Intravascular data acquisition system

Abstract

An optical element (or cap) is provided. [Solution] In part, the present invention relates to an optical cap. The cap has at least one lensed surface configured to direct and focus light outside the cap. The cap is placed over an optical fiber. Optical radiation travels through the fiber and interacts with one or more optical surfaces of the cap, resulting in a focused or substantially collimated beam at a distance outside the cap. Optical elements, such as the elongated caps described herein, can be used with various data collection modalities, such as optical coherence tomography. In part, the present invention relates to a lens assembly including a microlens; a beam director in optical communication with the microlens; and a substantially transparent film or cover. The substantially transparent film can transmit light bidirectionally and generate a controlled amount of backscatter. The film can surround a portion of the beam director.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates generally to optical elements, the design and manufacture of optical elements, and methods of using the same. Additionally, the present invention relates to using optical elements to collect data about a sample of interest. [Background technology]

[0002] Optical analysis methods, such as interferometry, require the delivery of light to a sample of interest and the collection of a portion of the light returning from the sample. Due to their size and complexity, many light sources and optical analysis devices are typically located far from the sample of interest. This is particularly evident when the sample of interest is an internal portion of a larger object, such as biological tissue within a living organism. One method for optically analyzing internal portions is to guide light from a distant light source to the sample using thin optical fibers. Thin optical fibers, due to their small cross-section, minimally interfere with the normal function of the sample. One example of such a method is the optical analysis of hollow organs, such as blood vessels, using fiber-optic catheters. Here, a fiber-optic catheter is connected at one end to a light source outside the body and inserted at the other end into the blood vessel.

[0003] A significant barrier to performing optical analysis of interior regions, such as lumens, is the design and low-cost production of compact optical devices for focusing or collimating light. Many types of optical analysis, such as imaging and spectroscopy, require that light incident on a sample be focused or substantially collimated at a specific distance. Because light emanating from the tip of a standard optical fiber diverges rapidly, compact optics can be coupled to the fiber to provide the focusing or collimating function. Furthermore, it is often desirable to analyze sample locations that do not lie directly on the optical axis of the fiber, such as the analysis of the lumen wall of a small blood vessel. In these situations, in addition to a means to focus or collimate the light emanating from the tip of the optical fiber, a means to substantially change the direction of the light is used.

[0004] Many methods have been described for fabricating miniature optics suitable for attachment to optical fibers that provide some of the above functions. These methods generally provide beam focusing in one of three ways: 1) using graded-index (GRIN) fiber segments; 2) directly shaping the fiber tip into a lens; or 3) using a compact bulk lens. Beam directing is generally provided in one of four ways: 1) using total internal reflection (TIR) ​​from the angled end face of the fiber or using an angled reflective surface; 3) using a compact bulk mirror; or 4) using a reflective coating on the fiber tip. However, these methods have numerous inherent limitations, including excessive manufacturing costs, excessive size or limited flexibility for selecting the focal spot size and focal length.

[0005] Many miniature optical systems are known in the art that can be used for the analysis of internal lumen structures. Each optical system is conceptually divided into a beam focusing means and a beam directing means. Light is passed from an external light source into the internal lumen through one or more optical illumination fibers. The optical illumination fibers may be single-mode or multimode in nature. The illumination fibers communicate with a miniature optical system that focuses and directs the beam into the lumen wall. Light is returned from the lumen to an analysis device outside the body using the same fiber or another fiber co-located with the illumination fiber. In one type of miniature optical system design, the focusing means and directing means are implemented by separate optical elements. In another type of design, the focusing means and directing means are implemented by the same element. Summary of the Invention [Problem to be solved by the invention]

[0006] Several characteristics of existing optical systems are undesirable. For example, in some devices, to minimize overall system size, all of the optical elements must be similar in diameter to the optical fiber (often around 125 μm). This reduces the options available for selecting focusing elements, beam expanders, and beam directors, thereby limiting the range of focal spot sizes and working distances achievable with the design. In addition, these extremely small elements are fragile, difficult to handle, and prone to breakage during fabrication and operation. Third, in many embodiments, using TIR to redirect the beam requires the creation of an air gap. This requires that a tight seal be maintained between the fiber and other elements to maintain the air gap. This can be problematic when the device is immersed in water, blood, or stomach acid, or when the device is rotated or translated at high speeds to form an image. Fourth, GRIN focusing elements have a rotationally symmetric refractive index profile, making it impossible to correct for cylindrical aberrations induced on the beam. The overall effect of these drawbacks is that some miniature optics are expensive, difficult to manufacture, prone to damage, and do not produce a circular output at the focal plane.

[0007] In addition to the drawbacks listed above, conventional lensed surfaces can only provide small radii of curvature and are limited to roughly spherical geometries. Furthermore, the beam cannot expand to a size significantly larger than the diameter of a single-mode fiber (often 125 μm) at any point within the optical system. These limitations lead to lens systems with limited working distances and significant spherical aberration.

[0008] As noted above, currently known miniature optical systems used to perform optical analysis or imaging have significant limitations. Thus, there is a need for optical elements that overcome the limitations of existing optical devices. [Means for solving the problem]

[0009] In part, the present invention provides a unitary optical element (or cap) with an internal cavity that slides over the end of an optical fiber for internal or external analysis of a sample. The cap includes integrated surface features for redirecting the beam and focusing or collimating the light to a defined width at a defined distance from the cap. The cap is small enough to prevent destruction or damage to sensitive samples, such as internal body tissue or hollow organs. Because the cap is a single, monolithic element in some embodiments, it can be fabricated using low-cost methods, such as injection molding. Significant cost advantages and improvements in manufacturing repeatability are achieved compared to previously described methods.

[0010] Some embodiments of the present invention provide an optical element, such as a cap, cover, or elongated member, with a curved distal end face or surface. The optical element can be fabricated from a single piece of material that can be secured to and accept a section of optical fiber. In particular, the cap has an open end that accepts the fiber, a length of solid material selected to be substantially optically transparent, and a curved reflective end surface that acts as both a lens and a mirror. In some embodiments, the curved reflective surface is shaped to have the focusing attributes of a lens and is coated to reflect (or partially reflect) incident light.

[0011] Light is emitted from the optical fiber, travels through the solid material, and strikes a curved, reflective end surface. The curvature of the lensed surface can be designed to focus or substantially collimate the incident light. The lensed surface can also be tilted relative to the propagation direction of the light emitted from the fiber tip. The tilt angle is selected to reflect the light so that it exits the cap through a side and reaches a focal point a desired distance from the side.

[0012] The above-described reflective attributes of the distal surface are obtained by coating the outer surface of the curved end surface with a reflective material, such as a metal or dielectric material. Furthermore, the curvature of the lensed surface can be different along each of two orthogonal axes. Furthermore, the curvature along one axis can be independently adjusted to compensate for optical distortions imparted to light as it exits through the substantially cylindrical side of the cap. The single-piece construction of the cap makes it amenable to manufacturing by low-cost methods such as injection molding.

[0013] In one embodiment, the invention relates to an optical beam directing element including an elongated one-piece cap having a cylindrical outer surface with a longitudinal axis, the elongated one-piece cap having a proximal end face defining an annular opening and a distal end face with a beam directing surface, the elongated one-piece cap defining a solid section and a first cavity section defining a volume extending to a boundary of the solid section, the volume sized to surround and receive an optical fiber having a fiber end face, the beam directing surface angled and positioned relative to the fiber end face such that light received from the fiber end face is directed from the cylindrical outer surface at a working distance D to form a focal spot of diameter w.

[0014] In some embodiments, the elongated, one-piece cap is formed from a material selected from the group consisting of acrylic, polycarbonate, polystyrene, polyetherimide, polymethylpentene, and glass. D can range from about 0 μm to about 30 mm. In some embodiments, w ranges from about 3 μm to about 100 μm. The beam-directing element can further include a stationary sheath and an optical fiber fixedly disposed within the volume, the optical fiber and the elongated, one-piece cap configured to rotate within the stationary sheath. In some embodiments, at least a portion of the beam-directing surface is coated with a reflective coating. The beam-directing element can further include a lensing surface disposed within the cylindrical outer surface and formed from the boundary. In some embodiments, the beam-directing surface is substantially flat. The reflective coating can include a partially transmissive coating.

[0015] In some embodiments, the partially transmissive coating splits light from the fiber end face into a first beam directed from the cylindrical outer surface at the working distance D, forming the focal spot with diameter w, and a second beam directed from the cylindrical outer surface at a working distance D', forming a focal spot with diameter w'. Furthermore, the beam incident on the fiber end face can be split based on the intensity of the incident beam or the wavelength of the incident beam. In some embodiments, a partially reflective coating is disposed on a distal section of the cylindrical outer surface, positioned such that a beam directed from the beam-forming surface passes through the partially reflective coating and is reflected back from the partially reflective coating. A partially reflective coating can be disposed within the volume along a portion of the boundary. In some embodiments, the beam-directing surface is located within the volume or the solid section. A second cavity section can be defined within the solid section, such that the beam-directing surface is partially obscured by a portion of the cylindrical outer surface surrounding the second cavity section. Furthermore, the beam directing surface is shaped to substantially eliminate cylindrical optical distortion induced by light propagating from the beam directing surface through the cylindrical outer surface and the stationary sheath. In some embodiments, the beam directing surface is selected from the group consisting of a biconic asphere, an aspheric surface, a biconic Zernike, a Fresnel, and a non-uniform rational B-spline.

