Jens Hofrichter

A 90nm CMOS integrated Nano-Photonics technology for 25Gbps WDM optical communications applications

The first sub-100nm technology that allows the monolithic integration of optical modulators and germanium photodetectors as features into a current 90nm base high-performance logic technology node is demonstrated. The resulting 90nm CMOS-integrated Nano-Photonics technology node is optimized for analog functionality to yield power-efficient single-die multichannel wavelength-mulitplexed 25Gbps transceivers.

Synthesis of Graphene on Silicon Dioxide by a Solid Carbon Source

We report on a method for the fabrication of graphene on a silicon dioxide substrate by solid-state dissolution of an overlying stack of a silicon carbide and a nickel thin film. The carbon dissolves in the nickel by rapid thermal annealing. Upon cooling, the carbon segregates to the nickel surface forming a graphene layer over the entire nickel surface. By wet etching of the nickel layer, the graphene layer was allowed to settle on the original substrate. Scanning tunneling microscopy (STM) as well as Raman spectroscopy has been performed for characterization of the layers. Further insight into the morphology of the layers has been gained by Raman mapping indicating micrometer-size graphene grains. Devices for electrical measurement have been manufactured exhibiting a modulation of the transfer current by backgate electric fields. The presented approach allows for mass fabrication of polycrystalline graphene without transfer steps while using only CMOS compatible process steps.

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.

Slotted photonic crystal nanobeam cavity with an ultrahigh quality factor-to-mode volume ratio

We describe the design, fabrication, and characterization of a 1-dimensional silicon photonic crystal cavity with a quality factor-to-mode volume ratio greater than 10(7), which exceeds the highest previous values by an order of magnitude. The maximum of the electric field is outside the silicon in a void formed by a central slot. An extremely small calculated mode volume of 0.0096 (λvac/n)(3) is achieved through the abrupt change of the electric field in the slot, despite which a high quality factor of 8.2 × 10(5) is predicted by simulation. Quality factors up to 1.4 × 10(5) are measured in actual devices. The observation of pronounced thermo-optic bistability is consistent with the strong confinement of light in these cavities.

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.

An integrated silicon photonics technology for O-band datacom

A manufacturable platform of CMOS, RF and opto-electronic devices fully PDK enabled to demonstrate a 4×25 Gb/s reference design is presented. With self-aligned fiber attach, this technology enables low-cost O-band data-com transceivers. In addition, this technology can offer enhanced performance and yield in hybrid-assembly for applications at 25 Gbaud and beyond.

Electro-Optical Active Barium Titanate Thin Films in Silicon Photonics Devices

We demonstrate the integration of single-crystalline barium titanate thin films on silicon substrates, with Pockels coefficients of rEff ~ 148 pm/V. We further show the implementation of such layers into silicon photonic devices such as ring resonators.

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.

Grating couplers as optical probe pads in a standard CMOS process

To enable in-line nanophotonic device monitoring, grating couplers for near-vertical wafer-scale optical probing are fabricated in a standard CMOS process. These partially etched “optical probes” demonstrate a robust 3-dB-bandwidth larger than 80 nm allowing for photonic device characterization over the entire C-band throughout the fabrication process.