DYNAMIC APERTURE HOLOGRAPHIC MULTIPLEXING
Systems and methods for dynamic aperture holographic multiplexing are disclosed. One example process may include recording a set of holograms in a recording medium by varying both the reference beam angular aperture and the signal beam angular aperture. The angular aperture of the signal beam may be dynamically changed such that the closest edge of each signal beam angular aperture is selected to be a threshold angle different than the angular aperture of the reference beam used to record it. In some examples, the dynamic aperture holographic multiplexing process may include dynamic aperture equalization to reduce cross-talk, to improve error correction parity distribution for improved recovery transfer rate, to provide multiple locus aperture sharing for increased recording density, and to provide polarization multiplexed shared aperture multiplexing for increased transfer rate in both recording and recovery.
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This application claims priority to U.S. Provisional Patent Application Ser. No. 61/755,893, filed Jan. 23, 2013, the entire disclosure of which is hereby incorporated by reference in its entirety for all purposes as if put forth in full below.
BACKGROUND1. Field
The present disclosure relates generally to holography and, more specifically, to holographic multiplexing.
2. Related Art
Holography is a technique for storing both phase and amplitude information of light by recording the interference pattern generated between a coherent object beam and a reference beam as a hologram in a photosensitive medium. During recovery, a probe beam (which is a replica of the reference beam) illuminates the hologram, and a diffracted beam (which is a replica of the object beam) may be generated. In the original “in line” configuration described by Dennis Gabor in “A new microscopic principle,” Nature 161, 777 (1948), the object and reference beams shared an optical axis, creating a diffracted “ambiguity” beam from the conjugate interference term, as well as resulting in a superposition of the diffracted beam with the probe beam. However, as described in E. N. Leith and J. Upatnieks, “Reconstructed wavefronts and communication theory,” J. Opt. Soc. Amer. 52, 1123-30 (1962), an “off-axis” configuration—one in which the object and reference beams have axes with different angles of incidence—would naturally allow for the separation of the diffracted beam from the other components. Such beams might be said to issue from separate, rather than shared, apertures in angle space. Off-axis holography subsequently became the dominant configuration, and is used for virtually all holographic systems, including holographic data storage systems.
Holography is attractive for digital data storage because many holograms may be written into the same volume (or overlapping volumes) of a thick recording medium using a process known as multiplexing, which is described by G. Barbastathis and D. Psaltis, “Volume holographic multiplexing methods,” in Holographic Data Storage, H. J. Coufal, D. Psaltis, and G. Sincerbox, eds. Springer (2000), pp. 21-62. Many different holographic multiplexing techniques have been developed. For example, using angle multiplexing, described by F. H. Mok, “Angle-multiplexed storage of 5000 holograms in lithium niobate,” Opt. Lett. 18, 915-917 (1993), one may record hundreds or thousands of different holograms in the same volume of media by using collimated (plane wave) reference beams that differ slightly from each other by their angle of incidence. Each hologram may record a different object beam (or signal beam) that has been modulated with a different digital data pattern. During recovery, the hologram may be illuminated by a probe beam. Due to the Bragg effect, only a hologram recorded with a reference beam angle at the same angle of incidence as the probe beam will produce substantial diffraction. Each signal beam may thus be reconstructed independently, allowing the digital data to be recovered without cross-talk from the rest of the multiplexed holograms.
Other holographic multiplexing techniques, such as wavelength multiplexing described by D. Lande, J. F. Heanue, M. C. Bashaw, and L. Hesselink, “Digital wavelength-multiplexed holographic data storage system,” Opt. Lett. 21, 1780-1782 (1996), shift multiplexing described by D. Psaltis, A. Pu, M. Levene, K. Curtis, and G. Barbastathis, “Holographic storage using shift multiplexing,” Opt. Lett. 20, 782-784 (1995), and polytopic multiplexing described by K. Anderson and K. Curtis, “Polytopic multiplexing,” Opt. Lett. 29, 1402-1404 (2004), have been developed. These multiplexing techniques may be used alone or in combination with other multiplexing techniques to increase the amount of data stored in a recording medium.
