MXPA99001665A - Apparatus and method for coupling high intensity light into low temperature optical fiber - Google Patents

Abstract

A method and apparatus for coupling high intensity light (82) to a low melting temperature optical fiber (80) which uses a high temperature, low NA optical fiber (84), a spatial filter between a source of high intensity light and a low melting temperature, low NA optical fiber. The source of light may be a high intensity arc lamp or may be a high NA, high melting temperature optical fiber transmitting light from a remote light source. The spatial filter not only allows the low, melting temperature optical fiber to be removed from the focus point of the high intensity light, but also dissipates unguided modes of light transmission before they enter the low temperature optical fiber. The spatial filter may be placed between the focus of a high intensity light source and a low melting temperature optical fiber, and alternatively may be placed between a high NA, high melting temperature optical fiber and a low temperature, low NA optical fiber. The source of high intensity light may be a direct source focused to a spot of less than 2 mm or alternatively may be from a second single fiber coupled to a high intensity light source. If the numerical aperture of the receiving fiber is less than that of the spatial filter, a spaced apart configuration is required with a mechanical heat sink (66) if the light intensity is higher than about 400 mW/mm2.

Description

APPARATUS AND METHOD FOR COUPLING HIGH INTENSITY LIGHT TO A LOW TEMPERATURE OPTICAL FIBER BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates generally to high intensity lighting systems and more particularly relates to optical transmission systems that use fiber optic light guides to drive high intensity and high temperature light sources. More specifically, this invention relates to apparatuses and methods for coupling light from a high intensity light source to low temperature optical fibers.

DESCRIPTION OF THE RELATED TECHNIQUE In the field of optical fiber transmission systems, it is known to use high intensity light sources and high thermal output such as, for example, mercury arc lamps, metal halide arc lamps or arc lamps. of xenon, which have typical operating power in the range of 35 to 1000 watts. See the patent of E.U.A. No. 4,757,431, issued July 12, 1988 and assigned to the same assignee hereof. These light sources are used with a fiber optic light guide that can consist of a single fiber or a bundle of many small fibers. Regular fiber bundles typically consist of low melting temperature glass, in contrast to silica or fused quartz for which the melting temperature is about 1000 ° C higher. Such systems have particular use in medical and industrial applications and are used in connection with instruments such as endoscopes, borescopes and the like. The coupling of light from a high intensity light source to a light guide requires condensation and focusing of light, and its concentration results in high power density at the focal point. The temperature rise at the focal point depends on the degree to which the light is observed. Larger site sizes are associated with a lower temperature rise and a lower degree of absorption will result in a large temperature increase. To reduce the temperature rise, the power density associated with larger site sizes must be reduced. To prevent a fiber bundle from melting, IR filters are typically placed between the light source and the beam. As the focal point decreases in size, higher melting temperature materials, such as quartz, are necessary. As indicated in the patent of E.U.A. No. 4,757,431, there are effective methods to focus light up to a diameter of 1 mm or smaller and raise the need for much higher power in the optical fiber objective than is found in light transmitting lighting systems. through a bundle of fibers.

Such high power intensities require that light guides consisting of materials with higher melting temperatures avoid the fusion of the optical fiber at the point of the coupling of the light to the fiber. This applies either to single fiber light guides or to small diameter fiber bundles (2 mm or smaller). Optical fibers made of quartz are expensive and it is necessary that such optical fibers are used for a sufficiently long period to justify their cost. In a surgical environment, this means that such optical fibers are sterilized after each use. Since sterilization techniques typically involve the use of autoclaves or high-temperature chemical disinfectants, optical fiber optic light guides must be made to withstand thermal damage and damage from the use of such chemicals. Additionally, quartz fibers are relatively brittle and difficult to bend without rupture, requiring a high degree of care during handling. Although the bundles of regular glass fibers (eg borosilicate) are made of relatively inexpensive materials, their performance in the transmission over long fiber sections is limited by the transmissivity of the materials and the losses in the stacking. In addition, the low melting temperature of the glass places limitations on the smaller sized beam that can be coupled to a high intensity light source.

