Patent Application
20190025492
The present disclosure relates to optical fibers and light sources, and in particular relates to an optical fiber apparatus that has a high divergence angle for use as a high-divergence-angle light source, and a light source system that uses the optical fiber apparatus.
Optical fibers are used for a variety of applications to convey light from a light source to a remote location. While the main application of optical fibers is for optical telecommunications, optical fibers are also used as sources of illumination and are especially useful for illuminating regions that are difficult to access using conventional illumination systems and methods.
Optical-fiber illumination is defined in part by the divergence angle of the light leaving the optical fiber end. Generally, the divergence angle of an optical fiber is determined by the index difference between the core and cladding of the optical fiber and the index of refraction of the medium in which the light-emitting end of the optical fiber is immersed. In many applications, such as biomedical applications, the illumination needs to have a very high divergence angle, e.g., of about 90 to 100 degrees in air. This is particularly challenging in biomedical applications because the light-emitting end of the optical fiber is immersed in biological fluids, which have indices of refraction of about 1.33 (e.g., about that of water), while the silica fiber core has a refractive index of nominally 1.45.
For an optical fiber to have such a high divergence angle in media like water and biological materials, the index of refraction difference between the core and cladding needs to be very high, e.g., >0.25 or >0.3. To have such very high refractive index difference while meeting other illumination requirements is very difficult. For example, for high-brightness illumination applications, the optical fiber needs to withstand high power levels, e.g., several hundreds of milliwatts over the operating wavelength range, which for visible light is from 400 nm to 700 nm. In addition, wavelength-dependent absorption or scattering needs to be avoided, as does the damage threshold of the biological media in which the light travels.
In addition, in cases where the optical fiber is to be immersed in biological media, it is preferred that the optical fiber not have materials, such as adhesives or like binding materials, that can aversely react with the biological media or remain in the biological media after the optical fiber has been removed.
An aspect of the disclosure is a high-divergence-angle (HDA) optical fiber apparatus that consists of: a multimode optical fiber having glass core, a lower-index glass cladding surrounding the glass core, a proximal end and a distal end, wherein the optical fiber has a divergence angle θ′; a light-redirecting structure operably disposed at the distal end and consisting of an array of fused glass microspheres having diameters in the range from 3 microns to 25 microns, wherein the array is fused to the distal end and has between 1 layer and 10 layers of microspheres; and wherein the light-redirecting structure defines a divergence angle θ, wherein θ≥2θ′. In an example, a majority of the microspheres is within a size range from 3 microns to 5 microns.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein the optical fiber has a core diameter D1 of nominally 40 microns and a cladding outer diameter D2 of nominally 50 microns.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein the glass microspheres, the glass core and the glass cladding are each made of a silica-based glass.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein the array has between 1 layer and 6 layers of microspheres.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein the microspheres are solid.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein θ≥3θ′.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein the core has a diameter D1 and includes adjacent the distal end a widened core section that has a diameter D1′ that is at least 5% greater than the core diameter D1.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein the distal end of the optical fiber is curved.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein the distal end of the optical fiber includes depressions and protrusions that have a size substantially the same as the glass microspheres.
Another aspect of the disclosure is the HDA optical fiber apparatus described above, wherein the fused microspheres define air-filled interstices within the light-redirecting structure.
Another aspect of the disclosure is a light source system that includes the HDA optical fiber apparatus described above and a light source optically coupled to the proximal end of the optical fiber. The light source includes a light emitter that emits light that is coupled into the optical fiber, wherein the light is emitted from the light-redirecting structure as divergent light over the second divergence angle θ.
Another aspect of the disclosure is the light source system as described above, wherein the light emitter emits non-polarized visible light in the range from 440 nm to 650 nm.
Another aspect of the disclosure is a method of forming an HDA optical fiber apparatus using a multimode optical fiber having a glass core, a lower-index glass cladding surrounding the glass core, a proximal end and a distal end, wherein the optical fiber has a first divergence angle θ′. The method includes: arranging an array of glass microspheres adjacent the distal end, the microspheres having diameters in the range from 3 microns to 25 microns; and applying heat to the microspheres and to the distal end to fuse the microspheres to each other and to the distal end to form a light-redirecting structure that consists only of the microspheres and that defines a second divergence angle θ, wherein θ≥2θ′.
