Optical transmission system, optical transmission path, and photoelectric composite cable

This optical transmission system is provided with: an optical signal transmitter that transmits an optical signal output from a light source; the optical signal receiver is used for receiving the optical signal; and an optical transmission path that optically connects the optical signal transmitter and the optical signal receiver and transmits the optical signal, the first optical transmission path having a product of a scattering loss and a length with respect to the optical signal of 6 dB or less; and a first optical transmission path that is disposed next to the light source and optically connected to the second optical transmission path, and that expands the beam diameter by three times or more and outputs the Gaussian beam when the Gaussian beam emitted from the single-mode fiber is input by center excitation. 光传输系统具备：发送从光源输出的光信号的光信号发送机；接收所述光信号的光信号接收机；和将所述光信号发送机和所述光信号接收机光学连接且传输所述光信号的光传输路，第1光传输路使相对于所述光信号的散射损耗与长度之积为6dB以下，在从单模光纤出射的高斯光束以中心激振而输入的情况下将光束直径扩大到3倍以上而输出，该第1光传输路配置在紧挨所述光源之后，进而与第2光传输路光学连接。