Chunhe Zhao

Bi-directional optical backplane bus for general purpose multi-processor board-to-board optoelectronic interconnects

We report for the first time a bidirectional optical backplane bus for a high performance system containing nine multi-chip module (MCM) boards, operating at 632.8 and 1300 nm. The backplane bus reported here employs arrays of multiplexed polymer-based waveguide holograms in conjunction with a waveguiding plate, within which 16 substrate guided waves for 72 (8/spl times/9) cascaded fanouts, are generated. Data transfer of 1.2 Gbt/s at 1.3-/spl mu/m wavelength is demonstrated for a single bus line with 72 cascaded fanouts. Packaging-related issues such as transceiver size and misalignment are embarked upon to provide a reliable system with a wide bandwidth coverage. Theoretical treatment to minimize intensity fluctuations among the nine modules in both directions is further presented and an optimum design rule is provided. The backplane bus demonstrated, is for general-purpose and therefore compatible with such IEEE standardized buses as VMEbus, Futurebus and FASTBUS, and can function as a backplane bus in existing computing environments. >

General purpose bidirectional optical backplane: high-performance bus for multiprocessor systems

We report the first bidirectional optical backplane bus for a high performance multiprocessor system operating at wavelengths of 632.8 nm and 1300 nm. The optical backplane employs an array of multiplexed holograms, in conjunction with a waveguiding plate within which cascaded fanouts are generated. Data transfer rate of 1.2 Gbit/sec at 1300 nm is demonstrated with a single bus line for a system composed of nine processor/memory boards. To provide a reliable system, packaging-related issues, such as the detector size and misalignment effects are addressed. Theoretical treatment to minimize fluctuations among the received power at each processor/memory board is further presented and an optimum design rule is provided. The backplane demonstrated here is for general-purpose. It can support standard multiprocessor buses such as Futurebus+, Multibus II, etc. It also can function as a backplane bus in existing computing systems and significantly reduce the bottlenecks that accompany electrical interconnects.

Shrinkage-corrected volume holograms based on photopolymeric phase media for surface-normal optical interconnects

The film shrinkage effect of photopolymeric phase media failed to provide the desired volume holograms for point-to-point optical interconnects. In this letter, we report a compensation method to physically correct the shrinkage effect that resulted from the holographic recording and the postbaking. Dupont photopolymer HRF-600X001 is studied. The correction of the Bragg diffraction angle shift of 1°21′, which is induced by a 5.25% film shrinkage, is successfully demonstrated with the surface-normal configuration. A shrinkage-corrected volume hologram with 80% diffraction efficiency is experimentally confirmed. The methodology reported herein is applicable to other phase media when the associated film shrinkage data are experimentally determined.

Cross-link optimized cascaded volume hologram array with energy-equalized one-to-many surface-normal fan-outs

Achieving a uniform fan-out energy distribution is critical to the successful applications of substrate guided-wave optical interconnects. Using Dupont photopolymer film HRF-600X00120, we investigated the optimum recording beam intensity for obtaining a large dynamic region of diffraction efficiency relative to exposure dosage. Based on the experimental diffraction efficiency curve, 1-to-5 and 1-to-9 surface-normal fan-out devices were fabricated that operated at a wavelength of 850nm, and output nonuniformities of +/-4 % and +/-10 % were obtained for the two devices.

Performance consideration of three-dimensional optoelectronic interconnection for intra-multichip-module clock signal distribution.

The structure, fabrication, and theory of a three-dimensional planarized optoelectronic clock signal distribution device, based on a thin light-guiding substrate in conjunction with a two-dimensional polymer holographic grating array, are described. We have demonstrated previously a 25-GHz 1-to-42 (6 × 7) highly parallel fan-out interconnect with a signal-to-noise ratio of 10 dB. We present theoretical research that focuses on generating a globally uniform fan-out distribution. An objective function aimed at equalizing the intensities among the fan-out beams is established. For an arbitrary M × N fan-out distribution, there are M + N + 1 sets of holograms needed to be recorded independently to provide the required equal fan-outs. The efficiency of each hologram is determined precisely. The angular misalignment, wavelength dispersion, and spot-size problems are discussed further, together with their tolerance requirements on the size of the photoreceivers integrated on the multichip modules. Employment of 0.25-pitch gradient index (GRIN) lenses as a collimator and as a focusing element is demonstrated experimentally. Optical beam profile manipulation and packaging tolerance are enhanced greatly with GRIN lenses. Finally, clock skew problems associated with the proposed system are discussed, and schemes to minimize the skew are proposed.

