Optical fibers, fiber connectors, and optical detection systems

Abstract

The present disclosure provides an endoscopic fiber having a proximal end and a distal end, comprising a plurality of cores, one or more of which are excitation cores(s), one or more of which are focusing cores(s), each of which is an excitation core(s), each of which is an excitation core(s), each of which is a focusing core(s), each of which is a focusing core(s), each of which is a solid core, each of which is a solid core having a refractive index different from that of the excitation core(s), each of which is an excitation core(s), each of which is a solid The invention also provides a fiber connector configured to connect to a fiber, a detection system including a laser light source or other excitation light source connected to the excitation core(s) of the fiber, and a method for performing Raman spectroscopy, which includes transmitting an excitation signal to a target region via the excitation core(s) of the fiber.

Description

Technical Field

[0001] The present invention relates to an optical fiber device, such as a multi-core optical fiber device for Raman sensing.

Background Art

[0002] Optical fiber devices having a plurality of cores and used for imaging are known. In order to reduce the diameter of the optical fiber device for endoscopic use, the cores of the fiber can be arranged together. However, in such known devices, there may be a limit to how close the cores can be arranged to each other. If the cores are too close to each other, light in one core may leak out of the core and enter another core by coupling. Such coupling of light between cores can degrade the transmission signal.

[0003] Measurement of Raman spectra via an optical fiber is usually complicated because the intrinsic Raman scattering of the fiber material is large. When the fiber material is silica or doped silica, the generation of unwanted Raman light is called the "silica background". This background can become so large as to overwhelm any signal collected from the biological sample of interest at the distal end of the system. For example, many useful carbon-based Raman bands spectrally overlap with this background. Therefore, in such systems, different fibers are used for excitation and collection in order to spatially separate the background from the collected signal. This can be a problem because the two fibers do not physically point to the same location, and a distal optical system is required not only to correct this but also to remove the Raman signal generated by the fibers. This increases the size of the probe. General solutions, such as the use of multiple fibers and distal optical systems, are complex and bulky.

[0004] One way to reduce coupling effects is to increase the refractive index contrast between the core and the surrounding cladding, which is generally evaluated using the numerical aperture (NA) of the fiber. In known fibers, an NA greater than 0.3 can be obtained by using expensive glass doping and tempering techniques. It should also be noted that, in more rigorous propagation models, a single refractive index cannot be assigned to the core or cladding (and thus to the NA) because different modes propagating within the fiber undergo different combinations of interactions at the core / cladding interface. That is, each different mode propagating within the fiber will have a different effective refractive index. Therefore, while it is convenient to represent each material with a single refractive index and the fiber with a single NA, the actual effective refractive index and effective NA experienced by individual modes may be higher or lower than the nominal values. The effective refractive index of a mode lies midway between the refractive indices of the core and the cladding. The effective refractive index will never be greater than the refractive index of the core.

[0005] Yerolatsitis et al. (Ultra-low background Raman sensing using a negative-curvature fiber and no distal optics, Journal of Biophotonics (2019)) demonstrated that excitation of Raman-derived silica background can be minimized by using a single hollow-core fiber containing an excitation hollow core and multiple Ge-doped light-collecting cores. In a hollow core, the interaction between light and silica is weak, so the generation of silica background is minimized. However, this type of fiber needs to be sealed to avoid capillary action caused by liquid passing through the hollow core of the fiber.

[0006] Yerolatsitis et al. (Sub millimetre flexible fiber probe for background and fluorescence-free Raman spectroscopy, Journal of Biophotonics (2021)) demonstrated a configuration in which a short solid core fiber is spliced ​​onto a hollow core fiber for excitation. To maintain the required light-gathering efficiency, the solid core fiber needs to be on the order of several hundred micrometers. This complicates the manufacturing process, especially in single-use probes, particularly when splicing procedures must be performed at both the distal and proximal ends of the fiber. Furthermore, multi-core fibers and hollow core fibers have different underlying guiding mechanisms. Light is guided by total internal reflection within the multi-core fiber. [Overview of the Initiative]

[0007] According to the first embodiment, an endoscopic fiber having a proximal end and a distal end, comprising a plurality of cores, one or more of the cores being excitation cores (multiple cores are possible), and one or more of the cores being focusing cores (multiple cores are possible), Each excitation core (one or more) contains a solid core. Each light-gathering core (one or more) includes a solid core having a refractive index different from that of the excitation core (one or more), The excitation core(s) are configured to transmit the optical excitation signal from the proximal end to the distal end or a target region in its vicinity. The focusing core(s) are configured to transmit the photodetection signal from the distal end or a nearby target region to the proximal end. An endoscopic fiber is provided in which the difference in refractive index between the excitation core(s) and the focusing core(s) is such that it reduces or eliminates crosstalk between the modes(s) of the excitation core(s) and the modes(s) of the focusing core(s).

[0008] Crosstalk reduction or elimination may occur such that, at the operating wavelength(s), the magnitude of the signal present in the focusing core(s) due to crosstalk from the excitation core(s) is less than 10%, e.g., less than 1%, e.g., less than 0.1%, or optionally less than 0.01%, of the corresponding signal in the excitation core(s). For example, crosstalk reduction or elimination may occur such that, due to crosstalk from the excitation core(s) of the Raman signal generated in the excitation core(s) by the excitation signal, the magnitude of the Raman signal present in the focusing core(s) is less than 10%, e.g., less than 1%, e.g., less than 0.1%, or optionally less than 0.01%, of the corresponding Raman signal generated in the excitation core(s).

[0009] The effective refractive index experienced by electromagnetic modes propagating within the excitation core(s) at the operating wavelength may differ from the effective refractive index experienced by the corresponding electromagnetic modes propagating within the focusing core(s).

[0010] The difference in refractive index between the excitation core(s) and the focusing core(s) may be such that, in the wavelength range of 200 nm to 1200 nm, and optionally in the range of 532 nm to 1064 nm, there is substantially no crosstalk and / or mode coupling between the optical excitation signal and the optical focusing signal.

[0011] The refractive index of the excitation core(s) can be within the range of 1.41 to 1.48. The refractive index of the focusing core(s) can be within the range of 1.41 to 1.48. The absolute difference in refractive index between the excitation core(s) and focusing core(s) can be within the range of 0.0003 to 0.07.

[0012] Each excitation core(s) may be positioned at a distance of at least 10 μm and / or between 10 μm and 125 μm from the nearest focusing core(s).

