Optical component, preferably with improved degradation resistance, and method for producing same

Abstract

An optical component with improved degradation resistance is provided. The optical component includes an optical material and a coating. The optical material has a native surface that is susceptible to degradation processes. The coating is a layer of an inorganic material and is applied so as to be substantially contiguous so that there are no continuous paths between fluid surrounding the optical component and the optical material.

Claims

1. An optical component, comprising: an optical material, wherein the optical material has a native surface that is susceptible to degradation processes; a first coating on the optical material comprising a first layer being produced by an atomic layer deposition (ALD) process and comprising an inorganic material, the first coating being substantially contiguous so that there are no continuous paths between an environment surrounding the optical component and the optical material; a second coating that overlaps at least a portion of the first coating, wherein the at least the portion of the first coating is disposed under the second coating, and wherein the second coating comprises at least one layer produced by a physical vapor deposition (PVD) process; and a degradation resistance after storage of at least 24 hours at a temperature of 85° C. and a relative humidity of 85% and/or after storage in deionized water for six months at a temperature of 25° C. selected from the group consisting of: a functionality of the optical component that does not deviate by more than 5% from an initial value of the functionality; a formation of no additional defects greater than 10 μm determined according to standard ISO 10110; no detachment of the first coating from the optical material; no strong change in color of the optical material as determined as a change in color coordinates in the CIE 1931 system; no strong change in color of the first coating as determined as a change in color coordinates in the CIE 1931 system; and any combinations thereof.

2. The optical component as claimed in claim 1, wherein the optical material comprises a material selected from the group consisting of an inorganic non-metallic material, an organic material, an amorphous inorganic non-metallic material, and glass.

3. The optical component as claimed in claim 1, wherein the optical material comprises a glass selected from the group consisting of: phosphate glass, phosphate glass including color-imparting components, phosphate glass including filtering components, phosphate glass including optically laser-active components, LG750 glass, LG760 glass, LG770 glass, APG1 glass, LG940 glass, LG950 glass, LG960 glass, S8612 glass, BG39 glass, BG50 glass, BG55 glass, BG56 glass, BG57 glass, BG60 glass, BG61 glass, and any combinations thereof.

4. The optical component as claimed in claim 1, wherein the optical material comprises a phosphate glass having a content of at least 10 wt % of P.sub.2O.sub.5 and a content of at most 80 wt % of P.sub.2O.sub.5.

5. The optical component as claimed in claim 1, wherein the optical material comprises a phosphate glass having a content of P.sub.2O.sub.5 from 50 wt % to 80 wt %.

6. The optical component as claimed in claim 1, wherein the first layer comprises a layer selected from the group consisting of: an inorganic oxidic layer; an inorganic amorphous oxidic layer; an Al.sub.2O.sub.3 oxide layer; an SiO.sub.2 oxide layer; an Nb.sub.2O.sub.5 oxide layer; an Ta.sub.2O.sub.5 oxide layer; an HfO.sub.2 oxide layer; an Sc.sub.2O.sub.5 oxide layer; a TiO.sub.2 oxide layer; and any combinations thereof.

7. The optical component as claimed in claim 1, wherein the optical component comprises a multi-layer coating system comprising at least one layer of a high refractive index material and/or at least one layer of a low refractive index material.

8. The optical component as claimed in claim 7, wherein the multi-layer coating system comprises the at least one layer of the high refractive index material and the at least one layer of the low refractive index material, and wherein the at least one layer of the high refractive index material and the at least one layer of the low refractive index material are arranged alternately.

9. The optical component as claimed in claim 7, wherein the low refractive index material comprises SiO2 and wherein the high refractive index material comprises a material selected from the group consisting of: Ta.sub.2O.sub.5; Al.sub.2O.sub.3; HfO.sub.2; Nb.sub.2O.sub.5; TiO.sub.2; and ZrO.sub.2.

10. The optical component as claimed in claim 1, wherein the first coating has a thickness of at least 1 nm and at most 10,000 nm or a thickness of at least 20 nm and at most 200 nm.

11. The optical component as claimed in claim 1, wherein the first coating covers at least part of a surface area of the optical component, wherein the surface area is configured for contact with a fluid reactive with the optical material.

12. The optical component as claimed in claim 1, wherein the first coating covers or encloses the optical material over an entire surface area thereof.

13. The optical component as claimed in claim 1, wherein the first coating covers one or more optical faces of the optical material.

14. The optical component as claimed in claim 1, wherein the first coating comprises a multi-layer system having consecutive layers of at least partially a different composition.

15. The optical component as claimed in claim 1, wherein the first coating and the second coating define an optically active layer system that reduces reflection or enhances reflection.

16. The optical component as claimed in claim 1, wherein the optical material has at least one face with a portion comprising a roughness determined as a root mean square roughness of not more than 8 nm, wherein the portion is at least partially provided with the coating.

