Electrical crosstalk cancellation in acousto-optic modulators

Abstract

A method for operating a multi-channel acousto-optic modulator includes obtaining (S20) print data for a plurality of channels of the multi-channel acousto-optic modulator. The radio frequency signal is modulated (S30) for each of the plurality of channels based on the print data. The modulated radio frequency signal is provided (S40) via the electrical input connector to a corresponding transducer of the multi-channel acousto-optic modulator. For at least one channel, the modulation of the radio frequency signal comprises crosstalk cancellation (S32). Wherein the modulated radio frequency signal is compensated by a modulated radio frequency signal of at least electrically adjacent channels among the electrical input connectors scaled by a predetermined factor and phase shifted by a predetermined phase difference. A method for calibrating a multi-channel acousto-optic modulator, a control unit for a multi-channel acousto-optic modulator and a pattern generator are also presented.

Description

Technical Field

[0001] The present technology relates generally to pattern printing, and in particular to apparatus and methods for pattern printing using an acousto-optic modulator. Background Art

[0002] In the field of pattern printing, multiple channels are commonly used, usually to increase the overall printing speed. Therefore, several channels must be modulated simultaneously. One way to manage this multi-channel modulation is to utilize an acousto-optic modulator (AOM). Acousto-optic modulation is commonly used in laser scanners, providing a reasonable compromise between cost, speed, and efficiency. An AOM uses acoustic waves within a crystal to create a diffraction grating. When the power of the applied RF signal varies, the amount of diffracted light varies proportionally. An acousto-optic multi-channel modulator allows multiple beams to be modulated independently by integrating a transducer array with a single acousto-optic crystal.

[0003] One problem that occurs by using a single common acousto-optic crystal is that there is a risk of crosstalk between channels. "Crosstalk" can refer to acoustic crosstalk and / or electrical crosstalk. Acoustic crosstalk occurs within the acousto-optic crystal as interference between different sound waves. Electrical crosstalk can occur all the way from the modulated signal source, via connecting cables, and at the acousto-optic crystal itself. Electrical crosstalk can also be capacitive (electrostatic) and / or inductive (electromagnetic).

[0004] The problem of acoustic crosstalk has been addressed in different ways. Published international patent application WO 2020 / 120725 Al discloses a method in which applying different frequencies to adjacent transducers is introduced.

[0005] In addition, a frequently used method for reducing some electrical crosstalk is to arrange the electrical input connectors of adjacent channels on the crystal away from each other. One method is to divide the AOM channels into two groups that are well separated on opposite sides of the device. In this way, crosstalk between channels that are physically adjacent on the crystal is reduced. However, there is still inevitable electrical crosstalk between channels that are not physically adjacent on the crystal but are electrically adjacent, for example, in the electrical connectors. Summary of the invention

[0006] A general object of the present technology is to provide improved crosstalk reduction in an apparatus and method for acousto-optic modulation for multi-beam pattern printing.

[0007] The above objects are achieved by a method and an arrangement according to the independent claims. Preferred embodiments are defined in the dependent claims.

[0008] In summary, in a first aspect, a method for operating a multi-channel acousto-optic modulator includes obtaining print data for a plurality of channels of the multi-channel acousto-optic modulator. A radio frequency signal is modulated for each of the plurality of channels based on the print data. The modulated radio frequency signal is provided to each transducer of the multi-channel acousto-optic modulator via an electrical input connector. For at least one channel, the modulation of the radio frequency signal includes crosstalk cancellation. Wherein the modulated radio frequency signal is compensated by a modulated radio frequency signal of an electrically adjacent channel among the electrical input connectors that is scaled by a predetermined factor and phase-shifted by a predetermined phase difference.

[0009] In a second aspect, a method for calibrating a multi-channel AOM includes operating one channel of the multi-channel AOM with a modulated radio frequency signal. Another channel of the multi-channel AOM is operated with a modulated radio frequency signal scaled by a factor and phase-shifted by a phase difference. The intensity through the other channel of the multi-channel AOM is measured. The factor and phase that give the lowest intensity are determined as a predetermined factor and a predetermined phase difference. The predetermined factor and the predetermined phase difference are used for crosstalk cancellation between the two measured channels of the multi-channel AOM.