Other features of the recording geometry may be varied to record data in the recording medium. For example, a page-oriented system is one in which the signal beam is modulated as a two-dimensional array of pixels, the modulation typically being imparted by a spatial light modulator (SLM). A Fourier architecture is one in which the recording medium is placed at or near an optical Fourier plane of the page image. A monocular system is one in which both the reference and signal beams pass through a single, shared objective lens before illuminating the recording medium, as described in U.S. Pat. No. 7,742,209, “Monocular holographic data storage system architecture,” Jun. 22, 2010.
SUMMARYMethods for recording a set of multiplexed holograms are provided. One example method may include: recording a first hologram of the set of multiplexed holograms to a recording medium using a first signal beam angular aperture and a first reference beam; and recording a second hologram of the set of multiplexed holograms to the recording medium using a second signal beam angular aperture and a second reference beam, wherein the second signal beam angular aperture is varied in at least one characteristic from the first signal beam angular aperture.
In one example, the first hologram and the second hologram may each comprise a data page of pixel information. In another example, the first signal beam angular aperture and the second signal beam angular aperture may vary in one or more of shape, size, and position.
In one example, the method may further include: recording a third hologram of the set of multiplexed holograms to the recording medium using a third signal beam angular aperture and a third reference beam, wherein the third signal beam angular aperture may be varied in at least one characteristic from the first signal beam angular aperture and the second signal beam angular aperture; and recording a fourth hologram of the set of multiplexed holograms to the recording medium using a fourth signal beam angular aperture and a fourth reference beam, wherein the fourth signal beam angular aperture may be varied in at least one characteristic from the first signal beam angular aperture, second signal beam angular aperture, and the third signal beam angular aperture.
In one example, an edge of the first signal beam angular aperture may be separated from an angular aperture of the first reference beam by a first angle; an edge of the second signal beam angular aperture may be separated from an angular aperture of the second reference beam by a second angle; an edge of the third signal beam angular aperture may be separated from an angular aperture of the third reference beam by a third angle; and an edge of the fourth signal beam angular aperture may be separated from an angular aperture of the fourth reference beam by a fourth angle. In another example, the first angle, the second angle, the third angle, and the fourth angle may be substantially equal. In yet another example, the first angle and the third angle may be substantially equal; the second angle and the fourth angle may be substantially equal; and the first angle and the third angle may be different than the second angle and the fourth angle.
In one example, using the first signal beam angular aperture may include using a signal beam with an angular range. In another example, at least a portion of an angular locus of a set of reference beams used to record the set of multiplexed holograms may overlap at least a portion of an angular locus of a set of signal beams used to record the set of multiplexed holograms.
In one example, a first portion of the set of multiplexed holograms may be used to store error parity data and a second portion of the set of multiplexed holograms may be used to store input data, wherein the holograms of the first portion may be smaller than the holograms of the second portion.
Systems for recording a set of multiplexed holograms are also provided
The present application can be best understood by reference to the following description taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals.
The following description is presented to enable a person of ordinary skill in the art to make and use the various embodiments. Descriptions of specific devices, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described herein and shown, but are to be accorded the scope consistent with the claims.
Various embodiments are described below relating to dynamic aperture holographic multiplexing. One example dynamic aperture holographic multiplexing process may include recording a set of holograms in a recording medium by varying both the angular aperture of a reference beam and the angular aperture of a signal beam. The angular aperture of the signal beam may be dynamically changed such that the closest edge of each signal beam angular aperture is selected to be a threshold angle different than the reference beam angular aperture used to record it. Thus, at least a portion of the reference beam locus (e.g., the aggregate coverage of the individual reference beam angular apertures) may be shared with the signal beam locus (e.g., the aggregate coverage of the individual signal beam angular apertures), resulting in a greater number of holograms being recorded in the same volume of recording medium than obtainable without the use of dynamic aperture holographic multiplexing. In some examples, the dynamic aperture holographic multiplexing process may include dynamic aperture equalization to reduce cross-talk, to improve error correction parity distribution for improved recovery transfer rate, to provide multiple locus aperture sharing for increased recording density, and to provide polarization multiplexed shared aperture multiplexing for increased transfer rate in both recording and recovery.
