Method and system for writing voxels onto a transparent substrate

Abstract

A method for writing voxels onto a substrate using a laser writing system includes: forming a first voxel at a first position in the substrate using a first laser pulse; detecting light emitted or scattered by the substrate as a result of the formation of the first voxel; determining whether the detected light satisfies predetermined constraints; and adjusting the amplitude of a second laser pulse if the detected light does not satisfy the predetermined constraints. The light emission or scattering from the substrate as a result of voxel formation is related to the properties of the formed voxel. By monitoring such emission or scattering, it is possible to compensate for changes in the performance of the laser writing system. A laser writing system and a computer program product implementing the method are also provided herein.

Description

[Background technology]

[0001] background

[0001] There is a great demand for data storage. Cloud storage providers are estimated to need zettabyte-level data storage capacity in the near future, where zettabyte is 1 trillion gigabytes (10 21 This is in bytes. Much of the data will need to be stored for long periods of time.

[0002]

[0002] Examples of widely used data storage technologies today include hard disk drives, magnetic tapes, flash memory, and optical discs. All of these technologies have the drawback that data must be periodically copied onto replacement media. This is costly in terms of both energy use and hardware requirements.

[0003]

[0003] Magnetic storage devices such as hard drives and magnetic tapes have the problem of gradual demagnetization. Flash memory has the problem of read disturbance, in which repeated reading from a particular flash cell causes damage to surrounding flash cells. Reflective materials used for data storage in optical media such as DVDs degrade over time. [Overview of the project] [Problems that the invention aims to solve]

[0004]

[0004] Birefringent optical data storage media have been proposed as a solution to these drawbacks. Birefringent optical data storage media have a substrate such as a quartz glass substrate. Data is encoded in three-dimensional nanostructures formed within the substrate. These nanostructures are referred to as voxels.

[0005]

[0005] The voxels have different optical properties than those of the surrounding bulk substrate. Specifically, the voxels are birefringent, in other words, they exhibit different refractive indices depending on the polarization and / or direction of the incident light. The optical properties of the voxels can be controlled at the time the voxels are written into the substrate. The optical properties of the voxels are used to encode data.

[0006]

[0006] The substrate is transparent in the sense that it is transparent to light at the wavelengths used to read and write voxels.

[0007]

[0007] Birefringent optical data storage media and their manufacture are described, for example, in "Anderson et al, Glass: A New Media for a New Era - 10th USENIX Workshop on Hot Topics in Storage and File Systems (HotStorage 18), 2018" and U.S. Patent No. 10,236,027. [Means for solving the problem]

[0008] overview

[0008] In one embodiment, a method is provided for writing voxels onto a substrate using a laser writing system. The method includes: forming a first voxel at a first position in the substrate using a first laser pulse; detecting light emitted or scattered by the substrate as a result of the formation of the first voxel; determining whether the detected light satisfies predetermined constraints; and adjusting the amplitude of a second laser pulse in response to the determination that the detected light does not satisfy the predetermined constraints.

[0009]

[0009] One aspect of the present invention provides a computer program product having instructions performed on a non-temporary computer-readable medium, which, when executed by one or more processors operably linked to a laser writing system for writing voxels to a transparent storage medium, causes the laser writing system to perform the method described above.

[0010]

[0010] Yet another embodiment provides a system for writing data onto a transparent substrate. The system comprises a pulsed laser source, a first amplitude modulator downstream of the pulsed laser source along an optical path, a beam scanner positioned on the optical path downstream of the first amplitude modulator, a sample stage for holding the substrate on the optical path downstream of the amplitude modulator and a movable optical element, a detector for detecting light emitted or scattered by the substrate as a result of voxel formation in the substrate by modulated laser pulses, and a controller. When in use, the controller controls the system to perform the method defined herein.

[0011]

[0011] This “Summary” is provided in a general form to introduce the selection of concepts that are further described later in the “Detailed Description.” This “Summary” is not intended to identify any major or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Nor is the claimed subject matter limited to any implementation that solves any or all of the defects described herein.

[0012] Brief explanation of the drawing

[0012] The following drawings are referenced only as examples to aid in understanding embodiments of the present disclosure and to illustrate how such embodiments may be carried out. [Brief explanation of the drawing]

[0013] [Figure 1]This is a schematic cross-section of an example optical data storage medium. [Figure 2] This is a flowchart illustrating the general method for writing voxels onto a transparent substrate. [Figure 3A] This image shows the light emission obtained as a result of the formation of scan lines in voxels, along with a plot of emission amplitude measured as a function of position along the scan line. [Figure 3B] This is a plot of the amplitude of photo-induced emission as a function of position along a scanline using laser pulses of different energies. [Figure 4] This flowchart outlines the calibration phase of the voxel writing method, which is adapted to allow for repeatable systematic error correction. [Figure 5] This flowchart outlines the voxel writing phase that can be performed following the method shown in Figure 4. [Figure 6A] This is a plot of the intensity of photo-induced emission in voxel formation as a function of laser pulse energy. [Figure 6B] This shows the change in photo-induced emission intensity over time in the absence of feedback control. [Figure 6C] It exhibits photo-induced emission over time with feedback control. [Figure 7] This is a block diagram of an illustrative laser writing system. [Figure 8] This is a block diagram of an example controller for a laser writing system. [Figure 9A] This is a heatmap showing the observed emission intensity as a function of position when writing voxels using the comparative example method. [Figure 9B] This is a heatmap showing the observed emission intensity as a function of position when writing voxels using the method described herein. [Figure 10] This plot shows voxel quality as a function of the amplitude of photo-induced emission during voxel formation. [Figure 11]A plot showing the change in the amplitude of light-induced emission and the voxel quality over time in the absence of feedback control. [Figure 12] A plot showing the change in the amplitude of light-induced emission and the voxel quality over time in the presence of feedback control. [Figure 13] Visualization of the state space described in Example 3.

Best Mode for Carrying Out the Invention

[0014] Detailed Description

[0013] Terms indicating directions such as "upper", "lower", "left", "right", "above", "below", "horizontal direction", and "vertical direction" are used in this specification for convenience of explanation and mean the directions shown in the figures of the described drawings. To avoid any doubts, this terminology is not intended to limit the orientation of the device in an external reference frame.

[0015]

[0014] The position of the voxels within the substrate can be described using Cartesian x, y, z coordinates. The laser pulses used to form the voxels propagate in the z-axis direction.

[0016]

[0015] The data processing steps are implemented using hardware such as a processing device, for example, a processing device 810, a digital or analog signal processor, or other suitable circuitry.

[0017]

[0016] First, referring to FIG. 1 which is a schematic cross-section of an optical data storage medium, the structure of an exemplary optical data storage medium will be described. [[ID=X]] [[ID=Y]]

[0018] [[ID=Z]]

[0017] The optical data storage medium 100 has a substrate 110 with voxels 120 embedded therein.

[0019]

[0018] The substrate 110 may be glass, specifically fused silica. Fused silica may also be called silica glass. Glass has excellent chemical stability, and data storage media based on glass substrates have an expected lifespan of several hundred years. Therefore, optical data storage media are useful for long-term data storage.

[0020]

[0019] The shape and dimensions of the substrate are not particularly limited. Figure 1 shows a cubic substrate. In deformation, the substrate can have any shape (for example, cylindrical).

[0021]

[0020] The substrate typically has a thickness t of up to 10 mm in the z direction, optionally up to 5 mm, and optionally in the range of 200 μm to 2 mm. More generally, the thickness of the substrate can be appropriately selected based on the capabilities of the imaging system used to image the voxels. The z direction is the direction in which light is transmitted through the substrate when imaging the voxels. The attenuation of light passing through the substrate increases as a function of the distance traveled, and providing relatively thin equipment can limit such attenuation.

[0022]

[0021] Multiple voxels 120 are embedded in the substrate 110. The voxels 120 may have phase voxels and / or birefringence voxels.