[0013] Each excitation core(s) may have a diameter in the range of 3 μm to 120 μm, and / or each focusing core(s) may have a diameter in the range of 3 μm to 120 μm, and / or the excitation core(s) may be positioned substantially collinearly and / or parallel to the longitudinal axis of the fiber, and / or the focusing core(s) may be positioned substantially collinearly and / or parallel to the axis of the fiber.

[0014] The fiber may include multiple focusing cores arranged concentrically around one or more excitation cores.

[0015] The fiber may include a focusing core with an annular cross-section, which is substantially concentrically arranged around the fiber axis and / or has a central axis collinear with the central longitudinal axis of the fiber.

[0016] The focusing core may have an inner diameter in the range of 10 μm to 150 μm and / or greater than 10 μm. The focusing core may have an outer diameter in the range of 13 μm to 1000 μm and / or less than 1000 μm.

[0017] The excitation core(s) may be configured to transmit light with wavelengths in the range of 200 nm to 1200 nm, and optionally light with wavelengths in the range of 532 nm to 1064 nm. The focusing core(s) may be configured to transmit light with wavelengths in the range of 200 nm to 1200 nm, and optionally light with wavelengths in the range of 532 nm to 1500 nm.

[0018] The fibers may have an outer diameter ranging from 125 μm to 1000 μm and / or less than 1000 μm.

[0019] The excitation core(s) may include at least one of silica or doped silica. There may be a difference of 0.001 to 0.02 between the absolute refractive index of the excitation core(s) and the absolute refractive index of the cladding of the excitation core(s).

[0020] The light collecting core(s) may include doped silica, such as germanium doped silica. There may be a difference of 0.003 to 0.03 between the absolute refractive index of the light collecting core(s) and the absolute refractive index of the clad of the light collecting core(s).

[0021] The excitation core(s) and the light collecting core(s) may be disposed inside the first clad material in the longitudinal direction and / or may be substantially encapsulated by the first clad material.

[0022] The first clad material may include fluorine doped silica.

[0023] The second clad material may surround each of the excitation core(s) and / or may be disposed between the excitation core(s) and the first clad material.

[0024] The second clad material may include fluorine doped silica.

[0025] The third clad material may surround each of the light collecting core(s) and / or may be disposed between the light collecting core(s) and the first clad material.

[0026] The third clad material may include silica or doped silica, such as fluorine doped silica.

[0027] The distal end of the fiber may be tapered in the longitudinal direction, whereby the diameter of the fiber decreases as the distance along the longitudinal direction increases at the distal end.

[0028] The lateral spread of the taper may be in the range of 10% to 40% of the maximum diameter of the fiber and optionally in the range of 5% to 70% of the maximum diameter of the fiber. The longitudinal spread of the taper may extend over a length of at least 5 mm from the distal end of the fiber.

[0029] The fiber can be configured for collection of detection signals from a target region at or near its distal end, optionally Raman detection signals. The refractive index difference between the excitation core(s) and the collection core(s) can be such that there is substantially no crosstalk of Raman signals generated in the excitation core(s) by the excitation signal into the collection core(s).

[0030] In a further aspect, there is provided a fiber connector configured to connect to a fiber as claimed or described herein, the fiber connector including at least one collection fiber, the at least one collection fiber being arranged such that when the face of the fiber connector engages the proximal end of the fiber, the collection core(s) is aligned with the collection fiber(s).

[0031] The numerical aperture of the collection fiber or each collection fiber is substantially the same as the numerical aperture of the corresponding one or more collection core(s).

[0032] The fiber connector includes at least one excitation fiber, the at least one excitation fiber being arranged such that when the face of the excitation connector engages the proximal end of the fiber, the excitation core(s) is aligned with the excitation fiber(s).

[0033] The fiber connector can be arranged such that when the fiber connector is connected to the fiber, the at least one excitation core of the fiber extends through the fiber connector.

[0034] The collection fiber(s) and the excitation fiber(s) or excitation core(s) can be bundled together or otherwise attached at the distal end of the connector, separated from each other and / or movable relative to each other at the proximal end of the connector, and such that the collection fiber(s) and the excitation fiber(s) or excitation core(s) can be connected to different connectors and / or devices.

[0035] In a further embodiment, a detection system is provided that includes a laser light source or other excitation light source connected to an excitation core(s) of a fiber as claimed or described herein, and a detection device connected to a focusing core(s) of a fiber.

[0036] The system may be a Raman spectroscopy system, and the detection device may consist of a Raman spectrometer.

[0037] A laser light source or other excitation light source may be connected to the excitation core(s) of the fiber via a fiber connector as claimed or described herein, and / or a detection device may be connected to the focusing core(s) of the fiber via a fiber connector as claimed or described herein.

[0038] In a further embodiment, a method is provided for performing Raman spectroscopy, comprising: transmitting an excitation signal to a target region via an excitation core(s) of a fiber as claimed or described herein; receiving a detection signal via the focusing core(s) of the fiber, including a signal(s) generated in response to the excitation signal; and determining a Raman spectrum from the detection signal.

[0039] In a further embodiment, a multicore optical fiber is provided having one or more cores with a lower refractive index for excitation and one or more cores with a higher refractive index for focusing, thereby preventing coupling between the two regions and enabling background-free Raman signal acquisition from a distal sample. A single all-solid-state fiber may be used for excitation.

[0040] Excitation cores typically have higher optical output than the focusing core(s) and generate a higher silica background. Therefore, it is beneficial to reduce the coupling of waveguide modes in the excitation fiber to waveguide modes in the focusing fiber, as such coupling, due to its intensity, can mask the received signal of interest.

[0041] For example, in one embodiment, the effective refractive index of the modes in the excitation core is lower than that of silica, while the effective refractive index of the modes in the focusing core is higher than that of silica, thereby preventing coupling between these two regions.

[0042] A multicore optical fiber may consist of a single all-solid low-refractive-index excitation core containing a silica core and fluorine-doped silica cladding, and multiple high-refractive-index focusing cores containing germanium-doped cores and silica cladding. In some embodiments, the excitation core may contain fluorine-doped silica. The fiber can be used to excite and focus Raman light from a distal sample. The refractive index difference between the two regions (excitation region and focusing region) prevents unwanted coupling between the excitation core and the focusing core, thereby enabling the collection of the Raman signal from the distal sample without background (silica background).

