Controller 160 is configured to modulate the amplitudes of the electric AC signals applied to the multiple electrodes on the substrates causing a low-electric field region to move with respect to the electrodes.

In conventional driving of the electrodes of an optical modulator, including during AC driving, the electric field potential shows regions in the optical layer where the electric field is much lower than at other regions in the optical layer. Such low-electric field region are disadvantageous as particles are hard to control in such a region. In particular, due to the low electric field in the low-electric field region, particles move slower there. Most of the time needed to transition from one optical state to another optical state is caused by the slow movement of particles in low-electric field regions.

For example, in a low-electric field region of the optical layer the electric field strength may be only 25% or less than elsewhere in the optical layer. For example, in some regions of the optical layer the electric field strength may be only 15% or less, 10% or less, 1% or less, compared to the maximal electric field in the optical layer, etc. For example, in a low-electric field regions of the optical layer the electric field strength may be less than 2*10{circumflex over ( )}6 V/m, less than 1*10{circumflex over ( )}6 V/m, less than 1*10{circumflex over ( )}5 V/m, etc. For example, the low-electric field region may be taken to be the region in the optical layer where electric field is minimal. For example, the low-electric field region may be taken to be the region in the optical layer where electric field is minimal, or a predetermined percentage larger than minimal, e.g., at most 10%, at most 15%, etc.

Electric field may be measured directly, however computer simulation of the electric field turns out to be sufficiently accurate for practical applications. For example, one may use the well-known COMSOL software for simulation electric field diagrams. Herein, the strength of electric field may be generated using Electrostatic study under the AC/DC module of COMSOL Multiphysics. Electric field diagrams shown herein were created with the above-mentioned software.

In particular, in the optical layer there may be regions where the electric field is absent, e.g., is null, or substantially null. Such a region is called a dead region. Particles in a dead region, essentially do not respond to electrophoretic control. Through other means, e.g., slow entropic movement, a particle can drift out of a dead region, and become susceptible to controlled movement again. Dead regions are particularly problematic for quick transitions between optical modes of the optical modulator. The dead region is sometimes referred to as an electric field neutral region, or neutral point. The neutral point may be a point in the 2D intersection as shown in the figures; however in a physical 3D embodiment, the neutral point may be a neutral curve or a neutral volume.

In embodiments problems caused by low electric field regions, and in particular dead regions, are addressed by variations of the potential differences between electrodes. By modulating the relative magnitude of signals applied to electrodes this electric field neutral point or volume is moved in the optical layer between the substrates.

In an embodiment, the overall drive may use AC signals and maintain current neutrality and a balance in the various electric fields in time. This is advantageous as it reduces erosion of the electrodes.

In an embodiment, electric field lines are modulated such that neutral points shift in position in the optical layer so that the total volume under electric field influence, e.g., electrophoretic control, increases.

In an embodiment, the main parameter varied in the signals is the amplitude, e.g., the amplification level of the signal. Other parameters to vary in an asymmetric way between electrodes include frequencies, signal shape (square, sinusoidal, etc.), durations, phase.

Asymmetric driving of the electrodes, as further explained herein has the advantage of faster transition between optical states. Asymmetric driving of the electrodes further gives the advantage of more uniform transition, as the differences between slow and fast transitioning location on the panel is reduced. An additional advantage of asymmetric driving is the reduced cumulation of particles on electrodes. In a conventional optical modulator, especially in a DC driving modulator, particles may accumulate on electrodes and may be compacted there locally. This may lead to particle interaction there and the particles forming non-reversible aggregations. Such aggregations of particles are undesirable. The aggregation effect causes issues such as of non-homogeneity and gravity effects. However, with asymmetric drive as in an embodiment, particles are increasingly in motion and therefore annealing into aggregations is limited. Moreover, particle movement is more uniform.

A dead region, e.g., a neutrality point or volume, also leads to optical aberrations due to particle accumulation during operations. By increasing particle mobility, aggregation is less, and the particles are less likely to fall due to gravity. Improved particle mobility allows better closing and dispersion of particles to reach a non-transparent state, while maintaining a particle distribution that is closer to the initial state of dispersion at manufacture.

Interestingly, asymmetric drive can be added to an existing algorithm used to drive a panel to a target gray scale. Moreover, introducing asymmetric drive can still maintain current neutrality. For example, one could use the algorithms described in say, PCT/EP2021/071346 with title “Light Modulator, Light Modulator Method And Smart Glazing” and introduce scaling of signals to move low-electric field regions, and in particular dead regions.

For example, a controller may be configured with a set of algorithms, e.g., for one or more of the functions: going up in transparency, going down in transparency, maintaining a present transparency, etc. There may be more or fewer algorithms. For example, algorithms may differ depending on the size of the jump in transparency that is desired. For example, a maintaining algorithm may be omitted. For example, in a simplified embodiment, the controller may have an algorithm for driving towards full transparency, and algorithm for driving to full opacity. For example, computer program code may be stored in a memory of the controller to implement said algorithms. In an embodiment, the controller is configured to apply a programmed driving algorithm for a certain duration, which may depend on, e.g., present transparency, target transparency, and measured sensor values, e.g., as explained in the cited PCT application.