[0023]

[0022] A voxel is a separate volume of a substrate that has been modified to have one or more non-inherent optical properties, in other words, one or more optical properties that are different from those of the bulk substrate material.

[0024]

[0023] Voxels are formed by focusing one or more pulses of laser light at a location within the substrate 110. The pulses induce physical changes in the structure of the material at that location. These physical changes may include the creation of denser or less dense areas, localized changes in glass composition, crystallization, and the formation of nanoscale voids.

[0025]

[0024] A phase voxel is a voxel having a refractive index different from that of an unmodified bulk substrate material. Phase voxels are so named because the electromagnetic waves (i.e., light) passing through the voxel experience a phase change. A phase voxel can be obtained by focusing a single laser pulse on the location of the voxel, but multiple laser pulses (e.g., from a GHz burst laser) may be useful as appropriate.

[0026]

[0025] Phase voxels may be used to implement a simple 1-bit encoding scheme, and the presence or absence of a voxel may be interpreted as logical 1 and logical 0, respectively, and vice versa.

[0027]

[0026] Alternatively, phase voxels can be used to implement multi-bit encoding schemes. The magnitude of the phase shift induced as light passes through a phase voxel is referred to as the voxel's "intensity". The intensity is determined by the refractive index of the phase voxel and the size of the voxel (more specifically, the path length through the voxel).

[0028]

[0027] The intensity of a phase voxel varies as a function of the amplitude (in other words, energy) of the laser pulse used to write the voxel. By modulating the amplitude of the laser pulse, phase voxels with different intensities can be obtained. Each different intensity is employed to encode different symbols. Such voxels are referred to as amplitude-modulated phase voxels.

[0029]

[0028] A pair of phase voxels is considered to have “different” intensities when the voxels produce sufficiently different phase changes that are useful for encoding different data symbols. The difference is above the noise floor of the writing system so that random fluctuations (e.g., in the laser power output) do not cause inaccurate symbols to be written to the substrate. The difference is also sufficiently large to be revealed by a phase-sensitive microscope. Very small fluctuations in intensity due to random noise are not considered to be “differences” in the context of this application.

[0030]

[0029] A birefringent voxel is a voxel that has non-intrinsic birefringence, that is, birefringence different from that of the bulk material. A birefringent voxel exhibits different refractive indices for light of different polarizations.

[0031]

[0030] Birefringent voxels produce a change in the polarization angle of light. Birefringent voxels have a linear retardance, which is a measure of the magnitude of the shift between the orthogonal polarization components of light when light interacts with the birefringent voxel. The linear retardance is a result of birefringence and has a magnitude related to the birefringence and size of the voxel.

[0032]

[0031] Typically, birefringent voxels are formed by focusing at least two laser pulses at the location of the voxel. The first laser pulse is a relatively large amplitude pulse called a seed pulse. The seed pulse results in the formation of a seed change. The seed pulse is followed by one or more data pulses of relatively small amplitude. The data pulses have polarization that determines the birefringence of the birefringent voxel. By modulating the polarization of the data pulses, voxels having different birefringent properties and, therefore, encoding different data symbols can be obtained.

[0033]

[0032] In terms of structure, a seed change is similar to a phase voxel. When writing multiple phase voxels, the laser pulse energy is modulated so that different phase voxels have different intensities. When forming multiple seed changes, the laser pulse energy remains nominally constant so that the seed changes have equal intensities within an acceptable range.

[0034]

[0033] Alternatively, if the shape of the laser beam is modulated, a single laser pulse can be used to obtain voxels with different birefringence properties.

[0035]

[0034] Alternatively or in addition to this, other parameters such as voxel position (e.g., distance from a reference location or reference axis) can also be modulated to encode the data.

[0036]

[0035] In the illustrated example, the voxel 120 is configured as a laminate of layers. The laminate has an upper layer 130, an intermediate layer 132, and a lower layer 134. Any number of layers of voxels can exist. For example, an optical data storage medium may contain 1 to 100 layers of voxels, or possibly even more.

[0037]

[0036] Voxels within a layer can be separated from each other laterally. The distance between adjacent voxels within a layer can be referred to as the pitch p. Generally, the closer the spacing between voxels, the greater the density of data that can be stored in the optical data storage medium per unit area. At least in the case of amplitude-modulated phase voxels, the voxels may be arranged in a superimposed arrangement, that is, they may partially overlap in space.

[0038]

[0037] The amount of data that can be stored in an optical data storage medium is determined in part by the number of bits that can be stored per voxel. The number of bits per voxel is determined by the number of distinct voxel states that can be reliably written to the transparent substrate. In order to allow data retrieval, these states must be distinguishable from one another after taking into account the effects of variations in the properties of the writing system.

[0039]

[0038] There are many possible factors that can cause variation. The variation may be spatial, temporal, or spatial-temporal.

[0040]

[0039] Sources illustrating spatial variations include focal aberration and component misalignment. Specifically, pulse supply efficiency often varies as a function of the position of the beam scanner in the writing system. Temporal variations include changes in laser intensity due to laser source warm-up, changes in the transmittance or reflectivity of optical components, and changes in component alignment due to the effects of thermal expansion or vibration.

[0041]

[0040] One method for mitigating fluctuations includes using a beam sampler to measure the intensity of light emitted by the laser source and adjusting the power output of the laser source based on the measured intensity. Consistent intensity measurements are difficult in the case of optical systems including scanners and / or polarization modulators because different laser pulses will reach different locations on the photodetector of the beam sampler. Therefore, the effectiveness of this method is somewhat limited.

[0042]

[0041] This specification provides a method for writing voxels onto a transparent substrate that allows for improved voxel reproducibility. In the method, light-induced emission from the substrate and / or light scattering by the substrate are monitored when forming the voxels. The energy of the laser pulse used to form the voxels is tuned based on the detected emission or scattering. By directly monitoring the effects on the substrate, it is possible to compensate for variations originating from any or all components of the writing system.

[0043]

[0042] The examples are described by specifically referring to the monitoring of photo-induced emission resulting from voxel formation, but instead of this, or in addition to this, light scattering resulting from voxel formation can also be monitored.

[0044]

[0043] Furthermore, the examples are described with reference to the formation of voxels in a transparent substrate. The use of a transparent substrate allows for the formation of multiple layers of voxels, which in turn allows for an increase in data density per unit volume. However, the methods described are equally applicable to the formation of voxels on a surface, such as the surface of an opaque substrate.

[0045]

[0044] The following describes an exemplary method with reference to Figure 2, which is a flowchart showing an overview of the method.

[0046]

[0045] In block 201, the first voxel is formed at a first position in the substrate using a first laser pulse.

[0047]

[0046] The substrate is most commonly a transparent substrate. The transparent substrate may have glass, glass-ceramic, or organic polymer. Specifically, the substrate may have glass such as fused silica.

[0048]

[0047] Alternatively, the substrate may be an opaque substrate.

[0049]

[0048] When the substrate is transparent, the first position may be located within the substrate or on its surface. When the substrate is opaque, the first position is located on the surface of the substrate.

[0050]

[0049] The first voxel may be a phase voxel. When it is required that multiple phase voxels be written to a transparent substrate, the laser pulse energy is modulated, and as a result, two or more voxels encoding different data symbols can be obtained.

[0051]

[0050] The first voxel may be a birefringent voxel. In such an implementation, the method can be applied when using a seed pulse to form a seed change and / or when applying one or more data pulses to a seed change to convert the seed change into a birefringent voxel.

[0052]

[0051] In block 202, light emitted or scattered by the transparent substrate as a result of the formation of the first voxel is detected. Specifically, this operation involves determining the intensity of the emitted or scattered light.

[0053]

[0052] Forming voxels in a transparent substrate using laser pulses results in photo-induced emission from the substrate material at the location of the voxels. Photo-induced emission may be, for example, the result of fluorescence, plasma formation, and / or blackbody emission. Light may be emitted over a given range of wavelengths, often in the range of 200 nm to 3000 nm. A color filter can be used to separate the light generated by photo-induced emission from the light emitted by the laser source.

