The present invention generally relates to a photonics diffractive memory. In particular, the present invention relates to an apparatus for reading information from the photonics diffractive memory.
The large storage capacities and relative low costs of CD-ROMS and DVDs have created an even greater demand for still larger and cheaper optical storage media. Holographic memories have been proposed to supersede the optical disc as a high-capacity digital storage medium. The high density and speed of the holographic memory comes from three-dimensional recording and from the simultaneous readout of an entire packet of data at one time. The principal advantages of holographic memory are a higher information density (1011 bits or more per square centimeter), a short random access time (˜100 microseconds and less), and a high information transmission rate (109 bit/sec).
In holographic recording, a light beam from a coherent monochromatic source (e.g., a laser) is split into a reference beam and an object beam. The object beam is passed through a spatial light modulator (SLM) and then into a storage medium. The SLM forms a matrix of shutters that represents a packet of binary data. The object beam passes through the SLM which acts to modulate the object beam with the binary information being displayed on the SLM. The modulated object beam is then directed to one point on the storage medium by an addressing mechanism where it intersects with the reference beam to create a hologram representing the packet of data.
An optical system consisting of lenses and mirrors is used to precisely direct the optical beam encoded with the packet of data to the particular addressed area of the storage medium. Optimum use of the capacity of a thick storage medium is realized by spatial and angular multiplexing. In spatial multiplexing, a set of packets is stored in the storage medium shaped into a plane as an array of spatially separated and regularly arranged subholograms by varying the beam direction in the x-axis and y-axis of the plane. Each subhologram is formed at a point in the storage medium with the rectangular coordinates representing the respective packet address as recorded in the storage medium. In angular multiplexing, recording is carried out by keeping the x- and y-coordinates the same while changing the irradiation angle of the reference beam in the storage medium. By repeatedly incrementing the irradiation angle, a plurality of packets of information is recorded as a set of subholograms at the same x- and y-spatial location.
Previous holographic devices for recording information in a highly multiplexed volume holographic memory, and for reading the information out, require components and dimensions having a large size which places a limit on the ability to miniaturize these systems. Because previous holographic devices use motors and large-scale components such as mirrors and lenses, the addressing systems of these previous devices are slow. Furthermore, the mechanical components of these previous devices need frequent maintenance to correct errors and dysfunction coming, for instance, from wear and friction (i.e., tribology effect). Furthermore, previous addressing systems are expensive because they use complex systems for control. Thus, their prices cannot be lowered by mass production. Moreover, previous devices are not economical in their energy consumption. Even when previous addressing devices are accurate when new, the wear and friction of the interacting surfaces that are in relative motion lowers their accuracy with time.
In view of the foregoing, it would be desirable to provide one or more techniques which overcomes the above-described inadequacies and shortcomings of the above-described proposed solutions.
In view of the foregoing, it is an object of the present invention to provide an improvement in higher speed and smaller size of photonics diffractive memory reading systems.
It is a further object of the present invention to provide a miniaturization of a photonics diffractive memory reading system.
It is another object of the present invention to reduce the addressing system of a photonics diffractive memory reading system to a matchbox size.
It is a still a further object of the present invention to design a solid state reading system that can be rapidly manufactured in large quantities and low cost out of existing resources.
In order to achieve the above-mentioned objectives, the present invention comprises a solid-state system for reading information from a photonics diffractive memory. A coherent light source generates a convergent light beam which is then deflected by an acousto-optic deflector. A plurality of micro-mirrors receives the deflected light beam from the acousto-optic deflector at one of the micro-mirrors. A photonics diffractive memory having a plurality of points receives at one of the points the reflected light beam which is reflected from the micro-mirror. A detector has a plurality of light-detecting cells. At least one of the cells receives a portion of the reflected light beam transmitted through the point.
In a further aspect of the present invention, the micro-mirrors are configured as a matrix.
In another aspect of the present invention, there is a lens which forms the convergent light beam from the light source.
In still another aspect of the present invention, the convergent light source is selected from the group consisting of a low power laser and a light-emitting diode.
In yet another aspect of the present invention, the detector is a CCD detector array.
