Diffractive optical element and bidirectional optical communication module using the same

Abstract

A diffractive optical element 1 has a diffraction grating which multiplexes the light beam of the different wavelength, and the diffraction grating is structured by a binary structure in which the diffraction surface top part 2 and the diffraction surface bottom part 4 repeat the concave and convex shape through a rising surface 3 part along the optical axis direction P, and the diffraction surface top part and the diffraction surface bottom part are inclined to the rising surface part. By this diffractive optical element 1 , the diffraction angle of the light beam is maintained, and the diffraction efficiency of the light beam can be improved. Then, by using this diffractive optical element 1 , the optical communication module in which, while the separation angle of the light beam of the different wavelength is maintained, the signal receiving performance is increased, can be provided.

1 . A diffractive optical element having a diffraction grating by which the light beams of different wavelengths are demultiplexed, and the diffraction grating has a binary structure in which the diffraction surface top part and the diffraction surface bottom part repeat the concave and convex shape through a rising surface part along the optical axis direction, and the diffraction surface top part and the diffraction surface bottom part are inclined by a predetermined angle to the direction perpendicular to the rising surface part.  
   
   
       2 . A diffractive optical element according to  claim 1 , wherein the diffraction grating is structured in such a manner that the incident light beam is transmitted.  
   
   
       3 . A diffractive optical element according to  claim 2 , wherein the inclination angle in which the diffraction surface top part and the diffraction surface bottom part are to the direction perpendicular to the rising surface part is within the range of 2° to 7°.  
   
   
       4 . A diffractive optical element according to  claim 3 , wherein the inclination angle in which the diffraction surface top part and the diffraction surface bottom part are to the direction perpendicular to the rising surface part is within the range of 3° to 6°.  
   
   
       5 . A diffractive optical element according to  claim 2 , wherein the height H 1  in the optical axis direction of the concave and convex shape satisfies the following expression.  
         H 1={λ 0 /( n− 1)}× K    
     Where, λ 0  one of the wavelength of the incident light beams,  
     n: the refractive index of the material of the diffraction grating, k: 3 or 4.  
   
   
       6 . A diffractive optical element according to  claim 1 , wherein the diffraction grating is structured in such a manner that the incident light beam is reflected.  
   
   
       7 . A diffractive optical element according to  claim 6 , wherein the inclination angle in which the diffraction surface top part and the diffraction surface bottom part are to the direction perpendicular to the rising surface part is within the range of 1° to 3°.  
   
   
       8 . A diffractive optical element according to  claim 7 , wherein the height H 2  in the optical axis direction of the concave and convex shape satisfies the following expression.  
         H 2={λ 0 /(2· n )}× K    
     Where, λ 0 : one of the wavelength of the incident light beams,  
     n: the refractive index of the material of the diffraction grating, K: 3 or 4.  
   
   
       9 . A diffractive optical element according to  claim 7 , wherein the height H 1  in the optical axis direction of the concave and convex shape satisfies the following expression.  
         H 3=(λ 0 /2)× K    
     Where, λ 0 : one of the wavelength of the incident light beams,  
     n: the refractive index of the material of the diffraction grating, K: 3 or 4  
   
   
       10 . An optical communication module having a diffractive optical element having a diffraction grating for demultiplexing light beams of different wavelength, wherein the diffraction grating has a binary structure in which the diffraction surface top part and the diffraction surface bottom part repeat the concave and convex shape through a rising surface part along the optical axis direction, and the diffraction surface top part and the diffraction surface bottom part are inclined by a predetermined angle to the direction perpendicular to the rising surface part.  
   
   
       11 . A optical communication module according to  claim 10 , further comprising: a light emitting element which sends the optical signal to the end of the optical fiber; and a light receiving element which receives the optical signal from the end of the optical fiber, wherein the diffraction optical element separates the first optical path between the end of the optical fiber and the light emitting element and the second optical path between the end of the optical fiber and the light receiving element.  
   
   
       12 . A optical communication module according to  claim 11 , wherein the diffraction grating is structured in such a manner that the incident light beam transmits.  
   
   
       13 . A optical communication module according to  claim 12 , wherein the inclination angle in which the diffraction surface top part and the diffraction surface bottom part are to the direction perpendicular to the rising surface part is within the range of 2° to 7°.  
   
   
       14 . A optical communication module according to  claim 13 , wherein the inclination angle in which the diffraction surface top part and the diffraction surface bottom part are to the direction perpendicular to the rising surface part is within the range of 3° to 6°.  
   
   
       15 . A optical communication module according to  claim 11 , wherein the height H 1  in the optical axis direction of the concave and convex shape satisfies the following expression.  
         H 1={λ 0 /( n− 1)}× K    
     Where, λ 0 : one of the wavelength of the incident light beams,  
     n: the refractive index of the material of the diffraction grating, K: 3 or 4.  
   
   
       16 . A optical communication module according to  claim 11 , wherein the wavelength λ 0  of the optical signal sent from the light emitting element to the end of the optical fiber and the wavelength λ 1  of the optical signal received from the end of the optical fiber satisfy the following expression.  
       1260 nm≦λ 0 ≦1360 nm  1480 nm≦λ 1 ≦1580 nm  
   
   
       17 . A optical communication module according to  claim 11 , wherein the wavelength λ 0  of the optical signal sent from the light emitting element to the end of the optical fiber and the wavelength λ 1  of the optical signal received from the end of the optical fiber satisfy the following expression.  
       1480 nm≦λ 0 ≦1580 nm  1260 nm≦λ 1 ≦1360 nm