Patent Publication Number: US-11640027-B2

Title: Enhancing imaging by multicore fiber endoscopes

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/631,750, filed Jan. 16, 2020 as a U.S. National Phase Application of PCT International Application No. PCT/IL2018/050779, International Filing Date Jul. 16, 2018, claiming the benefit of and priority to U.S. Provisional Patent Application No. 62/533,155, filed Jul. 17, 2017, each of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to the field of endoscopy, and more particularly, to multicore fiber endoscopes. 
     2. Discussion of Related Art 
     Endoscopes in various configurations allow efficient treatment of a range of medical problems, as well as means for manipulating different situations with limited access. Endoscope operations are challenging in that illumination, detection and treatment are confined to long and narrow operations modes. Fiber optics technology is a central enabler for such techniques, and fiber-based endoscope experience continuous improvements. 
     SUMMARY OF THE INVENTION 
     The following is a simplified summary providing an initial understanding of the invention. The summary does not necessarily identify key elements nor limit the scope of the invention, but merely serves as an introduction to the following description. 
     Various aspects of the present invention provide multicore fibers and endoscope configurations, along with corresponding production and usage methods, which any of adiabatically tapered proximal fiber tips and/or proximal optical elements, for improving the interface between the multicore fiber and the sensor, photonic crystal fiber configurations which reduce the attenuation along the fiber, jointed rigid links configurations which reduce attenuation while maintaining required flexibility and optical fidelity, image processing methods, spectral multiplexing approaches, which increase the information content of the radiation delivered through the fibers and endoscope, as well as fiber-based wave-front sensors. 
     These, additional, and/or other aspects and/or advantages of the present invention are set forth in the detailed description which follows; possibly inferable from the detailed description; and/or learnable by practice of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of embodiments of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout. 
       In the accompanying drawings: 
         FIG.  1 A  is a high level schematic illustration of a multicore imaging fiber having a proximal tapered end, according to some embodiments of the invention. 
         FIG.  1 B  is a high level schematic illustration of a multicore imaging fiber having a proximal optical element, according to some embodiments of the invention. 
         FIG.  2    is a high level schematic illustration of a cross section of a multicore photonic crystal fiber, according to some embodiments of the invention. 
         FIG.  3    is a high level schematic illustration of a hybrid endoscope, according to some embodiments of the invention. 
         FIGS.  4 A- 4 D  are high level schematic illustrations of an endoscope and illumination sources thereof, according to some embodiments of the invention. 
         FIGS.  5 A- 5 C  are high level schematic illustrations of endoscopes and illumination sources thereof, configured to implement wavelength multiplexing super resolved imaging, according to some embodiments of the invention. 
         FIG.  6    is a high level schematic illustration of endoscopes with multimode, multicore illumination fibers, according to some embodiments of the invention. 
         FIGS.  7 A and  7 B  are high level schematic illustrations of endoscopes with multicore fibers with multimode cores having tens of modes, according to some embodiments of the invention. 
         FIGS.  8 A and  8 B  are high level schematic illustrations of endoscopes with enhanced field of view, according to some embodiments of the invention. 
         FIGS.  9 A- 9 C  are high level schematic illustrations of longitudinally-sensing endoscopes, according to some embodiments of the invention. 
         FIG.  10    is a high level schematic illustration wave-front sensing endoscopes, according to some embodiments of the invention. 
         FIG.  11    is a high level flowchart illustrating a method, according to some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, various aspects of the present invention are described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well known features may have been omitted or simplified in order not to obscure the present invention. With specific reference to the drawings, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. 
     Before at least one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments that may be practiced or carried out in various ways as well as to combinations of the disclosed embodiments. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
     Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “processing”. “computing”, “calculating”, “determining”, “enhancing”, “deriving” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulates and/or transforms data represented as physical, such as electronic, quantities within the computing system&#39;s registers and/or memories into other data similarly represented as physical quantities within the computing system&#39;s memories, registers or other such information storage, transmission or display devices. Any of the disclosed modules or units may be at least partially implemented by a computer processor. 
     Multicore fibers and endoscope configurations are provided, along with corresponding production and usage methods. Various configurations include an adiabatically tapered proximal fiber tip and/or proximal optical elements for improving the interface between the multicore fiber and the sensor, photonic crystal fiber configurations which reduce the attenuation along the fiber, image processing methods and jointed rigid links configurations for the endoscope which reduce attenuation while maintaining required flexibility and optical fidelity. Various configurations include spectral multiplexing approaches, which increase the information content of the radiation delivered through the fibers and endoscope, and configurations which improve image quality, enhance the field of view, provide longitudinal information. Various configurations include fiber-based wave-front sensors. Many of the disclosed configurations increase the imaging resolution and enable integration of additional modes of operation while maintain the endoscope very thin, such as spectral imaging and three dimensional imaging. It is noted that while the following refers to tissue as the imaging object, any other element, object, surface or part may be imaged by the disclosed fibers and endoscopes, and the term “tissue” is not to be taken as limiting the invention in any way. It is further noted that configurations are disclosed separately to merely to simplify the respective explanations, and configurations may be combined to for endoscopes with two or more of the configurations which may be illustrated in different figures and/or disclosed in different embodiments, 
     Tapered End 
       FIG.  1 A  is a high level schematic illustration of a multicore imaging fiber  100  having a proximal tapered end  120 , according to some embodiments of the invention. Multicore imaging fiber  100  receives radiation  95 A from imaged tissue  90  (as a non-limiting example) at a distal end  100 A of fiber  100 , transmits the radiation throughout the fiber&#39;s length and delivers radiation  95 B to a sensor  80  at a proximal end  100 B of fiber  100 . Multicore imaging fiber  100  may comprise a large number of cores  110  within a common cladding and/or multiple cladding structures  112 , e.g., multicore imaging fiber  100  may comprise tens or hundreds of thousands cores  110 .  FIG.  1 A  illustrates schematically only few cores  110  for explanatory purposes. Certain embodiments comprise endoscopes comprising multicore imaging fiber  100 . 
