This application generally relates to systems and methods for performing linear algebra operations.
Randomized numerical linear algebra (RNLA) is a recently developed technique for reducing the dimensions of matrices on which linear algebra operations are performed, by using random sampling. For example, “matrix sketching” can include multiplying a matrix by a pseudo random matrix so as to reduce the dimension of the matrix in a linear algebra operation, while retaining important information within the matrix. RNLA techniques can include the matrix multiplication of a wide pseudo random matrix times a tall measurement or data matrix. However, when matrix dimensions can be on the order of 1000s by 100000s or more, multiplying matrices can take a significant amount of computational time.
Embodiments of the present invention provide systems and methods for performing linear algebra operations using multi-mode optics. For example, optical speckle in a multimode optical waveguide can be used as a photonic hardware accelerator to optically perform matrix multiplication faster, even up to orders of magnitude faster, than presently can be performed computationally. Illustratively, a plurality of matrix elements (such as elements of a matrix and a vector) can be modulated on an optical beam, and random matrix multiplication such as used in RNLA (or matrix sketching) can be performed in a multimode optical waveguide using the properties of time-wavelength mapping and optical speckle. A bank of photodiodes, integrators, and analog-to-digital converters can convert the resulting randomized version of the matrix elements (such as matrix and vector) back into the electronic domain for further processing.
Under one aspect, a method for performing a linear algebra operation includes imposing matrix elements onto a chirped optical carrier; and inputting into a multi-mode optic the matrix elements imposed on the chirped optical carrier. The method also can include outputting by the multi-mode optic a speckle pattern based on the matrix elements imposed on the optical carrier; and performing a linear algebra operation on the matrix elements based on the speckle pattern.
Illustratively, the matrix elements can include matrix elements of a first matrix and a second matrix. Optionally, the first matrix can include a matrix A of dimension m,n; the second matrix can include a vector b of dimension m; and the linear algebra operation can include approximating the equation Ax=b. Optionally, the multi-mode optic optically transforms each of matrix A and vector b by a speckle transformation S. Optionally, the speckle pattern output by the multi-mode optic can include matrix elements of a matrix SA of dimension p,n and matrix elements of a vector Sb of dimension p; and the linear algebra operation can include generating {tilde over (x)}=(SA)†Sb, where {tilde over (x)} is approximately equal to x, and wherein † indicates a pseudo-inverse operation. The speckle transformation S optionally includes at least one negative value.
Optionally, the method further includes receiving the speckle pattern output by the multi-mode optic at an array of p optical sensors coupled to n analog-to-digital converters (ADCs), and generating {tilde over (x)}=(SA)†Sb based on respective digital outputs of the p ADCs. Optionally, the p optical sensors concurrently receive a first portion of the speckle pattern corresponding to matrix elements of a first column of the matrix SA a first time; the p optical sensors concurrently receive a second portion of the speckle pattern corresponding to matrix elements of a second column of the matrix SA at a second time that is different from the first time; the p optical sensors concurrently receive a third portion of the speckle pattern corresponding to matrix elements of the vector Sb at a third time that is different from the first and second times; and the first, second, and third portions of the speckle pattern have different spatial distributions than one another. As a still further option, the matrix elements of the first column of the matrix SA can be imposed on one or more first pulses of the chirped optical carrier; the matrix elements of the second column of matrix SA can be imposed on one or more second pulses of the chirped optical carrier; and the matrix elements of the vector Sb can be imposed on one or more third pulses of the chirped optical carrier.
As additional or alternative options, the multi-mode optic can include a multi-mode guided-wave optic configured so as to control a rank of the speckle transformation S. A length and width of the multi-mode guided-wave optic optionally can be selected so as to control a correlation between columns and rows of the speckle transformation S.
Additionally, or alternatively, at least some of the matrix elements can be imposed onto the chirped optical carrier at different wavelengths than one another. Optionally, at least some of the matrix elements are imposed onto the chirped optical carrier at different times than one another.
Additionally, or alternatively, at least one of the matrix elements optionally has a negative value. The multi-mode optic optionally can transform at least one of the matrix elements by a negative value. Additionally, or alternatively, at least one of the matrix elements optionally has a positive value. The multi-mode optic optionally can transform at least one of the matrix elements by a positive value. In still further options, at least one of the matrix elements can have a negative value. The multi-mode optic and optical sensors can transform at least one of the matrix elements.
