Optical data transmission

Abstract

In an optical data transmission system, a beam modulator is configured to embed a data set into an input optical beam. A multimode optical waveguide network has an in-coupling region for receiving the input optical beam. The multimode optical waveguide network is configured to direct the input optical beam to an out-coupling region of the multimode optical waveguide network. A spatially coherent detector is configured to measure a phase and an amplitude of an output optical field at a plurality of locations. The output optical field is at least partially defined by the input optical beam and thus exhibits distortion effects caused by the propagation of the optical beam through the multimode waveguide network. Signal processing is applied to the output of the spatially coherent detector to compensate for the distortion effects, thereby recovering the data set embedded in the input optical beam from the output of the spatially coherent detector.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to optical data transmission. BACKGROUND

[0002] An optical waveguide is an optical element that can guide a beam of light by total internal reflection. A waveguide can be "multimode" in the sense that it has 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 a simple single-mode optical waveguide, such as a thin optical fiber used in fiber-optic systems, whose purpose is 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, while multimode optical waveguides allow for more data to be conveyed (e.g., entire images with potentially millions of pixels) through angular variations within the waveguide. In other words, multimode waveguides provide greater bandwidth through increased 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).

[0003] For example, multimode waveguides have been widely used in head-mounted displays (HMDs) and waveguide-based display systems. In this case, the multimode waveguide will typically carry an image from a display or light engine to the user's eye in a form such that the image can be reconstructed by the eye's optical system, to be perceived by the human user. Micro-optics can be used to provide beam expansion and ensure that the light beams entering and exiting the waveguide preserve the original image, so that the eye can reconstruct it. SUMMARY

[0004] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the. 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 disadvantages noted herein.

[0005] A first aspect herein provides an optical data transmission system. A beam modulator is configured to embed a data set into an input light beam. A multimode optical waveguide network has an in-coupling region for receiving the input light beam. The multimode optical waveguide network is configured to guide the input light beam to an out-coupling region of the multimode optical waveguide network. A spatially coherent detector is configured to measure a phase and an amplitude of an output light field at a plurality of locations. The output light field is at least partially defined by the input light beam and therefore exhibits distortion effects caused by the beam passing through the multimode waveguide network. At least one processor is coupled to the spatially coherent detector and configured to apply signal processing to outputs of the spatially coherent detector to compensate for the distortion effects, thereby recovering the data set embedded in the input light beam from the outputs of the spatially coherent detector.

[0006] This has the advantage of significantly increasing the optical data transfer capacity, the ability to transfer potentially large amounts of data in parallel (e.g. images with millions of pixels) and the ability to exploit potentially complex waveguide networks (e.g. to provide spatial multiplexing). The use of coherent detection enables this by providing sufficient flexibility for waveguide distortions because more effective distortion compensation can be applied to the measured phase and amplitude of the output light field. One example application of the present waveguide network is in a holographic data storage / retrieval system to carry light beams to / from a holographic recording medium. In this case, the ability to use the multimode capability of the waveguide(s), e.g. to read / write an entire image simultaneously, and to effectively compensate for waveguide distortions in the output of the spatially coherent detector increases the capacity and robustness of the system.

[0007] Other examples include optical communications or optical computing, any other optical data transfer environment using multimode waveguide(s) and in which data is embedded in a light beam and subsequently recovered. BRIEF DESCRIPTION OF DRAWINGS

[0008] 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:

[0009] FIG. 1A and FIG. 1B shows a schematic perspective view of a holographic recording medium;

[0010] Figure 2A shows a schematic perspective view of a holographic storage system comprising a set of waveguides which can be used to direct light beams to / from different sub-volumes of a holographic recording medium to provide spatial multiplexing on the medium; Figures 2B, 2C and 2D show plan and alternative side views of the system during a write interval, respectively; Figures 2E-2G show plan and alternative side views during a read interval;

[0011] FIGS. 3A-3D shows a schematic side view of various configurations of active light pipe; FIG. 3E and FIG. 3F shows a plan (cross-sectional) view of an active light pipe;

[0012] FIG. 4A and FIG. 4B shows an alternative side view of a (partial) optical waveguide network;

[0013] FIG. 5 shows a schematic view of a multiple waveguide network example for multiplexing over multiple holographic storage medium segments;

[0014] FIG. 6AAn example of an emission system for providing input and reference beams in a holographic storage system is shown; FIG. 6B A variant of the emission system with simplified optics is shown;

[0015] FIG. 7 An example of a data retrieval system using spatially coherent detection to measure the optical field of the output beam and signal processing to mitigate waveguide distortions in the measured optical field is shown;

[0016] FIG. 8 A functional block diagram representing the functions performed within a holographic storage system is shown;

[0017] FIG. 9 Another holographic storage system is shown in which at least one waveguide network is used for spatial multiplexing on a two-dimensional holographic recording medium slab;

[0018] FIG. 10A And FIG. 10B How spatial multiplexing is achieved with passive guiding elements is shown, in which the spatial multiplexing is achieved by modulating the properties of the light beam(s);

[0019] FIG. 11A And FIG. 11B An optical conduit with passive filters having different frequency responses is shown; and

[0020] FIG. 12 An example of a waveguide network with three levels is shown. DETAILED DESCRIPTION

[0021] One example application of the waveguide networks taught herein is holographic storage. 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 pattern. For example, a region of the medium (subvolume) can be exposed to an optical interference pattern resulting from the interference between a reference beam and an input beam with a data set embedded in it. 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 in the non-visible parts of the electromagnetic spectrum, for example.

[0022] 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 a persistently recorded or written subvolume). The changed state of the subvolume enables, at a later time, when the subvolume is exposed to a substantially matching reference beam, interference between the matching reference beam and the subvolume to produce an output beam that is substantially matched to the original input beam, in the sense that the data set originally embedded in the input beam can be recovered from the output beam (this can be referred to herein as reading the recorded pattern).

