Abstract: This optical coupler for coupling a plurality of visible light beams having different wavelengths includes: a substrate made of a material different from lithium niobate; and an optical coupling function layer formed on a main surface of the substrate. The optical coupling function layer includes: two multimode-interference-type optical coupling parts; optical-input-side waveguides and an optical-output-side waveguide connected to one multimode-interference-type optical coupling part, and optical-input-side waveguides and an optical-output-side waveguide connected to the other multimode-interference-type optical coupling part. The multimode-interference-type optical coupling parts, the optical-input-side waveguides, and the optical-output-side waveguides are made of a lithium niobate film.

Abstract: A light emitting device includes a light emitting element having a dominant wavelength in a range of 400 nm or more and 500 nm or less, and a wavelength conversion member that is arranged on a light emitting side of the light emitting element and includes a rare earth aluminate fluorescent material having a composition represented by the following formula (I), wherein the light emitting device emits light having a dominant wavelength in a range of 475 nm or more and 500 nm or less, and wherein the light emitting device emits light having an S/P ratio of 6.5 or less derived from the formula (1), which is the ratio of a luminous flux in scotopic vision relative to a luminous flux in photopic vision: (Lu1-p-nLnpCen)3(Al1-mGam)5kO12??(I) wherein in the formula (I), Ln represents at least one rare earth element selected from the group consisting of Y, La, Gd, and Tb, and the parameters k, m, n, and p satisfy 0.95?k?1.05, 0.05?m?0.70, 0.002?n?0.050, and 0?p?0.30, respectively.

Abstract: A method for producing a rare earth aluminate fluorescent material, including: preparing, as raw materials, cerium oxide having a crystallite diameter in a range of 200 ? or more and 1,600 ? or less, a compound containing at least one kind of a rare earth element Ln selected from the group consisting of Y, La, Lu, Gd, and Tb, a compound containing Al, and depending on necessity a compound containing at least one kind of an element M1 selected from the group consisting of Ga and Sc, wherein a total molar ratio of the rare earth element Ln and cerium is 3, a total molar ratio of Al and the element M1 is a product of a parameter k in a range of 0.95 or more and 1.05 or less and 5, a molar ratio of cerium is a product of a parameter n in a range of 0.005 or more and 0.050 or less and 3, and a molar ratio of the element M1 is a product of a parameter m in a range of 0 or more and 0.02 or less, the parameter k, and 5; and subjecting a mixture of the raw materials to a heat treatment to provide a calcined product.

Abstract: A light emitting device includes a light emitting element having a dominant wavelength in a range of 400 nm or more and 500 nm or less, and a wavelength conversion member that is arranged on a light emitting side of the light emitting element and includes a rare earth aluminate fluorescent material having a composition represented by the following formula (I), wherein the light emitting device emits light having a dominant wavelength in a range of 475 nm or more and 500 nm or less, and wherein the light emitting device emits light having an S/P ratio of 6.5 or less derived from the formula (1), which is the ratio of a luminous flux in scotopic vision relative to a luminous flux in photopic vision: (Lu1-p-nLnpCen)3(Al1-mGam)5kO12??(I) wherein in the formula (I), Ln represents at least one rare earth element selected from the group consisting of Y, La, Gd, and Tb, and the parameters k, m, n, and p satisfy 0.95?k?1.05, 0.05?m?0.70, 0.002?n?0.050, and 0?p?0.30, respectively.

Abstract: A method for producing a rare earth aluminate fluorescent material includes: subjecting a compound containing Ln that is at least one rare earth element to a first heat treatment at a temperature in a range of 1,000° C. or more and 1,600° C. or less; preparing a raw material containing an oxide containing Ln having a crystallite diameter of 1,500 ? or more obtained through the first heat treatment, a compound containing Ce, a compound containing Al, and optionally a compound containing Ga, having a chemical composition having a total molar ratio of Ln and Ce of 3, a total molar ratio of Al and Ga of a product of 5 and a parameter k of 0.95 or more and 1.05 or less, a molar ratio of Ce of a product of 3 and a parameter n of 0.005 or more and 0.050 or less, and a molar ratio of Ga of a product of a parameter m of 0 or more and 0.6 or less, the parameter k, and 5, and providing a mixture containing the raw material and a compound containing an alkaline earth metal element as a flux in an amount of 2.

Abstract: A method for producing a rare earth aluminate fluorescent material, including: preparing, as raw materials, cerium oxide having a crystallite diameter in a range of 200 ? or more and 1,600 ? or less, a compound containing at least one kind of a rare earth element Ln selected from the group consisting of Y, La, Lu, Gd, and Tb, a compound containing Al, and depending on necessity a compound containing at least one kind of an element M1 selected from the group consisting of Ga and Sc, wherein a total molar ratio of the rare earth element Ln and cerium is 3, a total molar ratio of Al and the element M1 is a product of a parameter k in a range of 0.95 or more and 1.05 or less and 5, a molar ratio of cerium is a product of a parameter n in a range of 0.005 or more and 0.050 or less and 3, and a molar ratio of the element M1 is a product of a parameter m in a range of 0 or more and 0.02 or less, the parameter k, and 5; and subjecting a mixture of the raw materials to a heat treatment to provide a calcined product.