Signal light transmission member
A signal light transmission member includes an AR coated lens, a light transmission part, and an optical fiber. The refractive index of the light transmission part has a specific relationship with the refractive index of a core material of the optical fiber. An anti-reflective coating is formed at an interface portion between the lens of the AR coated lens and the light transmission part.
1. A signal light transmission member comprising:
a lens that has a refractive index n1 and is configured to collimate signal light;
a housing part that houses the lens;
a light transmission part that has light permeability, has a refractive index n2 smaller than n1, is made of a light transmission material filling the housing part, and has the lens embedded therein;
an optical fiber through which the signal light passes, the optical fiber being inserted into the housing part and having an end portion fixed by the light transmission part at a position facing the lens on an optical axis of the lens in the housing part; and
an anti-reflective coating that is formed at least at a portion of the optical path of the signal light at the interface between the lens and the light transmission part, wherein
if the refractive index of a core material of the optical fiber is designated as n4, a following equation (1) is satisfied:
n 4−0.14≤ n 2≤ n 4+0.14 (1).
2. The signal light transmission member according to claim 1 , wherein a following equation (2) is satisfied:
n 1− n 2≥0.19 (2).
3. The signal light transmission member according to claim 1 , wherein the anti-reflective coating is a single-layer coating made of at least inorganic fine particles.
4. The signal light transmission member according to claim 3 , wherein if an average refractive index of the anti-reflective coating is designated as n3, a following equation (3) below is satisfied:
[Mathematical Equation 1]
√{square root over (( n 1× n 2))}−0.02≤ n 3≤√{square root over (( n 1× n 2))}+0.02 (3).
5. The signal light transmission member according to claim 3 , wherein
the anti-reflective coating includes:
antimony particles or mixed particles of antimony particles and silica particles;
a binder component curing agent that binds the antimony particles or the mixed particles; and
a light transmission material that fills gaps between the antimony particles or the mixed particles and the binder component curing agent.
6. The signal light transmission member according to claim 3 , wherein the anti-reflective coating made of the single-layer coating is formed on an entire surface of the interface.
7. The signal light transmission member according to claim 1 , wherein the lens is a ball lens.
8. The signal light transmission member according to claim 1 , wherein
the housing part includes a main body having one end opened, a transparent window that closes the one end, and a coupling part that couples the housing part to a housing part of another signal light transmission member, and
the coupling part is coupled to the housing part of the other signal light transmission member such that the transparent window faces the transparent window of the other signal light transmission member and is parallel or in close contact with the transparent window.
9. The signal light transmission member according to claim 8 , wherein the main body part includes a plurality of recesses arranged in a planar direction as viewed along the optical axis, the lens and the light transmission part are arranged in each of the recesses, and an optical fiber is connected in each of the recesses.