[0054]

[0053] It was found that the amplitude of photo-induced emission correlates with the degree of modification to the substrate material. Generally, the amplitude of photo-induced emission increases with voxel intensity.

[0055]

[0054] In block 203, it is determined whether the detected light satisfies the predetermined constraints. For example, it may be determined whether the intensity of the emitted light falls within a predetermined range, in which case the predetermined range corresponds to the target voxel intensity.

[0056]

[0055] The operation of this block can be implemented using a computer.

[0057]

[0056] Subsequently, in block 204, the amplitude of the second laser pulse is adjusted in response to the determination that the detected light does not satisfy the predetermined constraints.

[0058]

[0057] The second laser pulse may be for forming a second voxel. The second voxel may be formed at a second position located within the same substrate as the first position. Alternatively, the second voxel may be formed in a different substrate.

[0059]

[0058] Alternatively, the second laser pulse may be a data pulse for converting the first voxel from seed change to birefringent voxel.

[0060]

[0059] The adjustment may be an increase or decrease in amplitude depending on whether the voxel formed in block 201 is excessively strong (typically corresponding to the detected light intensity that falls below the lower limit of a predetermined range) or excessively weak (typically corresponding to the detected light intensity that is above the upper limit of a predetermined range).

[0061]

[0060] The amplitude of light can be adjusted by adjusting the output power of the laser and / or adjusting the intensity modulator associated with the laser. The intensity modulator may have an intensity attenuator. Examples of intensity attenuators include an acoustic-optical deflector or a combination of an electro-optical modulator and a polarizer. Alternatively or in addition to this, the intensity modulator may have an amplifier.

[0062]

[0061] The implementation of the method shown in Figure 2 allows for the correction of repeatable systematic errors within the laser writing system.

[0063]

[0062] Repeatable systematic errors may include spatial variations. For example, voxel intensity may vary with position along the scanline, as shown in Figure 3A. Figure 3A shows an image of light emission resulting from the formation of a scanline of a voxel, along with a plot of emission amplitude measured as a function of position along the scanline.

[0064]

[0063] A typical laser writing system includes a beam scanner. The beam scanner is one potential source of spatial variation. This is because the laser pulses follow different optical paths through the system depending on the orientation of the beam scanner. For example, different laser pulses may have different path lengths and / or pass through different points on one or more optical components. Example 1 further provides a more detailed explanation of how a beam scanner can cause spatial variation by using an example of a polygon scanner below.

[0065]

[0064] Therefore, repeatable systematic errors may be associated with the position within the substrate that the laser writing system is targeting.

[0066]

[0065] Other operating parameters may contribute to repeatable systematic errors. This is shown in Figure 3B, which is a plot of the amplitude of photoinduced emission as a function of position along the scanline using laser pulses of different energies.

[0067]

[0066] Figure 3B shows that the systematic error in this example had a spatial component, and the peak in the emission amplitude curve is observed at almost the same position regardless of the laser pulse energy. However, in the illustrated example, the change is relatively more pronounced in the case of a relatively high-energy laser pulse.

[0068]

[0067] To allow for repeatable systematic error correction, a variation of the method in Figure 2 may involve the generation of a calibration model. The calibration model associates the state of the laser writing system with a correction to apply to the amplitude of the light output by the laser. The correction is then applied during the voxel writing process.

[0069]

[0068] The "state" has a value that describes at least one operating parameter of the laser writing system. It may be preferable that the state represents as many operating parameters as possible.

[0070]

[0069] For illustrative purposes, the state may have values ​​representing one or more of the following: laser power output, attenuator setting, amplifier setting, spatial light modulator setting, beam scanner orientation, movable mirror orientation, variable focus lens focus, and / or the position of the sample stage of the laser writing system.

[0071]

[0070] Specifically, the state may describe at least one operating parameter of the beam scanner of the laser writing system.

[0072]

[0071] Alternatively, or in addition to this, the state may describe the target location within the transparent substrate by using, for example, one or more coordinates.

[0073]

[0072] The state may further have values ​​for specific parameters that describe the operating environment of the laser writing system. Examples of specific parameters include ambient temperature, humidity, and similar ones.

[0074]

[0073] The following describes an exemplary method adapted to compensate for repeatable systematic errors such as spatial variations, with reference to Figures 4 and 5. Figure 4 is a flowchart illustrating the calibration phase of the method. Figure 5 is a flowchart illustrating the voxel writing phase.

[0075]

[0074] The calibration phase of the method generates a calibration model of the type described above. The method in this example includes steps that can be iteratively repeated for N different states of the laser writing system (where N≧1). For ease of explanation, an arbitrary counter i is used to identify the current iteration.

[0076]

[0075] Each iteration writes a voxel to a location in the substrate and collects data representing the photo-induced emission or light scattering resulting from the writing of the voxel. A calibration model is constructed using the collected data, associating different locations (corresponding to different states of the laser writing system) with corresponding adjustments to the laser pulse energy. A configuration model is then used to determine the adjustments to apply when writing further voxels.

[0077]

[0076] In block 401, the laser writing system is positioned in the i-th state. The i-th state is the calibration state.

[0078]

[0077] The i-th state may correspond to a specific target position for a voxel within a transparent substrate. The i-th state may further have a target voxel intensity.

[0079]

[0078] Specifically, the i-th state may be the state of the write head of the laser writing system. The write head has the optical components of the laser writing system. The optical components may be the most important source of repeatable systematic errors.

[0080]

[0079] The i-th state may describe the operating parameters of the mechanical components of the laser writing system (e.g., a movable sample stage or a movable support for the writing head). In some implementations, the operating parameters of the mechanical components can be omitted.

[0081]

[0080] Next, in blocks 402, 403, and 404, a voxel is formed in the transparent substrate by the laser writing system in the i-th state, light emitted or scattered by the transparent substrate resulting from the formation of the voxel is detected, and it is determined whether the detected light satisfies predetermined constraints. These operations can be described by blocks 201 to 203 in Figure 2.

[0082]

[0081] When it is determined that the detected light does not satisfy the predetermined constraints, in block 405 an expression for adjustment to the laser pulse energy is calculated. For example, when the amplitude of the photo-induced emission is less than a predetermined target value, the adjustment may be an increase in the laser pulse energy.

[0083]

[0082] The amplitude of the photo-induced emission is related to the intensity of the formed voxel. The adjustment can be determined based on this relationship. The relationship may be a predetermined empirical relationship, as described in Example 2, for example.

[0084]

[0083] The relationship can be learned by a machine learning model that spans two or more instances of this method. The machine learning model can be trained, for example, by gradient descent.

[0085]

[0084] The default empirical relationships can be used in combination with machine learning models. For example, the machine learning model can be used for fine-tuning the relationships.

[0086]

[0085] Subsequently, in block 406, the representation of the adjustment is stored in relation to the representation of the i-th state, and the state and adjustment may be embedded within the calibration model. The state and adjustment can be stored in related data structures such as lookup tables or dictionaries. The state and adjustment can be transmitted as input to a machine learning model.

[0087]

[0086] In block 407, the i-th iteration is completed. If it is necessary to investigate further states of the laser writing system, in block 408 a further state is selected, and the operations of blocks 401 to 406 are repeated for the further state.

[0088]

[0087] The method shown in Figure 4 can construct a calibration model that associates the state of the laser writing system with the corresponding adjustment to the laser pulse energy.

[0089]

[0088] Data collected from multiple instances of the method can be used. For example, an average adjustment over two or more instances of a given state may be calculated and used in a calibration model.

[0090]

[0089] In implementations where machine learning is used, the machine learning model can be trained by reinforcement learning. Specifically, a reward function can be used that calculates a relatively large modulo reward that more closely approaches the target value.

[0091]

[0090] The calibration model generated using the method shown in Figure 4 is used to determine adjustments to the laser pulse energy when writing data voxels. The method for writing data voxels using the calibration model will be described below with reference to Figure 5.

[0092]

[0091] The state of the laser writing system used to write data voxels will be referred to as the j-th state.

