Optical elements

Abstract

An optical element (100) is provided, comprising a first surface (102) for transmitting and / or receiving electromagnetic radiation, the first surface (102) being configured or optically coupled to a portion of an optical fiber (104) having an axis. The optical element (100) comprises a second surface (106) arranged to transmit and / or receive electromagnetic radiation in a direction transverse to the axis of the optical fiber (104), the optical element (100) having a first focal length for electromagnetic radiation transmitted and / or received by an inner portion of the second surface (106) and a second focal length for electromagnetic radiation transmitted and / or received by an outer portion of the second surface (106), the first focal length and the second focal length being different. A method of forming an optical device comprising the optical element (100) and further comprising an optical fiber coupled to the optical element is also provided.

Description

[Technical Field]

[0001] The present invention relates generally to optical elements, particularly but not exclusively to optical elements (such as lenses) for optical fibers that may be part of biomedical devices. [Background technology]

[0002] Optical imaging and characterization techniques are of increasing interest in medical device applications. Optical fibers and fiber optic components enable the design of miniature optical probes for use in these devices—optical probes that can be inserted into tissues or body lumens for imaging or characterization while being less invasive than traditional, larger devices. Such devices may be suitable for characterization or imaging, or for using multiple different techniques simultaneously, sometimes using a single optical fiber to carry multiple optical signals associated with the different techniques. Using a single fiber to achieve multiple different imaging and characterization techniques allows for measurements and imaging to be performed in the same location using a small device, thereby improving access to delicate and narrow luminal organs such as coronary arteries and small airways.

[0003] Recently, optical probes for optical coherence tomography (OCT) have been developed. In these optical probes, OCT signals are captured by the core of a double-clad optical fiber. The inner cladding of this double-clad optical fiber is used to simultaneously guide multiple optical signals or intensities associated with other characterization techniques, including spectroscopic techniques such as fluorescence and absorption spectroscopy. Such single-fiber OCT plus fluorescence techniques have been successfully used in animal and human blood vessels. This technique is a promising candidate for accurately diagnosing high-risk plaque, a major precursor to heart attacks.

[0004] However, OCT has optical requirements that are the polar opposite of those of fluorescence technology. While obtaining high-quality OCT data or images requires focusing optics with a small numerical aperture, which allows for a long working distance (and a large depth of field), fluorescence technology benefits from a large numerical aperture to improve the collection efficiency of the fluorescence radiation. However, probes with lenses with a large numerical aperture typically have a small depth of field. As a result, probes with ideal optical properties for fluorescence technology do not have ideal properties for OCT technology. Other optical technologies also have optical configurations unique to their optical systems, which may be incompatible when multiple technologies are implemented in a single system. These optical techniques include OCT, fluorescence spectroscopy, confocal microscopy, multiphoton microscopy, diffuse optical tomography, total internal reflection fluorescence microscopy, phase contrast microscopy, stimulated emission depletion microscopy, near-field scanning optical microscopy, differential interference contrast microscopy, second harmonic imaging microscopy, reflectance spectroscopy, Raman spectroscopy, and optical coherence elastography.

[0005] There is a need for technological improvement. Summary of the Invention

[0006] In a first aspect of the present invention, there is provided an optical element: a first surface for transmitting and / or receiving electromagnetic radiation, the first surface being configured to be or is optically coupled to a portion of an optical fiber having an axis; a second surface arranged to transmit and / or receive electromagnetic radiation in a direction transverse to the axis of the optical fiber, The optical element has a first focal length for electromagnetic radiation transmitted and / or received by an inner portion of the second surface and a second focal length for electromagnetic radiation transmitted and / or received by an outer portion of the second surface, the first focal length and the second focal length being different focal lengths. the law of nature, the inner and outer portions of the second surface are optimized for use with the optical element to acquire measurements at a plurality of different acquisition parameters using one or more optical techniques; Optical elements.

[0007] In one embodiment, the inner and outer portions of the second surface are optimized for use with the optics to acquire measurements at a plurality of different acquisition parameters using at least two different optical techniques.

[0008] The optical element may be integrally formed.

[0009] The outer portion of the second surface may entirely surround the inner portion of the second surface.

[0010] One or both of the first surface and the second surface may have one or more surface portions adjacent to each other, and the surface portions adjacent to each other may be smooth surface portions.