An existing algorithm can be modified by periodically scaling one or more of signals down or up, so that the low-electric field region moves, and in particular, the dead region. For example, an existing driving algorithm may be modified to be asymmetric by introducing asymmetric scaling, and after a predetermined period changing the direction of asymmetric scaling. As the asymmetry of the drive changes, the low-electric field region moves. In an embodiment, the volume in the optical layer is scanned by a higher strength electric field line, causing all particles in the volume to be susceptible to electric control at some point during the scan. Asymmetric drive can be used advantageously both for driving towards a target transparency and for maintaining a gray scale. An open drive can also vary in asymmetry while maintaining gray scale.

Asymmetric drive allows faster transition, in particular a much faster closing of the device (that is, driving toward opacity) since a larger part of the particle population is moved irrespective of a particle's initial location, including middle position between electrodes and electrodes surfaces.

Typically, scaling of signals is applied to pairs of electrode signals. For example, a pair of signals X and Y may be applied to a pair of electrodes. The electrodes may be, e.g., a pair of opposite electrodes, a pair of neighboring electrodes, a pair of diagonally opposed electrodes. The electrode signals before scaling typically have the same phase, and have the same amplitude; in fact the pair of signal may be the same signal. However, there may be a difference in phase or amplitude even before scaling. For example, phase differences may be used to trap particle. For example, scaling differences may be used to compensate for hardware differences, e.g., between substrates amplification and the like. In particular the signals X and Y may be conventional AC driving signals for an electrophoretic optical modulator. The signals X and Y may be scaled to move low-electric field regions in the optical layer. For example, a time varying scaling factor may be applied to a signal. FIGS. 1c.1-1c.4 schematically shows example of an embodiment of scaling factors.

In FIG. 1c.1, the scaling factors are chosen such that one signal is scaled up (amplified) when the other is scaled down (de-amplified). In an embodiment, the product of the scaling factors may be 1. In an embodiment the sum of the logarithms of the scaling factors may be 0.

In FIG. 1c.2, the scaling factors are chosen such that only one of the two signals is amplified while the other is kept constant. In the figure, the scaling alternates. Note, that in these examples, instead of scaling-up, scaling down may be used. In fact, using scaling-down is easier, as the signals stay within predetermined bounds.

FIG. 1c.3, is the same as FIG. 1c.2, except that scaling is alternated with a period in which no scaling is used.

In FIG. 1c.4, only one of the signals is scaled, while the other is kept constant. In FIG. 1c.5, only one of the signals is scaled, while the other is kept constant. In FIG. 1c.5 a signal is scaled up and down alternatingly. In this example, scaling is combined with periods of no scaling.

Many other variations are possible. For example, a slight noisy scaling may be added to randomize slightly the location of low-electric field regions. These examples, use triangular changing scaling factors, but other shapes are possible, e.g., square wave, sinus, etc.

FIGS. 2a-2c schematically shows an example of AC signals in an embodiment of an optical modulator arranged for closing the panel, that is for reducing transparency of the panel. FIGS. 2a.1, 2b.1 and 2c.1 show an example of an electric field in an embodiment of an optical modulator. The electric field is shown in the same plane as shown in FIG. 1b. FIGS. 2a.2, 2b.2 and 2c.2 schematically show an example of AC signals corresponding to the electric field diagram. Note that FIGS. 2a.2, 2b.2 and 2c.2 schematically show the signals after scaling, whereas FIGS. 1c.1-1c.4 schematically show scaling factors.

The movement of particles is to a large extend dictated by the electric field, and its shape, as indicated by the electric field diagrams, although some other factors may also have some influence on the motion of the particles, e.g., Brownian motion, temperature, and so on.

The y-axis in FIG. 2a.2, and in similar diagrams, indicate schematically the voltage of a signal applied to an electrode. The dashed horizontal line in the four signals indicate the neutral voltage, e.g., zero voltage line for each signal. The x-axis schematically indicates time. Note that the four signals are AC signals. The FIG. 2 show square signals but other AC type signals, such as triangle, sinusoidal and combination thereof, can be used. The driving shown in FIG. 2a.2 is configured for closing the optical modulator, e.g., decreasing transparency, increasing the gray level. If the driving shown in FIG. 2a.2 were continued for a long time, the substrate would eventually approach maximum opacity. Driving does not need to continue, until full opacity though; driving can be terminated at some desired gray level before that time.

Note that signals 1 and 4 are equal, so that halfway between substrates 1 and 4, there is a dead region. The same holds for signals 2 and 3. Particles in the dead region do not respond to the electric field, as the electric field is absent there. Near the zero electric field points, electric field is low, e.g., there is a low electric field region. Particles in the low electric field region respond to electric field, but do so slowly.

