Intermediate infrared magneto-optical isolator and preparation method thereof

Abstract

The embodiment of the invention provides a mid-infrared magneto-optical isolator and a preparation method thereof, and belongs to the technical field of optical devices, the mid-infrared magneto-optical isolator comprises a polarizer, a Faraday rotator and a polarization analyzer, the Faraday rotator comprises a single-crystal optical fiber and a permanent magnet magnetic ring, the single-crystal optical fiber passes through the permanent magnet magnetic ring in a surrounding manner for many times, and the polarization analyzer is connected with the single-crystal optical fiber; the rotation angle of the deflection direction of light passing through the Faraday rotator is 45 degrees, the polarizer and the polarization analyzer are located at the light input end and the light output end of the Faraday rotator respectively, and the polarization direction of the polarizer and the polarization direction of the polarization analyzer form an included angle of 45 degrees. According to the scheme, the requirements of efficient Faraday rotation, high power tolerance and high energy tolerance can be met in a compact structure.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and in particular to a mid-infrared magneto-optical isolator and a preparation method thereof. Background Art

[0002] The magneto-optical isolator, also known as the Faraday isolator, is an optical device that uses the magneto-optical effect to achieve unidirectional transmission of optical signals. It can effectively prevent the reflected light in the laser system from returning to the light source and avoid the reflected light from damaging the laser source, thereby ensuring the stable operation of the laser system. High-peak power mid-infrared laser pulses are commonly used in laser surgery, laser industrial processing, and nonlinear optics. For example, the 2μm band laser corresponds to the absorption peaks of gas molecules and water molecules and is widely used in gas detection, optical communications, laser surgery, lidar and other fields. In particular, the 2μm band laser can be used as a pump source for the 3-5μm mid-infrared optical parametric oscillator (OPO), and a continuously adjustable mid-infrared band output in a wide range can be achieved through the nonlinear optical effect.

[0003] The Master Oscillator Power Amplifier (MOPA) is a laser system consisting of a master oscillator and a power amplifier, which can make the output laser have higher power. In MOPA, a magneto-optical isolator is generally added before the amplifier stage to prevent the laser returning from the amplifier stage from damaging the previous stage. Currently, 2um lasers are limited by the lack of high-performance Faraday isolators, which restricts the widespread application of MOPA solutions and also restricts the further improvement of 2um laser pulse energy and power.

[0004] In the design of mid-infrared magneto-optical isolators, the selection of magneto-optical crystals is crucial to the performance of the device. Currently, YIG (Bismuth Iron Garnet) crystals have long been widely used in Faraday isolators due to their high Verdet constant, especially in applications in the near-infrared to mid-infrared band (1-5μm). The magneto-optical effect of YIG comes from the transitions of Fe3+ ions, which are much faster than other common crystal materials (such as Tb 3+) makes a greater contribution to the electronic transition of YIG, making the Verdet constant of YIG much higher than other crystal materials. Since YIG crystals are inhomogeneous molten compounds, there are great difficulties in the growth of high-quality, large-sized YIG single crystals, and the size of the grown crystals is still limited, so it is not suitable for use in large-sized magneto-optical isolators. In addition, YIG crystals have certain absorption in the mid-infrared band, which may lead to heat accumulation and optical damage in high-power and high-energy laser applications. Fluoride magneto-optical crystals such as CeF3, NTF, LTF, KTF, etc. have the characteristics of high transmittance, low absorption, high resistance to light damage, and low thermal effect, and are more advantageous in high-power and high-energy laser scenes. However, the Verdet constant of such fluoride magneto-optical crystals will decrease with the increase of wavelength. For example, the magneto-optical coefficient of CeF3 crystal at 2μm is 10rad / T·m, which is much smaller than 200rad / T·m of YIG. If a Faraday isolator is made of fluoride magneto-optical crystals such as CeF3, its volume will be much larger than that of a mid-infrared Faraday isolator made of YIG, which seriously restricts its use in lasers.