Under another aspect, a system for performing a linear algebra operation includes a modulator configured to impose matrix elements onto a chirped optical carrier; and a multi-mode optic configured to receive the matrix elements imposed on the chirped optical carrier and to output a speckle pattern based on the matrix elements imposed on the chirped optical carrier. The system also can include a processor configured to perform a linear algebra operation on the matrix elements based on the speckle pattern.
Optionally, the matrix elements can include matrix elements of a first matrix and a second matrix. Optionally, the first matrix can include a matrix A of dimension m,n; the second matrix can include a vector b of dimension m; and the linear algebra operation can include numerically approximating the equation Ax=b. The multi-mode optic optionally can be configured to optically transform each of matrix A and vector b by a speckle transformation S. The speckle pattern output by the multi-mode optic optionally can include matrix elements of a matrix SA of dimension p,n and matrix elements of a vector Sb of dimension p; and the linear algebra operation optionally can include generating {tilde over (x)}=(SA)†Sb, where {tilde over (x)} is approximately equal to x, and wherein † indicates a pseudo-inverse operation. The multi-mode optic optionally is configured such that the speckle transformation S include at least one negative value.
The system optionally also can include an array of p optical sensors coupled top analog-to-digital converters (ADCs), the p optical sensors being configured to receive the speckle pattern output by the multi-mode optic, the p ADCs each respectively being configured to generate a digital output based on the speckle pattern received by the optical sensor coupled thereto, and the processor being configured to generate {tilde over (x)}=(SA)†Sb based on the digital outputs of the p ADCs. The p optical sensors optionally can be configured to receive concurrently a first portion of the speckle pattern corresponding to matrix elements of a first column of the matrix SA a first time; the p optical sensors optionally can be configured to receive concurrently a second portion of the speckle pattern corresponding to matrix elements of a second column of the matrix SA at a second time that is different from the first time; the p optical sensors optionally can be configured to receive concurrently a third portion of the speckle pattern corresponding to matrix elements of the vector Sb at a third time that is different from the first and second times; and the first, second, and third portions of the speckle pattern can have different spatial distributions than one another. In one optional configuration, the matrix elements of the first column of the matrix SA are imposed on one or more first pulses of the chirped optical carrier; the matrix elements of the second column of matrix SA are imposed on one or more second pulses of the chirped optical carrier; and the matrix elements of the vector Sb are imposed on one or more third pulses of the chirped optical carrier.
Additionally, or alternatively, the multi-mode optic can include a multi-mode guided-wave optic configured so as to control a rank of the speckle transformation S. Optionally, a length and width of the multi-mode guided-wave optic are selected so as to control a correlation between columns and rows of the speckle transformation S.
Additionally, or alternatively, at least some of the matrix elements can be imposed onto the chirped optical carrier at different wavelengths than one another. At least some of the matrix elements can be imposed onto the chirped optical carrier at different times than one another.
In still further options, at least one of the matrix elements can have a negative value. The multi-mode optic can transform at least one of the matrix elements by a negative value. Additionally, or alternatively, at least one of the matrix elements optionally has a positive value. The multi-mode optic optionally can transform at least one of the matrix elements by a positive value. In still further options, at least one of the matrix elements can have a negative value. The multi-mode optic and optical sensors can transform at least one of the matrix elements.
In yet another aspect, an integrated system for performing a linear algebra operation is provided. The integrated system can include a substrate; a source of a chirped optical carrier; and a modulator configured to impose matrix elements onto the chirped optical carrier. The integrated system also can include a multi-mode optic defined within the substrate and configured to receive the chirped optical carrier having the matrix elements imposed thereon and to output a speckle pattern based on the chirped optical carrier having the matrix elements imposed thereon. The integrated system also can include an array of optical sensors configured to be irradiated with the speckle pattern; and a linear algebra processor coupled to the array of optical sensors and configured to perform the linear algebra operation based on the speckle pattern.
In one optional configuration, one or more of the source, the modulator, the linear algebra processor, and the optical sensor are defined in or disposed on the substrate.
