Passive optical limiter having nonlinear material
The invention relates to a passive optical limiter having a nonlinear material capable of switching in a predetermined optical band from a transparent state to an opaque state as a function of the power of an incident laser beam. The nonlinear material is an organic dye which comprises molecules derived from 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene into which a nitrogen atom is inserted at the meso position, referred to as aza-bodipy molecules, and which have conjugated π chains functionalized so as to exhibit absorption for two photons around an incident beam wavelength lying between 1.45 μm and 1.6 μm.
1. A passive optical limiter comprising a nonlinear material capable of switching in a predetermined optical band from a transparent state to an opaque state as a function of the power of an incident laser beam, wherein the nonlinear material is an organic dye which comprises aza-bodipy molecules derived from 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene into which a nitrogen atom is inserted at the meso position and which have conjugated π chains functionalized so as to exhibit absorption for two photons around an incident beam wavelength lying between 1.45 μm and 1.6 μm.
2. A passive optical limiter according to claim 1 , wherein the conjugated π chains functionalized by aromatic electron donor or acceptor groups are introduced into the aza-bodipy molecules at position 1,7 or 3,5.
3. A passive optical limiter according to claim 2 , wherein the aromatic groups are NMe 2 , or OHex or NHex 2 at position 3,5.
4. A passive optical limiter according to claim 2 , wherein the functional groups are alkoxyphenyl or dialkylaniline or dialkylaminofluorenyl.
5. A passive optical limiter according to claim 2 , wherein the donor groups are different.
6. A passive optical limiter according to claim 1 , wherein heavy atoms are introduced into the aza-bodipy at position 2,6.
7. A passive optical limiter according to claim 6 , wherein the heavy atoms are halogens.
8. A passive optical limiter according to claim 7 , wherein the heavy atoms are Cl or Br or I.
9. A passive optical limiter according to claim 1 , wherein the aza-bodipy molecules are functionalized by a reactive hydroxyl or amino or trimethylsilyl function.
10. A passive optical limiter according to claim 1 , wherein the dye is used in liquid solution or as bulk material obtained by doping a polymer film, or as the active part of a monomer for producing an active polymer film, or by doping a matrix of the sol-gel type, or as the active part of a matrix of the sol-gel type, or as a crystal, or as nanocrystals dispersed in a polymer or sol-gel matrix.
11. A passive optical limiter according to claim 10 , further comprising an optical structure ( 30 ) with a resonant cavity, in the middle of which the said aza-bodipy used as bulk material is deposited.
12. A passive optical limiter according to claim 11 , wherein the optical structure with a resonant cavity is a photonic crystal, in the middle of which is deposited the said aza-bodipy used as a dopant of a matrix in which the photonic crystal is produced.
13. A passive optical limiter according to claim 12 , wherein the optical structure with a resonant cavity is a multilayer structure comprising a plurality of coupled resonant cavities as well as a layer exhibiting a nonlinear response.
14. A passive optical limiter according to claim 13 , wherein the multilayer optical structure is a structure with K cavities, which has Bragg mirrors with M layers, each layer having an optical thickness equal to λ/4 or a multiple of λ/4, λ being the wavelength of the incident beam, with M>2.
15. A passive optical limiter according to claim 14 , wherein the multilayer optical structure is of the type X (A) LL (A) L (A) N (A) L (A) LL (A), where (A) is a Bragg mirror with 2n layers of the type (LH) n , where L and H respectively describe a layer of optical thickness λ/4 having a low refractive index and a high refractive index, N describes a layer of the said dye with an optical thickness λ/2, X describes an apodization layer and n>1.
16. A passive optical limiter according to claim 15 , wherein the layer L is a layer of SiO 2 and the layer H is a layer of Ta 2 O 5 or TiO 2 .
17. A passive optical limiter according to claim 14 , wherein the multilayer optical structure is of the type X (A) HH (A) H (A) N (A) H (A) HH (A), where (A) is a Bragg mirror with 2n′ layers of the type (HL) n′ , where L and H respectively describe a layer of optical thickness λ/4 having a low refractive index and a high refractive index, N describes a layer of the said dye with an optical thickness λ/2, X describes an apodization layer and n′>1.
18. An optronic system which comprises a reception device equipped with a limiter according to claim 1 .
19. An optronic system according to claim 18 claim, further comprising a device for emitting a laser beam having a wavelength of between 1.45 and 1.6 μm, and in which the limiter is adapted to be blocking around the said wavelength.
20. An active optronic system according to claim 19 , wherein, the reception device having a detector located in a focal plane, the nonlinear material is placed in an intermediate focal plane or in a collimated beam.
21. An optronic system according to claim 18 , wherein, the reception device having a detector, the nonlinear material is deposited on the surface of this detector.