[0023] 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 certain forms of holographic recording media 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 media, when an interference pattern is created using a reference beam at a given angle, only a reference beam that is very closely matched to the reference beam originally used to create it can be used to read the recorded pattern. 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 millimeter, and ultraviolet potentially reaching tens of gigabytes per cubic millimeter. In practice, there can be other limiting factors, but high-density data storage still has great potential.

[0024] To achieve spatial multiplexing on one or more holographic storage media, in a manner that reduces or eliminates the need for mechanical motion, either “active” light pipes, “passive” light pipes, or a combination of active and passive light pipes can be used. Note that the terms “waveguide” and “light pipe” are used interchangeably herein.

[0025] An "active optical conduit" 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 can in turn be configured (i.e., have variable optical properties) to enable "one-to-many" optical transport, i.e., in the case where light is guided from a first surface region to one of a plurality of 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 transport, 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 optical conduit" refers to an optical conduit with guiding elements having 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., so that it is guided along a different route by guiding elements having different wavelength / polarization responses, etc.; e.g., using a tunable laser). The term "passive optical guide" is just 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).

[0026] Digital images (or data encoded as digital images) can be propagated as beams along active or passive optical conduits. The guiding elements of an active optical conduit can be individually controlled to either transmit or reflect an incident beam.

[0027] Many such optical conduits (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 optical conduits can be created using a spatial light modulator (SLM), and the output 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 to provide more effective waveguide distortion mitigation in conjunction with such techniques.

[0028] 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 steered and made to interfere at any desired location in the holographic storage medium. As mentioned before, using passive optical conduits can achieve the benefit of simplicity, where the switches are applied at the transmitter stage.

[0029] 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 are designed 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).

[0030] 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 motion between the medium and the waveguide network(s). Examples of such systems are described below, which use active and / or passive optical conduits. In the described examples, multi-mode waveguides can be used to simultaneously carry entire digital images to / from the holographic recording medium, or to carry a reference beam at one of multiple possible angles.

[0031] However, the optical waveguide networks taught herein are not limited to their application to holographic storage. Other applications include, for example, optical communications and optical computing.

[0032] Active optical conduits:

[0033] FIGS. 3A-3DA schematic side view is shown of an example form of an active light pipe 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.

[0034] The active light pipe 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 body-embedded. In this example, two such SBGs 300-1, 300-2 are shown on a first surface 300-S1 of the waveguide 300, although it will be appreciated that a greater number of SBGs can be provided at suitable locations on the waveguide 300 and / or surface 300-S1 within the body of the waveguide 300. Each SBG 300-1, 300-2 can be individually controlled to change its reflective / transmissive properties, so as to transmit or reflect an incident light beam. The SBGs 300-1, 300-2 form respective surface regions of the active light pipe 300, at which light can enter the waveguide 300 (in-couple) or leave the waveguide 300 (out-couple), depending on how the waveguide 300 is being used.

[0035] 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 an axis 301 of the waveguide 300.

[0036] 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-S2, 300-S4 extending along an axis 301 of the waveguide 300. In this example, as shown in the figures, the SBGs 300-1, 300-2 are both located at a position 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.

[0037] The SBGs 300-1, 300-2 are located at positions along the first side surface 300-S1, increasingly distant from the first region 300-0, with the first SBG 300-1 being located closest to the first region 300-0.

[0038] 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 enter the waveguide body 300 through the first surface region 300-0 at an angle sufficient to achieve total internal reflection at each of the side surfaces 300-1,..., 300-4 within the waveguide 300.

[0039] 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 incident light ray 300 to reflect therefrom, back into the waveguide 300, and to 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 light ray 304 to diffract out of the waveguide 300 through the second SBG 300-2, and thus to be coupled 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.

[0040] 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, and thus is coupled 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.

[0041] 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 any of the SBGs 300-1, 300-2. Although described for simplicity with respect to only two SBGs 300-1, 300-2, it should be understood that the same principles can be applied to a larger number of SBGs.

[0042] 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.

[0043] AsFIG. 3C , FIG. 3D and FIG. 3F As shown, using the depicted active light pipe 300, a many-to-one optical transmission is equally feasible.

[0044] 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 leaving 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.

[0045] 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.

[0046] FIG. 3F A cross-section is shown of how the second light ray 308 propagates within the waveguide 300, and the same description as FIG. 3E applies, but with the light ray directions reversed.

[0047] 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.

[0048] Although described as separate elements, the SBGs 300-1, 300-2 can in fact be separate, independently controllable areas of a single large SBG extending over all or most of the first side surface 300-S1.

[0049] 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.

[0050] 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.

[0051] Note that even if the steering elements themselves are mechanical, this still avoids the need for mechanical movement of the entire waveguide 300.

[0052] Active optical conduit network

[0053] 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 transport.

[0054] FIG. 4A and FIG. 4B An alternative side view of a (partial) waveguide network comprising a first active optical conduit 400 and a second active optical conduit 420 is shown. The second optical conduit 420 has a first surface area 420-0 located adjacent to and aligned with a surface area of the corresponding first optical conduit 400 for receiving a light beam from or directing a light beam to the second waveguide 420 through the first surface area 400-0. By way of example only, a light ray 404 is shown propagating through the first waveguide 400 to a corresponding surface area of the first waveguide 400 adjacent to the first surface area 420-0 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 area of the first waveguide 400 and enters the second waveguide 420 via the first surface area 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 direct 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.

[0055] 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.

[0056] More generally, the surface areas of the media can be optically coupled to the corresponding surface areas of the waveguides 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).

[0057] Holographic storage

[0058] Applications of active light pipes in holographic storage will now be described.

[0059] FIG. 1A and FIG. 1B A schematic perspective view of a holographic recording medium 102 is shown, which is a relatively thick volume of 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 persistent 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 later reproduced therefrom. The hologram is persistent 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).

[0060] 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.

[0061] 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.

[0062] 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 110. The output beam 108 propagates out of the sub-volume 110 via the third side surface 102-8 of the medium 102.

[0063] 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 two different holograms can be created 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.

