Plastic optical fiber, optical fiber cable and optical transmission device

A plastic optical fiber having a first core, a second core with a different refractive index from the first core, disposed concentrically on the outside of the first core, and a clad disposed concentrically on the outside of the second core, wherein:

• a ratio X (r1/r2) of a first core radius r1 to a second core radius r2 and a ratio Y (n2/n1) of a refractive index difference n2 between the second core and the clad to a refactive index difference n1 between the first core and the clad are in a range that satisfies the following expressions:
• Y≧−1.134X+1.0518 (1)
• X≦−1.4842Y2+1.1097Y+0.7097 (2)
• Y≦0.7, and (3)
• X≧0.5 (4)
• provided that coordinate pairs of X=0.8 and Y=0.35;
• X=0.8 and Y=0.45;
• and X=0.6 and Y=13/22 are excepted.

A plastic optical fiber having a first core, a second core with a different refractive index from the first core, disposed concentrically on the outside of the first core, and a clad disposed concentrically on the outside of the second core, wherein:

• a ratio X (r1/r2) of a first core radius r1 to a second core radius r2 and a ratio Y (n2/n1) of a refractive index difference n2 between the second core and the clad to a refractive index difference n1 between the first core and the clad are in a range where the following Expressions
• Y≦−3.333X+3.1 (5)
• Y≧2.5X −1.625 (6)
• Y≧−0.833X+0.975 (7)
• Y≧−1.429X+1.386 (8)
• Y≦0.5 (9)
• Y≧0.35 (10)
• are satisfied.

A plastic optical fiber having a first core, a second core with a different refractive index from the first core, disposed concentrically on the outside of the first core, and a clad disposed concentrically on the outside of the second core, wherein:

• a ratio X (r1/r2) of a first core radius r1 to a second core radius r2 and a ratio Y (n2/n1) of a refractive index difference n2 between the second core and the clad to a refractive index difference n1 between the first core and the clad are in a range where the following Expressions
• Y≧−1.429X+1.429 (11)
• Y≦−2.5X+2.4 (12)
• Y≦0.5 (13)
• Y≧0.4 (14)
• are satisfied.

A plastic optical fiber having a first core, a second core with a different refractive index from the first core, disposed concentrically on the outside of the first core, and a clad disposed concentrically on the outside of the second core, wherein:

• a ratio X (r1/r2) of a first core radius r1 to a second core radius r2 and a ratio Y (n2/n1) of a refractive index difference n2 between the second core and the clad to a refractive index difference n1 between the first core and the clad are in a range that satisfies the following expressions
• Y≧−1.134X+1.0518 (1)
• X≦−1.4842Y2+1.1097Y+0.7097 (2)
• Y≦0.7 (3)
• X≧0.5 (4);
• the first core and the second core are each composed of one kind of polymer;
• a compatibly blended layer of a polymer blend which consists of polymers constituting neighboring layers, respectively, is each formed between layers of the first core and the second core and between layers of the second core and the clad;
• and
• a thickness of either of said compatibly blended layers is not greater than 10 μm.

An optical transmission device, comprising:

• a plastic optical fiber having a first core, a second core with a different refractive index from the first core, disposed concentrically on the outside of the first core, and a clad disposed concentrically on the outside of the second core, wherein a ratio X (r1/r2) of a first core radius r1 to a second core radius r2 and a ratio Y (n2/n1) of a refractive index difference n2 between the second core and the clad to a refractive index difference n1 between the first core and the clad are in a range satisfying the following expressions
• Y≧−1.134X+1.0518 (1)
• X≦−1.4842Y2+1.1097Y+0.7097 (2)
• Y≦0.7 (3)
• X≧0.5 (4);
• a light emitting element with an excitation numerical aperture (NA) of not less than 0.3, disposed at one end of the plastic optical fiber;
• and
• an optical receiver disposed at the other end of the plastic optical fiber.