BEAM-SHAPING ELEMENTS FOR OPTICAL COHERENCE TOMOGRAPHY PROBES

A beam-shaping optical system suitable for use with optical coherence tomography having a beam-shaping insert having a polymeric material, the beam-shaping insert integrally defining a beam-shaping element. The beam-shaping element has a reflective element positioned on a curved surface. A light source generates an electromagnetic beam. An optical fiber having a core and a cladding, the optical fiber having first end optically coupled with the light source and a fiber end. The fiber end is configured to emit the electromagnetic beam toward the beam-shaping element. The reflective element has a reflectivity greater than about 98% for both a first wavelength band of the electromagnetic beam and a second wavelength band of the electromagnetic beam.

BACKGROUND

The present disclosure relates to optical coherence tomography, and in particular, to beam-shaping elements for an optical coherence tomography probe.

Optical coherence tomography (OCT) is used to capture a high-resolution cross-sectional image of biological tissues and is based on fiber-optic interferometry. The core of an OCT system is generally known as a Michelson interferometer, which typically includes a first optical fiber which is used as a reference arm and a second optical fiber which is used as a sample arm. The sample arm includes the sample to be analyzed, as well as a probe that contains optical components therein. A light source upstream of the probe provides light used in imaging. A photodetector is arranged in the optical path downstream of the sample and reference arms. The probe is used to direct light into or onto the sample and then to collect scattered light from the sample.

Optical interference of light from the sample arm and the reference arm is detected by the photodetector only when the optical path difference between the two arms is within the coherence length of the light from the light source. Depth information from the sample is acquired by axially varying the optical path length of the reference arm and detecting the interference between light from the reference arm and scattered light from the sample arm. A three-dimensional image is obtained by transversely scanning in two dimensions the optical path in the sample arm. The axial/depth resolution of the process is determined by the coherence length, while the overall transverse resolution is dictated by the size of the image spot formed by the optical components of the probe.

Because the probe typically needs to be inserted into a small cavity of the body, generally it must be small and preferably have a simple optical design. Exemplary designs for the probe include a transparent cylinder in which the miniature probe optical components are contained and through which light is transmitted and received. However, light may be lost due to back reflection when it passes through materials having a different refractive index, thus decreasing image spot intensity. Additionally, back reflections decrease the signal to noise ratio in the data. Moreover, having multiple and separate optical components in the probe is generally problematic because the small optical components have to be assembled and aligned, which adds to the cost and complexity of manufacturing the probe.

SUMMARY

According to one embodiment of the present disclosure, a beam-shaping optical system suitable for use with optical coherence tomography having a beam-shaping insert having a polymeric material, the beam-shaping insert integrally defining a beam-shaping element. The beam-shaping element has a reflective element positioned on a curved surface. A light source generates an electromagnetic beam. An optical fiber having a core and a cladding, the optical fiber having first end optically coupled with the light source and a fiber end. The fiber end is configured to emit the electromagnetic beam toward the beam-shaping element. The reflective element has a reflectivity greater than about 98% for both a first wavelength band of the electromagnetic beam and a second wavelength band of the electromagnetic beam.

According to another embodiment of the present disclosure, an optical coherence tomography probe has a sheath defining a central cavity, a beam-shaping insert positioned in the central cavity, the insert having a polymeric material and defining a curved surface, and a reflective element positioned on the curved surface. The reflective element includes a barrier layer having at least one layer of aluminum, chromium or alumina positioned on the curved surface. A metal layer is positioned on the barrier layer. At least one stack of alternating dielectric materials is positioned on the metal layer. A ferrule is positioned within the central cavity. An optical fiber, the fiber supported by the ferrule including a fiber end configured to emit an electromagnetic beam toward the reflective element.

According to another aspect of the present disclosure, a method of forming an optical coherence tomography probe includes the steps of forming a polymeric beam-shaping insert defining a curved surface, depositing a barrier layer on the curved surface, the barrier layer comprising at least one layer of chromium, aluminum, and alumina, depositing a metallic layer on the barrier layer, and depositing a dielectric stack on the metallic layer to form a reflective element. The reflective element is configured to reflect greater than about 98% of both a first wavelength band of an electromagnetic beam and a second wavelength band of an electromagnetic beam.

According to another aspect of the present disclosure, a beam-shaping optical system suitable for use with optical coherence tomography includes a sheath defining a central cavity, a beam-shaping insert having a first beam-shaping element and a second beam-shaping element, the insert positioned within the cavity, and an optical fiber having a core and a cladding disposed within the central cavity. The optical fiber has a fiber end configured to emit an electromagnetic beam toward the beam-shaping insert. The first beam-shaping element reflects a first portion of the electromagnetic beam and the second beam-shaping element refracts a second portion of the electromagnetic beam.

According to another aspect of the present disclosure, an optical coherence tomography probe includes a sheath defining a central cavity, a beam-shaping insert positioned near an end of the central cavity, a beam-shaping element positioned on the beam-shaping insert, and an optical fiber having a core and a cladding disposed within the central cavity. The optical fiber has a fiber end configured to emit an electromagnetic beam toward the beam-shaping element. The beam-shaping element is configured to focus a first portion of the electromagnetic beam to a side of the sheath and focus a second portion of the electromagnetic beam forward of the sheath.

