Optical data transfer

Abstract

To provide an optical data transfer system.SOLUTION: In a holographic storage system incorporating multi-waveguide networks, an input waveguide network includes a first input light pipe 203 to which a plurality of second input light pipes 204A, 204B are coupled. An input beam 104 from an emitter system 504 is coupled into the first input waveguide 203 through an in-coupling region thereof, and can be guided from there into the second input waveguide 204A or 204B. A reference waveguide network includes a first reference waveguide 205 to which a plurality of second reference waveguides 206A, 206B are coupled. A reference beam 106, 116 from the emitter system 504 is similarly coupled into the first reference waveguide 205, and can be guided into the second reference waveguide 206A or 206B. An output waveguide network includes a first output waveguide 207 to which a plurality of second output waveguides 208A, 208B are coupled.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] Technical Field

[0001] The present disclosure relates generally to optical data transfer. [Background technology]

[0002] background

[0002] An optical waveguide is a form of optical component capable of guiding a beam of light via total internal reflection. A waveguide can be "multimode" in the sense that it has sufficient physical dimensions to support a wide range of "modes" (i.e., spatial paths through the waveguide for a given channel, e.g., corresponding to different propagation directions). This contrasts with simple single-mode optical waveguides, such as thin optical fibers used in fiber optic systems, whose purpose is to essentially confine light entering the fiber to a single propagation mode. While single-mode optical waveguides can only carry data using amplitude, phase, or frequency modulation, multimode optical waveguides can carry much more data (e.g., potentially entire images of millions of pixels) through angular variations within the waveguide. Stated differently, multimode waveguides offer greater bandwidth through increased angular and / or spatial diversity by providing multiple optical paths through the waveguide from emitter to detector for any given channel (different paths corresponding to different propagation modes).

[0003]

[0003] Multimode waveguides are more commonly used in, for example, head-mounted displays (HMDs) and waveguide-based display systems. In this context, the multimode waveguide typically carries an image from a display or optical engine to a user's eye, in a form that allows the image to be reconstructed by the eye's optics and thus perceived by a human user. Differentiated optics may be used to provide beam expansion and ensure that the beams entering and exiting the waveguide preserve the original image so that it can be reconstructed by the eye. Summary of the Invention [Means for solving the problem]

[0004] overview

[0004] This Summary is provided to introduce selected concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Nor is the claimed subject matter limited to implementations that solve any or all of the disadvantages described herein.

[0005]

[0005] A first aspect of the present specification provides an optical data transfer system. A beam modulator is configured to embed a set of data in an input beam. A multimode optical waveguide network has an in-coupling region for receiving the input beam. The multimode optical waveguide network is configured to direct the input beam to an out-coupling region of the multimode optical waveguide network. A spatially coherent detector is configured to measure the phase and amplitude of an output optical field at multiple locations. The output optical field is at least partially defined by the input 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 an output of the spatially coherent detector to compensate for the distortion effects and thereby recover the set of data embedded in the input beam from the output of the spatially coherent detector.

[0006]

[0006] This has the advantage of significantly increasing optical data transfer capacity, due to the ability to transfer potentially large amounts of data in parallel (e.g., images of millions of pixels) and using potentially complex waveguide networks (e.g., to provide spatial multiplexing). This is made possible by providing appropriate resilience to waveguide distortions, since the use of coherent detection allows more effective distortion compensation to be applied to the measured phase and amplitude of the output optical field. One application of this waveguide network is to convey beams to / from holographic recording media in holographic data storage / retrieval systems. In this context, the multimode capability of the waveguide can be used, for example, to read / write an entire image simultaneously, and the ability to effectively compensate for waveguide distortions at the output of the spatially coherent detector increases the capacity and robustness of the system.

[0007]

[0007] Other examples include optical communications or optical computing and any other optical data transfer situation using multimode waveguides where data is embedded in a beam and then recovered.

[0008] Brief description of the diagram

[0008] For a better understanding of the present disclosure and to show how embodiments of the disclosure may be put into practice, reference is made, by way of example only, to the following figures: [Brief explanation of the drawings]

[0009] [Figure 1A]

[0009] A schematic perspective view of a holographic recording medium is shown. [Figure 1B]

[0009] A schematic perspective view of a holographic recording medium is shown. [Figure 2A]

[0010] FIG. 1 shows a schematic perspective view of a holographic storage system including a set of waveguides that can be used to direct beams to / from different sub-volumes of a holographic recording medium to provide spatial multiplexing across the medium. [Figure 2B]

[0010] A plan view of the system during a write period is shown. [Figure 2C]

[0010] A side view of one side of the system during a write period is shown. [Figure 2D]

[0010] A side view of one side of the system during a write period is shown. [Figure 2E]

[0010] A plan view during a reading period is shown. [Figure 2F]

[0010] A side view of one side during a reading period is shown. [Figure 2G]

[0010] A side view of one side during a reading period is shown. [Figure 3A]

[0011] 1 shows a schematic side view of an active light pipe in one configuration. [Figure 3B] 1 shows a schematic side view of an active light pipe in one configuration. [Figure 3C] 1 shows a schematic side view of an active light pipe in one configuration. [Figure 3D] 1 shows a schematic side view of an active light pipe in one configuration. [Figure 3E]

[0011] A plan (cross-sectional) view of an active light pipe is shown. [Figure 3F]

[0011] A plan (cross-sectional) view of an active light pipe is shown. [Figure 4A]

[0012] 1 shows a side view of one side of a portion of an optical waveguide network. [Figure 4B]

[0012] A side view of one side of an optical waveguide network (part thereof) is shown. [Figure 5]

[0013] 1 shows a schematic diagram of an example of a multiplexed waveguide network used to multiplex across multiple pieces of holographic storage media. [Figure 6A]

[0014] 1 illustrates an example of an emitter system for providing input and reference beams in a holographic storage system. [Figure 6B]

[0014] A variant of the emitter system with simplified optics is shown. [Figure 7]

[0015] An example data recovery system is presented that uses spatially coherent detection to measure the optical field of the output beam and uses signal processing to mitigate waveguide distortions in the measured optical field. [Figure 8]

[0016] FIG. 1 shows a functional block diagram illustrating the functions performed within a holographic storage system. [Figure 9]

[0017] An alternative holographic storage system is presented that uses at least one waveguide network to spatially multiplex in two dimensions across a slab of holographic recording medium. [Figure 10A]

[0018] It is shown how spatial multiplexing can be achieved using passive inductive elements, where spatial multiplexing is achieved by modulating the beam characteristics. [Figure 10B]

[0018] It is shown how spatial multiplexing can be achieved using passive inductive elements, where spatial multiplexing is achieved by modulating the beam characteristics. [Figure 11A]

[0019] 1 shows a light pipe with passive optical filters having different frequency responses. [Figure 11B] 1 shows a light pipe with passive optical filters having different frequency responses. [Figure 12]

[0020] 1 shows an example of a waveguide network with three hierarchical levels. DETAILED DESCRIPTION OF THE INVENTION

[0010] Detailed Description of Example Embodiments

[0021] One 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 a light pattern. For example, a region (subvolume) of the medium can be exposed to an optical interference pattern resulting from the interference of an input beam embedded with a data set and a reference beam. The beam can be, for example, a laser beam generated using a single laser and a beam splitter. Spatial light modulation (SLM) can be used to embed the data set in the input beam (e.g., an image encoding the data set can be spatially modulated and embedded in the input beam). For the avoidance of doubt, the terms "light," "optical," and similar terms used herein are not limited to visible light. Holographic storage can be implemented using, for example, infrared or ultraviolet beams in the non-visible portion of the electromagnetic spectrum.

[0011]

[0022] With sufficient beam power and exposure time, the optical interference pattern will produce a persistent state change within the sub-volume (at which point the interference pattern is said to be persistently recorded or written to the sub-volume herein). The state change of the sub-volume is such that, upon subsequent exposure of the sub-volume to a substantially matching reference beam, the interaction between the matching reference beam and the sub-volume will produce an output beam that is essentially matching with the original input beam, in the sense that the set of data originally embedded in the input beam can be recovered from the output beam (this may be referred to herein as reading the recorded pattern).

[0012]

[0023] Rather than storing individual bits as discrete units, a single interference pattern can encode many (e.g., millions) of bits. For example, a set of data could be a megapixel image embedded in an input beam. Moreover, by exploiting the sensitivity of certain forms of holographic recording media to small changes in the angle of a reference beam, it is possible to record many (e.g., hundreds or thousands) of such patterns in the same subvolume. For such media, once an interference pattern is generated with a reference beam at a given angle, the recorded pattern can only be read using a reference beam that closely matches the reference beam originally used to generate it. This effect can be exploited to record multiple patterns (encoding different sets of data) in the same subvolume at different reference beam angles. Theoretically, data storage capacity is limited only by the wavelength of the beam, potentially hundreds of megabytes per cubic millimeter for red light and tens of gigabytes for ultraviolet light. In practice, there may be other limiting factors, but nevertheless, there is great potential for high-density data storage.

