Holographic storage

Abstract

A holographic data storage system comprises an emitter system, a holographic recording medium and an input waveguide network formed by one or more multimode optical waveguides. The holographic recording medium has a plurality of recording regions, each recording region being optically coupled to a corresponding out-coupling region of a plurality of out-coupling regions of the input waveguide network, the holographic data storage system being arranged to durably write data of an input light beam received at any one out-coupling region to the corresponding recording region. A controller is coupled to at least one of the emitter system and at least one controllable steering element of the input waveguide network and controls at least one optical property of the input light beam or at least one steering element in order to direct the input light beam from the in-coupling region to any selected out-coupling region of the plurality of out-coupling regions. Similar waveguide networks are provided to carry reference light beams and output light beams.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to holographic storage. BACKGROUND

[0002] Holographic storage is a form of computer storage in which information is recorded in a photosensitive holographic recording medium by exposing the medium to an optical interference pattern. For example, a region (subvolume) of the medium can be exposed to an optical interference pattern resulting from interference between a reference beam and an input beam having a data set embedded therein. The beams can be laser beams generated using a single laser and a beam splitter, for example. A spatial light modulator (SLM) can be used to embed the data set into the input beam, for example an image encoding the data set can be spatially modulated into the input beam. For the avoidance of doubt, the terms "light", "optical" and the like herein are not limited to visible light. Holographic storage can be implemented using infrared or ultraviolet beams within the invisible portions of the electromagnetic spectrum, for example.

[0003] With sufficient beam power and exposure time, the optical interference pattern causes a persistent state change within the subvolume (at this point, the interference pattern is referred to herein as recording or writing the subvolume). The altered state of the subvolume enables the data set originally embedded in the input beam to be recovered from an output beam that substantially matches the input beam, in the sense that a substantially matching reference beam and the subvolume interact to produce the output beam when the subvolume is later exposed to the substantially matching reference beam (this can be referred to herein as reading the recorded pattern).

[0004] A single interference pattern can encode a large number (e.g. millions) of bits rather than storing a single bit as a discrete unit. For example, the data set can be a million-pixel image embedded in the input beam. Furthermore, by exploiting the sensitivity of a particular form of holographic recording medium to small changes in the angle of the reference beam, many such patterns (e.g. hundreds or thousands) can be recorded into the same subvolume. For such a medium, when an interference pattern is created using a reference beam at a given angle, the recorded pattern can only be read using a reference beam that closely matches the reference beam originally used to create it. This effect can be exploited to record multiple patterns (encoding different data sets) into the same subvolume at different reference beam angles. In theory, the data storage capacity is limited only by the wavelength of the beam, with red light potentially reaching hundreds of megabytes per cubic millimetre and ultraviolet potentially reaching tens of gigabytes per cubic millimetre. In practice, there can be other limiting factors, but there is still great potential for high-density data storage. SUMMARY

[0005] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all of the disadvantages mentioned herein.

[0006] Holographic data storage / retrieval systems providing spatial multiplexing of holographic data on a holographic recording medium typically require some form of mechanical actuator(s) to enable controlled mechanical movement of the holographic medium, in the sense of writing / reading different physical sub-volumes of the medium, to move the medium relative to e.g. the system's read / write head from which the input beam and reference beam are launched and at which the output beam is detected, or to move the read / write head relative to the medium. This in turn limits the speed of data writing / reading, as well as the scalability and reliability of such systems. Aspects of the technology disclosed herein reduce or eliminate the need for such mechanical movement.

[0007] A first aspect herein provides a holographic data storage system comprising a transmitter system, at least one holographic recording medium, and an input waveguide network formed by one or more multimode optical waveguides for simultaneously carrying a plurality of propagation modes. The transmitter system is configured to launch an input beam in the form of a multimode optical signal encoding a plurality of image pixels as a plurality of propagation modes of the input beam propagating in different directions. The input waveguide network has a plurality of out-coupling regions and an in-coupling region for receiving the input beam from the transmitter system. The at least one holographic recording medium has a plurality of recording regions, each recording region being optically coupled to a corresponding out-coupling region of the plurality of out-coupling regions of the input waveguide network, the holographic data storage system being arranged to durably and simultaneously write the plurality of image pixels encoded in the input beam received at any one of the out-coupling regions to the corresponding recording region. A controller is coupled to at least one of the transmitter system and at least one controllable steering element of the input waveguide network, the controller being configured to control at least one optical property of the input beam or the at least one steering element so as to direct the input beam from the in-coupling region to any one of the plurality of out-coupling regions. With this arrangement, different ones of the plurality of recording regions can be written from the same in-coupling region by changing the at least one optical property or controlling the at least one steering element to direct the input beam to different ones of the plurality of out-coupling regions while the plurality of out-coupling regions of the multimode optical waveguide network remain in fixed positions relative to the corresponding recording regions of the holographic recording medium.

[0008] Thus, in a first aspect, spatial multiplexing on a holographic recording medium is achieved for a write option without requiring any mechanical movement of the emitter system, the holographic recording medium or the input waveguide network. Where the directing element(s) are controllable, the input light beams can be controlled to be directed along different paths through the input waveguide network to different regions of the medium; where the optical properties of the light beams are varied, the input waveguide network can or can not be active (i.e. it can be passive or active), but in either case the input waveguide network responds to the optical property(ies) of the input light beam(s) such that such variation likewise causes the input light beams to be directed along different paths.

[0009] A second aspect herein provides a holographic data retrieval system comprising an emitter system, at least one detector array for detecting images, at least one holographic recording medium and a reference waveguide network formed of one or more multimode optical waveguides. The reference waveguide network has an in-coupling region for receiving a reference light beam from the emitter system and a plurality of out-coupling regions optically coupled to respective recording regions of the at least one holographic recording medium. A controller is coupled to the emitter system and at least one controllable directing element of the reference network and is configured to control at least one optical property of the reference light beam or the at least one directing element to direct the reference light beam to any selected recording region to be read, thereby creating an output light beam via interaction of the reference light beam with a pattern stored at that recording region, for reception at the detector array to recover data of the stored pattern from the output light beam. With this arrangement, different recording regions of a plurality of recording regions can be read using the same emitter system by varying the at least one optical property of the reference light beam or controlling the at least one directing element of the reference network while the plurality of out-coupling regions of the multimode optical waveguide network remain in fixed positions relative to the corresponding recording regions of the holographic recording medium. The controller is configured to vary an angle of the reference light beam to read different patterns stored at the same selected recording region, the multimode optical waveguides of the reference waveguide network being for carrying the reference light beam at any one of a plurality of possible angles.

[0010] A third aspect of the present document provides a holographic data retrieval system comprising at least one detector array, at least one holographic recording medium and an output waveguide network formed by one or more multimode optical waveguides. The output waveguide network has an out-coupling region for providing an output beam to the detector array, and a plurality of in-coupling regions optically coupled to respective recording regions of the at least one holographic recording medium. A controller is configured to cause the output beam to be directed through the output waveguide network from any selected recording region via an in-coupling region optically coupled to the recording region to the out-coupling region for reception at the detector array by controlling at least one controllable steering element of the output waveguide network or at least one optical property of a reference beam used to generate the output beam. With this arrangement, by varying the at least one optical property or controlling the at least one steering element while the plurality of out-coupling regions of the output waveguide network remain in fixed positions relative to the corresponding recording regions of the holographic recording medium, it is possible to read from different ones of the plurality of recording regions using the same detector array without the need to move the detector array or the holographic recording medium. The holographic data retrieval system is configured to cause the output beam to be created by causing the reference beam to interact with a pattern stored at the selected recording region, the stored pattern encoding a plurality of image pixels which are encoded in the output beam as a plurality of propagating modes which propagate simultaneously in different directions through the output waveguide network.

[0011] In the second and third aspects, spatial multiplexing on the holographic recording medium is achieved without the need for any mechanical movement of the emitter system / detector array, the holographic recording medium or the reference waveguide network / output waveguide network. Where the steering element(s) are controllable, the steering of the reference beam / output beam along different paths through the reference waveguide network / output waveguide network to and from different regions of the medium can be controlled; where the optical property(ies) of the beam are varied, the reference waveguide network / output waveguide network can or can not be active (i.e. it can be passive or active), but in either case the reference waveguide network / output waveguide network responds to the variation in the optical property(ies) of the reference beam / output beam such that the variations similarly cause the reference beam / output beam to be steered along different paths. BRIEF DESCRIPTION OF DRAWINGS

[0012] For a better understanding of the present disclosure, and to show how embodiments of the present disclosure can be implemented, reference is made to the following drawings, which are presented by way of example only, and in which:

[0013] FIG. 1A and 1B shows a schematic perspective view of a holographic recording medium;

[0014] FIG. 2AA schematic perspective view of a holographic storage system is shown, including a set of waveguides that can be used to guide a beam of light to / from different sub-rolls of a holographic recording medium to provide spatial multiplexing on the medium.

[0015] FIG. 2B , FIG. 2C and FIG. 2D The plan view and alternating side view of the system during the write interval are shown respectively;

[0016] FIG. 2E-FIG. 2G The plan view and alternating side views are shown during the reading interval;

[0017] FIG. 3A-FIG. 3D A schematic side view of an active light guide in various configurations is shown; FIG. 3E and FIG. 3F A planar (cross-sectional) view of the active light guide tube is shown;

[0018] FIG. 4A and FIG. 4B Alternating side views of (partial) optical waveguide networks are shown;

[0019] FIG. 5 A schematic diagram illustrating an example of a multi-waveguide network for multiplexing multiple segments of holographic storage medium is shown.

[0020] FIG. 6A An example of a transmitting system for providing an input beam and a reference beam in a holographic storage system is shown; FIG. 6B A variant of the emission system with simplified optics is shown;

[0021] FIG. 7 An example of a data retrieval system is shown that uses spatial coherent detection to measure the optical field of the output beam and signal processing to mitigate waveguide distortion in the measured optical field.

[0022] FIG. 8 This diagram illustrates the functional block diagram representing the functions performed within the holographic storage system.

[0023] FIG. 9 An alternative holographic storage system is shown, in which at least one waveguide network is used for spatial multiplexing on a two-dimensional holographic recording medium.