[0093]

[0092] In block 501, the method identifies that a voxel is written by a laser writing system in the j-th state, in which case the j-th state has a predetermined relationship to at least one of the N states sampled when the calibration model was generated according to Figure 4.

[0094]

[0093] This operation may involve identifying one or more of N states that are similar to the j-th state. The states may be represented as vectors, and the vector distance may be used as a measure of similarity. Different parameters may be assigned different weights when determining similarity. For example, a parameter describing the state of an optical component of a laser writing system (e.g., a beam scanner) may be assigned a greater weight than a parameter describing the state of a mechanical component (e.g., a sample stage).

[0095]

[0094] The adjustment can be calculated based on multiple calibration voxels. For example, block 501 may have the ability to identify two or more of the closest adjacent states of the j-th state out of N calibration states.

[0096]

[0095] As a more specific example, calibration data may be collected by writing voxels to a first substrate, and then data voxels may be written to a second substrate. When writing data voxels, it may be determined that the data voxels must be formed at a location in the second substrate that matches the location of one of the calibration voxels written to the first substrate.

[0097]

[0096] In another specific example, the location of a voxel is described by x, y, and z coordinates. The x position is controlled by positioning the sample stage of the laser writing system. The y position is controlled by the orientation of the beam scanner of the laser writing system. The z position is controlled by the focus of the objective lens of the laser writing system. It may be determined that the data voxel must be formed using orientation and focus (y and z positions) that match those of the calibration voxel. The adjustment can be selected based on the measured photo-induced emission for the calibration voxel. In this example, the difference in the positioning (x position) of the sample stage may be ignored, except that the motion of the sample stage provides an offset between the lines of voxels so that laser pulses are supplied to different parts of the substrate.

[0098]

[0097] To ensure that it is understood that these specific examples are illustrative and not limiting.

[0099]

[0098] After this, in block 502, the adjustment for the j-th state is determined based on the calibration model.

[0100]

[0099] When the calibration model is a lookup table, this operation may involve obtaining a calculated adjustment for one of the N calibration states that best matches the j-th state.

[0101]

[0100] When the calibration model is a machine learning model, the representation of the j-th state may be transmitted as input to the machine learning model, and the machine learning model may output the adjustment. The operations of blocks 501 and 502 can be combined in such an implementation.

[0102]

[0101] In block 503, the j-th voxel is written to the transparent substrate using a laser pulse. The adjustment determined in block 502 is applied, thereby correcting for repeatable systematic errors such as spatial variations.

[0103]

[0102] The method shown in Figure 5 can be repeated any number of times to write any number of voxels onto a transparent substrate.

[0104]

[0103] Voxels can encode data. In addition, voxels can also have voxels that are configured as reference marks, also called preambles.

[0105]

[0104] A reference mark is a group of voxels configured in a default pattern. Typically, the pattern is a one-dimensional ("1D") or two-dimensional ("2D") pattern, but a three-dimensional pattern may be used instead. The default pattern may be, for example, a Barker sequence or a Frank-Zadoff-Chu sequence. The size of the group is not particularly limited, as long as the number of voxels is large enough to allow the pattern to be identified when reading the optical data storage medium. An illustrative 2D reference mark is at least 4 voxels wide and 4 voxels high.

[0106]

[0105] The position of the voxels within the reference marks can be used as input to a processing / decoding method for recovering data from an optical data storage medium. These positional data allow the processing / decoding method to recover the data relatively easily.

[0107]

[0106] For example, when voxels are placed within a sector, a reference mark having a predetermined spatial relationship to the sector can be provided. For example, the reference mark can be placed along one or more edges of the sector or at the center of the sector. This allows the processing / decoding method to distinguish the sectors from one another relatively easily.

[0108]

[0107] Since the reference mark has a default pattern for the voxel, the processing / decoding method can use the reference mark to allow for correction of residual errors in the voxel characteristics.

[0109]

[0108] Another use case for reference marks is to allow fine-tuning of the calibration model. Additional calibration data can be collected when writing reference marks.

[0110]

[0109] Voxels may be arranged within sectors, in which case the sector is part of a layer. 2D reference marks may have a predetermined spatial relationship to the sectors.

[0111]

[0110] In addition to repeatable systematic errors, the laser writing system may experience errors that are not repeatable or are virtually random. The most prominent source of such errors is temporal variation. For example, the laser output power may change over time, and / or heating or cooling of optical components may result in changes in their properties.

[0112]

[0111] Temporal changes can be compensated for by using feedback control. As voxels are written, the light emission from the transparent substrate can be measured. When the emission intensity deviates from a predetermined target value, the amplitude of the laser pulse is adjusted to compensate for the deviation. Generally, when the emission intensity decreases, the amplitude of the laser pulse increases, and vice versa. Various feedback control methods are suitable. Examples include additive increase / multiplicative decrease and proportional-integral-derivative.

[0113]

[0112] The default target value may be based on an empirical measurement of voxel quality as a function of emission intensity. One metric for voxel quality is the maximum number of bits per voxel that can be encoded and successfully recovered.

[0114]

[0113] The emission intensity can be continuously monitored. Alternatively, the emission intensity may be sampled at an arbitrarily selected time interval.

[0115]

[0114] Figures 6A to 6C show the feedback control process.

[0116]

[0115] Figure 6A is a plot of the intensity of photo-induced emission during voxel formation as a function of laser pulse energy. The plot shows that the intensity of photo-induced emission increases with laser pulse energy, but these two are not necessarily directly proportional to each other. By measuring the intensity of the written voxels, the range of photo-induced emission values ​​corresponding to acceptable voxels has been empirically identified.

[0117]

[0116] Figure 6B shows the photo-induced emission intensity over time in the absence of feedback control. The emission intensity is found to deviate from the target range at certain points in time, which indicates the formation of voxels with intensities outside the acceptable range.

[0118]

[0117] Figure 6C shows the time-dependent photo-induced emission when feedback control is implemented. In this method, the laser pulse energy is adjusted to counteract the change in emission intensity over time. The emission intensity and, therefore, the voxel intensity are maintained within the target range.

[0119]

[0118] Hereinafter, with reference to Figure 7, an exemplary laser writing system 700 useful in the method described herein will be described. Figure 7 is a schematic block diagram of the laser writing system. The laser writing system may instead be referred to as a writing head.

[0120]

[0119] The illustrative laser writing system 700 includes a laser source 710, an amplitude modulator 720, a scanner 730, a relay optical system 740, a dichroic mirror 750, an objective lens 760, a sample stage 770, an imaging optical system 780, and a photodetector 790. The figure shows the system in use, in which the optical data storage medium 100 is mounted on the sample stage 770.

[0121]

[0120] The laser source 710 generates pulses of laser light and emits pulses along the optical path LP. Typically, the laser pulses have a period t p It is generated at a constant repetition rate having [a certain characteristic]. For illustrative purposes, the repetition rate may be at the level of 10 MHz. The laser light has a defined wavelength.

[0122]

[0121] The laser source 710 may be a femtosecond laser.

[0123]

[0122] The amplitude modulator 720 receives a laser pulse from the laser source and modulates the intensity of the laser pulse, thereby resulting in a modulated laser pulse. The amplitude modulator is adjustable so that a modulated laser pulse with a desired energy can be obtained. Where it is said that the amplitude of the laser pulse is adjustable, the adjustment can be implemented by controlling the amplitude modulator. The amplitude modulator may have an intensity attenuator and / or an amplifier.

[0124]

[0123] The intensity attenuator may include, for example, an acoustic-optical deflector, a liquid crystal modulator, a combination of an electro-optical modulator and a polarizer, or a combination of a pocket cell and a polarizer. Further examples of the intensity attenuator include a combination of a motor-driven stage and a variable neutral density filter, and a combination of a polarizer and a waveplate having a motor-driven stage.

