Magneto-optical isolator with low thermal lens effect

Abstract

The invention relates to a magneto-optical isolator with a low thermal lens effect, in particular to the technical field of optical instruments. The device comprises an optical fiber collimator, a first polarized light beam splitter, a neodymium iron boron permanent magnet, an optical rotation crystal, a wave plate, a second polarized light beam splitter, a concave lens and a convex lens which are sequentially arranged along a light forward transmission path, wherein the optical rotation crystal is a CS: CaFoptical rotation crystal.

Description

Technical Field

[0001] This invention relates to the field of optical instrument technology, and in particular to a low-heat lens effect magneto-optical isolator. Background Technology

[0002] In high-power laser optical systems, in order to prevent the returning light from returning into the system and affecting the stable operation of the system or even damaging the internal components of the optical system, fiber optic isolators are usually added to allow light to pass through in only one direction.

[0003] A typical fiber optic isolator is connected after the output stage of a laser. Its main purpose is to prevent reflected light from returning to the laser. It is equipped with a beam rotator and a beam polarization splitter. When strong reflected light returns, the beam rotator and the beam polarization splitter work together to prevent the light from returning to the laser along the same path. The fiber optic isolator can effectively isolate reflected light and prevent it from returning to the laser.

[0004] Based on the principle of fiber optic isolators, in order to ensure unidirectional light transmission during laser transmission, fiber optic isolators also need to be added to the optical transmission system. One end of the fiber optic isolator is connected to a pigtail, and the other end can be connected to a collimator for output, or the other end is also connected to a pigtail. Through the pigtail, it is easy and quick to splice with other devices, which makes fiber optic isolators increasingly widely used.

[0005] Meanwhile, with the development of technology, the output power of fiber lasers is getting higher and higher. In fiber lasers in the 1.0µm band, the optical rotator crystal used in the isolator is TGG. The weak absorption value of TGG crystal in this band is usually greater than 2000ppm / cm. Therefore, as the power is getting higher and higher, the crystal will absorb a large amount of light energy, which will lead to an increase in device temperature, which will lead to an increase in device refractive index, and then the light will be deflected.

[0006] The temperature distribution gradually decreases from the center to the outside, causing the refractive index of the device to also exhibit a Gaussian distribution from the center to the outside. This phenomenon of temperature causing changes in the refractive index is called the thermal lensing effect. In high-power optical systems, the thermal lensing effect will inevitably affect the performance of the isolator, impacting the insertion loss of high-power in-line isolators and the beam quality of collimated output isolators, among other things.

[0007] To mitigate the thermal lensing effect and improve the power load capacity of the isolator, the conventional approach is to increase the output beam diameter of the collimator, thereby reducing the power density of the device. However, a larger beam diameter means that the aperture of all optical components must be increased, which in turn leads to a significant increase in the cost of optical components. Furthermore, the magnets used with the TGG magneto-optical crystal also need to be redesigned, resulting in an overall increase in the size of the isolator and higher costs. Summary of the Invention

[0008] (1) Technical solution To address the aforementioned technical problems, this invention provides a low-heat lens effect magneto-optical isolator, comprising an optical fiber collimator, a first polarizing beam splitter, a neodymium iron boron permanent magnet, an optical rotator crystal, a waveplate, a second polarizing beam splitter, a concave lens, and a convex lens arranged sequentially along the forward optical transmission path, wherein the optical rotator crystal is a CS:CaF2 optical rotator crystal.

[0009] Preferably, the optically active crystal uses CaF2 with a Ce³⁺ ion doping concentration of 0.5-5 mol% as the magneto-optical crystal.

[0010] Preferably, the absorption coefficient of the optically active crystal is 50±30ppm / cm.

[0011] Preferably, the forward optical path transmission process of the low-thermal lens effect magneto-optical isolator is as follows: the optical signal is output from the fiber collimator, the laser is incident on the first polarization beam splitter, and the first polarization beam splitter splits the freely polarized optical signal into beams.

[0012] Preferably, a P-beam and an S-beam with mutually perpendicular polarization states are then output, with the P-beam propagating along the first beam splitting path and the S-beam propagating along the second beam splitting path.

[0013] Preferably, the P-beam and the S-beam pass sequentially through the optical rotator crystal and the waveplate along their respective optical paths, and the waveplate and the optical rotator crystal will rotate and adjust the polarization direction of the beams.

[0014] Preferably, the first and second split beams, after optical rotation adjustment, are incident on the second polarized beam splitter, which combines the P-splitter and the S-splitter.

[0015] Preferably, the laser beam, after being combined, passes through the concave lens and the convex lens to expand the beam and output it outward.

[0016] (2) Beneficial effects This invention provides a low-thermal lens effect magneto-optical isolator. Compared with the traditional use of TGG crystal as optical rotation element, the CS:CaF2 magneto-optical crystal used has very small weak absorption. When the laser power output reaches hundreds or even thousands of watts, the focus of its output beam will not change much, thus greatly improving the beam quality of the laser. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the forward transmission optical path and structure of the low-thermal lens effect magneto-optical isolator of the present invention; Figure 2 This is a schematic diagram of the structure of an optically active crystal in the prior art; Figure 3 This is a schematic diagram of the optically rotating crystal structure of the low-heat lens effect magneto-optical isolator of the present invention.

