WO2009088984A1

WO2009088984A1 - Novel optical filters for use with mercury arc lamp monitoring applications

Info

Publication number: WO2009088984A1
Application number: PCT/US2009/000036
Authority: WO
Inventors: Jamie Knapp
Original assignee: Newport Corporation
Priority date: 2008-01-08
Filing date: 2009-01-05
Publication date: 2009-07-16

Abstract

The application is directed to devices and methods of for producing novel optical filters devices for use with Mercury arc lamp applications and systems and includes at least one substrate, at least one optical coating deposited on at least one surface of the substrate, the coating configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 10% for wavelengths between about 300nm to about 450nm.

Description

NOVEL OPTICAL FILTERS FOR USE WITH MERCURY ARC LAMP MONITORING APPLICATIONS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to United States Provisional

Patent Application Serial No. 61/010,530, filed January 7, 2008, the entire contents of which is hereby incorporated by reference in its entirety herein.

BACKGROUND

[0002] Purified water is essential for numerous industrial applications. For example, purified water is required in drug and food manufacturing, semiconductor processing, critical cleaning applications, heat exchanger coolant use, purification of swimming pool water, etc. Most importantly, however, clean, potable water is necessary for sustaining life. While clean, potable water is readily available in most developed countries the lack of drinkable water continues to plague developing countries.

[0003] In response thereto, a number of water purification devices and methods have been developed. One popular purification process requires the exposure of germ-laden water to the germicidal wavelength of an ultraviolet source. Exposing flowing water to the ultraviolet germicidal wavelengths of 200nm-300nm alters and damages a bacteria's DNA, thereby preventing its reproduction. More specifically, the bacteria's DNA absorbs ultraviolet light strongly in the ultraviolet spectrum centered at 260nm. Fig. 1 graphically shows the spectral emissions for a typical mercury lamp having a dominant emission wavelength of about 254nm. Thus, mercury vapor lamps have been employed for this purpose. The U.S. Public Health Service requires that ultraviolet water purification equipment have a minimum 254nm ultraviolet dosage of 16,000 micro-watt-seconds per square centimeter. In order to insure that this minimum criterion is satisfied, an ultraviolet mercury lamp is often monitored with an optically filtered silicon photosensor, which is configured to directly measure the 254nm emission of a mercury lamp. If the photosensor measures a low 254nm emission, a warning is activated to replace the substandard ultraviolet lamp. Determining when an ultraviolet mercury lamp has aged to the point where its germicidal effectiveness has diminished is critical.

[0004] Presently, there are a number of UV water purification systems which employ ultraviolet enhanced photodiodes fitted with standard optical bandpass filters to monitor the life of the mercury lamp. These optical bandpass filters refine the performance of the optical system by selecting the critical 254nm emission, while optically blocking the remaining full UV/VIS/IR spectral region (200nm to 1200nm).

[0005] While these ultraviolet enhanced photodiode devices have proven somewhat successful in the past, a number of shortcomings have been identified. For example, these devices typically employ one or more narrow bandpass filters centered at 254nm positioned proximate to the photodiode. Exemplary filters include MDM (Metal-Dielectric -Metal) filters and Solar Blind Filters. Unfortunately, the substandard durability of these devices limits their longevity, field lifetime and versatility. In addition, these optical bandpass filters have poor resistance to environmental exposure (e.g. moisture and temperature) and, thus, need to be very carefully hermetically sealed within the housing of the photosensor.

[0006] Moreover, the widespread use of ultraviolet enhanced photodiodes fitted with standard optical bandpass filters for water purification application is largely limited by the cost of manufacture of the bandpass filters. For example, MDM filters cost approximately $88.00 (USD) per filter, while Solar Blind Filters cost approximately $250.00 (USD) per filter. Thus, such optical filters are not suitable in water purification devices and processes in third world or developing countries, which require utmost reliability at the lowest possible cost.

[0007] Thus, in light of the foregoing, there is an ongoing need for improved optical filters for ultraviolet water purification systems that are capable of producing large volumes of highly purified water with utmost reliability and at the lowest possible cost.

SUMMARY

[0008] The application is directed to devices and methods of for producing novel optical filters devices for use with Mercury arc lamp applications and systems. For example, in one embodiment, the present application discloses a variety of optical filters configured to be positioned proximate to the active region of a photodiode used in a Mercury lamp-based UV water purification system. In one embodiment, the present application discloses an optical filter device for use within an UV water purification device and includes at least one substrate, at least one optical coating deposited on at least one surface of the substrate, the coating configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 10% for wavelengths between about 300nm to about 450nm.