[0064] Figure 2A shows a schematic perspective view of an example holographic storage system 200 incorporating the particular principles of the present disclosure. 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 variety 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 FIGS. 3A-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 active light pipe 300 of FIGS. 3A-3E

[0065] 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.

[0066] ​Figures 2B-2D show how the input waveguide 204 and reference waveguide 206 are used to write data into the medium 102 in a one-to-many fashion. Figure 2B shows a schematic plan view of the system 200, and Figures 2C and 2D show alternative side views in which the input waveguide 204 and reference waveguide 206 are visible, respectively. The input waveguide 404 is used to direct the input beam 104 into any of the multiple sub-volumes of the medium 102 via any of the SBGs 404-1, 404-2 of the input waveguide 204 in the manner described above. The reference waveguide 406 is configured to direct the reference beam 106 into the same sub-volume at the same time, in order to create the desired interference pattern to be written into that sub-volume. In the example depicted, both the input waveguide 204 and reference 206 are currently configured to direct the input beam 104 and reference beam 106 into the sub-volume represented by reference numeral 110 via the second SBGs 204-2, 206-2 of each waveguide 204, 206.

[0067] Figures 2E-2G show how the reference waveguide 206 and output waveguide 208 are used to read data from the medium 102. Figure 2E is a plan view, and Figures 2F and 2G show alternative side views in which the reference waveguide 204 and output waveguide 206 are visible, respectively. The reference waveguide 206 is used in exactly the same way as depicted in Figures 2B-2D, but now the reference beam 116 is directed into any sub-volume from which a hologram is to be read - in this case, sub-volume 110. The output waveguide 208 is used in a one-to-many fashion to direct the resulting output beam 108 from the sub-volume 110 and through the pass-through waveguide 208 for subsequent detection.

[0068] For example, each sub-volume 110 can have a height and width of a few millimeters measured along any of the side surfaces, which is typically sufficient to store several million pixels per data "page" (e.g., multiplexed angle) - in this case, the volume of the sub-volume is sufficient to store (million pixels)*(# multiplexed angles).

[0069] The directing elements of the input waveguide 204 and reference waveguide 206 (SBGs in this example) are configured as needed to provide a path from the beam source (emission system) to be read to the sub-volume 108 for the input beam 104 and reference beam 106, 116. For SBGs, this is a matter of setting the SBGs to a transmissive or reflective state as needed to create the path. Similarly, the directing elements of the output waveguide 208 (also SBGs in this example) are similarly set to provide a path from the sub-volume 108 being read to the detector. To provide additional context, this will be described in more detail below with respect to the multi-waveguide network depicted in FIG. 5 Figure 3. However, the principles described apply more generally to other waveguide network topologies, both simpler networks (e.g., a single waveguide) or more complex waveguide networks. FIG. 5 Figure 3. However, the principles described apply more generally to other waveguide network topologies, both simpler networks (e.g., a single waveguide) or more complex waveguide networks.

[0070] As noted above, this allows spatial multiplexing 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 element takes (as noted above, the directing element itself can be mechanical or non-mechanical).

[0071] Holographic storage using a multi-waveguide network

[0072] FIG. 5 An example of a holographic storage system containing a multi-waveguide network of the type shown in Figure 4 is shown.

[0073] 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 waveguide 203 via its in-coupling region, and can be directed from there into any of the second input waveguides 204A, 204B.

[0074] 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 directed into any of the second reference waveguides 206A, 206B.

[0075] 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.

[0076] The arrangement depicted allows the beams to be directed to / from different sub-volumes of the multi-piece holographic storage medium 102A, 102B.

[0077] 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 Figures 2A-2G.

[0078] The first set of second waveguides 204A, 204B, 204C (each of the input, reference, and output) are located around the first segment of holographic storage medium 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 in FIGS. 2A-2G. Thus, the input beam 104 and the reference beams 106, 116 can be directed to any subvolume of any medium 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 subvolume of the medium segment of the adjacent desired waveguide.

[0079] The output waveguide network can be used to direct the output beam 108 from any subvolume of any 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 subvolume, the SBGs are configured to provide a passageway from that subvolume to the detector; thus, in this case, the SBGs 204A-2 and 207A-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 the passageway for the output beam 108 to the detector 508 (e.g., in this case, the SBG 207-2 of the first output waveguide 207 is set to the reflective state to prevent the output beam 104 from propagating into the 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 medium segment 102A or from "leakage" of the different medium segment(s) 102B (e.g., in this example, the SBG 204A-1, which is proximate to the subvolume being read, is shown set to the reflective state to prevent unwanted leakage).

[0080] 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 required. 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.

[0081] 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 108A, 108B. For example, the fourth network can be used to carry erase beams to the desired sub-volumes, suitable for erasing at least holograms therefrom (in the case of erasable holographic storage).

[0082] FIG. 9 An alternative physical architecture is shown, in which a single "slab" of holographic medium 102 is used instead of FIG. 5 single segments 102A, 102B. An input waveguide network is described, which has substantially the same physical configuration, but the second input waveguides 204A, 204B are now configured to direct the input beams 104 to different sub-volumes of the same slab 102. Whereas in FIG. 5 each second input waveguide 204A, 204B provides multiplexing in a single dimension along the length of a different single-segment medium 102A, 102B, in FIG. 9 the second waveguides 204A, 204B provide two-dimensional spatial multiplexing on the slab of holographic medium 102 (each waveguide provides one dimension of multiplexing individually, but as a whole on the slab 102 provides 2D multiplexing).

[0083] FIG. 9 The system of

[0084] Data encoding

[0085] FIG. 6A An example of an emitter system 504 that provides both the input beams 104 and the reference beams 106 is shown. The input beams are extended, spatially modulated laser beams. A laser 600 emits a coherent, narrow laser beam, which is split using a beam splitter 604.

[0086] A portion of the beam from the beam splitter 602 is used as the reference beam 106. In this example, a controllable reference beam steering element 612 is used to turn the reference beam 106 at the desired angle into the reference waveguide 106. 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.