[0010] In a third aspect, a control unit for a multi-channel acousto-optic modulator comprises an input, a modulator device and a multi-channel output. The input is configured to obtain print data for a plurality of channels of the multi-channel acousto-optic modulator. The modulator device has a multi-channel modulator controller for modulating a radio frequency signal for each of the plurality of channels according to the obtained print data. The multi-channel output is configured to provide the modulated radio frequency signal to a corresponding transducer of the multi-channel acousto-optic modulator via an electrical input connector. The modulator device is configured to provide crosstalk cancellation for at least one channel, the crosstalk cancellation giving a modulated radio frequency signal, the modulated radio frequency signal being compensated by a modulated radio frequency signal of at least one electrically adjacent channel among the electrical input connectors scaled by a predetermined factor and phase shifted by a predetermined phase difference.

[0011] In a fourth aspect, a pattern generator includes a multi-channel AOM and a control unit of the multi-channel AOM according to the third aspect.

[0012] One advantage of the proposed technique is that electrical crosstalk is significantly reduced. Other advantages will be understood when reading the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

[0014] Figure 1 An embodiment of a pattern generator is schematically shown;

[0015] Figure 2An embodiment of a connection to an acousto-optic modulator is schematically shown;

[0016] Figure 3 is an image showing electrical crosstalk between electrically adjacent channels;

[0017] Figure 4 is an image showing partially cancelled electrical crosstalk between electrically adjacent channels;

[0018] Figure 5 is an image showing complete elimination of electrical crosstalk between electrically adjacent channels;

[0019] Figure 6 is a schematic diagram of an embodiment of a control unit for a multi-channel acousto-optic modulator;

[0020] Figure 7 is a flow chart of steps of an embodiment of a method for calibrating a multi-channel acousto-optic modulator;

[0021] Figure 8 is a flow chart of steps of an embodiment of a method for operating a multi-channel acousto-optic modulator;

[0022] Fig. 9 is a flow chart of steps of an embodiment of a crosstalk cancellation step;

[0023] Fig.10 An embodiment of a signal compensation device is schematically shown;

[0024] Fig.11 is a flow chart of steps of another embodiment of a crosstalk cancellation step;

[0025] Fig.12 Another embodiment of a signal compensation device is schematically shown;

[0026] Fig.13 is a schematic diagram of another embodiment of a control unit for a multi-channel AOM. DETAILED DESCRIPTION

[0027] Throughout the drawings, the same reference numerals are used for similar or corresponding elements.

[0028] To better understand the proposed technique, it may be useful to start with a brief overview of a model system of pattern generator 1, as Figure 1 This embodiment of the pattern generator 1 shown is only an example of a system in which the present technique can be applied. The present technique can be used in any pattern generator using a multi-channel AOM.

[0029] A laser beam is generated by a laser device 30. A diffractive optical element (DOE) 32 splits the laser beam into a plurality of separate beams 90. A set of mirrors 34, 36, 38 and other optical elements direct the separate beams 90 to illuminate a photosensitive target 42 at a substrate holder 40 to produce an exposed pattern 44 in the photosensitive target 42. Each lens, mirror, optical crystal, etc. has some error, thereby giving energy spread. Print data 100 is provided to a control unit 10 for a multi-channel acousto-optic modulator 20.

[0030] In the AOM 20, the transducer 24 is used to generate an acoustic wave through the AOM crystal 22. Based on the interaction between the acoustic wave and the separated laser beam 90 within the AOM crystal 22, the separated laser beam 90 can be turned on and off in registration with the movement of the separated laser beam 90 on the photosensitive target 42, thereby producing a desired pattern.

[0031] The control unit 10 provides the modulated RF signals 102 based on the print data to the corresponding transducers 24 of the multi-channel AOM 20 via the electrical input connector.