[0043] The core may be made of silica glass, which may be doped or undoped. In some embodiments, the core rod is made from at least one of silica, Ge-doped silica, fluorine-doped silica, boron-doped silica, aluminum-doped silica, silicate glass, or silica doped with any suitable dopant. Any suitable combination of materials may be used to obtain the desired difference in refractive index between the excitation core(s) and the focusing core(s). Any suitable doping level may be used. For example, in some embodiments using Ge as the dopant, the doping level may be, for example, 1 to 20 mol%, or for example, about 4 mol%. In some embodiments, when F is used as the dopant, the doping level may be, for example, 0.05 to 2.5 mol%.

[0044] The clad rod(s) may be a hollow silica capillary. In some embodiments, the clad rod is made from at least one of silica, Ge-doped silica, fluorine-doped silica, boron-doped silica, aluminum-doped silica, silicate glass, or silica doped with any suitable dopant. Any suitable material for the clad may be used to obtain the desired optical properties. In some embodiments, the core and the clad may contain silica doped with the same dopant at different concentrations, resulting in a refractive index difference between the core and the clad.

[0045] Using all-solid-state excitation fibers can eliminate the need for splicing. Multicore optical fibers can simplify the requirements for developing endoscopic fiber probes for in vivo sensing, thereby facilitating mass production and shortening turnaround times. While hollow core fibers require many processing steps in manufacturing, all-solid-state multicore fibers are far simpler to manufacture.

[0046] The multicore region that functions as a light-collecting fiber may be replaced with a ring-shaped core.

[0047] The device may be configured to transmit at least one of the following: visible light, ultraviolet light, or infrared light.

[0048] The optical coupler may be coupled to an optical fiber device and / or to a light source and / or a photodetector.

[0049] Furthermore, according to another embodiment that may be provided independently, the effective refractive index of light traveling through the excitation core(s) is significantly different from and decoupled from the effective refractive index of light traveling through the focusing core(s). The excitation core(s) may have a higher, lower, or the same absolute refractive index as undoped silica, provided that the effective refractive index of modes traveling through the excitation core(s) does not couple with that of modes in the focusing core(s).

[0050] Undoped silica can be used as the core material or the cladding material, but any other suitable material may be used, provided that a suitable difference is achieved between the effective refractive indices of the excitation core and the focusing core. For example, each core may be arranged to have a suitable cladding having a refractive index lower than that of the corresponding core.

[0051] Features of one aspect of the present invention can be applied to other aspects of the present invention in any suitable combination. For example, features of an apparatus can be applied as features of a method, and vice versa.

[0052] Next, embodiments of the present invention will be described as non-limiting examples and are shown in the following figures. [Brief explanation of the drawing]

[0053] [Figure 1] This is a cross-sectional microscope image of a multicore optical fiber according to one embodiment, showing one excitation fiber and six focusing fibers. [Figure 2] This is a schematic diagram showing the comparison of the refractive indices of an excitation fiber and a collecting fiber according to one embodiment. [Figure 3] Figures A and B are schematic diagrams showing the refractive indices of the excitation fiber and focusing fiber in the relevant example. [Figure 4] This graph shows experimentally obtained spectra of the silica background generated when light is coupled to excitation cores of two different lengths. [Figure 5] This is a schematic diagram of a detection system according to one embodiment. [Figure 6] This is a schematic diagram illustrating the effect of tapering the distal end of a multicore optical fiber. [Figure 7] This graph shows experimentally obtained spectra of silica background generated in ethanol for multicore optical fibers with and without tapered distal ends. [Figure 8] This is a near-field image of the cross-section of the tapered distal end tip of a multicore fiber that has been photoexcited at its proximal end. [Figure 9] This is a schematic diagram of a fiber stretching device. [Figure 10] This is a schematic diagram of the cross-section of the tip of a multicore optical fiber. [Figure 11] This is a schematic diagram showing the comparison of the refractive indices of the excitation fiber and the collecting fiber according to a further embodiment. [Figure 12] Figures A through C are schematic diagrams of further embodiments. [Figure 13] This is a schematic diagram showing the tip of one embodiment of a multicore optical fiber. [Modes for carrying out the invention]

[0054] Figure 1 is a cross-sectional microscope image of a multicore optical fiber 10 according to one embodiment. The fiber 10 has one excitation core 14 and six focusing cores 12. In this embodiment, the excitation core 14 is positioned on the substantially central longitudinal axis of the multicore optical fiber 10.

[0055] The excitation core 14 has a radius considerably smaller than the radius of the focusing core 12 in the embodiment of Figure 1. In other embodiments, the diameter of the excitation core(s) may be smaller, larger, or equal to that of the focusing core(s) 12. Depending on the radius and NA, the excitation core can be single-mode, minority-mode, or multi-mode. Similarly, the focusing core can be single-mode, minority-mode, or multi-mode.

[0056] The focusing core 12 can be arranged concentrically around the excitation core 14. The excitation fiber 14 and the focusing fiber 14 are bundled together to form a multicore optical fiber 10.

[0057] The excitation fiber 14 shown in Figure 1 includes a single all-solid low refractive index excitation core containing a silica core and a fluorine-doped silica cladding, and six high refractive index focusing cores 12 containing germanium-doped silica cores and silica cladding.

[0058] The ratio of core dimensions to cladding dimensions (for example, the ratio of core diameter to cladding diameter) can be referred to as the core-to-cladding ratio. Cladding dimensions can also be referred to as outer dimensions.

[0059] Figure 2 is a schematic diagram showing a comparison of the refractive indices of an excitation core and a focusing fiber core in one embodiment. The vertical axis represents the refractive index of the core material, and the horizontal axis extends along the diameter of the multicore optical fiber and represents its width. In the configuration shown in Figure 2, the refractive indices of one excitation core and two focusing cores are shown relative to undoped silica.

[0060] The shaded areas in the figure represent the focusing core, the two excitation cores, and the cladding material surrounding them. The vertical extent of these shaded areas indicates the absolute refractive index. The cladding material surrounding the focusing core is silica (its absolute refractive index is equal to that of pure silica), and it can be seen that its absolute refractive index is lower than that of the focusing core. Similarly, the absolute refractive index of the cladding material surrounding the excitation core is lower than that of the excitation core. The dashed lines represent the effective refractive index of the relevant operating modes of the focusing core and excitation core. It can be seen that the absolute refractive index of the material in the focusing core is different from that of the material in the excitation core. Furthermore, it can be seen that the effective refractive index of the mode of interest in the focusing core (dashed line) is significantly different from that of the mode of interest in the excitation core (dashed line).

