Liquid crystal on silicon array controlling method and device

Abstract

The invention relates to optical communication and provides a controller for controlling a liquid crystal on silicon (LCOS) array. The controller is configured to generate a plurality of digital driving sequences, each comprising a plurality of thermometer bits (T-bits) and one or more binary bits (B-bits). Each digital driving sequence controls a respective pixel of the LCOS array to achieve a desired gray level. The controller further swaps the positions of the T-bits in one or more of the digital driving sequences, introducing variability in the driving patterns, which can reduces phase flicker and improves power stability while maintaining phase accuracy. This approach can enhance the performance of LCOS-based optical systems, particularly in applications where minimizing power fluctuations is critical.

Description

[0001] LIQUID CRYSTAL ON SILICON ARRAY CONTROLLING METHOD AND DEVICE

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to the field of optical technology. For instance, the present disclosure provides a controller and method for controlling a liquid crystal on silicon (LCOS) array.

[0004] BACKGROUND

[0005] LCOS arrays (or panels) have become an integral component in optical communication systems, particularly in wavelength selective switches (WSS) used for steering and power control in Wavelength Division Multiplexing (WDM) channels. LCOS panels operate by modulating the phase delay of impinging light through precise control of liquid crystal molecule orientation. In WSSes, phase front control is applied to steer different spectral slices of light to designated output ports. To meet the requirements of modem optical networks, a single LCOS panel shall handle abroad spectral range. Thus a large number of pixels is required to accommodate C and L-band. As pixel sizes shrink, so does the available space for electronic control underneath each pixel.

[0006] SUMMARY

[0007] For controlling LCOS panels, digital driving technology has replaced analog circuits to manage pixel sizes. Digital driving switchs the pixel voltage between two levels, allowing precise control of the liquid crystal's phase shift by varying the on / off ratio in the driving sequence. However, this method can introduce phase fluctuations. Such phase flicker can affect power flicker in diffraction and beam-steering applications caused by interference of a multitude of involved phase levels.

[0008] Finally, power fluctuations negatively affect WDM signal quality, especially at higher attenuation settings.

[0009] In view of the above, an objective of this disclosure is to improve LCOS panel controlling. Further objectives include reducing power flicker in digital-drive LCOS panels.

[0010] This and other objectives are achieved by the solutions of the present disclosure, as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

[0011] A first aspect of the present disclosure provides a controller for controlling an LCOS array. The controller is configured to generate a plurality of digital driving sequences. Each digital driving sequence comprises a plurality of thermometer bits (T-bits) and one or more binary bits (B-bits). Each digital driving sequence is used to control a respective pixel of the LCOS to achieve a desired gray level. The controller is configured to swap positions of the T-bits in one or more of the digital driving sequences. Swapping the positions of the T-bits introduces spatial variability in the digital driving sequences. This results in enhanced optical performance, particularly in minimizing power fluctuations.

[0012] Within this disclosure, “gray level” refers to a level of phase shift (or brightness) that can be achieved by a pixel controlled by a respective digital driving sequence; “T-bits” are of identical total duration and are used to provide coarse control over the liquid crystal tilt angle of each pixel; “B-bits” denote binary bits that are used to fine tune the phase shift between the coarse angle steps set by the T-bits.

[0013] The controller may be further configured to maintain the positions of the B-bits unchanged while swapping the positions of the T-bits in one or more of the digital driving sequences.

[0014] After swapping the positions of the T-bits in one or more of the digital driving sequences the controller can be configured to provide the digital driving sequences to the LCOS array.

[0015] In an implementation form of the first aspect, for swapping positions of the T-bits, the controller is configured to divide a plurality of gray levels into a first group and a second group based on a threshold gray level. The first group comprises gray levels below the threshold gray level. The second group comprises gray levels equal to or above the threshold gray level. For each digital driving sequence: if the desired gray level is in the second group, the controller is configured to swap positions of the T-bits; if the desired gray level is in the first group, the controller is configured to maintain positions of the T- bits. The controller is configured to provide the plurality of digital driving sequences to the LCOS array. Thus, the digital driving sequences provided to the LCOS array comprise at least one sequence with T- bits that are swapped by the controller.

