| CPC G02B 21/33 (2013.01) [G02B 21/02 (2013.01); G02B 21/24 (2013.01); G02B 21/06 (2013.01); G02B 2207/109 (2013.01)] | 21 Claims |

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1. An optical signal detection device comprising:
an objective; and
a gel unit including a gel and an assisting member, wherein
the assisting member includes a first surface, a second surface, and an opening,
the opening has a diameter smaller than an outer diameter of the gel and larger than an effective diameter of the objective,
the first surface faces the gel,
a part of the first surface is fixed to a bottom surface of the gel by an adhesive force,
a center of the bottom surface is not in contact with the assisting member, and
in a state where the gel unit is attached to a frame member of the objective, the second surface faces the frame member of the objective, a part of the first surface is fixed to the gel outside the effective diameter of the objective, and the gel is in close contact with the objective.
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