Frequency-dependent propagation characteristics of coplanar waveguide electrode on 100 GHz Ti:LiNbO3 optical modulator

Wide-bandwidth lasers and modulators for RF photonics

“…If the length of the same device is increased to 3 cm, decreases to 3.5 V, but the electrical and optical bandwidths also decrease to 30 and 45 GHz, respectively. Recently, a careful loss measurements up to 110 GHz revealed that up to 20-GHz loss is dominated by conductor losses [59]. Above 20 GHz, dielectric and radiation losses become important.…”

“…Above 20 GHz, dielectric and radiation losses become important. The SiO buffer layer is found to have a loss tangent four times higher than that of the LiNbO substrate [59]. Therefore, the quality of this buffer layer needs to be carefully controlled.…”

Ultra-high-speed LiNbO3 modulators

“…The microwave index was effectively lowered to 3.8, and the modulation bandwidth is 12 GHz. Figure 11 shows the ridge structure developed by Noguchi et al, where the LiNbO 3 substrate was etched between the center conductor and the ground of the CPW electrode in the interaction region [11,12,33]. With this structure, they obtained not only velocity-and impedance-matching but also a low driving voltage because the microwave field is concentrated in the ridged section, where the optical wave propa- gates in the Ti-diffused waveguide.…”

“…The origins of the dielectric loss lie in both the LiNbO 3 substrate and the silicon oxide buffer layer. It should be noted that the contribution of the silicon oxide buffer layer to the dielectric loss is twice as large as that of the LiNbO 3 substrate because the microwave confinement factor in the buffer layer is more than 4 times as large as that in the substrate [12]. …”

“…The LiNbO 3 modulator has several features that make it suitable for use as a component in both TDM and WDM systems: It works at very broadband from DC to microwave or millimeter-wave frequency range [12], and its modulation characteristics, such as insertion loss, driving voltage (half-wave voltage), and frequency response, depend little on wavelengths from 1.3 to 1.5 μm. In addition, the frequency chirping of modulated optical signal is very small or almost zero.…”