[0016] This selective swapping of T-bits for grey levels above or equal to the threshold gray level preserves the neighbor pixels’ interaction and the original pixels’ phase settings. Accordingly, the multitude of different interfering phase flicker patterns reduces the power flicker of the diffracted beam while the original cross-talk value is preserved.

[0017] T-bits of a digital driving sequence in the second group can comprise one or more common T-bits and multiple mobile T-bits. A common T-bit is a T-bit that can be commonly activated in sequences of the first group and the second group. T-bits that are not shared by the first group and are exclusively activated in the second group are mobile T-bits. In this disclosure, the controller may be configured to swap positions of the mobile T-bits only, and leave positions of the one or more common T-bits unchanged. The controller may be further configured to select the threshold grey level based on minimizing phase flicker and cross-talk in the LCOS array.

[0018] The threshold grey level may be dynamically adjustable based on the operating conditions of the LCOS array, such as but not limited to temperature, input signal strength, or application-specific requirements.

[0019] In a further implementation form of the first aspect, for swapping the positions of the T-bits, the controller is configured to cyclically shift the positions of the T-bits (e.g., the mobile T-bits mentioned above).

[0020] In a further implementation form of the first aspect, for swapping the positions of the T-bits (e.g., the mobile T-bits), the controller is configured to randomize the positions of the T-bits while preserving a minimum Hamming distance between the T-bits of adjacent digital driving sequences (for controlling adjacent pixels).

[0021] In a further implementation form of the first aspect, for swapping the positions of the T-bits, the controller is configured to maintain the first bit (TO) of the T-bits unchanged; and swap the remaining bits of the T-bits.

[0022] In a further implementation form of the first aspect, for generating a plurality of digital driving sequences, the controller is configured to initially set the T-bits such that a duty cycle of each digital modulation pattern of a digital driving sequence increases linearly with increasing gray levels.

[0023] A second aspect of this disclosure provides an optical device comprising an LCOS array and a controller. The controller is according to the first aspect or any implementation form thereof and is configured to control the LCOS array.

[0024] In a further implementation form of the second aspect, the optical device is a wavelength selective switch or an optical cross-connect.

[0025] A third aspect of this disclosure provides a method for controlling an LCOS array. The method is applied to a controller and comprises the following steps: generating a plurality of digital driving sequences, in which each digital driving sequence comprises a plurality of T-bits, and one or more B-bits, and each digital driving sequence is used to control a respective pixel of the LCOS to achieve a desired gray level; and swapping positions of the T-bits in one or more of the digital driving sequences. In an implementation form of the third aspect, the step of swapping positions of the T-bits comprises dividing a plurality of gray levels into a first group and a second group based on a threshold gray level. The first group comprises gray levels below the threshold gray level. The second group comprises gray levels equal to or above the threshold gray level. For each digital driving sequence: if the desired gray level is in the second group, positions of the T-bits are swapped; if the desired gray level is in the first group, positions of the T-bits are maintained. The method further comprises providing the plurality of digital driving sequences to the LCOS array.

[0026] In a further implementation form of the third aspect, the step of swapping the positions of the T-bits comprises cyclically shift the positions of the T-bits.

[0027] In a further implementation form of the third aspect, the step of swapping the positions of the T-bits comprises randomizing the positions of the T-bits while preserving a minimum Hamming distance between the T-bits of adjacent digital driving sequences (for controlling gray levels of adjacent pixels).

[0028] In a further implementation form of the third aspect, the step of swapping the positions of the T-bits comprises: maintaining the first bit (TO) of the T-bits unchanged; and swapping the remaining bits of the T-bits.

[0029] In a further implementation form of the third aspect, the step of generating a plurality of digital driving sequences comprises initially setting the T-bits such that a duty cycle of each digital modulation pattern of a digital driving sequence increases linearly with increasing gray levels.

[0030] The method of the third aspect may share the same optional features and advantages of the controller of the first aspect.

[0031] A fourth aspect of this disclosure provides a plurality of digital driving sequences for controlling an LCOS array. The digital driving sequences are obtained by the method according to the third aspect or any implementation form thereof.