[0016] In one aspect, the present invention relates to a method for collecting optical data from a test sample in situ. The method includes the steps of: providing an optical fiber including a core adapted to transmit a light beam at a first diameter; providing an elongated one-piece cap having a cylindrical outer surface and an annular opening, the cap fixedly and optically coupling a length of the optical fiber to the optical fiber by receiving and surrounding the length within a cavity defined within the cap; and transmitting the light beam to a beam-directing surface such that a first light beam is directed from the cylindrical outer surface at a working distance D to form a focal spot having a diameter w. In one embodiment, the method further includes splitting the light beam such that a second light beam is directed from the cylindrical outer surface at a working distance D' to form a focal spot having a diameter w'. In one embodiment, the method further includes collecting optical coherence tomography data using the first light beam. In some embodiments, the method further includes generating one of the reference signals in response to a reflective element disposed within the one-piece cap, the reflective element acting as an interferometer arm in an optical coherence tomography system. In some embodiments, the method further includes generating one of the calibration signals in response to a reflective element disposed within the one-piece cap, the calibration signal being used to adjust a reference arm optical path length to match a sample arm optical path length in an optical coherence tomography system.

[0017] Overview of Reference Reflector / Scattering Element Embodiments In one aspect, the invention relates to a fiber optic imaging probe having an elongated section and proximal and distal ends, the probe having a thin strip of light-scattering material applied to the distal end.

[0018] In another aspect, the invention relates to an optical element. The optical element includes a film or cover having a first surface and a second surface. The film includes a polymer and at least one backscattering element disposed therein for controlled optical backscattering. Furthermore, the film allows transmission of imaging light substantially undistorted.

[0019] Aspects of the invention described herein can include further embodiments. For example, the optical element can further include a plurality of backscattering elements, wherein the at least one backscattering element and each of the plurality of backscattering elements are particles having a particle size, and the plurality of backscattering elements are disposed within the polymer. In some embodiments, the film is shaped to form a curved surface suitable for wrapping, enclosing, enveloping, or otherwise covering an optical fiber end face or a microlens.

[0020] The particle size is less than about 1.5 μm in some preferred embodiments. Furthermore, the particles can include titanium, zinc, aluminum, and / or other materials suitable for scattering light. The plurality of scattering elements can have a volume doping concentration of about 0.1%. The optical element can further include an elongated member, where the membrane is shaped to form a sheath within which the elongated member is disposed and forms a portion of the probe tip.

[0021] In one aspect, the invention relates to an optical element including a curved cover having a first surface and a second surface, the cover forming a portion of an imaging probe, the cover including a polymer and at least one backscattering element disposed therein for controlled backscattering of light, whereby a reference point is generated for an imaging system from the backscattering of light, and the cover allowing transmission of imaging light substantially undistorted.

[0022] In another aspect, the invention relates to an imaging probe including an elongated section having a first end and a second end, the second end forming a probe tip having endoluminal imaging capabilities, the probe tip having a scattering material, the elongated section adapted to transmit light reflected by the scattering material to the first end of the elongated section.

[0023] In some embodiments, the elongated section is an optical fiber. The elongated section can also be a sheath. The probe can further include an optical fiber disposed within the sheath. The scattering material can include a plurality of light-scattering particles dispersed within a matrix. The scattering particles can include titanium and / or other materials known to scatter light. The matrix can also include other polymers, such as polyethylene terephthalate and / or urethane derivatives.

[0024] In some embodiments of this aspect of the invention, the controlled amount of backscattering is an amount of light at least sufficient to generate a reference point in the imaging system for calibration of at least one imaging system parameter. The substantially transparent film can also include a plurality of scattering particles.

[0025] In yet another aspect, the present invention relates to a method for calibrating an optical coherence tomography system, the method including generating scan data in response to light reflected from a sample, the reflected light passing through a bidirectional substantially transparent optical element; generating reference data in response to scattered light reflected from a scattering element disposed within the bidirectional substantially transparent optical element; and calibrating the optical coherence tomography system to determine a relative longitudinal position of the scattering element.

[0026] In one aspect, the invention relates to a method of fabricating an optical element, the method comprising the steps of selecting a material suitable for intraluminal use in an animal, selecting a dopant suitable for dispersion within the material, the dopant adapted to scatter light in response to a light source, and determining a volume concentration of the dopant such that a radial scan of the doped material produces a defined backscatter.

[0027] Some embodiments of the present invention provide an optical cap that can be secured to the end of a section of optical fiber, the cap having an open end to receive the fiber, an internal curved surface in line with the optical fiber that acts as a lens, a length of solid material, and a closed end with a flat reflective end surface that acts as a mirror. In some embodiments, the reflective end surface is coated, and in other embodiments, it is uncoated. The curvature of the internal lensed surface is selected to focus or substantially collimate light emanating from the end of the optical fiber. The reflective end surface is made reflective by coating the exterior of the end face with a metal or dielectric material. In some embodiments, the tilt angle between the end face and the axis of the fiber is typically about 45 degrees plus or minus about 20 degrees.

[0028] Another embodiment of the present invention provides an optical cap that can be secured to the end of a section of optical fiber, the cap having an open end for receiving the fiber, an internal curved surface aligned with the optical fiber to act as a lens, a length of solid material, and a closed end with a curved reflective end surface that acts as a second lens and mirror. The internal lensed surface is curved along one or two orthogonal axes to provide a first focusing means for light emanating from the tip of the fiber. The end surface is also curved along one or more orthogonal axes to provide a second focusing means for light transmitted from the first lensed surface through the length of solid material. In some embodiments, the end surface is made reflective by coating it with a reflective material. In some embodiments, the reflective material may be a metal or a dielectric material. In some embodiments, the optical cap is a one-piece cap. Furthermore, the optical cap can be made from one or more pieces of material in some embodiments.

[0029] Yet another embodiment of the present invention provides an optical cap that can be secured to the end of a section of optical fiber, the cap having an open end to receive the fiber, a length of solid material, and a closed end with a curved, partially reflective surface. Light emerges from the tip of the fiber, travels through the solid material, and strikes the partially reflective surface. A portion of the light is focused and reflected by the curve of the surface and exits through the side of the cap. Another portion of the light is refracted and transmitted through the end face of the cap. In this way, optical measurements can be made simultaneously along two different axes. The end face can be made partially reflective by coating it with a thin metal layer, a patterned metal layer, or a thin dielectric film designed to partially transmit light.

[0030] A further embodiment of the present invention provides an optical cap that can be secured to the end of a section of optical fiber, the cap having an open end to receive the fiber, a length of solid material, a closed end with a curved reflective surface, and a side with a partially reflective or backscattering coating. Light is emitted from the tip of the fiber, travels through the solid material, and strikes the reflective surface. The light is focused and reflected by the curve of the surface, striking the coated side of the cap. A portion of this light is transmitted by the coating and reaches a focal spot a desired distance from the cap. Another portion of the light is directly back-reflected or back-scattered by the coating and travels internally back toward the curved end face. The light is again reflected from the end face, refocused, and partially coupled back into the end tip of the optical fiber.

[0031] In this way, a controlled amount of reflected or backscattered light can be generated at a known distance from the focal spot. This is advantageous for use as a calibration signal or interference reference field in analytical techniques such as optical coherence tomography. The end facets are made reflective by coating them with a metal or dielectric material. The sides are made partially reflective by partially coating them with materials such as gold, aluminum, or other metals, by coating them with a thin dielectric film designed to partially transmit light, or by coating them with a layer of small backscattering particles. Alternatively, the partially reflective attribute can be provided by a thin polymer tube impregnated with backscattering particles, which is secured over the exterior of the optical cap. The thin polymer tube can be polyethylene terephthalate (PET), and the backscattering particles can be titanium dioxide. The reflective coating can also be selected from suitable dielectric reflective coatings. These dielectric reflective coatings can include multiple layers of dielectric materials. For example, in some embodiments, alternating layers of TiO2 and SiO2 can be used to form the reflective coating.

[0032] Yet another embodiment of the present invention provides an optical cap that can be secured to the end of a section of optical fiber, the cap having an open end to receive the fiber, an interior surface with a partially reflective coating aligned with the optical fiber, a length of solid material, a closed end with a curved reflective surface, and a side surface with a partially reflective coating. Light is emitted from the tip of the fiber and strikes the interior partially reflective surface. A portion of the light is reflected or backscattered back into the fiber, while another portion of the light is transmitted through the solid material. In this manner, a first amount of reflected or backscattered light can be generated at a known distance from the focal spot. The transmitted portion of the light then strikes the reflective surface. The light is focused by the curve of the surface and reflected to strike the coated side of the cap.

[0033] In this embodiment, a portion of this light is transmitted by the coating and reaches a focal spot a desired distance from the cap. Another portion of the light is directly back-reflected or back-scattered by the coating and travels internally back toward the bent end face. The light is again reflected from the end face, refocused, and partially coupled back into the end tip of the optical fiber. In this way, a second amount of reflected or back-scattered light can be generated at a known distance from the focal spot and a known distance from the internal partially reflective surface. This is advantageous for use as a calibration signal or interference reference field in analytical techniques such as optical coherence tomography. The end face is made reflective by coating it with a metal or dielectric material. The side faces are made partially reflective by partially coating them with a metal material, or by coating them with a thin dielectric film designed to partially transmit light, or by coating them with a layer of small back-scattering particles.

[0034] In another embodiment, the present invention also provides a method of using various embodiments of the optical cap as a component in a fiber optic imaging catheter, the fiber optic imaging catheter being inserted into a luminal structure of a living body and connected to an optical coherence tomography system to obtain high resolution images of the luminal structure.

[0035] Yet another embodiment provides a means for protecting the lensing surface of the optical cap by locating it partially or completely within the body of the cap. The cap may have any suitable geometry and is not limited to a cylindrical cap. Partial protection of the lensing surface can be achieved by including an extension of the cylindrical body slightly proximal to the lensing surface. In some embodiments, partial protection of the lensing surface can be achieved by locating the lensing surface completely within the cavity that receives the optical fiber. It is understood that any of the above embodiments can be modified to include partial or complete protection of the lensing surface. These embodiments of the invention are not limited to protection-related features. For example, recessing the lensing surface can make it easier to guide the cap distally in some embodiments.

