Optical data transfer

Abstract

In an optical data transfer system, a beam modulator is configured to embed a set of data into 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. Signal processing is applied to the 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.

Description

Technical Field

[0001] Technical Field

[0001] This disclosure generally relates to optical data transfer.

Background Art

[0002] Background

[0002] An optical waveguide is a form of an optical component that can guide a beam through total internal reflection. The 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, corresponding to different propagation directions for example). This is in contrast to simple single-mode optical waveguides such as thin optical fibers used in optical fiber systems, whose purpose is to essentially limit the light entering the fiber to a single propagation mode. A single-mode optical waveguide can only carry data using amplitude, phase, or frequency modulation, while a multimode optical waveguide can carry more data (e.g., potentially an entire image of millions of pixels) by means of angular variations within the waveguide. In other words, a multimode waveguide provides a larger bandwidth by increasing angular and / or spatial diversity by providing multiple optical paths (different paths corresponding to different propagation modes) through the waveguide from the emitter to the detector for any given channel.

[0003]

[0003] Multimode waveguides are more generally used, for example, in head-mounted displays (HMDs) and waveguide-based display systems. In this context, a multimode waveguide typically carries an image from a display or optical engine to the user's eye, and the image is reconstructed by the eye's optical system and thus in a form perceivable by a human user. A diffractive optical system can be used to ensure that the beam entering and exiting the waveguide preserves the original image so that the original image can be reconstructed by the eye, providing beam expansion.

Summary of the Invention

Means for Solving the Problems

[0004] Summary

[0004] This summary is provided to introduce selected concepts in a simplified form, and these concepts are further described in the following 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. Also, the claimed subject matter is not 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. The beam modulator is configured to embed a set of data into the input beam. The multimode optical waveguide network has an incoupling region for receiving the input beam. The multimode optical waveguide network is configured to direct the input beam to the outcoupling region of the multimode optical waveguide network. The spatial coherent detector is configured to measure the phase and amplitude of the output optical field at a plurality of locations. The output optical field is at least partially defined by the input beam and thus exhibits distortion effects caused by the beam passing through the multimode waveguide network. At least one processor is coupled to the spatial coherent detector and applies signal processing to the output of the spatial coherent detector to compensate for the distortion effect, thereby recovering the set of data embedded in the input beam from the output of the spatial coherent detector.

[0006]

[0006] This has the advantage of significantly increasing the optical data transfer capacity due to the ability to transfer potentially large amounts of data in parallel (e.g., an image of millions of pixels) and using a potentially complex waveguide network (e.g., to provide spatial multiplexing). By using coherent detection, more effective distortion compensation can be applied to the measured phase and amplitude of the output optical field, which becomes feasible by providing appropriate resilience to waveguide distortion. One example of the application of this waveguide network is in a holographic data storage / retrieval system, where a beam is carried to / from a holographic recording medium. In this context, the multimode capability of the waveguide can be used, for example, to simultaneously read / write an entire image, and the ability to effectively compensate for waveguide distortion in the output of a spatially coherent detector increases the capacity and robustness of the system.

[0007]

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

[0008] Brief Description of the Drawings

[0008] For a better understanding of the present disclosure and to show how embodiments of the present disclosure may be implemented, the following figures are referred to by way of example only.

Brief Description 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] A schematic perspective view of a holographic storage system including a set of waveguides that can be used to direct a beam to / from different sub-volumes of a holographic recording medium to provide spatial multiplexing across the medium is shown.

Figure 2B

[0010] Shows a plan view of the system during the writing period.

Figure 2C

[0010] Shows a side view of one side of the system during the writing period.

Figure 2D

[0010] Shows a side view of one side of the system during the writing period.

Figure 2E

[0010] Shows a plan view during the reading period.

Figure 2F

[0010] Shows a side view of one side during the reading period.

Figure 2G

[0010] Shows a side view of one side during the reading period.

Figure 3A

[0011] Shows a schematic side view of an active light pipe of a certain configuration.

Figure 3B

[0011] Shows a schematic side view of an active light pipe of a certain configuration.

Figure 3C

[0011] Shows a schematic side view of an active light pipe of a certain configuration.

Figure 3D

[0011] Shows a schematic side view of an active light pipe of a certain configuration.

Figure 3E

[0011] Shows a plan (cross-sectional) view of the active light pipe.

Figure 3F

[0011] Shows a plan (cross-sectional) view of the active light pipe.

Figure 4A

[0012] Shows a side view of one side of the optical waveguide network (a part thereof).

Figure 4B

[0012] Shows a side view of one side of the optical waveguide network (a part thereof).

Figure 5

[0013] Shows a schematic diagram of an example of a multiplex waveguide network used for multiplexing over multiple pieces of a holographic storage medium.

Figure 6A

[0014] Shows an example of an emitter system for providing input and reference beams in a holographic storage system.

Figure 6B

[0014] Shows a modified form of an emitter system with a simplified optical system.

Figure 7

[0015] An example of a data recovery system is shown that measures the optical field of an output beam using spatial coherent detection and reduces waveguide distortion in the measured optical field using signal processing.

Figure 8

[0016] A functional block diagram showing the functions performed within a holographic memory system is shown.

Figure 9

[0017] An alternative holographic memory system is shown that uses at least one waveguide network to spatially multiplex two-dimensionally across a slab of a holographic recording medium.

Figure 10A

[0018] Shows how spatial multiplexing can be achieved using passive guiding elements, where spatial multiplexing is achieved by modulating beam characteristics.

Figure 10B

[0018] Shows how spatial multiplexing can be achieved using passive guiding elements, where spatial multiplexing is achieved by modulating beam characteristics.

Figure 11A

[0019] A light pipe with a passive optical filter having different frequency responses is shown.

Figure 11B

[0019] A light pipe with a passive optical filter having different frequency responses is shown.

Figure 12

[0020] An example of a waveguide network having three hierarchical levels is shown.

Best Mode for Carrying Out the Invention

[0010] Detailed Description of Example Embodiments

[0021] One example of an application of the waveguide network taught herein is a holographic memory device. A holographic memory device is in the form of a computer memory device, and information is recorded on a photosensitive holographic recording medium by exposing the medium to an optical pattern. For example, a region (subvolume) of the medium can be exposed to an optical interference pattern created by the interference of an input beam and a reference beam in which a set of data is embedded. 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 a set of data in the input beam (e.g., an image encoding the set of data can be spatially modulated and embedded in the input beam). To avoid misunderstanding, in this specification, the terms "light," "optical," and the like are not limited to visible light. The holographic memory device can be implemented, for example, using infrared or ultraviolet beams within the non-visible portion of the electromagnetic spectrum.

[0011]

[0022] With sufficient beam output and exposure time, the optical interference pattern causes a persistent state change within the subvolume (at this point, the interference pattern is said to be persistently recorded or written to the subvolume in this specification). The state change of the subvolume is such that at a later time, upon exposing the subvolume to a substantially matching reference beam, the interaction between the matching reference beam and the subvolume can recover the set of data originally embedded in the input beam from the output beam (this can be referred to as reading the recorded pattern in this specification), resulting in an output beam that is essentially matched to the original input beam.