[0087] 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 particular reference beam angle and / or phase characteristic. All the descriptions regarding reference beam angle modulation apply equally to phase modulation.

[0088] Another portion of the beam from the beam expander 602 is expanded using a beam expander 604, the expanded beam passing 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 a Fourier lens 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 particular point in the plane of the SLM 606. The different propagation modes are coupled into the input waveguide 202, through which they are guided as described above in a manner that depends on the data. Using the in-coupling optic 608, the data is "angle encoded" in the sense that a point in the digital image corresponds essentially 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 infinitely far away. 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.

[0089] Note that the term "multi-mode" does not necessarily imply the use of such an in-coupling optic 608, nor does it require a one-to-one correspondence between each image point and a given direction of propagation. That is, multi-mode does not necessarily imply a one-to-one correspondence between the propagation modes and the image / data points. For example, FIG. 6B Another possible transmitter system is shown, in which the spatially modulated beam is coupled directly into the input waveguide 204. In this case, there are still multiple modes (i.e. multiple spatial paths through the waveguide for any given channel), but there is no one-to-one correspondence between the direction of propagation and the image points, nor can there be any one-to-one correspondence between the image / data points and the modes. This provides a form of spatial diversity based on a MIMO (multiple-input multiple-output) transmission form, provided by the multiple pixels of the SLM 606 and the detector array of the spatially coherent detector 508.

[0090] Data decoding

[0091] FIG. 7A spatially coherent detector 508 is shown that is used to measure the optical field of the output beam 108. In contrast to a conventional "direct detection", the spatially coherent detector 508 comprises an array of pixels (or more generally, detector elements), each pixel being 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 spatially coherent detector 508. The array of pixels is thus able to measure the phase and amplitude 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 the optical field of the output beam 108 that is guided to the spatially coherent detector 208 by the output waveguide 208.

[0092] Although only a single array is depicted, in practice there can be multiple physical arrays that cooperate as a single "logical array". For example, this logical array can be divided into two physical cameras.

[0093] 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.

[0094] As noted, the path from a particular in-coupling region of the beam into the waveguide network to a particular out-coupling region of the beam 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 multimode 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. Furthermore, it will be generated by a hologram created using an input beam that is guided from an in-coupling region of the input waveguide network to its particular out-coupling region. The hologram will be created and read using a reference beam that is similarly guided through a particular channel by a reference waveguide network. The input beam 104, the reference beam 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 analogue signal processing 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 is guided to the detector 508, but also the channel volume through which the input beam 104 used to write the hologram is guided to that sub-volume and the channels through which the reference beams 106, 116 used to write / read the hologram are guided to that sub-volume.

[0095] 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 a representation of the measured light 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 to eliminate or reduce 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.

[0096] For example, the signal processing 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.

[0097] Using a learning approach, the path from the emitter system 504 to the spatially coherent detector 508 is treated as a channel to be modeled. The channel can be modeled in terms of a function (e.g. an inverse transfer function) that inverts the channel distortion effects to be learned. The input to such a function is the distorted field (phase and amplitude) of the output beam measured by the spatially coherent detection, while the output of such a function is the undistorted field (phase and amplitude) of the input beam. Given a sufficient number of training examples, i.e. (distorted output field, clean input field) pairs, a model can be trained to approximate this inverse function, i.e. when given a distorted output field (phase and amplitude) as input, the trained model will approximately recover the original input field. This is the case because such a model is able to generalize from the set of sufficient training examples, even if the model did not encounter that exact form of distorted output field during training. For example, the output and input fields can be represented as input and output tensors of a convolutional neural network (CNN), and the CNN can be trained on a loss function that penalizes the difference between the output tensor (as generated by applying the CNN to the input tensor of that training example) and the known corresponding input field of that training example. As will be appreciated, this approach can be applied not only to holographic storage, but to any environment where the output field exhibits waveguide distortions, provided that such training examples can be collected.

[0098] Although described in the context of holographic storage, the use of such a combination of signal processing 700 and 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 where the received output beam is susceptible to distortions introduced in one or more waveguide networks.

[0099] FIG. 7 It is shown that the arrangement is arranged to substantially invert FIG. 6Bout-coupling optics 715 of the effect of the in-coupling optics 608, i.e. resolving each propagating mode to essentially a single point in the plane of the spatially coherent detector 508. Again, this is not essential and can be omitted for FIG. 6B

[0100] Although not depicted in FIG. 6A FIG. 6B some level of pre-processing can be applied to the digital image before it is modulated into the input beam 104. 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.

[0101] Dynamic scheduling

[0102] 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 108 or within each piece of the medium 108A, 108B 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.

[0103] 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 the first element represents a particular sub-volume within the medium 102 or one of the pieces of the medium 102A, 102B and the second element represents a particular reference beam direction (e.g. defining a beam direction by one angle or a set of multiple angles; the term "angle" can be used as shorthand for referring to a 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 a potentially 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 an address corresponding to a sub-volume and a 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.

[0104] 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.

[0105] ​​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.

[0106] Reference numerals 804, 806 and 808 are used to denote the input waveguide network, the reference waveguide network and the output optical waveguide network, respectively. As mentioned above, each is a single waveguide network or a multi-waveguide network (e.g., as shown in FIG. 5 The illustrated example considers frequency (or equivalently, wavelength) modulation. In this case, the light conduit(s) themselves (as such) can be passive, with static wavelength-dependent out-coupling (e.g., continuous longer pass dichroic interference filters, or varying center wavelength bandpass filters).

[0107] 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, through the input network 804 and the reference network 806, respectively, a channel volume for the input beam 104 and the reference beam 106 to the respective sub-volume of the emitter system 504; in addition, the reference beam steering element 612 is set to direct the reference beam 106 in the respective direction into the reference network 806. This results in the creation of 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.

[0108] During the interval in which a read operation pertaining to a specific address is scheduled (read time interval), the steering elements within the reference network 806 and the output 808 are similarly set to create, through the reference network 806, a channel volume for the reference beam 116 to the sub-volume and through the output network 808, a channel for the output beam 108 from the sub-volume to the detector 508; the reference beam steering 612 is similarly set to direct the reference beam 116 in the respective direction into the reference network 806, so as to read the intended hologram at the sub-volume and the reference beam angle.