     For example, multicore imaging fiber  100  may comprise at least 10,000 cores  110  (possibly 50,000 cores, 100,000 cores or any intermediate or other number) with a common cladding  112  and have proximal tip  100 A configured to deliver image radiation  95 A from tissue  90  at distal end  100 B of fiber  100 . Image radiation  105 A may be confined to cores  110 A (having a diameter d 1 . e.g., between 0.5-2 μm, between 1-1.5 μm etc.) and cores  110 A may be interspaced within fiber cross-sectional area A 1  (having a diameter D 1 , with cores  110 A interspaced, L 1 . e.g., by several μm. e.g., 3-5 μm) to prevent cross-talk between cores  110 A. Cross section  100 A may be prevalent from distal end  100 A and throughout all of fiber  100 , but for tapered end  120  thereof, and is illustrated to show each core  110 A surrounded by cladding material or structures  112 A and with image radiation  105 A confined to core  110 A. It is noted that cores  110  may have a varying degree of order, and may be dispersed through the fiber cross section with a certain degree of randomness. The interspacing, or pitch L 1  between cores  110  may be understood as average or median interspacing. 
     Proximal tip with tapered end  120  may be very short, e.g., shorter than e.g., 2 cm, lcm, 0.5 cm etc. as indicated by the length T. and be adiabatically tapered to reduce the fiber cross-sectional area (e.g., from fiber diameter D 1  and cross-sectional area A 1  to a fiber diameter D 2  and cross-sectional area A 2 ) and to reduce the core diameter (e.g., from core diameter d 1  of cores  110 A to a core diameter d 2  of cores  110 B, and correspondingly pitch L 1  to reduced pitch L 2 ) by a factor of at least 3, allowing image radiation  105 B to exit narrowed cores  110 B. Proximal tip with tapered end  120  may be further configured to deliver image radiation  105 B as radiation  95 B to an adjacent sensor  80 , with an effective image area to sensor area ratio (A 3 :A 2 ) which is much larger than the ratio of original fiber cross sectional area to sensor area ratio (A 3 :A 1 ). For example, effective image area to sensor area ratio (A 3 :A 2 ) may be at least 1:3, 1:2 or even larger, possibly approaching 1:1. The larger ratio of image area to sensor area enables any of: using smaller sensors  80  (as sensor coverage by the image is more efficient), using large sensors  80  more efficiently (with more pixels sensing image data) and/or using simpler sensors  80  (without gaps between pixels, as interspaces between cores  110 A are reduced and radiation  105 B may be delivered over most or all of the tapered end&#39;s cross sectional area A 2 ). Radiation  105 B may exit smaller cores  110 B at tapered end  120  to deliver radiation  95 B to sensor  80  over an area which is larger than the cumulative area of cores  110 B, while avoiding crosstalk due to the shortness of proximal end  100 B and due to the fact that tapered end  120  is mechanically fixed and cannot bend. 
     For example, in certain non-limiting embodiments, an effective area of adjacent sensor  80 , which receives image radiation  95 B from proximal tip  120 , may be at least 50% of the total area (A 3 ) of adjacent sensor  80 , possibly even at least 70%, 80% or 90% thereof. In certain embodiments, proximal tip  120  may be is shorter than 0.5 cm and/or stiff. In certain embodiments, reduced fiber cross-sectional area A 2  may be smaller than 0.1 mm 2 , reduced core diameter d 2  may be smaller than smaller than the optical wavelength in order to cause light to get out of the core and to travel in the cladding area (e.g., smaller than 0.5 μm-500 nm, smaller than 0.4 μm-400 nm, or other values.), and/or reduced core pitch L 2  may be smaller than 2 μm. 
     Advantageously, disclosed designs improve sensor efficiency using multicore fibers. Applying sensing array  80  to present multicore fibers having their proximal end similar of distal end  100 A—requires the imaging camera to have enough pixels to sample cores  110 A as well as cladding  112 A between cores  110 A. Moreover, as the camera samples the space uniformly but cores  110 A are not completely ordered, regions between cores  110 A require waste of camera hardware, namely the sensors have a number of pixels which is much larger than the number of cores  110 A in the fiber. In disclosed embodiments however, not only is cross-sectional area  100 B much smaller than cross-sectional area  100 A, but the spaces between cores  110 B are significantly reduced or even avoided, to deliver radiation  95 B over most or all of cross-sectional area  100 B adjacent to sensor  80  because due to the tapering the light propagating in the tapered section is not confined any more to the core region but rather leaks out to the cladding area. It is noted that while the spreading of radiation  105 B beyond narrowed cores  110 B provides more efficient use of sensor  80 , it does not result in crosstalk between cores  110 B and does not limit the bending of fiber  100 , as proximal tapered end  120  is very short (and may further be made stiff to prevent bending). For example, in fiber  100  having 80,000 cores  110 , sensors  80  may have only one or few 100,000 pixels to detect all radiation  95 B.  95 A, while prior art fibers (having proximal cross-section  100 A) may require several megapixels to detect all radiation from tissue  90 . 
     Optical Reduction of the Effective Fill Factor 
       FIG.  1 B  is a high level schematic illustration of a multicore imaging fiber  100  having a proximal optical element  122 , according to some embodiments of the invention. Multicore imaging fiber  100  receives radiation  95 A from imaged tissue  90  (as a non-limiting example) at distal end  100 A of fiber  100 , transmits the radiation throughout the fiber&#39;s length and delivers radiation  95 B to sensor  80  at proximal end  100 B of fiber  100 . Multicore imaging fiber  100  may comprise a large number of cores  110  within a common cladding and/or multiple cladding structures  112 . e.g., multicore imaging fiber  100  may comprise tens or hundreds of thousands cores  110 . Sensor  80  may be part of a detector  85  connected to a processing unit  180  configured to process delivered radiation  95 B and form images therefrom. 
       FIG.  1 B  illustrates schematically only few cores  110  for explanatory purposes. Certain embodiments comprise endoscopes comprising multicore imaging fiber  100 . 
     For example, multicore imaging fiber  100  may comprise at least 10,000 cores  110  (possibly 50,000 cores, 100,000 cores or any intermediate or other number) with a common cladding  112  and have proximal tip  100 A configured to deliver image radiation  95 A from tissue  90  at distal end  100 B of fiber  100 . Image radiation  105 A may be confined to cores  110 A (having a diameter d 1 , e.g., between 0.5-2 μm, between 1-1.5 μm etc.) and cores  110 A may be interspaced within fiber cross-sectional area A 1  (having a diameter D 1 , with cores  110 A interspaced, L 1 , e.g., by several μm, e.g., 3-5 μm) to prevent cross-talk between cores  110 A. Cross section  100 A may be prevalent from distal end  100 A and throughout all of fiber  100  and is illustrated to show each core  110 A surrounded by cladding material or structures  112 A and with image radiation  105 A confined to core  110 A. It is noted that cores  110  may have a varying degree of order, and may be dispersed through the fiber cross section with a certain degree of randomness. The interspacing, or pitch L 1  between cores  110  may be understood as average or median interspacing. 
     Proximal optical element  122  may be set between distal fiber end  100 B and sensor  80  and be configured to collect image radiation from cores  110  into a smaller area than the area of distal fiber end  100 B, to effectively reduce the fill factor of radiation  95 B reaching sensor  80  (the fill factor may be seen as the ration between the image radiation delivering cross sectional area and the total cross sectional area of fiber  100 ). For example, proximal optical element  122  may comprise one or more prism(s) and/or grating(s) configured to shift closer image radiation from individual cores so that image radiation  95 B reaching sensor  80  is at a smaller effective pitch than L. In certain embodiments, delivered radiation  95 B may be shifted in a way that mixing the spatial order of cores  110 , and detector  85  and/or processing unit  180  may be configured to re-arrange shifted core image radiation to form a correct image. For example, prism(s) with multiple orientations or Dammann grating(s) (see also  FIG.  5 C  for an analogous solution) may be used to implement proximal optical element  122 . For example, proximal optical element  122  may be configured to reduce, optically, a fill factor of cores  110  in the fiber cross section by re-orienting the delivered image radiation from cores  110  to fill a smaller area on adjacent sensor  80  with respect to the area of fiber cross section  100 B, e.g., to enable using sensor  80  with an area of a third or less of fiber cross section  100 B (e.g., the area delimited by cores  110 ). 