[0032] A fifth aspect of the present disclosure provides a computer program product comprising a program code for performing the method according to the third aspect or any implementation form thereof, when executed on a computer. A sixth aspect of the present disclosure provides a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the third aspect or any implementation form thereof.

[0033] A seventh aspect of the present disclosure provides a chipset comprising instructions which, when executed by the chipset, cause the chipset to carry out the method according to the third aspect or any implementation form thereof.

[0034] The present disclosure provides a controller and a method to drive digital LCOS panels using digital sequences with spatially varied digital patterns while preserving neighboring pixel correlations without changing values represented by the digital sequences.

[0035] It has to be noted that all apparatus, devices, elements, units, and means described in the present application could be implemented in software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity, which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

[0036] BRIEF DESCRIPTION OF DRAWINGS

[0037] The above-described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

[0038] FIG. 1 shows an example of thermometer scheme-based digital driving sequences for controlling an LCOS panel;

[0039] FIG. 2 shows a controller for controlling an LCOS array;

[0040] FIG. 3 shows an example of mobile T-bits based on a threshold gray level;

[0041] FIG. 4 shows a further example of mobile T-bits based on another threshold gray level;

[0042] FIG. 5A shows an example of driving sequences without spatial variation;

[0043] FIG. 5B shows an example of driving sequences with spatial variation;

[0044] FIG. 6 shows a flow chart of a method for controlling an LCOS array; and

[0045] FIG. 7 shows a flow chart for swapping positions of T-bits. DETAILED DESCRIPTION OF EMBODIMENTS

[0046] FIG. 1 shows an example of thermometer scheme-based digital driving sequences for controlling an LCOS panel.

[0047] LCOS panels are commonly applied in wavelength selective switches (WSS) for steering and power control of wavelength-division multiplexing (WDM) channels, also referred to as spectral slices. Efficient WSS devices typically cover the C and L bands, necessitating a large number of pixels to accommodate the substantial bandwidth. As a result, the pixel sizes in LCOS panels have progressively reduced, which consequently limits the available space for electronic control circuits under each pixel. Currently, analog circuits become inadequate when pixel sizes fall below 4 pm. However, digital electronics and driving schemes are able to manage this scaling effectively.

[0048] In digital driving, the voltage applied to each pixel switches between two levels. The average phase shift of the liquid crystal can be precisely adjusted by controlling the on / off ratio of the digital driving sequence. This method allows for fine control of the pixel’s phase shift but introduces phase fluctuations around the intended average phase value. These phase fluctuations can become problematic in beam steering applications, where phase wedges that emulate the phase profile of a tilted mirror are used. In such cases, phase fluctuations result in corresponding power fluctuations in the diffracted beam.

[0049] Typically, the peak-to-peak (P2P) power flicker is a key metric of concern. The P2P power flicker is defined as: in which p denotes the average power, and ppeak-to-peak denotes the (highest) peak to (lowest) peak difference.

[0050] For LCOS panels specifically designed for fast switching operations, for example through the selection of liquid crystal material or liquid crystal layer thickness, the P2P power fluctuation may reach 1 dB or higher, which is an unacceptable level that degrades WDM signal quality and system performance.

[0051] To suppress power flicker, the phase flicker at each grey level, or phase delay value addressable by the digital video signal (e.g., an HDMI signal), must first be minimized. A typical digital driving sequence operates within the time slots of a video frame (typically at a 60 Hz frame rate), where time slots are set to high (“white voltage”) or low (“black voltage”) to achieve the required duty cycle and to minimize phase excursions. It is desirable to optimize the on and off patterns independently for each grey level. However, in practical implementations, neighbouring pixels can have different phase delay values, and fringe-field effects must be considered as they can significantly modify the resulting average phase delay. Therefore, the "Hamming distance" (e.g., the number of differing on / off settings between consecutive time slots) is minimized between subsequent grey levels. This can be achieved using a so-called "thermometer scheme" in which thermometer bits (T-bits), representing unit time slots, once set to a high state, remain high for all subsequent higher grey levels. Only the interpolating terminated time slots, referred to as binary bits (B-bits), which follow a binary-weighted scheme and have shorter, decreasing durations, are excluded from this rule. Thus, minimizing phase fluctuations between grey levels while preserving driving consistency is crucial for ensuring stable and accurate LCOS panel performance, e.g. in WSS applications.