[0009] In another embodiment, the present application discloses an optical filter device for use within an UV water purification device and includes at least one photodiode device, at least one optical coating deposited on at least one surface of the photodiode device, the coating configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 5% for wavelengths between about 300nm to about 450nm.

[0010] In still another embodiment, the present application is directed to an optical filter device for use within an UV water purification device and includes at least one substrate configured to be positioned proximate to at least one photodiode device of an UV water purification device, at least one optical coating deposited on at least one surface of the substrate, the coating configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 5% for wavelengths between about 300nm to about 450nm.

[0011] In addition, the present application discloses a process for manufacturing an optical filter device for use with a Mercury Lamp-based UV water purification system, comprising depositing a multilayered optical coating comprised of alternating layers of low index material and high index material onto the active region of a photodiode device, the multilayer coating configured to configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 5% for wavelengths between about 300nm to about 450nm.

[0012] Other features and advantages of the embodiments of the novel optical filters for use with Mercury arc lamp monitoring applications as disclosed herein will become apparent from a consideration of the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Various novel optical filters for use with Mercury arc lamp monitoring applications will be explained in more detail by way of the accompanying drawings, wherein

[0014] FIG. 1 shows graphically the emission spectrum of a typical Mercury arc lamp commonly used in water purification applications;

[0015] FIG. 2 shows a cross-sectional view of an embodiment of a photodiode assembly having a novel optical filter positioned on or proximate to a photodiode device;

[0016] FIG. 3 shows a cross-sectional view of an embodiment of a photodiode assembly having a novel optical filter positioned within the housing of the photodiode assembly;

[0017] FIG 4 shows a cross-sectional view of an embodiment of a photodiode assembly having a novel optical filter positioned on or proximate to the optical window of a photodiode device;

[0018] FIG. 5 shows a cross-sectional view of an embodiment of a novel multilayered optical filter applied to at least one surface of a photodiode device;

[0019] FIG. 6 shows a cross-sectional view of an embodiment of a novel multilayered optical filter applied to at least one surface of a substrate configured to be positioned within a photodiode assembly;

[0020] FIG. 7 shows a cross-sectional view of an embodiment of the novel multilayered optical filter shown in FIG. 6 applied to a substrate coupled to a photodiode device;

[0021] FIG. 8 shows graphically the optical transmission of a Mercury arc lamp through the novel optical filter disclosed herein at wavelengths between 200nm and 300nm; [0022] FIG. 9 shows graphically the optical transmission of a Mercury arc lamp through the novel optical filter disclosed herein at wavelengths between 300nm and 425nm; and

[0023] FIG. 10 shows graphically the optical transmission of a Mercury arc lamp through the novel optical filter disclosed herein at wavelengths between 250nm and 1200nm.

DETAILLED DESCRIPTION

[0024] Figs. 2-4 show various embodiments of a spectrally tuned optical filter which may be used with a photodiode assembly incorporated into a mercury arc lamp-based water purification system. As shown in Figs. 2-4, the photodiode assembly 10 includes a housing body 12 having a base member 14 and at least one optical window 16. The housing body 12, base member 14, and optical window 16 define at least one housing cavity 18. One or more photodiode devices or chips 20 may be positioned within the housing cavity 18. In one embodiment, the photodiode device 20 comprises a Silicon Carbide photodiode. In an alternate embodiment, the photodiode comprises a Gallium Nitride photodiode. Those skilled in the art will appreciate that any variety of photodiode or light detecting devices may be used.

[0025] Referring again to Figs. 2-4, one or more optical filter devices or materials may be incorporated into the photodiode assembly 10. For example, as shown in Fig. 2, the optical filter device 22 may be applied to or otherwise positioned proximate to at least one surface of the photodiode device 20. For example, the optical filter device 22 may be positioned proximate to the active region of the photodiode device 20. In an alternate embodiment, the optical filter device 22 may be directly applied to the photodiode device 20. Optionally, the optical filter device 22 may be applied to a substrate which may then be affixed to of otherwise coupled to the photodiode device 20. Fig. 3 shows an alternate embodiment of a photodiode assembly 10 wherein one or more optical filters devices 22 may be positioned within the housing body 12 between the photodiode device 20 and the optical window 16. In another embodiment, Fig. 4 shows an embodiment of a photodiode assembly 10 wherein the optical filter device 22 is applied to at least one surface of the optical window 16. For example, in the illustrated embodiment, the optical filter device 22 is applied to a surface of the optical window 16 located within the housing cavity. Optionally, multiple optical filters may be positioned at various locations within the housing cavity 18. In another embodiment, the optical filter device 22 may form the optical window 16 of the photodiode assembly 10. As such, in each of the preceding embodiments, the optical filter device 22 may comprise one or more layers of an optical coating applied to an optical substrate or, in the alternative, applied directly to a component within the photodiode assembly 10.