17. The optical component as claimed in claim 1, wherein the optical material has at least one face with a portion comprising a roughness determined as a root mean square roughness of at least 0.5 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained by way of example with reference to the figures, wherein the same reference numerals designate the same or equivalent elements, and wherein:

(2) FIG. 1 schematically illustrates a longitudinal sectional view through an optical component;

(3) FIG. 2 schematically illustrates an optical component encapsulated by encapsulation;

(4) FIG. 3 schematically illustrates an optical component encapsulated by encapsulation;

(5) FIG. 4 schematically illustrates an optical component with a coating;

(6) FIG. 5 schematically illustrates an optical component with a high-index barrier layer;

(7) FIG. 6 schematically illustrates an optical component with a coating; and

(8) FIG. 7 schematically illustrates an optical component with a layer.

DETAILED DESCRIPTION

(9) FIG. 1 schematically illustrates a longitudinal sectional view through an optical component 1 according to an embodiment of the invention, not drawn to scale. Optical component 1 comprises an optical material 10 and a coating 2. This coating 2 comprises a layer comprising an inorganic material and was applied to the optical material 10 by a CVD process in a manner so as to completely encloses it. This coating 2 produced by a CVD process may be in the form of a low-index coating as well as a high-index coating.

(10) By way of example, the here illustrated optical component 1 comprises, as the optical material 10, a phosphate-containing glass which furthermore comprises active components in the form of rare-earth ions. Thus, the optical material 10 is a so-called laser glass in this case, by way of example, which is used to generate laser radiation.

(11) In order to generate laser radiation by so-called “optical pumping”, it is furthermore necessary to partially cool the optically active medium, in the present case the optical material 10, using a liquid. By way of example, the optical material 10 is provided in the form of a cylindrical rod. This rod is encapsulated by an encapsulation 3 such that a portion of the lateral surface of the cylinder is surrounded by a liquid, such as water, for cooling purposes. Thus, the encapsulation 3 divides the environment of optical component 1 into at least two regions 31, 32, and in one region 31 the optical component comes into contact with a fluid which might degrade the optical material. For example, in the case of the phosphate-containing glass such as a glass comprising phosphate which is doped with rare-earth ions and serves to generate laser radiation, this fluid may entirely consist of water or comprise water. More generally, however, it is also possible that organic liquids are used as a coolant. Alternatively, the optical material may be provided in the form of a plate, e.g. a rectangular plate. This plate may now be surrounded by coolant on one side or on both sides. Both the laser beam and the pumping light beam pass through the large surfaces which are in contact with the cooling medium.

(12) In the second region 32, the optical component 1 is surrounded by a less reactive fluid, for example normal ambient air. However, here too, the coating 2 improves the degradation resistance of the optical component 1. If the optical material 10 is a phosphate-containing glass, atmospheric moisture may already cause corrosion or degradation of the optical material.

(13) Coating 2 is preferably applied by a CVD process.

(14) FIG. 2 is a further schematic view, not drawn to scale, of an optical component 1 encapsulated by encapsulation 3. Here, optical component 1 consists of the optical material 10 which is provided with two coatings 21, 22. These two coatings 21, 22 enclose the optical material 10 completely, at least in portions thereof. Here, the optical material 10 is exemplified as a cylindrical rod made of a phosphate-containing glass, for example a phosphate-containing glass doped with rare-earth ions, which can be employed to generate laser radiation.

(15) The two coatings 21, 22 were each obtained by CVD. Coating 21 which is directly disposed on the optical material 10 is designed as a high refractive index layer, for example consisting of TiO.sub.2 or comprising TiO.sub.2, and coating 22 applied thereon is designed as a low refractive index layer, for example consisting of or comprising SiO.sub.2. The system of the two coatings 21, 22 thus provides a water barrier as well as an optically active layer system which is formed on the end face of optical component 1 as an antireflection system.

(16) Furthermore, the two regions 31 and 32 are indicated representing different environments of the optical component 1. By way of example, region 31 may be a particularly degrading region here, where the optical component 1 is surrounded by a liquid that degrades the optical material 10, for example. Region 32, by contrast, will usually be less degrading. For example, optical component 1 may be surrounded by air in this region, by way of example.

(17) A further refinement is shown in FIG. 3, which is a further schematic view, not drawn to scale, of an optical component 1 encapsulated by encapsulation 3. Here, the optically active layer system comprises more than two coatings, namely four coatings, by way of example, wherein these coatings are each formed as single layers here, so that the third layer 21 again comprises TiO.sub.2, and the fourth layer 22 again comprises SiO.sub.2, as illustrated. More generally, without being limited to the example illustrated herein, the high-index layers 21 may as well comprise other materials than TiO.sub.2, for example they may comprise Al.sub.2O.sub.3, additionally or alternatively, or another material. Furthermore, it is generally possible for the high-index and/or low-index layers 21, 22 to differ from each other in terms of their composition. For example, a first low-index layer 22 may have a different composition than a further low-index layer 22 in a layer system. This similarly also applies to the high-index layers 21.

