Multi-core fiber geometry and isotropic cooling environment to mitigate thermal gradients in coherent beam combinations

Abstract

The invention relates to a multi-core fiber geometry and isotropic cooling environment to mitigate thermal gradients in coherent beam combinations. In some implementations, an optical system includes a multi-core optical fiber having a plurality of cores arranged along one or more isotherms and an isotropic cooling environment housing the multi-core optical fiber. In some implementations, the isotropic cooling environment includes a cold plate having a recess shaped to fit the multi-core optical fiber and a structure for enclosing the multi-core optical fiber within the recess.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 553 / 886, filed on February 15, 2024, entitled “MULTI-CORE FIBERGEOMETRY WITHOUT THERMAL GRADIENTS FOR COHERENT BEAM COMBINING.” The disclosure of that prior application is considered a part of and incorporated by reference into this patent application. Technical Field

[0003] The present disclosure generally relates to coherent beam combining, as well as multi-core fiber geometries and isotropic cooling environments for mitigating temperature gradients that might otherwise cause group delay mismatch. Background Art

[0004] Coherent beam combining (CBC) is an optical technique used in optical devices to merge multiple laser beams into a single output beam with higher power and / or desired beam quality. CBC is particularly useful in applications where the power of a single laser is insufficient and scaling the power of a single emitter is challenging due to physical and / or technological limitations. The basic principle of CBC involves superimposing individual laser beams in a way that produces constructive interference, thereby increasing the intensity of the combined beam. In order to achieve the increase in intensity, the phase and amplitude of each individual laser beam need to be carefully controlled. For example, phase and / or amplitude control can be achieved through active and / or passive phase-locking mechanisms, which can include an electronic feedback system that adjusts the phase of the laser in real time based on the observed beam interference pattern. The implementation of CBC can be divided into two main architectures: stitched aperture combining and filled aperture combining. In stitched aperture combining, the individual laser beams are arranged in a two-dimensional array, and the phases of the laser beams are controlled to constructively interfere at a distant target to effectively produce a single high-power beam. The stitched aperture approach is beneficial in high-power laser systems, such as those used in directed energy applications. Filled aperture combining involves overlapping beams with the same spatial pattern of a single aperture, which is advantageous for applications requiring high beam quality and brightness, such as in fiber laser systems. However, CBC introduces challenges, including the need to control group delay and phase delay to maintain coherence (for example, for pulsed lasers), and the complexity of scaling the system with a large number of emitters. Summary of the Invention

[0005] In some implementations, an optical system includes a multi-core optical fiber having a central axis and a plurality of cores, the plurality of cores being equidistant from the central axis and arranged in a symmetrical pattern relative to the central axis; and an isotropic cooling environment that houses the multi-core optical fiber, wherein the isotropic cooling environment includes: a cold plate having a groove shaped to fit the multi-core optical fiber; and a cover structure for enclosing the multi-core optical fiber within the groove.

[0006] In some implementations, an optical system includes a multi-core optical fiber having multiple cores arranged along one or more isotherms; and an isotropic cooling environment that houses the multi-core optical fiber, wherein the isotropic cooling environment includes: a cold plate having a groove shaped to fit the multi-core optical fiber; and a structure for enclosing the multi-core optical fiber within the groove.

[0007] In some implementations, a coherent beam combining system includes a laser source configured to generate a seed laser; a splitting stage including one or more optical devices configured to split the seed laser into a beam array including a plurality of input beams; a multi-core optical fiber for receiving the plurality of input beams, wherein the multi-core optical fiber includes a plurality of cores arranged along one or more isotherms; an isotropic cooling environment member that houses the multi-core optical fiber, wherein the isotropic cooling environment member includes: a cold plate having a groove shaped to fit the multi-core optical fiber; and a structure for enclosing the multi-core optical fiber within the groove; an amplification stage including a plurality of amplifiers configured to amplify the plurality of input beams to generate a plurality of amplified beams; and a combining stage including one or more optical devices configured to combine the plurality of amplified beams into a single output beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a diagram illustrating an example of controlling group delay and phase delay in a coherent beam combining system.

[0009] Figure 2 is a diagram illustrating examples of multi-core fiber geometries that induce thermal gradients and example implementations of multi-core fiber geometries that mitigate thermal gradients.

[0010] Figure 3 is a diagram illustrating an example implementation of a multi-core fiber geometry and an isotropic cooling environment for mitigating thermal gradients in a coherent beam combining system.

[0011] Figure 4 is a diagram illustrating an example implementation of a polarization-maintaining multi-core optical fiber having a geometry for mitigating thermal gradients.

