Patent Application
20110274438
Computer performance is increasingly restricted by the ability of computer processors to quickly and efficiently access off-chip memory or communicate with other peripheral devices. The restriction is due, in part, to inherent physical limitations in the number of electrical pins that can fit into a connector of a defined size and surface area, which in turn determines the maximum electrical bandwidth. Saturation in the density of electrical pins results in “pin-out bottleneck” for a processor or chip, which describes the situation when the electrical bandwidth of a chip package becomes a performance limiting factor.
a is an illustration of a point-to-point optical communications link between optical engines formed on a first chip and a second chip, according to an exemplary embodiment of the present invention;
b is an illustration of a point-to-point optical communications link between optical engine chips bonded to first and second computing devices, according to an exemplary embodiment of the present invention;
The following detailed description of exemplary embodiments of the invention makes reference to the accompanying drawings, which form a part thereof and in which are shown exemplary embodiments in which the invention may be practiced. While these exemplary embodiments are described, by way of illustration, in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. As such, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as it is claimed, but is presented for purposes of illustration only; to describe the features and characteristics of the present invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the present invention is to be defined solely by the appended claims.
The following detailed description and exemplary embodiments of the invention will be best understood by reference to the accompanying drawings, wherein the elements and features of the invention are designated by numerals throughout.
Illustrated in
The optical engine is a combination of components which provides greatly improved performance at a reduced manufacturing cost. As will be described in more detail hereinafter, the optical engine can include a light source optically coupled to a modulation chip. The light source can be in a separate location from the modulation chip and can be optically coupled to the modulation chip by various means as are known in the art. The light source can generate an optical beam. At least one modulator may be carried on the modulation or optical engine chip and can modulate the optical beam generated by the light source. The modulator may be of any suitable type, including, but not limited to ring modulators and Mach-Zehnder modulators. For instance, the type of modulator may include one or more evanescent micro-ring modulators which are formed in a plane parallel to a plane of the optical engine chip or substrate. The modulator can modulate the optical beam to create an optical signal.
In addition, a waveguide can be carried on the modulation chip may be for guiding the modulated optical beam from the modulator to a defined location or region of the modulation chip (e.g. in the center of the chip or at the chip-edge). The defined region can have one or more out of plane couplers, such as grating couplers or the like, for optically coupling the modulated optical beam to an optical or electrical device. The modulated optical beam may be optically coupled from the out of plane coupler to the optical or electrical device through multi-core optical fibers for transport to the optical device. A plurality of out of plane couplers can be grouped in a relatively small, defined area. The out of plane couplers have a smaller size than an optical signal generator such as an LED or laser. This allows them to be grouped in a small area. A plurality of modulated optical signals can be coupled to a single optical waveguide, such as a multi-core fiber, fiber ribbon, or hollow metal waveguide using the plurality of out of plane couplers.
Photonic detectors can also be included in the defined area to receive optical signals broadcast from the optical or computing device. As a photonic optical signal detector, or photo-detector, is generally less complex than an optical signal generator (i.e. laser, LED, etc.) the photo-detectors can be located at the defined region to directly receive the input signals traveling through the multi-core optical fiber, or they can be distributed over the surface of the chip and similarly coupled to the multi-core optical fiber with grating coupling pads or tapered waveguides.
The optical engine of the present invention can help resolve the “pinout bottleneck” facing computer designers today, resulting from the approximate upper limit of a few thousand electrical pins per chip. Some of these electrical pins are used for CPU-to-memory traffic or other secondary communications which may lend themselves to point-to-point links. By providing direct optical connections between two computing devices and off-loading the CPU-to-memory or secondary communications into separate multi-channel, point-to-point optical links, a significant number of input/output pins can be reassigned to other uses, resulting in a substantial increase in bandwidth available for other internal computer operations.
The present invention provides further advantages over the prior art, which can include both traditional wired connectors and more recent developments in optical fiber communications technology. One benefit is lower manufacturing costs, since each component of the optical engine, including photo-detectors, waveguides, and optical couplers, can be manufactured using cost-effective, high-volume fabrication processes, such as VLSI (Very Large Scale Integration) fabrication techniques.
