Patent Application
20060114791
The present invention relates to optical media systems and more particularly, this invention relates to an optical media system using multiple-wavelength light detection for dramatically improved data density capabilities.
Optical media presently include compact discs (CDs), digital video discs (DVDs), laser discs, and specialty items. Optical media has found great success as a medium for storing music, video and data due to its durability, long life, and low cost.
A CD typically comprises an underlayer of clear polycarbonate plastic. During manufacturing, the polycarbonate is injection molded against a master having protrusions (or pits) in a defined pattern that creates an impression of microscopic bumps arranged as a single, continuous, spiral track of data on the polycarbonate. Then, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Next a thin acrylic layer is sprayed over the aluminum to protect it. A label is then printed onto the acrylic.
During playback, the reader's laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light. The steps between the bumps reflect light differently than the lands, and an opto-electronic sensor detects that change in reflectivity. The electronics in the reader interpret the changes in reflectivity in order to read the bits that make up the data.
A DVD is very similar to a CD, and is created and read in generally the same way (save for multilayer DVDs, as described below). However, a single-sided, single-layer DVDs can store about seven times more data than CDs. A large part of this increase comes from the pits and tracks being smaller on DVDs. Table 1 illustrates a comparison of CD and DVD specifications.
To increase the storage capacity even more, a DVD can have multiple layers, several layers being readable on each side. The laser that reads the disc can actually focus on the inner layers through the outer layers. Table 2 lists the capacities of several typical forms of DVDs.
A DVD is composed of several layers of plastic, totaling about 1.2 millimeters thick.
An emerging technology known as Blu-ray uses blue-violet laser light to achieve data storage capacities of up to 27 GB. The Blu-ray Disc enables the recording, rewriting and play back of up to 27 gigabytes (GB) of data on a single sided single layer 12 cm CD/DVD size disc using a 405 nm blue-violet laser. The companies that established the basic specifications for the Blu-ray Disc are: Hitachi Ltd., LG Electronics Inc., Matsushita Electric Industrial Co., Ltd., Pioneer Corporation, Royal Philips Electronics, Samsung Electronics Co. Ltd., Sharp Corporation, Sony Corporation, and Thomson Multimedia.
A DVD player functions similarly to the CD player described above. However, in a DVD player, the laser can focus either on the semi-transparent reflective material behind the closest layer, or, in the case of a double-layer disc, through this layer and onto the reflective material behind the inner layer. The laser beam passes through the polycarbonate layer, bounces off the reflective layer behind it and hits an opto-electronic device, which detects changes in light.
One problem with optical media is that current read technology only allows reading of a single laser wavelength. The result is that the data density of current optical media is limited. What is therefore needed is a way to increase the data density of optical media, and the ability to read the increased data density.
Accordingly, the present invention provides a system and corresponding method for reading an optical medium by reading different wavelengths of light as it reflects off of the medium. The system includes a light source for emitting light at an optical medium having features representing data, the features on the optical medium causing variations in the way the light is reflected. An optical filter separates the light reflected from the optical medium into multiple wavelengths. One or more sensors (e.g., photo diodes) detect changes in the light in the different wavelengths, the changes representing data.
In one embodiment, the optical filter and sensor(s) are present on a single substrate. The reflected light can enter the filter directly or via a medium such as a fiber optic cable.
The filter acts as a demultiplexer to separate the light into at least two different wavelengths, and can separate the light into many different wavelengths, e.g., 2, 3, 4, 5, 6, 8 or more. Multiple sensors can simultaneously detect changes in the light in the different wavelengths, thereby providing at least a 2× or more improvement over standard optical media systems.
In one embodiment, the surface features on the optical medium are positioned on the same layer of material of the optical medium, the surface features having differing dimensions for reflecting the light differently for each wavelength. In another embodiment, the surface features on the optical medium are positioned on different layers of material of the optical medium, the surface features having differing dimensions for reflecting the light differently for each wavelength.
A circuit is coupled to the at least one sensor. The circuit interprets signals created by the sensor(s) for converting the signal into digital data. The circuit can also be formed on the same substrate as the optical filter and sensors.
The optical medium can have physical dimensions substantially the same as a standard CD or DVD, mini-CD, etc. Preferably, the system can also read data from standard CDs and DVDs for backward compatibility.
Another embodiment is capable of reading transmissive media. A system for reading a transmissive optical medium includes a light source for emitting light at an optical medium having features representing data, the light passing through the optical medium, the features on the optical medium causing variations in the way the light passes through the optical medium. An optical filter separates the light passing through the optical medium into multiple wavelengths. One or more sensors detect changes in the light in the different wavelengths, the changes representing the data.
Other aspects and advantages of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention.
For a fuller understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings.
The following description is the best embodiment presently contemplated for carrying out the present invention. This description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein.
The present invention is directed to use of an optical demultiplexer and a method for separating an input optical signal into a plurality of channels by wavelength for reading data from optical media.
An optical filter (not shown) separates the light reflected from the optical medium into multiple wavelengths. One or more sensors (e.g., photo diodes, not shown) detect changes in the light in the different wavelengths, and outputs signals representing data based on the changes. During playback, the system 300 functions in generally the same way as a standard CD or DVD reader, moving the light source 304, filter and sensors along the medium to follow the data track(s) thereon.