In closing operations, as shown in FIGS. 2a-2c, the low-electric field region comprises a dead region between the substrates, e.g., within the optical layer. The dead region is moved by introducing asymmetry in the driving.

In FIG. 2a.2, the AC signals applied to opposite electrode pair 1 and 4 and to opposite electrode pair 2 and 3 is equal. In FIG. 2a.2, the AC signals applied to neighboring electrode pair 1 and 2 and to neighboring electrode pair 4 and 3 are equal except for a phase shift, in this case a phase shift over 180 degrees. An opposite electrode pair are two different electrodes opposite each other on opposite substrates. A neighboring electrode pair are two different electrodes next to each other on the same substrate. There is a dead region halfway between electrodes 1 and 4, and halfway between electrodes 2 and 3.

FIG. 2b.2 show an asymmetry introduced in the driving of the panel. In FIG. 2b.2, the AC signals applied to opposite electrode pair 1 and 4 and to opposite electrode pair 2 and 3 are equal except for scaling. For example, the driving in FIG. 2b.2 can be obtained from the driving in FIG. 2a.2 by scaling down the driving on electrodes 1 and 2, e.g., by scaling down the driving of one of the electrodes in a pair of opposite electrodes. In this case, the signal to electrodes 1 and 2 has been scaled down. Scaling up or down can be done using an amplifier, by a variable resistor, or by changing parameters in a signal generator, etc. In FIG. 2b.2, the AC signals applied to neighboring electrode pair 1 and 2 and to neighboring electrode pair 4 and 3 are equal except for a phase shift, in this case a phase shift over 180 degrees.

The effect of the driving shown in FIG. 2b.2 is still to close the panel. Note that the low-electric field region in FIG. 2a.1 has moved up in FIG. 2b.1; in particular a dead region has moved up.

In FIG. 2c.2 the direction of scaling is reversed. The asymmetry introduced in a pair of opposite electrodes during a closing operation, is now in the opposite direction. This means that the dead region is now moved down, e.g., toward the bottom substrate. Note that the directions up and down are relative. These terms relate here to the panel as shown in the figure and are short for towards the first substrate or towards the second substrate; in an embodiment a panel could be vertical so that directions like up and down might be front and back, or the like.

To decrease transparency, e.g., to close the panel, the panel may be driven by alternating between the three types of signals. For example, a driving may have a middle dead region as in FIG. 2a, a top dead region as in FIG. 2b, or a bottom dead region as in FIG. 2c. For example, in an embodiment driving may repeat a cycle like: middle dead region driving, top dead region driving, middle dead region driving, and bottom dead region driving.

Closing a panel using this type of two-direction asymmetric driving makes reaching dark grays significantly faster. With conventional symmetric drive, transitioning from 10% gray to 1% gray, that is from light gray to full dark, may take about ten times as long as in an embodiment.

Using a two-directional asymmetric drive is preferable as a larger part of the volume is scanned, and mixing of particles is thereby improved. It is not necessary though; improved driving may be achieved by repeating a cycle such as: middle dead region driving, top dead region driving.

FIGS. 3a-3c show an example of an electric field in an embodiment of an optical modulator. The electric field diagrams in FIGS. 3a-3c are the same as in FIGS. 2a.1-2c.1. Shown in the FIGS. 3a-3c is a low-electric field region schematically indicated by a circle. The center of the circle correspond with a portion of the field where electric field is absent, e.g., a dead region. Note that the position of the dead region moves with respect to the electrodes. In this case, the dead region moves substantially orthogonal to the substrates. Orthogonal movement is convenient, though not necessary, by introducing asymmetry in a neighboring pair of electrodes as well as in opposite pairs of electrodes the dead region can be moved parallel to a substrate as well. For improved mixing orthogonal movement is sufficient though.

FIGS. 3a-3c show different stages in a closing operation using asymmetric driving. The dead region moves within the optical layer between two opposite substrates, e.g., towards and away from any of the two substrates. For example, the controller may be configured to apply a scaling operation to the signals applied to the electrodes. For example, the signals applied to opposite electrodes may be the same except for a scaling applied to one or both of them. The amount of scaling depends on the application, e.g., on the size of the panel and the thickness of the optical layer. As an example, a first AC signal applied to a first electrode may be scaled with respect to a second AC signal applied to a second electrode, e.g., opposite the first electrode, wherein the lower amplitude of the first and second AC signal is at most 70%, 50%, 45%, 40%, 30% of the higher amplitude.

The signals schematically shown in the figures are square waves, though in practice this is not at all necessary. The signals may be sine waves instead. For example, a low-pass filter may be applied to the signals as shown in the figures. The low-pass threshold may be chosen in dependence on the size of the panel, e.g., 1 kHz for a larger panel.

