CHIP TO CHIP OPTICAL INTERCONNECT
An apparatus for optical communication is provided. The apparatus includes a first waveguide formed on a first surface and a second waveguide formed on a second surface. The first and second surfaces are bonded together to form an air gap between the first and second surfaces and diffraction gratings of the first and second waveguides are facing each other
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1. Field
The present embodiments relate to optical connections and, more particularly, to optical connections between microchips.
2. Brief Description of Related Developments
Large symmetric multiprocessor machines such as blade servers are running out of bandwidth for blade-to-blade, module-to-module and eventually chip-to-chip interconnections. The bandwidth required for these interconnections is growing more rapidly than Moore's law because this bandwidth is the product of the increasing number of processors, the increasing complexity of each processor and the increasing clock speed of those processors. In order to build a complete optical interconnection hierarchy several levels of connections should be addressed. The optical signal travels from the chip to the module, from the module to the board, from the board to the backplane, across the backplane and then back through these levels in the reverse order.
In conventional mainframe and high-end applications, chips interconnect via a substrate using controlled collapse chip connection (C4 or flip chip) bonding. The substrate may be, for example, a glass ceramic multichip module or silicon interposer. Chip to chip electrical connections flow from a chip through the C4 interconnect to the multichip module and then back through the C4 interconnect to the next chip. These C4 electrical connections are not sufficient to accommodate the necessary increase in bandwidth.
Existing optical connections rely on multimode waveguides or multimode fibers because the large cores of multimode waveguides do not require tight mechanical tolerances during assembly, the losses within the short range between chips is negligible and the sources are often multimode. These existing optical connections use volume holographic gratings that are not a feasible manufacturing approach to the problem of the increasing bandwidth requirements because these volume holographic gratings cannot be easily created using microlithography.
It would be advantageous to replace some of the chip to chip electrical connections with easily manufactured optical connections to allow higher speeds over chip to chip distances.
SUMMARYIn one exemplary embodiment, a method for chip to chip communication is provided. The method includes forming a first waveguide on a first surface, forming a second waveguide on a second surface, bonding the first surface to the second surface so an air gap exists between the first and second surface and diffraction gratings of the first and second wave guides face each other and passing a light beam through the first waveguide, across the air gap and into the second waveguide.
In another exemplary embodiment, an apparatus for optical communication is provided. The apparatus includes a first waveguide formed on a first surface and a second waveguide formed on a second surface. The first and second surfaces are bonded together to form an air gap between the first and second surfaces and diffraction gratings of the first and second waveguides are facing each other.
In one exemplary embodiment, an apparatus for optical chip to chip communication is provided. The apparatus includes a first waveguide formed on a first surface, a second waveguide formed on a second surface, the second waveguide having at least two diffraction grating sections and a third waveguide formed on a third surface. The first and third surfaces are bonded to the second surface so an air gap exists between the first and second surfaces and the third and second surfaces, a diffraction grating section of the first waveguide is facing a first diffraction grating of the second waveguide and a diffraction grating of the third surface is facing a second diffraction grating of the second surface.
In still another exemplary embodiment, an apparatus for optical chip to chip communication is provided. The apparatus includes a first waveguide formed on a first surface and a second waveguide formed on a second surface. The first and second surfaces are bonded together to form an air gap between the first and second surfaces and diffraction gratings of the first and second waveguides are facing each other, the first waveguide having three elements.
The foregoing aspects and other features of the present embodiments are explained in the following description, taken in connection with the accompanying drawings, wherein:
The chips 110A and 110B and the multichip module, carrier or interposer 100 may contain the waveguide 300 of
The waveguide 300 may be made of any suitable material capable of transmitting light, such as for example silicone, silicon/SiO2 or a polymer.
The waveguide 300 may be a multimode waveguide or any other suitable waveguide. The waveguide 300 may include a rectangular waveguide 410 and a grating terminal or section 430 that are longitudinally connected by a tapered waveguide 420. The rectangular waveguide 410 may have, for example, a width of about 0.4 microns. The tapered waveguide 420 may, for example, extend longitudinally away from the rectangular waveguide 410 while expanding the lateral dimension of the rectangular waveguide by, for example, approximately twenty degrees to mate with the grating terminal or section 430. The grating section 430 may be, for example, approximately ten microns wide and approximately ten microns long. In alternate embodiments the waveguide 300 and its sections 410-430 may have any suitable shape, dimensions and/or configuration. The grating terminal 430 may contain diffraction gratings 440 having a directional selectivity to send the propagated light in and out of the chip in the direction of 100A, 110B rather than into the body of chip 110A, 110B. For example, as shown in
The waveguide 300 may propagate any suitable wavelength of light such as for example the infrared 1.5 micron or 3 micron communication wavelengths. In alternate embodiments the waveguide 300 may be configured through suitable material choices to propagate visible light.
The chips 110A and 110B containing the wave guide 300 may be bonded to the carrier 100, which also contains a waveguide 300, in any suitable manner such as by C4 connection 120 (
Referring to
As noted above, for each optical connection two waveguides 300A, 300B are used in pairs and oriented to face each other across the gap 340 as shown in
In the exemplary configuration shown in
By expanding the guided light beam 330 in the exit region up to a sufficient diameter, such as for example, a 10 or 20 micron diameter that is focused some distance away from the surface, the alignment tolerances of the chip/carrier bonding process are accommodated. In addition, the light beam may be configured so that uncertainties in the distance between the chip 110 and the carrier 100 (i.e. the air gap 340) due to variations in the solder volume in each C4 joint are within the depth of focus of the beam 330 leaving the exit region.
