Optical element for Mie scattering light from an optical fiber

Abstract

The invention relates to an optical scattering element suitable for dispersing or scattering light transmitted by optical device by Mie scattering. The optical scattering element comprises a phase-separated or porous borosilicate glass having dispersed phase particles with a particle size of 200 to 500 nanometers or pores with a size of 200 to 500 nanometers, at a number density of 10.sup.8 to 10.sup.12 mm.sup.3. The optical scattering element can be prepared by subjecting a borosilicate glass to a controlled heat treatment to induce phase separation, and then optionally leaching out one of the phases with an acid leach. The optical scattering element can be, for example, attached to an end of an optical fiber or bundle of optical fibers. The invention also relates to a method of dispersing or scattering light by transmitting the light through the optical scattering element.

Claims

1. A device comprising one or more optical fibers and one or more Mie scattering optical elements for dispersing light, emitted from said at least one optical fiber, predominantly in the forward direction, wherein at least one of said one or more optical fibers has one of said one or more Mie scattering elements attached to an end thereof, and wherein said one or more Mie scattering optical elements each comprise a phase-separated glass having dispersed phase particles with a particle size of 200 to 500 nanometers or a porous glass having pores with a size of 200 to 500 nanometers, at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

2. A device according to claim 1, wherein said phase-separated glass or porous glass is a phase-separated or porous borosilicate glass.

3. A device according to claim 1, wherein said phase-separated glass or porous glass is a phase-separated or porous alkali borosilicate glass.

4. The device according to claim 1, wherein said one or more Mie scattering optical elements each comprise a phase-separated borosilicate glass wherein the particles of the dispersed phase have particle size of 200 to 500 nanometers at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

5. The device according to claim 4, wherein said one or more Mie scattering optical elements each comprise an alkali phase-separated borosilicate glass wherein the particles of the dispersed phase have particle size of 200 to 500 nanometers at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

6. The device according to claim 1, wherein said at one or more Mie scattering optical elements each comprise a porous borosilicate glass wherein glass have pores with a pore size of 200 to 500 nanometers at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

7. The device according to claim 6, wherein said one or more Mie scattering optical elements each comprise an alkali porous borosilicate glass wherein glass have pores with a pore size of 200 to 500 nanometers at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

8. The device according to claim 4, wherein said particles of the dispersed phase have particle size of 300 to 500 nanometers.

9. The device according to claim 4, wherein said particles of the dispersed phase have particle size of 300 to 450 nanometers.

10. The device according to claim 6, wherein said pores have a pore size of 300 to 500 nanometers.

11. The device according to claim 6, wherein said pores have a pore size of 300 to 450 nanometers.

12. The device according to claim 1, wherein said dispersed phase particles or said pores have a number density of 10.sup.9 to 10.sup.11 mm.sup.3.

13. The device according to claim 12, wherein said dispersed phase particles or said pores have a number density of 10.sup.10 to 10.sup.11 mm.sup.3.

14. The device according to claim 1, wherein said device is capable of providing a scattering cross section of 10.sup.4 to 10.sup.2 m.sup.2 for light emitted though said at least one Mie scattering optical element.

15. The device according to claim 14, wherein said device is capable of providing a scattering cross section of 510.sup.3 to 510.sup.2 m.sup.2.

16. The device according to claim 2, wherein said one or more Mie scattering optical elements are prepared by subjecting an annealed borosilicate glass to a phase separation using a controlled thermal treatment, and optionally subjecting the phase-separated borosilicate glass to an acid leach to create pores and a caustic leach to clean the resultant pores.

17. The device according to claim 16, wherein said controlled thermal treatment comprising heating the annealed borosilicate glass at a temperature of 500-800 C. for a time period of 1 to 150 hours.

18. The device according to claim 16, wherein said controlled thermal treatment comprising heating the annealed borosilicate glass at a temperature of 600-800 C. for a time period of 1 to 150 hours.

19. The device according to claim 16, wherein said controlled thermal treatment comprising heating the annealed borosilicate glass at a temperature of 650-750 C. for a time period of 1 to 150 hours.

20. The device according to claim 16, wherein said controlled thermal treatment comprising heating the annealed borosilicate glass at a temperature of 700-725 C. for a time period of 1 to 150 hours.