[0036] Various embodiments described herein relate to subsystems for transmitting and receiving various types of electromagnetic radiation that can be directed through an optical fiber or similar waveguide. Thus, while reference may be made to radiation, optical radiation, light, or other types of electromagnetic radiation, these terms are not intended to limit the scope of the invention and instead encompass any type of light or electromagnetic radiation that can be transmitted or received by a lens or optical fiber or similar waveguide. [Brief explanation of the drawings]

[0037] The objects and features of the present invention may be better understood with reference to the drawings and claims set forth below. The drawings are not necessarily to scale, with emphasis generally being placed upon illustrating the principles of the invention. In the drawings, like numerals are used to refer to like parts throughout the various views. The drawings accompanying this disclosure are addressed individually at the time they are introduced within this disclosure. [Figure 1] 1 is a two-dimensional cross-sectional schematic diagram depicting an optical subsystem that directs a beam of light along an optical fiber and through an elongated member that defines a cavity, according to an exemplary embodiment of the present invention. [Figure 2A] 1 is a three-dimensional view illustrating a reflective lensed end surface according to an exemplary embodiment of the present invention. [Figure 2B] 1 is a three-dimensional view illustrating an optical element or cap according to an exemplary embodiment of the present invention. [Figure 3] 1A-1C show an optical cap surrounding an optical fiber such that the cap is inside a transparent sheath, according to one embodiment of the present invention. [Figure 4] FIG. 10 illustrates exemplary ranges of focal spot size and working distance for lensed reflective surfaces and three different lengths of solid material on fiber optic tips and optical caps according to an exemplary embodiment of the present invention. [Figure 5] FIG. 1 illustrates an optical cap including a transmissive lensed inner surface and angled reflective end surfaces to direct a beam through the side of the cap and produce a focal spot at a desired distance from the cap, according to an exemplary embodiment of the present invention. [Figure 6] FIG. 1 illustrates an optical cap including a transmissive lensed inner surface and angled reflective end surfaces to direct a beam through the side of the cap and produce a focal spot at a desired distance from the cap, according to an exemplary embodiment of the present invention. [Figure 7]FIG. 1 illustrates an optical cap including a curved, partially reflective, lensed end surface for generating two focused beams directed through the side and end faces of the cap, according to an exemplary embodiment of the present invention. [Figure 8] FIG. 1 illustrates an optical cap including a curved, reflective, lensed end surface for directing a beam through a coating disposed on the outer cylindrical surface of the cap and out the side of the cap, according to an exemplary embodiment of the present invention. [Figure 9] FIG. 1 illustrates an optical cap including a reflective or partially reflective surface in addition to a curved reflective lensed surface, according to an exemplary embodiment of the present invention. [Figure 10] FIG. 1 illustrates an optical cap in accordance with an exemplary embodiment of the present invention, in which a reflective lensed surface is protected from damage by being located within a volume defined within the cap. [Figure 11] FIG. 1 illustrates an optical cap in accordance with an exemplary embodiment of the present invention, in which a reflective lensed surface is partially protected from damage by being partially located within the body of the cap. [Figure 12] 1 illustrates an apparatus for performing optical coherence tomography data acquisition in accordance with an exemplary embodiment of the present invention. [Figure 13] FIG. 2 illustrates a second apparatus for performing optical coherence tomography data acquisition in accordance with an exemplary embodiment of the present invention. [Figure 14A] FIG. 1 illustrates a mold for fabricating an embodiment of the present invention. [Figure 14B] 14B illustrates an embodiment of the present invention fabricated using the mold depicted in FIG. 14A. [Figure 15A] FIG. 1 illustrates a mold for fabricating an embodiment of the present invention. [Figure 15B] 15B illustrates an embodiment of the present invention fabricated using the mold depicted in FIG. 15A. [Figure 16]1 is a schematic diagram of an optical fiber tip with a microlens and protective cover. [Figure 17] Figure 1 depicts an image taken with a doped plastic lens cover. DETAILED DESCRIPTION OF THE INVENTION

[0038] The following description refers to the accompanying drawings which illustrate certain embodiments of the invention. Other embodiments are possible, and modifications may be made to these embodiments without departing from the spirit and scope of the invention. Therefore, the following detailed description is not intended to limit the invention, the scope of which is defined by the claims.

[0039] The sections and headings herein are not intended to limit the invention, and each section and heading may apply to any aspect, embodiment, or feature of the invention.

[0040] It should be understood that the order of steps of the methods of the present invention is not important so long as the invention remains functional. Moreover, unless otherwise specified, two or more steps may be performed simultaneously or in a different order than described herein.

[0041] When a range or list of values ​​is given, each intervening value between the upper and lower limits of that range or list of values ​​is considered individually and is encompassed by the present invention as if each value were expressly recited herein. Additionally, smaller ranges between and including the upper and lower limits of a given range are contemplated and encompassed by the present invention. The recitation of exemplary values ​​or ranges does not exclude other values ​​or ranges between and including the upper and lower limits of a given range.

[0042] Unless otherwise specified, the terms "a" and "an" should be understood to mean "one or more."

[0043] These and other features and advantages of the present invention, as well as the invention itself, will be more fully understood from the description, drawings and claims.

[0044] Developments in advanced optical analysis or imaging, such as confocal microscopy, single-photon and multiphoton fluorescence imaging, harmonic imaging, optical spectroscopy, and optical coherence tomography (OCT), have had a tremendous impact on industrial inspection, basic biological research, and in vivo imaging in animals and humans. While these methods differ in many respects, they share a common design feature: the incident light used to illuminate the sample of interest is focused or collimated. Focused light offers many advantages over unfocused light, including improved localization of the incident light for better spatial resolution and increased optical power density for generating increased signal levels.

[0045] A focused or collimated beam is produced by passing the output of a light source through a series of optical elements that together form an optical system. The elements of the optical system are selected to achieve a desired focal spot size that appears a desired distance, referred to as the "working distance," from the last element of the optical system. The working distance is shown as an angle in the drawings. This is the preferred way to define the working distance (parallel to the direction of beam propagation). One preferred embodiment uses a beam that exits the side of the cap at a forward angle of approximately 10 degrees. Each individual optical analysis application has its optimal spot size and working distance. For example, confocal microscopy requires a small spot size approaching 1 μm. On the other hand, OCT requires a moderate spot size of approximately 5 to approximately 100 μm.

[0046] Although it is possible to obtain a wide range of spot sizes and working distances using optics constructed from conventional bulk lenses, many applications require flexible and miniaturized optics to analyze samples located inside larger objects. Biomedicine is one example of an area where this requirement is often found: the esophagus, intestine, urinary tract, airway, lungs, and Optical analysis of luminal structures such as blood vessels can use light from an external light source that is transmitted through a flexible probe, focused using miniature optics, and returned through the flexible probe to a data analysis system outside the body.

[0047] Furthermore, it is often desirable to analyze the lumen wall rather than its contents—for example, to use OCT to image the intima and media of a vessel wall rather than the blood contained within it. This provides an additional design objective to direct the beam away from the longitudinal axis of the optical system or along another preferred direction (or range of directions). These types of optical probes are often referred to as "side-firing," "side-directed," "side-imaging," or "side-looking." The dimensions of these lumens, like blood vessels, can be as small as a few millimeters, making the design of compact optical systems extremely challenging. Furthermore, the embodiments described herein are suitable for use with various multi-fiber or fiber bundle embodiments. The various embodiments described below address these and other needs related to probe components and beamforming.

[0048] Overview In general, the present invention relates to an optical element having an elongated, three-dimensional shape, such as a cap. The optical element defines a cavity or channel. The optical element can be sized to receive a portion of an optical fiber and operatively direct and focus light. The optical element can be affixed to the optical fiber and used to redirect and focus light outside the cap and receive light from a sample of interest. The present invention provides a method for using a miniature optical cap and fiber as part of an insertable probe. The insertable probe, in turn, can be used to perform optical analysis of luminal structures in vivo. Other embodiments of the present invention also relate to the design, manufacture, and use of devices for delivering focused or substantially collimated light to a sample and returning a portion of the light from the sample for processing in an imaging or data collection system. One illustrative, non-limiting example of such a system is an optical coherence tomography (OCT) system.

[0049] <Beam forming element> FIG. 1 illustrates an embodiment of the present invention suitable for forming a beam at a predetermined location. In particular, an optical system 10 suitable for directing light, collecting light, or otherwise gathering data about a sample of interest is shown. In the illustrated example, an optical fiber is connected at its proximal end to a light source (not shown). The optical fiber includes a light-guiding core with a coated region 12 and a cladding region 14. In one embodiment, the coated region 12 includes a polyimide material. As shown in FIG. 1, the coating has been partially removed to expose a portion of the core and cladding distal to the coated region 12. As shown in FIG. 1, a protective material 16, such as an adhesive, also surrounds the core and cladding 14 and / or the coated region 12. The optical fiber guides optical radiation from the light source to a distal fiber segment, where a length of the coating has been removed by mechanical or chemical stripping. The fiber end face (or fiber tip) can be flat or can be cleaved at a small angle, typically between about 8° and about 15°, to prevent aberrations and unwanted back reflections. This cleaving action can be performed by a fiber cleaver, and in certain embodiments, such a cleaving action is fast and consistent, providing cost savings and manufacturing advantages.

[0050] In general, in part, the present invention relates to a one-piece optical element (or optical probe element or cap) 18 formed from a transparent material. In some embodiments, the one-piece optical element or cap has an elongated shape. In other embodiments, the optical element or cap is spherical or hemispherical. For example, in some embodiments, the cap is a sphere or partially flattened sphere with a fiber-receiving hole formed in an off-diagonal direction, specifically one-half radius down from the center of the sphere. However, any suitable cap geometry is possible. The optical element defines a bore or channel that extends through a portion of the optical element 18 to terminate in a wall or region 19 formed from the transparent material. As shown, the fiber core and cladding 14 and coated region 12 are disposed within a volume defined within the cap 18 and enter the cap 18 through an annular opening 17 shown on the left side of the figure. The present invention relates to various types and shapes of such optical elements that define a channel, cavity or bore that partially surrounds or contains an optical fiber, although the terms "cap," "cover," "optical assembly," "beam former," "lens assembly," or other terms may be used herein in a non-limiting manner.