[0026] Figs. 5-7 show various embodiments of an optical filter device shown in Figs. 2-4 above. As shown in Fig. 5, the optical filter device 22 may be directly applied to at least one surface of a device or component 20 used in forming the photodiode assembly 10. For example, Fig. 5 shows an embodiment of photodiode device 20 having an optical filter device 22 which is comprised of a multilayer coating applied thereto. In one embodiment, the multiplayer coating comprises alternating layers of hafnium oxide and silicon dioxide. In one embodiment, optical filter device 22 comprises alternating layers of coating materials having a low index of refraction 30 (hereinafter low index materials) and materials having a high index of refraction 32 (hereinafter high index materials). Exemplary low index materials 30 include, without limitation, SiO₂, Al₂O₃, SiO, fluorides such as barium fluoride and lanthanum fluoride, MgO, and the like. Exemplary high index materials 32 may include, without limitation, for example, TiO₂, ZrO₂, Ta₂O₅, and HfO₂.

[0027] Fig. 6 shows an alternate embodiment of an optical filter device 42. As shown, the optical filter device 42 may comprise at least one substrate 44 having multiple layer optical coating applied thereto. Like the previous embodiment, the multiple layer optical coating comprises alternating layers of low index materials 46 and high index coating materials 48. Exemplary substrate materials include, without limitation, synthetic fused silica substrates, fused silica substrates, ultraviolet transparent glass substrates, optical crystals, polymer substrates, glass substrates, composite material substrates, film substrates, metal substrates, and the like. Like the previous embodiment, the low refractive index materials include, for example, SiO₂, Al₂O₃, SiO, fluorides such as barium fluoride and lanthanum fluoride, MgO, and the like., while high index materials may include, without limitation, for example, TiO₂, ZrO₂, Ta₂O₅, and HfO₂. During use, the optical filter device 42 may be positioned on or in proximity to the photodiode or detector device 20 of the photodiode assembly 10 (See Fig. 2-4). For example, Fig. 7 shows an embodiment of the optical filter 42 shown in Fig. 6 affixed to a surface of the photodiode device 48. Optionally, the optical filter 42 may be positioned within the housing cavity 18 or, in the alternative, affixed to a surface of the optical window 20. (See Figs. 3 and 4). Optionally, the optical filter 42 of Fig. 7 may replace the optical window 16 shown in Fig. 2.

[0028] As stated above, the optical filters devices shown in Figs. 5-7 may be used with any variety of photodiode devices. As shown in Fig. 1, in addition to outputting radiation having a wavelength of about 254nm, mercury lamps often emit radiation having wavelengths of 300nm or greater. During use, wavelengths of about 300nm to about 450nm may be detected by a silicon carbide or gallium nitride photodetector device. As shown in Fig. 8, the optical filter devices disclosed herein may be easily configured to reduce or prevent the transmission of wavelengths between about 300nm and about 450nm. As such, the optical filter devices disclosed herein may be configured to eliminate those discreet mercury lamp emission lines (313nm, 365nm and 405nm) which are within the short spectral detection band (200nm - 400nm) of a silicon carbide or gallium nitride photodiode device. For example, in one embodiment the optical filter device disclosed herein has an optical transmittance of no greater than about 10% for wavelengths between about 300nm to about 450nm. In an alternate embodiment, the optical filter device disclosed herein has an optical transmittance of no greater than about 5% for wavelengths between about 300nm to about 450nm. In still another embodiment, the optical filter device disclosed herein has an optical transmittance of no greater than about 2% for wavelengths between about 300nm to about 450nm.

