Jan Ingenhoff

Integrated optical Mach-Zehnder biosensor

We present measurements on biomolecular surface multilayers using an integrated optical sensor based on the Mach-Zehnder interferometer (MZI). The sensor design is unique in that it incorporates a three-waveguide coupler structure at the interferometer output which gives advantages in terms of signal referencing and in establishing and maintaining a sensitive operating point. The sensor performance is characterized with respect to bulk superstrate index and by the formation of multiple protein adlayers using a biotin-avidin-based biochemical system. The detection limit for protein loading is estimated as 5 pg/mm/sup 2/.

A gas sensor based on an integrated optical Mach-Zehnder interferometer

Abstract In this paper we demonstrate a sensor system for measuring gaseous compounds using an integrated optical Mach-Zehnder interferometer (IO-MZ chip). One of the surface waveguide arms of the IO device is covered with a polysiloxane layer, sensitive to organic solvents. The refractive index of the polymer layer changes continuously when exposed to the vapours of such solvents. The influence on the evanescent field of the guided mode causes a change in the optical pathlength in the covered arm. Incoupled light of a semiconductor laser diode results in an interference pattern at the output of the IO-MZ chip. The phase shift of the signal is dependent on the gas concentration and the solvent type. We have determined the values for some hydrocarbons, chlorohydrocarbons and aromatic compounds. The extremely short response time of the system allows it to be used like a gas chromatographic detector. The applicationn of Maxwells equations for the propagation of light in waveguides offers a simulation of the interference signals. By this means, the experimental signal obtained can be correlated to changes in refractive index of the polymer layer. The dependence of the interference patterns on wavelength is explained. White light interference is obtained by use of a xenon lamp.

Integrated optical Mach-Zehnder interferometers as simazine immunoprobes

Abstract Immunoassay has become a versatile tool in several fields of analytical chemistry. We describe the characterization and the application of different integrated optical channel waveguide Mach-Zehnder interferometers (MZIs) as label-free immunoprobes. The performance of the classical MZI is compared with that of a modified structure which incorporates a 3 × 3 coupler. Characterization of the devices demonstrates a dramatic improvement gained by using the 3 × 3 coupler. Two main advantages are achieved by the modified device. First, the possibility of referencing the output signal allows the elimination of signal fluctuations due to coupling and light-source instabilities. An increase of the signal-to-noise ratio by a factor of up to 10 is achieved. Secondly, the phase shift between the three outputs allows unambiguous detection with optimum sensitivity. For the detection of the herbicide simazine, the functional properties of the transducer surface are optimized by an appropriate chemical modification. Using this improved device, a simazine immunoassay has been carried out with a test midpoint of 0.3 ppb and a detection limit of approximately 0.1 ppb. The excellent performance, established manufacturing techniques and the potential for simplification and parallelization make the device attractive for further development.

Direct monitoring of antigen-antibody interactions by spectral interferometry

Abstract Spectral interferometry as a tool for on-line monitoring of immunoreactions is described. The setup consists of a light source, a thin transparent light interference layer as the sensing interface and a diode array spectrometer. Optical coupling is achieved by means of a bifurcated fiber optics. The basic principle is the measurement of the reflection spectra perpendicular to the sensing film. Incident light is partially reflected at the adjacent and remote surfaces of this film. The reflected partial beams show interference resulting in an interference spectrum. Deposition of a layer of protein at the interface during an immunoreaction changes the reflected spectrum. If the refractive indices of film and protein layer are matched, the change in the interference spectrum can be calculated as an increase in the thickness of the film. The reaction of rabbit-IgG with anti-rabbit-IgG on polystyrene shows high specificity. All steps of the test protocol can be clearly identified by changes in layer thickness. Quantitative evaluation of concentration dependency shows a linear correlation between antibody concentrations and initial rate of thickness increase. Investigated concentrations range from 0.5–25 μg/ml. Data can be calculated from a time interval of 100 s incubation time, indicating the capability of this rapid label-free system.

Modeling and properties of an ion-exchanged optical variable attenuator

The optical signal power needs to be regulated at some locations in transmission lines. That can be done with the help of optical variable attenuators (OVA), devices which allows for the control of their insertion loss. This work describes the design and properties of some OVAs fabricated by the ion-exchange technique. The OVA functionality relies on a Mach-Zehnder structure, where the output optical intensity is tuned via the change in optical path along one of the two interferometer arms. Here, the optical path is varied through thermo-optic effect (change of refractive index with temperature). Modelling is first addressed: a mostly qualitative theoretical investigation is used to clarify how the fabrication parameters (burial depth and Mach-Zehnder arm separation distance) can be related to the OVAs properties (attenuation dynamic, switching power, settling time, PDL). Properties of fabricated OVAs are presented in a second part. They are compared with other existing products. The relationship between fabrication parameters and properties is also re-examined in light of these results.

Spectral interferometric sensors for gases and liquids using integrated optical devices

Investigations for a sensor application with an integrated optical (IO) interferometric arrangement are presented. One of the two waveguide arms of an IO-Mach-Zehnder- interferometer is covered with a thin layer of polysiloxane (superstrate), which is sensitive to hydrocarbons. The dielectric IO-devices are fabricated by IOT. Gases of organic compounds including halogenated and non-halogenated hydrocarbons cause a change of the polysiloxans refractive index followed by an increase or decrease of the effective refractive index of the covered waveguide arm. The resulting phase shift between the guided light in the measuring and the reference arm depends on the detection wavelength and the concentration of gas. Using an LED as the light source the spectral interferogram becomes observable and so order and phase of the signal can be determined. The aim of this work is the development of a reversibly working, miniaturized sensor with a short response time. The advantages of spectral observation of the interference are discussed. A comparison between measured and calculated spectral interference signals is given.