Patent ID: 6781740
Filing Date: 2004-08-24
Classification: G02B

Abstract:
Achromatic phase shift device for introducing a wavelength independent optical phase shift in a first optical beam during operation, comprising at least one dispersive element,the at least one dispersive element comprising k element pairs (55k), k being an integer between 1 and M, each element pair being formed by respective first refractive means (2k) and second refractive means (4k), the respective first refractive means (2k) having a first refractive means input plane (6) for receiving a first optical beam (40) and a first refractive means output plane (8), the first refractive means input plane (6) and the first refractive means output plane (8) being at a predetermined angle &bgr;k to each other, 0kthe respective second refractive means (4k) having a second refractive means input plane (10) and a second refractive means output plane (12), said second refractive means input plane (10) being positioned equidistant to the first refractive means output plane (8) and the second refractive means output plane (12) being positioned parallel to the first refractive means input plane (6), characterised in that the device (1) introduces a predetermined phase shift &psgr;0 between the first optical beam (40) and a second optical beam (41), the second optical beam (41) running substantially parallel to the first optical beam (40) over an optical path length w0, a first optical axis (50) being defined from a device input surface (51) to a device output surface (52), the first refractive means (2k) having a first distance dkâ€² along the first optical axis (50) and the second refractive means having a second distance dkâ€³ along the first optical axis (50), the first optical beam (40) being at an angle &thgr;k with the first optical axis (50) and a modified refractive index ak being defined as ak=nk cos &thgr;k, in which the sum dk of the first and second distance of the first and second refractive means (2k, 4k), respectively and the required optical path w0 are determined by solving the following equations for the wavelengths (&lgr;0 . . . &lgr;M) at which the predetermined phase shift &psgr;0 should be obtained exactly: â€ƒ-w0+a0&af;(Î»0)&it;d0+â€¦+aM-1&af;(Î»0)&it;dM-1=Ïˆ02&it;â€ƒ&it;Ï€&it;Î»0â€ƒ&vellip;&vellip;&vellip;â€ƒ-w0+a0&af;(Î»M)&it;d0+â€¦+aM-1&af;(Î»M)&it;dM-1=Ïˆ02&it;â€ƒ&it;Ï€&it;Î»Mâ€ƒ