阅读说明：本技术 共振光纤光束操纵器 (Resonant fiber optic beam manipulator ) 是由 M.H.门德尔 P.格雷格 R.D.福尔哈伯 J.J.莫雷海德 A.哈彻 于 2021-05-28 设计创作，主要内容包括：具有使光束以规则周期在渐变折射率光纤中重新成像的折射率分布的渐变折射率光纤可以包括一组弯曲部,其弯曲周期与渐变折射率光纤的节距匹配或几乎匹配。例如,可以使用一个或多个弯曲设备在渐变折射率光纤中形成该一组弯曲部,该弯曲设备包括一个或多个突起,该突起具有与渐变折射率光纤的节距匹配或几乎匹配的周期性。一个或多个弯曲设备的第一部分可以被致动以朝向一个或多个弯曲设备的第二部分移动,使得一个或多个突起导致在渐变折射率光纤中形成弯曲部。(A graded-index fiber having a refractive index profile that causes a beam to be re-imaged in the graded-index fiber at a regular period may include a set of bends whose bending period matches or nearly matches the pitch of the graded-index fiber. For example, the set of bends may be formed in the graded-index fiber using one or more bending devices that include one or more protrusions having a periodicity that matches or nearly matches the pitch of the graded-index fiber. The first portion of the one or more bending devices may be actuated to move toward the second portion of the one or more bending devices such that the one or more protrusions cause a bend to be formed in the graded-index optical fiber.)

1. An optical assembly, comprising:

an input optical fiber providing an optical beam; and

a graded-index fiber coupled to the input fiber, the graded-index fiber having a refractive index profile such that the beam is re-imaged in the graded-index fiber at a regular period having a pitch length, wherein the graded-index fiber comprises a set of bends having a bend period matching or nearly matching the pitch length of the graded-index fiber.

2. The optical assembly of claim 1, wherein the regular period of the light beam and the set of bends applied to the graded-index fiber are sinusoidal.

3. The optical assembly of claim 1, wherein the set of flexures includes one or more flexures in a first orientation and one or more flexures in a second orientation.

4. The optical assembly of claim 3, wherein the one or more bends in the first orientation control an angle at which the light beam exits the graded-index fiber on a first axis, and wherein the one or more bends in the second orientation control a spatial offset of the light beam on a second axis.

5. The optical assembly of claim 1, wherein the graded-index fiber includes a number of pitch lengths, and wherein each bend in the set of bends is spaced one-half pitch length from an adjacent bend in the set of bends.

6. The optical assembly of claim 1, wherein the graded index fiber includes a number of pitch lengths, and wherein a first bend of the set of bends is aligned with a first quarter pitch length of the graded index fiber.

7. The optical assembly of claim 1, wherein each bend in the set of bends has an opposite sign relative to an axis of the graded-index optical fiber than an adjacent bend in the set of bends.

8. The optical assembly of claim 1, wherein the set of bends includes only a single bend centered at a location of the graded-index fiber that is at least a quarter pitch from an end of the graded-index fiber.

9. The optical assembly of claim 1, wherein a number of pitch lengths in the graded-index fiber satisfies a threshold based on one or more metrics related to accumulating error per pitch of the graded-index fiber.

10. A method, comprising:

routing the graded-index optical fiber through one or more bending devices, wherein the one or more bending devices comprise one or more protrusions having a periodicity that matches or nearly matches a pitch of the graded-index optical fiber; and

actuating the first portion of the one or more bending devices to move toward the second portion of the one or more bending devices such that the one or more protrusions cause a series of bends to be formed in the graded-index fiber, wherein the periodicity of the one or more protrusions causes the series of bends to have a bend period that matches or nearly matches the pitch of the graded-index fiber.

11. The method of claim 10, wherein the one or more bending devices comprise a first bending device arranged to induce a first series of bends in the graded-index fiber in a first orientation and a second bending device following the first bending device to induce a second series of bends in the graded-index fiber in a second orientation.

12. The method of claim 11, wherein the first series of bends in the first orientation and the second series of bends in the second orientation are perpendicular or parallel to each other.

13. The method of claim 11, wherein the first series of bends manipulate the light beam passing through the graded index fiber in the near field, and wherein the second series of bends manipulate the light beam passing through the graded index fiber in the far field.

14. The method of claim 10, further comprising:

rotating the one or more bending devices relative to the graded-index fiber, wherein the periodicity of the one or more protrusions is shorter than the pitch of the graded-index fiber, and wherein rotating the one or more bending devices relative to the graded-index fiber extends the bending period to match or nearly match the bending period to the pitch of the graded-index fiber.

15. The method of claim 10, wherein a two-dimensional or three-dimensional series of bends are formed in the graded-index fiber.

16. A bending apparatus comprising:

a conditioning stage adapted to receive a graded-index optical fiber, wherein the conditioning stage comprises a first portion having a first set of protrusions and a second portion having a second set of protrusions, having a periodicity that matches or nearly matches the pitch of the graded-index optical fiber; and

an actuation mechanism for moving the first portion of the conditioning stage toward the second portion of the conditioning stage such that the first set of protrusions and the second set of protrusions form a series of bends in the graded-index optical fiber.

