The present disclosure aims to reduce the size and cost of this optical monitoring device that detects the intensity of light propagating through an optical fiber.
The present disclosure relates to an optical monitoring device for detecting the intensity of light propagating through an optical fiber, the optical monitoring device comprising an optical component that branches part of incident light in a first direction and branches the rest in a second direction at a specific branching ratio and emits the light, wherein the optical component includes: a single-layer film having a uniform thickness; an incident-side member provided on the incident side of the single-layer film; and an outgoing-side member provided on the outgoing side of the single-layer film, a first refractive index interface between the single-layer film and the incident-side member and a second refractive index interface between the single-layer film and the outgoing-side member are provided at a specific angle with an optical axis of the incident light, the first direction is a direction in which the light transmits through the first refractive index interface and the second refractive index interface, and the second direction is a direction in which the light is reflected on the first refractive index interface and the second refractive index interface.