(18) FIG. 4 is another schematic view, not drawn to scale, of the optical component 1, here exemplified as a cylindrical rod made of an optical material 10, which is provided with a coating, here the low-index barrier coating 22, for example consisting of or comprising SiO.sub.2. This coating 22 completely encloses the optical material 10 and is produced by a chemical vapor deposition process (CVD process).

(19) Furthermore, a coating 41 is applied on the end face of the cylindrical rod. This coating 41 was applied by a PVD process, i.e. by physical vapor deposition. Such PVD processes are directed processes which are not suitable for coating three-dimensional geometries, but only for approximately two-dimensional surfaces, e.g. by electron beam vapor deposition (also plasma-assisted), ion beam or magnetron sputter deposition.

(20) Coating 41 may be configured as a single layer, for example, but also as a layer system, i.e. may comprise a plurality of layers of materials having different refractive indices.

(21) FIG. 5 is a schematic view of a further embodiment of an optical component 1. Optical component 1 is again exemplified as a cylindrical rod made of an optical material 10 which is completely enclosed by a high-index barrier layer 21 in this example, which was produced by a chemical vapor deposition (CVD) process.

(22) Furthermore, a coating 42 is applied on the end face of the cylindrical rod. This coating 42 was applied by a PVD process, i.e. by physical vapor deposition. Coating 42 may consist of a low refractive index layer or may comprise a plurality of layers, and the combination of coating 21 and coating 42 on the end face of the rod defines an AR coating.

(23) More generally, without being limited to the example shown in FIG. 5, the optical component 1 can as well be provided in the form of a slice or disk, for example a slice comprising a blue glass, which is used as a filter, for example. In such an application, the optical component 1 may as well be provided in a form so that the component 1 is applied to and fixed on a substrate, for example by an adhesive including epoxy resin. In this case, the environment with normal environmental conditions is considered to be the area of the blue glass which is in contact with the adhesive, whereas the non-supported areas of the blue glass are considered to be in contact with a region 32 with degrading environmental conditions.

(24) Furthermore, FIG. 6 schematically shows yet another embodiment of an optical component 1 according to the present invention. Here, the optical component comprises the optical material 10 which is again provided in the form of a cylindrical rod, for example. In this case, first, a coating 43 is applied to the end face of the rod by a physical vapor deposition process (PVD process), consisting of multiple layers here, which form the basis of a layer system with an antireflective (AR) effect. Here, the coating 22 which completely encloses the optical material 10 and the coating 43 applied to at least the one of the end faces of the rod that is illustrated here, is effective as a final low refractive index coating for completing the AR layer system. Coating 22 is formed of a low refractive index material in this case, and is applied by a CVD process, i.e. by chemical vapor deposition.

(25) More generally, without being limited to the example shown in FIG. 6, the optical component 1 may as well be provided in the form a slice or disk, for example a slice comprising a blue glass which is used as a filter, for example. In such an application, the optical component 1 may as well be provided in a form so that the component 1 is applied to and fixed on a substrate, for example by an adhesive including epoxy resin. In this case, the environment with normal environmental conditions is considered to be the area of the blue glass which is in contact with the adhesive, whereas the non-supported areas of the blue glass are considered to be in contact with a region 32 with degrading environmental conditions.

(26) FIG. 7 is a further schematic view, not drawn to scale, of an optical component 1 according to an embodiment of the invention. Optical component 1 is made of an optical material 10 which is provided in the form of a layer here, by way of example. The layer may be a glassy layer, for example, such as a layer comprising a phosphate glass. In the present case, the layer is applied on a carrier or substrate 5. This carrier or substrate 5 may itself also comprise an optical material. Here, the optical material 10 is contiguously enclosed by a barrier coating 2, so that the strongly degrading environmental conditions in region 32 do not degrade the material 10.

(27) In order to determine the degradation resistance of the optical component, i.e. of the optical material and the coating applied thereto, environmental resistance tests were performed on a multitude of samples. For this purpose, different coating systems were applied onto a common blue filter glass S8612 as the substrate material, which is available from Schott AG, Mainz. This type of glass is considered to be very sensitive to moisture and thus to be a very critical type of glass with respect to a possible tendency to degradation. For example, this type of glass is significantly more sensitive to moisture than other blue filter glasses, such as BG55 or BG60.

