordingly, use can be made of such effects if desired.

[0071] It is noted that the index of refraction of the cavity defined by the cover and the substrate can be of influence on the optical behaviour of the optical element. The index of refraction of the cavity can be influenced by at least partially filling the cavity. To facilitate said filling the cavity may be enclosed by one or more of the support, the cover and the substrate, or may even be sealed entirely. If the cavity is indeed sealed, it can be filled with a substance. Different fillings of the cavity can lead to different refractive indices, and thus a different optical behaviour. The cavity may for this purpose be filled with a gas composition. Aside from a gas or gas mixture, the cavity may also be filled by a liquid (mixture) and / or liquid crystals, or even a solid filling, which may have a greater effect on the refractive index. Another option would be to instill a vacuum inside of the cavity. Definition of, and filling of the cavity may also be done for other reasons than influencing the index of reflection, i.e. to provide absorption, to provide structure rigidity, or other reasons.

[0072] Moreover, the substance filling a cavity can be of influence on other than the optical behaviour of the optical element, including but not limited to the mechanical response of the cover and the electrical influence of the means. A filled cavity can also be used to exert a pressure on the cover, in order to move it using pressure based means.

[0073] As a further remark, it is noted that the structure described herein as optical element can be used in a different and novel way as well, regardless of whether or not the characterizing portion of the claims is applied. In this novel way of using the device, a substrate opposite the cover is necessary, so that a cavity is formed between the cover and the substrate. The device is configured to allow entry of electromagnetic radiation, such as (visible) light, into the cavity between the support and the substrate, and to allow egress of the same, also between the support and the substrate. In contrast to the principles shown above, in which light interacts by being incident the cover (either from the first or second surface), the light now travels substantially parallel to the cover, through the cavity. In this case, the cavity acts like a waveguide. To form a waveguide, the skilled person is able to choose suitable materials for the support, the substrate and the material at the cover’s first surface and optionally for material to fill the cavity with, so that the light is influenced by the cover. This influence could for example result in a change in amplitude, phase or the state of the light. Suitably chosen characteristics, such as optical characteristics, of the cover allow interaction with light passing through the cavity. By changing the contour shape of the cover, or by changing its position, the waveguide formed in the cavity can be altered. The changing influence of the cover on waves passing through can be used to modulate the light.

[0074] It is noted that the cover need not actually move or change shape in order to affect the passing light differently. For instance, its strain may be altered for instilling different optical properties.

[0075] The invention will be further elucidated with reference to the attached drawings, in which: Figures 1A, IB and 1C show schematically interaction of light with an optical element known in the state of the art;

[0076] Figures 2A, 2B and 2C show schematically interference interaction of light with an optical element known in the state of the art;

[0077] Figures 3 - 4B show schematically an optical element, with its cover in different cover contour profiles; Figure 5 shows schematically the steps of a method of operating an optical element;

[0078] Figures 6 and 7 show schematically an optical element for different interferometric effects;

[0079] Figure 8 shows schematically in perspective view another way of using the optical element; and

[0080] Figures 9A - 9B show schematically different operations of an optical element to perform dithering.

[0081] Figure 1A shows interaction of light with of a flat cover 101, which is supported by supports 104. The parallel rays 601 and 602 are both deflected by the same angle and remain parallel after interaction with the cover 101. This constitutes specular reflection.

[0082] Figure IB shows interaction of light with a convex cover. Due to the rounded convex cover contour profile, a first ray 601 is deflected by almost 180° and the second ray 602 is only deflected by a small angle. The rays 601 and 602 are no longer parallel after reflection at the cover. This constitutes diffuse reflection.

[0083] Figure 1C shows interaction of light with a concave cover. Due to the rounded concave cover contour profile, a first ray 601 is deflected by an angle less than 90° and the second ray 602 is deflected by almost 180°. The rays 601 and 602 are no longer parallel after reflection at the cover. This constitutes diffuse reflection.

[0084] Figure 2A shows interference interaction with a flat cover. Aside from the supports 104, a substrate 106 is also present in this example of the state of the art, which lies on the bottom of the optical element. The support 104, cover 101 and substrate 106 define a cavity having a depth 205. The substrate 106 is transmissive and absorbing to an extent and the cover 101 is reflective, such that an incoming ray 601 undergoes interference which is dependent on the depth 205.