[0052] FIG. 1 illustrates an example of an relationship between grey levels, phase shift, and the corresponding digital driving sequences applied to an LCOS array. The grey levels represent different levels of phase shifts that are achieved by controlling the on / off states of the thermometer bits and binary bits in the digital driving sequence.

[0053] As depicted in FIG. 1, the phase shift of each pixel increases linearly with the grey level. Each grey level corresponds to a specific combination of T-bits and B-bits that determine the time slots during which the voltage is applied to the pixel. The T-bits, once switched on, remain on for all subsequent grey levels, providing a stable coarse control of the phase shift. The B-bits, which follow a binary- weighted scheme, are responsible for fine-tuning the phase shift by switching on and off at specific intervals.

[0054] FIG. 2 shows a controller 210 for controlling an LCOS array 230. The controller 210 is configured to generate a plurality of digital driving sequences. Each digital driving sequence comprises a plurality of T-bits, one or more B-bits. The LCOS array 230 comprises an array of LCOS pixels 231. Each digital driving sequence is used to control a respective pixel of the LCOS to achieve a desired gray level.

[0055] Optionally, the digital driving sequence may be generated based on the desired gray level of each pixel according to the thermometer scheme introduced in FIG. 1.

[0056] In LCOS, a gray level may refer to a specific level of phase shift (or brightness) that can be achieved by a pixel. Each gray level corresponds to a combination of on and off states of the T-bits and B-bits in the digital driving sequence. The number of addressable gray levels may be determined by the bit depth of the display driver.

[0057] In a digital driving sequence for an LCOS display, T-bits are bits that have an equal time duration and remain in an on-state for all higher gray levels once switched on. T-bits provide coarse control over the liquid crystal tilt angle and the resulting phase shift. Binary bits are bits that have unequal time durations following a binary-weighted scheme (e.g., 1:2:4:8) and can be switched on or off independently for each gray level. B-bits provide fine-tuning of the phase shift between the coarse steps set by the T-bits.

[0058] The controller 210 is further configured to swap positions of the T-bits in one or more of the digital driving sequences.

[0059] To preserve weak fringe-field-induced interactions between neighboring pixels, or to maintain these interactions without sequence changes, a driving scheme with constrained sequence modifications is introduced. In particular, positions of the T-bits are selectively swapped in a sub-group of the plurality of digital driving sequences.

[0060] Optionally, for swapping the positions of the T-bits, the controller 210 is configured to divide a plurality of gray levels into a first group and a second group based on a threshold gray level. The first group comprises gray levels below the threshold gray level, and the second group comprises gray levels equal to or above the threshold gray level. For each generated digital driving sequence: the controller 210 is configured to swap positions of the T-bits if the desired gray level (achieved by the sequence) is in the second group. In this case, the swapping of the T-bits is constrained to keep the minimum Hamming distance between neighbor pixels; the controller 210 is configured not to swap positions of the T-bits (i.e., to maintain positions of the T-bits) if the desired gray level is in the first group.

[0061] Then, the controller 210 is configured to provide the digital driving sequences to the LCOS array 230.

[0062] Optionally, for swapping the positions of the T-bits for sequence in the second group, the controller 210 is configured to cyclically shift the positions of the T-bits or randomize the positions of the T-bits while the minimum Hamming distance between the T-bits of adjacent digital driving sequences for controlling adjacent pixels is preserved.

[0063] This disclosure proposes two groups of T-Bits based on the threshold gray level. For a gray level above the threshold gray level, the T-bits in the sequence are spatially varied through swapping their positions in the sequence. The positions may be randomized or cyclic shifted (while keeping minimum Hamming distance).

[0064] Optionally, excessive T-bits that are not common with gray levels below the threshold may be swapped (randomized or cyclically shifted) with other T-bit positions in the sequence. Common T-bits may remain unchanged. For instance, the first T-bit (TO) of the T-bits may be maintained for sequences in the second group, while the remaining T-bits are swapped by the controller 210. In another example, the first and the second T-bits (TO and Tl) of the T-bits may be maintained for sequences in the second group, while the remaining T-bits are swapped.