[0024] FIG. 10A and FIG. 10B This demonstrates how spatial multiplexing can be achieved using passive guiding elements, where spatial multiplexing is achieved by modulating the characteristics of (multiple) beams;

[0025] FIG. 11A and FIG. 11B Optical guides showing passive filters with different frequency responses; and

[0026] FIG. 12 An example of a waveguide network with three tiers is shown. DETAILED DESCRIPTION

[0027] To achieve spatial multiplexing on one or more holographic storage media, in a manner that reduces or eliminates the need for mechanical motion, one can use “active” light pipes, “passive” light pipes, or a combination of active and passive light pipes. Note that the terms “waveguide” and “light pipe” are used interchangeably herein.

[0028] An “active light pipe” refers to a waveguide with one or more active switching elements or other guiding elements attached to the surface of the waveguide or within the body of the waveguide, which in turn can be configured (i.e., have variable optical properties) to achieve “one-to-many” optical transmission, i.e., in the case where light is guided from a first surface region to one of multiple possible second surface regions (in this case, the first surface region serves as an incoupling region, and the second regions serve as outcoupling regions), or “many-to-one” optical transmission, i.e., in the case where light can be guided from any one of the second surface regions (now serving as incoupling regions) to the same first surface region (now serving as an outcoupling region). The term “passive light pipe” refers to a light pipe with guiding elements that have different optical sensitivities (e.g., different wavelength and / or polarization sensitivities), such that a similar effect can be achieved by changing the optical property(s) or beam (e.g., changing its wavelength, polarization, etc., to cause it to be guided along a different route by guiding elements with different wavelength / polarization responses, etc.; e.g., using a tunable laser). The term “passive light pipe” is simply a convenient label, consistent with the fact that in this case the guiding elements need not be active—however, having different optical sensitivities (e.g., different wavelength and / or polarization sensitivities, etc.) can be used in this case (i.e., the guiding elements can be active and have different optical sensitivities).

[0029] Digital images (or data encoded as digital images) can be propagated as beams along active or passive light pipes. The guiding elements of an active light pipe can be individually controlled to either transmit or reflect an incident beam of light.

[0030] Many such light pipes (active, passive, or a combination of both types) can be combined into various geometrical shapes to create a switching network that can be used to direct beams and images to one of many addressable locations in one or more spatial dimensions. For example, an input to the light pipes can be created using a spatial light modulator (SLM), and the output can be read on a CCD (charge-coupled device). A combination of optical and computational techniques can be used to correct for phase interference and noise, including machine learning techniques, which would involve learning one or more signal processing parameters from training data. Particular embodiments use coherent detection in conjunction with such techniques to provide more effective waveguide distortion mitigation.

[0031] Compared to the kind of optical switches and optical fibers traditionally used for optical data communication, the described embodiments use optical conduits capable of transmitting entire images at once. This takes advantage of the high resolution of today's available optical equipment, such as SLMs and digital cameras. These devices have millions of pixels, can encode and decode gigabytes of data. This allows for high bandwidth transmission even at modest switching rates of the SLMs, cameras and active optical conduit elements (in case of active optical conduits) or beam(s) optical properties (in case of passive optical conduits). Furthermore, applications such as holographic storage require interference between multiple beams, at least one of which is modulated with an image. In holographic storage, using active optical conduits, the beams and images can be controlled efficiently at any desired location in the holographic storage medium and made to interfere. As mentioned before, using passive optical conduits can achieve the benefit of simplicity, where the switches are applied at the transmitter stage.

[0032] The optical conduits described below are "multi-mode" waveguides in the sense that they have physical dimensions sufficient to support a range of "modes" (i.e. spatial paths through the waveguide for a given channel, e.g. corresponding to different directions of propagation). This is in contrast to simple single-mode optical waveguides, such as the thin optical fibers used in fiber-optic systems, which aim to confine the light entering the fiber to a substantially single mode of propagation. Single-mode optical waveguides can only transmit data using amplitude, phase or frequency modulation, whereas multi-mode optical waveguides allow for the transmission of more data (e.g. entire images with potentially millions of pixels) through angular variations within the waveguide. In other words, multi-mode waveguides provide greater bandwidth by increasing the angular and / or spatial diversity, by providing multiple light paths from the transmitter to the detector for any given channel (different paths corresponding to different modes of propagation).

[0033] Another aspect disclosed herein is a holographic data storage system that uses one or more waveguide networks to spatially multiplex (i.e. read from / write to different sub-volumes of the medium) on a holographic recording medium without requiring any relative mechanical movement between the medium and the waveguide network(s). Examples of such a system are described below, which use active and / or passive optical conduits. In the described examples, multi-mode waveguides can be used to carry entire digital images to / from the holographic recording medium at once, or to carry a reference beam at one of multiple possible angles.

[0034] Active optical conduits:

[0035] FIG. 3A-FIG. 3D A schematic side view is shown of an example form of a waveguide 300 having a particular physical structure. As will be appreciated, this is merely one example of a suitable physical structure that can provide the required optical configurability. Further examples are considered below.

[0036] The waveguide 300 is shown as having at least a first surface region 300-0 and a plurality of active switches in the form of switchable Bragg gratings (SBGs), which can be on-surface or bulk-embedded. In this example, two such SBGs 300-1, 300-2 are shown on a first surface 300-S of the waveguide 300, but it will be appreciated that a greater number of SBGs can be provided at suitable locations of the waveguide 300 and / or surface 300-S embedded within the body of the waveguide 300. Each SBG 300-1, 300-2 can be individually controlled to change its reflective / transmissive properties, to thereby transmit or reflect an incident light beam. The SBGs 300-1, 300-2 form respective surface regions of the waveguide 300, at which light can enter (in-couple) or exit (out-couple) the waveguide 300, depending on how the waveguide 300 is being used.

[0037] The first surface region 300-0 is an end region of the waveguide 300 from which a first side surface 300-S1 of the waveguide extends along the axis 301 of the waveguide 300.

[0038] FIG. 3E and FIG. 3F Each shows a cross-sectional view of the waveguide 300, which in this example can be seen to have a rectangular shape in cross-section, with four side surfaces 300-S1, 300-S2, 300-S3, 300-S4 extending along the axis 301 of the waveguide 300. In this example, as shown in the figures, the SBGs 300-1, 300-2 are both located along the first side surface 300-S1, although in general such SBGs can be attached to multiple surfaces of the waveguide 300, depending on the application.

[0039] The SBGs 300-1, 300-2 are located along the first side surface 300-S1 of the waveguide, at increasingly greater distances from the first region 300-0, with the first SBG 300-1 being located closest to the first region 300-0.

[0040] FIG. 3A 、 FIG. 3B and FIG. 3EA "one-to-many" use case is depicted in which the first surface region 300-0 is used as an in-coupling region, while the second surface regions of the SBGs 300-1, 300-2 are used as out-coupling regions. As an example, FIG. 3 shows a first light ray 304 coupling into the waveguide 300 via the in-coupling region 300-0. In this example, the first surface region 300-0 is angled with respect to the side surfaces 300-S1,..., 300-S4 such that the first light ray 304 can pass through the first surface region 300-0 into the waveguide body 300 at an angle sufficient to achieve total internal reflection at each of the side surfaces 300-1,..., 300-4 within the waveguide 300.

[0041] Each of the SBGs 300-1, 300-2 can be configured to change it between a reflective state and a transmissive state. FIG. 3A A configuration is shown in which the first SBG 300-1 is in the reflective state, causing the first light ray 304 to reflect therefrom back into the waveguide 300 and be guided along the waveguide 300 until reaching the second SBG 300-2. The SBG 300-2 is shown as being in the transmissive state, causing the first light ray 304 to diffract out of the waveguide 300 through the second SBG 300-2, thereby coupling out of the waveguide 300-2 through the surface region of the second SBG 300. This configuration of the SBGs 300-1, 300-2 creates a "channel" through the waveguide 300 between the first surface region 300-0 and the surface region of the second SBG 300-2.

[0042] In contrast, FIG. 3B The first SBG 300-1 is shown as being in the transmissive state. Thus, when the first light ray 304 reaches the first SBG 300-1, it instead diffracts out of the waveguide 300 through the first SBG 300-1, thereby coupling out of the waveguide 300 through the surface region of the first SBG 300-1. This configuration creates a channel through the waveguide 300 between the first surface region 300-0 and the surface region of the first SBG 300-1.

[0043] In this way, the first light ray 304 can be guided from the first region 300-0 through the waveguide 300 and out of the waveguide 300 at the surface region of either of the SBGs 300-1, 300-2. Although described with respect to only two SBGs 300-1, 300-2 for simplicity, it will be appreciated that the same principles can be applied to a larger number of SBGs.

[0044] FIG. 3E An illustration is shown of how the first light ray 304 propagates via TIR from some or all of the side surfaces 300-S1,..., 300-S4 depending on the angle of the first light ray 304 when viewed in cross-section.

[0045] AsFIG. 3C , FIG. 3D and FIG. 3F As shown, a one-to-many optical transmission using the depicted waveguide 300 is equally feasible.

[0046] FIG. 3C The same SBG configuration as FIG. 3A is shown. The only difference is how the waveguide 300 is used: now a second light ray 308 is shown incident on the second SBG 300-2 from an external source (not shown). When the second SBG is in the transmissive state, the second light ray 308 is diffracted into the waveguide 300 by the second SBG (now providing in-coupling at its surface area), which is guided from the second SBG through the waveguide 300 to the first surface area 300-0 (now an out-coupling area); this includes a reflection from the first SBG 300-1, which is now in the reflective state. The reflective state of the first SBG 300-1 prevents the light ray 308 from exiting the waveguide via the first SBG 300-1. Furthermore, any external light ray 309 that happens to be incident on the first SBG 300-1 will be substantially reflected off it, and thus not enter the waveguide 300.

[0047] FIG. 3D The same configuration as FIG. 3B is shown, but now the second light ray 308 is incident on the first SBG 300-1 from an external source. In case the first SBG 300-1 is in the transmissive state, the third light ray 310 enters the waveguide 300 by diffraction into it, and is guided to the first surface area 300-0.

[0048] FIG. 3F A cross-section showing how the second light ray 308 propagates within the waveguide 300 is shown, and the same description as FIG. 3E applies, but with the light ray directions reversed.