[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 can be a megapixel image embedded in an input beam. Moreover, by taking advantage of the sensitivity of certain forms of holographic recording media to small changes in the angle of a reference beam, many (e.g., hundreds or thousands) of such patterns can be recorded in the same subvolume. For such media, when an interference pattern is generated with a reference beam at a given angle, the recorded pattern can be read only by using a reference beam that is precisely aligned with the reference beam originally used to generate it. This effect can be utilized to record multiple patterns (encoding different sets of data) in the same subvolume at different reference beam angles. In theory, the data storage capacity is limited only by the wavelength of the beam and potentially can be hundreds of megabytes per cubic millimeter for red light and tens of gigabytes for ultraviolet light. In practice, there can 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 way that reduces or eliminates the need for mechanical motion, an “active” light pipe, a “passive” light pipe, or a combination of an active light pipe and a passive light pipe can be used. Note that the terms “waveguide” and “light pipe” are used interchangeably herein.

[0014]

[0025] "Active light pipe" refers to a waveguide having one or more active switching elements or other guiding elements attached to the surface of the waveguide or within the bulk of the waveguide, and thus is capable of (i.e., can be changed to have) "one-to-many" light transmission (i.e., light is guided from a first surface area to one of a plurality of possible second surface areas, where the first surface area is an in-coupling area and the second area is an out-coupling area), or "many-to-one" light transfer (i.e., light is guided from any one of the second surface areas (here, the in-coupling area) to the same first surface area (here, the out-coupling area)). The term "passive light pipe" refers to a light pipe having guiding elements with different light sensitivities (e.g., different wavelength and / or polarization sensitivities), and can achieve a similar effect by changing the optical properties or the beam instead (e.g., using an adjustable laser to change its wavelength, polarization, etc. to be guided along different routes by guiding elements having, e.g., different wavelength / polarization responses). The term "passive light guiding" is merely a convenient label and in this case is consistent with the fact that the guiding elements do not need to be active, but in connection with this, active guiding elements or passive guiding elements having different light sensitivities (e.g., different wavelengths and / or polarization sensitivities, etc.) can be used (i.e., the guiding elements can be active and have different light sensitivities).

[0015]

[0026] A digital image (or data encoded as a digital image) can propagate as a beam along an active or passive light pipe. The guiding elements of the active light pipe can be individually controlled to transmit or reflect an 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 a switching network that can be used to manipulate beams and images to one of many addressable locations in one or more spatial dimensions. Inputs to the light pipe can be generated using a spatial light modulator (SLM), and outputs can be read, for example, in a charge-coupled device (CCD). Phase coherence and noise can be corrected using a combination of optical and computational techniques (including machine learning techniques), which will 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 conventionally used in optical data communication, the described embodiments use a light pipe that can transfer an entire image at once. This takes advantage of currently available high-resolution optical devices such as SLMs and digital cameras. These devices have millions of pixels and enable the encoding and decoding of megabytes of data. This enables high-bandwidth transmission even at a modest switching rate of the SLM, camera, and active light pipe elements (in the case of an active light pipe) or beam optical properties (in the case of a passive light pipe). Additionally, for applications such as holographic storage devices, interference between multiple beams is required, and at least one of the multiple beams is modulated with an image. In a holographic storage device, an active light pipe can be used to efficiently manipulate beams and images and cause interference at any desired location on the holographic storage medium. As described, simpler advantages can be achieved with a passive light pipe, in which 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 a 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 optical fiber systems, whose purpose is to essentially limit the light entering the fiber to a single propagation mode. A single-mode optical waveguide can only carry data using amplitude, phase, or frequency modulation, while a multimode optical waveguide can carry more data (e.g., potentially an entire image of millions of pixels) by means of angular variations within the waveguide. Put another way, a multimode waveguide provides a larger bandwidth through an increase in angular and / or spatial diversity by providing multiple optical paths (where different paths correspond to different propagation modes) through the waveguide from the emitter to the detector for any given channel.

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

[0020]

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

[0021] Active light pipe:

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

[0022]

[0033] The active light pipe 300 is shown as having at least a first surface region 300 - 0 and a plurality of active switches in the form of switchable Bragg gratings (SBGs) that can be surface - mounted 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 appropriate 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 so that its reflection / transmission characteristics change in order to transmit or reflect an incident beam. The SBGs 300 - 1, 300 - 2 form respective surface regions of the active light pipe 300, and in those regions, light can either enter (incouple) into the waveguide 300 or exit (outcouple) from the waveguide 300 depending on how the waveguide 300 is being used.

[0023]

[0034] The first surface region 300 - 0 is an 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] Figures 3E and 3F show cross - sectional views of the waveguide 300, which in this example has a rectangular - shaped cross - section, and it can be seen that four side surfaces 300 - S1, 300 - S2, 300 - S3, 300 - S4 extend along the axis 301 of the waveguide 300. In this example, as depicted in the figures, the SBGs 300 - 1, 300 - 2 are all located along the first side surface 300 - S1, but in general, such SBGs can be attached to multiple surfaces of the waveguide 300 depending on the application.

[0025]

[0036] SBG 300-1 and 300-2 are positioned along the first side surface 300-S1 of the waveguide such that the distance from the first region 300-0 increases, and the first SBG 300-1 is positioned closest to the first region 300-0.

[0026]

[0037] FIGS. 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 and 300-2 of the SBG serve as the out-coupling regions. As an example, FIG. 3 shows a first light ray 304 being coupled into the waveguide 300 through the in-coupling region 300-0. In this example, the first surface region 300-0 is angled with respect to the side surfaces 300-S1,..., 300-S4, such that the first light ray 304 enters the bulk of the waveguide 300 through the first surface region 300-0 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 and 300-2 can be configured to change between a reflective state and a transmissive state. FIG. 3A shows a configuration in which the first SBG 300-1 is in the reflective state, and the incident light ray 304 is reflected by the first SBG 300-1 and guided along the waveguide 300 until it reaches the second SBG 300-2. The SBG 300-2 is shown in the transmissive state, and the light ray 304 diffracts out of the waveguide 300 through the second SBG 300-2, thereby being extracted from the waveguide 300 through the surface region of the second SBG 300-2. With this configuration of the SBGs 300-1 and 300-2, a "channel" through the waveguide 300 is created between the first surface region 300-0 and the surface region of the second SBG 300-2.

[0028]

[0039] In contrast, FIG. 3B shows that the first SBG 300-1 is in a transmissive state. Accordingly, as soon as the first light ray 304 reaches the first SBG 300-1, instead, it diffracts out of the waveguide 300 through the first SBG 300-1, and thereby is taken out of the waveguide 300 through the surface region of the first SBG 300-1 instead. With this configuration, a channel through the waveguide 300 is created between the first surface region 300-0 and the surface region of the first SBG 300-1.

[0029]

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

[0030]

[0041] FIG. 3E shows, in cross-section, how the first light ray 304 can propagate from some or all of the side surfaces 300-S1, ..., 300-S4 depending on the angle of the first light ray 304 via TIR.

[0031]

[0042] As depicted in FIGS. 3C, 3D and 3F, it is equally feasible to use the depicted active light pipe 300 for many-to-one optical transfer.