[0085] Figure 2B shows interference interaction with a convex cover. The cover 101 of the optical element of figure 12 has been deformed into a convex shape (cover contour profile). This was brought about by a means pushing the cover 101 upwards. This increases the depth 205 and the interference behaviour of incoming light 601 is altered.

[0086] Figure 2C shows interference interaction with a concave cover. The cover 101 of the optical element of figure 12 has been deformed into a concave shape (cover contour profile). This was brought about by the means pushing the cover 101 downwards. This decreases the depth 205 and the interference behaviour of incoming light 601 is altered.

[0087] Now first referring to figures 6 and 7, it is noted that depending on the optical properties of the cover 101 and the substrate 106, different operational principles are also usable for influencing incident light. Figure 6 for instance, shows an optical element similar to that of figures 1 and 2, but with a cover 101 that is relatively absorbing, and a substrate 106 that that is relatively reflective. As a result, incident light 601 transmitted 602 through the cover 101 interacts with light reflected 604 from the substrate to form a pattern of nodes and antinodes. The cover can be controlled by means (not shown) to be placed at or away from a node or antinode, to accordingly absorb strongly or less strongly light, so that the intensity of exiting light 605 can be controlled. In figure 7 a cover 101 is present that is both transmissive and reflective, and a substrate that is reflective. Accordingly, use can be made of interferometric reflection, similar to figures 2A - 2C, however now the optical element is configured for light incident the cover 101. Otherwise, the optical element may be identical to that described above.

[0088] Figures 3 - 4B show an optical element 99 with support 4 and a cover 1. The cover 1 is actuated, i.e. made to move, by a means 7 in a substrate 6. The means 7 are controlled by a controller 12. In this case, the means 7 comprise an electrode, but other principles of operation are possible. In figure 3, the cover 1 in an unactuated position, that is to say a rest position in which the means are not or not strongly operated, is shown in dashed lines, whereas a solid line shows the cover 1 in a further cover contour profile. In practice the cover would likely show a more organic profile, but for the purpose of this explanation the exact cover shape is not relevant. Relevant is the position of the cover 1 with respect to the substrate 6, which defines at least in part the optical behaviour of the optical element 99 as was explained above in relation to figures 1A - 2C. As an example, assume that the position shown in solid lines in figure 3 makes the optical element appear predominantly orange. Figures 4A and 4B both show the cover 1 in different positions, i.e. at different cover contour profiles in solid lines, and show the position of the cover 1 of the other figure in dashed lines. Assume the profile shown in figure 4A makes the optical element appear predominantly red. Assume the profile shown in figure 4B makes the optical element appear predominantly yellow. By now operating the means 7 so that the cover 1 moves quickly back and forth between the positions in figures 4A and 4B, a fast switching between red and yellow occurs. If the switching is sufficiently fast, the result will appear orange. However, as opposed to the orange colour of figure 3, the result is actually made up of different wavelengths, may have a different intensity, and may therefore have other appearance or feel. As such, the switching behaviour allows more versatile use of the optical element 99.

[0089] Figure 5 shows the steps and process of the method, starting with the step 1001 of receiving a desired optical characteristic for the optical element, followed by step 1002 of calculating a cover contour profile and a further cover contour profile that, when assumed altematingly, result in the desired optical characteristic. After that, step 1003, controlling the means to alternate the cover from the first cover contour profile to the further cover contour profile repeatedly, takes place.

[0090] Finally, reference is made to figure 8, which shows a perspective view of a device, such as an optical element, similar to that described herein. Like before, the device has a substrate 106 and support 104, which in this case are monolithic. The support 104 defines a cavity C that is of longitudinal shape in this example. Cover 101 held by the support 104 spans the cavity C. Materials for the support 104, the substrate 106, the material at the cover’s first surface and material with which the cavity C is filled are chosen so that the cavity C acts as a waveguide. Incident waves 601, such as light, can therefore pass through from one side to another, and egress as exited light 602. Via means 107, in this case presented on top of the support 104, although not strictly necessary, the cover 101 can be moved, or its cover contour profile changed. As a result, the cover 101 at least locally influences the light passing through the cavity C in order to modulate it.

[0091] In figures 9A - 9D, an optical element 99 is shown, with a support 4, a cover 1, and a substrate 6, as is defined in the claims. A means is also present in the substrate 6 to move the cover 1, but is not shown.

[0092] In figure 9A, a dashed line represents schematically movement of the cover in response to the means activating. Accordingly, and as described above, a certain optical behaviour can be expected depending on the height of the cover.

