Laser induced refractive index change writing in non-hydrated hydrogels

Abstract

A method of forming an optical device with a modified refractive index pattern provided therein includes: providing an optical device comprising a polymeric lens hydrogel material in a non-hydrated form essentially devoid of free, non-bound water; forming at least one laser-modified pattern within the hydrogel material in the non-hydrated form by exposing regions of the hydrogel material to light pulses from a laser to cause changes in the polymeric lens hydrogel material in the exposed regions of the hydrogel material sufficient to cause a change in refractive index of the exposed regions relative to the refractive index of the polymeric lens hydrogel material in non-exposed regions upon hydration of the polymeric lens hydrogel material; hydrating the hydrogel material which has the laser-modified pattern formed there within; and heating the optical device having the resulting hydrated hydrogel material which has the laser-modified pattern formed there within to increase a change in refractive index between exposed and non-exposed regions of the polymeric hydrogel lens material. The laser exposure may be performed by scanning focused pulses from the laser along regions of the polymeric lens hydrogel material. The polymeric lens hydrogel material may comprise a silicone hydrogel material or a non-silicone based hydrogel material. The polymeric lens hydrogel material in a non-hydrated form may not have been previously hydrated and dried, and further be essentially devoid of bound water.

Description

LASER INDUCED REFRACTIVE INDEX CHANGE WRITING IN NON-HYDRATEDHYDROGELSRELATED FIELDS

[0001] Femtosecond micromachining for inducing refractive index (RI) or phase change in hydrogel-based materials.BACKGROUND

[0002] Femtosecond micromachining is a process that uses femtosecond lasers to deliver a large amount of energy to a small area, creating localized changes in a material’s properties. By scanning a tightly focused pulse in the material, a wide range of nano- and microstructures can be inscribed in metals, plastics, ceramics, and biological tissues. This technique is often used in the production of microfluidic devices, and other microscale components for various purposes, including data storage, drug delivery, and environmental monitoring. Furthermore, when the pulse energy is below the ablation threshold, femtosecond lasers can be used to create localized refractive index changes in transparent materials without the damage or removal of the material.

[0003] This technique has more recently been applied to alter the optical properties of ophthalmic materials, such as hydrogel-based contact lenses, intra-ocular lenses (IOL), and cornea tissues, by creating different refractive index shaping structures for vision correction applications. LIRIC (Laser Induced Refractive Index Change) writing is a process that uses femtosecond laser pulses, at energies below the damage threshold, to locally modify the refractive index of ophthalmic materials via multiphoton absorption. Gandara-Montano et al. (“Femtosecond laser writing of freeform gradient index micro-lenses in hydrogel-based contact lenses,” Optical Materials Express 5(10), 2257-2271 (2015)), e.g., successfully wrote arbitrary Zernike polynomials in hydrogel-based contact lenses. A phase- wrapped lens was written directly inside an IOL to alter the hydrophilicity of targeted areas, and also high-quality gradientindex (GRIN) Fresnel lenses with wide power range from -3.0 to +1.5 diopters were written in piano contact lens materials. NIR / Blue femtosecond lasers have further been used for noninvasive Intra-Tissue Refractive Index Shaping (IRIS) inside corneal tissue.

[0004] U.S. Publication No. 2008 / 0001320, the disclosure of which is incorporated herein by reference in its entirety, more particularly describes methods for modifying the refractive index of optical polymeric materials, such as intraocular lenses, corneal inlays, or contact lenses, using very short pulses from a visible or near-IR laser having a pulse energy from, e.g., 0.5 nJ to 1000 nJ, where the intensity of light is sufficient to change the refractive index of the material within the focal volume, whereas portions just outside the focal volume are minimally affected by the laser light. Irradiation within the focal volume results in refractive optical structures characterized by a change in refractive index of 0.005 or more relative to the index of refraction of the bulk (non-irradiated) polymeric material. Under certain irradiation conditions and in certain optical materials, a change in refractive index of 0.06 was measured. The change in refractive index can be used to form patterned desired refractive structures in the optical polymeric material.

[0005] U.S. Publication No. 2012 / 0310340, the disclosure of which is incorporated herein by reference in its entirety, further describes a method for providing changes in refractive power of an optical device made of an optical, polymeric material by forming at least one laser-modified, gradient index (GRIN) layer disposed between an anterior surface and a posterior surface of the device by scanning with light pulses from a visible or near-IR laser along regions of the optical, polymeric material. The at least one laser-modified GRIN layer comprises a plurality of adjacent refractive segments, and is further characterized by a variation in index of refraction of at least one of (i) a portion of the adjacent refractive segments transverse to the direction scanned; and (ii) a portion of refractive segments along the direction scanned.

[0006] Huang and Knox (“Femtosecond micro-machining of hydrogels: parametric study and photochemical model including material saturation,” Optical Materials Express, Vol. 9, No. 9 / 1, 3818-3834 (2019)), further studied the optimization of laser writing system parameters in the LIRIC writing technique. They examined the effects of various laser system parameters, including the laser repetition rate, wavelength, pulse duration and shape, scan speed, numerical aperture, and average power, on the induced refractive index change in ophthalmic hydrogels. They developed a photochemical model given in equation (2) relating the phase change induced A<b, a quantity related to refractive index change by equation (1), to various writing and material parameters.Where An is the refractive index change, L is the axial depth of the refractive index change region and A is the wavelength of the He-Ne laser used in the interferometer to image the phase change.Where A<h is the induced phase change measured in waves at the measurement wavelength, NA is the numerical aperture, Pavgis average power, m is nonlinear absorption factor, / ? is the nonlinear absorption coefficient, v is repetition rate of the laser,! is pulse width, A is the laser wavelength, S is scan speed, t is linespacing and y is material constant.

