Patent Publication Number: US-2022221708-A1

Title: Optical Instrument for Imaging and Sensing using Multicore Fiber

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 62/157,131 filed May 5, 2015; 62/163,522 filed May 19, 2015; 62/163,532 filed May 19, 2015; and 62/166,154 filed May 26, 2015 the entire contents of each are incorporated by reference in their entirety as if set forth at length herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to endoscopic devices and in particular to a fixed distal optics endoscope having multicore fiber. 
     BACKGROUND 
     Medical and non-medical applications of imaging endoscopes are well known and their importance to contemporary cardiology, gastroenterology, pulmonology, laparoscopy as well as nondestructive evaluation/nondestructive testing (NDE/NDT) is widely accepted. Given that importance, improvements to endoscopic devices and systems would represent a welcome addition to the art. 
     SUMMARY 
     An advance in the art is made according to an aspect of the present disclosure directed to endoscopic devices employing multicore optical fiber. 
     In contrast to contemporary, prior-art endoscopic devices and systems, devices constructed according to the present disclosure may employ—in addition to multicore optical fiber—employ a variety of measurement techniques including swept-source techniques, employ widely tunable source(s), include multiple functions, and—in some embodiments—critical complex optical functions may be performed by one or more photonic integrated circuit(s). 
     An illustrative endoscopic system and structure according to the present disclosure includes an optical receiver selected from the group consisting of spectral domain optical coherence tomography (OCT) receiver, time domain OCT receiver, confocal receiver, fluorescence receiver, and Raman receiver; an endoscope body including fixed distal optics; and a multicore optical fiber optically coupling the fixed distal optics to the receiver. 
     Notably, term endoscope is used throughout the disclosure to describe structures according to the present disclosure. Those skilled in the art will readily appreciate that the disclosure is not specifically limited to endoscopes. More particularly, the disclosure and underlying principles herein are equally applicable to catheters, laparoscopes, imaging guidewires as well as other medical and non-medical devices and structures. Accordingly, when the term endoscope is used, it is intended that it be interchangeable with any instrument or system used to examine the inside of something—oftentimes a body for medical reasons. Such instruments advantageously permit the interior of an organ or other cavity of the body. Of further advantage, endoscopes are capable of being inserted directly into an organ for subsequent examination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       A more complete understanding of the present disclosure may be realized by reference to the accompanying drawings in which: 
         FIG. 1  shows exemplary Prior Art endoscopes; 
         FIG. 2(A) ,  FIG. 2(B)  and  FIG. 2(C)  show a series of exemplary single-mode fiber scanning endoscopes as known in the Prior Art; 
         FIG. 3  shows a schematic diagram of a multi-core fiber endoscope employing an array of swept-source optical coherence tomography (SS-OCT) receivers according to an aspect of the present disclosure; 
         FIG. 4  shows a schematic diagram of a multi-core fiber endoscope employing a single SS-OCT receiver and distinct delays according to an aspect of the present disclosure; 
         FIG. 5  shows a schematic diagram of another multi-core fiber endoscope employing a single SS-OCT receiver and 1:N switch(es) interconnecting the receiver to the endoscope according to an aspect of the present disclosure; 
         FIG. 6  shows a schematic diagram of an illustrative distal portion of a five-core optical fiber endoscope according to an aspect of the present disclosure; 
         FIG. 7(A) ,  FIG. 7(B) ,  FIG. 7(C) ,  FIG. 7(D)  and  FIG. 7(E)  show a series of illustrative arrangements as schematic diagrams other illustrative multi-core fiber endoscope employing:  FIG. 7(A)  a collimating lens,  FIG. 7(B)  a fiber/lens coupling element including a passive or active beam steering elements,  FIG. 7(C)  a graduated index (GRIN) lens or section of multimode fiber,  FIG. 7(D)  a multi-element collimating lens, and  FIG. 7(E)  a beam deflector element according to aspects of the present disclosure; 
         FIG. 8  shows a schematic diagram of an illustrative multi-core fiber endoscope wherein the multi-core fiber is connected to a photonic integrated circuit (PIC) according to an aspect of the present disclosure; 
         FIG. 9  show another schematic diagram illustrating a multi-core fiber endoscope wherein the multi-core fiber is connected to a PIC according to an aspect of the present disclosure; 
         FIG. 10  shows yet another schematic diagram illustrating a multi-core fiber endoscope wherein the multi-core fiber is connected to a PIC according to an aspect of the present disclosure; 
         FIG. 11  show a schematic diagram illustrating a multi-core fiber endoscope having a pull-back and/or rotational or twisting proximal motor according to an aspect of the present disclosure; 
     
    
    
     DETAILED DESCRIPTION 
     The following merely illustrates the principles of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its spirit and scope. More particularly, while numerous specific details are set forth, it is understood that embodiments of the disclosure may be practiced without these specific details and in other instances, well-known circuits, structures and techniques have not been shown in order not to obscure the understanding of this disclosure. 
     Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. 
     Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently-known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 
     Thus, for example, it will be appreciated by those skilled in the art that the diagrams herein represent conceptual views of illustrative structures embodying the principles of the invention. 
     In the claims hereof any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements which performs that function or b) software in any form, including, therefore, firmware, microcode or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. Applicant thus regards any means which can provide those functionalities as equivalent as those shown herein. Finally, and unless otherwise explicitly specified herein, the drawings are not drawn to scale. 
     Thus, for example, it will be appreciated by those skilled in the art that the diagrams herein represent conceptual views of illustrative structures embodying the principles of the disclosure. 
     By way of some additional background, it is noted that many contemporary imaging endoscopes, catheters, laparoscopes, and imaging guidewires—such as those employed in optical coherence tomography systems—typically employ single mode optical fiber. Such systems perform scanning and imaging by either: 1) spinning the fiber or 2) employing distal optics—for example, motor(s) and actuator(s)—along with a stationary single mode optical fiber. As may be appreciated, configurations such as 1) and 2), above, provide necessary beam deflection(s) to effect the scanning. 
     Turning now to  FIG. 1  there is shown several illustrations of contemporary optical endoscopes that are known in the art. While not specifically identified in that Figure, such endoscopes may include an eyepiece, a light post, and an objective assembly. Alternative configurations may include—among other things—an access port for instrument(s) and an “umbilical” connection. 
       FIG. 2(A) ,  FIG. 2(B)  and  FIG. 2(C)  show in schematic form several illustrative examples of single-mode, or multi-mode fiber scanning endoscopes as known in the art. As may be appreciated such endoscopes must be capable of delivering, focusing, scanning and collecting a single spatial-mode optical beam. In addition, the catheter employed oftentimes is flexible—but not always—and has a sufficiently small diameter to facilitate its entry into internal spaces such as arteries. Generally, such endoscopes will include optical control and coupling element(s) at a proximal end, a single-mode fiber running the length of the catheter, and optical focusing and beam directing elements at the distal end. As is generally known by those skilled in the art, the endoscope is configured to scan the beam in a circumferential pattern such that a cross-section image may be made of structure(s) into which it is positioned such as—for example—an artery. 
     As shown in  FIG. 2(A) , such illustrative examples generally include—at a proximal end—a system  210  which may include light source(s), detector(s) and controlling circuitry and/or operating software(s). Such a system is optically, mechanically, and electrically coupled to a catheter body  230  by a rotary fiber optical joint  220  which includes a spinning optical fiber  231  which in turn is connected—at a distal end—to one or more lens(es)  240  and prism  241  which in turn produces a spatial mode optical beam  250 . 
     The illustrative example shown in  FIG. 2(B)  includes—at its proximal end—system  212 , stationary fiber optical joint  213  which is coupled to catheter body  232  and includes a fixed, or stationary, otherwise non spinning single mode optical fiber  233  which in turn is coupled—at the distal end—to one or more lens(es)  242  which in turn is optically coupled to a prism  243  which is spun by distal motor  253 . 
     Similarly, the illustrative example shown in  FIG. 2(C)  includes system  214 , stationary fiber optical joint  224 , catheter body  234  including stationary single mode optical fiber  235  optically coupled at a distal end to lens(es)  244  and optical phased array(s)  245  thereby producing scanning beam  256 . 
     As may be appreciated, spinning optical fibers—such as those employed in configurations such as that in  FIG. 2(A) , exhibit several disadvantages including non-uniform rotation distortion (NURD), fragility/breakage, cost, reliability, rotational speed limitations along with certain safety considerations that accompany such configurations. Distal motors—such as those employed in  FIG. 2(B) —likewise are disadvantaged by cost, size, scanning flexibility, the need for control line(s) and power delivered to the distal end. Distal optical phased arrays—such as those employed in  FIG. 2(C) —while offering optimistic promise nevertheless exhibit limitations with respect to image quality, efficiency sidelobes, electrical power requirements and size. 
