Faraday rotator, its preparation method and isolator

Abstract

This application relates to the field of optical device technology, and discloses a Faraday rotator, its fabrication method, and an isolator. The Faraday rotator comprises multiple magneto-optical crystals and multiple heat-dissipating crystals, which are alternately stacked along the optical path. Embodiments of this application can overcome the thermal focus shift defect of the isolator without increasing the output beam diameter of the collimator.

Description

Technical Field

[0001] This application relates to the field of optical device technology, and in particular to a Faraday rotator, its preparation method and isolator. Background Technology

[0002] Optical isolators, as core components of laser systems, play a crucial role in blocking reverse light propagation and maintaining unidirectional optical path operation, holding irreplaceable application value in high-power fiber lasers and solid-state lasers. With the continuous increase in laser output power demands from industrial manufacturing and scientific research, the light energy absorption effect in Faraday rotatable plates of magneto-optical crystals is significantly enhanced, leading to uneven temperature distribution within the crystal and inducing a strong thermal lensing effect. This effect manifests as an unintended shift in the focal position of the output beam, known as thermal focal shift, which not only degrades beam quality but can also trigger a chain reaction of problems such as laser system instability and reduced energy conversion efficiency. To mitigate thermal focal shift, current technologies primarily rely on increasing the collimator output beam diameter to distribute the heat load per unit area. However, this strategy forces a simultaneous increase in the aperture of all optical elements, resulting in an expansion of the overall isolator structure, increased material consumption, and significantly higher manufacturing costs and assembly complexity. Furthermore, the enlarged design limits the application potential of optical systems in compact devices, making it difficult to meet the urgent demands of modern high-power laser technology for miniaturization and high reliability. Summary of the Invention

[0003] The purpose of this application is to provide a Faraday rotator, its preparation method, and an isolator that can overcome the thermal focal shift defect of the isolator without increasing the output beam diameter of the collimator.

[0004] This application provides a Faraday rotatable sheet, comprising multiple magneto-optical crystals and multiple heat-dissipating crystals, wherein the magneto-optical crystals and the heat-dissipating crystals are stacked alternately along the optical path direction.

[0005] In some embodiments, the magneto-optical crystal and the heat dissipation crystal are bonded together using a bonding process.

[0006] In some embodiments, the light-transmitting surface of the Faraday rotator is provided with an anti-reflection film, which is used to compensate for the refractive index deviation between the magneto-optical crystal and the heat dissipation crystal.

[0007] In some embodiments, the thickness of both the magneto-optical crystal and the heat dissipation crystal is [10 μm, 200 μm].

[0008] In some embodiments, the roughness of both the magneto-optical crystal and the heat dissipation crystal is less than 0.5 nm, and the flatness is better than λ / 10.

[0009] In some embodiments, the magneto-optical crystal is one or more of TGG crystal, YIG crystal, TAG crystal, TYAG crystal, and TSAG crystal.

[0010] In some embodiments, the heat dissipation crystal is one or more of sapphire, rutile, YAG crystal, GGG crystal, and work-off crystal.

[0011] This application also provides a method for preparing a Faraday rotatable plate, used to prepare the above-mentioned Faraday rotatable plate, the method comprising: Multiple magneto-optical crystals and multiple heat dissipation crystals that meet the target thickness, target roughness, and target flatness are prepared by slicing, grinding, and polishing processes. The surfaces of the magneto-optical crystal and the heat dissipation crystal are bombarded with an ion beam or a plasma beam to remove the surface adsorption layer, resulting in a cleaned magneto-optical crystal and a clean heat dissipation crystal. A nanometer-precision vision alignment system is used to alternately stack and pre-bond the cleaned magneto-optical crystal and the heat dissipation crystal to obtain the pre-bonded magneto-optical crystal and the heat dissipation crystal. A pressure of 1 MPa to 5 MPa is applied to the pre-bonded magneto-optical crystal and the heat dissipation crystal, and heat treatment is performed at 200°C to 400°C to obtain the Faraday rotator.

[0012] In some embodiments, after obtaining the Faraday rotator, the method further includes: depositing an antireflection film of a target wavelength on the light-transmitting surface of the Faraday rotator, so that the reflectivity of the Faraday rotator is less than 0.1%.

[0013] This application embodiment also provides an isolator, including a first polarizing prism, an optical waveplate, a second polarizing prism, and the aforementioned Faraday rotator, wherein the first polarizing prism, the Faraday rotator, the optical waveplate, and the second polarizing prism are arranged sequentially along the optical path direction.

[0014] The beneficial effects of this application are: instead of relying on increasing the beam diameter to reduce the overall power density, it achieves localization and rapid dissipation of heat at the microscopic level by using a Faraday rotation plate composed of multiple magneto-optical crystals and multiple heat dissipation crystals stacked alternately along the optical path. The heat generated by each magneto-optical crystal can be quickly absorbed and conducted by the adjacent heat dissipation crystal, thereby effectively avoiding the accumulation of heat inside the magneto-optical crystal and fundamentally suppressing the occurrence of thermal lensing effect and thermal focal shift. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the Faraday rotator provided in the first embodiment of this application.

[0016] Figure 2 This is a schematic diagram of the structure of the Faraday rotator provided in the second embodiment of this application.

[0017] Figure 3 This is a flowchart of the preparation method of the Faraday rotatable plate provided in the embodiments of this application.

[0018] Figure 4 This is a schematic diagram of the isolator provided in the embodiments of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] It should be noted that the terms "first," "second," "third," "fourth," etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a system, product, or device that includes a series of circuits is not necessarily limited to those explicitly listed, but may include other circuits not explicitly listed or inherent to such systems, products, or devices.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0022] In traditional optical isolator applications, as laser output power continues to increase, the absorption of light energy by the magneto-optical crystal is intensified, leading to a thermal lensing effect and causing a shift in the output beam focus—a phenomenon known as thermal focal shift. The essence of thermal focal shift lies in the refractive index change caused by the uneven temperature gradient distribution within the magneto-optical crystal. This change directly interferes with the beam propagation path, negatively impacting the beam quality and operational stability of the laser system, making it impossible for the system to reliably maintain unidirectional operation. For example, in the actual operation of high-power fiber lasers, as output power gradually increases, the magneto-optical crystal experiences localized temperature rise due to light energy absorption, resulting in a thermal lensing effect and an uncontrollable shift in the output beam focus. This shift causes a mismatch in the coupling process between the beam and the subsequent collimator, leading to fluctuations in the system output power. Simultaneously, the aperture of optical components is forced to enlarge to compensate for the power density, increasing the overall structural size of the device and raising assembly complexity.

[0023] If the thermal focal shift problem is not effectively suppressed, the performance of the optical isolator will gradually degrade, the laser system may lose its unidirectional operation capability, the output beam quality will continue to decline, and the reliability will fail to meet the basic requirements of high-power applications. As a result, the system stability is fundamentally threatened, and the feasibility of long-term device operation is constrained.

[0024] Based on this, embodiments of this application provide a Faraday rotator, its preparation method, and an isolator, which can overcome the thermal focal shift defect of the isolator without increasing the output beam diameter of the collimator.