[0032] The separated laser beam 90 is moved over the photosensitive target by several mechanisms. The Y interferometer 50 uses the laser beam 54 from the laser source 52 to determine the position of the separated laser beam 90 in the Y direction. The X interferometer 56 similarly determines the position in the X direction. A mirror 58 at the movable print head is used for this purpose. The print head in the X carriage can be moved in the X direction along the X bridge 46, as shown by arrow 48, and the substrate holder 40 can be moved in steps in the Y direction relative to the X bridge 46, as shown by arrow 78. Therefore, the X carriage scans in the X direction (scan strip). During the return stroke of the X carriage, the Y stage carrying the substrate holder 40 moves a step length (scan strip width). Micro-sweeping 90 can also be obtained in the Y direction by sweeping the separated laser beam 90 as shown by arrow 72, thereby moving the impingement point 70 of the separated laser beam. In this embodiment, the micro-sweeping is achieved by an acousto-optic deflector 60 with an acousto-optic crystal 62. The transducer 64 is provided with a sweep signal 66 which is coordinated with the other movements and the print data 100. Thus, exposure is performed by writing several microsweeps in one scan swath. The AOD deflection crystal 62 generates the sweep for all separate beams 90 together and controls the power and linearity on the sweep.

[0033] The printed pattern 44 on the photosensitive target 42 thus depends on the separate laser beams 90 being given the correct modulation consistent with the micro-scanning and other movement actions of the print head. The AOM modulator crystal 22 controls the power of each separate beam 90 and converts the pattern data 100 into exposure light. The present technology focuses on the control unit 10 for the multi-channel acousto-optic modulator 20 and the method thereof.

[0034] Figure 2 An embodiment of an AOM 20 is schematically shown. The AOM 20 may be used, for example, in Figure 1 The pattern generator shown. In this particular embodiment, the AOM 20 includes 15 channels. Each channel is mechanically connected to an acousto-optical crystal 22 for enabling the transmission of acoustic waves into the acousto-optical crystal 22. Depending on, for example, the frequency of the acoustic wave, the light passing perpendicular to the wave, i.e. horizontally in the figure, may be affected. Thereby, the light beam can be switched on and off. Each transducer 24 defines a channel of the AOM 20, and each of these channels can thereby be controlled more or less independently of each other. A separate single-frequency control signal to each transducer 24 determines the modulation of a single light beam passing through the AOM 20.

[0035] This method generally works quite well. However, there is some crosstalk between channels. One way to avoid crosstalk between adjacent channels in an AOM crystal 22 is to set the electrical input connectors of adjacent channels on the crystal generally away from each other. In the figure, it can be seen that the transducer is connected by two connectors 21A, 21B, which are well separated in opposite sides of the device, respectively having 8 and 7 separate channels 23. In one connector 21A that manages the first group of channels 23, the order of the channel connectors is 7, 5, 3, 1, 2, 4, 6 and 8, as shown in the box on the right. The numbers refer to the actual mechanical position at the AOM crystal 22. Since the channel number indicates how the channel is placed on the crystal, channel 1 is physically adjacent to 2, 2 is physically adjacent to 3, and so on. The order of the channels 23 of the connector group 21B is similarly 9, 11, 13, 15, 14, 12 and 10, as shown in the box on the left. In this way, the electrical crosstalk between physically adjacent channels is reduced. This is because the connectors of the channels are positioned according to the above order. Thus, for example, channel 7 is electrically adjacent to 5, 5 to 3 and 7, 3 to 1 and 5, 1 to 2 and 3, 2 to 1 and 4, 4 to 2 and 6, and 6 to 4 and 8, and 8 to 6. The same applies to the other group.

[0036] The channels are positioned in a way that reduces crosstalk between adjacent channels on the crystal, but on the contrary inevitably introduces electrical crosstalk between channels that are not adjacent but electrically adjacent on the crystal. It is therefore found that if only one channel is controlled to allow light to pass through the AOM, and all surrounding channels are turned off, a certain amount of light still passes through the electrically adjacent channels. This is in Figure 3 The picture shows where light through different channels is detected.