[0061] In Figure 2, the fiber 20a includes a single all-solid low refractive index excitation fiber core 24a containing silica and at least two focusing fiber cores 22a containing germanium-doped silica. In other embodiments, the cores may include any other suitable material. The refractive index of the excitation fiber core 24a may be lower than that of the corresponding focusing fiber core 22a. In the embodiment shown in Figure 2, including the fiber 20a, all modes of the excitation fiber are spaced apart from the modes of the focusing fiber.

[0062] Figures 3A and 3B show related examples that do not constitute part of the present invention and have a structure similar to the embodiment in Figure 2. However, in these examples, although fibers 20b and 20c are structurally similar to fiber 20a, all modes of the excitation fiber (24b and 24c, corresponding to 24a in Figure 2) cannot be sufficiently separated from the modes of the focusing fiber (22b and 22c, corresponding to 22a in Figure 2, respectively).

[0063] In other embodiments, the core may include any other suitable material. Further embodiments are shown in Figure 11.

[0064] In other embodiments, the multicore optical fiber may have any preferred number of focusing fiber cores, e.g., one focusing fiber core 22, e.g., six focusing fiber cores 22, e.g., 20 focusing fiber cores 22, 1 to 20 focusing cores, or any other preferred number of focusing fiber cores 22. One excitation core 24 is shown in Figure 2. In other embodiments, the device may have multiple excitation cores 24. The excitation core 14 in Figure 1 is positioned substantially in the center of the focusing fiber cores 12 in a direction perpendicular to the axis of the multicore optical fiber 0 and is surrounded by the focusing fiber cores 12. In other embodiments, the excitation core may be offset from the central axis of the multicore optical fiber 10, such as in the outer region of the multicore optical fiber 10. In other embodiments, the excitation core 14 may not be surrounded by the focusing fiber cores 12, but may only be partially surrounded by them.

[0065] The dashed lines in Figure 2 represent the effective refractive indices of different orders of waveguide modes within the core, with higher-order modes labeled. The height of the blue solid bars in Figure 2 represents the absolute refractive index of the material constituting the multicore optical fiber 20.

[0066] Figure 2 shows an optical fiber 20a according to a first embodiment of the present invention, in which the refractive index of the excitation core 24a is lower than that of the focusing core 22a. The difference in refractive index eliminates or reduces coupling between the waveguide modes in the excitation core and the focusing core. Because the effective refractive index of the excitation mode and the focusing mode, including higher-order modes, are significantly different, this hinders mode mixing and thus prevents background interference. In the excitation core 24, relatively high optical power is transmitted through the core and coupled to the focusing fiber core 22, and as it proceeds to the proximal end, it obscures the received optical signal, resulting in silica background. However, this refractive index contrast eliminates or reduces this silica background. In Figure 2, it can be seen that light is emitted from each fiber core, represented by vertical arrows, without coupling to each other.

[0067] Crosstalk reduction or elimination may occur such that, at the operating wavelength(s), the magnitude of the signal present in the focusing core(s) due to crosstalk from the excitation core(s) is less than 10%, e.g., less than 1%, e.g., less than 0.1%, or optionally less than 0.01%, of the corresponding signal in the excitation core(s). For example, crosstalk reduction or elimination may occur such that, due to crosstalk from the excitation core(s) of the Raman signal generated in the excitation core(s) by the excitation signal, the magnitude of the Raman signal present in the focusing core(s) is less than 10%, e.g., less than 1%, e.g., less than 0.1%, or optionally less than 0.01%, of the corresponding Raman signal generated in the excitation core(s).

[0068] Figures 3A and 3B show further optical fibers 20b and 20c. In the relevant example of Figure 3A, the cores have the same refractive index, and as a result, the coupling of waveguide modes between the excitation fiber core 24 and the focusing fiber core 22 is represented by a curved arrow between the cores. In the relevant example of Figure 3B, the cores have modes with similar effective refractive indices (shown as dashed lines), which results in the coupling of waveguide modes between the excitation fiber core 24 and the focusing fiber core 22, also represented by a curved arrow between the cores. In each of Figures 3A and 3B, the silica background generated in the excitation fiber core 24 may obscure, at least partially, the signal received at the proximal end of the focusing fiber core 22b or 22c.

[0069] Figure 4 is a graph showing experimentally obtained spectra of the silica background generated when light is coupled to excitation cores of two different lengths (in this case, 2 m and 1.8 m) of the fiber according to the embodiment of Figure 1. It can be seen that the silica background is stronger for longer lengths than for shorter lengths because the distance over which the light interacts with the core material is longer.

[0070] A feature of the embodiments is that by providing a difference in effective refractive index between the excitation core(s) and the focusing core(s), crosstalk and / or mode coupling between the optical excitation signal transmitted through the excitation core(s) and the optical focusing signal passing through the focusing core(s) can be substantially eliminated or reduced at the operating frequency, which can be achieved for signals having wavelength(s) within the operating range, for example, in the wavelength range of 200 nm to 1200 nm. In some embodiments, the excitation signal has a wavelength selected from at least one of 248, 266, 355, 405, 457, 473, 491, 515, 532, 561, 640, 660, 785, 830, 980, or 1064 nm.

[0071] Crosstalk reduction or elimination may occur such that, at the operating wavelength(s), the magnitude of the signal present in the focusing core(s) due to crosstalk from the excitation core(s) is less than 10%, e.g., less than 1%, e.g., less than 0.1%, or optionally less than 0.01%, of the corresponding signal in the excitation core(s). For example, crosstalk reduction or elimination may occur such that, due to crosstalk from the excitation core(s) of the Raman signal generated in the excitation core(s) by the excitation signal, the magnitude of the Raman signal present in the focusing core(s) is less than 10%, e.g., less than 1%, e.g., less than 0.1%, or optionally less than 0.01%, of the corresponding Raman signal generated in the excitation core(s).

[0072] In some embodiments, the focusing signal has a wavelength in the range above or below the excitation wavelength, and the Raman signal is shifted between 50 cm⁻¹ and 4500 cm⁻¹ or -50 cm⁻¹ and -4500 cm⁻¹, for example, if excited at 532 nm, it will be focused in the range of 535 to 700 nm or 430 to 530 nm.

[0073] In other embodiments, the wavelength of the focused signal is in the range of 245 nm to 275 nm, or 260 nm to 300 nm, or 480 nm to 600 nm, or 550 nm to 730 nm, or 670 nm to 950 nm, or 700 nm to 1020 nm, or 860 nm to 1390 nm, or any other appropriate wavelength range.