[0009] With the developed photochemical model, it is possible to carefully chose laser writing system parameters to induce desired refractive corrections to produce customized contact lenses.

[0010] While most prior work has been performed on hydrogel materials in their hydrated form, Savage (“A Non-Ablative Technique for Femtosecond Laser-Based Refractive Correction: Development, Efficacy, and Tissue Effects”, PhD Thesis, Daniel Savage, University of Rochester (2018)) reported that index changes in dehydrated air-dried Hydroxy ethyl Methyl Acrylate (HEMA) based contact lenses (Akreos®) were obtained with an 80 MHz 800 nm laser at scan speeds of 5-50mm / s. Refractive index changes after rehydration were lower but comparable to the index change induced under hydrated conditions with similar writing parameters. The research was limited to the inscription of diffraction gratings, and while writing in silicone based dehydrated hydrogel materials was also reported, index changes in such materials were not determined, as slippage of the dehydrated samples during writing made it difficult to measure refractive index change from the written grid pattern.

[0011] One method of manufacturing hydrogel -based contact lenses involves pressing a monomer solution between convex and concave parts of a mold and polymerizing the mixture under ultraviolet radiation. The resulting lens is then peeled off, hydrated in a saline solution, and packaged in a sealed blister. Manufacturers create contact lenses with different powers by shaping the ophthalmic hydrogel in molds with specific curvatures, a process that requires a different mold shape for each refractive correction. This method is limited in the range of lenspowers that can be produced, especially for uncommon prescriptions, due to cost considerations. In contrast, the LIRIC technique allows for more precise control of the refractive index and the ability to create a wider range of lens powers.

[0012] It would be desirable to provide new ways of incorporating a LIRIC writing process into hydrogel lens materials, and in particular enable incorporating LIRIC writing process into hydrogel contact lens manufacturing systems in ways that allow for new kinds of customization of the lens properties.SUMMARY

[0013] In one embodiment of the disclosure, a method of forming an optical device with a modified refractive index pattern provided therein is described, where the method comprises: providing an optical device comprising a polymeric lens hydrogel material in a non-hydrated form essentially devoid of free, non-bound water; forming at least one laser-modified pattern within the hydrogel material in the non-hydrated form by exposing regions of the hydrogel material to light pulses from a laser to cause changes in the polymeric lens hydrogel material in the exposed regions of the hydrogel material sufficient to cause a change in refractive index of the exposed regions relative to the refractive index of the polymeric lens hydrogel material in non-exposed regions upon hydration of the polymeric lens hydrogel material; hydrating the hydrogel material which has the laser-modified pattern formed there within; and heating the optical device having the resulting hydrated hydrogel material which has the laser-modified pattern formed there within to increase a change in refractive index between exposed and nonexposed regions of the polymeric hydrogel lens material.

[0014] In various further specific embodiments of the disclosure, the laser exposure may be performed by scanning focused pulses from the laser along regions of the polymeric lens hydrogel material; the polymeric lens hydrogel material may comprise a silicone hydrogel material or a non-silicone based hydrogel material; the polymeric lens hydrogel material may be a silicone hydrogel material; the polymeric lens hydrogel material may be a non-silicone based hydrogel material; and / or the polymeric lens hydrogel material in a non-hydrated form may not have been previously hydrated and dried, and is further essentially devoid of bound water.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Fig. 1.1 is a schematic illustrating steps of manufacture of ophthalmic contact lens via injection molding.

[0016] Fig. 1.2 is a schematic illustrating structural changes in a hydrogel during different stages of the dehydration process, adapted from Y. Sekine and T. Ikeda-Fukazawa, “Structural changes of water in a hydrogel during dehydration,” The Journal of Chemical Physics, vol. 130, no. 3, p. 034501, Jan. 2009.

[0017] Fig. 2.1(a) is a schematic illustrating a configuration of a 400nm femtosecond laser writing system.

[0018] Fig. 2.1(b) is a schematic of a MZI setup used to image phase bars, adapted from G. A. Gandara-Montano, A. Ivansky, D. E. Savage, J. D. Ellis, and W. H. Knox, “Femtosecond laser writing of freeform gradient index microlenses in hydrogel-based contact lenses,” Optical Materials Express, vol. 5, no. 10, pp. 2257-2271, 2015.

[0019] Figures 2.2(a)-(c) are bright field lOx images of phase bars written with decreasing scan speeds of 30, 25, 20 and 15mm / s, 50mW 80MHz 400nm (a) in fully dehydrated (b) in rehydrated and (c) hydrated in Narafilcon A silicone hydrogels.

[0020] Figures 2.3(a)-(b) are Interferogram and Wavefront maps of rectangular regions of phase change for (a) dehydrated silicone post 3 days hydration and (b) hydrated silicone writing at an average laser power of 50mW and scan speed of 15mm / s.