[0005] According to the Faraday effect, the angle θ of the polarization direction rotation of light after passing through a magneto-optical crystal placed in a magnetic field is proportional to the product of the crystal length L and the magnetic field strength B (B·L): θ=VLB, where V is the Verdet constant of the crystal, B is the applied magnetic field strength, and L is the length of the crystal. When a magneto-optical crystal is selected (the Verdet constant is determined), if you want to achieve a polarization direction rotation angle of 45°, you must either increase the crystal length or increase the magnet strength. Increasing the crystal length will make the magneto-optical isolator too large in length, and crystals that are too long are not easy to obtain, or even impossible to obtain. The magnetic field strength is related to the size of the magnet. Strong magnetic fields often require larger magnets to generate, which will significantly increase the radius and weight of the magneto-optical isolator. Summary of the invention

[0006] In order to achieve efficient Faraday rotation and withstand high power and high energy requirements in a compact structure, this scheme proposes a mid-infrared magneto-optical isolator and a preparation method thereof. By making the fluoride magneto-optical crystal into a slender single-crystal optical fiber, the single-crystal optical fiber is passed through a permanent magnet ring in a multiple-circular manner to achieve the purpose of rotating the polarization direction of light by 45 degrees. This can effectively solve the problems of large size, poor heat dissipation, and low damage threshold of traditional mid-infrared Faraday isolators.

[0007] According to a first aspect of the present invention, a mid-infrared magneto-optical isolator is provided, comprising: a polarizer, a Faraday rotator and an analyzer, the Faraday rotator comprising a single crystal optical fiber and a permanent magnet magnetic ring, the single crystal optical fiber passes through the permanent magnet magnetic ring multiple times, so that the polarization direction of light passing through the Faraday rotator is rotated by an angle of 45°, the polarizer and the analyzer are respectively located at the light input end and the light output end of the Faraday rotator, and the polarization directions of the polarizer and the analyzer form an angle of 45°.

[0008] Through the above technical solution, the single crystal optical fiber passes through the permanent magnet ring multiple times, which can increase the interaction path between light and magnetic field. Multiple passes can accumulate the polarization rotation angle of light, thereby achieving a larger polarization rotation in a relatively small volume. The overall design is more compact and can be applied to high-power, high-energy mid-infrared lasers.

[0009] Optionally, in the mid-infrared magneto-optical isolator provided by the present invention, the single crystal optical fiber is prepared by stretching a fluoride magneto-optical crystal, and the fluoride magneto-optical crystal adopts a magneto-optical material including but not limited to CeF3, NTF, LTF, and KTF.

[0010] Optionally, in the mid-infrared magneto-optical isolator provided by the present invention, the single crystal optical fiber can be bent multiple times, and light is transmitted in the form of a waveguide inside the single crystal optical fiber.

[0011] Optionally, in the mid-infrared magneto-optical isolator provided by the present invention, each time the single crystal optical fiber wraps around the permanent magnet ring, the polarization direction of the light produces a rotation angle, and multiple wraps make the accumulated rotation angle reach 45°.

[0012] Optionally, in the mid-infrared magneto-optical isolator provided by the present invention, the mid-infrared magneto-optical isolator further includes a compensator, and the compensator is located before the polarizer.

[0013] Optionally, in the mid-infrared magneto-optical isolator provided by the present invention, the incident light of the mid-infrared magneto-optical isolator includes but is not limited to that generated by a 2-5 μm mid-infrared band laser source.

[0014] According to a second aspect of the present invention, a method for preparing a mid-infrared magneto-optical isolator is provided, comprising: drawing a fluoride magneto-optical crystal into a single crystal optical fiber, allowing light to pass through a polarizer and then be transmitted in the form of a waveguide in the single crystal optical fiber; passing the single crystal optical fiber through a permanent magnet magnetic ring multiple times to form a Faraday rotator, so that the polarization direction of the light after passing through the Faraday rotator is rotated by an angle of 45 degrees.

[0015] The mid-infrared magneto-optical isolator and the preparation method thereof provided by the present invention can at least achieve the following beneficial effects: 1. Single crystal optical fiber is prepared by using fluoride magneto-optical crystals with high loss threshold and low absorption. While maintaining its crystalline properties, the single crystal optical fiber is passed through the permanent magnet ring in a multiple-circling manner to achieve the purpose of rotating the polarization direction of light by 45 degrees. It can achieve efficient Faraday rotation and withstand high power and high energy requirements in a compact structure.