In some examples, the processes for dynamic aperture holographic multiplexing may be combined with other multiplexing techniques, such as angle multiplexing, polytopic multiplexing, and the like. In one example, a page-oriented, monocular, Fourier geometry may be used to perform dynamic aperture holographic multiplexing. However, dynamic aperture holographic multiplexing may similarly be used with other architectures, such as collinear holography systems, common aperture holography systems, and the like.
k-Space Formalism for Holography
Holographic recording and diffraction can be analyzed using k-space formalism, as described in M. R. Ayres, “k-Space Formalism,” in K. Curtis, L. Dhar, W. L. Wilson, A. Hill, M. R. Ayres, Holographic Data Storage: From Theory to Practical Systems, John Wiley & Sons, Ltd. (2010), pp. 26-31. In k-space, propagating optical waves and holographic gratings may be represented by three-dimensional Fourier transforms of their distributions in real space. For example, a collimated monochromatic reference beam can be represented in real space and k-space by
where Er ({right arrow over (r)}) is the optical scalar field distribution at all {right arrow over (r)}={x,y,z} 3D spatial vector locations, and its transform Er({right arrow over (k)}) is the optical scalar field distribution at all {right arrow over (k)}={kx,ky,kz} 3D spatial frequency vectors. Ar is the complex amplitude of the field, and {right arrow over (k)}r is a vector whose length indicates the spatial frequency of the light waves, and whose direction indicates the direction of propagation. In some examples, all beams may be composed of light of the same wavelength, so all optical k-vectors may have the same length (e.g., |{right arrow over (k)}r|=kn). Thus, all optical propagation vectors may lie on a sphere of radius kn. This construct is known as the k-sphere.
The other important k-space distribution is that of the holograms themselves. Holograms for data storage usually include spatial variations of the index of refraction within the recording medium, typically denoted Δn({right arrow over (r)}). Ideally, this index modulation pattern is proportional to the spatial intensity of the recording interference pattern, i.e.,
Δn({right arrow over (r)})∝|Es({right arrow over (r)})+Er({right arrow over (r)})|2=|Es({right arrow over (r)})2+|Er({right arrow over (r)})|2+Es*({right arrow over (r)})Er({right arrow over (r)})+Es({right arrow over (r)})Er*({right arrow over (r)}), (2)
where Es({right arrow over (r)}) is the spatial distribution of the signal beam field. The final term in this expansion, Es({right arrow over (r)})Er*({right arrow over (r)}), is the signal-bearing (data band) term. Thus we can write
where is the 3D cross-correlation operator. This is to say, the product of one field and the complex conjugate of another in the spatial domain become a cross-correlation of their respective Fourier transforms in the frequency domain.
The internal structure of the data bands is also indicated. The entire data band (along with the conjugate data band) represents the k-space locus of the holographic fringes for all of the holograms in an angle-multiplexed hologram stack, and each hologram occupies an Es({right arrow over (k)}) 112 patch-shaped layer within each of the bands. Each layer has a slight thickness (determined by the Bragg selectivity imparted by the medium thickness) and may be packed in a nested fashion similar to the layers of an onion within the data band to maximize density. It should be noted that while
Using a holographic data storage system having a monocular architecture like that shown in
To illustrate,
In contrast,
In some examples, the signal beam angular aperture may be dynamically changed by changing the subset of the SLM pixels that are included in the holographic data page. In some examples, regions of the signal angular aperture that are not included in the holographic data page may be darkened to prevent their illuminating the recording medium. In some examples, this darkening may be accomplished by setting SLM pixels corresponding to the excluded regions to a dark, or “off” state. In other examples, this darkening may be accomplished using a knife edge shutter or similar device to selectively block illumination from excluded aperture regions while passing illumination from included regions. Such a method might be used if, for example, the SLM employed does not produce an appropriate dark pixel state. In still other examples, this darkening may be accomplished by a beam shaping device that dynamically redirects light from dark regions to illuminated regions.
Employing the same reference beam angular spacing design rule that was used in the preceding discussion of
System 500 may include an aperture sharing element to combine the reference 516 and signal beam 512 paths in the regions that are shared between the two. In the illustrated example of
While passive aperture sharing methods are described above, in other examples, an active aperture sharing element employing a switchable element, such as a MEMS-actuated micro-mirror array, to dynamically select the desired beam source for each region of the shared aperture, may be used. In yet other examples, a single SLM may be used to generate both signal and reference beams, and may thus itself be considered to be an active aperture sharing element. Moreover, other architectures, potentially employing other methods of either passive or active aperture sharing, may additionally or alternatively be used.
