Optical switch networks based on silicon photonics can provide high bandwidth, low latency, low power, and low cost interconnect fabrics for datacenter, cloud, and high-performance computing by eliminating the pin-constrained electronic switches and the multiple electrical-optical conversions necessary in traditional networks. Silicon photonics is also compatible with wavelength division multiplexing (WDM) allowing simultaneous routing of large bandwidth data streams. Adoption of photonic switches requires scaling to large port counts compared to current 4x4 and 8x8 demonstrations. For example, a 64-port switch implemented using thirty-two 4x4 and four 16x16 switches will be limited by losses in numerous subcomponents, including optical couplers, waveguide propagation losses, waveguide crossings, and phase shifters. To enable viable optical-link-loss budgets requires incorporation of optical gain in addition to improved efficiency in all subcomponents. We have developed a silicon photonic switch platform with integrated gain based on a carrier with active photonics. Optical switches are monolithically integrated into photonic carrier while semiconductor optical amplifiers (SOAs) and CMOS drive ICs are flip-chip attached. We demonstrated non-blocking 4x4 Si photonic switches with < 3-dB on-chip loss and < -20 dB crosstalk with about 4ns switching time. Photonic carriers and 4-channel SOA arrays were co-designed with custom precision packaging features enabling flip-chip bonding with high accuracy. The photonic carrier incorporates low-loss SiN waveguides with inverse taper structures for efficient coupling to/from the SOA arrays and off-carrier coupling. Photonic carriers with integrated 4-channel SOA arrays were fabricated achieving over 10 dB gain and demonstrating error-free 4x25-Gb/s WDM links for all 4 channels.
Future fiber systems in computer communications applications must meet growing bandwidth requirements, while
maintaining feasible power and cost targets in addition to maintaining manageable volumes of fiber cabling. Therefore,
bandwidth-per-fiber represents a critical design metric for next-generation systems. Here, a multicore fiber technology
based on multimode graded-index cores is reviewed. A full link demonstration using six cores transmitting up to 20 Gb/s
each is achieved between custom transmitter and receiver assemblies, which interface directly to the multicore fiber. The
demonstrated technology may provide the added bandwidth per link required in next generation HPC systems.
A novel, compact 48-channel optical transceiver module has been designed and fabricated based on a "holey" Optochip
- a single-chip CMOS transceiver IC with 24 receiver and 24 laser driver circuits each with a corresponding throughsubstrate
optical via (hole). The holes enable 24-channel 850-nm VCSEL and photodiode arrays to be directly flip-chip
soldered to the CMOS IC to maximize high-speed performance and facilitate direct fiber-coupling to a standard 4 x 12
MMF array. The Optochips were packaged into complete modules by flip-chip soldering to high-density, high-speed
organic carriers. All 48-channels showed good performance up to 12.5 Gb/s/ch providing a 300 Gb/s bidirectional
aggregate data rate.
We report developments at Emcore on serial 850 nm vertical-cavity surface-emitting lasers (VCSELs) operated up to 25
Gb/s. They have been designed to provide a solution not only to meet stringent 10 Gb/s IEEE and Fiber Channel
specifications but also for emerging demands of 17 Gb/s Fiber Channel serial and 100 Gb/s (4x25 Gb/s or 5x20 Gb/s)
parallel applications in local and storage area networks. This paper covers 10 Gb/s GenX production distributions and
improved GenX VCSEL device design to meet low-power requirements at 20 Gb/s. We have successfully demonstrated
low threshold current of 0.65 mA at 25°C using nominal 7.3 μm oxide-aperture GenX VCSELs. They can be directly
modulated up to 25 Gb/s with open eyes at 6 mA bias. With the same design, open eyes of 20 Gb/s is achieved at bias
current as low as 4 mA (9 KA/cm2) at 25°C and 8 mA (18 KA/cm2) at 70°C. These operation conditions are comparable
to current 10 Gb/s GenX VCSELs in production which have been shown a great field history.
Scaling computing systems to Exaflops (1018 floating point operations per second) will require tremendous increases in
communications bandwidth but with greatly reduced power consumption per communicated bit as compared to today's
petaflop machines. Reaching the required performance in both density and power consumption will be extremely
challenging. Electrical and optical interconnect technologies that may be part of the solution are summarized, including
advanced electrical printed circuit boards, VCSEL-array based optical interconnects over multimode fibers or
waveguides, and singlemode silicon photonics. The use of optical interconnects will play an ever-larger role in
intrasystem communications. Although optics is used today primarily between racks, it will gradually migrate into
backplanes, circuit cards, and eventually even on-chip.