[0013]

[0024] To achieve spatial multiplexing across one or more holographic storage media in a manner that reduces or eliminates the need for mechanical movement, "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.

[0014]

[0025] An "active light pipe" refers to a waveguide having one or more active switching or other guiding elements attached to the surface of the waveguide or within the bulk of the waveguide, and thus configurable (i.e., having changeable optical properties) to cause "one-to-many" light transfer (i.e., light is guided from a first surface region to one of multiple possible second surface regions (where the first surface region becomes an in-coupling region and the second region becomes an out-coupling region)) or "many-to-one" light transfer (i.e., light is guided from any one of the second surface regions (here becoming an in-coupling region) to the same first surface region (here becoming an out-coupling region)). The term "passive light pipe" refers to a light pipe with guiding elements having different light sensitivities (e.g., different wavelength and / or polarization sensitivities); a similar effect can be achieved by instead varying the optical properties or beam (e.g., using a tunable laser to change its wavelength, polarization, etc. so that it is guided along different routes by guiding elements with different wavelength / polarization responses, etc.). The term "passive light induction" is merely a convenient label to coincide with the fact that in this case the induction element does not need to be active, but in this context active or passive induction elements with different light sensitivities (e.g., different wavelength and / or polarization sensitivities, etc.) can be used (i.e., the induction elements can be active and have different light sensitivities).

[0015]

[0026] A digital image (or data encoded as a digital image) can be propagated as a beam along an active or passive light pipe, whose guiding elements can be individually controlled to transmit or reflect the incident light beam.

[0016]

[0027] Many such light pipes (active, passive, or a combination of both types) can be combined in various geometries to create switching networks that can be used to steer beams and images to one of many addressable locations in one or more spatial dimensions. The input to the light pipe can be generated using a spatial light modulator (SLM), and the output is read, for example, on a CCD (charge-coupled device). Phase interference and noise can be corrected using a combination of optical and computational techniques (including machine learning techniques), which would involve learning one or more signal processing parameters from training data. Some embodiments use coherent detection in combination with such techniques to provide more effective waveguide distortion mitigation.

[0017]

[0028] In contrast to the types of optical switches and fibers traditionally used in optical data communications, the described embodiments use light pipes that can transmit entire images at once. This takes advantage of currently available high-resolution optical devices, such as SLMs and digital cameras. These devices have millions of pixels, allowing for the encoding and decoding of megabytes of data. This enables high-bandwidth transmission even with modest switching rates of the SLM, camera, and active light pipe elements (in the case of active light pipes) or beam optics (in the case of passive light pipes). In addition, applications such as holographic storage require interference between multiple beams, at least one of which is modulated with an image. In holographic storage, active light pipes can be used to efficiently steer beams and images to interfere at any desired location in the holographic storage medium. As described, simpler advantages can be achieved with passive light pipes, where switching is instead applied at the emitter stage.

[0018]

[0029] The light pipes described below are “multimode” waveguides in the sense that they have sufficient physical dimensions to support a wide range of “modes” (i.e., spatial paths through the waveguide for a given channel, e.g., corresponding to different propagation directions). This is in contrast to simple single-mode optical waveguides, such as thin optical fibers used in fiber optic systems, whose purpose is to essentially confine light entering the fiber to a single propagation mode. While single-mode optical waveguides can only carry data using amplitude, phase, or frequency modulation, multimode optical waveguides can carry much more data (e.g., potentially entire images of millions of pixels) through angular variations within the waveguide. Stated differently, multimode waveguides offer greater bandwidth through increased angular and / or spatial diversity by providing multiple optical paths through the waveguide from emitter to detector for any given channel (different paths corresponding to different propagation modes).

[0019]

[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) across a holographic recording medium without requiring any relative mechanical motion between the medium and the waveguide network. Examples of such systems are described below and utilize active and / or passive light pipes. In the described examples, multimode waveguides can be used to simultaneously carry an entire digital image to / from the holographic recording medium or to carry a reference beam at one of several possible angles.

[0020]

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

[0021] Active Light Pipe:

[0032] 3A-D show schematic side views of example configurations of active light pipes 300 having particular physical structures. As will be appreciated, this is merely one example of a suitable physical structure that can provide the desired optical configurability. Further examples are considered below.

[0022]

[0033] The active light pipe 300 is shown having at least a first surface region 300-0 and a plurality of active switches in the form of switchable Bragg gratings (SBGs), which may be surface or volume-embedded. In this example, two such SBGs 300-1, 300-2 are shown on the first surface 300-S1 of the waveguide 300, but it will be understood that more SBGs can be placed at suitable locations on the surface 300-S1 of the waveguide 300 and / or embedded within the bulk of the waveguide 300. Each SBG 300-1, 300-2 can be individually controlled to change its reflection / transmission characteristics to transmit or reflect an incident beam. The SBGs 300-1, 300-2 form respective surface regions of the active light pipe 300 where light can enter (incouple) or exit (outcouple) the waveguide 300, depending on how the waveguide 300 is used.

[0023]

[0034] The first surface region 300-0 is the end region of the waveguide 300 from which the first side surface 300-S1 of the waveguide extends along the axis 301 of the waveguide 300.

[0024]

[0035] 3E and 3F each show a cross-sectional view of waveguide 300, which in this example has a rectangular shaped cross-section, with four sides 300-S1, 300-S2, 300-S3, and 300-S4 extending along axis 301 of waveguide 300. In this example, as depicted in the figures, SBGs 300-1, 300-2 are all located along first side 300-S1, although in general such SBGs can be attached to multiple surfaces of waveguide 300 depending on the application.

[0025]

[0036] The SBGs 300-1, 300-2 are located at increasing distances from the first region 300-0 along the first side 300-S1 of the waveguide, with the first SBG 300-1 being located closest to the first region 300-0.

[0026]

[0037] 3A, 3B, and 3E depict a "one-to-many" use case, where the first surface region 300-0 serves as the in-coupling region and the second surface regions 300-1, 300-2 of the SBG serve as out-coupling regions. As an example, FIG. 3 shows a first light ray 304 being coupled into the waveguide 300 via the in-coupling region 300-0. In this example, the first surface region 300-0 is angled relative to the side surfaces 300-S1, ..., 300-S4, such that the first light ray 304 passes through the first surface region 300-0 and into the bulk of the waveguide 300 at an angle sufficient to achieve total internal reflection at each of the side surfaces 300-S1, ..., 300-S4 within the waveguide 300.

[0027]

[0038] Each of the SBGs 300-1, 300-2 can be configured to change between a reflective state and a transmissive state. Figure 3A shows a configuration in which the first SBG 300-1 is in a reflective state, where an incident light ray 304 is reflected off the first SBG 300-1, back into the waveguide 300, and guided along the waveguide 300 until it reaches the second SBG 300-2. SBG 300-2 is shown in a transmissive state, where the light ray 304 is diffracted out of the waveguide 300 through the second SBG 300-2, thereby extracting it from the waveguide 300 through the surface region of the second SBG 300-2. 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.

[0028]

[0039] 3B shows the first SBG 300-1 in a transmissive state. Thus, upon reaching the first SBG 300-1, the first light ray 304 is instead diffracted out of the waveguide 300 via the first SBG 300-1, and thereby instead extracted from the waveguide 300 via 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.

[0029]

[0040] In this manner, a first light ray 304 can be guided through the waveguide 300 from the first region 300-0 until it exits the waveguide 300 at a surface region of the SBG 300-1 or 300-2. For simplicity, only two SBGs 300-1, 300-2 are described in relation to each other, but it will be understood that the same principles can be applied to many more SBGs.

[0030]

[0041] FIG. 3E shows, when viewed in cross section, how first light ray 304 may propagate through TIR from some or all of sides 300-S1, ..., 300-S4 depending on the angle of first light ray 304.

[0031]

[0042] It is equally feasible to use the depicted active light pipe 300 for many-to-one light transfer, as depicted in Figures 3C, 3D and 3F.

[0032]

[0043] Figure 3C shows the same SBG configuration as Figure 3A. The only difference is the use of the waveguide 300; here, a second light ray 308 is shown entering a second SBG 300-2 from an external source (not shown). With the second SBG in a transmissive state, the second light ray 308 is diffracted into the waveguide 300 through the second SBG (which now provides incoupling at its surface region) and from there is guided through the waveguide 300 to the first surface region 300-0 (which now serves as the outcoupling region). This includes reflection from the first SBG 300-1, which is now in a reflective state. The reflective state of the first SBG 300-1 prevents the light ray 308 from exiting the waveguide through the first SBG 300-1. Moreover, external light rays 309 that happen to be incident on the first SBG 300-1 are essentially reflected away from the first SBG 300-1 and therefore do not enter the waveguide 300.

