Diffraction grating element

Abstract

The present invention provides a diffraction grating element that allows the temperature control mechanism to be dispensed with or simplified. The diffraction grating element of the present invention comprises a transparent plate having a first surface and a second surface that are substantially parallel with one another; and a diffraction grating which is formed on a first surface side with respect to the second surface and is substantially parallel with the first surface. At any temperature within a temperature range −20° C. to +80° C., the sum of the rate of change in the period per unit length of the diffraction grating with respect to a temperature change, and the temperature coefficient of the refractive index of a medium that surrounds the diffraction grating element is 0.

1 - 36 . (canceled)  
   
   
       37 . A diffraction grating element, comprising: 
 a transparent plate having a first surface and a second surface that are substantially parallel with one another; and    a diffraction grating which is formed on a first surface side with respect to the second surface and is substantially parallel with the first surface,    wherein:    the diffraction grating element is disposed in a hermetically sealed gas or in a vacuum; and    the rate of change in the period per unit length of the diffraction grating with respect to a temperature change is 2.4×10 −7 /K or less.    
   
   
       38 . The diffraction grating element according to  claim 37 , wherein the diffraction grating is formed on the first surface.  
   
   
       39 . The diffraction grating element according to  claim 37 , wherein the diffraction grating is supported by the first surface.  
   
   
       40 . The diffraction grating element according to  claim 37 , wherein the diffraction grating is formed within the transparent plate.  
   
   
       41 . The diffraction grating element according to  claim 37 , wherein the transparent plate is made of silica glass or crystallized glass to which an impurity has been added.  
   
   
       42 . The diffraction grating element according to  claim 41 , wherein the impurity is the element Ti.  
   
   
       43 . The diffraction grating element according to  claim 37 , wherein the transparent plate is constituted by laminating a plurality of optical glasses with different linear expansion coefficients.  
   
   
       44 . The diffraction grating element according to  claim 43 , wherein the section of the transparent plate where the diffraction grating is formed is made of silica glass.  
   
   
       45 . The diffraction grating element according to  claim 43 , wherein the distribution of material in the thickness direction of the transparent plate is symmetrical.  
   
   
       46 . The diffraction grating element according to  claim 45  wherein the diffraction grating is formed in the center in the thickness direction of the transparent plate.  
   
   
       47 . The diffraction grating element according to  claim 37 , wherein the diffraction efficiency is substantially polarization-independent.  
   
   
       48 . The diffraction grating element according to  claim 37 , wherein the rate of change in the period per unit length of the diffraction grating with respect to a temperature change is 1.2×10 −7 /K or less.