[0021] Figure 2.4 is a plot of magnitude of induce phase written at different scan speeds in two different silicone hydrogel materials: Narafilcon A and Stenfilcon A.

[0022] Figures 2.5(a)-(b) are Interferogram and Wavefront maps of rectangular regions of phase change for writing at an average laser power of 5 ImW and scan speed of 30mm / s with (a) dehydrated silicone post 3 days saline solution hydration and (b) dehydrated silicone post 13 days saline solution + autoclave heat treatment at 121 C, 15 3psi for 30 mins.

[0023] Figures 2.6(a)-(d) are Bright Field and interferograms images for phase bars written with 25mW, 80MHz, 400nm, scan speeds 12-18mm / s, where Bright Field image (a) and interferogram image (b) are for Dehydrated LIRIC followed by hydrated reading, and BrightField image (c) and interferogram image (d) are for hydrated LIRIC in Contamac 58 - a HEMA based material. The interferograms correspond to phase bars written at 16mm / s scan speed.

[0024] Figures 2.7(a)-(b) are Bright field images of (a) phase bars inscribed via hydrated LIRIC (out of focus) and dehydrated LIRIC (in focus) in Contamac 58 - a HEMA based hydrogel, and (b) y-z cross sections of the same phase bars within the rectangular dotted lines.

[0025] Figures 2.8(a)-(b) are Bright Field and interferograms for phase bars written with 380mW, 515nm, 8.3 MHz, 40x objective in dehydrated Etafilcon A, where (a) Bright Field images showing phase bars writing with 10, 20 and 30mm / s and (b) interferograms of phase bar at 20mm / s.

[0026] Figures 2.9(a)-(b) are Bright Field and interferogram images of phase bars written with 400nm, 25mW, 80 MHz, in dry, never hydrated Contamac 58 - a HEMA based material, where (a) Bright Field images showing phase bars written with 4 and 8 mm / s and (b) interferogram of phase bar at 4 mm / s.

[0027] Figures 2.10(a)-(b) are Interferograms of a phase bar written with 400nm, 80MHz, 25mW, 12mm / s in (a) dry, never hydrated Contamac58 and (b) dehydrated Contamac58.DETAILED DESCRIPTION

[0028] The traditional method of manufacturing hydrogel-based contact lenses, shown in figure 1.1 stages numbered (l)-(5), involves pressing a monomer solution 111 between convex 112 and concave 113 parts of a mold and polymerizing the mixture under ultraviolet radiation 114. The resulting lens 115 is then peeled off, hydrated in a saline solution 116, sterilized and packaged in a sealed blister pack 117. In accordance with one embodiment of the present disclosure, it is possible to incorporate a LIRIC writing system into such a contact lens production process in a way that reduces the need for a variety of mold shapes and allows for the manufacturing of a wider range of lens powers. For some specialized lenes, such as multifocal lenses, writing LIRIC structures such as gradient index Fresnel lens patterns directly into a polymeric lens material during manufacturing also advantageously can result in a better fit onto a user’s eye compared to multifocal lenses manufactured with ridged surface patterns to provide multifocality, which may tend to cause user discomfort. One method of integrating LIRIC into this process involves inserting a femtosecond micromachining system between stages (3) and (4), and performingLIRIC in a contact lens in dry form. While it was not clear based on prior disclosures whether LIRIC technique could be used to inscribe high quality refractive corrections into dry hydrogel based contact lenses, the present disclosure demonstrates such ability.

[0029] It has previously been proposed that two different active chemical components - a dopant and a quencher - are involved in femtosecond writing in a hydrogel (see, e.g., G. A. Gandara- Montano, V. Stoy, M. Dudic, V. Petrak, K. Haskovcova, and W. H. Knox, “Large optical phase shifts in hydrogels written with femtosecond laser pulses: elucidating the role of localized water concentration changes,” Opt. Mater. Express, vol. 7, no. 9, p. 3162, Sep. 2017). The dopant nonlinearly absorbs the laser photons while the quencher redirects the energy into the polymer main chain to break bonds. Increased Raman water peaks post LIRIC writing indicate that water in a hydrogel material is necessary to create regions of lower refractive index once bonds have been broken (see, e g., Yu, D., Huang, R. and Knox, W. H., “Femtosecond laser micromachining in ophthalmic hydrogels: spectroscopic study of materials effects,” Opt. Mater. Express, OME 9(8), 3292-3305 (2019)), but may not be directly involved in the bond breaking process. It is accordingly proposed in accordance with the present disclosure to use LIRIC techniques on dry contact lens materials and hydrating the hydrogel after the writing process, which parallels the hydration in stage (4) of the contact lens production process shown in Figure 1.1. This would allow for easy integration of LIRIC technology into the production process without need to significantly alter the existing machinery and stages.

[0030] The previous inscription of grid lines in dehydrated HEMA supports the dopant-quencher model, suggesting that presence of water in a hydrogel material may not be required in writing mechanisms of refractive index change. Moreover, it is proposed that the presence of water can lead to conditions that decrease the maximum achievable index change. Water has a high heat capacity, and the absence of water during the femtosecond micromachining process accordingly could lead to a higher accumulation of heat at the focal volume, resulting in enhanced photothermal effects and hence have an impact on the resultant index change.