[0033]

[0044] 3D shows the same configuration as FIG. 3B, but here a second light ray 308 is incident on the first SBG 300-1 from an external source. With the first SBG 300-1 in a transmissive state, the second light ray 308 enters the waveguide 300 at that location by diffraction and is guided to the first surface region 300-0.

[0034]

[0045] FIG. 3F shows in cross section how a second light ray 308 may propagate within the waveguide 300, with the same explanation as in FIG. 3E being true, but with the light ray direction reversed.

[0035]

[0046] The above description assumes perfect reflectivity / transmittance of the SBGs in the transmission / reflection state. As will be appreciated, this is not an absolute requirement in practice, and more typically, systems have some tolerance for imperfections in the SBGs 300-1, 300-2 and the waveguide 300. Suitable signal processing techniques for compensating for distortions introduced in the waveguide 300 are described below.

[0036]

[0047] Although SBGs 300-1, 300-2 are depicted as separate elements, in reality separate, independently controllable regions of a single larger SBG may extend across all or most of first side 300-S1.

[0037]

[0048] SBGs are just one possible form of active switching element. For example, with polarized light beams, the same effect can be achieved using controllable polarizing filters attached to the surface of the waveguide 300 or embedded within the bulk of the waveguide. SBGs and controllable polarizing filters are examples of non-mechanical active switches that can change the optical properties of the waveguide 300 through non-mechanical effects. Other examples of inductive elements include controllable mirrors such as micromirror devices or other microelectromechanical systems (MEMs), which are examples of mechanical inductive elements.

[0038]

[0049] When using polarizing filters as the steering elements, the SBGs 300-1, 300-2 can be replaced with passive diffractive elements, with the polarizing filters operating to steer beams towards or away from the passive diffractive elements in a controllable manner as needed, without the need to reconfigure the diffractive elements.

[0039]

[0050] Note that even though the inductive elements themselves are mechanical, this still avoids the need for mechanical movement of the waveguide 300 as a whole.

[0040] Active Light Pipe Network

[0051] As used herein, a "waveguide network" can take the form of a single waveguide or multiple interconnected waveguide networks. Waveguide networks comprising multiple active light pipes have particular advantages in terms of flexible optical data transfer.

[0041]

[0052] 4A and 4B show side views of one side of a waveguide network (portion thereof) including first and second active light pipes 400, 420. The second light pipe 420 has a first surface area 420-0 positioned so as to be aligned adjacent to a corresponding surface area of ​​the first light pipe 400, for receiving a beam from or directing a beam to the second waveguide 420 via the first surface area 400-0. Purely by way of example, a light ray 404 is shown propagating through the first waveguide 400 to a corresponding surface area of ​​the first waveguide 400, which is adjacent to the first surface area 420-0 of the second waveguide 420. A light ray 404 is extracted from the first waveguide 400 via SBG 400-1 attached to an adjacent surface region of the first waveguide 400 and is coupled into the second waveguide 420 via first surface region 400-0. From there, the light ray 404 can be directed to any one of multiple SBGs 420-1, 420-2 of the second waveguide 420 in a one-to-many manner. The same arrangement can also be used to reverse the direction of the light ray and direct the beam in the other direction from the second waveguide 420 to the first waveguide 400 in a many-to-one manner.

[0042]

[0053] Although this example considers two interconnected waveguides 400, 420, the principles can be applied to many more interconnected waveguides to enable flexible data routing through a waveguide network.

[0043]

[0054] More generally, the surface region of the medium may be optically coupled to a corresponding surface region of the waveguide in another manner, such as via an air interface or one or more other optical components (which may themselves be waveguides and may or may not provide active or passive switching functionality).

[0044] Holographic Storage

[0055] Here we describe the application of active light pipes to holographic storage.

[0045]

[0056] 1A and 1B show schematic perspective views of a holographic recording medium 102 (which for simplicity may be referred to simply as medium 102), which is a volume of relatively thick photosensitive material capable of persistently storing a light pattern as a “hologram” embodied within the holographic recording medium 102. A hologram is generated by exposing a subvolume 110 (region) of the medium 102 to a light pattern, such that a persistent state change occurs within that subvolume 110. The hologram generated in the subvolume 110 by that state change records the light pattern into the medium 102, from which the light pattern can be reproduced at a later time. The hologram is persistent in that, once generated, the medium 102 requires no power to maintain it. The composition and structure of the medium 102 can be such that the hologram cannot be erased once generated (thus providing a form of “write-once-read-many” (WORM) storage) or such that the hologram can be erased and replaced (but persists unless and until erased).

[0046]

[0057] A single hologram can record a light pattern that encodes a very large number (e.g., millions) of bits, allowing very large amounts of data to be written to / read from the holographic recording medium 102 in parallel (simultaneously). Another advantage of holographic storage is that many holograms can be written to the same sub-volume 110 of the holographic recording medium 102, thereby greatly increasing the data storage capacity per unit volume of the holographic recording medium 102.

[0047]

[0058] More specifically, FIG. 1A shows how an input beam 104 and a reference beam 106 are directed toward a subvolume 110 via first and second sides 102-4 and 102-6 of the medium 102, respectively, to write a set of data to the medium 102. This generates a light pattern in the form of an interference pattern caused by interference between the input beam 104 and the reference beam 106. If the beams 104 and 106 have sufficient power and the subvolume 110 is exposed for a sufficient duration, the interference pattern created by the interfering beams 104 and 106 will be persistently recorded in the subvolume 110 as a hologram. As explained below, the set of data is embedded in the input beam 104 and can be recovered from the resulting hologram. In this manner, an encoded set of data is written to the subvolume 110. In the following example, the set of data is encoded as a digital image and then embedded in the input beam 104 via spatial modulation.

[0048]

[0059] 1B, to read data from subvolume 110, a matched reference beam 116 is directed into subvolume 110 via second side 102-6 of medium 102, where it interacts with the hologram to produce output beam 108 that is essentially matched to the input beam 104 used to write the hologram, to the extent that the embedded data is recoverable from output beam 108. Output beam 108 propagates out of subvolume 110 via third side 102-8 of medium 102.

[0049]

[0060] The reference beam 116 used to read the data is substantially aligned with the reference beam 106 originally used to write the data, and in particular is oriented at an angle (or, more generally, a direction) that closely matches the angle of the original reference beam 106. This is because the ability to read a hologram (i.e., to generate an output beam 108 from which the data can be recovered) is sensitive to angular deviations between the reference beam 106 used to write the hologram and the reference beam 116 used to read the hologram. This sensitivity can be exploited to record multiple holograms in the same subvolume 110, each hologram generated using a different reference beam angle, so that two entirely different holograms can be generated using only slight differences in the reference beam angle. In this way, many (e.g., hundreds or thousands) holograms can be written to the same subvolume 110, each encoding many (e.g., millions) of bits.

[0050]

[0061] 2A shows a schematic perspective view of an example holographic storage system 200 incorporating certain 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 106 and 116, and the output beam 108; the three separate waveguides 204, 206, and 208 may be referred to individually as the input waveguide 204, the reference waveguide 206, and the output waveguide 208. As noted, 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 and 206) or from (in the case of the output waveguide 208) any one of multiple subvolumes 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 the waveguides 204, 206, 208 relative to the holographic recording medium 102. To avoid the need for such mechanical movement, inductive elements are located on or within each waveguide 204, 206, 208, and can be configured to vary the optical properties of the waveguides 204, 206, 208 in order to direct signals to or from different sub-volumes of the medium 102, i.e., to create different channels within the waveguides 204, 206, 208 as desired. In this particular example, the inductive elements take the form of active optical switching elements (switches). The forms that the switches can take are varied. In this example, the switches take the form of SBGs located on different surface regions of the waveguides 204, 206, 208 in the same general arrangement as in FIGS. 3A-F. That is, each waveguide 204, 206, 208 takes the form of an active light pipe, and each waveguide 204, 206, 208 has the same general physical structure as active light pipe 300 of Figures 3A-F.

[0051]

[0062] Each waveguide 204, 206, 208 is positioned such that its first surface (i.e., the surface on which its SBG is located) is adjacent to a different side of the medium 102, thereby causing its SBG to extend along that side of the medium 102. The first and second SBGs of each waveguide 204, 206, 208 are indicated by reference numerals 204-1, 204-2, 206-1, 206-2, 208-1, and 208-2, respectively, and are all configurable in the manner described above. Additional SBGs are depicted without reference numerals, and the number of SBGs can be selected to accommodate any size of holographic recording medium 102. The following description will refer to the first and second SBGs of each waveguide 204, 206, and 208 for simplicity, but it will be understood that the description applies to more SBGs.

