DE9400445U1 - Illumination device with liquid light guide - Google Patents

Description

LIGHTING DEVICE WITH LIQUID LIGHT GUIDE

The invention relates to a lighting device with a light source and a liquid light guide.

Such a lighting device is known from US-A-4 009 382. DE-A-40 24 445 Al discloses a liquid light guide which contains a tube made of an amorphous fluoroplastic which is available under the trade name TEFLON AF from the Dupont company and which has the following formula

--C—c

•C C--

Teflon AF

■ 0 0

FCF FCF I

and is based on a combination of tetrafluoroethylene and a fluorinated, cyclic ether, which acts as a spacer to the polymer main chain, whereby crystallization is sterically hindered. This amorphous fluoroplastic is crystal clear and has a low refractive index η (with increasing glass transition temperature from η = 1.315 down to η = 1.29). This fluoroplastic is not only relatively stiff, so that light guides made with it can also be used with a relatively thin wall thickness of the tube.

Not only are the granules easy to handle due to their shape, but this material is also difficult to extrude into tubes (the Teflon AF 2400 modification cannot be extruded at all) and is extremely expensive: 1 g of granulate currently costs around US$10, so that a batch of 20 kg required for extrusion costs around US$240,000, which, with an achievable extrusion length of 1000 to 2000 m depending on the thickness of the sheath, results in a price per meter of around US$100.

The invention is based on the object of creating a lighting device that is cost-effective and easy to handle and ensures very good utilization of the radiation emitted by the light source.

It has been shown that a suitable light source in combination with a light guide that contains a liquid-filled tube made of a fluorocarbon polymer and in which a very thin inner coating of the tubular jacket of the liquid light guide with Teflon AF, which is available in the modifications AFl600 with a refractive index n=1.31, or AF2000 with n=1.30 or AF2400 with n=1.29 from the world-famous company Dupont, with an extraordinarily small layer thickness in the order of approx. 3 µm, i.e. in the order of a small multiple of the wavelength of the light to be guided, not only leads to very considerable savings in the manufacturing costs, but surprisingly also improves the transmission of the light guide and thus the optical efficiency of the lighting device. In particular, bending the light guide results in significantly lower transmission losses, which is of great practical importance because a light guide of a lighting device is often strongly bent during handling, for example as a probe or in dental applications, whereby light losses are of course undesirable.

The inner coating according to the invention also allows

much greater freedom in the selection of the flexible hose material than in the above-mentioned prior art, since the hose itself only has to serve as a substrate for the Teflon layer. Fluorocarbon polymers with a low refractive index (around n=1.35) are preferred as the substrate material for the Teflon AF layer, so that in the event of any defects in the inner layer and direct contact between the optical fiber fluid and the hose material, the light leakage is as low as possible (the aim is therefore to achieve the greatest possible difference between the refractive indices η of the optical fiber fluid and the substrate material of the jacket). Preferred substrate materials are the terpolymer Hostafion TFB ^(Wz) from Hoechst or the Teflon FEP, PTFE, PFA with the following structural formulas, or TEFZEL ETFE ^(WZ) from Dupont or PCTFE (polychlorotrifluoroethylene or PVDF (3M).

I I --C C--

"TeCIon" PTFE

--(
N &eegr; F
I
-C
p. e = F
- :-
F
•

Teflon· F£P

F—C—F

! T C-

F
I

■c-

-c-f-

PFA

F—C F

F-C—F

F—&Ogr; F

F ·

Glycols are preferred as optical fiber fluids

such as monoethylene, diethylene, triethylene and tetraethylene glycol and mixtures thereof, which have a high refractive index that is significantly higher than that of the layer material according to the invention, in order to provide the best possible total reflection properties. However, since the hose materials are not completely water vapor-tight, over time in environments with high humidity, water vapor can diffuse through the hose into the liquid and undesirably increase the internal pressure. However, if a little water is added to the glycols from the outset, the vapor pressure difference is reduced accordingly, so that less water vapor diffuses into the interior of the hose and increases the internal pressure less. This reduces the risk of the quartz or glass plugs that serve as light windows and are inserted into the ends of the light guide jacket being pushed out. However, with the usual hose materials for the optical fiber jacket, at 8% water addition, a limit is reached at which the difference between the refractive indices becomes too small. However, the inner layer according to the invention contains the reserves for this difference range, so that higher water additions are possible and the undesirable diffusion of water vapor from the environment into the hose can be reduced even further. Water additions of at least about 6 to 7% up to 10%, 15%, 20% or 30% to triethylene glycol and other glycols have proven effective in this regard; the resulting reduction in the refractive index can be accepted here.