[0025] This application provides a Faraday rotator plate for use in an isolator. For example... Figure 1 As shown, the Faraday rotatable plate includes multiple magneto-optical crystals 10 and multiple heat-dissipating crystals 20. The magneto-optical crystals 10 and heat-dissipating crystals 20 are stacked alternately along the optical path direction.

[0026] The magneto-optical crystal 10 refers to a crystal material that can produce the Faraday effect under the influence of a magnetic field. When light passes through the magneto-optical crystal 10, its polarization plane rotates. However, the magneto-optical crystal 10 generates heat when absorbing light energy, which may lead to a degradation in device performance. The heat dissipation crystal 20 refers to a crystal material with high thermal conductivity and low absorption coefficient. This crystal is mainly used to absorb and conduct the heat generated by the magneto-optical crystal 10 during operation to maintain the temperature stability of the device and thus suppress the generation of thermal effects.

[0027] This embodiment provides a Faraday rotation sheet, whose structural design aims to optimize thermal management performance. The core of this Faraday rotation sheet lies in its unique composition and arrangement, namely, it is composed of multiple magneto-optical crystals 10 and multiple heat-dissipating crystals 20 stacked alternately along the optical path. Specifically, the magneto-optical crystals 10 constituting this Faraday rotation sheet can be implemented in various ways. For example, a single type of magneto-optical material can be selected and processed into thin sheets with specific thicknesses and dimensions. Alternatively, materials with different magneto-optical properties can be combined to form crystal sheets with specific magneto-optical responses. These magneto-optical crystal sheets 10 are designed to effectively generate the Faraday rotation effect. Simultaneously, the crystals used for heat dissipation can also be prepared in various ways. For example, a transparent crystal material with excellent thermal conductivity can be selected and processed into a size and shape matching the magneto-optical crystal sheets 10. The main function of these heat-dissipating crystal sheets 20 is to efficiently absorb and conduct the heat generated by the magneto-optical crystals 10 during operation.

[0028] Structurally, this Faraday rotatable sheet is constructed by alternating the aforementioned magneto-optical crystal 10 and heat dissipation crystal 20 sheets along the optical path. For example, a magneto-optical crystal 10 can be placed first, followed by a heat dissipation crystal 20, and then another magneto-optical crystal 10, and so on, until the required number of stacked layers is formed. This alternating stacking structure can be achieved in various ways. For instance, the crystal sheets can be placed and initially fixed one by one using a precise mechanical positioning device. Alternatively, optical contact can be used to create a tight physical contact between the crystal sheets, ensuring optical path continuity and effective heat transfer.

[0029] The following example will provide a more detailed explanation of the above technical solution: In a high-power laser system, an optical isolator is needed to protect the laser source from interference from backlighting. Traditional isolators typically use a thick magneto-optical crystal 10 as a Faraday rotator. However, when the laser system operates at high power, the absorption of light energy by this thick magneto-optical crystal 10 leads to a significant increase in its internal temperature, resulting in severe thermal lensing and thermal focal shift. This causes the focus of the laser output beam to deviate, affecting the system's stability and efficiency. To address this problem, the Faraday rotator provided in this embodiment is introduced into the laser system.

[0030] The Faraday rotator is composed of multiple magneto-optical crystals 10 and multiple heat-dissipating crystals 20 stacked alternately along the optical path. Specifically, when a high-power laser beam passes through the Faraday rotator, the laser first enters the first magneto-optical crystal 10. Within the magneto-optical crystal 10, the polarization plane of the laser rotates, and due to the absorption of light energy, a certain amount of heat is generated inside the magneto-optical crystal 10. However, because the magneto-optical crystal 10 is designed as a thin sheet and is adjacent to a heat-dissipating crystal 20, the generated heat can be rapidly conducted from the magneto-optical crystal 10 to the adjacent heat-dissipating crystal 20.

[0031] Subsequently, the laser beam passes through the heat dissipation crystal 20 and enters the next magneto-optical crystal 10, repeating the above process. The heat dissipation crystal 20 has excellent thermal conductivity, effectively absorbing and dispersing heat from the magneto-optical crystal 10, thereby preventing heat accumulation within a single magneto-optical crystal 10. Through this alternating stacking of magneto-optical crystals 10 and heat dissipation crystals 20 along the optical path, heat is continuously and locally managed and dissipated throughout the entire Faraday rotator. The heat generated by each magneto-optical crystal 10 can be promptly carried away by its adjacent heat dissipation crystal 20, thereby significantly reducing the overall temperature rise and internal temperature gradient of a single magneto-optical crystal 10. Thus, the Faraday rotator can effectively suppress the thermal lensing effect and thermal focal shift, ensuring stable transmission of the high-power laser beam and the accuracy of the focal position.

[0032] Based on the above examples, the Faraday rotator provided in this embodiment demonstrates a significant technical contribution. In conventional high-power laser systems, to address the thermal lensing effect and thermal focal shift generated by the magneto-optical crystal 10, it is typically necessary to reduce the power density of the device by increasing the output beam diameter of the collimator. While this method can alleviate the thermal effect to some extent, its drawback is that it requires enlarging the aperture of all optical elements, resulting in an increased device structure size and a significant increase in the manufacturing cost of the isolator.

[0033] In contrast, the Faraday rotator in this embodiment provides a more efficient and compact thermal management solution by employing a structure in which magneto-optical crystals 10 and heat dissipation crystals 20 are alternately stacked along the optical path. The core advantage of this solution is that it no longer relies on reducing overall power density by increasing the beam diameter, but rather on achieving localization and rapid dissipation of heat at the microscopic level. The heat generated by each magneto-optical crystal 10 can be rapidly absorbed and conducted by the adjacent heat dissipation crystal 20, effectively preventing heat accumulation within the magneto-optical crystal 10 and fundamentally suppressing thermal lensing and thermal focal shift.

[0034] Therefore, this Faraday rotator can significantly improve the thermal stability of high-power laser systems without increasing the overall size and cost of the device. This innovative structural design not only solves the problems of low thermal management efficiency, large device size, and high cost in existing technologies, but also provides a completely new approach to the design of high-power optical isolators, ensuring the stability and reliability of laser systems under high-power operation.

[0035] In some embodiments, the magneto-optical crystal 10 and the heat dissipation crystal 20 are bonded together by a bonding process.

[0036] Bonding is a technique that tightly connects two or more solid surfaces through atomic or molecular forces. Its main function is to achieve a strong bond between different material layers, thereby forming a monolithic structure with excellent mechanical stability, optical continuity, and long-term reliability. This process can be implemented in various ways. For example, direct bonding can be used, where the crystal surface is activated (e.g., by plasma treatment) to form atomic-level bonds upon contact, followed by appropriate annealing to enhance bond strength. Alternatively, eutectic bonding can be used, where a low-melting-point metal layer is introduced at the crystal interface, forming a eutectic liquid phase at a specific temperature, followed by solid-state bonding upon cooling. Furthermore, diffusion bonding can be used, where atomic diffusion allows crystal surfaces to interpenetrate and bond under high temperature and pressure conditions.