Another aspect of the disclosure is the method described above, and further including: prior to the act of applying heat, using a binding material to bind the microspheres to each other and to the distal end of the optical fiber; and wherein the act of applying heat includes burning off substantially all of the binding material.
Another aspect of the disclosure is the method described above, wherein the optical fiber has a core diameter of nominally 40 microns and a cladding outer diameter of nominally 50 microns.
Another aspect of the disclosure is the method described above, wherein the glass microspheres, the core and the cladding are made of a silica-based glass.
Another aspect of the disclosure is the method described above, wherein the array has between 1 layer and 6 layers of microspheres.
Another aspect of the disclosure is the method described above, wherein the microspheres are solid.
Another aspect of the disclosure the method described above, wherein the fused microspheres define air-filled interstices within the light-redirecting structure.
Another aspect of the disclosure is the method described above, wherein the core has a diameter D1 and further including a widened core section adjacent the distal end, the widened core section having a diameter D1′ that is at least 5% greater than the core diameter D1.
Another aspect of the disclosure is the method described above, and further including forming the distal end of the optical fiber to have a convex curvature.
Another aspect of the disclosure is the method described above, and further including forming protrusions and depressions on the distal end of the optical fiber, wherein the protrusion and depressions have a size substantially the same as the microspheres.
Another aspect of the disclosure is the method described above, and further including operably arranging a light source relative to the proximal end of the optical fiber and emitting a divergent light beam from the light-redirecting structure.
Another aspect of the disclosure is the method described above, wherein the light source emits non-polarized broadband visible light over a spectral range from 440 nm to 650 nm.
Another aspect of the disclosure is the method described above, and further including immersing the light-redirecting structure in a biological fluid.
Another aspect of the disclosure is a light source system that emits divergent light of a visible wavelength λ, the light source system including: a multimode optical fiber having a proximal end and a distal end, and a divergence angle θ′; a light-redirecting structure operably disposed at the distal end and consisting of an array of fused glass microspheres having diameters in the range from 3 microns to 25 microns, wherein the light-redirecting structure is fused to the distal end and has between 1 layer and 10 layers of microspheres and defines a divergence angle θ, wherein θ≥2θ′; and a light source optically coupled to the proximate end of the optical fiber and that emits light of the visible wavelength λ.
Additional features and advantages are set forth in the Detailed Description that follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the Detailed Description serve to explain principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which:
Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure.
The claims as set forth below are incorporated into and constitute part of this Detailed Description.
Cartesian coordinates are shown in some of the Figures for the sake of reference and are not intended to be limiting as to direction or orientation.
In the discussion below, the phrase “between M and N” includes the values of M and N, e.g., “between 1 and 10 layers” includes 1 layer and also includes 10 layers.
The optical fiber “distal end” is also referred to herein as the “fiber end” or “fiber end face.”
In the discussion below, the divergence angle θ of the HDA optical fiber apparatus and the divergence angle θ′ of the optical fiber used in the HAD optical fiber apparatus are each measured from the central axis of the optical fiber. In an example, the divergence angle θ is measured as the full-width half-maximum (FWHM) of the intensity distribution of the emitted light, and in various examples the divergence angle θ as measured in air is greater than 40 degrees, or greater than 50 degrees, or greater than 60 degrees, or greater than 70 degrees, or greater than 80 degrees. Also in an example, the divergence angle θ is in the range from 40 degrees to 110 degrees, or 60 degrees to 90 degrees. The divergence angle θ as measured in a liquid is reduced as a function of the refractive index of the liquid. In an example, a “high divergence angle” θ is one that is at least twice the divergence angle θ′ of the optical fiber, i.e., θ≥2θ′.
In the discussion below, reference to an increase in the divergence angle θ is relative to the divergence angle θ′ of the optical fiber, i.e., the optical fiber alone, without the light-redirecting structure at the distal end of the optical fiber.
In an example, optical fiber 51 can be made of one or more of the following glasses: silica, soda-lime, titania, borosilicate glass (e.g., PYREX glass), alumina, and silicon oxynitride.
In an example, optical fiber 51 is a multimode fiber with a step refractive index and a core diameter D1 of nominally 40 microns and cladding outer diameter D2 of nominally 50 microns (see
The microspheres 102 need not all have the same size, i.e., a range of sizes can be used within the stated diameter range. Thus, in an example, microspheres 102 can have a size (diameter) distribution, with the majority of the microspheres having a diameter of between 3 and 10 microns or between 3 and 5 microns, or the average diameter of the microspheres is between 3 and 10 microns or between 3 and 5 microns. In an example, microspheres 102 are not perfect spheres, i.e., they are substantially spherical to within manufacturing tolerances. In an example, 10% or fewer of the microspheres in light-directing structure 106 can have a diameter smaller than 3 microns.