According to another aspect of the present disclosure, a method of forming multiple image spots includes the steps of positioning an optical fiber having a core and a cladding within a ferrule, positioning the ferrule within a central cavity of a sheath, and emitting an electromagnetic beam from a fiber end of the optical fiber toward a beam-shaping insert. The beam-shaping insert is configured to form a first image point at a first image plane and a second image point at a second image plane, the image planes being different working distances from the beam-shaping insert.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferred embodiments, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

Depicted inFIGS. 1A-6is an embodiment of the beam-shaping optical probe10suitable for use in OCT and the making of OCT images. The optical probe10includes a sheath14defining a central cavity16within which an optical fiber18is disposed. The sheath14is comprised of a first portion22and a second portion26. The optical fiber18includes a cladding34, a core40, and a coating44. In various embodiments the coating44is polymeric, but may also comprise metal. The optical fiber18includes a first end (not shown) optically coupled to a light source (not shown) and a fiber end48. The light source is configured to generate and emit an electromagnetic beam52into the optical fiber18such that the fiber end48emits the electromagnetic beam52. The electromagnetic beam52may be a light beam (e.g., visible, ultraviolet, infrared or light). The electromagnetic beam52is emitted along an optical axis OA defined by the optical probe10. In assembly, the optical fiber18enters the optical probe10through a torque tube58and is coupled to a ferrule62. A beam-shaping insert66is positioned at a distal end of the optical probe10and defines a beam-shaping element70.

Referring now toFIGS. 1A and 1B, the sheath14is an assembly of the first portion22and the second portion26aligned on axis OA and in abutment with one another. In the depicted embodiment, the second portion26defines a window82through which the electromagnetic beam52(FIG. 3) may exit and enter the optical probe10. Optionally, the window82may include a transparent material through which the electromagnetic beam52can pass, yet prevents foreign matter out of the optical probe10. The sheath14may comprise a transparent or opaque material. In some embodiments the sheath14may comprise a polymeric material such as latex, polyethylene, or polyurethane or a metal such as304or306stainless steel. The central cavity16of the sheath14is defined by an inner wall90. The first and second portions22,26each define an abutment surface94configured to be in contact or close proximity when the optical probe10is in the assembled configuration. The ferrule62, the torque tube58and the beam-shaping insert66are shaped to precisely mirror the inner wall90of the sheath14such that the ferrule62, torque tube58and the beam-shaping insert66precisely fit within the central cavity16in a flush and substantially concentric manner. In assembly, the optical fiber18travels through the torque tube58from an upstream light source (not shown) to the ferrule62. The ferrule62defines an aperture98extending though the ferrule62into which the optical fiber18is positioned. The aperture98is configured to accept the cladding34and the core40of the optical fiber18. By positioning the optical fiber18within the ferrule62, a central axis of the fiber18along which the electromagnetic beam52is emitted may be quickly aligned to the optical axis OA of the optical probe10due to the high concentricity between the ferrule62and the inner wall90of the sheath14.

The beam-shaping insert66is configured to be inserted into the central cavity16of the distal end of the sheath14such that a flange102is in abutting contact with the sheath14. It will be understood that various embodiments of the optical probe10and beam-shaping insert66do not necessarily have a flange102. The flange102is positioned on the beam-shaping insert66such that the flange102contacts the second portion26of the sheath14as the beam-shaping element70is positioned proximate the window82. In this manner, the flange102may aid in the positioning of the beam-shaping insert66within the sheath14as well as the beam-shaping element70. Optionally, a forward surface106of the beam-shaping insert66and/or the flange102includes one or more markings (e.g., degree dial, an index line, hash marks) designed to aid an operator in correctly orienting the beam-shaping insert66within the sheath14. Additionally or alternatively, the sheath14(e.g., second portion26) may include the same, similar, or complimentary markings configured to aid in orientation of the beam-shaping insert66. Orientation of the beam-shaping insert66within the sheath14is performed such that the beam-shaping element70is aligned with the optical axis OA of the optical probe10and the window82of the sheath14. A gap110is defined between the ferrule62and the beam-shaping insert66when in assembly. The gap110may be a void having air or a transmissive liquid or solid. In embodiments where the gap110is filled with a transmissive liquid or solid, the refractive index of the liquid or solid may be chosen to aid in propagation and/or shaping of the electromagnetic beam52.

In various embodiments, the beam-shaping insert66and/or the ferrule62includes a polymeric composition having a glass transition temperature greater than about 150° C. Exemplary thermoset classes of polymeric materials that may be used to form the beam-shaping element66include epoxy, polyester, cyanate ester, phenolic, melamine, bismalemide, and polyimide. Exemplary thermoplastic polymeric materials for the beam-shaping insert66include ZEONOR® (available from Zeon Chemicals L.P., Louisville, Ky.), polyetherimide (PEI), polyethylene, polypropylene, polycarbonate, engineered polymers (e.g., liquid crystal), acrylonitrile butadiene styrene, polyetheretherketone, nylon12, polybutylene terephthalate, polyethylene terephthalate, polysulfones, thermoplastic polyimide, cyclo olefinic copolymer, polyphenylene ether, polyphenylene sulfide, syndiotactic polystyrene, as well as any other polymeric material or combination of polymeric materials capable of forming the beam-shaping insert66and producing a smooth surface. In polymeric embodiments, the beam-shaping insert may also include filler including mineral fillers, glass fibers, or a combination of mineral and glass fibers. In other embodiments, the beam-shaping insert66may include metals, ceramics, or composites thereof. The beam-shaping insert66and/or the ferrule62is capable of formation by conventional manufacturing techniques such as injection molding, casting, machining, thermoforming, diamond turning, or extrusion.