     Given such noted infirmities with these prior art endoscopes, scanning optical endoscopes exhibiting low cost, small size and acceptable (albeit lower) scanning resolution may be may be constructed according to aspects of the present disclosure. More particularly, and with reference to  FIG. 3 , there is shown in schematic an illustrative multi-core fiber endoscope  300  according to an aspect of the present disclosure employing an array of swept-source optical coherence tomography (OCT) receivers. As shown in that figure, a multi-core optical fiber is employed and—in sharp contrast to the prior art—no distal mechanical element(s), controllable phased array(s), and/or spinning fibers are used. Of further advantage, individual optical fibers employed may be single-mode fiber(s) or multi-mode fiber(s). It is noted at this point that while specific illustrative examples disclosed herein employ SS-OCT systems and techniques—the disclosure is not so limited. More particularly, other OCT systems and non-OCT systems such as Raman, fluorescence, near-infrared, confocal, and other types of imaging systems that connect similar multicore fiber endoscopes with multicore optical fiber are contemplated and within the scope of this disclosure as well. 
     A multi-core fiber (MCF) has multiple cores positioned within a cladding. Such MCF have been employed in telecommunications applications and shown considerable promise. Advantageously, the number of cores comprising a MCF may differ from application to application—as those individual application needs dictate. By way of illustrative example only—a seven core MCF may have one center and six outer cores. The distance between two neighboring cores is known as the core pitch. By altering the core pitch—it is known by those skilled in the art—that the amount of crosstalk between neighboring cores may be changed. 
     In the illustrative example shown in  FIG. 3 , a swept-source optical coherence tomography system  310  is coupled to a multi-core optical fiber endoscope  330 . As previously noted either single-mode or multi-mode fibers may be employed however for SS-OCT systems such as the one illustrated single-mode fibers are preferably used. Additionally, and as previously noted, while we have shown illustratively an SS-OCT system in this Figure and described in this description, those skilled in the art will readily appreciate that any of a variety of measurement system(s) may be employed and remain consistent with one or more aspect(s) of the present disclosure. 
     As depicted in  FIG. 3 , a swept source laser  312  is split into N different channels through the effect of splitter  313  or other suitable optical structure(s), each of the N channels optically coupled to a multi-core optical fiber  324  via a proximal end connected (shown in Figure as a dotted line). The N channels are conveyed via the multi-core optical fiber to distal optical structure(s)  370  that may focus light through a transparent, protective cover  360 —or transparent windows in a transparent cover—such that output light  380  is conveyed into any external sample, i.e., body tissue(s) or cavities. 
     As will be now understood, light reflected from the sample(s) is collected along the same optical path(s), combined with light directed to a reference arm  315  and interferometrically detected in N separate, opto-electronic receivers  316 ( 1 ) . . .  316 ( n ), the output of which is directed into a digital signal processing sub-system  317  and other computer(s), controller(s), instrumentation—as necessary (not specifically shown)—for analysis and/or display. Notably, an endoscope such as the one illustrated  330  may include a protective and/or structural jacket  340  to ensure integrity and/or smooth operation/insertion of the device as it is routed through other instruments or directly into a body lumen or other sample environment. Of further note that while this portion of the description has been directed to an SS-OCT type system those skilled in the art will appreciate that systems according to the present disclosure are not so limited. In particular, other types of optical sensing, ranging, or imaging modalities may be employed (e.g., fluorescence, Raman, near-infrared spectroscopy, etc.) in systems according to the present disclosure. 
     As may be further appreciated by those skilled in the art, the distal optical structures may advantageously include one or more passive lens assemblies or photonic integrated circuit(s) (PIC). Additionally, planar lightwave circuits (PLC) comprising those optical structures may advantageously be fabricated from InP or Si photonic materials—among others. By employing one or more PICs fabricated from well-known materials using highly evolved fabrication technologies contemporary design tools may be employed to design, simulate and manufacture the distal optical structures while producing benefits related to high precision, small size and low-cost. Still further, such distal optics according to the present disclosure may be fabricated—either in whole or in part—from molded optical materials and components thereby further lowering their cost and manufacturability. 
     Notably, while the distal optics of the system so described may comprise one or more PICs—so may elements of the SS-OCT portion  310  of the system. More particularly, on one illustrative embodiment according to the present disclosure—the SS-OCT portion of the system  310  shown schematically within the dotted line of  FIG. 3 , (excluding any elements/components not suitable for PIC fabrication presently—i.e., computers, etc.) may comprise one or more PICs such that a compact, robust, low-cost structure(s) result. As those skilled in the art will further appreciate and as will become apparent to those skilled in the art, such PIC fabrication methodologies may advantageously be applied to other designs/configurations according to the present disclosure including those described herein. 
