Optical isolator for multi-path polarization beam splitting and combining

Abstract

The invention provides a multi-path polarization beam splitting and combining optical isolator, which comprises a polarization beam splitting device, an isolation processing device and a polarization beam combining device which are sequentially arranged along an optical path, and is characterized in that the polarization beam splitting device is used for splitting an incident beam into N paths of sub-beams which are propagated in parallel, and N is an integer greater than or equal to 4; the isolation processing device comprises at least one Faraday rotator and at least one isolation half-wave plate which are sequentially arranged along a light path, and the N sub-beams simultaneously pass through the Faraday rotator and the isolation half-wave plate in a spatial parallel mode; and the polarization beam combining device is used for combining the N sub-beams processed by the isolation processing device into one emergent beam. By means of the structure of beam splitting, parallel processing and beam combining, energy of a single high-power laser beam is dispersed into N parallel light paths to be processed, so that local optical power density passing through a Faraday rotator is greatly reduced from the physical principle, and the problem of thermal management under high power is effectively solved by restraining the thermal lens effect.

Description

Technical Field

[0001] This invention relates to the field of passive optical device technology, and specifically to an optical isolator for multi-path polarization beam splitting and combining. Background Technology

[0002] Optical isolators are key passive devices in laser systems used to protect light sources from backlight interference. Their core working principle relies on the non-reciprocal polarization rotation characteristics of Faraday rotators.

[0003] However, in high-power laser applications, the core Faraday magneto-optical crystal (such as TGG, TSAG, YIG, etc.) will generate significant thermal effects due to the absorption of laser energy. This will lead to the formation of a refractive index gradient inside the crystal, resulting in a thermal lensing effect, causing a series of problems such as beam quality degradation and reduced isolation, which seriously restricts the further improvement of high-power laser performance.

[0004] Currently, mainstream solutions for the aforementioned thermal lensing effect all have significant limitations. While enhanced cooling technologies improve heat dissipation through optimized crystal clamping structures and thermal management, they cannot reduce the power density in the central region of the laser spot, thus only addressing the symptoms, not the root cause. Optical compensation technologies, although introducing complex lens groups to counteract the thermal lensing effect, increase system complexity and manufacturing costs. Furthermore, separate optical isolators are required for each of the multiple laser beams, resulting in a large system size, high cost, and low integration.

[0005] Therefore, it is necessary to design a method that can directly reduce the power density of Faraday crystals at the time of operation from a physical principle, thereby suppressing the thermal lensing effect and achieving high-performance, high-power optical isolation. Summary of the Invention

[0006] The purpose of this invention is to provide an optical isolator that reduces the thermal lensing effect by utilizing multi-path polarization beam splitting and combining.

[0007] To achieve the objective of this invention, a multi-path polarization beam splitter and combiner isolator is provided, comprising a polarization beam splitter, an isolation processing device, and a polarization beam combiner arranged sequentially along the optical path; the polarization beam splitter is used to split an incident beam into N parallel propagating sub-beams, where N is an integer greater than or equal to 4; the isolation processing device includes at least one Faraday rotator and at least one isolation half-wave plate arranged sequentially along the optical path, wherein the N sub-beams pass through the Faraday rotator and the isolation half-wave plate simultaneously in a spatially parallel manner; the polarization beam combiner is used to combine the N sub-beams processed by the isolation processing device into a single outgoing beam.

[0008] As can be seen from the above, this scheme disperses the energy of a single high-power laser beam into N parallel optical paths for processing through a beam splitting-parallel processing-beam combining architecture. This significantly reduces the local optical power density through the Faraday rotator from a physical perspective and effectively solves the problem of thermal management under high power by suppressing the thermal lensing effect.

[0009] A further approach is to include a Faraday rotator in the isolation processing device, through which N sub-beams simultaneously pass through different positions of the same Faraday rotator in a spatially parallel manner.

[0010] As can be seen from the above, by allowing multiple beams to share the same Faraday rotator, not only is the thermal load spatially distributed, but the system structure is also greatly simplified and the cost is reduced. At the same time, since all beams experience the physical environment of the same crystal, it helps to ensure the consistency of polarization rotation.