     It is noted that throughout the disclosure, the term “distal” is used to refer to the ends and associated parts of fiber  100  and/or endoscope  150  which are far from the endoscope&#39;s interface (with the detector or the eye of the user) and close to the imaged tissue and to its surroundings, while the term “proximal” is used to refer to the ends and associated parts of fiber  100  and/or endoscope  150  which are close to the endoscope&#39;s interface (with the detector or the eye of the user) and far from the imaged tissue and to its surroundings. Concerning cores  110 , it is noted that cores  110  may support a single radiation mode, or in certain embodiments, cores may be multimodal, and support more than one radiation mode, as determined by the numerical aperture (NA) and diameter of cores  110  and the delivered wavelength. 
     It is further noted that fiber  100  and/or endoscope  150  in any of the disclosed embodiments may be used for near or far filed imaging, or any imaging position therebetween. Near field imaging refers to the formation of an image (of imaged objects, tissues and/or their surroundings) at the distal end of the endoscope fiber, typically at the fiber&#39;s tip. The image is then typically transferred through the fiber to the detector, possibly through proximal optical elements. Far field imaging refers to the formation of a Fourier transform of imaged objects, tissues and/or their surroundings at the distal end of the endoscope fiber (e.g., the distal end of the endoscope fiber may be at the aperture or pupil plane of the endoscope&#39;s optical system), typically at the fiber&#39;s tip. The image of the imaged objects, tissues and/or their surroundings may be formed at the proximal end of the endoscope fiber, typically at the fiber&#39;s proximal tip or directly on the detector, possibly through proximal optical elements. Near and/or far field imaging may be implemented by various embodiments of optical systems, e.g., direct imaging without any optical elements between the imaged object or tissue and the fiber tip or imaging through any optical element(s) (e.g., lenses). Optical elements may be positioned between the imaged object or tissue and the distal fiber tip, with the distal fiber tip being at least approximately at the Fourier plane (for far field imaging, also termed aperture plane and pupil plane in different contexts) or at the focus plane (for near field imaging, also termed image plane in different contexts) of the optical elements. Intermediate imaging may also be applicable for fiber(s)  100  and/or endoscope(s)  150 , with a processing unit being configured to determine the spatial configuration (e.g., relative positions of the Fourier and/or image planes with respect to the fiber&#39;s distal tip) and process the delivered radiation from the tissue respectively. 
     Improving the Resolution 
     In certain embodiments, endoscope  150  may be operated to provide far field imaging, with distal tip  100 A of fiber  100  being at the Fourier plane of the imaging system (deliver Fourier transform of imaged tissue as the delivered radiation), with the output resolution at detector  85  determined by the number of the pixels in the delivered radiation (rather than by the number of cores  110  as in near field imaging), because the Fourier domain is sparse and a small number of cores is sufficient to transmit the spectral information (especially in cases cores  110  are not periodically ordered and thus the sampling of the Fourier is sparse and not uniform/periodic which is even better for properly representing the information of the object that is to be imaged). In certain embodiments, sparse sampling of the Fourier plane, by setting distal end  100 A of fiber  100  at a corresponding position with respect to tissue  90  (far field imaging) may be used to improve the resolution of resulting images. e.g., by implementing compressed sensing algorithms, with respect to near field imaging, by overcoming the difficulty of imaging tissue  90  that corresponds to gaps between cores  110  (see e.g., pitch L 1  in  FIGS.  1 A and  1 B ). 
     Photonic Crystal Fibers 
       FIG.  2    is a high level schematic illustration of a cross section of a multicore photonic crystal fiber  100 , according to some embodiments of the invention. Certain embodiments comprise endoscopes comprising multicore imaging fiber  100 . 
     In certain embodiments, multicore fiber  100  may have a photonic crystal structure composed of multiple air holes  101  in at least two types: core-type air holes  110  interspaced within the fiber cross-sectional area at a specified core-pitch P 1  selected to confine image radiation  105  within core-type air holes  110 , and cladding air-holes  112  (between core-type air holes  110 ) which are interspaced within the fiber cross-sectional area at a specified cladding-pitch P 2  selected to prevent cross-talk between core-type air holes  110 . The core diameters (denoted by D&#39;s for core-type air holes  110  and cladding air-holes  112 ) may also be configured to support image radiation confinement within core-type air holes  110  (e.g., the diameter of core-type air holes  110  may be between 0.7-1 μm, e.g., 0.9 μm). 
     Advantageously, using air holes  101  to provide core-type air holes  110  reduces the attenuation of radiation  105  travelling through cores  110  which are made e.g., of polymer material such as poly(methyl methacrylate) (PMMA), polystyrene (PS) etc. Cladding air-holes  112  are designed to form a periodic structure around each core-type air hole  110  to confine radiation  105  therein due to the spatial periodicity of the cladding structure rather than due to differences in the refraction index as in polymer cores. In effect, multicore fiber  100  may be seen as providing multicore photonic crystal fibers for the first time. For example, in certain embodiments, multicore fiber  100  may have an attenuation coefficient which is smaller by e.g., a factor of 2 per length of 10 cm than a comparable multicore fiber having a same number of polymer cores. 
     Rigid Links and Joints Structure 
       FIG.  3    is a high level schematic illustration of a hybrid endoscope  150 , according to some embodiments of the invention. Endoscope  150  may comprise distal multicore fiber  100  optically coupled to a plurality of rigid image-relay elements  130 , interconnected by a respective plurality of joints  140 . 
     Distal multicore fiber  100 , e.g., an imaging fiber, may be configured to receive image radiation  95 A from tissue  90  at distal end  100 A thereof and deliver the image radiation to proximal end  100 B of proximal multicore imaging fiber  100 . It is notes that rigid image-relay elements  130  are made of materials which are more transparent in the respective wavelength range than core material of fiber  100 , providing overall reduction of attenuation along endoscope  150  (e.g., rigid image-relay elements  130  may be made of glass while fiber cores  110  may be made of polymers which are less transparent). For example, rigid image-relay elements  130  may be GRIN (graded index) rods and/or lenses made of glass. 
     Rigid image-relay elements  130  interconnected by respective plurality of joints  140 , may be configured to deliver radiation travelling through fiber  100  as radiation  95 B to a detector  85  (e.g., sensor  80  with corresponding optical element(s)). A distal one of rigid image-relay elements  130  may be connected via a corresponding joint  140 A to proximal end  100 B of distal multicore imaging fiber  100 . 
     Joints  140 A,  140  may be configured to preserve the delivered image radiation from proximal end  100 B of distal multicore imaging fiber  100  upon angular movements  136 A of rigid image-relay elements  130  with respect to each other, to deliver the image radiation at a proximal end  100 C of endoscope  150 . 
     Optionally, endoscope  150  may further comprise a proximal multicore imaging fiber  100 - 1  connected to a proximal one of rigid image-relay elements  130  via corresponding joint  140 B, and configured to deliver the image radiation from proximal rigid image-relay element  130  to detector  85 . 