[0032]

[0043] Figure 3C shows the same SBG configuration as in Figure 3A. The only difference is in the way the waveguide 300 is used, where a second light ray 308 incident on the second SBG 300-2 from an external source (not shown) is depicted. Due to the second SBG being in a transmissive state, the second light ray 308 diffracts into the waveguide 300 through the second SBG (which provides incoupling in its surface region here) and is then guided from there through the waveguide 300 to the first surface region 300-0 (which is the outcoupling region here). This includes reflections from the first SBG 300-1 which is in a reflective state here. 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, incidentally, an external light ray 309 that might be incident on the first SBG 300-1 essentially reflects away from the first SBG 300-1 and thus does not enter the waveguide 300.

[0033]

[0044] Figure 3D shows the same configuration as in Figure 3B, but here the second light ray 308 is incident on the first SBG 300-1 from an external source. Due to the first SBG 300-1 being 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] Figure 3F shows how the second light ray 308 can propagate within the waveguide 300 in cross-section. The same explanation as in Figure 3E applies, but the direction of the light ray is reversed.

[0035]

[0046] The above description assumes perfect reflectivity / transmissivity of the SBG in the transmit / reflection states. As is understood, this is not actually an absolute condition, and more generally, the system has a certain tolerance for imperfections in the SBGs 300-1, 300-2, and the waveguide 300. Appropriate signal processing techniques for compensating for the distortion introduced into the waveguide 300 will be described later.

[0036]

[0047] Although SBG 300-1 and 300-2 are depicted as separate elements, in fact, separately controllable regions of a single large SBG can extend across all or most of the first side 300-S1.

[0037]

[0048] SBG is only one possible form of an active switching element. For example, in a polarized beam, the same effect can be achieved using a controllable polarization filter attached to the surface of the waveguide 300 or embedded within the bulk of the waveguide. SBG and the controllable polarization filter are examples of non-mechanical active switches that can change the optical properties of the waveguide 300 via non-mechanical effects. Other examples of guiding elements include controllable mirrors such as micro-mirror devices or other micro-electro-mechanical systems (MEMS), and micro-electro-mechanical systems (MEMS) are examples of mechanically induced elements.

[0038]

[0049] When using a polarization filter as the guiding element, SBG 300-1 and 300-2 can be replaced with passive diffraction elements, and the polarization filter operates to direct the beam to or away from the passive diffraction element in a controllable manner as needed without the need to reconfigure the diffraction element.

[0039]

[0050] Note that even if those guiding elements themselves are mechanical, the need for mechanical operation of the entire waveguide 300 is still avoided.

[0040] Active Light Pipe Network

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

[0041]

[0052] Figures 4A and 4B show a side view of one side of a waveguide network (a part of it) including first and second active light pipes 400, 420. The second light pipe 420 has a first surface region 420-0 positioned adjacent to a corresponding surface region of the first light pipe 400 to receive a beam from the second waveguide 420 or direct a beam to the second waveguide 420 via the first surface region 400-0. By way of pure example, a light ray 404 is shown propagating through the first waveguide 400 to a corresponding surface region of the first waveguide 400, and the corresponding surface region of the first waveguide 400 exists adjacent to the first surface region 420-0 of the second waveguide 420. The light ray 404 is taken out from the first waveguide 400 via an SBG 400-1 attached to an adjacent surface region of the first waveguide 400 and taken into the second waveguide 420 via the first surface region 400-0. From there, the light ray 404 can be directed to any one of a plurality of SBGs 420-1, 420-2 of the second waveguide 420 in a one-to-many fashion. In a many-to-one fashion, the same arrangement can be used to direct a beam in the other direction from the second waveguide 420 to the first waveguide 400 by reversing the direction of the light ray.

[0042]

[0053] This example considers two mutually coupled waveguides 400, 420, but the principle can be applied to more mutually coupled waveguides to enable flexible data routing through the waveguide network.

[0043]

[0054] More generally, the surface region of the medium can optically couple to the corresponding surface region of the waveguide in other ways, 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 device

[0055] Here, the application of an active light pipe to a holographic memory device will be described.

[0045]

[0056] FIGS. 1A and 1B show a schematic perspective view of a holographic recording medium 102, which is a volume of a relatively thick photosensitive material that can persistently store an optical pattern as a "hologram" embodied within the holographic recording medium 102 (which can simply be referred to as medium 102 for simplicity). The hologram is generated by exposing that sub - volume 110 (region) of the medium 102 to an optical pattern such that a persistent state change occurs within the sub - volume 110. The hologram generated in the sub - volume 110 by that state change records the optical pattern to the medium 102 and can reproduce the optical pattern from there at a later time. The hologram is persistent in that the medium 102 does not require power to maintain it once it is generated. The composition and structure of the medium 102 can be such that the hologram cannot be erased once it is generated (thus providing the form of a "write - once read - many" (WORM) memory device) or such that the hologram can be erased and replaced (however, it persists until erased and not otherwise).

[0046]

[0057] A single hologram can record an optical pattern encoding a very large number (e.g., millions) of bits, thereby writing / reading a very large amount of data to / from the holographic recording medium 102 in parallel (simultaneously). Another advantage of the holographic memory device is that many holograms can be written to the same sub - volume 110 of the holographic recording medium 102, thereby significantly increasing the data storage capacity per unit volume of the holographic recording medium 102.

[0047]

[0058] More specifically, FIG. 1A shows how input beam 104 and reference beam 106 are directed at sub-volume 110 through first and second sides 102-4, 102-6 of medium 102, respectively, to write a set of data to medium 102. Thereby, an optical pattern in the form of an interference pattern resulting from the interference between input beam 104 and reference beam 106 is generated. If beams 104, 106 have sufficient power and sub-volume 110 is exposed for a sufficient duration, the interference pattern generated by interfering beams 104, 106 will be permanently recorded as a hologram within sub-volume 110. As will be explained below, the set of data is embedded in input beam 104 and can be recovered from the resulting hologram. Thus, the set of encoded data is written to sub-volume 110. In the following example, the set of data is encoded as a digital image and then embedded in input beam 104 through spatial modulation.

[0048]

[0059] As shown in FIG. 1B, to read data from sub-volume 110, a collimated reference beam 116 is directed at sub-volume 110 through second side 102-6 of medium 102, and collimated reference beam 116 interacts with the hologram to generate output beam 108, which essentially matches input beam 104 used for writing the hologram to the extent that the embedded data can be recovered from output beam 108. Output beam 108 propagates out of sub-volume 110 through 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 is directed at an angle (or more generally a direction) that is precisely aligned with the angle of the original reference beam 106. This is because the ability to read the hologram (i.e., generate the output beam 108 from which the data can be recovered) is highly sensitive to the angular deviation between the reference beam 106 used for writing the hologram and the reference beam 116 used for reading the hologram. This sensitivity can be utilized to record multiple holograms within the same subvolume 110, each hologram being generated using a different reference beam angle, and two completely different holograms can be generated using only a very small difference in the reference beam angles. In this way, many (e.g., hundreds or thousands) of holograms can be written into the same subvolume 110, each encoding many (e.g., millions) of bits.