[0011] In some embodiments, the focal lengths may be defined as a function of electromagnetic radiation wavelength. In one embodiment, the first focal length is greater than the second focal length, where the depth of field associated with an inner portion of the second surface is greater than the depth of field associated with an outer portion of the second surface.

[0012] The optical element is configured to receive at least one of the electromagnetic radiation received within an inner portion of the second surface. The optical fiber may be configured such that a portion or a majority of the electromagnetic radiation received within the outer portion of the second surface is guided within a central region, such as a core region, of the optical fiber, and at least a portion or a majority of the electromagnetic radiation received within the outer portion of the second surface is guided within a region of the optical fiber surrounding the central region, such as a cladding or inner cladding region of the optical fiber.

[0013] Thus, optical elements according to embodiments of the present invention provide at least partially separate paths for electromagnetic radiation received by the outer portion of the second surface and electromagnetic radiation received by the inner portion of the second surface.

[0014] Embodiments of the present invention have the advantage that the optical properties of each portion of the lens can be customized for multiple different optical measurement techniques. This is an advantage over lens systems with only one focal length, where the different optical requirements of multiple techniques can result in suboptimal performance. For example, OCT is an optical technique that desires a large depth of field, which may be associated with a large focal length. On the other hand, detection of fluorescence radiation emitted in random directions requires a large numerical aperture to enable sensitive measurements, which may be associated with a small focal length. The inner portion of the second surface may have a large focal length at each wavelength of electromagnetic radiation, thereby achieving a large depth of field when used with OCT. The outer portion may have a short focal length at each wavelength of electromagnetic radiation, thereby achieving a large numerical aperture that allows fluorescence radiation to be collected by the outer portion with high efficiency.

[0015] In one embodiment, the optical fiber may comprise an inner core for use in OCT measurements and an inner cladding used to collect fluorescence radiation.

[0016] In one embodiment, the outer portion may have a focal length that results in a numerical aperture that is at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8 greater than the numerical aperture of the inner portion.

[0017] The optical element may have any suitable diameter along the axis of the optical fiber, but in certain embodiments of the invention, the optical element has a diameter of less than 1 mm, less than 0.5 mm, less than 0.2 mm, or less than 0.1 mm.

[0018] The second surface of the optical element may be constrained to lie within a circle and may have a diameter of less than 1 mm, less than 0.5 mm, less than 0.2 mm, or less than 0.1 mm. An inner portion of the second surface may be constrained to lie within a circle and may have a diameter of less than 1 mm, less than 0.5 mm, less than 0.2 mm, less than 0.1 mm, or less than 0.01 mm. An outer portion of the second surface may be constrained to lie within a circle and may have an outer diameter of less than 1 mm, less than 0.5 mm, less than 0.2 mm, less than 0.1 mm, or less than 0.01 mm.

[0019] The optical element may be configured such that the second surface is positioned to transmit and / or receive electromagnetic radiation in a direction substantially perpendicular to the axis of the optical fiber.

[0020] The second surface of the optical element may be a spherical or aspherical lens, an axicon lens, a Fresnel lens, a total internal reflection lens, a diffractive optical element, a metalens, or a combination thereof, and may be configured to correct chromatic and / or spherical aberration and / or astigmatism. For example, the inner and outer portions of the optical element may comprise different zones of a Fresnel lens or may have lens portions of different curvatures. The optical element may also have a grating for correcting chromatic aberration or for wavelength-specific separation of radiation.

[0021] The optical element may further comprise at least one reflective surface, which may have a reflective coating, a dichroic coating, or a surface arranged for total internal reflection of electromagnetic radiation. The at least one reflective surface may be configured to direct electromagnetic radiation between a direction along an axis of the optical fiber and a direction transverse to the axis of the optical fiber.

[0022] In some embodiments, the reflective surface may be planar. In other embodiments, the reflective surface may include smooth surface portions that are not planar. The reflective surface may be piecewise continuous.

[0023] The reflective surface may be shaped to correct optical aberrations, such as those caused by other surfaces (e.g., an enclosing catheter sheath) through which the electromagnetic radiation must pass to make the optical measurement, and may also have focusing or defocusing functions.

[0024] The optical element may be configured to couple directly or indirectly optically and mechanically with an optical fiber.

[0025] Noise in the optical signal or crosstalk between the optical signal received by the outer portion of the second surface and the optical signal received by the inner portion of the second surface may be reduced by optimizing the ratio of the diameters of the outer portion and the inner portion of the second surface, for example, the ratio of the outer diameters of the outer portion and the inner portion of the second surface may be 3:1.

