Randy W. Wickman

Fully embedded board-level guided-wave optoelectronic interconnects

A fully embedded board-level guided-wave optical interconnection is presented to solve the packaging compatibility problem. All elements involved in providing high-speed optical communications within one board are demonstrated. Experimental results on a 12-channel linear array of thin-film polyimide waveguides, vertical-cavity surface-emitting lasers (VCSELs) (42 /spl mu/m), and silicon MSM photodetectors (10 /spl mu/m) suitable for a fully embedded implementation are provided. Two types of waveguide couplers, titled gratings and 45/spl deg/ total internal reflection mirrors, are fabricated within the polyimide waveguides. Thirty-five to near 100% coupling efficiencies are experimentally confirmed. By doing so, all the real estate of the PC board surface are occupied by electronics, and therefore one only observes the performance enhancement due to the employment of optical interconnection but does not worry about the interface problem between electronic and optoelectronic components unlike conventional approaches. A high speed 1-48 optical clock signal distribution network for Cray T-90 super computer is demonstrated. A waveguide propagation loss of 0.21 dB/cm at 850 nm was experimentally confirmed for the 1-48 clock signal distribution and for point-to-point interconnects. The feasibility of using polyimide as the interlayer dielectric material to form hybrid three-dimensional interconnects is also demonstrated. Finally, a waveguide bus architecture is presented, which provides a realistic bidirectional broadcasting transmission of optical signals. Such a structure is equivalent to such IEEE standard bus protocols as VME bus and FutureBus.

1-GHz clock signal distribution for multi-processor super computers

In this paper, we present our efforts to construct an optoelectronic interconnection layer for high-speed optical clock signal distribution in a Gray T-90 supercomputer board. The optoelectronic interconnection layer under investigation employs optical channel waveguides and cascaded 3 dB 1-to-2 waveguide splitters in conjunction with surface-normal waveguide grating couplers. The planarization requirement for the optical interconnection layer required by multi-layer integration is fulfilled. Furthermore, the difficulties associated with the complicated 3-D multiple alignments are significantly reduced by the surface-normal fanout beams and the unique planarized device feature. An 1-GHz optical clock signal operating at 1.3 /spl mu/m was transmitted through a 45 cm long polymer-based channel waveguide. Some new techniques to fabricate large-area optical channel waveguides and surface-normal waveguide grating couplers are also presented.

Board-level optical clock signal distribution based on guided-wave optical interconnects in conjunction with waveguide holograms

In this paper, we represent our effort to construct an optoelectronic interconnection layer for high-speed optical clock signal distribution in a Cray supercomputer board. The optoelectronic interconnection layer under investigation employs optical channel waveguides and 3 dB waveguide splitters in conjunction with surface-normal waveguide couplers. The difficulties associated with the complicated 3D multiple alignments are significantly reduced by the surface-normal fanout beams and the unique planar device feature. 1-GHz clear optical clock signal is demonstrated experimentally with a guided-wave interconnection length of 45 cm. Some new techniques to fabricate large-area optical channel waveguides and surface-normal waveguide grating couplers are also presented.

Si CMOS process-compatible guided-wave optical interconnects

We report the formation of polyimide-based H-tree waveguides for a multi-GBit/sec optical clock signal distribution in a Si CMOS process compatible environment. Such a clock distribution system is to replace the existing electronic counterpart associated with high-speed supercomputers such as Cray T-90 machine. A waveguide propagation loss of 0.21 dB/cm at 850 nm was experimentally confirmed for the 1-to-48 waveguide fanout device. The planarization requirement of the optical interconnection layer among many electrical interconnection layers makes the employment of tilted grating a choice of desire. Theoretical calculation predicts the 1-to-1 free-space to waveguide coupling with an efficiency as high as 95 percent. Currently, a coupling efficiency of 35 percent was experimentally confirmed due to the limited index difference between guiding and cladding layers. Further experiments aimed at structuring a larger guiding/cladding layer index differences are under investigation. To effectively couple an optical signal into the waveguide through the tilted grating coupler, the accuracy of the wavelength employed is pivotal. This makes the usage of the vertical cavity surface-emitting lasers (VCSELs) and VCSEL arrays the best choice when compared with edge-emitting lasers. Modulation bandwidth as high as 6 GHz was demonstrated at 850 nm. Such a wavelength is compatible with Si-based photodetectors.

Guided-wave Si CMOS process-compatible optical interconnects

We report the formation of polyimide-based H-tree waveguides for a multi-GBit/sec optical clock signal distribution in a Si CMOS process compatible environment. Such a clock distribution system is to replace the existing electronic counterpart associated with high-speed supercomputers such as Cray T-90 machine.