Hybrid optoelectronic backplane bus for multiprocessor-based computing systems

The architecture of a hybrid electrical and optical backplane with multiple bus lines for high performance bus is proposed and bus systems with 2-bus lines at a wavelength of 850 nm are experimentally demonstrated, with a size of collimation lens (here we used graded index (GRIN) lenses) and level of collimation-limited separation of 1.5 mm between the two bus lines. For the new bus system containing multiple bus lines and 9 processor/memory boards, VCSELs (vertical cavity surface emitting lasers) and photodetector arrays, such parameters as power budget, misalignment and packaging related issues are discussed. With the introduction of GRIN lenses into the backplane system, it is found that not only can the signal beam from the VCSELs get collimated, but the angular tolerance of the system is greatly enhanced. The optical backplane bus system developed here is transparent to higher level bus protocols, thus can support standard backplane buses such as Futurebus/sup +/, Multi-bus II, and VMEbus.

Cascaded energy-optimized linear volume hologram array for 1-to-many surface-normal even fan-outs

Optimization of fan-out energy distribution for substrate guided wave optical interconnects with a surface-normal configuration is addressed in this paper. Up to nine optimized waveguide holograms are independently fabricated on the same substrate. Energy fluctuation affected by the deviation of the designed diffraction efficiency is theoretically analysed. Using DuPont photopolymer film HRF-600X001-20, we demonstrate 1-to-5 and 1-to-9 surface-normal fan-out devices operating at 850 nm. The output non-uniformities of ±4% and ±10% are experimentally confirmed for the two devices, respectively.

Implementation of optical perfect shuffle with substrate guided-wave optical interconnects

The vulnerability in optoelectronic packaging of free space optical interconnects fail to provide a reliable interconnection for highly parallel system. In this letter, we report, for the first time, a substrate-guided-wave-based perfect shuffle (PS) having an 8-to-8 interconnection, is demonstrated at 632.8-nm wavelength. Sixteen waveguide holograms are fabricated with the full functionality of the PS. The diffraction efficiencies of the waveguide holograms are all within 80%/spl plusmn/5%, The surface-normal configuration of the demonstrated PS makes the integration with vertical-cavity surface-emitting lasers (VCSELs) and other surface-mountable processing elements (PEs) highly feasible.

Design limitations of highly parallel free-space optical interconnects based on arrays of vertical-cavity surface-emitting laser diodes, microlenses, and photodetectors

The packing density of a highly parallel free-space multi-stage optical interconnect network involving arrays of vertical cavity surface-emitting lasers (VCSELs), microlenses, and photodetectors is analyzed for the first time, based on a crosstalk model involving the diffraction-induced crosstalk among pixels. Variations of channel packing density, interconnection distance, and optical transmission efficiency are evaluated to provide optimum design parameters for the arrays of VCSELs, microlenses, and photodetectors. It is shown that it is pivotal to optimize the photodetector diameter in such an optical interconnect network. Photodetector array misalignment effects on system performance are further investigated, providing both transverse and longitudinal alignment tolerance. Several experiments are also conducted to verify the theory developed herein.

INTRAPLANE TO INTERPLANE OPTICAL INTERCONNECTS WITH A HIGH DIFFRACTION EFFICIENCY ELECTRO-OPTIC GRATING

We report on a new optical interconnect architecture for three-dimensional, multiple electro-optic gratings with LiNbO(3) used in conjunction with substrate guided waves. First the operating mechanism of the system is studied in detail, and the momentum mismatch in the operating process of the system is also demonstrated. We then derive a new method for calculating coupling efficiency by introducing a compensation for the mismatch. This theoretical research allows the new optical interconnect architecture to provide a higher design accuracy and an optimized coupling efficiency, even though it is under the case of momentum mismatch. We achieve this result by introducing a substrate guided wave with 45 degrees bouncing angle and 100-V applied voltage. The successful design and its theoretical analysis will be helpful for research on the grating coupler.