17. The bending apparatus according to claim 16, wherein the periodicity of the one or more protrusions causes the series of bends to have a bend period that matches or nearly matches a pitch of the graded-index fiber.

18. The bending apparatus according to claim 16, wherein the first and second sets of protrusions do not exert a force on the graded-index fiber when the first and second portions of the conditioning stage are in a neutral state in which the graded-index fiber is routed through the conditioning stage.

19. The bending apparatus according to claim 16, further comprising:

a rotation stage adapted to rotate the bending apparatus relative to the graded-index fiber.

20. The bending apparatus according to claim 16, wherein the actuation mechanism is capable of adjusting the shape of the series of bends such that a light beam output by the graded-index fiber has at least two states.

Technical Field

The present disclosure relates generally to steering or otherwise routing an optical beam through an optical fiber, and more particularly, to steering or otherwise routing an optical beam through a graded index fiber (graded index fiber) having a set of bends with a bend period that matches or nearly matches the pitch (pitch) of the graded index fiber.

Background

Laser material processing may be used for cutting, drilling, welding, brazing, surface annealing, alloying, hardening, and/or other applications. In particular, laser material processing typically includes the use of one or more optical fibers to deliver a high power and/or high intensity laser beam to a workpiece on which the laser material processing is to be performed. For example, a typical fiber optic delivery laser material processing system may include a laser source (e.g., one or more fiber optic laser modules), an optical coupler unit, a delivery fiber (typically 10-50 meters in length and contained in a delivery cable that may be spliced at one or both ends), and a processing head. The processing head is an optical assembly that includes a receiver for delivering optical fibers, optics for projecting laser power, and any components required for laser-based processing. In operation, the laser source transmits laser emission into the optical coupler unit (e.g., through free space or through a separate optical fiber), and the laser emission can be coupled into the delivery fiber through the optical fiber or through the optical coupler unit that transmits the emission internally through free space and can amplify or reduce the emission. The delivery fiber then transmits the laser light to a processing head, which projects the laser light onto a workpiece associated with performing a material processing task. Thus, advantages of laser material processing may include high productivity, non-contact nature of the process, improved quality, high precision and mobility of the delivery point of the laser beam, and the like.

One challenge that arises in the context of laser material processing relates to fiber optic bundle shaping (e.g., for cutting, welding, etc.), an increasingly important aspect of high power laser material processing. For example, in some cases, the high power and excellent beam quality of fiber lasers can be used to perform "keyhole welding" with high aspect ratio penetration profiles in a narrow fusion zone with low distortion and minimal heat affected zone. In other examples, larger laser spot sizes with lower power densities may be used to perform shallower "conduction welds" that may be used for aesthetic welding, to minimize the need for post-processing steps, etc. In other examples, processing different materials or materials with different thicknesses may require different properties of the beam (e.g., some materials may require a high brightness, small spot size, while other materials may require a larger, higher divergence beam). Accordingly, there may be a need for a laser system having beam shaping capabilities and the ability to cycle or switch between multiple states in order to control and/or alter the characteristics of the beam.

Disclosure of Invention

According to some embodiments, an optical assembly may comprise: an input optical fiber providing an optical beam; and a graded-index fiber coupled to the input fiber, the graded-index fiber having a refractive index profile such that the beam is re-imaged in the graded-index fiber at a regular period having a pitch length, wherein the graded-index fiber comprises a set of bends having a bend period matching or nearly matching the pitch length of the graded-index fiber.

According to some embodiments, a method may comprise: routing (routing) the graded-index fiber through one or more bending devices, wherein the one or more bending devices comprise one or more protrusions having a periodicity that matches or nearly matches a pitch of the graded-index fiber; and actuating a first portion of the one or more bending devices to move toward a second portion of the one or more bending devices such that the one or more protrusions cause a series of bends to be formed in the graded-index fiber, wherein a periodicity of the one or more protrusions causes the series of bends to have a bend period that matches or nearly matches a pitch of the graded-index fiber.

According to some embodiments, the bending apparatus may comprise: a conditioning stage (stage) adapted to receive the graded-index fiber, wherein the conditioning stage comprises a first portion having a first set of protrusions and a second portion having a second set of protrusions, having a periodicity that matches or nearly matches the pitch of the graded-index fiber; and an actuation mechanism for moving the first portion of the conditioning stage toward the second portion of the conditioning stage such that the first set of protrusions and the second set of protrusions form a series of bends in the graded-index optical fiber.

Drawings

FIG. 1 is a schematic illustration of a graded-index fiber;

FIG. 2 is a schematic view of one or more example embodiments of a bending apparatus that may be used to apply one or more bends in a graded-index optical fiber;

FIG. 3 is a schematic diagram of one or more example embodiments of a plurality of bending devices arranged in a cascade configuration;

4A-4C are exemplary diagrams relating to the propagation length of a graded-index optical fiber manipulated using the bending apparatus and methods described herein;

FIG. 5 is a flow chart of an example process for applying a set of bends in a graded-index fiber using one or more bending devices.

Detailed Description

The following detailed description of example embodiments refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements.