[0026] In embodiments in which optical element 100 has a reflective surface configured for total internal reflection, noise in the optical signal or crosstalk between the optical signal received by the outer portion of the second surface and the optical signal received by the inner portion of second surface 106 may be reduced by optimizing the angle between the total internal reflection surface and the axis of the optical fiber. For example, the angle of the total internal reflection surface may be a critical angle for particular wavelengths of electromagnetic radiation, such that some wavelengths are not totally internally reflected.

[0027] Additionally or alternatively, noise in the optical signals or crosstalk between the optical signals received by the outer portion of the second surface 106 and the optical signals received by the inner portion of the second surface may be reduced by using a separating member on the reflective surface or between the inner and outer portions of the second surface. The separating member may be configured to reflect or absorb electromagnetic radiation over a particular wavelength range.

[0028] The optical element may be formed using any suitable method, but in certain embodiments, it is formed using a 3D printing method such as multiphoton lithography. In this embodiment, the optical element 100 may be formed directly on one end of an optical fiber or may be formed separately. The optical element may be formed from any suitable material, such as a photosensitive material, and in certain embodiments, it is formed from "Nanoscribe IP-S."

[0029] In a second aspect of the present invention, there is provided an optical device comprising an optical element according to the first aspect of the present invention, further comprising an optical fiber coupled to the optical element.

[0030] The optical fiber may be of any suitable type, but in one embodiment is a coreless optical fiber. The optical fiber may include a coating (e.g., a coating having a refractive index similar to that of the outer portion of the optical fiber, but including a coating material selected to absorb electromagnetic radiation in a particular wavelength range of interest) to reduce the effects of stray electromagnetic radiation in a particular wavelength range of interest.

[0031] In a third aspect of the present invention, there is provided a method of forming an optical device according to the second aspect of the present invention, comprising the steps of: providing a design for an optical element; providing an optical fiber and positioning one end of the optical fiber relative to a multiphoton 3D printing system; instructing a multiphoton 3D printing system to form an optical element according to the provided design; A method comprising:

[0032] The present invention will be more fully understood from the following description of specific embodiments thereof, the description of which is made with reference to the accompanying drawings. [Brief explanation of the drawings]

[0033] [Figure 1]1 is a microscope image of an optical element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic side view of the optical element shown in FIG. [Figure 3] FIG. 2 is a schematic top view of the optical element shown in FIG. [Figure 4] 1(a) to 1(d) are diagrams showing optical components according to several embodiments of the present invention. [Figure 5] 1 is a graph showing measurement data obtained using an apparatus according to one embodiment of the present invention. [Figure 6] 10(a) to 10(c) are images acquired using a device according to one embodiment of the present invention. [Figure 7] 10A and 10B show optical elements according to further embodiments of the present invention. [Figure 8] 1 is a flowchart illustrating a method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] First, an optical element 100 according to one embodiment of the present invention will be described with reference to Figures 1 to 3. The optical element 100 has a first surface 102 for transmitting and / or receiving electromagnetic radiation, and the first surface 102 is optically coupled to one end of an optical fiber 104. In this embodiment, the optical fiber 104 is a coreless fiber connected to a double-clad optical fiber 105. The optical element 100 is formed directly on the one end of the optical fiber 104.

[0035] The optical element 100 also has a second surface 106 that is positioned to transmit and / or receive electromagnetic radiation in a direction transverse to the axis of the optical fiber 104. In this embodiment, the second surface 106 is positioned to transmit and / or receive electromagnetic radiation in a direction substantially perpendicular to the axis of the optical fiber 104.

[0036] Optical element 100 has a first focal length for electromagnetic radiation transmitted and / or received by an inner portion of second surface 106 and a second focal length for electromagnetic radiation transmitted and / or received by an outer portion of second surface 106. The first focal length and the second focal length are different focal lengths.

[0037] The inner portion of the second surface 106 has a larger focal length and a larger depth of field, which is advantageous for optical coherence tomography (OCT) imaging. The outer portion of the second surface 106 has a shorter focal length than the inner portion, but a larger numerical aperture than the inner portion, thereby allowing for efficient collection of fluorescent radiation. Other combinations of focal lengths are also possible. The focal lengths may be selected to optimize the optical performance of the optical element 100 for one or more optical techniques, including OCT, fluorescence spectroscopy, confocal microscopy, multiphoton microscopy, diffuse optical tomography, total internal reflection fluorescence microscopy, phase contrast microscopy, and stimulated emission depletion microscopy. These include mirror microscopy, near-field scanning optical microscopy, differential interference contrast microscopy, second harmonic imaging microscopy, reflectance spectroscopy, Raman spectroscopy, and optical coherence elastography.