[0037] The present application employs a bonding process to bond the magneto-optical crystal 10 and the heat dissipation crystal 20, creating a tight, atomic- or molecular-level connection between the originally simply stacked crystal layers. This connection significantly enhances the overall mechanical strength and structural stability of the Faraday rotator, effectively preventing interlayer misalignment or separation caused by external vibrations or temperature changes. Simultaneously, the bonding process minimizes air gaps and impurities at the crystal interfaces, thereby reducing reflection loss and scattering of light during transmission between different crystal layers, ensuring the continuity of the optical path and the stability of optical performance. Furthermore, the tight bonding interface facilitates efficient heat conduction between the magneto-optical crystal 10 and the heat dissipation crystal 20, thus improving the heat dissipation efficiency and operational stability of the Faraday rotator in high-power applications.

[0038] In one specific implementation, during the fabrication of the Faraday rotatable sheet, the bonding surfaces of the magneto-optical crystal 10 and the heat dissipation crystal 20 can first be ultra-precision polished to achieve extremely low surface roughness and high flatness. Subsequently, these surfaces are subjected to plasma activation treatment to remove surface adsorbates and increase surface activity. Next, the activated magneto-optical crystal 10 and the heat dissipation crystal 20 are alternately aligned and lightly contacted along the optical path, allowing preliminary pre-bonding to occur at room temperature. Finally, the pre-bonded crystal stack is annealed at a specific temperature, such as heating to several hundred degrees Celsius in an inert atmosphere, to promote diffusion and reconstruction between interface atoms, thereby forming strong covalent bonds or van der Waals bonds and achieving permanent adhesion between crystal layers.

[0039] Through the above technical solution, a tight and stable connection is achieved between the magneto-optical crystal 10 and the heat dissipation crystal 20, effectively solving the problems of mechanical instability, optical interface loss, and low thermal management efficiency that may be caused by simple stacking. This bonding method significantly improves the overall structural integrity and shock resistance of the Faraday rotatable sheet, while optimizing the light transmission efficiency at the crystal interface and reducing insertion loss. In addition, the tight bonding interface also promotes efficient heat conduction, thereby improving the thermal stability of the Faraday rotatable sheet in high-power laser applications and extending the device's lifespan.

[0040] In some embodiments, such as Figure 2 As shown, the light-transmitting surface of the Faraday rotator is provided with an anti-reflection film 30, which is used to compensate for the refractive index deviation between the magneto-optical crystal 10 and the heat dissipation crystal 20.

[0041] The light-transmitting surface of a Faraday rotator refers to the surface on which the Faraday rotator exchanges light with the external environment; that is, the interface through which light enters and leaves the device. These surfaces typically require fine optical processing to ensure the quality of light transmission.

[0042] An antireflective coating 30 is a thin film applied to the surface of optical components. Its main function is to reduce light reflection at the interface between different media, thereby improving light transmittance. The antireflective coating 30 can be achieved by stacking single or multiple dielectric films. The materials are typically chosen to have specific refractive indices and thicknesses, such as magnesium fluoride, silicon dioxide, titanium dioxide, or aluminum oxide. By precisely controlling the thickness and refractive index of the film layers, the interference effect of light can be used to counteract reflected light, thus achieving the antireflective effect.

[0043] Compensating for the refractive index mismatch between the magneto-optical crystal 10 and the heat dissipation crystal 20 refers to mitigating or eliminating optical losses caused by the refractive index mismatch between them. When light travels from one refractive index medium to another, partial reflection occurs. The antireflection coating 30 forms one or more thin film layers with specific optical properties on the light-transmitting surface of the Faraday rotation plate, causing incident light to interfere within these layers, thereby reducing reflected light and increasing transmitted light. This compensation effect not only targets the external interface but also indirectly optimizes the transmission efficiency of light within the internal crystal stack structure, as reduced reflection at the external interface helps maximize the light energy entering and leaving the crystal stack.

[0044] The present application proposes an antireflection coating 30 on the light-transmitting surface of a Faraday rotator, which causes interference of incident light within the coating layer, thereby significantly reducing light reflection on the outer light-transmitting surface of the Faraday rotator. This reduction in reflection not only directly improves light transmittance, but more importantly, the design of the antireflection coating 30 takes into account the refractive index deviation between the magneto-optical crystal 10 and the heat dissipation crystal 20. By optimizing the refractive index and thickness of the coating layer, the light transmission loss of the entire Faraday rotator as a whole optical system is minimized. In this way, the antireflection coating 30 effectively compensates for the refractive index deviation effect that may be introduced by the internal crystal stacking structure, ensuring that light energy can pass through the entire Faraday rotator efficiently, thereby improving the overall optical performance of the device.

[0045] As a specific implementation, one or more antireflection films 30 can be deposited on the light-transmitting surface of the Faraday rotator. For example, physical vapor deposition techniques such as ion-assisted deposition or magnetron sputtering can be used to deposit multiple dielectric films on the incident and exit surfaces of the Faraday rotator. These films can be composed of alternating low-refractive-index materials (such as silicon dioxide) and high-refractive-index materials (such as titanium dioxide or tantalum pentoxide). By precisely controlling the thickness of each film layer, optimal antireflection effect can be achieved within the target wavelength range. For example, for a Faraday rotator operating in the near-infrared band, a broadband antireflection film 30 composed of multiple layers of silicon dioxide / titanium dioxide can be designed. Its film structure and thickness are optimized to ensure that the reflectivity of light on the light-transmitting surface is less than 0.1% throughout the entire operating wavelength range, thereby effectively compensating for the possible refractive index difference between the magneto-optical crystal 10 and the heat dissipation crystal 20 and maximizing the transmission of light energy.

[0046] By employing the aforementioned technical solution, an antireflection film 30 is applied to the light-transmitting surface of the Faraday rotatable plate to compensate for the refractive index deviation between the magneto-optical crystal 10 and the heat dissipation crystal 20. This significantly reduces light reflection loss when entering and exiting the device. This not only improves the overall transmittance of the Faraday rotatable plate and reduces light energy waste, but also, through effective compensation for the refractive index deviation of the internal crystal stacking structure, allows light to pass through the entire device more efficiently and stably. Ultimately, this helps improve the isolation of the Faraday rotatable plate, reduce insertion loss, and thus optimize its performance in applications such as optical communication and laser systems.

[0047] In some embodiments, the thicknesses of both the magneto-optical crystal 10 and the heat dissipation crystal 20 are [10 μm, 200 μm].