21. The device according to claim 17, wherein said time period is 24 to 48 hours.

22. The device according to claim 17, wherein said time period is 48 to 80 hours.

23. The device according to claim 16, wherein said annealed borosilicate glass comprises (based on wt. %): TABLE-US-00006 B.sub.2O.sub.3 15.00-40.00 SiO.sub.2 45.00-80.00 R.sub.2O 0.0-20.0 RO 0.0-20.00 RO.sub.2 0.0-10.00 Al.sub.2O.sub.3 0.0-10.00 wherein R.sub.2O is the sum of Li.sub.2O, Na.sub.2O, K.sub.2O, and Cs.sub.2O, RO is the sum of BaO, CaO, MgO, SrO, and ZnO, and RO.sub.2 is the sum of TiO.sub.2, ZrO.sub.2, and HfO.sub.2.

24. The device according to claim 16, wherein said annealed borosilicate glass is an annealed alkali borosilicate glass.

25. The device according to claim 16, wherein said annealed borosilicate glass comprises (based on wt. %): 40-80% SiO.sub.2, 5-35% B.sub.2O.sub.3 and 1-10% Na.sub.2O.

26. The device according to claim 25, wherein said annealed borosilicate glass comprises (based on wt. %): 45-65% SiO.sub.2, 20-30% B.sub.2O.sub.3 and 2-8% Na.sub.2O.

27. The device according to claim 26, wherein said annealed borosilicate glass comprises (based on wt. %): 50-55% SiO.sub.2, 25-27% B.sub.2O.sub.3 and 5-7% Na.sub.2O.

28. The device according to claim 1, wherein said device includes a plurality of optical fibers and each of said optical fibers has one of said Mie scattering optical elements attached to an end thereof.

29. The device according to claim 1, wherein said device comprises a plurality of said optical fibers in the form of an optical fiber bundle, and one of said Mie scattering optical elements is attached to an end of said optical fiber bundle.

30. A process for preparing a device according to claim 1, said process comprising: preparing one of said Mie scattering optical elements by subjecting an annealed glass to a phase separation using a controlled thermal treatment, and optionally subjecting the phase-separated borosilicate glass to an acid leach to create pores and a caustic leach to clean the resultant pores, and attaching the resultant Mie scattering optical element to the end of one of said optical fibers or to an end of a bundle of said optical fibers.

31. The process according to claim 30, wherein said resultant Mie scattering optical element is attached to the end of said one of said optical fibers or to an end of said bundle of said optical fibers by fusion splicing.

32. The process according to claim 30, wherein said resultant Mie scattering optical element is attached to the end of said one of said optical fibers or to an end of said bundle of said optical fibers by an optically clear silicone adhesive.

33. The process according to claim 30, wherein said resultant Mie scattering optical element is attached to the end of said one of said optical fibers or to an end of said bundle of said optical fibers by a nanofoil.

34. A method for dispersing or scattering light transmitted by an optical device comprising an optical fiber and a Mie scattering optical element for dispersing light, said process comprising: transmitting the light emitted from an end of said optical fiber, through said Mie scattering optical element, whereby said light is dispersed predominantly in the forward direction, said Mie scattering optical element comprising a phase-separated or porous glass having dispersed phase particles with a particle size of 200 to 500 nanometers or pores having a size of 200 to 500 nanometers, at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

35. The method according to claim 27, wherein said optical device is an optical fiber.

36. The method according to claim 27, wherein said optical device is an optical fiber bundle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and further details, such as features and attendant advantages, of the invention are explained in more detail below on the basis of the exemplary embodiments which are diagrammatically depicted in the drawings, and wherein:

(2) FIG. 1 shows a scanning electron microscope image of a porous glass derived from composition A of Table 1;

(3) FIG. 2 shows an embodiment wherein several optical fibers are each provided with a Mie scattering element attached to an end thereof; and

(4) FIG. 3 shows an embodiment wherein a single Mie scattering element is attached to the ends of a plurality of optical fibers.

EXAMPLES

(5) The base glasses can be made by combining the components in their metal oxide forms and melting the resultant mixture with the help of stirring using a platinum stirrer for better homogeneity. The glasses can then be cast into moulds and appropriately annealed in order to remove the stress as the liquid cools to the amorphous state. The resulting glass slabs can then be shaped into forms required for use with the instruments that measure the various properties of the glasses, drawn to fiber, or machined to numerous geometries for joining to optical fiber or optical fiber bundles.

(6) The following Tables 1A-1D present examples of suitable base glasses for use in with invention.