Still referring toFIGS. 1A and 1B, the beam-shaping element70is integrally defined by the beam-shaping insert66such that in assembly, the beam-shaping element70is positioned inside of the central cavity16of the sheath14. The beam-shaping element70includes a reflective element114positioned on a curved surface118defined from the beam-shaping insert66. The beam-shaping insert66extends in an upwardly and inwardly curved manner with respect to the forward surface106to define the curved surface118. The beam-shaping element70is substantially conic in shape and curves inwardly toward the optical axis OA of the optical probe10. The conic shape of the beam-shaping element70is defined by a radius of curvature and conic constant along an axis of the beam-shaping element70with respect to the optical axis OA of the optical probe10.

In order to properly shape the electromagnetic beam52, the beam-shaping element70may have a radius of curvature along the X-axis that is the same or different than a radius of curvature in the Y-axis. The radius of curvature of the X- and Y-axes of the curved surface118of the beam-shaping element70may have an absolute value of between about 0.5 millimeters and about 10 millimeters, and more specifically, about 1.0 millimeter to about 4.0 millimeters. The conic constant of the X- and Y-axes of the beam-shaping element70may independently range from about 1 to about −2, and more specifically between about 0 and about −1. It should be understood that the radii and conic constants of the curved surface118explained above describe the overall shape of the beam-shaping element70, and do not necessarily reflect local radii or conic constants of the curved surface118. The radius of curvature of the X-axis and Y-axis of the beam-shaping element70may be adjusted independently in order to correct for any material disposed around the optical probe10. The conic shape of the beam-shaping element70may be decentered along the Y- or Z-axes between about 0.01 millimeters and about 0.8 millimeters. Additionally, the conic shape of the beam-shaping element70may have a rotation between the Y- and Z-axes of between about 70° and 120°.

Referring now toFIG. 2, the beam-shaping element70is configured to collect and shape (e.g., collimate, converge, and/or change the optical path of) through reflection the electromagnetic beam52(FIG. 3) emitted from the optical fiber18, as explained in greater detail below. Positioned on the curved surface118of the beam-shaping element70is the reflective element114. In the depicted embodiment, the reflective element114includes a barrier layer122, a metal layer126, a first dielectric sack130and a second dielectric stack134. The barrier layer122comprises a chromium layer122A, an aluminum layer122B, and an alumina layer122C. In some embodiments, the barrier layer122includes only one or two of the layers122A,122B,122C (e.g., only the chromium layer122A or only the aluminum layer122B and the alumina layer122C). The order of the layers122A,122B,122C may also be different than that depicted. For example, the alumina layer122C may be proximate the curved surface118of the aluminum layer122B may be proximate the metallic layer126. Each of the layers122A,122B,122C may have a thickness between about 1 nanometers and about 100 nanometers, more particularly between about 10 nanometers and about 60 nanometers, and more particularly about 20 nanometers to about 40 nanometers. In a specific example, the layers122A,122B,122C are each about 30 nanometers thick. In some embodiments, the thickness of the layers122A,122B,122C may all be approximately the same, while in other embodiments each layer122A,122B,122C may have a different thickness. The chromium layer122A may include metallic chromium, alloys of chromium, oxides of chromium, or high chromium concentration (e.g., greater than about 30 weight %) materials. Similarly to the chromium layer122a,the aluminum layer122B may include metallic aluminum, oxides of aluminum, aluminum alloys, and high aluminum concentration (e.g., greater than about 30 weight %) materials. The alumina layer122C may include various oxides of aluminum, metallic aluminum, aluminum alloys, and high alumina concentration (e.g., greater than about 30 weight %) materials and other metal oxides. The chromium layer122A, aluminum layer122B and the alumina layer122C of the barrier layer122may be sprayed, dipped, spun, or brushed onto the curved surface118of the beam-shaping insert66.

Traditional applications utilizing a metal (e.g., metal layer126) or dielectric stack as a beam-shaping element70on a polymeric component (e.g., beam-shaping insert66) suffer from low adhesion strength and are prone to chipping or peeling off. However, application of the barrier layer122to the curved surface118of the beam-shaping insert66offers several advantages over simply applying the metal layer126or the first and second dielectric stacks130,134directly to the curved surface118. The barrier layer122may increase the adhesion strength with which the metal layer126is held to the curved surface118. For example, use of the barrier layer122may allow the metal layer126and the first and second dielectric stacks130,134to survive military specification adhesion requirements (e.g., a ½″ wide strip of cellophane tape is pressed against the reflective element114and quickly removed). Additionally, the use of the barrier layer122may prevent the transfer of thermal energy to the beam-shaping insert66from the electromagnetic beam52during beam-shaping thus preventing possible damage from occurring to the beam-shaping insert66or element70.

Positioned on top of the barrier layer122is the metal layer126. The metal layer126may have a thickness from about 50 nanometers to about 200 nanometers, or from about 75 nanometers to about 150 nanometers, or from about 80 nanometers to about 120 nanometers. In a specific embodiment, the metal layer126is about 100 nanometers thick. The metal layer126may include silver, gold, aluminum, platinum, copper, alloys thereof and other lustrous metals capable of reflecting the electromagnetic beam52. In various embodiments, the metal layer126may be applied via physical vapor deposition or by spray coating. Use of the metal layer126offers a general broadband reflection to the reflective element114.