In a further aspect of the present invention, each of the plurality of points stores one or more diffraction patterns.
In yet another aspect of the present invention, the photonics diffractive memory comprises stored therein information located at the plurality of points of the memory and at a plurality of angles at each one of the points so as to form a plurality of packets of information at each one of the points.
In another aspect of the present invention, each of the micro-mirrors is a oscillatory scanning micro-mirror.
In a further aspect of the present invention, a computer is configured to coordinate the synchronization of the acousto-optic deflector and the oscillatory micro-mirrors so that the reflected light beam is directed to one of the points with a specific angle for a sufficient time to retrieve information from the point.
In yet another aspect of the present invention, each of the micro-mirrors is a oscillatory micro-mirror and the oscillation cycle of the micro-mirror is coordinated with the scanning of the acousto-optical deflector so as to direct said reflected light beam onto one of the points of the storage medium.
In order to facilitate a fuller understanding of the present invention, reference is now made to the appended drawings. These drawings should not be construed as limiting the present invention, but are intended to be exemplary only.
a shows a close up view of the actuator of the micro-mirror assembly according to the present invention.
a shows adding an epitaxial layer to a wafer as part of the MEMS fabrication process according to the present invention.
b shows the formation of the starting electrodes and deposition of a metal layer as part of the MEMS fabrication process according to the present invention.
c shows an anisotropical etch to remove the substrate underneath the designed mirror plate as part of the MEMS fabrication process according to the present invention.
d shows a cross section of the micro-mirror chip according to the present invention.
a shows a starting electrode of a micro-mirror assembly according to the present invention.
b shows operation of a micro-mirror being driven by a saw tooth signal according to the present invention.
The compact architecture for diffractive optics systems in accordance with the present invention integrates a number of components into a compact package, including an acousto-optic deflector and a microoptoelectromechanical system (MOEMS) device which reduces the addressing component of a reading system for a photonics diffractive memory to a matchbox size. The reading system is made of solid-state components. The mirrors are built in CMOS technology resulting in the advantage that the reading system can be mass-produced at low cost.
Various diffractive recording/reading processes have been developed in the art and further details can be found in the book Holographic Data Storage, Springer (2000) edited by H. J. Coufal, D. Psaltis, and G. T. Sincerbox. In this specification, the term “diffractive” is used throughout to differentiate prior art holographic technology used for 3-D image generation from diffractive technology necessary for the generation of a storage medium. For example, diffraction efficiency is critical to the viability of any material to be used as a diffractive storage medium. The quality of interference constituting a 3D-hologram is simple to achieve compared to the quality required to realize a storage medium. Moreover, a storage diffractive pattern can also be implemented by using other techniques than the interference of a reference and object beam, such as using as an e-beam etched on a material to generated diffraction patterns. For all these reasons, the specification herein introduces the concept of a broader diffractive optics technology.
The variation of the capacitance C 125 (C varies with angle φ) between the mirror plate 102 and the comb like driving electrodes 105a, 105b is used to generate the plate tortional movement. If a voltage U is applied by an energy source (not shown) to the driving electrodes 105a, 105b, the generated electrostatic torque M is:
M=½dC/dφU2
where φ is the deflection angle of the plate.
The mirror plate 102 can have a size from 0.5×0.5 mm up to 3×3 mm. The actuators (the movement between mirror plate 102 and electrodes 105 as driven by the energy source) are resonantly excited, i.e., they are continuously oscillating. The scan frequency depends on the size of the mirror plate (0.14 KHz up to 20 KHz) and a mechanical scan angle of ±15° can be achieved at a driving voltage of only 20V.
When the actuator works in synchronous mode, it is possible to control the angular position of the mirror plate 102 by controlling the maximum deflection amplitude and oscillating period. Advantages of these mirrors is that the amplitude of the deflection can be monitored with the driving voltage U. For a large scan angle, the deflection angle varies linearly with the excitation voltage.
