Connection unit, optical fiber line unit, optical cable, and optical transmission system

An optical fiber line unit comprising a plurality of optical fibers accommodated in an optical cable sheath portion and constituting an optical cable together with said optical cable sheath portion, each of said optical fiber lines having a length of not less than 30 km, wherein

• each of said optical fiber lines is formed by connecting a plurality of optical fibers, and
• a difference between a highest transmission loss and a lowest transmission loss among transmission losses in said optical fiber lines is not more than 0.005 dB/km.

An optical cable constituted by a plurality of optical transmission lines each including an optical fiber line having a first mode field diameter, wherein

• at least one of said plurality of optical transmission lines includes an optical fiber connected to one end of said optical fiber line and having a second mode field diameter smaller than the first mode field, and a loss adjusting section for adjusting an overall transmission loss in said selected optical transmission line including said optical fiber line and said optical fiber, and
• a difference between a highest transmission loss and a lowest transmission loss among transmission losses in said plurality of optical transmission lines is not more than 0.005 dB/km.

An optical cable constituted by a plurality of optical transmission lines each including an optical fiber line having a portion having a first mode field diameter and a portion having a second mode field diameter larger than the first mode field diameter, wherein

• at least one optical transmission line selected from said plurality of optical transmission lines includes an optical fiber connected to one end of said optical fiber line and having a third mode field diameter larger than the first mode field diameter and smaller than the second mode field diameter, and a loss adjusting section for adjusting an overall transmission loss in said selected optical transmission line including said optical fiber line and said optical fiber, and
• a difference between a highest transmission loss and a lowest transmission loss among transmission losses in said plurality of optical transmission lines is not more than 0.005 dB/km.

An optical transmission system comprising an optical cable having a plurality of optical fiber lines, an optical amplifier, and a plurality of optical fibers extending from said optical amplifier, wherein

• at least one of optical transmission lines including one optical fiber line selected from said plurality of optical fiber lines and one optical fiber selected from said plurality of optical fibers includes a loss adjusting section for adjusting a difference between a highest transmission loss and a lowest transmission loss among transmission losses in said plurality of optical transmission lines to not more than 0.005 dB/km.