[0011] A further approach involves an isolation processing device comprising an isolation half-wave plate, through which N sub-beams simultaneously pass through different positions of the same isolation half-wave plate in a spatially parallel manner.

[0012] As can be seen from the above, allowing multiple beams to share the same half-wave plate, similar to the design of a shared Faraday rotator, further demonstrates the system's integrated and compact design, reduces the number of optical components, and helps improve system stability and reduce assembly complexity.

[0013] A further approach is to include an isolation processing device comprising multiple Faraday rotators, with one or more sub-beams passing through a single Faraday rotator.

[0014] As can be seen from the above, this scheme provides greater design flexibility. It can configure independent rotators for one or more beams to achieve physical isolation of heat sources and avoid thermal crosstalk. It can also group and manage beams according to power levels, which facilitates modular design and power expansion.

[0015] A further approach is to include an isolation processing device comprising multiple isolation half-wave plates, through which one or more sub-beams pass.

[0016] As can be seen from the above, the scheme of using multiple half-wave plates allows for independent polarization fine-tuning of different optical paths, which helps to compensate for the polarization state deviation of each path caused by processing or assembly errors, thereby optimizing the overall beam combining efficiency and isolation performance.

[0017] A further proposed approach is to include a polarization beam splitter comprising a first-stage polarization beam splitter, a first-stage input half-wave plate, and two second-stage polarization beam splitters. The first-stage input half-wave plate is located between one polarization beam splitting surface of the first-stage polarization beam splitter and one of the second-stage polarization beam splitters, while the other polarization beam splitting surface of the first-stage polarization beam splitter is opposite to the other of the second-stage polarization beam splitters.

[0018] As can be seen from the above, by unifying the polarization through the first-stage half-wave plate and providing the correct incident polarization state for the second-stage beam splitter, the balance and stability of the splitting ratio are ensured, laying the foundation for an efficient and low-loss 4-way beam splitting design for subsequent parallel processing and high-quality beam combining.

[0019] A further approach is to include two second-stage input half-wave plates and four third-stage polarization beamsplitters, with one second-stage input half-wave plate located between one polarization beamsplitter plane of the second-stage polarization beamsplitter and one third-stage polarization beamsplitter, and the other polarization beamsplitter plane of the second-stage polarization beamsplitter opposite to another third-stage polarization beamsplitter.

[0020] As can be seen from the above, based on the 4-way beam splitting, a complete 8-way polarization beam splitting tree structure has been extended. By increasing the number of beam splitting stages and corresponding half-wave plates for polarization management, the system has systematically and efficiently expanded one beam into more beams, demonstrating the excellent scalability of the architecture of this invention.

[0021] A further proposed approach is to include a polarization beam combiner comprising a first-stage polarization beam combiner, a first-stage output half-wave plate, and two second-stage polarization beam combiners. The first-stage output half-wave plate is located between one polarization beam combiner surface of the first-stage polarization beam combiner and one of the second-stage polarization beam combiners, while the other polarization beam combiner surface of the first-stage polarization beam combiner is opposite to the other of the second-stage polarization beam combiners.

[0022] As can be seen from the above, the beam combining device is the reverse process of the 4-way beam splitting device. Its mirror-symmetric design ensures the optical path symmetry of the beam combining process and the beam splitting process, so that the optical path of all sub-beams remains consistent. This is crucial for achieving low-loss coherent beam combining and maintaining the quality of the final output beam.

[0023] A further approach is to include two second-stage output half-wave plates and four third-stage polarization combiners, with one second-stage output half-wave plate located between one polarization combining surface of the second-stage polarization combiner and one third-stage polarization combiner, and the other polarization combining surface of the second-stage polarization combiner opposite to another third-stage polarization combiner.

[0024] As can be seen above, this 8-way beam combining structure also demonstrates precise symmetry with the beam splitter. Through careful polarization design, the complex multi-stage beam combining structure can efficiently recombine up to 8 sub-beams into a single beam, achieving ultra-high power processing capabilities while maintaining high efficiency and performance comparable to a single-path isolator. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the optical path of the first embodiment of the optical isolator of the present invention.

