Multiphoton curing to provide encapsulated optical elements
Methods of fabricating optical elements that are encapsulated in monolithic matrices. The present invention is based, at least in one aspect, upon the concept of using multiphoton, multi-step photocuring to fabricate encapsulated optical element(s) within a body of a photopolymerizable composition. Imagewise, multi-photon polymerization techniques are used to form the optical element. The body surrounding the optical element is also photohardened by blanket irradiation and/or thermal curing to help form an encapsulating structure. In addition, the composition also incorporates one or more other, non-diffusing binder components that may be thermosetting or thermoplastic. The end result is an encapsulated structure with good hardness, durability, dimensional stability, resilience, and toughness.
1. A method of fabricating an encapsulated optical element, said method comprising the steps of:
(a) providing a body comprising:
(i) a photopolymerizable precursor comprising a diffusing species, said precursor forming a polymer matrix upon photopolymerization, and said polymer matrix having an index of refraction;
(ii) a substantially non-diffusing binder component having an index of refraction that is lower than the index of refraction of the polymer matrix and that is miscible with the photopolymerizable precursor; and
(iii) a multiphoton photoinitiator system;
(b) imagewise exposing at least a portion of the body to energy under conditions effective to multiphoton photopolymerize the polymer precursor in a pattern effective to form a three-dimensional optical element; and
(c) after imagewise exposing the body; nonimagewise exposing at least a portion of the body to a photopolymerizing fluence of energy.
2. The method of claim 1 , wherein the binder is derived from ingredients comprising a thermoplastic polymer.
3. The method of claim 1 , wherein the binder is derived from ingredients comprising a thermosetting polymer having substantially no photocurable functionality.
4. The method of claim 1 , wherein the multiphoton photoinitiator system comprises a multiphoton photosensitizer.
5. The method of claim 4 , wherein the multiphoton photoinitiator system further comprises a single photon photoinitiator.
6. The method of claim 5 , wherein the multiphoton photoinitiator system further comprises an electron donor.
7. The method of claim 1 , wherein the nonimagewise exposing step comprises causing single photon polymerization.
8. The method of claim 1 , wherein the nonimagewise exposing step comprises causing multiphoton polymerization.
9. The method of claim 1 wherein the imagewise exposing step comprises causing a depletion zone to be formed at a boundary of the optical element, said depletion zone comprising a reduced amount of the diffusing species.
10. The method of claim 1 , wherein the imagewise exposing step comprises causing a plurality of femtosecond laser pulses to be directed into the body.
11. The method of claim 1 wherein said body comprises a homogeneous admixture of ingredients comprising said precursor and said binder.
12. The method of claim 1 , wherein said optical element is a waveguide.
13. The method of claim 1 , wherein said imagewise exposure step occurs non-holographically.
14. The method of claim 1 , wherein the precursor comprises at least one aromatic (meth)acrylate monomer.
15. The method of claim 1 , wherein the precursor comprises at least one aromatic, (meth)acrylate comprising a fluorinated moiety.
16. The method of claim 1 , wherein the precursor comprises 10 to 100 parts by weight of at least one of 2-(1-napthoxy)ethyl(meth)acrylate, 2-(2-napthoxy)ethyl (meth)acrylate, phenoxy(meth)acrylate, and mixtures thereof per (b) 0.5 to 50 parts by weight of at least one multifunctional (meth)acrylate monomer.
17. The method of claim 1 , wherein the multifunctional (meth)acrylate monomer comprises at least one of trimethylolpropane tri(meth)acrylate (TMPTA), hexanediol di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, and mixtures thereof.