Optical fiber
An optical fiber that communicates in a predetermined communication band includes: a signal light propagation core that propagates light beams of up to (x+1)-th order LP mode, where x is an integer of two or more; and a coupler that propagates a light beam that is: coupled with a light beam of the (x+1)-th order LP mode propagating through the signal light propagation core, and suppressed from being coupled with light beams of up to the x-th order LP mode propagating through the signal light propagation core, wherein, mode coupling of the light beams of up to the x-th order LP mode propagating through the signal light propagation core is performed, and mode coupling between the light beam of the x-th order LP mode and the light beam of (x+1)-th order LP mode is suppressed.
1. An optical fiber that communicates in a predetermined communication band, the optical fiber comprising:
a signal light propagation core oriented along a central axis of the optical fiber that propagates light beams of up to (x+1)-th order LP mode, where x is an integer of two or more; and
a side core that is parallel to the signal light propagating core and that propagates a light beam that is:
coupled with a light beam of the (x+1)-th order LP mode propagating through the signal light propagation core, and
suppressed from being coupled with light beams of up to the x-th order LP mode propagating through the signal light propagation core, wherein,
mode coupling of the light beams of up to the x-th order LP mode propagating through the signal light propagation core is performed, and
mode coupling between the light beam of the x-th order LP mode and the light beam of (x+1)-th order LP mode is suppressed.
2. The optical fiber according to claim 1 , wherein the signal light propagation core comprises:
an inner core having a center axis; and
an outer core that surrounds an outer circumferential surface of the inner core and has a refractive index higher than that of the inner core.
3. The optical fiber according to claim 1 , wherein the side core loses more of a light beam propagating therethrough than the signal light propagation core.
4. The optical fiber according to claim 1 , wherein the side core is a clad that surrounds an outer circumferential surface of the signal light propagation core.
5. The optical fiber according to claim 4 , wherein relationships (1) and (2) below are satisfied:
Δn eff a<Δn eff c; and (1):
Δn eff b<Δn eff c, where (2):
Δn eff a is a maximum value among effective refractive index differences between light beams of LP modes having effective refractive indexes that are adjacent to each other except for the x-th order LP mode and the (x+1)-th order LP mode,
Δn eff b is a difference between an effective refractive index of a light beam of the highest order LP mode propagating through the signal light propagation core and a refractive index of the clad, and
Δn eff c is a difference between an effective refractive index of the light beam of the x-th order LP mode and an effective refractive index of the light beam of (x+1)-th order LP mode.
6. The optical fiber according to claim 5 , wherein relationship (3) below is satisfied:
Δn eff b<Δn eff a (3):.
7. The optical fiber according to claim 1 , wherein relationships (1) to (4) below are satisfied:
Δn eff a<Δn eff c; (1):
Δn eff a<Δn eff d; (2):
Δn eff b<Δn eff c; and (3):
Δn eff b<Δn eff d, where (4):
Δn eff a is a maximum value among effective refractive index differences between light beams of LP modes having effective refractive indexes that are adjacent to each other except for the x-th order LP mode and the (x+1)-th order LP mode,
Δn eff b is a minimum value among differences between the effective refractive indexes of the light beams of (x+1)-th order LP mode and higher propagating through the signal light propagation core and an effective refractive index of a light beam of at least one mode propagating through the side core,
Δn eff c is a difference between an effective refractive index of the light beam of the x-th order LP mode and an effective refractive index of the light beam of (x+1)-th order LP mode, and
Δn eff d is a minimum value among differences between the effective refractive index of the light beam of the x-th order LP mode and the effective refractive indexes of the light beams of the modes propagating through the side core.
8. The optical fiber according to claim 7 , wherein relationship (5) below is satisfied:
Δn eff b<Δn eff a (5):
9. The optical fiber according to claim 1 , wherein the side core is a single mode core.
10. An optical fiber that communicates in a predetermined communication band, the optical fiber comprising:
a signal light propagation core oriented along a central axis of the optical fiber that propagates light beams of (x+2)-th order LP mode and higher, where x is an integer of two or more; and
a side core that is parallel to the signal light propagation core and that propagates a light beam that is:
coupled with a light beam of any of (x+1)-th order LP mode and higher propagating through the signal light propagation core, and
suppressed from being coupled with light beams of up to the x-th order LP mode propagating through the signal light propagation core, wherein,
mode coupling of the light beams of up to the x-th order LP mode propagating through the signal light propagation core is performed,
mode coupling between the light beam of the x-th order LP mode and the light beam of (x+1)-th order LP mode is suppressed, and
mode coupling of the light beams of the (x+1)-th order LP mode and higher propagating through the signal light propagation core is performed.
11. An optical fiber that communicates in a predetermined communication band, the optical fiber comprising:
a signal light propagation core that propagates light beams of up to (x+1)-th order LP mode, where x is an integer of two or more; and
a side core that is parallel to the signal light propagation core and that propagates a light beam that is:
coupled with a light beam of the (x+1)-th order LP mode propagating through the signal light propagation core, and
suppressed from being coupled with light beams of up to the x-th order LP mode propagating through the signal light propagation core, wherein
mode coupling of the light beams of up to the x-th order LP mode propagating through the signal light propagation core is performed,
mode coupling between the light beam of the x-th order LP mode and the light beam of (x+1)-th order LP mode is suppressed, and
the side core is a single mode core.
12. An optical fiber that communicates in a predetermined communication band, the optical fiber comprising:
a signal light propagation core that propagates light beams of (x+2)-th order LP mode and higher, where x is an integer of two or more; and
a side core that is parallel to the signal light propagation core and that propagates a light beam that is:
coupled with a light beam of any of (x+1)-th order LP mode and higher propagating through the signal light propagation core, and
suppressed from being coupled with light beams of up to the x-th order LP mode propagating through the signal light propagation core, wherein
mode coupling of the light beams of up to the x-th order LP mode propagating through the signal light propagation core is performed,
mode coupling between the light beam of the x-th order LP mode and the light beam of (x+1)-th order LP mode is suppressed,
mode coupling of the light beams of the (x+1)-th order LP mode and higher propagating through the signal light propagation core is performed, and
the side core is a single mode core.