[0050]

[0061] FIG. 2A shows a schematic perspective view of an example of a holographic memory system 200 incorporating certain principles of the present disclosure. In this particular example, three separate waveguides 204, 206, 208 are used to carry input beam 104, reference beams 106, 116, and output beam 108, and the three separate waveguides 204, 206, 208 can be individually referred to as input waveguide 204, reference waveguide 206, and output waveguide 208. As described, the terms “optical waveguide” and “light pipe” are used interchangeably herein. Each of waveguides 204, 206, 208 provides spatial multiplexing in the sense that it can direct a signal to (in the case of input and reference waveguides 204, 206) or from (in the case of output waveguide 208) any one of a plurality of sub-volumes within holographic recording medium 102. Thereby, spatial multiplexing is provided across the volume of holographic recording medium 102 without any mechanical movement of waveguides 204, 206, 208 with respect to holographic recording medium 102. To avoid the need for such mechanical movement, the guiding elements are located on or within each of waveguides 204, 206, 208 and are configurable to vary the optical properties of waveguides 204, 206, 208 to direct a signal to or from different sub-volumes of medium 102. That is, to create different channels within waveguides 204, 206, 208 as needed. In this particular example, the guiding elements take the form of active optical switching elements (switches). The forms that the switches can take are various. In this example, the switches take the form of SBGs located in different surface regions of waveguides 204, 206, 208 in the same general arrangement as FIGS. 3A - F. That is, each of waveguides 204, 206, 208 takes the form of an active light pipe, and each of waveguides 204, 206, 208 has the same general physical structure as active light pipe 300 of FIGS. 3A - F.

[0051]

[0062] Each of the waveguides 204, 206, 208 is arranged such that its first surface (i.e., the surface on which its SBG is located) is adjacent to a different side surface of the medium 102, whereby the SBG extends along that side surface of the medium 102. The first and second SBGs of each of the waveguides 204, 206, 208 are respectively indicated by reference numerals 204-1, 204-2, 206-1, 206-2, 208-1, 208-2, and they can all be configured in the manner described above. Additional SBGs are depicted without reference numerals, and the number of SBGs can be selected to adapt to holographic recording media 102 of any size. The following description will, for the sake of brevity, refer to the first and second SBGs of each of the waveguides 204, 206, 208, but it will be understood that the explanation also applies to more SBGs.

[0052]

[0063] FIGS. 2B to 2D show how the input and reference waveguides 204, 206 are used to write data to the medium 102 in a one-to-many fashion. FIG. 2B shows a schematic plan view of the system 200, and FIGS. 2C and 2D show side views of one side on which the input and reference waveguides 204, 206 can be seen, respectively. The input waveguide 204 is used to direct the input beam 104 to any one of a plurality of sub-volumes of the medium 102 through any one of the SBGs 204-1, 204-2 of the input waveguide 204 in the manner described above. The reference waveguide 206 is configured to simultaneously direct the reference beam 106 to the same sub-volume, and a desired interference pattern to be written to that sub-volume is generated. In the example depicted, both the input waveguide 204 and the reference waveguide 206 are here configured to direct the input and reference beams 104, 106 respectively to the sub-volume indicated by reference numeral 110 through the second SBGs 204-2, 206-2 of each of the waveguides 204, 206.

[0053]

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

[0054]

[0065] Each sub - volume 110 can have a height and width of several millimeters, for example, as measured along any side, which would generally be sufficient to store millions of 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 guiding elements (SBG in this example) of the input waveguide 204 and the reference waveguide 206 are configured to provide channels for the input beam 104 and the reference beams 106, 116 from the beam source (emitter system) to the sub - volume 110 to be read, as needed. In SBG, the SBG is set to a transmission or reflection state as needed to create the channels. Similarly, the guiding element (also SBG in this example) of the output waveguide 208 is set in the same way to provide a channel from the sub - volume 110 being read to the detector. For additional context, this will be described in more detail below with reference to the multi - waveguide network depicted in Figure 5. However, the principles described in relation to the specific example of Figure 5 apply more generally to other waveguide network topologies, such as both simpler networks (e.g., a single waveguide) and more complex waveguide networks.

[0056]

[0067] As described above, this enables spatial multiplexing across the medium 102 without mechanical movement of the medium 102 with respect to the waveguides 204, 206, 208. This holds true regardless of the form taken by the guiding elements (as described above, those guiding elements themselves can be either mechanical or non - mechanical).

[0057] Holographic storage device using a multi - waveguide network

[0068] FIG. 5 shows an example of a holographic storage system incorporating a multi - waveguide network of the type shown in FIG. 4.

[0058]

[0069] The input waveguide network is shown to include a first input light pipe 203 (“parent” waveguide) to which a plurality of second input light pipes 204A, 204B (“child” waveguides) are coupled. The input beam 104 from the emitter system 504 is taken into the first input waveguide 203 through its in - coupling region and can be directed therefrom to the second input waveguide 204A or 204B.

[0059]

[0070] The reference waveguide network is shown to include a first reference waveguide 205 to which a plurality of second reference waveguides 206A, 206B are coupled. The reference beams 106, 116 from the emitter system 504 can similarly be taken into the first reference waveguide 205 and directed to the second reference waveguide 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] With the described arrangement, beams can be directed to / diverted from different sub - volumes of a plurality of pieces 102A, 102B of the holographic storage medium.

[0062]

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

[0063]

[0074] The first group 204A, 206A, 208A of the second waveguides (one each of input, reference, and output) are located around the first piece 102A (first medium) of the holographic storage medium, and the second group 204B, 206B, 208B of the second waveguides are located around the second piece 102B (second medium), each having the same general arrangement as FIGS. 2A - G. Thus, the input and reference beams 104, 106, 116 can be directed to any sub-volume of any medium piece 102A, 102B by first guiding those beams to the desired second waveguide of the input and reference networks respectively, and then to the desired sub-volume of the medium piece adjacent to the desired waveguide.

[0064]

[0075] The output waveguide network can be used to direct an output beam 108 from any sub-volume of any of the media pieces 102A, 102B to a first output waveguide 207 from applicable second output waveguides 208A, 208B and then from the first output waveguide 207 through the out-coupling region of the first output waveguide 207 to a detector 508. To perform a read from a particular sub-volume, the SBGs are configured to provide a channel from that sub-volume to the detector and thus, in this case, SBGs 204A-2 and 207-1 are set to a transmissive state and the other SBGs of the output waveguide network are set to a reflective state as necessary 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 the waveguide 208B). The other SBGs of the output waveguide network can be set to reflect to the extent necessary to prevent transmission (i.e., “leakage”) of unwanted light from other regions of the same media piece 102A or from a different media piece 102B (e.g., in this example, SBG 204A-1, which is close to the sub-volume being read, is shown as being set to reflect to prevent unwanted leakage).

[0065]

[0076] In the example above, three separate waveguide networks are used for the input, reference, and output beams 104, 106, 116, 108, but this is not necessarily required. For example, the same waveguide network can be used to carry both the input beam 104 and the reference beams 106, 116, and / or the same waveguide network can be used to carry the input beam 104 and the output beam 108, and / or the same waveguide network can be used to carry the output beam 108 and the input beam 104. Generally, having three separate networks is expected to provide optimal performance, but nevertheless, fully functional implementations exist that use only one or two waveguide networks.

[0066]

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

[0067]

[0078] FIG. 9 shows an alternative physical structure where, instead of the individual pieces 102A, 102B of FIG. 5, a single “slab” of the holographic medium 102 is used. An input waveguide network is depicted and has essentially the same physical configuration, but here the second input waveguides 204A, 204B are configured to direct the input beam 104 to different subvolumes of the same slab 102. In FIG. 5, each of the second input waveguides 204A, 204B provides multiplexing in one dimension along the length of a different single media piece 102A, 102B, while in FIG. 9, the second waveguides 204A, 204B provide spatial multiplexing in two dimensions across the slab 102 of the holographic medium 102 (each waveguide provides multiplexing in one dimension individually, but there is two-dimensional multiplexing across the slab 102 as a whole).

