Polarization-insensitive optical filter which has resonant gratings and is adjustable according to the incidence angle

摘要

The invention relates to a polarization-insensitive optical filter centered on a wavelength measured in vacuum, comprising: first and second waveguides each having a propagation mode; a first grating formed in or on the surface of the first waveguide, the first grating being periodical at least along a first axis Ox defining a first orthonormal base Oxyz; a second grating formed in or on the surface of the second waveguide, the second grating being periodical at least along a second axis Ox′ defining a second orthonormal base Ox′y′z; wherein the first and second grating are provided one above another and are such that the first axis Ox and the second axis Ox′ define an angle ξ different from ±π/2 radians so that, when the first grating is illuminated by a light beam, the propagation modes are excited and have orthogonal fields for an angle of incidence of the light beam.

主权项

1. An optical filter insensitive to polarisation centred on a wavelength (λ0) measured in a vacuum, comprising:
a first waveguide supporting a first propagation mode; a second waveguide supporting a second propagation mode; a first grating formed in or on the surface of the first waveguide, the first grating being periodic of period d1 at least along a first axis Ox defining a first orthonormal base Oxyz; a second grating formed in or on the surface of the second waveguide, the second grating being periodic of period d2 at least along a second axis Ox′ defining a second orthonormal base Ox′y′z; wherein the first and the second gratings are arranged one above another and are such that a third axis Oz is normal to the surface of the waveguides and that the first axis Ox and the second axis Ox′ form an angle ξ different than +−π/2 radians such that when the first grating is illuminated by a light beam the first and second propagation modes are excited and their fields are orthogonal for an angle of incidence of the light beam, and the first and second gratings have respective diffraction orders n and m, wherein the respective directions of propagation V1 and V2 of the diffraction orders n and m are defined by the formulae:V1=[sin⁡(θ)⁢cos⁡(Φ)-n⁢⁢λd1]⁢x^+[sin⁡(θ)⁢sin⁡(Φ)]⁢y^V2=[sin⁡(θ)⁢cos⁡(π2-Φ+ξ)-m⁢⁢λd2]⁢y^′+[sin⁡(θ)⁢sin⁡(π2-Φ+ξ)]⁢x^′with θ and Φ being polar and azimuth angles, respectively, and λ being the wavelength of the light beam, and
wherein the condition of excitation of the first mode via the first grating is ∥V1∥≈nf1, the condition of excitation of the second mode via the second grating is ∥V2∥≈nf2, and the condition of orthogonality between the fields of both excited modes is V1·V2=0.