[0016] 2. The design of multiple single-crystal optical fibers passing through the magnetic ring and the optimization of the magnetic ring structure reduce the dependence on magnetic field strength and optical fiber length, while ensuring efficient optical isolation through precise polarization control.

[0017] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings: Figure 1 A schematic structural diagram of a mid-infrared magneto-optical isolator according to an embodiment of the present invention is shown; Figure 2 A schematic diagram showing a single crystal optical fiber surrounding a permanent magnet ring according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0019] In order to address the volume and performance bottlenecks of traditional magneto-optical isolator designs, the embodiments of the present disclosure propose a mid-infrared magneto-optical isolator, which prepares the magneto-optical crystal into a single crystal optical fiber, and then rotates the polarization direction of the light by 45 degrees by passing through a magnetic field multiple times, taking into account the application requirements of high power, high isolation and compact structure. The exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0020] Figure 1 FIG. 2 shows a schematic diagram of the structure of a mid-infrared magneto-optical isolator according to an embodiment of the present invention. Figure 1 As shown, the mid-infrared magneto-optical isolator includes: a polarizer, a Faraday rotator and an analyzer. The Faraday rotator includes a single crystal optical fiber and a permanent magnet ring. The single crystal optical fiber passes through the permanent magnet ring for multiple times, so that the deflection direction of light passing through the Faraday rotator rotates by an angle of 45°. The polarizer and the analyzer are respectively located at the light input end and the light output end of the Faraday rotator, and the polarization directions of the polarizer and the analyzer form an angle of 45°.

[0021] Among them, the polarizer is used to convert the incident natural light into linearly polarized light, and adjust the polarization direction of the light to a specific initial direction so that the subsequent optical process can operate according to this direction. The analyzer cooperates with the polarizer and forms a 45-degree angle with the polarization axis of the polarizer, allowing the rotated polarized light to pass through. When the light propagates in the forward direction, it can pass through the isolator smoothly after passing through the polarizer, Faraday rotator and analyzer; while the light propagating in the reverse direction cannot pass through the analyzer due to the rotation of the polarization plane, and is thus blocked, realizing unidirectional isolation of light. The polarizer and analyzer can use polarizers or Glan prisms. In the mid-infrared band, polarizers made of special materials such as quartz and lithium niobate can be used to avoid light loss.

[0022] Single crystal optical fiber is one of the core components of the entire Faraday isolator, which is used to achieve polarization rotation of light through the Faraday effect. Since fluoride magneto-optical crystals have low absorption losses and good light transmittance, they can ensure stable transmission of optical signals under high power conditions and reduce the loss of light energy. At the same time, the low thermal effect of fluoride materials helps to improve the power handling capacity of the system and can effectively prevent material damage. However, since the Verdet constant of these materials is relatively low, in order to achieve sufficient Faraday rotation, the rotation effect needs to be enhanced through appropriate fiber length, magnetic field strength and bending design.

[0023] According to one embodiment of the present invention, the single crystal optical fiber is prepared by stretching a magneto-optical crystal, and the fluoride magneto-optical crystal uses magneto-optical materials including but not limited to CeF3 (cerium-doped fluoride), NTF (sodium yttrium fluoride doped with ytterbium), LTF (lithium lanthanum fluoride doped with ytterbium), and KTF (potassium-doped fluoride). By making the fluoride magneto-optical crystal into a slender single crystal optical fiber form, the damage threshold can be increased and the volume of the material can be reduced. At the same time, since the optical fiber has a higher specific surface area, it is helpful for heat dissipation and can work stably at a higher power, and is suitable for mid-infrared band laser systems including but not limited to 2-5μm.

[0024] In order to further improve the utilization rate of the magnetic field and achieve a compact structure, this scheme uses a permanent magnet with a ring structure, and the direction of the magnetic field is always along the axial direction, ensuring that the magneto-optical crystal is subjected to a consistent magnetic field during each crossing process. In order to enhance the strength and stability of the magnetic field, materials with high magnetization strength (such as neodymium iron boron NdFeB) are selected as magnet materials. Highly magnetic materials can generate a strong magnetic field in a smaller volume, thereby effectively reducing the limitation of the magnet size.

