Patent Application
20060274419
The present invention relates to optical filters (demultiplexers) and multiplexers and more particularly, this invention relates to a new optical filter and multiplexer and use thereof in an optical media system.
Existing optical filtering systems use a collection of thin film filters to demultiplex multiple optical channels on a single fiber. In such devices, a plurality of filters are deposited individually on a single substrate with a sequence of masking and deposition operations to create each filter. Each filter is designed to pass a single wavelength channel. Those channels that are not passed through the first filter are reflected toward the next filter which is designed to pass a single channel which is different from the single channel that passes through the first filter. Those channels that are not passed through the second filter are reflected in a similar manner and either pass through or are reflected by each subsequent filter. Existing optical multiplexers work similarly, but the optical signals flow in an opposite direction. As those skilled in the art will appreciate, the execution of this process for making such devices is complicated by the fact that each filter is manufactured separately, thereby requiring precise alignment of each separate filter on the substrate during deposition in order to ensure proper operation of the device. The present specification discloses novel optical filters and multiplexers, and methods for performing optical filtering and optical multiplexing that represent simplified and more reliably, processes when compared to existing systems and methods. Also disclosed are methods of using the novel optical filters and multiplexers in optical media systems.
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.
One problem with optical media is that current read technology only allows reading of a single light 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.
The present invention is directed to a new optical multiplexer and filter (demultiplexer), and use thereof for writing data to and reading data from optical media. An optical filter according to a first embodiment includes a receiving port for receiving incoming light, and a plurality of substantially transparent spacers coupled together to form an assembly, the assembly having a light input surface positioned towards the receiving port. A plurality of specular devices are coupled to the spacers, each specular device being designed to reflect a single wavelength channel in a new direction and allow light of other wavelengths to pass therethrough. A plurality of sensors can be provided to detect changes in the reflected light.
The specular devices can be thin film interference mirrors, e.g., metal mirrors, dielectric mirrors, metal-dielectric mirrors, cold mirrors, or combinations thereof. As an option, the final specular device positioned farthest from the receiving port can be about 100% reflective across all wavelengths. The specular devices are preferably arranged such that each specular device reflects a longer wavelength than any preceding specular device positioned closer to the receiving port. Alternatively, the specular devices can be arranged so that each specular device reflects a shorter wavelength than any preceding specular device positioned closer to the receiving port.
The assembly of spacers is preferably coupled to a single substrate. The assembly of spacers is also preferably linear along a path of the incoming light.
In one embodiment, the light input and/or output surfaces of the spacers are coated with an antireflection coating.
An optical multiplexer has a similar structure and features, and includes an outgoing port for passing outgoing light. A plurality of spacers are coupled together to form an assembly, the assembly having a light output surface positioned towards the outgoing port. A plurality of specular devices are coupled to the spacers, each specular device being designed to reflect a single wavelength channel and allow light of other wavelengths to pass therethrough. A plurality of light sources can be provided to emit light towards the specular devices.
In other embodiments, 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 chip. The reflected light can enter the chip 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., 4, 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 chip 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 translucent media. A system for reading a translucent 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.
Yet other embodiments are capable of writing to an optical medium. In these embodiments, light in various wavelengths is multiplexed and directed onto an optical medium, as a single beam, or demultiplexed and directed to the medium. The light in the various wavelengths creates readable surface features on the medium.
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 a new optical multiplexer and filter (demultiplexer), and use thereof for writing data to and reading data from optical media.
With continued reference to
On the filtering surface of each spacer, which is preferably oriented at about a 45° angle to the incident light beam, a thin film specular device (e.g., thin film interference mirror) 120 is deposited on or laminated thereto. Each specular device 120 is spectrally selective, i.e., designed to reflect a selected wavelength channel (range) as shown in
In one embodiment, cold mirrors are used. A cold mirror reflects shorter wavelengths and transmits longer wavelengths. Illustrative cold mirrors can be formed of layers of SiO2 and/or TiO2. One illustrative cold mirror includes a coating consisting of multiple layers of SiO2 and TiO2 on a glass substrate.
In a variation, alternating spacers can have two filtering surfaces with mirrors, one on either end. For example, in
The light input and output surfaces of each spacer are preferably coated with a broadband antireflection (BBAR) coating 121 for decreasing any back reflection in a whole range of used light wavelengths. Table 2 lists several suitable BBAR coatings and their properties.
These BBAR coatings are available for purchase from Red Optronics, P.O. Box 2032, Mountain View, Calif. 94042, USA.