[0026] Figure 2 This is a schematic diagram of the optical path of the second embodiment of the optical isolator of the present invention.

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0028] First embodiment of optical isolator: Reference Figure 1 The optical isolator includes a polarization beam splitter, an isolation processing device, and a polarization beam combiner arranged sequentially along the optical path. The polarization beam splitter is used to split an incident beam into N parallel sub-beams, where N is an integer greater than or equal to 4. The isolation processing device includes at least one Faraday rotator 4 and at least one isolation half-wave plate 5 arranged sequentially along the optical path. The N sub-beams pass through the Faraday rotator 4 and the isolation half-wave plate 5 simultaneously in a spatially parallel manner. The polarization beam combiner is used to combine the N sub-beams processed by the isolation processing device into a single outgoing beam.

[0029] Specifically, in this embodiment, the propagation of four parallel sub-beams is used as an example. The polarization beam splitter includes a first-stage polarization beam splitter 11 (PBS), a first-stage input half-wave plate 21 (HWP), and two second-stage polarization beam splitters 31 (PBS) arranged sequentially along the optical path. The first-stage polarization beam splitter 11 has two parallel polarization beam splitting surfaces, and the second-stage polarization beam splitter 31 (PBS) has two parallel polarization beam splitting surfaces. The first-stage input half-wave plate 21 is located between one polarization beam splitting surface of the first-stage polarization beam splitter 11 and one polarization beam splitting surface of one second-stage polarization beam splitter 31. The other polarization beam splitting surface of the first-stage polarization beam splitter 11 is opposite to one polarization beam splitting surface of the other second-stage polarization beam splitter 31.

[0030] The isolation processing device includes a Faraday rotator 4 and an isolation half-wave plate 5. Four sub-beams pass through different positions of the same Faraday rotator 4 in a spatially parallel manner. After passing through the Faraday rotator 4, the four sub-beams pass through different positions of the same isolation half-wave plate 5 in a spatially parallel manner.

[0031] The polarization beam combiner includes a first-stage polarization beam combiner 12 (PBS), a first-stage output half-wave plate 22, and two second-stage polarization beam combiners 32 (PBS) arranged sequentially along the optical path. The first-stage polarization beam combiner 12 (PBS) has two parallel polarization beam-splitting surfaces, and the second-stage polarization beam combiner 32 (PBS) has two parallel polarization beam-splitting surfaces. The first-stage output half-wave plate 22 is located between one polarization beam combining surface of the first-stage polarization beam combiner 12 and one polarization beam-splitting surface of one of the second-stage polarization beam combiners 32. The other polarization beam combining surface of the first-stage polarization beam combiner 12 is opposite to one polarization beam-splitting surface of the other second-stage polarization beam combiner 32.

[0032] When the optical isolator is transmitting in the forward direction, a beam of unpolarized light is incident on the first-stage polarization beam splitter 11 and is split into s-beams and p-beams. The p-beams pass through a first-stage input half-wave plate 21 placed at a fast axis of 45°, and the polarization states of the two beams are unified, both becoming s-beams.

[0033] Subsequently, the two beams are incident on the second-stage polarization beamsplitter 31. The first-stage polarization beamsplitter 11 is rotated 45° relative to the second-stage polarization beamsplitter 31, so that the incident S-beam is at a 45° angle relative to its optical axis, thus being split again by the second-stage polarization beamsplitter 31 into two sub-beams with orthogonal polarization states. The same process occurs in another second-stage polarization beamsplitter 31, so that the incident S-beam is at a 45° angle relative to its optical axis.

[0034] Four sub-beams L1 pass in parallel through different regions of a large-diameter Faraday rotator 4, which can be made of TGG crystal. Under the action of a suitable magnetic field, the TGG crystal provides a non-reciprocal polarization rotation of 45°. The isolating half-wave plate 5 provides a polarization rotation of 45° opposite to the direction of the above-mentioned 45° polarization rotation. After the four beams pass through the Faraday rotator 4 and the isolating half-wave plate 5 in the forward direction, the polarization rotation angle is 90°.

