A double-stage isolator and optical communication device

Abstract

The utility model relates to the field of optical fiber communication technology, in particular to a double-stage isolator and an optical communication device. The double-stage isolator includes: a first birefringent crystal plate, one side of which is used as a light input / output side, and an incident port and an output port are respectively arranged along the two ends of the light input / output side perpendicular to the light transmission direction; a half-wave plate assembly, including a first half-wave plate and a second half-wave plate arranged in succession perpendicular to the light transmission direction; a Faraday rotator, when the light passes through the first half-wave plate and the Faraday rotator in sequence, the polarization angle will be deflected by 90°, and when the light passes through the Faraday rotator and the second half-wave plate in sequence, the polarization angle will be deflected by 90°; a second birefringent crystal plate, which has the same birefringence characteristics as the first birefringent crystal plate; a reflector. The utility model has a stable isolation effect, a low setting cost, and the light output end and the incident end are located on the same side, which meets the personalized needs of users.

Description

Technical Field

[0001] The utility model relates to the technical field of optical fiber communication, in particular to a double-stage isolator and an optical communication device. Background Art

[0002] A double-stage isolator is an optical device used to isolate input and output light in an optical system to prevent light reflection and interference. Double-stage isolators are usually composed of multiple isolation cascades, each with a specific function to ensure unidirectional transmission of light and optimization of system performance.

[0003] The common double-stage isolator currently is realized by two single-stage isolator cores. The isolation of the reflective double-stage isolator is adjusted by controlling the relative angle of the two single-stage isolator cores. The closer the relative angle is to 45 degrees, the better the isolation effect. This requires high accuracy of adjustment, and requires precise adjustment devices and accurate measurement methods to ensure the accuracy of angle adjustment, and the adjustment cost is high. And once adjusted to the ideal position, the relative angle of the two isolator cores needs to be kept stable. Any vibration, temperature change or mechanical stress may cause changes in the angle, thereby affecting the performance of the isolator. Utility Model Content

[0004] The technical problem to be solved by the embodiments of the utility model is to provide a double-stage isolator and an optical communication device to solve the problems of unstable isolation performance of the isolator and high cost of adjusting the isolator in the prior art.

[0005] The utility model discloses a double-stage isolator, comprising:

[0006] A first birefringent crystal plate, one side of which is used as a light input / output side, and an incident port and an output port are respectively provided along two ends of the light input / output side perpendicular to the light transmission direction;

[0007] A half wave plate assembly is located on a side of the first birefringent crystal plate far from the light input / light output side, and includes a first half wave plate and a second half wave plate which are arranged in series perpendicular to the light transmission direction;

[0008] A Faraday rotator is located on a side of the half wave plate assembly away from the first birefringent crystal plate, and when linear polarized light passes through the first half wave plate and the Faraday rotator in sequence, the polarization angle will be deflected by 90°; when linear polarized light passes through the Faraday rotator and the second half wave plate in sequence, the polarization angle will be deflected by 90°;

[0009] a second birefringent crystal plate, located at a side of the Faraday rotator away from the half wave plate group, and having the same birefringence characteristics as the first birefringent crystal plate;

[0010] A reflecting mirror is located on a side of the second birefringent crystal plate away from the Faraday rotator.

[0011] Optionally, a polarization angle change value of the first half wave plate for linear polarized light passing in a forward direction is the same as a polarization angle change value of the second half wave plate for linear polarized light passing in a reverse direction.

[0012] Optionally, the absolute values ​​of the optical axis angle of the first half-wave plate and the optical axis angle of the second half-wave plate are equal.

[0013] Optionally, the optical axis angle of the first half wave plate is -22.5°, and the optical axis angle of the second half wave plate is 22.5°.

[0014] Optionally, the Faraday rotator is capable of rotating the polarization state of linearly polarized light passing through in the forward or reverse direction by 45°.

[0015] Optionally, the first birefringent crystal plate and the second birefringent crystal plate have equal widths along the light transmission direction.