[0048] The solution in this application optimizes the overall performance of the Faraday rotation plate by precisely controlling the thickness of the magneto-optical crystal 10 and the heat dissipation crystal 20 between 10 μm and 200 μm, combined with a structure in which multiple magneto-optical crystals 10 and multiple heat dissipation crystals 20 are alternately stacked along the optical path. In the alternately stacked structure, the magneto-optical crystal 10 is the core component for generating the Faraday rotation effect, but it generates heat due to light absorption during operation. The heat dissipation crystal 20 is responsible for dissipating this heat from the magneto-optical crystal 10. By controlling the thickness of the magneto-optical crystal 10 between 10 μm and 200 μm, it is ensured that it has sufficient optical interaction length to achieve the required rotation angle, while being thin enough so that the heat generated inside can be quickly conducted to the adjacent heat dissipation crystal 20. Correspondingly, the thickness of the heat dissipation crystal 20 is also controlled between 10 μm and 200 μm, which ensures that it can effectively absorb and dissipate heat from the magneto-optical crystal 10 without becoming a bottleneck for heat conduction or significantly increasing the optical path due to its own excessive thickness. This precise thickness control enables each pair of magneto-optical crystals 10 and heat dissipation crystals 20 to form a highly efficient optical-thermal unit, thereby achieving uniform and efficient heat management throughout the entire Faraday rotator, effectively suppressing thermal effects, and ensuring the stability and reliability of the optical performance of the Faraday rotator under long-term high-power operation.

[0049] The following is a specific example. In one embodiment, the Faraday rotatable sheet can be formed by alternating stacks of a 50 μm thick magneto-optical crystal 10 and an 80 μm thick heat-dissipating crystal 20. These crystal layers can be initially diced using high-precision wafer dicing technology, and then the thickness can be precisely controlled within the aforementioned range through fine grinding and chemical mechanical polishing processes. For example, a double-sided polishing device can be used, along with grinding and polishing slurries of specific particle sizes, to process the crystal step-by-step until the required micron-level thickness is achieved. During processing, a non-contact optical thickness gauge can be used to monitor the crystal thickness in real time, ensuring it meets the requirement of a range of 10 μm to 200 μm.

[0050] By precisely limiting the thickness of the magneto-optical crystal 10 and the heat dissipation crystal 20 in the Faraday rotatable sheet to between 10 μm and 200 μm, the overall performance of the Faraday rotatable sheet can be significantly improved. This precise thickness control allows the Faraday rotatable sheet to maintain a compact structure while effectively optimizing thermal management efficiency, reducing thermal birefringence and thermal lensing effects caused by heat accumulation, thereby ensuring the optical performance stability and reliability of the Faraday rotatable sheet under long-term high-power operation. In addition, this thickness range also helps to reduce the overall size and weight of the device, facilitating integration into more compact optical systems, reducing optical absorption loss, and improving light energy utilization.

[0051] In some embodiments, the roughness of both the magneto-optical crystal 10 and the heat dissipation crystal 20 is less than 0.5 nm, and the flatness is better than λ / 10.

[0052] Surface roughness refers to the degree of undulation in the microscopic geometry of an object's surface, usually measured by the root mean square (RMS) value or the arithmetic mean deviation (Ra). For optical components, extremely low surface roughness is crucial for ensuring high-quality beam transmission. When surface roughness is less than 0.5 nm, it can effectively suppress light scattering at crystal surfaces and interfaces, reduce energy loss, and maintain good beam directivity and wavefront quality. Achieving such low surface roughness typically requires ultra-precision machining techniques, such as chemical mechanical polishing (CMP) or ion beam polishing (IBP). CMP combines mechanical abrasion and chemical etching, enabling the removal of submicron-level defects to obtain an atomically smooth surface. IBP, on the other hand, uses a high-energy ion beam to bombard the material surface, removing material through physical sputtering, achieving precise control over surface morphology and the fabrication of ultra-smooth surfaces.

[0053] Flatness refers to the degree of deviation of the surface of an optical element from its ideal geometry. λ / 10 indicates that the maximum deviation of the surface from the ideal plane is less than one-tenth of the wavelength of light. For the visible light band (e.g., 500 nm), a flatness of λ / 10 means a surface deviation of less than 50 nm. High flatness is crucial for maintaining the wavefront integrity of the light beam passing through the optical element, preventing severe wavefront distortion during transmission, and thus ensuring the collimation, focusing, and mode purity of the emitted beam. Achieving flatness better than λ / 10 typically requires precision optical processing techniques, such as Computer-Controlled Optical Surface Shaping (CCOS) or Magnetorheological Fluid Polishing (MRF). CCOS precisely controls the movement trajectory and pressure of the polishing tool, combined with real-time interferometer feedback, to locally shape the surface, achieving extremely high surface accuracy. MRF utilizes a magnetically confined abrasive stream to perform non-contact polishing of the optical surface, enabling nanometer-level surface finishing.

[0054] The solution presented in this application significantly improves the overall optical performance of the Faraday rotator by controlling the roughness of both the magneto-optical crystal 10 and the heat dissipation crystal 20 to less than 0.5 nm and achieving a flatness better than λ / 10. Specifically, when the magneto-optical crystal 10 and the heat dissipation crystal 20 have extremely low surface roughness, the scattering loss of light at the crystal surface and the inter-crystal interface can be minimized. Scattering is one of the main factors leading to optical power attenuation and beam quality degradation. By reducing the roughness to the nanometer level, it is possible to ensure that the beam passes through each crystal layer with minimal loss, thereby improving the light transmission efficiency of the Faraday rotator. At the same time, the excellent surface flatness ensures that the wavefront distortion of the beam is strictly controlled within a very small range when passing through the multi-layer crystal stack structure. This means that the outgoing beam can maintain good collimation and focusing characteristics, avoiding aberrations and beam divergence caused by wavefront distortion, which is crucial for applications requiring high beam quality, such as laser systems. Furthermore, high surface quality facilitates close contact between crystals, forming high-quality interfaces through bonding processes or optical contact, further reducing interface losses and thermal resistance, thereby improving the overall performance and reliability of the Faraday rotator. This high-surface-quality crystal stacking structure enables the Faraday rotator to maintain extremely high optical transmission efficiency and beam quality while achieving Faraday rotation functionality, effectively solving the problem of optical performance degradation caused by surface defects.

[0055] In one specific implementation, when preparing the magneto-optical crystal 10 and the heat dissipation crystal 20, a crystal substrate can first be obtained using precision cutting and grinding processes, followed by multi-stage polishing. For example, rough polishing can be performed first to remove most surface damage, followed by fine polishing to achieve preliminary optical surface quality. To achieve a roughness of less than 0.5 nm and a flatness better than λ / 10, chemical mechanical polishing (CMP) technology can be further used for final ultra-precision machining of the crystal surface. During CMP, by precisely controlling the chemical composition of the polishing slurry, the abrasive particle size, the polishing pressure, and the polishing disc rotation speed, atomic-level removal of material from the crystal surface can be achieved, resulting in an ultra-smooth surface. Simultaneously, an online or offline interferometer detection system, such as a Fizeau interferometer, can be used to monitor and provide feedback on the flatness of the crystal surface in real time or periodically, guiding subsequent polishing processes until a surface accuracy requirement better than λ / 10 is achieved. For example, an interferometer from Zygo can be used to inspect the crystal surface to ensure that its surface accuracy meets the requirements.