     Joints  140 ,  140 A.  140 B may be designed according to the illustrated design principles, as mechanical-optical joints which preserve the imaging condition between adjacent rigid image-relay elements  130  (as well as thereto and therefrom, relating to joints  140 A.  140 B to fibers  100 ,  100 - 1 , respectively) so that light is continuously coupled from one link to the next, at different angles of rotation of rigid image-relay elements  130 . It is emphasized that in endoscope  150 , imaging is maintained as well as a certain degree of flexibility between rigid elements  130 , which may suffice for most of the length of endoscope  150 . Multicore fibers  100  may be used only at imaging end  100 A of endoscope  150 , and possibly at its detector end  100 C. Such configurations may be used to yield long endoscopes  150 , without limitations resulting from the length of multicore fiber  100  (e.g., attenuation, price, optical performance etc. which at least partly are due to light attenuation through polymer cores  110 ). Endoscope  150  may further comprise sleeves (not shown) to support the disclosed structure mechanically. 
     In certain embodiments, at least some, or all of rigid image-relay elements  130  may comprise glass GRIN links and joints  140  may comprise spherical ball lenses  135  positioned within mechanical joints  136  which are connected mechanically to adjacent rigid image-relay elements  130  or fibers  100 ,  100 - 1  (for joints  140 ,  140 A.  140 B, respectively). Spherical ball lenses  135  may be positioned to preserve, proximad (in proximal direction), the delivered image radiation in any angular relation between adjacent rigid links  130 . For example, spherical ball lens  135  may be positioned in the center of mechanical sliding ring  136  in distances fulfilling the imaging condition between an exit face  130 A of one link  130  positioned on one side of joint  140  and an entrance face  130 B of next adjacent link  130  positioned on the other side of joint  140 . Alternatively, optical elements  135  may be used in place of spherical ball lenses  135 . Optical elements  135  such as spherical ball lens  135  may be configured to create coupling of light from one link  130  to the next link  130  for any possible angle (or angles within a specified range which is limited mechanically) created between links  130 . 
     Spectral Multiplexing 
       FIGS.  4 A- 4 D  are high level schematic illustrations of endoscope  150  and illumination sources  160  thereof, according to some embodiments of the invention. 
     Certain embodiments comprise endoscopes  150  comprising an illumination source  160  (see  FIG.  4 A ), configured to deliver illumination  65  (e.g., via one or more illumination fiber(s)  60 ) at a specified plurality of distinct wavelengths, detector  85  comprising a spectrometer  162  (in addition to sensor  80  and optionally optical elements  82 ) configured to decode detected radiation  95 B in the specified plurality of distinct wavelengths, multicore imaging fiber  100  configured to deliver, through cores  110  to detector  85 , image radiation  95 A received from tissue  90  illuminated by illumination  65  from illumination source  160 , and processing unit  180  configured to derive, from the decoded detected image radiation of each of cores  110 , image data corresponding to the specified plurality of distinct wavelengths. Applying illumination at the plurality of distinct wavelengths, simultaneously or sequentially and analyzing received images with respect to the plurality of wavelengths for each core  110 , is referred to herein as spectral, or wavelength, multiplexing. 
     For example, as illustrated schematically in  FIG.  4 B , multiple input fibers  162  may be configured to deliver the distinct wavelengths (denoted λ 1  . . . λ N ) as narrowband radiation to a multiplexer  165 , e.g., a wavelength-division multiplexer (WDM), which combines the radiation into illumination  65 , delivered through illumination fiber  60  to tissue  90 . Narrowband input fibers  162  may thus be coupled through multiplexer  165  to deliver multiple distinct wavelengths simultaneously or temporally separated. Correspondingly, as illustrated schematically in  FIG.  4 C , spectrometer  170  may receive radiation  95 B from multicore fiber  100  and separate it into the distinct wavelengths  172  (denoted λ 1  . . . λ N ), by a de-multiplexer  175 , e.g., a wavelength-division multiplexer/de-multiplexer (WDM) (possibly even the same as WDM  165 ). The resulting narrowband radiation channels  172  may be delivered to sensor(s)  80 . e.g., via optics  82 , and the resulting data may be delivered to processing unit  180  which may be configured to derive multiple data channels from each core  110 . Wavelength multiplexing may thus be configured to increase the information content passed through each core  110  significantly, possibly by factors of tens, hundreds or even thousands, depending on the number of the distinct wavelengths and the ability to crowd narrowband wavelength ranges within the spectrum used for imaging (e.g., in the visible range of ca. 400-700 nm, bandwidths of 3 nm provide N=100 distinct wavelengths denoted λ 1  . . . λ 100 ). 
     Disclosed wavelength multiplexing may be used to enhance resolution of endoscope  150  and/or to incorporate additional functionalities or modalities such as OCT (optical coherence tomography), spectroscopical analysis etc. in addition to imaging—to implement multi-functional micro-endoscope  150 . For example, an OCT application may be used to extract depth information for internal tissues  90 . In certain embodiments, endoscope  150  may be configured to implement Fourier domain OCT with illumination source  160  being configured to have spectral scanning capability to enable capturing and processing a plurality of 2D images at the range of scanned wavelengths by full field Fourier domain OCT application. In certain embodiments, illumination source  160  may be configured to be spectrally tunable, and images at the plurality of wavelengths may be captured and assembled by processing unit  180  after each (time scanning) of the range of wavelengths, to provide a 2D spatial image with spectral information per each pixel. In certain embodiments, various spectral ranges may be scanned, e.g., fluorescence bands for fluorescent microscopy or other specific ranges—further enhancing the versatility and number of functionalities of endoscope  150 . 
     Multicore imaging fiber  100  and endoscope  150  may be implemented as any of the embodiments disclosed herein, e.g., as multicore imaging fiber  100  having a proximal tapered end  120 , as multicore photonic crystal fibers  100  and/or as endoscope  150  with distal multicore fiber  100  optically coupled to jointedly-interconnected rigid image-relay elements  130 . 
       FIG.  4 D  is a high level schematic illustration of temporal spectral multiplexing in illumination source  160 , according to some embodiments of the invention. Illumination source  160  may comprise a fiber laser  162  comprising a broadband Bragg filter mirror  161  for a range of the specified plurality (N) of distinct wavelengths (denoted λ 1 -λ N ), a controllable 1-to-N switch  164  connected to N narrowband Bragg filter mirrors  167  (denoted λ 1  . . . λ N ), for the corresponding distinct wavelengths, each of narrowband Bragg filter mirrors  167  designed to reflect only the corresponding distinct wavelength. 1-to-N switch  164  may be controlled electrically (or mechanically, optically etc.). Illumination source  160  may further comprise a pumped gain in-fiber medium  163  connected between Bragg filter mirror  161  and controllable 1-to-N switch  164  with connected N narrowband Bragg filter mirrors  167 . Illumination source  160  may further comprise multiplexer  165  (e.g., WDM) configured to combine illumination radiation from N narrowband Bragg filter mirrors  167  and provide illumination  65 , delivered through illumination fiber  60  to tissue  90 —simultaneously or in a temporally tunable manner with respect to the range or sub-ranges of the distinct wavelengths. 
     It is emphasized that the configuration illustrated in  FIG.  4 D  may also be reversed to be used as spectrometer  170 , as shown schematically in  FIG.  4 C  with respect to  FIG.  4 B , for example, spectrometer  170  configured to provide narrow band imaging detection. In certain embodiments, narrow band imaging detection may be used for improved diagnosis of cancerous tissues. 