[0038] The inner portion of the second surface 106 is configured to guide the received radiation (e.g., OCT signal) primarily into the inner portion of the coreless fiber 104 and then into the core region of the optical fiber 105. The outer portion of the second surface 106 (the portion associated with a larger numerical aperture) is configured to guide the radiation (fluorescence radiation) primarily into the outer portion of the coreless fiber 104 and then into the inner cladding region of the fiber 105. For example, for fluorescence measurements, the achievable signal-to-noise ratio (S / N ratio) is related to the numerical aperture of the collection cone. In this embodiment, the outer portion of the second surface 106 has a numerical aperture greater than 0.4, which results in a relatively high S / N ratio and correspondingly high sensitivity.

[0039] Optical element 100 is shaped to use total internal reflection at surface 110 to guide light from a transverse direction to a direction along the axis of optical fiber 104. In variations of this embodiment, surface 110 may be modified to have a reflective or dichroic coating, or surface 110 may be a freeform surface.

[0040] The optical element 100 may be used in so-called "side-viewing" endoscopic or intravascular probes, which are typically housed within a transparent catheter sheath. This is to protect the tissue as the probe moves inside during examination and to prevent contamination of the probe. Such a transparent sheath acts as an optically negative cylindrical lens, generating astigmatism. The surface 110 may be shaped to optically correct the astigmatism. The optical element 100 may also have a grating structure to correct chromatic aberration or achieve color separation.

[0041] The optical element 100 may have any suitable dimensions. For example, the second surface 106 of the optical element 100 may have an outer diameter in the range of 1 mm to 0.1 mm, or may have an outer diameter less than this range. The first surface 102 may have an outer diameter that matches the outer diameter of the optical fiber 104 to which the optical element 100 is coupled. For example, the first surface 102 may have an outer diameter of less than 1.5 mm to 0.1 mm, or may have an outer diameter less than this.

[0042] Optical element 100 may be configured such that the inner portion of second surface 106 has a focal length in the range of 0.5 mm to 2 mm in the wavelength range of 500 nm to 1900 nm. While the inner portion may have any suitable shape, in one embodiment, the inner portion is circular with an outer diameter that is 10% to 90% smaller than the outer diameter of the outer portion of second surface 106.

[0043] Additionally, optical element 100 may be configured such that the outer portion of second surface 106 has a focal length of 0.1 mm to 0.5 mm in the wavelength range of 400 nm to 1000 nm. The outer portion of optical element 100 may have a numerical aperture that is at least 0.1 to 0.8 or more greater than the numerical aperture of the inner portion. While the outer portion may have any suitable shape, in this embodiment the outer portion is annular.

[0044] In one embodiment, optical element 100 is configured to reduce or prevent crosstalk between electromagnetic waves or radiation (hereinafter simply referred to as "radiation") received by an outer portion of optical element 100 and radiation received by an inner portion of optical element 100. Such crosstalk, which may have a detrimental effect on measurements or image quality, can be reduced, for example, by optimizing the ratio between the diameter of the aperture in the outer portion of second surface 106 and the diameter of the aperture in the inner portion of second surface 106, or by optimizing the tilt angles of the inner and outer portions. In one example, this The ratio of the tilt angles is 3:1, and the tilt angles are selected so that radiation having a particular wavelength range is not totally internally reflected at the reflective surface of the optical element 100 .

[0045] Additionally, an optical isolating element (not shown) may be used that selectively absorbs or selectively transmits (filters) radiation over a particular wavelength range. The optical isolating element may be disposed, for example, on a surface from which received electromagnetic radiation is reflected. Additionally or alternatively, a coating may be applied to the outer surface of the fiber 104 or fiber 105. The coating may be configured to absorb unwanted radiation. For example, the coating may be configured to absorb stray light that is totally internally reflected at the interface of the optical fiber 104 or fiber 105. Such stray light can be minimized or reduced by using a coating on the exterior of the optical fiber 104 or optical fiber 105 that has a refractive index similar to that of the exterior of the optical fiber 104 or optical fiber 105 but that absorbs light in a particular wavelength range.