[0056] By employing the aforementioned technical solution, the roughness of both the magneto-optical crystal 10 and the heat dissipation crystal 20 is controlled to less than 0.5 nm, and the flatness is better than λ / 10, which significantly improves the overall optical performance of the Faraday rotator. Specifically, the extremely low surface roughness minimizes light scattering losses at the crystal surface and interface, thereby improving the light transmission efficiency and isolation of the Faraday rotator. Simultaneously, the excellent surface flatness ensures that the wavefront distortion of the beam is strictly controlled when passing through the multilayer crystal stack structure, ensuring good collimation and focusing characteristics of the emitted beam and avoiding aberrations and beam divergence caused by surface defects. This high-surface-quality crystal stack structure enables the Faraday rotator to maintain extremely high optical transmission efficiency and beam quality while achieving the Faraday rotation function, effectively solving the problem of optical performance degradation caused by surface defects, thus enhancing the application value and reliability of the Faraday rotator in precision optical systems.

[0057] In some embodiments, the magneto-optical crystal 10 is one or more of TGG crystal, YIG crystal, TAG crystal, TYAG crystal and TSAG crystal.

[0058] Specifically, TGG (Terbium Gallium Garnet) crystal is a magneto-optical material widely used in Faraday rotators and isolators, characterized by a high Verdet constant and low optical absorption loss, particularly excelling in the visible and near-infrared bands. YIG (Yttrium Iron Garnet) crystal exhibits significant magneto-optical effects in the microwave and infrared bands, making it suitable for magneto-optical devices within specific wavelength ranges. TAG (Terbium Aluminum Garnet), as a novel magneto-optical material, possesses a high Verdet constant and good thermal properties, contributing to improved device stability at high power. TYAG (Terbium Yttrium Aluminum Garnet) crystal is a solid solution of TGG and YAG, designed to combine the advantages of both for superior overall performance. TSAG (Terbium Scandium Aluminum Garnet) crystal is renowned for its high Verdet constant and excellent thermal conductivity, effectively addressing the thermal management challenges in high-power laser applications. These crystals can be prepared using various crystal growth techniques such as molten salt method, Czochralski method or liquid phase epitaxy, and undergo precise cutting, grinding and polishing processes to achieve the required size and surface quality.

[0059] The present application constructs a Faraday rotator by alternately stacking the aforementioned specific types of magneto-optical crystals 10 and heat-dissipating crystals 20 along the optical path. These selected magneto-optical crystals 10, such as TGG, YIG, TAG, TYAG, and TSAG crystals, are renowned for their excellent magneto-optical properties, such as high Verdet constants and low optical absorption. A high Verdet constant ensures that the required polarization plane rotation angle can be achieved within a short optical path, thereby reducing the overall size and weight of the device. Low optical absorption minimizes energy loss and heat generation when light passes through the crystal, which is crucial for maintaining stable device operation. When a beam of light passes through these magneto-optical crystals 10, its polarization plane rotates under the influence of an external magnetic field. Simultaneously, because these magneto-optical crystals 10 and heat-dissipating crystals 20 are alternately stacked, even if a small amount of heat is generated during operation, it can be quickly conducted away through the heat-dissipating crystals 20, effectively preventing performance degradation or damage to the magneto-optical crystals 10 due to temperature increases. This structural design, combined with the high-performance magneto-optical crystal 10, ensures that the Faraday rotator achieves efficient magneto-optical rotation while possessing excellent thermal management capabilities and long-term stability, thus overcoming the limitations of traditional Faraday rotators in terms of performance and thermal stability.

[0060] In one specific implementation, the magneto-optical crystal 10 can be a TGG crystal. Due to its high Verdet constant and low optical loss characteristics in the visible and near-infrared bands, TGG crystals can effectively achieve rotation of the optical polarization plane, making them an ideal choice for constructing high-performance Faraday rotators. During fabrication, high-quality TGG single crystals can be grown using the Czochralski method, then cut into thin slices with a thickness of 10 μm to 200 μm, and subjected to precise grinding and polishing to ensure a surface roughness of less than 0.5 nm and a flatness better than λ / 10. These TGG crystal slices are then alternately stacked with a heat-dissipating crystal 20 (e.g., sapphire crystal) and bonded together to form a Faraday rotator.

[0061] Through the above technical solutions, the Faraday rotator can achieve a stronger magneto-optical effect and higher rotational efficiency, while effectively reducing light absorption loss in the crystal. Furthermore, the selected magneto-optical crystal 10 has good thermal stability, and in conjunction with the heat dissipation crystal 20, further improves the reliability and stability of the Faraday rotator under long-term operation or high-power applications, thereby significantly improving the overall performance of the Faraday rotator.

[0062] In some embodiments, the heat dissipation crystal 20 is one or more of sapphire, rutile, YAG crystal, GGG crystal and work-off crystal.

[0063] The heat dissipation crystal 20 can be sapphire. Sapphire has excellent thermal conductivity, high hardness, and good optical transmittance over a wide spectral range, which can efficiently conduct away the heat generated by the magneto-optical crystal 10 while maintaining low optical loss. The heat dissipation crystal 20 can also be rutile. Rutile is a crystal material with high refractive index and good thermal conductivity. Its unique birefringence properties also have application potential in certain optical designs, helping to achieve effective heat management. The heat dissipation crystal 20 can also be YAG crystal. YAG crystal, or yttrium aluminum garnet, is known for its good thermal conductivity, mechanical strength, and optical homogeneity. It is often used in laser gain media and optical components, and as a heat dissipation material, it can effectively maintain the temperature stability of the Faraday swivel plate. The heat dissipation crystal 20 can also be GGG crystal. GGG crystal, or gadolinium gallium garnet, has good thermal conductivity and a lattice constant similar to some magneto-optical garnet crystals. This allows it to reduce interfacial stress when bonded to the magneto-optical crystal 10, thereby improving the long-term reliability of the device. The heat dissipation crystal 20 can also be a work-off crystal. Work-off crystals typically refer to crystals that have undergone special processing or have a specific crystal orientation, designed to optimize their thermal properties. For example, by controlling the crystal growth or cutting direction to enhance the heat conduction efficiency in a specific direction, thereby more effectively managing the heat distribution inside the Faraday rotation plate.

[0064] The present application constructs a highly efficient thermal management structure by alternately stacking the aforementioned heat dissipation crystal 20, which possesses excellent thermal and optical properties, and the magneto-optical crystal 10 along the optical path. When a light beam passes through the Faraday rotator, the magneto-optical crystal 10 generates heat due to the absorption of light energy. Because the heat dissipation crystal 20 is tightly bonded to the magneto-optical crystal 10, and the material of the heat dissipation crystal 20 (such as sapphire, rutile, YAG crystal, GGG crystal, or work-off crystal) has high thermal conductivity, heat can be rapidly conducted from the magneto-optical crystal 10 to adjacent heat dissipation crystals 20. This alternately stacked structure provides multiple layers of heat conduction paths, allowing heat to be quickly and uniformly distributed throughout the entire Faraday rotator and ultimately dissipated to the external environment. Simultaneously, the materials of these heat dissipation crystals 20 have good optical transmittance within the target wavelength range, ensuring low loss of the optical signal during transmission. In this way, the temperature inside the Faraday rotator can be effectively controlled, avoiding performance degradation of the magneto-optical crystal 10 due to temperature increases, thereby ensuring the stability and reliability of the Faraday rotator in high-power applications.