     Alternative or complementary implementations of spectral multiplexing may comprise a plurality of wavelength specific beam splitters or gratings, configured to provide the multiple narrowband spectral ranges at λ 1  . . . λ N . 
     Spectral multiplexing may be used to enhance any of various characteristics of fiber(s)  100  and endoscope(s)  150  such as resolution, field of view, working distance, depth of focus, 3D capability etc.—by multiplying the amount of information delivered through each core  110  by a factor of 10, 100 or even 1000 (depending on the spectral range and spectral resolution). These enhancements may be carries out with respect to one or more fiber modules in endoscope  150  and/or replace the need to use several fiber modules in the endoscope (fiber modules referring to associated fibers  100  which handle image delivery cooperatively). Spectral multiplexing may also be used to implement super resolved imaging achieved by various means, utilizing the multiple inputs per core  110  which correspond to the multiple wavelengths. 
     Wavelength Multiplexing Super Resolved Imaging 
       FIGS.  5 A- 5 C  are high level schematic illustrations of endoscope  150  and illumination sources  160  thereof, configured to implement wavelength multiplexing super resolved imaging, according to some embodiments of the invention. Endoscope  150  may be configured to have broadband illumination source  160 , e.g., a white light source, and comprise a spatial encoder  166  configured to split the broadband illumination spatially, delivering different narrowband wavelength ranges to different locations on tissue  90  (illustrated schematically in  FIG.  5 A  as pattern  66 ,  FIG.  5 B  illustrates a non-limiting example for pattern  66 ). Spatial encoder  166  may comprise e.g., dispersive optical elements such as one or more gratings, transmissive optical elements such as one or more prisms and/or may possibly comprise de-multiplexer  175  as disclosed above for separating individual wavelengths λ 1  . . . λ N  from the broadband illumination in combination with elements such as DLP (digital light processing elements), mirror arrays etc.—and delivering different λ 1  . . . λ N  to different locations on tissue  90 . 
     For example, the wavelength range λ 1  . . . λ N  may be scanned at a folded linear pattern  66  exemplified in  FIG.  5 B  to cover given region  90 A with different locations illuminated by different wavelengths λ 1  . . . λ N . The spatio-spectral resolution may be configured to cover larger region  90 A with larger locations per wavelength, or smaller region  90 A with smaller locations per wavelength; or alternatively or complementarily, the number of distinct wavelengths (N) and/or the wavelength range (λ 1 , . . . λ N ) may be configured to increase or reduce the spectrally-encoded spatial resolution. 
     Illumination  65  may therefore be configured to be spatially encoded by wavelength, illuminating each location on tissue  90  at a different wavelength, possibly according to a specified pattern  66 .  FIG.  5 C  illustrates schematically a non-limiting example for the optical implementation of illuminating pattern  66 , namely by using a first grating  168  for implementing the spectral raster splitting and a second Dammann-like grating  169  configured to replicate the spectral raster encoding to fully illuminate the full field of view of tissue  90 , illuminating pattern  66  on all tissue regions  90 A of tissue  90  (illustrated in a highly schematic manner in  FIG.  5 C ). Spatial encoder  166  may be configured to use white light illumination  64  with grating  168 ,  169  to deliver multiple illuminating patterns  66  to all tissue regions  90 A of tissue  90 , with radiation from each tissue region  90 A delivered to a different core  110 . Encoded radiation  65  may be delivered to tissue  90  through one or more optical element(s)  168 A, e.g., configured to delivered focused encoded radiation  65 , to project pattern  66  of tissue regions  90 A (with the distance of optical element(s)  168 A from tissue  90  being equal to the focus length, F, of optical element(s)  168 A). 
     It is emphasized that fiber  100  may be configured to have sparse cores  110  (see  FIGS.  1 A,  1 B ), with some or each of cores  110  receiving radiation  105 A from region  90 A illuminated by full pattern  66  (or possibly a part thereof) so that the region between any two cores  110  may be multiplexed with wavelengths λ 1  . . . λ N  to make each spatial pixel guided in core  110  include actually many spatial points of information encoded by the different wavelengths according to pattern  66 . The resulting is image, analyzed by spatial decoder  176 , may therefore have much more spatial pixels of information than the number of cores  110  (e.g., maximally N times the number of cores). 
     Radiation  95 A from tissue  90  may therefore be likewise spatio-spectrally encoded, and multicore fiber  100  may be configured to deliver radiation  95 A from a region  90 A (indicated schematically) of tissue  90 , including multiple wavelengths which encode different locations in region  90 A, to detector  85 . Each core  110  may therefore be configured (e.g., by focusing and de-focusing) to deliver spectrally-encoded information from multiple locations on tissue  90 , e.g., region  90 A). Detector  85  may comprise spectrometer  170  (e.g., implemented as disclosed above, using principles disclosed in  FIGS.  4 C and/or  4 D ) and a spatial decoder  176  configured to decode spatial reflectivity information from the spectral information—providing N data points for each core  110 . Therefore each core  110  may be used to deliver data for multiple pixels on sensor  80 , which correspond to the spectrally encoded region  90 A of tissue  90 . 
     Certain embodiments comprise endoscope  150  comprising illumination source  160  comprising spatial encoder  166 , configured to deliver illumination  65  at specified plurality of spatially-encoding distinct wavelengths λ 1  . . . λ N , with different wavelengths illuminating different locations on a tissue according to specified spatio-spectral pattern  66 ; detector  85  comprising spectrometer  170  and spatial decoder  176 , configured to decode detected radiation  95 B in specified plurality of distinct wavelengths λ 1  . . . λ N  according to specified spatio-spectral pattern  66 ; multicore imaging fiber  100  comprising cores  110  and configured to deliver ( 95 B), through cores  110  to detector  85 , image radiation  95 A received from tissue  90  illuminated by illumination source  160 , wherein at least some, or each core  110  is configured to deliver image radiation  95 A from a tissue region illuminated by specified spatio-spectral pattern  66 ; and processing unit  180  configured to derive, from spatio-spectrally decoded detected image radiation  95 B of single cores  110 , image data corresponding to specified plurality of distinct wavelengths λ 1  . . . λ N  from image radiation delivered by each core  110 . In certain embodiments, spatial encoder  166  may be implemented by first grating  168  configured to split broadband (e.g., white light) illumination into specified plurality of distinct wavelengths λ 1  . . . λ N  and second grating  169  configured to replicate the split broadband illumination to multiple patterns  66  corresponding to different regions of tissue  90 . 
     Speckle Reduction 
       FIG.  6    is a high level schematic illustration of endoscope  150  with a multimode, multicore illumination fiber  102 , according to some embodiments of the invention. In certain embodiments, illumination source  160  may be configured to deliver illumination  104  through single mode, multicore illumination fiber  102  to generate a speckle pattern  108  on tissue  90  which is more uniform and with larger speckles than different types of illumination, such as by a multimode illumination fiber with a large-area core. Single mode, multicore illumination fiber  102  may be configured to have about the same area as a single core multimode illumination fiber, to deliver a comparable amount of illumination or energy, while delivering the illumination through multiple cores having almost identical axial lengths of the respective light channels (due to the fabrication process). As the optical paths are practically identical, resulting speckle pattern  108  consists of large speckles (due to interference of light coming from the different cores which are small in dimensions) and is more uniform than single core multimode illumination. Advantageously, larger speckles require simpler speckle averaging and reduction and are therefore advantageous with respect to resulting image quality and required processing power. Moreover, cores of single mode, multicore illumination fiber  102  may be optimized with respect to core size and number to maximize the size of speckles in the illumination channel and in pattern  108 . Processing of the distal tip of illumination fiber  102  (e.g., may also be configured to enhance the coherence of illumination radiation delivered through different cores. 