K-Space SeparabilityAs shown in
In some examples, dynamic aperture equalization may be performed by interleaving data page sizes. For example, the edge of the signal beam angular aperture may be changed every other hologram so that only the odd (or alternatively even) numbered holograms have the lowest allowable frequency components. In the example described with respect to
In other examples, dynamic aperture equalization may be performed with or without shared aperture multiplexing. Additionally, interleaving patterns of different lengths (not just odd/even), and patterns that are not cyclical may also be performed. In general, any technique that equalizes the k-space modulation distribution may be performed and may be referred to as dynamic aperture equalization.
Error Correction Parity DistributionHolographic storage devices typically employ error correcting codes in order to achieve robust data recovery in the presence of recovery errors. For example, systematic codes may be used to append parity data to the input data to allow for reconstruction when some part of the whole cannot be recovered. Examples of systematic codes include low density parity check (LDPC) codes and Reed-Solomon codes.
In some examples using dynamic aperture holographic multiplexing, the parity portion of the data recorded may be preferentially distributed to some subset of the data pages, while input data may be preferentially distributed to some other subset. In one example, parity data may be preferentially distributed to smaller data pages, while input data may be preferentially distributed to larger ones. Distributing the parity data in this way advantageously improves the recovery transfer rate because in the event of error-free recovery of the input data, the parity data residing on the smaller data pages need not be recovered. When used in a dynamic aperture system, the parity pages may be selectively distributed to lower data rate (smaller) pages.
Multiple Locus Aperture SharingIn some examples, regions of the aperture may be shared multiple times. Multiple sharing of the signal and/or reference angular apertures can be used to access grating space that is inaccessible to the “singly shared” methods discussed above. Multiple sharing in this context is distinct from the “sharing” of an underlying multiplexing scheme, such as the angle multiplexing described above.
In one example, multiple locus aperture sharing may include double sharing and may be performed with the dynamic aperture holographic multiplexing described above.
While a specific locus shared aperture example is provided above, it should be appreciated that other multiple locus shared aperture schemes may be used. The multiple locus hologram distributions may or may not be symmetric in k-space, and three, four, or even more distributions may be employed. The method may be practiced in combination with multiplexing methods other than angular multiplexing and/or polytopic multiplexing.
Polarization Multiplexed Shared Aperture MultiplexingIn some examples in which multiple locus shared aperture techniques are used, multiple locus multiplexing may be performed simultaneously, rather than sequentially, by employing substantially orthogonal polarization states for the recording or recovery of two shared apertures simultaneously. In some examples, the shared apertures of
The examples described above relate to systems employing angle and polytopic multiplexing. However, it should be appreciated that the present disclosure may also be applied to other system architectures. For example, dynamic aperture holographic multiplexing may similarly be applied to a collinear holography system, such as that described in H. Horimai, X. Tan, and J. Li, “Collinear holography,” Appl. Opt. 44, 2575-2579 (2005). According to Horimai et al., “[t]he unique feature of this technology is that 2-D page data are recorded as volume holograms generated by a coaxially aligned information beam and a reference beam, which are displayed simultaneously by one SLM and interfere with each other in the recording medium through a single objective lens.”
During the write process, a combined image of the signal beam and the reference beam, as shown in the angular aperture map of
During the read process, only the outer reference beam may be generated by SLM 904 and passed through PBS 906, QWP 910, and objective lens 912 onto holographic recording media 914. A reconstructed signal beam may be produced and may be reflected back through objective lens 912 and passed through QWP 908, where it may be converted from a circularly polarized state to an s-polarized state. The reconstructed signal beam may be then reflected by PBS 906 and detected using CMOS or CCD sensor 922. Laser source 916 may be used for optical servo control to adjust the focal point of the objective lens 912.