Positioned above the metal layer126are the first and second dielectric stacks130,134. It should be understood that although depicted with two dielectric stacks, the reflective element114may have only one stack (e.g., the first or second dielectric stacks130,134) or have three or more stacks. The first dielectric stack130is positioned on the metal layer126and includes at least one first dielectric layer130A and at least one second dielectric layer130B. The first dielectric stack130may contain between two and ten layers (e.g., the first and second dielectric layers130A,130B). The first and second dielectric layers130A,130B are positioned in an alternating manner and comprise a dielectric material. Exemplary dielectric materials include SiO2, Ta2O5, NbO5, TiO2, HfO2, and combinations thereof. In some embodiments, each layer130A,130B may be a single dielectric material. In a specific embodiment, the first dielectric layer130A may be SiO2and the second dielectric layer130B may be Ta2O5. The thickness of the first and second dielectric layers130A,130B may be between about 50 nanometers and about 500 nanometers. In some embodiments, the thickness of the first and second dielectric layers130A,130B may be different than one another and optionally vary across the thickness of the first dielectric stack130. In some embodiments, the choice of which dielectric material to use for the alternating first and second dielectric layers130A,130B may be based on the refractive index of the material in order to increase a reflectivity of the reflective element114. For example, a high refractive index material (e.g., Ta2O5, NbO5, TiO2, HfO2) may be included in the first dielectric layer130A and a low refractive index material (e.g., SiO2) may be included in the second dielectric layer130B. In some embodiments, the upper most layer (e.g., first or second dielectric layer130A,130B) comprises a high refractive index material (e.g., Ta2O5, NbO5, TiO2, HfO2). Additionally or alternatively, the upper most layer may be thinner (e.g., half or quarter the thickness of the wavelength of the beam52) or thicker than the other layers (e.g., first or second dielectric layers130A,130B).

Similarly to the first dielectric stack130, the second dielectric stack134also includes alternating layers of dielectric materials. In the depicted embodiment, the second dielectric stack134includes at least one third dielectric layer134A and at least one fourth dielectric layer134B. The second dielectric stack134may contain between two and ten layers (e.g., the third and fourth dielectric layers134A,134B). The third and fourth dielectric layers134A,134B of the second dielectric stack134may comprise any of the dielectric materials and have any of the thicknesses mentioned in connection with the first dielectric stack130. In some embodiments, the thickness or ratio of thicknesses of the third and fourth dielectric layers134A,134B may be different (e.g., smaller or larger) than that of the first or second dielectric layers130A,130B of the first dielectric stack130. It will be understood that more than two types of layers may be used in the construction of the reflective element114. As explained in connection with the first dielectric stack130, the material chosen for the third and fourth dielectric layers134A,134B may be chosen based on index of refraction in order to increase reflectivity of the reflective element114. Further, in embodiments utilizing the second dielectric stack134, an uppermost layer of the stack may be thicker or thinner than the rest of the layers (e.g., third or fourth dielectric layers134A,134B). Additionally, it will be understood that dielectric materials having a suitable index of refraction not specified here may be used with a variety of thicknesses in order to approximate the dielectric materials disclosed in connection with the first and second dielectric stacks130,134.

Use of dielectrics (e.g., the first and/or second dielectric stacks130,134) within the reflective element114may allow the beam-shaping element70to be a dual-channel beam-shaping element70. In such an embodiment, the reflective element114may have a reflectivity of greater than about 98% for two different wavelength bands of the electromagnetic beam52. For example, the two different wavelength bands may be an imaging band and a high power band. In such embodiments, the imaging band of the electromagnetic beam52may have a wavelength of between about 700 nanometers and about 830 nanometers, or between about 1200 nanometers to about 1400 nanometers. Imaging wavelength bands of the electromagnetic beam52may be useful for the formation of images using the optical probe10. High power bands of the electromagnetic beam52may have a wavelength of between about 1430 nanometers and about 1550 nanometers. High power bands of the electromagnetic beam52may also cover water absorption spectrums. High power bands of the electromagnetic beam52may be useful in the optical probe10for marking or ablation purposes. During operation at the high power bands, the electromagnetic beam52may have a peak intensity as measured at the beam-shaping element70of between about 500 watts per square centimeter to about 15,000 watts per square centimeter, or from about 1,000 watts per square centimeter to about 11,000 watts per square centimeter. In a specific example, the electromagnetic beam power may be about 8,000 watts per square centimeter as measured at the beam-shaping element70. The reflectance of the reflective element114may vary based on the angle of incidence of the electromagnetic beam52on the element114. The reflective element114may also include a capping layer to protect it from environmental conditions (e.g., water, oxygen, and/or sterilization procedures).

Referring now toFIG. 3, the optical fiber18is depicted as defining the fiber end48flush with a face150of the ferrule62. In operation, the optical fiber18is configured to act as a wave guide for electromagnetic radiation, specifically light at an operating wavelength λ. The optical fiber18carries light from an upstream light source (not shown) to the fiber end48where the light is emitted as the electromagnetic beam52. In one embodiment, the operating wavelength λ includes an infrared wavelength such as one in the range from about 830 nanometers to about 1,600 nanometers, with exemplary operating wavelengths λ being about 1300 nanometers and about 1560 nanometers. In various embodiments, the operating wavelengths λ may be as low as about 700 nanometers. The optical fiber18may be a single mode or a multimode configuration. The optical fiber18may have a mode field diameter of between about 9.2 microns+/−0.4 microns at a wavelength of 1310 nanometers and have a mode field diameter of about 10.4 microns+/−0.5 microns at 1550 nanometers. The diameter of the cladding34may be between about 120 microns and about 130 microns.