In addition, frost-proof light guides can be produced using a glycol-water mixture, which is of great importance for winter-proof outdoor applications. The greater reserve of the refractive index difference achieved by the inner layer according to the invention allows a light guide effect even with pure water as the light guide fluid, especially if Teflon AF 2400 is used, i.e. the AF material with the highest glass transition temperature and the lowest refractive index.

index of n=1.29 is used, which is however somewhat more complex to apply as a layer. A physiological saline solution has also proven to be useful for such a coating of a jacket that is open on one side, as is known from the above-mentioned DE-A-4 0 24 445.

Aqueous solutions of salts such as alkali and alkaline earth halides, especially chlorides and fluorides, are also suitable light-conducting liquids, e.g.

CaCl ₂ solutions with &eegr;_< 1.45

KF solutions with &eegr; _< 1, 4

CsF solutions with &eegr; £ 1.42

NaCl solutions with &eegr; _< 1.40,

Fluoride solutions are more resistant to short-wave radiation (UVB) than chloride solutions, of which sodium chloride solution is important as a physiological saline solution in medical light guide applications. Phosphate solutions such as

p Solutions with &eegr;_< 1,42 Na ₃ HPO ₄ Solutions with &eegr;_< 1,42 NaH ₂ PO. Solutions with &eegr;_< 1,42,

which are also more resistant to short-wave radiation (UVB) than chloride solutions. However, chloride solutions are well suited to the transmission of UVA radiation. Short-wave radiation is provided in particular by excimer lasers and high-pressure mercury lamps, whose radiation tends to decompose the chlorine-containing compounds, thereby reducing the transmission of the light guide. The above solutions are usually used in highly concentrated form in order to achieve the highest possible refractive indices for the light guide fluid.

For the transmission of near infrared radiation, a combination of FEP tubing, AF 1600 inner layer and a polychlorotrifluoroethylene oil (PCTFE oil) with the formula

Cl

and a refractive index of up to about 1.40 or 1.41; this gives usable acceptance angles of about 60°.

The three mentioned modifications of the Teflon AF 16 00, AF 2000 and AF 2400 used for the layer according to the invention have different glass transition temperatures of 160 ⁰ C, 200 ⁰ C and 240 ⁰ C respectively, according to the modification designations. Teflon AF 1600 dissolves in liquids consisting of fluorinated hydrocarbons up to 6 wt.%, Teflon AF 2 40 0 only up to 2 wt.%. The three times higher solubility of the first-mentioned layer material allows easier application of the layer according to the invention, since it builds up more quickly with a higher proportion.

Fluoride and phosphate solutions, which are more resistant to short-wave radiation (UVB) than chlorides, have a relatively low refractive index and are therefore not as suitable for conventional tube materials. It is only through the inner layer according to the invention that these solutions become interesting as light guide fluids and produce usable transmissions, especially in the UVB range (280nm <λ.< 330nm). --&mdash;

The application of the layer according to the invention can be carried out by applying a solution of Teflon AF powder. It has been shown, quite surprisingly, that

a very stable adhesion of the Teflon AF layer to the inside of the tube of fluorocarbon polymers can be achieved, which was not to be expected at all, since fluorocarbon polymers are known to have very poor adhesion properties (but very good sliding properties). This good adhesion remains even when wetted with the above-mentioned optical fiber fluids and does not deteriorate even when the optical fiber is frequently bent sharply, which is of great importance for a long service life. The adhesion of the layer to the tube materials is so good that even when the window plugs are fitted tightly into the tube ends, the layer is not damaged or comes off. The layer according to the invention even improves the fit of the window plugs in the tube ends, so that the risk of them being pushed out when the internal pressure increases is reduced. This astonishingly good and secure adhesion is a great advantage for sheath materials made of fluorocarbons, such as Teflon FEP with a refractive index of n=1.34 and Hostafion TFB with a refractive index of 1.36, as well as Teflon PTFE (n=1.34), Teflon PFA (n=1.34) and Teflon ETFE (n=1.42), as well as PCTFE and PVDF. If the bond between the Teflon AF layer according to the invention and the inside of the sheath made of such materials is not quite perfect in places, the light losses in such places can still be kept low with light guide fluids with η > 1.4, so that no significant transmission losses need to be feared.

The invention is illustrated by means of an embodiment in the only accompanying drawing.

The lighting device shown in the drawing in a highly simplified form contains a light source 10, a condenser 12 with three lenses made of quartz, which are coated with an anti-reflective layer designed for 3 65 nm, a light filter 14 and a light guide 16.

