||Due to the dramatic increase in the need of optical communications, it becomes more important on developing the core of photonics integration elements. Among the elements in photonic integration circuits, electro-absorption modulator (EAM) is one of the key elements. To get high performance of EAM, low-loss and high-electrical-and-optical conversion efficiency optical waveguide thus plays an essential part. In this paper, quantum well intermixing (QWI) based on InGaAsP/InGaAsP material is applied for fabricating the waveguide of EAM with the buried semiconductor heterostructure. QWI with Impurity free vacancy diffusion (IFVD) enhanced by depositing SiO2 is used for changing the bandgap of InGaAsP/InGaAsP quantum well toward the blue shift regime, reducing refractive index. Therefore, patterning SiO2 could define both electrical and optical confinement optical waveguide.|
The SiO2 film is sputtered on top of the wafer as dielectric material and also the pattern area of optical waveguide. After rapid thermal annealing, the reaction of Ga atom with SiO2 will induce vacancy, improving the interdiffusion in atom of quantum well. By increasing bandgap in SiO2 region, the accompanied index change defines the optical waveguide area. Above 80nm wavelength shift between in and outside SiO2 region was observed, where the window of 3, 5, and 7μm were used for setting optical waveguide. Through bias-dependent transmission, quadratic relation indicates the quantum confined Stark effect (QCSE) in quantum will, which can be used for developing high efficiency EAM. Besides, the SiO2 patterned area with large blue shift induces as high as 0.07 of refractive index change, suitably defining optical waveguide. Higher than 20dB of modulation efficiency within 3V voltage bias was shown in the devices. And through the observations on near field and far field of 3, 5 and 7um waveguide, it shows that the waveguide indeed possesses good optical confinement.