For example, in an embodiment, a controller may have a signal generator that is configured for a dead region in the middle of the optical layer. An asymmetry modulator may modulate the signals to move the dead region towards or away from one of the substrate. The asymmetry modulator may cycle through different scaling. For example, a scaling between two AC signals applied to an opposite pair of electrodes may cycle between a lower scaling factor and an upper scaling factor. The controller may also directly generate scaled signals.

Scaling may keep one signal constant while decreasing and/or increasing the other signal. For example, the first AC signal may have a constant amplitude, and the second AC signal may be scaled with respect to the first AC signal. The signal to keep constant and the signal to scale may switch in time. Scaling may be done on low voltage signals, but may also be introduced during amplification of the signals. In an embodiment, scaling of the signals is randomized to randomize the position of dead region. In an embodiment, scaling of the signals is controlled to move the position of the low-electric field region in a controlled way, e.g., along a predetermined path through the optical layer.

Once a target gray level is reached, e.g., as indicated by sensors associated with the panel, e.g., optical and/or electric sensors. The driving signals may be aborted. The panel will keep its gray level for some time, though the appearance of the panel may decay with time, so that a conventional maintenance driving may be used. Maintenance driving may comprise a slow, and low power driving of the panel to grayness level near the target gray level. Maintenance driving may be alternated with no driving at all. During maintenance, asymmetric signals may also be used, as this will improve mixing and increase the durability of the panel.

FIGS. 4a-4b schematically shows an example of AC signals in an embodiment of an optical modulator arranged for opening the panel, that is for increasing transparency of the panel. FIGS. 4a.1, and 4b.1 show an example of an electric field in an embodiment of an optical modulator. The electric field is shown in the same plane as shown in FIG. 1b. FIGS. 4a.2, and 4b.2 schematically show an example of AC signals corresponding to the electric field diagram.

In FIG. 4a.2, the AC signals applied to neighboring electrode pair 1 and 2 and to neighboring electrode pair 3 and 4 is equal. In FIG. 4a.2, the AC signals applied to opposite electrode pair 1 and 4 and to opposite electrode pair 2 and 3 are equal except for a phase shift, in this case a phase shift over 180 degrees. There is a low-electric field region halfway between electrodes 1 and 2, and between electrodes 3 and 4, stretching from substrate to substrate. FIG. 4a.1 also shows two dead regions: a dead region between electrodes 1 and 2, and a dead region between electrodes 3 and 4. These two dead regions are located outside of the optical layers. As there are no particles relevant for the shown electrodes 1-4, these dead regions are not a problem on their own. However, stretching between these two dead regions, there is a low-electric field region. Particles in the low-electric field region respond to the electric field quicker than particles in a dead region, but the particles in the low-electric field region still move slower than those elsewhere in the optical layer. For example, the electric field in the low-electric field region between the two dead regions, maybe 25% lower than the field midway and directly between the electrodes.

FIG. 4b.2 shows an asymmetry introduced in the driving of the panel. In FIG. 4b.2, the AC signals applied to neighboring electrode pair 1 and 2 and to neighboring electrode pair 3 and 4 are equal except for scaling. For example, the driving in FIG. 4b.2 can be obtained from the driving in FIG. 4a.2 by scaling down the driving on electrodes 2 and 3, e.g., by scaling down the driving of one of electrodes in a pair of neighboring electrodes. In this case, the signal to electrodes 2 and 3 has been scaled down. In FIG. 4b.2, the AC signals applied to opposite electrode pair 1 and 4 and to neighboring electrode pair 2 and 3 are equal except for a phase shift, in this case a phase shift over 180 degrees.

The effect of the driving shown in FIG. 4b.2 is still to open the panel. Note that the low-electric field region in FIG. 4a.1 has moved to the right in FIG. 4b.1. The size of the low-electric field has also somewhat increased. If only driving of the type shown in FIG. 4b.2 were used this could make moving particles near electrodes 2 and 3 harder, but as the driving is combined with asymmetric driving in the other direction this is not a problem.

In FIG. 4b.2 the direction of scaling could also be reversed, e.g., by scaling down signals 1 and 4 instead of signals 2 and 3. The asymmetry introduced in a pair of neighboring electrodes during an opening operation, will then be in the opposite direction, e.g., the low-electric field region will move to the left.

To increase transparency, e.g., to open the panel, the panel may be driven by alternating between the three types of signals. For example, a driving may have a center low-electric field region as in FIG. 4a, a right low-electric field region as in FIG. 4b, or a left low-electric field region (not shown in a separate figure). For example, in an embodiment driving may repeat a cycle between a low-electric field: center, left, center right; or just center, left. The time spent in different phases need not be equal. For opening, the time in spent in center may be higher than the time spent in driving with a left or right low-electric field.