While glass microspheres 102 are generally preferred, the microspheres can be made of other materials, such as polymers (e.g., PMMA or polystyrene), ceramics or crystalline materials. The type of glass used can also vary, e.g., silica, soda-lime, borosilicate glass (e.g., PYREX), titania, alumina, silicon oxynitride, any one of the optical glasses known in the art, etc. The microspheres 102 can be solid or hollow, as described below. In an example, array 100 can consist of both solid microspheres and hollow microspheres.
The fusing of microspheres 102 to form array 100, as described in greater detail below, results in the formation of light-redirecting structure 106 that does not have any binding material to keep the microspheres attached to each other and to fiber end 54. Thus, in an example, there is no other material in bare end section 55 other than the glass of glass guiding section 52 and microspheres 102, and in particular there is no material used for binding, adhering, fusing, etc. the microspheres to each other and to fiber end 54 other than the glass of the glass guiding section 52 and the glass that makes up microspheres 102.
For strong and reliable fusing of microspheres 102 to fiber end 54, it is preferred that the coefficients of thermal expansion (CTEs) and the softening points of optical fiber 51 and microspheres 102 be similar. If the CTEs are significantly different, the microspheres 102 and/or the fiber end 54 can experience large stresses when heated and may cause fractures and degrade the adhesion of the microspheres to the fiber end. The stresses depend on the contact area, the CTE mismatch and the softening point. In an example, the softening points of fiber end 54 and microspheres 102 are within 300° C. to 500° C. of each other. In one example, the CTEs are within 5×10−6 of each other, while in another example the CTEs are within 1×10−6 of each other.
In an example, microspheres 102 are disposed on fiber end 54 in 1 to 10 layers, e.g., in 1 and 6 layers or in 2 to 3 layers. In an example, the layers can be relatively loose, i.e., not perfectly ordered or particularly well defined, especially in cases where the sizes of microspheres 102 vary.
Method of Making the Microsphere Array
In an example, microspheres 102 can be substantially evenly distributed over fiber end 54 using a mixture in the form of a pH-controlled solution having dispersants. The binding material 110 can be an epoxy or a low-viscosity glue. In this case, the fiber end 54 can be dipped in a thin layer (e.g., <5 microns) of binding material 110 and then dipped in a substantially uniform layer of microspheres 102, which attach to the thin layer of binding material. The latter step can be performed by pressing fiber end 54 and the microspheres 102 adhered thereto onto a flat surface to spread the microspheres out substantially evenly, as well as to remove any excess layers of the microspheres.
Because optical fiber 51 and microspheres 102 are made of dielectric materials, in another example, electrostatic techniques can be used to attach the microspheres to fiber end 54 as an initial step prior fusing the microspheres to the fiber end and to each other. In an example, an electrostatic charge is created at fiber end 54 (e.g., by rubbing bare end section 55 with a cloth) and then bringing the charged fiber end into contact with microspheres 102.
Once microspheres 102 are disposed on fiber end 54 using the binding material 110 or electrostatic means, the array 100′ of microspheres (which can also include binding material 110), as well as the fiber end, are subjected to a heating process to fuse the microspheres to each other and to the fiber end. In the example where binding material 110 is used in array 100′, the heating process is used to burn off substantially all of the binding material (i.e., only trace amounts, if any, may remain). In this regard, glass-based optical fibers 51 are preferred over plastic or polymer optical fibers since the latter have lower softening temperatures and can be damaged during the heating process that removes the binding material.
In an example, a first spark 126 is used to burn off binding material 110 and to create an initial fusion of microspheres 102 to fiber end 54 and to each other. The heating process can then be repeated a number of times with additional sparks 126 to increase the fusing strength between microspheres 102 and to fiber end 54. In an experiment, an arc current of about 12 milliamps for an arc time of 250 milliseconds was used to fuse silica microspheres 102 (Bangs SS05N dry silica beads) having an average diameter d of 3.93 microns. The binding material 110 was a low-viscosity ultraviolet epoxy. A total of 4 sparks 126 were used in the heating process to perform the fusion and to burn off binding material 110. In an example, a single spark 126 can be used to process fiber end 54 and array 100′ by employing a higher arc current and a longer arc time. The result of the arc thermal processing is the formation of light-redirecting structure 106 of
In an example, laser source 142 is a CO2 laser that emits at an infrared wavelength of nominally 10.6 microns or an ND-YAG laser that emits infrared wavelength of nominally 1.06 microns. Other lasers that emit a laser beam 144 that can heat and fuse microspheres 102 to each other and to fiber end 54 while burning off binding material 110 can be effectively employed.
