Tuneable grating assisted directional optical coupler
View Patent ↗A tuneable grating assisted directional optical coupler to couple a transmission signal has a first waveguide including a first core and a first cladding, the first waveguide having a first effective refractive index. The coupler also has a second waveguide including a second core and a second cladding, the second waveguide having a second effective refractive index different from the first effective index and being in substantially close proximity to the first waveguide in a predetermined region to provide coupling therebetween. A periodic perturbation is positioned in the coupling region to cause the coupling to be wavelength selective for one given wavelength function of the first and/or the second effective refractive index. Additionally, the second cladding of the second waveguide has a tuneable material and the first cladding of the first waveguide has a non-tuneable material.
1. A tuneable grating assisted directional optical coupler to couple a transmission signal, comprising:
a first waveguide comprising a first core and a first cladding, said first waveguide having a first effective refractive index;
a second waveguide comprising a second core and a second cladding, said second waveguide having a second effective refractive index, different from said first effective index, and being in substantially close proximity to said first waveguide in a predetermined region to provide coupling therebetween; and
a periodic perturbation positioned in said coupling region for causing said coupling to be wavelength selective for a given wavelength as a function of said first and/or said second effective refractive index;
said second cladding of said second waveguide comprising a tuneable material and said first cladding of said first waveguide comprising a non-tuneable material.
2. The coupler according to claim 1 , wherein said tuneable material has a refractive index which can be varied upon variation of an external parameter.
3. The coupler according to claim 2 , wherein the tuneable material is variable with temperature and said tuneable material has a ratio
Δ
n
n
between the refractive index variation Δn and the refractive index n of said tuneable material, the ratio not smaller than 10 −2 for a temperature variation not greater than 100° C.
4. The coupler according to claim 2 , wherein the tuneable material is variable with an electric field and said tuneable material has a ratio
Δ
n
n
between the refractive index variation Δn and the refractive index n of said tuneable material, the ratio not smaller than 10 −2 for an electric field variation not greater than 1 V/μm.
5. The coupler according to claim 2 , wherein the refractive index n of said tuneable material is variable with temperature T and said tuneable material has a thermo-optic coefficient
ⅆ
n
ⅆ
T
greater than or equal to 10 −4 /° C.
6. The coupler according to claim 2 , wherein said tuneable material variable with temperature is a polymer.
7. The coupler according to claim 2 , wherein the refractive index of said tuneable material is variable with electric field and said tuneable material has an electro-optic coefficient greater than or equal to 2.5 nm/V.
8. The coupler according to claim 1 , wherein said first and said second waveguides are vertically stacked on a substrate.
9. The coupler according to claim 8 , wherein said first waveguide is the lower waveguide, while said second waveguide is the upper waveguide.
10. The coupler according to claim 1 , wherein said first and/or said second core comprises silicon compound material.
11. The coupler according to claim 1 , wherein said first cladding of said first waveguide comprises silica glass.
12. The coupler according to claim 1 , wherein said given wavelength is in the range of about 1530 nm to about 1565 nm.
13. The coupler according to claim 1 , wherein said transmission signal carries a given number of optical channels having wavelengths comprising about 1530 to about 1565 nm.
14. The coupler according to claim 1 , wherein said periodic perturbation is a Bragg grating having a grating period (Λ) and said given wavelength (λ 0 ) is given by λ 0 =Λ(n 1 ±n 2 ), where n 1 is said first effective refractive index and n 2 is said second effective refractive index.
15. The coupler according to claim 1 , wherein said transmission signal is supplied to said first waveguide and a coupled signal of said given wavelength is outputted by said second waveguide.
16. The coupler according to claim 15 , wherein said transmission signal and said coupled signal are contra-propagating and said given wavelength (λ 0 ) is given by λ 0 =Λ(n 1 +n 2 ), where Λ is a grating period of said periodic perturbation, n 1 is said first effective refractive index, and n 2 is said second effective refractive index.
17. The coupler according to claim 16 , wherein said transmission signal comprises one or more wavelengths between a lower wavelength value λ min and an upper wavelength value λ max , and wherein said first effective refractive index n 1 and said second effective refractive index n 2 satisfy the following equation:
n
2
-
n
1
>
2
n
1
(
λ
max
λ
min
-
1
)
.
18. The coupler according to claim 15 , wherein said transmission signal and said coupled signal are co-propagating and said given wavelength (λ 0 ) is given by λ 0 =Λ(n 1 −n 2 ), where Λ is a grating period of said periodic perturbation, n 1 is said first effective refractive index, and n 2 is said second effective refractive index.
19. The coupler according to claim 1 , wherein said periodic perturbation is realised on the first waveguide.
20. The coupler according to claim 19 , wherein said periodic perturbation is realised on said first core of said first waveguide.
21. An add/drop optical device comprising one or more tuneable grating assisted directional optical couplers, at least one of the tuneable grating assisted directional optical couplers comprising:
a first waveguide comprising a first core and a first cladding, said first waveguide having a first effective refractive index;
a second waveguide comprising a second core and a second cladding, said second waveguide having a second effective refractive index, different from said first effective index, and being in substantially close proximity to said first waveguide in a predetermined region to provide coupling therebetween; and
a periodic perturbation positioned in said coupling region for causing said coupling to be wavelength selective for a given wavelength as a function of said first and/or said second effective refractive index;
said second cladding of said second waveguide comprising a tuneable material and said first cladding of said first waveguide comprising a non-tuneable material.