[0074] Reducing or eliminating crosstalk and / or mode coupling can be particularly important in the context of endoscopic measurements. For example, when both the excitation and focusing signals need to travel relatively long distances from a light source / detector located outside the patient or other object to a target area inside the patient or other object, or vice versa, such as in the lungs, stomach, or other anatomical regions. For example, the fiber length may be greater than 30 cm, optionally greater than 50 cm, or greater than 1 m, optionally in the range of 30 cm to 3 m, 50 cm to 4 m, or 50 cm to 2 m. As shown in Figure 4, a significant silica background signal from the silica core can occur over such distances. Furthermore, considering the frequencies often used in Raman measurements, this background signal can significantly affect the acquired signal and, consequently, the Raman spectrum or other measurements. Such effects can be mitigated by providing an appropriate refractive index difference between the excitation and focusing cores.

[0075] Figure 5 is a schematic diagram of the detection system 40 (Raman spectroscopy system in this embodiment) including the multicore optical fiber 10 shown in Figure 1. The multicore optical fiber 10 takes the form of an endoscopic fiber probe for insertion into a patient or other object.

[0076] The system in Figure 5 includes a fiber connector 42 configured to connect to the proximal end of a multicore optical fiber 10 at its distal end and to a detection device at its proximal end. In the system shown in Figure 5, the fiber connector 42 is in the form of an all-fiber reformatter. In the system shown in Figure 5, the detection device includes a spectrometer 44.

[0077] The fiber connector 42 includes a configuration in which a single-mode (low refractive index) excitation fiber 52 and six multimode (high refractive index) focusing fibers 50 are bundled together. Figure 5 shows an image of the distal end face 46 of the fiber connector 42 (a) and an image of the proximal end face 48 of the fiber connector 42 (b).

[0078] The design of the fiber connector 42 is consistent with the design of the multicore fiber 10. In the system shown in Figure 5, at the distal end of the fiber connector 42, the excited low refractive index core 14 is at the center of the multifiber structure of the connector 42, surrounded by six focusing fibers 50 that have the same numerical aperture (NA) as the focusing core 12 of the multicore fiber 10.

[0079] Figure 5 also shows a cross-sectional image (c) of the proximal end face 54 of the multicore fiber 10. The fiber connector 42 is configured such that when the distal end face 46 of the fiber connector 42 engages with the proximal end face 54 of the multicore fiber 10, the light-gathering core 12 of the multicore fiber 10 is aligned with the light-gathering fiber of the fiber connector 42, thereby enabling the detection signal received via the light-gathering core 12 to pass through to the light-gathering fiber 50.

[0080] A key feature of the system in Figure 5 is that the excitation core 14 does not terminate at the proximal end face 54 of the multicore fiber 10. Instead, the excitation core 14 extends through the distal end face 46 of the fiber connector 42 and exits from the main part of the fiber connector 42 at the branching point 56.

[0081] Next, the excitation core extends from the branch point 56 to an excitation source in the form of a laser light source 58 included in the system 40. The laser light source 58 is capable of transmitting an excitation signal in the form of laser light at or within a range of operating frequencies through the excitation core to the distal end of the multicore fiber 10, thereby exciting a target region as desired. In the system of Figure 5, additional cladding and / or outer layers are provided around the excitation core 14 between the branch point 14 and the proximal end of the excitation core 14 to protect the excitation core.

[0082] In a modified version of the system, the excitation core 14 is terminated at the proximal end face 54 of the multicore fiber 10 and is aligned with an additional excitation fiber or core included in the fiber connector 42 in that modified version. The additional excitation fiber or core can be connected to a laser light source 58 or other excitation light source. In some embodiments, this laser light source may be a single-frequency light source operating at wavelengths of 532 nm, 633 nm, 785 nm, 830 nm, or 1064 nm. In some embodiments, the laser light source 58 may be a 785 nm VHG stabilized laser diode (part number: FPV785S) sold by Thor Labs. In other embodiments, the laser light source 58 may be a 1060-1083 nm DBR laser diode (part number: DBR1064S) sold by Thor Labs. In other embodiments, the interface between the excitation core(s) and the corresponding further excitation fiber(s) or core(s) occurs at any desired point between the proximal end face 54 of the multicore fiber 10 and the connection to the excitation light source.

[0083] Figure 5 also shows a cross-sectional image (b) of the proximal end face 46 of the fiber connector 42, showing additional dummy fibers 52 between the focusing fibers 50, positioned corresponding to the location of the excitation core 14 at the distal end of the fiber connector 42. In some modifications, the dummy fibers 52 terminate before reaching the distal end fiber connector 42. In other embodiments, the proximal end face 46 of the fiber connector 42 may have a different configuration than that shown in Figure 5, for example, focusing fibers 50 arranged symmetrically around the dummy fibers 52, or focusing fibers 50 arranged linearly on the proximal end face 46, or any other preferred configuration. The dummy fibers are used to achieve a dense pack arrangement when bundling the focusing cores and connecting them to the detection device.

[0084] The proximal end of the fiber connector 42 is connected to a detection device in the form of a spectrometer 44 in the system shown in Figure 5. In some embodiments, the spectrometer 44 may be a WP 785 ER Raman spectrometer (part number: WP-785-ER-IC) sold by Wasatch Photonics. In other embodiments, the spectrometer 44 may be a QE Pro Raman series spectrometer (part number: QEPRO-RAMAN-638 Spectrometer) sold by Ocean Insight.

[0085] The reformatter, in the form of a fiber connector 42, is positioned so that light from the light source 58 can be coupled to the excitation core 14, and is configured to receive the resulting Raman signal from a distal sample or other target region via the focusing core 12 of the fiber probe 10. By branching the excitation core from the focusing fiber at the branching point, the excitation light and focused light can be separated and supplied to different components / elements, such as the light source 58 and the spectrometer 44 in the system shown in Figure 5.

[0086] The fiber connector 42 can be tapered at its distal end if necessary, depending on the design of the multicore fiber, thereby ensuring that the focusing core 14 is properly aligned with the focusing fiber 50.

[0087] In the system shown in Figure 5, the multicore fiber 10 may also be tapered at its distal end. Figure 5 also shows a cross-sectional image (d) of the distal end face 62 of the multicore fiber 10. In other modifications or embodiments, the distal end tip of the multicore fiber 10 may not be tapered or may have another preferred shape.

[0088] Figure 6 is a schematic diagram illustrating the effect of tapering the distal end of a multicore optical fiber. The field of view (FoV) of an optical fiber core can be understood as a three-dimensional boundary that defines the spatial extent of light radiated from the core. For example, in the case of a circular core end face, it may be conical. Similarly, it can be understood as a three-dimensional boundary that defines the region in which a detection signal can be received by coupling the optical signal into a waveguide mode. The dashed lines in Figure 6 define the range of the FoV shown in the figure, as well as the reception and emission angles of light from the core. The emission and reception angles depend on the numerical aperture of the core. Reducing the diameter of the core does not change the numerical aperture of the core.

[0089] The overlapping region of FoV of the excitation fiber and the condensing fiber(s)(or more) may represent a target region that can be effectively investigated by the multicore optical fiber. Such an overlapping region 70 is shown in Figure 6 for the multicore fiber 10, and is indicated as a shaded region where the FoV of the excitation fiber core 24 and the condensing fiber core(s) 22(s) spatially overlap.

[0090] Similarly, the overlapping region 72 is also shown for a multicore optical fiber 74 having the same characteristics as the multicore optical fiber 10, except that the multicore optical fiber 74 has a tapered region 76 near the distal end of the fiber 74. In the tapered region, the excitation core 12 and the focusing core 14 gradually approach each other. For clarity, the cores 12 and 14 are not shown in the tapered region 76 in Figure 6. Due to the tapered region, the diameter of the distal end of the multicore optical fiber is smaller than the diameter of the proximal end.

[0091] As schematically shown in Figure 6, tapering causes the overlapping region 72 of the tapered multicore optical fiber 74 to be closer to the distal end compared to the overlapping region of the untapered multicore optical fiber 10. Therefore, by using such a tapered fiber 73, the system shown in Figure 5 can collect Raman signals or other signals from a position closer to the distal end than is possible with the corresponding untapered multicore optical fiber 10. This allows for improved light collection efficiency, particularly when attempting to investigate a sample through a scattering medium or a relatively opaque medium, as can occur with biological samples. Light of the wavelength of interest in biological samples often travels only a few millimeters. Therefore, being able to effectively collect such light can significantly improve the light collection efficiency of the system.

[0092] Figure 7 is a graph showing experimentally obtained spectra of silica background generated in ethanol for multicore optical fiber 10 with and without tapered distal ends. As shown in the enlarged portion of the graph, the tapered multicore optical fiber 74 exhibits superior performance compared to optical multicore fiber 10 at the 845 nm ethanol spectral peak. A 2 to 3 times improvement was achieved compared to the non-tapered distal end. In this embodiment, the distal end tip of the fiber is tapered to 40% of its original diameter. In other embodiments, the tapering may be greater or less than 40%. Further embodiments may provide additional post-processing of the collected signals, lensing of the end faces / apers of the fiber core, and / or angular polishing of the end faces / apers of the fiber core, which can result in further performance improvements for at least some measurements.

[0093] Figure 8 is a near-field image of the distal end of a tapered multicore fiber 74 in which the excitation fiber core 14 is photoexcited at its proximal end. The configuration of the tapered multicore optical fiber 74 is the same as that shown in Figure 1, and it has one low refractive index excitation fiber 14 and six concentrically arranged focusing fibers 12.

[0094] Tapering this structure allows light to spread from the excitation fiber core 14 to the fluorine-doped cladding, resulting in better illumination of the target region. Furthermore, the separation distance between the focusing fiber core 22 and the excitation fiber core 24 is locally reduced. By reducing this separation distance, enhanced focusing can be achieved, as explained in relation to Figure 6. As also shown in Figure 8, although the light spreads to the fluorine-doped cladding region, the surrounding structure remains considerably darker, confirming that the difference in refractive index prevents unwanted coupling to the surrounding focusing fiber core 12.

[0095] Any suitable method can be used to form the multicore fiber 10, for example, known fiber stretching methods or other techniques. As an example, Figure 9 is a schematic diagram of a fiber stretching apparatus 80 including a heating element 82 and a fiber stretching mechanism 84. The fiber stretching apparatus 80 can be used to form multicore fibers using lamination and stretching techniques. Other components of the fiber stretching apparatus 80 are omitted for clarity. Figure 9 is not drawn to scale.

[0096] In this embodiment, the fiber stretching device 80 is a type of communication equipment and is configured to control the diameter of the stretched fiber in microns. In other embodiments, any suitable fiber stretching device may be used.

[0097] The fiber stretching device 80 is configured to stretch a fiber preform 86 which includes a core portion 88 including a plurality of suitably arranged core rods and a cladding portion 34 including cladding rods.

[0098] To stretch the fiber preform 86, it is pulled by a tension mechanism in the direction indicated by arrow 40 (downward in Figure 1).

[0099] The fiber preform 86 is heated to a temperature of 2000 degrees Celsius by a heating element 82, softened, and stretched. In other embodiments, the fiber preform 86 may be heated to any other suitable temperature. The fiber preform 86 is stretched by a tensioning mechanism 22, increasing in length and decreasing in cross-section. The output of the fiber tensioning device 10 is a core rod 102, which has a much smaller cross-sectional area while having substantially the same core-to-clad dimension ratio as the original fiber preform 86. In some embodiments, the final diameter of the core rod 102 may be on the order of a few millimeters. The tensioning mechanism includes a tensioning belt (not shown). Tapering can also be provided, for example, by selecting heating and / or further stretching of a selected area of ​​the fiber, or by using other known techniques.

[0100] Figure 10 is a schematic diagram of a cross-section of the distal or proximal end of a multicore optical fiber 10. The configuration of the multicore optical fiber 10 is the same as that shown in Figure 1, and it has one low refractive index excitation fiber core 14 and six concentrically arranged focusing fiber cores 12. The excitation fiber core 14 is disposed within and / or substantially enclosed by the excitation core cladding 64 in the longitudinal direction, and the excitation core cladding 64 is referred to as the second cladding material. Each focusing fiber core 12 is disposed within and / or substantially enclosed by the focusing core cladding 66 in the longitudinal direction, and the focusing core cladding 66 is referred to as the third cladding material. Each of the focusing core and excitation core, as well as the cladding, is disposed within and / or substantially enclosed by the main cladding 68 in the longitudinal direction, the main cladding 68 being referred to as the first cladding material. In some embodiments, the main cladding 68 or the first cladding material comprises fluorine-doped silica. Any suitable material may be used for the first cladding material to obtain the desired optical properties.