[0035] Beam combining is the reverse process of beam splitting. Four beams are incident in pairs onto the second-stage polarization combiner 32, where they are efficiently combined into two linearly polarized beams. One of the s-beams output from the second-stage polarization combiner 32 is rotated into a p-beam by a first-stage output half-wave plate 22 positioned at a 45° fast axis. Finally, the two s-beams and the p-beam are combined into a single output beam by the first-stage polarization combiner 12.

[0036] In reverse isolation, any light transmitted in the reverse direction will have its polarization state rotated by 45° after passing through the Faraday rotator for the second time, resulting in it being orthogonal to the polarization state of the forward light. As a result, it will be reflected at the two second-stage polarization beam splitters 31 and will not be able to return to the light source from the inlet of the isolator.

[0037] As can be seen from the above, the incident beam can be divided into four sub-beams by the beam splitting of the first-stage polarization beam combiner 12 (PBS) and the two second-stage polarization beam combiners 32 (PBS). There is a 45° rotation angle difference between the beam splitting of the first-stage polarization beam combiner 12 (PBS) and the two second-stage polarization beam combiners 32 (PBS). The polarization state of each sub-beam is controlled to be consistent by the first-stage input half-wave plate 21. Before the beam combining of the first-stage polarization beam combiner 12, the polarization state of one of the parallel sub-beams is controlled to be orthogonal to the polarization state of the other sub-beam by the first-stage output half-wave plate 22. Finally, the four sub-beams after isolation are recombined into a single laser output beam.

[0038] The polarization beam splitter, the isolation processing device, and the polarization beam combiner together form an optically symmetrical system, ensuring that the optical path length of all sub-optical paths is equal.

[0039] The polarization beam splitter adopts a tree structure of multi-stage polarization beam splitters. The first-stage polarization beam combiner 12 splits the incident light into two orthogonally polarized beams, and then the polarization state is unified by a half-wave plate. The second-stage polarization beam combiner 32 splits each beam into two beams again, and so on, to achieve 1x4 beam splitting.

[0040] The polarization beam combiner is the mirror inverse structure of the polarization beam splitter. Before beam combining, the polarization state of the sub-laser is pre-rotated by a half-wave plate to meet the beam combining conditions of the polarization beam splitter (PBS), thereby achieving low-loss coherent beam combining.

[0041] Second embodiment of optical isolator: Reference Figure 2 Based on the first embodiment of the optical isolator described above, a second-stage input half-wave plate 71 and a third-stage polarization beam splitter 61 are added after the second-stage polarization beam splitter 31, and a second-stage output half-wave plate 72 and a third-stage polarization beam combiner 62 are added before the second-stage polarization beam combiner 32.

[0042] Specifically, the polarization beam splitter includes two second-stage input half-wave plates 71 and four third-stage polarization beam splitters 61. One second-stage input half-wave plate 71 is located between one polarization beam splitting surface of the second-stage polarization beam splitter 31 and one third-stage polarization beam splitter 61, and the other polarization beam splitting surface of the second-stage polarization beam splitter 31 is opposite to another third-stage polarization beam splitter 61.

[0043] The polarization beam combiner includes two second-stage output half-wave plates 72 and four third-stage polarization beam combiners 62. One second-stage output half-wave plate 72 is located between one polarization beam combining surface of the second-stage polarization beam combiner 32 and one third-stage polarization beam combiner 62, and the other polarization beam combining surface of the second-stage polarization beam combiner 32 is opposite to another third-stage polarization beam combiner 62.

[0044] After the two second-stage polarization beam splitters 31 output four sub-beams, two of the sub-beams pass through the second-stage input half-wave plate 71 and are then respectively input to the third-stage polarization beam splitter 61. After polarization and beam splitting, they output eight beams toward the Faraday rotator 4.

[0045] Eight sub-beams L2 pass in parallel through different regions of the Faraday rotator 4. Then, the eight sub-beams pass forward through the isolation half-wave plate 5, with a polarization rotation angle of 90°. Beam combining is the reverse process of beam splitting. Based on the above beam combining principle, the eight sub-beams are finally combined into a single beam for output.