A collinear system similar or identical to that shown in
Modifying the collinear system in this way may advantageously provide at least two benefits:
1) Though the k-space hologram distributions generated by the three patterns are substantially overlapping, the overall volume of the data bands and conjugate data bands of the holograms so multiplexed may be larger than in the conventional case. This may result in a higher theoretical recording density.
2) According to a theoretical analysis as described in T. Shimura, M. Terada, Y. Sumi, R. Fujimura, and K. Kuroda, “Inter-page cross-talk noise in collinear holographic memory,” Joint Int. Symp. on Opt. Memories and Opt. Data Storage, Waikoloa, Hi., July (2008), paper TuPO4, inter-page cross-talk noise in collinear holography goes as an incoherent sum of contributions from the multiplexed pages. The k-space hologram distributions for conventional collinear holograms are completely overlapping, but the distributions of, e.g.,
Collinear holography relies on a correlation effect for holographic multiplexing. In contrast to angle multiplexing where individual holograms occupy disjoint regions of k-space, individual holograms in collinear recording are broadly distributed and densely overlapped with other holograms, leading to cross-talk expressions such as that of Shima et al. Dynamic aperture holographic multiplexing described herein serves to slightly reduce the overlap of these distributions, and thus serves to slightly reduce cross-talk by driving the design toward a more disjoint k-space partitioning scheme. Other variations of this technique may be implemented under the scope of the present disclosure.
Dynamic Aperture Holographic Multiplexing ProcessAt block 1202, a first hologram may be recorded to a recording medium using a first signal beam angular aperture and a first reference beam having a first reference beam angular aperture.
In one example, using a system similar or identical to that shown in
In another example, using a collinear system similar or identical to that shown in
In some examples, the reference beam angular aperture and the edge of the signal beam angular aperture nearest the reference beam angular aperture may be separated by a threshold angle.
In one example, using a system similar or identical to that shown in
In another example, using a collinear system similar or identical to that shown in
At block 1204, a second hologram may be recorded to the recording medium using a second signal beam angular aperture and a second reference beam having a second reference beam angular aperture. It should be appreciated that the second reference beam may be similar to the first reference beam used to record the first hologram at block 1202, except that a characteristic of the first reference beam may be modified to generate the second reference beam at block 1204. Similarly, the second signal beam angular aperture may be similar to the first signal beam angular aperture used to record the first hologram at block 1202, except that a characteristic of the first signal beam angular aperture may be modified to generate the second signal beam angular aperture at block 1204.
In one example, using a system similar or identical to that shown in
In another example, using a system similar or identical to that shown in
At block 1206, a third hologram may be recorded to the recording medium using a third signal beam angular aperture and a third reference beam having a third angular aperture. It should be appreciated that the third reference beam may be similar to the first reference beam used to record the first hologram at block 1202, except that a characteristic of the first reference beam may be modified to generate the third reference beam at block 1206. Similarly, the third signal beam angular aperture may be similar to the first signal beam angular aperture used to record the first hologram at block 1202, except that a characteristic of the first signal beam angular aperture may be modified to generate the third signal beam angular aperture at block 1206.
In one example, using a system similar or identical to that shown in
In another example, using a system similar or identical to that shown in
At block 1208, a fourth hologram may be recorded to the recording medium using a fourth signal beam angular aperture and a fourth reference beam having a fourth angular aperture. It should be appreciated that the fourth reference beam may be similar to the first reference beam used to record the first hologram at block 1202, except that a characteristic of the first reference beam may be modified to generate the fourth reference beam at block 1208. Similarly, the fourth signal beam angular aperture may be similar to the first signal beam angular aperture used to record the first hologram at block 1202, except that a characteristic of the first signal beam angular aperture may be modified to generate the fourth signal beam angular aperture at block 1208.
In one example, using a system similar or identical to that shown in
In another example, using a system similar or identical to that shown in
In some examples, additional holograms may be recorded in a manner similar to that described with respect to blocks 1204, 1206, and 1208. Each additional hologram may be recorded using a reference beam that is different than any of those previously used to record holograms and a signal beam that has been dynamically adjusted accordingly, as described above. In some examples, the threshold angle offset between the reference beam angular aperture and the edge of the signal beam angular aperture nearest the reference beam may be the same or substantially the same as the threshold angles used in each of the previous recordings. In other examples, the threshold angle offset may be interleaved such that even numbered holograms may use the same or substantially the same threshold angle and odd numbered holograms may use the same or substantially the same threshold angle (different from the angle used for the even numbered holograms) in order to perform dynamic aperture equalization to reduce cross-talk between holograms. In yet other examples, other non-uniform distributions of threshold angles may be used to generate the holograms.