[0031] The present disclosure accordingly is directed towards forming at least one laser- modified pattern within a hydrogel material in a non-hydrated form by exposing regions of the hydrogel material to light pulses from a laser to cause changes in the polymeric lens hydrogel material in the exposed regions of the hydrogel material sufficient to cause a change in refractiveindex of the exposed regions relative to the refractive index of the polymeric lens hydrogel material in non-exposed regions upon hydration of the polymeric lens hydrogel material.

[0032] With regard to the non-hydrated form of the hydrogel material, there are several possible states of water present in a hydrogel, which may be broadly categorized into free, weakly bound and bound water, where each state of water has unique thermodynamic properties and freeze at different temperatures (see, e.g., V. M. Gun’ko, I. N. Savina, and S. V. Mikhalovsky, “Properties of Water Bound in Hydrogels,” Gels, vol. 3, no. 4, Art. no. 4, Dec. 2017). Figure 1.2, e.g., illustrates a schematic of the different kinds of water present in a polymer network 120 at different stages of a hydrogel dehydration process (adapted from Y. Sekine and T. Ikeda- Fukazawa, “Structural changes of water in a hydrogel during dehydration,” The Journal of Chemical Physics, vol. 130, no. 3, p. 034501, Jan. 2009), where (a) represents a hydrated hydrogel, (b) represents a partially dehydrated hydrogel, and (c) represents a dehydrated hydrogel with only bound water remaining. The present disclosure demonstrates successful refractive index writing in hydrogel materials which were previously hydrated and subsequently air dried to remove essentially all free water (while potentially maintaining at least some bound water, as schematically illustrated in Fig. 1.2 section (c)), as well as never hydrated hydrogel based polymeric materials (which are thus essentially devoid of both free and bound water). Accordingly, in embodiments of the present disclosure, the hydrogel material in a non-hydrated form will be at least essentially devoid of free, non-bound water, and in more particular embodiments will additionally be essentially devoid of bound water as well as of free, nonbound water. Such condition of being essentially devoid of bound water as well as of free, nonbound water will apply, e.g., to manufactured contact lens materials formed in a lens mold prior to hydration thereof.

[0033] The present disclosure more particularly expands upon LIRIC writing in hydrogel materials in non-hydrated forms by inscribing regions of continuous refractive index change in a range of air-dried commercial hydrogel lens materials, as well as in dry, never-hydrated hydrogel polymeric materials. Further, writing in the absence of water with subsequent hydration and heating of the hydrated material is shown to lead to distinct effects, resulting in thermal contributions to phase change that do not depend on writing parameters in the same way as photochemical phase changes.

[0034] Dry Sample Preparation and Rehydration Technique

[0035] The present disclosure demonstrates creation of measurable rectangular regions of refractive index change, known as phase bars, in commercial contact lenses after they have been air-dried to remove essentially all free, non-bound water from the hydrogel material prior to laser exposure, and hydrated after laser exposure. This facilitates understanding how low or near-zero water content can impact the resulting localized index change during femtosecond micromachining, even if the properties of an air-dried hydrogel (with retained bound water) may not fully match those of a dry, never-hydrated hydrogel based material.

[0036] The ophthalmic contact lenses are first cut into rectangular pieces to release strain and then left to air dry between a coverslip and microscope slide for at least seven days. Sensitive scale measurements showed that the total mass of the contact lens halved after 3 hours of air drying, indicating that a week of air drying should be sufficient to remove essentially all the free water from the hydrogel. The dried sample is then mounted on a x-y-z translation stage for micromachining. After inscribing the phase bars, the samples are rehydrated by first submerging them in a Petri dish of distilled water and then placing them in a vial of saline solution for three days or subjecting them to heat treatment in saline solution (e.g., greater than 50°C, and more particularly greater than 100°C, for 5-60 minutes, and in specific embodiments autoclaving them in saline solution at 121°C under increased pressure (e.g., 15.3 psi) for 30 minutes). Such heat treatments in saline solution have been found to be particularly advantageous in certain embodiments in order to provide increased refractive index changes, as well as sharper written phase bars. The process of LIRIC in an air-dried hydrogel followed by rehydration will be referred to as "dehydrated LIRIC, hydrated reading" or "dehydrated writing," while the process of LIRIC in a hydrated hydrogel will be referred to as "hydrated LIRIC," and the process of LIRIC in a dry hydrogel followed by hydration will be referred to as “Dry LIRIC writing”.

[0037] Dehydrated LIRIC Writing Experiments

[0038] LIRIC was performed on commercial silicone and hydroxy ethylmethacryl ate (HEMA) based air-dried hydrogels. To inscribe refractive patterns, 400nm femtosecond laser pulses at 80MHz with an average power of below 50mW were focused through a 0.7 NA objective 216(LUCPlanFLN60x, Center Valley, PA, USA) into the dried sample 214 as shown in Fig. 2. l.(a). A mode locked Ti:Sapphire laser 211 (Vitesse; Coherent Corporation, Santa Clara, CA, USA) emitting 800nm, ~ lOOfs pulses at 80MHz was employed, where the 800nm beam was first frequency doubled to 400nm with a second harmonic generator 212. A variable neutral density filter 213 is introduced into the beam path to vary the writing power of the system. The air-dried sandwiched sample 214 is mounted on to a three-dimensional x-y-z translation stage 215 (Aerotech Inc., Pittsburgh, PA, USA) to raster scan the focused 400nm beam inside of the sample. By attaching the sample to the stage and programming the stage to move in the horizontal plane, rectangular bars of uniform refractive index change are created.