The coupling of a fiber optic device, such as a microendoscope having an illumination aperture of 2 mm or less, to a typical light-transmitting fiber beam of 3 to 5 mm in diameter is inefficient and results in inefficient light transmission to an optical device. Inefficiency results from area inequality. Reducing the size of the fiber bundle to equal that of the device causes substantial losses of coupling of the source, while narrowing the focus of a small diameter beam results in beam fusion. In general, the size of the light guide coupled to a fiber optic device should be matched to the diameter of the device. Therefore, for small diameter fiber optic devices (eg less than 2 mm), a single high temperature fiber or a single high temperature fiber beam is required. Single fiber light guides having a diameter of 1 mm or less coupled to a light source are more effective than a beam of similar size since the bundles have inherent losses of stacking. Since single quartz or glass fibers greater than 1 mm in diameter are generally too rigid for practical use, bundles of fibers are typically used for applications requiring diameters greater than 1 mm. Although single quartz fibers and glass fiber bundles are useful and effective in transmitting light, they are not the least expensive way to transmit light. Plastic optical fibers are both economical and highly flexible, even at diameters greater than 1 mm. According to the above, it would be desirable to use these low cost plastic fibers together with sources} of high intensity light. Like glass beams, however, plastic has a much lower melting temperature than quartz. Therefore, the use of a single plastic fiber to transmit sufficient illumination requires an intermediate system of light transmission between the plastic fiber and the light source. An example of an application, in which low-cost plastic fibers or low-cost, small diameter glass fiber bundles would be useful, is the medical field. The use of low cost fibers would allow light guides for illuminated instruments in medicine to be sold as sterile single use product, eliminating the need for sterilization after each use. The use of small beams coupled to a single high intensity quartz fiber would allow smaller devices to be manufactured. However, neither plastic fibers nor small diameter fiberglass bundles can withstand the high temperature generated at the focal point of a light source that is condensed and focused to a small site of equal size to the diameter of such light guides. The patent of E.U.A. No. 4,986,622 issued January 22, 1991, mentions an attempt by the prior art to solve the problem and avoid thermal damage to low temperature plastic fibers. The '622 patent mentions a light transmitting apparatus which is coupled to a beam of heat-resistant glass optical fibers at the output of a high intensity light source. The fiber optic fiber bundle is then mechanically tightly coupled to a bundle of plastic optical fibers in a regular connector. The '622 patent requires a mechanical adjustment of the glass fiber bundle to the bundle of plastic fibers in order to avoid the generation of a significant amount of heat at the coupling point, which would damage the bundle of plastic fibers. The '622 patent requires that the diameter of the glass bundle be less than or equal to the diameter of the plastic bundle. This is to allow the cone of light emanating from the glass beam to be transmitted to the plastic beam without loss of light. In practice, however, this is effective only if there is also an optical specification with respect to the light cone angle (ie, the numerical aperture AN) for each beam or optical fiber and the spacing between them. The '622 patent fails to recognize this requirement. Furthermore, if the diameter of the glass bundle were significantly smaller than that of the plastic bundle, thermal damage to the plastic fiber would occur at higher power densities, if a sufficient amount of light from the light source were coupled. . In the context of the '622 patent, it appears that typical beams with diameters of 3 or 5 mm are used, since the connection between the fiberglass and plastic bundles is that which is typically found in medical lighting equipment. Such connectors make use of a proximity coupling between the bundles of fibers with minimum separation in the joint and are based on an adjustment of the relative diameters of the bundles. For higher power densities, such connectors would cause damage to the low melting temperature fiber bundle. Additionally, the '622 solution is insufficient to maximize the light output of the low temperature fiber coupled to a single high temperature fiber that transmits light from a high intensity source. There remains a need for the technique of improving the methods and apparatuses for coupling high intensity light to high melting temperature optical fibers.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a method and apparatus for coupling high intensity light to a high melting temperature optical fiber using a specific numerical aperture (AN) high temperature optical fiber as a spatial filter between a high intensity light source (at least 400 m / mm) and an optical fiber with low melting temperature and low AN. The spatial filter not only allows the low fusing temperature optical fiber to be removed from the focal point of high intensity light, but also dissipates unguided modes of light transmission before it enters the low temperature optical fiber . The spatial filter can be placed between the focus of the high intensity light source and a low melting temperature optical fiber and can alternatively be placed between a high AN and high melting temperature optical fiber and a temperature optical fiber low and low AN. The high intensity light source can be a direct source focused to a site of less than 2 mm or alternatively it can be of a second single fiber coupled to a high intensity light source. If the numerical aperture of the receiver fiber is smaller than that of the spatial filter, a spaced configuration with a mechanical thermal collector is required if the light intensity is higher than approximately 400 m / mm. If the numerical openings are equal or the receiving fiber is larger than that of the spatial filter, then the degree to which the fibers are spaced apart and the mechanical thermal collection requirement are dependent on the relative diameters of the fibers, the length of wave of light and power density.