[0065] In one specific implementation, the Faraday rotatable sheet can be formed by alternately stacking multiple TGG magneto-optical crystals 10 and multiple sapphire heat dissipation crystals 20 along the optical path. The sapphire heat dissipation crystals 20 are chosen for their excellent thermal conductivity and optical transparency, ensuring efficient heat dissipation in the optical path without introducing significant optical losses. In another specific implementation, the heat dissipation crystal 20 can be YAG crystal, which maintains good thermal conductivity while also possessing excellent mechanical strength and chemical stability, further improving the overall reliability of the Faraday rotatable sheet. In some applications with high requirements for lattice matching, GGG crystals can be used as the heat dissipation crystal 20, forming a more stable interface with the magneto-optical crystal 10.

[0066] Through the above technical solution, the Faraday rotator effectively solves the problem of performance degradation caused by heat generation in the magneto-optical crystal 10 under high-power illumination. Specifically, by selecting sapphire, rutile, YAG, GGG, or work-off crystals as the heat dissipation crystal 20, the thermal management capability of the Faraday rotator is significantly improved. This allows the operating temperature of the magneto-optical crystal 10 to be maintained within a more stable range, thereby effectively suppressing the generation of thermally induced birefringence and thermal lensing effects, and reducing beam distortion and polarization state degradation. At the same time, the stability of the Faraday rotation angle is also ensured, avoiding rotation angle drift caused by temperature fluctuations. Therefore, the Faraday rotator of this application has higher performance, longer service life, and stronger environmental adaptability in fields such as high-power laser isolation, fiber optic communication, and optical sensing.

[0067] This application also provides a method for preparing a Faraday rotatable plate, used to prepare the aforementioned Faraday rotatable plate. For example... Figure 3 As shown, the preparation method includes, but is not limited to, steps S301 to S304.

[0068] Step S301 involves using slicing, grinding, and polishing processes to prepare multiple magneto-optical crystals and multiple heat dissipation crystals that meet the target thickness, target roughness, and target flatness.

[0069] In step S302, the surfaces of both the magneto-optical crystal and the heat dissipation crystal are bombarded with an ion beam or a plasma beam to remove the surface adsorption layer, resulting in a cleaned magneto-optical crystal and a heat dissipation crystal.

[0070] In step S303, a nanometer-precision vision alignment system is used to alternately stack and pre-bond the cleaned magneto-optical crystal and heat dissipation crystal to obtain pre-bonded magneto-optical crystal and heat dissipation crystal.

[0071] Step S304: Apply a pressure of 1 MPa to 5 MPa to the pre-bonded magneto-optical crystal and heat dissipation crystal, and perform heat treatment at 200℃ to 400℃ to obtain a Faraday rotator.

[0072] The slicing process can employ diamond wire cutting technology, using high-precision cutting equipment to cut the crystal material into thin slices of the required thickness. The grinding process utilizes a precision grinding machine, along with grinding fluids of varying grit sizes, to mechanically remove impurities from the wafer surface, achieving the target thickness and initially improving surface smoothness. The polishing process can employ chemical mechanical polishing (CMP) or magnetohydrodynamic polishing (MRP) techniques, using the synergistic effect of chemical etching and mechanical friction to remove microscopic defects and subsurface damage from the wafer surface, thereby obtaining extremely low surface roughness and excellent smoothness.

[0073] Ion beam bombardment can use argon ion beams to physically sputter crystal surfaces, removing the surface atomic layer through high-energy ion bombardment and exposing fresh surfaces. Plasma beam bombardment can use oxygen plasma or mixed gas plasma treatment, where active free radicals chemically react with surface contaminants, converting them into volatile substances for removal.

[0074] The vision alignment system can use a high-resolution CCD camera combined with image processing algorithms to monitor the wafer edge or preset marker points in real time, and perform sub-micron or even nanometer-level XYZ axis adjustments through a precision motion platform (such as a piezoelectric ceramic drive platform). Pre-bonding, after precise alignment, involves applying slight contact or minimal pressure to utilize van der Waals forces or hydrogen bonds activated on the crystal surface to form a preliminary physical adsorption bond between the wafers.

[0075] External pressure and high-temperature heat treatment promote the diffusion and reconstruction of atoms on the crystal surface, forming covalent or ionic bonds, thereby obtaining an integrated Faraday rotation sheet. Pressure can be applied using hydraulic or pneumatic devices, with a precise control system applying uniform and stable pressure to the stacked crystals to ensure tight contact at the bonding interfaces. Heat treatment can be carried out in a high-temperature furnace under vacuum or inert gas atmosphere. By precisely controlling the heating rate, holding time, and cooling rate, interfacial atomic diffusion and bonding strengthening are achieved without phase transitions or damage to the crystals.

[0076] This application's method first involves high-precision slicing, grinding, and polishing of the magneto-optical crystal and the heat-dissipating crystal, ensuring that each wafer meets stringent requirements for thickness, roughness, and flatness, laying the optical foundation for subsequent bonding. Subsequently, the crystal surface is deeply cleaned and activated using an ion beam or plasma beam, removing surface adsorption layers and contaminants that could affect bonding quality, significantly enhancing the crystal surface activity and enabling high-strength direct bonding. Next, a nanometer-precision vision alignment system is used to achieve precise alternating stacking and pre-bonding between the magneto-optical crystal and the heat-dissipating crystal, effectively avoiding optical performance degradation due to alignment deviations. Finally, heat treatment under specific pressure and temperature conditions promotes atomic diffusion and reconstruction at the crystal interface, forming strong covalent or ionic bonds, thereby integrating the multilayer crystal structure and eliminating problems such as stress, absorption, and thermal expansion mismatch that may be introduced by traditional adhesives. This fabrication method allows Faraday rotatable wafers to meet the stringent requirements of high-power laser applications for optical components, especially in scenarios requiring thin layers, high precision, high thermal conductivity, and low optical loss, where their performance advantages are even more pronounced.

[0077] The following is a specific example. As a particular implementation, TGG crystal can be used as the magneto-optical crystal, and sapphire crystal as the heat dissipation crystal. First, using a diamond wire saw with a diameter of 100μm, the TGG crystal and sapphire crystal raw materials are cut into thin slices with a thickness of approximately 250μm. Next, a double-sided polishing machine is used for coarse polishing with an alumina polishing slurry with a particle size of 3μm, followed by fine polishing with a silica polishing slurry with a particle size of 0.5μm, reducing the wafer thickness to approximately 120μm. Subsequently, a chemical mechanical polishing (CMP) device is used with an alkaline silica polishing slurry to polish the wafer surface roughness to below 0.3nm, achieving a flatness better than λ / 15, with the final thickness controlled at 100μm. After wafer fabrication, an ion beam cleaner is used in a vacuum environment to bombard the wafer surface with an argon ion beam with an energy of 500eV for 5 minutes to remove adsorbed hydrocarbons and oxide layers. Then, using an automated alignment and bonding system equipped with a high-resolution microscope and a piezoelectric ceramic displacement stage, cleaned TGG and sapphire crystals were alternately stacked to ensure that the lateral alignment deviation between adjacent wafers was less than 50 nm. Pre-bonding was achieved using van der Waals forces on the crystal surface under slight contact. Finally, the pre-bonded crystal stack was placed in a hot press bonding furnace, where a uniform pressure of 2 MPa was applied under a vacuum better than 10^-4 Pa, and the temperature was increased to 300 °C at a rate of 5 °C / min. After holding at that temperature for 2 hours, the temperature was slowly reduced to room temperature at a rate of 2 °C / min to obtain an integrated Faraday rotatable wafer.

