Traveling-wave modulator test results: TW-2.

摘要

This device is a single Mach-Zehnder interferometer with two independent electrode sets, one for DC bias and one for RF modulation. The operating wavelength is 0.83 (mu)m. The RF electrodes are a ''coplanar waveguide'' emission line with approximately a 5 (mu)m gap and 20 (mu)m center electrode width, made with 3.0 (mu)m thick gold. There is a 3500 (Angstrom) thick SiO(sub 2) isolation layer. The electrodes are coated with a few microns of polyamide to increase their breakdown voltage. The characteristic impedance of this transmission line is about 22 (Omega). The modulator length is 4.0 mm, and the transmission line extends approximately 16 mm beyond this before termination by two 40 (Omega) BeO chip resistors in parallel. The extra length is to damp out reflections from the termination at high frequencies. The DC resistance of the electrode is 10 (Omega), so the DC input impedance is about 30 (Omega). The DC and RF connections use the Wiltron K connector, which is compatible with SMA and 3.5 mm connectors. The input fiber is York 125 (mu)m OD HB800/2 polarization-preserving fiber (obtained from LANL). The output fiber is 125 (mu)m OD single-mode fiber (obtained from LANL). The fiber-to-device bond was made by putting the fibers in silicon V-grooves and cementing the V-grooves to the LiNbO(sub 3) with no other support (strain relief is provided near the fiber exit from the package). This method has been found to be mechanically rugged and wig withstand temperatures of 0 to 120 (degrees)F (this was tested with short duration cycling only). The package has been hermetically sealed, evacuated, and backfilled with dry nitrogen at 1 psig.