[0037] In this experiment, a plane wave of light is sent through the modulator crystal and an RF signal is applied to only one of the modulator channels, channel 5 in this example. An imaging system is provided to image the acoustic waves generated within the crystal onto the camera sensor. This is achieved by filtering out the 0th diffraction order and letting only the 1st diffraction order pass to the camera. When the image is analyzed, it is clearly seen that in addition to the acoustic wave CH5 of channel 5, acoustic waves from channels 3 CH3 and 7 CH7 are also visible. These correspond to channels electrically adjacent to channel 5, CH5. In this picture, another acoustic wave of much lower intensity can also be seen corresponding to channel 1, which is electrically adjacent to channel 3 CH3. The reason these acoustic waves exist is because part of the energy of the RF signal CH5 sent to channel 5 couples to the circuits of the adjacent channels, reaches the corresponding transducers, and then the transducers generate waves in the crystal. It can also be noted that no light is detected in the physically adjacent channels between channels CH5 and CH7.

[0038] According to the idea of ​​the present technology, the electrical crosstalk can be eliminated by adding a cancellation signal to the original desired signal before sending it to the AOM. The cancellation signal is a scaled-down and phase-shifted copy of the signal of the electrically adjacent channel. If the channel has two electrically adjacent channels, a cancellation signal can be added to each.

[0039] Figure 4 is similar to Figure 3 The image of the case of , but the added cancellation signal in channel CH7 consists of a copy of the CH5 signal, scaled to 1.7% in amplitude (0.028% power) and phase shifted by 203 degrees. There is a noticeable drop in intensity at CH7. The phase shift is also varied, and in this particular case, the maximum cancellation is found at a phase shift of 211 degrees. In theory, if all connectors are exactly the same in terms of, for example, length, construction, etc., then the best cancellation will occur at 180 degrees. However, due to differences between connectors in a practical setup, there may be a small phase shift between specific electrically adjacent channels, in this case 31 degrees.

[0040] However, the same test was repeated with a constant phase shift of 211 degrees while the scaling was varied. At an amplitude scaling of 2,9% (0.085% power), the light through channel CH7 essentially disappeared, as Figure 5 As shown in FIG. 1 , the result is the same regardless of how the signal in channel CH5 is constructed, as long as the cancellation signal is a scaled and phase-shifted copy of it.

[0041] This shows that electrical crosstalk is possible to cancel. Since the crosstalk conditions in the device are constant during operation, the crosstalk cancellation parameters - phase shift and scaling factor - are the same for each pair of channels. Therefore, each individual device can be measured and calibrated to cancel electrical crosstalk.

[0042] The proposed method thus results in complete elimination of electrical crosstalk between electrically adjacent channels. This method will eliminate crosstalk even in situations where pure phase control methods fail, for example when the desired signal has zero amplitude and the crosstalk signal has maximum amplitude.

[0043] Figure 6 A control unit 10 for a multi-channel AOM is schematically shown. An input terminal 9 is configured to obtain print data 100 for a plurality of channels 23 of the multi-channel AOM. The modulator device 8 has a multi-channel modulator controller 12 for modulating a radio frequency signal 101 for each of the plurality of channels based on the obtained print data 100.

[0044] The modulator means 8 are configured to provide, for at least one channel 23, crosstalk cancellation, giving a modulated radio frequency signal which is compensated by a modulated radio frequency signal of at least one electrically adjacent channel in the electrical input connector scaled by a predetermined factor and phase-shifted by a predetermined phase difference. This compensation is added to the modulated radio frequency signal 101 to form a compensated radio frequency signal 102. This is typically performed in a corresponding signal compensation means 14 for each channel.

[0045] The multi-channel output 7 is configured to provide the modulated and compensated radio frequency signals 102 to the respective transducers of the multi-channel AOM via the electrical input connector 6 .

[0046] Preferably, the modulator arrangement 8 is configured for performing crosstalk cancellation on all channels 23 of the electrical input connector 6 .

[0047] Preferably, the modulator device 8 is configured to provide crosstalk cancellation by giving, except for the electrically outermost channel 23X, a modulated radio frequency signal 102 which is composed of the modulated radio frequency signals of two electrically adjacent channels among the electrical input connectors scaled by respective predetermined factors and shifted in respective phase by a predetermined phase difference.

[0048] Different, more detailed embodiments will be presented further below.