[0109] Alternative waveguide networks:

[0110] 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.

[0111] FIG. 10A The illustrated example considers frequency (or equivalently, wavelength) modulation. In this case, the light conduit(s) themselves (as such) can be passive, with static wavelength-dependent out-coupling (e.g., continuous longer pass dichroic interference filters, or varying center wavelength bandpass filters).

[0112] FIG. 11A A light pipe 1100 is shown having an outer surface 1100-S along which a plurality of passive optical filters 1100-1, 1100-2 are placed. The configuration of the light pipe 1100 is identical to that of FIGS. 3A-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 having a frequency within the range of the second filter 1100-2 but outside the range of the first filter 1100-1. Thus, the beam 1104 is reflected from the former but transmitted by 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 by the first filter 1100-1.

[0113] Such a light pipe 1100 can be used in place of the active light pipe described above, and the above description applies equally to the following modification of the system.

[0114] FIG. 10A A scheduler 800 is shown communicatively coupled to the lasers 600 of the transmitter system, for changing the frequencies (or equivalently, wavelengths) of the input beam 104 and the reference beams 106, 116. In this case, either beam can be directed to obtain the desired holographic storage region by setting the frequency accordingly. Different 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.

[0115] In this case, wavelength is used as the switching dimension. The lasers 600 are fast-tunable lasers used as active elements.

[0116] In such an implementation, the switching can be in only one spatial dimension (i.e. along a single pipe). However, using a laser with sufficient range and line-narrowing, the first optical pipe can be coarsely filtered (i.e. over a relatively wide wavelength range), with subsequent optical pipes 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. polarization).

[0117] 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.

[0118] FIG. 10B An example of such an implementation with controllable polarization elements 601 is shown, which can be used to change the polarization of the input beam 104 and reference beams 106, 116. This can be combined with passive polarization filters on or in the optical pipes. This can be implemented as an alternative or supplement to the passive frequency filters in the examples of FIG. 10A Such polarization modulation will provide two independent paths, and can be effectively combined, e.g. with passive wavelength filtering and / or active optical pipe(s). The polarization modulation of the beams can also be combined with active polarization filter(s).

[0119] 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.

[0120] Other hierarchies:

[0121] 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 a parent waveguide or child waveguide, respectively; that is, a child / grandchild waveguide can be optically coupled to a parent / child waveguide not only directly (immediate offspring), but also through one or more other child / grandchild waveguides (indirect offspring).

[0122] FIG. 12An example of a waveguide network with three levels of hierarchy is shown. A parent waveguide 1200 has two direct child waveguide networks 1202A, 1202B optically coupled to it in the manner described above, and each of those child waveguides 1202A / 1202B has two grandchild networks 1204A-A, 1204A-B / 1204B-A, 1204B-B optically coupled to it in the same manner.

[0123] An extreme example is a "binary tree" architecture, in which each waveguide has exactly two direct children, possibly with more than three levels of waveguides. However, in practice, it can also be the case that it is preferable to increase the number of direct children to reduce the number of levels required.

[0124] FIG. 8 、 FIG. 10A and FIG. 10B The scheduler 800 shown in FIGS. 1-3 is a functional component of the system. Similarly, the encoder 610, the decoder 704, and the signal processing component 700 are functional components. Such components can be implemented in software (i.e., as program code executing on one or more programmable hardware processors such as CPUs, accelerators, e.g., GPUs, etc.), 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., the channel model 702) can be encoded in a computer-readable storage. Examples of computer-readable storage include optical, magnetic, and / or solid-state storage, where the code, data, etc. can be stored in a non-transitory form. This is in contrast to transitory media, such as signals propagating through a cache (e.g., over a bus).

[0125] A first aspect herein provides an optical data transmission system, comprising: a beam modulator configured to embed a data set into an input light beam; an input waveguide network formed of one or more multimode optical waveguides, the input waveguide network having an in-coupling region for receiving the input light beam, the input waveguide network configured to guide the input light beam to an out-coupling region network of the input waveguide; a spatially coherent detector configured to measure phase and amplitude of an output light field at a plurality of locations, the output light field being at least partially defined by the input light beam and thus exhibiting a distortion effect caused at least in part by a propagation of the input light beam through the input waveguide network; at least one processor coupled to the spatially coherent detector and configured to apply signal processing to an output of the spatially coherent detector to compensate for the distortion effect, thereby recovering the data set embedded in the input light beam from the output of the spatially coherent detector.

[0126] In embodiments, the optical data transmission system can comprise at least one holographic recording region, the input waveguide network being configured to direct the input light beam to the holographic recording region for storing embedded data in a pattern recorded within the region via interference between the input light beam and a reference light beam, the output light field being subsequently created via interference between the recorded pattern and the reference light beam in order to read the embedded data from the holographic recording region.

[0127] The optical data transmission system can be configured to direct the reference light beam to the holographic recording region by one of: the input waveguide network, and a reference waveguide network formed by one or more further multi-mode optical waveguides, wherein the passing of the reference light beam through the input waveguide network or the reference waveguide network can also contribute to said distortion effects compensated by the signal processing.

[0128] The optical data transmission system can be configured to direct the output light beam, defined at least in part by the input light beam, to the spatially coherent detector by one of: the input waveguide network formed by one or more further multi-mode optical waveguides, the above reference waveguide network, and the output waveguide network, wherein the passing of the output light beam through the input waveguide network, the reference waveguide network, or the output waveguide network can also contribute to said distortion effects compensated by the signal processing.

[0129] At least one of the input waveguide network, the above reference waveguide network, and the above output waveguide network can comprise at least one steering element, which is configurable and / or responsive to at least one light beam property, whereby different channel selections can be implemented, the at least one processor being configured to apply said signal processing in accordance with the channel selection associated with the output light field by reconfiguring the at least one steering element and / or modulating the at least one beam property for the at least one waveguide network.