[0025] According to one embodiment of the present disclosure, the permanent magnet ring is a whole magnetic ring or a combination of multiple magnetic rings, and the magnetic field strength direction of the permanent magnet ring is the axial direction of the magnetic ring. When multiple magnetic rings are used, it is necessary to ensure that the polarization direction of light in the magneto-optical crystal remains unchanged when it is deflected counterclockwise or clockwise. In addition, the relative position between the magnet and the single crystal optical fiber or other optical components does not shift, so as to avoid changes in the magnetic field direction caused by mechanical vibration or thermal expansion.

[0026] Single crystal optical fiber can be bent, and light is transmitted as a waveguide inside the single crystal optical fiber. Each time the single crystal optical fiber wraps around the permanent magnet ring, the polarization direction of the light rotates by an angle, and multiple wraps make the cumulative rotation angle reach 45°.

[0027] Figure 2 FIG. 2 shows a schematic diagram of a single crystal optical fiber surrounding a permanent magnet ring according to an embodiment of the present invention. Figure 2 As shown in the figure, the single crystal fiber passes through the magnetic ring many times, and the rotation angle is increased by continuously increasing the interaction with the magnetic field. The single crystal fiber passes through the permanent magnet ring in a curved manner. Each series will cause the polarization of the light to rotate to a certain extent. By passing through the magnetic field many times, the rotation angle accumulates until it reaches the required 45 degrees.

[0028] It should be noted that the strength of the magnetic field, the length of the optical fiber, and the configuration of the magnetic field can all be adjusted to optimize the polarization rotation effect and maximize the properties of the fluoride magneto-optical crystal.

[0029] return Figure 1 As shown, the mid-infrared magneto-optical isolator also includes a compensator, which is located in the front stage of the polarizer and is used to compensate for the phase difference or polarization effect introduced in the laser system due to thermal effects, polarization loss or birefringence, so that the polarization direction of the light remains consistent.

[0030] According to one embodiment of the present invention, a method for preparing a mid-infrared magneto-optical isolator is provided, comprising: drawing a fluoride magneto-optical crystal into a single crystal optical fiber, and transmitting light in the form of a waveguide in the single crystal optical fiber after passing through a polarizer.

[0031] Fluoride magneto-optical crystals are selected as magneto-optical materials, such as cerium fluoride (CeF3) and calcium fluoride (CaF2). They have good light transmittance and low absorption loss in the mid-infrared band. Although the Verdet constant of fluoride magneto-optical crystals is low, this problem can be compensated by increasing the optical path by making them into optical fiber structures. These magneto-optical crystals are converted into single-crystal optical fibers through drawing technology. The fiber shape of the optical fiber helps guide light and stabilize the structure, while also improving the efficiency of the magneto-optical effect. Single-crystal optical fiber not only has high light transmission efficiency, but also avoids light loss and scattering.

[0032] Then, the single crystal optical fiber is passed through the permanent magnet ring multiple times to form a Faraday rotator, so that the polarization direction of the light after passing through the Faraday rotator is rotated by 45 degrees.

[0033] Among them, the ring structure of the permanent magnet can effectively provide a stable and uniform magnetic field, ensuring that the direction of the magnetic field is consistent along the axial direction when the light passes through, and is not easily affected by external disturbances. The single crystal optical fiber travels through the magnetic ring many times, that is, the optical fiber turns back or detours many times in a magnetic field area, which can increase the time or path for the interaction between the light and the magnetic field, thereby accumulating sufficient polarization rotation angles. Each time the light passes through the magnetic field, the polarization of the light will rotate to a certain extent. Multiple crossings will accumulate the polarization rotation angles of the light, and ultimately achieve a 45-degree polarization rotation.

[0034] Through the optimization of single crystal fiber design and magnetic ring structure, a larger polarization rotation angle can be achieved in a shorter space, thus effectively solving the problem of low Verdet constant of fluoride magneto-optical crystals.