     Processing unit  180  may be configured to identify and remove from delivered image radiation  95 B, speckle pattern  108  from illumination  104  by single mode, multicore illumination fiber  102 . 
     In certain embodiments, illumination may be implemented by one or more multimode multicore illumination fiber  102  with cores having a small number of multiple modes (e.g., 2-10 modes, or few tens, e.g., 10-30 modes) to provide additional flexibility in enhancing the uniformity of the speckle&#39;s formation altogether. 
     In certain embodiments, the shape of the illumination spot may be modulated to remove secondary speckle patterns, which depend on the spot size, by image processing. In certain embodiments, processing unit  180  may be configured to modulate, via illumination source  160 , illumination  104  with respect to at least one illumination spot parameter such as any of the shape, the diameter and/or the spatial modes of the illumination spot, e.g., according to a specified pattern. Processing unit  180  may be further configured to use the specified pattern to analyze resulting changes in the image of the illumination spot, as detected by detector  85 , and remove features of the image that fluctuate according to the specified pattern, as being related to secondary speckle patterns rather than to the imaged tissue. Advantageously, the contrast of the secondary speckle patterns may be significantly reduced and the image quality significantly improved. It is noted that removable secondary speckle patterns relate to features that may be modified by modulating illumination  104 , while some residual, primary speckle patterns may remain, such as features relating e.g., to the size of the diffuser (not shown) through which illumination  104  is performed. 
     Hybrid Imaging Fiber 
       FIGS.  7 A and  7 B  are high level schematic illustrations of endoscope  150  with multicore fiber  100  with multimode cores having tens of modes, according to some embodiments of the invention. Multicore fiber  100  may be configured to have a relatively small number of cores. e.g., several tens of modes (e.g., 10, 30, 50, 80) or a few hundred modes (e.g., 100, 150, 200) to implement a hybrid multicore fiber  100  in the sense that cores  110  are not single mode cores, but also not the customary multimode cores supporting many hundreds or thousands of modes. Complementarily, processing unit  180  may comprise a mode-decoupling module  184 , configured to remove distortions which may be caused by mode mixing at bends of hybrid multicore fiber  100 . Advantageously, while the use of multimode cores increases the information content of delivered radiation  95 B, endoscope  150  does not become as sensitive to bending of fiber  100  as are prior art fibers supporting thousands or even tens of thousands of modes, because the computational effort in removing the distortions due to mode mixing is tolerable, and achievable by available processors for such applications. 
     When fiber  100  is bended in operation, the different modes are mixed and the image guided by through them is distorted, yet the distortions may be inverted by applying e.g., deep learning neural network algorithms by mode coupling module  184 . Since every core  110  has small number of modes (e.g., tens of modes, much less than regular multimode fibers) the inversion of the modes-mixing due to bending may be carried out in real time. 
     In certain embodiments (see e.g.,  FIG.  7 B  as a non-limiting example), illumination source  160  may be configured to project a point (or any pattern)  67  on tissue  90  and processing unit  180  may be configured to estimate distortions by analyzing a distortion of illuminated point (or pattern)  67  in its image  97  (illustrated schematically) delivered through fiber  100  (within region  90 B of tissue  90  imaged by fiber  100  and indicated schematically as image  95 B). Mode coupling module  184  may be configured to enhance distortion cleaning calculations using the distortion estimation of illuminated point or pattern  67 . Advantageously, the overall resolution is significantly increased without adding too much overload to the processing power of processing unit  180 . For instance, in an illustrative non-limiting example, assuming a 450×450 micron fiber  100  with 20,000 cores  110 , with every core  110  having 100 modes, the received image ( 95 B) would have of  2 M pixels instead of only 20K pixels when cores  110  are single mode. Certain embodiments of hybrid fiber  100  avoid both the difficulty in producing single mode cores in the multicore fiber and the requirement for rigidity in multimode fibers (to prevent mixing of modes which not feasible to correct) to combine the benefits of information increase when using multimode multicore fibers with reduced sensitivity to bending due to the relatively small number of modes. 
     Field of View Enhancing and Zooming 
       FIGS.  8 A and  8 B  are high level schematic illustrations of endoscope  150  with enhanced field of view, according to some embodiments of the invention. In certain embodiments, endoscope  150  may be configured to have a large field of view without need to bend the distal tip of endoscope  150  and fiber  100 . It is noted that the common practice of bending the distal tip of endoscope  150  to increase the field of view requires a large volume near tissue  90  for handling the distal tip of endoscope  150  (due to the limited bending radius thereof), while in disclosed embodiments a much smaller volume is required to accommodate disclosed distal tip optical elements  190  which provide a large enhancement of the field of view. Distal tip optical elements  190  may be configured to be controllably displaceable with respect to each other (perpendicularly to their optical axes), with relative displacement  192 A configured to change the field of view ( 192 B) of fiber  100 , as illustrated schematically in  FIG.  8 A . 
     As illustrated schematically in  FIG.  8 B , in a non-limiting example, distal tip optical elements  190  may comprise a first lens  191 A with a negative focal length and a second lens  191 B with a positive focal length at distal tip  100 A of fiber  100 . Shifting  192 A of the relative position of lenses  191 A.  191 B may be configured to implement a tunable prism (see Equation 1 below). With distal tip optical elements  190 , shifting ( 192 A) lenses  191 A.  191 B with respect to each other increases the field of view ( 192 B) of endoscope  150  by increasing only the size of the distal tip of endoscope  150  without requiring to bend the distal tip of endoscope  150 , which requires large free volume available. Moreover, changing the distance ( 192 A) between lenses  191 A.  191 B may be configured to realize optical zooming (alternatively or possibly in addition to field of view enhancement). A mechanism  194  may be configured to perform shifts  192 A between lenses  191 A,  191 B (perpendicularly to their optical axes). For example, mechanical implementations of mechanism  194  may comprise controllably movable sleeves connected to lenses  191 A,  191 B and/or by springs similar to existing springs connected to the navigation shield (not shown) of endoscope  150  which may transfer a longitudinal shift  192 C of these elements to perpendicular shift  192 A of lenses  191 A,  191 B. 
     The following Equation 1 demonstrates that changing a relative shift between lenses  191 A,  191 B (left-hand expression in Equation 1) is equivalent to a prism (right-hand expression in Equation 1) with an angle that is proportional to the amount of the relative shift ( 192 A) between lenses  191 A,  191 B, with T(x) denoting the overall transmission expression of lenses  191 A.  191 B as illustrated schematically in  FIG.  8 B , having the same focal length F in absolute value (lens  191 A with −F and  191 B with +F), positioned sequentially with a relative transversal shift of 2Δx between them, and λ denoting the optical wavelength. 
     