[0046] Of course, the above embodiments are only preferred embodiments of this invention. In practical applications, the number of Faraday rotators 4 and isolation half-wave plates 5 can be adjusted according to actual application requirements. Two or more can be arranged, and one or more sub-beams can selectively pass through one or more Faraday rotators 4 and one or more sub-beams can selectively pass through one or more isolation half-wave plates 5. In addition, for the selection of the number of sub-beams, besides using 4, 8, 16, 32..., an integer greater than or equal to 4 can also be selected, which can also achieve the purpose of this invention.

[0047] As can be seen from the above, this scheme disperses the energy of a single high-power laser beam into N parallel optical paths for processing through a beam splitting-parallel processing-beam combining architecture. This significantly reduces the local optical power density through the Faraday rotator from a physical perspective and effectively solves the problem of thermal management under high power by suppressing the thermal lensing effect.

Claims

1. An optical isolator for multi-path polarization beam splitting and combining, characterized in that, It includes a polarization beam splitter, an isolation processing device, and a polarization beam combiner arranged sequentially along the optical path; The polarization beam splitter is used to split an incident beam into N parallel propagating sub-beams, where N is an integer greater than or equal to 4. The isolation processing device includes at least one Faraday rotator and at least one isolation half-wave plate arranged sequentially along the optical path, and the N sub-beams pass through the Faraday rotator and the isolation half-wave plate simultaneously in a spatially parallel manner; The polarization beam combiner is used to combine the N sub-beams processed by the isolation processing device into a single outgoing beam.

2. The optical isolator according to claim 1, characterized in that: The isolation processing device includes a Faraday rotator, and the N sub-beams pass through different positions of the same Faraday rotator simultaneously in a spatially parallel manner.

3. The optical isolator according to claim 1, characterized in that: The isolation processing device includes an isolation half-wave plate, and N sub-beams pass through different positions of the same isolation half-wave plate simultaneously in a spatially parallel manner.

4. The optical isolator according to claim 1, characterized in that: The isolation processing device includes multiple Faraday rotators, and one or more of the sub-beams pass through one of the Faraday rotators.

5. The optical isolator according to claim 1, characterized in that: The isolation processing device includes multiple isolation half-wave plates, and one or more sub-beams pass through one isolation half-wave plate.

6. The optical isolator according to any one of claims 1 to 5, characterized in that: The polarization beam splitter includes a first-stage polarization beam splitter, a first-stage input half-wave plate, and two second-stage polarization beam splitters. The first-stage input half-wave plate is located between one polarization beam splitting surface of the first-stage polarization beam splitter and one of the second-stage polarization beam splitters, and the other polarization beam splitting surface of the first-stage polarization beam splitter is opposite to the other second-stage polarization beam splitter.

7. The optical isolator according to claim 6, characterized in that: The polarization beam splitter includes two second-stage input half-wave plates and four third-stage polarization beam splitters. One second-stage input half-wave plate is located between one polarization beam splitting surface of the second-stage polarization beam splitter and one of the third-stage polarization beam splitters, and the other polarization beam splitting surface of the second-stage polarization beam splitter is opposite to another of the third-stage polarization beam splitters.

8. The optical isolator according to any one of claims 1 to 5, characterized in that: The polarization beam combiner includes a first-stage polarization beam combiner, a first-stage output half-wave plate, and two second-stage polarization beam combiners. The first-stage output half-wave plate is located between one polarization beam combining surface of the first-stage polarization beam combiner and one of the second-stage polarization beam combiners, and the other polarization beam combining surface of the first-stage polarization beam combiner is opposite to the other second-stage polarization beam combiner.

9. The optical isolator according to claim 8, characterized in that: The polarization beam combiner includes two second-stage output half-wave plates and four third-stage polarization beam combiners. One second-stage output half-wave plate is located between one polarization beam combiner surface of the second-stage polarization beam combiner and one of the third-stage polarization beam combiners, and the other polarization beam combiner surface of the second-stage polarization beam combiner is opposite to another of the third-stage polarization beam combiners.

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