PLANAR OPTICAL SYSTEM FOR WIDE FIELD-OF-VIEW POLYCHROMATIC IMAGING

• US 20120127577A1
• Filed: 07/29/2010
• Published: 05/24/2012
• Est. Priority Date: 07/31/2009
• Status: Active Grant

• Current Assignee: HORIBA Jobin Yvon S.A.S.
• Original Assignee: HORIBA Jobin Yvon S.A.S.
• Inventors: Desserouer, Frédéric
• Granted Patent: US 8,934,171 B2
• Time in Patent Office: Days
• US Class Current: 359/566
• CPC Class Codes: G02B 2027/0112 comprising device for genereting colour display
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/0101 characterised by optical features G02B27/0172 takes precedence
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• CPC Class Codes: G02B 5/1861 Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 6/0011 the light guides being planar or of plate-like form

Abstract

A planar optical system for wide field-of-view polychromatic imaging includes a planar waveguide including two plane parallel faces, an entry coupler including a first diffraction grating, and an exit coupler including a second diffraction grating. The diffraction gratings are low line density diffraction gratings that have a pitch greater than the wavelength of use such that the grating is adapted to couple an entry beam having a mean angle of incidence i₀ ranging between 30 to 60 degrees into the waveguide by positive first order (+1) diffraction, the coupled beam defining an internal angle of incidence greater than the angle of total internal reflection and less than γ=80 degrees, and the second grating is adapted to receive the coupled beam and to diffract it out of the waveguide by negative first order (−1) diffraction at a mean exit angle i₁ ranging between 30 to 60 degrees.

Claims

1. A planar optical system (10) for wide field-of-view polychromatic imaging, comprising:

a planar waveguide (3) including two faces (4, 5) that are plane and parallel;

an entry coupler including a first diffraction grating (1);

an exit coupler including a second diffraction grating (2);

the planar optical system (10) being adapted to receive an incident optical beam (6, 16) having an optical spectrum of spectral width Δ

λ

(Δ

λ

=λ

₃−

λ

₁) and an angular field ±

Δ

θ and

defining a mean angle of incidence i₀ with the normal to a face (4, 5) of the waveguide (3);

said first grating (1) being adapted to couple said incident beam (6, 16) into the planar waveguide (3) as a beam (7, 17) adapted to propagate in the waveguide (3) by total internal reflection at the faces (4, 5) of the waveguide (3), and the second grating (2) being adapted to receive the coupled beam and to diffract said coupled beam out of the waveguide as an exit beam (9, 19);

characterized in that;

the first grating (1) is adapted to couple an entry beam (6, 16) of mean angle of incidence i₀ in the range 30 degrees to 60 degrees into the waveguide (3) by positive first order (+1) diffraction, said coupled beam (7, 17, 8, 18) defining an internal angle of incidence greater than the angle of total internal reflection and less than a limit angle γ

, and the second grating (2) being adapted to receive the coupled beam (7, 17, 8, 18) and to diffract it by negative first order (−

1) diffraction out of the waveguide (3) at a mean exit angle i₁ relative to the normal to an exit face (4, 5) of the waveguide (3) in the range 30 degrees to 60 degrees.

2. A planar optical system according to claim 1, characterized in that the gratings (1, 2) are diffraction gratings of low line density, having a pitch greater than the wavelength of use (λ

₁, λ

₃).

3. A planar optical system according to claim 2, characterized in that the line density is less than 1200 lines/mm.

4. A planar optical system according to claim 1, characterized in that the refractive index of the waveguide (3) is less than 1.65 over the spectral range [λ

₁, λ

₃].

5. A planar optical system according to claim 1, characterized in that the line density of the gratings (1, 2) is equal to N=1000 lines/mm, the refractive index of the waveguide (3) being equal to 1.6, and wherein the mean angle of incidence i₀ of the incident beam (6, 16) is 50 degrees, the limit angle γ

is 80 degrees, the spectral range is at least 450 nm to 630 nm and the angular field 2·

Δ

θ

is ±

15 degrees.

6. A planar optical system according to claim 1, characterized in that the first diffraction grating (1) and the second diffraction grating (2) are placed on respective faces (4, 5) of the planar waveguide (3), the lines of the grating (1, 2) being disposed perpendicularly to the longitudinal direction of the waveguide (3).

7. A planar optical system according to claim 1, characterized in that the first grating (1) and the second (2) have the same line density.

8. A planar optical system according to claim 1, characterized in that the second grating (2) has a diffraction efficiency that varies so as to render the optical flux uniform over the exit pupil.

9. A planar optical system according to claim 8, characterized in that the depth of modulation of the second grating (2) varies.

10. A planar optical system according to claim 8, characterized in that the second grating (2) includes a thin dielectric layer deposited on the profile of the grating (2), said thin dielectric layer having a continuously varying thickness.

11. A planar optical system according to claim 1, characterized in that the first diffraction grating (1) is a reflection grating and the second grating (2) is a reflection grating.

12. A planar optical system according to claim 1, characterized in that the first diffraction grating (1) is a reflection grating and the second grating (2) is a transmission grating.

13. A planar optical system according to claim 1, characterized in that the first diffraction grating (1) is a transmission grating and the second grating (2) is a reflection grating.

14. A planar optical system according to claim 1 any one of claims 1 to 10, characterized in that the first diffraction grating (1) is a transmission grating and the second grating (2) is a transmission grating.

15. Method of using a planar optical system to transport a wide field-of-view polychromatic image, comprising the following steps:

providing the planar optical system of claim 1;

directing an incident beam (6, 16) towards the entry coupler of the waveguide (3) so that said incident beam (6, 16) defines an angle of incidence i₀±

Δ

θ

with a face (4, 5) of the waveguide (3) and is diffracted by the first grating (1) and coupled into the interior of the waveguide (3) with an internal angle of incidence greater than the angle of total internal reflection and less than a limit angle γ

of 80 degrees, said incident beam (6) defining a mean angle of incidence i₀ in the range 30 degrees to 60 degrees, having a total angular field 2*Δ

θ

greater than or equal to 30 degrees, and a having spectral bandwidth Δ

λ

greater than or equal to 100 nm;

guiding the coupled beam (7, 17, 8, 18) towards the exit coupler in the interior of the waveguide (3) by total internal reflection at the internal faces (4, 5) of the waveguide (3) so that the second diffraction grating (2) receives said coupled beam and is adapted to diffract it by negative first order (−

1) diffraction to extract it from the waveguide (3) and form an exit beam (9, 19);

receiving said exit beam (9) extracted from the waveguide (3) by diffraction at the second grating (2), said exit beam (9) defining an exit angle i₁±

Δ

θ

′

with a face (4, 5) of the waveguide (3), i₁ being greater than or equal to 30 degrees, and having total angular field 2*Δ

θ

′

greater than or equal to 30 degrees over the spectral band Δ

λ

.

16. Method according to claim 15 wherein the mean directions of the incident beam (6, 16) and of the exit beam (9, 19) define an angle in the range 80 degrees to 100 degrees.