       
         
           
             
               
                 
                   
                     T 
                     ⁡ 
                     
                       ( 
                       x 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         exp 
                         ⁡ 
                         
                           ( 
                           
                             
                               - 
                                
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             i 
                             ⁢ 
                             
                               
                                 
                                   ( 
                                   
                                     x 
                                     - 
                                     
                                       Δ 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       x 
                                     
                                   
                                   ) 
                                 
                                 2 
                               
                               
                                 λ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 F 
                               
                             
                           
                           ) 
                         
                       
                       ⁢ 
                       
                         exp 
                         ⁡ 
                         
                           ( 
                           
                              
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             i 
                             ⁢ 
                             
                               
                                 
                                   ( 
                                   
                                     x 
                                     + 
                                     
                                       Δ 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       x 
                                     
                                   
                                   ) 
                                 
                                 2 
                               
                               
                                 λ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 F 
                               
                             
                           
                           ) 
                         
                       
                     
                     = 
                     
                       exp 
                       ⁡ 
                       
                         ( 
                         
                           
                             4 
                             ⁢ 
                              
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             iΔ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             xx 
                           
                           
                             λ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             F 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     The overall transmission expression of the emulated prism (right-hand expression in Equation 1) reflects a prism positioned on the aperture plane of an imaging lens which shifts the obtained image by a factor of 2Δx which is exactly the relative shift between two lenses  191 A.  191 B. By tuning ( 192 A) the amount of shift (by changing Δx), the field of view of fiber  100  may be scanned, providing a larger field of view than merely the physical field of view of the given imaging lens. 
     Longitudinally-Sensing Endoscope 
       FIGS.  9 A- 9 C  are high level schematic illustrations of longitudinally-sensing endoscope  150 , according to some embodiments of the invention. In certain embodiments, endoscope  150  may be configured to have sensing capabilities along at least part of its length. For example, fiber  100  may be configured to have a plurality of peripheral radiation entrance locations  195  (“windows”), configured to allow radiation from the sides of fiber  100  to enter peripheral cores  110 C of fiber  100 , as illustrated schematically in  FIGS.  9 A- 9 C . Different peripheral cores  110 C may be configured along fiber  100  to receive radiation  95 C from different locations, e.g., from locations along a body conduit  91  such as a blood vessel, by corresponding configuration of peripheral radiation entrance locations  195  along endoscope  150 . Illumination fiber  60  may be configured to emit radiation  65 A along endoscope  150 , to improve or enable sensing reflected radiation  95 C from surrounding tissue  91  by fiber  100 . 
     For example, peripheral radiation entrance locations  195  may be arranged in circles  195 , each circle  195  being connected to a different peripheral core  110 C as illustrated schematically in  FIG.  9 B . Such configurations may be used to extract the distance of fiber  100  from tissue  91  along its longitudinal axis by extracting the readout of peripheral cores  110 C while internal cores  110  are used to imaging explained above. The longitudinal sensing may therefore be used to improve the control of endoscope  150 , avoiding lateral damage to tissue  91  and provide data concerning tissue  91 . In certain embodiments, peripheral radiation entrance locations  195  such as circles  195  may be formed by controlled twisting of the pre-form during its drawing to yield fiber  100 .  FIG.  9 C  provides a non-limiting example for such actual fiber  100  with slits  195  produced by the inventors. 
     Endoscope  150  may further comprise processing unit  180  configured to derive longitudinal data  198  from radiation  95 C delivered through the specified peripheral cores, in addition to image data  197  delivered from the distal tip of fiber  100 . Illumination fiber  60  may correspondingly be configured to emit radiation  65 A along endoscope  150 , in addition to illuminating  65  tissue  90  at the distal end thereof. Endoscope  150  may be further configured, e.g., via processing unit  180 , to derive indications for tissue  91  in proximity to fiber  100  along its length. 
     Wave-Front Sensing 
       FIG.  10    is a high level schematic illustration wave-front sensing endoscopes  150 , according to some embodiments of the invention. 
     Endoscope  150  may comprise illumination source  160 , configured to deliver illumination  65  at a specified plurality of spatially distinct locations on tissue  90 , detector  85  and multicore imaging fiber  100  comprising multimode cores  110  which are configured to support more than one radiation mode in core  110 , e.g., any of 2-6 modes, or possibly between 2-10 or 2-20 modes (configured, without being bound by theory, according to V=π·A·(NA/λ) 2 , with V the number of modes, A the cross sectional area of core  110 . NA the numerical aperture of core  110  and λ the corresponding wavelength, see the detailed analysis below). Multicore imaging fiber  100  may be configured to deliver, through multimode cores  110  to detector  85 , wave-front radiation  96  received from tissue  90  illuminated by illumination source  180 . Wave-front radiation  96  may be delivered though cores  110  without any optical elements at distal fiber tip  100 A, or as modified wave-front radiation  96 A which may be modified by optical elements  114  between distal fiber tip  100 A and tissue  90  (e.g., perforations, lenslets, Shack Hartmann interferometer configurations, pinholes array configurations, etc.). For example, optical elements  114  may be configured to focus sections of wave-front radiation % into cores  110 , to generate modified wave-front radiation % A in which phase information in wave-front radiation % is modified to spatial information (e.g., orthogonal focus point translations illustrated schematically by the double-headed arrow), which is delivered through cores  110  along multicore fiber  100 . Endoscope  150  may further comprise processing unit  180  configured to derive, from the delivered wave-front radiation % and/or % A, three dimensional (3D) image data  182  derived from wave-front radiation %, e.g., according to spot position changes associated with each or some of cores  110 . The spot position changes indicate the angle of the wave-front entering respective cores  110 . 
     An example for such configurations follows. The number of modes supported by multimode cores  110  may be selected as a tradeoff between information delivery capacity of cores  110  and the sensitivity of the delivered modes to bending of fiber  100  (e.g., configurations less prone to bending, cores  110  may be configured to support more modes). This tradeoff is described below, and fibers  100  may be configured to implement various tradeoffs, with cores supporting a range of number of modes. The number of modes (V) may be expressed by Equation 2, with NA denoting the numerical aperture, a is the radius of a core, λ denoting the wavelength of the light, and n core  and n cladding  denoting the corresponding refractive indices. 
     
       
         
           
             
               
                 
                   V 
                   = 
                   
                     
                       
                         
                           2 
                           ⁢ 
                            
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           a 
                         
                         λ 
                       
                       ⁢ 
                       NA 
                     
                     = 
                     
                       
                         
                           2 
                           ⁢ 
                            
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           a 
                         
                         λ 
                       
                       ⁢ 
                       
                         
                           
                             
                               n 
                               core 
                             
                             2 
                           
                           - 
                           
                             
                               n 
                               clading 
                             
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
     
     The single mode condition requires V&lt;2.405 and the number of modes (M) is proportional to 2·(V/2.405) 2 , or specifically for a step index fibers M=4V 2 /π 2 . The tradeoff of the number of modes with respect to crosstalk between cores  110  may be expressed in terms of the width of the Gaussian profile of the field propagating through optical core  110  (denoted by W, defined for a field value that is 1/e of its maximal value) and the pitch L between cores  110 —expressed in Equations 3 in terms of V (number of modes) and a (core radius). For example, a condition for preventing crosstalk between cores  110  may be defined as L≥2W, providing a relation between pitch (L) and core radius (a). 
     
       
         
           
             
               
                 
                   
                     W 
                     = 
                     
                       a 
                       ⁡ 
                       
                         ( 
                         
                           0.65 
                           + 
                           
                             1.619 
                             
                               V 
                               1.5 
                             
                           
                           + 
                           
                             2.879 
                             
                               V 
                               6 
                             
                           
                         
                         ) 
                       
                     
                   
                   ; 
                   
                     L 
                     = 
                     
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                       ⁢ 
                       
                         a 
                         ⁡ 
                         
                           ( 
                           
                             
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                               ⁢ 
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                               ⁢ 
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                                 ⁢ 
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                                 6 
                               
                             
                           
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                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
               
             
           
         
       
     
     Such condition may be balanced in fiber design with respect to the 3D resolution achievable by the core multimode configuration, which may be expressed as follows. The 3D resolution in space equals to the pitch size L (related to the core size) and the resolution in phase #sensitivity to wavefront 96 equals to 2π/√M in every axis (y and x). Thus, the angular sensitivity in the direction of propagation along the axial direction Z, Δθ z , may be expressed and approximated and expressed in to Equation 4. 
     