In some examples, process 1200 may include the use of error correcting codes. In these examples, some of the data pages or holograms may be used to store parity information, while the other data pages are used to store input data. For example, the smaller data pages may be used to store the parity information, while the remaining data pages may be used to store input data. This may advantageously improve the recovery transfer rate because in the event of error-free recovery of the input data, the parity data residing on the smaller data pages need not be recovered.
In some examples, process 1200 may include multiple locus aperture sharing, as discussed above. In these examples, regions of the aperture may be shared multiple times. For example, process 1200 may include double sharing, as described above with respect to
In some examples in which multiple locus shared aperture techniques are used in process 1200, multiple locus multiplexing may be performed simultaneously, rather than sequentially, by employing substantially orthogonal polarization states for the recording or recovery of two shared apertures simultaneously. In some examples, the shared apertures of
At least some values based on the results of the above-described processes can be saved for subsequent use. Additionally, a non-transitory computer-readable medium can be used to store (e.g., tangibly embody) one or more computer programs for performing any one of the above-described processes by means of a computer. The computer program may be written, for example, in a general-purpose programming language (e.g., Pascal, C, C++, Java) or some specialized application-specific language.
Although only certain exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this disclosure. For example, aspects of embodiments disclosed above can be combined in other combinations to form additional embodiments. Accordingly, all such modifications are intended to be included within the scope of this disclosure.
Claims
1. A method for recording a set of multiplexed holograms, the method comprising:
- recording a first hologram of the set of multiplexed holograms to a recording medium using a first signal beam angular aperture and a first reference beam; and
- recording a second hologram of the set of multiplexed holograms to the recording medium using a second signal beam angular aperture and a second reference beam, wherein the second signal beam angular aperture is varied in at least one characteristic from the first signal beam angular aperture.
2. The method of claim 1, wherein the first hologram and the second hologram each comprise a data page of pixel information.
3. The method of claim 1, wherein the first signal beam angular aperture and the second signal beam angular aperture vary in one or more of shape, size, and position.
4. The method of claim 1, further comprising:
- recording a third hologram of the set of multiplexed holograms to the recording medium using a third signal beam angular aperture and a third reference beam, wherein the third signal beam angular aperture is varied in at least one characteristic from the first signal beam angular aperture and the second signal beam angular aperture; and
- recording a fourth hologram of the set of multiplexed holograms to the recording medium using a fourth signal beam angular aperture and a fourth reference beam, wherein the fourth signal beam angular aperture is varied in at least one characteristic from the first signal beam angular aperture, second signal beam angular aperture, and the third signal beam angular aperture.
5. The method of claim 4, wherein:
- an edge of the first signal beam angular aperture is separated from an angular aperture of the first reference beam by a first angle;
- an edge of the second signal beam angular aperture is separated from an angular aperture of the second reference beam by a second angle;
- an edge of the third signal beam angular aperture is separated from an angular aperture of the third reference beam by a third angle; and
- an edge of the fourth signal beam angular aperture is separated from an angular aperture of the fourth reference beam by a fourth angle.
6. The method of claim 5, wherein the first angle, the second angle, the third angle, and the fourth angle are substantially equal.
7. The method of claim 5, wherein:
- the first angle and the third angle are substantially equal;
- the second angle and the fourth angle are substantially equal; and
- the first angle and the third angle are different than the second angle and the fourth angle.
8. The method of claim 1, wherein using the first signal beam angular aperture comprises using a signal beam with an angular range.
9. The method of claim 1, wherein at least a portion of an angular locus of a set of reference beams used to record the set of multiplexed holograms overlaps at least a portion of an angular locus of a set of signal beams used to record the set of multiplexed holograms.
10. The method of claim 1, wherein a first portion of the set of multiplexed holograms are used to store error parity data and a second portion of the set of multiplexed holograms are used to store input data, wherein the holograms of the first portion are smaller than the holograms of the second portion.