[0039] The sample 214 is then rehydrated in saline solution for three days and the phase bars are imaged using a Mach-Zehnder interferometer at 633nm as shown in Figure 2.1(b), adapted from G. A. Gandara-Montano, A. Ivansky, D. E. Savage, J. D. Ellis, and W. H. Knox, “Femtosecond laser writing of freeform gradient index microlenses in hydrogel-based contact lenses,” Optical Materials Express, vol. 5, no. 10, pp. 2257-2271, 2015, where identical microscope objectives 217, 218 in both the sample and the reference arms are employed where the pattern plane is conjugate to the detector plane. The microscope objectives in both arms are located at the same distance with respect to the detector plane to ensure that no curvature in the measured interference wavefront is induced. The average phase change per bar is computed using a carrier fringe technique with a Goldstein phase unwrapping algorithm (see R. M. Goldstein, H. A.Zebker, and C. L. Werner, “Satellite radar interferometry: Two-dimensional phase unwrapping,” Radio Science, vol. 23, no. 4, pp. 713-720, 1988; and D.E. Savage, “A Non-Ablative Technique for Femtosecond Laser-Based Refractive Correction: Development, Efficacy, and Tissue Effects”, PhD Thesis, University of Rochester (2018), p. 365). For refractive error corrections, it is most useful to determine if IX of average phase change can be induced. This is one criterion for viability of the dry writing process, since with one full wave, phase wrapping can be employed to make a Fresnel lens structure (see D. R. Brooks, K. T. Wozniak, W. H. Knox, K. R. Huxlin, and J. D. Ellis, “Measurement and design of refractive corrections using ultrafast laser- induced intra-tissue refractive index shaping in live cats,” in Ophthalmic Technologies XXVIII, F. Manns, P. G. Soderberg, and A. Ho, Eds., San Francisco, United States: SPIE, Mar. 2018, p. 46).

[0040] Dehydrated Silicone Writing: Narafilcon A and Stenfilcon A

[0041] The setup in Figure 2.1(a) was used to inscribe phase bars at different scan speeds in two different commercially available silicone contact lenses, with trademark names of 1- DAY Acuvue ©TruEye® (Narafilcon A) and CooperVision MyDay®(Stenfilcon A).

[0042] Narafilcon A Silicone Dehydrated Writing

[0043] The results suggest that dehydrated LIRIC writing using 400nm laser light in Narafilcon A hydrogels induced greater phase changes compared to hydrated LIRIC writing. This differs from previous research on dehydrated writing in hydrogels, which found either similar or lower index changes compared to hydrated LIRIC. Illustrated in Figures 2.2(a)-2.2(c) are Bright field lOx images of phase bars written with decreasing scan speeds of 30, 25, 20 and 15mm / s, 50mW 80MHz 400nm in (a) fully dehydrated, (b) fully dehydrated and then rehydrated after writing, and (c) hydrated Narafilcon A silicone hydrogels. Illustrated in Figures 2.3(a)-(b) are interferograms and wavefront maps of rectangular regions of phase change for both writing in a dry and wet sample of a silicone Narafilcon A contact lens at an average laser power of 50mW and scan speed of 15mm / s, where Figure 2.3(a) shows results for writing in dehydrated silicone post 3 days hydration, and Fig. 2.3(b) shows results for writing in hydrated silicone. The average phase change computed for dehydrated LIRIC writing and hydrated LIRIC writing were found to be -IX and -0.35k respectively. To compare the effect of water content on LIRIC writing, similar experiments were conducted at a lower average power of 25mW on three pieces of dried Narafilcon A hydrogel and the resulting average phase changes at different scan speeds were compared to data from LIRIC writing in hydrated Narafilcon A hydrogel at an average power of 50mW. The results are plotted in Figure 2.4. While measurable continuous regions of refractive index change could be observed after writing in a dehydrated silicone based ophthalmic hydrogel material with simple subsequent rehydration, the phase bars obtained were not as sharp as may be desired. Furthermore, the ability to further increase average phase change obtainable, or enable desired average phase changes of Ik and more at faster scanning speeds, would be desirable, as inducing Ik and more of average phase change in a single layer is preferable in order to meet preferred criteria for creating customized refractive error corrections.

[0044] It is noteworthy that dehydrated LIRIC writing in silicone carried out with 25mW average power resulted in greater induced phase change at all scan speeds than LIRIC writing inhydrated silicone with 50mW average power. This supports the idea that water is not directly involved in the LIRIC writing mechanism, and rather may suppress photothermal effects that would otherwise have contributed to refractive index change. The larger phase changes observed may be due to an increase in thermal accumulation at the focal volume, leading to a unique photothermal contribution to the refractive index change. This hypothesis is further supported by the fact that the induced phase change by dehydrated LIRIC plotted in figure 2.4 does not follow the 1 / (scan speed) relationship predicted by the photochemical model in equation 2. However, there may be additional factors at play, as the air drying reduces the volume of the silicone hydrogel by almost half. This could result in complex changes to the hydrogel matrix which could alter the interaction between the polymer matrix and incident laser pulses during femtosecond micromachining.