       
         
           
             
               
                 
                   
                     
                       Δθ 
                       z 
                     
                     ≈ 
                     
                       λ 
                       
                         4 
                         ⁢ 
                         
                           a 
                           ⁡ 
                           
                             ( 
                             
                               
                                 0.65 
                                 ⁢ 
                                 V 
                               
                               + 
                               
                                 1.619 
                                 
                                   V 
                                   0.5 
                                 
                               
                               + 
                               
                                 2.879 
                                 
                                   V 
                                   5 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                     ≈ 
                     
                       
                         1.21 
                         ⁢ 
                         λ 
                       
                       aV 
                     
                   
                   = 
                   
                     0.2 
                     ⁢ 
                     
                       
                         λ 
                         2 
                       
                       
                         NAa 
                         2 
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
             
           
         
       
     
     The reciprocal relation between Δθ z  and V indicates that increasing the number of modes (V) improves sensitivity (as smaller angles Δθ can be sensed) but as shown above, increasing V also increases the sensitivity to fiber bending (increases crosstalk through modes coupling). The reduction in the bending angle (affects the bending radius of the fiber) is proportional to the root of the number of modes, √M, which is proportional to 4a·NA/λ. 
     Equations 2-4 and the considerations presented above clearly describe the ways specific fiber configurations may be carried out to optimize endoscope performance with respect to mechanical requirements and wave-front sensing (3D resolution) requirements. Various applications of endoscope may imply different fiber configurations with respect to fiber rigidness, core parameters (size and pitch) and achieved spatial resolution. 
     It is noted that wave-front sensing endoscopes  150  may be implemented as any of the embodiments disclosed herein, e.g., as multicore imaging fiber  100  having a proximal tapered end  120 , as multicore photonic crystal fibers  100  and/or as endoscope  150  with distal multicore fiber  100  optically coupled to jointedly-interconnected rigid image-relay elements  130 . 
       FIG.  11    is a high level flowchart illustrating a method  200 , according to some embodiments of the invention. The method stages may be carried out with respect to endoscopes  150  and/or fibers  100  described above, which may optionally be configured to implement method  200 . Method  200  may be at least partially implemented by at least one computer processor. Certain embodiments comprise computer program products comprising a computer readable storage medium having computer readable program embodied therewith and configured to carry out of the relevant stages of method  200 . Method  200  may comprise stages for producing, preparing and/or using device endoscopes  150  and/or fibers  100 , such as any of the following stages, irrespective of their order. 
     Method  200  may comprise adiabatically tapering a proximal tip of a multicore imaging fiber (stage  210 ) comprising at least 10,000 cores with a common cladding, configured to deliver image radiation from tissue at a distal end of the fiber, wherein the image radiation is confined to the cores and the cores are interspaced within a fiber cross-sectional area to prevent cross-talk therebetween, and configuring the adiabatically tapered proximal tip (stage  215 ) to be shorter than lcm and have a fiber cross-sectional area and a core diameter which are reduced by a factor of at least 3 with respect to the multicore imaging fiber, to allow the image radiation exit the narrowed cores and deliver the image radiation to an adjacent sensor. Certain embodiments comprise reducing, optically, the fill factor of the delivered image by re-orienting delivered image radiation from the cores to fill a smaller area on the sensor (stage  217 ). 
     Method  200  may comprise configuring multicore fiber from a photonic crystal structure (stage  220 ) composed of multiple air holes, by designing the air holes to be in at least two types: core-type air holes, interspaced within a fiber cross-sectional area at a specified core-pitch selected to confine image radiation within the core-type air holes, and cladding air-holes between the core-type air holes, the cladding air-holes interspaced within the fiber cross-sectional area at a specified cladding-pitch selected to prevent cross-talk between the core-type air holes. 
     Method  200  may comprise configuring an endoscope from a distal multicore imaging fiber and a plurality of rigid image-relay elements (stage  230 ), wherein the distal multicore imaging fiber is configured to receive image radiation from tissue at a proximal end thereof and deliver the image radiation to a distal end of the distal multicore imaging fiber, and interconnecting the rigid image-relay elements by a respective plurality of joints (stage  235 ), wherein a distal one of the rigid image-relay elements is connected via a corresponding joint to the proximal end of the distal multicore imaging fiber. The joints are configured to preserve the delivered image radiation from the proximal end of the distal multicore imaging fiber upon angular movements of the rigid image-relay elements with respect to each other, to deliver the image radiation at a proximal end of the endoscope. 
     Method  200  may further comprise connecting a proximal multicore imaging fiber (stage  237 ) to a proximal one of the rigid image-relay elements via a corresponding joint, to deliver the image radiation from the proximal rigid image-relay element. 
     Method  200  may comprise using spectral multiplexing to enhance the information content of the delivered radiation (stage  240 ) and encoding, spectrally, the radiation delivered through each of the cores, and decoding therefrom multiple data points per core (stage  245 ). For example, method  200  may comprise illuminating tissue by a specified plurality of distinct wavelengths, delivering image radiation received from illuminated tissue through each of a plurality of cores of a multicore imaging fiber, decoding, for each of the cores, detected radiation in the specified plurality of distinct wavelengths, and deriving from the decoded detected image radiation of each of the cores, image data corresponding to the specified plurality of distinct wavelengths. Method  200  may further comprise implementing super resolved imaging utilizing multiple inputs per core which correspond to the multiple wavelengths (stage  247 ). 
     Method  200  may comprise using spatio-spectral encoding and decoding of illumination to enhance spatial resolution by spatio-spectral patterned illumination (stage  250 ), e.g., by illuminating tissue by a specified plurality of distinct wavelengths at a specified spatio-spectral pattern, delivering image radiation received from illuminated tissue through each of a plurality of cores of a multicore imaging fiber, decoding, for each of the cores, detected radiation in the specified plurality of distinct wavelengths according to the specified spatio-spectral pattern, and deriving from the decoded detected image radiation of each of the cores, image data corresponding to the specified plurality of distinct wavelengths and according to the specified spatio-spectral pattern. 
     Method  200  may comprise illuminating the tissue by a single mode, multicore illumination fiber to increase speckle size and possibly removing speckle effects (stage  260 ), e.g., by using a single mode, multicore illumination fiber to illuminate a tissue imaged by a multicore imaging fiber and optionally identifying and removing from image radiation delivered by a multicore imaging fiber, a speckle pattern from the illumination by the single mode, multicore illumination fiber. Method  200  may further comprise modulating the shape of the illumination spot and removing secondary speckle patterns, which depend on the spot size, by image processing (stage  262 ). 
     Method  200  may comprise imaging an illuminated tissue by a multicore imaging fiber having cores configured to support between 10-100 modes, and decoupling the modes by removing mode-mixing distortions from image radiation delivered by the fiber (stage  270 ). 
     Method  200  may comprise increasing a field of view of an imaging fiber (stage  280 ) by implementing a tunable prism at a distal tip thereof. e.g., by controllably displacing distal tip optical elements with respect to each other to change a field of view of the fiber, possibly using distal tip optical elements with opposite focal lengths +F and −F. 
     Method  200  may comprise introducing radiation laterally into peripheral cores to derive indications of the proximity of surrounding tissue (stage  290 ), e.g., by enabling radiation to enter through sides of a multicore imaging fiber and into specified peripheral cores thereof, and deriving longitudinal data concerning tissue surrounding the fiber from radiation delivered through the specified peripheral cores. For example, method  200  may comprise designing peripheral slits in the fiber to enable the radiation enter the specified peripheral cores. 
     Method  200  may comprise implementing wave-front sensing by a multicore imaging fiber having at least 10,000 multimode cores, by detecting image radiation delivered therethrough, measuring a spot position associated with the cores and deriving 3D image data therefrom (stage  300 ). 
     In the above description, an embodiment is an example or implementation of the invention. The various appearances of “one embodiment”, “an embodiment”, “certain embodiments” or “some embodiments” do not necessarily all refer to the same embodiments. Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. Certain embodiments of the invention may include features from different embodiments disclosed above, and certain embodiments may incorporate elements from other embodiments disclosed above. The disclosure of elements of the invention in the context of a specific embodiment is not to be taken as limiting their use in the specific embodiment alone. Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in certain embodiments other than the ones outlined in the description above. 
     The invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described. Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined. While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents.