PHOTO MODULE

PROBLEM TO BE SOLVED: To provide a technique for condensing signal light guided to a photo module into a photo detector without increasing a manufacturing process and increasing costs, and not allowing reflected light returned from the photo module to re-enter a transmission route in the photo module for measuring signal intensity in the transmission route.SOLUTION: A photo module comprises: an incident optical fiber 1 for guiding incident light; a gradient index lens 2 having an optical axis 21 different from that of the incident optical fiber 1 and a period length larger than a 1/4 period length and smaller than a 1/2 period length to the wavelength of the incident light, bonded with the incident optical fiber 1 on a surface forming a finite angle to a surface perpendicular to the optical axis 21, and having a surface approximately perpendicular to the optical axis 21 as an emission surface of emission light; and a photo detector 3 arranged at a condensing position of emitted light and for measuring intensity of the emission light.