Ridge-Type Zn-Indiffused Mach-Zehnder Modulator in LiNbO3

Integrated Mach-Zehnder modulators are essential components in optical communication systems and waveguide sensors [1]. For the demands on high-speed and low driving voltage operations, commercially available optical modulators were fabricated with Ti indiffusion (TI) in LiNbO3. As we know, the TI modulators have such advantages of low propagation and small polarization dependent losses. However, the typical diffusion temperature (> 1050◦C) and diffusion time (> 8 hr), still make low product throughput and out diffusion suppressing is needed. Moreover, the photorefractive characteristics not only cause the unstable bias voltage of modulators used in the short wavelengths (< 0.8 μm) but also limit the conversion efficiency of wavelength converters via nonlinear optics [2]. Recently, an alternative Zn indiffusion (ZI) process has been proposed to make waveguide devices exhibiting higher damage-resistant, which use for the efficient wavelength converters and waveguide lasers [3], [4]. There, the wavelength converters employing the mechanism of difference frequency generation (DFG) are key elements in wavelength-division-multiplexed (WDM) and alloptical time-division-multiplexed (OTDM) networks [3], [5]. In this paper, a ridge-type Zn-indiffused Mach-Zehnder modulator operating at 1.55 μm wavelength is demonstrated on a z-cut LiNbO3 substrate for the first time. The results show that the overlap integral factors between electrical and optical fields can be improved from 0.37 to 0.43 with a ridge structure of 1.7 μm etched depth. Also, the values