One distinct advantage of the present invention over the prior art is the capability to generate an optical beam at a location separate from the modulation chip. This allows for the use of a wide variety of types of lasers to be used. Oftentimes, lasers and other optical sources have a fairly limited operating temperature range. In some environments, it is necessary to locate the modulation chip near a heat generating computing component, such as a processor. This creates a less than optimal performance in the laser. Modulators are often operable in a wider temperature range than lasers. Thus, while the processor temperature may be within the acceptable range for modulator operation, it may be advantageous to move the laser to a location with a more suitable temperature. The laser or other optical source can create an optical beam that is carried to the modulation chip through a fiber optic cable, large core hollow metal waveguide, free space, or other optical transport device. The optical beam can be coupled to the modulation chip using any of a variety of different components as are known in the art. Some such components may include grating couplers, taper couplers or edge couplers.
It is an advantage of the present invention that a light source, such as a laser, may be located in a separate location from a modulation chip and that modulators and/or photo-detectors can be distributed over the surface of the optical engine chip, along with waveguides for guiding the optical signals to and from a defined region, so that a large number of optical signals can be concentrated and organized into a small footprint configurable for coupling into a single multi-core optical fiber, such as a photonic crystal fiber or an optical fiber ribbon. With prior optical systems, therefore, a separate chip with detectors may be required to receive an incoming signal and complete the duplex communications link. In contrast, each component of the present invention can be fabricated using silicon based or III-V group semiconductor materials, allowing for the micro-ring modulators, the receiving photo-detectors and their associated components to be integrated into the same chip. In alternate embodiments, the modulators and photodetectors may be fabricated from silicon, germanium, silicon germanium or combinations of these materials.
The present invention offers additional benefits that can be attractive to computer designers and engineers. For instance, all the point-to-point traffic between the two computing devices can be handled by a single multi-core optical fiber, such as a photonic crystal fiber or optical fiber ribbon, which can be actively or passively aligned to the optical couplers, and which can be attached to the defined region on the optical engine using proven adhesive materials and methods. Moreover, the present invention provides the convenience and flexibility of directly integrating the optical engine into the computing device, or fabricating the engine on a separate chip for subsequent wafer-mounting to the computing device.
Each of the above-recited advantages and improvements will be apparent in light of the detailed description set forth below, with reference to the accompanying drawings. These advantages are not meant to be limiting in any way. Indeed, one skilled in the art will appreciate that other benefits and advantages may be realized, other than those specifically recited herein, upon practicing the present invention.
Illustrated in
After being coupled to the modulation chip 6, the optical beam may be modulated by a modulator 21. The modulator may be carried on the modulation chip and configured to modulate the optical beam generated by the light source 24. The modulator may be any of a variety of types of modulators, as are known in the art. Some contemplated examples of modulators include micro-ring modulators, Mach-Zehnder modulators, Alexander modulators, or absorption modulators. While the figures and much of the discussion herein is directed towards use of micro-ring modulators, it is to be understood that any suitable type of modulator for modulating an optical beam may be used to modulate the optical beam of the present invention.
Also carried on the modulation chip 6 is a waveguide 30, configured to guide the modulated optical beam from the modulator 21 to at least one of a plurality of out-of-plane couplers 40 grouped in a defined region of the modulation chip. The waveguide structure may be formed in a number of configurations as are known to one having skill in the art. In one embodiment, the waveguide may be a Silicon-on-Insulator waveguide. Alternatively, a polymer waveguide may be used.
In one aspect, the optical beam may travel along the waveguide before reaching the modulator and then continue along the waveguide as a modulated optical beam, or optical signal. In another aspect, the optical beam may travel along a first waveguide to the modulator, and then travel along a second waveguide from the modulator to the defined region. In another aspect, the optical beam may be modulated by the modulator upon being coupled to the modulation chip, such that the optical beam does not pass through a waveguide until after modulation.
At an end of the waveguide 30 is a defined region 48 wherein is grouped a plurality of out-of plane couplers 40. In one aspect, the out-of-plane couplers may be grating couplers. The modulated optical beam, or optical signal, can travel parallel to a plane of the modulation chip 6 within the waveguide 30 to the out-of-plane coupler. The out-of-plane coupler then redirects the optical beam to travel out-of-plane to the modulation chip. It is contemplated that a plurality of optical beams may be modulated by a plurality of modulators and travel to the defined region to respective out-of-plane couplers all grouped and configured to be located within the region. In one embodiment, an end of a multi-core optical fiber may cover the region when coupled to the modulation chip.
