Optical fiber cable

1. An optical fiber cable comprising:

a sheath; and

a core that is housed in the sheath and comprises an intermittently-adhered optical fiber ribbon comprising:

optical fibers; and

adhesive portions that intermittently adhere the optical fibers together in a longitudinal direction, wherein

recesses and protrusions are disposed alternately in a circumferential direction on an outer circumferential surface of the sheath,

the recesses each comprise:

two connecting portions respectively connected to radial inner ends of two adjacent protrusions; and

a bottom surface positioned between the two connecting portions, and

in a transverse cross-sectional view, a cross-sectional area of the recesses that is enclosed by closed curves tangent to radial outer ends of the protrusions and all the recesses is 1.3 mm 2 or greater and 4.8 mm 2 or less.

2. The optical fiber cable according to claim 1 , wherein the two connecting portions have a convex surface shape that is radially inward.

3. The optical fiber cable according to claim 1 , wherein the optical fiber cable has a compressive strength of 12.8 N/mm 2 or greater and 32.4 N/mm 2 or less.

4. The optical fiber cable according to claim 1 , wherein the core further comprises a wrapping tube that wraps the intermittently-adhered optical fiber ribbon.

5. The optical fiber cable according to claim 4 , wherein the wrapping tube comprises:

a wrap portion where a first end portion of the wrapping tube overlaps with a second end portion of the wrapping tube; and

a non-wrap portion positioned between the first end portion and the second end portion.

6. The optical fiber cable according to claim 5 , wherein

a wrap rate R of the optical fiber cable is calculated as R=W 1 ÷(W 1 +W 2 )×100, where W 1 is a circumferential length of the wrap portion and W 2 is a circumferential length of the non-wrap portion, and

the wrap rate R is 5% or greater and 20% or less.

7. The optical fiber cable according to claim 1 , wherein a twist angle of the sheath per 1 m along the longitudinal direction of the optical fiber cable is 10 degrees/m or greater and 180 degrees/m or less.

8. The optical fiber cable according to claim 1 , wherein a radius of curvature of each outer circumferential surface of the protrusions is smaller than a radius of the sheath.

9. The optical fiber cable according to claim 1 , further comprising:

tensile strength members embedded inside the protrusions on the sheath, wherein

the protrusions and the tensile strength members have a spirally twisted shape centered on a central axis of the optical fiber cable.

10. The optical fiber cable according to claim 1 , further comprising:

tensile strength members embedded inside the protrusions on the sheath, wherein

the tensile strength members are made of poly-paraphenylene benzobisoxazole fiber reinforced plastics (PBO-FRP).

11. The optical fiber cable according to claim 1 , further comprising:

tensile strength members embedded in the sheath, wherein

in a transverse cross-sectional view, the tensile strength members are disposed inside each of the protrusions on the sheath.

12. The optical fiber cable according to claim 1 , further comprising:

intermittently-adhered optical fiber ribbons, wherein

an SZ-shaped twist is applied to the sheath by twisting the intermittently-adhered optical fiber ribbons in an SZ shape.

13. The optical fiber cable according to claim 1 , wherein the sheath comprises:

a base material; and

a low friction material having a friction coefficient smaller than a friction coefficient of the base material, and

the low friction material is disposed at least on tops of the protrusions.

14. An optical fiber cable comprising:

a sheath;

a core that is housed in the sheath and comprises an intermittently-adhered optical fiber ribbon comprising:

optical fibers; and

adhesive portions that intermittently adhere the optical fibers together in a longitudinal direction; and

tensile strength members and ripcords embedded in the sheath, wherein

recesses and protrusions are disposed alternately in a circumferential direction on an outer circumferential surface of the sheath,

the recesses each comprise:

two connecting portions respectively connected to radial inner ends of two adjacent protrusions; and

a bottom surface positioned between the two connecting portions, and

in a transverse cross-sectional view, the ripcords are positioned inside some of the protrusions,

and the tensile strength members are positioned inside the remaining protrusions.