[0046] Optical element 100 may be integrally formed from an optically transparent material using 3D printing techniques, as described in more detail below.

[0047] 4(a) to 4(d), we describe examples of lens surfaces that may form the second surface 106 of the optical element 100. In each example, the lens surface is shaped such that the inner portion has a longer focal length, a larger depth of field, and a smaller numerical aperture, while the outer portion has a shorter focal length, a larger numerical aperture, and a shorter depth of field.

[0048] Figure 4(a) is a schematic cross-sectional view of a conventional lens 402, illustrating a possible shape of a surface 403 that may form the second surface 106 of the optical element 100 described above with reference to Figures 1 to 3. The surface 403 has a non-uniform curvature, such that the inner portion has a greater focal length than the outer portion.

[0049] Figure 4(b) is a schematic cross-sectional view of a Fresnel lens 404, illustrating the possible shapes of a surface 405 that may form the second surface 106 of the optical element 100 described above with reference to Figures 1 to 3. Surface 405 has an inner Fresnel zone, which provides a larger focal length, and an outer Fresnel zone, which provides a shorter focal length.

[0050] Figure 4(c) is a schematic cross-sectional view of a metalens 406 having a surface 407. Surface 407 may also form second surface 106 of optical element 100 described above with reference to Figures 1-3. Surface 407 is structured such that the inner portion has a greater focal length than the outer portion.

[0051] As a further option, surface 407 may be the surface of a diffractive optical element (DOE) that has diffractive properties that result in a larger focal length in the inner portion than in the outer portion, for example.

[0052] FIG. 4(d) is a schematic side view of second surface 106, which includes two or more lenses. In this example, outer portion 108 is a total internal reflection (TIR) ​​lens, and inner portion 109 is a refractive lens. Each TIR facet of the TIR lens uses TIR to direct light into optical element 100 (see the close-up inset of FIG. 4(d)). Light passing through the outer portion of the lens may be further refracted at the surface of the lens. Advantageously, using a combination of refraction and TIR in a single lens allows for very compact optical designs with large numerical apertures.

[0053] As a further example, the inner portion of the second surface 106 may be a diffractive optical element and the outer portion of the second surface 106 may be a refractive lens.

[0054] 5 is a graph showing the intensity of fluorescence radiation 502 detected by an apparatus including an optical element according to the present invention compared to the intensity of fluorescence radiation 504 detected using a conventional apparatus. Figure 5 illustrates that an apparatus including an optical element according to the present invention can perform more sensitive fluorescence measurements than a conventional apparatus, which is due to the larger numerical aperture of the outer portion of the second surface of an optical element according to an embodiment of the present invention. Meanwhile, the depth of field of the inner portion of the second surface is advantageous for OCT imaging.

[0055] Those skilled in the art will appreciate that optical elements according to embodiments of the present invention can be used in a variety of applications, including but not limited to OCT and fluorescence imaging. For example, the optical elements can also be used in autofluorescence imaging, autofluorescence sensing, fluorescence imaging with contrast agents, fluorescence sensing with contrast agents, confocal microscopy, multiphoton microscopy, diffuse optical tomography, total internal reflection fluorescence microscopy, phase contrast microscopy, stimulated emission depletion microscopy, near-field scanning optical microscopy, differential interference contrast microscopy, second harmonic imaging microscopy, reflectance spectroscopy, Raman spectroscopy, and optical coherence elastography.

[0056] FIG. 6(a) is an example of an integrated OCT and autofluorescence image acquired using an apparatus including an optical element according to one embodiment of the present invention. FIGS. 6(b) and 6(c) show the corresponding OCT and autofluorescence images, respectively. These images show an atherosclerotic plaque acquired using one embodiment of the present invention. The presence of the plaque was confirmed by the strong intensity of the detected fluorescent radiation from the 6 o'clock to 9 o'clock direction (see FIGS. 6(a) and 6(c)). In this embodiment, the inner portion of the optical element may be designed to optically transmit radiation with a bandwidth greater than 50 nm, and the outer portion of the optical element may be designed to optically transmit radiation with a bandwidth greater than 20 nm.