[0051] Thus, in one embodiment, optical cap (or optical element) 18 includes a fiber-containing section 20 and a beam-forming (or solid) section 21. Because a continuous, monolithic material is typically used, a notional boundary, indicated by a dotted line or boundary 22, distinguishes first section 20 from second section 21. Boundary 22 of optical cap 18 can be imagined as defining a plane located distal to adhesive or protective material 16, which fills the gap between core 14 and optical cap 18. As shown, in one embodiment, a gap exists between fiber end face 23 (which may be tilted from about 8° to about 15°) and cavity wall 19. Furthermore, as shown, adhesive or protective material 16 fills the cavity, including coated region 12 and core with cladding 14. The optical element has a curved surface 25 distal to the fiber core with cladding 14. The closed distal surface / curved end face 25 can include one or more coatings, such as a reflective or partially reflective coating. Additionally, the optical element and fiber assembly are typically disposed within a sheath 28. In some embodiments, the optical element 18 and other elements connected or fused thereto rotate together relative to the sheath. In another embodiment, both the sheath 28 and the optical element 18 rotate. In another embodiment, the sheath and optical element 18 are fixed and do not rotate. Additionally, the region between the sheath and the optical element can be filled with a fluid.

[0052] In certain preferred embodiments, the optical element is a monolithic or one-piece material. While combinations of materials, such as blends of polymers or glasses, can be used to create an optical element, the composition of the element is generally designed to be substantially the same throughout in certain embodiments. Coatings or other materials may be applied, fused, or otherwise bonded or connected to a one-piece optical element.

[0053] As shown in the embodiment of FIG. 1 , an optical fiber core with cladding 14 and coated region 12 is inserted into the cavity proximal to optical element 18. Proximal and distal refer to positions relative to the end of the fiber that will be connected to the device outside the body. The cavity (or fiber-receiving chamber of the optical element) defined by wall 19 can be filled with a protective material or adhesive 16 as shown. Adhesive 16 is selected to be substantially optically transparent and can be cured by exposure to ultraviolet light, heat, air, or any other curing method. To reduce the possibility of bubble formation between the fiber end face 23 and the cavity wall 19, application of adhesive 16 can be performed under a partial vacuum. To reduce back reflections, material or adhesive 16 can be selected to have a refractive index close to that of fiber 14 and optical element 18. Alternatively, to generate back reflections with a controlled amplitude, material or adhesive 16 can be selected to have a refractive index different from that of fiber 14 and optical element 18. In one embodiment, the adhesive is an acrylic-based adhesive. In another embodiment, an adhesive that can be cured with ultraviolet light is used.

[0054] In one embodiment, the cavity size is chosen to be very close to the size of the fiber to prevent tilt problems. The fiber end face is placed in contact with the end of the cavity to prevent longitudinal alignment problems. In one embodiment, the material 16 is an adhesive with a refractive index similar to that of the material used to form the optical fiber core and element 18, so that back reflections from the fiber tip 23 are further reduced.

[0055] Once the adhesive hardens (such as by exposure to heat, light, or ultraviolet radiation), the fiber is secured to the cap in the volume or cavity shown. Alternatively, the cap can be formed in place over the optical fiber core with cladding 14 and coated region 12 using a process such as injection molding. Forming the cap directly on the fiber can eliminate the bonding step and lead to lower manufacturing costs. Thus, in some embodiments, region 16 has the same material-filled region 18. That is, when adhesive 16 is not used, the region defined in FIG. 1 is removed and the cap directly contacts the fiber.

[0056] The cap has the general shape of a cylindrical tube with a closed distal face. The outer diameter of the optical element 18 is typically on the order of twice the diameter of the optical fiber, giving an outer diameter range of about 160 μm to about 500 μm. The inner diameter of the optical element 18, in turn, can range from about 80 μm to about 250 μm.

[0057] In one embodiment, the cap 18 is fabricated from a single piece of material selected to be optically transparent in the spectral band used for the particular imaging or analysis application. Generally, the optical elements or caps described herein are suitable for use in imaging applications using wavelengths of electromagnetic radiation ranging from about 350 nm to about 2000 μm. To facilitate low-cost, high-volume manufacturing, the material can be a resin or polymer rather than glass. If low aberration levels and high transmission are desired for a given application, the cap can also be formed from glass. Preferred materials include acrylic, polycarbonate, polystyrene, polyetherimide, or polymethylpentene. These materials can be injection molded into parts on the size scale of optical caps using methods known in the art of micromolding. Furthermore, these materials are suitable for forming one-piece caps. Generally, some embodiments of elongated one-piece caps can include an optically transparent material. As used herein, an optically transparent material means a material that has low absorption and scattering in the spectral bands used for a particular application and through which a significant percentage of the light emanating from the optical fiber is transmitted.

[0058] In some embodiments, the single-piece molded part provides significantly reduced manufacturing costs and times and improved part-to-part uniformity compared to miniature optics known in the art, such as those described above. In some embodiments, the length of the optical cap ranges from about 0.25 mm to about 5 mm. The gap between wall 19 and end face 23 ranges from about 0 μm to about 1000 μm.

[0059] Light traveling along the optical fiber exits the fiber end face 23 and cavity wall 19 and propagates a length L into the solid material of the second section 21 of the optical element 18. Length L is equal to the distance from the cavity wall 19 to the center of the closed distal surface 25. As the light travels, it diverges, as indicated by the first set of dashed lines. Upon reaching the closed distal surface 25, the light interacts with a coating deposited on the outer surface of the distal face.

[0060] The coating is designed to be highly reflective in the spectral band used for the particular imaging or analytical application. The coating can be a metal, a single dielectric layer, or a multi-dielectric stack. An optically non-functional layer may be deposited between the distal surface and the reflective coating to improve adhesion. For example, such a layer may include chromium, titanium, or a dielectric. An additional optically non-functional layer may be deposited on the reflective coating to protect the coating from oxidation, delamination, or other damage.

[0061] The normal to the center of distal surface 25 is oriented at an oblique angle θ relative to the longitudinal axis of the cap. As a result, the reflected light is directed at an angle 2θ relative to the incident light (see Figures 2A and 3). Distal surface 25 is further curved to form a focusing surface. Specific details of the focusing surface are discussed below. After interacting with distal surface 25 and the reflective coating, the light begins to focus or become collimated. As the light passes through cap side surface 29 and sheath 28, it is affected by cylindrical distortion due to the substantially cylindrical shapes of the cap and sheath. This distortion causes the beam to be oval in cross section rather than circular, resulting in a different focal plane for each of the beam's two major axes. These two focal planes are separated in space along the direction of beam propagation.

[0062] Cylindrical distortion is detrimental to many optical analysis applications because it leads to anisotropic lateral resolution, reduced peak incident power density, and degraded axial resolution. However, the curvature of the distal surface 25 can be different in two orthogonal axes in the plane of the distal surface, so the lens can be optimized to pre-compensate for cylindrical distortion before it occurs. In this way, a circularly symmetric beam is obtained outside the cap, and the undesirable effects of cylindrical distortion are avoided. Details of the distal surface 25 geometry are described more fully below.

[0063] Once the light exits the cap, it continues to focus, eventually reaching a focal plane or spot that is a working distance D away from the nearest edge of the optical element 18. If the fiber is single-mode, the beam is Gaussian, and its size at the focal plane is defined by a focal diameter w equal to twice the radius of the beam's Gaussian profile. In some embodiments, the length L and distal surface geometry can be selected to provide a wide range of focal spot sizes and working distances. In some embodiments, D is measured as the distance from the side of the cap to the focal plane along the direction of beam propagation (not necessarily perpendicular to the cap). This approach is consistent with how D is shown in FIG. 1.

[0064] If a longer working distance is desired for a particular application, the length L can be increased, thereby allowing the beam to expand to a larger diameter before striking the distal face 25. The beam can expand to a maximum diameter equal to the outer diameter of the cap, which can range from about 160 μm to about 500 μm. Increased beam expansion at the distal end is equivalent to increasing the numerical aperture of the optical system. Increasing the numerical aperture allows for an increased working distance D for a given focal diameter w. If a smaller focal diameter w is desired for a particular application, the radius of curvature of the distal face can be decreased, which effectively increases the focusing power of the optical system.

[0065] <Geometric structure of the end face> Figure 2A is a three-dimensional perspective view of lensed surface 40 (see surface 25 in Figure 1) with a first focal point F1 and a second focal point F2. Figure 2B is a three-dimensional perspective view of an entire optical element or compact optical cap 50 with outer and inner diameters A and Di and an overall length B. As shown, the cap includes an annular opening 17 sized to receive and securely couple to an optical fiber. Focusing or beam-forming surface 40 from Figure 2A is implemented, in one embodiment, as surface 52 in Figure 2B.

[0066] Generally, in certain embodiments, the optical element is designed to form or direct a substantially circularly symmetric beam with substantially no distortion outside the optical element or cap. To facilitate this design feature, the distal surface is chosen to have different curvatures along the arcs struck by rays Ax and Ay, corresponding to curves C1 and C2, respectively, on surface 40. Ax and Ay emanate from different focal points F1 and F2, respectively. Several surface geometries 25, 40 are suitable for the optical elements / caps described herein, including biconic aspheric, biconic Zernike, Fresnel, or non-uniform rational B-spline. Biconic aspheric surfaces are generally suitable for applications requiring focal spot sizes of about 3 μm to about 100 μm and working distances of about 0 μm to about 30 mm, and where correction for cylindrical distortions caused by the sides of the cap and other materials located between the cap and the focal plane is desired.

[0067] Returning to FIG. 2A, the deviation of the lensing surface away from a flat plane, such as the xy plane, commonly referred to as surface sag, is defined for a biconic asphere as follows:

[0068]

number

[0069] In this equation, x, y, and z are local coordinates with origin O at the center of the surface. R x and R y are the radii of curvature of the sphere along the x-axis and y-axis, respectively. In the embodiment of FIG. 2A, A x and A y is R x and R y This is an example of k x and k yare the conic constants along the x and y axes, respectively, giving a total of four free parameters for the surface sag z. Surface 40 is also rotated around the x axis by an angle θ to orient the beam at the surface by an angle 2θ. The surface is also rotated by a quantity y to further reduce the aberrations of the optical system. off can only be offset in the y direction.