     Of particular interest to those skilled in the art is that while employing a PIC a vertical cavity surface emitting laser (VCSEL) or other laser structure such as verner tuned laser may be integrated into an SS-OCT PIC such that a single PIC includes a VCSEL transmitter, waveguide(s) for beam handling and one or more optical receivers such as a dual-balanced, dual-polarization, I/Q receiver—among other(s). In sharp contrast to contemporary configurations, such PICs may be designed so that VCSEL emission light is coupled into a silicon waveguide. 
     With reference now to  FIG. 4 , there is shown a schematic of an illustrative embodiment of a multi-core fiber endoscope system  400  employing a single SS-OCT receiver and distinct delay(s) according to an aspect of the present disclosure. As depicted in that Figure, a single receiver  410  is employed and SS-OCT information from each optical fiber comprising the multi-core fiber  425  is extracted through the utilization of distinct delays  414  (D Dn). By employing different delays in each fiber path, information about optical properties from each path is transformed into distinct intermediate frequencies (i.f.) at any photodetector(s) used. Such an approach of encoding two signals into different i.f. frequencies has been employed in polarization sensitive OCT (PS-OCT) but has not—prior to the present disclosure—been employed in optical endoscopes and in particular not in conjunction with multi-core optical endoscopes according to the present disclosure. 
     As may be appreciated with continued reference to  FIG. 4 , DSP unit  417  may process these n distinct i.f. frequencies as they arrive as different—and substantially non-overlapping—frequency bands. Those skilled in the art will readily appreciate that such a configuration results in considerable advantage over the prior art as it utilizes only one receiver and exhibits only a 1/n loss in reflected signal power and transmitted power. Note further that while this illustrative configuration is shown, those skilled in the art will now appreciate from this disclosure that alternative configurations according to the present disclosure may be constructed that achieve the same result(s). 
     Similar to the system shown previously with respect to  FIG. 3 , the receiver  410  is coupled to the endoscope  430  by the multicore optical fiber  425 , wherein each of the individual fibers comprising the multicore optical fiber includes one or more distinct delay elements  414  (D . . . . Dn) which produces a distinct delay for each of the individual fibers. The endoscope  430  generally includes a body—providing a protective and structural jacket  440  to the multicore fiber  425  as well as other elements positioned therein and comprising the overall endoscope  430 . Notably, distal optics  470  produce optical scan beams  480  and is generally protected through the effect of cap,  460 . As will become apparent to those skilled in the art, a variety of distal optical configurations are contemplated according to the present disclosure. 
       FIG. 5  shows yet another illustrative embodiment of a multi-core optical endoscope system  500  according to the present disclosure wherein an illustrative SS-OCT sub-system  510  is coupled to a multi-core optical fiber endoscope sub-system  530  through the effect of a 1:N switch  524 . As depicted in that Figure, the illustrative sub-system  510  includes a number of circulators  514  along with receiver  516  and DSP  518  for receiving and processing return signals from samples illuminated by beams  580  and under examination by endoscope system  500 . In a particular illustrative embodiment of the system  500  shown in the Figure, repetition rate of laser  512  may be synchronized to the switching rate of the 1:N switch  524  such that light is transmitted and received substantially during a single frequency sweep (or multiple thereof). In this manner, inefficiencies associated with switching dynamics are incurred during a period when the laser is blanked—at lower power. In this manner, unused portion(s) of the laser frequency sweep is overlapped in time with unusable portions of the switching during switching transients. 
     With this disclosure, those skilled in the art will readily appreciate that this approach has the advantage of higher optical sensitivity as all of the laser light and sample reflected light is coupled to one (or more) of the optical fibers comprising the multi-core optical fiber. As noted previously, other alternative optical systems and components such as spectral-domain OCT, time-domain OCT, confocal systems, fluorescence sensors, Raman sensors and other may be used in place of the SS-OCT system shown illustratively. Of course, the SS-OCT system including the 1:N switch may be constructed using integrated optical technologies—e.g. silicon photonics—to achieve a compact, reliable, low-cost system. Similarly—and as noted previously—these same techniques/structures/methodologies may be employed with any/all of the illustrative examples disclosed herein. 