In embodiments where the modulation chip 6 comprises multiple waveguides 30, a single light source 24 may generate an optical beam which is then split and carried to each of the waveguides. The beam may be split at a splitter on the modulation chip, or may be split before (as is shown in
Any number of modulators may be used in series, and it is not necessary that the frequencies be modulated in a particular order. As shown in
Illustrated in
It can be further appreciated that, other than the optical source, the components of the transmitting base unit can be embedded within the optical engine layer 6 as illustrated, or can be formed to extend above the top of the layer and be surrounded by empty space or a transparent protective coating. Electrical connections between the optical engine and a driving computing device can be provided for in the underlying base layer(s) 4.
Another aspect of the present invention's flexibility is the micro-ring laser's configurability for both single and multi-mode operation. In an exemplary embodiment, for instance, the optical engine of the present invention can be configured for single-mode operation centered around the 1310 nm or 1550 nm wavelengths.
The operation and functionality of the micro-ring laser 20, including its configurability for both single and multi-mode operation, are more specifically set forth in commonly owned and co-pending PCT Patent Application No. PCT/US081/62791, filed May 6, 2008, and entitled “System and Method For Micro-ring Laser,” which is incorporated by reference in its entirety herein.
In the embodiment illustrated in
The out-of-plane transmitting optical coupler 40 is used to redirect the output optical signal out-of-plane relative to the plane of the underlying substrate 2. Differing types of optical coupling devices, such as silvered mirrors, beamsplitters, optical grating pads, etc., can be used to redirect the optical beam out-of-plane. In an exemplary embodiment, the optical signal can be redirected to be substantially perpendicular, or 90 degrees, to the plane of the substrate, but it is to be appreciated that re-directing the optical beam at angles of about 30 degrees or more for coupling into a multi-core optical fiber can also be considered to fall within the scope of the present invention.
One low-cost but highly effective device for coupling the output optical signal 12 out-of-plane to the plane of the substrate can be a grating pad coupler 42. The grating pad coupler can generally comprise an expanded section or pad 44 of the optical waveguide 30 that can be made from the same or differing material and which can be formed integrally with or separate from the waveguide. The pad 44 can have a width much greater than its thickness. A grating pattern of slots 46 can be etched or otherwise formed in the top surface of the grating pad coupler and extend downward into the body of the grating pad coupler. The grating coupler can operate on the principle of light diffraction, wherein an optical signal contacting a single slot as it travels through the pad material will be split into several components, including a transmitted component, a reflected component, and an out-of-plane component. By using multiple slots which are precisely dimensioned and spaced along the top surface of the grating pad, a substantial portion of the optical beam can be re-directed into a transmitted optical signal 14 traveling out-of-plane to the plane of the waveguide.
The efficiency of the grating coupler in redirecting the optical signal 12 out-of-plane relative to the plane of the substrate 2 can be optimized through control of the dimensions and spacing of the grating slots relative to the wavelength of the optical beam. Thus, the grating coupler can be tuned or optimized for the center wavelength of laser light emitted by the micro-ring laser, as can the waveguide which connects the two devices together. Tuning the entire transmitting base unit to the wavelength of light generated by the micro-ring laser, such as to the 1310 nm or 1550 nm wavelengths described above, can simultaneously maximize the output of the base unit while minimizing the loss of the optical signal moving through each component, resulting in an optical engine with reduced power requirements.
Illustrated in
The receiving optical coupler 70 can be used to redirect an incoming optical beam or input optical signal 16 traveling out-of-plane relative to the plane of the substrate 2 into a received optical signal 18 moving through the waveguide 80 and parallel to the plane of the substrate 2. The receiving optical coupler 70 can be substantially identical to the transmitting optical coupler, and can further include various types of optical coupling devices, including a silvered mirrors, beam splitters, optical grating pads, etc.
In the exemplary embodiment illustrated in
Once the input optical signal 16 has been captured and coupled into the receiving base unit by the grating coupler 72, the received optical signal 18 can be transported along the waveguide 80 to the photo-detector 90. The photo-detector can include differing types of optical detecting devices, such as a layer of germanium, silicon germanium, or III-V material, a p-i-n or Schottky diode, a photo-transistor, etc. In an exemplary embodiment, however, the photo-detector can be made from the same III-V group semiconductor materials as the micro-ring modulator, or a micro-ring laser, to facilitate the fabrication of the optical engine.