[0012] Figure 5 is a diagram illustrating an example of a coherent beam combining system. DETAILED DESCRIPTION

[0013] The following detailed description of example implementations refers to the accompanying drawings, in which the same reference numerals in different drawings may identify the same or similar elements.

[0014] Figure 1 is a diagram illustrating an example 100 of controlling group delay and phase delay in a coherent beam combining system.

[0015] Fiber laser technology has many properties that can be used in a variety of light-induced applications in science, industry, and other fields. For example, fiber laser systems have the characteristics of being able to achieve power scalability, excellent beam quality and stability, high quantum efficiency, wide gain bandwidth and / or thermal management, which leads to fiber laser systems being frequently used as versatile laser sources in both continuous wave (CW) and pulsed regimes. For example, due to the power scalability of fiber laser systems, fiber laser systems are often used in applications requiring high power levels (e.g., in the kilowatt (kW) range), such as advanced materials processing and laser particle accelerators. For example, fiber laser systems using high brightness laser diodes and double-clad fibers can provide much higher output powers than fiber laser systems pumped by single-clad fibers, and chirped pulse amplification technology can achieve further power scalability for ultrafast (e.g., femtosecond) pulses in a single amplification channel (e.g., a single-core amplifier).

[0016] However, due to various physical limitations, including nonlinear effects, polarization losses, mode instabilities, thermal issues, optical damage and / or pump power limitations, ultrafast fiber laser technology is approaching the power scaling limits of single-core amplifiers. Therefore, in some cases, beam combining techniques can be used to achieve further power scaling in fiber laser systems. For example, beam combining techniques can use several fibers or several cores to split the seed laser beam before the amplification stage to distribute the intensity of the beam across several fibers or several cores, and then each beam (or sub-beam) is individually amplified and combined into a single output. Typically, multiple amplifier channels can be used for amplification, which can be individual fibers, or can be multi-core fibers (MCFs) where multiple cores are embedded in a single larger fiber and the beams are amplified in parallel before being recombined. However, fiber-based amplifiers for ultrafast lasers are reaching intensity limits due to nonlinearities inside the active cores, which can lead to self-phase modulation and thus beam quality degradation.

[0017] Therefore, coherent beam combining (CBC) techniques can be used to (re)combine multiple beams more efficiently. For example, in a CBC system, power scaling can be achieved by combining multiple laser amplifiers seeded by a common laser source into a single high-power output beam while maintaining beam quality and preserving the spatial and spectral characteristics of the laser. For example, in a CBC system, there is a phase relationship between the multiple laser amplifiers, and the parallel amplifiers effectively operate as a single laser. The general concept is to split the seed beam into several copies (e.g., N channels), which are then amplified to the highest possible power and / or energy by parallel amplifier sections, and then the amplified copies of the seed beams are combined into a single beam. The peak intensity limitation can be overcome by spatially multiplexing and coherently recombining the seed lasers through multiple individual cores (and / or fibers). However, in order to maximize the combining efficiency and avoid intensity fluctuations, the time delay (e.g., phase difference) between the beamlets in different cores or different fibers needs to be stable to as low as a fraction of the wavelength. For example, a CBC system can use active phase control, where a phase detector is used at the output side of the amplifier stage to detect the phase difference between adjacent beams, and a phase modulator (e.g., before or after the amplifier stage) is used to correct the phase difference detected using the phase detector. However, before phase control can be performed to produce efficient recombination interference conditions, the group delay (e.g., arrival time difference) needs to be small enough to avoid temporal mismatches that would otherwise cause coherence loss between the beamlets. For example, for ultrashort pulses, the group delay (or arrival time difference) between individual beams (or beamlets) needs to be at least an order of magnitude shorter than the pulse length.

[0018] More specifically, group delay is typically caused by optical path difference (OPD), which can originate from factors such as fiber length variations and / or refractive index variations, which can be manufacturing-related or thermally induced. In order to generate efficient recombination interference conditions, phase control needs to provide a group delay that satisfies (e.g., is less than) a threshold. Otherwise, the time mismatch will result in a loss of coherence between the beamlets. For example, in Figure 1, curve 110 corresponds to two pulse trains (e.g., associated with respective beams) associated with a first OPD (e.g., 15 micrometers (μm)) and a first temporal overlap (e.g., 78% overlap). Thus, as shown in reference numeral 120, the CBC system can implement group delay control and phase delay control to compensate for the OPD and produce two temporally overlapping pulse trains. For example, the group delay control can provide a coarse adjustment of the OPD to ensure that the two pulse trains overlap in time such that the OPD meets a first threshold to ensure that the temporal overlap meets a second threshold (e.g., such that the two pulse trains in FIG110 have an OPD below 7 μm to ensure that the two pulse trains have at least 90% temporal overlap). The phase delay control can then perform a fine adjustment of the OPD to ensure that the pulses constructively interfere (e.g., providing additional fine adjustment over a range of 2π with a resolution of at least λ / 10, where λ is the wavelength). In this manner, as shown in curve 130, the two pulse trains can have an OPD that enables coherent beam combining (e.g., an OPD of 0 μm, resulting in 100% temporal overlap).