     Turning now to  FIG. 6 , there is shown in schematic form another illustrative embodiment (both side and end view(s)) of a distal end of multi-core fiber endoscope  600  according to an aspect of the present disclosure. As may be observed from that Figure, the distal end of the endoscope includes a protective cap  670  and distal optics including collimating lens(es)  673 , fold mirrors  672 , and substrate  671  coupled to the multi-core fiber,  625  which in this illustrative embodiment includes 5 (five) single optical fibers shown arranged as a central fiber with four perimeter fibers. Of course, those skilled in the art will appreciate that the number of individual fibers and number(s) of individual distal optical elements may be changed as specific application needs dictate. Additionally, the arrangement of the individual fiber(s) and distal optical element(s) may change from application to application as well. Shown further in that Figure is the light beam patters  675  which emanate from the distal optics. 
     With continued reference to  FIG. 6 —and as will be appreciated by those skilled in the art—certain details of structural and protective jacket (body) of the endoscope is not shown for simplicity. Operationally, light emanating from each fiber core is collected and directed into tissue/structures through the effect(s) of lens(es)  673  and mirrors  672 . Notably, while the term “mirrors” is used herein—the disclosure is not so specifically limited. Other optical structures which redirect and/or the light in a desired manner such as prisms, light guides, photonic integrated circuits, etc., are contemplated for such structures and purpose as well. 
     Accordingly, there exist numerous approaches to the distal optics of a multi-core fiber optic endoscope according to the present disclosure. In particular, lens(es) may be graduated index (GRIN) lenses, ball lenses, fiber lenses, and/or lens arrays including multimode, multicore fiber lens that may be affixed or fusion spliced to the distal end of the multi-core fiber. Optional fold mirrors (or prisms or other structures) may be used to redirect light from optical fiber core(s) substantially away from endoscope axis—as desired. Also, one or more center cores may be coupled to optical structures (lenses, etc) that direct light substantially along the endoscope axis. 
     Advantageously, and as will be readily appreciated by those skilled in the art, all distal optical elements—or selected components thereof—may be made from discrete components, one or more molded components, photonic integrated circuit(s) or combinations thereof. As shown in the Figure(s), a protective cap may be fully or partially transparent or include windows to allow light to traverse from optical fibers and/or optical elements to/from samples under examination while providing a smooth, sufficiently strong, and appropriately shaped character such that it may be presented/inserted/retrieved from anticipated pathways such as the interior of a bodily lumen. Furthermore—as shown in  FIG. 6 , the entire distal optics may be assembled and/or fabricated as part of or on top of a substrate. Advantageously, the substrate may allow beam expansion from fiber to lens(es) such that a desired focus, beam waist etc. may be realized. As an illustrative example—and not considered limiting—if a multicore fiber is operating in a single mode regime at 1300 nm, then the core size is ˜9 um. As is known in the art, to a achieve a ˜20 um beam waist (1/e{circumflex over ( )}2) at a ˜1 mm focal length requires ˜28 um diameter (1/e{circumflex over ( )}2) at a face of a lens (in air). Longer focal lengths require a correspondingly larger beam diameter at the lens face where requires a larger lateral separation between fiber cores in the multicore fiber. As may be appreciated, it is desirable that light propagating along the fiber cores and up to and out of any lense(s) does not have substantial leakage from one channel to another. 
     Of further note, alternative illustrative embodiments of the arrangement of  FIG. 6  may not necessarily include the lens(es) depicted in that Figure. In particular, one or more fold mirrors may be employed to redirect light into/away from the fiber axes—as appropriate. Advantageously, such a configuration is not only simple, but limited imaging range may be achieved (˜0.3 um the Rayleigh range assuming a 1310 nm wavelength and a ˜9 um beam waist at fiber facet). Accordingly—and as will be readily understood by those skilled in the art—there are a variety of other focal length/focal spot size width exit beam diameter design tradeoffs that may be made depending on the desired operating parameters. 
     As may be appreciated, there are many medical and non-medical applications that would benefit from a simple, low-cost, compact, reusable and/or disposable endoscope such as one(s) constructed according to the present disclosure. Such applications include where a precise, continuous profile of an intimal surface of a lumen is not needed but a measurement of 2, 4, or 8 cross sectional dimensions of the lumen opening is sufficient. For example, when using a nine core optical fiber with one fiber as a central fiber and eight fibers positioned concentrically around the perimeter of that central fiber—each perimeter fiber having a fold mirror associated with it—then four cross-sectional measurements along the 0, 45, 90 and 135 degree axis may be made along with one forward axial measurement. Such measurement(s) may be combined with fiber pull-back mechanism(s) to pull (or push) the endoscope substantially along the axis of the fiber. As will be shown and discussed, it is possible to perform a manual or automated twisting action—back and forth—to sample more of the circumferential area of interest. In this manner four cross-sectional measurements may continuously be made as the endoscope/fiber is pulled back. Such measurement(s) may be useful for a variety of applications including sizing lumens for stents or other therapeutic or interventional procedures. Of further advantage, such endoscope(s) may be combined with other measurement devices/techniques including optical measurements (fluorescence, NIR, Raman) or non-optical devices (e.g., pressure, temperature, pH, etc.) It is also possible to combine such device(s) with therapeutic devices such as surgical lasers, cryo or RF ablation, mechanical cutting tools, and/or other devices/structures. Of distinct advantage, it is possible to position such devices within the inside of a needle—due to its small size. 
