Photo module

Abstract

A photo module which measures a signal strength in a transmission path, and this technique collects a signal light, guided to a photo module, on a light receiving element without increasing the number of manufacturing processes and the cost and, at the same time, prevents reflected light returned from the photo module from entering inside the transmission path again. The photo module is provided with an incident light fiber guiding incident light, a gradient index lens having an optical axis different from the incident light fiber, having a period length larger than a ¼ period length and smaller than a ½ period length with respect to the wavelength of the incident light, joined to the incident light fiber on a surface forming a finite angle with a surface vertical to the optical axis, and having, as a light exit surface of emitting light, a surface substantially vertical to the optical axis, and a light receiving element disposed at a position where the emitting light is collected and measuring the strength of the emitting light.

Dependencies are inferred from the claim text.