The patent or application file includes at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
Embodiments of the present invention include systems and methods for performing linear algebra operations using multi-mode optics. Elements of the matrix or matrices to be operated upon can be converted into the optical domain, e.g., imposed on a chirped optical carrier. A multi-mode optic can receive the matrix elements imposed on the chirped optical carrier, and based thereon can transform the matrix elements by a speckle transformation that can reduce the size of the matrix or matrices to be operated upon. The linear algebra operation can be performed in the digital domain based upon the reduced-dimension matrix or matrices, optionally using randomized numerical linear algebra (RNLA) techniques.
An exemplary numerical linear algebra problem can include approximating a solution to the equation:
Ax=b (1)
for the vector x, given A and b under conditions in which A is a relatively large, tall matrix of dimension m,n (for example, m=40,000 rows by n=2000 columns) and b is a relatively large vector of dimension m (for example, with m=40,000 elements). Illustratively, m can be 1,000 or more, e.g., in the range of 1,000 to 1,000,000, or more. Additionally, or alternatively, n can be 100 or more, e.g., in the range of 100 to 100,000, or more.
The least squares solution for such an overdetermined problem is obtained with the pseudoinverse A† such that x=A†b. For large matrices A, computing the pseudoinverse can be computationally intensive. In comparison, such linear algebra operations can be accelerated by multiplying both sides of equation (1) by a pseudo-random matrix S of dimension p,m to obtain a matrix SA of dimension p,n and a vector Sb of dimension p, and approximately solving the reduced dimensionality equation:
SAx=Sb (2)
for x. For example, the linear algebra operation can include generating the solution:
{tilde over (x)}=(SA)†Sb (3)
where {tilde over (x)} is approximately equal to x. In a nonlimiting example where p=n, the matrix SA is square, and the solution for x can be obtained using the matrix inverse of the n by n matrix SA provided SA has a good condition number.
The systems and methods provided herein can provide further accelerations of such linear algebra operations by performing certain of said operations in the optical domain, using time/wavelength mapping. For example, the matrix elements being operated upon can be imposed on an optical carrier, such as a chirped optical carrier, and can include matrix elements of a first matrix and a second matrix. Illustratively, the first matrix can include matrix A of dimension m,n and the second matrix can include vector b of dimension m, and the linear algebra operation can include approximating the equation Ax=b. According to the present systems and methods, elements of such matrices can be imposed on a chirped optical carrier using an optical modulator, e.g., in a manner such as described herein with reference to
As described in greater detail herein, and further below with reference to
propagation through the multimode optical and integration for the duration of the modulation
yields the products
at two different spatial locations in the output plane of the multimode optic. Similarly, modulation of the second column of A,
on the second optical pulse, propagation through the multimode guide and integration yield the products
which completes the matrix multiplication SA for this illustrative case.
For details of exemplary RNLA techniques that can be adapted for use with the present systems and methods, see the following references, the entire contents of which are incorporated by reference herein: Mahoney, “Randomized algorithms for matrices and data,” Foundation and Trends in Machine Learning, Now Publishers: 1-54 (2011); and Drineas et al., “RandNLA: Randomized Numerical Linear Algebra,” Communications of the ACM 59(6): 80-90 (June 2016).
An overview of exemplary systems for performing linear algebra operations using multi-mode optics will be described, along with exemplary signals that can be formed therein. An exemplary method for performing linear algebra operations will be described. Additionally, some illustrative performance characteristics of exemplary multi-mode optics suitable for use in the present systems and methods, and comparative accelerations that can be achieved using the present systems and methods as compared with previously known techniques, will be described.
Optical carrier source 110 illustrated in
Referring again to
In one illustrative embodiment, optical carrier source 110 can include a theta laser such as disclosed in Shinwook Lee et al., Extreme Chirped Pulse Oscillator (XCPO) Using a Theta Cavity Design, IEEE Photonics Technology Letters, Vol. 18, No. 7, 799-801 (Apr. 1, 2006), the entire contents of which are incorporated by reference herein. The theta laser disclosed in Lee includes two optical circulators, an intensity modulator, an output coupler, a bandpass filter, a polarization controller, a semiconductor optical amplifier, an electric comb generator, and chirped FBG. The theta laser can be used to generate a sequence of chirped optical pulses.