[0052]

[0063] 2B-2D illustrate how input and reference waveguides 204, 206 are used to write data to medium 102 in a one-to-many fashion. FIG. 2B shows a schematic plan view of system 200, while FIGS. 2C and 2D show side views of one side showing input and reference waveguides 204, 206, respectively. Input waveguide 204 is used to direct input beam 104 to any one of multiple subvolumes of medium 102 via any one of SBGs 204-1, 204-2 of input waveguide 204 in the manner described above. Reference waveguide 206 is configured to simultaneously direct reference beam 106 to the same subvolume, generating the desired interference pattern to be written in that subvolume. In the depicted example, both the input waveguide 204 and the reference waveguide 206 are configured to direct the input and reference beams 104, 106, respectively, to the subvolume indicated by reference numeral 110 via the second SBGs 204-2, 206-2 of each waveguide 204, 206, respectively.

[0053]

[0064] Figures 2E-2G show how reference and output waveguides 206, 208 can be used to read data from medium 102. Figure 2E is a plan view, and Figures 2F and 2G show side views of one side showing reference and output waveguides 206, 208. Reference waveguide 206 is used in exactly the same way as depicted in Figures 2B-2D, except here, reference beam 116 is directed to the subvolume where the hologram is to be read (in this case, subvolume 110). Output waveguide 208 is used in a one-to-many fashion to direct the resulting output beam 108 from subvolume 110 through waveguide 208 for subsequent detection.

[0054]

[0065] Each sub-volume 110 may have, for example, a height and width of a few millimeters as measured along any side, which would generally be sufficient to store several million pixels per data "page" (e.g., multiplexing angle). In this case, the volume of the sub-volume is sufficient to store (millions of pixels) * (# number of multiplexing angles).

[0055]

[0066] The inductive elements of the input waveguide 204 and the reference waveguide 206 (SBGs in this example) are configured to provide channels for the input beam 104 and the reference beam 106, 116, as needed, from the beam source (emitter system) to the sub-volume 110 being read. The SBGs are set to a transmissive or reflective state as needed to create the channels. Similarly, the inductive elements of the output waveguide 208 (also SBGs in this example) are similarly configured to provide channels from the sub-volume 110 being read to the detector. To provide additional context, this will be described in more detail below with reference to the multiple waveguide network depicted in FIG. 5. However, the principles described in connection with the specific example of FIG. 5 apply more generally to other waveguide network topologies, including both simpler networks (e.g., a single waveguide) and more complex waveguide networks.

[0056]

[0067] As noted above, this allows spatial multiplexing across medium 102 without mechanical movement of medium 102 relative to waveguides 204, 206, 208. This is true whatever form the inductive elements take (which, as noted above, can themselves be mechanical or non-mechanical).

[0057] Holographic storage using multiple waveguide networks.

[0068] FIG. 5 shows an example of a holographic storage system incorporating a multiplexed waveguide network of the type shown in FIG.

[0058]

[0069] The input waveguide network is shown to include a first input light pipe 203 (a "parent" waveguide) to which multiple second input light pipes 204A, 204B ("child" waveguides) are coupled. An input beam 104 from an emitter system 504 is coupled into the first input waveguide 203 through its incoupling region, from which it can be directed to a second input waveguide 204A or 204B.

[0059]

[0070] The reference waveguide network is shown to include a first reference waveguide 205 to which multiple second reference waveguides 206A, 206B are coupled. Reference beams 106, 116 from an emitter system 504 can similarly be coupled into the first reference waveguide 205 and directed to the second reference waveguides 206A or 206B.

[0060]

[0071] The output waveguide network is shown to include a first output waveguide 207 to which a plurality of second output waveguides 208A, 208B are coupled.

[0061]

[0072] The depicted arrangement allows beams to be directed to / from different sub-volumes of multiple pieces 102A, 102B of holographic storage media.

[0062]

[0073] Although Figure 5 shows input beam 104, reference beams 106, 116 and output beam 108, it will be understood that the sub-volumes would typically be written and read at different times in the manner described above with reference to Figures 2A-G.

[0063]

[0074] A first group of second waveguides 204A, 206A, 208A (one each for input, reference, and output) are positioned around a first piece 102A (first medium) of holographic storage media, and a second group of second waveguides 204B, 206B, 208B are positioned around a second piece 102B (second medium), each in the same general arrangement as in Figures 2A-G. Thus, input and reference beams 104, 106, 116 can be directed to any subvolume of any media piece 102A, 102B by first directing those beams into the desired second waveguides of the input and reference networks, respectively, and then directing them into the desired subvolume of the media piece adjacent to the desired waveguide.

[0064]

[0075] The output waveguide network can be used to direct the output beam 108 from any subvolume of any medium piece 102A, 102B from the applicable second output waveguide 208A, 208B to the first output waveguide 207, and then from the first output waveguide 207 through the outcoupling region of the first output waveguide 207 to the detector 508. To read from a particular subvolume, the SBGs are configured to provide a channel from that subvolume to the detector; thus, in this case, SBGs 204A-2 and 207-1 are set to a transmissive state, and other SBGs of the output waveguide network are set to a reflective state as needed to provide a channel for the output beam 108 to the detector 508 (e.g., in this case, SBG 207-2 of the first output waveguide 207 is set to a reflective state to prevent propagation of the output beam 108 to waveguide 208B). Other SBGs in the output waveguide network can be set to be reflective to the extent necessary to prevent unwanted light transmission (i.e., "leakage") from other areas of the same media piece 102A or from different media pieces 102B (e.g., in this example, SBG 204A-1, which is close to the subvolume being read, is shown to be set to be reflective to prevent unwanted leakage).

[0065]

[0076] Although the above example uses three separate waveguide networks for the input, reference, and output beams 104, 106, 116, 108, this is not necessary. For example, the same waveguide network could be used to carry both the input beam 104 and the reference beams 106, 116, and / or the same waveguide network could be used to carry the input beam 104 and the output beam 108, and / or the same waveguide network could be used to carry the output beam 108 and the input beam 104. Generally, having three separate networks is expected to provide optimal performance, although there are nevertheless perfectly viable implementations using only one or two waveguide networks.

[0066]

[0077] Although not depicted in any of the figures, a fourth waveguide network can be used to deliver beams to the remaining sides of media pieces 102A, 102B. For example, a fourth network can be used to deliver an erase beam to a desired sub-volume that is at least suitable for erasing a hologram therefrom (in the case of erasable holographic storage).

[0067]

[0078] Figure 9 shows an alternative physical structure in which a single "slab" of holographic medium 102 is used in place of the individual pieces 102A, 102B of Figure 5. An input waveguide network is depicted, having essentially the same physical configuration, but here second input waveguides 204A, 204B are configured to direct input beams 104 to different subvolumes of the same slab 102. While in Figure 5, each of the second input waveguides 204A, 204B provides multiplexing in one dimension along the length of a different single piece of medium 102A, 102B, in Figure 9, the second waveguides 204A, 204B provide spatial multiplexing in two dimensions across the slab of holographic medium 102 (each waveguide individually provides one-dimensional multiplexing, but there is two-dimensional multiplexing across the slab 102 as a whole).

[0068]

[0079] The system of Figure 9 is limited to a maximum of two waveguide networks (one on each side of the slab 102). As noted above, this is still a viable arrangement because the same network can be used to carry multiple beams.

[0069] Data Encoding

[0080] 6A shows an example of an emitter system 504 that provides both the input beam 104 and the reference beam 106. The input beam is an expanded, spatially modulated laser beam. A laser 600 emits a coherent, narrow laser beam that is split using a beam splitter 602.

[0070]

[0081] A portion of the beam from beam splitter 602 is used as reference beam 106. In this example, controllable reference beam steering element 612 is used to steer reference beam 106 to enter reference waveguide 206 at a desired angle. By changing the angle of reference beam 106 before it is introduced into reference waveguide 206, different holograms can be written to / read from the same sub-volume of media in the manner described above.

[0071]

[0082] As an alternative or in addition to beam angle multiplexing, multiple patterns can be stored in and read from the same sub-volume with different phases of the reference beams 106, 116 (phase multiplexing). Thus, a logical address may correspond to a particular reference beam angle and / or phase characteristic. All discussion regarding modulation of the reference beam angle applies equally to phase modulation.

[0072]

[0083] The other portion of the beam from the beam splitter 602 is expanded using a beam expander 604, and the expanded beam passes through a spatial light modulator (SLM) 606. An encoder 610 receives a set of data to be encoded and encodes the set of data as a digital image, which is then modulated via the SLM 606 and embedded in the expanded beam. An incoupling optic (in this case, a Fourier lens 608) positioned so that the plane of the SLM 606 is substantially in the focal plane of the Fourier lens 608 is used to separate the expanded beam into distinct propagation modes, where each mode corresponds to a unique propagation direction, where each mode corresponds to a specific point in the plane of the SLM 606. The distinct propagation modes are introduced into the input waveguide 204 and guided therefrom in the manner described above. Using the incoupling optics 608, data is "angularly encoded" within the input beam in the sense that points in the digital image essentially correspond to unique propagation directions (i.e., unique propagation modes of the input beam 104). This is analogous to a ray of light from a distant object viewed as infinity. The angle-encoded input beam 104 of Figure 6A is an example of multiple propagation modes (i.e., components propagating in different directions) of a "multimode" optical signal; this arrangement provides a form of angular diversity.