In the embodiment shown, the light source 10 contains a 200W Hg ultra-high pressure lamp 18, type HBO200 with a concave, spherical reflector 20.

The light source can also contain another gas or vapor discharge lamp, e.g. a xenon high-pressure lamp or a tungsten halogen lamp. The light filter is an ion-plated thin-film filter that reflects long-wave radiation, i.e. longer-wave visible light and near infrared.

The spectral transmission range of the light filter depends on the application of the lighting device. For example, in polymerization devices for industrial adhesives and for dental plastics, radiation in the UVA range (approx. 330 to 380 nm) or in the UVA range plus the blue spectral range (approx. 330 to 480 nm) or UVB+UVB+blue (approx. 280-480 nm) is required. Such transmission ranges can be realized with thin-film interference filters.

The liquid conductor contains a flexible tubular jacket 21 made of a fluorocarbon polymer of the type explained above. This jacket can have a thickness suitable for the respective application, e.g. 0.5 mm, and serves as a substrate for a thin layer 22 according to the invention, with which the inside of the jacket 21 is lined. The interior of the tube constructed in this way is filled with a light-conducting liquid 23 and closed on both sides with quartz or glass plugs 24, which are expediently firmly connected to the jacket 21 by a mechanical seal not shown here.

If the layer 22 is made of Teflon AF 2400, which has a relatively low refractive index of η = 1.2 9, then due to the reserve with regard to the refractive index difference, a light-conducting liquid 23 with a low refractive index, such as a fluoride or phosphate solution, can be used.

use a solution that has good resistance to short-wave light, e.g. UVB light (280 nm <A< 320 nm). Chloride-containing solutions with a lower chloride content can also be used, in which only a correspondingly smaller amount of chloride can be broken down by short-wave radiation and the transmission deteriorates only slightly.

The following are some results from tests that lasted for many months. In particular, tubular jackets 21 made of Teflon FEP and Hostafion TFB were coated with a thin layer 22 of <5μm, in particular 3 μιγ, made of both Teflon AF 2400 and Teflon AF 1600 and filled with various light-conducting liquids 23. It was found that layers made of Teflon AF 1600 in particular produced particularly good results in terms of improving transmission, i.e. lower light losses, increasing the numerical aperture, which makes it easier to couple light into the light guide, reducing transmission losses when bending the light guide and the quality of the adhesion of the layer 22 to the substrate jacket 21.

Although Teflon AF 2400 is less easy to process, it can still be used to form layers 22, making it possible to produce light guides whose light-conducting liquid consists of the purest water.

Long-term tests of such light guides with a jacket 21 made of fluorocarbon polymers and a layer 22 made of Teflon AF also showed that after more than half a year no signs of detachment of the layer 22 from the jacket 21 could be observed. The consistent transmission of the light guides and the continued independence of the transmission from sharp bends in the light guides are proof of the stability and durability of the layer, even under the influence of the light-conducting liquids that wet it. Even after functional testing,

Tests with focused radiation from 150 watt halogen lamps, 200 watt Hg high pressure lamps and 250 watt HTI lamps over several hundred hours showed no reduction in transmission, i.e. no impairment of layer 22 even with these energy loads. Even bending tests involving several thousand bends did not lead to damage to the layer or even to a detachment of the layer from the substrate. The adhesion of layer 22 to the substrate of the jacket 21 is so good that the layer did not detach even when the tightly fitting cylindrical quartz plugs 24, which form the entry and exit windows for the light, were pressed into the light guide tube.

Apart from the special case of the water light guide, for which AF 2400 is required, coating a sheath made of FEP material with Teflon AF 1600 is particularly effective, especially in connection with the usual light guide liquids (salt solutions, in particular CaClp solution, glycols), whose refractive indices cannot be increased significantly above n=1.45. The Teflon AF inner layer increases the transmission of the light guide, especially in its bent state, by up to 25%, since Teflon AF - in contrast to the slightly crystalline structure of FEP - has a glassy structure and thus results in less scattering losses during total reflection. This advantage also applies to the other tube materials to a greater or lesser extent.

Since TFB material has a higher optical refractive index of 1.3 6 than Teflon FEP, the effective refractive index of the optically thinner cladding medium can be reduced by 5/100 by coating it with Teflon AF 1600. When using a light-conducting liquid with n=1.45", the total aperture angle for the incident light beam increases from 60° to 80°, and the bending losses are reduced from 15% to less than 5% for a light guide with 5 mm active diameter and curvature with R = 7 cm.