Still other exemplary chirped optical carrier sources suitable for use as optical carrier source 110 are described in the following references, the entire contents of each of which are incorporated by reference herein: Coldren et al., “Tunable Semiconductor Lasers: A Tutorial,” Journal of Lightwave Technology 22(1): 193-202 (2004); Coldren, “Scalable and Reliable Photonic Integrated Circuits for Scalable and Reliable WDM Networks,” Proc. Contemporary Photonics Technology Conference, paper no. A1, Tokyo, Japan: 2 pages (2004); Johansson et al., “Sampled-grating DBR laser integrated with SOA and tandem electroabsorption modulator for chirp-control,” Electronics Letters 40(1): 2 pages (2004); Johansson et al., “High-Speed Optical Frequency Modulation in a Monolithically Integrated Widely-Tunable Laser—Phase Modulator,” Proc. OFC 2004, paper no. FL2, Los Angeles, Calif.: 3 pages (2004); Akulova et al., “10 Gb/s Mach-Zender modulator integrated with widely-tunable sampled grating DBR Laser,” Proc. OFC 2004, paper no. TuE4, Los Angeles, Calif.: 3 pages (2004); Fish et al., “Wavelength Agile, Integrated Analog Optical Transmitters,” Proc. GOMACTech, Monterey, Calif.: 225-228 (2004); Coldren et al., “High-efficiency ‘receiverless’ optical interconnects,” Proc. GOMACTech, paper no. 9.4, Monterey, Calif.: 2 pages (2004); Wang et al., “Efficient, Integrated Optical Transmitters for High-Speed Optical Interconnect Applications,” Proc. IEEE/LEOS Workshop on Interconnections Within High Speed Digital Systems,” Santa Fe, N. Mex.: 3 pages (2004); Johansson et al., “Monolithically integrated 40 GHz pulse source with >40 nm wavelength tuning range,” Proc. Integrated Photonics Research, paper no. IPD4, San Francisco, Calif.: 3 pages (2004).
Matrix element source 102 is coupled to optical modulator 120, and can be configured to generate elements of one or more matrices to be operated upon. Matrix element source 102 can be any device capable of generating matrix elements, which matrix elements can be received from another component. For example, matrix element source 102 can be configured to receive remotely generated matrix elements via a suitable wired or wireless signaling pathway and to provide those matrix elements to optical modulator 120, e.g., via a wired or wireless signaling pathway (not illustrated). Matrix element source 102 is suitably coupled to optical modulator 120 such that modulator 120 can impose the matrix elements upon the optical carrier generated by optical carrier source 110. Matrix element source 102 need not necessarily be considered to be part of system 100, and indeed can be remote from system 100. Exemplary sources of matrix elements include, but are not limited to, network models, cryptography, computer games, genetic calculations, image processing, computer graphics, coding theory, graph theory, graphical transformations, face morphing, detection and tracking, and compression.
Optical modulator 120 can be configured to impose the matrix elements onto the optical carrier (e.g., chirped optical carrier) generated by optical carrier source 110. As noted above, the matrix elements imposed on the optical carrier can include elements of a first matrix and a second matrix, such as matrix A and vector b described above. For example,
In optical modulator 120 illustrated in
Note that the matrix elements can be imposed on the optical carrier such that at least some of the matrix elements can be imposed onto the chirped optical carrier at different wavelengths as one another, and optionally can be imposed onto the chirped optical carrier at different times than one another. For example, the matrix elements can be sequentially imposed onto the optical carrier at different times than one another. Illustratively, each individual matrix element of a first column of a matrix sequentially can be imposed onto a chirped optical carrier in sequence, followed by each individual matrix element of a second column of the matrix, and so on. The value of each matrix element can be imposed on the chirped optical carrier as a corresponding intensity level. In configurations in which the matrix elements are binary, then on-off keying can be used to individually impose the matrix elements sequentially on the chirped optical carrier. In another example, a plurality of the matrix elements of a matrix (e.g., a column of the matrix elements) can be encoded using any suitable encoding technique, and the encoded matrix elements imposed onto the chirped optical carrier. Illustratively, higher order modulations that can be used to impose arbitrary matrix element values on an optical carrier include amplitude modulation, pulse width modulation, pulse position modulation, differential phase shifting, code division multiplexing, double-sideband modulation, single-sideband modulation, vestigial sideband modulation, quadrature amplitude modulation, angle modulation, frequency modulation, and phase modulation or any other suitable analog encoding format such as used in the telecommunications industry. Such encoding techniques optionally can include combining any suitable number of matrix elements with one another over a selected bandwidth. Additionally, or alternatively, any suitable number of the matrix elements can have negative values in a manner such as described below with reference to
Referring back to
Multi-mode optic 130 is configured so as to output a speckle pattern based on the matrix elements imposed on the optical carrier. By “multi-mode optic” it is meant a passive optical component that supports a plurality of electromagnetic propagation modes for each of a plurality of wavelengths, in which different of such propagation modes coherently interfere with one another so as to produce a speckle pattern. By “speckle pattern” it is meant an irregular, aperiodic pattern in which at least a first portion of the pattern includes an optical intensity profile that is different than an optical intensity profile of at least a second portion of the pattern that is spatially separated from the first portion of the pattern. By “optical intensity profile” it is meant the respective intensities (amplitudes) of different wavelengths in an optical pulse at a selected region of space.