       FIG. 7(A) ,  FIG. 7(B) ,  FIG. 7(C) ,  FIG. 7(D)  and  FIG. 7(E)  show a series of illustrative arrangements as schematic diagrams other illustrative multi-core fiber endoscope employing:  FIG. 7(A)  a collimating lens,  FIG. 7(B)  a fiber/lens coupling element including a passive or active beam steering elements,  FIG. 7(C)  a graduated index (GRIN) lens or section of multimode fiber,  FIG. 7(D)  a multi-element collimating lens, and  FIG. 7(E)  a beam deflector element—as part of distal optics all according to certain aspects of the present disclosure. 
     More particularly  FIG. 7(A)  shows another illustrative example of a multi-core fiber endoscope  700  according to the present disclosure wherein a single, shared collimating lens  710  is employed to collimate multiple outputs  715  from multi-core optical fiber  730 . Advantageously, the lens may be a single element lens that is coupled to the multi-core fiber  730  via a free-space or solid coupling mechanism(s)  720  including direct fusion splice of a graded index lens constructed of optical fiber or cementing a GRIN lens to the end of the multi-core fiber. Of further advantage, the lens so coupled may be a single element or multiple, separate elements. Such lens(es) may be a GRIN lens, ball lens or aspheric molded glass lens—among other types as well. One additional possibility is the construction of lensing element(s) using fiber gratings within the core or cladding material of the multi-core fiber. 
     With reference now to  FIG. 7(B) , there is shown yet another illustrative example of a multi-core fiber endoscope  701  according to an aspect of the present disclosure wherein a fiber/lens coupling element  720  includes a passive or active beam steering element(s)  721 , i.e., a prism element, to adjust the focus location of light emanating from each of the individual fibers comprising the multi-core fiber (shown emanating onto a collimating lens  710 ) such that the focus location(s) are nearly identical with respect to any sample(s) being examined. 
     Advantageously, there are a number of approaches to this illustrative example. In particular, if there are N cores in the multi-core fiber then all N cores may be utilized in parallel using receiver structure(s) shown previously. Alternatively, if only a single fiber—for example the center fiber—emits light and the remaining fibers—or a subset of the remaining fibers—may simultaneously be used to collect light reflected from the sample(s). One particular advantage to this approach that will be readily appreciated by those skilled in the art is that beam waists are in the same—but not necessarily exact same) location and additional information about angular scattering and back reflection of light from the sample may be obtained and used to differentiate tissue structure. Of further advantage, using one (or more) of the individual fibers comprising the multi-core optical fiber to illuminate and using other fibers to collect light reflected from the sample(s) may be extended to any of the embodiments contemplated herein or derivatives thereof. 
       FIG. 7(C)  shows yet another illustrative embodiment of a multi-core optical fiber endoscope  702  according to an aspect of the present disclosure. In particular, a lens employed may advantageously be a GRIN lens or a section of multimode fiber exhibiting a property to image facets of the multi-core fiber at an appropriate distal beam focus. The use of a multimode fiber, as is known in the art, is particularly attractive since it may be fusion spliced or otherwise easily secured to the end of the multicore fiber. 
     As may be appreciated, it is sometimes advantageous to use a section of coreless fiber positioned before the multimode fiber in the optical path to allow beam(s) to more freely expand. Once the beam diameter is of sufficient size to achieve the focal depth and confocal parameter the beam may enter a beam propagation region  735 . Once the beam(s) are sufficiently spatially separated an optional distal beam deflector  740  element can be used to deflect some of the beams  742  substantially away from the axis of the endoscope and allow one or more or no beam to pass through substantially uninterrupted to allow for forward ranging  743 . The endoscope can have transparent windows at appropriate beam exit locations and as noted previously—when smooth—allows for easier insertion into tight spaces. Similarly, an outer sheath of the endoscope body may be made transparent and constructed from a biocompatible materials. Finally, it is noted that while the particular application of the principles provided in this disclosure have used endoscopes as examples, the disclosure is not so limited. In particular, aspects of this disclosure will apply equally well to using sensors and imaging within catheters, guidewires, needles, laparoscopes and other medical—and non-medical—devices. 
