Integrated Mach-Zehnder interferometers (MZIs) based on flexible polymer materials have been demonstrated as evanescent field sensors for the detection of refractive indices and molecule concentrations. The used application of a measurement window in classical MZIs is difficult in a roll-to-roll fabrication process. We have previously demonstrated foil-based asymmetric MZIs with different widths in sensing and reference arm which do not need a measurement window. Here we present the use of a multimode interference structure (MMI) inserted into the sensing arm of the interferometer to increase the sensitivity. We consider the expected interference signal from numerical simulations and optimize the system in terms of sensitivity, dimensions and absorption losses. The fabricated MMI-MZI foils are tested experimentally to demonstrate the function of the MMI-MZI system by applying water/glucose solutions with different refractive indices.
Two new design concepts for all-polymer-based integrated optical Mach-Zehnder interferometers in foil as chemical or bio-chemical sensors are presented. Fabricated with hot-embossing and printing techniques, these all polymer optical components are designed for low-cost fabrication and yield highly sensitive response to external refractive index changes. Compared to traditional semiconductor based systems, these polymer sensors do not need the interaction window and do not require a cleanroom for fabrication. The optical response of the asymmetric interferometers to temperature variations is determined theoretically and compared for two designs. Using the designed asymmetric interferometer, a chemical micro-fluidic test system with temperature controller experimentally demonstrates the sensors’ temperature characteristics.
In contrast to established semiconductor waveguide-based or glass fiber-based integrated optical sensors, polymerbased optical systems offer tunable material properties, such as refractive index or viscosity, and thus provide additional degrees of freedom for sensor design and fabrication. Of particular interest in sensing applications are fully-integrated optical waveguide-based temperature sensors. These typically rely on Bragg gratings which induce a periodic refractive index variation in the waveguide so that a resonant wavelength of the structure is reflected.1,2 With broad-band excitation, a dip in the spectral output of the waveguide is thus generated at a precisely-defined wavelength. This resonant wavelength depends on the refractive index of the waveguide and the grating period, yet both of these quantities are temperature dependent by means of the thermo-optic effect (change in refractive index with temperature) and thermal expansion (change of the grating period with temperature). We show the design and fabrication of polymer waveguide-integrated temperature sensors based on Bragggratings, fabricated by replication technology on flexible PMMA foil substrates. The 175 μm thick foil serves as lower cladding for a polymeric waveguide fabricated from a custom-made UV-crosslinkable co-monomer composition. The fabrication of the grating structure includes a second replication step into a separate PMMA-foil. The dimensions of the Bragg-gratings are determined by simulations to set the bias point into the near infrared wavelength range, which allows Si-based detectors to be used. We present design considerations and performance data for the developed structures. The resulting sensor's signal is linear to temperature changes and shows a sensitivity of -306 nm/K, allowing high resolution temperature measurements.
Integrated Mach-Zehnder interferometers (MZI) based on semiconductors or glasses have been widely used as evanescent field sensors for the monitoring of liquid or gas concentrations. In these systems the upper cladding of the sensing arm is removed partially to form an interaction window by means of subtractive fabrication techniques like etching. The use of polymer materials implicates new options and challenges. Polymers are tunable in terms of refractive index and viscosity offering a great flexibility in design and fabrication in a certain range. They enable a cost-efficient and large-scale roll-to-roll manufacturing of integrated optics on flexible foils as substrate material. The foils can be pre-patterned for example by hot-embossing. Additive steps such as printing a pattern or dispensing a homogeneous layer of liquid monomer material followed by a UV induced polymerization can be used to define the optical structure. However, when a large scale fabrication is required, the reliable production of small lateral structures and thin layers is challenging. Thus the fabrication according to the classical MZI design including an interaction window is difficult so that new design approaches are required. We present here the design and systematic evaluation of MZI sensors without interaction window based on polymer materials. The phase shift at the recombining Y-splitter of the MZI upon a refractive index change of an analyte, which serves as upper cladding of the entire system, is generated by a geometrical asymmetricity of the MZI. The waveguides in the sensing and the reference arm have different width leading to different effective refractive indices and sensitivities. We consider theoretically the expected interference signal and show results from numerical simulations of the whole system using commercial software. The simulations include the material as well as propagation losses and give an overall optimal system length.
