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    A Ymeti@tn · Utwente · A Nl · J S Ymeti · J Kanger · R Greve · P V Wijn · Lambeck
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    ABSTRACT: Your picture An integrated channel waveguide Y-splitter with two output parallel branches is used as the basic optical component for building of the integrated optical Young Interferometer. Integrated channel waveguide is realized on SiON technology as has been developed at MESA+. The ridge-type channel waveguides have a ridge height of 1 nm and channel width of 2 m, being mono-modal both in transversal and lateral directions In order to get rid of the slab light a bend input waveguide is implemented. The sensing window is realized on the top of the core layer of the measuring channel by locally removing the PECVD Silicon Oxide layer using the wet etching procedure. for the TE polarized light with a wavelength of 647 nm. The objective of the project is to develop a highly sensitive Multichannel Integrated Interferometer Immunosensor on top of a Si-wafer. New aspects of a MULTICHANNEL device are: 1. In one experiment, a complete binding curve can be recorded by applying different analyte concentrations to different channels. 2. Different analyte molecules can be detected simultaneously by applying different receptor molecules for different channels. 3. One or more channels can be used as internal reference, e.g. for compensating non-specific adhesion of analyte molecules. PRINCIPLES The core-cover interface of an optical waveguide structure is coated with a receptor layer, which can selectively bind to a certain type of analyte molecule. When binding of an analyte occurs, an increase of the refractive index at the core-cover interface takes place, which is probed by the evanescent field of a guided mode. Consequently the propagation constant of the mode within the interaction length will be changed, and the resulting phase change can be measured accurately by using an interferometer. INTEGRATED OPTICAL YOUNG INTERFEROMETER The laser light with vacuum wavelength of 647 nm is end-fire coupled into the sensor chip by using a microscope objective with an NA of 0.65. A cylindrical lens is collimating two output dive-rgent beams within the plane of the sensor chip. The interference pattern is recorded by a Teli CS-3440 CCD camera, which has 767x575 pixels. The recorded interference signal is digi-tized with 12-bit resolution and is further analyzed by a personal computer. Signal processing consists of performing a 2D-Fast Fourier transform of the recorded image from which the phase information is extracted. A flow-through cuvette is used for applying liquid samples onto the sensing window of the device. RESULTS We have measured the response of the sensor to refractive index change between water and water in which a certain amount of glucose is dissolved. Water is flown through the cuvette before a new sample is introduced. Solutions of glucose in water with concentrations of 0.07, 0.14 and 0.21 % in weight were applied in the sensing area of the measuring channel in combination with water. The measured and theoretically calculated phase shifts are plotted versus the glucose concentration. Experimental results are in good agreement with the theoretical calculations. The measurements as has been realized up to now show a short-term phase resolution of 1.5x10 fringes, which corresponds to a refractive index resolution of 3x10 Long-term phase stability (drift) is about 1x10 fringes/h, corresponding to a refractive index change of 2x10 -5 -9 -3 -7 . . The stability can be further improved by having windows in both measuring and reference arms, the first provided with an active chemo-optical transducer layer, and the second with an inactive layer of similar thickness and refractive index. In this way, environmental changes like temperature drift will be canceled. The output parallel channels will be positioned at different distances from each other in such a way that channels of each pair are separated by a unique distance. Since in this way all spatial frequencies can be made different, it is possible to well-separate different peaks in the amplitude of the Fourier transformed interference signal. d p By looking at the same spatial frequency on the phase of the Fourier Transform, the phase shift between both channels of one pair can be monitored independently from the other channel pairs. ij ij Calculated interference pattern in case of a four-channel Young interferometer. Amplitude and phase of the Fourier transform in case of a four-channel Young interferometer.
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