[0057] FIG. 7 illustrates an optical element 700 according to a further embodiment of the present invention. In this example, an inner portion 702 of a second surface 704 of the optical element 700 is a diffractive optical element (DOE) surface optimized for chromatic confocal imaging, allowing different wavelength bands to be focused at different locations. In FIG. 7, the different wavelength bands are indicated by different shades of gray. In this manner, depth-resolved confocal signals can be detected using a spectrometer (not shown), which separates signals from various wavelengths onto different pixels of a detector (not shown). An outer portion 706 of the second surface 704 may be a DOE surface or, for example, a Fresnel zone with a shorter focal length and a larger numerical aperture than the inner portion 702.

[0058] It will be apparent to those skilled in the art that optical elements according to embodiments of the present invention can be used to examine biological tissues, both in vivo and ex vivo. For example, the optical elements can be used for intravascular imaging, diagnosis, and treatment. They can also be used for other endoscopic applications, such as examining the digestive, respiratory, urinary, and reproductive systems and the ear, and for diagnosing and treating cancer and other diseases. They can also be used to examine any type of object, such as a pipe, tank, or other structure.

[0059] Additionally, an optical element according to an embodiment of the present invention and at least a portion of an optical fiber optically coupled to the optical element may be disposed within a metal tube or needle that is transparent to at least electromagnetic radiation and has an inlet.

[0060] Additionally, an optical element does not necessarily have to be used to simultaneously perform multiple measurements associated with multiple different measurement or imaging techniques. The optical element may be used to acquire multiple measurements or images using a single technique, with the inner and outer portions of the optical element optimized for multiple different acquisition parameters (also referred to as "focusing parameters"). For example, the inner and outer portions of the second surface of the optical element may be optimized to acquire fluorescence radiation at multiple different depths within the object or tissue of interest.

[0061] A method 800 for forming an optical device according to an embodiment of the present invention is described below. The optical device comprises an optical fiber. In this embodiment, an optical element is formed on the optical fiber. The optical element may be, for example, the optical element 100 described above.

[0062] Method 800 includes an initial step 802 of preparing a design for an optical element. Step 802 includes designing the optical element using, for example, optical design software "Zemax®" and exporting the resulting design in a computer-aided design (CAD) file format. The design may also be further refined using software "Solidworks®" (Dassault Systemes, France).

[0063] Method 800 further includes step 804 of providing an optical fiber and positioning one end of the optical fiber relative to a multiphoton 3D printing system. Step 804 may include providing a length of coreless or step-index fiber spliced ​​onto a double-clad or single-mode optical fiber.

[0064] The method 800 also includes a step 806 of instructing a multiphoton lithography system to 3D print an optical element according to the provided design.

[0065] Multiphoton lithography systems allow for the printing of optical elements directly onto one end of an optical fiber. After the optical fiber is attached to the multiphoton lithography system using a suitable fiber holder, the system is aligned with the end of the optical fiber. This is easily done by directing light into the opposite end of the fiber. The other end of the optical fiber can then be identified using a CCD camera. The optical element is then printed onto the end of the optical fiber. In this way, the optical element is printed using the Nanoscribe It is integrally formed using a suitable photosensitive material such as IP-S.

Claims

1. a first surface for transmitting and / or receiving electromagnetic radiation, the first surface being configured to be or is optically coupled to a portion of an optical fiber having an axis; a second surface positioned to transmit and / or receive electromagnetic radiation in a direction transverse to the axis of the optical fiber, the optical element has a first focal length for electromagnetic radiation transmitted and / or received by an inner portion of the second surface and a second focal length for electromagnetic radiation transmitted and / or received by an outer portion of the second surface, the first focal length and the second focal length being different focal lengths; the optical element is used to obtain measurements using at least two different imaging techniques; each of the first focal length and the second focal length is customizable for use with a corresponding one of the at least two different imaging techniques; the first focal length is greater than the second focal length; a depth of field associated with the inner portion of the second surface is greater than a depth of field associated with the outer portion of the second surface; Optical elements.

2. The optical element of claim 1 , wherein the optical element is integrally formed.

3. The optical element according to claim 1 , wherein the outer portion of the second surface entirely surrounds the inner portion of the second surface.

4. 4. The optical element according to claim 1, wherein one or both of the first surface and the second surface has one or more smooth surfaces adjacent to each other.

5. The optical element is at least a portion or a majority of the electromagnetic radiation received within the inner portion of the second surface is directed within a central region of the optical fiber, including a core region of the optical fiber; at least a portion or a majority of the electromagnetic radiation received within the outer portion of the second surface is guided within a region of the optical fiber surrounding the central region, including a cladding or inner cladding region of the optical fiber; The optical element according to any one of claims 1 to 4, which is configured as follows.