[0049] The above description assumes perfect reflectivity / transmissivity of the SBGs in the reflective / transmissive state. As will be understood, this is not an absolute requirement in practice, and the system will have some tolerance for more general imperfections in the SBGs 300-1, 300-2 and the waveguide 300. Suitable signal processing techniques for compensating for distortions introduced within the waveguide 300 are described later.

[0050] Although described as separate elements, the SBGs 300-1, 300-2 can in fact be separate, independently controllable regions of a single large SBG extending over all or most of the first side surface 300-S1.

[0051] SBGs are just one possible form of active switching element. For example, for polarized light beams, the same effect can be achieved using controllable polarization filters attached to the surface of the waveguide 300 or embedded within the waveguide body. SBGs and controllable polarization filters are examples of non-mechanical active switches, which can change the optical properties of the waveguide 300 through non-mechanical effects. Other examples of steering elements include controllable mirrors such as micro-mirror devices or other micro-electro-mechanical systems (MEMs), the latter being examples of mechanical steering elements.

[0052] When using polarization filters as steering elements, the SBGs 300-1, 300-2 can be replaced with passive diffractive elements, with the polarization filters used to controllably steer the light beams in and out of the passive diffractive elements as needed, without the need to reconfigure the diffractive elements.

[0053] Note that even if the steering elements themselves are mechanical, this still avoids the need for mechanical movement of the entire waveguide 300.

[0054] Active optical conduit network

[0055] Here, a “waveguide network” can take the form of a single waveguide or a network of multiple waveguides coupled to each other. A waveguide network with multiple active optical conduits has particular advantages for flexible optical data transmission.

[0056] FIG. 4A And FIG. 4B An alternating side view of a (partial) waveguide network comprising a first waveguide 400 and a second waveguide 420 is shown. The second waveguide 420 has a first surface region 400-0 located adjacent to and aligned with a corresponding surface region of the first waveguide 400 for receiving a light beam from or directing a light beam to the second waveguide 420 through the first surface region 400-0. By way of example only, a light ray 404 is shown propagating through the first waveguide 400 to a corresponding surface region of the first waveguide 400 adjacent to the first surface region 400-0 of the second waveguide 420. The light ray 404 is out-coupled from the first waveguide 400 via an SBG 400-1 connected to the adjacent surface region of the first waveguide 400 and enters the second waveguide 420 via the first surface region 400-0. From there, it can be steered in a one-to-many fashion to any of a plurality of SBGs 420-1, 420-2 of the second waveguide 420. The same arrangement can be used to steer a light beam in the other direction from the second waveguide 420 to the first waveguide 400 in a many-to-one fashion, with the light ray directions reversed.

[0057] Although this example considers two mutually coupled waveguides 400, 402, these principles can be applied to a larger number of mutually coupled waveguides to allow flexible data routing through a waveguide network.

[0058] More generally, surface areas of the medium can be optically coupled to corresponding surface areas of the waveguide in other ways, e.g., through an air interface or one or more other optical components (which themselves can or can not provide active or passive switching functionality).

[0059] Holographic storage

[0060] Applications of active light pipes in holographic storage will now be described.

[0061] FIG. 1A and FIG. 1B A schematic perspective view of a holographic recording medium 102 is shown, which is a relatively thick volume of a photosensitive material capable of durably storing an optical pattern as a "hologram" (which can be referred to simply as the medium 102 for brevity) embodied within the holographic recording medium 102. The hologram is created by exposing a sub-volume 110 (region) of the medium 102 to an optical pattern that causes a durable state change within that sub-volume 110. The hologram is created with the sub-volume 110 by the state change recording the optical pattern onto the medium 102, so that the optical pattern can be reproduced therefrom later. The hologram is durable in that once created, the medium 102 does not require electrical power to maintain it. The composition and structure of the medium 102 can be such that the hologram, once created, cannot be erased, thus providing a form of "write once, read many" (WORM) storage, or can be such that the hologram can be erased and replaced (but still exist unless and until they are erased).

[0062] A single hologram can record an optical pattern that encodes a very large number (e.g., millions) of bits, allowing a large amount of data to be written / read to / from the holographic recording medium 102 in parallel (simultaneously). Another benefit of holographic storage is that many holograms can be written to the same sub-volume 110 of the holographic recording medium 102, which greatly increases the data storage capacity per unit volume of the holographic recording medium 102.

[0063] In more detail, FIG. 1AIt is shown how, in order to write a data set into the medium 102, the input beam 104 and the reference beam 106 are directed into the sub-volume 110 through the first side surface 102-4 and the second side surface 102-6, respectively, of the medium 102. This results in an optical pattern in the form of an interference pattern caused by the interference between the input beam 104 and the reference beam 106. Assuming that the beams 104, 106 have sufficient power and that the sub-volume 110 is exposed for a sufficient duration, the pattern resulting from the interference of the beams 104, 106 will be recorded permanently as a hologram within the sub-volume 110. The data set is embedded in the input beam 104 and can be recovered from the resulting hologram as described below. In this way, the encoded data set is written into the sub-volume 110. In the example below, the data set is encoded as a digital image, which is then embedded into the input beam 104 by spatial modulation.

[0064] As FIG. 1B shown, in order to read data from the sub-volume 110, a matching reference beam 116 is directed into the sub-volume 110 through the second side surface 102-6 of the medium 102, where it interacts with the hologram to create an output beam 108 that will substantially match the input beam 104 used to write the hologram to the extent that the embedded data can be recovered from the output beam 108. The output beam 108 propagates out of the sub-volume 110 via the third side surface 102-8 of the medium 102.

[0065] The reference beam 116 used to read the data substantially matches the reference beam 106 used to write the data initially, and in particular is oriented at an angle (or more generally, direction) that very closely matches the angle of the original reference beam 106. This is because the ability to read the hologram (i.e., to produce an output beam 108 from which data can be recovered from the hologram) is highly sensitive to the angular difference between the reference beams 106, 116 used to write and read the hologram, respectively. It is this sensitivity that can be exploited to record multiple holograms within the same sub-volume 110— each hologram created using a different reference beam angle, and it is possible to create two different holograms with only slight differences in the reference beam angle. In this way, a large number (e.g., hundreds or thousands) of holograms can be written into the same sub-volume 110, each encoding a large number (e.g., millions) of bits.

[0066] FIG. 2AA schematic perspective view of an example holographic storage system 200 incorporating certain principles of the present disclosure is shown. In this particular example, three separate waveguides 204, 206 and 208 are used to carry the input beam 104, the reference beams 116, 126 and the output beam 118, and can be referred to as the input waveguide 204, the reference waveguide 206 and the output waveguide 208 respectively. As mentioned above, the terms "optical waveguide" and "light pipe" are used interchangeably herein. Each of the waveguides 204, 206 and 208 provides spatial multiplexing in the sense that it can direct signals to (in the case of the input and reference waveguides 204, 206) or from (in the case of the output waveguide 208) any one of a plurality of sub-volumes within the holographic recording medium 102. This provides spatial multiplexing across the volume of the holographic recording medium 102 without requiring any mechanical movement of any of the waveguides 204, 206, 208 relative to the holographic recording medium 102. In order to avoid the need for such mechanical movement, a directing element is located on or within each waveguide 204, 206, 208 and is configurable to change the optical properties of the waveguide 204, 206, 208 in order to direct signals to or from different sub-volumes of the medium 102. That is, different channels are created within the waveguides 204, 206, 208 as required. In this particular example, the directing element takes the form of an active optical switching element (a switch). The switch can take a number of forms. In this example, the switch takes the form of an SBG located in a different surface region of the waveguide 204, 206, 208, the overall arrangement being identical to that of FIG. 3A-FIG. 3E That is, each of the waveguides 204, 206 and 208 takes the form of an active light pipe, and each of the waveguides 204, 206, 208 has the same general physical structure as the waveguide 300 of FIG. 3A-FIG. 3E

[0067] Each waveguide 204, 206, 208 is arranged so that its first surface (i.e. the surface on which its SBG is located) is adjacent to a different side surface of the medium 102 so that its SBG extends along that side surface of the medium 102. The first and second SBGs of each waveguide 204, 206, 208 are denoted by reference numerals 204-1, 204-2; 206-1, 206-2; and 208-1, 208-2 respectively, all of which can be configured in the manner described above. Further SBGs are depicted without reference numerals, and the number of SBGs can be selected to accommodate a holographic recording medium 102 of any size. For brevity, the following description refers to the first and second SBGs of each waveguide 204, 206, 208, but it will be appreciated that the description applies to a greater number of SBGs.

[0068] FIG. 2B to FIG. 2D ​The diagram illustrates how input waveguide 204 and reference waveguide 206 can be used to write data to medium 102 in a one-to-many manner. FIG. 2B A schematic plan view of system 200 is shown, and FIG. 2C and FIG. 2D Alternating side views are shown, in which input waveguide 204 and reference waveguide 206 are visible. Ray 404 is used to guide input beam 104 to any of a plurality of sub-rolls of medium 102 via either SBG 204-1, 204-2 of input waveguide 204 in the manner described above. Reference waveguide 406 is configured to simultaneously guide reference beam 106 to the same sub-roll in order to create the desired interference pattern to be written into that sub-roll. In the depicted example, both input waveguide 204 and reference 206 are currently configured to guide input beam 104 and reference beam 106 to sub-roll 110 via second SBG 204-2, 206-2 of each waveguide 204, 206.

[0069] FIG. 2E to FIG. 2G The reference waveguide 206 and the output waveguide 208 are shown to be used to read data from the medium 102. FIG. 2E It's a floor plan. FIG. 2F and FIG. 2G Alternating side views are shown, in which reference waveguide 204 and output waveguide 206 are visible. The usage of reference waveguide 206 is similar to... FIG. 2B to FIG. 2D The process is exactly the same as depicted in the previous section, but now the reference beam 116 is directed to any sub-roll from which the hologram is to be read—in this case, sub-roll 110. The output waveguide 208 is used in a one-to-many manner to guide the resulting output beam 108 from sub-roll 110 and to use it for subsequent detection.

[0070] For example, each subvolume 110 may have a height and width of a few millimeters measured along any side surface, which is typically sufficient to store millions of pixels per data “page” (e.g., multiplexed angle) – in this case, the subvolume is sufficient to store (megapixels) * (#multiplexed angle).

