E. Voges

Periodically structured metallic substrates for SERS

Abstract The detection of organic traces by surface-enhanced Raman scattering (SERS) requires rough metallic substrates with structures in the nanometer range. Regular metallic structures generated by electron-beam lithography are better reproducible than electrochemical roughened surfaces, island films or films over deposited particles. The lithography also allows optimisation of the dimensions of these structures. The SERS enhancement of optimised periodic structures was found to be at least one order of magnitude larger than that of island films.

A new low-power microwave plasma source using microstrip technology for atomic emission spectrometry

A new low-power, compact microwave-induced plasma source for applications in atomic emission spectrometry at atmospheric pressure using microstrip technology is described. The gas channel of about 1 mm2 is integrated in a fused silica dielectric wafer. The microstrip transmission lines are fabricated by sputtering and electro-plating. For example, a unit operates at an input power of 15 W with an argon gas flow of about 500 ml min-1 at atmospheric pressure. Rotational (OH) and excitation (Fe) temperatures of 650 K and 8000 K, respectively, were measured at these conditions. The emitted radiation can be taken up by an optical fibre positioned in the plasma-gas channel thus enabling an axial observation and coupling to a miniaturized spectrometer. The first devices showed an operation time of at least several hundred hours. Further investigations will lead to even smaller dimensions and lower power consumption and open the way for integrated microwave plasma sources with low detection limits as integrable parts of miniaturized total analytical systems applications.

Bistable micromechanical fiber-optic switches on silicon with thermal actuators

Abstract A new bistable moving-fiber switch for applications in optical communication systems is developed by employing advanced bulk silicon micromachining. The bistable switch utilizes actuators based on thermal expansion and the bimetal effect. Switches and switch arrays are successfully fabricated and tested. Due to the low number of process steps and the high yield and reliability, the process technology is suitable for low-cost single- and multi-mode fiber optic switches. A typical fiber-to-fiber insertion loss of 2±0.5 dB (single-mode fibers at 1300 nm wavelength, including MT-connector losses of typically 0.5–1.5 dB) is achieved in an array of 12 switches. The cross talk is below the detection limit (

X-ray refractive planar lens with minimized absorption

Silicon refractive planar parabolic lenses with minimized absorption were fabricated by a combination of photolithography and dry-etching techniques. Focusing and spectral properties of the lenses were studied with synchrotron radiation in the energy range 8–25 keV at the European Synchrotron Radiation Facility. A focal spot of 1.8 μm with a gain of 18.5 and transmission of more then 80% was measured at 15.6 keV. The spectral characteristics were analyzed taking into account material dispersion and photon-energy attenuation in the hard x-ray range.

All-silicon bistable micromechanical fiber switch based on advanced bulk micromachining

Bulk silicon micromachining is used to fabricate bistable optical fiber switches. The switches are based on a silicon device consisting of an actuator for fiber movement and a V-groove fiber clamp for bistable operation. The complete mechanical structures including thermal actuators are etched into standard silicon wafers using anisotropic wet etching in KOH. While switching is caused by asymmetric thermal expansion of a U-shaped silicon cantilever, the fiber clamp is driven by the bimaterial effect. The efficient process technology allows a low cost batch fabrication of these devices. The switches exhibit an insertion loss <1 dB and a crosstalk of <-60 dB using standard single-mode fibers. A switching power below 1 W is required during switching.

Dynamics of electrooptic bistable devices with delayed feedback

The dynamic behavior of electrooptic bistable devices with delayed feedback is investigated theoretically and experimentally. The operation principle of the system is analyzed by the method of iterated maps. Stable, bistable, periodic, higher periodic, and chaotic solutions are discussed and realized experimentally by using an integrated Mach-Zehnder interferometer on LiNbO 3 as a basic nonlinear element. Taking into account the periodic modulator characteristic, the application of this device as a simple and fast bistable and monostable multivibrator is demonstrated. In addition, the synchronization properties of the astable multivibrator are investigated.

Low-loss fiber-matched low-temperature PECVD waveguides with small-core dimensions for optical communication systems

Plasma-enhanced chemical vapor deposition (PECVD) offers a simple way of fabricating (doped) silica layers on silicon. A new design of the waveguide core allows low-loss fiber matched waveguides with low birefringence without high-temperature annealing. The increased loss of doped plasma deposited silica due to hydrogen incorporation is overcome by reducing the core dimensions and increasing the refractive index contrast. The waveguides can easily be fabricated using standard PECVD technologies and resist masked reactive ion etching (RIE) etching. Integrated optical devices such as 1/spl times/8 power splitters, 1300/1550-nm wavelength multiplexers and thermooptical switches were successfully fabricated and tested.

Bulk silicon micromachining for MEMS in optical communication systems

Crystalline silicon has become more and more important for optical MEMS. The increased need of bandwidth in optical communication networks has led to a number of new optical MEMS devices such as moving-fibre and moving-waveguide switches, optical cross-connects, mirrors, resonators, optical benches and fibre alignment structures which are based on wet anisotropic micromachining techniques and deep reactive ion etching of single-crystal silicon. The excellent mechanical properties as well as the optical properties and orientation-dependent etching behaviour of crystalline silicon attract attention for reliable optical components based on surface micromachining, silicon-on-insulator, integrated optics and bulk micromachining. Anisotropic etching is especially useful for the batch fabrication of large opto-mechanical devices with sub-μm precision.

Three-dimensional semi-vectorial wide-angle beam propagation method

A wide-angle Beam Propagation Method (BPM) based on the series expansion technique is proposed. The method employs a finite difference approach and allows extremely dense discretizations. A theoretical analysis supporting this numerical technique is demonstrated. Semi-vectorial formulations are included in this BPM algorithm. It is easily applicable to 3-D simulations. Following an accuracy test with a 2-D problem, several 3-D examples for quasi-TE and -TM modes are demonstrated. >

FLOX—an oxygen-flux-measuring system using a phase-modulation method to evaluate the oxygen-dependent fluorescence lifetime

The direct relationship between the oxygen supply by skin blood flow and oxygen uptake (O 2 uptake) through the skin could be of importance for the diagnosis of circulatory disturbances and their consequences. A new measuring system has been developed to obtain simultaneously at three places the local O 2 uptake through the skin. It uses the principle of the O 2 -flux optode to measure the O 2 flux into the tissue. This luminescence-based-O 2 sensor has the well-known advantages (1) to be permeable for the analyte O 2 , (2) to be flexible to cover larger areas of the surface and (3) not to consume the analyte O 2 . To avoid the problems inherent to fluorescence intensity measurements the FLOX system (an oxygen-flux-measuring system) uses a phase-modulation measuring method to evaluate the oxygen-dependent fluorescence lifetime. The evaluation is based on the quadrature or incoherent envelope detection, which enables both phase angle (lifetime) and amplitude (intensity) to be received. The three sensor modules of the system consist of a light-emitting diode (LED) (λ peak = 470 nm) as light source, optical filters, a bifurcated glass fibre bundle to transport the light for excitation and emission, a photomultiplier tube as a detector and additional circuits. The main frequency generation of the modulation and reference signals is performed by a direct digital synthesizer (DDS) with dual output. The system is PC-based and works at modulation frequencies in the range of 5-900 kHz. Depending on the used indicator dye and the measuring purpose, the frequency is adjusted for the optimum phase angle range. The first O 2 -flux measurements on human skin with the multilayer O 2 -flux sensor and reproducibility measurements with the FLOX system prove the ability of the method.