The ferrule62is configured to couple with the inner wall90of the sheath14such that when the optical fiber18is within the aperture98, the electromagnetic beam52is emitted from the fiber end48on an optical path OP that is both substantially coaxial with the optical axis OA of the optical probe10, and directed toward the beam-shaping element70. As the beam52is emitted from the fiber end48, it propagates through the gap110and the diameter of the optical path OP widens with increasing distance from the fiber end48. A distance D1between the fiber end48and the reflective element114of the beam-shaping element70is set based on a desired size of a beam spot154. The beam spot154is the area of light the electromagnetic beam52forms as it strikes the beam-shaping element70. The beam spot154grows in diameter with increasing distance D1from the fiber end48. In order for the beam-shaping element70to properly shape the electromagnetic beam52, the beam spot154must be have the proper diameter when contacting the reflective element114(e.g., approximately half the diameter of the reflective element114). Accordingly, the ferrule62and the fiber end48must be placed a predetermined distance from the beam-shaping element70for the beam52to be properly shaped. In various embodiments, the distance D1between the fiber end48and the reflective element114may range between about 0.2 millimeters and about 2.6 millimeters. In one embodiment, the distance D1is about 1.314 millimeters. The diameter of the beam spot154may range from about 200 microns to about 2000 microns and more specifically, between about 400 microns to about 600 microns.

As the electromagnetic beam52enters the beam-shaping element70, its optical path OP is folded by an angle β from reflection off of the reflective element114. In the depicted embodiment, the angle β is approximately 90°, but in various embodiments can vary greater than or less than about 25°, about 20°, and about 10° on either side of 90°. The radius of curvature and position of the beam-shaping element70determine both the angle β that the optical path OP of beam52will be folded by, and also a working distance D2to an image plane IMP where the beam52converges to form an image spot160. Accordingly, the emitted beam52is shaped into the image spot160solely by reflection from the beam-shaping element70.

Still referring toFIG. 3, the fiber end48of the optical fiber18may terminate at an angle in order to prevent undesired back reflection of light into the fiber18. OCT is particularly sensitive to back reflections of light which have not been scattered off of a sample to be tested (i.e., reflections from the optical probe10, fiber end48, or refractive surfaces along the optical path OP). The back reflected light may lead to increased noise and artifacts in the OCT image. Terminating the fiber end48at an angle minimizes the coupling of the back reflected light back into the optical fiber18. The fiber end48may be prepared at an angle between about 0° to about 10°, and more particularly between about 6° to 9°. Angling of the fiber end48may be accomplished, for example, by cleaving the fiber end48before or after insertion into the ferrule62, or by polishing the face150of the ferrule62with the fiber end48at an angle, as depicted. In some embodiments, the ferrule62or beam-shaping element70may be angled with respect to the optical axis OA of the optical probe10in order to compensate for the angled fiber end48. The angled ferrule62would keep the optical path OP of the beam52substantially coaxial with the optical axis OA of the optical probe10. Additionally or alternatively, the fiber end48may include an anti-reflection film to reduce the amount of reflected light absorbed by the optical fiber18. The anti-reflection film may include a single or multilayer dielectric material configured to cancel light reflected back to the optical probe10.

In various embodiments, the fiber end48of the optical fiber18may be locally tapered with respect to the rest of the optical fiber18. Tapering of the fiber end48may be accomplished through laser heating, plasma heating, resistance heating, or flame heating a portion of the optical fiber18, and placing the fiber18in tension. The heated portion of the fiber18then necks down as it is pulled. The fiber18may be pulled until the fiber18is separated or the heated portion of the fiber18may be cut while in the necked down position. Tapering of the core40may have an axial length along the optical fiber18of about 1 millimeter to about 5 millimeters, and in a specific example of about 4 millimeters. The tapering of the fiber end48should be such that the fiber end48does not experience adiabatic loss. Tapering of the optical fiber18at the fiber end48may locally increase the mode field diameter of the fiber end48. The mode field diameter at a beam52wavelength of 1310 nanometers of the tapered fiber end48may range from about 10 microns to about 40 microns and in specific examples be about 10 microns, about 11 microns, about 12 microns, about 13 microns, about 14 microns, about 15 microns, about 16 microns, about 17 microns, about 18 microns, about 19 microns, or about 20 microns. The mode field diameter of the fiber end48may expand about 5%, about 10%, about 100%, about 400%, or about 500%. Tapering of the optical fiber18at the fiber end48may locally increase the mode field diameter of the fiber end48. The mode field diameter at a beam52wavelength of 1310 nanometers of the tapered fiber end48may range from about 10 microns to about 40 microns and in specific examples be about 10 microns, about 11 microns, about 12 microns, about 13 microns, about 14 microns, about 15 microns, about 16 microns, about 17 microns, about 18 microns, about 19 microns, or about 20 microns. Tapering and angling the fiber end48of the optical fiber18may decrease the back reflection from about −10 dB to about −350 dB, and in specific examples to below about −80 dB, −90 dB, −100 dB, −110 dB, −120 dB and below about −130 dB depending on the level of tapering. Additionally or alternatively, the fiber end48may be tapered and positioned at locations other than at the face150of the ferrule62. For example, a second optical fiber having similar dimensions to that of the tapered fiber end48may be positioned in the aperture98of the ferrule62and be optically coupled to the fiber end48. In such embodiments, the optical coupling may take place at any point along the aperture98(e.g., inside the ferrule62) as well as at the entrance to the aperture98. The second optical fiber may then have an angled end, from which the electromagnetic beam52exits, to reduce back reflection.