(7) TABLE-US-00002 TABLE 1A Glass compositions on an oxide-weight percent basis Oxide A B C D E F SiO.sub.2 52.40 52.77 50.93 56.85 54.85 56.85 B.sub.2O.sub.3 25.99 25.87 25.73 30.31 30.31 30.31 Al.sub.2O.sub.3 3.42 3.41 3.39 Na.sub.2O 5.92 5.89 5.86 6.90 6.90 6.90 CaO 5.14 5.12 5.09 ZnO 3.00 4.00 2.00 TiO.sub.2 2.00 2.00 2.00 ZrO.sub.2 5.14 6.94 7.00 3.00 4.00 2.00

(8) TABLE-US-00003 TABLE 1B Glass compositions on an oxide-weight percent basis Oxide G H I J K L SiO.sub.2 54.85 58.92 57.68 58.69 57.69 60.19 B.sub.2O.sub.3 30.31 28.41 27.81 28.30 27.82 29.02 Al.sub.2O.sub.3 Na.sub.2O 6.90 6.47 6.33 6.44 6.33 6.61 CaO ZnO 3.00 3.10 4.09 2.06 3.05 2.10 TiO.sub.2 2.00 1.33 1.97 ZrO.sub.2 3.00 3.09 4.09 3.18 3.14 2.80

(9) TABLE-US-00004 TABLE 1C Glass compositions on an oxide-weight percent basis Oxide M N O P Q R SiO.sub.2 56.86 57.47 53.28 50.61 52.70 52.12 B.sub.2O.sub.3 27.43 27.72 26.43 26.23 26.14 25.86 Al.sub.2O.sub.3 Na.sub.2O 6.24 6.31 6.02 5.97 5.95 5.89 CaO ZnO 5.41 5.49 5.23 5.20 5.18 5.12 TiO.sub.2 2.00 6.98 2.00 2.01 ZrO.sub.2 4.03 3.01 7.03 5.00 8.02 8.99

(10) TABLE-US-00005 TABLE 1D Glass compositions on an oxide-weight percent basis Oxide S T SiO.sub.2 60.19 54.15 B.sub.2O.sub.3 29.02 26.11 Al.sub.2O.sub.3 3.45 Na.sub.2O 6.61 5.68 CaO ZnO 2.10 5.17 TiO.sub.2 ZrO.sub.2 2.08 5.18

Example 1

(11) Glass-in-glass phase separation is employed to create in the glass features on the order of 250 nm to induce Mie scattering primarily in the forward direction. A base glass of composition A from Table 1 is exposed to a carefully controlled heat treatment wherein the base glass is subjected to a soak temperature of 700 C. for 24 hours. The resultant glass is opaque and white in color.

(12) To support the proposed Mie scattering behavior of the phase separated glass in the visible region of the electromagnetic spectrum (400-800 nm), Mie scattering calculations were performed using the approach outlined in Bohren and Huffman (Absorption and Scattering of Light by Small Particles, Wiley-VCH, 1983, pp. 82-89). Assuming a typical observation wavelength of 550 nm, 300-nm feature sizes and 50% volume proportions of the two phases as actually observed in the phase-separated samples, calculated refractive indices for the two glassy phases (1.53 and 1.46) based on the model of Huggins and Sun (J. Amer. Ceram. Soc., vol. 26, p 4-11, 1943) with compositions estimated from mass-balance consideration of the phase-separated glass, calculations reveal a feature number density of 3.510.sup.13 mm.sup.3, a scattering cross-section of 1.510.sup.3 m.sup.2, and a scattering coefficient of 523 cm.sup.1. Further, for this particular parameter set, the forward scatter component is over 100 times stronger than the back-scatter component, a desirable feature to increase the efficiency of the out-coupled light and to reduce the thermal load of the fiber. Note that this scenario (550 nm, 300-nm feature sizes, 50% volume proportions of the two phases, and the calculated refractive indices) is meant solely as an example of what can be attained using phase-separated glass.

Example 2

(13) A plate of composition A from Table 1 is fabricated and exposed to the same phase separation heat treatment as described in Example 1. The phase separated sample is then exposed to a chemical leaching process comprised of an acid wash (e.g., 10% hydrochloric acid, 95 C.) to create open porosity and a basic wash (e.g., 0.5 N sodium hydroxide, room temperature) to remove any residual material in the porous matrix. The product of this process is a porous glass that exhibits pores on the order of 250 nm (FIG. 2).

(14) In this example, the Mie scattering is the result of the size of the nanoscale features that yield the open porosity, i.e., the pores (average pore size approximately 250 nm), and the difference in refractive index between the silica matrix and the air filled pores. Assuming the same set of conditions as in Example 1, but now with refractive indices of 1.50 and 1.00 (for the voids), the calculated Mie scattering turbidity coefficient is around 2000 mm.sup.1 at 400 nm wavelength and 850 mm.sup.1 at 800 nm, much higher than the glass of Example 1 due to the larger refractive index differential.

