Sven Mahnkopf

Tuning localized plasmons in nanostructured substrates for surface-enhanced Raman scattering

Reflectivity measurements of gold nanostructures graded in pitch and aperture size allow investigation of localized plasmons. A simple model confirmed by simulations explains the plasmon resonances. Such arrays are highly suitable Raman scattering substrates.

Two-channel tunable laser diode based on photonic crystals

We report the development of a tunable laser diode array monolithically integrated with a Y-coupler structure based on photonic crystals. The laser diodes consist of two longitudinally coupled photonic crystal waveguide segments that are separated by a photonic crystal mirror section. Quasicontinuous tuning is achieved in a 30.6-nm window with 100-GHz channel spacing as typically required by wavelength-division-multiplexing applications. The sources can be operated independently allowing the simultaneous transmission of two freely selectable wavelengths.

Tunable distributed feedback laser with photonic crystal mirrors

We report the development of a tunable laser diode based on InP using photonic crystal mirrors. The laser consists of two longitudinally coupled ridge waveguide segments that are coupled through a photonic crystal mirror segment. A laterally defined binary superimposed grating provides a distributed feedback in each of the cavities. Quasi-continuous tuning is achieved in a 24.5 nm window with 56 channels as typically required by wavelength division multiplexing applications.

Tunable photonic crystal coupled-cavity laser

We report the development of a tunable photonic crystal coupled-cavity laser diode based on InP. The laser consists of two photonic crystal channel waveguides that are coupled through a photonic crystal mirror segment in /spl Gamma/-M direction. The cavity lengths define the respective mode spacings in the cavities. The tuning characteristics of the device are compared with results obtained from a transfer matrix model. Quasi-continuous tuning is achieved in a 29.6-nm window with 36 wavelength division multiplexing channels spaced 0.8 nm apart (ITU grid). The simplicity of fabrication and promising output characteristics should make this tunable laser design an interesting source for monolithic integration into highly integrated photonic circuits.

Probing molecules by surface-enhanced Raman spectroscopy

A new class of Surface-Enhanced Raman Scattering (SERS) substrates have been engineered by exploiting both Photonic Crystal (PC) and semiconductor technologies. Gold coated inverted pyramids nanotextured substrates allow reproducibility <10% and enhancement factors > 106 over large areas. Modelling and optical characterization of the engineered structures is demonstrated. Examples of applications to amino acids and illicit drug detection are given. Concentrations as low as ppm-ppb (mg/mL to ng/mL) have been measured depending on the adsorbed analytes. Information on structure and conformation of the molecule is inferred due to the richer nature of SERS spectra.

Widely tunable complex-coupled distributed feedback laser with photonic Crystal mirrors and integrated optical amplifier

We report the development of a current-controlled widely tunable laser diode based on InP with photonic crystal mirrors and an integrated amplifier section for stabilized power output. The laser consists of three longitudinally coupled ridge waveguide cavities that are coupled through photonic crystal mirror segments. A laterally defined binary superimposed grating provides complex-coupled distributed feedback into two of the laser cavities. The wavelength can be switched over a range of 26 nm. Through adjustment of the current into a third amplifier section, the output power can be stabilized over the tuning range of the laser.

Integration of active and passive photonic-crystal-based optoelectronic components

Two examples of integrating active and passive photonic crystal devices are discussed. A first example integrates two tunable laser diodes with a passive photonic crystal Y-coupler structure. The tunable laser diode is defined by two photonic crystal channel waveguides that are coupled longitudinally through photonic crystal coupling sections. The waveguides have slightly different lengths and hence exhibit slightly different longitudinal mode spacings. The front and rear reflectors are realized by photonic crystal mirrors with lattice dimensions chosen to achieve the desirable mirror reflectivities. Secondly, a passive superprism structure is discussed that can be integrated with an array of photo diodes to build highly integrated receivers for optical networks.

Technology and properties of photonic-crystal-based active and passive optoelectronic devices

We have investigated tunable photonic crystal waveguide lasers and their integration with a photonic crystal based combiner. The devices were fabricated on a layer structure with active and passive sections. The lasers are formed in the active part and consist of two longitudinally coupled photonic crystal waveguide segments. Photonic crystals based waveguides and a combiner, both defined in the passive sections, are used to direct the light of the two sources into a single output waveguide. Tuning over a 30 nm range is demonstrated. The two sources can be operated independently, allowing the simutaneous transmission of two freely selectable wavelengths.