Polyimide-based waveguides for guided-wave multi-GBit/sec MCM optoelectronic interconnects

We present the fabrication of polyimide-based H-tree waveguides for a multi-GBit/sec optical clock signal distribution in a Si CMOS process compatible environment. Such a clock distribution system is to replace the existing electronic counterpart associated with high-performance computers. A waveguide propagation loss of 0.21 dB/cm at 850 nm was experimentally confirmed for the l-to-48 waveguide fanout device, l-to-2 splitting loss and bending loss were measured to be 0.25 dB and higher. The planarization requirement of the optical interconnection layer among many electrical interconnection layers makes the employment of tilted grating a choice of desire. Theoretical calculation predicts the 1-to-l free-space to waveguide coupling with an efficiency as high as 95%. Currently, a coupling efficiency of 35% was experimentally confirmed due to the limited index difference between guiding and cladding layers. Further experiments aimed at structuring a larger guiding/cladding layer index differences are under investigation. To effectively couple an optical signal into the waveguide through the tided grating coupler, the accuracy of the wavelength employed is pivotal. This makes the usage of the vertical cavity surface-emitting lasers (VCSELs) and VCSEL arrays the best choice when compared with edge-emitting lasers. Modulation bandwidth as high as 6 GBit/sec was demonstrated at 850 nm. Such a wavelength is compatible with Si-based photodetectors. Temperature dependence of the threshold current up to 155 °C was measured which will determine the power dissipation issue of the optoelectronic packaging. Finally, the first fully monolithic Si-MOSFET integrated receiver was made as the optical clock signal detector. To further enhance the bandwidth of such a detector, a resonant cavity structure with Si/Si02 as the bottom mirror was employed. The measured demodulation bandwidth is over 10 GHz. A fully integrated guided-wave optical clock signal distribution system having planarized grating couplers, H-tree Si- CMOS process compatible waveguides, VCSELs and Si-based photo-receivers will be demonstrated in the near future.

Polymer waveguide-based high-speed clock signal distribution system

The increasing demand for clock speed is rapidly exhausting capabilities of interconnection techniques currently employed for high performance supercomputers. In order to address the bottleneck problem at the board level, we have taken a systems approach in developing optoelectronic interconnection layer for board-level high speed optical clock signal distribution. The reported approach employs polymer optical channel waveguides, waveguide clock signal distribution. The reported approach employs polymer based optical channel waveguides, waveguide splitters, and surface-normal waveguide couplers. This paper describes the system architecture, material choice, and fabrication process of board-level waveguides devices to achieve a synchronous global clock signal distribution.

Flip chip VCSEL arrays on transparent substrates

In this report, we will discuss a method utilized by Emcore to flip-chip VCSEL die arrays onto transparent substrates, which contain integrated lensing and hybrid drive circuits. This process enables very dense hybrid packages.

Clustering supercomputer nodes using high-density parallel optic interconnects

Clustering supercomputer nodes requires a large amount of bandwidth in as small an area as possible. The distance between nodes can be quite varied, and interconnects covering 30 meters between nodes are not uncommon. Current advances in parallel optic interconnects allow these devices to be given consideration to replace the more traditional electrical and copper cable interconnect. However, supercomputer communication boards often need to support and route 1,000 to 1,200 communications lines. We build and demonstrate a parallel optic interconnect module with a bandwidth density of 15Gb/s/inch2 and an optical connector housing supporting 16 MT ferrules to satisfy the needs of a system communication module.

Polyimide-based guided-wave multigigabit per second optical clock signal distribution system for Cray T-90 supercomputer

We report the formation of polyimide-based H-tree waveguides for a multi-GBit/sec optical clock signal distribution in a Si CMOS process compatible environment. Such a clock distribution system is to replace the existing electronic counterpart associated with high-speed supercomputers such as Cray T-90 machine. A waveguide propagation loss of 0.21 dB/cm at 850 nm was experimentally confirmed for the 1-to-48 waveguide fanout device. The planarization requirement of the optical interconnection layer among many electrical interconnection layers makes the employment of tilted grating a choice of desire. Theoretical calculation predicts the 1-to-1 free-space to waveguide coupling with an efficiency as high as 95 percent. Currently, a coupling efficiency of 35 percent was experimentally confirmed due to the limited index difference between guiding and cladding layers. Further experiments aimed at structuring a larger guiding/cladding layer index differences are under investigation. To effectively couple an optical signal into the waveguide through the tilted grating coupler, the accuracy of the wavelength employed is pivotal. This makes the usage of the vertical cavity surface-emitting lasers (VCSELs) and VCSEL arrays the best choice when compared with edge-emitting lasers. Modulation bandwidth as high as 6 GHz was demonstrated at 850 nm. Such a wavelength is compatible with Si-based photodetectors.