In other embodiments, the core40of the fiber end48may be locally expanded in addition to being prepared with an angle. The core40of the optical fiber18may be locally expanded at the fiber end48such that the mode field diameter of the fiber18locally increases. In expanded core40embodiments, the fiber end48may have a mode field diameter at a beam52wavelength of 1310 nanometers between about 10 microns to about 40 microns with specific examples being about 10 microns, about 11 microns, about 12 microns, about 13 microns, about 14 microns, about 15 microns, about 16 microns, about 17 microns, about 18 microns, about 19 microns, and about 20 microns. The mode field diameter and diameter of the core40of the fiber end48may expand by about 5%, about 10%, about 100%, about 400%, or about 500%. Local expansion of the core40within the fiber end48may take place via laser heating, plasma heating, resistance heating, or flame heating a portion of an optical fiber and allowing sufficient time to pass for a portion of the core40to diffuse into the cladding34. Expansion of the core40may have an axial length along the optical fiber18of about 1 millimeter to about 5 millimeters, and in a specific example of about 4 millimeters. Expanding the core40and angling the fiber end48of the optical fiber18may decrease the back reflection from about −10 dB to about −350 dB, and in specific examples to below about −80 dB, −90 dB, −100 dB, −110 dB, −120 dB and below about −130 dB. Additionally or alternatively, the core40of the fiber end48may be expanded and positioned at locations other than at the face150of the ferrule62. For example, a second optical fiber having similar dimensions to that of the expanded core40fiber end48may be positioned in the aperture98of the ferrule62and be optically coupled to the fiber end48. In such embodiments, the optical coupling may take place at any point along the aperture98(e.g., inside the ferrule62) as well as at the entrance to the aperture98. The second optical fiber may then have an angled end, from which the electromagnetic beam52exits, to reduce back reflection.

Referring now toFIGS. 4A-D, the beam-shaping insert66of the optical probe10may take a variety of configurations which form a second image spot172at a second image plane IMP2having a second working distance D3away. The second working distance D3may be between about 1.0 millimeters and about 20.0 millimeters. In such an embodiment, the electromagnetic beam52may be split into a first portion156which forms the image spot160and a second portion158which forms the second image spot172. In side-viewing embodiments (FIGS. 4A and 4B), both the first and second portions156,158of the electromagnetic beam52may be directed to the side of the sheath14such that the second image spot172may be formed to a side of the optical probe10similar to that of the image spot160. Such embodiments may be advantageous in that multiple locations of a sample being tested by the optical probe10may be in focus simultaneously, allowing a depth of the sample to be perceived. In forward-viewing embodiments (FIGS. 4C and 4D), the first portion156of the beam52may be directed to the side of the probe10to form image spot160and the second portion of the beam158may be directed along the Z-direction to form the second image spot172at the second image plane IMP2forward of the probe10. Such embodiments may be advantageous in that sample material in front of and to the side of the optical probe10may be scanned simultaneously, thus allowing an operator of the optical probe10greater flexibility in how to position the probe10relative to the sample. All of the depicted embodiments of FIGS.4A-D allow for the simultaneous formation of the image spot160and the second image spot172, but may also allow selective formation of the image spot160and second image spot172. It will be understood that elements of the depicted embodiments inFIGS. 4A-Dmay be combined with one another without departing from the spirit of this disclosure (e.g., forming multiple image spots to a side of the optical probe10while retaining forward viewing or forming multiple image spots forward of the optical probe10).

Referring now to the depicted embodiment ofFIGS. 4A and 4B, the beam-shaping element70may be configured as a dual zone reflector. In such an embodiment, the beam-shaping element70may define a first reflection zone164and a second reflection zone168. In the embodiment ofFIG. 4A, the first reflection zone164is depicted as encircling the second reflection zone168, but the first and second reflection zones164,168may take a variety of positional configurations. For example,FIG. 4Bdepicts the first reflection zone164above the second reflection zone168. In yet other embodiments, the first and second reflection zones164,168may be in a side by side configuration. The curved surface118may have a different conic constant or radius of curvature for each of the reflection zones164,168. The different conic constants and curvature radii allow the first reflection zone164to form the image spot160at the image plane IMP the working distance D2away from the first portion156of the beam52, while the second reflection zone168forms the second image spot172at the second image plane IMP2the second working distance D3away from the second portion158of the beam52. The image spot160and the second image spot172are depicted as being formed above one another, but may also be formed at the same image plane in a side by side configuration. The relative sizes of the first reflection zone164and the second reflection zone168may be different such that a greater portion of the electromagnetic beam52is captured by either of the first reflection reflective portion174or the refractive portion176and a more intense image spot (e.g., image spot160or the second image spot172) may be formed from the corresponding portion.