[0049] Figure 7 A flow chart showing steps of an embodiment of a method for calibrating a multi-channel AOM is shown. In step S10, one channel of the multi-channel AOM, here denoted as channel N, is operated with a modulated RF signal. In a simultaneous step S12, another channel of the multi-channel AOM, here denoted as channel M, is operated with a modulated RF signal scaled by a factor and phase shifted by a phase difference.

[0050] In step S14, the intensity of another channel, channel M, through the MAC is measured. In step S16, the factor and phase difference that give the lowest intensity are determined. This is typically performed by repeating steps S12 and S14 with different scaling factors and phase shifts, as indicated by dashed arrow S15. These determined factors and phase differences that give the lowest intensity are assigned as predetermined factors and predetermined phase differences for the channel pair N and M for crosstalk cancellation between the two test channels N and M of the MAC.

[0051] Preferably, the predetermined factor and the predetermined phase difference are determined for each pair of electrically adjacent channels.

[0052] This principle of course applies to all pairs of channels, even if the electrical crosstalk with electrically non-adjacent channels is extremely small. Therefore, in one embodiment, a predetermined factor and a predetermined phase difference are determined for each pair of channels. If the factor is very small, this is an indication that the electrical crosstalk is also very small, and may be an indication that cancellation between such channels may not be necessary. The predetermined factors and predetermined phase differences between different pairs of channels may then be used in the operation of the multi-channel acousto-optic modulator.

[0053] Figure 8 is a flow chart of steps of an embodiment of a method for operating a multi-channel acousto-optic modulator. In step S20, print data of a plurality of channels of the multi-channel acousto-optic modulator is obtained. In step S30, a radio frequency signal is modulated for each of the plurality of channels based on the print data. The step S30 of modulating the radio frequency signal further includes crosstalk cancellation S32 for at least one channel. Thereby, the modulated radio frequency signal is compensated by a modulated radio frequency signal of at least one electrically adjacent channel among the electrical input connectors that is scaled by a predetermined factor and phase-shifted by a predetermined phase difference. In step S40, the modulated radio frequency signal is provided to each transducer of the multi-channel acousto-optic modulator via the electrical input connector.

[0054] Preferably, crosstalk cancellation is performed on all channels of the electrical input connector.

[0055] It is also preferred that crosstalk cancellation is performed for all electrically adjacent channels. In most cases, a channel has two electrically adjacent channels, whereby electrical crosstalk from these two electrically adjacent channels is compensated. For channels associated with connectors arranged at the side of the connector, i.e. for the outermost channels, there is only one electrically adjacent channel, and compensation for electrical crosstalk is performed only for one electrically adjacent channel. Therefore, crosstalk cancellation preferably gives a modulated radio frequency signal other than the electrically outermost channel, which is compensated by the modulated radio frequency signals of the two electrically adjacent channels in the electrical input connector, which are scaled by a corresponding predetermined factor and correspondingly phase shifted by a predetermined phase difference.

[0056] The crosstalk cancellation described above can be achieved in different ways. The exact, absolute phase of the modulated signal to the multichannel AOM can be achieved to be arbitrary. The operation of the channels of the multichannel AOM does depend only on the frequency of the applied signal. Therefore, applying a phase shift to the signal supplied to a single channel of the multichannel AOM will not change the modulation characteristics of the channel. The modulator device can then be designed in such a way that each channel is designed to have a certain phase difference with respect to the electrically adjacent channels. If this phase difference is equal to the measured calibrated predetermined phase shift, a simple setting of the signal compensation device can be utilized. Since the basic phase shift between the different channels has been set to a predetermined phase shift, simply adding an amplitude proportional to the signal of the electrically adjacent channel will automatically achieve the expected phase difference.

[0057] Fig. 9 is a partial flow chart of an embodiment of step S32 showing crosstalk cancellation between electrically adjacent channels. In step S33, the channels are arranged to have a fixed relative phase difference with the electrically adjacent channel(s) among the electrical input connectors. The fixed relative phase difference is equal to the corresponding predetermined phase difference. In step S34, the print data amplitude of each channel is summed with the print data amplitude of the electrically adjacent channel scaled by a predetermined factor. In this way, a total channel signal including a cancellation signal with an appropriate phase difference relative to the electrically adjacent channels will be given by RF modulation with a fixed relative phase difference.

