Christian Koos

Nonlinear silicon-on-insulator waveguides for all-optical signal processing

Values up to gamma=7 x 10(6)/(W km) for the nonlinear parameter are feasible if silicon-on-insulator based strip and slot waveguides are properly designed. This is more than three orders of magnitude larger than for state-of-the-art highly nonlinear fibers, and it enables ultrafast all-optical signal processing with nonresonant compact devices. At lambda=1.55 microm we provide universal design curves for strip and slot waveguides which are covered with different linear and nonlinear materials, and we calculate the resulting maximum gamma.

Error Vector Magnitude as a Performance Measure for Advanced Modulation Formats

We examine the relation between optical signal-to-noise ratio (OSNR), error vector magnitude (EVM), and bit-error ratio (BER). Theoretical results and numerical simulations are compared to measured values of OSNR, EVM, and BER. We conclude that the EVM is an appropriate metric for optical channels limited by additive white Gaussian noise. Results are supported by experiments with six modulation formats at symbol rates of 20 and 25 GBd generated by a software-defined transmitter.

High-speed low-voltage electro-optic modulator with a polymer-infiltrated silicon photonic crystal waveguide

A novel electro-optic silicon-based modulator with a bandwidth of 78GHz, a drive voltage amplitude of 1V and a length of only 80 microm is proposed. Such record data allow 100Gbit/s transmission and can be achieved by exploiting a combination of several physical effects. First, we rely on the fast and strong nonlinearities of polymers infiltrated into silicon, rather than on the slower free-carrier effect in silicon. Second, we use a Mach-Zehnder interferometer with slotted slow-light waveguides for minimizing the modulator length, but nonetheless providing a long interaction time for modulation field and optical mode. Third, with this short modulator length we avoid bandwidth limitations by RC time constants. The slow-light waveguides are based on a photonic crystal. A polymer-filled narrow slot in the waveguide center forms the interaction region, where both the optical mode and the microwave modulation field are strongly confined to. The waveguides are designed to have a low optical group velocity and negligible dispersion over a 1THz bandwidth. With an adiabatic taper we significantly enhance the coupling to the slow light mode. The feasibility of broadband slow-light transmission and efficient taper coupling has been previously demonstrated by us with calculations and microwave model experiments, where fabrication-induced disorder of the photonic crystal was taken into account.

Surface plasmon polariton absorption modulator.

A new compact electrically controlled surface plasmon polariton (SPP) absorption modulator operating at communication wavelengths is introduced. The modulator is controlled by changing the free carrier density and thereby the propagation loss of the SPP.

Real-time Nyquist pulse generation beyond 100 Gbit/s and its relation to OFDM.

Nyquist sinc-pulse shaping provides spectral efficiencies close to the theoretical limit. In this paper we discuss the analogy to optical orthogonal frequency division multiplexing and compare both techniques with respect to spectral efficiency and peak to average power ratio. We then show that using appropriate algorithms, Nyquist pulse shaped modulation formats can be encoded on a single wavelength at speeds beyond 100 Gbit/s in real-time. Finally we discuss the proper reception of Nyquist pulses.

Silicon Organic Hybrid Technology—A Platform for Practical Nonlinear Optics

A cost-effective route to build electrically as well as optically controlled modulators in silicon photonics is reviewed. The technology enables modulation at bit rates beyond 100 Gbit/s. This platform relies on the well-established silicon-based complementary metal-oxide-semiconductor processing technology for fabricating silicon-on-insulator (SOI) waveguides, while an organic cladding layer adds the required nonlinearity. The strength of this hybrid technology is discussed, and two key devices in communications are exemplarily regarded in more detail. The first device demonstrates demultiplexing of a 120 Gbit/s signal by means of four-wave mixing in a slot-waveguide that has been filled with a highly nonlinear chi(3)-organic material. The second device is a 100 Gbit/s/1 V electrooptic modulator based on a slow-light SOI photonic crystal covered with a chi(2) -nonlinear organic material.

Photonic wire bonding: a novel concept for chip-scale interconnects.

Photonic integration requires a versatile packaging technology that enables low-loss interconnects between photonic chips in three-dimensional configurations. In this paper we introduce the concept of photonic wire bonding, where polymer waveguides with three-dimensional freeform geometries are used to bridge the gap between nanophotonic circuits located on different chips. In a proof-of-principle experiment, we demonstrate the fabrication of single-mode photonic wire bonds (PWB) by direct-write two-photon lithography. First-generation prototypes allow for efficient broadband coupling with average insertion losses of only 1.6 dB in the C-band and can carry wavelength-division multiplexing signals with multi-Tbit/s data rates. Photonic wire bonding is well suited for automated mass production, and we expect the technology to enable optical multi-chip systems with enhanced performance and flexibility.Photonic integration has witnessed tremendous progress over the last years, and chip-scale transceiver systems with Terabit/s data rates have come into reach. However, as on-chip integration density increases, efficient off-chip interfaces are becoming more and more crucial. A technological breakthrough is considered indispensable to cope with the challenges arising from large-scale photonic integration, and this particularly applies to short-distance optical interconnects. In this letter we introduce the concept of photonic wire bonding, where transparent waveguide wire bonds are used to bridge the gap between nanophotonic circuits located on different chips. We demonstrate for the first time the fabrication of three-dimensional freeform photonic wire bonds (PWB), and we confirm their viability in a multi-Terabit/s data transmission experiment. First-generation prototypes allow for efficient broadband coupling with overall losses of only 1.6 dB. Photonic wire bonding will enable flexible optical multi-chip assemblies, thereby challenging the current paradigm of highly-complex monolithic integration.

Real-Time Software-Defined Multiformat Transmitter Generating 64QAM at 28 GBd

We demonstrate a software-defined real-time optical multiformat transmitter. Here, eight different modulation formats are shown. Data rate and modulation formats are defined through software accessible look-up tables enabling format switching in the nanosecond regime without changing the transmitter hardware. No data are lost during the switching process. SP-64 quadrature amplitude modulation at 28 Gbd has been generated and tested. This allows us to generate a 336-Gb/s real-time pseudorandom bit sequence in a dual polarization setup.

Single-laser 32.5 Tbit/s Nyquist WDM transmission

Single-laser 32.5 Tbit/s 16QAM Nyquist-WDM transmission with 325 carriers over 227 km at a net spectral efficiency of 6.4 bit/s/Hz is reported.

Slow and fast dynamics of gain and phase in a quantum dot semiconductor optical amplifier

Gain and phase dynamics in InAs/GaAs quantum dot semiconductor optical amplifiers are investigated. It is shown that gain recovery is dominated by fast processes, whereas phase recovery is dominated by slow processes. Relative strengths and time constants of the underlying processes are measured. We find that operation at high bias currents optimizes the performance for nonlinear cross-gain signal processing if a low chirp is required.