[0016] Optionally, the first half wave plate and the second half wave plate have equal widths along the light transmission direction and equal lengths perpendicular to the light transmission direction.

[0017] Optionally, the light incident from the incident port and the light emitted from the emission port are both circularly polarized lights.

[0018] Optionally, the first birefringent crystal plate and the second birefringent crystal plate are made of yttrium yttrium vanadate.

[0019] The utility model also discloses an optical communication device, comprising an incident optical fiber, an output optical fiber and the double-stage isolator as described above;

[0020] The incident optical fiber and the exit optical fiber are respectively arranged vertically at the incident port and the exit port of the double-click isolator.

[0021] Compared with the prior art, the beneficial effects of 2222 provided by the embodiment of the utility model are:

[0022] By matching the optical axis angles of the first half wave plate and the second half wave plate with the Faraday rotator, when the light passes through the first half wave plate and the Faraday rotator in sequence, and when the light passes through the Faraday rotator and the second half wave plate in sequence, the polarization angle will be deflected by 90°. Since the half wave plate has different deflection values ​​for the polarization angles of light incident from different directions, the polarization angle deflection by 90° cannot be achieved when the light transmission direction is reverse. Therefore, the light input in the forward direction can be combined into circularly polarized light again after being divided into e-light and o-light and then emitted from the output port, while the light input in the reverse direction cannot be combined into circularly polarized light and cannot be emitted from the input port, thereby realizing the isolation function of unidirectional light passage. By reasonably setting the optical elements, it does not rely on two single-stage isolators, the structure is stable, the isolation effect is stable, and no complex and fine adjustment is required, and the setting cost is low. By setting a reflector, the output end and the incident end of the light can be located on the same side to meet the personalized needs of users. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The scheme of the utility model will be further described in detail below with reference to the accompanying drawings and embodiments, in which:

[0024] Figure 1 It is a structural schematic diagram of an embodiment of a double-stage isolator provided by the utility model;

[0025] Figure 2 This is a schematic diagram of the principle of forward light transmission provided by the utility model;

[0026] Figure 3 It is a schematic diagram of the principle of reverse light transmission provided by the utility model.

[0027] The reference numerals in the figures are:

[0028] 1. Double-stage isolator; 11. First birefringent crystal plate; 111. Incident port; 112. Exit port; 12. Half-wave plate assembly; 121. First half-wave plate; 122. Second half-wave plate 13. Faraday rotator; 14. Second birefringent crystal plate; 15. Reflector. DETAILED DESCRIPTION

[0029] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. Now, in conjunction with the accompanying drawings, a preferred embodiment of the present utility model is described in detail.

[0030] See also Figure 1 , Figure 11 is a schematic diagram of the structure of an embodiment of a double-stage isolator provided by the utility model. The double-stage isolator 10 includes a first birefringent crystal plate 11, a half-wave plate assembly 12, a Faraday rotator 13, a second birefringent crystal plate 14 and a reflector 15 arranged along the light transmission direction. Among them, the half-wave plate assembly 12 includes a first half-wave plate 121 and a second half-wave plate 122 arranged in series perpendicular to the light transmission direction.

[0031] The first birefringent crystal plate 11 is made of birefringent crystal material and has special optical properties, which can separate the incident light into o light and e light. Birefringence means that when light passes through a crystal, it will be divided into two beams of light, namely o light (ordinary ray) and e light (extraordinary ray), and their propagation speeds and refractive indices are different. This phenomenon is caused by the non-central symmetry of the crystal. When light passes through the crystal, photons with different polarization directions will be affected to different degrees, resulting in the separation of light. In this implementation scenario, the first birefringent crystal plate 11 is made of YVO4 crystal material. The reason why the incident light can be divided into o light and e light is that the structure of the YVO4 crystal has a special optical symmetry, which causes birefringence to occur during the propagation of photons inside the crystal. YVO4 has the characteristics of a wide light transmission range, high transmittance, large birefringence coefficient, and easy processing. In other implementation scenarios, the material of the first birefringent crystal plate 11 can also be rutile (CaCO3), calcite (TiO3), etc.