As shown in
a-3d show the process for manufacturing a micro-mirror element 200 on a substrate 230 with starting electrodes 210a, 210b. The fabrication is achieved using a CMOS-compatible technology. Referring to
a illustrates the operation of the micro-mirror element 100.
b shows synchronization of the mirror plate 102 as driven by a saw tooth signal 300. The saw tooth signal 300 comprises the voltage U applied with a predetermined frequency per second. The operation of the mirror plate 102 is shown at five different positions 301-305 as the mirror plate 102 is driven by saw tooth wave 300 applied across the drive electrodes 105a, 105b (see
Table 1 shows the eigenfrequency (resonance frequency) of the micro-mirror element 100 as a function of mirror size. The eigenfrequency depends on the mechanical and electrical characteristics of the micro-mirror element 100. In the synchronized mode, the mirror oscillates at two times the eigenfrequency.
The operation of the reading system proceeds with the light source 410 emitting a light beam 480a which is focused by the converging lens 420 from a plane wave to spherical wave 480b. The spherical wave 480b is a convergent beam. The convergent beam 480b is deflected by the acousto-optic deflector 430 to form beam 480c which impinges on one of the micro-mirror elements of the MEOMS matrix 440. The MEOMS mirror matrix 440 has a size that fits the constraints of the memory matrix addressing system. The matrix of micro-mirrors 440 is used to address the matrix of points of the memory 450 in which data are recorded by spatial and angular multiplexing. The beam 480c coming from the acousto-optic deflector 430 forms an area with a diameter that can fit within the diameter of each one of the mirror elements of the MEOMS matrix 440. Additionally, the memory matrix 450 is spatially adjusted in such a way that the size of the laser beam 480d fits exactly the size of every point of the memory matrix 450.
Thus, as shown in
The storage medium 8 is typically a three-dimensional body made up of a material sensitive to a spatial distribution of light energy produced by interference of the object light beam 4 and the reference light beam 1. A hologram may be recorded in a medium as a variation of absorption or phase or both. The storage material must respond to incident light patterns causing a change in its optical properties. In a volume hologram, a large number of packets of data can be superimposed, so that every packet of data can be reconstructed without distortion. A volume (thick) hologram may be regarded as a superposition of three dimensional gratings recorded in the depth of the layer of the recording material each satisfying the Bragg law (i.e., a volume phase grating). The grating planes in a volume hologram produce change in refraction and/or absorption.
Several materials have been considered as storage material for optical storage systems because of inherent advantages. These advantages include a self-developing capability, dry processing, good stability, thick emulsion, high sensitivity, and nonvolatile storage. Some materials that have been considered for volume holograms are photorefractive crystals, photopolymer materials, and polypeptide material.
Referring now to
In this case, a 1 mm2 image 8a is obtained by focusing the object beam 4 onto the storage medium 8 centered at its coordinate. Due to this interference between the two beams 1,4, a diffractive image 8a 1 mm2 in size is recorded in the storage material 8 centered at the coordinates of the matrix. Spatial multiplexing is carried out by sequentially changing the rectilinear coordinates. The object beam 4 focuses on the storage material 8 so that a separate image 8a is recorded at a unique position in the plane defined by its coordinates (x, y). This spatial multiplexing results in a 10 by 10 matrix of diffractive images 8a. Angle multiplexing is carried out by sequentially changing the angle of the reference beam 1 by means of the mirror elements of the MEOMS matrix 440. Angle multiplexing is used to create 15-20 packets of information 8b corresponding to 15 discrete variations of the angle of incidence of the reference beam. Additionally, it is possible to reach 20-25 packets by simple multiplexing and 40-50 packets by using double symmetrical angular multiplexing. A data packet is reconstructed by shinning the reference beam 1 at the same angle and spatial location in which the data packed was recorded. The portion of the reference beam 1 diffracted by the storage material 8 forms the reconstruction, which is typically detected by a detector array. The storage material 8 may be mechanically shifted in order to store data packets at different points by its coordinates (x, y).
Two representative micro-mirrors 440a, 440b of the micro-mirror array 440 of
The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the present invention, in addition to those described herein, will be apparent to those of skill in the art from the foregoing description and accompanying drawings. Thus, such modifications are intended to fall within the scope of the appended claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP01/15421 | 12/7/2001 | WO | 6/7/2004 |