Referring now to the depicted embodiment ofFIG. 4C, the beam-shaping insert66includes a lens180in addition the beam-shaping element70. The lens180may be integrally formed within the beam-shaping element66, or maybe a separate structure configured to mate with the beam-shaping element66and the inner wall90. Additionally or alternatively, the lens180may be positioned within the beam-shaping insert66such that it protrudes through the curved surface118and reflective element114. The lens180may be a gradient index lens, a diffractive optical element, a Fresnel lens, and/or a refractive element such as that described above. As the electromagnetic beam52contacts the beam-shaping insert66, the second portion158of the beam52passes through the lens180and exits the optical probe10to form the second image spot172at the second image plane IMP2the second working distance D3away. In optical coherence tomography applications of the optical probe10, a computer which analyzes a signal from the optical probe10can distinguish between the data of the first image spot160and the second image spot170based on a time difference in the signal due to the different lengths of the working distances D2and D3of the image spot160and the second image spot172.

Referring now to the depicted embodiment ofFIG. 4D, the beam-shaping insert66includes a beam splitter184configured to reflect and focus the first portion156portion of the electromagnetic beam52while simultaneously refracting and focusing the second portion158of the electromagnetic beam52. The beam-splitter184may be a dichroic lens, a polarization beam splitter, a half-silvered mirror, or any other form of beam splitter. The beam-splitter184may be altered to have a predetermined reflection vs refraction ratio, including 10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20, 90/10 or smaller subdivisions thereof. By altering the ratio of reflection to refraction, the intensity of the image spot160and the second image spot172can be changed. The beam-splitter184may be integrally formed by the beam-shaping insert66(e.g., via half silvering of a clear polymeric embodiment of the beam-shaping insert66) or may be mounted to the beam-shaping insert66. In the depicted embodiment, the beam-shaping insert66defines a passage188through which the second portion158of the emitted beam52passes in order to form the second image spot172forward of the optical probe10.

Referring now toFIG. 5, the optical probe10is depicted in use within an OCT alignment system200. As explained above, light traveling within the optical fiber18exits the fiber end48and is emitted as beam52along the optical axis OA. The optical path OP of the beam52diverges as it passes through the gap110until it enters the beam-shaping element70and reflects from the reflective element114. The curvature of the beam-shaping element70causes the light to converge uniformly to the image spot160due to the curved surface118being conic. In the depicted embodiment, as the beam52converges, it passes through the window82of the sheath14and forms the image spot160at the image plane IMP. The working distance D2is measured between the horizontal portion of the optical axis OA of the probe and the image plane IMP and may be between about 1 millimeter and about 20 millimeters.

The proper orientation of the optical probe10during manufacturing is facilitated by the use of the ferrule62, the beam-shaping insert66, and the OCT alignment system200. In an exemplary method for alignment of the optical fiber18, a photo detector204(e.g., camera or a rotating slit) can be used to capture at least one image of image spot160and generate a detector signal SD representative of the captured image. The captured image(s) can be analyzed, e.g., via a computer208that is operably connected to photodetector204. The computer208can be used to analyze and display information about the captured image spot(s)160. In an example, a plurality of image spots160are detected and compared to a reference spot (e.g., as obtained via optical modeling based on the design of the optical probe10) to assess performance. If the detected image spots160are incorrect, an operator assembling the optical probe10may adjust a distance in the Z direction between the first and second portions22,26of the sheath14, or use the markings on the forward surface106of the beam-shaping insert66, to adjust its orientation relative to the sheath14. The use of the ferrule62and the beam-shaping insert66allow for near precise alignment of the optical probe10upon initial assembly.

The mode field diameter MFD is a measure of the spot size or beam width of light propagating in a single mode fiber or at another location in an optical system. The mode field diameter MFD within an optical fiber is a function of the source wavelength, fiber core radius and fiber refractive index profile. In the depicted embodiment, the optical probe10is capable of producing an image spot160having a mode field diameter MFD of between about 20 microns to about 100 microns at a 1/e2threshold at the image plane IMP. In a specific embodiment, the mode field diameter MDF may be about 22 microns. An exemplary mode field diameter of the optical fiber18may be 9.2 microns at a 1/e2threshold. The mode field diameter MFD may be sensed as an indicator of the quality of the image spot160.

The position of optical fiber18can be axially adjusted within the optical probe10(e.g., by adjusting the first and second portions22,26or moving the ferrule62or beam-shaping insert66) based on making one or more measurements of image spot160until an acceptable or optimum image spot160is formed. In an example, the one or more measured image spots160are compared to a reference image spot or a reference image spot size. The ferrule62and the beam-shaping insert66can then be fixed in their respective aligned positions and orientations within the sheath14via one or more attachment methods (e.g., set screws, epoxies, adhesives, UV curable adhesives, friction fit, etc.).

In an exemplary embodiment of optical probe10, the beam-shaping element26has an X-axis radius of curvature of about 1.16 millimeters and an X-axis conic constant of about 0.5858 and a Y-axis radius of curvature of about 1.2935 millimeters and a Y-axis conic constant of about 0.8235. Further, the conic shape of the beam-shaping element70is decentered along the Y-axis by about 0.7 millimeters, decentered along the Z-axis by about 0.089 millimeters, and has a rotation between the Y- and Z-axes of about 89.7°. The distance D1between the fiber end40and reflective element114is about 1.314 millimeters. Such an optical probe is capable of forming the image spot160at a working distance D2of about 9.0 millimeters with a mode field diameter MFD of about 64 microns at the 1/e2threshold.

