Patent ID: 7106508

Claim:
An optical device through which propagates a first beam and a second beam, the first beam propagating through the optical device along a first optical path and the second beam propagating through the optical device along a second optical path, the optical device comprising: a first optical component having a first length, the first optical component receiving the first beam along the first optical path; a second optical component optically coupled to said first optical component, said second optical component having a second length and being adapted to receive the first beam and the second beam, and a first polarizing beam splitter and a second polarizing beam splitter, said first polarizing beam splitter being optically coupled to said first optical component and said second polarizing beam splitter being disposed between said first optical component and said second optical component, wherein said first length of said first optical component and said second length of said second optical component are selected such that an optical path difference between the first optical path length of said first optical path and a second optical path length of said second optical path is approximately inversely proportional to a free spectral range of a target wavelength of either the first beam or the second beam, and wherein said first length and said second length are defined by the equations ( n air - n g ) ⁢ L w + ( n o - n e ) ⁢ L c = c FSR - 4 ⁢ n g ⁢ d ⁢ ⁢ sin ⁢ ⁢ α ⁢ ⁢ and [ ( n air - n g ) ⁢ α 1 - β 1 ] ⁢ L w + ( β 2 + α 2 ⁡ ( n o - n e ) ) ⁢ L c = - 4 ⁢ d ⁢ ⁢ sin ⁢ ⁢ α ⁡ ( β 1 + α 1 ⁢ n g ) , where n air = refractive index of air. n g = group index of the glass. L 2 = length of first optical component. n o = ordinary index of refraction of the second optical component. n e = extraordinary index of refraction of the second optical component. L c = length of the second optical component. c = speed of light in a vacuum. FSR = free spectral range. d = distance between a first interface and a second interface of the first polarizing beam splitter. α = angle of the first interface with respect to horizontal. α 1 = thermal expansion coefficient of said first and said second polarizing beam splitters. α 2 = thermal expansion coefficient of said second optical component. β 1 = ∂ n g ∂ T , where ⁢ ⁢ ∂ T ⁢ ⁢ is the change in ambient temperature. β 2 = ∂ ( n o - n e ) ∂ T , where ⁢ ⁢ ∂ T ⁢ ⁢ is the change in ambient temperature.