11. A system for recording a set of multiplexed holograms, the system comprising:
- an aperture sharing element configured to output a modulated signal beam and a reference beam;
- a recording medium; and
- a controller configured to: cause the recording of a first hologram of the set of multiplexed holograms to the recording medium by causing the aperture sharing element to output a first signal beam having a first signal beam angular aperture and a first reference beam having a first reference beam angular aperture; and cause the recording of a second hologram of the set of multiplexed holograms to the recording medium by causing the aperture sharing element to output a second signal beam having a second signal beam angular aperture and a second reference beam having a second reference beam angular aperture, wherein the second signal beam angular aperture is varied in at least one characteristic from the first signal beam angular aperture.
12. The system of claim 11, wherein the aperture sharing element comprises a spatial light modulator, and wherein causing the aperture sharing element to output the first signal beam having the first signal beam angular aperture and the first reference beam having the first reference beam angular aperture comprises controlling the spatial light modulator to output the first signal beam having the first signal beam angular aperture and the first reference beam having the first reference beam angular aperture.
13. The system of claim 11, further comprising:
- a laser source for generating a beam;
- a beam directing device coupled to receive the beam; and
- a spatial light modulator coupled to receive the beam, wherein: causing the aperture sharing element to output the first signal beam having the first signal beam angular aperture comprises controlling the spatial light modulator to cause the aperture sharing element to output the first signal beam having the first signal beam angular aperture; and causing the aperture sharing element to output the first reference beam having the first reference beam angular aperture comprises controlling the beam directing device to output the first reference beam having the first reference beam angular aperture
14. The system of claim 11, wherein the controller is further configured to:
- cause the recording of a third hologram of the set of multiplexed holograms to the recording medium by causing the aperture sharing element to output a third signal beam having a third signal beam angular aperture and a third reference beam having a third reference beam angular aperture, wherein the third signal beam angular aperture is varied in at least one characteristic from the first signal beam angular aperture and the second signal beam angular aperture; and
- cause the recording of a fourth hologram of the set of multiplexed holograms to the recording medium by causing the aperture sharing element to output a fourth signal beam having a fourth signal beam angular aperture and a fourth reference beam having a fourth reference beam angular aperture, wherein the fourth signal beam angular aperture is varied in at least one characteristic from the first signal beam angular aperture, second signal beam angular aperture, and the third signal beam angular aperture.
15. The system of claim 14, wherein:
- an edge of the first signal beam angular aperture is separated from an angular aperture of the first reference beam by a first angle;
- an edge of the second signal beam angular aperture is separated from an angular aperture of the second reference beam by a second angle;
- an edge of the third signal beam angular aperture is separated from an angular aperture of the third reference beam by a third angle; and
- an edge of the fourth signal beam angular aperture is separated from an angular aperture of the fourth reference beam by a fourth angle.
16. The system of claim 15, wherein the first angle, the second angle, the third angle, and the fourth angle are substantially equal.
17. The system of claim 15, wherein:
- the first angle and the third angle are substantially equal;
- the second angle and the fourth angle are substantially equal; and
- the first angle and the third angle are different than the second angle and the fourth angle.
18. The system of claim 11, wherein the first signal beam angular aperture comprises an angular range of the signal beam.
19. The system of claim 11, wherein at least a portion of an angular locus of a set of reference beams used to record the set of multiplexed holograms overlaps at least a portion of an angular locus of a set of signal beams used to record the set of multiplexed holograms.
20. The system of claim 11, wherein a first portion of the set of multiplexed holograms is used to store error parity data and a second portion of the set of multiplexed holograms is used to store input data, wherein the holograms of the first portion are smaller than the holograms of the second portion.
Type: Application
Filed: May 1, 2013
Publication Date: Jul 24, 2014
Applicant: AKONIA HOLOGRAPHICS LLC (Longmont, CO)
Inventors: Mark R. AYRES (Boulder, CO), Kenneth E. ANDERSON (Boulder, CO), Fredric R. ASKHAM (Loveland, CO), Bradley Jay SISSOM (Boulder, CO)
Application Number: 13/875,071
International Classification: G03H 1/26 (20060101);