Laurent Schares

Group index and group velocity dispersion in silicon-on-insulator photonic wires

We determine group index and group velocity dispersion (GVD) of SOI single-mode strip waveguides (photonic wires) with 525x226nm cross-section over the entire telecommunication bandwidth by employing an integrated Mach-Zehnder interferometer. The measured GVD yields 4400 ps/(nm*km) at 1550 nm and exceeds that of standard single-mode fibers by almost three orders of magnitude. In the photonic wires the GVD is mainly determined by strong light confinement rather than by material dispersion. Our results indicate that despite this high GVD, dispersion-induced signal impairment is negligible in photonic circuits for data rates up to 100-Gb/s and total waveguide lengths as long as about 1 meter. The measured group index and GVD are used as benchmarks to compare model calculations originating from four different theoretical methods.

160 Gb/s Bidirectional Polymer-Waveguide Board-Level Optical Interconnects Using CMOS-Based Transceivers

We have developed parallel optical interconnect technologies designed to support terabit/s-class chip-to-chip data transfer through polymer waveguides integrated in printed circuit boards (PCBs). The board-level links represent a highly integrated packaging approach based on a novel parallel optical module, or Optomodule, with 16 transmitter and 16 receiver channels. Optomodules with 16 Tx+16 Rx channels have been assembled and fully characterized, with transmitters operating at data rates up to 20 Gb/s for a 27-1 PRBS pattern. Receivers characterized as fiber-coupled 16-channel transmitter-to-receiver links operated error-free up to 15 Gb/s, providing a 240 Gb/s aggregate bidirectional data rate. The low-profile Optomodule is directly surface mounted to a circuit board using convention ball grid array (BGA) solder process. Optical coupling to a dense array of polymer waveguides fabricated on the PCB is facilitated by turning mirrors and lens arrays integrated into the optical PCB. A complete optical link between two Optomodules interconnected through 32 polymer waveguides has been demonstrated with each unidirectional link operating at 10 Gb/s achieving a 160 Gb/s bidirectional data rate. The full module-to-module link provides the fastest, widest, and most integrated multimode optical bus demonstrated to date.

Chip-to-chip optical interconnects

Terabus is based on a silicon-carrier interposer on an organic card containing 48 polymer waveguides. We have demonstrated 4times12 arrays of low power optical transmitters and receivers, operating up to 20 Gb/s and 14 Gb/s per channel respectively

Phase dynamics of semiconductor optical amplifiers at 10-40 GHz

The phase dynamics that occur in bulk InGaAsP-InP semiconductor optical amplifiers (SOAs) in response to picosecond pulse excitations at 10 and 40 GHz are studied experimentally and numerically for various amplifier lengths. The time dependencies of the phase changes and of the absolute gain of the amplifier are measured simultaneously. The total phase shifts induced by 1.5-ps pulses at 10 GHz are higher than /spl pi/ in SOAs with active region lengths between 0.5 and 2 mm and exceed 2/spl pi/ in a 1.5-mm-long amplifier. Phase shifts above /spl pi/ are measured at 40 GHz in 1.5- and 2-mm-long SOAs. The dependence of the total phase shift on the amplifier bias current and length and on pump pulse energy is investigated. Numerical simulations based on a comprehensive time-domain SOA model allow us to confirm the experimental results for a wide range of amplifier parameters. In particular, SOAs with lengths up to 5 mm have been modeled, and the calculations suggest that the maximum phase shifts occur in amplifiers of approximately 2-mm length. The phase dynamics measurements are illustrated at the example of an optical time division multiplexing add-drop multiplexer, based on a SLALOM switch, gated by 10- or 40-GHz control pulses. We find that simultaneous good dropping and clearing is possible if the length and the operating conditions of the SOA in the switch are chosen such as to induce a full /spl pi/ phase shift.

