This paper reports the feasibility of optical coherence tomography (OCT) technology for inspection of bonding quality of microfluidic devices in manufacturing environments. A compact optical-fiber-based OCT is developed and its measurement performance is characterized. A series of microfluidic devices respectively bonded by adhesive tape, thermal method, and oxygen plasma, are inspected. The defects of geometry deformation and sealing completeness are emphasized during measurements. Based on the inspection results, some discoveries related to the production of microfluidic devices are discussed.
We present a way to identify distortions of transparent
micro-patterned substrates using a desktop document scanner and
a set of image processing routines. The method requires neither expensive optical equipment nor precise positioning of
the part. It is therefore ideally suited to rapid process monitoring. A 5000-dpi imagesetter is used to print a square
reference grid of lines having a known pitch ~100 μm. This reference pattern is used to produce a hard stamp that is
subsequently embossed into a sheet of thermoplastic polymer. The pattern transferred to the polymer may include
distortions resulting from contraction of the sheet after separation from the stamp. To measure these distortions, the
embossed polymeric part is placed on a document scanner. The reference grid is laid on top of the part and rotated by
hand until moire fringes are seen. At least two scans are made, each with a different relative reference-part rotation. For
each scan, the orientation of the part relative to the reference grid may be arbitrarily chosen within an allowable range of
a few degrees. These orientations may be extracted from the captured images, and, together with the moire fringes'
orientations and spacings, provide enough information to obtain the part's distortions. Estimates of part strains may be
improved, at the expense of measurement time, by capturing more images. The approach can detect isotropic shrinkage
of the part with a strain resolution ~10-3.
Microfluidic devices play a crucial role in biology, life sciences and many other fields. Three aspects have to be
considered in production of microfluidic devices: (i) material properties before and after processing, (ii) tooling and
processing methodologies, and (iii) measurements for process control. This paper presents a review of these three areas.
The key properties of materials are reviewed from both the production and device performance point of views in this
paper. The tooling and processing methodologies considered include both the direct tooling methods and the mold based
processing methods. The response of material on the production parameters during hot embossing process are simulated
for process control and product quality prediction purpose. Finally, the measurements for process control aspect discuss
different measurement approaches, especially the defect inspection, critical dimensional measurements, bonding quality
characterization and checking functionality. Simulation and experimental results are used throughout the paper to
illustrate the effectiveness of such approaches.
Polarization mode dispersion (PMD) is becoming major system impairment in high speed and long distance optical fiber transmission systems. As the bit rate climbs from 10 to 40Gb/s per channel and beyond, optical pulses are increasingly distorted by 1st and higher order PMD. We report on the experimental mitigation of pulse distortion due to 1st and higher order PMD effect based on one tunable differential group delay (DGD) element, which is a compact concatenation via six magneto-optic polarization rotators (Faraday rotators) of six YVO4 birefringence crystals whose lengths decrease in a binary power series. Two different experiments are carried out, with and without an electric polarization controller set before the tunable DGD element. Optical pulses with width of 41ps are broadened and distorted by the PMD emulator which generates 1st and 2nd order PMD with mean magnitude of 30.28 ps and 483.31 ps2, respectively, and then reshaped by the compensation device. Degree of polarization (DOP) is used as the feedback signal, which is significantly increased from around 0.15 to around 0.85. The experiment results show that pulse distortion due to 1st and higher order PMD is successfully mitigated.
Polarization mode dispersion is becoming major system impairment in high speed and long distance optical fiber transmission systems. As the bit rate climbs from 10 to 40 Gb/s per wavelength division multiplexed channel and beyond, optical pulses are increasingly distorted by polarization mode dispersion effect. We report on polarization mode dispersion compensation experiments in 10 Gb/s, 40 Gb/s optical communication systems. The polarization mode dispersion compensator used in the experiments is a compact variable differential group delay element base on concatenation via six magneto-optic polarization rotators (Faraday rotators) of six YVO4 birefringence crystals whose lengths decrease in a binary power series. Feedback scheme is used to optimize the performance of polarization mode dispersion compensation, using degree of polarization as the feedback signal. In the experiments in 10 Gb/s and 40 Gb/s optical transmission systems, eye-diagrams and bit error rate curves of the code sequences before and after polarization mode dispersion compensation are analyzed. The experimental results demonstrate that the polarization mode dispersion effect induced by the polarization mode dispersion emulator is feasibly mitigated. Separate experiment to reshape the 39ps pulses distorted by polarization mode dispersion is also carried out. The incident optical pulses with width of 39ps are broadened and distorted by polarization mode dispersion effect and then reshaped by the polarization mode dispersion compensator. The relationship between the feedback signal degree of polarization and differential group delay is also analyzed.
The PMD at a wide range of optical frequencies and statistics of all-order PMD, especially the first-, second- and third-order PMD, of a n-segment DGD units combination separated by PCs or PRs are fully analysed with Poincare sphere, Mueller matrix and Fourier transform methods. The results show that, to simulate all-order PMD in DWDM systems as truly as possible, the number of n should be as large as possible, the least value of 4 is preferred. The DGD units should be variable or unequal. Choosing PC or PR just affects the probability density function of PMD when n is not too much and the DGD values of the DGD units are unchangeable. At last, a simple, practical, and low cost all-order PMD emulator in DWDM systems is proposed.