In a preferred embodiment, the optical filter and sensor(s) are present on a single substrate 306, and can be formed as a single chip. The reflected light can enter the filter directly or via a medium such as a fiber optic cable. The substrate, filter and sensors are described in more detail below, but will be described briefly to provide context.
In brief, the filter acts as a demultiplexer to separate the light into at least two different wavelengths, and can separate the light into many different wavelengths, e.g., 2, 3, 4, 5, 6, 7, 8 or more. Multiple sensors can simultaneously detect changes in the light in the different wavelengths, thereby providing at least a 2× or more improvement in data density over standard optical media systems.
A circuit 308 is coupled to the at least one sensor. The circuit interprets signals created by the sensor(s) for converting the signal into digital data, much in the same way as a standard DVD player interprets data signals during playback. The circuit can also be formed on the same substrate or chip as the optical filter and sensors.
The optical medium itself is much like the CDs and DVDs described above. However, the surface features on the optical medium have differing properties and/or dimensions for instance for reflecting the light differently for each wavelength. For example, one set of features can be set with dimensions for a first wavelength and another set of features can be set with dimensions for a second wavelength. The characteristics of the reflected light will vary based on these features, the variations being readable by detecting changes at particular wavelengths in the reflected light. When reading the features set to the first wavelength, the system will recognize a coherent data stream coming from the sensor for that wavelength, and variations in the other wavelengths at that particular sensor will either be blocked by optical filtration, or will be recognized and filtered out by the system. The other sensors will likewise provide a stream of data for the other wavelengths.
The surface features can be positioned on the same layer of material of the optical medium, and aligned in vertical layers and/or in horizontal spirals. The surface features can also be positioned on different layers of material of the optical medium but along the same data track, much in the same way multi-layer DVDs are created. Note
The optical medium can have physical dimensions substantially the same as a standard CD or DVD, mini-CD, etc. Preferably, the system can also read data from standard CDs and DVDs for backward compatibility.
Another embodiment is capable of reading transmissive media. This embodiment is shown in
In
2(T)/tan θ
where T=the transport region thickness, and θ=incident angle of light with respect to a plane of the substrate. This assumes parallelism between the reflector 410 and the optical structures 406a, 406b, 406c, 406d.
T(tan θ1)+T(tan θ2)
Each optical structure 406 in the first plurality is composed of a plurality of thinfilm layers. The thickness of each layer in any given optical structure 406 in the first plurality of structures is associated with the wavelength of one of the optical signal channels 404.
The optical filter 400 further comprises a reflector 410 having a surface 412 parallel to a surface 414 of the first common substrate 408. A transport region 416 separates the reflector 410 from the first plurality of the optical structures 406. The transport region 416 may be glass or any other transport media having the property of transparency, flatness and rigidity which are commonly known to those skilled in the art. Note that the parallelism of the surfaces can be varied in practice to accomplish the spacing of the transport region 416.
An aperture 418 is disposed at one end of the transport region 416. Such aperture may comprise a combination of lenses, prisms (e.g., to provide input beam deflection) or other optical elements. When the input optical signal 402 is provided to the aperture 418, output optical signals at different wavelengths (i.e. λ1, λ2, λ3, λ4,) associated with different ones of the channels are generated at separate positions along a length of the transport region 416. The action is known as demultiplexing. In one embodiment each of the first plurality of optical structures 406 on the first common substrate 408 corresponds to a different one of the channels 404, and transmits light at a wavelength corresponding to that channel but reflects light at all of the other wavelengths corresponding to channels 404.
In one embodiment of the present invention, the reflector 410 of the optical filter 400 is a specular reflector. Where the reflector 410 is a specular reflector, it may be a metal specular reflector or a dielectric mirror.
In
In the embodiment shown in
The invention also includes a method of separating an input optical signal 402 into a plurality of channels by wavelength using, for example, a multi-channel optical filter such as filter 400, 400a, or 400b. Devices performing this function are commonly called demultiplexers. The method comprises the step of providing a first plurality of simultaneously deposited optical structures 406. The optical structures 406 are disposed on different regions of a first common substrate 408. Each optical structure 406 in the first plurality is composed of a plurality of thin-film layers. In this method, the thickness of each layer in a given optical structure 406 in the first plurality is associated with one of the channels. A reflector having a surface parallel to a surface of the first common substrate 408 is also provided. The optical filter has a transport region 416 between the first plurality of the optical structures 406 and the reflector 410, and an aperture 418 disposed at one end of the transport region. When the input optical signal is provided to the aperture, output optical signals are generated at separate positions along a length of the transport region, each of the output optical signals being associated with a different one of the channels.
Referring now to
Other embodiments of integrated receivers may stack and bond separate substrates containing optical filters 400 and arrays of photo diodes 702. In these embodiments, multiple device units might be stacked and bonded and then diced from the resulting structure to yield individual devices. The purpose of such assemblies and techniques is to reduce size and cost, improve alignment of the separate optical structures, and improve performance of the resulting assemblies. These assemblies may then be packaged or mounted directly on an optical circuit board to function with other optical and electrical elements.
The methodology for forming the filter is described in PCT Patent Application No. WO 02/075996 to Baldwin et al., which is herein incorporated by reference for all purposes.
One preferred single chip device having a filter and sensors is the MUX/DEMUX MULTI-FILTER CHIP available from 4Wave, Inc., 22977 Eaglewood Court, Suite 120, Sterling, Va. 20166, USA.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