[0125]

[0124] The scanner 730 receives the attenuated laser pulse from the amplitude modulator and deflects the attenuated laser pulse. The deflection angle is swept in a reciprocating manner so that a laser pulse moving along the scan line can be obtained. The sweep may be at a constant speed or at a speed that changes in a known manner.

[0126]

[0125] The scanner 730 may have a spinning polygon mirror, a resonant scanner, a microelectromechanical system ("MEMS") mirror, a galvanometer scanner, an electro-optical scanner, an acoustic-optical scanner, or something similar.

[0127]

[0126] The scanner guides the attenuated laser pulse to the relay optical system 740. The relay optical system 740 may have a scanning lens, a spherical lens, and a tube lens.

[0128]

[0127] After passing through the relay optical system 750, the attenuated laser pulse reaches the dichroic mirror 750. The dichroic mirror is configured to reflect light at the wavelength output by the laser light source 710. In deformations where it is necessary to detect light scattered by the substrate, it may be desirable for the dichroic mirror to transmit a portion of the light at the wavelength output by the laser source.

[0129]

[0128] The laser pulse reflected by the dichroic mirror then passes through the objective lens 760. The objective lens 760 focuses the laser pulse at a predetermined location within the optical data storage medium 100.

[0130]

[0129] The objective lens 760 may have one or more lenses. The objective lens 760 may have a variable depth of focus to allow control over the positioning of the voxels in the z direction.

[0131]

[0130] The optical data storage medium 100 is mounted on the sample stage 770. The sample stage 770 can move the optical data storage medium 100 in the y direction, for example.

[0132]

[0131] Voxels can be formed at any location within the optical data storage medium 760 based on the orientation of the scanner 730, the focal point of the objective lens 760, and the position of the sample stage 770.

[0133]

[0132] The formation of voxels within the optical data storage medium generates photo-induced emission of light from the optical data storage medium. This light has a different wavelength from that of the laser pulses generated by the laser source 710.

[0134]

[0133] At least a portion of the emitted light travels along the return path RP. In the illustrated example, the emitted light passes through the objective lens 760 and the dichroic mirror 750 and is focused onto the photodetector 790 by the imaging optical system 780.

[0135]

[0134] The imaging optical system 780 may have one or more lenses.

[0136]

[0135] The characteristics of the photodetector 790 are not particularly limited. The photodetector 790 may have, for example, a single photodiode, a photodiode array, a photomultiplier tube, an image sensor, or something similar thereto.

[0137]

[0136] Various changes can be made to the example system.

[0138]

[0137] As an alternative to providing a movable sample stage, the sample stage may be fixed, and at least the objective lens 760 may be mounted on an actuator that moves the objective lens in relation to the sample stage.

[0139]

[0138] The photodetector can be placed at any position where light generated by photo-induced emission as a result of voxel formation can be detected. For example, the photodetector can be placed below or to the side of the optical data storage medium. In such an implementation, the dichroic mirror 750 can be omitted. Instead, the laser writing system may include a color filter to prevent light having a wavelength emitted by the laser source from reaching the photodetector.

[0140]

[0139] The described example is suitable for writing phase voxels. To allow the formation of birefringent voxels, one modification may further include a modulation state generator that modulates the polarization of laser pulses supplied to a transparent substrate.

[0141]

[0140] The exemplary laser writing system supplies a single beam of laser pulses to a transparent substrate. Modulations allow for the supply of multiple beams simultaneously. For example, the laser writing system may further include a beam splitter that splits the laser pulse into two or more split pulses. Each split pulse can be transmitted via an individual amplitude modulator. Each amplitude modulator may be controlled independently. The modulated pulses can be combined in a common scanner 730 having different incident angles. Downstream of the scanner, the pulses may be guided through a relay optical system 740 to an objective lens 750 and focused at individual different locations within the substrate 100.

[0142]

[0141] The laser writing system described herein can be controlled by a controller to perform the method described herein.

[0143]

[0142] The controller may have a processor and a memory for storing computer executable instructions, the computer executable instructions causing the laser writing system to perform one or more operations as described herein when executed by the processor. The controller may have hardware circuitry for controlling the laser writing system to perform one or more operations as defined herein. The controller may have a combination of processor / memory and hardware circuitry.

[0144]

[0143] Figure 8 shows an illustrative block diagram of a controller 800.

[0145]

[0144] The controller 800 includes a data storage 820 and a processing unit 810 operably linked to an optional user terminal 830. The data storage 820 stores a computer program 822 for execution by the processing unit 810. When executed by the processing unit 810, the computer program 822 causes the controller 800 to perform the method described herein. The performance of the method may include communicating with and / or controlling one or more components of the laser writing system 700.

[0146]

[0145] The user terminal 830 may include a user input device and a display device.

[0147]

[0146] A user input device may have any one or more suitable input devices known in the art to receive input from a user. Examples of input devices include pointing devices such as a mouse, stylus, touchscreen, trackpad, and / or trackball. Other examples of input devices include a keyboard, a microphone when used with a speech recognition algorithm, and / or a video camera when used with a gesture recognition algorithm.

[0148]

[0147] Where the receipt of user input through a user input device is referred to in this specification, this may mean any one or more user input devices that constitute a user input device.

[0149]

[0148] User input devices may be useful to allow a user to specify data to be encoded and written to an optical data storage medium and / or to allow a user to specify parameters that describe the optical data storage medium, such as identifying the properties of a transparent substrate material.

[0150]

[0149] The display device may have any suitable form for outputting an image, such as a light-emitting diode (LED) screen, a liquid crystal display (LCD), a plasma screen, or a cathode ray tube (CRT). The display device may have a touchscreen and therefore may form at least part of a user input device. The touchscreen may allow input by contact with the user's finger and / or by the use of a stylus.

[0151]

[0150] Inclusion of a display device is optional. A display device is useful in cases where it is desirable to display human-readable output to the user.

[0152]

[0151] The processing unit 810 includes one or more processing units mounted in one or more dies, IC (integrated circuit) packages, and / or housings at one or more geographic sites.

[0153]

[0152] Each of the one or more processing units may have any suitable form known in the art, such as a general-purpose central processing unit (CPU), or a dedicated form of a coprocessor or accelerator processor such as a graphical processing unit (GPU), digital signal processor (DSP), etc. Each of the one or more processing units may have one or more cores.

[0154]

[0153] When it is stated that a computer program is executed on a processing unit, this may mean execution by any one or more processing units that make up the processing unit 810. Generally, when it is stated that a calculation or decision is performed, the calculation or decision may be performed using one or more processing units.

[0155]

[0154] The processing unit 810 typically further has working memory such as random access memory and / or one or more memory caches in one or more processing units.

[0156]

[0155] The data storage 820 has one or more memories implemented in one or more memory media within one or more housings at one or more geographic sites.

[0157]

[0156] Each of the one or more memory units may utilize any suitable storage medium known in the art, such as a magnetic storage medium like a hard disk drive or magnetic tape drive, or an electronic storage medium like a solid-state drive (SSD), flash memory, or electrically erasable programmable read-only memory (EEPROM), or an optical storage medium like an optical disk drive, or storage based on glass or memory crystal.

[0158]

[0157] Whenever in this specification it is stated that any item of data is stored in or within the data storage 810, this may mean that it is stored in any part of any one or more memory devices that make up the data storage 820.

[0159]

[0158] The processing unit 810 and the data storage 820 are operably linked. The processing unit and the data storage are configured such that the processing unit 810 has the ability to read data from at least a portion of the data storage 820 and write data to at least a portion of the data storage 820. The processing unit 810 can communicate with the data storage 820 over a local connection such as a physical data bus and / or over a network such as a local area network or the Internet. In the latter case, the network connection may be wired or wireless.

[0160] Example 1: Compensation for spatial changes

[0159] A two-dimensional array of voxels was written onto a glass substrate using a laser writing system of the type described with reference to Figure 7.

[0161]

[0160] The scanner of the laser writing system was a spinning polygon scanner with 24 faces. Laser pulses were focused along the scan lines in the glass only 24 times per rotation of the polygon scanner. The amplitude modulator of the system was a combination of a pocket cell and a linear polarizer.