Reference will now be made to
Shown in
The positioning of the transmitting grating couplers 140 and the photo-detectors 190 within the central location or defined region 108 as shown in
The multi-core optical fiber 150 can have a proximate end 156 for coupling to the central location or defined region 108 of the optical engine chip 106, and a distal end 158 for coupling to one or more passive optical devices, active optical devices, additional optical engines, and the like. The proximate end 156 can be coupled to the defined region 108 of the optical engine chip 106 so that the optical cores 154 align with the out-of-plane optical couplers 140, 170 located within the defined region. The proximate end 156 of the fiber 150 can also be attached to the top surface of the optical engine chip 106 with an appropriate adhesive, attachment method or attachment structure.
Alignment of the optical cores 154 with the out-of-plane optical couplers 140, 170 can be accomplished through passive, or self-alignment methods, as well as active methods that monitor the strength of one or more optical signals passing through the multi-core optical fiber 150, such as a photonic crystal fiber, as the fiber is coupled to the chip. More detail on the various aspects and methods for aligning and coupling the multi-core optical fiber to the optical engine is specifically set forth in commonly owned and co-pending U.S. patent application Ser. No. 12/254,490, filed Oct. 20, 2008, and entitled “Method for Connecting Multicore Fibers to Optical Devices,” which is incorporated by reference in its entirety herein.
Illustrated in
b further illustrates another aspect of the present invention, in which separate optical engine chips 260 have been wafer mounted to the two adjacent computing devices 210, 220, and then linked with the multi-core optical fiber 250 to create the point-to-point optical communications link 202. Forming the optical engines on separate chips 260 which are later attached to the computing devices can provide for greater control over the manufacturing processes used in fabricating the chip and for economies of scale in reducing fabrication costs. Separate optical engine chips 260 can also allow for the creation of a communications protocol that is substantially independent of the computing device upon which the optical engine is mounted. It is also noted here that in some embodiments, a single optical source or laser may be optically coupled to a plurality of optical engine chips. The optical source beam may be split at a splitter 230 on the optical engine chips as is shown. Alternatively, as has been previously discussed, a separate optical fiber may transport an optical beam to each transmitting waveguide on each of the optical engine chips.
The optical fiber ribbon 350 can carry the output signal to the receiving portion of a similar optical engine chip 300 mounted on another computing device 308 (see FIG. 10). And in a reciprocal duplex fashion, the off-chip laser coupled to the second optical engine chip can be used to send an optical signal to the second optical engine, where a desired form of modulation can occur and a modulated signal can be sent back through the optical fiber ribbon 350 to the optical engine chip mounted on the first computing device 306 for reception through waveguide tapers 370 (see
The method may further include one or more additional steps such as: detecting an optical signal at detectors located in the defined region; splitting the optical beam before modulation and recombining the optical beam after modulation; modulating a plurality of frequencies of the optical beam using a plurality of micro-ring laser modulators; or coupling the modulated optical beam into a multi-core optical fiber, wherein the multi-core optical fiber is configured to transmit the modulated optical beam to an optical or electronic device.
In some embodiments, photonic crystal resonators may be used to modulate an optical beam. Illustrated in
The foregoing detailed description describes the invention with reference to specific exemplary embodiments. However, it will be appreciated that various modifications and changes can be made without departing from the scope of the present invention as set forth in the appended claims. The detailed description and accompanying drawings are to be regarded as merely illustrative, rather than as restrictive, and all such modifications or changes, if any, are intended to fall within the scope of the present invention as described and set forth herein.
More specifically, while illustrative exemplary embodiments of the invention have been described herein, the present invention is not limited to these embodiments, but includes any and all embodiments having modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the foregoing detailed description. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the foregoing detailed description or during the prosecution of the application, which examples are to be construed as non-exclusive. For example, in the present disclosure, the term “preferably” is non-exclusive where it is intended to mean “preferably, but not limited to.” Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2009/030664 | 1/9/2009 | WO | 00 | 7/8/2011 |