[0065] By leaving the common T-bits (between the first and the second group) unchanged and changing the T bits in the second group according to the rule above preserving the duty cycle and the Hamming distance of T bits of neighbor pixels, the initial phase delay of the liquid crystal remains unaffected by the driving pattern changes. Thus, the initial typically very low cross-talk value to other ports is preserved while the superposition of more spatially varying phase fluctuations suppresses power fluctuations.

[0066] The LCOS array 230 and the controller 210 may be comprised in an optical device 200. The optical device may be a wavelength selective switch or an optical cross-connect.

[0067] It is noted that the connection and the position of the LCOS array 230 and the control 210 shown in FIG. 2 are schematic and does not necessarily reflect a real implementation configuration. The controller 210 may be connected to the LCOS array 230 by any suitable means as long as the controller 210 is able to provide the digital drive sequences to the LCOS array. For instance, the controller 210 may be positioned beneath the LCOS array 230, such as in a substrate of the LCOS array 230.

[0068] FIG. 3 shows an example of mobile T-bits based on a threshold gray level. The initial digital driving sequence of FIG. 3 is generated according to the thermometer scheme as shown in FIG. 1. When applying the solution in FIG. 2, the threshold gray level is set to gray level 4 in the example of FIG. 3. In this example, gray level 0-3 are in the first group, while gray level 4 and above are in the second group. According to this disclosure, T-bits of sequences for gray level 0-3 are not changed, while T-bits of sequences for gray level 4 and above are swapped. B-bits remain unchanged for both groups.

[0069] Optionally, common T-bits of the first and the second group are not changed. In FIG. 3, the common T- bits are the first T-bit (TO). Thus, TO remains unchanged for both the first and the second group. The remaining T-bits (referred to as mobile T-bits or excessive T-bits) are swapped by the controller 210 before being provided to the LCOS array 230.

[0070] FIG. 4 shows a further example of mobile T-bits based on a further threshold gray level. In the example of FIG. 4, the further threshold gray level is set to gray level 6. Thus, T-bits of sequences for gray level 0-5 are not changed, while T-bits of sequences for gray level 6 and above are swapped. In this example, the first and the second T-bits (TO and Tl) are common T-bits of the first and the second group, and thus, remain unchanged. The remaining T-bits (T2 and above) are excessive / mobile T-bits that can be swapped before being provided to the LCOS array. It is noted that similar applies when, e.g., the threshold gray level is set to gray level 8. In this case, the common T-bits (that remain unchanged) are TO, Tl, T2. The mobile T-bits (that can be swapped) are T3 and above.

[0071] FIG. 5A shows an example of driving sequences without spatial variation. FIG. 5A visualizes the T-bits and B-bits switched on (marked as black in the figures) for a plurality of pixels to achieve different gray levels, which are generated based on the thermometer scheme as shown in FIG. 1. It can be seen that each pixel is driven by an identical driving sequence for a particular gray level (e.g., the four pixels of gray level 4 in FIG. 5 A share the same pattern of driving sequence). The phase fluctuations in this pattern are highly correlated with the period of the blazed grating related to the target beam steering angle resulting in significant peak-to-peak (P2P) power flicker of the diffracted beam, measured at 0.6 dB as an example.

[0072] FIG. 5B shows an example of driving sequences with spatial variation according to this disclosure. The threshold gray level is set to gray level 4 like the example shown in FIG. 3. In this example, the T-bits of the second group are swapped in a cyclic way while preserving the minimum Hamming distance. This introduces variability in the driving sequences, reducing the correlation between neighboring pixels' phase fluctuations.

[0073] By applying the solution of this disclosure, the P2P power flicker can be significantly reduced (e.g., from 0.6 dB (as shown in FIG. 5A) to 0.17 dB (as shown in FIG. 5B)).

[0074] As an example for illustrating the cyclic shifting: initially the sequences for different gray levels above or equal to the threshold gray level (as an example of gray level 4) are as depicted in Table 1.

[0075] Table 1

[0076] One possible way of cyclic shifting the T-bits in the second group is shown in Table 2 (in this example, threshold gray level is gray level 4 and thus, TO is the common T-bit and remains unchanged).