[0058] As an example, a simplified approach could be the following. The data channel adds the main signal and the scaled adjacent signal and provides them to RF modulation, usually in a so-called transmit board. The transmit board has an appropriate phase difference set. Figure 2 In the embodiment of the arrangement, ideally, all electrically adjacent channels are arranged to have a phase difference of 180 degrees, as shown in Table 1:

[0059]

[0060] Table 1: Ideal channel phases, in physical order.

[0061] According to Table 2, by arranging them in electrical order, the phase difference between electrically adjacent channels becomes apparent.

[0062]

[0063] Table 2: Ideal channel phases, in electrical order.

[0064] In a real situation the phase difference will not always be 180, as seen in the experiment mentioned above, so if for example channel 5 needs to be 200 degrees below channel 7 and 170 degrees above channel 3, the table would have to change to (along with the other experimentally determined phase shifts):

[0065]

[0066] Table 3: Calibrated channel phases, in physical order.

[0067] In electrical sequence, the shift then becomes:

[0068]

[0069] Table 4: Calibrated channel phases, in electrical order.

[0070] Fig.10 An embodiment of the signal compensation device 14 is schematically shown. Three electrically adjacent channels 101 N-1 , 101 N and 101 N+1 The print data 100 is provided to the signal compensation device 14 at the input end. In the adding part 18, the print data 101 N-1 In multiplier 11 N-1 and scaling factor β N-1 Similarly, print data 101 N+1 In multiplier 11 N+1 and scaling factor β N+1 Multiply. Two scaled print data and print data 101 N The compensated print data are summed in the summer 15. In other words, in the adding section 18, the print data amplitude of each channel is added to the print data amplitude of the electrically adjacent channel scaled by a predetermined factor;

[0071] In the modulator 13 of the phase shifter 16, the compensated print data is transmitted with a frequency f and a phase φ N RF modulation is performed. An RF modulated signal 102 is provided at the output for connection to channel N of the multi-channel acousto-optic modulator via a connector in which channels N-1 and N+1 are electrically adjacent. In other words, the phase shifter 16 is configured to arrange the channels to have a fixed relative phase difference equal to the corresponding predetermined phase difference with the electrically adjacent channels in the electrical input connector.

[0072] Alternatively, the implementation can be done entirely in the transfer board. In this case, the transfer board must store three times the normal data.

[0073] Fig.11A flow chart of an embodiment of step S32 of crosstalk cancellation between electrically adjacent channels is shown. In step S35, a radio frequency signal modulated according to the print data of a channel among the electrical input connectors and a radio frequency signal modulated according to the print data of at least one other channel are provided. In step S36, the modulated radio frequency signal according to the print data of at least one other channel is scaled by a corresponding predetermined factor and the modulated radio frequency signal according to the print data of at least one other channel is phase shifted by a corresponding predetermined phase difference. In step S37, the modulated radio frequency signal according to the print data of the channel and the scaled and phase-shifted modulated radio frequency signal according to the print data of at least one other channel are added, which gives a modulated radio frequency signal for crosstalk cancellation to be provided to the respective transducers.

[0074] Fig.12 An embodiment of the signal compensation device 14 is schematically shown. The compensation bridge 19 is connected to the output of the multi-channel modulator controller 12 and is configured to scale the modulated RF signal according to the print data of the channel with a corresponding predetermined factor and phase shift the modulated RF signal according to the print data of the channel with a corresponding predetermined phase difference. The signal adder 17 is connected to one or more of the compensation bridges 19 and is configured to add the scaled and phase shifted modulated RF signal according to the print data of the channel from one or more compensation bridges to the modulated RF signal according to the print data of another channel. The respective output of the signal adder 17 providing the crosstalk-canceled modulated RF signal is connected to a respective one of the transducers via an electrical input connector.

[0075] As mentioned above, the elimination of electrical crosstalk can also be generalized to more than electrically adjacent channels. Typically, for each channel that separates two interfering channels, crosstalk is significantly reduced. Therefore, more than two closest channels on each side will be unlikely to give a crosstalk large enough to be compensated. However, in theory it can be performed for all channels.

