An optical spatial differentiator based on subwavelength high-contrast gratings (HCGs) is proposed experimentally. The spatial differentiation property of the subwavelength HCG is analyzed by calculating its spatial spectral transfer function based on the periodic waveguide theory. By employing the FDTD solutions, the performance of the subwavelength HCG spatial differentiator was investigated numerically. The subwavelength HCG differentiator with the thickness at the nanoscale was fabricated on the quartz substrate by electron beam lithography and Bosch deep silicon etching. Observed under an optical microscope with a CCD camera, the spatial differentiation of the incident field profile was obtained by the subwavelength HCG differentiator in transmission without Fourier lens. By projecting the images of slits, letter “X,” and a cross on the subwavelength HCG differentiator, edge detections of images were obtained in transmission. With the nanoscale HCG structure and simple optical implementation, the proposed optical spatial differentiator provides the prospects for applications in optical computing systems and parallel data processing.

The hyperbranched polytriazole (hb‐PTA) containing second‐order nonlinear optical chromophore was synthesized through “A2 + B3” approach based on “click reaction.” Its corresponding linear analogue (l‐PTA) was prepared for comparison. The hb‐PTA has better solubility in common organic solvents than the l‐PTA. Both the polymers exhibit good thermal stability with 5% weight loss temperatures over 260 °C. The poled film of hb‐PTA exhibits much higher second‐harmonic coefficient (96.8 pm/V) than that of l‐PTA (23.5 pm/V). The three‐dimensional spatial isolation effect resulting from the highly branched structure and the crosslinking of the terminal acetylene groups at moderate temperature play important roles in the enhancement of optical nonlinearity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1140–1148, 2008

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BACKGROUND: The 'A 2 + B 3 ' type of polymerization has been demonstrated to be an alternative route towards hyperbranched polymers. Some highly crosslinked hyperbranched polymers have been prepared via copper(I)catalyzed click reactions of multivalent azides and alkynes. To obtain hyperbranched polymers without gelation and develop the A 2 + B 3 type of polymerization based on click reactions, the specific reaction conditions need to be investigated. RESULTS:In this work, a hyperbranched polytriazole (hb-PTA) was synthesized through the A 2 + B 3 approach using a click reaction. 4-N,N -bis(2-azidoethyl)amino-4 -nitroazobenzene and 1,3,5-tris(alynyloxy)benzene were synthesized for use as the A 2 and B 3 monomers, respectively. This was a 'one-pot' polymerization carried out using a slow-addition method. The obtained hb-PTA was soluble in common organic solvents. The molecular structure was characterized using 1 H NMR, Fourier transform infrared and gel permeation chromatography analyses. The degree of branching of hb-PTA was determined to be around 0.50. CONCLUSION:The hb-PTA was successfully synthesized via the A 2 + B 3 approach based on a click reaction. The polymerization conducted in dilute solution adopting slow addition of A 2 to B 3 resulted in hb-PTA in the absence of gelation. The obtained hb-PTA exhibited high thermal stability.