[0068]

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

[0069] Data Encoding

[0080] FIG. 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. Laser 600 emits a coherent narrow laser beam, and the coherent narrow laser beam is split using beam splitter 602.

[0070]

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

[0071]

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

[0072]

[0083] Another portion of the beam from beam splitter 602 is expanded using beam expander 604, and the expanded beam passes through spatial light modulator (SLM) 606. Encoder 610 receives a set of data to be encoded, encodes that set of data as a digital image, and then the digital image is modulated via SLM 606 and embedded in the expanded beam. An in-coupling optical system (in this case, Fourier lens 608) positioned such that the plane of SLM 606 is substantially at the focal plane of Fourier lens 608 is used to separate the expanded beam into a completely different propagation mode, and in this example, the modes correspond to unique propagation directions, and here each mode corresponds to a particular point in the plane of SLM 606. The different propagation modes are captured in input waveguide 204 and induced therefrom in the manner described above. With in-coupling optical system 608, the data is "angle encoded" within the input beam in the sense that points within the digital image essentially correspond to unique propagation directions (i.e., unique propagation modes of input beam 104). This is similar to light rays from a distant object that can be thought of as an infinite point. The angle-encoded input beam 104 of FIG. 6A is an example of a plurality of propagation modes (i.e., components propagating in different directions) of a "multimode" optical signal, and this arrangement provides a form of angular diversity.

[0073]

[0084] The term "multimode" should be noted not necessarily to imply the use of such an in-coupling optical system 608, nor necessarily that all image points need to uniquely correspond to a given propagation direction. That is, multimode does not necessarily imply a one-to-one correspondence between propagation modes and image points / data points. For example, FIG. 6B shows an alternative executable emitter system in which a spatially modulated beam is directly captured into the input waveguide 204. In this case, there are still multiple modes (i.e., multiple spatial paths through the waveguide for any given channel), but there is no one-to-one correspondence between the propagation direction and the image points, and in some cases, there is also no one-to-one correspondence between the image / data points and the modes. Thereby, a form of spatial diversity based on the form of MIMO (multiple-input multiple-output) transfer through a plurality of pixels of the SLM 606 and the detector array of the spatial coherent detector 508 is provided.

[0074] Data decoding

[0085] FIG. 7 shows the spatial coherent detector 508 used to measure the optical field of the output beam 108. In contrast to conventional "direct detection", the spatial coherent detector 508 includes an array of pixels (or more generally detector elements), each of which is configured to measure both the amplitude and phase (not just the intensity) of the optical field at the location of that pixel. These can be measured, for example, using the local oscillator 712 of the spatial coherent detector 508. Thus, the array of pixels can measure the phase and amplitude variations of the optical field in both time and space, and thus can provide an analog or digital representation of the measured optical field. In this case, the optical field to be measured is the optical field of the output beam 108 induced into the spatial coherent detector 508 via the output waveguide 208.

[0075]

[0086] Only a single array is depicted, but in fact, there can be multiple physical arrays that cooperate as a single "logical array". For example, this logical array can be split across two physical cameras.

[0076]

[0087] The physical detector array can take the form of a single camera (where each detector element is a pixel or set of pixels of the camera) or the form of multiple cameras. In an extreme case, each detector element could be a separate camera, in which case the logical detector array can potentially be split over a very 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) can 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 guided through a particular channel of the output waveguide network (i.e., from its particular incoupling region to the outcoupling region of output waveguide 208). Moreover, the output beam 108 will be generated from a hologram generated using the input beam that was guided from the incoupling region of the input waveguide network to its particular outcoupling region. The hologram will be generated and read using a reference beam that was similarly guided through a particular channel through a reference waveguide network. All of the input beam 104, reference beams 106, 116, and output beam 108 are susceptible to the effects of distortion within the associated waveguide network that is specific to the channel through which they are guided. To compensate for such distortion, signal processing component 700 applies analog and / or digital signal processing to the measured representation of the field. Signal processing component 700 does this using the channel model associated with the subvolume that is currently being read (i.e., where output beam 108 was generated). The channel model associated with a particular subvolume models not only the channel through which output beam 108 is guided to detector 508, but also the channels through which input beam 104, used for writing the hologram, is guided to that subvolume and the channels through which reference beams 106, 116, used for writing / reading the hologram, are guided to that subvolume.

[0078]

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

[0079]

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

[0080]

[0091] Using a learning method, the path from the emitter system 504 to the spatial coherent detector 508 is treated as a channel to be modeled. The channel can be modeled with a learned function (such as an inverse transfer function) that inverts the channel distortion effect. The input to such a function is the distorted field (phase and amplitude) of the output beam measured through spatial coherent detection, and the output of such a function is the non-distorted field (phase and amplitude) of the input beam. Given a sufficient number of training examples (i.e., pairs of distorted output fields and clean input fields), the model can be trained to approximate this inverse function (i.e., when a distorted output field (phase and amplitude) is given as input, the trained model approximately recovers the original input field). This holds even if the model does not encounter the exact form of the distorted output field during training, because such a model can be generalized from a sufficient set of training examples. For example, the output and input fields can be represented as the input and output tensors of a convolutional neural network (CNN), and the CNN can be trained based on a loss function that penalizes the difference between the output tensor of the training example (such as generated by applying the CNN to the input tensor of the training example) and the known corresponding input field. As understood, this method can be applied not only in holographic memory devices, but also in any situation where the output field exhibits waveguide distortion, provided that such training examples can be collected.

[0081]

[0092] Although described in the context of a holographic memory device, the use of such signal processing 700 combined with spatial coherent detection is not limited in this regard and can be applied in other contexts such as optical communication or optical computing, or any other context where the received output beam is susceptible to the effects of distortion introduced in one or more waveguide networks.

[0082]

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

[0083]

[0094] Although not depicted in FIGS. 6A or 6B, a level of preprocessing can be applied to the digital image before modulating and embedding it into the input beam 104. This can reduce the required compensation level on the detector side. Even if such preprocessing is performed, some level of detector-side processing may be applied to account for different distortion effects between different channels.

[0084] Dynamic Scheduling

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

[0085]

[0096] First, as described above, a single sub-volume can store a plurality of holograms at different reference beam angles. To accommodate this, each address uniquely corresponds to a particular sub-volume in combination with a particular reference beam direction (i.e., a unique address is assigned to each available tuple), indicating a particular sub-volume within medium 102 or within any one of medium pieces 102A, 102B, and indicating a particular reference beam direction (e.g., an angle or a set of angles that define the beam direction, where the term "angle" is used as a concise expression for referring to the direction of the reference beam, but it will be understood that the direction can in fact be defined by a plurality of angles depending on the configuration of the system). Thus, a sub-volume can be associated with potentially many addresses corresponding to different reference beam angles. A tuple defines a logical storage location, and the same sub-volume at different reference beam angles provides a plurality of logical storage locations at the physical level. Each of the logical storage locations has a unique address (ADDR). This notation is used as a concise expression for meaning the address corresponding to the sub-volume and the reference beam angle, but it will be understood that this does not imply a particular form of address. Any address space and addressing mechanism that uniquely identifies the logical storage locations of this nature can be used.