[0018] The attached figures are labeled as follows: 1-fiber collimator, 2-first polarizing beam splitter, 3-neodymium iron boron permanent magnet, 4-optical rotator crystal, 5-wave plate, 6-second polarizing beam splitter, 7-concave lens, 8-convex lens. Detailed Implementation

[0019] The present invention will be further described in conjunction with the accompanying drawings and embodiments.

[0020] like Figure 1 As shown, the low-heat lens effect magneto-optical isolator of the present invention includes an optical fiber collimator 1, a first polarizing beam splitter 2, a neodymium iron boron permanent magnet 3, an optical rotator crystal 4, a waveplate 5, a second polarizing beam splitter 6, a concave lens 7, and a convex lens 8 arranged sequentially along the forward optical transmission path. The optical rotator crystal 4 is a CS:CaF2 optical rotator crystal.

[0021] Furthermore, such as Figure 3 As shown, the optical rotator crystal 4 uses CaF2 with a Ce³⁺ ion doping concentration of 0.5-5 mol% as a magneto-optical crystal. The absorption coefficient of the optical rotator crystal 4 is 50±30 ppm / cm, and its weak absorption is very small, only 1 / 40 of that of the TGG crystal. Therefore, the energy absorbed when the light signal passes through the optical rotator crystal is very small, which will not cause the temperature to rise. Its refractive index remains basically unchanged, so the beam will not be deflected by the focusing device and will not produce a thermal lensing effect.

[0022] like Figure 2 As shown, terbium gallium garnet crystals are traditionally used as optical rotators. They have a large weak absorption value, so when the light signal passes through the optical rotator, some of its energy will be absorbed, which will lead to an increase in temperature and a larger refractive index. Therefore, it can be equivalent to the light signal passing through a convex lens, causing the light beam to be deflected and focused.

[0023] Furthermore, the forward optical path transmission process of the low-thermal lens effect magneto-optical isolator is as follows: the optical signal is output from the fiber collimator 1, and the laser is incident on the first polarization beam splitter 2. The first polarization beam splitter 2 splits the freely polarized optical signal into beams; then, P-beams and S-beams with mutually perpendicular polarization states are output. The P-beam propagates along the first beam splitting path, and the S-beam propagates along the second beam splitting path; the P-beams and S-beams pass sequentially through the optical rotator crystal 4 and the waveplate 5 along their respective optical paths. The waveplate 5 and the optical rotator crystal 4 will rotate and adjust the polarization direction of the split beams; the first and second split beams after optical rotation adjustment are incident on the second polarization beam splitter 6, and the second polarization beam splitter 6 combines the P-beams and S-beams; finally, the combined laser passes through the concave lens 7 and the convex lens 8 to expand the beam and output it outward.

[0024] The embodiments described above are merely preferred embodiments of the present invention, and are described in a relatively specific and detailed manner. However, the present invention is not limited to these embodiments. It should be noted that for those skilled in the art, any modifications made without departing from the spirit of the present invention fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A low-thermal lens effect magneto-optical isolator, characterized in that, The optical fiber collimator (1), the first polarizing beam splitter (2), the neodymium iron boron permanent magnet (3), the optical rotator (4), the waveplate (5), the second polarizing beam splitter (6), the concave lens (7), and the convex lens (8) are arranged sequentially along the forward optical transmission path. The optical rotator (4) is a CS:CaF2 optical rotator.

2. The low-thermal lens effect magneto-optical isolator according to claim 1, characterized in that, The optically active crystal (4) uses CaF2 with a Ce³⁺ ion doping concentration of 0.5-5 mol% as a magneto-optical crystal.

3. A low-thermal lens effect magneto-optical isolator according to claim 2, characterized in that, The absorption coefficient of the optically active crystal (4) is 50±30ppm / cm.

4. A low-thermal lens effect magneto-optical isolator according to claim 1 or 2, characterized in that, The forward optical path transmission process of the low-thermal lens effect magneto-optical isolator is as follows: the optical signal is output from the optical fiber collimator (1), the laser is incident on the first polarization beam splitter (2), and the first polarization beam splitter (2) splits the free polarization state optical signal into beams for output.

5. A low-thermal lens effect magneto-optical isolator according to claim 4, characterized in that, Subsequently, P-beams and S-beams with mutually perpendicular polarization states are output. The P-beam propagates along the first beam splitting path, and the S-beam propagates along the second beam splitting path.

6. A low-thermal lens effect magneto-optical isolator according to claim 5, characterized in that, The P-beam and S-beam pass sequentially through the optical rotator crystal (4) and the waveplate (5) along their respective optical paths. The waveplate (5) and the optical rotator crystal (4) will rotate and adjust the polarization direction of the beams.

7. A low-thermal lens effect magneto-optical isolator according to claim 5, characterized in that, The first and second beams, after optical rotation adjustment, are incident on the second polarized beam splitter (6), which combines the P beam and the S beam.

8. A low-thermal lens effect magneto-optical isolator according to claim 6, characterized in that, Finally, the combined laser beam passes through the concave lens (7) and the convex lens (8) to expand the beam and output it outward.

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