[0101] Figure 11 is a schematic diagram showing a comparison of the refractive indices of the excitation fiber core and the focusing fiber core in a further embodiment of the present invention. The vertical axis represents the refractive index, and the horizontal axis extends along the diameter of the multicore optical fiber 20d and represents its width. The refractive indices of one excitation core 24d and two focusing cores 22d are shown relative to undoped silica, and for clarity, the refractive index of the relative cladding is omitted. In this embodiment, the excitation core 24d has a higher refractive index than the focusing cores 22d. In the excitation core 24d, a relatively high optical power is transmitted through the core, coupled to the focusing fiber core 22d, and proceeds to the proximal end, causing silica background to occur, but this refractive index contrast eliminates or reduces this silica background. In Figure 11, it can be seen that light is emitted from each fiber core, represented by vertical arrows, without coupling to each other. The effective refractive indices in the operating modes (horizontal dashed lines) differ significantly between the excitation core and the focusing core, resulting in little to no crosstalk.

[0102] Figures 12A to C schematically illustrate further embodiments. In each embodiment, the effective refractive index of the operating mode (horizontal dashed line) differs significantly between the excitation core and the focusing core, resulting in little to no crosstalk.

[0103] Figure 12B shows an excitation core fabricated using only f-doped silica (a lightly doped core and a highly doped cladding), while Figure 12C shows a fiber fabricated using graded-index fibers. The graded index can be defined using the standard formula for graded-index fibers.

number

[0104] The operating mode of the excitation core may be a mode corresponding to the operating wavelength of the excitation signal input to the fiber to generate a Raman response from the target. The operating mode of the focusing core may be a mode corresponding to the wavelength(s) of the Raman signal generated by the target in response to the excitation signal.

[0105] If there is an absolute difference in the refractive index of the focusing core and the excitation core, a refractive index difference will occur between the effective refractive indices of the waveguide modes. For example, if the excitation core has a core refractive index of 1.45 and a cladding refractive index of 1.44, and the focusing core has a core refractive index of 1.46 and a cladding refractive index of 1.45 (similar to embodiment A in Figure 12), this absolute difference will completely isolate the core modes. Furthermore, even if the opposite is true, and the excitation core has a higher refractive index than the focusing core (as in Figure 11), this will still work as long as there is a refractive index difference between the cores.

[0106] Figure 13 is a schematic diagram of a cross-section of the distal or proximal end of one embodiment of a multicore optical fiber 10. The multicore optical fiber 10 comprises one low refractive index excited fiber core 120 made of undoped silica and one annular focusing core 124 made of germanium-doped silica. The annular focusing core 124 has an annular cross-section. In various embodiments, the inner radius of the annular focusing core may be between 10 μm and 125 μm, and the outer radius of the annular focusing core may be between 20 μm and 600 μm. The excited fiber core 120 is disposed in the longitudinal direction within and / or substantially enclosed by an excited core cladding 122 having an annular cross-section, the excited core cladding 122 referred to as a second cladding material and formed of fluorine-doped silica. The annular light-gathering core 124 is disposed within and / or substantially enclosed by the light-gathering core cladding 126 in its longitudinal direction, the light-gathering core cladding 126 is referred to as the third cladding material and is formed of undoped silica. Any suitable material may be used for the second and third cladding, as well as for the excitation core and the light-gathering core, in order to obtain the desired optical properties.

[0107] In the above, the terms core rod and clad rod are used. A core rod may refer to a rod comprising a central portion and a clad, wherein the central portion consists of at least one material and is characterized by a first refractive index profile, and the clad comprises a second material characterized by a second refractive index profile. The clad has an effective refractive index lower than that of the first portion, thereby confining light to the central portion.

[0108] A clad rod may include a hollow silica tube. In some embodiments, a clad rod may refer to a rod comprising a core material characterized by a first effective refractive index profile and a clad material characterized by a second effective refractive index, the second being higher than the first effective refractive index.

[0109] In further embodiments, any desired number of stacking and stretching operations may be used. For example, the rods may be stacked, otherwise arranged, and / or stretched two, three, four, or five times.

[0110] The core may be made of silica glass, which can be doped or undoped. In some embodiments, the core rod is made from at least one of silica, Ge-doped silica, fluorine-doped silica, boron-doped silica, aluminum-doped silica, or silicate glass. Any suitable combination of materials can be used to obtain the desired difference in refractive index between the excitation core(s) and the focusing core(s).

[0111] The clad rod(s) may be a hollow silica capillary. In some embodiments, the clad rod is made from at least one of silica, Ge-doped silica, fluorine-doped silica, boron-doped silica, aluminum-doped silica, or silicate glass. Any suitable material for the clad may be used to obtain the desired optical properties.

[0112] The embodiment can provide a multicore optical fiber having multiple core regions within a cladding region. The cladding region of the fiber may be formed from a hollow, air-filled tube or capillary. The formed multicore optical fiber has a longitudinal length with a distal end for receiving light and a proximal end for transmitting light.

[0113] During use, light is introduced into the proximal end of the fiber and guided to the distal end. The light is transmitted through the fiber via the core region. Light traveling through the fiber is substantially restricted by the cladding region to travel through the core region. The core region can also be called the optical confinement region.

[0114] In some embodiments, a multicore fiber may be packaged with one or more sensing fibers and / or capillary tubes to form a multifunctional fiber device. The imaging fiber and / or sensing fiber and / or capillary tube may be further arranged in another glass or polymer tube, which may be referred to as a package. This further glass or polymer tube may be shorter than the imaging fiber and / or sensing fiber and / or capillary tube. The package includes the imaging fiber, sensing fiber and capillary tube, which are fixed in place by epoxy. The package may form an endoscope. Optionally, any suitable additional outer protective layer may be provided.

[0115] Each feature disclosed herein and (as appropriate) in the claims and drawings may be provided independently or in any suitable combination.

Claims

1. An endoscope fiber having a proximal end and a distal end, comprising a plurality of cores, one or more of the cores being excitation cores (multiple cores are possible), and one or more of the cores being focusing cores (multiple cores are possible), Each of the excitation cores (one or more) includes a solid core. Each of the light-gathering cores (one or more) includes a solid core having a refractive index different from that of the excitation cores (one or more), The excitation core(s) The light-gathering core(s)(s)(s) are configured to transmit the photodetection signal from the target region at or near the distal end to the proximal end. The difference in refractive index between the excitation core(s) and the focusing core(s) is such that it reduces or eliminates crosstalk between the modes(s) of the excitation core(s) and the modes(s) of the focusing core(s). Endoscope fiber.

2. A fiber according to claim 1, wherein the effective refractive index of an electromagnetic mode propagating within the excitation core(s) at the operating wavelength is different from the effective refractive index of a corresponding electromagnetic mode propagating within the focusing core(s).