In an embodiment, during an opening operation the low-electric field region may move parallel to the substrates. As discussed for closing operations, similar options for generating the signals are possible for opening operations. For example, a signal may be scaled, and a scaling factor may repeatedly run through a range of scaling factors.

FIGS. 5a-5b show an example of an electric field in an embodiment of an optical modulator. The electric field diagrams in FIGS. 5a-5b are the same as in FIGS. 4a.1-4b.1. Shown in the FIGS. 5a-5c is a low-electric field region schematically indicated by an oval. The electric field in the ovals is about 1.5*10{circumflex over ( )}6 V/m. Note that low-electric field region moved to the right, when comparing FIGS. 5a and 5b. For example, the center of the low-electric field region, e.g., a center of gravity or a center weighted by electric field strength moved to the right, in this case parallel to the substrates. Note also that the dead regions outside the optical layer moved to the right.

FIGS. 6a-6b schematically shows an example of AC signals in an embodiment of an optical modulator arranged for a diagonal drive. Diagonal drive may be used for closing of the panel. Diagonal drive may be used to mix the particles in the optical layer. Mixing particles is advantageous for the lifespan of the panel. Mixing particles may also be used as a phase during closing of the panel. For example, a period of diagonal driving as in FIGS. 6a and 6b may be followed by driving as in FIGS. 2a-2c. Diagonal driving may also be used to reach a gray in between a closed and open panel.

FIGS. 6a.1, and 6b.1 show an example of an electric field in an embodiment of an optical modulator. The electric field is shown in the same plane as shown in FIG. 1b. FIGS. 6a.2, and 6b.2 schematically show an example of AC signals corresponding to the electric field diagram.

In FIG. 6a.2, the AC signals applied to diagonal electrode pair 1 and 3 and to diagonal electrode pair 2 and 4 is equal. In FIG. 6a.2, the AC signals applied to neighboring electrode pair 1 and 2 and to neighboring electrode pair 3 and 4 are equal except for a phase shift, in this case a phase shift over 180 degrees. There is a dead region halfway between electrodes 1, 2, 3, and 4. In the dead region the electric field is substantially null.

FIG. 6b.2 show an asymmetry introduced in the driving of the panel. In FIG. 6b.2, the AC signals applied to diagonal electrode pair 1 and 3 and to diagonal electrode pair 2 and 4 are equal except for scaling. For example, the driving in FIG. 6b.2 can be obtained from the driving in FIG. 6a.2 by scaling down the driving on electrodes 1 and 2, e.g., by scaling down the driving of one of electrodes in a pair of diagonal electrodes. In FIG. 6b.2, the AC signals applied to neighboring electrode pair 1 and 2 and to neighboring electrode pair 3 and 4 are equal except for a phase shift, in this case a phase shift over 180 degrees. Note that all signals applied to electrodes on one substrate, in this case the upper substrate, have been scaled down. For example, in an embodiment signals applied to one of the two substrates has a lower amplitude than signals applied to the other of the two substrates. As a result the dead region in FIG. 6a.1 has moved up in FIG. 6b.1. In this case, the dead region moved orthogonal to the substrate, though non-orthogonal movement is possible as well, e.g., by scaling signals 1 and 2 in FIG. 6b.2 a different amount.

In an embodiment, the controller is configured for a closing operation of the optical modulator, in the closing operation the AC signal applied to opposite electrodes on opposite substrates are scaled with respect to each other, the controller modulating the scaling thus moving the low-electric field region. In an embodiment, the AC signal applied to neighboring electrodes on the same substrates are phase shifted with respect to each other.

In an embodiment, the controller is configured for an opening operation of the optical modulator, in the closing operation the AC signal applied to neighboring electrodes on the same substrates are scaled with respect to each other, the controller modulating the scaling thus moving the low-electric field region. In an embodiment, the AC signal applied to opposite electrodes on opposite substrates are phase shifted with respect to each other.

In an embodiment, asymmetric driving comprises applying a different amplitude signal to at least some of the electrodes in the optical modulator. Other asymmetric driving type is also possible, e.g., asymmetric driving with different frequencies. For example, the same amplitudes may be used on all electrodes, but the frequencies may be varied between at least some pairs. Frequency can also be varied in addition to amplitude.

In an embodiment, the optical modulator is an electrophoretic modulator, wherein particles are moved due to the electrophoretic effect. In an embodiment, a high frequency component may be added to the signals. For example, in an embodiment, the electrophoretic driving uses frequencies of, say, up to 100 Hz. Using only comparatively low frequency signals is sufficient to obtain efficient driving of the optical modulator. In an embodiment, at least some of the AC signals comprise a high frequency component. For example, in an embodiment, the high frequency component may have a frequency of at least 500 Hz, or at least 750 Hz, preferably at least 1 kHz. The high frequency component causes particles to move due to the dielectrophoretic effect in addition to the electrophoretic effect.