[0078] Through the above technical solutions, this application can precisely control the thickness, roughness, and flatness of the magneto-optical crystal and the heat dissipation crystal in the Faraday rotatable sheet, ensuring excellent optical performance. Activation treatment of the crystal surface using an ion beam or plasma beam greatly improves the cleanliness and activity of the crystal surface, providing ideal interface conditions for subsequent direct bonding. The use of a nanometer-precision vision alignment system for alternating stacking and pre-bonding ensures highly accurate alignment of the multilayer crystal structure, effectively avoiding optical loss and performance degradation caused by alignment deviations. Combined with precisely controlled pressure and heat treatment processes, high-strength, adhesive-free bonding between the magneto-optical crystal and the heat dissipation crystal is achieved, eliminating problems such as stress, absorption, and thermal expansion mismatch that may be introduced by traditional adhesives, thereby significantly improving the overall optical performance, thermal stability, and long-term reliability of the Faraday rotatable sheet.

[0079] In some embodiments, after obtaining the Faraday rotatable sheet, the method further includes: depositing an antireflection film of the target wavelength on the light-transmitting surface of the Faraday rotatable sheet, so that the reflectivity of the Faraday rotatable sheet is less than 0.1%.

[0080] The antireflective coating can be achieved using physical vapor deposition (PVD) techniques, such as electron beam evaporation or magnetron sputtering, by precisely controlling the type of deposited material, film thickness, and number of layers to achieve the desired optical performance. Alternatively, wet chemical techniques such as chemical vapor deposition (CVD) or sol-gel methods can also be used to prepare the antireflective coating.

[0081] This application's solution effectively solves the problem of surface reflection loss in Faraday rotatable plates by depositing an antireflection coating of the target wavelength on the light-transmitting surface. When light is incident from one medium (such as air) to another medium (such as a Faraday rotatable plate), some light is reflected at the interface due to the difference in refractive index between the two media. The principle of the antireflection coating is to utilize the thin-film interference effect by introducing one or more dielectric thin films with specific refractive indices and thicknesses onto the surface of the Faraday rotatable plate. These thin film layers enable a specific phase difference between the reflected light waves generated at different interfaces of the incident light, thereby causing destructive interference at the target wavelength and significantly reducing the intensity of the reflected light. At the same time, the reduction of reflected light means an increase in transmitted light, thus improving the optical transmittance of the Faraday rotatable plate. By reducing the reflectivity to below 0.1%, it is ensured that the vast majority of incident light can effectively pass through the Faraday rotatable plate, greatly improving the optical efficiency and performance of the device. This processing method, combined with the aforementioned precision fabrication method for Faraday rotators, results in Faraday rotators that not only possess excellent internal structure and material properties, but also exhibit extremely high light transmittance on their optical surfaces, thereby enhancing the overall performance of the Faraday rotator in the optical path.

[0082] The following is a specific example. After the Faraday rotatable sheet is fabricated, one or more antireflective coatings can be deposited on its light-transmitting surface using ion-assisted electron beam evaporation (IBE). For example, for the 1064 nm wavelength commonly used in laser applications, a multilayer dielectric film system composed of alternating silicon dioxide (SiO2) and tantalum oxide (Ta2O5) can be designed. By precisely controlling the deposition rate and thickness of each thin film, for example, to achieve a specific total film thickness, optimal destructive interference can be achieved at the 1064 nm wavelength. During the coating process, the optical thickness of the film can be monitored in real time to ensure its accuracy. Ultimately, the surface reflectivity of the coated Faraday rotatable sheet at the 1064 nm wavelength can be precisely controlled and stably maintained below 0.1%.

[0083] By employing the aforementioned technical solution, an antireflection film of the target wavelength is deposited on the light-transmitting surface of the Faraday rotatable sheet, achieving a reflectivity of less than 0.1%, significantly reducing surface reflection loss in the optical path. This directly improves the transmission efficiency of optical signals and reduces energy loss, which is of great significance for applications requiring high optical transmittance, such as high-power laser systems or precision optical measurement equipment. Especially considering that the aforementioned fabrication method already ensures excellent crystal quality and bonding interfaces within the Faraday rotatable sheet, further optimization of its optical surface properties elevates the overall optical performance of the Faraday rotatable sheet to a higher level. This ensures the stability and reliability of the device during actual operation and effectively avoids the risk of system instability or component damage caused by excessively high reflectivity.

[0084] This application also provides an isolator. For example... Figure 4 As shown, the isolator includes a first polarizing prism 1, an optical waveplate 2, a second polarizing prism 3, and the aforementioned Faraday rotator 4. The first polarizing prism 1, the Faraday rotator 4, the optical waveplate 2, and the second polarizing prism 3 are arranged sequentially along the optical path. Magnetic field generators 5 are also arranged on both sides of the Faraday rotator 4 perpendicular to the optical path.

[0085] The first polarizing prism 1 is used to select the polarization state of incident light. It can convert unpolarized light into light with a specific polarization state, or allow only light with a specific polarization state to pass through. For example, a Wollaston prism or a Glan-Taylor prism can be used, which can efficiently separate or transmit light with a specific polarization direction.

[0086] An optical waveplate 2 is an optical element used to change the polarization state of light waves. It works by introducing a phase delay between different polarization components. For example, a quarter-wave plate or a half-wave plate can be used, which can convert linearly polarized light into circularly polarized light, or rotate the polarization direction of linearly polarized light by an angle.

[0087] Similar to the first polarizing prism 1, the second polarizing prism 3 is also used to select or analyze the polarization state of the light beam. It is usually placed at the end of the optical path to block or transmit light with a specific polarization state. For example, a Wollaston prism or a Glan-Taylor prism can also be used, whose transmission axis is usually set at a specific angle relative to the transmission axis of the first polarizing prism 1 to block reverse light.