[0070] <Optimization of design parameters> Referring to FIG. 3 , an optical system 70 is shown that includes a beam-directing surface 72 for directing a beam out the side of cap 75 and generating a focal spot at a desired distance from the outer surface of sheath 76. Thus, in some embodiments, the beam-directing surface both directs and focuses a beam of light or other radiation. Furthermore, the curvature of lensed surface 72 can be adjusted to compensate for distortions caused by transmission through sheath 76 and the outer cylindrical surface of cap 75. The following section describes a process for designing a compact optical cap of the type shown in FIG. 3 to achieve a desired focal spot size and working distance that is optimized for a particular optical analysis application. The optical analysis application chosen for this illustrative example is OCT imaging of coronary vessels, which requires the optical fiber and compact optical cap to rotate and translate longitudinally. This approach offers numerous advantages, including: Reduced production time saves costs and eliminates the need for fusion splicing -Provides non-rotationally symmetric lens shapes that compensate for cylindrical distortion Potentially improved repeatability in focal spot size and working distance.

[0071] Figure 3 shows a miniature optical cap 75 encased within a flexible, transparent sheath 76 with an inner diameter M and wall thickness T. The fiber core with cladding 14, coated region 12, and cap 75 are rotated and translated within the sheath by an external actuator, while the sheath 76 remains stationary within the vessel to prevent damage to the vessel wall.

[0072] In this illustrative example, the desired focal spot diameter w is approximately 30 μm. It is desired that the beam arrive at the focal plane a distance D' from the side of the sheath 76 and a distance D from the cap, where D' is approximately 1.6 mm and D is approximately 1.857 mm. The sheath wall thickness T is approximately 102 μm and the inner diameter M is approximately 710 μm. The cap outer diameter A is chosen to be approximately 400 μm to allow sufficient clearance between the cap and the sheath inner surface 77. In one embodiment, the cap material is chosen to be acrylic because it is optically clear at one wavelength of interest, approximately 1310 nm.

[0073] In this example, the distal surface bevel angle θ is selected to be approximately 50° to prevent unwanted back-specular reflections from the inner surface 77 of the sheath 76. This redirects incident light striking the distal surface at an angle of approximately 100° relative to the longitudinal axis of the fiber. The angle θ is shown as being formed between the longitudinal axis of the fiber and the normal vector to surface 72. Thus, light strikes the inner surface of the sheath 77 at an angle of approximately 10° from normal incidence, avoiding back-specular reflections. In one embodiment, the lumen 78 between the cap and sheath is filled with a radio-opaque contrast fluid having a refractive index of approximately 1.449. Furthermore, in one embodiment, the lumen between the sheath 76 and the vessel wall is filled with the same contrast material or salt. Contrast material may be provided by a proximal flushing mechanism to temporarily evacuate blood from the vessel, allowing for clear OCT images.

[0074] The design parameters that remain to be optimized are the distance from the fiber tip to the lensing surface, L, and the surface sag parameter, R. x , R y , kx and k y and y offset y off (If any). An optical simulation tool such as ZEMAX (ZEMAX Development, Bellevue, WA, USA) or equivalent can be used to find the optimal combination of the remaining design parameters to produce the desired focal spot diameter of approximately 20 µm at a distance of approximately 1.4 mm from the sheath. This software can also be used to ensure that the output beam striking the vessel wall is circular and aberration-free. To achieve this, an iterative optimization algorithm is used that searches for the best combination of free parameters that minimizes the value of a user-defined error function.

[0075] The error function measures several attributes of the simulated beam at the focal plane along the local x' and y' axes (see Figure 3). The measured values ​​are compared to desired values, and a weighted sum of the differences between the measured and desired values ​​is generated to provide the value of the error function. The error function incorporates simulated values ​​of the beam radius (Rx and Ry) at the 13.5% intensity level (corresponding to the characteristic radius ω of the beam) along the x' and y' axes, which corresponds to the characteristic beam waist ω, a Gaussian fit (Gx and Gy) along the x' and y' axes, and the distance between the desired and actual focal planes (Fx and Fy) along the x' and y' axes. The error function is constructed to provide a value of zero when the beam diameters along the x' and y' axes are equal, a Gaussian fit is achieved, and the distance between the desired and actual focal planes along the x' and y' axes is equal to zero. A beam is circularly symmetric if the beam diameters along the x' and y' axes are equal. This is desirable for producing an isotropic focal spot. If a Gaussian fit is achieved along the x' and y' axes, the system will have minimal distortion. This is desirable for maximizing image quality and optimizing the amount of optical power returned to the system for analysis. When these conditions are met, the beam will be substantially free of aberrations and will have the desired focal spot size w at the desired working distance D.

[0076] In this illustrative example, the error function E may be selected to incorporate six parameters, including Rx, Ry, Gx, Gy, Fx, and Fy. Each parameter is further assigned a weight W1 through W6 to control the relative importance of each parameter within the error function E. Each parameter is also assigned a target value Rxt, Ryt, Gxt, Gyt, Fxt, and Fyt. Rx, Ry, Rxt, Ryt, Fx, Fy, Fxt, and Fyt can be measured in millimeters. Gx, Gy, Gxt, and Gyt are unitless parameters that range from 0 to 1, with 1 representing a perfect Gaussian fit. The error function E is defined as the weighted sum of each parameter minus its corresponding target value. Therefore, E = W1 (Rx - Rxt) + W2 (Ry - Ryt) + W3 (Gx - Gxt) + W4 (Gy - Gyt) + W5 (Fx - Fxt) + W6 (Fy - Fyt).

[0077] In this illustrative example, Rxt and Ryt may be 0.017 mm, which corresponds to a full width at half maximum beam diameter of 0.020 mm. Gxt and Gyt may be 1. Fxt and Fyt may be 0. W1 and W2 may be 50, W3 and W4 may be 0.1, and W5 and W6 may be 1. The optical design values ​​L, R x , R y , k x , k y and y off Each selection of R gives a set of beam parameters Rx, Ry, Gx, Gy, Fx, and Fy, which in turn give a particular value of the error function E. Once the parameter targets and weights have been selected, one or more approaches can be used to find the optical design values ​​L, R that lead to the smallest error function. x , R y , k x , k y and y offThis can be achieved by finding a local minimum in the error function or a minimum in the error function. Many optical design packages, such as ZEMAX, contain built-in optimization algorithms that are sufficient to perform this step.

[0078] In this illustrative example, the optimization process results in an L of approximately 721 μm and an R of approximately 772 μm. x , R of approximately -1675 μm y , k of approximately -3797 μm x , k of approximately -15,970 μm y and y of approximately −23 μm off These values, when realized in the fiber optic cap embodiment, result in a focal spot size of approximately 29.6 μm at a distance D' of approximately 1600 μm. Such a focal spot size is suitable for performing OCT imaging and data collection in coronary vessels.

[0079] Example focal spot sizes and working distances The embodiments of optical components, such as caps or beam-shaping elements, described herein enable a wide range of focal spot sizes and working distances by constructing compact optical caps with various distal surface geometries and various distances L (L1, L2, and L3) between the fiber tip and the distal face. L1, L2, and L3 are selected for illustrative purposes and are not intended to limit the scope of the present invention. In one embodiment, L2 is selected to be half of L1, and L3 is selected to be half of L2. As an illustrative example, various data points are plotted in Figure 4 using an acrylic cap with an outer diameter of approximately 400 μm. In particular, Figure 4 shows a subset of design parameters available for the acrylic caps discussed above. Here, the distance L from the fiber tip to the distal end face is selected to be one of approximately 2.10 mm, approximately 1.05 mm, or approximately 0.56 mm, respectively. These specific values ​​of L are selected merely for illustrative purposes and are not intended to limit the scope of the present invention. To obtain a focal spot at a given working distance, at each point on each curve, the end face geometry was optimized according to the method described above using the error function as above.

[0080] Figure 4 shows that for this particular type of end cap, focal spot sizes of about 4.3 μm to about 110 μm can be achieved at working distances of about 0 mm to about 11 mm. For any given length L, the maximum working distance D' occurs when the focal spot size approaches the size of the beam incident on the distal end face. Under this condition, the focusing power of the optical system is weak and the working distance cannot be extended any further.

[0081] Internal Lensing Surface FIG. 5 shows another optical subsystem 80 of the present invention. Here, beam focusing is provided not by the distal end facet but by an internal lensed surface 83 at the end of the cavity. Cap 85 has a different cavity shape due to the additional lensed surface 83. Surface 83 can be concave or convex, have different radii of curvature in the x- and y-axes, be spherical or aspherical, or any other type of surface commonly known in the art of lens design. Surface 83 allows for beam collimation or beam focusing and other features. In general, the shape of surface 83 can be the same as that shown in FIG. 2A. Surface 83 can be any type of lens surface. Surface 83 can be the same as that shown in FIG. 2A, where the tilt angle θ can be as low as 0 degrees. This surface 83 serves as a boundary between the cavity and the beam-forming section of cap 85, similar to boundary 19 in FIG. 1. Beam direction is still provided by distal end face 25′. However, in this embodiment, the end faces are angled and planar.

[0082] In one embodiment, end face 25' is made reflective by coating it with a reflective material, such as a metal or dielectric coating. In this embodiment, light emanating from the fiber tip spreads into gap G. The gap may be filled with an optical adhesive to bond fiber 14 to cap 85, or alternatively, the gap may be filled with air to allow for more rapid beam expansion. The length of gap G is set by the length S of the fiber with the protective coating removed and the length S+G of the cavity.