       FIG. 7(D)  shows yet another illustrative embodiment of a forward imaging multicore fiber endoscope  703  having a multi-element collimating lens and distal beam deflector element  740 . More particularly—and as depicted in that Figure—a multi-element fiber/lens coupling element  720  is employed to individually collect light from each of the individual multicore fiber outputs  715  and direct/focus it such that the light may be more particularly directed onto/into a sample (not specifically shown). In a particular illustrative embodiment, such multi-element fiber/lens coupling element  720  may comprise a multi-mode, multicore optical fiber that is fusion spliced or otherwise connected to a single mode multi-core fiber. In an illustrative embodiment, the outside diameter of the multi-mode multicore fiber is substantially the same as the outside diameter of the single-mode multicore fiber. Of course, other applications may advantageously utilize configurations in which the outer diameters are not the same—for example, those applications in which a larger exit beam diameter is desired. 
     With continued reference to  FIG. 7(D) , it may be observed that in an illustrative embodiment the multi-mode multi-core fiber is configured with an appropriate GRIN-like profile to achieve appropriate beam parameters for example, focal distance, confocal parameter, etc. for imaging light onto/into the sample (not specifically shown). Additionally, it may be observed that the illustrative embodiment shown in the  FIG. 7(E)  includes a beam deflector element, that is configured to direct one or more light beams  742  in a direction substantially away from the endoscope axis  751  such that they may be directed to the sample. 
       FIG. 8  shows yet an additional illustrative example according to the present disclosure in which a multicore fiber  810  is coupled to a photonic integrated circuit (PIC—or Integrated Optical Substrate)  820 . As will be readily appreciated by those skilled in the art, there exist a wide variety of PIC technologies and materials including PLC, InP and the entire family of Silicon Photonics materials. As depicted in the Figure, light from the multicore fiber  810  is butt coupled to the integrated optic substrate through which it propagates via light guides  830  formed therein, and subsequently impinges on respective surface grating coupler(s)  835 . Those skilled in the art will readily understand and appreciate the operation of 1D and 2D surface grating couplers and that any among a variety of same may advantageously be employed in structures according to the present disclosure. Further appreciated, is the fact that the surface grating couplers individually collect diverging light from each of the fibers in the multicore fiber and simultaneously reemit it in such that it is directed into a sample (not shown). Conversely, such surface grating coupler(s) operate in the reverse direction by collecting light from sample(s) and directing it to the fibers comprising the multicore fiber. 
     Turning now to  FIG. 9 , there is shown an additional illustrative example of multicore optical fiber endoscope distal end  900  according to yet another aspect of the present disclosure. More particularly and as depicted in that Figure, the multicore optical fiber  930  is shown coupled to a photonic integrated circuit  920 . As depicted therein, light from the multicore fiber (not specifically shown)—which is butt coupled to the integrated substrate of the PIC  920  wherein it propagates via waveguide structures  925  to one or more surface grating coupler(s)  935 . As depicted in this illustrative example, inner grating couplers  935  couple light to/from the waveguides  930  and multicore optical fiber as well as additional waveguides  939  which convey light from inner couplers  935  to/from outer surface grating couplers  937  which emit/receive light to/from sample(s). 
     For simplicity, only a single waveguide is shown connecting optical fibers to respective inner surface grating couplers and subsequently to outer grating couplers. Notably, two or more waveguides may be employed to couple the optical fibers to the inner grating as well as two or more waveguides to couple the inner grating couplers to the outer grating couplers such that one or two polarization modes are conveyed. Note further that the number of waveguides connecting the couplers does not have to be the same for each. As will be appreciated, configurations according to the present disclosure such as that shown in  FIG. 9  provide an advantage namely that the radius of the multicore fiber employed may be smaller and still provide a large aperture on emitting surface grating coupler. 