[0019] Therefore, in order to maintain coherence between beamlets in a CBC system, reducing the group delay mismatch (e.g., to a threshold level) is a prerequisite for avoiding time mismatch and achieving phase delay control to produce effective recombination (constructive) interference conditions. In some cases, group delay compensation can be performed using active techniques, such as piezoelectric actuators and / or other linear delay stages equipped with one or more retro-reflective mirrors. However, using active techniques to reduce group delay mismatch can increase the size, cost, and complexity associated with the CBC system. Therefore, some implementations described herein involve one or more passive techniques that can be used to reduce group delay mismatch. For example, as further described in detail herein, a multi-core optical fiber can include multiple cores arranged according to a geometry that can eliminate or reduce temperature variations between the multiple cores (e.g., which can result in refractive index variations that contribute to OPD). In some implementations, the multi-core optical fiber can be used in combination with one or more other passive techniques to reduce group delay mismatch. For example, in some implementations, the multi-core fiber can be mounted or housed in an isotropic cooling environment, such as a cold plate with a groove design, to efficiently extract heat from the multi-core fiber and reduce absolute temperature and gradients, thereby achieving power scaling. Additionally or alternatively, in some implementations, the multi-core fiber can have a symmetrical bend layout to eliminate or reduce geometry-induced OPD. In this way, some implementations described herein can reduce group delay mismatch in a CBC system and ensure that the beams or beamlets to be recombined have temporal overlap, thereby achieving fine-tuned phase delay control.

[0020] Figure 1 Provided as an example. Other examples can be found in the Figure 1 Different from what is described.

[0021] Figure 2 2 is a diagram illustrating an example 200 of a multi-core fiber geometry that induces a thermal gradient and an example implementation 250 of a multi-core fiber geometry that mitigates the thermal gradient. For example, as described herein, multiple beams or beamlets to be combined in a CBC system may experience group delays caused by OPD. In a multi-core fiber having multiple cores, beams or beamlets propagating in respective cores may be associated with OPDs caused by factors such as refractive index variations. Furthermore, in some cases, refractive index variations between cores in a multi-core fiber may be caused by thermal gradients (e.g., temperature differences in respective cores). For example, in a multi-core fiber having a geometry having one or more central (or inner) cores and one or more outer cores (e.g., a square array, three cores arranged in a line, a core ring surrounding a central core, etc.), the central or inner core tends to exhibit a higher temperature than the outer cores. Thus, the core geometry in the multi-core fiber can result in thermal gradients, which can cause refractive index variations that increase group delay mismatch. Group delay mismatch can severely degrade the recombination efficiency and output pulse duration of sub-picosecond (ps) laser pulses.

[0022] For example, Figure 2 An example 200 of a multi-core optical fiber geometry having one or more central cores that may induce a thermal gradient is depicted. For example, the multi-core optical fiber includes a core arrangement 202 having three cores that produces a temperature distribution 204 within the multi-core optical fiber (shown as a finite element (FE) simulation). As shown in reference numeral 206, a geometry having a three-core arrangement and a central core exhibits a temperature increase in the central core. For example, reference numeral 206 relates to a first curve in which the vertical or y-axis represents heat load (in watts (W) per cubic meter (m)) and the horizontal or x-axis corresponds to the x-coordinate along which heat flows (e.g., typically corresponding to the x-coordinate of the three cores). Additionally, reference numeral 206 relates to a second curve in which the vertical or y-axis represents a temperature difference (e.g., using the notation T-T0 (K)). For example, the second curve depicts a temperature difference with respect to a material (e.g., a cold plate) surrounding a multi-core optical fiber having a three-core arrangement and a central core that corresponds to a temperature increase that occurs when the multi-core optical fiber is active.

[0023] Typically, the thermo-optic coefficient (i.e., the change in refractive index with respect to temperature at constant pressure, expressed as dn / dT) of glass and yttrium aluminum garnet (YAG) is typically 10 -5 Kelvin -1 (K -1 For example, under certain operating conditions (e.g., a pump power of approximately 600 W and a peak heat load of 70 W / m 3), for a fiber with a length of 1 meter and a temperature difference of several K between the cores, the group delay mismatch can be expected to be as high as tens of microns. Group delay mismatch can severely degrade the recombination efficiency and output pulse duration of sub-ps laser pulses. For example, in Example 200, the central (hotter) core can have a time delay of about 1 micron per 50 W of pump power, which is manifested by a phase drift during the power ramp. In addition, although Example 200 depicts a temperature gradient that may contribute to the group delay mismatch, similar temperature gradients can appear in any multi-core fiber geometry with one or more central (or inner) cores and one or more outer cores (e.g., a 3×3 or larger square array, a concentric ring array, a hexagonal layout with 7, 19, 37, or other suitable number of cores, etc.). In particular, in this case, the thermal load in the outer cores may increase the temperature of the central or inner core, which may result in a refractive index variation and larger OPD across the multiple cores, thereby increasing the group delay mismatch.

[0024] Thus, in some implementations, a multi-core optical fiber can be associated with a geometry (e.g., core layout) that can eliminate or significantly reduce transverse temperature gradients in the multi-core optical fiber, which can achieve optimal group delay matching. For example, Figure 2 An example implementation 250 of a multi-core optical fiber geometry is depicted having multiple cores arranged along one or more isotherms and having no center core, which can provide the same temperature distribution in each core. For example, in the example implementation 250, the multi-core optical fiber includes a core arrangement 252 having six cores arranged in a circular or hexagonal layout and having no center core, which results in a thermal profile 254 showing the same or uniform temperature across the cores (e.g., no core experiences an increase in temperature due to an imbalance in the number of adjacent or neighboring cores). More generally, some implementations described herein relate to multi-core optical fiber geometries in which multiple cores are arranged along one or more isotherms, which generally correspond to one or more cross-sectional lines or points having the same temperature. For example, where each core has the same diameter, the one or more isotherms can be along a circle around a central axis of the multi-core optical fiber, whereby the multiple cores can be equidistant from the central axis and arranged in a symmetrical pattern relative to the central axis. For example, in Figure 2 In the embodiment shown, core arrangement 252 is a circular or hexagonal arrangement, but other suitable geometries may be used (e.g., a 2×2 square arrangement inscribed in a circle). Additionally or alternatively, in some cases, the isotherms may be arranged in an asymmetric pattern, such as when there is variation in the size or diameter of the individual cores. For example, the temperature may be higher in cores with relatively larger diameters, and thus the isotherms associated with a multi-core optical fiber (e.g., locations with the same temperature) may result in multiple cores being located at different distances from the central axis and / or being arranged in an asymmetric pattern.

[0025] Thus, as described herein, a multi-core optical fiber can generally include a plurality of optical fibers arranged according to a geometry that results in the temperature being the same in each core. For example, as shown at 256, a geometry having six cores arranged in a circular (e.g., annular) or hexagonal geometry and having no central or inner core results in the temperature being the same in each core. For example, 256 relates to a first curve in which the vertical or y-axis depicts the heat load (in W / m²). 3 ), showing two x-coordinates along which heat flows (e.g., generally corresponding to the x-coordinates of the three leftmost cores and the x-coordinates of the three rightmost cores). In addition, reference numeral 256 relates to a second graph in which the vertical or y-axis represents temperature difference (e.g., using the notation T-T0 (K)), wherein a first temperature difference at the x-coordinates of the three leftmost cores is the same as a second temperature difference at the x-coordinates of the three rightmost cores.

[0026] In this manner, arranging multiple cores in a multi-core optical fiber according to a geometry that results in identical temperatures in each core can eliminate or mitigate thermally induced group delay mismatch, which can enable phase delay control and improve the performance of CBC systems (e.g., ultrafast CBC lasers). Furthermore, in some implementations, identical temperature profiles in each core can enhance spatial mode matching between beamlets propagating in the respective cores. For example, higher temperatures typically result in reduced mode field diameters due to enhanced refractive index profiles (self-focusing), and mode field matching can affect recombination efficiency and output beam quality in CBC systems. Furthermore, as described in further detail herein, the multi-core optical fiber can be embedded in an isotropic cooling environment, which can efficiently extract heat from the multi-core optical fiber and reduce temperature gradients across the multiple cores.

[0027] Figure 2 Provided as an example. Other examples can be found in the Figure 2 There is a difference as described.

[0028] Figure 3 is a diagram illustrating an example implementation 300 of a multi-core fiber geometry and an isotropic cooling environment for mitigating thermal gradients in a CBC system. Figure 3 As shown, the example implementation 300 includes a multi-core optical fiber 310 having a plurality of cores 312 (eg, doped signal cores) arranged along one or more isotherms. Figure 3, the multi-core optical fiber 310 includes a central axis and six cores 312 that are equidistant from the central axis and arranged in a symmetrical pattern (e.g., a circular or hexagonal pattern) relative to the central axis. Alternatively, in some implementations, the multiple cores 312 can be arranged in an asymmetrical pattern relative to the central axis (e.g., where one or more cores 312 have a larger diameter or a smaller diameter relative to the other cores 312, which affects the temperature within one or more cores 312). Thus, as described herein, the individual cores 312 can be arranged in any suitable geometry along one or more isotherms of the multi-core optical fiber 310 to produce the same temperature distribution in each core 312. Figure 3 As further shown, the multi-core optical fiber 310 may include a pump region 314 , and a cladding may surround the pump region 314 to guide the pump light.

[0029] In some implementations, the core 312 of the multi-core optical fiber 310 can be polarization maintaining (PM) or non-polarization maintaining (non-PM). For example, in some implementations, the core 312 can be polarization maintaining (PM) or non-PM by placing one or more stress rods ( Figure 3 To produce birefringence, the core 312 of the multi-core optical fiber 310 can be made into a PM. For example, an example layout of stress rods is as follows: Figure 4 As shown in FIG. 1 and described in more detail herein, the size and refractive index of the individual cores 312 can determine whether the multi-core optical fiber 310 is single-mode or multi-mode. For example, peak intensity decreases with increasing core diameter, but a large core diameter can also lead to the guidance of higher-order modes. Depending on the application, the diameter and / or refractive index of the cores 312 can be configured to ensure single-mode operation. Additionally or alternatively, depending on the application, the diameter and / or refractive index of the cores 312 can be configured to ensure multi-mode operation.

[0030] As described herein, the multi-core optical fiber 310 can arrange the multiple active cores 312 and heat sources into a ring, hexagon, square, or other suitable symmetrical geometry (e.g., when the cores 312 have the same diameter) or an asymmetrical geometry (e.g., when the cores 312 have different diameters or refractive indices, such as in multimode operation), wherein the cores 312 are generally arranged along one or more isotherms. In this manner, the geometry of the cores 312 can eliminate or reduce temperature gradients (e.g., temperature differences) across the individual cores 312. Furthermore, in some implementations, the multi-core optical fiber 310 can be housed or mounted in a cooling environment for extracting heat from the multi-core optical fiber 310 in an isotropic or nearly isotropic manner, thereby generating the same temperature between the individual cores 312. For example, as Figure 3As shown, the isotropic cooling environment can include a cold plate 320 (e.g., water-cooled aluminum, copper, or other suitable material) having a groove shaped to fit the multi-core optical fiber 310. For example, in some implementations, the groove can be U-shaped to fit the circular shape of the multi-core optical fiber 310. Additionally, in some implementations, the isotropic cooling environment can include a cover structure 322, as shown as a top cover closure, to achieve isotropic cooling. In some implementations, the metal-to-fiber gap between the multi-core optical fiber 310 and the metal of the cold plate 320 can be filled with an adhesive (e.g., glue) that is transparent (e.g., at the laser wavelength) and thermally conductive (e.g., having a thermal conductivity that meets a threshold associated with heat dissipation or heat removal applications). In some implementations, the adhesive can be applied in a manner that ensures that no bubbles are formed in the adhesive filling the gap between the multi-core optical fiber 310 and the cold plate 320. For example, in some implementations, the adhesive filler can be cured under vacuum conditions.

[0031] As described herein, the width of the gaps between the multi-core optical fiber 310 and the cold plate 320, and between the multi-core optical fiber 310 and the cover structure 322, strongly influences heat extraction. Therefore, in some implementations, the U-shaped groove and the cover structure 322 can be manufactured to a desired precision to ensure that the size of the fiber-to-metal gap around the multi-core optical fiber 310 is uniform around the circumference of the multi-core optical fiber 310. For example, Figure 3 As shown, the shape of the cover structure 322 can closely follow the shape of the multi-core optical fiber 310 (e.g., Figure 3 The middle cover structure 322 has an inverted U-shape. Additionally or alternatively, other cooling techniques may be used to reduce temperature variations between the multiple cores 312. For example, cooling techniques to reduce temperature variations between the cores may include using materials with high thermal conductivity (e.g., diamond) and / or active heat extractors (e.g., Peltier elements). In some implementations, such elements may be placed in carefully designed locations around the multi-core optical fiber 310 to maintain the same temperature across the multiple cores 312. For example, in the case of extracting heat from a first group of cores 312 located relatively close to the cold plate 320 (more efficiently than extracting heat from a second group of cores 312), the thermally conductive material and / or active heat extractor may be located closer to the second group of cores 312 so that the heat extraction in each core 312 is uniform or nearly uniform.

[0032] Thus, as described herein, the multi-core optical fiber 310 can include a core arrangement or core geometry to ensure an isotropic thermal gradient. Furthermore, in some implementations, the multi-core optical fiber 310 can be used with an isotropic cooling environment. In this manner, the multi-core optical fiber 310 and the isotropic cooling environment can be suitable for applications such as high-power ultrafast laser amplifiers used in CBC systems. In this manner, the multi-core optical fiber 310 and the isotropic cooling environment can define an optical system that provides passive group delay compensation.

[0033] Figure 3 Provided as an example. Other examples can be found in the Figure 3 Different from what is described. Figure 3 The number and arrangement of the devices shown are provided as examples only. Figure 3 There may be more devices, fewer devices, different devices, or differently arranged devices than shown. Figure 3 Two or more of the devices shown may be implemented in a single device, or Figure 3 The single device shown may be implemented as multiple distributed devices. Additionally or alternatively, Figure 3 The illustrated set of devices can perform the functions described as being Figure 3 Another group of devices is shown performing one or more functions.

[0034] Figure 4 4 is a diagram illustrating example implementations 400A and 400B of polarization-maintaining multi-core optical fibers having geometries for mitigating thermal gradients. For example, as described herein, a multi-core optical fiber can have a plurality of isotherms along one or more isotherms (e.g., Figure 4 The multiple cores 410 may be arranged in a manner similar to that shown in FIG. 400A (shown as dashed circles in FIG. 400A ) or in any suitable geometry that results in the same temperature across the multiple cores 410 (e.g., a symmetrical pattern and / or an asymmetrical pattern about a central axis, and / or a pattern without any central or internal cores that may otherwise have a higher temperature than the outer cores). Additionally, as described herein, the cores 410 of the multi-core optical fiber may be made PM by placing one or more stress rods around the cores 312 to induce birefringence. For example, in example 400A, stress rods 420 (e.g., boron-doped stress rods) may be positioned on opposite sides of the cores 410 to induce linear birefringence 430, and the arrangement of the stress rods 42 may be repeated for each core 410 of the multi-core optical fiber. In example 400A, one or more stress rods 420 may be positioned on the sides of different cores 410. For example, in the top row of the annular, circular, or hexagonal geometry shown in example 400A, intermediate stress rods 420 are placed to the left of the first (rightmost) core 410 and to the right of the second (leftmost) core 410. Alternatively, in example 400B, a single central stress rod 425 can be positioned along the central axis of the multi-core optical fiber to induce radial birefringence 435. In this manner, a single stress rod 425 can be used to provide PM properties, which can simplify the fabrication and production of the multi-core optical fiber.

[0035] Figure 4 Provided as an example. Other examples can be found in the Figure 4 Different from what is described. Figure 4 The number and arrangement of the devices shown are provided as examples only. Figure 4There may be more devices, fewer devices, different devices, or differently arranged devices than shown. Figure 4 Two or more of the devices shown may be implemented in a single device, or Figure 4 The single device shown may be implemented as multiple distributed devices. Additionally or alternatively, Figure 4 The illustrated set of devices can perform the functions described as being Figure 4 Another group of devices is shown performing one or more functions.

[0036] Figure 5 is a diagram illustrating an example CBC system 500. In some implementations, as described herein, the CBC system can include a multi-core optical fiber having multiple cores arranged along one or more isotherms, and an isotropic cooling environment housing the multi-core optical fiber, wherein the isotropic cooling environment can include a cold plate having a groove shaped to fit the multi-core optical fiber, and a cover structure for enclosing the multi-core optical fiber within the groove.

