Abstract: Compositions, containing glycine and serine and having a content ratio of glycine to serine (glycine/serine) of not less than 0.6 in weight ratio are effective for improving cognitive function, and have an effective preventive or improving effect on a decline in cognitive function and cognitive dysfunction, are highly safe, and enable continuous ingestion or administration.

Abstract: An optical device incorporating an incident-side optical waveguide portion having an incident terminal port and an outgoing terminal port which are connected with a fiber array, and an outgoing-side optical waveguide portion having another outgoing terminal port. Between the incident-side and outgoing-side optical waveguide portions, there is disposed a wavelength division multiplexer for sending back an incident beam from the incident-side optical waveguide portion to the incident-side optical waveguide portion and permitting a part of the incident beam to pass therethrough. Between the wavelength division multiplexer and the outgoing-side optical waveguide portion, a polarization-independent type optical isolator is disposed. Between the wavelength division multiplexer and the incident-side optical waveguide portion, a first lens is disposed, and between the wavelength division multiplexer and the polarization-independent type optical isolator, a second lens is disposed.