We report on the fabrication of all-polymer inverted rib waveguides by hot-embossing and inkjet printing. Inkjet printing as an additive fabrication technique is well suited for a fast, selective and automated patterning of large areas. In general, the lines that can be printed with polymer inks can serve as waveguides themselves but the dimensions are too big to form single-mode waveguides. To overcome this limitation we apply hot-embossed grooves as assist structures to ensure the lateral confinement of the guided wave. We show the waveguide design, spin-coated single-mode waveguides as an intermediate result and finally inkjet printed all-polymer waveguides and their optical performance.
Integrated optical Mach-Zehnder interferometers (MZI) can be used as high sensitivity sensors through the
interaction of the evanescent field of the waveguide with liquids or gases surrounding the sensor. We present
here the design of polymer-based MZIs fabricated by hot-embossing and printing technologies. Simulations of an
integrated MZI system with regard to variations of the waveguide cross-section and the refractive indices of the
core layer are carried out to guarantee single mode behavior and optimize high sensitivity to external refractive
index changes of analytes. The simulation of propagation losses induced by the Y-coupleres is also presented.
Furthermore, transmission as a function of different interaction window lengths are also simulated on the entire
MZI structure using a mixture of water and ethanol as an analyte on the sensing arm. Finally, we calculate the
coupling efficiency of a laser diode into a tapered waveguide and estimate that a value of 30% is possible.
Illumination uniformity is one of the key specifications of lithography illumination system because of its strong influence on the critical dimension (CD) uniformity in optical lithography. Refractive microlens array (MLA) has been extensively adopted in lithography system to achieve highly homogeneous illumination field with less light loss relative to diffractive element. Off-line homogenization inspection of the MLA provides important data for entire system integration. It is still a challenge work to investigate the optical performance for such high-end MLA with large clear aperture and high sensitivity to the incident light parameters. In order to address these issues, subaperture stitching method has been proposed to be applied and studied in this work. The feasibility of this method has been verified by theoretical simulation of a diffracting homogenizer. In the experiment, a corresponding optical setup is constructed, and a crossed-cylindrical single-plate MLA has been tested. The experimental results are consistent with the simulation ones. It could be concluded that subaperture stitching method is a powerful method to evaluate the homogeneous performance of MLA.
Diffractive optical element (DOE) is used for off-axis illumination extensively in DUV lithographic system. A method for testing the optical performance of DOE using a visible laser is proposed to simplify the test process. In principle, the optical performance of DOE with a visible laser is analyzed with scalar diffraction theory and numerically simulated using MATLAB program. Compared with the DUV condition, the diffractive pattern distribution is enlarged proportionally with a zero-order spike under the visible laser condition. In experiments, the DOE is tested under He-Ne laser. Its far field diffractive pattern is compared and analyzed with the result tested under the working wavelength of 193.368nm. The shape, the opening angle, the azimuth angle and the pole balance coincide with the values tested in DUV condition. The usefulness of method is verified.
An optical detecting technique to identify bio-aerosol particles is proposed in this paper by normalized fluorescence
value which correlates to its size and intrinsic fluorescence. With the bio-aerosol detecting system developed, we test and
analyze three types of aerosols, while each of them contains fluorescent microspheres of a certain size. The result
indicates that different fluorescent microspheres containing the same fluorescent substances have the same normalized
fluorescence voltage to unit particle size in diameter. The normalized fluorescence value of other species aerosols is
tested for comparing. The research results can be applied to identification of bio-aerosols preliminarily.
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