As noted above, fiber optic bundle shaping is an increasingly important aspect of high power (e.g., greater than 100 watts (W)) laser material processing and/or other applications (e.g., light detection and ranging (LIDAR), endoscopic microscopy, and/or the like) that may require a rasterizeable fiber optic source. For example, in the context of laser material processing, it is desirable for the laser to be able to control and alter the laser light of the beam characteristics, as different materials or materials having different thicknesses may require different characteristics of the beam. For example, thin stainless steel (e.g., stainless steel less than 3 millimeters (mm) thick) typically requires a high brightness, small spot, while thicker low carbon steel (e.g., steel greater than 12mm thick) may require a larger, higher divergence beam.

Thus, an important factor in designing a laser system with beam shaping capabilities is the ability to provide cycling or switching between multiple states that produce beams with different characteristics. However, an actuation method is required to switch between different states, which is a challenge for kilowatt (kW) lasers, as the actuation method must be substantially lossless. For example, switches used in telecommunications and/or data communications applications may result in losses of 0.5 decibels (dB) or higher, which is unacceptable for such high powers. In addition to the desire to keep the entire system in the fiber to improve manufacturability and reduce alignment tolerances, there is also a need to provide a non-destructive actuation method to switch between different states, which greatly limits the possible actuation options. While a simple actuation method may be to have two laser engines that can be independently turned on and off, this actuation method adds significantly to the cost of the system.

Graded index fiber is one possible alternative to two independently controlled laser engines. In particular, graded index fibers typically have a refractive index profile that is parabolic or approximately parabolic in square, as shown by the following equation:

wherein n is₁Is the peak (or maximum) index, r is the radial coordinate (e.g., distance from the center of the graded-index fiber), and f is the focal length of the graded-index fiber, related to the pitch of the graded-index fiber. Thus, bending a graded-index fiber typically results in a translation of the center of the beam, and a curvature of the bend (1/local bend radius (R))_bend) Proportional). The shift (Δ x) also depends on the characteristics of the graded-index fiber, such as the focal length (f) and peak/maximum refractive index (n) of the graded-index fiber₁) As shown in the following formula:

thus, one potential approach to providing an all-fiber beam switch is to use a graded-index fiber and bend the graded-index fiber adiabatically to different degrees, so that different beam-offset locations within the fiber can be implemented depending on the curvature of the bend. However, for larger deflections, adiabatic bending requires a longer bent fiber length and a larger overall bend angle, and can cause significant stress on the fiber, which can lead to breakage. Furthermore, if such an offset is desired to achieve variable offset launch into a second fiber (e.g., a multi-core fiber, a multi-spin fiber, etc.), stress occurs right at the splice point, which makes splice (spice) optimization more difficult and makes splices more prone to failure.

Some embodiments described herein relate to an apparatus and method that uses periodic re-imaging properties of graded-index fibers to route a beam within the fiber or to spatially translate the beam using a series of well-controlled bends. In this way, some embodiments described herein may achieve a greater range of beam steering (e.g., relative to a single bend) by using a series of less intense bends rather than a single long adiabatic bend, as large bends may be limited by local stresses applied to the fiber. In addition, or alternatively, a single short bend (rather than a series of bends) can be formed in the graded-index fiber at well-controlled locations, which can reduce stress on the graded-index fiber and reduce the need for precise adjustment of the bending apparatus to accommodate the periodicity or pitch of a particular graded-index fiber. Furthermore, by routing the optical beams within the optical fibers, some embodiments described herein may eliminate or reduce input/output coupling losses into the routing device and improve manufacturability by reducing alignment tolerances. Furthermore, some embodiments described herein may be used to route a beam in space and angle, thereby steering a controlled two-dimensional beam out of an optical fiber. In some embodiments, the apparatus and methods described herein may be used in kilowatt-scale fiber optic beam forming or other fields, such as laser radar, endoscopic microscopy, and/or any other suitable application where a rasterizeable fiber optic source is desired.

FIG. 1 shows an example 100 of a graded-index fiber. More specifically, as described herein, the square of the refractive index profile of a graded-index fiber can be parabolic or approximately parabolic (e.g., in the core region), with the refractive index varying smoothly in the radial direction from the axis of the graded-index fiber to a particular radial position. In other words, a graded-index fiber has a refractive index profile that is parabolic or approximately parabolic in cross-section and is uniform along the length of the graded-index fiber. Thus, light propagating through a graded-index fiber follows a periodic trajectory of a parabolic or near-parabolic refractive index profile (profile) through the graded-index fiber. For example, as shown in fig. 1, one or more light rays originating from a point source (e.g., a laser source, an input fiber coupled to the laser source, and/or the like) may propagate through a graded-index fiber.

Due to the periodic imaging nature of the graded index fiber, the point source is accurately re-imaged at each pitch (and each half pitch is imaged but inverted). Mathematically, the light rays passing through a single pitch of the graded index fiber are computed as four consecutive Fourier transforms, representing collimation (e.g., in the first quarter pitch), focusing onto the inverse image (e.g., in the second quarter pitch), collimation (e.g., in the third quarter pitch), and refocusing (e.g., in the fourth quarter pitch). In some embodiments, when the graded-index fiber is stretched, the pitch of the graded-index fiber is determined by the core diameter and the numerical aperture (aperature). In some embodiments, as described herein, periodic bending of a graded-index fiber with a bending period that matches or nearly matches the pitch of the graded-index fiber results in stronger and more versatile optical path modifications than adiabatic bending.

As noted above, fig. 1 is provided as an example. Other examples may be different than that depicted in fig. 1.

FIG. 2 is a schematic diagram of one or more example embodiments 200 of a bending device 210, which bending device 210 may be used to apply one or more bends in a graded-index fiber 215. In some embodiments, the bending device 210 can be designed to apply a series of bends to the graded-index fiber 215 in alternating directions every odd number of quarter pitches (e.g., every half pitch, starting with the first quarter pitch) based on the periodic imaging behavior of the graded-index fiber 215, as described herein. In this manner, the series of bends may have a bend period that matches or nearly matches the pitch of the graded-index fiber 215. For example, for an ideal fiber, the period of the bending device 210 would be equal to the pitch of the graded-index fiber 215. However, due to fiber manufacturing tolerances, the pitch of the manufacturing may shift from the nominal value. To correct for deviations between the manufactured pitch and the nominal value, the bending apparatus 210 may be manufactured with a shorter period than the pitch of the graded-index fiber 215, and the bending apparatus 210 may be placed on a rotary stage 220. In some embodiments, the rotational stage 220 may include a knob or other rotational mechanism to rotate the bending apparatus 210 relative to the graded-index fiber 215 to extend the effective period applied to the graded-index fiber 215 and to enable in situ adjustment of the period of perturbation that causes the bend to form in the graded-index fiber 215.

As described herein, for a given acceptable level of curvature imposed on the graded-index fiber 215, the bending apparatus 210 can allow the beam to be displaced by approximately 4N times than using a single adiabatic bend, where N is the number of pitches in the graded-index fiber 215. In other words, the bending device 210 can use a bending curvature on the graded-index fiber 215 of approximately 1/4N times to achieve the beam shift for the target amount of beam shift. Thus, the bending apparatus 210 utilizes the bending characteristics of the graded-index fiber 215 more efficiently than adiabatic bending. In this way, the bending device 210 exerts much less stress on the graded-index fiber 215, provides much greater performance, and significantly simplifies mechanical implementation.

As shown in fig. 2, a graded-index fiber 215, nominally N-pitch in length, is routed through the bending device 210. In some embodiments, the bending device 210 has one or more protrusions 235, 245, the period (Λ) of the protrusions 235, 245 matching or nearly matching (e.g., a threshold amount shorter than) the pitch of the graded-index fiber 215. In the neutral setting, the protrusions 235, 245 of the bending device 210 are not in contact with the graded-index fiber 215, or are barely in contact with the graded-index fiber 215. Thus, in the neutral setting, the protrusions 235, 245 do not exert a force on the graded-index fiber 215. Generally, as described above, light emitted coaxially (on-axis) at the entrance of the graded-index fiber 215 leaves the coaxial axis (Δ x ═ 0) and is accurately re-imaged. This fiber state is particularly useful for producing a nominally undisturbed high beam quality output state.

In some embodiments, bending device 210 includes an actuation mechanism 225, such as a micrometer knob and/or the like, that can be adjusted to move a first portion 230 of bending device 210 toward a second portion 240 of bending device 210. In some embodiments, the protrusions 235, 245 cause the graded-index fiber 215 to bend in a wavy pattern when the actuation mechanism 225 is adjusted to move the first portion 230 toward the second portion 240. In some embodiments, the bending device 210 may be aligned (align) such that the one or more protrusions 235 of the first portion 230 and the one or more protrusions 245 of the second portion 240 are aligned with an odd quarter pitch length of the graded-index fiber 215. As such, when the protrusions 235, 245 cause the graded-index fiber 215 to bend in a wave-like pattern, a series of bends may be formed in the graded-index fiber 215, a first bend in the series of bends being aligned with a first quarter-pitch length of the graded-index fiber 215, and each bend in the series of bends being spaced from an adjacent bend by a half-pitch length. Thus, the series of bends formed in the graded-index fiber 215 resonate with the inherent periodicity of the graded-index fiber 215. The small local bend is equivalent to introducing a tilt in the graded-index fiber 215, and because the fourier transform of the tilt is a shift, the net effect is that the beam propagating through the graded-index fiber 215 is gradually shifted from the center of the graded-index fiber 215 every half pitch, as shown in graph 250. The bending (or tilt) that occurs per half pitch is opposite in sign (sign) with respect to the axis of the graded-index fiber 215, which complements the image flipping behavior of the graded-index fiber 215 per half pitch and allows the offset to increase long. Thus, the total offset may be controlled by the number of cycles of the bending device 210 and the degree to which the two portions 230, 240 of the bending device 210 are moved towards each other.

In some embodiments, configuring the bending device 210 as shown in FIG. 2 can provide a bend having an intensity independent of the focal length of the first order graded-index fiber 215. In this manner, the graded-index fiber 215 may be freely selected according to other system constraints, such as better mode matching with an input fiber coupled to the graded-index fiber 215 to provide the light beam to the graded-index fiber 215, an output fiber coupled to the graded-index fiber 215 to receive the light beam after passing through the graded-index fiber 215, and so forth. In this case, the period of the bending device 210 (e.g., the period of the protrusions 235, 245 that cause the bends in the graded-index fiber 215 to be formed) may be adjusted to correspond to the pitch of the graded-index fiber 215. In general, the beam-shifting behavior of the bending device 210 is not strongly dependent on the precise shape of the periodic curve induced in the graded-index fiber 215. For example, the graded-index fiber 215 may be bent in a sinusoidal pattern or another smoothly varying oscillating curve, a sequence of alternating circular arcs, a sequence of straight or nearly straight segments connected by tight bends near odd quarter-pitch locations, or the like. For example, as shown in FIG. 2, when bent by a near point contact actuator, the graded-index fiber 215 may have a natural elastic bend shape, which produces a smoothly varying curve that approximates a sinusoidal curve.