Because optical probe10and the exemplary optical coherence tomography alignment system200has a beam-shaping insert66which defines a reflective beam-shaping element70, the system has no need for the use of spacers, GRIN lenses or refractive elements, such as lenses. Further, eliminating the use of multiple optical components is beneficial because there are fewer material interfaces which may result in optical back reflections or vignetting of the image spot160. Additionally, by shaping the beam52into the image spot160solely based on reflection, higher power light sources may be used than conventional optical probes. Optical probes utilizing polymers as a refractive element are limited in the intensity of light they may refract; however, reflective systems do not have such limitations.

FIG. 6illustrates an exemplary OCT system220that includes an embodiment of the optical probe10as disclosed herein. OCT system220includes a light source224and an interferometer228. The light source224is optically connected to a fiber optic coupler (“coupler”)232via a first optical fiber section FI. OCT probe10is optically connected to coupler232via optical fiber18and constitutes the sample arm SA of the interferometer228. OCT system220also includes a movable mirror system236optically connected to coupler232via an optical fiber section F2. Mirror system236and optical fiber section F2constitute a reference arm RA of the interferometer228. Mirror system236is configured to alter the length of the reference arm, e.g., via a movable mirror (not shown). OCT system220further includes the photodetector204optically coupled to coupler232via a third optical fiber section F3. Photodetector204in turn is electrically connected to computer208.

In operation, light source224generates light240that travels to interferometer228over optical fiber section FI. The light240is divided by coupler232into light240RA that travels in reference arm RA and light240SA that travels in sample arm SA. The light240RA that travels in reference arm RA is reflected by mirror system236and returns to coupler232, which directs the light to photo detector204. The light240SA that travels in sample arm SA is processed by optical probe10as described above (where this light was referred to as just emitted beam52) to form image spot160on or in a sample244. The resulting scattered light is collected by optical probe10and directed through optical fiber18to coupler232, which directs it (as light240SA) to photodetector204. The reference arm light240RA and sample arm light240SA interfere and the interfered light is detected by photodetector204. Photodetector204generates an electrical signal SI in response thereto, which is then sent to computer208for processing using standard OCT signal processing techniques.

The optical interference of light240SA from sample arm SA and light240RA from reference arm RA is detected by photodetector204only when the optical path difference between the two arms is within the coherence length of light240from light source224. Depth information from sample244is acquired by axially varying the optical path length of reference arm RA via mirror system236and detecting the interference between light from the reference arm and scattered light from the sample arm SA that originates from within the sample244. A three-dimensional image is obtained by transversely scanning in two dimensions the optical path in the sample arm SA. The axial resolution of the process is determined by the coherence length.

It should be understood that although the use of the optical probe10was described in connection with only one OCT technique, the optical probe10may be used in a wide variety of applications, including other OCT techniques (e.g., Frequency Domain OCT, Spectral Domain OCT).

EXAMPLES

FIGS. 7A-8Bare graphs and charts depicting computed data about specific examples of the reflective element114as made according to various aspect of this disclosure.FIGS. 7A-Bcorrespond to a dual-channel mirror (e.g., reflective element114) having a reflectance greater than about 98% for two different wavelength bands light (e.g., electromagnetic beam52).FIG. 7Adepicts a graph showing that the dual-channel mirror has a reflectance greater than about 98% at an angle of incidence of about 55° over a first wavelength band from about 1200 nanometers to about 1400 nanometers and a second wavelength band of from about 1450 nanometers to about 1550 nanometers.FIG. 7Bdepicts that the dual-channel mirror has a single dielectric stack (e.g., first dielectric stack130) of alternating dielectric materials (e.g., the first dielectric layer and the second dielectric layer130A,130B), the layers having alternating thicknesses. In this example, the dielectric materials are SiO2and Ta2O5, with the SiO2layers having a refractive index n of 1.47 and the Ta2O5layers having a refractive index n of about 2.06.

FIGS. 8A and 8Balso depicts a dual channel mirror (e.g., reflective element114) having a reflectance greater than about 98% for two separate wavelength bands of a light source (e.g., electromagnetic beam52).FIG. 8Adepicts a graph showing that the dual-channel mirror has a reflectance greater than about 98% over a first wavelength band from about 700 nanometers to about 800 nanometers and a second wavelength band of from about 1450 nanometers to about 1550 nanometers.FIG. 8Bdepicts that the dual-channel mirror has a two dielectric stacks (e.g., first dielectric stack130and second dielectric stack134) of alternating dielectric materials (e.g., the first, second, third and fourth dielectric layers130A,130B,134A,134B), the stacks being separated based on dielectric layer thicknesses. In this example, the dielectric materials are SiO2and Ta2O5, with the SiO2layers having a refractive index n of 1.47 at 750 nanometers and the Ta2O5layers having a refractive index n of about 2.06 at 1480 nanometers.

While the embodiments disclosed herein have been set forth for the purpose of illustration, the foregoing description should not be deemed to be a limitation on the scope of the disclosure or the appended claims. It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the claims.

It will be understood by one having ordinary skill in the art that construction of the described invention and other components is not limited to any specific material. Other exemplary embodiments of the invention disclosed herein may be formed from a wide variety of materials, unless described otherwise herein. In this specification and the amended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise.

For purposes of this disclosure, the term “coupled” (in all of its forms, couple, coupling, coupled, etc.) generally means the joining of two components (electrical or mechanical) directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two components (electrical or mechanical) and any additional intermediate members being integrally formed as a single unitary body with one another or with the two components. Such joining may be permanent in nature or may be removable or releasable in nature unless otherwise stated. It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the claims.