[0130] The at least one processor can be configured to select a channel model corresponding to the associated channel selection from a plurality of channel models corresponding to different channel selections, and to apply the signal processing in accordance with the selected channel model.

[0131] Each channel model can comprise a set of signal processing parameters learned for a respective channel selection.

[0132] A second aspect of the present document provides an optical data transmission system, comprising: a beam modulator configured to embed a data set into an input beam; a spatially coherent detector and configured to measure a phase and an amplitude of an optical field of an output beam at a plurality of locations, the output beam being at least partially defined by the input beam; an output waveguide network formed of one or more multimode optical waveguides, the output waveguide network having an in-coupling region for receiving the output beam and being configured to guide the output beam to an out-coupling region of the output waveguide network for reception at the spatially coherent detector; at least one processor coupled to the spatially coherent detector and configured to apply signal processing to an output of the spatially coherent detector to compensate for distortion effects caused at least in part by a propagation of the output beam through the output waveguide network, thereby to recover from the output of the spatially coherent detector the data set embedded in the input beam.

[0133] The optical data transmission system can comprise a plurality of holographic recording regions, the output waveguide network having at least one guiding element, the at least one guiding element being configurable and / or responsive to at least one beam property, using the same spatially coherent detector such that reading from any one of the plurality of holographic recording regions can be selected by reconfiguring the at least one guiding element and / or modulating the at least one beam property to direct the output beam from the selected holographic recording region to the spatially coherent detector, wherein the at least one processor is configured to apply the signal processing in dependence on the holographic recording region being read.

[0134] Each holographic recording region can be associated with at least one channel model, and the at least one processor can be configured to apply the signal processing using the channel model associated with the holographic recording region being read.

[0135] Each holographic recording region can have at least one logical address, and the channel model can be selected based on a logical address associated with a current read operation and identifying the holographic recording region being read.

[0136] The optical data transmission system can be configured to direct a reference beam to one of the selected holographic recording regions by one of: the output waveguide network, and a reference waveguide network formed of one or more further multimode optical waveguides, wherein a propagation of the reference beam through the output waveguide network or the reference waveguide network can also contribute to the distortion effects compensated for by the signal processing.

[0137] The optical data transmission system can be configured to direct the input beam to one of the selected holographic recording regions by one of: the output waveguide network, and an input waveguide network formed of one or more further multimode optical waveguides, wherein a propagation of the input beam through the output waveguide network or the input waveguide network can contribute to the distortion effects compensated for by the signal processing.

[0138] A third aspect herein provides an optical data transmission system comprising: a beam modulator configured to embed a data set into an input light beam; a spatially coherent detector configured to measure phase and amplitude of the output light field at a plurality of locations of the output light field, the output light field being defined at least in part by the input light beam and a reference light beam; a reference waveguide network formed of one or more multimode optical waveguides, the reference waveguide network having an in-coupling region for receiving the reference light beam, the reference waveguide network being configured to guide the reference light beam to an out-coupling region of the reference waveguide network for defining the output light field; at least one processor coupled to the spatially coherent detector and configured to apply signal processing to the output of the spatially coherent detector to compensate for distortion effects caused at least in part by the propagation of the reference light beam through the reference waveguide network, thereby recovering the data set embedded in the input light beam from the output of the spatially coherent detector.

[0139] An optical communication system or an optical computing system can comprise at least one such optical data transmission system.

[0140] In the above particular embodiments, a waveguide network(s) as described below can be used.

[0141] A multimode optical waveguide network can comprise: a parent waveguide; and a plurality of child waveguides; wherein the parent waveguide and each of the child waveguides is a multimode optical waveguide having a first surface region, a plurality of second surface regions, and at least one guiding element attached to a surface of the waveguide or embedded within the waveguide, each parent waveguide of the second surface regions is optically coupled to the first surface region of a respective one of the child waveguides; and wherein the at least one guiding element of the parent waveguide is arranged to direct a light beam from its first surface region to any selected one of its plurality of second surface regions or to direct a light beam from any selected one 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 a second surface region of the parent waveguide and a first surface region of a corresponding child waveguide optically coupled to the second surface region of the parent waveguide, the at least one guiding element of each child waveguide is arranged to direct a light beam from its first surface region to any selected one of its plurality of second surface regions or to direct a light beam from any selected one of its plurality of second surface regions to its first surface region, wherein the at least one guiding 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 at least one light beam property.

[0142] 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 region, a plurality of second surface regions, and at least one guiding element attached to a surface of the grand waveguide or embedded within the grand waveguide, each second surface region of each grand waveguide being optically coupled to the first surface region of a respective one of the grand waveguides; wherein the at least one guiding element of each grand waveguide can be arranged to direct a light beam from its first surface region to any selected one of its plurality of second surface regions or to direct a light beam from any selected one of its plurality of second surface regions to its first surface region, the light beam being in-coupled or out-coupled the grand waveguide through its first surface region and the second surface region of a 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 region of the grand waveguide and / or in response to at least one light beam characteristic, for selecting the second surface region of the grand waveguide via modulation of the at least one light beam characteristic.

[0143] Each waveguide can have at least one active guiding element configurable for selecting the second surface region of the waveguide.

[0144] Each waveguide can have at least one guiding element responsive to at least one light beam characteristic for selecting the second surface region of the waveguide via modulation of the at least one light beam characteristic.

[0145] At least one waveguide can have at least one active guiding element configurable for selecting the second surface region 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 region of the another waveguide via modulation of the at least one light beam characteristic.

[0146] 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.

[0147] The or each active guiding element can have at least one of: a configurable transmissivity or reflectivity, or a configurable refractive index.

[0148] The or each active guiding element can be a switchable grating or grating region.

[0149] 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.

[0150] 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.

[0151] An optical system comprising such 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 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.

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] In, for example, an optical communication or optical computing context, at least one optical system component of the first and / or second optical system components can comprise: a signal transducer configured to convert an optical beam to an electrical signal or vice versa, or an optical processor.

