Ultra-high speed electro-optic modulators have been fabricated and tested with integrated electrode transitions for W-band operation. These devices use new polymer systems that are low loss, stable and have electro-optic coefficients exceeding that of LiNbOa.Recently we have fabricated and tested modulators that have worked as high as 113 GHz. These were prototype devices, based upon DR19 were contacted using high frequency coplanar probes. In this paper we have extended these measurements to integrated optical modulators which directly couple to W-band waveguide. Further, we have fabricated these devices from a new class of chromophores that have been designed to have a shape that reduces dipole-dipole pairing. This leads to structures that have large loading densities and relatively high electro-optic coefficients. In particular, this paper reports results with APII and FTC materials.The materials that we have been working with have also been developed with an additional emphasis on high thermal stability and low optical loss. These typically are about 1 dB/cm and are only slightly higher in going from 1.3 to 1.5 pm. The r33 for these materials range up to 55 pm/volt with V, as low as 4.5 volts.The basic structures are shown in Fig. 1. Note that it is very straightforward to make arrays of modulators with polymer materials. Fig. 1: Photograph of Integrated W-band Modulator (a) before insertion and (b) after insertion into rectangular waveguide.
Recent advances in polymer materials and in the fabrication of polymer integrated optical structures have made possible some significant improvements in the performance of high speed traveling wave electro-optic modulators and in the achievement of practical three dimensional integrated optical circuits. Hiah Speed Travelina Wave ModulatorsProfessor Dalton's group has developed a new electro-optic polymer using a high-pp choromophore based on a novel tricyanobutadiene acceptor incorporating a furan-derivative ring; FTC (2-dicyanomethylen-3-cyano-4-(2-[frans-(4-Nl N-diacetoxyethyl-amino) phenylene-3, 4-dibutylthien-51vinyl) -5 3 dimethyl -2, 5-dihydrofuran). In addition to a high EO coefficient, the chromophore is structured so as to reduce the electro-static interaction between the chromophores may reduce the achievable EO coefficients. The FTC chromophore showed a large EO effect (rS > 55 pmN @ 1060 nm) in a PMMA-doped polymer system, excellent solubility (which is essential for materials processibility), high chromophore thermostability (> 300 "C), and relatively short wavelength h,,, resulting in a low optical loss @ 1300 nm (< 1 dB/cm). To make a device quality material with higher thermal poling stability, Dalton's group has synthesized hydroxyl functionalized FTC monomers for incorporation into a thermoset polyurethane. Two crosslinkers;. toluene diisocyanate (TDI) and triethanolamine (TEA), used to achieve the aligned three dimensional EO polyurethanes with the R-C covalently attatched Traveling wave Mach Zehnder modulators have been fabricated using this new polymer. Good processing yield has been achieved and Vn of 4.5V @ 1300 nm have been measured. We will review the fabrication techniques used, the selection of cladding and substrate materials, and electrode design. The modulator response to 40 GHz and been measured and shows only small variations due to the RF coupling as shown in Fig 1. Earlier modulators using similar structures were measure at frequencies over 100 GHz.Low loss fiber packaging of the modulators has been achieved using small 3 pm core fiber. The latest results on the RF response, optical insertion loss, and thermal stability will be presented.(TS-PU-FTC). Three Dimensional lntearated OpticsConventional two dimensional guided wave integrated optics provides a reliable and structurally stable method for interconnecting optical devices for photonic circuits and for 3 0-7803-4947-4/98/$10.00 01 998 IEEE
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