[0045] Narafilcon A Silicone Dehydrated Writing with subsequent heat treatment

[0046] In further examples of dehydrated LIRIC writing using 400nm laser light in Narafilcon A hydrogels, the resulting written hydrogels were rehydrated in saline solution and further subjected to a heat treatment while in the saline solution (autoclaving in saline solution at 121 °C and 15.3psi for 30 minutes). Notably, in comparison to rehydration in saline solution alone (Fig. 2.5(a)), rehydration in saline solution + the heat treatment (Fig. 2.5(b)) enabled increased phase change (-1.09X vs. -0.66X), as well as sharper written phase bars. Significantly, the heat treatment enabled the desired induced phase change of at least -I at the higher scanning speed of 30mm / s.

[0047] It is proposed in accordance with the present disclosure to use LIRIC techniques on dry contact lens materials, such as polymerized hydrogel materials formed in a lens mold during a manufacturing process, and hydrating the hydrogel after the writing process, with subsequent heat treatment, which parallels the autoclaving step in stage 5 of the contact lens production process shown in Figure 1.1. This would allow for further easy integration of LIRIC technology into the production process.

[0048] Stenfilcon A Dehydrated writing

[0049] LIRIC performed on dehydrated Stenfilcon A hydrogels using the system in Figure 2.1(a) was able to induce low but measurable phase changes whereas in hydrated Stenfilcon Ahydrogels, resulted in phase bars below the noise floor of the MZI. Thus, increased phase change resulting from writing in dehydrated silicon hydrogel material in comparison to writing in hydrated silicon hydrogel materials has been demonstrated in a variety of silicone-based hydrogel materials.

[0050] Dehydrated HEMA Writing: Two different writing systems

[0051] Two Hema-based contact lens materials were used for dehydrated LIRIC writing experiments: Acuvue2 ® (Etafilcon A) and Contamac® Contaflex. “Etafilcon A” is a copolymer of 2 -hydroxy ethyl methacrylate and methacrylic acid cross-linked with 1, 1, 1 -trimethylol propane trimethacrylate and ethylene glycol dimethacrylate.

[0052] HEMA 400nm High NA 80MHz Dehydrated Writing

[0053] The setup in Figure 2.1(a) was used to inscribe phase bars at different scan speeds in two different commercially available HEMA based contact lens materials. It was not possible to discern any changes under the bright field or phase contrast microscope in the dehydrated HEMA contact lens materials after performing LIRIC writing with 400nm, 25mW at scan speeds ranging from 5-30mm / s. This contrasts with the observation in fully dehydrated silicone material, where the phase bars could be faintly seen under bright field in figure 2.2a. However, once rehydrated, the phase bars became visible in both HEMA-based materials. The phase bars contained striations as shown in Figure 2.6(a), while the corresponding interferograms of those phase bars in figure 2.6(b) showed distorted fringes which prevented any phase change measurements to be taken. Dehydrated LIRIC writing carried out at a lower average power of 15mW still had similar striations and distorted fringes. Under identical writing parameters, hydrated LIRIC writing produced smooth phase bars as illustrated in the bright field image in figure 2.6(c) but interferograms indicated a phase change lower than 0.1 waves.

[0054] A further experiment was carried out in which LIRIC writing was performed on a hydrated sample of Contamac58, followed by 3 days of air-drying, and LIRIC writing was again performed in the same area of the hydrogel to compare the phase bars written under different levels of hydration. The bright fields in figure 2.7(a) shows both phase bars induced via dehydrated LIRIC writing (in focus phase bars) and hydrated LIRIC writing (out of focus phasebars) at different depths of the sample. In figure 2.7(b), a y-z cross-sectional analysis of the rehydrated sample showed that the axial (z) depth of the LIRIC phase bars within the rectangular dotted line region of (a) via dehydrated writing was nearly three times greater than phase bars inscribed via hydrated writing. While the 1.36 swelling ratio of Contamac58 could account for some of the increase in axial depth, it cannot completely explain such a large increase, indicating that other factors associated with dehydrated LIRIC writing are involved. In accordance with an embodiment of the disclosure, such increased phase bar depth may be employed to achieve an associated increased resulting phase change at relatively lower laser powers due to the refractive index change upon hydration being present over a greater depth.

[0055] HEMA 515nm Low NA 8.3MHz Dehydrated Writing

[0056] Smooth phase bars with an induced phase change of greater than one wave were successfully inscribed in dehydrated Acuvue2 ® (Etafilcon A) using LIRIC writing with 515nm, 8.3 MHz, 40x objective at an average power of 380mW using scan speeds ranging from 10- 30mm / s, as shown in Figures 2.8 (a)-(b) Bright Field and interferogram imagess for phase bars written with 380mW, 515nm, 8.3 MHz, 40x objective in dehydrated Etafilcon A, where the interferogram image (b) is of phase bars written at 20mm / s. This is an interesting result because previous experiments using the 400nm writing system in figure 2. la were unable to produce smooth phase bars in dehydrated HEMA with the average power and scan speed used. This demonstrates that the repetition rate, numerical aperture, and wavelength, which all may affect phase change according to the photochemical model, may be varied to achieve useful results for LIRIC writing in HEMA based non-hydrated hydrogel materials, and accordingly the applicability of dehydrated LIRIC to a range of hydrogel based materials.