[0157] In the above particular embodiments, the waveguide network(s) can be used as described below.

[0158] A multi-mode optical waveguide network can comprise: a parent waveguide; and a plurality of child waveguides; wherein each of the parent and child waveguides is a multi-mode optical waveguide 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 is optically coupled to a first surface region of a respective one of the child waveguides; and wherein at least one steering element of the parent waveguide is arranged to steer an optical beam from its first surface region to any selected one of its plurality of second surface regions or to steer an optical beam from any selected one of its plurality of second surface regions to its first surface region, the optical beam being coupled to or received from a respective child waveguide whose first surface region is optically coupled to the second surface region of the parent waveguide by the second surface region of the respective child waveguide, at least one steering element of each child waveguide is arranged to steer an optical beam from its first surface region to any selected one of its plurality of second surface regions or to steer an optical beam from any selected one of its plurality of second surface regions to its first surface region, wherein 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 optical beam characteristic, for selecting a second surface region of that waveguide by modulating at least one optical beam characteristic.

[0159] A multi-mode optical waveguide network can comprise a plurality of grandchild waveguides, each grandchild waveguide being a multi-mode optical waveguide having a first surface region, a plurality of second surface regions, and at least one steering element attached to a surface of the grandchild waveguide or embedded within the grandchild waveguide, each child waveguide of the second surface regions is optically coupled to a first surface region of a respective one of the grandchild waveguides; wherein at least one steering element of each grandchild waveguide can be arranged to steer an optical beam from its first surface region to any selected one of its plurality of second surface regions or to steer an optical beam from any selected one of its plurality of second surface regions to its first surface region, the optical beam being in-coupled or out-coupled the grandchild waveguide by its first surface region and a second surface region of a child waveguide with which it is optically coupled, at least one steering element of each grandchild waveguide is configurable for selecting a second surface region of that grandchild waveguide and / or in response to at least one optical beam characteristic, for selecting a second surface region of that grandchild waveguide by modulating at least one optical beam characteristic.

[0160] Each waveguide can have at least one active steering element configurable for selecting a second surface region of that waveguide.

[0161] Each waveguide can have at least one steering element responsive to at least one optical beam characteristic for selecting a second surface region of that waveguide by modulating at least one optical beam characteristic.

[0162] At least one waveguide can have at least one active guiding element configurable for selecting a second surface area of the waveguide, and at least another waveguide can have at least one guiding element responsive to at least one beam property for selecting a second surface area of the other waveguide by modulating the at least one beam property.

[0163] One of the parent waveguides and one of the child waveguides can have at least one wavelength- responsive guiding element such that a beam in a first wavelength range is guided from its first surface area to the first child waveguide or grandchild waveguide or from the first child waveguide or grandchild waveguide to its first surface area, and such that a beam in a second wavelength range is guided from its first surface area to the second child waveguide or grandchild waveguide or from the second child waveguide or grandchild waveguide to its first surface area; wherein the first child waveguide or grandchild waveguide can have at least one wavelength- responsive guiding element such that a beam in a first sub-range of the first wavelength range is guided from its first surface area to its second surface area or from its second surface area to its first surface area, and such that a beam in a second sub-range of the first wavelength range is guided from its first surface area to another second surface area thereof or from another second surface area thereof to its first surface area; and wherein the second child waveguide or grandchild waveguide can have at least one wavelength- responsive guiding element such that a beam in a first sub-range of the second wavelength range is guided from its first surface area to its second surface area or from its second surface area to its first surface area, and such that a beam in a second sub-range of the second wavelength range is guided from its first surface area to another second surface area thereof or from another second surface area thereof to its first surface area.

[0164] The or each active guiding element can have at least one of: a configurable transmissivity or reflectivity, or a configurable refractive index.

[0165] The or each active guiding element can be a switchable grating or grating region.

[0166] 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.

[0167] At least one waveguide can have two or more guiding elements and three or more second surface areas, any of which can be selected by configuring one or both of the two or more guiding elements and / or modulating the at least one beam property.

[0168] 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 second optical system component of the plurality of second optical system components or from any selected second optical system component of the plurality of second optical system components to the first optical system component; and 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 the first optical system component to the selected second optical system component or from the selected second optical system component to 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.

[0169] 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.

[0170] 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.

[0171] 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 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.

[0172] 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 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.

[0173] In, for example, an optical communication or optical computing context, at least one optical system component of the first and / or second optical system components can comprise: a signal transducer configured to convert an optical beam to an electrical signal or vice versa, or an optical processor.

[0174] Note that the above embodiments are described by way of example only. Other variations or uses of the disclosed technology can become apparent to those skilled in the art once given this disclosure. The scope of the disclosure is not to be limited by the described embodiments, but only by the claims that follow.

Claims

1. An optical data transmission system comprising: a beam modulator configured to embed a data set into an input beam; an input waveguide network formed of one or more multimode optical waveguides, the input waveguide network having an in-coupling region for receiving the input beam, the input waveguide network being configured to direct the input beam to an out-coupling region of the input waveguide network; a spatially coherent detector configured to measure phase and amplitude of an output optical field at a plurality of locations, the output optical field being at least partially defined by the input beam and exhibiting a distortion effect therefrom, the distortion effect being at least partially caused by a propagation of the input beam through the input waveguide network; and at least one processor coupled to the spatially coherent detector and configured to compensate for the distortion effect using signal processing applied to an output of the spatially coherent detector and thereby recover the data set embedded in the input beam from the output of the spatially coherent detector, wherein compensating for a distortion effect comprises compensating for a distortion effect caused by a propagation of a reference beam through at least one of a reference waveguide network formed of further multimode optical waveguides or the input waveguide network.

2. The optical data transmission system of claim 1, comprising at least one holographic recording region, the input waveguide network being configured to direct the input beam to the holographic recording region for storing the embedded data in a recorded pattern within the region via interference between the input beam and the reference beam, the output optical field being subsequently created via interference between the recorded pattern and a reference beam in order to read the embedded data from the holographic recording region.