[0073]

[0084] Note that the term "multimode" does not necessarily imply the use of such incoupling optics 608, nor does it necessarily require that all image points uniquely correspond to a given propagation direction. That is, multimode does not necessarily imply a one-to-one correspondence between propagation modes and image / data points. For example, FIG. 6B shows an alternative viable emitter system in which the spatially modulated beam is directly coupled 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 propagation directions and image points, and possibly no one-to-one correspondence between image / data points and modes. This provides a form of spatial diversity based on a form of MIMO (multiple-input, multiple-output) transfer through multiple pixels of the SLM 606 and the detector array of the spatially coherent detector 508.

[0074] Data Decryption

[0085] 7 illustrates a spatially coherent detector 508 used to measure the optical field of the output beam 108. In contrast to conventional "direct detection," the spatially coherent detector 508 includes an array of pixels (or, more generally, detector elements), each configured to measure both the amplitude and phase (rather than just intensity) of the optical field at that pixel's location. These can be measured, for example, using the spatially coherent detector's 508 local oscillator 712. The array of pixels can thus measure the phase and amplitude variations of the optical field in both time and space, and thus provide an analog or digital representation of the measured optical field. In this case, the optical field being measured is the optical field of the output beam 108 directed to the spatially coherent detector 508 via the output waveguide 208.

[0075]

[0086] Although only a single array is depicted, there may in fact be multiple physical arrays working together as a single "logical array." For example, this logical array may be split across two physical cameras.

[0076]

[0087] The physical detector array can take the form of a single camera (each detector element is a pixel or set of pixels in 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 potentially be split across a large number of physical detectors.

[0077]

[0088] As described, the route from a particular incoupling region where a beam enters a waveguide network to a particular outcoupling region where the beam exits the waveguide network (these regions may be in the same or different waveguides) may be referred to herein as a "channel." As described, in a multimode waveguide network, a single channel encompasses multiple spatial paths. The output beam 108 will be directed through a particular channel of the output waveguide network (i.e., from that particular incoupling region to the outcoupling region of the output waveguide 208). Moreover, the output beam 108 will be generated from a hologram generated using an input beam directed from the incoupling region of the input waveguide network to that particular outcoupling region. The hologram will be generated and read using a reference beam similarly directed through a particular channel through a reference waveguide network. The input beam 104, the reference beams 106, 116, and the output beam 108 are all subject to distortions within the associated waveguide network specific to the channel through which they are directed. To compensate for such distortions, the signal processing component 700 applies analog and / or digital signal processing to the representation of the measured field. The signal processing component 700 does so using a channel model associated with the subvolume currently being read (i.e., from which the output beam 108 was generated). The channel model associated with a particular subvolume models not only the channels through which the output beam 108 is directed to the detector 508, but also the channels through which the input beam 104 used to write the hologram was directed to that subvolume and the channels through which the reference beams 106, 116 used to write / read the hologram were directed to that subvolume.

[0078]

[0089] Each channel model can take the form of, for example, a transfer function (which models the channel directly) or an inverse transfer function (which models the channel with its approximate inverse). Note that the transfer function is applied to a representation of the measured light field (i.e., both its measured phase and amplitude at different spatial points), not just the light intensity. Spatially coherent detection offers greater scope for removing or reducing such channel distortions, with the goal of recovering the original digital image accurately enough to allow the decoder 704 to easily decode the encoded data from the recovered image.

[0079]

[0090] The signal processing 700 can correct for phase interference and noise, for example, using a combination of optical and computational techniques (which may include, for example, machine learning techniques).

[0080]

[0091] Using a training 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 with a trained function (e.g., an inverse transfer function) that inverts the channel distortion effects. The input to such a function is the distorted field (phase and amplitude) of the output beam measured through spatially coherent detection, and 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., pairs of distorted output field and clean input field), a model can be trained to approximate this inverse function (i.e., when the distorted output field (phase and amplitude) is given as input, the trained model nearly recovers the original input field). This is true even if the model did not encounter that exact form of the distorted output field during training, because such a model can generalize from a sufficient set of training examples. 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 based on a loss function that, for each training example, penalizes the difference between that training example's output tensor (as generated by applying the CNN to that training example's input tensor) and the known corresponding input field. As will be appreciated, this approach can be applied not only in holographic storage, but also in any situation where the output field exhibits waveguide distortions, provided such training examples can be collected.

[0081]

[0092] Although described in the context of holographic storage, the use of such signal processing 700 in combination with spatially coherent detection is not limited in this respect and may be applied in other contexts such as optical communications or optical computing, or any other context in which a received output beam is susceptible to distortions introduced in one or more waveguide networks.

[0082]

[0093] Figure 7 shows outcoupling optics 715 arranged to essentially reverse the effect of incoupling optics 608 of Figure 6B (i.e., to essentially resolve each propagation mode to a single point in the plane of spatially coherent detector 508). Again, this is not required, and outcoupling optics 715 can be omitted by using the alternative emitter system of Figure 6B.

[0083]

[0094] Although not depicted in Figures 6A or 6B, some level of pre-processing can be applied to the digital image before it is modulated and embedded into the input beam 104. This can reduce the level of compensation required at the detector side. Even with such pre-processing, some degree of detector-side processing can be applied to account for different distortion effects between different channels.

[0084] Dynamic Scheduling

[0095] 8 shows a controller in the form of a scheduler 800 that can schedule read and write operations within a holographic storage system of the type described above. To facilitate effective scheduling, sub-volumes within the medium 102, or within each media piece 102A, 102B, are assigned unique addresses. This provides a form of addressable holographic storage that is similar to more conventional forms of addressable electronic storage. However, there are many features that go beyond conventional addressing.

[0085]

[0096] First, as described above, a single subvolume can store multiple holograms at different reference beam angles. To accommodate this, each address uniquely corresponds to a specific subvolume in combination with a specific reference beam direction (i.e., each available tuple is assigned a unique address), indicates a specific subvolume within media 102 or one of media pieces 102A, 102B, and indicates a specific reference beam direction (e.g., an angle or set of angles defining a beam direction; the term "angle" can be used as shorthand to refer to the direction of the reference beam, but it will be understood that a direction can effectively be defined by multiple angles depending on the system configuration). Thus, a subvolume can be associated with potentially many addresses corresponding to different reference beam angles. A tuple defines a logical storage location, and the same subvolume at different reference beam angles provides multiple logical storage locations at the physical level. Each logical storage location has a unique address (ADDR). This notation is used as shorthand to mean an address corresponding to a subvolume and a reference beam angle, but it will be understood that this does not imply a specific address representation. Any address space and addressing mechanism that uniquely identifies logical storage locations of this nature can be used.

[0086]

[0097] Second, in contrast to conventional storage devices, each logical memory location can store an entire image, and thus a single logical memory location can potentially store a very large number (e.g., thousands or millions) of bits.

[0087]

[0098] Scheduler 800 operates at the logical storage level and schedules incoming read and write operations for different addresses within appropriate time intervals.

[0088]

[0099] Reference numerals 804, 806, and 808 are used to denote input, reference, and output optical waveguide networks, respectively. As described above, each can be a single waveguide network or a multiple waveguide network (e.g., similar to FIG. 5), with one or more configurable inductive elements (e.g., SBG or other active switching elements) that can be used to create channels to different sub-volumes of a piece (or pieces) of holographic storage media.

[0089]

[0100] During the period when a write operation for a particular address is scheduled (the write period), the inductive elements in the input and reference waveguide networks 804, 806 are configured to create a channel for the input beam 104 and the reference beam 106 from the emitter system 504 through the input and reference networks 804, 806, respectively, to the corresponding sub-volume. In addition, the reference beam steering element 612 is configured to steer the reference beam 106 in a corresponding direction toward the reference network 806. This generates a desired interference pattern at the reference beam angle within the sub-volume, and therefore, if the sub-volume is exposed to the interference pattern for a sufficiently long duration, the interference pattern will be persistently stored as a hologram.

[0090]

[0101] During the period when a read operation for a particular address is scheduled (the read period), the steering elements in the reference and output networks 806, 808 are similarly configured to create a channel for the reference beam 116 through the reference network 806 to the sub-volume, and a channel for the output beam 108 from the sub-volume through the output network 808 to the detector 508. The reference beam steering element 612 is similarly configured to steer the reference beam 116 to the reference network 806 in a corresponding direction to read the intended hologram in the sub-volume at the reference beam angle.