[0086]

[0097] Second, in contrast to conventional storage devices, each of the logical storage locations can store the entire image, and thus a single logical storage 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 an appropriate time interval.

[0088]

[0099] Reference numerals 804, 806, and 808 are each used to denote an input, a reference, and an output optical waveguide network. As described above, each may be a single waveguide network or a multiplexed waveguide network (e.g., similar to FIG. 5), and may have one or more configurable guiding elements (e.g., SBG or other active switching elements) that can be used to create channels to different subvolumes of one piece (or pieces) of the holographic storage medium.

[0089]

[0100] During a period (write period) in which a write operation for a particular address is scheduled, the guiding elements in the input and reference waveguide networks 804, 806 are set to create channels for the input beam 104 and the reference beam 106 from the emitter system 504 through each of the input and reference networks 804, 806 to the corresponding subvolume. Additionally, the reference beam steering element 612 is set to direct the reference beam 106 in a corresponding direction toward the reference network 806. Thereby, a desired interference pattern is generated at the reference beam angle within the subvolume, and thus, if the subvolume is exposed to the interference pattern for a sufficiently long duration, the interference pattern is persistently stored as a hologram.

[0090]

[0101] During a period (read period) in which a read operation for a particular address is scheduled, the guiding elements in the reference and output networks 806, 808 are similarly set to create a channel for the reference beam 116 from the reference network 806 to the subvolume, and a channel for the output beam 108 from the subvolume through the output network 808 to the detector 508. The reference beam steering element 612 is similarly set to direct the reference beam 116 in a corresponding direction toward the reference network 806 for reading the intended hologram at the reference beam angle within the subvolume.

[0091] Alternative waveguide network:

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

[0092]

[0103] The example of FIG. 10A contemplates frequency (or equivalently wavelength) modulation. In this case, the light pipes themselves are passive and have static wavelength-dependent outcoupling (such as a continuous long-pass dichroic interference filter or a variable center wavelength band-pass filter).

[0093]

[0104] FIG. 11A shows a light pipe 1100 having an outer surface 1100-S along which there are a plurality of passive filters 1100-1, 1100-2. The configuration of the light pipe 1100 is the same as FIGS. 3A - D, apart from the fact that the filters 1100-1, 1100-2 replace the SBGs 300-1, 300-2. The filters 1100-1, 1100-2 have different frequency responses (i.e., they act as frequency filters). More specifically, each filter 1100-1, 1100-2 essentially transmits a relatively narrow range of optical frequencies and essentially reflects 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, the beam 1104 is reflected by the first filter 1100-1 but transmitted through the second filter 1100-2 (and thus exits the light pipe 1100 at that location). FIG. 11B shows a beam 1104' of a different frequency, where its frequency is within the range of the first filter 1100-1 and thus is transmitted through the 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 equally applies to modified forms of the following systems.

[0095]

[0106] FIG. 10A shows a scheduler 800 communicatively coupled to a laser 600 of an emitter system for varying the frequencies (or equivalently wavelengths) of input and reference beams 104, 106, 116. In this case, any of the beams can be directed to a desired holographic memory region by correspondingly setting the frequency. Here, different beam frequencies correspond to different routes through the waveguide network (defined by different frequency characteristics of the passive filters), and the frequencies 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 fast tunable laser that functions as an active element.

[0097]

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

[0098]

[0109] In relation to the reading operation, the frequency of the output beam 108 is matched to the frequency of the reference beam 116 used to read a particular sub-volume, and the same principle can be applied to use an appropriate filter in the output waveguide network 808 to return it to the detector.

[0099]

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

[0100]

[0111] Note that all of the various "passive" and "active" implementations described above can be implemented separately or in combination (for example, a combination of active and passive guiding elements can be used). That is, the waveguide can have both passive and active elements, and / or it is possible to combine active and passive waveguides within the same network.

[0101] Additional hierarchical level:

[0112] The above example considers a waveguide network having two hierarchical "levels" of a parent waveguide and child waveguides. However, a multi-level waveguide network can 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" can refer to any waveguide at any hierarchical level below a respective parent or child waveguide. That is, the child / grandchild waveguides can be optically coupled to the parent / child waveguides not only via, for example, an air interface (direct grandchild), but also via one or more other child / grandchild waveguides (indirect grandchildren).

[0102]

[0113] FIG. 12 shows an example of a waveguide network having three hierarchical levels. The parent waveguide 1200 has two direct child waveguide networks 1202A and 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 waveguides 1202A / 1202B in the same manner.

[0103]

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

[0104]

[0115] The scheduler 800 shown in FIGS. 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 can be implemented in software (i.e., as program code executed on one or more programmable hardware processors such as a CPU, an accelerator, e.g., a GPU), or using other forms of processor hardware such as a field programmable gate array and / or an application specific integrated circuit. The signal processing performed by the signal processing component 700 can be analog or digital signal processing, or any combination thereof. Such program code and other data (e.g., the channel model 702) can be encoded in a computer-readable storage device. Examples of computer-readable storage devices include optical, magnetic, and / or solid state storage devices, which can store code, data, and the like in a non-transitory form. This is in contrast to transitory media such as a transitory signal carrier wave.

[0105]

[0116] A first aspect of the present specification is 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, having an incoupling region for receiving the input beam, and configured to direct the input beam to an outcoupling region of the input waveguide network; a spatial coherent detector configured to measure the phase and amplitude of an output optical field at a plurality of locations, the output optical field being at least partially defined by the input beam, and thus exhibiting at least partially a distortion effect caused by the input beam passing through the input waveguide network; and at least one processor coupled to the spatial coherent detector, the at least one processor being configured to apply signal processing to the output of the spatial coherent detector to compensate for the distortion effect, and thereby recover the set of data embedded in the input beam from the output of the spatial coherent detector.

[0106]

[0117] In an embodiment, the optical data transfer system may include at least one holographic recording region, and 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 therein via interference between the input beam and a reference beam, and the output optical field is generated at a later time via interaction between the recorded pattern and the reference beam to read the embedded data from the 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 the input waveguide network and a reference waveguide network formed from one or more additional multimode optical waveguides, and the passage of the reference beam through the input or reference waveguide network may also contribute to the distortion effect compensated by signal processing.

[0108]

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

[0109]

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

[0110]

[0121] At least one processor can be configured to select a channel model corresponding to an associated channel selection from a plurality of channel models corresponding to different channel options and apply the signal processing according to the selected channel model.

[0111]

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

[0112]

[0123] A second aspect of the present specification is an optical data transfer system, comprising a beam modulator configured to embed a set of data in an input beam, a spatial coherent detector configured to measure the phase and amplitude of the optical field of the output beam at a plurality of locations, the output beam being at least partially defined by the input beam, a spatial coherent detector, an output waveguide network formed from one or more multimode optical waveguides, the output waveguide network having an incoupling region for receiving the output beam and being configured to direct the output beam to an outcoupling region of the output waveguide network for reception by the spatial coherent detector, and at least one processor coupled to the spatial coherent detector, the at least one processor being configured to apply signal processing to the output of the spatial coherent detector to compensate for at least partially a distortion effect caused 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 spatial coherent detector.