[0029] Referring again to Figs. 5-7, the optical filter devices 22, 42, respectively, may be fabricated of coating materials recognized by those skilled in the art including low and high refractive index materials. In one embodiment the coating materials are thin films of ultraviolet transparent refractory metal oxides (e.g. hafnium oxide, zirconium oxide, silicon dioxide, etc.). For example, in one embodiment the optical filter devices 22, 42, respectively, comprises a multiplayer coating of alternating layers of hafnium oxide and silicon dioxide. [0030] Those skilled in the art will appreciate that various manufacturing processes may be employed to deposit the optical coating layers forming the optical filter devices disclosed herein, including, without limitation, physical vapor deposition (thermal evaporation employing electron-beam technology), ion assisted deposition, sputtering, chemical vapor deposition, and/or reactive ion plating. Further, the thicknesses of the one or more optical coating layers, for example, the optical coating layers 30, 32 shown in Fig. 5, may range from about a nanometer per layer to about hundreds of nanometers per layer, depending on applications. In addition, the various optical filter devices disclosed herein may be manufactured in any variety of sizes. For example, in the embodiment shown in Fig. 6, the transverse dimension of the optical filter 42 is less than 2mm², thereby to enabling the optical filter 42 to be directly mounted onto the active surface of the photodiode device 20 (See Figs. 2-4). In another embodiment, the optical filter devices 22, 42 (See Figs. 5-7) may be sized to replace the optical window 16 of the photodiode assembly 10 (See Figs. 2-4). As the size of the photodiode housing window varies, the size of the optical filter 22 may be varied accordingly. Similarly, the thickness of the optical filter devices 22, 42 may range from about lOμm to about 20mm. For example, in the embodiment shown in Fig. 6, the thickness of the optical filter device 42 ranges from about 0.5mm to about lmm. The optical thin films formed by alternating high and low index layers 46, 48, respectively, may have thicknesses ranging from .lnm to lOOOOnm. For example, in the embodiment shown in Fig. 6, the thicknesses of the high index layers 46 are in the range of about 36nm to about 45nm, and the low index layers 48 are in the range of about 55nm to about 115nm.

[0031] Figs. 9 and 10 show the wavelength transmittance of the optical filter devices 22, 42 shown in Figs. 5-7. As shown in Fig. 9 and 10, the optical filter devices 22, 42 disclosed herein are configured to transmit at least about 40% of optical radiation having a wavelength of about 254nm. In another embodiment, the optical filter devices 22, 42 are configured to transmit at least about 70% of optical radiation having a wavelength of about 254nm. In still another embodiment, the optical filter devices 22, 42 disclosed herein are configured to transmit at least about 75% of optical radiation having a wavelength of about 254nm. Further, such transmittance may be maintained over extended periods of exposure to ultraviolet radiation. For example, in one embodiment, a germicidal mercury vapor lamp may be used as an ultraviolet radiation source. The output power of the UV source may range from about lμw to about 500Kw. One or more optical filter devices 42 (See Fig. 6) may be positioned at any variety of positions relative to the mercury vapor lamp. For example, the optical filter device 42 may be positioned about 0.1 inches to about several yards from the mercury vapor lamp. As a result, the optical filter device 42 may be configured to withstand exposure to UV radiation for at least 100 minutes without suffering a substantial deterioration of performance. In another embodiment, the optical filter devices 22, 42 described herein may be configured to withstand exposure to UV radiation for at least one thousand hours without suffering a substantial deterioration of performance.

EXAMPLE l :

[0032] A multilayer optical filter having layers of Hafnium Oxide and Silicon Dioxide deposited on a synthetic fused Silica substrate was fabricated as follows:

A. A simplified UV/VIS rejection coating was deposited on one surface of the synthetic fused silica substrate as follows, (see also Fig. 6, reference number 44):

[0033] SUBSTRATE/ .30076H / .12755L / (.125L .25H .125L)12 / .1216L /

.2857H / .0904L / (.157L .314H .157L)12 / .118L / .2954H / .12159L /AIR

wherein:

Substrate: Synthetic Fused Silica (approximately 0.7mm thick)

High Index Material (H): Hafnium Oxide (.25H = 1 Quarter Wave Optical Thickness of Hafnium Oxide)

Low Index Material (L): Silicon Dioxide (.25L = 1 Quarter Wave Optical Thickness of Silicon Dioxide)

Design Wavelength = 330nm [0034] The filter was produced by the ion plating deposition of hafnium oxide and silicon dioxide onto 2.0" square synthetic fused silica substrates. The thickness of the synthetic fused silica substrate was approximately 0.7mm.

[0035] Thicknesses of the hafnium oxide layers and of the silicon dioxide layers were as shown above. After dicing, the overall size of the optical filter was approximately 2mm x 2mm SQ. Other sizes produced included 0.240" diameters.

[0036] The measured performance of the thus formed multilayer optical filter was tested with the following results, as graphically shown in Fig. 9. The measured transmission percentage at 254nm is 94.3%. Further, the transmission percentage at the following wavelengths may be as follows:

%T = 0.014% at 313nm; %T = 0.005% at 365nm; and %T = 0.007% at 405nm.