[0083] In one embodiment, a taper 87 at the proximal side of the cavity acts as a stop for the coated portion of the fiber, allowing precise control of the fiber insertion length. Alternatively, a cylindrical stop may be used instead of a taper, although tapered shapes are generally preferred for the micromolding fabrication process, where sharp edges are difficult to fabricate. The gap length G and the surface sag of the interior surface can be optimized in a similar manner as described above using an error function. It will be appreciated that if cap 85 is placed inside a sheath (not shown), the gap length G and the surface sag for surface 83 can be further optimized to compensate for distortions caused by transmission through the sheath.

[0084] This cap embodiment 85 offers several advantages in addition to those discussed above for the cap design shown in FIG. 3. First, the lensing surface 83 is located within a cavity, protecting it from accidental damage during handling or manipulation. Second, the area of ​​the inner lensing surface 83 is smaller than the area of ​​the distal end face 25′, which simplifies the tooling design used to fabricate the cap. Third, because the distal end face 25′ is flat rather than curved, achieving a uniform coating thickness is simplified. Coating adhesion may also be improved due to the flatness of the end face.

[0085] Double lens surface FIG. 6 shows another optical subsystem 90 with a cap embodiment 95. Here, beam focusing is provided by a combination of one internal lensing surface 96 at the end of the cavity and a reflective lensing surface 97 formed on the distal end face. Beam direction is still provided by making the end face 97 reflective by coating it with a reflective material, such as a metallic or dielectric coating. In this embodiment, light emanating from the fiber tip 23′ spreads into the air gap G. Upon interacting with the internal lensing surface 96, the light refracts and propagates through a length L′ of solid material. The light then strikes the distal end face 97, where it is further focused and redirected to exit the side of the cap. The air gap length G, the length L′ of the solid material, and the surface deflections of the internal surface 96 and distal end face 97 can be optimized in a similar manner as above using an error function. It will be appreciated that if cap 95 is placed inside the sheath, the gap length G and the surface deflection of both surfaces 96 and 97 can be further optimized to compensate for distortion caused by transmission through the sheath.

[0086] This cap embodiment 95 offers several advantages in addition to those discussed above for the cap designs shown in FIGS. 3 and 5. First, the use of two lensing surfaces 96, 97 provides more design parameter freedom, allowing for a wider range of focal spot sizes w and working distances D. Second, the use of two lensing surfaces leads to fewer geometric aberrations than a comparable design using a single lensing surface, improving the optical quality of the resulting beam. Third, the internal lensing surface 96 and air gap G can be configured such that light transmitted through the length L' of solid material is substantially collimated. In this way, the exact value of L' is less critical to the overall optical performance of the system, thereby improving the design's tolerance to manufacturing errors. Under certain manufacturing conditions, the embodiments shown in FIGS. 3, 8, or 11 are preferred.

[0087] Partially Reflective Endface for Dual Beam Scanning FIG. 7 shows another system embodiment 100 of the present invention using a cap 105. Here, light emanating from the fiber tip 23 is split into two focused beams B1 and B2 by a partially reflective coating on the distal end face 107 of the compact optical cap 105. In this embodiment, light emanating from the fiber tip 23 propagates through a length L of solid material. The light strikes the distal end face 107, where it interacts with the partially reflective coating. The coating transmits a portion of the light through the end face and reflects another portion of the light through the side of the cap. The reflected portion of light B1 reaches a focal plane at a first working distance D with a focal spot size w. The transmitted portion of light B2 reaches a second focal plane at a second working distance D'' with a second focal spot size w''. It will be appreciated that if the cap is placed inside the sheath, the solid length L and distal end face surface deflection can be further optimized to compensate for distortions caused by transmission through the sheath.

[0088] The partially reflective coatings mentioned above can be formed in several ways. First, a highly reflective material, such as a metal, can be applied in a pattern on the distal end face such that the metal covers less than 100% of the end face area exposed by the beam. The pattern can include a checkerboard, annulus, concentric rings, or any other pattern. Second, a dielectric coating can be applied to a continuous portion of the end face area. The properties of the dielectric material can be selected to partially reflect a fixed percentage of the incident optical power. Alternatively, the dielectric coating can be selected to substantially reflect one wavelength band and substantially transmit a second wavelength band. This type of coating is commonly referred to as a "dichroic" or "dichroic mirror" coating.

[0089] The embodiment of FIG. 7 offers several advantages in addition to those described above for the cap designs shown in FIGS. 3, 5, and 6. First, the generation of two beams B1, B2 along different axes allows for simultaneous analysis of two different sample locations. This facilitates examining luminal structures within the body. One illustrative example is OCT imaging of a blood vessel containing an occlusive lesion. Using this embodiment, a forward-looking annular image can be obtained simultaneously with a side-looking radial image by rotating the catheter about the fiber axis. In this way, OCT images can be obtained from the front of the catheter as it is advanced into the lesion to analyze the lesion structure.

[0090] More generally, forward imaging is useful for guiding the placement of the imaging catheter to avoid perforating the lumen wall. When a dichroic coating is used, an additional advantage is the ability to perform optical analysis of samples in front of the cap using one set of wavelengths and samples to the side of the cap using a second set of wavelengths. Thus, using such an approach, it becomes possible to perform multimode imaging of the luminal structure. OCT imaging can be performed using light at approximately 1310 nm directed through the side of the cap, while confocal fluorescence imaging can be performed using light at approximately 800 nm directed through the front of the cap.

[0091] <Fixed reflective surface> In some optical analysis and data collection applications, including OCT imaging, it is desirable to include one or more surfaces that generate a reflection of known intensity at a known location relative to the focal plane. This facilitates calibration and interferometric calculations in some embodiments. A fixed reflection can be used in OCT applications to generate a calibration signal for adjusting the reference arm length to match the sample arm length (see U.S. Patent Application Publication No. 2009 / 0122320 to Petersen et al., the disclosure of which is incorporated by reference in its entirety). A fixed reflection can also be used in OCT applications to generate a reference field that interferes with light returned from the sample. As a result, this forms a common-path interferometer within the imaging catheter, avoiding the need for a separate reference arm.

[0092] In part, the present invention allows for the generation of a fixed reflection that includes only the calibration signal, only the reference field, or both the calibration signal and the reference field. Figure 8 shows a system 110 embodiment of the present invention in which a coating 111 is applied to a region of the side of a compact optical cap 113. Typically, a partially reflective or backscattering coating 111 is applied to a portion of the side of the optical cap to create a controlled reflection at a known distance from the focal spot. As shown, the coating 111 overlaps the region of the side where the beam exits the cap 113. The coating 111 is chosen to be partially transmissive. This can be achieved using a patterned metal coating, a thin-film dielectric stack, or small backscattering particles. By using the coating 111, a fixed portion of the light is reflected from the coated portion of the side. This reflected light re-impacts the curved distal surface 115 and is coupled back into the optical fiber 14.

[0093] The amount of reflected light desired to be coupled back into fiber 14 depends on whether the fixed reflector is used to generate a calibration signal or a reference field. If an OCT calibration signal is desired, the intensity of the light coupled back into fiber 14 from fixed reflector 115 should be similar to the intensity of the light returned from the sample to prevent saturation of the detection system.

[0094] If an OCT reference field is desired, the intensity of the light coupled back into fiber 14 from fixed reflector 115 should be several orders of magnitude higher than the intensity of the light returned from the sample. This provides sufficient heterodyne gain for the sample light, thereby obtaining sufficient detection sensitivity for imaging in scattering tissue. However, because coating 111 is not located in the focal plane of the optical system but rests on the cylindrically curved side of the cap, the back-reflected light is not perfectly coupled into the fiber. Therefore, the reflectivity or backscattering fraction of the coating is typically selected to be high enough to compensate for these fiber coupling losses, which can be calculated using optical design tools commonly used in the art.

[0095] 9 shows another system embodiment 120 in which two coatings provide two fixed reflections. Specifically, in one embodiment, partially reflective or backscattering coatings are applied to portions of the sides and interior surfaces of an optical cap 121 to generate two controlled reflections at known distances from the focal spot. One coating 123 is located on a portion of the side of the cap, and the other coating 124 is located on a portion of the interior surface of the cavity that receives the optical fiber 14. By generating two fixed reflections, the miniature optical cap 14 can provide one calibration signal and one reference field. Alternatively, two calibration signals can be provided, or two reference signals can be provided.

[0096] Distal tip design for protection of optical surfaces For some analytical applications, it is desirable to protect the optical surfaces of the miniature end cap from damage that may occur during catheter assembly or during functional use of the device. Figure 10 shows a system 130 in which the optical surface 131 is protected by being placed within an optical element or cap 133. Beam focusing is provided by an internal lensed surface at the end of the cavity that receives the fiber. Beam direction is provided by the same internal surface by tilting the surface with respect to the longitudinal axis of the fiber. The internal surface is made reflective by coating it with a reflective material, such as a metal or dielectric coating.

[0097] 11 shows a system 140 with an optical element 141 that provides partial protection for the optical surface 142. This may be sufficient to prevent damage in many applications. In this embodiment, the optical surface 142 is located within a recess formed by extending the cylindrical wall 144 of the cap distally beyond the end face. In this embodiment, the fiber 14 resides within a first cavity formed within the optical element or cap 141, and the light-directing surface 142 is formed within a second cavity formed at the distal end of the cap 141.

[0098] Optical Coherence Tomography Imaging Various embodiments of the compact optical cap described herein are suitable for performing OCT imaging of internal luminal structures. A flexible OCT imaging catheter can be constructed by encasing the optical cap and fiber in a transparent sheath that covers the length of the catheter. The fiber and cap can then be rotated about the longitudinal axis of the fiber to perform sideways spiral imaging. These various combinations of elements can operate as data collection probes as shown in the system embodiments of the appropriate figures. Forward-directed annular images may also be obtained if the cap is configured to generate a forward-looking beam in addition to a side-looking beam as shown in FIG. 11 .

