Antonio La Porta

Polymer waveguides for electro-optical integration in data centers and high-performance computers.

To satisfy the intra- and inter-system bandwidth requirements of future data centers and high-performance computers, low-cost low-power high-throughput optical interconnects will become a key enabling technology. To tightly integrate optics with the computing hardware, particularly in the context of CMOS-compatible silicon photonics, optical printed circuit boards using polymer waveguides are considered as a formidable platform. IBM Research has already demonstrated the essential silicon photonics and interconnection building blocks. A remaining challenge is electro-optical packaging, i.e., the connection of the silicon photonics chips with the system. In this paper, we present a new single-mode polymer waveguide technology and a scalable method for building the optical interface between silicon photonics chips and single-mode polymer waveguides.

Flip-chip optical couplers with scalable I/O count for silicon photonics

A scalable and tolerant optical interfacing method based on flip-chip bonding is developed for silicon photonics packaging. Bidirectional optical couplers between multiple silicon-on-insulator waveguides and single-mode polymer waveguides are designed and fabricated. Successful operation is verified experimentally in the 1530-1570 nm spectral window. At the wavelength of 1570 nm, the coupling loss is as low as 0.8 dB for both polarization states and the planar misalignment loss is less than 0.6 dB for TE and 0.3 dB for TM polarization in a lateral silicon-polymer waveguide offset range of ± 2 µm. The coupling loss does not exhibit any temperature dependence up to the highest measurement point of 70°C.

Laser Direct Writing of Single-Mode Polysiloxane Optical Waveguides and Devices

Using a custom-built laser direct writing system, single-mode polymer optical waveguides, and devices for board-level optical interconnects were fabricated. A novel photopatternable polysiloxane material was developed that combines low-loss, simple, and large-area processability, and reliability during manufacturing and system operation. The polysiloxane waveguides were designed with quadratic cross sections of 5.5 × 5.5 μm2 and a refractive index contrast of 0.0086 between core and cladding polymer for single-mode operation at the wavelength of 1.3 μm. A straight waveguide propagation loss of 0.28 dB/cm was achieved. A wide range of passive optical devices, including Y-splitters, directional couplers, and Mach-Zehnder interferometers were successfully fabricated and characterized. The results prove that the presented combination of material and process technology is a viable implementation for short distance board-level optical links.

A low-power high-speed InP microdisk modulator heterogeneously integrated on a SOI waveguide

We report on the modulation characteristics of indium phosphide (InP) based microdisks heterogeneously integrated on a silicon-on-insulator (SOI) waveguide. We present static extinction ratios and dynamic operation up to 10 Gb/s. Operation with a bit-error rate below 1 × 10(-9) is demonstrated at 2.5, 5.0 and 10.0 Gb/s and the performance is compared with that of a commercial modulator. Power penalties are analyzed with respect to the pattern length. The power consumption is calculated and compared with state-of-the-art integrated modulator concepts. We demonstrate that InP microdisk modulators combine low-power and low-voltage operation with low footprint and high-speed. Moreover, the devices can be fabricated using the same technology as for lasers, detectors and wavelength converters, making them very attractive for co-integration.

A single InP-on-SOI microdisk for high-speed half-duplex on-chip optical links

We demonstrate for the first time that a single compact, electrically contacted indium phosphide based microdisk heterogeneously integrated on a silicon-on-insulator waveguide can be used as both a high-speed modulator and photo detector. We demonstrate high-speed operation up to 10 Gb/s and present bit-error rate results of both operation modes.

Optical interconnects for disaggregated resources in future datacenters

In future datacenters with disaggregation, dynamic allocation and reconfiguration of resources, I/O and networks will become both enabling elements - and bottlenecks. We discuss latency in optical data transmission and photonics integration and packaging, which will become particularly critical.

Optical coupling between polymer waveguides and a silicon photonics chip in the O-band

We present a silicon photonics optical I/O interfacing solution based on adiabatic optical coupling between silicon and polymer waveguides. A transition loss of -0.9 dB and back-reflection <; -45 dB were found at 1310 nm.

Scalable Optical Coupling between Silicon Photonics Waveguides and Polymer Waveguides

We present a silicon photonics optical I/O interfacing solution based on adiabatic optical coupling between silicon waveguides in a silicon photonics chip and polymer waveguides. Three different assembly methods were investigated for the evaluation of the coupling loss. A coupling loss as low as 0.9 dB was found at 1310 nm.

Broadband and scalable optical coupling for silicon photonics using polymer waveguides

Abstract We present optical coupling schemes for silicon integrated photonics circuits that account for the challenges in large-scale data processing systems such as those used for emerging big data workloads. Our waveguide based approach allows to optimally exploit the on-chip optical feature size, and chip- and package real-estate. It further scales well to high numbers of channels and is compatible with state-of-the-art flip-chip die packaging. We demonstrate silicon waveguide to polymer waveguide coupling losses below 1.5 dB for both the O- and C-bands with a polarisation dependent loss of <1 dB. Over 100 optical silicon waveguide to polymer waveguide interfaces were assembled within a single alignment step, resulting in a physical I/O channel density of up to 13 waveguides per millimetre along the chip-edge, with an average coupling loss of below 3.4 dB measured at 1310 nm.

Scalable and broadband silicon photonics chip to fiber optical interface using polymer waveguides

We present a silicon photonics optical I/O interfacing solution based on adiabatic optical coupling between silicon and polymer waveguides working for both O- and C-band. In the O-band, a fiber-to-chip coupling loss < 4 dB was found, with a polarization dependent loss < 0.5 dB.