Jan-Michael Brosi

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.

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.

Microwave-Frequency Experiments Validate Optical Simulation Tools and Demonstrate Novel Dispersion-Tailored Photonic Crystal Waveguides

A new experimental method in the microwave regime is introduced to verify the performance of guided-wave photonic devices with high-index contrast. In particular, a novel broadband slow-light or high-dispersion photonic-crystal (PC) waveguide (WG) is studied. By scaling up the structure dimensions, the equivalent fabrication uncertainty can be reduced to 0.5 nm, which, in combination with the available microwave equipment, allows the conduction of reference measurements with a precision that is not possible in optics. Based on these experiments, several numerical band calculation methods for designing the PC-WGs are evaluated, and out of three accurate methods, we identify a fast tool. Furthermore, we check the accuracy of PC device simulations with the finite integration technique using the aforementioned PC-WG. We demonstrate that the device exhibits a region with a low group velocity of 4% of the vacuum speed of light and a region with a high chromatic dispersion of 4 ps/(mm ldr nm), both in a 1-THz bandwidth. For the first time, we quantify by experiments that a random disorder of the hole radii by 5%, which can be caused by fabrication imperfections, does not significantly degrade the group velocity behavior.

100 Gbit/s electro-optic modulator and 56 Gbit/s wavelength converter for DQPSK data in silicon-organic hybrid (SOH) technology

CMOS-compatible silicon photonics combined with covers of χ⁽²⁾ or χ⁽³⁾-nonlinear organic material allows electro-optic modulators and all-optical wavelength converters for data rates of 100 Gbit/s and beyond. The devices are not impaired by free carriers.

Silicon-Organic Hybrid (SOH) Devices for Optical Signal Processing

Silicon-organic hybrid (SOH) integration allows overcoming insufficient nonlinear optical properties of silicon-on-insulator waveguides. We discuss 100Gbit/s electro-optic modulation and demonstrate 120Gbit/s all-optical signal processing with SOH devices.

Broadband Slow Light in a Photonic Crystal Line Defect Waveguide

Pulse transmission at 4% of the vacuum light velocity is shown for a slow-light line-defect waveguide with 1300GHz bandwidth. We prove the concept for an upscaled microwave model with disorder both theoretically and experimentally.

Inhomogeneous magnetization of a superconducting film measured with a gradiometer

The magnetic flux generated by the screening currents of a superconducting Nb film in the Meissner state is measured with a coaxial gradiometer in a weak magnetic field B. A peculiar position dependence is found when the sample surface is only slightly tilted away from the parallel field orientation and shifted with respect to the center axis of the gradiometer. This is due to the inhomogeneous magnetization with a strong out-of-plane contribution measured by the two pick-up coils as confirmed by numerical finite-element calculations. The unusual position dependence has important consequences for interpreting the diamagnetic screening of superconducting films measured by a coaxial gradiometer near the parallel-field orientation.

Design and fabrication of nanophotonic devices

High index contrast integratable optical devices are investigated. Simulations are run on a parallel computer using an efficient wavelet FDTD code. For 2D photonic crystals with line defects and random perturbations, we have developed a numerically fast semi-analytical method. The effects due to sidewall roughnesses are studied for straight strips and for 2D photonic crystal line defect waveguides. For a microring filter and a photonic crystal slab, we compare numerical results to measurements using an upscaled microwave model. Fabrication steps for the material systems SOI and InGaAsP/InP are discussed, and FIB milling is demonstrated for GaAs/AlGaAs.