Integrated Broadband Passive Optical Nonreciprocal Device

With the rapid development of communication and computing technology, optical communication and computing devices get increasingly widely used due to its many excellent properties like ultra-large bandwidth, ultra-high speed and anti-interference. Optical nonreciprocal device, which could be used in the design of fundamental elements including optical isolator, optical rotator, and optical diode, plays a very significant role in optical communication and computing. With the optical integration technology development in the 21 st century, there come new requirements for the optical nonreciprocal device. The traditional optical nonreciprocal device which is based on discrete magneto-optic device is no longer stratified the requirements. Therefore it is urgent to design novel optical nonreciprocal device, which is both all-optical and integrated. This thesis mainly includes the research content as follows:Deducing from Lorentz reciprocal theorem, we discuss the principles to realize optical nonreciprocity in devices. Then we introduce three main categories of methods to realize optical nonreciprocity including the magneto-optic method, the spatial-temporal refractive index modulations method and the nonlinear optical method. To addressing the weakness that operating bandwidths of the current designs are too narrow, we proposed two novel integrated passive nonreciprocal schemes with large operating bandwidths.One scheme based on asymmetric hybrid slot waveguide coupler is proposed. The two branches are filled with different materials, which leads to very different optical nonlinear coefficients, and finally causes the distinct transmission for the light in the forward direction and the backward direction. The device based on hybrid slot waveguide has ultra-large operating bandwidth(66 nm), and could function properly for both continuous wave and sub-picosecond pulse of 200 fs.The other scheme based on optical gradient force is proposed. Asymmetric coupler is also involved, and one of the coupler branches is a suspended waveguide. Due to the existence of optical gradient force, the suspended waveguide may deform, and thus its effective index changes correspondingly. This is the so-called mechanical Kerr effect. Since Mechanical Kerr effect is much stronger than optical nonlinear effect, the operating power gets reduced in this device. The device based on optical gradient force effect has ultra-low operating power(390 ?W), and large operating bandwidth(13.1 nm).