[0037] The foregoing description of the invention is merely illustrative thereof, and it should be understood that variations and modifications can be affected without departing from the scope or spirit of the invention as set forth in the following claims.

Claims

What is claimed is

1. An optical filter device for use within an UV water purification device, comprising:

at least one substrate;

at least one optical coating deposited on at least one surface of the substrate, the coating configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 10% for wavelengths between about 300nm to about 450nm.

2. The device of claim 1 wherein the substrate comprises a photodiode device.

3. The device of claim 1 wherein the substrate comprises fused silica.

4. The device of claim 1 wherein the substrate is manufactured from the group consisting of synthetic fused silica, ultraviolet transparent glass, optical crystals, polymer materials, glass, composite materials, film materials, and metal substrates.

5. The device of claim 1 wherein the optical coating comprises a multilayered optical coating.

6. The device of claim 5 wherein the multilayered coating comprises alternating layers of low index of refraction materials and high index of refraction materials.

7. The device of claim 6 wherein the low index material comprises Silicon Dioxide.

8. The device of claim 6 wherein the low index material is selected from the group consisting of Aluminum Oxide, Silicon Oxide, Barium Fluoride, Lanthanum Fluoride, and Magnesium Oxide.

9. The device of claim 6 wherein the high index material comprises Hafnium Oxide.

10. The device of claim 6 wherein the high index material is selected from the group consisting of Titanium Oxide. Zirconium Dioxide, and Tantalum Pentoxide.

1 1. The device of claim 5 wherein the coating is configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 5% for wavelengths between about 300nm to about 450nm.

12. The device of claim 5 wherein the coating is configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 2% for wavelengths between about 300nm to about 450nm.

13. An optical filter device for use within an UV water purification device, comprising:

at least one photodiode device;

at least one optical coating deposited on at least one surface of the photodiode device, the coating configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 5% for wavelengths between about 300nm to about 450nm.

14. The device of claim 13 wherein the optical coating comprises a multilayered optical coating.

15. The device of claim 14 wherein the multilayered coating comprises alternating layers of low index of refraction materials and high index of refraction materials.

16. The device of claim 15 wherein the low index material comprises Silicon Dioxide.

17. The device of claim 15 wherein the low index material is selected from the group consisting of Aluminum Oxide, Silicon Oxide, Barium Fluoride, Lanthanum Fluoride, and Magnesium Oxide.

18. The device of claim 15 wherein the high index material comprises Hafnium Oxide.

19. The device of claim 15 wherein the high index material is selected from the group consisting of Titanium Oxide. Zirconium Dioxide, and Tantalum Pentoxide.

20. The device of claim 13 wherein the coating is configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 2% for wavelengths between about 300nm to about 450nm.

21. An optical filter device for use within an UV water purification device, comprising:

at least one substrate configured to be positioned proximate to at least one photodiode device of an UV water purification device;

at least one optical coating deposited on at least one surface of the substrate, the coating configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 5% for wavelengths between about 300nm to about 450nm.

22. The device of claim 21 wherein the substrate comprises fused silica.

23. The device of claim 21 wherein the substrate is manufactured from the group consisting of synthetic fused silica, ultraviolet transparent glass, optical crystals, polymer materials, glass, composite materials, film materials, and metal substrates.

24. The device of claim 21 wherein the optical coating comprises a multilayered optical coating.

25. The device of claim 24 wherein the multilayered coating comprises alternating layers of low index of refraction materials and high index of refraction materials.

26. The device of claim 25 wherein the low index material comprises Silicon Dioxide.

27. The device of claim 25 wherein the low index material is selected from the group consisting of Aluminum Oxide, Silicon Oxide, Barium Fluoride, Lanthanum Fluoride, and Magnesium Oxide.

28. The device of claim 25 wherein the high index material comprises Hafnium Oxide.

29. The device of claim 25 wherein the high index material is selected from the group consisting of Titanium Oxide. Zirconium Dioxide, and Tantalum Pentoxide.

30. The device of claim 21 wherein the coating is configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 2% for wavelengths between about 300nm to about 450nm.

31. A process for manufacturing an optical filter device for use with a Mercury Lamp-based UV water purification system, comprising depositing a multilayered optical coating comprised of alternating layers of low index material and high index material onto the active region of a photodiode device, the multilayer coating configured to configured to have an optical transmittance of at least about 40% at a wavelength of about 254nm and optical transmittance of no greater than about 5% for wavelengths between about 300nm to about 450nm.