Nonreciprocal Devices For Integrated Optics

Recent development of waveguide nonreciprocal devices, i.e. , isolator and circulator, is reviewed. Two major difficulties exist for their fabrication. First, form birefringence must be overcome to obtain high TE-TM mode conversion efficiency. Secondly, both of input and output light must be either TE or TM mode. A variety of methods and device structures have been proposed to solve these difficulties. However, experimental demonstration of waveguide isolator has been limited. After a brief discussion on advantages and drawbacks of proposed methods and device structures, a new fabrication process of waveguide isolator is described. A device structure which ensures TE mode operation was achieved by making adjoining nonreciprocal and reciprocal mode converters by using laser annealing technique. Faraday and Cotton-Mouton effects of Bi-substituted iron garnet film were used for nonreciprocal and reciprocal mode converters, respectively. Growth-induced and stress-induced birefringences of the film were used to cancel the form birefringence. An isolation ratio of 12.5dB was achieved at wavelength of 1.15μm with external magnetic field of 100 Gauss.