3. The optical data transmission system of claim 2, configured to direct the reference beam to the holographic recording region via one of: the input waveguide network, and the reference waveguide network.

4. The optical data transmission system of claim 1, configured to direct an output beam at least partially defined by the input beam to the spatially coherent detector via one of: the input waveguide network, the reference waveguide network, and an output waveguide network formed of one or more further multimode optical waveguides, wherein a propagation of the output beam through the input waveguide network, the reference waveguide network, or the output waveguide network also contributes to the distortion effect compensated for by the signal processing.

5. The optical data transmission system of claim 1, wherein at least one of: the input waveguide network, the reference waveguide network, and an output waveguide network, comprises at least one directing element, the directing element being responsive to at least one beam characteristic, wherein the at least one processor is configured to apply the signal processing in accordance with a channel selection associated with the output optical field.

6. The optical data transmission system of claim 5, wherein the at least one processor is configured to select a channel model corresponding to the associated channel selection from a plurality of channel models corresponding to different channel selections, and to apply the signal processing in accordance with the selected channel model.

7. The optical data transmission system of claim 6, wherein each channel model comprises a set of signal processing parameters learned for the respective channel selection.

8. An optical data transmission system, comprising: a beam modulator configured to embed a data set into an input beam; a spatially coherent detector and configured to measure a phase and an amplitude of an optical field of an output beam at a plurality of locations, the output beam being at least partially defined by the input beam; an output waveguide network formed of one or more multimode optical waveguides, the output waveguide network having an in-coupling region for receiving the output beam and being configured to guide the output beam to an out-coupling region of the output waveguide network for reception at the spatially coherent detector; and at least one processor coupled to the spatially coherent detector and configured to use signal processing applied to an output of the spatially coherent detector to compensate for distortion effects caused at least in part by a transfer of the output beam through the output waveguide network, and to recover the data set embedded in the input beam from the output of the spatially coherent detector thereby.

9. The optical data transmission system of claim 8, comprising a plurality of holographic recording regions, the output waveguide network having at least one guiding element, the guiding element being responsive to at least one beam characteristic, wherein each holographic recording region of the plurality of holographic recording regions is selected to be read using the same spatially coherent detector by reconfiguring the at least one guiding element and / or modulating the at least one beam characteristic to guide an output beam from the selected holographic recording region to the spatially coherent detector, wherein the at least one processor is configured to apply the signal processing in accordance with the holographic recording region being read.

10. The optical data transmission system of claim 9, wherein each holographic recording region is associated with at least one channel model, and the at least one processor is configured to apply the signal processing using the channel model associated with the holographic recording region being read.

11. The optical data transmission system of claim 10, wherein each holographic recording region has at least one logical address, and the channel model is selected based on a logical address associated with a current read operation and identifying the holographic recording region being read. ​ 12. The optical data transmission system of any of claims 9 to 11, configured to direct a reference beam into a selected one of the holographic recording regions via one of: the output waveguide network, and a reference waveguide network formed by one or more further multimode optical waveguides, wherein the passage of the reference beam through the output waveguide network or the reference waveguide network contributes to the distortion effects compensated for by the signal processing.

13. The optical data transmission system of claim 9, configured to direct the input beam into a selected one of the holographic recording regions via one of: the output waveguide network, and an input waveguide network formed by one or more further multimode optical waveguides, wherein the passage of the input beam through the output waveguide network or the input waveguide network contributes to the distortion effects compensated for by the signal processing.

14. An optical data transmission system, comprising: a beam modulator configured to embed a data set into an input beam; a spatially coherent detector configured to measure phase and amplitude of an output optical field at a plurality of locations, the output optical field being defined at least in part by the input beam and a reference beam; a reference waveguide network formed by one or more multimode optical waveguides, the reference waveguide network having an in-coupling region for receiving the reference beam, the reference waveguide network configured to direct the reference beam to an out-coupling region of the reference waveguide network for defining the output optical field; and at least one processor coupled to the spatially coherent detector and configured to recover the data set embedded in the input beam from an output of the spatially coherent detector using signal processing applied to the output of the spatially coherent detector to compensate for distortion effects caused at least in part by the passage of the reference beam through the reference waveguide network. a holographic recording region, the optical data transmission system comprising an output waveguide network having a steering element responsive to a beam property, wherein each of the holographic recording regions is selected to be read using the same spatially coherent detector at least one of: reconfiguring the steering element or modulating the beam property to direct an output beam from the selected holographic recording region to the spatially coherent detector, wherein the processor is configured to apply the signal processing in dependence on the holographic recording region being read.

15. The optical data transmission system of claim 14, comprising:

16. The optical data transmission system of claim 15, wherein each holographic recording region is associated with a channel model, and the processor is configured to apply the signal processing using the channel model associated with the holographic recording region being read.

17. The optical data transmission system of claim 16, wherein each holographic recording region has a logical address, and the channel model is selected based on a logical address associated with a current read operation and identifying the holographic recording region being read. ​ 18. The optical data transmission system of claim 14, configured to direct an output light beam, defined at least in part by the input light beam, to the spatially coherent detector via one of: an input waveguide network, the reference waveguide network, and an output waveguide network formed by a further multi-mode optical waveguide, wherein the passing of the output light beam through the input waveguide network, the reference waveguide network, or the output waveguide network also contributes to the distortion effects compensated by the signal processing.

19. The optical data transmission system of claim 14, wherein at least one of: the input waveguide network, the reference waveguide network, and an output waveguide network comprises a directing element, the directing element being responsive to a light beam property, wherein the processor is configured to apply the signal processing in accordance with a channel selection associated with the output light field.

20. The optical data transmission system of claim 19, wherein the processor is configured to: select, from a plurality of channel models corresponding to different channel selections, a channel model corresponding to the associated channel selection, and apply the signal processing in accordance with the selected channel model, wherein each channel model comprises signal processing parameters learned for the corresponding channel selection. ​ ​ ​ ​

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