[0037] For example, in some implementations, the CBC system may include or may be coupled to a laser source configured to generate the seed laser 505. Figure 5 As shown, the CBC system may include a splitting stage 510 comprising one or more optical devices configured to split the seed laser 505 into a beam array 515 comprising individual input beams co-propagating in parallel with a particular polarization (e.g., horizontal or vertical). Figure 5 As further shown, the CBC system includes an amplification stage 520 including a plurality of amplifiers, each amplifier being arranged to amplify an individual input beam in the beam array to form a set of amplified beams 525. As further shown, the CBC system 500 includes a combining stage including one or more optical devices configured to combine the amplified beams 525 into a single output beam 535. Additionally, as shown, there may be energy or power losses 540 after the combining stage 530 (e.g., due to phase delays between the individual beams in the beam array 515). Thus, as shown Figure 5 As shown, a phase detector 545 may be provided after the amplification stage 520 to measure the phase difference between the beams in the beam array 515. Specifically, the phase detector 545 may generate one or more signals indicative of the phase difference between the beams in the beam array 515. Figure 5 As shown, (multiple) signals indicating the phase differences between beams in the beam array 515 can be provided to a control system 550, which can control one or more phase modulators 555 to stabilize the phase of each beam in the beam array 515 and thereby minimize losses 540.

[0038] As described herein, in order to achieve phase control that results in constructive interference (e.g., via phase detector 545, control system 550, and phase modulator 555), the group delay associated with each beam in beam array 515 may need to be sufficiently small. Therefore, in some implementations, a multi-core optical fiber can be provided after the dividing stage 510 to receive each input beam in beam array 515, wherein the multi-core optical fiber can have a design that eliminates or reduces temperature gradients across the multiple cores (e.g., the input beam propagates in the multiple cores before amplification). For example, as described herein, the multi-core optical fiber includes multiple cores arranged along one or more isotherms, and the multi-core optical fiber can be housed or mounted in an isotropic cooling environment to ensure uniform heat extraction across the multiple cores. For example, the isotropic cooling environment can include a cold plate having a groove shaped to fit the multi-core optical fiber and a structure to enclose the multi-core optical fiber within the groove. In addition, the multi-core optical fiber and the isotropic cooling environment can have other features to ensure uniform temperature distribution across the multiple cores, as described elsewhere herein.

[0039] Figure 5 Provided as an example. Other examples can be found in the Figure 5 Different from what is described. Figure 5 The number and arrangement of the devices shown are provided as examples only. Figure 5 There may be more devices, fewer devices, different devices, or differently arranged devices than shown. Figure 5 Two or more of the devices shown may be implemented in a single device, or Figure 5 The single device shown may be implemented as multiple distributed devices. Additionally or alternatively, Figure 5 The illustrated set of devices can perform the functions described as being Figure 5 Another group of devices is shown performing one or more functions.

[0040] The above disclosure provides illustration and description, but is not intended to be exhaustive or to limit implementations to the precise forms disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of implementations. Furthermore, any implementations described herein may be combined, unless the above disclosure explicitly provides reasons why one or more implementations cannot be combined.

[0041] As used herein, satisfying a threshold may refer to a value being greater than a threshold, greater than or equal to a threshold, less than a threshold, less than or equal to a threshold, equal to a threshold, not equal to a threshold, etc., depending on the context.

[0042] Although specific combinations of features are cited in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features can be combined in a manner that is not specifically cited in the claims and / or disclosed in the specification. Although each dependent claim listed below can only directly depend on one claim, the disclosure of various implementations includes the combination of each dependent claim with each other claim in the claim set. As used herein, the phrase "at least one" in a list of reference items refers to any combination of these items, including single members. For example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as the combination of multiple items in the same item.

[0043] When a component or one or more components (e.g., a laser emitter or one or more laser emitters) is described or claimed (either within a single claim or across multiple claims) as performing multiple operations or being configured to perform multiple operations, such language is intended to broadly encompass a variety of architectures and environments. For example, unless otherwise expressly claimed (e.g., by using "a first component" and "a second component" or other language that distinguishes components in a claim), the language is intended to encompass a single component performing or being configured to perform all operations, a group of components collectively performing or being configured to perform all operations, a first component performing or being configured to perform a first operation and a second component performing or being configured to perform a second operation, or any combination of components performing or being configured to perform operations. For example, when a claim has the form "one or more components configured to: perform X; perform Y; and perform Z," the claim should be interpreted as "one or more components configured to perform X; one or more (possibly different) components configured to perform Y; and one or more (possibly different) components configured to perform Z."