[0077] Table 2

[0078] In general, the controller 210 may be configured to cyclic shifting the T-bits of the second group sequence that are not in common with the first group across adjacent grating periods. Notably, the grating period is a spatial interval over which a phase modulation applied by the LCOS array repeats. In LCOS applications, especially for beam steering or wavelength-selective switches, the liquid crystal pixels are arranged to create a phase grating. This means that the phase shift applied across the array of pixels creates a pattern that is periodic (e.g., like a sinusoidal or linear phase gradient). This phase grating steers the light in a particular direction or diffracts it to specific angles.

[0079] As can be seen in FIG. 5B, a pixel of gray level 7 of the first grating period (firstly appears in FIG. 5B) is activated by a sequence of T0+T2+T3+B0. A pixel of gray level 7 of the second grating (secondly appears in FIG. 5B) is activated by a different sequence of T0+T3+T4 +B0.

[0080] It is noted that the FIG. 5B only illustrates one possible way of swapping T-bits. The T bit changes can follow any other sequence change scheme as long as it preserves (a) the duty cycle, i.e. the total duration of “on” time, for each pixel and (b) the minimum Hamming distance for T bits of neighbor pixels.

[0081] FIG. 6 shows a flow chart of a method 600 according to this disclosure. The method is applied to the controller 210 for controlling the LCOS array 230 and comprises the following steps.

[0082] Step 610: generating a plurality of digital driving sequences. Each digital driving sequence comprises a plurality of T-bits, and one or more B-bits. Each digital driving sequence is used to control a respective pixel of the LCOS to achieve a desired gray level.

[0083] Step 620: swapping positions of the T-bits in one or more of the digital driving sequences.

[0084] FIG. 7 shows a flow chart for swapping positions of T-bits.

[0085] Optionally, for swapping the positions of the T-bits, the method may comprise: dividing a plurality of gray levels into a first group and a second group based on a threshold gray level. The first group comprises gray levels below the threshold gray level, and the second group comprises gray levels equal to or above the threshold gray level.

[0086] As depicted in FIG. 7, for each digital driving sequence:

[0087] Step 621: maintaining positions of the T-bits if the desired gray level is in the first group;

[0088] Step 622: swapping positions of the T-bits if the desired gray level is in the second group.

[0089] The step of swapping positions of the T-bits may comprise randomizing the positions of the T-bits, or cyclic shifting the positions of the T-bits, while preserving the minimum Hamming distance between the T-bits of adjacent digital driving sequences (for controlling adjacent pixels).

[0090] In FIGs 1-7, corresponding elements may share the same optional features and function likewise.

[0091] The present disclosure provides a solution for reducing power flicker in LCOS panels through spatial variation of digital driving sequences. The driving scheme involves the use of thermometer bits and binary bits to control the phase shifts of the liquid crystal pixels. By introducing constrained position changes of the T-bits, particularly for grey levels above a threshold, the invention significantly reduces peak-to-peak power flicker while preserving pixel-to-pixel interactions and phase stability. For grey levels below the threshold, the T-bits remain fixed to maintain phase consistency. However, for grey levels above the threshold, the T-bits are swapped to introduce variability in the phase control, reducing correlation between neighboring pixels and thereby minimizing phase flicker. This approach ensures that phase flicker is reduced without negatively impacting cross-talk or the accuracy of phase settings.

[0092] An application scenario of this application is in the field of optical communication systems, such as wavelength-selective switches and optical cross-connects, where LCOS panels are used for beam steering and power control of wavelength-division multiplexing channels. By reducing phase flicker and improving power stability, this disclosure can enhance signal quality and reduce cross-talk between optical channels, which is essential in dense WDM systems operating at high baud rates.

[0093] This application may also be applied in beam steering applications, where precise control of the phase shift across pixels is required to direct light beams at specific angles. This is highly relevant in firee- space optical communication, laser-based projection systems, and optical sensors where maintaining stable power levels and reducing flicker are crucial for system performance.