[0091] Alternative Waveguide Networks:

[0102] 10A and 10B show an alternative system in which spatial multiplexing is achieved instead by modulating one or more optical properties of the input and reference beams 104, 106, 116. In such a system, passive (non-switchable) inductive elements may be used instead of the active (switchable) inductive elements of the previous figures.

[0092]

[0103] The example in Figure 10A considers frequency (or equivalently wavelength) modulation. In this case, the light pipes themselves are passive, with static wavelength-dependent outcoupling (such as continuous long-pass dichroic interference filters or variable center wavelength bandpass filters).

[0093]

[0104] FIG. 11A shows a light pipe 1100 having an outer surface 1100-S, along which are located multiple passive filters 1100-1 and 1100-2. The configuration of the light pipe 1100 is the same as that shown in FIGS. 3A-D, except that the filters 1100-1 and 1100-2 replace the SBGs 300-1 and 300-2. The filters 1100-1 and 1100-2 have different frequency responses (i.e., they act as frequency filters). More specifically, each filter 1100-1 and 1100-2 essentially transmits a relatively narrow range of optical frequencies and is essentially reflective to frequencies outside that range. FIG. 11A shows an incoupling beam 1104, whose frequency is within the range of the second filter 1100-2 but outside the range of the first filter 1100-1. Thus, beam 1104 is reflected by first filter 1100-1 but is transmitted through second filter 1100-2 (and thus exits light pipe 1100 at that location). Figure 11B shows a different frequency beam 1104', where the frequency is within the range of first filter 1100-1 and is therefore transmitted through first filter 1100-1.

[0094]

[0105] 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 system variations.

[0095]

[0106] 10A shows a scheduler 800 communicatively coupled to the laser 600 of the emitter system for varying the frequency (or equivalently, wavelength) of the input and reference beams 104, 106, 116. In this case, either beam can be directed to a desired holographic storage region by setting the frequency accordingly. Here, different beam frequencies correspond to different routes through the waveguide network (defined by different frequency characteristics of the passive filters), and the frequency can be set to correspond to any desired route.

[0096]

[0107] In this case, wavelength is used as the switching dimension. Laser 600 is a high speed tunable laser that functions as the active element.

[0097]

[0108] In such a realization, switching can be in only one spatial dimension (i.e., along a single pipe). However, with a laser having sufficient range and narrow linewidth, the first light pipe can filter coarsely (i.e., over a relatively wide wavelength range), and subsequent light pipes sample more finely (i.e., over a narrower wavelength range). Another factor limiting the linewidth is the requirement for a relatively long coherence length, so that in any event, the linewidth can be sufficiently narrow. In the context of holographic storage, this implementation can be combined with a second implementation using, for example, a different switchable parameter (e.g., polarization) to achieve replication of an input field to addressable locations across a two-dimensional output space.

[0098]

[0109] In connection with the readout operation, the frequency of the output beam 108 is matched to the frequency of the reference beam 116 used to read the particular sub-volume, and the same principles can be applied to return it to the detector using an appropriate filter in the output waveguide network 808.

[0099]

[0110] Figure 10B shows an example of such an implementation with a controllable polarizing element 601 that can be used to change the polarization of the input and reference beams 104, 106, 116. This can be combined with passive polarization filters on or within the light pipe. This can be implemented as an alternative to or in addition to the passive frequency filters of the example of Figure 10A. Such polarization modulation provides two independent routes and can be useful in combination with, for example, passive wavelength filtering and / or active light pipes. Beam polarization modulation can also be combined with active polarization filters.

[0100]

[0111] It should be noted that the various "passive" and "active" implementations described above can all be implemented separately or in combination (e.g., a combination of active and passive inductive elements can be used), i.e., a waveguide can have both passive and active elements and / or it is possible to combine active and passive waveguides in the same network.

[0101] Additional hierarchy levels:

[0112] The above example considers a waveguide network having two hierarchical “levels”: a parent waveguide and a child waveguide. However, a multiplexed waveguide network may have three (parent, child, grandchild) or more levels. Note that the terms “child,” “parent,” and “grandchild” do not necessarily imply a direct hierarchical relationship. That is, the term child or grandchild may refer to any waveguide at any hierarchical level below the parent or child waveguide, respectively. That is, a child / grandchild waveguide may be optically coupled to a parent / child waveguide, for example, not only via an air interface (direct descendant) but also via one or more of its other child / grandchild waveguides (indirect descendants).

[0102]

[0113] 12 shows an example of a waveguide network with three hierarchical levels: a parent waveguide 1200 has two direct child waveguide networks 1202A, 1202B optically coupled to the parent waveguide 1200 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 the child waveguide 1202A / 1202B in the same manner.

[0103]

[0114] An extreme example is a "binary tree" architecture where every waveguide has exactly two direct children, potentially with more than three levels of waveguides, but in practice there may be situations where it is preferable to increase the number of direct children in order to reduce the number of hierarchical levels required.

[0104]

[0115] The scheduler 800 shown in Figures 8, 10A, and 10B is a functional component of the system. Similarly, the encoder 610, the decoder 704, and the signal processing component 700 are also functional components. Such components may be implemented in software (i.e., as program code executing on one or more programmable hardware processors, such as a CPU, accelerator, or GPU) 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 may be analog or digital signal processing, or any combination thereof. Such program code and other data (e.g., the channel model 702) may be encoded in a computer-readable storage device. Examples of computer-readable storage devices include optical, magnetic, and / or solid-state storage devices, capable of storing code, data, and the like in a non-transitory form. This is in contrast to a transitory medium, such as a transient signal carrier wave.

[0105]

[0116] A first aspect of the present specification provides an optical data transfer system including: a beam modulator configured to embed a set of data in an input beam; an input waveguide network formed from one or more multi-mode optical waveguides, the input waveguide network having an in-coupling region for receiving the input beam and configured to direct the input beam to an out-coupling region of the input waveguide network; a spatially coherent detector configured to measure the 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 therefore exhibiting distortion effects caused at least in part by the input beam passing through the input waveguide network; and at least one processor coupled to the spatially coherent detector, the at least one processor configured to apply signal processing to an output of the spatially coherent detector to compensate for said distortion effects and thereby recover the set of data embedded in the input beam from the output of the spatially coherent detector.

[0106]

[0117] In an embodiment, the optical data transfer system may include at least one holographic recording region, wherein an input waveguide network is configured to direct an input beam to the holographic recording region to store embedded data in a pattern recorded in that region through interference between the input beam and a reference beam, and an output optical field is generated at a later time through interaction between the recorded pattern and the reference beam to read the embedded data from that holographic recording region.

[0107]

[0118] The optical data transfer system may be configured to direct a reference beam to the holographic recording region via one of an input waveguide network and a reference waveguide network formed from one or more further multimode optical waveguides, and passage of the reference beam through the input or reference waveguide network may also contribute to said distortion effects that are compensated for by signal processing.

[0108]

[0119] The optical data transfer system may be configured to direct an output beam, at least partially defined by the input beam, to a spatially coherent detector via one of an input waveguide network, a reference waveguide network as described above, and an output waveguide network formed from one or more further multimode optical waveguides, and the passage of the output beam through the input, reference or output waveguide network may also contribute to said distortion effects that are compensated for by signal processing.

[0109]

[0120] At least one of the input waveguide network, the reference waveguide network and the output waveguide network may include at least one inductive element that is configurable and / or responsive to at least one beam characteristic, whereby different channel options for the at least one waveguide network may be realized by reconfiguring the at least one inductive element and / or modulating the at least one beam characteristic, and at least one processor may be configured to apply the signal processing in response to a channel selection associated with the output optical field.

[0110]

[0121] The at least one processor may be configured to select a channel model corresponding to the associated channel selection from a plurality of channel models corresponding to different channel options, and to apply the signal processing in accordance with the selected channel model.

[0111]

[0122] Each channel model may include a set of signal processing parameters learned for the corresponding channel selection.

[0112]

[0123] A second aspect of the present specification provides an optical data transfer system including: a beam modulator configured to embed a set of data in an input beam; a spatially coherent detector configured to measure the phase and amplitude of an optical field of an output beam at a plurality of locations, the output beam being defined at least in part by the input beam; an output waveguide network formed from one or more multi-mode optical waveguides, the output waveguide network having an in-coupling region for receiving the output beam and configured to direct the output beam to an out-coupling region of the output waveguide network for reception by the spatially coherent detector; and at least one processor coupled to the spatially coherent detector, the at least one processor configured to apply signal processing to an output of the spatially coherent detector to compensate for distorting effects caused, at least in part, by the output beam passing through the output waveguide network, thereby recovering the set of data embedded in the input beam from the output of the spatially coherent detector.

[0113]

[0124] The optical data transfer system may include a plurality of holographic recording regions, and the output optical waveguide network has at least one directing element that is configurable and / or responsive to at least one beam characteristic, whereby by reconfiguring the at least one directing element and / or modulating the at least one beam characteristic, any region of the plurality of holographic recording regions can be selected for readout using the same spatially coherent detector to direct an output beam from the selected holographic recording region to the spatially coherent detector, and at least one processor is configured to apply said signal processing in response to the holographic recording region being readout.