The high frequency component may be removed when a target gray level is reached. Doing so save energy, and reduced heat up of the optical modulator. A low pass filter may be applied to the AC signals. For example, the low-pass filter may be set to a threshold of just above the frequency of the high frequency component. FIGS. 7a-7c schematically show an example of AC signals in an embodiment of an optical modulator. FIGS. 7a-7c correspond to FIGS. 2a.2, 2b.2, 2c.2 with a schematic HF component. FIGS. 4a.2, 4b.2, 6a.2 and 6b.2 could likewise be enhanced with an HF component.

FIG. 8a schematically shows an example of an embodiment of an optical modulator. FIG. 8b schematically shows an example of AC signals in an embodiment of an optical modulator. The optical modulator shown in other figures use two phases for all signals. This is not necessary however, and in fact, using different phases for more than 2 signals may b advantageous. For example, FIG. 8b shows a first signal on electrode. A second signal on the neighboring electrode 2 is the same but is shifted over a first phase shift. A third signal on electrode 3 is the same as the electrode 2 signal, but is phase shifted over a second phase shift. The signal for electrode 4 is phase shifted over a third phase shift compared to signal 3. The first signal is the same as the fourth signal shifted over a fourth phase shift. The four phase shifts could all be equal to 360/4=90 degrees, but this is not necessary. In an embodiment, the phase differences are varied over time.

An advantage of having increasing phase shifts for the four signals is that particles are kept in the cell gap better. As a result, a given transparency or lack thereof can be maintained with lower power. In FIG. 8b the amplitudes of the four signals as shown are equal, but the amplitudes could be varied as in an embodiment.

Using different phase for more than two signals may be used to trap particles in the gap between neighboring electrodes; this is especially advantageously when closing the panel, and in maintaining a gray level.

For example, taking the signal on electrode 4 as a reference, signal 1 may have phase shift and an amplitude scaling, signal 2 may have a further phase shift and an amplitude scaling (possibly the same scaling), signal 3 may have a further phase shift without the amplitude scaling.

FIG. 9a schematically shows an embodiment of a light modulator 10, which may be applied in smart glazing. A light modulator is an example of an optical modulator.

Reference is made to patent application PCT/EP2020/052379, which is included herein by reference; this application comprises advantageous designs for light modulator, which may be further improved, e.g., by including electrodes, building blocks, and/or substrates as explained herein.

Light modulator 10 can be switched electronically between a transparent state and a non-transparent state and vice versa, or between a reflective state and a non-reflective state and vice versa. Light modulator 10 comprises a first substrate 11 and a second substrate 12 arranged opposite to each other. On an inner-side of first substrate 11 at least two electrodes are applied: shown are electrodes 13a, 13b. These at least two electrodes are together referred to as electrodes 13. On an inner-side of second substrate 12 at least two electrodes are applied: shown are electrodes 14a, 14b. These at least two electrodes are together referred to as electrodes 14. The configuration of electrodes is interdigitated, but may otherwise be greatly varied. In particular, it is not necessary that main lines of the electrodes stretch across the substrate in parallel.

A fluid 15 is provided in between said substrate. The fluid comprises particles 30, e.g., nanoparticles and/or microparticles, wherein the particles are electrically charged or chargeable. For example, particles may carry a charge on their surface intrinsically. For example, the particle may be surrounded by a charged molecule.

The electrodes are arranged for driving particles 30 to move towards or away from electrodes, depending on the electric field applied. The optical properties, in particular the transparency or reflectivity of the light modulator depends on the location of particles 30 in the fluid. For example, a connection may be provided for applying an electro-magnetic field to the electrodes.

In an example, substrate 11 and substrate 12 may be optically transparent outside of the electrodes, typically >95% transparent at relevant wavelengths, such as >99% transparent. Taking electrodes into account, transparency can be much lower, e.g., 70%. The term “optical” may relate to wavelengths visible to a human eye (about 380 nm-about 750 nm), where applicable, and may relate to a broader range of wavelengths, including infrared (about 750 nm-1 μm) and ultraviolet (about 10 nm-380 nm), and sub-selections thereof, where applicable. In an exemplary embodiment of the light modulator a substrate material is selected from glass, and polymer. A transparent material may be used for electrodes as well. In an embodiment of an optical modulator, only of the substrates 11 and substrate 12 is transparent.

In another example, one substrate, such as a bottom substrate 12, may be reflective or partially reflective, while the top substrate 11 is transparent. The optical properties, in particular the reflectivity of the light modulator depends on the location of particles 30 in the fluid. When the panel is in the open state (vertical drive), the particles will mostly be located between opposite electrodes of the two substrates, such that incident light can pass through the transparent top substrate and the optical layer relatively unhindered, and is reflected or partially reflected on the bottom substrate.

The distance between the first and second substrate is typically smaller than 30 μm, such as 15 μm. In an exemplary embodiment of the light modulator a distance between the first and second substrate is smaller than 500 μm, preferably smaller than 200 μm, preferably less than 100 μm, even more preferably less than 50 μm, such as less than 30 μm.