Keywords: optical interconnects, supercomputers, exascale,
Aggregate chip bandwidths in server and high performance computing have exceeding Tb/s, and if present trends are to
continue would lead to doubling the number of signal pins in each generation. For high bandwidth switch and server
applications, bandwidth requirements could exceed the package pin limit as early as 2012.
We defined metrics to compare the performance of electrical and optical interconnects, which includes bandwidth
density (Gb/s/mm2/port), media bandwidth*distance product (GHz*m), power consumption (mW/Gb/s/Port), and
technology comparison metric (Gb/s/mm2/port * GHz*m/mW/Port). We will show that optical interconnects offer a
performance metric improvement factor of greater than 25 over electrical interconnects.
The IBM Terabus program has developed parallel optical interconnects for terabit/sec-class chip-to-chip
communications through printed circuit boards with integrated optical waveguides. 16 TX + 16 RX channel transceiver
"Optomodules" were assembled and fully characterized, with fiber-coupled full links operating up to 15 Gb/s, for an
aggregate bi-directional data transfer rate of 240 Gb/s. Furthermore, we have demonstrated a complete link between two
Optomodules through polymer waveguides on a printed circuit board, with all 32 uni-directional links operating error-free
at 10Gb/s, for a 160 Gb/s bidirectional aggregate data rate. This is the fastest, widest, and most integrated
multimode optical bus ever demonstrated.
In this paper we summarize production data from serial 10 Gb/s devices and report on 850 nm VCSEL arrays with
channel speeds up to 25 Gb/s. The production data demonstrates that robustness of the basic technology as well as its
suitability for cost effective, high volume production. The >10 Gb/s measurements on two dimensional arrays show that
850 nm VCSEL technology can be extended well beyond the 10 Gb/s links currently beginning to be deployed by
volume field users.
The UV stability of a-C:H films was investigated by irradiating them with a 248 nm excimer laser or a DUV lamp with a 248 nm filter. Both transmittance and phase angle of the film at 248 nm were measured at different UV dose intervals up to a cumulative dose of 10,000 J/cm2. We found that film stability was dependent on processing conditions. Excellent stability was achieved when the a-C:H films were sputtered from a graphite target in a Ar/hydrocarbon process gas mixture with the substrate held at an rf bias. If no substrate bias was used, films were stable only up to a maximum of 1,000 J/cm2 for a nominal transmittance of about 6%. These instabilities were attributed to adsorption of oxygen on the film and its subsequent diffusion into the films. X-ray photoelectron spectroscopy (XPS) shows that under DUV irradiation the oxygen content increases from 13 to 29 at.% on the carbon surface. Secondary ion mass spectrometry (SIMS) shows also oxygen diffusion into the carbon film. It appears that the oxygen first removes the graphitic content since film transmittance was found to increase. It is believed that rf bias sputtering results in denser films that are more impervious to oxygen penetration and hence more durable to this UV assisted oxidative degradation process. The sputtered films with no substrate bias were found stable when irradiated in a nitrogen atmosphere.
The feasibility of using thin films of organic material as a protective cover for x-ray lithography masks has been demonstrated. A pellicle structure that fits unobtrusively inside the mask-wafer gap and on the x-ray lithography NIST standard ring was developed. The pellicle solves several problems: 1) protects the mask absorber from direct contact to external sources of possible damage without itself contacting the absorber, 2) allows effective cleaning of the x-ray mask by preventing dust or debris particles from getting imbedded in the absorber pattern, 3) reduces contamination of the stepper and wafers by absorber metal debris in the event of catastrophic breakage of the mask membrane, 4) reduces contamination of the absorber pattern by debris generated by the resist or the stepper environment during x-ray exposure, and 5) reduces photoelectrons generated by the absorber during x-ray exposure from reaching the resist. Furthermore, pellicles may offer inspection advantages by providing a flat surface without absorber topography. Several approaches for the fabrication of suitable pellicles using organic and inorganic films will be presented in this paper. Pellicles have been successfully tested in the SVGL and SUSS steppers in the IBM Advanced Lithography Facility in the East Fishkill, NY. Results on pellicle's performance together with radiation damage measurements to estimate a pellicle's lifetime are presented in this paper.
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