       FIG. 10  shows yet another illustrative example according to the present disclosure of a multicore optical fiber endoscope configuration  1000  wherein the multicore optical fiber  1030  is coupled to a photonic integrated circuit (integrated optical substrate)  1020 . Here, the individual cores  1031  of the multicore fiber  1030  are directly butt coupled to a surface grating coupler(s)  1035  fabricated in/on the circuit substrate  1020 . The surface grating coupler(s) so coupled to the fibers  1031  are further coupled to respective end facet emitter(s)  1037  via respective optical waveguide(s)  1039 . As configured, the end facet emitter(s)  1037  emit light substantially orthogonally to the axis of the multicore fiber (except for a center core). As will be understood and appreciated by those skilled in the art, there exist a number of end facet (horizontal) couplers that may be used including adiabatic coupling approaches. Advantageously—with a configuration such as that depicted—if the wavelength employed is 1300 nm and a focal distance of 2 mm is desired, with a beam waist of ˜20 um, then a beam waist at the exit facet is ˜46 um. 
     At this point it is noted that a number of the illustrative embodiments shown exhibit a central fiber comprising the multicore fiber which is shown in the Figures to emit light along the axis of the fiber (forward). As will be appreciated, such emission—while desirable in certain applications—is not necessary in all. Additionally, it is noted that the individual fibers comprising the multicore fiber do not all have to be the same. In particular, a combination of different fibers may be employed where—for example—some fibers are single mode while others are multimode fibers. Further, some of the fibers may be employed for imaging and sensing while others may be used for invasive or other therapeutic procedures or other diagnostic modalities. 
     As will be appreciated, in many optical systems, including OCT systems, there is a tradeoff made between the measurement range (e.g. the confocal parameter or 2× the Rayleigh Range) and the resolution at the beam waist. Generally, the tighter the beam waist, the higher the lateral resolution but the shorter the measurement range. One of the attractive features of PIC and other integrated optical designs is that by using the high-resolution lithographic techniques for manufacturing the PICs one can make very complex amplitude and/or phase masks in the surface gratings. 
     For example, Bessel beam generation, and other similar depth-of-filed extension techniques, may be designed into the phase mask to provide extended measurement range for a given lateral resolution. Such depth-of-field extension techniques, can be designed into the surface grating couplers using PIC design tools and are advantageously applicable embodiments according to the present disclosure shown and described. 
     As noted previously, one of the advantages of using a multicore fiber is that it allows several simultaneous beams to be guided up/down the endoscope for sensing, imaging, and ranging. One application of such an endoscope acquires several readings of an interior dimensions of a lumen and/or measures properties of interest of the lumen wall. While a single core configuration having a distal motor or a rotating fiber (as is known in SS-OCT cardiovascular and gastroenterology systems) can produce a continuous measurement of a lumen, such an approach comes with noted disadvantages including increased cost, size, and complexity of the endoscopic probe. Multicore fiber configurations according to the present disclosure have the potential to be smaller and therefore be employed into tighter lumens and medical devices (e.g. imaging needles). 
     Of further advantage, it is possible to include additional measurement or imaging capability to multi-core fiber endoscopes constructed according to the present disclosure. Turning now to  FIG. 11  there is shown a multicore fiber endoscope  1100  including a pull-back (or push-back) and/or torsional element  1150  Such an element allows for the manual and/or automated pulling-back (or pushing forward) of the distal end of the endoscope along the axis of the endoscope body and lumen in which it is positioned. In this manner, optical measurements may be made along the axis of the lumen which advantageously allows several two-dimensional images to be obtained. Alternatively, and in another illustrative embodiment, the entire multi-core fiber may be rotated back and forth (to and fro) as to radially scan the distal end of the endoscope and therefore the lumen/sample. This advantageously allows additional regions of the sample to be measured. It is also contemplated to have both pullback capability and twisting back and forth capability. 
     Note further that illustrative embodiments according to the present disclosure have depicted a number of ways to image light from a multicore fiber into a sample. There are of course other methods and combinations of the methods shown that may be implemented and are contemplated herein. Additionally, there are also many other aspects of a fiber endoscope design known in the art while not specifically shown and described. Such aspects include protective jackets (metal or plastic), torque cables, markers for x-ray, CT, or MM imaging, etc. With this disclosure and teachings in place, those skilled in the art will readily understand and appreciate that there are numerous applications of structures and techniques according to the present disclosure in addition to SS-OCT and endoscopes including—but not limited to—catheters, guidewires, imaging needles, laparoscopes, and other medical and non-medical devices. 
     At this point those skilled in the art will readily appreciate that while the methods, techniques and structures according to the present disclosure have been described with respect to particular implementations and/or embodiments, those skilled in the art will recognize that the disclosure is not so limited. Accordingly, the scope of the disclosure should only be limited by the claims appended hereto.