[0057] Dry, Never Hydrated Hydrogel LIRIC Writing Experiment

[0058] In order to more closely simulate the conditions of freshly molded contact lenses in a production line, dry ophthalmic HEMA-based Contamac58 hydrogel discs (not previously hydrated, and thus essentially devoid of bound water as well as free, non-bound water) were obtained from Contamac™, a hydrogel manufacturing company. Phase bars were written into the dry, never hydrated hydrogels with laser parameters of 400nm, 80MHz, 25mW, and scan speeds ranging from 4-20mm / s. After being subsequently hydrated, faint phase bars were visible asshown in Figures 2.9(a)-(b), where (a) Bright Field images show phase bars written with 4 and 8 mm / s and (b) interferogram of phase bar at 4 mm / s. As further shown in the Figures 2.10(a)-(b), at 25mW and a scan speed of 12mm / s, LIRIC in the dry, never hydrated hydrogel more particularly produced a faint but smooth phase bar below one-tenth of a wave, while under similar writing parameters, LIRIC writing in dehydrated Contamac58 hydrogels produced visibly distorted phase bars as seen under the MZI. The improved smoothness of the obtained phase bars further supports applicability of LIRIC writing in dry, never hydrated hydrogels in a hydrogel lens production line in accordance with an embodiment of the present disclosure.

[0059] The above examples demonstrate the ability to write refractive index changes in polymeric lens hydrogel materials with femtosecond lasers while the hydrogel material is in a non-hydrated form essentially devoid of free, non-bound water, as well as in a non-hydrated form essentially devoid of both bound water and free, non-bound water. In accordance with the present disclosure, known LIRIC writing parameters may be optimized for writing in such materials in such states.

[0060] The forming of the refractive structures is particularly suited for modifying the refractive index in select and distinct regions of a polymeric, optical silicone-based hydrogel, or a polymeric, optical non-silicone based hydrogel.

[0061] The term “hydrogel” as employed in the present disclosure refers to an optical, polymeric material that can absorb greater than 10% by weight water based on the total hydrated weight. In fact, many of the optical, hydrogel polymeric materials will be able to absorb a water content greater than 15% or greater than 20%. For example, many commercially available hydrogel polymeric materials will have a water content from 15% to 80%, or from 15% to 60%, or from 15% to 40% in their fully hydrated states. For use in an optical device, the polymeric hydrogel materials are of sufficient optical clarity, and may have a relatively high refractive index of approximately 1.40 or greater, particularly 1.48 or greater.

[0062] Without exclusion as to any lens materials or material modifications, e.g., the inclusion of a photosensitizer, or laser parameters described herein, the foregoing disclosed techniques and apparatus can be used to modify the refractive properties, and thus, the dioptric power, of an optical polymeric material, by creating (or machining) a refractive structure with a gradient indexin one, two or three dimensions of the optical material, as more fully described in U.S. Publication Nos. 2012 / 0310340 and 2012 / 0310223, incorporated by reference herein. The gradient refractive structure can be formed by continuously scanning a continuous stream of femtosecond laser pulses having a controlled focal volume in and along at least one continuous segment (scan line) in the optical material while varying the scan speed and / or the average laser power, which creates a gradient refractive index in the polymer along the segment. Accordingly, rather than creating discrete, individual, or even grouped or clustered, adjoining segments of refractive structures with a constant change in the index of refraction in the material, a gradient refractive index is created within the refractive structure, and thereby in the optical material, by continuously scanning a continuous stream of pulses. As described in greater detail in U.S. Publication No. 2012 / 0310340, since the refractive modification in the material arises from a multiphoton absorption process, a well-controlled focal volume corrected for spherical (and other) aberrations will produce a segment having consistent and, if desired, constant depth over the length of the scan. As further noted, when a tightly focused laser beam consisting of femtosecond pulses at high repetition rate impinges on a material that is nominally transparent at the incident laser wavelength, there is little if any effect on the material away from the focal region. In the focal region, however, the intensity can exceed one terawatt per square centimeter, and the possibility of absorbing two or more photons simultaneously can become significant. In particular, the amount of two-photon absorption can be adjusted by doping or otherwise including in the irradiated material with selected chromophores that exhibit large two-photon absorption cross-section at the proper wavelength (e.g., between 750 nm and 1100 nm), which can significantly increase the scanning speed as already described. Also, multiple segments can be written into the material in a layer using different scan speeds and / or different average laser power levels for various segments to create a gradient index profile across the layer, i.e., transverse to the scan direction. Further, multiple, spaced gradient index (GRIN) layers can be written into the material along the z-direction (i.e., generally the light propagation direction through the material) to provide a desired refractive change in the material that provides a significant added dioptric power or that otherwise corrects for some, most, or all higher order aberrations of a patient’s eye. Such abilities to write continuously varying gradient index layers are particularly advantageous in forming refractive correctors having wavefront cross-sectionprofiles. For ophthalmic applications, it is of particular interest that GRIN refractive structures are low scattering (as discussed above) and are of high optical quality.

