Coupling the signal to the electrodes of an integrated electro-optical modulator with an array of antennas is used to velocity-match the modulation and optical waves, greatly extending the length-to-modulation frequency product of the modulator. In addition, antenna coupling eliminates the parasitic elements associated with coax connectors, matching trainsformers and bond wires. This paper summarizes the results obtained to date with this techinique at 20 to 100 GHz, with phase modulators, Mach-Zehnder modulators, and delta-beta directional coupler modulators.
AGENCY USE ONLY (Leaveblank)2. REPORT DATE MARCH 2001 REPORT TYPE AND DATES COVEREDFinal Report Feb 96 -Jun 00 TITLE AND SUBTITLE WAVE-COUPLED MILLIMETER-WAVE ELECTRO-OPTIC TECHNIQUES AUTHOR(S)William B. Bridges, Lee J. Burrows, and Uri V. Cummings FUNDING NUMBERSC -F30602-96-C-O020 PE-63726F PR-2863 TA-92 WU-81 PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)California Institute of Technology Office of Sponsored Programs 1201 East California Blvd, MC 213-6 Pasadena CA 91125 PERFORMING ORGANIZATION REPORT NUMBERN/A SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)Air 12b. DISTRIBUTION CODE ABSTRACT (Maximum 200 words)This report details results on two antenna-coupled millimeter-wave electro-optic modulators, the slot-vee antenna-coupled modulator and a 94 GHz directional coupler modulator. The slot-vee-coupled modulator gave 0.17 m-squared per Watt sensitivity, but known defects in the chip imply much better performance is possible. The 94 GHz directional coupler improvements anticipated were not realized due to fabrication problems. A detailed theoretical study of the effects of velocity mismatch on linearized electr-optic modulators was made and the results published. A key result was that directional-coupler based modulators were found to be significantly more easily degraded than some Mach-Zehnder-based modulators. An experimental study of bias drift in electro-optic modulators was made and protons were determined to be the cause. Several inventions were made to reduce or eliminate proton-caused bias drift. Gain of Y-fed DCM below 6 = 1.5 n 42 SUBJECT TERMSComparison of vee and slot-vee antennas on a dielectric substrate 46Schematic drawing of slot-vee antenna elements overlaying one waveguide of a Mach-Zehnder modulator 48Schematic view of the slot-vee modulator 49Schematic drawing of the slot-vee modulator and its microwave feed system 50Antenna mask for 5 slot-vee modulators 51Assembly drawing of modulator support and feed structure 54Photograph of slot-vee modulator test setup with fiber-input coupling and lens output coupling 55 in List Of Tables Table 6.1 Comparison of Experimental and Theoretical Diffusion Depths 78 IV EXECUTIVE SUMMARYThis report documents the progress made in improving antenna-coupled modulators for mmwave, analyzing linearized modulators, and studying and countering bias drift in electro-optic modulators.We demonstrated for the first time a modulator at 24 GHz using the slot-vee antenna coupled arrangement suggested by F. T. Sheehy in a previous Rome Laboratory contract. The actual performance was measured as 0.17 m 2 /Watt, comparable to other antenna coupled modulators we have built. However, known defects in this particular chip suggest that future performance would be much better, comparable to commercial low microwave frequency modulators.Our attempts to correct the known defects in the 94 GHz directional coupler modulator first demonstrated in the previous contract were unsuccessful, due to difficulties in developing the skills needed to transfer the fabrication tec...
We have demonstrated slot vee antenna-coupled electro-optic (Mach-Zehnder amplitude) modulators at 24 GHz (optical wavelength 1 .3 tim). The slot vee antenna design allows for a more robust microwave signal feed into the LiNbO3 chip, where the modulator itself acts as a slab waveguide for the microwave signal. The antenna-coupled design overcomes the velocity mismatch problems inherent in LiNbO3 traveling-wave electro-optic modulators.
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