摘要:
An encryption method and apparatus for holographic data storage are disclosed. In a system using orthogonal phase-code multiplexing, data is encrypted by modulating the reference beam using an encryption key K represented by a unitary operator. In practice, the encryption key K corresponds to a diffuser or other phase-modulating element placed in the reference beam path, or to shuffling the correspondence between the codes of an orthogonal phase function and the corresponding pixels of a phase spatial light modulator. Because of the lack of Bragg selectivity in the vertical direction, the phase functions used for phase-code multiplexing are preferably one dimensional. Such phase functions can be one-dimensional Walsh functions. The encryption method preserves the orthogonality of reference beams, and thus does not lead to a degradation in crosstalk performance.
摘要:
A method for encoding and decoding digital data for storage in a holographic medium (12). Digital data, consisting of binary data (B.sub.i) or grey scale data (A.sub.i), is encoded in bit groups or digit groups (B.sub.k, A.sub.k) containing at least k=1 bits or digits, respectively, by assigning to each bit group (B.sub.k) one reference bit (B.sub.r) and to each digit group (A.sub.k) two reference digits (A.sub.r1, A.sub.r2), assigning the bits of group (B.sub.k) to information bits (B.sub.j), assigning the digits of group (A.sub.k) to information digits (A.sub.j), assigning the reference bit (B.sub.r) and information digits (B.sub.j) to a reference pixel (P.sub.r) and information pixels (P.sub.j) chosen from pixels (24) of a holographic signal modulator (18), and assigning the reference digits (A.sub.r1, A.sub.r2) and information digits (A.sub.j) to reference pixels (P.sub.r1, P.sub.r2) and information pixels (P.sub.j) chosen from pixels (24) of the holographic signal modulator (18). Storing all pixels (24) by illuminating the holographic signal modulator (18) with a signal beam (22) which impresses upon the signal beam (29) pixels (24), guiding the signal beam (22) to the holographic medium (12) and storing the pixels (24) by directing a reference beam (26) at the holographic medium (12) from a predetermined angle .beta. and at a predetermined part of the holographic medium (12). Decoding the encoded binary data (B.sub.i) and encoded grey scale data (A.sub.i) by aiming the reference beam (26) at the holographic medium (12) at the same angle .beta. and location as during storage, recovering pixels (24) and recovering from them using a decoding unit (38) reference bits (B.sub.r) and information bits (B.sub.j) for each bit group (B.sub.k), and recovering reference digits (A.sub.r1, A.sub.r2) and information digits (A.sub.j) for each digit group (A.sub.k). Reconstructing the original binary data (B.sub.i) by differentiating the binary values of bits (B.sub.r) and (B.sub.j). Reconstructing the grey scale data (A.sub.i) by differentiating the reference digits (A.sub.r1, A.sub.r2) to obtain a benchmark (D.sub.r) and applying a binary operation on the benchmark (D.sub.r) and each of the information digits (A.sub.j).
摘要:
A method for coded-wavelength multiplexing according to which a signal waves S.sub.i (r) is recorded in a holographic medium in a counter-propagating geometry using corresponding writing reference waves R.sub.i (r). The method involves selecting discrete wavelengths .lambda. and encoding reference wave vectors .rho..sub.l which make up writing reference waves R.sub.i (r) such that the writing reference waves R.sub.i (r) at each wavelength .lambda. are orthogonal. The stored signal waves S.sub.i (r) are reconstructed in the form of reconstruction waves A.sub.c (.sigma.) with reconstruction reference waves R.sub.c (r) selected from among the writing reference waves R.sub.i (r). In the event of angular multiplexing of the reference wave vectors .rho..sub.l, it is possible to use one reference wave to produce a number of reconstruction waves A.sub.c (.sigma.) and generate a mosaic of desired holographic pages.
摘要:
Ionic and impurity concentrations in a photorefractive holographic storage medium are optimized such that electronic and ionic Debye numbers match an expected grating wave number K, at fixing and recording temperatures, respectively. Simultaneous and sequential recording and fixing are evaluated. The photovoltaic effect is reduced, subject to response time and absorption constraints, by matching reduced and oxidized impurity concentrations.
