Christophe Kopp

Zero-bias 40Gbit/s germanium waveguide photodetector on silicon

We report on lateral pin germanium photodetectors selectively grown at the end of silicon waveguides. A very high optical bandwidth, estimated up to 120GHz, was evidenced in 10 µm long Ge photodetectors using three kinds of experimental set-ups. In addition, a responsivity of 0.8 A/W at 1550 nm was measured. An open eye diagrams at 40Gb/s were demonstrated under zero-bias at a wavelength of 1.55 µm.

Silicon Photonic Circuits: On-CMOS Integration, Fiber Optical Coupling, and Packaging

Silicon photonics is a new technology that should at least enable electronics and optics to be integrated on the same optoelectronic circuit chip, leading to the production of low-cost devices on silicon wafers by using standard processes from the microelectronics industry. In order to achieve real-low-cost devices, some challenges need to be taken up concerning the integration technological process of optics with electronics and the packaging of the chip. In this paper, we review recent progress in the packaging of silicon photonic circuits from on-CMOS wafer-level integration to the single-chip package and input/output interconnects. We focus on optical fiber-coupling structures comparing edge and surface couplers. In the following, we detail optical alignment tolerances for both coupling architecture, discussing advantages and drawbacks from the packaging process point of view. Finally, we describe some achievements involving advanced-packaging techniques.

Nanophotonic Devices for Optical Interconnect

We review recent progress in nanophotonic devices for compact optical interconnect networks. We focus on microdisk-laser-based transmitters and discuss improved design and advanced functionality including all-optical wavelength conversion and flip-flops. Next we discuss the fabrication uniformity of the passive routing circuits and their thermal tuning. Finally, we discuss the performance of a wavelength selective detector.

Efficient beamshaper homogenizer design combining diffractive optical elements, microlens array and random phase plate

We propose a new approach that combines original techniques to achieve a very efficient laser beam homogenizer and shaper. The three retained concepts are microlens array, random phase plate and diffractive optical elements. The performance of usual homogenizers are improved in terms of efficiency, homogenization and shaping abilities. We report on the theory and the development of such diffractive beamshaper homogenizers. Finally, an application concerning laser to fibre coupling is described.

Chip-to-chip optical interconnections between stacked self-aligned SOI photonic chips

Photonic silicon devices are key enabling technologies for next generation High Performance Computers. In this paper, we report the possibility to stack and optically interconnect SOI based photonic chips for future System-In-Package photonic architecture. Combining vertical grating couplers and state-of-the-art flip-chip technology, we demonstrated low loss penalties and wide spectral range optical interconnections between stacked photonic chips.

Enhanced Fiber Grating Coupler Integrated by Wafer-to-Wafer Bonding

The ultimate goal of silicon photonics development is the monolithical integration of a photonic layer with optical functions onto silicon IC chips. This 3-D stacking can be obtained by wafer-to-wafer bonding leading to the photonic layers to be embedded into the last levels of metalization above the IC layer. We present a method that takes advantage of this integration process in order to realize enhanced fiber grating couplers. Indeed, grating structures are very attractive to couple the light between tiny silicon wires to the external world, which is dominated by optical fibers. Moreover, the insertion of a mirror below the grating is a well-known solution to increase significantly the coupling efficiency. We propose a method to obtain this bottom mirror by anticipating the grating coupler flip due to the wafer-to-wafer bonding. To this end, the mirror is formed above the encapsulation layer of the fiber grating coupler in order to appear below it after the optical layers integration onto an IC wafer. In this way, the thickness between the grating and the bottom mirror, which is a very sensitive parameter, remains under control whatever wafer-to-wafer bonding process tolerances. Experimental results with one single silicon layer as a bottom mirror exhibit coupling efficiency up to 69%.

A fluxless bonding process using AuSn or Indium for a miniaturized hermetic package

In the field of high speed data transmissions or in the industrialisation of MEMS devices a hermetic package is often required. However this technological achievement represents an important part of the package price and usually limits the freedom of design and miniaturization. In this paper we propose a localized hermetic sealing method adapted to batch process, that uses either Eutectic AuSn (AuSn20) or pure Indium for the seal ring. A novel fluxless controlled thermocompression process is developed to achieve simultaneously a hermetic bonding and interconnection of I/Os located within the sealing ring through the capping part. Different designs are tested using a standard He aspersion leak test and additionally some reliability tests are performed. Leak rate ≪5.10−8 mbar l/s are obtained with both AuSn20 and In seal rings.

Packaged hybrid III-V/silicon SOA

We present a hybrid III-V/silicon SOA, mounted in a planar package, with a fiber-to-fiber gain up to 10 dB, maximum internal gain of 28±2 dB, an internal noise figure of 10-11 dB and an output saturation power around 9 dBm.

40Gbit/s germanium waveguide photodetector on silicon

We report a Germanium lateral pin photodiode integrated with selective epitaxy at the end of silicon waveguide. A very high optical bandwidth estimated at 120GHz is shown, with internal responsivity as high as 0.8A/W at 1550nm wavelength. Open eye diagram at 40Gb/s was obtained under zero-bias at wavelength of 1.55μm.

Design and Implementation of an Integrated Reconfigurable Silicon Photonics Switch Matrix in IRIS Project

This paper aims to present the design and the achieved results on a CMOS electronic and photonic integrated device for low cost, low power, transparent, mass-manufacturable optical switching. An unprecedented number of integrated photonic components (more than 1000), each individually electronically controlled, allows for the realization of a transponder aggregator device which interconnects up to eight transponders to a four direction colorless-directionless-contentionless ROADM. Each direction supports 12 200-GHz spaced wavelengths, which can be independently added or dropped from the network. An electronic ASIC, 3-D integrated on top of the photonic chip, controls the switch fabrics to allow a complete and microsecond fast reconfigurability.