JP2827128B

PURPOSE:To realize an effect equivalent to elevation of saturation point and to make the title item to be applicable on lights impinging from both directions by providing a light path where light propagates in single mode and by providing an activation region for amplifying light along a light path in region other than that where strength of light propagating this light path within light path is greatest. CONSTITUTION:Current is injected into a light-amplification device 200 through first and second electrodes 11 and 12 and a carrier is injected into an activation layer 6 for keeping an inversion distribution (excitation) state. In this state, light signal which propagates within a light transmission path is coupled from an end face where a reflection-preventing film 13 is formed to a waveguide path layer 3 using a lens etc., for allowing wave to be guided. The incidence light signal is guided through the waveguide path layer 3, is irradiated from the end face which is opposite to the incidence end face, and then is coupled to the original light transmission path through the lens, etc. Thus, a wavelength of light which travels through the waveguide path layer 3 is that to be amplified by inversion distribution which is formed at the activation layer 6, light signal which travels within the waveguide path layer 3 is amplified.