Ge-on-SOI-Detector/Si-CMOS-Amplifier Receivers for High-Performance Optical-Communication Applications

In this paper, an overview and assessment of high-performance receivers based upon Ge-on-silicon-on-insulator (Ge-on-SOI) photodiodes and Si CMOS amplifier ICs is provided. Receivers utilizing Ge-on-SOI lateral p-i-n photodiodes paired with high-gain CMOS amplifiers are shown to operate at 15 Gb/s with a sensitivity of -7.4 dBm (BER=10-12) while utilizing a single supply voltage of only 2.4 V. The 5-Gb/s sensitivity of similar receivers is constant up to 93 degC, and 10-Gb/s operation is demonstrated at 85 degC. Error-free (BER<10-12) operation of receivers combining a Ge-on-SOI photodiode with a single-ended high-speed receiver front end is demonstrated at 19 Gb/s, using a supply voltage of 1.8 V. In addition, receivers utilizing Ge-on-SOI photodiodes integrated with a low-power CMOS IC are shown to operate at 10 Gb/s using a single 1.1-V supply while consuming only 11 mW of power. A perspective on the future technological capabilities and applications of Ge-detector/Si-CMOS receivers is also provided

Phase modeling based on the /spl alpha/-factor in bulk semiconductor optical amplifiers

Different approaches based on the /spl alpha/-factor to model the phase of the optical fields in bulk semiconductor optical amplifiers are analyzed. Our time-domain numerical model is presented and it is calibrated by means of experimental characterizations of the device gain, of the amplified spontaneous emission spectra, and of the effective /spl alpha/-factor. We then compare the phase modulation at the SOA output for three cases. In the first one, the /spl alpha/-factor is always taken as constant. In the second case, the /spl alpha/-factor is set according to the SOA working point and then kept fixed. In the last case, we take into account the dependence of the /spl alpha/-factor on the carrier density and on the wavelength for every simulated time step. We shall identify when the first two approximations listed above deliver reliable results. In particular cases, the use of a constant value for the /spl alpha/-factor can lead to phase errors up to 50%.

A 15-Gb/s 2.4-V Optical Receiver Using a Ge-on-SOI Photodiode and a CMOS IC

We report the fastest (15 Gb/s) and lowest voltage (2.4V) all-silicon-based optical receiver to date. The receiver consists of a lateral, interdigitated, germanium-on-silicon-on-insulator (Ge-on-SOI) photodiode wire-bonded to a 0.13-mum complementary metal-oxide-semiconductor (CMOS) receiver integrated circuit (IC). The photodiode has an external quantum efficiency of 52% at lambda=850 nm and a dark current of 10 nA at -2 V. The small-signal transimpedance of the receiver is 91-dBOmega and the bandwidth is 6.6 GHz. At a bit-error rate of 10-12 and lambda=850 nm; the receiver exhibits sensitivities of -11.0, -9.6, and -7.4 dBm at 12.5, 14, and 15 Gb/s, respectively. The receiver operates error-free at rates up to 10 Gb/s with an IC supply voltage as low as 1.5 V and with a photodiode bias as low as 0.5 V. The power consumption is 3 to 7 mW/Gb/s. The Ge-on-SOI photodiode is well suited for integration with CMOS processing, raising the possibility of producing high-performance, low-voltage, monolithically integrated receivers based on this technology in the future

160-Gb/s, 16-Channel Full-Duplex, Single-Chip CMOS Optical Transceiver

We report a single-chip CMOS optical transceiver incorporating sixteen 10-Gb/s transmitter and receiver channels for a 160 Gb/s aggregate bit rate. The transceiver consumes 15.6 mW/Gb/s with an area efficiency of 9.4 Gb/s/mm2 per link.

Silicon Photonic Switch Fabrics in Computer Communications Systems

We discuss silicon photonic switch fabric designs that target data-intensive computing networks, reviewing recent results, and projecting future performance goals. We analyze the achievements of demonstrated hardware in terms of switching time, footprint, crosstalk, and power consumption, concluding that the most crucial metric to improve upon is net loss. We propose integrating semiconductor optical amplifiers into the switch fabric using either flip-chip or wafer-bonding technology, and investigate its potential merits alongside several challenges in implementation. Furthermore, we explore the dominant causes of crosstalk, and discuss manners for reducing it. We perform switch simulations that project a 7-dB reduction in crosstalk, when using a push-pull, rather than a single-ended phase shifter drive scheme. We also evaluate crosstalk effects on transmission performance using a full-link model that incorporates multiple crosstalk-accumulating photonic switch hops. The study demonstrates the degree to which crosstalk may degrade signal integrity after just a few occurrences. Finally, a comparison of four topologies highlights tradeoffs in physical-layer design and scheduling complexity, illustrating the scales that may be accomplished with the simplest topologies, and the device improvements required to achieve the more robust architectures.

Optical interconnects in future servers

Optical interconnects are common in todays petascale supercomputers, and will become pervasive at the exascale during this decade. Technologies that can meet the challenging technological and economic requirements for the exascale will be reviewed.