Patent ID: 7941025

Claim:
A semiconductor photonic device comprising: a semiconductor photonic element having an effective refractive index n c and including an active layer through which light having a wavelength λ propagates; and a coating film including a plurality of layers and located on an end surface of said semiconductor photonic element, wherein said coating film has an amplitude reflectivity r having a magnitude component and a phase component so that the amplitude reflectivity can be expressed as a complex number with a real part and an imaginary part and the amplitude reflectivity has a non-zero real part and a non-zero imaginary part, said coating film has a power reflectivity R=|r| 2 , said coating film includes a multi-layer film, said multi-layer film including a first layer having a refractive index n 1 and a thickness d 1 , and a second layer having a refractive index n 2 and a thickness d 2 , arranged in a stack, said first and second layers of said multi-layer film have a thickness ratio equal to d 1 /d 2 , the amplitude reflectivity, r, is r = ( m 11 + m 12 ) ⁢ n c - ( m 21 + m 22 ) ( m 11 + m 12 ) ⁢ n c + ( m 21 + m 22 ) , where m 11 , m 12 , m 21 , and m 22 are elements of the characteristic matrix of said coating film having λ, n 1 , n 2 , d 1 , d 2 and d 1 /d 2 as variables, the characteristic matrix satisfies [ m 11 m 12 m 21 m 22 ] = [ cos ⁢ ⁢ ϕ 1 - i n 1 ⁢ sin ⁢ ⁢ ϕ 1 - in 1 ⁢ sin ⁢ ⁢ ϕ 1 cos ⁢ ⁢ ϕ 1 ] × [ cos ⁢ ⁢ ϕ 2 - i n 2 ⁢ sin ⁢ ⁢ ϕ 2 - in 2 ⁢ sin ⁢ ⁢ ϕ 2 cos ⁢ ⁢ ϕ 2 ] where φ 1 is phase change of light having the wavelength λ and passing through said first layer of said multi-layer film and φ 2 is phase change of light having the wavelength λ and passing through said second layer of said multi-layer film, ϕ 1 = 2 ⁢ π λ ⁢ n 1 ⁢ d 1 , ⁢ and ⁢ ⁢ ϕ 2 = 2 ⁢ π λ ⁢ n 2 ⁢ d 2 .