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A photodefinable polymer of benzocyclobutene (BCB 4024-40) from Dow Chemical™ has been demonstrated as a waveguiding material in a new structure of optical wavelength filter. The filter structure is based on the combination of restricted interference and general interference schemes of multimode interference technique. The filter is capable in optical wavelength filtering particularly for 1550/1310 nm. Because of the photosensitive nature of the polymer, the chemical wet-etching fabrication technique needs to be adopted. For the purpose of laser coupling, a new facet polishing technique has been proposed and it is based on the combination of mechanical and chemical polishing. It is shown that the fabricated device works well with improved crosstalk of −15.7 dB (1310 nm) and −21.8 dB (1550 nm). © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1301–1313, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26781

A novel 1 A— 2 multimode interference (MMI) optical wavelength filter for 1310 and 1550 nm operation based on photodefinable BenzoCyclobutene (BCB 4024-40) polymer is demonstrated. The device is fabricated on BK7 glass substrate with thin layer of SiO2 as cover. A cost effective chemical etching technique is used in the fabrication process to take advantage of the photosensitive nature of the polymer. The filter length is significantly reduced by adopting the restricted MMI scheme, lower beat length ratio, and cascaded MMI couplers. At 1550 nm filtering operation, the measured crosstalk is -20.6 dB and at 1310 nm filtering is -14.4 dB. The measured insertion loss is around 3.2-3.5 dB for both ports.

The main objective of the study was to determine the kinetics of the polyphenol oxidation reaction in cocoa beans during air drying at various air temperatures and humidities. The temperatures used were between 40 and 60 °C and the relative humidities were between 50 and 80%. The higher the temperature and relative humidity of the drying air, the lower the amount of polyphenol residue in the cocoa beans, because of enzymatic oxidation of polyphenols. At higher drying temperatures, non-enzymatic oxidation of polyphenols could also occur. Computer simulation results gave rate constants for the polyphenol oxidation reaction (k 1 ) and the condensation reaction (k 2 ), at various air conditions, in the range of 0.055-0.200 and 0.136-0.155 h -1 respectively. The activation energies obtained for the polyphenol oxidation reaction were in the range of 27 800-30 312 J K -1 mol -1 . The reaction kinetics of the enzymatic browning reaction fitted a pseudo first-order reaction.

The fabrication and characterization process of BenzoCyclobutene (BCB 4024-40) polymer waveguides are described. The polymer film thickness for various coating speed and refractive index are measured by the method of prism coupling. A cost effective chemical etching technique is used in the waveguide fabrication process to take advantage of the photosensitive nature of the polymer. The waveguide loss is measured using the conventional cut back method which results on an average loss of 3.5 dB/cm.