[0099] FIG. 12 shows a data collection system 150 for performing OCT imaging using a flexible catheter that includes a miniature optical cap 155 at its distal tip. The optical cap 155 is secured to a flexible optical fiber 153 to form an insertable imaging catheter that directs light to a sample 157 and returns sample arm light to an OCT interferometer. A light source is in optical communication with the OCT interferometer, which may be a Michelson interferometer or any variation thereof known in the art. The light source can be a broadband superluminescent diode, a tunable laser with a narrow instantaneous linewidth and a wide tuning range, a supercontinuum light source, or any source of low-coherence optical radiation. The OCT interferometer is in optical communication with a reference arm that generates a reference field that interferes with the sample light returned from the sample arm.

[0100] The sample arm contains an optical coupler and a flexible imaging catheter. The optical coupler connects to the proximal end of the catheter and directs a portion of the radiation from the light source into the catheter. The optical coupler also provides rotational and translational motion, which is transferred to the distal end of the catheter and into a miniature optical cap. Light is guided through the fiber, focused and redirected by the miniature optical cap 155, and impinges on the sample. As shown, the fiber and cap combination can be rotated. Backscattered and backreflected light from the sample is collected by the miniature optical cap and transmitted back through the fiber, through the optical coupler, and into the OCT interferometer. The sample arm light and reference arm light interfere and are then detected, processed, and displayed by a data acquisition and display system.

[0101] FIG. 13 shows another system 170 for performing OCT imaging using a flexible catheter that includes a miniature optical cap 173 at its distal end. The optical cap has at least one fixed reflective surface, as shown in FIG. 8 or FIG. 9. The optical cap is secured to a flexible optical fiber 175 to form an insertable imaging catheter that directs light to the sample and returns sample arm light to the OCT interferometer. Additionally, the optical cap 173 generates a fixed reference reflection at a known position relative to the focal plane. The reference reflection acts as an interference reference field and interferes with the sample light to form optical coherence tomography image lines. This configuration is known in the field of OCT imaging as a "common-path" interferometer. Common-path interferometer embodiments offer the advantage of matching optical aberrations, such as chromatic dispersion and polarization-induced dispersion, in the sample and reference arms because they are common-mode (the sample and reference fields are generated after traveling substantially the same physical path). Matching these types of aberrations improves image resolution and contrast. However, certain types of common-mode noise can no longer be canceled. Overall, the advantages of common-path interferometry often outweigh the disadvantages once a practical method for constructing a common-path design is established.

[0102] In this case, the fixed reflective surface is configured to generate a reference field that interferes with the sample light returned from the sample. Thus, the optical coupler and flexible catheter have an integrated reference arm and sample arm. This configuration has many advantages over the apparatus shown in FIG. 12. First, the absence of a separate reference arm reduces the cost and complexity of the system. Traditional OCT interferometers require a reference arm that is the same length as the sample arm. In this embodiment, the reference field is generated very close to the sample, and therefore the reference arm path length is inherently matched to the sample arm path length.

[0103] Manufacturing Process and Molding Embodiments Any of the embodiments of the present invention can be manufactured from a single piece of material in one or more steps and then applying a coating in a subsequent step. Alternatively, multiple pieces of material can be combined in a single or multiple steps. To achieve low manufacturing costs and rapid manufacturing times, the manufacturing process can be any type of molding, including injection molding, compression molding, or a special type of injection molding known as micromolding. Figure 14A shows a mold 200 containing four components used to manufacture certain embodiments of the present invention using a molding process. A large, two-part clamshell can be used to form the elongated cylindrical shape of the cap. A first core pin, whose diameter gradually changes from approximately the outer diameter of the coated fiber region to the outer diameter of the core and cladding region, can be used to form the cavity that receives the optical fiber. A second core pin, whose diameter is approximately equal to the diameter of the closed end face of the cap, can be used to form the optical surface at the end of the cap. Essentially, these core pins are placed in a mold, and the material that forms the final molded part flows around the pins and solidifies. FIG. 14B shows a molded part 205 that can be obtained using the mold tool 200 shown in FIG. 14A.

[0104] An optical-quality surface finish can be achieved by diamond-turning the end of the core pin. This process reduces aberrations caused by surface roughness, thereby improving image quality. Furthermore, the use of the core pin allows the optical surface to be formed from a single mold piece, rather than machining half of the optical surface in each of the two clamshell mold pieces that form the cylindrical body of the cap. Alternatively, the first core pin may be replaced by the optical fiber itself in a micromolding process. This configuration, known in the art as "molding in place" or "over-molding," places the optical fiber within a half-cavity formed in the two clamshell components of the mold.

[0105] FIG. 15A shows a three-component mold 210 used to fabricate one embodiment of the present invention using an over-molding process. In the over-molding process, an optical fiber replaces the core pin that would otherwise form the cavity to receive the optical fiber. During the molding process, a molten polymer flows directly onto the fiber and hardens in situ, forming a part molded directly onto the fiber. This process incorporates the fiber into the molded part, eliminating the need to glue or separately bond the fiber into the molded part's cavity during subsequent assembly steps. FIG. 15B shows a molded part 215 that can be obtained using the mold tool shown in FIG. 15A. Here, the optical fiber is bonded directly to the elongated cap during the over-molding process.

[0106] Integrated Reference Reflector and Scattering Particle Embodiments Figure 16 illustrates one embodiment of the imaging wire tip of the probe. An optical fiber 270 terminates in a microlens assembly 326, which focuses the light at a distance from the microlens assembly 326. Light emitted from the microlens assembly 326 is reflected by a beam deflector 330 and travels substantially perpendicular to the optical axis of the fiber 270. The entire fiber assembly is covered by a protective transparent sheath 334 doped with a small amount of scattering material to provide a reference reflection corresponding to the sample arm path length. This reflection is extremely useful in non-common path interferometers (more typical types of interferometers), where the sample and reference paths are physically distinct yet must be matched in path length to generate the desired interference signal.

[0107] Several materials are suitable as dopants. Titanium dioxide (TiO2) is particularly advantageous. TiO2 is used in many paint formulations due to its excellent light scattering properties. Furthermore, it is inert and can be manufactured in large quantities. The particle size can be much smaller than the optical wavelength of interest (nominally 1.3 μm), resulting in a "Rayleigh" scattering effect. In this way, the wavefronts of the outgoing and returning light are not significantly perturbed, thereby minimizing potential image degradation at sufficiently low dopant concentrations.

[0108] Furthermore, because OCT imaging has extraordinary sensitivity and a large dynamic range (typically 100 dB sensitivity and >60 dB dynamic range can be achieved with practical instruments), care must be taken to calculate and then achieve the optimal doping level of TiO2 in the material.

[0109] Basic scattering theory can be used to arrive at the doping concentration in a material. In a typical OCT image of a coronary artery, the instrument's minimum noise is about -100 dB, i.e., about one part in 10 billion of the optical output power applied to the object of interest, and a typical image has a useful dynamic range of about 40 dB. Image processing electronics and software are optimized for this range, so the probe reflector element should be optimized near the maximum detectable peak of image intensity, which is about -60 dB (-100 + 40). This means that the probe reflector should be the brightest object in the image.

[0110] As described herein, probe reflector elements can include, but are not limited to, membranes, films, caps, covers, or other materials. In some embodiments, the reflector elements are flexible or non-flexible. The reflector elements can be shaped into a variety of geometries. Reflector portions can be curved, planar, or substantially planar.

[0111] Basic scattering theory for particles and classical radar cross section theory states that the fraction of light reflected from a single TiO2 particle is given by the formula L R =(σ b / V i )l c ΔΩ where L R is the proportion of reflected light, σ b is the scattering cross section (calculated from standard MIE theory), V i is the volume of the particle, l c is the interaction length (from radar theory), in this case the coherence length of the OCT light, and ΔΩ is the acceptance angle (solid angle) of the microlens. Therefore, if the particle size is about 45 nm and the scattering cross section is about 4.26 × 10 -7 μm 2 When light with a coherence length of approximately 15 μm is irradiated onto a particle through a microlens with a solid angle of approximately 0.004, the proportion of reflected light L R is approximately 0.006 or -32dB.

[0112] Therefore, the total light returned from the probe reference reflector element material should be equal to the volume fraction (doping concentration) multiplied by the fraction of single particle light. This should equal approximately -60 dB (from above), so a reduction of -30 dB (or 0.001) is required. The volume fraction should therefore be approximately 0.001 or approximately 0.1% doping volume concentration. This should lead to a strong, but not overwhelming, reference reflection by the TiO2 particles, as shown in Figure 17.