[0035] The mid-infrared magneto-optical isolator and the preparation method thereof provided by the present invention can at least achieve the following beneficial effects: 1. By using fluoride magneto-optical crystals with high loss threshold and low absorption to prepare single crystal optical fibers, while maintaining the properties of the crystal, the single crystal optical fiber is allowed to pass through the permanent magnet ring in a multiple-circling manner to achieve the purpose of rotating the polarization direction of light by 45 degrees, which can achieve efficient Faraday rotation and withstand high power and high energy requirements in a compact structure; 2. The design of multiple single-crystal optical fibers passing through the magnetic ring and the optimization of the magnetic ring structure reduce the dependence on magnetic field strength and optical fiber length, while ensuring efficient optical isolation through precise polarization control.

[0036] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0037] Those skilled in the art will appreciate that the modules or units or components of the devices in the examples disclosed herein may be arranged in the devices described in the embodiment, or alternatively may be located in one or more devices different from the devices in the examples. The modules in the foregoing examples may be combined into one module or may be divided into multiple submodules.

[0038] Those skilled in the art will appreciate that the modules in the devices in the embodiments may be adaptively changed and arranged in one or more devices different from the embodiments. The modules or units or components in the embodiments may be combined into one module or unit or component, and furthermore may be divided into a plurality of submodules or subunits or subcomponents.

[0039] Furthermore, those skilled in the art will appreciate that although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features from different embodiments is meant to be within the scope of the present invention and to form different embodiments.

[0040] As used herein, unless otherwise specified, the use of ordinal numbers "first," "second," "third," etc. to describe common objects merely indicates that different instances of similar objects are involved, and is not intended to imply that the objects so described must have a given order in time, space, order, or in any other manner.

[0041] Although the present invention has been described according to a limited number of embodiments, it will be apparent to those skilled in the art, with the benefit of the above description, that other embodiments may be envisioned within the scope of the invention thus described. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching purposes, rather than for explaining or defining the subject matter of the present invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is illustrative and not restrictive with respect to the scope of the present invention, and the scope of the present invention is defined by the appended claims.

Claims

1. A mid-infrared magneto-optical isolator, comprising: A polarizer, a Faraday rotator and an analyzer, characterized in that the Faraday rotator comprises a single crystal optical fiber and a permanent magnet ring, the single crystal optical fiber passes through the permanent magnet ring multiple times, so that the deflection direction of light passing through the Faraday rotator rotates by an angle of 45°, the polarizer and the analyzer are respectively located at the light input end and the light output end of the Faraday rotator, and the polarization directions of the polarizer and the analyzer form an angle of 45°.

2. The mid-infrared magneto-optical isolator according to claim 1, characterized in that: The single crystal optical fiber is prepared by stretching a fluoride magneto-optical crystal, and the fluoride magneto-optical crystal adopts magneto-optical materials including but not limited to CeF3, NTF, LTF, and KTF.

3. The mid-infrared magneto-optical isolator according to claim 1, characterized in that: The single crystal optical fiber can be bent multiple times, and light is transmitted in the single crystal optical fiber in the form of a waveguide.

4. The mid-infrared magneto-optical isolator according to claim 1, characterized in that: Each time the single crystal optical fiber is wrapped around the permanent magnet ring, the polarization direction of the light is rotated by an angle, and multiple wrappings make the accumulated rotation angle reach 45°.

5. The mid-infrared magneto-optical isolator according to claim 1, characterized in that: The permanent magnet ring is a whole magnet ring or a combination of multiple magnet rings, and the magnetic field intensity direction of the permanent magnet ring is the axial direction of the magnet ring.

6. The mid-infrared magneto-optical isolator according to claim 1, characterized in that: The mid-infrared magneto-optical isolator further includes a compensator, which is located in the front stage of the polarizer.

7. The mid-infrared magneto-optical isolator according to any one of claims 1 to 6, characterized in that: The incident light of the mid-infrared magneto-optical isolator includes but is not limited to that generated by a 2μm-5μm mid-infrared band laser source.

8. A method for preparing a mid-infrared magneto-optical isolator, characterized in that: include: Drawing the fluoride magneto-optical crystal into a single crystal optical fiber, so that light passes through a polarizer and is transmitted in the single crystal optical fiber as a waveguide; The single crystal optical fiber is passed through a permanent magnet ring for multiple times to form a Faraday rotator, so that the polarization direction of light after passing through the Faraday rotator rotates by an angle of 45 degrees.

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