[0114]

[0125] Each holographic recording region may be associated with at least one channel model, and the at least one processor may be configured to apply the signal processing using the channel model associated with the holographic recording region being read.

[0115]

[0126] Each holographic recording region may have at least one logical address, and the channel model may be selected based on a logical address associated with the current read operation that identifies the holographic recording region being read.

[0116]

[0127] The optical data transfer system may be configured to direct a reference beam to selected ones of the holographic recording regions via one of an output waveguide network and a reference waveguide network formed from one or more further multimode optical waveguides, and the passage of the reference beam through the output or reference waveguide network may also contribute to said distortion effects that are compensated for by signal processing.

[0117]

[0128] The optical data transfer system may be configured to direct an input beam to selected ones of the holographic recording regions via one of an output waveguide network and an input waveguide network formed from one or more further multimode optical waveguides, and the passage of the input beam through the output or input waveguide network may contribute to said distortion effects that are compensated for by signal processing.

[0118]

[0129] A third aspect of the present specification provides an optical data transfer system including: a beam modulator configured to embed a set of data in an input beam; a spatially coherent detector configured to measure the 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 from one or more multi-mode optical waveguides, the reference waveguide network having an in-coupling region for receiving the reference beam and configured to direct the reference beam to an out-coupling region of the reference waveguide network to define the output optical field; and at least one processor coupled to the spatially coherent detector, the at least one processor configured to apply signal processing to an output of the spatially coherent detector to compensate for distorting effects caused, at least in part, by passage of the reference beam through the reference waveguide network, thereby recovering the set of data embedded in the input beam from the output of the spatially coherent detector.

[0119]

[0130] An optical communication system or an optical computing system may include at least one such optical data transfer system.

[0120]

[0131] In certain embodiments described above, a waveguide network such as that described below may be used.

[0121]

[0132] A multimode optical waveguide network may include a parent waveguide and a plurality of child waveguides, each of the parent and child waveguides being 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, wherein each of the second surface regions of the parent waveguide is optically coupled to a first surface region of a corresponding one of the child waveguides, and the at least one guiding element of the parent waveguide is arranged to guide a beam from or to its first surface region to or from a selected second surface region of the plurality of second surface regions, the beam being coupled to or from a selected second surface region of the second surface region of the parent waveguide. a first surface region of a corresponding daughter waveguide optically coupled to a second surface region of the parent waveguide, the first surface region of the corresponding daughter waveguide being coupled to the second surface region of the parent waveguide, and at least one directing element of each daughter waveguide being arranged to direct the beam from or to its first surface region to or from a selected second surface region of the plurality of second surface regions, the at least one directing element of each waveguide being configurable to select the second surface region of that waveguide and / or to select the second surface region of that waveguide via modulation of at least one beam characteristic in response to at least one beam characteristic.

[0122]

[0133] The multimode optical waveguide network may include a plurality of grandchild waveguides, each of which is a multimode optical waveguide having a first surface region, a plurality of second surface regions, and at least one inductive element attached to a surface of the grandchild waveguide or embedded within the grandchild waveguide, wherein each of the second surface regions of each grandchild waveguide is optically coupled to a first surface region of a corresponding one of the grandchild waveguides, and the at least one inductive element of each grandchild waveguide is coupled to or from its first surface region through a selected second surface region of its plurality of second surface regions. The waveguides may be arranged to direct a beam to or from a selected second surface region, the beam being introduced into or extracted from the grandchild waveguide via its first surface region and via the second surface region of a grandchild waveguide optically coupled thereto, and at least one directing element of each grandchild waveguide may be configured to select the second surface region of its grandchild waveguide and / or to select the second surface region of its grandchild waveguide via modulation of at least one beam characteristic in response to at least one beam characteristic.

[0123]

[0134] Each of the waveguides may have at least one active inductive element configurable to select a second surface region of that waveguide.

[0124]

[0135] Each of the waveguides may have at least one inductive element responsive to the at least one beam characteristic to select a second surface region of that waveguide through modulation of the at least one beam characteristic.

[0125]

[0136] At least one of the waveguides may have at least one active inductive element configurable to select a second surface region of that waveguide, and at least another of the waveguides may have at least one inductive element responsive to at least one beam characteristic to select a second surface region of the other waveguide via modulation of the at least one beam characteristic.

[0126]

[0137] One of the parent waveguides and one of the child waveguides may have at least one wavelength-responsive directing element, whereby a beam in a first wavelength range is directed from or to its first surface region to or from a first of the child or grandchild waveguides, and a beam in a second wavelength range is directed from or to its first surface region to or from a second of the child or grandchild waveguides, and the first child or grandchild waveguide may have at least one wavelength-responsive directing element, whereby a beam in a first sub-range of the first wavelength range is directed from or to its first surface region to or from one of its second surface regions. The second waveguide may have at least one wavelength-responsive directing element, whereby a beam within a first sub-range of the second wavelength range is directed from or to the first surface region to or from one of the second surface regions, and a beam within a second sub-range of the second wavelength range is directed from or to the first surface region to or from another of the second surface regions.

[0127]

[0138] The or each active inductive element may have at least one of a configurable transmittance and reflectance and a configurable refractive index.

[0128]

[0139] The or each active inductive element may be a switchable grating or grating region.

[0129]

[0140] At least one of the inductive elements may be a wavelength and / or polarization filter having a fixed or configurable wavelength response and / or a fixed or configurable polarization axis.

[0130]

[0141] At least one of the waveguides may have two or more guiding elements and three or more second surface regions, any of which may be selected by configuring one or both of the two or more guiding elements and / or modulating at least one beam characteristic.

[0131]

[0142] An optical system incorporating such a waveguide network may include: a first optical system component; a plurality of second optical system components; at least one multimode optical waveguide network according to any of the aspects or embodiments described above, the multimode optical waveguide network being arranged to direct a beam from or to the first optical system component to or from a selected second optical system component of the plurality of second optical system components; and a controller configured to select one second optical system component of the plurality of second optical system components, and to direct the beam from or to the first optical system component to or from the selected second optical system component by configuring at least one of the directing elements of the multimode optical waveguide network and / or modulating at least one beam characteristic.

[0132]

[0143] The first system component may include an emitter system for emitting and directing the beam to a selected second system component or a detector array from which the beam is directed from the selected second system component.

[0133]

[0144] The optical system may include one or more holographic recording media, and at least some of the second system optical components may be respective sub-volumes of the one or more holographic recording media.

[0134]

[0145] The optical system may include a second multimode optical waveguide network according to any of the aspects or embodiments described above, and the controller may be configured to direct a second beam from or to the first optical system component to or from the same selected second optical system component by configuring at least one of the directing elements of the second multimode optical waveguide network and / or modulating at least one beam characteristic.

[0135]

[0146] The optical system may include a third multimode optical waveguide network according to any of the aspects or embodiments described above, and the controller may be configured to direct a third beam from or to the first optical system component to or from the same selected second optical system component by configuring at least one of the directing elements and / or modulating at least one beam characteristic of the third multimode optical waveguide network.

[0136]

[0147] For example, in the context of optical communications or optical computing, at least one of the first and / or second optical system components may include a signal converter or optical processor configured to convert the beam into an electrical signal (or vice versa).

[0137]

[0148] In certain embodiments described above, a waveguide network such as that described below may be used.

[0138]

[0149] The multimode optical waveguide network may include a parent waveguide and a plurality of child waveguides, each of the parent and child waveguides being 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 of the second surface regions of the parent waveguide being optically coupled to a first surface region of a corresponding one of the child waveguides, the at least one guiding element of the parent waveguide being arranged to guide a beam from or to its first surface region to or from a selected second surface region of the plurality of second surface regions, the beam passing through and through the second surface region of the parent waveguide. a beam is introduced into or received from a corresponding child waveguide, the first surface region of which is optically coupled to the second surface region of the parent waveguide, via its first surface region of the corresponding child waveguide, the at least one directing element of each child waveguide being arranged to direct the beam from or to its first surface region to or from a selected second surface region of the plurality of second surface regions, the at least one directing element of each waveguide being configurable to select the second surface region of that waveguide and / or to select the second surface region of that waveguide via modulation of at least one beam characteristic in response to at least one beam characteristic.

[0139]

[0150] The multimode optical waveguide network may include a plurality of grandchild waveguides, each of which is a multimode optical waveguide having a first surface region, a plurality of second surface regions, and at least one inductive element attached to a surface of the grandchild waveguide or embedded within the grandchild waveguide, wherein each of the second surface regions of each grandchild waveguide is optically coupled to a first surface region of a corresponding one of the grandchild waveguides, and the at least one inductive element of each grandchild waveguide is coupled to or from its first surface region by a selected second surface region of its plurality of second surface regions. The optical waveguides may be arranged to direct a beam onto or from a selected second surface region, the beam being introduced into or extracted from the grandchild waveguide via its first surface region and via the second surface region of a grandchild waveguide optically coupled thereto, and at least one directing element of each grandchild waveguide may be configured to select the second surface region of its grandchild waveguide and / or to select the second surface region of its grandchild waveguide via modulation of at least one beam characteristic in response to at least one beam characteristic.