[0094] In summary, the invention provides a robust and efficient method for improving the performance of LCOS panels with benefits such as reduced flicker and improved signal quality, making it ideal for use in modem optical communication and imaging systems. It is noted that the entities (e.g., the controller 210) in the present disclosure may comprise processing circuitry configured to perform, conduct or initiate the various operations of the device described herein, respectively. The processing circuitry may comprise hardware and software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The digital circuitry may be a chipset. Optionally, the processing circuitry comprises one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the device to perform, conduct or initiate the operations or methods described herein, respectively.

[0095] This disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed subject matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. For example, the user-defined code indicated by the data request may comprise a series of executable binaries and / or commands. A single element or another unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A controller (210) for controlling a liquid crystal on silicon, LCOS, array (230), wherein the controller (210) is configured to: generate a plurality of digital driving sequences, wherein each digital driving sequence comprises a plurality of thermometer bits, T-bits, and one or more binary bits, B-bits, and each digital driving sequence is used to control a respective pixel of the LCOS to achieve a desired gray level; and swap positions of the T-bits in one or more of the digital driving sequences.

2. The controller (210) according to claim 1, wherein for swapping positions of the T-bits, the controller (210) is configured to: divide a plurality of gray levels into a first group and a second group based on a threshold gray level, wherein the first group comprises gray levels below the threshold gray level, and the second group comprises gray levels equal to or above the threshold gray level; for each digital driving sequence: if the desired gray level is in the second group, swap positions of the T-bits; if the desired gray level is in the first group, maintain positions of the T-bits; and wherein the controller (210) is further configured to provide the plurality of digital driving sequences to the LCOS array (230).

3. The controller (210) according to claim 2, wherein for swapping the positions of the T-bits, the controller (210) is configured to cyclically shift the positions of the T-bits.

4. The controller (210) according to claim 2, wherein for swapping the positions of the T-bits, the controller (210) is configured to randomize the positions of the T-bits while preserving a minimum Hamming distance between the T-bits of adjacent digital driving sequences.

5. The controller (210) according to claim 3 or 4, wherein for swapping the positions of the T-bits, the controller (210) is configured to: maintain the first bit (TO) of the T-bits unchanged; and swap the remaining bits of the T-bits.

6. The controller (210) according to any one of claims 1 to 5, wherein for generating a plurality of digital driving sequences, the controller (210) is configured to initially set the T-bits such that a duty cycle of each digital modulation pattern of a digital driving sequence increases linearly with increasing gray levels.

7. An optical device (200) comprising: a liquid crystal on silicon, LCOS, array; and a controller (210) according to any one of claims 1 to 6, wherein the controller (210) is adapted to control the LCOS array (230).

8. The optical device (200) according to claim 7, wherein the optical device is a wavelength selective switch or an optical cross-connect.

9. A method (600) for controlling a liquid crystal on silicon, LCOS, array, wherein the method is applied to a controller (210) and comprises: generating (610) a plurality of digital driving sequences, wherein each digital driving sequence comprises a plurality of thermometer bits, T-bits, and one or more binary bits, B-bits, and each digital driving sequence is used to control a respective pixel of the LCOS to achieve a desired gray level; and swapping (620) positions of the T-bits in one or more of the digital driving sequences.

10. The method (600) according to claim 9, wherein the step (620) of swapping positions of the T-bits comprises: dividing a plurality of gray levels into a first group and a second group based on a threshold gray level, wherein the first group comprises gray levels below the threshold gray level, and the second group comprises gray levels equal to or above the threshold gray level; for each digital driving sequence: if the desired gray level is in the second group, swapping (622) positions of the T-bits; if the desired gray level is in the first group, maintaining (621) positions of the T-bits; and wherein the method further comprises providing (630) the plurality of digital driving sequences to the LCOS array.

11. The method (700) according to claim 10, wherein the step of swapping the positions of the T- bits comprises cyclically shifting the positions of the T-bits or randomize the positions of the T-bits, while preserving a minimum Hamming distance between the T-bits of adjacent digital driving sequences.

12. A plurality of digital driving sequences for controlling a liquid crystal on silicon, LCOS, array, wherein the digital driving sequences are obtained by the method according to any one of claims 9 to 11.

13. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to perform the method according to any one of claims 9 to 11.

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