Optical device

Abstract

According to one embodiment, an optical device includes a first mirror, a second mirror, and a first member. The first mirror has a first planar surface. The second mirror is spaced from the first mirror in a first direction crossing the first planar surface. The second mirror has a concave surface including a first region and a second region around the first region. First distance between the first region and the first planar surface in the first direction is longer than second distance between the second region and the first planar surface in the first direction. The first distance is half or less of curvature radius of the concave surface. The first member is light transmissive and solid. The first member includes a first portion provided between the first mirror and the second mirror. The first portion is in contact with the first planar surface and the concave surface.

What is claimed is: 
     
         1 . An optical device comprising:
 a first mirror having a first planar surface;   a second mirror spaced from the first mirror in a first direction crossing the first planar surface, the second mirror having a concave surface including a first region and a second region around the first region, first distance between the first region and the first planar surface in the first direction being longer than second distance between the second region and the first planar surface in the first direction, and the first distance being half or less of curvature radius of the concave surface; and   a first member being light transmissive, being solid, and including a first portion provided between the first mirror and the second mirror, the first portion being in contact with the first planar surface and the concave surface.   
     
     
         2 . The device according to  claim 1 , wherein
 the first member further includes a second portion,   direction from the first portion to the second portion crosses the first direction, and   the second portion does not overlap the second mirror in the first direction.   
     
     
         3 . The device according to  claim 1 , wherein
 the first member further includes a second portion and a third portion,   the first portion is located between the second portion and the third portion in a second direction crossing the first direction, and   the second portion and the third portion do not overlap the second mirror in the first direction.   
     
     
         4 . The device according to  claim 3 , wherein length along the first direction of at least part of the first portion is longer than length along the first direction of the second portion and longer than length along the first direction of the third portion. 
     
     
         5 . The device according to  claim 3 , further comprising:
 a first prism,   wherein the first prism is spaced from the second mirror in the second direction, and   the first prism overlaps part of the second portion in the first direction.   
     
     
         6 . The device according to  claim 5 , wherein direction from part of the first mirror to the first prism lies along the first direction. 
     
     
         7 . The device according to  claim 1 , further comprising:
 a translucent second member; and   a translucent third member,   wherein the first member is located between the second member and the third member in a second direction crossing the first direction, and   the second member and the third member do not overlap the second mirror in the first direction.   
     
     
         8 . The device according to  claim 7 , wherein length along the first direction of at least part of the first member is longer than length along the first direction of the second member and longer than length along the first direction of the third member. 
     
     
         9 . The device according to  claim 7 , further comprising:
 a first prism,   wherein the first prism is spaced from the second mirror in the second direction, and   the first prism overlaps part of the second member in the first direction.   
     
     
         10 . The device according to  claim 9 , wherein direction from part of the first mirror to the first prism lies along the first direction. 
     
     
         11 . The device according to  claim 1 , wherein the first mirror contains at least one selected from the group consisting of TiO 2 , Ta 2 O 3 , SiO 2 , MgF 2 , TiO 3 , and Nb 2 O 5 . 
     
     
         12 . The device according to  claim 1 , wherein the second mirror contains at least one selected from the group consisting of TiO 2 , Ta 2 O 3 , SiO 2 , MgF 2 , TiO 3 , and Nb 2 O 5 . 
     
     
         13 . The device according to  claim 1 , wherein the first member contains at least one selected from the group consisting of Y 2 SiO 5 , LF 3 , SiO 2 , and C. 
     
     
         14 . An optical device comprising:
 a first mirror having a first concave surface including a first region and a second region provided around the first region;   a second mirror spaced from the first mirror in a first direction, the second mirror having a second concave surface including a third region and a fourth region provided around the third region, first distance between the first region and the third region in the first direction being longer than second distance between the second region and the fourth region in the first direction, and the first distance being 0.5 times or less of sum of curvature radius of the first concave surface and curvature radius of the second concave surface; and   a first member being light transmissive, being solid, and including a first portion provided between the first mirror and the second mirror, the first portion being in contact with the first concave surface and the second concave surface.