[0032] One side of the first birefringent crystal plate 11 serves as the light input / output side, and an incident port 111 and an output port 112 are respectively arranged on the light input / output side, and the incident port 111 and the output port 112 are arranged perpendicular to the light transmission direction. In this implementation scenario, the light enters the first birefringent crystal plate 11 perpendicularly to the light input / output side, the incident port 111 is arranged at the upper half of the light input / output side, and is used to receive the incident light, and the output port 112 is arranged at the lower half of the light input / output side, and is used to output the emitted light. It should be noted that the light may also be emitted from the incident port 111 or from the output port 112, but the light cannot be emitted from the rest of the positions of the light input / output side.

[0033] The first half wave plate 121 and the second half wave plate 122 are arranged vertically, wherein the first half wave plate 121 is arranged in the upper part of the half wave plate assembly 12 and is located on the same side as the incident port, and is used to change the polarization angle of the incident light, and the second half wave plate 122 is arranged in the lower part of the half wave plate assembly 12 and is located on the same side as the exit port to change the polarization angle of the light to be emitted. A half wave plate is an optical element, which is usually used to change the polarization state of light. It can convert linear polarized light into rotated polarized light, or convert rotated polarized light into linear polarized light. The name of the half wave plate comes from its ability to extend the wavelength of light by half, so it is called a "half" wave plate.

[0034] The Faraday rotator 13 is also used to change the polarization angle of light. The Faraday rotator 13 is a device that uses the Faraday effect to rotate the polarization direction of light. The Faraday effect refers to the rotation phenomenon that occurs when polarized light propagating in a medium is affected by a magnetic field. In the Faraday rotator 13, when light passes through a medium (usually a material with a Faraday effect), the application of a magnetic field causes the polarization direction of the light to rotate. This rotation is due to the influence of the magnetic field on the charge in the medium, thereby changing the way the light propagates in the medium. By adjusting the intensity of the magnetic field applied to the Faraday rotator 13, the angle of the polarization direction of the light can be controlled.

[0035] In this implementation scenario, when the linear polarized light sequentially passes through the first half wave plate 121 and the Faraday rotator 13, the polarization angle will be deflected by 90°, that is, if the linear polarized light is e-light, it will become o-light, and if the linear polarized light is o-light, it will become e-light. When the linear polarized light sequentially passes through the Faraday rotator 13 and the second half wave plate 122, the polarization angle will be deflected by 90°, that is, if the linear polarized light is e-light, it will become o-light, and if the linear polarized light is o-light, it will become e-light.

[0036] The second birefringent crystal plate 14 has the same birefringent property as the first birefringent crystal plate 11, for example, the refraction angles of the linearly polarized light in the second birefringent crystal plate 14 and the first birefringent crystal plate 11 are consistent, and the transmission path lengths are consistent. In order to achieve the same birefringent property of the second birefringent crystal plate 14 and the first birefringent crystal plate 11, the second birefringent crystal plate 14 and the first birefringent crystal plate 11 are made of the same material (for example, both are YVO4), and have the same width along the light transmission direction and the same length perpendicular to the light transmission direction.

[0037] The reflector 15 is located on a side of the second birefringent crystal plate 14 away from the Faraday rotator 13 , and is used to reflect the light emitted from the second birefringent crystal plate 14 .

