Electrooptic polymeric digital optical switches and hybrid integration of EO polymeric devices

Optical switches are vital in the optical communication networks and optical signal processing systems. High-speed, large extinction ratio, low switching voltage and ease of control are desired properties for optical switches.;As the result of the development of polymer materials with high nonlinearity, the application of EO polymers in photonic devices becomes more common. EO polymeric devices can work at high frequency because of the better velocity match between microwave and lightwave in the devices. The high nonlinearity of new EO materials result in a lower voltage requirement to achieve a certain change of refractive index. The required voltage-length product for switches is lower.;Digital optical switch (DOS) based on EO polymer is a promising candidate for high-performance optical switch. Based on adiabatic propagation phenomenon in slow-changing waveguide structures, DOS's are tolerant to fabrication errors and material property changes. The device is easy to switch between ON and OFF state because of the step-like modulation curve.;The classical design of DOS's includes an active Y-branch. The refractive index of either or both arms is changed to make the Y-branch asymmetric. The input wave, while propagating along this changing structure, will change its shape. If the product of refractive index change and length is large enough, the optical power will be output from the desired port.;DOS's can also be fabricated by replacing the Y-branch with a full 1 x 2 adiabatic coupler. Our work shows that this approach can lower the driving voltage and the bias of DOS's.;To lower the insertion loss of EO polymeric devices, a waveguide transition structure between passive and active polymers is proposed. This easy-to-fabricate, in-plane and self-aligned transition can handle a moderate refractive index difference between two different materials. Excess loss around 0.1dB has been demonstrated experimentally.;This transition is utilized in hybrid integration of waveguide devices. The test results show that the loss of the devices is improved by about 2.5dB without affecting the EO effect. As an application, the hybrid integrated cascaded 1 x 2 x 4 DOS's have been fabricated and tested.