Optical receptacle and optical transceiver

1. An optical receptacle, comprising:

a fiber stub including an optical fiber, a ferrule, and a first elastic member, the optical fiber including cladding and a core for transmitting light, the ferrule having a through-hole where the optical fiber is fixed, the first elastic member fixing the optical fiber in the through-hole;

a holder holding the fiber stub; and

a sleeve, the sleeve being configured to hold the fiber stub at one end and hold a plug ferrule at another end,

the fiber stub having one end surface and another end surface, the one end surface being on a side of the ferrule optically connected to the plug ferrule, the other end surface being on a side opposite to the one end surface,

the optical fiber including a first portion on the other end surface side, a third portion on the one end surface side, and a second portion between the first portion and the third portion,

the first portion extending in an axis direction, the axis direction being a direction in which the first portion, the second portion, and the third portion are arranged,

the second portion extending in the axis direction,

the third portion extending in the axis direction,

a core diameter at the first portion being smaller than the core diameter at the third portion,

the core diameter at the second portion increasing from the first portion side toward the third portion side,

a change of the core diameter at the first portion in the axis direction being smaller than a change of the core diameter at the second portion in the axis direction,

a change of the core diameter at the third portion in the axis direction being smaller than the change of the core diameter at the second portion in the axis direction,

the first elastic member being provided between the optical fiber and an inner wall of the through-hole,

the holder holding the other end surface side of the fiber stub,

the sleeve holding the one end surface side of the fiber stub,

the optical fiber including, at a central portion in the axis direction of the second portion,

a finest portion where an outer diameter is smallest,

a change of an inner diameter of the through-hole being smaller than a change of the outer diameter of the optical fiber,

a thickness of the first elastic member being largest at the finest portion, increasing gradually from the first portion toward the finest portion, and increasing gradually from the third portion toward the finest portion,

the core diameter at the first portion being 10 μm or less and 0.5 to 4 μm smaller than an incident beam waist, and

a length of the second portion in the axis direction being 100 μm or more.

2. The optical receptacle according to claim 1 , wherein a refractive index of the core at the first portion, the refractive index of the core at the second portion, and the refractive index of the core at the third portion are equal to each other, a refractive index of the cladding at the first portion is smaller than the refractive index of the cladding at the third portion, and the refractive index of the cladding at the second portion increases from the first portion side toward the third portion side.

3. The optical receptacle according to claim 1 , wherein a refractive index of the cladding at the first portion, the refractive index of the cladding at the second portion, and the refractive index of the cladding at the third portion are equal to each other, a refractive index of the core at the first portion is larger than the refractive index of the core at the third portion, and the refractive index of the core at the second portion decreases from the first portion side toward the third portion side.

4. The optical receptacle according to claim 1 , wherein the core at the second portion includes a level difference at a portion of a region where the core diameter at the second portion increases from the first portion side to the third portion side.

5. The optical receptacle according to claim 1 , wherein a difference between a refractive index of the core and a refractive index of the cladding at the first portion is larger than a difference between the refractive index of the core and the refractive index of the cladding at the third portion.

6. The optical receptacle according to claim 1 , wherein a difference between a refractive index of the core and a refractive index of the cladding at the first portion is larger than a difference between the refractive index of the core and the refractive index of the cladding at the second portion.

7. The optical receptacle according to claim 1 , wherein a difference between a refractive index of the core and a refractive index of the cladding at the second portion decreases from the first portion side toward the third portion side.

8. The optical receptacle according to claim 1 , wherein an outer diameter of the optical fiber at the second portion is smaller than the outer diameter of the optical fiber at the first portion.

9. The optical receptacle according to claim 1 , wherein an outer diameter of the optical fiber at the second portion is smaller than the outer diameter of the optical fiber at the third portion.

10. The optical receptacle according to claim 1 , further comprising a transparent member fixed to the ferrule, the through-hole including a small diameter portion and a large diameter portion, the large diameter portion being provided on the other end surface side and having a diameter larger than a diameter of the small diameter portion, the entire optical fiber being disposed in the small diameter portion, at least a portion of the transparent member being disposed in the large diameter portion, the first elastic member being provided between the optical fiber and the transparent member.

11. The optical receptacle according to claim 1 , wherein the first portion includes a portion protruding from the ferrule, and the second portion and the third portion are disposed inside the through-hole over the entire regions of the second portion and the third portion.

12. The optical receptacle according to claim 11 , wherein the through-hole of the ferrule includes a first region and a second region, a width in an orthogonal direction of the first region corresponding to a width in the orthogonal direction of the optical fiber, the orthogonal direction being orthogonal to an axis direction of the through-hole, the second region being disposed on the other end surface side of the first region and having a width in the orthogonal direction widening toward the other end surface, and an axis-direction central portion of the second portion is disposed to overlap the first region.

13. The optical receptacle according to claim 11 , wherein the through-hole of the ferrule includes a first region and a second region, a width in an orthogonal direction of the first region corresponding to a width in the orthogonal direction of the optical fiber, the orthogonal direction being orthogonal to an axis direction of the through-hole, the second region being disposed on the other end surface side of the first region and having a width in the orthogonal direction widening toward the other end surface, and the second portion is disposed to overlap the first region.

14. The optical receptacle according to claim 11 , further comprising a fixing member provided on an end surface side of the portion of the first portion protruding from the ferrule, the fixing member fixing the optical fiber, the fixing member being disposed to be separated from the ferrule.

15. The optical receptacle according to claim 12 , wherein the holder holds a portion of an outer side surface of the ferrule on the other end surface side of the first region.

16. The optical receptacle according to claim 12 , wherein the holder holds only a portion of an outer side surface of the ferrule opposing the first region.

17. The optical receptacle according to claim 11 , further comprising: a protective member covering a portion of the optical fiber extending outside the ferrule; and a tube covering the protective member, a space being provided between the protective member and the tube.

18. The optical receptacle according to claim 1 , wherein the first portion, the second portion, and the third portion are formed as one body.

19. The optical receptacle according to claim 1 , wherein in the axis direction of the optical fiber, a length of the first elastic member provided between the second portion and the inner wall is shorter than at least one of the length in the axis direction of the first elastic member provided between the first portion and the inner wall or the length in the axis direction of the first elastic member provided between the third portion and the inner wall.

20. The optical receptacle according to claim 1 , wherein the core diameter of the first portion is substantially constant in the axis direction, and the core diameter of the third portion is substantially constant in the axis direction.