Diffractive polarizing mirror device
A polarizing mirror device including an optical substrate ( 1 ) of real refractive index n s ; a dielectric multilayer mirror ( 2 ), composed of dielectric layers of low and high refractive index; and a corrugated grating layer ( 6 ) of local period Λ at the side of a cover medium of refractive index n c . The local period Λ is selected such that upon substantially normal incidence of an incident wave at wavelength λ from the cover medium there is no diffraction order other than the 0 th reflected order in the cover medium, such that the field of the +1 st and −1 st orders diffracted into the layers of the multilayer and into the optical substrate have a non-evanescent propagating character, and such that the respective angles under which the +1 st and −1 st orders propagate in each layer of said multilayer have an absolute value larger than or equal to the angle corresponding to the angular band edge of the central TM reflection band and, if a central TE reflection band of finite angular width exits, smaller than the angle corresponding to the angular band edge of this central TE reflection band in the angular spectrum of the multilayer at the wavelength λ with a fictive incident medium having the index of the considered layer of this multilayer.
1. A polarizing mirror device comprising:
an optical substrate of refractive index real part n s ;
a dielectric multilayer mirror composed of layers of high and low refractive index n h and n l ,; and
a grating layer arranged at the side of a cover medium and defining a corrugated grating of local period Λ,
wherein said local period Λ is selected such that upon substantially normal incidence of an incident wave, at a wavelength λ in the laser range, from the cover medium there is no diffraction order other than the 0 th reflected order in this cover medium, such that the field of the +1 st and −1 st orders diffracted into the layers of said multilayer and into the optical substrate have a non-evanescent propagating character, and such that the respective angles θ 1h and θ 1l , under which the +1 st and −1 st orders propagate in any layer of said multilayer have an absolute value, arc sin(λ/n l ·Λ) in the layers of low index and arc sin(λ/n h ·Λ) in the layers of high index, which is larger than or equal to the angle corresponding to the angular band edge of the central TM reflection band and, if a central TE reflexion band of finite angular width exists, smaller than the angle corresponding to the angular band edge of this central TE reflection band in the angular reflexion spectrum of the multilayer at the wavelength λ.
2. The polarizing mirror device according to claim 1 , wherein said absolute value of said respective angles in said each layer is substantially equal to an angle corresponding to a TM reflection dip in said angular reflection spectrum of the multilayer.
3. The polarizing mirror device according to claim 2 , wherein said local period Λ of the grating is arranged such that the +1 st and −1 st orders diffracted in said multilayer impinge at the interfaces between its layers substantially under the Brewster incidence.
4. The polarizing mirror device according to claim 3 , wherein it exhibits substantially 100% TE 0 th order reflection.
5. The polarizing mirror device according to claim 2 , wherein it exhibits substantially 100% TE 0 th order reflection.
6. The polarizing mirror device according to claim 1 , wherein the last layer of said multilayer at the cover side is of low index.
7. The polarizing mirror device according to claim 1 , wherein said multilayer is composed of a stack of quarter wave layers at the wavelength of said incident wave under normal incidence.
8. The polarizing mirror device according to claim 1 , wherein said multilayer is composed of a stack of quarter wave layers at said wavelength Λ under oblique incidence from an incidence medium of refractive index equal to the refractive index of the low index layers of this multilayer.
9. The polarizing mirror device according to claim 8 , wherein said oblique incidence is smaller than or equal to 30 degrees.
10. The polarizing mirror device according to claim 1 , wherein said substrate has a refractive index substantially equal to one of said low and high refractive index.
11. The polarizing mirror device according to claim 1 , wherein it exhibits substantially 100% TE 0 th order reflection.
12. The polarizing mirror device according to claim 1 , wherein said grating has radially periodic circular lines for azimuthal polarization generation.
13. The polarizing mirror device according to claim 1 , wherein said grating is segmented in concentric rings, each ring containing radial lines of essentially identical period, for radial polarization generation.
14. The polarizing mirror device according to claim 1 , wherein the grating layer propagates a guided mode excited by the corrugation.
15. The polarizing mirror device according to claim 14 , wherein the phase difference between the TE and TM field reflection coefficients is approximately equal to π.