6. The optical element of any one of claims 1 to 5, wherein the outer portion has a focal length that results in a numerical aperture that is at least 0.1 greater than the numerical aperture of the inner portion.

7. 7. The optical element according to claim 1, wherein the second surface of the optical element is constrained to lie within a circle and has a diameter of less than 1 mm.

8. The optical element according to any one of claims 1 to 7, wherein the inner portion of the second surface is constrained to lie within a circle and may have a diameter of less than 1 mm.

9. The optical element according to any one of claims 1 to 8, wherein the outer portion of the second surface is constrained to lie within a circle and may have an outer diameter of less than 1 mm.

10. 10. The optical element of claim 1, wherein the optical element is configured such that the second surface is positioned to transmit and / or receive electromagnetic radiation in a direction substantially perpendicular to the axis of the optical fiber.

11. 11. The optical element according to claim 1, wherein the second surface of the optical element is a surface of a spherical or aspherical lens, an axicon lens, a Fresnel lens, a total internal reflection lens, a diffractive optical element, a metalens, or a combination thereof.

12. An optical element described in any one of claims 1 to 10, wherein the inner portion of the second surface includes a refractive lens and the outer portion of the second surface includes an internal total reflection lens.

13. The optical element of claim 12, wherein the total internal reflection lens has at least one total internal reflection (TIR) ​​facet, and the at least one TIR facet is configured to utilize TIR to guide light into the optical element.

14. The outer portion of the second surface includes a circular protrusion extending in a direction approximately perpendicular to the second surface, the annular projection has an outer minor surface further from the center of the second surface and an inner minor surface closer to the center of the second surface; The optical element of any one of claims 1 to 10, wherein the outer facets comprise total internal reflection (TIR) ​​facets.

15. An optical element described in any one of claims 1 to 10, wherein the inner portion of the second surface includes a diffractive optical element and the outer portion of the second surface includes a refractive lens.

16. 16. The optical element according to any one of claims 1 to 15, wherein the optical element comprises at least one reflective surface, the reflective surface having a reflective or dichroic coating or arranged for total internal reflection of electromagnetic radiation.

17. 17. The optical element of claim 16, wherein the reflective surface is configured to guide electromagnetic radiation between the direction along the axis of the optical fiber and the direction transverse to the axis of the optical fiber.

18. 18. The optical element according to claim 16 or 17, wherein the reflecting surface is a flat surface.

19. 18. The optical element according to claim 16, wherein the reflecting surface includes a smooth surface portion that is not flat.

20. 18. An optical element according to claim 16 or 17, wherein the reflective surface is piecewise continuous.

21. The optical element according to any one of claims 1 to 20, wherein the optical element is configured to be directly coupled or indirectly optically and mechanically coupled to the optical fiber.

22. An optical element described in any one of claims 1 to 21, wherein noise in an optical signal or crosstalk between an optical signal received by the outer portion of the second surface and an optical signal received by the inner portion of the second surface is adjustable by customizing the ratio of the diameters of the outer portion and the inner portion of the second surface.

23. An optical element described in any one of claims 1 to 22, which reduces noise in an optical signal or crosstalk between an optical signal received by the outer portion of the second surface and an optical signal received by the inner portion of the second surface by using a separating member or a reflective surface between the inner portion and the outer portion of the second surface.

24. 24. The optical element of claim 23, wherein the separating member is configured to reflect or absorb electromagnetic radiation having a particular range of wavelengths.

25. The optical element according to any one of claims 1 to 24, wherein the optical element is formed directly on one end of the optical fiber.

26. An optical device comprising the optical element according to any one of claims 1 to 25, further comprising an optical fiber coupled to the optical element.

27. 27. The optical device of claim 26, wherein the optical fiber is a coreless optical fiber.

28. 28. An optical device according to claim 26 or 27, wherein the optical fiber is provided with a coating selected to absorb electromagnetic radiation having a particular wavelength range, in order to reduce the effects of stray electromagnetic radiation in said wavelength range.

29. A method for forming the optical device according to any one of claims 26 to 28, comprising the steps of: providing a design for the optical element; providing an optical fiber and positioning one end of the optical fiber relative to a multiphoton lithography system; instructing the multiphoton lithography system to 3D print the optical element according to the provided design; A method comprising:

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