[0076] In other words, in one embodiment, crosstalk cancellation gives a modulated RF signal that is compensated by modulated RF signals of more than two channels between electrical input connectors, which are scaled by respective predetermined factors and phase shifted by respective predetermined phase differences.

[0077] Fig.13 Schematically an embodiment is shown in which crosstalk from more than two channels on each side is compensated. In other words, the modulator means 8 is configured to provide crosstalk cancellation, giving a modulated radio frequency signal compensated by a modulated radio frequency signal of at least one electrically adjacent channel in the electrical input connector scaled by a predetermined factor and phase shifted by a predetermined phase difference.

[0078] The current crosstalk compensation concept has been shown to give a complete elimination of electrical crosstalk on electrically adjacent channels. Furthermore, there are implementations that are easy to implement without having to introduce hardware modifications. It is possible to implement the necessary modifications only in software / firmware.

[0079] The above embodiments are to be understood as several exemplary embodiments of the present invention. It will be appreciated by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different component solutions in different embodiments may be combined in other configurations where technically possible. However, the scope of the present invention is defined by the appended claims.

Claims

1. A method for operating a multi-channel acousto-optic modulator (20), comprising the following steps: - obtaining (S20) printing data (101) of a plurality of channels (23) of the multi-channel acousto-optic modulator (20); - modulating (S30) a radio frequency signal (102) for each of the plurality of channels (23) based on the print data (101); and - providing (S40) the modulated radio frequency signal (102) to the corresponding transducer (24) of the multi-channel acousto-optic modulator (20) via the electrical input connector (6), Characterized in that the step of modulating (S20) the radio frequency signal (102) comprises crosstalk cancellation (S32) for at least one channel (23), wherein the modulated radio frequency signal is compensated by the modulated radio frequency signal of at least an electrically adjacent channel (23) among the electrical input connectors scaled by a predetermined factor (β) and phase shifted by a predetermined phase difference (φ).

2. The method according to claim 1, characterized in that The crosstalk cancellation (S32) is performed for all channels (23) of the electrical input connector (6).

3. The method according to claim 1 or 2, characterized in that: The crosstalk cancellation (S32) gives a modulated radio frequency signal (102) other than the electrically outermost channel (23X), which is compensated by the modulated radio frequency signals of two electrically adjacent channels (23) in the electrical input connector (6) scaled by a corresponding predetermined factor (β) and phase-shifted by a corresponding predetermined phase difference (φ).

4. The method according to any one of claims 1 to 3, characterized in that The crosstalk elimination (S32) comprises the following steps: - arranging (S33) said channels (23) in said electrical input connector (6) with a fixed relative phase difference equal to said electrically adjacent channels (23), said fixed relative phase difference being equal to said corresponding predetermined phase (φ) difference; and - summing (S34) the print data amplitude of each channel (23) with the print data amplitude of the electrically adjacent channel (23) scaled by the predetermined factor (β).

5. The method according to any one of claims 1 to 3, characterized in that The crosstalk cancellation (S32) gives a modulated radio frequency signal which is compensated by the modulated radio frequency signals of more than two channels (23) among the electrical input connector scaled by a respective predetermined factor (β) and phase-shifted by a respective predetermined phase difference (φ).

6. The method according to any one of claims 1, 2, 3 or 5, characterized in that: The crosstalk elimination (S32) comprises the following steps: - providing (S35) in the electrical input connector (6) a modulated radio frequency signal according to the print data (101) of a channel (23) and a modulated radio frequency signal according to the print data (101) of at least one other channel (23); - scaling (S36) the modulated radio frequency signal (101) according to the print data of the at least one other channel (23) with the corresponding predetermined factor (β), and phase shifting the modulated radio frequency signal (101) according to the print data of the at least one other channel (23) with the corresponding predetermined phase difference (φ); - adding (S37) the modulated radio frequency signal according to the print data of the channel (23) and the scaled and phase-shifted modulated radio frequency signal according to the print data of the at least one other channel (23) to give the crosstalk-canceled modulated radio frequency signal (102) to be provided to the respective transducer.