3. A fiber according to claim 1, wherein the difference in refractive index between the excitation core(s) and the focusing core(s) is such that it substantially does not provide crosstalk and / or mode coupling between the optical excitation signal and the optical focusing signal in the wavelength range of 200 nm to 1200 nm, and optionally in the range of 532 nm to 1064 nm.

4. A fiber according to claim 1, wherein the refractive index of the excitation core(s) (one or more) is within the range of 1.41 to 1.

48. The refractive index of the aforementioned focusing core (one or more) is within the range of 1.41 to 1.

48. A fiber in which the absolute difference in refractive index between the excitation core(s) and the focusing core(s) is within the range of 0.0003 to 0.

07.

5. A fiber according to claim 1, wherein each excitation core (one or more) is spaced at a distance of at least 10 μm and / or 10 μm to 125 μm from the nearest focusing core (one or more).

6. A fiber according to claim 1, wherein each of the excitation cores (one or more) has a diameter in the range of 3 μm to 120 μm, and / or Each of the aforementioned focusing cores (one or more) has a diameter in the range of 3 μm to 120 μm. The excitation core(s) (one or more) are positioned substantially collinearly and / or parallel to the longitudinal axis of the fiber, A fiber in which the light-gathering core(s)(s) are positioned substantially collinearly and / or parallel to the axis of the fiber.

7. A fiber according to claim 6, comprising a plurality of focusing cores concentrically arranged around one or more excitation cores.

8. A fiber according to claim 1, comprising a focusing core having an annular cross-section, substantially concentrically arranged around the axis of the fiber and / or having a central axis collinear with the central longitudinal axis of the fiber.

9. A fiber according to claim 8, wherein the focusing core has an inner diameter in the range of 10 μm to 150 μm and / or greater than 10 μm, and an outer diameter in the range of 13 μm to 1000 μm and / or less than 1000 μm.

10. A fiber according to claim 1, wherein the excitation core(s) (one or more) is configured to transmit light with a wavelength in the range of 200 nm to 1200 nm, and optionally light with a wavelength in the range of 532 nm to 1064 nm. A fiber in which the light-collecting core(s) (one or more) is configured to transmit light in the wavelength range of 200 nm to 1200 nm, and optionally in the range of 532 nm to 1500 nm.

11. A fiber according to claim 1, wherein the fiber has an outer diameter in the range of 125 μm to 1000 μm and / or less than 1000 μm.

12. A fiber according to claim 1, wherein the excitation core(s) comprises at least one of silica or doped silica, and there is a difference of 0.001 to 0.02 between the absolute refractive index of the excitation core(s) and the absolute refractive index of the cladding of the excitation core(s).

13. A fiber according to claim 1, wherein the light-gathering core(s) comprises doped silica, for example, germanium-doped silica, and there is a difference of 0.003 to 0.03 between the absolute refractive index of the light-gathering core(s) and the absolute refractive index of the cladding of the light-gathering core(s).

14. A fiber according to claim 1, wherein the excitation core(s) and the focusing core(s) are disposed within and / or substantially enclosed by a first cladding material in the longitudinal direction.

15. The fiber according to claim 14, wherein the first cladding material comprises fluorine-doped silica.

16. A fiber according to claim 14, wherein the second cladding material surrounds each of the excitation cores (one or more) and is disposed between the excitation cores (one or more) and the first cladding material.

17. The fiber according to claim 16, wherein the second cladding material comprises fluorine-doped silica.

18. A fiber according to claim 14, wherein a third cladding material surrounds each of the light-gathering cores (one or more) and is disposed between the light-gathering cores (one or more) and the first cladding material.

19. The fiber according to claim 18, wherein the third cladding material comprises silica or doped silica, for example, fluorine-doped silica.

20. A fiber according to claim 1, wherein the distal end of the fiber is tapered in the longitudinal direction, and thereby the diameter of the fiber decreases with increasing distance along the longitudinal direction at the distal end.

21. The fiber according to claim 20, wherein the lateral spread of the tapered portion is in the range of 10% to 40% of the maximum diameter of the fiber, and optionally in the range of 5% to 70% of the maximum diameter of the fiber. A fiber in which the longitudinal extension of the tapered shape extends over a length of at least 5 mm from the distal end of the fiber.

22. A fiber according to claim 1, wherein the fiber is configured for collecting detection signals from the distal end or a target region in its vicinity, optionally for collecting Raman detection signals, and / or the difference in refractive index between the excitation core(s) and the focusing core(s) is such that there is substantially no crosstalk of the Raman signals generated in the excitation core(s) to the focusing core(s) by the excitation signals.

23. A fiber connector configured to connect to a fiber according to claim 1, comprising at least one focusing fiber, wherein the at least one focusing fiber is positioned such that the focusing core(s) align with the focusing fiber(s) when the surface of the fiber connector engages with the proximal end of the fiber.

24. A fiber connector according to claim 23, wherein the numerical aperture of the said or each focusing optical fiber is substantially the same as the numerical aperture of the corresponding one or more focusing cores.

25. A fiber connector according to claim 23, comprising at least one excitation fiber, wherein the at least one excitation fiber is positioned such that the excitation core(s) aligns with the excitation fiber(s) when the surface of the excitation connector engages with the proximal end of the fiber according to claim 1.

26. A fiber connector according to claim 23, wherein when the fiber connector is connected to the fiber, the at least one excitation core of the fiber according to claim 1 is arranged to extend through the fiber connector.

27. A fiber connector according to claim 23, wherein the focusing fiber(s) and the excitation fiber(s) or excitation core(s) are bundled together or otherwise attached at the distal end of the connector, spaced apart from each other and / or movable at the proximal end of the connector, and the focusing fiber(s) and the excitation fiber(s) or excitation core(s) are connected to different connectors and / or devices.

28. A detection system comprising a laser light source or other excitation light source connected to the excitation core(s) of the fiber described in claim 1, and a detection device connected to the focusing core(s) of the fiber described in claim 1.

29. A detection system according to claim 28, wherein the system is a Raman spectroscopy system and the detection device includes a Raman spectrometer.

30. A detection system according to claim 28, wherein the laser light source or other excitation light source is connected to the excitation core(s) of the fiber via the fiber connector according to claim 23, and / or the detection device is connected to the focusing core(s) of the fiber via the fiber connector according to claim 23.

31. A method for performing Raman spectroscopy, comprising: transmitting an excitation signal to a target region via an excitation core (or more) of a fiber according to claim 1; receiving a detection signal via the light-gathering core (or more) of the fiber according to claim 1, including a signal (or more) generated in response to the excitation signal; and determining a Raman spectrum from the detection signal.

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