[0071] The guiding elements of the input waveguide 204 and reference waveguide 206 (SBG in this example) are configured as needed to provide a path from the beam source (emission system) to the output beam 108 to be read for the input beam 104 and reference beams 106, 116. For the SBG, this is the case where the SBG is set to either transmission or reflection mode to create the path as needed. Similarly, the guiding element of the output waveguide 208 (also an SBG in this example) is similarly configured to provide a path from the read output beam 108 to the detector. For additional context, this will be referred to below. FIG. 5 The multi-waveguide network depicted in the diagram is described in more detail. However, regarding specific examples...FIG. 5 The principles described are more generally applicable to other waveguide network topologies, both simpler networks (e.g. a single waveguide) or more complex waveguide networks.

[0072] As noted above, this allows spatial multiplexing to be performed on the medium 102 without any mechanical movement of the medium 102 relative to the waveguides 204, 206, 208. This is true regardless of the form that the directing elements take (as noted above, the directing elements themselves can be mechanical or non-mechanical).

[0073] Holographic storage using a multi-waveguide network

[0074] FIG. 5 An example of a holographic storage system incorporating a multi-waveguide network of the type shown in Figure 4 is shown.

[0075] The input waveguide network is shown as comprising a first input light pipe 203 (a "parent" waveguide), to which a plurality of second input light pipes 204A, 204B ( "child" waveguides) are coupled. The input beam 104 from the emitter system 504 is coupled into the first input light pipe 203 via its in-coupling region, and can be guided from there into any of the second input waveguides 204A, 204B.

[0076] The reference waveguide network is shown as comprising a first reference waveguide 205, to which a plurality of second reference waveguides 206A, 206B are coupled. The reference beams 106, 116 from the emitter system 504 are similarly coupled into the first reference waveguide 205, and can be guided into any of the second reference waveguides 206A, 206B.

[0077] The output waveguide network is shown as comprising a first output waveguide 207, to which a plurality of second output waveguides 208A, 208B are coupled.

[0078] The arrangement depicted allows beams to be directed to / from different sub-volumes of the plurality of holographic storage medium segments 102A, 102B.

[0079] Although FIG. 5 Input beam 104, reference beams 106, 116 and output beam 108 are shown, but it will be appreciated that the sub-volumes will typically be written to and read from at different times in the manner described above with reference to FIG. 2A-FIG. 2G

[0080] ​The first set of second waveguides 204A, 204B, 204C (each of the input, reference, and output) are located around holographic storage medium segment 102A (the first medium), and the second set of second waveguides 204B, 206B, 208B are located around the second segment 102B (the second medium), each medium having the same overall arrangement as FIG. 2A-FIG. 2G Thus, the input beam 104 and the reference beams 106, 116 can be directed to any sub-volume of any holographic storage medium segment 102A, 102B by first directing these beams to the desired second waveguides of the input network and the reference network, respectively, and then to the desired sub-volume of the medium segment of the adjacent desired waveguide.

[0081] The output waveguide network can be used to direct the output beam 108 from any sub-volume of any holographic storage medium segment 102A, 102B from the applicable second output waveguide 208A, 208B to the first output waveguide 207, and from there to the detector 508 via the out-coupling region of the first output waveguide 207. To read from a particular sub-volume, the SBGs are configured to provide a channel from that sub-volume to the detector; thus, in this case, SBGs 204A-2 and 207-1 are set to the transmissive state, and the other SBGs of the output waveguide network are set to the reflective state as needed in order to provide a channel for the output beam 108 to the detector 508 (e.g., in this case, SBG 207-2 of the first output waveguide 207 is set to the reflective state to prevent the input beam 104 from propagating into waveguide 207-2). The other SBGs of the output waveguide network can be set to the reflective state to the extent needed to prevent any unwanted light transmission, i.e., from other areas of the same holographic storage medium segment 102A or from "leakage" of the different medium segment(s) 102B (e.g., in this example, SBG 204A-1, which is proximate to the sub-volume being read, is shown set to the reflective state to prevent unwanted leakage).

[0082] Although in the above example three separate waveguide networks are used for the input beam 104, the reference beams 106, 116, and the output beam 108, this is not necessary. For example, the same waveguide network can be used to carry the input beam 104 and the reference beams 106, 116 and / or the same waveguide network can be used to carry the input beam 104 and the output beam 108 and / or the same waveguide network waveguides can be used to carry the output beam 108 and the input beam 104. It is generally expected that having three separate networks will provide the best performance, but there are still fully viable implementations that use only one or two waveguide networks.

[0083] Although not depicted in any of the figures, a fourth waveguide network can be used to carry light beams to the remaining side surfaces of the media segments 102A, 102B. For example, the fourth network can be used to carry erase light beams to the desired sub-volumes, suitable for erasing at least holograms therefrom (in the case of erasable holographic storage).

[0084] FIG. 9 An alternative physical structure is shown, in which a single "board" of holographic medium 102 is used instead of FIG. 5 a single segment 102A, 102B. The input waveguide network is described, which has substantially the same physical configuration, but the second input waveguides 204A, 204B are now configured to direct input light beams 104 to different sub-volumes of the same board 102. Whereas in FIG. 5 each second input waveguide 204A, 204B provides multiplexing in a single dimension along the length of a different single holographic storage medium segment 102A, 102B, in FIG. 9 the second waveguides 204A, 204B provide two-dimensional spatial multiplexing on the board of holographic medium 102 (each waveguide provides one-dimensional multiplexing separately, but as a whole on the board 102 provides 2D multiplexing).

[0085] FIG. 9 The system of

[0086] FIG. 9 Another benefit of using waveguides is illustrated. Certain existing holographic storage systems use light beams that propagate in free space, with individually placed optical components (reflectors, beam splitters, etc.) to direct the light beams. Such systems are not easily scalable - in fact, they are only suitable for a lab-type environment. This is because the individual components must be placed and calibrated individually. In contrast, using waveguides can more easily manufacture and deploy a "stand-alone" system. FIG. 9 The system of FIG. 9 is similar in some respects to an "off-the-shelf" solid-state storage device - not only is the system free of moving parts, but it can be constructed and provided as a complete unit, significantly reducing the time and effort required to deploy it (e.g., in a data center). Because using multi-mode waveguides allows for reading / writing entire images at once, and allows for angular multiplexing over multiple reference beam angles, this greatly improves the scalability of holographic storage, and does so without impacting bandwidth or storage capacity.

[0087] Data encoding

[0088] FIG. 6AAn example of an emitter system 504 that provides both the input beam 104 and the reference beam 106 is shown. The input beam is an extended, spatially modulated laser beam. A laser 600 emits a coherent, narrow laser beam, which is split using a beam splitter 602.

[0089] A portion of the beam from the beam splitter 602 is used as the reference beam 106. In this example, a controllable reference beam control element 612 is used to divert the reference beam 106 at a desired angle. By changing the angle of the reference beam 106 before it is coupled into the reference waveguide 206, different holograms can be written to / read from the same sub-volume of the medium in the manner described above.

[0090] Alternatively or in addition to beam angle multiplexing, multiple patterns can be stored to / read from the same sub-volume with different phases of the reference beam 106, 116 (phase multiplexing). Thus, a logical address can correspond to a specific reference beam angle and / or phase characteristic. All the descriptions regarding reference beam angle modulation apply equally to phase modulation.

[0091] Another portion of the beam from the beam splitter 602 is expanded using a beam expander 604, the expanded beam passes through a spatial light modulator (SLM) 606. An encoder 610 receives a data set to be encoded and encodes it into a digital image which is then modulated into the expanded beam by the SLM 606. A coupling-in optic - in this case, the position of the in-coupling optic 608 is such that the plane of the SLM 606 lies substantially in the focal plane of the in-coupling optic 608 - is used to separate the expanded beam into different propagation modes; in this example, the modes correspond to unique directions of propagation, each mode now corresponding to a specific point in the plane of the SLM 606. The different propagation modes are coupled into the input waveguide 204, through which they are guided in the manner described above. Using the in-coupling optic 608, the data is "angle encoded" within the input beam, in the sense that a point within the digital image substantially corresponds to a unique direction of propagation, i.e. a unique propagation mode of the input beam 104. This is analogous to a light ray from a distant object being considered as being infinite. FIG. 6A The angle encoded input beam 104 is one example of a "multi-mode" optical signal, multiple propagation modes (i.e. components propagating in different directions), and this arrangement provides a form of angular diversity.

[0092] Note that the term "multi-mode" does not necessarily imply the use of such an in-coupling optic 608, nor does it require that each image point uniquely corresponds to a given direction of propagation. That is, multi-mode does not necessarily imply a one-to-one correspondence between propagation modes and image points / data points. For example, FIG. 6BAnother possible transmitter system is shown, in which the spatially modulated light beam is directly coupled to the input waveguide 204. In this case, there are still multiple modes (i.e. for any given channel, multiple spatial paths through the waveguide), but there is no one-to-one correspondence between the direction of propagation and the image point, and there can be no one-to-one correspondence between the image / data point and the mode. This provides a form of spatial diversity based on MIMO (Multiple Input Multiple Output) transmission forms, through the multiple pixels of the SLM 606 and the detector array of the spatially coherent detector 508.

[0093] Data decoding

[0094] FIG. 7 A detector 508 is shown for measuring the optical field of the output light beam 108. In contrast to conventional “direct detection”, the detector 508 comprises an array of pixels (or more generally, detector elements), each pixel configured to measure the amplitude and phase (rather than just the intensity) of the optical field at that pixel location. These can be measured, for example, using a local oscillator 712 of the detector 508. The array of pixels is thus able to measure the phase and amplitude variations of the optical field over time and space, and thus provide an analogue or digital representation of the measured optical field. In this case, the measured optical field is that of the output light beam 108 guided through the output waveguide 208 to the spatially coherent detector 508.

[0095] Although only a single array is depicted, in practice there can be multiple physical arrays cooperating as a single “logical array”. For example, this logical array can be divided into two physical cameras.

[0096] The physical detector array can take the form of a single camera (each detector element being a pixel or set of pixels of the camera) or multiple cameras. In the extreme case, each detector element can be a separate camera, in which case the logical detector array can be divided into a very large number of physical detectors.

[0097] As noted, the path from a particular in-coupling region of a beam into the waveguide network to a particular out-coupling region of it from the waveguide network (those regions can be in the same or different waveguides) can be referred to herein as a "channel". As previously noted, in a multi-mode waveguide network, a single channel will comprise multiple spatial paths. The output beam 108 will be guided through a particular channel of the output waveguide network, i.e. from its particular in-coupling region to the out-coupling region of the output waveguide 208. Moreover, it will be generated by a hologram created using the input beams that were guided from the in-coupling regions of the input waveguide network to their particular out-coupling regions. The hologram will be created and read using a reference beam that is similarly guided through a particular channel by the reference waveguide network. The input beams 104, the reference beams 106, 116 and the output beam 108 are all susceptible to distortions within the relevant waveguide network that is specific to the channel through which they are guided. The signal processing component 700 applies analog and / or digital signal processing to the representation of the measured field to compensate for such distortions; it does so using the channel model associated with the sub-volume from which it is currently reading (i.e. the sub-volume that produced the output beam 108). The channel model associated with a particular sub-volume models not only the channel through which the output beam 108 was guided to the detector 508, but also the channel volume through which the input beams 104 were guided to that sub-volume for writing the hologram and the channels through which the reference beams 106, 116 were guided to that sub-volume for writing / reading the hologram.

[0098] For example, each channel model can take the form of a transfer function (modeling the channel directly) or an inverse transfer function (modeling the channel in terms of an approximate inverse of the channel). Note that the transfer function is applied to the representation of the measured optical field, i.e. its measured phase and amplitude at different spatial points, and not just the intensity of the light. Spatially coherent detection provides a greater scope for eliminating or reducing such channel distortions, with the aim of recovering the original digital image sufficiently accurately to facilitate the decoder 704 decoding the encoded data from the recovered image.

[0099] For example, the signal processing component 700 can use a combination of optical and computational techniques to correct for phase disturbances and noise, which can for example include machine learning techniques.

[0100] Although described in the context of holographic storage, the use of such a signal processing component 700 in combination with spatially coherent detection is not limited in this respect and can be applied to other contexts, such as optical communications or optical computing, or any other context in which a received output beam is susceptible to distortions introduced in one or more waveguide networks.

[0101] FIG. 7 It is shown that the arrangement is arranged to substantially invert FIG. 6Bout-coupling optics of the in-coupling optics 608, i.e. resolving each propagating mode to essentially a single point in the plane of the detector 508. Again, this is not essential and can be omitted for FIG. 6B for alternative emission systems, the out-coupling optics can be omitted.

[0102] Although not depicted in FIG. 6A or FIG. 6B Before the digital image is modulated into the input beam 104, some level of pre-processing can be applied to the digital image. This can reduce the degree of compensation required on the detector side. Even with such pre-processing, some amount of detector-side processing can be applied to account for different distortion effects between different channels.

[0103] Dynamic scheduling

[0104] FIG. 8 A controller, in the form of a scheduler 800, is shown which can schedule read and write operations within a holographic storage system of the type described above. To facilitate efficient scheduling, sub-volumes within the medium 102 or within each medium segment 102A, 102B are assigned unique addresses. This provides a form of addressable holographic storage similar to more conventional forms of addressable electronic storage. However, there are a number of differences compared to conventional addressing.

[0105] Firstly, as described above, a single sub-volume can store holograms for a plurality of different reference beam angles. To accommodate this, each address uniquely corresponds to a particular sub-volume in conjunction with a particular reference beam direction, i.e. each available tuple is assigned a unique address where ADDR represents a particular sub-volume within the medium 102 or one of the holographic storage medium segments 102A, 102B and REFBEAM represents a particular reference beam direction (e.g. a set of one or more angles defining the beam direction; the term "angle" can be used as shorthand for referring to the reference beam direction, although it will be appreciated that the direction can in fact be defined by a plurality of angles depending on the configuration of the system). Thus, a sub-volume can be associated with potentially a large number of addresses corresponding to different reference beam angles. The tuple defines a logical storage location, a plurality of which are provided at a physical level by the same sub-volume for different reference beam angles. Each logical storage location has a unique address (ADDR). This notation is used as shorthand for representing the address corresponding to a sub-volume and reference beam angle, although it will be appreciated that this does not imply any particular representation of the address. Any address space and addressing mechanism which uniquely identifies logical storage locations of this nature can be used.

[0106] Secondly, each logical storage location can store an entire image compared to conventional storage, so a single logical storage location can potentially store a large number (e.g. thousands or millions) of bits.

[0107] The scheduler 800 operates at the logical storage level and schedules the income read and write operations pertaining to different addresses at appropriate time intervals.

[0108] Reference numerals 804, 806, and 808 are used to denote the input, reference, and output waveguide networks, respectively. As mentioned above, each is a single- or multi-waveguide network (e.g., as shown in FIG. 5 with one or more configurable steering elements (e.g., SBGs or other active switching elements) that can be used to create a channel volume to a volume of a sub-volume of a different segment (or multi-segment) holographic storage medium.

[0109] During the time interval in which a write operation pertaining to a specific address is scheduled (write time interval), the steering elements within the input waveguide network 804 and the reference waveguide network 806 are set to create a channel from the emitter system 504 to the corresponding sub-volume through the input waveguide network 804 and the reference waveguide network 806 for the input beam 104 and the reference beam 106, respectively; in addition, the reference beam control element 612 is set to direct the reference beam 106 into the reference waveguide network 806 in the corresponding direction. This results in creating the desired interference pattern within the sub-volume at the reference beam angle, which in turn results in the interference pattern being stored as a hologram persistently, provided that the sub-volume is exposed to the interference pattern for a sufficient duration of time.

[0110] During the interval in which a read operation pertaining to a specific address is scheduled (read interval), the steering elements within the reference waveguide network 806 and the output waveguide network 808 are similarly set to create a channel to the sub-volume through the reference waveguide network 806 for the reference beam 116 and a channel from the sub-volume to the detector 508 through the output waveguide network 808 for the output beam 108; the reference beam control element 612 is similarly set to direct the reference beam 116 into the reference waveguide network 806 in the corresponding direction so as to read the intended hologram at the sub-volume and the reference beam angle.

[0111] Alternative waveguide networks:

[0112] FIG. 10A and FIG. 10B An alternative system is shown in which spatial multiplexing is achieved by modulating one or more optical properties of the input and reference beams 104, 106, 116. In such a system, passive (non-switchable) steering elements can be used instead of the active (switchable) steering elements in the previous figures.

[0113] FIG. 10AAn example considers frequency (or equivalently, wavelength) modulation. In this case, the light pipe(s) themselves (as such) can be passive, with static wavelength-dependent out-coupling (e.g. a continuous longer pass dichroic interference filter, or a varying center wavelength bandpass filter).

[0114] FIG. 11A A light pipe 1100 is shown with an outer surface 1100-S along which a plurality of passive filters 1100-1, 1100-2 are placed. The configuration of the light pipe 1100 is identical to that of FIG. 3A-FIG. 3D except for the fact that the filters 1100-1, 1100-2 replace the SBGs 300-1, 300-2. The filters 1100-1, 1100-2 have different frequency responses (i.e. they act as frequency filters). More specifically, each filter 1100-1, 1100-2 is substantially transmissive for a relatively narrow range of optical frequencies, and substantially reflective for frequencies outside this range. FIG. 11A An in-coupled light beam 1104 is shown with a frequency within the range of the second filter 1100-2, but outside the range of the first filter 1100-1. Thus, the light beam 1104 is reflected from the former, but transmitted through the latter (thereby exiting the light pipe 1100 at this location). FIG. 11B A light beam 1104' of a different frequency is shown, now within the range of the first filter 1100-1, and thus transmitted through the first filter 1100-1.

[0115] Such a light pipe 1100 can be used in place of the active light pipes described above, and the above description applies equally to the following modification of the system.

[0116] FIG. 10A A scheduler 800 is shown communicatively coupled to the lasers 600 of the transmitter system, for changing the frequency (or equivalently, wavelength) of the input light beam 104 and the reference light beams 106, 116. In this case, either light beam can be directed to obtain the desired holographic storage region by setting the frequency accordingly. Different light beam frequencies now correspond to different paths through the waveguide network (defined by the different frequency characteristics of the passive filters), and the frequency can be set to correspond to any desired path.

[0117] In this case, wavelength is used as the switching dimension. The lasers 600 are fast-tunable lasers that act as active elements.

[0118] In such an implementation, the switching can be in only one spatial dimension (i.e. along a single conduit). However, using a laser with sufficient range and line-narrowing, the first optical conduit can be coarsely filtered (i.e. over a relatively wide wavelength range), with subsequent optical conduits sampling more finely (i.e. over a narrower wavelength range). Another factor limiting the line is the need for a relatively long coherence length, so the line can be narrow enough in any case. To implement copying of the input field to an addressable location in the 2D output space in the holographic storage context, this implementation can for example be combined with a second implementation using a different switchable parameter (e.g. polarisation).

[0119] In the case of a read operation, the frequency of the output beam 108 will match that of the reference beam 116 used to read a particular sub-volume, and the same principle can be applied using suitable filters in the output waveguide network 808 to direct it back to the detector.

[0120] FIG. 10B An example of such an implementation with controllable polarisation elements 601 is shown, which can be used to change the polarisation of the input beam 104 and reference beams 106, 116. This can be combined with passive polarisation filters on or in the optical conduits. This can be implemented as an alternative or supplement to the passive frequency filters in the examples above. Such polarisation modulation will provide two independent paths, and can be effectively combined, e.g. with passive wavelength filtering and / or active optical conduit(s). Polarisation modulation of the beams can also be combined with active polarisation filter(s). FIG. 10A

[0121] Note that all the various “passive” and “active” implementations described above can be implemented separately or in combination, e.g. a combination of active and passive steering elements can be used. That is, a waveguide can have both passive and active elements, and / or active and passive waveguides can be combined in the same network. Other hierarchies:

[0122] The examples described above consider a waveguide network with two levels of “grades” of waveguides, with parent and child waveguides. However, a multi-waveguide network can have three grades (parent, child, grandchild) or more. Note that the terms “child”, “parent” and “grandparent” do not necessarily imply a direct hierarchical relationship, i.e. the term child or grandchild can refer to any waveguide at any hierarchical grade below the parent waveguide or child waveguide respectively; that is, a child / grandchild waveguide can be optically coupled to a parent / child waveguide not only by e.g. an air interface (direct descendant), but also through one or more other child / grandchild waveguides (indirect descendant).

[0123] FIG. 12 ​An example of a waveguide network with a three-level structure is shown. The parent waveguide 1200 has two direct sub-waveguide networks 1202A and 1202B optically coupled to it in the manner described above, and each of those sub-waveguides 1202A / 1202B has two grandchild networks 1204A-A, 1204A-B / 1204B-A, 1204B-B optically coupled to it in the same manner.

[0124] An extreme example is the "binary tree" architecture, where each waveguide has exactly two direct children, and there may be more than three levels of waveguides. However, in practice, there may be situations where it is best to increase the number of direct children to reduce the number of levels required.

[0125] FIG. 8 , FIG. 10A and FIG. 10B The scheduler 800 shown is a functional component of the system. Similarly, the encoder 610, decoder 704, and signal processing component 700 are functional components. Such components can be implemented in software (i.e., as program code that executes on one or more programmable hardware processors (such as CPUs, accelerators, e.g., GPUs), or using other forms of processor hardware (such as field-programmable gate arrays and / or application-specific integrated circuits). The signal processing performed by the signal processing component 700 can be analog or digital signal processing, or any combination thereof. Such program code and other data (e.g., channel model 702) can be encoded in computer-readable storage. Examples of computer-readable storage include optical, magnetic, and / or solid-state storage, where code, data, etc., can be stored in a non-transitory form. This contrasts with transient media such as transient signal carriers.

[0126] A holographic data storage system is provided in a first aspect of the present disclosure, comprising: a transmitter system; an input waveguide network formed by one or more multimode optical waveguides, the input waveguide network having a plurality of out-coupling regions and an in-coupling region for receiving an input beam from the transmitter system; at least one holographic recording medium having a plurality of recording regions, each recording region optically coupled to a corresponding out-coupling region of the plurality of out-coupling regions of the input waveguide network, the holographic data storage system being arranged to durably write data of the input beam received at any of the out-coupling regions to the corresponding recording region; and a controller coupled to at least one of the transmitter system and at least one controllable steering element of the input waveguide network, the controller being configured to control at least one optical property of the input beam or the at least one steering element so as to direct the input beam from the in-coupling region to any of the plurality of out-coupling regions, wherein different recording regions of the plurality of recording regions can be written from the same in-coupling region by changing the at least one optical property or controlling the at least one steering element to direct the input beam to different out-coupling regions of the plurality of out-coupling regions while the plurality of out-coupling regions of the multimode optical waveguide network are kept in fixed positions relative to the corresponding recording regions of the holographic recording medium.

[0127] In embodiments, the transmitter system can be configured to provide a reference beam, and the holographic data storage system can be configured to direct the reference beam to any of the recording regions, and the controller can be configured to cause the reference beam and the input beam to be directed to the same recording region in a write interval for storing data of the input beam as a pattern caused by interference between the input beam and the reference beam.

[0128] For example, the holographic data storage system can comprise a reference waveguide network formed by one or more further multimode optical waveguides, the reference waveguide network having a plurality of out-coupling regions and an in-coupling region for receiving a reference beam from the transmitter system, each of the plurality of recording regions of the holographic recording medium also being optically coupled to a corresponding out-coupling region of the plurality of out-coupling regions of the reference waveguide network, and the controller can be configured to control at least one optical property of the reference beam or at least one controllable steering element of the reference waveguide network so as to cause the reference beam to be directed from the in-coupling region of the reference waveguide network to any of the plurality of out-coupling regions of the reference waveguide network, the controller being configured to cause the reference beam to be directed to the out-coupling region optically coupled to the same recording region in the write interval.

[0129] Alternatively, the input waveguide network can be arranged to receive both the input beam and the reference beam, and the controller can be configured to control, in said writing interval, at least one optical property of the input beam and at least one optical property of the reference beam, or a directing element to direct both beams to the same recording region.

[0130] The controller can be coupled to the emitter system for controlling the phase properties and / or the angle of the reference beam coupled into the input waveguide network or the reference waveguide network to cause multiple patterns to be stored in a single recording region created with different phase properties and / or different angles of the reference beam.

[0131] The holographic data storage system can comprise at least one detector array, and the controller can be configured to cause, in a reading interval, the reference beam to be directed from the emitter system to one of the recording regions to be read, such that an output beam created by the interaction of the reference beam with a pattern stored therein is received at the detector array for recovering data of the stored pattern from the output beam.

[0132] The input waveguide network or the reference waveguide network can be arranged to receive the output beam, and the controller can be configured to control an optical property of the reference beam or at least one directing element of the input waveguide network or the reference waveguide network so as to cause the output beam to be directed to the detector array, whereby it is possible to read from different ones of the recording regions using the same detector array.

[0133] Alternatively, the holographic data storage system can comprise an output waveguide network formed by one or more further multimode waveguides, the output waveguide network having a plurality of in-coupling regions, each of the plurality of recording regions of the holographic recording medium also being optically coupled to a corresponding one of the plurality of in-coupling regions of the output waveguide network for receiving an output beam therefrom, and an out-coupling region for providing the output beam to a detector array. The controller can be coupled to at least one of the emitter system for controlling at least one optical property of the reference beam thereby controlling at least one corresponding optical property of the output beam, and at least one controllable directing element of the output waveguide network, and the controller can be configured to control, in said reading interval, at least one optical property of the reference beam or at least one directing element of the output waveguide network to cause the output beam to be directed to the detector array, wherein it is possible to read from different ones of the recording regions using the same said detector array while said in-coupling regions of said output waveguide network remain in fixed positions relative to said recording regions of said holographic recording medium.

[0134] The multi-mode waveguide of the input waveguide network can have a side surface extending along an axis of the waveguide that is aligned with a first side surface of the holographic recording medium, the out-coupling region of the input waveguide network being located at a different position on the side surface of the waveguide.

[0135] The second plurality of multi-mode optical waveguides of the input waveguide network can be optically coupled to the first multi-mode optical waveguide of the input waveguide network at different positions along a side surface of the first waveguide, the multi-mode optical waveguide of the input waveguide network being one of the second waveguides, wherein each of the other second waveguides can further have a plurality of out-coupling regions optically coupled to: a respective further recording region of the holographic recording medium, or a respective recording region of at least one further holographic recording medium, and the controller can be configured to control the at least one optical property of the input light beam or the at least one guiding element of the input waveguide network to cause the input light beam to be guided from the in-coupling region via the first waveguide into any one of the second waveguides and to the out-coupling region of that second waveguide.

[0136] The multi-mode optical waveguide of the reference waveguide network can have a side surface extending along an axis of the waveguide that is aligned with a second side surface of the holographic recording medium, the out-coupling region of the reference waveguide network being located at a different position on the side surface of the waveguide.

[0137] The second plurality of multi-mode optical waveguides of the reference waveguide network can be optically coupled to the first multi-mode optical waveguide of the reference waveguide network at different positions along a side surface of the first optical waveguide, the multi-mode optical waveguide of the reference waveguide network being one of the second waveguides of the reference waveguide network, wherein each of the other second waveguides of the reference waveguide network can further have a plurality of out-coupling regions optically coupled to: the respective further recording region of the holographic recording medium, or the respective recording region of at least one further holographic recording medium,

[0138] and the controller can be configured to control at least one optical property of the reference light beam or the at least one guiding element of the reference waveguide network to cause the reference light beam to be guided from the in-coupling region via the first waveguide of the reference waveguide network into any one of the second waveguides of the reference waveguide network and to the out-coupling region of that second waveguide.

[0139] A second aspect of this document provides a holographic data storage or retrieval system, comprising: a transmitter system; at least one detector array; at least one holographic recording medium; a reference waveguide network formed of one or more multimode optical waveguides, the reference waveguide network having an input coupling region and multiple output coupling regions, the input coupling region being used to receive a reference beam from the transmitter system, the multiple output coupling regions being optically coupled to corresponding recording regions of the at least one holographic recording medium; and a controller coupled to at least one controllable guiding element of the transmitter system and the reference network, the controller being configured to control at least one optical characteristic of the reference beam or the at least one guiding element. A guiding element is provided to guide the reference beam to any selected recording region of the recording region to be read, thereby creating an output beam by interacting with a pattern stored in the recording region via the reference beam, for receiving data at the detector array to recover the stored pattern from the output beam, wherein different recording regions of the plurality of recording regions can be read using the same transmitter system by maintaining the plurality of outcoupling regions of the multimode optical waveguide network in a fixed position relative to the corresponding recording regions of the holographic recording medium, changing the at least one optical characteristic of the reference beam, or controlling the at least one guiding element of the reference network.

[0140] In an embodiment, the holographic data retrieval system may include an output waveguide network in the form of one or more additional multimode optical waveguides having an outcoupling region and a plurality of incoupling regions optically coupled to the recording region of the at least one holographic recording medium, wherein the controller may be coupled to at least one of the transmitter system and at least one controllable guiding element of the output waveguide network and configured to control: the at least one guiding element of the output waveguide network, and at least one optical characteristic of the reference beam, and the corresponding optical characteristic of the output beam therefrom, so as to guide the output beam from the selected recording region via the incoupling region optically coupled to the outcoupling region of the output waveguide network for reception at the detector array, wherein while the incoupling region of the output waveguide network is held in a fixed position relative to the recording region of the holographic recording medium, it is possible to read from different recording regions within the recording region using the same detector array.

[0141] The multimode waveguide of the output waveguide network may have a side surface extending along the axis of the waveguide, which is aligned with the side surface (e.g., a third side surface) of the holographic recording medium, and the coupling region of the output waveguide network is located at different positions on the side surface of the waveguide.

[0142] The plurality of second multi-mode optical waveguides of the output waveguide network can be optically coupled to the first multi-mode optical waveguide of the output waveguide network at different locations along a side surface of the first waveguide, the multi-mode optical waveguide of the output waveguide network being one of: a second waveguide, wherein each other second waveguide can also have a plurality of coupling-in regions optically coupled to: a respective further recording region of the holographic recording medium, or a respective recording region of at least one further holographic recording medium, and the controller can be configured to control at least one optical property of the reference beam or at least one guiding element of the output waveguide network to cause the output beam to be guided from a coupling-in region optically coupled to a recording region being read through the second waveguide into the first waveguide and to the coupling-out region of the output waveguide network for reception at the detector array.

[0143] A third aspect herein provides a holographic data retrieval system comprising: at least one detector array; at least one holographic recording medium; an output waveguide network formed by one or more multi-mode optical waveguides, the output waveguide network having a coupling-out region for providing an output beam to the detector array and a plurality of coupling-in regions respectively optically coupled to corresponding recording regions of the at least one holographic recording medium; and a controller configured to cause the output beam to be guided through the output waveguide network from any selected recording region of the recording regions via the coupling-in region optically coupled to the recording region to the coupling-out region for reception at the detector array by controlling at least one controllable guiding element of the output waveguide network or at least one optical property of a reference beam used to create the output beam, wherein the same detector array can be used to read from different recording regions of the plurality of recording regions by varying the at least one optical property or controlling the at least one guiding element while the plurality of coupling-out regions of the output waveguide network are held in fixed positions relative to the corresponding recording regions of the holographic recording medium.

[0144] In embodiments, a multi-mode waveguide of the output waveguide network can have a side surface extending along an axis of the waveguide, the side surface being aligned with a side surface (e.g. a third side surface) of the holographic recording medium, the coupling-in regions of the output waveguide network being at different locations of the side surface of the waveguide.

[0145] The plurality of second multi-mode optical waveguides of the output waveguide network can be optically coupled to the first multi-mode optical waveguide of the output waveguide network at different locations along the side surface of the first waveguide, the multi-mode optical waveguide of the output waveguide network being one of: a second waveguide, wherein each other second waveguide can also have a plurality of in-coupling regions optically coupled to: a respective further recording region of the holographic recording medium, or a respective recording region of at least one further holographic recording medium, the controller being configured to control at least one optical property of the reference beam or at least one steering element of the output waveguide network to cause the output beam to be steered from an in-coupling region optically coupled to a recording region being read through the second waveguide into the first waveguide and into an out-coupling region of the output waveguide network for reception at the detector array.

[0146] In the above particular embodiments, the waveguide network(s) described below can be used.

[0147] The multi-mode optical waveguide network can comprise: a parent waveguide; and a plurality of child waveguides; wherein the parent waveguide and each of the child waveguides are multi-mode optical waveguides having a first surface region, a plurality of second surface regions and at least one steering element attached to a surface of the waveguide or embedded within the waveguide, each parent waveguide of the second surface regions being optically coupled to the first surface region of a corresponding child waveguide; and wherein the at least one steering element of the parent waveguide is arranged to steer a light beam from its first surface region to any selected second surface region of its plurality of second surface regions or to steer a light beam from any selected second surface region of its plurality of second surface regions to its first surface region, the light beam being coupled to or received from its first surface region through the second surface region of the parent waveguide and the first surface region of the corresponding child waveguide optically coupled to the second surface region of the parent waveguide, the at least one steering element of each child waveguide being arranged to steer a light beam from its first surface region to any selected second surface region of its plurality of second surface regions or to steer a light beam from any selected second surface region of its plurality of second surface regions to its first surface region, wherein the at least one steering element of each waveguide is configurable for selecting a second surface region of that waveguide and / or in response to at least one light beam property for selecting a second surface region of that waveguide by modulating the at least one light beam property.

[0148] A multi-mode optical waveguide network can comprise a plurality of grand waveguides, each grand waveguide being a multi-mode optical waveguide having a first surface area, a plurality of second surface areas, and at least one guiding element attached to a surface of the grand waveguide or embedded within the grand waveguide, each second surface area of each grand waveguide being optically coupled to the first surface area of the corresponding grand waveguide; wherein the at least one guiding element of each grand waveguide can be arranged to direct a light beam from its first surface area to any selected second surface area of its plurality of second surface areas or to direct a light beam from any selected second surface area of its plurality of second surface areas to its first surface area, the light beam being in-coupled or out-coupled the grand waveguide through the first surface area of the grand waveguide and the second surface area of the sub-waveguide with which it is optically coupled, the at least one guiding element of each grand waveguide being configurable for selecting the second surface area of the grand waveguide and / or responsive to at least one light beam characteristic, for selecting the second surface area of the grand waveguide via modulation of the at least one light beam characteristic.

[0149] Each waveguide can have at least one active guiding element configurable for selecting the second surface area of the waveguide.

[0150] Each waveguide can have at least one guiding element responsive to at least one light beam characteristic for selecting the second surface area of the waveguide via modulation of the at least one light beam characteristic.

[0151] At least one waveguide can have at least one active guiding element configurable for selecting the second surface area of the waveguide, and at least another waveguide can have at least one guiding element responsive to at least one light beam characteristic for selecting the second surface area of the another waveguide via modulation of the at least one light beam characteristic.

[0152] One of the parent waveguides and one of the child waveguides can have at least one wavelength-responsive guiding element such that light beams in a first wavelength range are guided from its first surface region to a first child waveguide or grandchild waveguide or from a first child waveguide or grandchild waveguide to its first surface region first, and such that light beams in a second wavelength range are guided from its first surface region to a second child waveguide or grandchild waveguide or from a second child waveguide or grandchild waveguide to its first surface region; wherein the first child waveguide or grandchild waveguide can have at least one wavelength-responsive guiding element such that light beams in a first sub-range of the first wavelength range are guided from its first surface region to its second surface region or from its second surface region to its first surface region, and such that light beams in a second sub-range of the first wavelength range are guided from its first surface region to its further second surface region or from its further second surface region to its first surface region; and wherein the second child waveguide or grandchild waveguide can have at least one wavelength-responsive guiding element such that light beams in a first sub-range of the second wavelength range are guided from its first surface region to one of its second surface regions or from one of its second surface regions to its first surface region, and such that light beams in a second sub-range of the second wavelength range are guided from its first surface region to its further second surface region or from its further second surface region to its first surface region.

[0153] The or each active guiding element can have at least one of: a configurable transmissivity or reflectivity, or a configurable refractive index.

[0154] The or each active guiding element can be a switchable grating or grating region.

[0155] At least one of the guiding elements can be a wavelength and / or polarization filter having a fixed or configurable wavelength response and / or a fixed or configurable polarization axis.

[0156] The at least one waveguide can have two or more guiding elements and three or more second surface regions, any one waveguide can be selected by configuring one or both of the two or more guiding elements and / or modulating the at least one light beam property.

[0157] An optical system comprising such a waveguide network(s) can comprise: a first optical system component; a plurality of second optical system components; at least one multi-mode optical waveguide network according to any of the above aspects or embodiments, arranged to direct an optical beam from the first optical system component to any selected selection second optical system component of the plurality of second optical system components or to direct an optical beam from any selected second optical system component of the plurality of second optical system components to the first optical system component; a controller configured to select a second optical system component of the plurality of second optical system components and to cause the optical beam to be directed from or to the selected second optical system component to or from the first optical system component by configuring at least one of the directing elements of the multi-mode optical waveguide network and / or modulating at least one optical beam property.

[0158] The first system component can comprise: an emitter system from which the optical beam is emitted and directed to the selected second system component, or a detector array to which the optical beam is directed from the selected second system component.

[0159] The optical system can comprise one or more holographic recording media, wherein at least some of the second system optical components can be respective sub-volumes of the one or more holographic recording media.

[0160] The optical system can comprise a second multi-mode optical waveguide network according to any of the above aspects or embodiments, and the controller can be configured to cause a second optical beam to be directed from the first optical system component to the same selected second optical system component or to cause the second optical beam to be directed from the same selected second optical system component to the first optical system component by configuring at least one of the directing elements of the second multi-mode optical waveguide network and / or modulating at least one optical beam property.

[0161] The optical system can comprise a third multi-mode optical waveguide network according to any of the above aspects or embodiments, and the controller can be configured to cause a third optical beam to be directed from the first optical system component to the same selected second optical system component or to cause the third optical beam to be directed from the same selected second optical system component to the first optical system component by configuring at least one of the directing elements of the third multi-mode optical waveguide network and / or modulating at least one optical beam property.

[0162] It will be appreciated that the above embodiments have been described by way of example only. Once the disclosure herein has been given, other variations or uses of the disclosed technology can become apparent to those skilled in the art. The scope of the disclosure is defined by the appended claims, not by the described embodiments.

Claims

1. A holographic data storage system, comprising: The transmitter system is configured to emit an input beam in the form of a multimode optical signal, which encodes multiple image pixels into multiple propagation modes of the input beam propagating in different directions; An input waveguide network is formed by one or more multimode optical waveguides for simultaneously carrying multiple propagation modes, the input waveguide network having multiple out-coupling regions and an in-coupling region for receiving an input beam from the transmitter system; At least one holographic recording medium having multiple recording regions, each recording region being optically coupled to a corresponding decoupling region among the multiple decoupling regions of the input waveguide network, the holographic data storage system being arranged to persistently and simultaneously write multiple image pixels encoded in an input beam received at any of the decoupling regions into the corresponding recording region. as well as A controller, coupled to at least one of the following: the transmitter system and at least one controllable guiding element of the input waveguide network, the controller being configured to: control at least one optical characteristic of the input beam or the at least one guiding element to guide the input beam from the input coupling region to any selected out-coupling region among the plurality of out-coupling regions, wherein by maintaining the plurality of out-coupling regions of the input waveguide network in a fixed position relative to corresponding recording regions of the holographic recording medium, changing the at least one optical characteristic or controlling the at least one guiding element to guide the input beam to different out-coupling regions among the plurality of out-coupling regions, writing can be performed from the same input coupling region to different recording regions among the plurality of recording regions.

2. The holographic data storage system of claim 1, wherein the transmitter system is configured to provide a reference beam, and the holographic data storage system is configured to guide the reference beam to any one of the recording regions, and the controller is configured to guide the reference beam and the input beam to the same recording region during a write interval for storing the input beam data as a pattern caused by interference between the input beam and the reference beam.

3. The holographic data storage system of claim 2, comprising a reference waveguide network formed by one or more additional multimode optical waveguides, the reference waveguide network having a plurality of outcoupling regions and an incoupling region for receiving the reference beam from the transmitter system, each of the plurality of recording regions of the holographic recording medium being optically coupled to a corresponding outcoupling region of the plurality of outcoupling regions of the reference waveguide network, the controller being configured to: control at least one optical characteristic of the reference beam or at least one controllable guiding element of the reference waveguide network to guide the reference beam from the incoupling region of the reference waveguide network to any selected outcoupling region of the plurality of outcoupling regions of the reference waveguide network, the controller being configured during the write interval to guide the reference beam to the outcoupling region optically coupled to the same recording region.

4. The holographic data storage system of claim 2, wherein the input waveguide network is arranged to receive both the input beam and the reference beam, and the controller is configured to control during the writing interval: The at least one optical characteristic of the input beam and the at least one optical characteristic of the reference beam, or The guiding element This guides both the input beam and the reference beam to the same recording area.

5. The holographic data storage system of claim 3, wherein the controller is coupled to the transmitter system for controlling the phase characteristics and / or angles of the reference beam coupled to the input waveguide network or the reference waveguide network, so that multiple patterns are stored in a single recording region created with different phase characteristics and / or different angles of the reference beam.

6. The holographic data storage system of claim 2, comprising at least one detector array, wherein the controller is configured during a readout interval to: guide the reference beam from the transmitter system to one of the recording regions to be read, such that an output beam created by the interaction of the reference beam with a pattern stored in the recording region is received at the detector array for retrieving data of the stored pattern from the output beam.

7. The holographic data storage system according to claim 6, wherein, The input waveguide network is arranged to receive the output beam, and the controller is configured to control the optical characteristics of the reference beam or at least one guiding element of the input waveguide network to guide the output beam to the detector array, thereby enabling reading from different recording areas in the recording area using the same detector array.

8. The holographic data storage system of claim 6, comprising an output waveguide network formed by one or more additional multimode waveguides, the output waveguide network having a plurality of input coupling regions, each recording region of the plurality of recording regions of the holographic recording medium further optically coupled to a corresponding input coupling region of the plurality of input coupling regions of the output waveguide network for receiving an output beam from the output waveguide network; and an output coupling region for providing the output beam to the detector array, the controller being coupled to at least one of the following: The transmitter system is configured to control at least one optical characteristic of the reference beam, thereby controlling at least one corresponding optical characteristic of the output beam, and At least one controllable guiding element of the output waveguide network, wherein the controller is configured during the readout interval to control at least one optical characteristic of the reference beam or at least one guiding element of the output waveguide network to guide the output beam to the detector array, wherein while the coupling region of the output waveguide network is held in a fixed position relative to the recording region of the holographic recording medium, it is possible to read from different recording regions in the recording region using the same detector array.

9. The holographic data storage system according to claim 3, wherein the multimode waveguide of the input waveguide network has a side surface extending along the axis of the waveguide, the side surface being aligned with a first side surface of the holographic recording medium, and the decoupling region of the input waveguide network is located at different positions on the side surface of the waveguide.

10. The holographic data storage system of claim 9, wherein a plurality of second multimode optical waveguides of the input waveguide network are optically coupled to the first multimode optical waveguide of the input waveguide network at different locations along the side surface of the first multimode optical waveguide, the multimode waveguide of the input waveguide network being one of the second multimode optical waveguides, wherein each of the other second multimode optical waveguides further has a plurality of decoupling regions optically coupled to: The corresponding additional recording area of ​​the holographic recording medium, or At least one corresponding recording area of ​​another holographic recording medium, The controller is configured to control at least one optical characteristic of the input beam or at least one guiding element of the input waveguide network to guide the input beam from the input coupling region via the first multimode waveguide into any one of the second multimode waveguides, and to any one of the out coupling regions of the second multimode waveguide.

11. The holographic data storage system of claim 10, wherein the multimode waveguide of the reference waveguide network has a side surface extending along the axis of the waveguide, the side surface being aligned with a second side surface of the holographic recording medium, and the decoupling regions of the reference waveguide network are located at different positions on the side surface of the waveguide.

12. The holographic data storage system of claim 11, wherein a plurality of second multimode optical waveguides of the reference waveguide network are optically coupled to the first multimode optical waveguide at different locations along the side surface of the first multimode optical waveguide of the reference waveguide network, the multimode waveguide of the reference waveguide network being one of the second multimode optical waveguides of the reference waveguide network, wherein each of the other second multimode optical waveguides of the reference waveguide network further has a plurality of decoupling regions optically coupled to: The corresponding additional recording area of ​​the holographic recording medium, or At least one additional holographic recording medium, in the corresponding recording area, The controller is configured to control at least one optical characteristic of the reference beam or at least one guiding element of the reference waveguide network to guide the reference beam from the input region via the first multimode waveguide of the reference waveguide network into any one of the second multimode waveguides of the reference waveguide network, and to any one of the output regions of the second multimode waveguide.

13. A holographic data retrieval system, comprising: Transmitter system; At least one detector array for detecting images; At least one holographic recording medium; as well as A reference waveguide network is formed by one or more multimode waveguides, the reference waveguide network having an input coupling region and multiple output coupling regions, the input coupling region being used to receive a reference beam from the transmitter system, and the multiple output coupling regions being optically coupled to corresponding recording regions of the at least one holographic recording medium. A controller, coupled to at least one of the following: the transmitter system and at least one controllable guiding element of the reference waveguide network, the controller being configured to control at least one optical characteristic of the reference beam or the at least one guiding element to guide the reference beam to any selected recording region of the recording region to be read, thereby creating an output beam via the interaction of the reference beam with a pattern stored in the recording region, for receiving at the detector array data to recover the stored pattern from the output beam, wherein different recording regions of the plurality of recording regions can be read using the same transmitter system by maintaining the plurality of decoupling regions of the reference waveguide network in a fixed position relative to the corresponding recording regions of the holographic recording medium, changing the at least one optical characteristic of the reference beam or controlling the at least one guiding element of the reference waveguide network, wherein the controller is configured to change the angle of the reference beam for reading different patterns stored in the same selected recording region, the multimode waveguide of the reference waveguide network being used to carry the reference beam at any of a plurality of possible angles.

14. The holographic data retrieval system of claim 13, comprising an output waveguide network in the form of one or more additional multimode optical waveguides, the output waveguide network having an out-coupling region and a plurality of input-coupling regions optically coupled to the recording region of the at least one holographic recording medium. The controller is coupled to at least one controllable guiding element of the transmitter system and the output waveguide network, and is configured to control: The at least one guiding element of the output waveguide network, and The at least one optical characteristic of the reference beam, and the corresponding optical characteristic of the output beam therefrom. So that the output beam from the selected recording region can be guided via the input region of the output waveguide network through optical coupling to the output waveguide network for reception at the detector array, wherein the input region of the output waveguide network is kept in a fixed position relative to the recording region of the holographic recording medium, while the same detector array can be used to read from different recording regions in the recording region.

15. The holographic data retrieval system of claim 14, wherein the multimode waveguide of the output waveguide network has a side surface extending along the axis of the waveguide, the side surface being aligned with the side surface of the holographic recording medium, and the coupling region of the output waveguide network is located at different positions on the side surface of the waveguide.

16. The holographic data retrieval system of claim 15, wherein a plurality of second multimode waveguides of the output waveguide network are optically coupled to the first multimode waveguide at different locations along the side surface of the first multimode waveguide of the output waveguide network, the multimode waveguide of the output waveguide network being one of the second multimode waveguides of the output waveguide network, wherein each of the other second multimode waveguides of the output waveguide network further has a plurality of coupling regions optically coupled to: The corresponding additional recording area of ​​the holographic recording medium, or At least one corresponding recording area of ​​another holographic recording medium, The controller is configured to control at least one optical characteristic of the reference beam or at least one guiding element of the output waveguide network to guide the output beam from the input region optically coupled to the recording region being read through the second multimode waveguide into the first multimode waveguide, and to the output region of the output waveguide network for reception at the detector array.

17. A holographic data retrieval system, comprising: At least one detector array; At least one holographic recording medium; An output waveguide network is formed by one or more multimode optical waveguides. The output waveguide network has an out-coupling region and multiple input-coupling regions. The out-coupling region is used to provide an output beam to the detector array. The multiple input-coupling regions are optically coupled to corresponding recording regions of the at least one holographic recording medium, respectively. as well as A controller is configured to guide the output beam through the output waveguide network to the decoupling region from any selected recording region of the recording region via the input coupling region optically coupled to the recording region, by controlling at least one controllable guiding element of the output waveguide network or at least one optical characteristic of a reference beam for creating the output beam, for reception at the detector array. This is for receiving the output beam at the detector array. The controller also allows reading from different recording regions of the plurality of recording regions using the same detector array by changing the at least one optical characteristic or controlling the at least one guiding element while maintaining the plurality of decoupling regions of the output waveguide network in a fixed position relative to the corresponding recording region of the holographic recording medium. The holographic data retrieval system is configured to create the output beam by causing the reference beam to interact with a pattern stored in the selected recording region, the stored pattern encoding a plurality of image pixels in the output beam as a plurality of propagation modes that propagate simultaneously in different directions through the output waveguide network.

18. The holographic data retrieval system of claim 17, wherein the multimode waveguide of the output waveguide network has a side surface extending along the axis of the waveguide, the side surface being aligned with the side surface of the holographic recording medium, and the coupling region of the output waveguide network is located at different positions on the side surface of the waveguide.

19. The holographic data retrieval system of claim 18, wherein a plurality of second multimode waveguides of the output waveguide network are optically coupled to the first multimode waveguide at different locations along the side surface of the first multimode waveguide of the output waveguide network, the multimode waveguide of the output waveguide network being one of the second multimode waveguides of the output waveguide network, wherein each of the other second multimode waveguides of the output waveguide network further has a plurality of coupling regions optically coupled to: The corresponding additional recording area of ​​the holographic recording medium, or At least one corresponding recording area of ​​another holographic recording medium, The controller is configured to control at least one optical characteristic of the reference beam or at least one guiding element of the output waveguide network to guide the output beam from the input region optically coupled to the recording region being read through the second multimode waveguide into the first multimode waveguide, and to the output region of the output waveguide network for reception at the detector array.

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