7. A method for calibrating a multi-channel acousto-optic modulator (20), comprising the following steps: - operating (S10) a channel (23) of a multi-channel acousto-optic modulator (20) with a modulated radio frequency signal; - operating (S12) another channel (23) of the multi-channel acousto-optic modulator (20) with the modulated radio frequency signal scaled by a factor and phase-shifted by a phase difference; - measuring (S14) the intensity of the other channel (23) through the multi-channel acousto-optic modulator (20); and - determining (S16) the factor and phase difference giving the lowest intensity as a calibration factor and calibration phase difference to be used for crosstalk cancellation between the two measured channels (23) of the multi-channel acousto-optic modulator.

8. The method according to claim 7, characterized in that The calibration factor and the calibration phase difference are determined for each pair of electrically adjacent channels (23).

9. The method according to claim 7 or 8, characterized in that: The calibration factor and the calibration phase difference are determined for each pair of channels (23).

10. A control unit (10) of a multi-channel acousto-optic modulator (20), comprising: - an input terminal (9) for obtaining printing data (100) of a plurality of channels (23) of the multi-channel acousto-optic modulator (20); - a modulator device (8) having a multi-channel modulator control (12) for modulating a radio frequency signal (102) for each of the plurality of channels (23) based on the obtained print data (100); and - a multi-channel output terminal (7) for providing the modulated radio frequency signal (102) to the corresponding transducer of the multi-channel acousto-optic modulator (20) via the electrical input connector (6); The modulator device (8) is configured to provide, for at least one channel (23), crosstalk cancellation by providing a modulated radio frequency signal (102) compensated by a modulated radio frequency signal of at least an electrically adjacent channel (23) among the electrical input connector (6) scaled by a predetermined factor (β) and phase shifted by a predetermined phase difference (φ).

11. The control unit according to claim 10, characterized in that The modulator device (8) is configured to perform the crosstalk cancellation for all channels (23) of the electrical input connector (6).

12. The control unit according to claim 10 or 11, characterized in that: The modulator device (8) is configured to provide crosstalk cancellation by giving, except for the electrically outermost channel (23X), a modulated radio frequency signal (102) compensated by the modulated radio frequency signals of two electrically adjacent channels (23) in the electrical input connector scaled by a respective predetermined factor (β) and phase shifted by a respective predetermined phase difference (φ).

13. The control unit according to any one of claims 10 to 12, characterized in that The modulator device (8) comprises: - an adding section (18) in which the print data (101) of each channel (23) N ) amplitude and the print data amplitude (I01) of the electrically adjacent channel (23) scaled by the predetermined factor (β) N-1 , 101 N+1 ) added together; and - a phase shifter (16) configured to arrange the channels (23) at a fixed relative phase difference with the electrically adjacent channels (23) among the electrical input connectors (6), the fixed relative phase difference being equal to the corresponding predetermined phase difference (φ).

14. The control unit according to any one of claims 10 to 12, characterized in that The modulator arrangement (8) is configured to provide crosstalk cancellation giving a modulated radio frequency signal (102) compensated by modulated radio frequency signals of at least an electrically adjacent channel (23) among the electrical input connector (6) scaled by a respective predetermined factor (β) and phase shifted by a respective predetermined phase difference (φ).

15. A control unit according to any one of claims 10, 11, 12 or 14, characterized in that The modulator device (8) comprises a signal compensation device, wherein the signal compensation device has: - a compensation bridge (19) connected to the output of the multi-channel modulator control (12) and configured to scale the modulated radio frequency signal according to the print data of the channel (23) with the corresponding predetermined factor (β) and to phase shift the modulated radio frequency signal according to the print data of the channel (23) with the corresponding predetermined phase difference (φ); as well as - a signal adder (17), connected to one or more of the compensation bridges (19), configured to add the modulated radio frequency signal from the one or more compensation bridges (19) scaled and phase-shifted according to the print data of the channel (23) to the modulated radio frequency signal according to the print data of another channel (23); Thereby, respective outputs of the signal adders (17) providing the crosstalk-canceled modulated radio frequency signals (102) are connected to respective transducers (24) via the electrical input connectors (6).

16. A pattern generator (1), comprising: A multi-channel acousto-optic modulator (20) and a control unit (10) for the multi-channel acousto-optic modulator (20) according to any one of claims 10 to 15.

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