In operation, for example, light enters the waveguide structure 300A in the chip 110 via the rectangular waveguide 410 section. The rectangular waveguide section mates with a grating terminal or section 430 through the tapered waveguide 420 section. As shown in
The disclosed embodiments may provide a cost effective, easily manufactured and practical method of bringing optical signals to and from a multichip module from outside the module as well as from chip to chip.
It should be understood that the foregoing description is only illustrative of the embodiments. Various alternatives and modifications can be devised by those skilled in the art without departing from the embodiments. Accordingly, the present embodiments are intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims.
Claims
1. A method for chip to chip communication, the method comprising:
- forming a first waveguide on a first surface;
- forming a second waveguide on a second surface;
- bonding the first surface to the second surface so an air gap exists between the first and second surface and diffraction gratings of the first and second wave guides face each other; and
- passing a light beam through the first waveguide, across the air gap and into the second waveguide;
- forming a third waveguide on a third surface; and
- bonding the third surface to the second surface so an air gap exists between the third and second surface and diffraction gratings of the third and second wave guides face each other;
- wherein the light beam passes from the second wave guide across the air gap and into the third waveguide.
2. (canceled)
3. The method of claim 1, wherein the first and third surfaces comprise microchips.
4. The method of claim 1, where the first surface and second surface are bonded by controlled collapse chip connection.
5. The method of claim 1 wherein forming the first and second waveguides comprises:
- forming a rectangular waveguide and a diffraction grating terminal connected by a tapered waveguide;
- wherein the rectangular waveguide and tapered waveguide are formed by lithography.
6. The method of claim, wherein the diffraction gratings are formed by a dual damascene process.
7. The method of claim 1 wherein the diffraction gratings are metal tuned.
8. The method of claim 1 further comprising the first waveguide and second waveguide being formed on a top surface area of the first surface and second surface, respectively.
9. An apparatus for optical communication comprising:
- a first waveguide formed on a first surface; and
- a second waveguide formed on a second surface;
- wherein the first and second surfaces are bonded together to form an air gap between the first and second surfaces and diffraction gratings of the first and second waveguides are facing each other; and
- a third waveguide formed on a third surface;
- wherein the third and second surfaces are bonded together to form an air gap between the first and second surfaces and diffraction gratings of the third and second waveguides are facing each other.
10. (canceled)
11. The apparatus of claim 9, wherein the waveguides are configured so the first waveguide and third waveguides are in communication with each other via the second waveguide.
12. The apparatus of claim 9, wherein the first and third surfaces comprise a microchip.
13. The apparatus of claim 9, wherein the first and second waveguides comprise at least:
- a rectangular waveguide section;
- a diffraction grating terminal; and
- a tapered waveguide section longitudinally connecting the rectangular waveguide to the diffraction grating terminal.
14. The apparatus of claim 13 wherein the rectangular waveguide section comprises a 0.4 micron dimension, the tapered waveguide section is tapered laterally 20 degrees and the diffraction grating terminal is 10 microns wide and 10 microns long.
15. The apparatus of claim 9, wherein the first waveguide comprises silicon or a polymer and second waveguide comprises silicon or a polymer.
16. The apparatus of claim 9, wherein the diffraction gratings comprise a two-dimensional diffraction grating made of a single metal layer.
17. The apparatus of claim 9, wherein the diffraction gratings of the first and second waveguides have non-uniform spacing.
18. The apparatus of claim 9 further comprising the first waveguide and the second waveguide being formed on a top surface area of the first surface and the second surface, respectively.
19. An apparatus for optical chip to chip communication comprising:
- a first waveguide formed on an outer area of a first surface;
- a second waveguide formed on an outer area of a second surface, the second waveguide having at least two diffraction grating sections; and
- a third waveguide formed on an outer area of a third surface;
- wherein the outer areas of the first and third surfaces are bonded to the outer area of the second surface so an air gap exists between the outer areas of the first and second surfaces and the third and second surfaces, a diffraction grating section of the first waveguide is facing a first diffraction grating of the second waveguide and a diffraction grating of the third surface is facing a second diffraction grating of the second surface.
20. An apparatus for optical chip to chip communication comprising:
- a first waveguide formed on a first surface; and
- a second waveguide formed on a second surface;
- wherein the first and second surfaces are bonded together to form an air gap between the first and second surfaces and diffraction gratings of the first and second waveguides are facing each other, the first waveguide having three elements; and
- a third waveguide formed on a third surface;
- wherein the third and second surfaces are bonded together to form an air gap between the first and second surfaces and diffraction gratings of the third and second waveguides are facing each other, the third waveguide having three elements.
21. (canceled)
22. The apparatus of claim 20, wherein the first, second and third waveguides comprise at least:
- a rectangular waveguide section;
- a diffraction grating terminal; and
- a tapered waveguide section longitudinally connecting the rectangular waveguide to the diffraction grating terminal.
23. The apparatus of claim 19 wherein the waveguides are configured so the first waveguide and third waveguides are in communication with each other via the second waveguide.
24. The apparatus of claim 19, wherein the first and second waveguides comprise at least:
- a rectangular waveguide section;
- a diffraction grating terminal; and
- a tapered waveguide section longitudinally connecting the rectangular waveguide to the diffraction grating terminal.
25. The apparatus of claim 19 further comprising the first waveguide and the second waveguide being formed on a top surface area of the first surface and the second surface, respectively.
Type: Application
Filed: Jun 28, 2007
Publication Date: Jan 1, 2009
Applicant: INTERNATIONAL BUSINESS MACHINES CORPORATION (Armonk, NY)
Inventors: Punit P. Chiniwalla (Ann Arbor, MI), Philip Hobbs (Briarcliff Manor, NY), Theodore G. van Kessel (Millbrook, NY)
Application Number: 11/770,299
International Classification: G02B 6/12 (20060101);