One skilled in the art will appreciate that other materials, currently sold and those yet to be invented, can be used to construct the specular devices 120 and BBAR coatings 121 without straying from the spirit and scope of the invention.
To construct the device 100, the spacers are glued together in a sequence of specular devices with design wavelength reflectivity increasing from the input to the final spacer. The assembly can be assembled on a single substrate piece by piece, or can be glued thereto as a partially or fully assembled assembly. Note
The device works to demultiplex an incoming light beam as follows. The collimated light beam with wavelengths λ1, or λ2>λ1, or λ3>λ2>λ1, or kn . . . >λ3>λ2>λ1 is directed from a multi-wavelength light source 122 (e.g., fiber optic cable) through a receiving port 123 into the light input surface of the device. The light having the shortest selected wavelength λ1 is nearly completely reflected by the first specular device to the accordable receiver. Those wavelengths λ2-λn that are not reflected pass through the first specular device to the next specular device which is designed to reflect a single channel λ2 which is different from the single channel λ1 reflected by the first specular device. The light having a wavelength λ2 (>λ1) is nearly completely transmitted by the first specular device and nearly completely reflected by the next specular device to the appropriate receiver. Those channels that are not reflected by the second specular device either pass through or are reflected by each subsequent specular device. Optical signals (each of which corresponds to a particular wavelength) then pass out of the device and are directed to the sensors 124 (e.g., photo diodes). Each sensor 124 converts one of the optical signals output from the filter into a corresponding electrical signal. As an option, lenses (not shown) may be placed between the sensors 124 and device to improve device performance.
The specular devices are preferably arranged such that each specular device reflects a longer wavelength than any preceding specular device positioned closer to the receiving port. Alternatively, the specular devices can be arranged so that each specular device reflects a shorter wavelength than any preceding specular device positioned closer to the receiving port.
The range of readable wavelengths can be as broad or narrow as desired, and can include visible as well as UV and IR light.
The process for multiplexing functions in a similar way, but the optical signals flow in an opposite direction. As shown in
As mentioned above, the device is suitable for use in a reader and/or writer for optical media. 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 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.
The data stored on the CD is retrieved by a CD player that focuses a laser on the track of bumps. The laser beam passes through the polycarbonate layer, reflects off the aluminum layer and hits an opto-electronic device that detects changes in light. The bumps reflect light differently than the lands, and the opto-electronic sensor detects that change in reflectivity. The electronics in the drive interpret the changes in reflectivity in order to read the bits that make up the bytes.
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 standard DVD holds about seven times more data than a CD.
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 3 illustrates a comparison of CD and DVD specifications.
To increase the storage capacity even more, a DVD can have up to four layers, two on each side. The laser that reads the disc can actually focus on the second layer through the first layer. Table 4 lists the capacities of different forms of DVDs.
A DVD is composed of several layers of plastic, totaling about 1.2 millimeters thick.
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.
An optical filter such as the one described above 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 output signals representing data based on the changes. During playback, the system 600 functions in generally the same way as a standard CD or DVD reader, moving the light source 604, 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 chip 606. 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, 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 over standard optical media systems.
A circuit 608 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 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 dimensions and/or properties 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 as junk. 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
Referring now to
Other embodiments of integrated receivers may stack and bond separate chips 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.
Yet other embodiments use the multiplexing embodiment 300 to write data to an optical medium. In one such embodiment, light of various selected wavelengths can be transmitted in the same beam onto the surface of the optical medium to create the aforementioned pits and lands or their equivalent. One preferred embodiment directs the multiplexed light onto a stack of layers, each layer being responsive to light in a particular wavelength. As the light travels through the layers, each wavelength channel modifies the surface of the corresponding optical medium such as by changing the color of a dye or by altering the physical or chemical structure of the particular layer in a readable way. In another embodiment, the multiplexed light is demultiplexed back into the various wavelength channels, and the various channels are emitted onto the optical medium to create the readable features.
The interior of the filter 800 can have an open configuration, i.e., can have a void in the central portion 808 below the receiving port 804. Alternatively, the central portion 808 can have a material therein that is transparent in the incoming wavelength range.
In the embodiments shown, the faces 812 of the specular devices 802 face inwardly. However, one skilled in the art will understand that the faces 812 could also face outwardly, be aligned in a linear fashion, etc. so long as the receivers 806 are appropriately positioned to receive the reflected light.
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.