[0093] Figure 9B shows two dashed positions for the cover 1, between which the cover 1 can alternate by suitable operation of the means. The resulting optical behaviour is an average of the optical behaviours at the two respective positions. This alternating, called grayscale dithering, can be performed of a relatively low frequency, for instance of < 20 Hz. Figure 9C shows schematically the cover 1 changing positions between positions that cause the acousto-optical device to output different colours. By changing between these positions rapidly, a mixture of colours can be output. This changing, called hue dithering, can be performed at a frequency of e.g. >20 Hz. A combination is shown in figure 9D, allowing many more colours to be output, for instance at > 500 Hz, and called gamut dithering.

[0094] It is noted that terms like “preferably”, “generally” and “typically” are not utilized herein to limit the scope of the claims or to imply that certain features are critical, essential, or even important to the structure or function of the claims. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present disclosure. Likewise, for the purposes of describing and defining the present disclosure, it is noted that the terms “substantially” and “approximately” and their variants are utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement or other representation, as well as to represent the degree by which a quantitative representation may vary without resulting in a change in the basic function of the subject matter at issue.

[0095] While certain representative embodiments and details have been shown for purposes of illustrating the present disclosure, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the disclosure, which is defined in the appended claims.

Claims

CLAIMS1. Method of operating an interferometric optical element, the optical element comprising a. a cover having a first surface and a second surface, b. a support, and c. a means; wherein: the cover is orientated with the first surface directed towards the support; a part of the first surface is attached to the support; a spatial arrangement of the cover as seen in a cross section of the cover defines a cover contour profile; the means is arranged to move the cover from a first cover contour profile to a further cover contour profile which is different from the first cover contour profile; wherein the optical element further comprises a substrate on a side of the support opposite the cover, a cavity being defined between the cover and the substrate, with a cavity height defined as a distance from the substrate to the cover, characterized in that the method comprises the steps of: i) receiving a desired optical characteristic for the optical element; ii) calculating a cover contour profile and a further cover contour profile that, when assumed altematingly, result in the desired optical characteristic; and iii) controlling the means to alternate the cover from the first cover contour profile to the further cover contour profile repeatedly.

2. Method according to the previous claim, wherein step ii) comprises calculating a desired ratio between respective residence times for the first cover contour profile and the second cover contour profile suitable for resulting in the desired optical characteristic, and wherein step iii) comprises controlling the means so that the cover exhibits the first cover contour profile during a first residence time and exhibits the further cover contour profile during a further residence time, wherein a ratio between the first and the further residence time corresponds to the desired ratio.

3. Method according to any of the preceding claims, wherein the desired optical characteristic is defined as a set of values, preferably less than five values, such as four values, preferably three values or alternatively two values or one value.

4. Method according to the previous claim, wherein the set of values reflects intensities of different colours, such as Red, Green and Blue (RGB), or wherein the set of values reflect parameters of a colour space such as HSV, NCS, RGB, such as sRGB or Adobe RGB, or CMYK.

5. Method according to claim 1 or 2, the desired optical characteristic is an intensity.

6. Method according to any of the preceding claims, wherein in step ii) the calculation is further based on an intensity of light incident the optical element.

7. Method according to any of the preceding claims, wherein a third cover contour profde is calculated and alternated with the first cover contour profile and further cover contour profile.

8. Method according to any of the preceding claims, wherein in step iii) the alternating is performed at a pixel framerate, and steps i) - ii) are performed at a display framerate, which is different from the pixel framerate.

9. Method according to the previous claim, wherein the pixel framerate is at least 100 Hz, preferably at least 1 kHz, more preferably at least 1 MHz, more preferably at least 1 GHz.

10. Method according to any of claims 8 - 9, wherein the pixel framerate is larger than the display framerate, preferably at least two times larger, more preferably at least 10 times larger, most preferably at least 20 times larger, even more preferably 100 times larger.

11. Optical modulator, comprising a plurality of optical elements and a controller, the controller being configured to perform, for each of the optical elements, the method of any of the preceding claims.

12. Optical modulator according to the previous claim, further comprising a light source.

13. Optical modulator according to the previous claim, wherein the controller is further configured to control the light source based on the desired characteristic received for each optical element.

14. Optical modulator according to any of claims 11 - 13, wherein the optical modulator is a display.1915. Optical modulator according to any of claims 11 - 13, wherein the optical modulator is a spatial light modulator.

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