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully understood with the detailed description given hereinafter of the accompanying drawings, which are given by way of illustration only and which are not limiting of the present invention, and in which: 1 is a diagram illustrates the general concept of the spatial filter according to the present invention; Figures 2a-2c illustrate respective alternative embodiments of the present invention as implemented with a proximal connector; Figure 3 is a diagram of a high intensity lighting system that can be used with the present invention; Figure 4 is a diagram showing a specific embodiment of a proximal connector for use in the present invention; and Figure 5 shows an alternative embodiment of the present invention in which the spatial filter is used to couple light from a high AN optical fiber to a low temperature and low AN optical fiber.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES In Figure 3, an example of a high intensity light source as contemplated in the present invention is shown. The housing 10 of the light source includes a light source (typically, a high intensity arc lamp such as a xenon or mercury arc lamp or any other source of visible electromagnetic radiation that can be focused at a power density. at least 400 mW / mm2) and a concave reflector for collecting and condensing light from the source on the inlet end 4 of an optical fiber 2. The operation of the collecting and condensing system in the US patent is described. No. 4,757,431, previously mentioned. A receiving block 6 made of metal of high thermal conductivity (ie aluminum) is fixed to the walls of the housing 10 to secure a connector 8 containing the optical fiber 2, inserted at the end 6a of the block 6, to the housing. The housing 10 also contains a nozzle 9 which is secured to the block 6 of the end 6b. The connector 8 is secured to the block 6 by means of a locking mechanism 11. A switch 54 with push button is arranged in block 6 for a button pressure 58 is provided to keep the closer closed from the light source in order to protect the user's eyes from high intensity light in the absence of a connector 8 that is present. The connectors 56 are connected to the circuit system to operate the closer when the push button 58 is depressed in the presence of the connector 8. The nature of the light source system 33 is such that a very high light flux density is focused on the small area of the entrance end 4 of fiber 2. The focused light room will include light with high divergence angles, which will cause a large number of modes of propagation to the fiber to enter. However, the number of modes that can be propagated or guided in the fiber is limited by the physical characteristics of the fiber, including factors such as the AN of the fiber and the radius of the core of the fiber. Due to the mismatch of the area and the mode, only a fraction of the focused light is actually taken in by the fiber. The remaining light is either absorbed in the area surrounding the input end of the fiber, causing the generation of a significant amount of heat, or entering the fiber in unguided ways, which the fiber can not propagate. Figure 1 illustrates a general concept of the present invention. High intensity light 82 containing components with high divergence angles is focused according to the short section of the heat resistant optical fiber made of a high melting temperature material. An example of such a high melting temperature fiber is a quartz fiber; however, any other suitable high melting temperature material can be used. The high temperature fiber 84 is surrounded by a thermal collector 66, which is made of thermally conductive material, for example metal. A high temperature fiber 84 can withstand the heat generated by light that does not enter the fiber but is incident on the area surrounding the fiber input end. Additionally, the section of the fiber is sufficiently long in such a way that the functions of the fiber as a spatial filter, in which all the unguided modes of light that enter the fiber input end, are completely dissipated, within the length of the fiber 84. Accordingly, the output of the fiber 84 will consist of guided modes of light which will be coupled only as guided modes of the low melting temperature optical fiber 80. The optical fiber 80 is made of materials such as plastic or soft glass such as borosilicate for example. Since only the guided modes are coupled to the low temperature fiber 80, there is no excess heat generation between the outlet end in the fiber 84 and the inlet end of the fiber 80. Ideally, the fiber numerical aperture High temperature must be equal to or less than the numerical aperture of the low melting temperature fiber. However, even if the numerical aperture of the high temperature fiber is higher, the spatial filtering of the source light will eliminate the high order modes that would become heat. Depending on the purity and melting temperature of the low temperature fiber, additional measures may be necessary to ensure that there is no thermal damage. Plastic fibers often have impurities that absorb light, cause thermal leakage. The effect is more noticeable when the numerical aperture of the high temperature fiber is larger than that of the low temperature fiber. For example, at high power densities, light that is readily absorbed within the surface of a plastic receiving fiber can cause melting and cratering of the surface of the plastic fiber. This effect is more pronounced when the AN within the plastic fiber is lower than the AN of the high temperature fiber. This effect can be eliminated by spacing the fibers together and providing a thermal collector to ward off the resulting thermal energy. The actual spacing depends on the power density and the AN. For example, for a quartz fiber with a diameter of 0.47 mm and with AN = 0.68 that transmits 2 watts of visible light (from 410 nm to 650 nm) to a polymethacrylate fiber with a diameter of 1 mm and with AN = 0.55, the Required spacing is at least 1.7 mm to avoid thermal damage to the plastic fiber. With this spacing, part of the light with the highest angle coming out of the high temperature fiber deviates from the opening of the plastic fiber, thus providing an additional means of spatial filtering. With the same spacing and a plastic fiber with a diameter of 1.5 mm, the total power transmitted will be twice that of the fiber of 1 mm. In both cases, the amount of light transmitted to the plastic fiber without damage is considerably larger than is possible by coupling directly to the light source. The spaced configuration decreases the intensity of light that hits the fiber surface and decreases the probability of reaching the minimum fusion, which would cause thermal damage. The heat generated by excess light requires the use of a thermal collector.