[0038] In one implementation scenario, since the effect of the Faraday rotator 13 on changing the polarization angle of linearly polarized light is independent of the incident direction of the light, that is, whether the linearly polarized light is incident from the side of the Faraday rotator 13 close to the half wave plate assembly 12 or from the side of the Faraday rotator 13 close to the second birefringent crystal plate 14, the change value of its polarization angle is the same. Therefore, in order to make the polarized light deflect by 90° when passing through the first half wave plate 121 and the Faraday rotator 13 in sequence, and when passing through the Faraday rotator 13 and the second half wave plate 122 in sequence, the polarization angle change value of the first half wave plate 121 for the linear polarized light passing forward is the same as the polarization angle change value of the second half wave plate 122 for the linear polarized light passing backward. For example, when the Faraday rotator 13 changes the polarization angle of linear polarized light by 60°, the polarization angle change value of the first half wave plate 121 for the linear polarized light passing forward and the polarization angle change value of the second half wave plate 122 for the linear polarized light passing backward are both 30°. For another example, when the Faraday rotator 13 changes the polarization angle of linear polarized light by 45°, the polarization angle change value of the first half wave plate 121 for the linear polarized light passing forward and the polarization angle change value of the second half wave plate 122 for the linear polarized light passing backward are both 45°.

[0039] Furthermore, the absolute value of the optical axis angle of the first half wave plate 121 and the optical axis angle of the second half wave plate 122 are equal. When linearly polarized light passes through a half wave plate, a rotation angle is generated, and this angle is related to the incident direction. For example, when the light is incident on a half wave plate with an optical axis of -22.5° in the forward direction, its polarization angle changes by 45°, and when the light is incident on a half wave plate with an optical axis of -22.5° in the reverse direction, its polarization angle changes by -45°. Therefore, in order to make the polarization angle change consistent after the light is incident on the first half wave plate 121 in the forward direction and on the second half wave plate 122 in the reverse direction, the absolute value of the optical axis angle of the first half wave plate 121 and the optical axis angle of the second half wave plate 122 are equal.

[0040] In one implementation scenario, the optical axis angle of the first half wave plate 121 is -22.5°, and the optical axis angle of the second half wave plate 122 is 22.5°. Then, the polarization angle of the light changes by 45° clockwise after passing through the first half wave plate 121 in the forward direction, and changes by 45° clockwise after passing through the second half wave plate 122 in the reverse direction, so that the polarization angle of the light passing through in the forward or reverse direction is changed by 45° clockwise, so that when the light passes through the first half wave plate 121 and the Faraday rotator 13 in sequence, the polarization angle will be deflected by 90° clockwise, and when the light passes through the Faraday rotator 13 and the second half wave plate 122 in sequence, the polarization angle will be deflected by 90° clockwise.

[0041] Furthermore, in order to ensure that the polarization angle changes of the light after passing through the first half wave plate 121 in the forward direction and the second half wave plate 122 in the reverse direction are the same, the first half wave plate 121 and the second half wave plate 122 have equal widths along the light transmission direction and equal lengths perpendicular to the light transmission direction.

[0042] Please refer to Figure 2 and Figure 3 , Figure 2 This is a schematic diagram of the principle of forward light transmission provided by the utility model. Figure 3 This is a schematic diagram of the principle of reverse light transmission provided by the utility model. Figure 2 As shown in FIG. 1 , circularly polarized light is incident on the first birefringent crystal plate 11 through the incident optical fiber from the incident port 111 and is split into o light and e light and then emitted. Figure 2 As shown in the figure, the dotted line represents the o light, and the solid line represents the e light. It can be seen that since the birefringent crystal has different refraction effects on different light rays, the transmission paths of the o light and the e light in the first birefringent crystal plate 11 are inconsistent, and the transmission deflection angles are also inconsistent. The o light and the e light are two parallel light beams when they are emitted from the first birefringent crystal plate 11.

[0043] The o-light and e-light respectively pass through the first half-wave plate 121 and the Faraday rotator 133 in sequence, and the polarization angle will be deflected by 90°, so the o-light will become e-light, and the e-light will become o-light. Specifically, when the o-light and the e-light are positively incident on the first half-wave plate 121 with an optical axis of -22.5°, the polarization angle will rotate 45 degrees clockwise, and after the deflected light passes through the Faraday rotator 133, the polarization angle will be rotated another 45 degrees clockwise, so that the o-light will become e-light, and the e-light will become o-light.