11
Example 1: Water light guide

Light-conducting liquid 23: deionized high-purity water n=1.33. Tube: AF 2400 as a thin layer 22 applied to the

Inside of a jacket 21 made of FE _- P material. Length 150 cm, 0. = 5 mm, 0 = 6 mm

1 3.

2 quartz plugs SiO ₂ each 20 mm long, thickness of layer 22 approx. 2 μm.

The transmission of the light guide at A=430 nm and a light incidence cone with a 60° opening was: T = 22% (the aperture of the light guide is only 36°). With a light incidence cone with a 10° opening only, the transmission increases to 60%. In the case of an excimer laser (XeCl) as a light source 10 with /\-=308 nm, the transmission was 60%. The light guide was bent in a U-shape with a radius of R = 30 cm in these measurements. Due to the small difference in the refractive index between the core of light-conducting liquid 23 and layer 22 (^n = 3/100 - 4/100), this water light guide is particularly suitable for radiation sources with very low light incidence divergence, i.e. for laser radiation, preferably UV laser radiation from an excimer laser with emission at =3 08 nm (XeCl), since H&ldquor;O has an excellent UV transmission. As a laser light guide, the active diameter of the water light guide should be less than 5 mm, e.g. 2 mm or 1 mm, in order to minimize bending losses. The substrate jacket 1 preferably has an inner diameter 0 of 2 mm and an outer diameter 0 of 4 mm and can be made of FEP, PTFE, PFA,

el

ETFE or TFB material. This water light guide with FEP substrate material described above has maintained its transmission precisely over a period of 5 months as a closed system. (Because the permeability of the hose wall for H&ldquor;O vapor means there is a risk of H&ldquor;O vapor diffusing from the inside of the hose to the outside, a thicker wall of e.g. 1 mm is advantageous for water light guides.)

12
Example 2:

Light guide with a core made of light-conducting liquid 23 triethylene glycol with 8% H&ldquor;0 additive (n=1.45), a jacket 21 made of fluorocarbon terpolymer TFB, 1 = 230 cm, 0. = 5 mm, 0 = 6 mm and an inner layer 22 made of AF 1600 (n = 1.31),

a thickness d _>. ll· ¹¹ * ^{1 un<} ^ with ends closed on both sides by quartz glass stoppers.

The transmission measurement was carried out with blue light = 430 nm at a light incidence cone angle of 60° and resulted in an average transmission value of 79.3% for 10 measured light guides with AF 1600 layer 22. The bending losses were measured for light guides wound twice around a circular cylinder with R = 7 cm and resulted in a reduction in transmission of only 3% to 76%. The measurement of 10 control light guides under the same conditions, but without the AF 1600 layer 22, resulted in an average transmission value of 72.5% and in the bending test of 64%. The average transmission value of the light guide coated with AF 1600 is 9.4% higher in the slightly bent or straight state, and a considerable 20% higher in the strongly bent state.

The invention therefore provides a lighting device that contains a light source and a liquid light guide. The liquid light guide has a tubular flexible jacket made of fluorocarbon polymer material, which is filled with a light-conducting liquid such as glycol, a chloride-, fluoride- or phosphate-containing salt solution, phenyl-methyl-silicone oil (n approx. 1.57), PCTFE oil, polychlorotrifluoroethylene oil (n approx. 1.40) or pure water. The tubular jacket is lined with a thin inner layer, preferably made of Teflon AF, whose refractive index is lower than that of the jacket material.

13 Example 3:

Hose material: copolymer of tetrafluoroethylene and hexafluoropropylene (FEP);

Coating material: Teflon AF 1600^ ^Wz) ; Liquid: Aqueous calcium chloride solution, η = 1.435.

Otherwise as example

Example 4:

Hose material: copolymer of tetrafluoroethylene and hexafluoropropylene (FEP);

Coating material Teflon AF 1600

(Wz)

Liquid: Triethylene glycol with a content of 10 wt.% water (the water content can vary between 8 and 15%) - Otherwise as Example 5:

Hose material: terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride;

Layer material and liquid as in example

Example 6:

Hose material and layer material as in example

Liquid: tetraethylene glycol; water content as in example 4.

14 Example 7:

Hose material: copolymer of tetrafluoroethylene and hexafluoropropylene (FEP);

Coating material: Teflon AF 1600 ^(Wz) ; layer thickness at least 3 pm, preferably 5 μιλ.

Liquid: Polychlorotrifluoroethylene oil with the general formula

F F

! I

II F Cl

and a refractive index of about 1.40 to 1.41. Example 8:

Hose and layer material as in example liquid: phenylmethylsilicone oil.