[0044] Unless explicitly stated, any element, behavior or instruction used in this article should not be interpreted as key or essential. In addition, as used in this article, the article "one" and "an" are intended to include one or more projects and can be used interchangeably with "one or more". In addition, as used in this article, the article "said" is intended to include one or more projects quoted in combination with the article "said", and can be used interchangeably with "one or more". In addition, the word "set" used in this article is intended to include one or more projects (for example, related projects, unrelated projects, or a combination of related and unrelated projects), and can be used interchangeably with "one or more". If only one project is intended to be used, phrase "only one" or similar language is used. In addition, as used in this article, the term "having", "having", "containing" etc. are intended to be open terms. In addition, unless explicitly stated otherwise, the word "based on" is intended to represent "at least partially based on". In addition, as used in this article, the term "or" is inclusive when used in series, and can be used interchangeably with "and / or", unless explicitly stated otherwise (for example, if used in combination with "any one of ... or "only one of ... "). Additionally, for ease of description, spatially relative terms (such as "below," "lower," "above," "upper," etc.) may be used herein to describe the relationship of one element or feature to other elements or features shown in the figures. Spatially relative terms are intended to encompass different orientations of the device, apparatus, and / or element in use or operation in addition to the orientation shown in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

Claims

1. An optical system comprising: a multi-core optical fiber having a central axis and a plurality of cores, the plurality of cores being equidistant from the central axis and arranged in a symmetrical pattern relative to the central axis; as well as an isotropic cooling environment element for accommodating the multi-core optical fiber, wherein the isotropic cooling environment element comprises: a cold plate having a groove having a shape adapted to the multi-core optical fiber; as well as A cover structure is used to enclose the multi-core optical fiber in the groove.

2. The optical system of claim 1, wherein the multi-core optical fiber is polarization-maintaining.

3. The optical system of claim 2 , wherein the multi-core optical fiber comprises a plurality of stress rods positioned such that each of the plurality of cores has a first stress rod and a second stress rod on opposite sides to produce birefringence in the corresponding core.

4. The optical system of claim 2, wherein the multi-core optical fiber includes a single stress rod positioned along the central axis to produce radial birefringence in the plurality of cores. The optical system of claim 1 , wherein the multi-core optical fiber is single-mode. The optical system of claim 1 , wherein the multi-core optical fiber is multimode.

7. The optical system of claim 1, wherein the fiber-to-metal gap is uniform around the circumference of the multi-core optical fiber.

8. The optical system of claim 7, wherein the fiber-to-metal gap is filled with an adhesive having high thermal conductivity and being transparent at the laser wavelength.

9. The optical system of claim 1, wherein one or more of the cold plate or the cover structure comprises one or more thermally conductive elements or materials such that a temperature difference between the plurality of cores satisfies a threshold value.

10. An optical system comprising: A multi-core optical fiber having a plurality of cores arranged along one or more isotherms; as well as an isotropic cooling environment element for accommodating the multi-core optical fiber, wherein the isotropic cooling environment element comprises: a cold plate having a groove having a shape adapted to the multi-core optical fiber; as well as A structure for enclosing the multi-core optical fiber in the groove. 11 . The optical system of claim 10 , wherein the multi-core optical fiber has a central axis, and wherein the plurality of cores are arranged in a symmetrical pattern with respect to the central axis.

12. The optical system of claim 10, wherein the multi-core optical fiber has a central axis, and wherein the plurality of cores are arranged in an asymmetric pattern relative to the central axis.

13. The optical system of claim 10, wherein the multi-core optical fiber is polarization-maintaining.

14. The optical system of claim 10, wherein the multi-core optical fiber is single mode.

15. The optical system of claim 10, wherein the multi-core optical fiber is multimode.

16. The optical system of claim 10, wherein the fiber-to-metal gap is uniform around the circumference of the multi-core optical fiber.

17. The optical system of claim 10, wherein one or more of the cold plate or the structure for enclosing the multi-core optical fiber comprises one or more thermally conductive elements or materials.

18. A coherent beam combining system comprising: a laser source configured to generate a seed laser; a splitting stage comprising one or more optical devices configured to split the seed laser into a beam array comprising a plurality of input beams; a multi-core optical fiber for receiving the plurality of input beams, wherein the multi-core optical fiber comprises a plurality of cores arranged along one or more isotherms; an isotropic cooling environment element for accommodating the multi-core optical fiber, wherein the isotropic cooling environment element comprises: a cold plate having a groove having a shape adapted to the multi-core optical fiber; and a structure for enclosing the multi-core optical fiber in the groove; an amplification stage comprising a plurality of amplifiers configured to amplify the plurality of input beams to generate a plurality of amplified beams; and A combining stage includes one or more optical devices configured to combine the multiple amplified beams into a single output beam.

19. The coherent beam combining system of claim 18, wherein the plurality of cores are arranged in a symmetrical pattern with respect to a central axis of the multi-core optical fiber.

20. The coherent beam combining system of claim 18, wherein the plurality of cores are arranged in an asymmetric pattern relative to a central axis of the multi-core optical fiber.

Images