Accordingly, within a speckle pattern output by multi-mode optic 130 illustrated in
A length and width of the multi-mode guided-wave optic can be selected so as to control a correlation between columns and rows of the speckle transformation S, and/or the multi-mode guided-wave optic can be configured so as to control a rank of the speckle transformation S. For example, note that multi-mode optics that are insufficiently wide may have an insufficient number of speckle lobes at the output of the optic, and that multi-mode optics that are insufficiently long may have insufficient variation with wavelength to randomize the number of matrix elements. Illustratively, in a multimode waveguide, there exist a large number of spatial modes, each of which has a unique spatial pattern in the direction or directions perpendicular to the guide. The interference of these modes gives rise to a speckle pattern that is generally the same for each optical wavelength at the entrance to the waveguide. Each spatial mode also has a unique phase that is inversely proportional to the optical wavelength and directly proportional to the distance of propagation along the guide. Then as the modes propagate along the guide, the speckle pattern changes and because of the wavelength-dependent phase, the speckle pattern varies from wavelength to wavelength. The longer the guide, the faster the speckle pattern changes with wavelength and this in turn allows more independent columns in the speckle transformation S or a higher rank in S. Likewise, making a guide wider allows it to support a larger number of modes and hence a larger number of independent rows in S or again a higher rank.
Although
The matrix elements can be recovered based on the speckle pattern. For example, referring again to
Linear algebra processor 140 can include at least one optical sensor that multi-mode optic 130 irradiates with a first portion of a speckle pattern, and that generates an analog electronic signal. Additionally, linear algebra processor 140 can include one or more electronic based devices configured to convert analog signals into digital signals, e.g., an analog-to-digital converter (ADC), for further processing. For example, the optical sensor can be coupled to an ADC so as to digitize an electrical output of the optical sensor. Additionally, linear algebra processor 140 can include any suitable device capable of performing linear algebra operations, e.g., a processor, and can include a memory device such as random access memory (RAM), a flash drive, or other recordable medium for storing the output of the ADC(s), as well as the results of the linear algebra operation on the matrix elements.