In an example the modulator may be provided in a flexible polymer, and the remainder of the device may be provided in glass. The glass may be rigid glass or flexible glass. If required, a protection layer may be provided on the substrate. If more than one color is provided, more than one layer of flexible polymer may be provided. The polymer may be polyethylene naphthalate (PEN), polyethylene terephthalate (PET) (optionally having a SiN layer), polyethylene (PE), etc. In a further example the device may be provided in at least one flexible polymer. As such the modulator may be attached to any surface, such as by using an adhesive.

Particles 30 may be adapted to absorb light and therewith preventing certain wavelengths from passing through. Particles 30 may reflect light; for example the reflecting may be specular, diffusive or in between. A particle may absorb some wavelengths, and reflect others. Particles may also or instead emit light, e.g., using phosphorescence, fluorescence, or the like. Even the fluid may emit light, which emittance is modulated by changing the location of particles.

In an exemplary embodiment of the light modulator a size of the nanoparticles is from 20-1000 nm, preferably 20-300 nm, more preferably smaller than 200 nm. In an exemplary embodiment of the light modulator the nanoparticles/microparticles may comprise a coating and/or a pigment, and preferably comprising a core. In an exemplary embodiment of the light modulator the coating of the particles is made from a material selected from conducting and semiconducting materials.

In an exemplary embodiment of the light modulator the particles are adapted to absorb light with a wavelength of 10 nm-1 mm, such as 400-800 nm, 700 nm-1 μm, and 10-400 nm, and/or are adapted to absorb a part of the light with a wavelength-range falling within 10 nm-1 mm (filter), and combinations thereof.

In an exemplary embodiment of the light modulator the particles are electrically charged or chargeable. For example, a charge on the particles may be 0.1e to 10e per particle (5*10-7-0.1 C/m2).

In an exemplary embodiment of the light modulator the fluid is present in an amount of 1-1000 g/m², preferably 2-75 g/m², more preferably 20-50 g/m², such as 30-40 g/m². It is a big advantage that with the present layout much less fluid, and likewise particles, can be used.

In an exemplary embodiment of the light modulator the particles are present in an amount of 0.01-70 g/m², preferably 0.02-10 g/m², such as 0.1-3 g/m2.

In an exemplary embodiment of the light modulator the particles have a color selected from cyan, magenta, and yellow, and from black and white, and combinations thereof.

In an exemplary embodiment of the light modulator the fluid comprises one or more of a surfactant, an emulsifier, a polar compound, and a compound capable of forming a hydrogen bond.

Fluid 15 may be an apolar fluid with a dielectric constant less than 15. In an exemplary embodiment of the light modulator the fluid has a relative permittivity r of less than 100, preferably less than 10, such as less than 5. In an exemplary embodiment of the light modulator, fluid 15 has a dynamic viscosity of above 10 mPa·s.

Electrodes 13a, 13b and electrodes 14a, 14b are in fluidic contact with the fluid. The fluid may be in direct contact the electrodes, or indirectly, e.g., the fluid may contact a second medium with the electrode, such as through a porous layer. In an embodiment, the electrodes cover about 1-30% of the substrate surface. In an embodiment, the electrodes comprise an electrically conducting material with a resistivity of less than 100 n□m (at 273K; for comparison typically used ITO has 105 n□m), which is similar to an electrical conductivity >1*107 S/m at 20° C.

In an embodiment of the light modulator electrodes comprise copper, silver, gold, aluminum, graphene, titanium, indium, and combinations thereof, preferably copper. The electrodes may be in the form of wires, e.g., microwires, embedded in a polymer-based substrate; for example, copper microwires.

A connection for applying an electro-magnetic field to the electrodes, wherein the applied electro-magnetic field to the electrodes provides movement of the nano- and microparticles from a first electrode to a second electrode and vice versa. A connection for applying an electro-magnetic field to the electrodes may be provided. For example, in an exemplary embodiment of the light modulator an electrical current is between −100−+100 μA, preferably −30−+30 μA, more preferably −25−+25 μA. For example, a power provider may be in electrical connection with the at least two electrodes. The power provider may be adapted to provide a waveform power. At least one of amplitude, frequency, and phase may be adaptable to provide different states in the light modulator. For example, the aspects of the power may be adapted by a controller.

Light modulator 10 may comprise one or more segments, a segment being a single optically switchable entity, which may vary in size. The substrates enclose a volume, which may be a segment, at least partly.

The present device may comprise a driver circuit for changing appearance of (individual) segments by applying an electro-magnetic field. As such also the appearance of the light modulator, or one or more parts thereof, may be changed. For example, a segment may have an area of at least 1 mm2. The present design allows for stacking to allow for more colors; e.g., for full color applications a stack of two or three modulators could provide most or all colors, respectively.