In one numerical example of a bending device 210, an input beam provided by an input fiber may have a spot diameter of 50 microns and a divergence of 0.1 radians. Using a fused silica graded index fiber 215 having a focal length of 750 microns and a Numerical Aperture (NA) of 0.21, and taking into account stress optical effects caused by bends in the graded index fiber 215, using 4 alternating bends (e.g., corresponding to two pitches of the graded index fiber 215, as shown in fig. 2), each bend being 2.4 degrees, separated by a half pitch length of 3.5 millimeters, can produce a beam position shift of 100 microns, which is a practical and useful amount compared to an actual beam size of 50 microns. The actual bend angle of 2.4 degrees is relatively small and actuation on the graded-index fiber 215 is simple, does not cause damage to the graded-index fiber 215, and does not require complex fiber handling or geometry.

In some embodiments, two multi-curving devices 210 may be cascaded, one after the other, with multi-curving devices 210 oriented in a perpendicular orientation to each other. For example, the axes of graded-index fibers 210 are aligned along direction z, a first multi-bending device 210 may operate in the x-z plane, and a second multi-bending device 210 may operate in the y-z plane. Thus, the two multi-bending devices 210 can be independently adjusted to allow the user to arbitrarily move the beam in the x-y plane, which provides useful capabilities in many applications where a rasterized or addressable beam position is desired. Additionally or alternatively, two-dimensional addressing capability may be implemented using a single multi-bending device 210, which multi-bending device 210 may be actuated in any laterally desired direction. For example, the bending device 210 shown in FIG. 2 can additionally be rotated about the fiber axis (e.g., using a rotating mechanism). In addition, or alternatively, the actuation surface contacting the graded-index fiber 215 may be a small ring or hole in a flat stack tab that can move the graded-index fiber 215 in two dimensions at each actuator. The applied motion of the ring or aperture can be adjusted in the x-and y-orientations using a two-dimensional adjustment stage instead of the one-dimensional stage shown in fig. 2.

In some embodiments, the bending apparatus 210 is made to high precision because simulations indicate that the desired deflection is on the order of 10 μm. Thus, the protrusions 235, 345 may be fabricated to have exactly the same height, or at least have an exact mirror image relationship between the various portions. For example, in some embodiments, the bending apparatus 210 may be manufactured to a high degree of precision using wire electrical discharge machining or the like.

As described above, fig. 2 is provided as one or more examples. Other examples may be different than that depicted in fig. 2. For example, the number and arrangement of components shown in FIG. 2 are provided as examples. Indeed, the arrangement shown in fig. 2 may include additional components, fewer components, different components, or components arranged differently than those shown in fig. 2. Additionally or alternatively, one set of components (e.g., one or more components) in fig. 2 may perform one or more functions described as being performed by another set of components in fig. 2.

Fig. 3 is a diagram of one or more example implementations 300 of a plurality of bending devices arranged in a cascade configuration. For example, as shown in FIG. 3, an input fiber 310 is coupled to a first bending device 320 and a second bending device 330 arranged in a cascade configuration with a quarter-pitch graded-index fiber 340 between the two bending devices 320, 330. In some embodiments, the bending devices 320, 330 may operate on the same axis, a vertical axis, or another mutual angle. For example, in fig. 3, the bending devices 320, 330 are arranged to operate on a vertical axis. Thus, the first bending device 320 can control the angle at which the beam leaves the quarter-pitch graded-index fiber 340 in the y-direction, and the second bending device 330 can control the spatial offset of the beam in the x-direction. Combining the two bending devices 320, 330 with the quarter-pitch graded-index fiber 340 between the two bending devices 320, 330 allows for control of beam offset and beam deflection angles (e.g., near field and far field, respectively) in the vertical axis, thereby producing oblique rays. If the two bending devices 320, 330 are oriented on the same axis, the two bending devices 320, 330 can generate meridian rays, again adjusting the beam offset and deflection angle independently. In some embodiments, the quarter-pitch graded-index fiber 340 between the two bending devices 320, 330 may be the same or different as in a multi-bending device, and/or the quarter-pitch graded-index fiber 340 may include multiple graded-index elements, the net effect of which is equivalent to one quarter-pitch graded-index element.

