Abstract: An optical delay line of a configuration in which a number of components such as a circulator and an optical coupler is reduced is to be provided. To this end, the optical delay line has a configuration in which, after an optical fiber diffraction grating having a core subjected to refractive index modulation and a cladding partly cleared of its outer circumference and an optical fiber having a cladding partly cleared of its outer circumference are brought close to each other so that the cores have mutually parallel directions of an optical axis to fabricate a directional coupler, both ends of the optical fiber are connected into an optical fiber loop. In this way, an optical delay line to generate a specific time delay for controlling optical signals can be provided in small dimensions and with a small number of components.

Abstract: An optical delay line of a configuration in which a number of components such as a circulator and an optical coupler is reduced is to be provided. To this end, the optical delay line has a configuration in which, after an optical fiber diffraction grating having a core subjected to refractive index modulation and a cladding partly cleared of its outer circumference and an optical fiber having a cladding partly cleared of its outer circumference are brought close to each other so that the cores have mutually parallel directions of an optical axis to fabricate a directional coupler, both ends of the optical fiber are connected into an optical fiber loop. In this way, an optical delay line to generate a specific time delay for controlling optical signals can be provided in small dimensions and with a small number of components.