[0113]

[0124] The optical data transfer system may include a plurality of holographic recording regions, the output optical waveguide network having at least one guiding element that is configurable and / or responsive to at least one beam characteristic, whereby, by reconfiguring the at least one guiding element and / or modulating the at least one beam characteristic, any region of the plurality of holographic recording regions is selected for being read using the same spatial coherent detector and the output beam can be directed from the selected holographic recording region to the spatial coherent detector, and the at least one processor is configured to apply the signal processing in accordance with the holographic recording region being read.

[0114]

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

[0115]

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

[0116]

[0127] The optical data transfer system may be configured to direct a reference beam to a selected one of the holographic recording areas via one of an output waveguide network and a reference waveguide network formed from one or more additional multimode optical waveguides, and the passage of the reference beam through the output or reference waveguide network may contribute to the distortion effect to be compensated by signal processing.

[0117]

[0128] The optical data transfer system may be configured to direct an input beam to a selected one of the holographic recording areas via one of an output waveguide network and an input waveguide network formed from one or more additional multimode optical waveguides, and the passage of the input beam through the output or input waveguide network may contribute to the distortion effect to be compensated by signal processing.

[0118]

[0129] A third aspect of the present specification is an optical data transfer system, comprising: a beam modulator configured to embed a set of data in an input beam; a spatial coherent detector configured to measure the phase and amplitude of an output optical field at a plurality of locations, wherein the output optical field is at least partially defined by the input beam and a reference beam; a reference waveguide network formed from one or more multimode optical waveguides, having an incoupling region for receiving the reference beam and configured to direct the reference beam to an outcoupling region of the reference waveguide network to define the output optical field; and at least one processor coupled to the spatial coherent detector and configured to apply signal processing to the output of the spatial coherent detector to compensate for at least partially a distortion effect caused by the reference beam passing through the reference waveguide network, thereby recovering the set of data embedded in the input beam from the output of the spatial 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 as 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 or embedded within the surface of the waveguide. Each of the second surface regions of the parent waveguide is optically coupled to the first surface region of the corresponding one of the child waveguides. At least one guiding element of the parent waveguide is arranged to direct a beam from or to its first surface region to or from a selected second surface region of its plurality of second surface regions. The beam is taken into or received from the corresponding child waveguide whose first surface region is optically coupled to the second surface region of the parent waveguide via the second surface region of the parent waveguide and the first surface region of the corresponding child waveguide. At least one guiding element of each child waveguide is arranged to direct a beam from or to its first surface region to or from a selected second surface region of its plurality of second surface regions. At least one guiding element of each waveguide is configurable to select the second surface region of its waveguide and / or to select the second surface region of its waveguide via modulation of at least one beam characteristic in response to at least one beam characteristic.

[0122]

[0133] A multimode optical waveguide network may include a plurality of sub-waveguides, each of which is a multimode optical waveguide having a first surface region, a plurality of second surface regions, and at least one guiding element attached to or embedded in the surface of the sub-waveguide. Each of the second surface regions of each sub-waveguide is optically coupled to the first surface region of the corresponding one of the sub-waveguides. At least one guiding element of each sub-waveguide can be arranged to guide a beam from or to its first surface region to or from a selected second surface region of its plurality of second surface regions. The beam is incorporated into or extracted from the sub-waveguide through its first surface region and through the second surface region of the sub-waveguide optically coupled thereto. At least one guiding element of each sub-waveguide can be configured to select the second surface region of the sub-waveguide and / or select the second surface region of the sub-waveguide through 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 guiding element configured to select the second surface region of the waveguide.

[0124]

[0135] Each of the waveguides may have at least one guiding element that selects the second surface region of the waveguide through modulation of at least one beam characteristic in response to at least one beam characteristic.

[0125]

[0136] At least one of the waveguides may have at least one active guiding element configured to select the second surface region of the waveguide, and at least another one of the waveguides may have at least one guiding element that selects the second surface region of the other waveguide through modulation of at least one beam characteristic in response to 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 guiding element, whereby a beam within a first wavelength range is guided from or to its first surface region to or from a first one of the child or grandchild waveguides, and a beam within a second wavelength range is guided from or to its first surface region to or from a second one of the child or grandchild waveguides. The first child or grandchild waveguide may have at least one wavelength-responsive guiding element, whereby a beam within a first sub-range of the first wavelength range is guided from or to its first surface region to or from one of its second surface regions, and a beam within a second sub-range of the first wavelength range is guided from or to its first surface region to or from another one of its second surface regions. The second child or grandchild waveguide may have at least one wavelength-responsive guiding element, whereby a beam within a first sub-range of the second wavelength range is guided from or to its first surface region to or from one of its second surface regions, and a beam within a second sub-range of the second wavelength range is guided from or to its first surface region to or from another one of its second surface regions.

[0127]

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

[0128]

[0139] That or each active guiding element may be a switchable grating or grating region.

[0129]

[0140] At least one of the guiding 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 can have two or more guiding elements and three or more second surface regions, any of which can be selected by forming 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 includes a first optical system component, a plurality of second optical system components, and at least one multimode optical waveguide network according to any of the above-described aspects or embodiments, the multimode optical waveguide network being arranged to direct a beam from the first optical system component or to the first optical system component, to a selected second optical system component of the plurality of second optical system components or from the selected second optical system component, and a controller configured to select one of the plurality of second optical system components, the controller comprising at least one of the guiding elements of the multimode optical waveguide network and / or modulating at least one beam characteristic to direct a beam from the first optical system component or to the first optical system component, to the selected second optical system component or from the selected second optical system component.

[0132]

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

[0133]

[0144] The optical system can include one or more holographic recording media, and at least some of the second system optical components can 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 above-described aspects or embodiments, and the controller may configure at least one of the guiding elements of the second multimode optical waveguide network and / or modulate at least one beam characteristic to guide a second beam from a first optical system component or to a first optical system component, to or from the same selected second optical system component or the same selected second optical system component.

[0135]

[0146] The optical system may include a third multimode optical waveguide network according to any of the above-described aspects or embodiments, and the controller may configure at least one of the guiding elements of the third multimode optical waveguide network and / or modulate at least one beam characteristic to guide a third beam from a first optical system component or to a first optical system component, to or from the same selected second optical system component or the same selected second optical system component.

[0136]

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

[0137]

[0148] In certain embodiments described above, an optical waveguide network as described below can be used.

[0138]

[0149] 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 or embedded in the surface of the waveguide. Each of the second surface regions of the parent waveguide is optically coupled to the first surface region of the corresponding one of the child waveguides. At least one guiding element of the parent waveguide is arranged to direct a beam from or to its first surface region to or from a selected second surface region of its plurality of second surface regions. The beam is taken into or received from the corresponding child waveguide whose first surface region is optically coupled to the second surface region of the parent waveguide through the second surface region of the parent waveguide and the first surface region of the corresponding child waveguide. At least one guiding element of each child waveguide is arranged to direct a beam from or to its first surface region to or from a selected second surface region of its plurality of second surface regions. At least one guiding element of each waveguide is configurable to select the second surface region of its waveguide and / or to select the second surface region of its waveguide through modulation of at least one beam characteristic in response to at least one beam characteristic.