(28) Different coating systems were applied onto the blue filter glass S8612, comprising different arrangements of high refractive index and low refractive index layers. SiO.sub.2 was selected as the low refractive index material, and one of the following materials was selected as the high refractive index material: Ta.sub.2O.sub.5, Al.sub.2O.sub.3, HfO.sub.2, Nb.sub.2O.sub.5, TiO.sub.2, or ZrO.sub.2. The coatings have a total thickness of between 5 and 100 nm.

(29) The substrates provided with the different coating systems were then placed in a climate chamber where they were exposed to different temperatures which were constant over the test period, at a relative humidity of 85%. The temperatures were 100° C., 200° C., and 250° C.

(30) A possible degradation of the coating systems was investigated and analyzed at regular intervals. This included a visual inspection of the coated substrates with the human eye according to standards ISO 10110 or MIL 13830 at 36 W cold light, color temperature 5600 K, fluorescent tube, not collimated, through an opal glass sheet, against a black background without additional ambient light. In such a test arrangement, relevant degradation signs such as delamination or cracks, but also a catastrophic failure, are clearly visible.

(31) An investigation of the substrates introduced into the climate chamber with regard to possible degradation signs of the substrates or the applied coating systems was performed after a period of 250 hours, after 500 hours, and after 1000 hours.

(32) For comparison, blue filter glasses S8612 were furthermore provided with commonly known AR coating systems and were also introduced into the climate chamber for comparison.

(33) It was found that the prior art AR coating systems exhibit catastrophic failure after only 250 hours. This included destruction of the layer and/or the formation of a matte, turbid surface, so that pure transmission of electromagnetic radiation is no longer possible in the visible wavelength range.

(34) By contrast, samples according to the invention with ALD coatings, i.e. where the layers were produced by atomic layer deposition, show hardly any degradation signs. In particular, the optical and/or mechanical functionality of the component deviates by not more than 5% from the initial values for optical and/or mechanical functionality. Also, there are no additional defects greater than 10 μm, and no additional defects greater than 5 μm, and no additional defects greater than 1 μm. Furthermore, neither were there observed any detachments of the ALD coatings and/or of individual layers of the ALD coating system, nor any color changes.

(35) After 500 hours, degradation signs could be observed on some samples with ALD coating systems. However, while in the case of samples with prior art AR coatings it was observed that the coating already delaminates or even has completely peeled off and the substrate is being dissolving, such signs have not been observed in samples with coating systems according to the present invention.

(36) The following overview lists some coating systems according to the invention, which showed only very slight degradation signs after 1000 hours, and these degradation signs did not occur over the whole surface but locally limited, while major portions of the surface showed no degradation at all.

(37) TABLE-US-00004 T Layer thickness Nano- Material [° C.] [nm] laminate Al.sub.2O.sub.3 plasma-assisted 100 100 Al.sub.2O.sub.3 plasma-assisted 200 100 Al.sub.2O.sub.3 thermal 100 100 Al.sub.2O.sub.3 thermal 250 25 HfO.sub.2 plasma-assisted 200 25 Ta.sub.2O.sub.5 thermal 250 25 Al.sub.2O.sub.3/HfO.sub.2 nl plasma-assisted 200 100 yes Al.sub.2O.sub.3/Ta.sub.2O.sub.5 nl thermal 250 100 yes

(38) These ALD coating systems were applied to both laser glass and blue filter glass.

(39) A high processing temperature of 100 to 350° C., preferably 200 to 350° C., and more preferably 250 to 300° C. during the coating process is considered to be favorable for a low degradation tendency of the ALD coating.

(40) Some coating systems are designed as a nanolaminate. This means that the involved layers are made very thin, preferably between 2 and 10 nm, with alternating high refractive index and low refractive index materials.

(41) An optical component according to the invention may additionally comprise further layers, preferably AR layers. It should be considered here, that ALD layers are under tensile stress and that standard electron beam or sputter coatings may exhibit lower layer adhesion on phosphate glasses than on silicate glasses, in particular quartz.

(42) Strong tensile stresses in a higher layer may therefore delaminate or rupture underlying layers. Even small cracks are therefore undesirable in the context of the invention.

(43) Even if such a sequence of layers of the coating system can be technically realized on the substrate as an optical material with a prior art AR layer applied thereon and furthermore the ALD coating system applied thereon, it is nevertheless advantageous to apply the ALD layer directly onto the substrate and the AR coating afterwards.

(44) It is of course also possible to form the entire AR system of ALD layers so that there is no need to deposit further layers above or below the ALD layer stack using a different coating technology.

LIST OF REFERENCE NUMERALS

(45) 1 Optical component 10 Optical material 2 Coating comprising a layer comprising an inorganic material 21 High-index coating 22 Low-index coating 3 Encapsulation 31 Region with highly degrading conditions 32 Region with normal environmental conditions 41, 42, 43 Layer or layer system with optical effect 5 Substrate