[0088] This isolator operates using the non-reciprocity principle of the Faraday effect. When forward light enters the isolator, it first passes through a first polarizing prism 1, which converts the incident light into linearly polarized light in a specific direction. This linearly polarized light then passes through a Faraday rotator 4, which, under the influence of an external magnetic field, rotates the polarization direction of the linearly polarized light by a fixed angle. Next, the light passes through an optical waveplate 2, which can further adjust the polarization state of the light, for example, converting it into circularly polarized light or rotating its linear polarization direction to match the transmission axis of a second polarizing prism 3. Finally, the light passes through the second polarizing prism 3, whose transmission axis is aligned with the polarization direction of the forward light after adjustment by the Faraday rotator 4 and the optical waveplate 2, thus allowing the forward light to pass smoothly. For reverse light, it propagates in the opposite direction in the optical path. When reverse light passes through the second polarizing prism 3, it will pass through if its polarization state matches the transmission axis of the second polarizing prism 3. Then, the reverse light passes through the optical waveplate 2 in the opposite direction, and its polarization state changes again. The key is that when the reverse light passes through the Faraday rotator 4 in the opposite direction, its polarization direction will rotate again in the same direction due to the non-reciprocity of the Faraday effect. This means that its polarization direction rotates by an angle relative to the propagation direction of the reverse light, resulting in a larger rotation relative to the initial polarization direction. Therefore, when the reverse light reaches the first polarizing prism 1, its polarization direction will be orthogonal to the transmission axis of the first polarizing prism 1, thus being blocked by the first polarizing prism 1 and unable to return to the light source. Through this structural configuration, the first polarizing prism 1, the Faraday rotator 4, the optical waveplate 2, and the second polarizing prism 3 work together to achieve low-loss transmission of forward light and efficient blocking of reverse light, thereby protecting the upstream optical components.

[0089] The following is a concrete example. In one specific implementation, the isolator may include a first polarizing prism 1, such as a Glan-Taylor prism, with its transmission axis set vertically. Following this is a Faraday rotator 4, which is composed of alternating stacks of the aforementioned magneto-optical crystal and heat-dissipating crystal, and rotates the polarization direction of the linearly polarized light by 45 degrees under the influence of an external magnetic field. Next, an optical waveplate 2, such as a tunable waveplate, is provided to fine-tune the polarization state of the beam after passing through the Faraday rotator 4, to compensate for residual birefringence in the system or to achieve more precise polarization matching. Finally, a second polarizing prism 3, such as another Glan-Taylor prism, is provided, with its transmission axis rotated 45 degrees relative to the transmission axis of the first polarizing prism 1. In this configuration, the normally incident vertically polarized light remains vertically polarized after passing through the first polarizing prism 1. After passing through the Faraday rotator 4, its polarization direction is rotated by 45 degrees, becoming 45-degree linearly polarized light. Subsequently, the 45-degree linearly polarized light is fine-tuned by optical waveplate 2 to ensure its polarization state precisely matches the transmission axis of the second polarizing prism 3. Finally, the light passes smoothly through the second polarizing prism 3. For the reverse light, it propagates in the reverse direction in the optical path. When the reverse light passes through the second polarizing prism 3, if its polarization state matches the transmission axis of the second polarizing prism 3, it will pass through. After passing through optical waveplate 2 in the reverse direction, its polarization state is fine-tuned again. Then, when passing through Faraday rotator plate 4 in the reverse direction, due to the non-reciprocity of the Faraday effect, its polarization direction will rotate again by 45 degrees, making its polarization direction orthogonal to the transmission axis of the first polarizing prism 1. Therefore, when the reverse light reaches the first polarizing prism 1, it will be completely blocked.

[0090] Through the above technical solution, the first polarizing prism 1, the Faraday rotator 4, the optical waveplate 2, and the second polarizing prism 3 are sequentially arranged along the optical path to form a complete isolator. This isolator can effectively achieve unidirectional transmission of light, blocking the interference and damage of reverse light to the light source or other optical components. In particular, due to the use of the Faraday rotator 4, which is composed of multiple magneto-optical crystals and multiple heat-dissipating crystals stacked alternately, the isolator can better manage thermal effects while achieving polarization rotation, improving the stability and reliability of the Faraday rotator 4 under high-power applications. Thus, the entire isolator can maintain excellent isolation performance and low insertion loss even under long-term operation or high-power laser transmission environments.

[0091] In summary, the Faraday rotatable plate, its preparation method, and isolator provided in this application no longer rely on reducing the overall power density by increasing the beam diameter. Instead, they achieve localization and rapid dissipation of heat at the microscopic level by using a Faraday rotatable plate composed of multiple magneto-optical crystals and multiple heat dissipation crystals stacked alternately along the optical path. The heat generated by each magneto-optical crystal can be quickly absorbed and conducted by the adjacent heat dissipation crystal, thereby effectively avoiding the accumulation of heat inside the magneto-optical crystal and fundamentally suppressing the occurrence of thermal lensing effect and thermal focal shift.

[0092] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0093] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A Faraday rotator plate, characterized in that, It includes multiple magneto-optical crystals and multiple heat-dissipating crystals, which are stacked alternately along the optical path.

2. The Faraday rotator plate according to claim 1, characterized in that, The magneto-optical crystal and the heat dissipation crystal are bonded together using a bonding process.

3. The Faraday rotator plate according to claim 1, characterized in that, The light-transmitting surface of the Faraday rotator is provided with an anti-reflection film, which is used to compensate for the refractive index deviation between the magneto-optical crystal and the heat dissipation crystal.

4. The Faraday rotator according to claim 1, characterized in that, The thicknesses of both the magneto-optical crystal and the heat dissipation crystal are [10 μm, 200 μm].

5. The Faraday rotator plate according to claim 1, characterized in that, The roughness of both the magneto-optical crystal and the heat dissipation crystal is less than 0.5 nm, and the flatness is better than λ / 10.

6. The Faraday rotator plate according to claim 1, characterized in that, The magneto-optical crystal is one or more of TGG crystal, YIG crystal, TAG crystal, TYAG crystal, and TSAG crystal.

7. The Faraday rotator plate according to claim 1, characterized in that, The heat dissipation crystal is one or more of sapphire, rutile, YAG crystal, GGG crystal, and work-off crystal.

8. A method for preparing a Faraday rotatable plate, used to prepare the Faraday rotatable plate according to any one of claims 1 to 7, characterized in that, The method for preparing the Faraday rotator includes: Multiple magneto-optical crystals and multiple heat dissipation crystals that meet the target thickness, target roughness, and target flatness are prepared by slicing, grinding, and polishing processes. The surfaces of the magneto-optical crystal and the heat dissipation crystal are bombarded with an ion beam or a plasma beam to remove the surface adsorption layer, resulting in a cleaned magneto-optical crystal and a clean heat dissipation crystal. A nanometer-precision vision alignment system is used to alternately stack and pre-bond the cleaned magneto-optical crystal and the heat dissipation crystal to obtain the pre-bonded magneto-optical crystal and the heat dissipation crystal. A pressure of 1 MPa to 5 MPa is applied to the pre-bonded magneto-optical crystal and the heat dissipation crystal, and heat treatment is performed at 200°C to 400°C to obtain the Faraday rotator.

9. The method for preparing the Faraday rotatable plate according to claim 8, characterized in that, After obtaining the Faraday rotator, the method further includes: depositing an antireflection film of the target wavelength on the light-transmitting surface of the Faraday rotator, so that the reflectivity of the Faraday rotator is less than 0.1%.

10. An isolator, characterized in that, It includes a first polarizing prism, an optical waveplate, a second polarizing prism, and a Faraday rotator as described in any one of claims 1 to 7, wherein the first polarizing prism, the Faraday rotator, the optical waveplate, and the second polarizing prism are arranged sequentially along the optical path direction.

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