[0139]

[0150] A multimode optical waveguide network may include a plurality of sub-waveguides, each of which is a multimode optical waveguide having a first surface region, a plurality of second surface regions, and at least one guiding element attached to or embedded within the surface of the sub-waveguide. Each of the second surface regions of each sub-waveguide is optically coupled to the first surface region of the corresponding one of the sub-waveguides. The at least one guiding element of each sub-waveguide can be arranged to direct a beam from or to its first surface region to or from a selected one of its plurality of second surface regions. The beam is captured by or extracted from the sub-waveguide via its first surface region and via the second surface region of the sub-waveguide optically coupled thereto. The at least one guiding element of each sub-waveguide can be configured to select the second surface region of the sub-waveguide and / or to select the second surface region of the sub-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 guiding element that can be configured to select the second surface region of the waveguide.

[0141]

[0152] Each of the waveguides may have at least one guiding element that selects the second surface region of the waveguide via modulation of at least one beam characteristic in response to at least one beam characteristic.

[0142]

[0153] At least one of the waveguides may have at least one active guiding element that can be configured to select the second surface region of the waveguide, and at least one other of the waveguides may have at least one guiding element that selects the second surface region of the other waveguide via modulation of at least one beam characteristic in response to 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 guiding element, whereby a beam within a first wavelength range is guided from or to its first surface region to or from a first one of the child or grandchild waveguides, and a beam within a second wavelength range is guided from or to its first surface region to or from a second one of the child or grandchild waveguides. The first child or grandchild waveguide may have at least one wavelength-responsive guiding element, whereby a beam within a first sub-range of the first wavelength range is guided from or to its first surface region to or from one of its second surface regions, and a beam within a second sub-range of the first wavelength range is guided from or to its first surface region to or from another of its second surface regions. The second child or grandchild waveguide may have at least one wavelength-responsive guiding element, whereby a beam within a first sub-range of the second wavelength range is guided from or to its first surface region to or from one of its second surface regions, and a beam within a second sub-range of the second wavelength range is guided from or to its first surface region to or from another of its second surface regions.

[0144]

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

[0145]

[0156] That or each active guiding element may be a switchable grating or a grating region.

[0146]

[0157] At least one of the guiding 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 guiding elements and three or more second surface regions, any of which can be selected by forming one or both of the two or more guiding elements and / or modulating at least one beam characteristic.

[0148]

[0159] An optical system incorporating such a waveguide network includes a first optical system component, a plurality of second optical system components, and at least one multimode optical waveguide network according to any of the above-described aspects or embodiments, which is arranged to guide a beam from the first optical system component or to the first optical system component, to a selected second optical system component of the plurality of second optical system components or from the selected second optical system component, and a controller configured to select one of the plurality of second optical system components, which forms at least one of the guiding elements of the multimode optical waveguide network and / or modulates at least one beam characteristic to cause the beam to be guided from the first optical system component or to the first optical system component, to the selected second optical system component or from the selected second optical system component.

[0149]

[0160] The first system component may include an emitter system for emitting a beam and guiding it to a selected second system component, or a detector array from which a beam is guided from a 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 above-described aspects or embodiments, and the controller may configure at least one of the guiding elements of the second multimode optical waveguide network and / or modulate at least one beam characteristic to direct a second beam from a first optical system component or to a first optical system component, to the same selected second optical system component or from the same selected second optical system component.

[0152]

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

[0153]

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

[0154]

[0165] It will be understood that the above-described embodiments are presented by way of example only. Other variations or use cases of the disclosed techniques will become apparent to those skilled in the art at the time of the disclosure of this specification. The scope of this disclosure is not limited by the described embodiments, but only by the appended claims.

Claims

Claim 1 An optical data transfer system, comprising: a beam modulator configured to embed data in an input beam; an input waveguide network formed from a multimode optical waveguide, having an incoupling region, and configured to direct the input beam to an outcoupling region of the input waveguide network; a spatial coherent detector configured to measure the phase and amplitude of an output optical field at a plurality of locations, the output optical field being at least partially defined by the input beam and thus exhibiting at least partially a distortion effect caused by passage of the input beam through the input waveguide network; a processor coupled to the spatial coherent detector and configured to compensate for the distortion effect using signal processing applied to the output of the spatial coherent detector, thereby recovering the data embedded in the input beam from the output of the spatial coherent detector; and compensating for the distortion effect includes compensating for a distortion effect caused by passage of a reference beam through at least one of a further multimode optical waveguide formed reference waveguide network and the input waveguide network. An optical data transfer system. Claim 2 The optical data transfer system according to claim 1, further comprising a holographic recording region, wherein the input waveguide network is configured to direct the input beam to the holographic recording region for storing the embedded data in a pattern recorded in the holographic recording region via interference between the input beam and the reference beam, and the output optical field is generated at a later time via interaction between the recorded pattern and the reference beam for reading the embedded data from the holographic recording region. Claim 3 The optical data transfer system according to claim 2, wherein the reference beam is configured to be directed to the holographic recording region via one of the input waveguide network and the reference waveguide network. Claim 4 An output beam at least partially defined by the input beam is configured to be directed to the spatial coherent detector via one of the input waveguide network, the reference waveguide network, and an output waveguide network formed from a further multimode optical waveguide, and the output beam passing through the input, reference, or output waveguide network also contributes to the distortion effect compensated by the signal processing. The optical data transfer system according to any one of claims 1 to 3.

5. The input waveguide network, the reference waveguide network, and the output waveguide network At least one of them includes an induction element that responds to beam characteristics, and the processor is configured to apply the signal processing according to the channel selection associated with the output optical field. The optical data transfer system according to any one of claims 1 to 4.

6. The processor is configured to select a channel model corresponding to the associated channel selection from a plurality of channel models corresponding to different channel options, and apply the signal processing according to the selected channel model. The optical data transfer system according to claim 5.

7. Each channel model includes signal processing parameters learned for the corresponding channel selection. The optical data transfer system according to claim 6.

8. A beam modulator configured to embed data in an input beam, an input waveguide network formed from a multimode optical waveguide, having an in-coupling region, and configured to direct the input beam to the out-coupling region of the input waveguide network. An input waveguide network, a spatial coherent detector configured to measure the phase and amplitude of the output optical field at a plurality of locations, the output optical field being at least partially defined by the input beam, and thus at least partially presenting a distortion effect caused by the input beam passing through the input waveguide network. The processor of an optical data transfer system comprising: Compensating the distortion effect using signal processing applied to the output of the spatial coherent detector, thereby recovering the data embedded in the input beam from the output of the spatial coherent detector. Compensating for the distortion effect includes compensating for the distortion effect caused by the reference beam passing through at least one of a reference waveguide network formed from a further multimode optical waveguide and the input waveguide network. A method. When executed by a processor, a beam modulator configured to embed data in an input beam, and an input waveguide network formed from a multimode optical waveguide, having an in-coupling region, and configured to direct the input beam to an out-coupling region of the input waveguide network. An input waveguide network, and a spatial coherent detector configured to measure the phase and amplitude of the output optical field at a plurality of locations, the output optical field being at least partially defined by the input beam, and thus at least partially exhibiting a distortion effect caused by the input beam passing through the input waveguide network. An optical data transfer system comprising: Compensating for the distortion effect using signal processing applied to the output of the spatial coherent detector, thereby recovering the data embedded in the input beam from the output of the spatial coherent detector. A computer-readable storage medium comprising data and instructions for causing the above to be executed. Compensating for the distortion effect includes compensating for the distortion effect caused by the reference beam passing through at least one of a reference waveguide network formed from a further multimode optical waveguide and the input waveguide network. A computer-readable storage medium.

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