[0140]

[0151] Each of the waveguides may have at least one active inductive element configurable to select a second surface region of that waveguide.

[0141]

[0152] Each of the waveguides may have at least one inductive element responsive to the at least one beam characteristic to select a second surface region of that waveguide through modulation of the at least one beam characteristic.

[0142]

[0153] At least one of the waveguides may have at least one active inductive element configurable to select a second surface region of that waveguide, and at least another of the waveguides may have at least one inductive element responsive to at least one beam characteristic to select a second surface region of the other waveguide via modulation of the at least one beam characteristic.

[0143]

[0154] One of the parent waveguides and one of the child waveguides may have at least one wavelength-responsive directing element, whereby a beam in a first wavelength range is directed from or to its first surface region to or from a first of the child or grandchild waveguides, and a beam in a second wavelength range is directed from or to its first surface region to or from a second of the child or grandchild waveguides, and the first child or grandchild waveguide may have at least one wavelength-responsive directing element, whereby a beam in a first sub-range of the first wavelength range is directed from or to its first surface region to or from one of its second surface regions. The second waveguide may have at least one wavelength-responsive directing element, whereby a beam within a first sub-range of the second wavelength range is directed from or to the first surface region to or from one of the second surface regions, and a beam within a second sub-range of the second wavelength range is directed from or to the first surface region to or from another of the second surface regions.

[0144]

[0155] The or each active inductive element may have at least one of a configurable transmittance and reflectance and a configurable refractive index.

[0145]

[0156] The or each active inductive element may be a switchable grating or grating region.

[0146]

[0157] At least one of the inductive elements may be a wavelength and / or polarization filter having a fixed or configurable wavelength response and / or a fixed or configurable polarization axis.

[0147]

[0158] At least one of the waveguides may have two or more inductive elements and three or more second surface regions, any of which can be selected by configuring one or both of the two or more inductive elements and / or modulating at least one beam characteristic.

[0148]

[0159] An optical system incorporating such a waveguide network may include: a first optical system component; a plurality of second optical system components; at least one multimode optical waveguide network according to any of the aspects or embodiments described above, the multimode optical waveguide network being arranged to direct a beam from or to the first optical system component to or from a selected second optical system component of the plurality of second optical system components; and a controller configured to select one second optical system component of the plurality of second optical system components, and to direct the beam from or to the first optical system component to or from the selected second optical system component by configuring at least one of the directing elements of the multimode optical waveguide network and / or modulating at least one beam characteristic.

[0149]

[0160] The first system component may include an emitter system for emitting and directing the beam to a selected second system component, or a detector array from which the beam is directed from the selected second system component.

[0150]

[0161] The optical system may include one or more holographic recording media, and at least some of the second system optical components may be respective sub-volumes of the one or more holographic recording media.

[0151]

[0162] The optical system may include a second multimode optical waveguide network according to any of the aspects or embodiments described above, and the controller may be configured to direct a second beam from or to the first optical system component to or from the same selected second optical system component by configuring at least one of the directing elements of the second multimode optical waveguide network and / or modulating at least one beam characteristic.

[0152]

[0163] The optical system may include a third multimode optical waveguide network according to any of the aspects or embodiments described above, and the controller may be configured to direct a third beam from or to the first optical system component to or from the same selected second optical system component by configuring at least one of the directing elements and / or modulating at least one beam characteristic of the third multimode optical waveguide network.

[0153]

[0164] For example, in the context of optical communications or optical computing, at least one of the first and / or second optical system components may include a signal converter or optical processor configured to convert the beam into an electrical signal (or vice versa).

[0154]

[0165] It will be understood that the above-described embodiments are described by way of example only. Other variations or uses of the disclosed techniques will be apparent to those skilled in the art given the disclosure herein. The scope of the present disclosure is not limited by the described embodiments, but only by the appended claims.

Claims

1. 1. An optical data transfer system, comprising: a beam modulator configured to embed a set of data in an input beam; an input waveguide network formed from one or more multimode optical waveguides, the input waveguide network having an in-coupling region for receiving the input beam and configured to direct the input beam to an out-coupling region of the input waveguide network; a spatially coherent detector configured to measure the 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 therefore exhibiting distortion effects caused at least in part by the input beam passing through the input waveguide network; and at least one processor coupled to the spatially coherent detector, the at least one processor configured to apply signal processing to an output of the spatially coherent detector to compensate for the distortion effects, thereby recovering, from the output of the spatially coherent detector, the set of data embedded in the input beam; An optical data transfer system comprising:

2. 2. The optical data transfer system of claim 1, comprising at least one holographic recording region, wherein the input waveguide network is configured to direct the input beam to the holographic recording region to store the embedded data in a pattern recorded in the region through interference between the input beam and a reference beam, and wherein the output light field is generated at a later time through interaction between the recorded pattern and a reference beam to read the embedded data from the holographic recording region.

3. 3. The optical data transfer system of claim 2, configured to direct the reference beam to the holographic recording region via one of the input waveguide network and a reference waveguide network formed from one or more further multi-mode optical waveguides, wherein the passage of the reference beam through the input or reference waveguide network also contributes to the distortion effect compensated for by the signal processing.

4. 4. An optical data transfer system according to claim 1, configured to direct an output beam defined at least in part by the input beam to the spatially coherent detector via one of the input waveguide network, a reference waveguide network according to claim 3, and an output waveguide network formed from one or more further multi-mode optical waveguides, wherein the passage of the output beam through the input, reference or output waveguide network also contributes to the distortion effect compensated for by the signal processing.

5. the input waveguide network; A reference waveguide network according to claim 3, and 5. An output waveguide network according to claim 4.

5. The optical data transfer system of claim 1, wherein at least one of the output optical fields comprises at least one inductive element that is configurable and / or responsive to at least one beam characteristic, whereby by reconfiguring the at least one inductive element and / or modulating the at least one beam characteristic different channel options for the at least one waveguide network can be realized, and wherein the at least one processor is configured to apply the signal processing in response to a channel selection associated with the output optical field.

6. 6. The optical data transfer 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 the different channel options, and apply the signal processing according to the selected channel model.

7. 7. The optical data transfer system of claim 6, wherein each channel model includes a set of signal processing parameters learned for the corresponding channel selection.

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

9. 9. The optical data transfer system of claim 8, comprising a plurality of holographic recording regions, wherein the output optical waveguide network has at least one directing element that is configurable and / or responsive to at least one beam characteristic, whereby by reconfiguring the at least one directing element and / or modulating the at least one beam characteristic, any of the plurality of holographic recording regions can be selected for readout using the same spatially coherent detector to direct an output beam from the selected holographic recording region to the spatially coherent detector, and wherein the at least one processor is configured to apply the signal processing depending on the holographic recording region being readout.

10. 10. The optical data transfer system of claim 9, wherein each holographic recording region is associated with at least one channel model, and wherein 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. 11. The optical data transfer 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 that identifies the holographic recording region being read.

12. 12. An optical data transfer system according to claim 9, configured to direct a reference beam to selected ones of the holographic recording regions via one of the output waveguide network and a reference waveguide network formed from one or more further multi-mode optical waveguides, the passage of the reference beam through the output or reference waveguide network contributing to the distortion effects compensated for by the signal processing.

13. 13. An optical data transfer system according to any one of claims 9 to 12, configured to direct the input beam to selected ones of the holographic recording regions via one of the output waveguide network and an input waveguide network formed from a further one or more multi-mode optical waveguides, wherein passage of the input beam through the output or input waveguide network contributes to the distortion effect compensated for by the signal processing.

14. 1. An optical data transfer system, comprising: a beam modulator configured to embed a set of data in an input beam; a spatially coherent detector configured to measure the phase and amplitude of an output light field at multiple locations, the output light field being defined at least in part by the input beam and a reference beam; a reference waveguide network formed from one or more multimode optical waveguides, the reference waveguide network having an in-coupling region for receiving the reference beam and configured to direct the reference beam to an out-coupling region of the reference waveguide network to define the output optical field; at least one processor coupled to the spatially coherent detector, the at least one processor configured to apply signal processing to an output of the spatially coherent detector to compensate for distortion effects caused, at least in part, by the reference beam passing through the reference waveguide network, thereby recovering, from the output of the spatially coherent detector, the set of data embedded in the input beam; An optical data transfer system comprising:

15. 15. An optical communication or computing system comprising at least one optical data transfer system according to any one of claims 1, 8 or 14.

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