(15) Following the examples listed above one skilled in the art can produce scattering optical elements in a variety of formats. For example, from melt, the original glass can be cast into plates, discs, other irregular geometries, or drawn to an optical fiber.

(16) Furthermore, glass compositions such as those found in Table I can be drawn to form an optical fiber using well-known, accepted industrial processes. Here, a single-fiber can be employed, where a porous fiber can be partially exposed to a pore closing heat treatment as taught by Hood and Nordberg (U.S. Pat. No. 2,106,744) to produce a high silica fiber with a porous end that act as the scattering optical element as described in Example 2. Thus, according to a further aspect of the invention there is provided a process of preparing an optical device comprising an optical fiber and a Mie scattering optical element, the process comprising preparing a porous glass, formed from a glass system that undergoes phase separation (for example, a borosilicate glass, preferably an alkali borosilicate glass), drawing the glass into a porous fiber and subjecting the drawn porous glass to a pore closing heat treatment to produce an optical fiber with a porous end, the porous end being a Mie scattering optical element having pores having a size of 200 to 500 nanometers, at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

(17) Additionally, a single fiber produced from glass compositions such as those found in Table 1 can be exposed to a thermal treatment to induce glass-in-glass phase separation. The phase separated fiber can then be partially chemically leached such that the end of the fiber remains phase separated (e.g., non-porous). The pores created by the chemical leaching procedure can then be closed with a pore closing thermal treatment such as that taught by Hood and Nordberg (U.S. Pat. No. 2,106,744). Here, the entire fiber is non-porous, and comprised of two regionsa high silica, non-scattering region and a phase separated Mie scattering region. Thus, according to another aspect of the invention there is provided a process of preparing an optical device comprising an optical fiber and a Mie scattering optical element, the process comprising preparing a glass, formed from a glass system that undergoes phase separation (for example, a borosilicate glass, preferably an alkali borosilicate glass), drawing the glass into a fiber, subjecting the fiber to controlled thermal treatment to induce phase separation, partially subjecting the phase-separated fiber to an acid leach to create pores to form a fiber having a porous region and a non-porous end, and subject the porous region of the fiber to a pore closing heat treatment to produce an optical fiber with a phase-separated non-porous end, the non-porous end being a Mie scattering optical element having dispersed phase particles with a particle size of 200 to 500 nanometers, at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

(18) Furthermore, glass compositions such as those found in Table 1 can be drawn to an optical fiber. The resultant optical fiber can be partially inserted into a furnace to be heat treated only at one end. Here, a single optical fiber is produced that is capable of Mie scattering light. Thus, according to a further aspect of the invention there is provided a process of preparing an optical device comprising an optical fiber and a Mie scattering optical element, the process comprising preparing a glass, formed from a glass system that undergoes phase separation (for example, a borosilicate glass, preferably an alkali borosilicate glass), drawing the glass into a fiber, subjecting one end of the fiber to controlled thermal treatment to induce phase separation in that end of the fiber, and optionally subjecting the phase-separated fiber end to an acid leach to create pores and a caustic leach to clean the resultant pores, to convert the treated end of the fiber to a Mie scattering optical element having dispersed phase particles with a particle size of 200 to 500 nanometers or pores having a size of 200 to 500 nanometers, at a number density of 10.sup.8 to 10.sup.12 mm.sup.3.

(19) Alternatively, rather than heating the fiber end in a furnace, the end of the single optical fiber can be irradiate with a high power laser to induce glass in glass phase separation.

(20) In order to close the pores of a porous glass, the glass is exposed to a multistep thermal treatment. Initially, the porous glass is held at a low temperature (200 C.) to vaporize water contained within the glass. Next, the temperature is slowly increased to consolidate the open porosity (i.e., sinter) to create a non-porous glass. Here, temperatures exceeding 1000 C. are employed.

(21) The scattering optical elements comprised of phase separated glass or porous glass, in accordance with the invention, have commercial value in the general field of illumination, optical devices and sensors. For example, affixing the scattering optical element of the present invention to an optical fiber, can be employed in medical devices, such as optical fibers for use in ocular surgery. Two specific advantages of the inventive scattering optical elements in the fields of optical devices and sensors are the tunability of the scattering features over a range of sizes (i.e., 200-500 nm) by varying the heat treatment/leaching conditions and the ability to fabricate the glass products in a variety of formats (e.g., plate, fiber, etc.).

(22) The entire disclosure[s] of all applications, patents and publications, cited herein, are incorporated by reference herein.

(23) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(24) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.