The melting threshold of a plastic fiber depends on the composition of the fiber and the level of impurities. Materials that absorb the wavelengths of light transmitted from the spatial filter tend to decrease the amount of light that can be coupled without damage. Similarly, if the AN of the spatial filter is larger than that of the plastic receiving fiber, the coupling efficiency is decreased and the damage threshold is reduced for the same spacing as when the AN of the spatial filter is smaller than that of the receiving plastic fiber. In contrast, the high intensity coupling light of a single quartz fiber with AN of 0.68 to a borosilicate beam of 1 mm with AN = 0.86 or 0.55 does not require specific spacing (the starting requirement of spacing is that the fiber is placed only so that the light only fills the beam opening) and can withstand 2 watts of transmitted light power for several hours. This result is primarily from the higher melting temperature of the borosilicate compared to that of the plastic. Similar results would be expected with a single borosilicate fiber (1 mm in diameter). Care should be taken to avoid contamination of the surface of the receiving fibers, since degradation and thermal leakage are highly likely due to the absorption of the contaminant. Figures 2a-2c illustrate several alternative specific embodiments of the present invention as described in connection with Figure 1. Figure 2a illustrates a first embodiment in which the connection of the spatial filter to the low melting temperature fiber is within a proximal connector 1, such that the use of a high temperature fiber is not apparent to the user. In Figure 4, an example of such a proximal connector is shown. The connector 1 is formed of a drum 3, a collar 5 and a protective sleeve 7 which protects the inlet end 4 of the optical fiber 84 when it is not connected to the hub 9. The thermal collector 66 is in the form of a support tube of fibers. More details of connector 1 are described in the U.S. patent. No. 5,452,392 and will not be repeated in the present. Figure 2b illustrates a second embodiment in which the low temperature fiber 80 is attached to a separate connector 86 that can be inserted into the connector 1. In this embodiment, the proximal connector 1 is usable, while the low temperature fiber 80 is usable. It is disposable. Figure 2c shows a third possible mode in which the high temperature fiber 84 extends out of the proximal connector 1 and is coupled to a low temperature fiber 80 through an external connector 88. In all three modes, the fiber-to-fiber connection requires a spaced configuration and a thermal collection at the connection when the low melting temperature fiber is composed of plastic. For higher temperature fibers such as borosilicate, the spacing is less critical.