Exemplary linear algebra processor 140 illustrated in
Each photodetector 661 can provide the electronic representation of the respective portion of the speckle pattern to a corresponding one of ADCs 662 via a suitable electronic pathway 663, e.g., a conductor. ADC 662 then generates a digital representation of the corresponding portion of the speckle pattern, and provides that digital representation to processor 664 via a suitable electronic pathway 665, e.g., a conductor. In some embodiments, ADCs 662 are synchronized to optical carrier source 110 illustrated in
Note that any suitable arrangement and types of optical carrier source 110, optical modulator 120, multi-mode optic 130, linear algebra processor 140, and substrate 150 illustrated in
The chirped optical carrier is received by optical modulator 121, such as a Mach-Zehnder modulator (MZM), which imposes matrix elements upon the chirped optical pulse such as represented in
then the stream of digits driving the modulator (e.g., MZM) can be {3,6,9,2,5,8,1,4,7}. In an example in which the duration of the pulse for each number in A is tip/m, where tip is the interpulse time of the laser and m is the large dimension A, the mapping of time onto wavelength in the repetitively chirped optical signal can map each matrix element in a given column of A to a different color in a manner such as shown below modulator 121 in
The multi-mode optic can include multi-mode waveguide/fiber 131 that receives as input the matrix elements imposed upon the chirped optical pulse, e.g., via a reticle, that optically transforms the matrix elements by a speckle transformation, and outputs (directly, or indirectly via guided-wave optics 132) a speckle pattern to a linear algebra processor that can include photodiode array 141 and ADCs 142 that can be configured analogously as those discussed herein with reference to
In embodiments in which SA is a square matrix, e.g., where p=n, the number of uncorrelated measurements in the speckle pattern at the output plane of the multi-mode optic 131 can be approximately equal to the small dimension n of A. In one nonlimiting example, a planar waveguide such as described in the Valley article and the Valley patent mentioned elsewhere herein, having 100 independent outputs from a 20 micron SOI wide waveguide can be used. The dimension n can be increased by using a larger waveguide or can be doubled by placing a 50/50 beamsplitter directly after the modulator (e.g., MZM 121), and injecting the modulated optical signal into a second waveguide. Different mode scramblers can be used for each guide, e.g., such as illustrated in
Note that the exemplary matrix element sequence shown schematically above MZM 121 in
It should be appreciated that systems such as described herein with reference to
At step 720 of method 700 illustrated in
At step 730 illustrated in
At step 740 illustrated in
As noted above, performing an optical speckle transformation S of matrix elements can significantly accelerate appropriate linear algebra operations, e.g., RNLA operations such as described herein with reference to equations (1)-(3).
Note that the RNLA calculation has 2 parts, the matrix multiply SA and the inverse operation (SA)†, assuming that the random matrix S is precalculated. If the matrix multiply SA can be calculated in a time that is short compared to the time to perform (SA)†, the RNLA acceleration can be much greater, and such factor can be referred to as “speckle acceleration” such as plotted in
It can be understood from
Additionally, any suitable combination of elements of the present systems can be integrated in one or more suitable substrates. For example,
In the configuration illustrated in
One or more of the optical carrier source, the modulator, the linear algebra processor, and the optical sensor (photodiode array) can be defined in or disposed on the substrate 1301. For example, in a hybrid integration implementation, the optical carrier and the modulator can be disposed on a first substrate, and the waveguide and photodiode array can be disposed on a second substrate that abuts the first substrate. In one example, a method is provided for performing a linear algebra operation that includes imposing matrix elements onto a chirped optical carrier; inputting into a multi-mode optic the matrix elements imposed on the chirped optical carrier; outputting by the multi-mode optic a speckle pattern based on the matrix elements imposed on the optical carrier; and performing a linear algebra operation on the matrix elements based on the speckle pattern. Nonlimiting examples of such a method are described further herein with reference at least to
In another example, a system is provided for performing a linear algebra operation that includes a modulator configured to impose matrix elements onto a chirped optical carrier; a multi-mode optic configured to receive the matrix elements imposed on the chirped optical carrier and to output a speckle pattern based on the matrix elements imposed on the chirped optical carrier; and a processor configured to perform a linear algebra operation on the matrix elements based on the speckle pattern. Nonlimiting examples of such a system are described further herein with reference at least to
In another example, an integrated system is provided for performing a linear algebra operation that includes a substrate; a source of a chirped optical carrier; a modulator configured to impose matrix elements onto the chirped optical carrier; a multi-mode optic defined within the substrate and configured to receive the chirped optical carrier having the matrix elements imposed thereon and to output a speckle pattern based on the chirped optical carrier having the matrix elements imposed thereon; an array of optical sensors configured to be irradiated with the speckle pattern; and a linear algebra processor coupled to the array of optical sensors and configured to perform the linear algebra operation based on the speckle pattern. Nonlimiting examples of such an integrated system are described further herein with reference at least to
While preferred embodiments of the invention are described herein, it will be apparent to one skilled in the art that various changes and modifications may be made. For example, it should be apparent that the systems and methods provided herein suitably may be used to perform any suitable type of linear algebra operation. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.
This invention was made with government support under Contract No. FA8802-14-C-0001 awarded by the Department of the Air Force. The government has certain rights in the invention.
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Number | Date | Country | |
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20180165248 A1 | Jun 2018 | US |