We proposed a compact design of cascade Y-branch splitter devices. The new device consists of a 1×N branching
region and a fan-out region. The length requirement of this new design is analyzed, the results show that the device
length can be sharply cut, when N is larger than 8. As an example of this new structure, we designed an 1×16
branching splitter by K<sup>+</sup>/Na<sup>+</sup> ion-exchange in BK7 glass, the smallest S-bend radius is 30mm, and the total bends length
is about 20mm, it is 69% length of ordinary splitter.
A novel structure ofGaAs/GaAIAs multi-quantum well (MQW) traveling wave (TW) Mach-Zehnder modulator (MZM) with coplanar strips is proposed. This device uses n<sup>+</sup> heavy doped layer to obtain velocity match. Then the Method of Lines is applied to characterize the influence ofmetallization thickness and conductivity loss on the velocity match and impedance match. With optimum parameters ofthe structure, the bandwidth over 80GHz is obtained.
We design and analyze a novel low-loss symmetric Y-branch in Lithium Niobate by heavily annealed proton exchange (APE). In this design, a wide transitional waveguide is used between the input and two S-shape output waveguides, making the field match with the mode in the two output waveguides by intentionally generating second-order mode and radiation. By this method, optical power can be coupled into the two output waveguides with high efficiency. simultaneously , the minimum gap between the two output waveguides is 2.7 microns, thus the stem region of this Y-branch has no sharp taper and the fabrication of the device is easy. The Y-branch is optimized by the method of three-dimensional FD-BPM, after optimization, losses can be less than 0.05dB.