In an example, laser source 142 emits light pulses so that the amount of energy in processing laser beam 150 can be precisely controlled, which in turn allows for the amount of heat delivered to array 100′ to be precisely controlled. The fusing process using process laser beam 150 can be carried out in a number of steps, e.g., a first step that burns off binding material 110 while performing an initial fusion of microspheres 102 to fiber end 54 and to each other, and then additional steps to increase the strength of the fusion of microspheres 102 to fiber end 54 and to each other. The fusion process can also be carried out in a single step that results formation of light-redirecting structure 106 of
Light Divergence by Refraction
As noted above, the size of microspheres 102 are selected so that they mainly if not entirely refract light rather than scatter light. This means that most if not all of microspheres 102 have a diameter d that is substantially larger than the wavelength of light used to form the divergent illumination. For example, if visible wavelengths of light are used (e.g., from 0.4 microns to 0.7 microns), then the diameter d of microspheres 102 is preferably at least four times the largest wavelength in the wavelength band, e.g., 2.8 microns. If a narrow-band green light having a wavelength of 0.5 microns is employed, then in an example, the diameter d of microspheres 102 is preferably at least 2 microns.
The depressions 54D and protrusions 54P can be formed on fiber end 54 using a number of techniques known in the art, including chemical etching or mechanical roughening. In an example, the chemical etching can employ a mask that allows for an etchant (e.g., an acid) to selectively act on fiber end 54. Example mask materials include an acid-resistant polymer or wax (e.g., wax microbeads).
The use of microspheres 102 allows for HDA fiber apparatus 50 to carry and emit a relatively large amount of optical power (e.g., up to about 300 milliwatts) because each microsphere only receives a small fraction of light 202 emitted from fiber end 202. In addition, the absence of a binding material in light-redirecting structure 106 avoids the problem of the high optical power burning off the binding material during use, especially during a biomedical-related use. A design that requires a binding material to bind the microspheres risks having the microspheres coming loose and being left behind in a biological medium if the optical power breaks down the binding material.
In an example, the diameter D1′ of widened core section 56W is at least 5% greater than the core diameter D1, and in another example is at least 10% greater than the core diameter D1. The increased core diameter D1′ of widened core section 56W results in an increase in the mode-field diameter of guided light 202G at fiber end 54. The increased mode-field diameter serves to increase the divergence angle θ of divergent light 214 formed by light-redirecting structure 106.
Light Source System
The light source 190 can also include an optical system 204 that couples light 202 from light emitter 200 into optical fiber 51 at input end 53, to form guided light 202G that travels down the optical fiber to fiber end (distal end) 54. As described above, guided light 202G exits fiber end 54 as light 202, which undergoes refraction by microspheres 102 in light-redirecting structure 106 to form divergent light 214.
The divergent light 214 from HDA fiber apparatus 50 serves to illuminate a wide section (volume) of vitreous humor 302 as well a wide surface portion of retina 304 so that the vitreous cutter probe 330 can be directed by a user to perform, for example, a vitrectomy or retinectomy.
The vitreous humor 302 is a fluid with a refractive index of 1.337, which is approximately the same as that of water. Consequently, the divergence angle θ of divergent light 214 from HDA fiber apparatus 50 is reduced when immersed in vitreous humor 302 (or any other liquid) as compared to an air environment. This reduction in the divergence angle θ when the output end of HDA fiber apparatus 50 is immersed in fluid is one reason why the divergence angle in air needs to be made very large. The vitreous humor 302 is one example of a biological fluid in which the light-redirecting structure 106 may be immersed during a biomedical procedure.
With reference again to
As also noted above, the absence of an organic binding material in light-redirecting structure 106 avoids possible complications (including contaminations) relating to introducing such material into eye 300 or other part of the body.
It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/288,858 filed on Jan. 29, 2016, the content of which is relied upon and incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/015292 | 1/27/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62288858 | Jan 2016 | US |