In some embodiments, the two stages 320, 330 may be combined into one multi-bend device, where the graded-index fiber 340 may be bent every quarter pitch, rather than every odd quarter pitch. In this case, the odd quarter-pitch bend can adjust the beam offset and the even quarter-pitch bend can adjust the beam angle, measured from the output end where the total length is not an integer number of half-pitches. If the orientation of the odd number of quarter-pitch bends is perpendicular to the even number, the overall bent fiber shape will approximate a spiral and the output light will be tilted. On the other hand, if the two sets of bends are parallel, the output light will be meridional. Typical quarter-pitch lengths are on the order of 1 mm or less, and such devices may require complex actuation systems, particularly if the design goal is to provide complete two-dimensional addressability in both beam deflection and beam deflection. Further, to provide equal sensitivity to offset and deflection, graded-index fiber 340 may have a focal length such that the quarter-pitch beam size is approximately the same as the input beam size provided by input fiber 310. Thus, the graded-index fiber 340 may have a focal length of several hundred microns for the beam size of interest. Additionally or alternatively, the input beam size may be first adjusted (e.g., using a single quarter-pitch graded-index fiber with appropriate focusing intensity) to change the beam size to the desired new beam size, and then the more preferred focal length of the expanded graded-index fiber may be used to bend the array.

In some embodiments, the bend formed in the graded-index fiber 340 can have any periodic bend shape with a bend period equal to or approximately equal to the pitch of the graded-index fiber 340, as described herein. In this manner, the bend formed in the graded-index fiber 340 may be used to manipulate the spatial characteristics of the light carried by the graded-index fiber 340. In some embodiments, the curvature may be two-dimensional (e.g., in the x-z plane, where z is the average propagation direction, such as a simple sinusoid), or the curvature may be three-dimensional (e.g., in the x, y, and z directions, such as a circular helix, an elliptical helix, a more complex three-dimensional shape periodic in the z direction, etc.). In some embodiments, the bend period may be exactly matched to the pitch of the graded-index fiber, or the bend period may be approximately matched to the pitch of the graded-index fiber by 25%, 10%, 3%, etc. Thus, in order to match or nearly match the pitch of the graded-index fiber, it may be desirable for the deviation between the bend period and the pitch of the graded-index fiber to meet (e.g., be less than and/or equal to) a threshold (e.g., ± 10% or less). In some embodiments, the bending device may steer the light beam in the near field (offset position), the far field (beam pointing direction), or both, depending on the bending shape. In this manner, forming a bend in the graded-index fiber 340 that matches or nearly matches the pitch of the graded-index fiber 340 provides more versatility than adiabatic bending, which is typically limited to manipulating the near field only.

Furthermore, in some embodiments, a single bend may be formed in the graded-index fiber 340. Typically, when a single bend is used, the single bend is substantially equal to or shorter than half the pitch of the graded-index fiber 340 and is centered at least one-quarter pitch away from one end of the graded-index fiber 215 in the graded-index fiber 215. In this case, some embodiments described herein may significantly enhance the bending effect as compared to adiabatic bending. For example, in some embodiments, a splice assembly can include an input fiber that provides a light beam, a graded-index fiber coupled to the input fiber and having a length that is one-half pitch relative to an imaging pitch length of the graded-index fiber, and an output fiber that can receive a modified light beam position from the graded-index fiber, wherein a bend is applied to the graded-index fiber, centered about and strongest at a middle of the graded-index fiber. In some embodiments, the bend may or may not extend into the input and/or output fiber, but may generally be weaker in the input and/or output fiber than in the graded-index fiber in order to minimize bending stresses applied to the splice point. In this case, the splice assembly may differ from a typical adiabatic bend fiber in that the majority of the length of the bend should be equal to or shorter than the half pitch of the graded index fiber, which is typically about 1-5 mm, and if the goal is to move only the near field, the strongest bend will not be applied at the output splice point, but about a quarter pitch before the output splice, similar to an adiabatic bend.

In some embodiments, the optical system may include an actuation mechanism that allows the curved shape to be adjusted, thereby enabling at least two states (e.g., an unperturbed state and a modified state) of the output beam. In the simplest case, however, a static periodic curved shape may be imparted to the graded-index fiber 340 such that a given input state is statically converted to a different output state (e.g., a different beam position and/or beam pointing direction than the input). One example of such a device may include an all-fiber rotating beam generator, where the induced fiber bend shape may be helical, and the output beam may be simultaneously offset from the fiber axis and tilted perpendicular to the offset, creating a skew characteristic and orbital angular momentum. If the graded-index fiber 340 is to be spliced to an output step-index or ring-index fiber with a radius that matches the spatial offset and an NA that matches the beam tilt angle, the offset, deflected beam will be captured and held in the rotating beam. Such a static rotating beam generator can be implemented in an integrated form by fabricating an optical fiber preform comprising a graded-index core offset from the central axis of the fiber, and rotating the fiber during stretching so that the offset core actually follows a helical path (even though the exterior of the fiber may appear straight). If the pitch of the helix, as determined by the rotation rate relative to the draw rate during fiber drawing, is equal or nearly equal to the graded-index pitch, the helical-core fiber can produce a static lateral offset and beam deflection (e.g., a tilted beam carrying orbital angular momentum), which can produce a ring-shaped rotating beam when the graded-index fiber 340 is coupled into an output fiber (e.g., a step-index or ring fiber) of appropriate diameter and NA to guide the rotating beam. As such, some embodiments described herein may produce a rotating beam that is compact and simple to manufacture. For example, the structure may be only a few millimeters or centimeters long, does not require tapering, has simple fiber preform fabrication, and may provide efficient conversion to a rotating beam in terms of power and brightness.