[0162]

[0161] The scan line was directed along the y-axis. The glass substrate was moved in parallel along the x-axis. Photo-induced emission during voxel formation was monitored.

[0163]

[0162] Figure 9A shows the photo-induced emission data collected in the comparative example without applying adjustment to the laser pulse amplitude.

[0164]

[0163] Changes in emission intensity were observed in both the y and x directions. This change generated a change in voxel amplitude.

[0165]

[0164] The change in the x-direction is mainly generated by the difference in reflectivity between the faces of the polygon scanner ("inter-face change"), while the change in the y-direction is mainly generated by a combination of changes in reflectivity within the plane and differences in beam supply to the plane ("in-plane change").

[0166]

[0165] Figure 9B shows photoinduced emission data collected when an adjustment is applied to the laser pulse amplitude. An adjustment to the laser pulse intensity was applied to compensate for spatial variations in the performance of the laser writing system. As can be observed, within the region where the adjustment was applied (the corrected region in Figure 9B), the change in emission amplitude not only within each plane but also between planes was reduced. The adjustment enables the writing of voxels with a consistent amplitude.

[0167]

[0166] In this example, the adjustment was calculated using subsequent procedures.

[0168]

[0167] A target emission intensity I target that gives good voxel quality was selected.

[0169]

[0168] The emission intensity was measured for various different states of the laser writing system. More specifically, the emission intensity at different laser pulse energies was measured for each location within each plane of the polygon scanner.

[0170]

[0169] The target pulse energy E Target at which the emission intensity is equal to the target emission intensity I target (k,y) is determined for the k-th in-plane location of the polygon scanner by interpolating the measurements.

[0171]

[0170] The maximum acceptable energy spanning all positions of all planes is selected and denoted as E max .

[0172]

[0171] When writing a voxel, the amplitude of the laser light is adjusted by the transmittance E target (k,y) / E max , where E target (k,y) is the target energy at the k-th in-plane location y of the polygon scanner currently being used. If the transmittance is greater than 1, a transmittance of 1 is used.

[0173] Example 2: Compensation for changes over time

[0172] Voxels were written to a transparent substrate using a laser writing system described with reference to Example 1, by using laser pulses of varying amplitude. The intensity of photo-induced emission was measured when forming the voxels. Voxel quality was measured by determining the number of bits per voxel that can be written and subsequently recovered ("BPV"). The results are shown in Figure 10.

[0174]

[0173] Based on measurements, it was found that the highest quality voxels were obtained when the photo-induced emission had a relative amplitude in the range of 60 to 90. A target amplitude of 75 was selected.

[0175]

[0174] As described with reference to Example 1, additional voxels were written onto the transparent substrate while measuring the light-induced emission intensity and applying compensation for spatial heterogeneity. Voxel quality was measured. The results are shown in Figure 11. In Figure 11, the sector position is a surrogate measurement for time because the sample stage was moved in parallel at a constant speed while writing the voxels.

[0176]

[0175] We found that the emission amplitude and voxel quality drifted over time, resulting in inter-sector variations. The amplitude of photo-induced emission decreased and then gradually increased. The number of bits per voxel changed over time.

[0177]

[0176] The experiment was repeated, and this time, feedback control was further applied. After every 100 data sectors, the energy of the laser pulse was adjusted to change the amplitude of the photo-induced emission toward the target value. This was found to be effective in significantly reducing the temporal drift of voxel quality, as shown by the data in Figure 12.

[0178] Example 3: Reinforcement Learning

[0177] The calibration model may be a machine learning model. Specifically, the machine learning model can be trained by reinforcement learning (RL).

[0179]

[0178] In RL, a software agent interacts with the environment, takes actions to investigate the environment, and adapts its behavior based on the feedback (or "rewards") it receives from the environment, in order to maximize its total reward (i.e., to encourage intended behavior).

[0180]

[0179] Reinforcement learning problems are typically modeled using the following three parts: 1) State space 2) Action space, and, 3) Reward function

[0181]

[0180] Both the correction of repeatable systematic errors, described with reference to Figures 4 and 5, and the correction of temporal changes, described with reference to Figures 6A to 6C, can be addressed by the same machine learning model. This can be achieved by "live" training of the machine learning model, i.e., training of the model as data is written, in a state where the behavior of the writing system is controlled by the machine learning model.

[0182]

[0181] The following describes one example machine learning model. Other models can also be used, as can be understood.

[0183]

[0182] This example concerns a calibration model that addresses spatial variations within a laser writing system, including a polygon scanner.

[0184]

[0183] The state space can be visualized as a table, as shown in Figure 13. The rows of the table correspond to each of the N faces of the polygon scanner. The columns represent different scan lines. The model may consider all scan lines or only sample groups of scan lines. Each entry (or "bucket") in the table holds a representation of the adjustment with respect to the laser energy.

[0185]

[0184] The action space can be represented by tuples, each identifying a bucket and the possible laser energy values ​​that can be used for that bucket. NOOP ("no action") is permitted, meaning the software agent can determine that it will not make any changes to the bucket.

[0186]

[0185] The reward signal is the mean square (RMS) error between the measured photo-induced emission amplitude and a predetermined target amplitude. The smaller the RMS error, the larger the reward value.

[0187]

[0186] The system starts in a uniform state (i.e., each bucket contains the same energy value).

[0188]

[0187] The policy network takes the current state as input and suggests an action to be taken. The action may be to adjust the laser energy value for the bucket.

[0189]

[0188] The voxel is written using the suggested modulation. Photo-induced emission is measured. The reward signal is calculated based on the measurement.

[0190]

[0189] After a batch of suggested actions, the policy network will be updated.

[0191]

[0190] Training can be performed periodically or continuously to improve the calibration model or to update the calibration model as a property of changes in components over time.

[0192]

[0191] It should be understood that the embodiments described above are for illustrative purposes only.

[0193]

[0192] More generally, according to one embodiment disclosed herein, a method is provided for writing voxels onto a substrate. The method includes: forming a first voxel at a first location in the substrate using a first laser pulse; detecting light emitted or scattered by the substrate as a result of forming the first voxel; determining whether the detected light satisfies predetermined constraints; and adjusting the amplitude of a second laser pulse if the detected light does not satisfy the predetermined constraints. It has been found that changes occur in the photo-induced emission and / or light scattering properties of the substrate when forming voxels, and that this is related to voxel quality.

[0194]

[0193] The first voxel may be a phase voxel, a seed change for a birefringent voxel, or a birefringent voxel.

[0195]

[0194] The second laser pulse can form a second voxel. The second voxel can be formed in the same substrate as the first voxel or in a different substrate.

[0196]

[0195] The substrate may be a transparent substrate. This allows for the formation of multiple layers of voxels.

[0197]

[0196] Detection of light emitted or scattered by the substrate may involve determining the intensity of the detected light. In such an implementation, the amplitude adjustment of the second laser pulse may involve adjusting the amplitude based on the intensity of the detected light.

[0198]

[0197] Detection may involve detecting photo-induced emission from the substrate.

[0199]

[0198] The method can be used to generate a calibration model for compensation of repeatable systematic errors.

[0200]

[0199] For example, the method may further include calculating a value representing adjustment to the amplitude of a second laser pulse in response to a determination that the detected light does not satisfy a predetermined constraint, and storing the value representing the adjustment in relation to a value representing the state of the laser writing system that formed the first voxel. The calculation may be performed using one or more processors, and the storage may be stored in a memory unit.

[0201]

[0200] The method may involve writing a plurality of first voxels at a plurality of different locations within a transparent substrate. For each of the plurality of first voxels, the method may further include calculating a value representing adjustment to the amplitude of a second laser pulse and storing the value representing the adjustment in relation to a value representing the state of the laser writing system that formed the voxel.

[0202]

[0201] The method can consequently yield a calibration model that associates the adjustment value with the position within the transparent substrate.

[0203]

[0202] Adjusting the amplitude of the second laser pulse may include identifying that further voxels are to be written using a second state of a laser writing system having a predetermined relationship to the first state, obtaining a value representing the adjustment in response, and applying the adjustment indicated by the value when forming further voxels at the second position.

[0204]

[0203] The default relationship is that the first and second positions share common values ​​for the operating parameters of the optical components. For example, the optical component may be a beam scanner, and the common value for the operating parameters is the common orientation of the beam scanner.

[0205]

[0204] The method can be used to compensate for temporal changes. For example, the method may include using a further laser pulse after a predetermined time interval to form further voxels at further locations in the substrate, detecting further light emitted or scattered by the substrate as a result of the formation of further voxels, and determining whether the detected further light satisfies predetermined constraints. If the detected further light does not satisfy the predetermined constraints, the amplitude of the third laser pulse can be adjusted.

[0206]

[0205] The third laser pulse can form a voxel. The voxel may be a phase voxel, a seed change for a birefringent voxel, or a birefringent voxel. The voxel can be formed in the same substrate as the first voxel or in a different substrate.

[0207]

[0206] Adjusting the amplitude of the laser pulse can be done by using a machine learning model to calculate an encoded value for adjusting the amplitude of the light output by the laser based on the detected light and the values ​​of related parameters. The machine learning model can be trained by reinforcement learning.

[0208]

[0207] The method can be parallelized so that two or more instances of the method are performed simultaneously. For example, the formation of a first voxel can consist of forming two or more first voxels simultaneously. An instance of the detection and determination step can be performed for each first voxel. Similarly, for example, two or more second laser pulses can be generated in parallel to write two or more second voxels onto a substrate.

[0209]

[0208] Another embodiment provides a computer program product having instructions performed on a non-temporary computer-readable medium, which, when executed by one or more processors operably linked to a laser writing system for writing voxels to a transparent storage medium, causes the laser writing system to perform the method defined herein. As understood, the method can be implemented using computer control. The determination step can be implemented in software or the like.

[0210]

[0209] In another embodiment, a laser writing system useful for implementing the method is provided. The system may include a laser source configured to emit laser pulses along an optical path; a first amplitude modulator configured to modulate the amplitude of the laser pulses to result in modulated laser pulses; a movable optical element configured to guide the modulated laser pulses to a controllable position in a transparent substrate; a sample stage configured to hold the substrate in the optical path downstream of the movable optical element and the amplitude modulator; a detector configured to detect light emitted or scattered by the substrate as a result of the formation of voxels in the substrate by the modulated laser pulses; and a controller configured to control the system to perform the method defined herein.

[0211]

[0210] As can be understood, the methods implemented by the controller may include any of the various selective steps described herein in any suitable combination.

[0212]

[0211] The controller may have at least one processor and at least one memory. The at least one memory may store instructions that cause the processor to control the system to perform one or more operations of the method when executed by the at least one processor. Alternatively, or in addition to this, the controller may have dedicated hardware circuitry.

[0213]

[0212] The system can be configured to allow parallelization of the method. For example, the system may further have a beam splitter for splitting a laser pulse into at least a first split laser pulse and a second split laser pulse, the first amplitude modulator can be configured to modulate the amplitude of the first split laser pulse, thereby resulting in a first modulated laser pulse. The system may further have a second amplitude modulator configured to modulate the amplitude of the second split laser pulse, thereby resulting in a second modulated laser pulse. The system may further have a combination optical element downstream of the first and second amplitude modulators and upstream of the movable optical element, in which case the combination optical element is configured to guide the first and second modulated laser pulses to the movable optical element at individual angles.

[0214]

[0213] The detector can be configured to measure the intensity of light emitted or scattered by the substrate as a result of the formation of voxels within the substrate.

[0215]

[0214] The detector can be configured to detect light-induced emission from a transparent substrate.

[0216]

[0215] The movable optical element may have, for example, a scanner such as a polygon scanner.

[0217]

[0216] This disclosure provides the following terms: Clause 1: Method, The first laser pulse is used to form a first voxel at a first position within the substrate, To detect light emitted or scattered by the substrate as a result of forming the first voxel, To determine whether the detected light satisfies the predetermined constraints, In response to the determination that the detected light does not satisfy the predetermined constraints, the amplitude of the second laser pulse is adjusted, Methods that include... Clause 2: The substrate is a transparent substrate, as described in Clause 1. Clause 3: The method according to Clause 1 or Clause 2, comprising determining the intensity of the detected light, for the detection of light emitted or scattered by the substrate. Clause 4: The method according to Clause 3, wherein the amplitude of the second laser pulse is adjusted based on the detected light intensity. Clause 5: Detection is the method according to any one of Clauses 1 to 4, comprising detecting photo-induced emission from a substrate. Clause 6: In response to the determination that the detected light does not satisfy the predetermined constraints, To calculate a value that represents the adjustment for the amplitude of the second laser pulse, In relation to a value representing the state of the laser writing system that formed the first voxel, a value representing the adjustment is stored, It further includes, In this case, the amplitude of the second laser pulse is adjusted as follows: Identifying that further voxels must be written using a second state of a laser writing system having a predetermined relationship to the first state (501), Based on the stored values, the adjustment for the second state is determined, and as a result, the adjusted second state is brought about (502), The method described in any one of clauses 1 to 5, including the method described in any one of clauses 1 to 5. Clause 7: The default relationship is the method described in Clause 6, where the first and second positions share common values ​​for the operating parameters of the optical components. Clause 8: The optical component is a beam scanner, and the common value of the operating parameter is the common orientation of the beam scanner, as described in Clause 7. Article 9: Writing multiple voxels at multiple different locations within a transparent substrate, For each individual voxel of a plurality of voxels, perform the method defined in claim 5 or claim 6, thereby obtaining a calibration model that associates the adjustment value with a position within the transparent substrate, The method described in any one of clauses 6 to 8, including the method described in any one of clauses 6 to 8. Clause 10: After a predetermined time interval, Further laser pulses are used to form additional voxels at further locations within the substrate, To detect further light emitted or scattered by the substrate as a result of the formation of further voxels, To determine whether the detected additional light satisfies the predetermined constraints, In response to the determination that the detected additional light does not satisfy the predetermined constraints, the amplitude of the third laser pulse is adjusted, The method described in any one of clauses 1 to 9, further including the method described in any one of clauses 1 to 9. Clause 11: The method according to any one of Clauses 1 to 10, wherein the amplitude adjustment of the second laser pulse is performed by using a machine learning model to calculate a value that encodes the adjustment to the amplitude of the light output by the laser based on the detected light and the values ​​of associated parameters. Clause 12: The machine learning model is trained by reinforcement learning as described in Clause 11. Clause 13: The method according to any one of Clauses 1 to 12, further comprising forming a further voxel simultaneously with the first voxel or the second voxel. Clause 14: A computer program product having instructions executed on a non-temporary computer-readable medium, wherein the instructions, when executed by one or more processors operably linked to a laser writing system having a pulsed laser source, an amplitude modulator configured to receive laser pulses from the pulsed laser source, and a photodetector, cause the laser writing system to perform the method defined in any prior claim. Clause 15: A system, A pulsed laser source, A first amplitude modulator located downstream of a pulsed laser source along an optical path, the first amplitude modulator configured to modulate the amplitude of a laser pulse from the pulsed laser source, thereby producing a modulated laser pulse; A beam scanner positioned downstream of the first amplitude modulator on the optical path, A sample stage for holding a substrate on the optical path downstream of a movable optical element and an amplitude modulator, A detector for detecting light emitted or scattered by a substrate as a result of voxel formation within the substrate, A controller for controlling the system to execute the method, It has, The method is, The first laser pulse is used to form a first voxel at a first position within the substrate, To detect light emitted or scattered by the substrate as a result of forming the first voxel, To determine whether the detected light satisfies the predetermined constraints, In response to the determination that the detected light does not satisfy the predetermined constraints, the amplitude of the second laser pulse is adjusted, A system that has Clause 16: The controller is the system described in Clause 15, having at least one processor and at least one memory. Article 17: A beam splitter positioned between the pulsed laser source and the first amplitude modulator, A second amplitude modulator is positioned on a parallel optical path to the first amplitude modulator, A combination optical element downstream of first and second amplitude modulators and upstream of a movable optical element, the combination optical element is configured to guide the first and second modulated laser pulses to the movable optical element at individual angles, The system described in Clause 15 or Clause 16, further comprising the above. Clause 18: Method, In response to the determination that the detected light does not satisfy the predetermined constraints, To calculate a value that represents the adjustment for the amplitude of the second laser pulse, In relation to a value representing the state of the laser writing system that formed the first voxel, a value representing the adjustment is stored, This further includes, in this case, the amplitude of the second laser pulse is adjusted, Identifying that further voxels require writing using a second state of a laser writing system having a predetermined relationship to the state, In response to this, obtain a value that encodes the adjustment, Applying adjustments when forming further voxels at the second position, The systems described in clauses 15-17, including those mentioned above. Clause 19: The system described in any one of Clauses 15-18, which modulates the amplitude of the second laser pulse, including using a machine learning model to calculate a value that encodes the adjustment to the amplitude of the light output by the laser, based on the detected light and the values ​​of associated parameters. Clause 20: Method, After a predetermined time interval, Further laser pulses are used to form additional voxels at further locations within the substrate, To detect further light emitted or scattered by the substrate as a result of forming additional voxels, To determine whether the detected additional light satisfies the predetermined constraints, In response to the determination that the detected light does not satisfy the predetermined constraints, the amplitude of the third laser pulse is adjusted, The system described in any one of clauses 15-20, including further details. Clause 21: The system according to any one of Clauses 15 to 20, wherein the detector is configured to measure the intensity of light emitted or scattered by the substrate as a result of the formation of voxels within the substrate. Clause 22: The system according to any one of Clauses 15 to 21, wherein the detector is configured to detect light-induced emission from a transparent substrate. Clause 23: A movable optical element is a system described in any one of Clauses 15 to 22, having a polygon scanner. Clause 24: The system described in any one of Clauses 15-23, which includes adjusting the amplitude of light output by a laser based on the detected light intensity.

