We are developing a 1x8 single mode (SM) optical interface to facilitate the adoption of dense wavelength division multiplexing (DWDM) silicon photonic (SiPh) optical interconnects in exascale computing systems. A common method for fiber attachment to SiPh transceivers is ‘pigtailing’- the permanent adhesive bonding of fiber/v-groove arrays to onchip grating couplers (GC). This approach precludes standard high throughput surface mounting and solder reflow assembly of the transceiver onto system printed circuit boards. Our approach replaces the fixed pigtail with a low profile, small form factor, detachable expanded beam optical connector which consists of four essential parts: a GC array, a surface mount glass microlens array chip, an injection molded solder reflowable optical socket, and an injection molded SM light turn ferrule. The optical socket and ferrule are supplied by US Conec Ltd. To design the GC, we developed an optical simulator that considers CMOS foundry constraints in the optimization process. On-wafer measurements of the GC coupling loss to SMF28 fiber at 1310nm is ~1.4dB with a 1dB bandwidth of ~22nm. This ensures a wide low loss spectral window for at least 16 DWDM channels. The geometry of the optical system is arranged so that only a simple spherical lens is required for efficient mode matching in the expanded beam space. The fiber to fiber insertion loss through the light turn ferrule, two microlenses and GCs, and a looped back SOI waveguide ranged from 4.1-6.3dB, with insertion loss repeatability of 0.2dB after multiple mating cycles.
The need for additional IO bandwidth for data center device interconnection is well established. Optical interconnects can deliver required bandwidth along with energy and space efficiency at a cost that encourages adoption. To this end, we are developing an optical transceiver incorporating multimode VCSEL emitters in a coarse wavelength division multiplex (CWDM) system capable of transmission at 25Gbps per channel, 100Gbps/fiber, and a maximum aggregate bidirectional data rate of 1.2Tbps. Electrical connection to the transceiver can be made by solder reflow or LGA connector, and optical connection is made by means of a custom optical connector supporting CWDM transmission.
A low cost, blind mate, injection molded optical backplane is presented. The optical backplane is comprised of 12
channel optical broadcast buses, operating at 10Gbps/channel with six blindmate optical output ports spaced 1U apart.
We describe the performance and reliability of multi-bar diode stacks assembled with hard solder attachment of the laser
diode bar to the conduction-cooled package substrate. The primary stack package design is based on a modular platform
that makes use of common piece parts to incorporate anywhere from 2-7 bars, operating at peak powers of 80W/bar to
200W/bar. In assembling monolithic type diode stack packages, it is typical to use a soft solder material such as indium
for P-side bar attachment into the package. Due to its low melting point and low yield stress, indium can provide a solder
joint that transfers low stress to the laser bar. However, during CW and QCW operation, indium is prone to migration
that can cause device failure due to a number of well-known mechanisms. This shortcoming of soft-solder bar
attachment can limit the number of shots the stack delivers over its operating life. By replacing the soft solder typically
used for P-side attachment with a hard solder, it is possible to greatly reduce or eliminate certain failure modes, thereby
increasing the operating life of the part. We demonstrate lifetime of > 1E9 shots at 80 W/bar, 250 us/40 Hz pulses, and
50C package operating temperature.
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