Figure 5 shows another alternative embodiment of the invention that increases the amount of light that can be transmitted through a plastic fiber without damage. Although quartz fiber with high AN can couple substantially more light from an arc source than a lower AN fiber, the resulting spatial filtration is less than optimal if the NA of the low melting temperature receiving fiber is less than that of quartz fiber. This situation can be remedied by either adjusting the AN of the spatial filtration fiber to be less than or equal to the AN of the receiving fiber of light plastic or by incorporating a second fiber with AN equal to or less than that of the plastic fiber. as a spatial filter between quartz fiber with high AN and the receiving plastic fiber. This configuration allows at least 50% more light to be coupled to the plastic receiving fiber than the direct coupling without such a spatial filter. In practice, there is a limit to which filtration will satisfactorily eliminate the fusion of plastic fiber, because heat absorption is centered within the plastic fiber. Finally, the upper limit is determined by the absorbance of the low melting temperature fiber, its purity and the presence of contaminants at the interface between the fibers. The maximum increase in the intensity of light transmitted from a plastic fiber is dependent on the power density of the light emitted by the spatial filter, the characteristics of the mechanical heat collector and the amount of spacing between the fibers. Generally, when the power density exceeds 400 mW / mm2 a spaced configuration is required and the connector must be capable of functioning as a thermal collector. In Figure 5, spatial filtering fiber 84a with low AN is used to couple the light of a high temperature optical fiber 90 and high AN to an optical fiber 80 of high temperature and low AN. The optimal ratio of the system AN is ANfiber 90 >; AN fiber 84a% ANfiber 80. The high AN light energy output by fiber 90 will not be propagated by the low AN spatial filter but will be dissipated within its length. The heat generated by such dissipation will be conducted away from the fiber 84a of the thermal collector 86. Only the guided modes of low AN will be output by the fiber 84a and coupled to the low temperature fiber 80. As such, a low temperature operation of the fiber 80 can be maintained. Compared to the prior art, the amount of light that can be coupled to a low melting temperature plastic fiber is 3 to 5 larger. In the preferred embodiments of the present invention, the optical fibers are single core fibers with a diameter of 0.1 mm to 1.0 mm. However, the principles of the invention can also be applied to optical fiber bundles. Having thus described the invention, it will be apparent to those skilled in the art that the same may be varied and modified in any manner without departing from the spirit and scope of the invention. It is intended that any and all such modifications be included within the scope of the following claims.