[0218]

[0217] Other variations or use cases of the disclosed techniques may become apparent to those skilled in the art at the time the disclosure in this Specification is granted. The scope of this disclosure is limited not by the embodiments described, but only by the appended claims.

Claims

1. It is a method, (201) Forming a first voxel (120) at a first position within the substrate (100) using a first laser pulse, Detecting (202) light emitted or scattered by the substrate (100) as a result of the formation of the first voxel (120), (203) Determining whether the detected light satisfies the predetermined constraints, In response to the determination that the detected light does not satisfy the predetermined constraints, the amplitude of the second laser pulse is adjusted (204), A method of having.

2. The method according to claim 1, wherein the substrate (120) is a transparent substrate.

3. The method according to claim 1 or claim 2, wherein detecting (202) the light emitted or scattered by the substrate (120) is determined to determine the intensity of the detected light.

4. The method according to claim 3, wherein adjusting the amplitude of the second laser pulse (204) is to adjust the amplitude based on the intensity of the detected light.

5. The method according to any one of claims 1 to 4, wherein the detection (202) comprises detecting photo-induced emission from the substrate.

6. In response to the determination that the detected light does not satisfy the predetermined constraints, (404) Calculate a value that represents the adjustment of the amplitude of the second laser pulse, In relation to a value representing the state of the laser writing system that formed the first voxel, the value representing the adjustment is stored (405), It further includes, Adjusting the amplitude of the second laser pulse is Identifying that further voxels must be written using a second state of the laser writing system having a predetermined relationship to the first state (501), Based on the stored values, determine the adjustment for the second state that results in the adjusted second state (502), The method according to any one of claims 1 to 5, comprising:

7. The method according to claim 6, wherein the predetermined relationship is that the first and second positions share a common value for the operating parameters of the optical components.

8. The method according to claim 7, wherein the optical component is a beam splitter, and the common value of the operating parameter is the common orientation of the beam splitter.

9. Writing multiple voxels at multiple different locations within the transparent substrate (120), For each of the plurality of voxels, the method described in claim 6 is performed, resulting in a calibration model that associates the adjustment value with its position within the transparent substrate. The method according to any one of claims 6 to 8, comprising:

10. After a predetermined time interval, Further laser pulses are used to form additional voxels at further locations within the substrate, To detect further light emitted or scattered by the substrate as a result of forming the further voxels, Determining whether the detected additional light satisfies the predetermined constraints, In response to the determination that the detected additional light does not satisfy the predetermined constraints, the amplitude of the third laser pulse is adjusted. The method according to any one of claims 1 to 9, further comprising:

11. Adjusting the amplitude of the second laser pulse is By using a machine learning model, a value is calculated that encodes the adjustment of the amplitude of the light output by the laser, based on the detected light and the values ​​of the associated parameters. The method according to any one of claims 1 to 10, comprising:

12. The method according to claim 11, wherein the machine learning model is trained by reinforcement learning.

13. The method according to any one of claims 1 to 12, further comprising forming a further voxel simultaneously with the first voxel or the second voxel.

14. A computer program product having instructions (822) executed on a computer-readable medium (820), wherein the instructions are executed by one or more processors (810) operably linked to a laser writing system (700) having a pulsed laser source (710), an amplitude modulator (720) arranged to receive laser pulses from the pulsed laser source (710), and a photodetector (790), and the laser writing system (700) A computer program product that causes the computer program to perform the method described in any one of claims 1 to 13.

15. System (700), A pulsed laser source (710), A first amplitude modulator (720) located downstream of the pulsed laser source (710) along the optical path (LP), A beam scanner (730) is positioned downstream of the first amplitude modulator (720) on the optical path, A sample stage (770) for holding a substrate (100) in the optical path (LP) downstream of the beam scanner (730) and the first amplitude modulator (720), A detector (790) for detecting light emitted or scattered by the substrate (110) as a result of the formation of voxels (120) within the substrate (100), A controller (800) for controlling the system (700) to perform the method described in any one of claims 1 to 13, A system that has

16. The system according to claim 15, wherein the controller (800) comprises at least one processor (810) and at least one memory (820).

17. A beam splitter is positioned between the pulsed laser source (710) and the first amplitude modulator (720), A second amplitude modulator is arranged on a parallel optical path to the first amplitude modulator, A combination optical element located downstream of the first and second amplitude modulators and upstream of the movable optical element, The system according to claim 15 or 16, further comprising, during use, the combination optical element guides the first and second modulated laser pulses to the movable optical element at individual angles.

18. The aforementioned method, In response to the determination that the detected light does not satisfy the predetermined constraints, (404) Calculate a value that represents the adjustment of the amplitude of the second laser pulse, In relation to a value representing the state of the laser writing system that formed the first voxel, the value representing the adjustment is stored (405), The further includes adjusting the amplitude of the second laser pulse, Identifying that further voxels must be written using a second state of the laser writing system having a predetermined relationship to the aforementioned state (501), Based on the stored values, determine the adjustment for the second state that will result in the adjusted second state (502), The system according to any one of claims 15 to 17, including the system described in any one of claims 15 to 17.

19. Adjusting the amplitude of the second laser pulse is By using a machine learning model, a value is calculated that encodes the adjustment of the amplitude of the light output by the laser, based on the detected light and the values ​​of the associated parameters. The system according to any one of claims 15 to 18, including the system described in any one of claims 15 to 18.

20. The aforementioned method, After a predetermined time interval, Further laser pulses are used to form additional voxels at further locations within the substrate (100), To detect further light emitted or scattered by the substrate (100) as a result of the formation of the further voxels, Determining whether the detected additional light satisfies the predetermined constraints, The amplitude of the third laser pulse is adjusted when the detected additional light does not satisfy the predetermined constraints. The system according to any one of claims 15 to 18, further comprising:

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