Having one or more segments allows the light modulator to be controlled locally; this is advantageous for some applications, but not necessary. For smart glazing a light modulator may be used with or without segments. For example, applied in smart glazing, transparency or reflectivity may be controlled locally, e.g., to block a sun-patch without reducing transparency or reflectivity in the whole window. Segments may be relatively large, e.g., having a diameter of at least 1 mm, or at least 1 cm, etc.

In an exemplary embodiment of the light modulator substrates (11,12) are aligned, and/or electrodes (13,14) are aligned. For example, electrodes 13a, 13b and electrodes 14a, 14b may be aligned to be opposite each other. In aligned substrates, electrodes on different substrates fall behind each other when viewed in a direction orthogonal to the substrates. When the light modulator is disassembled, and the substrates are both arranged with electrodes face-up, then the electrode patterns are each other's mirror image.

Aligning substrates may increase the maximum transparency or reflectivity of the light modulator; on the other hand, when selecting a light modulator for more criteria than the range of transparency or reflectivity, etc., it may be better not to align or not fully align the two substrates. Light modulators can be stacked. For example, two stacked light modulators can be made from three substrates, wherein the middles one has electrodes on both its surfaces. In an embodiment of the light modulator optionally at least one substrate 11,12 of a first light modulator is the same as a substrate 11,12 of at least one second light modulator. For stacked modulators, alignment may also increase maximum transparency or reflectivity, but is may be detrimental to other considerations, e.g., diffractions.

FIG. 9b schematically shows an example of an embodiment of a light modulator 40. Light modulator 40 is similar to light modulator 10, except that it comprises multiple optical layers; in the example as shown two optical layers. There may be more than two optical layers. Each optical layer is arranged between two substrates. Light modulator 40 can be regarded as a stack of two-substrate light modulators as in FIG. 9a. As shown, light modulator 40 comprises three substrates: first substrate 41, second substrate 42 and third substrate 43. Between substrates 41 and 42 is an optical layer, and between substrates 42 and 43 is an optical layer. The optical layers may be similar to those in light modulator 10. A controller 46 is configured to control electrical current on the electrodes of the substrates. For example, in FIG. 9b, controller 46 may be electrically connected to at least 4 times 2 equals 8 electrodes.

Interestingly, the particles in the multiple optical layers may be different so that the multiple layers may be used to control more optical properties of the light modulator. For example, particles in different optical layers may absorb or reflect at different wavelengths, e.g., may have a different color. This can be used to create different colors and/or different color intensities on the panel by controller 46. For example, a four-substrate panel may have three optical layers with different color particles, e.g., cyan, yellow and magenta, respectively. By controlling the transparency or reflectivity for the different colors a wide color spectrum may be created.

The surfaces of the substrates that face another substrate may be supplied with two or more patterns, e.g., as in an embodiment. For example, the outer substrates 41 and 43 may receive electrodes only on an inner side, while the inner substrate, e.g., substrate 42, may have electrodes on both sides.

Substrates 41 and 42 may together be regarded as an embodiment of a light modulator. Likewise, substrates 42 and 43 may together be regarded as an embodiment of a light modulator.

FIG. 9c schematically shows an example of an embodiment of a car 20 having smart glazing for windows 21. This is a particularly advantageous embodiment, since while driving the level of incident lighting can change often and rapidly. Using smart glazing in a car has the advantage that light levels can be maintained as a constant level by adjusting the transparency of the car windows. Faster and/or more uniform transition between optical states, e.g., faster transition towards non-transparency is particularly advantageous in a car, as it reduces driver distraction during transition. Car 20 may comprise a controller configured for controlling the transparency or reflectivity of windows 21.

The smart glazing can also be used in other glazing applications, especially, were the amount of incident light is variable, e.g., buildings, offices, houses, green houses, skylights. Skylights are windows arranged in the ceiling to allow sunlight to enter the room.

The light modulator may have two optical states, e.g., a transparent state and a non-transparent state, or a reflective state and a non-reflective state. The light modulator, e.g., light modulator 10 or light modulator 40 may be configured to

- switch to the second optical state, e.g., the non-transparent state or to the non-reflective state by creating an alternating voltage on at least one of the first and second substrates, applying an alternating current between at least a first electrode and a second electrode on the first substrate and/or between a first electrode and a second electrode on the second substrate, and
- switch to the first optical state, e.g., the transparent state or to the reflective state by creating an alternating voltage between the first and second substrate, applying an alternating current between a first electrode on the first substrate and a first electrode on the second substrate, and/or between a second electrode on the first substrate and a second electrode on the second substrate.

The electrode pattern on the first substrate is arranged at least in part in the same pattern as a second electrode on the second substrate. Typically, the electrodes oppose each other, but the pattern of the first electrode and second electrode may also be shifted with respect to each other.

A protective coating may be provided on at least a part of the inner surface area of at least one of the first substrate and the second substrate is provided.