Claims (28)

1 13671 Dr.v.B/Schä S8 PATENT CLAIMS 1. Lighting device with a light source and a with this optically coupled liquid light guide, which contains a cylindrical, tubular jacket made of carbon-fluoropolymer material and an active core surrounded by the jacket made of a light-conducting liquid, characterized in that the jacket (1) is provided on its inside with a thin layer (2) of an amorphous copolymer which is based on a combination of tetrafluoroethylene and a fluorinated cyclic ether (Teflon AF). 2. Lighting device according to claim 1, characterized in that the thickness of the layer (2) is >1 µm. 3. Lighting device according to claim 1 or 2, characterized in that the jacket (1) consists of TFB material (terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride). 4. Lighting device according to claim 1 or 2, characterized in that the jacket consists of FEP material (copolymer of tetrafluoroethylene and hexafluoropropylene). 5. Lighting device according to claim 1 or 2, characterized in that the sheath consists of PFA material (perfluoroalkoxy polymer). 6. Lighting device according to claim 1 or 2, characterized in that the jacket consists of PTFE material (polytetrafluoroethylene). 7. Lighting device according to claim 1 or 2, characterized in that the sheath consists of ETFE material (copolymer of ethylene and tetrafluoroethylene). 8. Lighting device according to claim 1 or 2, characterized in that the sheath consists of PVDF material (polyvinylidene fluoride) or PCTFE or PVDF. 9. Lighting device according to one of the preceding claims, characterized in that the material of the layer (2) has a glass temperature in the range of 160° to 240 ⁰ C. 10. Lighting device according to claim 3, characterized in that the glass temperature of the layer (2) is below 240 ^° C. 11. Lighting device according to one of the preceding claims, characterized in that the light-conducting liquid consists of mono- and/or di- and/or tri- and/or tetraethylene glycol. 12. Lighting device according to one of claims 1 to 9, preferably according to claim 3 or 4, characterized in that the light-conducting liquid (3) consists of a chloride- and/or fluoride-containing aqueous salt solution. 13. Lighting device according to one of the claims 1 to 9, preferably according to claim 3 or A, characterized in that the light-conducting liquid (3) consists of a phosphate-containing aqueous solution. 14. Lighting device according to claim 11, characterized in that the light-conducting liquid (3) contains a proportion of water which is more than 5%, preferably between 7 and 15%. 15. Lighting device according to one of the claims 4 to 7, characterized in that the material of the layer (2) has a glass transition temperature of 240 ⁰ C (Teflon AF 2400) and the light-conducting liquid (3) consists of pure water or water with fluoride or phosphate addition or with a small amount of chloride addition. 16. Lighting device according to claim 15, characterized in that the fluoride additive is formed by potassium and/or sodium and/or caesium and/or ammonium and/or calcium chloride with a concentration which gives a refractive index of up to n=1.44. 17. Lighting device according to claim 15, characterized in that the phosphate additive is formed by K&ldquor;HP0., Na&ldquor;HP0. or NaH ₂ PO, with a concentration which gives a refractive index up to n=1.42. 18. Lighting device according to one of claims 1 to 17, characterized in that the light source contains a very high pressure gas or vapour discharge lamp. 19. Lighting device according to one of claims 1 to 17, characterized in that the light source contains a tungsten-halogen lamp. 20. Lighting device according to one of claims 1 to 19, characterized in that a light filter (14) is arranged between the light source and the liquid light guide. 21. Lighting device according to claim 20, characterized in that the light filter has a transmission range of about 330 to 380 nm. 22. Lighting device according to claim 20, characterized in that the light filter has a transmission range of about 330 to 480 nm. 23. Lighting device according to claim 20, characterized in that the light filter has a transmission range of about 280 to 480 nm. 24. Lighting device according to claim 1, characterized in that the jacket (1) consists of a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), the inner layer (2) consists of AF 1600 and the liquid consists of a calcium chloride solution with a preferred refractive index η = 1.435. 25. Lighting device according to claim 1, characterized in that the casing (1) consists of a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP) or of a terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride, the inner layer (2) consists of AF 1600 and the liquid consists of tri- and/or tetraethylene glycol with an addition of 8-15% by weight, preferably about 10% water. 26. Lighting device according to claim 1, characterized in that the casing (1) consists of a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), the inner layer (2) consists of AF 1600 and the liquid consists of polychlorotrifluoroethylene oil. 27. Irradiation device according to claim 26, characterized in that the layer (2) has a thickness of at least 3 μm, preferably 5 μm. 28. Irradiation device according to claim 26, characterized in that the jacket (1) consists of a terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride, the layer consists of AF 1600 and the liquid consists of a phenylmethylsiliconol.