Claims (17)

NOVELTY OF THE INVENTION CLAIMS

1. - Apparatus for coupling high intensity light of at least 400 mW / rmt? to a low melting temperature optical fiber, comprising: a spatial filter composed of high melting temperature material to receive said high intensity light, dissipating unguided light modes within the length of said spatial filter and outputting substantial only to guided light modes; a thermal connector in proximity to said spatial filter to absorb the heat generated by said spatial filter and conduct said heat away from said spatial filter; and a low melting temperature optical fiber to substantially receive only light modes guided from said spatial filter in an inlet stoma thereof, propagating said light modes guided along a body of said optical fiber temperature of low melting and output to said guided light modes at an output end thereof.

2. Apparatus according to claim 1, further characterized in that said spatial filter comprises a single quartz optical fiber.

Apparatus according to claim 1, further characterized in that the numerical aperture of said low melting temperature optical fiber is equal to or greater than the numerical aperture of said spatial filter.

4. Apparatus according to claim 1, further characterized in that said spatial filter receives said high intensity light from a high intensity light source.

5. Apparatus according to claim 1, further characterized in that said spatial filter receives said high intensity light from a high AN optical fiber.

6. Apparatus according to claim 1, further characterized in that said low melting temperature optical fiber is made of borosilicate material.

7. Apparatus according to claim 1, further characterized in that said thermal connector is made of metal.

8. Apparatus according to claim 1, further comprising a connector attached to said low melting temperature optical fiber to connect said low melting temperature optical fiber to a light source system that provides said intensity light high, said spatial filter being located within said connector.

9. Apparatus according to claim 1, further comprising a first connector for attaching one end thereof to a light source system which provides said high intensity light, said spatial filter being located within said connector and said low melting temperature optical fiber being coupled to a second connector, said second connector being inserted to said first connector at a second end thereof, for coupling light of said spatial filter to said low melting temperature optical fiber.

10.- Fiber optic coupling device for 5 coupling high intensity light at least 400 m / mm2 from a light source system to a low melting temperature optical fiber, comprising: a connector coupled to said low melting temperature optical fiber to connect said fiber low melting temperature optics to said source system THE thing of light; a spatial filter composed of high melting temperature material, located within said connector between said light source system and said low melting temperature optical fiber, to receive said high intensity light, dissipate . Unguided light modes within the length of said filter 15 and give substantially only output to light modes guided to said low melting temperature optical fiber.

11. Apparatus according to claim 10, further characterized in that said spatial filter comprises a single quartz optical fiber.

12. Apparatus according to claim 10, further characterized in that said spatial filter comprises a single quartz optical fiber.

13. Apparatus according to claim 10, characterized in that said spatial filter comprises a single quartz optical fiber.

14. - A method for coupling high intensity light of at least 400 mW / mrrr to a low melting temperature optical fiber, comprising the steps of: providing a spatial filter composed of a single high melting temperature optical fiber to receive said high intensity light, dissipating unguided light modes within the length of said spatial filter and substantially only output to guided light modes; providing a thermal collector in proximity to said spatial filter to absorb the heat generated by said spatial filter and conduct said heat away from said spatial filter; and coupling an optical fiber at low melting temperature to said spatial filter to substantially receive only light modes guided from said spatial filter at an input end thereof, propagating said light modes guided along a body of said low melting temperature optical fiber and outputting said guided light modes at one exit end thereof.

15. Apparatus according to claim 1, further characterized in that said low melting temperature optical fiber comprises a beam of a plurality of optical fibers of small diameter and low melting temperature.

16. Apparatus according to claim 1, further characterized in that said low melting temperature optical fiber is made of light-transmitting plastic material.

17. Apparatus according to claim 1, further characterized in that said low melting temperature optical fiber is made of light-transmitting plastic material. SUMMARY OF THE INVENTION A method and apparatus for coupling high intensity light to a low melting temperature optical fiber using a low temperature and high temperature optical fiber, a spatial filter between a high intensity light source and a temperature optical fiber low melting and low numerical aperture; the light source can be a high intensity arc lamp or it can be a high numerical aperture optical fiber and high melting temperature that transmits light from a remote light source; the spatial filter not only allows the low fusing temperature optical fiber to move away from the focal point of high intensity light, but also dissipates unguided light transmission modes before they enter the low temperature optical fiber; the spatial filter can be placed between the focus of a high intensity light source and a high melting temperature optical fiber, and can alternatively be placed between an optical fiber of high numerical aperture and high melting temperature and an optical fiber of low temperature and low numerical aperture; the high intensity light source can be a direct source focused to a site of less than 2 mm or it can alternatively be of a second optical fiber coupled to a high intensity light source; if the numerical aperture of the receiving fiber is smaller than that of the spatial filter, a spatial configuration with a metallic thermal connector is required, if the intensity of the light is greater than about 400 mW / mm. GC / amm * mvh P99 / 84F