Integrated optical circuit with an off-center groove
An integrated optical circuit includes a substrate having an input face, an output face, a lower face and an upper face, an optical waveguide extending between a first end located on the input face of the substrate and a second waveguide end located on the output face of the substrate. The integrated optical circuit further includes at least one off-center groove, the off-center groove extending from the lower face to the inside of the substrate, the at least one off-center groove being located at a non-zero distance d from the median plane, the off-center groove replacing a central groove and the at least one off-center groove being capable of attenuating the non-guided optical beam transmitted by the substrate between the first end and the second end.
1. An integrated optical circuit comprising:
a substrate, said substrate including an input face, an output face, a lower face, an upper face and two side faces, said lower face, upper face and side faces extending between the input face and the output face, the upper face being planar and opposite to the lower face;
at least one optical waveguide located in a plane parallel to the upper face, said at least one optical waveguide extending between said input face and said output face;
at least one first waveguide end located on the input face of the substrate and at least one second waveguide end located on the output face of the substrate;
said integrated optical circuit being capable of receiving an incident optical beam on said first waveguide end, of forming a guided optical beam propagating in an optically guided manner, and of forming a non-guided optical beam propagating in a non-guided manner in the substrate,
wherein, there being defined a median plane perpendicular to the upper face and to a line segment joining the first and the second waveguide ends, said median plane passing through the middle of said line segment, and an incidence plane perpendicular to the median plane, said incidence plane passing through the first end and the second end,
said integrated optical circuit does not include a central groove but instead includes at least one groove off-centered with respect to the median plane, said at least one off-center groove extending from the lower face to an inside of the substrate, said at least one off-center groove being located at a non-zero distance d from said median plane, said at least one off-center groove having a height h in the incidence plane, said height h being higher than a minimum height h min , such that:
h
m
i
n
=
2
×
e
×
d
L
+
D
×
λ
2
where L represents the length of the substrate, e the thickness of the substrate, d the distance between said off-center groove and the median plane, λ the wavelength in the material of a non-guided optical beam in the substrate, and D is equal to (L/2−d), said at least one off-center groove being capable of attenuating said non-guided optical beam transmitted by said substrate between said first end and said second end.
2. The integrated optical circuit according to claim 1 , wherein said at least one off-center groove has a width w such that:
w
>>
λ
2
×
θ
S
×
(
θ
S
′
-
θ
S
)
so as to limit the angle of diffraction on the bottom of the off-center groove, where θ S represents the grazing incidence angle of a non-guided optical beam on the bottom of said off-center groove and θ′ S represents the angle formed between the upper face of the substrate and a segment extending from the middle of the bottom of the groove to the second end of the waveguide.
3. The integrated optical circuit according to claim 1 , wherein said at least one off-center groove extends in a plane parallel to the median plane.
4. The integrated optical circuit according to claim 1 , wherein said at least one off-center groove extends in a plane parallel to the input face and/or the output face of the substrate.
5. The integrated optical circuit according to claim 1 , wherein said at least one off-center groove includes a flat bottom.
6. The integrated optical circuit according to claim 5 , wherein said flat bottom has an optically polished surface so as to limit the diffusion towards the second end.
7. The integrated optical circuit according to claim 1 , including a single one off-center groove extending from the lower face to the inside of the substrate.
8. The integrated optical circuit according to claim 1 , wherein said at least one groove has a rectangular, trapezoidal or dovetail section.
9. The integrated optical circuit according to claim 1 , wherein said at least one off-center groove extends from a side face of the substrate to the opposite side face of the substrate.
10. The integrated optical circuit according to claim 1 , wherein said substrate is a lithium niobate crystal and said at least one waveguide is a polarizer waveguide formed by proton exchange.
11. The integrated optical circuit according to claim 2 , wherein said at least one off-center groove extends in a plane parallel to the median plane.
12. The integrated optical circuit according to claim 2 , wherein said at least one off-center groove extends in a plane parallel to the input face and/or the output face of the substrate.
13. The integrated optical circuit according to claim 2 , wherein said at least one off-center groove includes a flat bottom.
14. The integrated optical circuit according to claim 3 , wherein said at least one off-center groove includes a flat bottom.
15. The integrated optical circuit according to claim 4 , wherein said at least one off-center groove includes a flat bottom.
16. An integrated optical circuit comprising:
a substrate, said substrate including an input face, an output face, a lower face, an upper face and two side faces, said lower face, upper face and side faces extending between the input face and the output face, the upper face being planar and opposite to the lower face;
at least one optical waveguide located in a plane parallel to the upper face, said at least one optical waveguide extending between said input face and said output face;
at least one first waveguide end located on the input face of the substrate and at least one second waveguide end located on the output face of the substrate;
said integrated optical circuit being capable of receiving an incident optical beam on said first waveguide end, of forming a guided optical beam propagating in an optically guided manner, and of forming a non-guided optical beam propagating in a non-guided manner in the substrate,
wherein, there being defined a median plane perpendicular to the upper face and to a line segment joining the first and the second waveguide ends, said median plane passing through the middle of said line segment, and an incidence plane perpendicular to the median plane, said incidence plane passing through the first end and the second end,
said integrated optical circuit includes at least one groove off-centered with respect to the median plane, said at least one off-center groove extending from the lower face to an inside of the substrate, said at least one off-center groove being located at a non-zero distance d from said median plane, said at least one off-center groove having a height h in the incidence plane, said height h being higher than a minimum height h min , such that:
h
m
i
n
=
2
×
e
×
d
L
+
D
×
λ
2
where L represents the length of the substrate, e the thickness of the substrate, d the distance between said off-center groove and the median plane, λ the wavelength in the material of a non-guided optical beam in the substrate, and D is equal to (L/2−d), said at least one off-center groove being capable of attenuating said non-guided optical beam transmitted by said substrate between said first end and said second end; wherein the integrated optical circuit comprises only one or more off-center grooves.
17. The integrated optical circuit according to claim 16 , wherein said at least one off-center groove has a width w such that:
w
>>
λ
2
×
θ
S
×
(
θ
S
′
-
θ
S
)
so as to limit the angle of diffraction on the bottom of the off-center groove, where θ S represents the grazing incidence angle of a non-guided optical beam on the bottom of said off-center groove and θ′ S represents the angle formed between the upper face of the substrate and a segment extending from the middle of the bottom of the groove to the second end of the waveguide.
18. The integrated optical circuit according to claim 16 , wherein said at least one off-center groove extends in a plane parallel to the median plane.
19. The integrated optical circuit according to claim 16 , wherein said at least one off-center groove extends in a plane parallel to the input face and/or the output face of the substrate.
20. The integrated optical circuit according to claim 16 , wherein said at least one off-center groove includes a flat bottom.