摘要:
A video image F�k! is identified as a basis image and stored as a basis page S�k! in a holographic storage medium. A subsequent image F�k+n! is stored by recording in the medium a page S�k+n!=F�k+n!-a�k!F�k!, where a�k!.noteq.0 and preferably a�k!=1. The page S�k! is recorded with a reference beam R�k!, while S�k+n! is recorded with a reference beam R�k+n! orthogonal to R�k!. The basis page is reset whenever the average intensity of a page to be stored exceeds a predetermined threshold. An image F'�k! is retrieved by reading basis page S�k! and letting F'�k!=S�k!. Subsequent images F'�k+n! are retrieved as S�k+n!+b�k!S�k!, where b�k!.noteq.0 and preferably b�k!=a�k!=1. The page addition step is performed coherently, i.e. by accessing the medium with a reference wave function R�k+n!+b�k!R�k!. The coherent addition is achieved by using a compound phase-and-amplitude modulator in a phase-code-multiplexed system, and by simultaneously accessing the storage medium at two different angles in an angle-multiplexed system. Differential video compression leads to a reduction in interpage crosstalk and to a capacity increase in crosstalk-limited memories. Optical page-by-page addition allows fast readout and eliminates the need for a time-consuming electronic decompression step.
摘要翻译:视频图像F [k]被识别为基础图像并作为基本页S [k]存储在全息存储介质中。 通过在介质中记录S [k + n] = F [k + n] -a [k] F [k]来存储后续图像F [k + n],其中a [k] a [k] = 1。 以参考光束R [k]记录页S [k],而用与R [k]正交的参考光束R [k + n]记录S [k + n]。 每当要存储的页面的平均强度超过预定阈值时,基页被重置。 通过读取基本页S [k]并使F'[k] = S [k]来检索图像F'[k]。 随后的图像F'[k + n]被检索为S [k + n] + b [k] S [k],其中b [k] NOTEQUAL 0并且优选地b [k] = a [k] = 1。 相干地执行页面添加步骤,即通过访问具有参考波函数R [k + n] + b [k] R [k]的介质。 通过在相位码复用系统中使用复合相位和幅度调制器,并且在角度多路复用系统中以两个不同的角度同时访问存储介质来实现相干相加。 差分视频压缩导致分组串扰的减少和串扰限制存储器的容量增加。 光学逐页添加允许快速读出,并且不需要耗时的电子减压步骤。
摘要:
A method of choosing an angle between a reference beam and a signal beam in a holographic storage apparatus is presented. The angle between the reference and signal beams can be optimized in light of crosstalk, scattering and wavelength seperation considerations.
摘要:
Partially overlapping holograms are stored in a cylindrical volume holographic storage medium capable of rotation about and translation along its longitudinal axis. The reference and signal beams are mutually perpendicular, and each is perpendicular to the longitudinal axis. An index-matched housing encloses the medium laterally. An optional helically-varying optical axis (c-axis) orientation allows recording at constant angular intervals over a full revolution. Signals from stored pages are used to dynamically adjust the positioning of the medium relative to the light beams as the medium continuously spins at high velocity, and to control the access of the signal beam to the readout camera.
摘要:
A digital electronic camera includes a holographic medium, an imaging array disposed at a focal plane for converting optical information to digital information; and an optical system configured to store the digital information onto the holographic medium. An optical system for retrieving images stored in the medium may be provided inside the camera or as a separate appliance.
摘要:
A single monolithic semiconductor substrate comprises a first side and a second side. The first side includes an air bearing surface. A laser integrates with the first side. The laser has an emission facet substantially co-planer with the air bearing surface. A contact pad on the second side electronically bridges to the laser.
摘要:
A near-field optical system having one or more solid state lasers and an aerodynamically shaped slider which comprise a single integrated, monolithic device fabricated from the same base semiconductor material. The monolithic optical head can be quickly and easily attached to the read arm of an optical read/write device without requiring attachment of separate laser elements, and without micropositioning or use of optical microscopy for positioning the lasers. The optical head comprising a single semiconductor substrate including a first region which defines a slider having an air bearing surface, and at least one second, laser region which defines a diode laser, with the diode laser having an emission face which is substantially co-planar with the air bearing surface. A slider region of the semiconductor substrate includes an air bearing surface, adjacent the p-clad layer, which is aerodynamically structured and configured to define a slider. The integral lasers include a p-electrical contact and an n-electrical contact which are electrically accessible from one side of the laser, which allows the laser to be used directly with a drive circuit substrate.