In some embodiments, different options may be used as an actuation mechanism to provide two or more output states in addition to and/or in place of the actuation mechanism described above. For example, in some embodiments, the actuation mechanism may provide full addressability by controlling the two-dimensional lateral position of the graded-index fiber at each half-pitch position, each quarter-pitch position, using an array of micromanipulators, or the like. In another example, the actuation mechanism may be arranged to switch between a straight fiber shape and a helical fiber shape by holding the graded-index fiber straight and slightly tensioned to provide a straight state, and twisting the graded-index fiber while providing a slightly relaxed tension, such that the graded-index fiber adopts a helical state with a predetermined pitch. In another example, switching between a straight fiber shape and a spiral fiber shape may be achieved by twisting a graded-index fiber around a second (non-optical) fiber of suitable diameter and stiffness at a predetermined number of turns, and either tensioning the fiber while relaxing the non-optical fiber to provide a straight fiber state or relaxing the fiber while tensioning the non-optical fiber to force the fiber into a spiral configuration.

As described above, fig. 3 is provided as one or more examples. Other examples may be different than that depicted in fig. 3. For example, the number and arrangement of components shown in FIG. 3 are provided as examples. Indeed, the arrangement shown in fig. 3 may include additional components, fewer components, different components, or components other than the arrangement shown in fig. 3. Additionally or alternatively, one set of components (e.g., one or more components) in fig. 3 may perform one or more functions described as being performed by another set of components in fig. 3.

Fig. 4A-4C illustrate example graphs 400, 410, 420 relating to the propagation length of a graded-index fiber manipulated using one or more bending devices and/or one or more methods described herein. For example, as shown in FIG. 4A, graph 400 shows ray traces within a graded-index fiber, showing a single ray traveling around an integer number of pitches. The source NA was 0.1. As shown in FIG. 4B, graph 410 shows the lowest order linearly polarized fundamental mode (LP01) of a 50 μm and 0.22NA step index fiber launched into different graded index fibers, which propagates a certain number of pitches. Further, referring to fig. 4C, graph 420 shows how the "aberration" of even a perfect graded-index fiber affects the beam based on changing spot size. Higher order modes of the same input fiber propagate a certain number of pitches in the same graded index. Higher order modes experience more aberrations per pitch and spread out faster because the mode is not as well matched in size to the graded index.

Accordingly, one challenge of the bending apparatus and methods described herein is achieving precise lengths of graded-index fibers. If the length of the graded-index fiber is significantly longer or shorter than an integer multiple of the pitch, the input beam may have a "blurred" image with power at higher radii, which may result in a loss of Brightness (BPP) when coupled into the delivery fiber. As shown in fig. 4A, for tight dimensional tolerances of about 5 microns (μm), the length tolerance is independent of the graded-index fiber focal length and depends only on the input beam NA. For larger tolerances, the focal length may be a factor, with smaller focal lengths being more forgiving. The most tolerant configuration is to select a graded index focal length (e.g., to size match the graded index to the input beam) that produces exactly the same spot size in both the near and far fields. For input beam radius (w) and divergence (θ), a suitable graded index focal length is f ═ w/θ. In this case, the beam does not change size as it propagates (although the shape of the beam may oscillate slightly). In this case, the length of the graded-index fiber is not important, nor is the position of the start of the bend array relative to the start of the graded-index fiber. However, the period of the bend array is well matched to the graded-index pitch, and the position of the final bend relative to the end of the graded-index fiber is controlled, so that the desired steering of the near and/or far field can be achieved.

Furthermore, one additional design consideration is that the graded index "lens" has aberrations, similar to a free space element. For example, even a graded index fiber with a perfect parabolic refractive index profile cannot obtain an accurate image at every pitch, but small errors accumulate as more pitches are used. These errors depend to a large extent on the NA and size of the input beam. For example, if the input is a single fundamental mode in a 0.22NA step index fiber 50 microns in diameter, the input can be re-imaged almost perfectly even over 100 pitches in the correct focal length graded index, as shown in FIG. 4B. However, for the same graded-index fiber that maintains the spot size of the LP01 mode group of the input fiber, where a different mode is selected that has a poor overlap with the corresponding mode in the graded-index fiber, the aberration per pitch gradually increases, as shown in fig. 4C, even though the fiber length is perfectly selected. In general, for a given input fiber, as the NA increases, the number of graded-index pitches before significant aberrations occur will decrease. This is mathematically analogous to using a series of lenses, each with a small amount of spherical aberration. Thus, in some embodiments, the number of pitches in the length of the graded-index fiber may be selected to satisfy a threshold that is based on one or more metrics related to the error accumulated per pitch of the graded-index fiber. For example, as shown in fig. 4C, after a propagation length of about ten (10) pitches, the aberration significantly increases, whereby a series of bends may be formed in a length of graded-index fiber including ten or less pitches in one example.

In some embodiments, the exact length of the graded-index fiber may not be an integer multiple of the pitch in applications where brightness is to be maintained. In some embodiments, the device length may be selected to minimize spot size, rather than providing a perfect integer pitch (similar to aligning a free space system to a minimally confusing circle, as opposed to paraxial focusing). Furthermore, depending on the light source, small modifications can be made to the refractive index profile to correct for different aberrations. In this way, the refractive index profile design will not be an exact parabola, but a slightly different function, while still being a qualitative graded index.