[0063] In particular contemplated embodiments of the present disclosure, GRIN refractive structures in the form of Fresnel lens patterns may be LIRIC written in polymeric lens hydrogel material in a non-hydrated form essentially devoid of free, non-bound water, and more particularly wherein the polymeric lens hydrogel material in a non-hydrated form has not been previously hydrated and dried, and is further essentially devoid of bound water.

[0064] The laser may generate light with a wavelength in the range from violet to near-infrared. In various aspects, the wavelength of the laser may be in the range, e.g., from 340 nm to 1500 nm, from 400 nm to 1200 nm, from 400 to 600, or from 650 nm to 1100 nm, including more specifically wavelengths near 405 nm, 517 nm, 800 nm, and 1035 nm. Example pulsewidths include femtosecond scale pulsewidths, and, in some examples, pulsewidths less than 350 fs. Example repetition rates include repetition rates in the range of 1-80 MHz. Example lens NA include NA’s between 0.19 and 1.0. Any suitable scanning system may be utilized, including, without limitation, high speed XYZ translation stages, high speed galvanometer scanning systems, and shaker scanners (such as described in U.S. Patent Application Publication No. 2016 / 0144580 published May 26, 2016 to Wayne H,. Knox et al.). In some instances, the scanning speed may be in the range of 1 mm / sec to 10 meters / sec.

[0065] The laser scanning system may deliver short laser pulses of sufficient energy (e.g. above a minimal threshold but below a damage threshold) and at sufficient scan speeds (e.g. above a damage threshold but below an upper speed threshold) to cause a nonlinear absorption of photons (typically multi-photon absorption), leading to a change in the refractive index of the material at the focus point. The damage threshold may reflect a threshold in which a degradation in optical quality of the device is detectable. Moreover, the region of the material just outside the focal region is minimally affected by the laser light. Accordingly, select regions of an optical, polymeric material can be modified with a laser resulting in a change in the refractive index in the exposed regions. The irradiated regions may exhibit no significant differences in the Raman spectrum with respect to the non-irradiated regions. Also, the irradiated regions may exhibit little or no scattering loss, which means that the structures formed in the irradiated regions are not clearly visible under appropriate magnification without contrast enhancement.

[0066] The described writing systems may be utilized to create lenses or other optical constructs in the interior of the material to change their optical properties. Depending on the phase shift required, the lens or other optical construct can be written into the material in a single layer or in multiple layers. U.S. Patent 8,932,352, issued January 13, 2015 to Wayne H. Knox et al. for an “Optical Material and Method for Modifying the Refractive Index” and U.S. Patent 9,144,491, issued September 29, 2015 to Wayne H. Knox et al. for a “Method for Modifying the Refractive Index of an Optical Material,” describe additional examples of gratings and other optical constructs that may be written into materials.

[0067] A first step to determining material characteristics for planning desired writing parameters may be to measure written phase shifts obtainable in the material of interest after subsequent hydration as a function of, for example, average power and scan speed. Phase vs. power can be plotted on logdog scales to determine slope of nonlinear processes in small signal regime (below saturation). The determined slope may be indicative of the applicable photochemical model for the material of interest (e.g. a slope close to 2 may be indicative of a two photon model, a slope close to 4 may be indicative of a four photon model, etc.). The applicable photochemical models (e.g. the two and / or four photon regime models) may be fit to the data, and a maximum phase shift just below the damage threshold may be identified. This information may be subsequently used to establish a range of writing powers at desired scan speeds. It is noted that, while the best results for at least some systems and methods are obtained when the one-photon absorption is minimized, a small amount of one-photon absorption may be tolerable even in those instances.

Claims

Claims:

1. A method of forming an optical device with a modified refractive index pattern provided therein comprising: providing an optical device comprising a polymeric lens hydrogel material in a nonhydrated form essentially devoid of free, non-bound water; forming at least one laser-modified pattern within the hydrogel material in the nonhydrated form by exposing regions of the hydrogel material to light pulses from a laser to cause changes in the polymeric lens hydrogel material in the exposed regions of the hydrogel material sufficient to cause a change in refractive index of the exposed regions relative to the refractive index of the polymeric lens hydrogel material in non-exposed regions upon hydration of the polymeric lens hydrogel material; hydrating the hydrogel material which has the laser-modified pattern formed there within; and heating the optical device having the resulting hydrated hydrogel material which has the laser-modified pattern formed there within to increase a change in refractive index between exposed and non-exposed regions of the polymeric hydrogel lens material.

2. The method of claim 1 wherein the laser exposure is performed by scanning focused pulses from the laser along regions of the polymeric lens hydrogel material.

3. The method of claim 1 wherein the polymeric lens hydrogel material comprises a silicone hydrogel material.

4. The method of claim 1, wherein the polymeric lens hydrogel material in a non-hydrated form has not been previously hydrated and dried, and is further essentially devoid of bound water.

5. The method of claim 1, wherein the laser-modified pattern formed in the polymeric lens hydrogel material forms gradient index refractive structures in the form of a Fresnel lens pattern.

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