[0113] Having thus described certain embodiments of the present invention, various deviations, modifications, and improvements will be apparent to those skilled in the art. Such deviations, modifications, and improvements are intended to be within the spirit and scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. In order to maintain the disclosure of the present application as originally filed, the contents of claims 1 to 14 as originally filed are added below. (Claim 1) 1. An optical coherence tomography system, comprising: It is a flexible catheter, an elongated one-piece optical cap defining a bore; and a flexible optical fiber, the elongated one-piece optical cap secured to the flexible optical fiber, the flexible optical fiber being disposed within the bore, the elongated one-piece optical cap having a beam directing surface such that divergent light received from the flexible optical fiber positioned within the bore is directed out of the elongated one-piece optical cap to form a focal point; a flexible catheter having It is an interferometer, Reference arm, detector, It is an optical coupler, the optical coupler is connectable to a proximal end of the flexible optical fiber and is connected to a light source, the reference arm, and the detector; the optical coupler directs a portion of the light from the light source through a side of the elongated one-piece optical cap into the flexible optical fiber; Optical coupler, an interferometer having a data acquisition and display system in electrical communication with the detector; A system having: (Claim 2) The system of claim 1 , wherein the elongated one-piece optical cap has at least one fixed reflective surface. (Claim 3) 2. The system of claim 1, wherein backscattered and backreflected light from the sample is collected by the elongated one-piece optical cap and transmitted back to the fiber, through the optical coupler, into the interferometer, and detected, processed, and displayed by the data acquisition and display system after interference of the reflected light with reference arm light. (Claim 4) 10. The system of claim 1, wherein the beam-directing surface is selected from the group consisting of a biconic asphere, an aspheric surface, a biconic Zernike, a Fresnel, and a non-uniform rational B-spline. (Claim 5) 1. An optical coherence tomography system, comprising: It is a flexible catheter, an elongated one-piece optical cap defining a bore, the elongated one-piece optical cap having a reference reflector; and a flexible optical fiber, the elongated one-piece optical cap secured to the flexible optical fiber, the flexible optical fiber being disposed within the bore; a flexible catheter having It is an interferometer, Reference arm, detector, It is an optical coupler, the optical coupler is connectable to a proximal end of the flexible optical fiber and is connected to a light source, the reference arm, and the detector; the optical coupler directs a portion of the light from the light source through a side of the elongated one-piece optical cap into the flexible optical fiber; Optical coupler, an interferometer having a data acquisition and display system in electrical communication with the detector, the data acquisition system having imaging parameters that are calibratable using the reference reflector; A system having: (Claim 6) The system of claim 5 , wherein the elongated one-piece optical cap has at least one fixed reflective surface. (Claim 7) 6. The system of claim 5, wherein backscattered and backreflected light from the sample is collected by the elongated one-piece optical cap and transmitted back into the fiber, through the optical coupler, into the interferometer, and detected, processed, and displayed by the data acquisition and display system after interference of the reflected light with reference arm light. (Claim 8) 6. The system of claim 5, wherein the beam directing surface is selected from the group consisting of a biconic asphere, an aspheric surface, a biconic Zernike, a Fresnel, and a non-uniform rational B-spline. (Claim 9) The system of claim 5 , wherein the beam-directing surface is a biconic asphere. (Claim 10) 1. An optical coherence tomography system, comprising: It is a flexible catheter, an elongated one-piece optical cap defining a bore, the elongated one-piece optical cap adjacent to and in optical communication with a sheath having a reference reflector; and a flexible optical fiber, the elongated one-piece optical cap secured to the flexible optical fiber, the flexible optical fiber being disposed within the bore; a flexible catheter having It is an interferometer, Reference arm, detector, It is an optical coupler, the optical coupler is connectable to a proximal end of the flexible optical fiber and is connected to a light source, the reference arm, and the detector; the optical coupler directs a portion of the light from the light source through a side of the elongated one-piece optical cap into the flexible optical fiber; Optical coupler, an interferometer having a data acquisition and display system in electrical communication with the detector, the data acquisition system having imaging parameters that are calibratable using the reference reflector; A system having: (Claim 11) The system of claim 10 , wherein the elongated one-piece optical cap has at least one fixed reflective surface. (Claim 12) 11. The system of claim 10, wherein backscattered and backreflected light from the sample is collected by the elongated one-piece optical cap and transmitted back into the fiber, through the optical coupler, into the interferometer, and detected, processed, and displayed by the data acquisition and display system after interference of the reflected light with reference arm light. (Claim 13) 11. The system of claim 10, wherein the beam directing surface is selected from the group consisting of a biconic asphere, an aspheric surface, a biconic Zernike, a Fresnel, and a non-uniform rational B-spline. (Claim 14) The system of claim 10 , wherein the beam-directing surface is a biconic asphere.

[0114] I'll leave a few notes here. [Appendix 1] 1. A light beam directing element having an elongated one-piece cap having a cylindrical outer surface with a longitudinal axis, the cap comprising: the elongated one-piece cap has a proximal end face defining an annular opening and a distal end face having a beam-directing surface, the elongated one-piece cap defining a solid section and a first cavity section defining a volume extending to a boundary of the solid section, the volume sized to surround and receive an optical fiber having a fiber end face, the beam-directing surface being angled and positioned relative to the fiber end face such that light received from the fiber end face is directed from the cylindrical outer surface at a working distance D to form a focal spot of diameter w; Light beam directing element. [Appendix 2] 2. The light beam directing element of claim 1, wherein the elongated one-piece cap is formed from a material selected from the group consisting of acrylic, polycarbonate, polystyrene, polyetherimide, polymethylpentene, and glass. [Appendix 3] 2. The light beam directing element of claim 1, wherein D ranges from about 0 μm to about 30 mm. [Appendix 4] 2. The light beam directing element of claim 1, wherein w ranges from about 3 μm to about 100 μm. [Appendix 5] 2. The optical beam directing element of claim 1, further comprising a stationary sheath and an optical fiber fixedly positioned within the volume, wherein the optical fiber and the elongated one-piece cap are configured to rotate within the stationary sheath. [Appendix 6] 10. The optical beam directing element of claim 1, wherein at least a portion of the beam directing surface is coated with a reflective coating. [Appendix 7] 7. The light beam directing element of claim 6, having a lensed surface disposed within the cylindrical outer surface and formed from the boundary. [Appendix 8] 8. The optical beam directing element of claim 7, wherein the beam directing surface is substantially flat. [Appendix 9] 7. The light beam directing element of claim 6, wherein the reflective coating is a partially transmissive coating. [Appendix 10] 10. The optical beam directing element of claim 9, wherein the partially transmissive coating splits light from the fiber end face into a first beam directed from the cylindrical outer surface at the working distance D to form the focal spot having a diameter w, and a second beam directed from the cylindrical outer surface at a working distance D' to form a focal spot having a diameter w'. [Appendix 11] 11. The optical beam directing element of claim 10, wherein the beam incident on the fiber end face is split based on the intensity of the incident beam or the wavelength of the incident beam. [Appendix 12] 2. The optical beam directing element of claim 1, wherein a partially reflective coating is disposed on a distal section of the cylindrical outer surface, positioned such that a beam directed from the beam-forming surface passes through the partially reflective coating and is reflected back from the partially reflective coating. [Appendix 13] 2. The light beam directing element of claim 1, wherein a partially reflective coating is disposed within the volume and along a portion of the boundary. [Appendix 14] 2. The optical beam directing element of claim 1, wherein the beam directing surface is located within the volume or the solid section. [Appendix 15] 2. The optical beam directing element of claim 1, wherein a second cavity section is defined within the solid section such that the beam directing surface is partially obscured by a portion of the cylindrical outer surface surrounding the second cavity section. [Appendix 16] 6. The optical beam directing element of claim 5, wherein the beam directing surface is shaped to substantially eliminate cylindrical optical distortion induced by light propagating from the beam directing surface through the cylindrical outer surface and the stationary sheath. [Appendix 17] 6. The optical beam directing element of claim 5, wherein the beam directing surface is selected from the group consisting of a biconic asphere, an aspheric surface, a biconic Zernike, a Fresnel, and a non-uniform rational B-spline. [Appendix 18] 1. A method for collecting optical data from a test sample in situ, comprising: providing an optical fiber including a core adapted to transmit a light beam having a first diameter; providing an elongated one-piece cap having a cylindrical outer surface and an annular opening, said cap fixedly and optically coupled to said length of optical fiber by receiving and surrounding said length within a cavity defined within said cap; transmitting the light beams onto a beam-directing surface such that a first light beam is directed at a working distance D from the cylindrical outer surface to form a focal spot having a diameter w. method. [Appendix 19] 19. The method of claim 18, further comprising splitting the light beam so that a second light beam is directed at a working distance D' from the cylindrical outer surface to form a focal spot having a diameter w'. [Appendix 20] 19. The method of claim 18, further comprising collecting optical coherence tomography data using the first light beam. [Appendix 21] 19. The method of claim 18, further comprising generating one of the reference signals in response to a reflective element disposed within the integrated cap, the reflective element acting as an arm of an interferometer in an optical coherence tomography system. [Appendix 22] 19. The method of claim 18, further comprising generating one of the calibration signals in response to a reflective element disposed within the integrated cap, the calibration signal being used to adjust a reference arm path length to match a sample arm path length in an optical coherence tomography system.

Claims

1. 1. An intravascular data acquisition system comprising: a fiber having a core and a fiber end face, the fiber transmitting a beam at a first diameter; a beam directing element comprising an elongated one-piece cap having a curved beam directing surface at a first end, a cylindrical outer surface having a constant outer diameter, and an annular opening coupled to the fiber at a second end; comprising a first working distance D from the outer cylindrical surface to form a first focal spot.

2. 2. The intravascular data acquisition system of claim 1, wherein the annular aperture is fixedly and optically coupled to the fiber by receiving and surrounding the length of the fiber and the fiber end face within a cavity defined in the beam directing element.

3. 10. The intravascular data acquisition system of claim 1, wherein the beam directing element further comprises a partially transmissive coating that splits the beam so that a second beam is directed a working distance D′ from the cylindrical outer surface to form a second focal spot.

4. The intravascular data acquisition system of claim 3 , wherein the second focal spot has a diameter w′.

5. The intravascular data acquisition system of claim 1 , further comprising a data acquisition unit that acquires intravascular data using the first beam.

6. The intravascular data collection system of claim 5 , wherein the intravascular data includes optical coherence tomography data.

7. The endovascular data collection system of claim 5 , wherein the data acquisition unit provides an output of the collected endovascular data.

8. The intravascular data acquisition system of claim 1 , wherein the beam directing element further comprises a reflective element that generates at least one reference signal, the reflective element acting as an arm of an interferometer in an intravascular imaging system.

9. 10. The intravascular data collection system of claim 1, wherein the beam directing element further comprises a reflective element that generates at least one calibration signal, the at least one calibration signal being used to adjust a reference arm optical path length to match a sample arm optical path length in an intravascular imaging system.

10. The intravascular data acquisition system of claim 1 , wherein at least a portion of the beam directing surface is coated with a reflective coating.

11. The intravascular data acquisition system of claim 10 , wherein the reflective coating is a partially transmissive coating.

12. 12. The intravascular data acquisition system of claim 11, wherein the partially transmissive coating splits the diverging light into the first and second beams.

13. The intravascular data acquisition system of claim 1 , wherein the first focal spot has a diameter w.

14. The intravascular data acquisition system of claim 1 , wherein the annular aperture is sized to receive the beam directing element and couple it to the fiber.

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