Furthermore, the aberration considerations may affect the number of perturbation periods used. High NA sources may only provide a small number of pitches before the beam "blurs", while low NA sources may use more pitches. In addition, the required deflection and tolerances on the micrometer platform are also a factor. In automated systems, the micrometer may be replaced with a piezo or the like, enabling sub-second level actuation. Furthermore, some embodiments described herein may have mechanisms to change the effective length to avoid excessive cleaving and polishing to achieve a precise length (e.g., change the optical path length by heating, longitudinal stress, compressive stress, etc.).

4A-4C are provided as one or more examples. Other examples may be different than that depicted in fig. 4A-4C.

FIG. 5 is a flow diagram of an example process 500 for applying a set of bends in a graded-index fiber using one or more bending devices.

As shown in fig. 5, process 500 may include routing a graded-index fiber through one or more bending devices, where the one or more bending devices include one or more protrusions having a periodicity that matches or nearly matches a pitch of the graded-index fiber (block 510). For example, in some embodiments, the graded-index fibers 100, 215, 340, etc. may be routed through one or more bending devices 210, 320, 330, etc., as described above. In some embodiments, one or more bending devices 210, 320, 330 and/or the like include one or more protrusions 235, 245 and/or the like having a periodicity that matches or nearly matches the pitch of the graded-index fiber 100, 215, 340 and/or the like.

As further shown in fig. 5, the process 500 may include actuating a first portion of one or more bending devices to move toward a second portion of the one or more bending devices such that the one or more protrusions cause a series of bends to be formed in the graded-index fiber, wherein a periodicity of the one or more protrusions causes the series of bends to have a bending period that matches or nearly matches a pitch of the graded-index fiber (block 520). For example, in some embodiments, the first portion 230 of the one or more bending devices 210, 320, 330 may be actuated to move toward the second portion 240 of the one or more bending devices 210, 320, 330 such that the one or more protrusions 235, 245 cause a series of bends to be formed in the graded-index fiber 100, 215, 340, etc. In some embodiments, the periodicity of the one or more protrusions 235, 245 is such that the series of bends have a bend period that matches or nearly matches the pitch of the graded-index fibers 100, 215, 340, etc.

Process 500 may include additional embodiments, such as any single embodiment or any combination of embodiments described below and/or in conjunction with one or more other processes and/or embodiments described elsewhere herein.

For example, in a first embodiment, the one or more bending devices may include a first bending device 320 and a second bending device 330, the first bending device 320 arranged to induce a first series of bends in the graded-index fiber in a first orientation, the second bending device 330 following the first bending device 320 to induce a second series of bends in the graded-index fiber in a second orientation.

In a second embodiment, alone or in combination with the first embodiment, the first series of bends in the first orientation and the second series of bends in the second orientation may be perpendicular or parallel to each other.

In a third embodiment, alone or in combination with one or more of the first and second embodiments, the first series of bends manipulate the light beam passing through the graded index fiber in the near field and the second series of bends manipulate the light beam passing through the graded index fiber in the far field.

In a fourth embodiment, alone or in combination with one or more of the first through third embodiments, the process 500 includes rotating one or more bending devices relative to the graded-index fiber, wherein the periodicity of the one or more protrusions is shorter than the pitch of the graded-index fiber, and rotating the one or more bending devices relative to the graded-index fiber extends the bending period to match or nearly match the bending period to the pitch of the graded-index fiber.

In a fifth embodiment, a series of bends in graded-index fiber, either two-dimensional or three-dimensional, are formed in the graded-index fiber, either alone or in combination with one or more of the first through fourth embodiments.

Although fig. 5 shows example blocks of the process 500, in some implementations, the process 500 may include additional blocks, fewer blocks, different blocks, or a different arrangement of blocks than those depicted in fig. 5. Additionally or alternatively, two or more blocks of process 500 may be performed in parallel.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the embodiments.

As used herein, depending on the context, meeting a threshold may refer to a value that is greater than the threshold, greater than or equal to the threshold, less than or equal to the threshold, not equal to the threshold, and the like.

Even though specific combinations of features are disclosed in the present application, these combinations are not intended to limit the disclosure of the various embodiments. Indeed, many of these features may be combined in ways not specifically recited and/or disclosed in this application. While each listed embodiment may be directly dependent on only one embodiment, the disclosure of each embodiment includes a combination of the embodiments in any way.

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. In addition, as used herein, the articles "a" and "an" are intended to include one or more items, and may be used interchangeably with "one or more". Further, as used herein, the article "the" is intended to include one or more items associated with the article "the" and may be used interchangeably with "the one or more". Further, as used herein, the term "group" is intended to include one or more items (e.g., related items, unrelated items, combinations of related and unrelated items, etc.) and may be used interchangeably with "one or more. When only one item is intended, the phrase "only one" or similar language is used. Furthermore, as used herein, the terms "having," "possessing," and the like are intended to be open-ended terms. Further, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise. Furthermore, as used herein, the term "or" when used in a serial manner is intended to be inclusive and may be used interchangeably with "and/or" unless specifically stated otherwise (e.g., if used in conjunction with "either" or "only one of").