[0044] The o-light and the e-light are incident on the second birefringent crystal plate 14. Since the second birefringent crystal plate 14 has the same birefringent characteristics as the first birefringent crystal plate 11, the deflection angle and the transmission path of the o-light and the e-light are the same as those in the first birefringent crystal plate 11. The o-light and the e-light will be combined into circularly polarized light by the second birefringent crystal plate 14, and the circularly polarized light will be reflected by the reflector 15 and incident on the second birefringent crystal plate 14 again.

[0045] exist Figure 2 In the example, the o-light is deflected upward at a certain angle, and the e-light is emitted straight. In the first birefringent crystal plate 11, the o-light is emitted above the e-light, and after passing through the first half-wave plate 121 and the Faraday rotator 13, the o-light will become e-light, and the e-light will become o-light, so it is emitted below the e-light. In the second birefringent crystal plate 14, since the o-light is deflected upward at a certain angle and the e-light is straight, the o-light below will be deflected upward and will intersect with the e-light and then be combined into circularly polarized light and emitted.

[0046] As in the case of the first birefringent crystal plate 11, the circularly polarized light is divided into o-light and e-light in the second birefringent crystal plate 14. When the o-light and the e-light pass through the Faraday rotator 13 and the second half-wave plate 122 in sequence, the polarization angle will be deflected by 90°, the o-light will become the e-light, and the e-light will become the o-light. The specific deflection reasons are similar to those mentioned above and will not be repeated here. The o-light and the e-light are incident on the first birefringent crystal plate 11. Since the second birefringent crystal plate 14 has the same birefringence characteristics as the first birefringent crystal plate 11, the deflection angle and transmission path of the o-light and the e-light are the same as those in the second birefringent crystal plate 14. The o-light and the e-light will become circularly polarized light through the first birefringent crystal plate 11, and the circularly polarized light is emitted through the exit port 112, realizing forward light transmission.

[0047] Specifically, at this time, the o-light is incident in the reverse direction into the second birefringent crystal plate 14, so the o-light is deflected downward, and the e-light continues to be emitted straight, so the o-light is emitted below the e-light. After passing through the Faraday rotator 13 and the second half-wave plate 122, the o-light will become the e-light, and the e-light will become the o-light, so the o-light is emitted above the e-light, and in the first birefringent crystal plate 11, since the o-light is deflected downward at a certain angle, the e-light is straight, so the o-light above will be deflected downward and will intersect with the e-light and then be combined into circularly polarized light and then emitted.

[0048] like Figure 3 As shown in FIG. 1 , the circularly polarized light enters the first birefringent crystal plate 11 from the exit port 112 and Figure 2Similarly, the circularly polarized light is divided into o-light and e-light, and the polarization angles of o-light and e-light do not change when they pass through the second half-wave plate 122 and the Faraday rotator 13 in sequence. Specifically, when the light passes through the second half-wave plate 122 with an optical axis of +22.5° in the forward direction, the polarization angle will rotate clockwise by -45°, and after passing through the Faraday rotator 133, the polarization angle will rotate clockwise by 45 degrees again, and the two will cancel each other out, so the polarization angles of o-light and e-light do not change.

[0049] After the o-light and the e-light are transmitted to the second birefringent crystal plate 14, since the second birefringent crystal plate 14 has the same birefringent characteristics as the first birefringent crystal plate 11, the deflection angle and transmission path of the o-light and the e-light are the same as those in the first birefringent crystal plate 11, so the difference between the o-light and the e-light will be larger. The o-light and the e-light are respectively incident on the reflector 15, and are reflected by the reflector 15 to the second birefringent crystal plate 14.

[0050] Specifically, in Figure 2 In the example, the o-light is deflected upward at a certain angle, while the e-light is emitted straight. In the first birefringent crystal plate 11, the o-light is emitted above the e-light, and when it passes through the second half-wave plate 122 and the Faraday rotator 13 in sequence, the polarization angle does not change, and the o-light is still emitted above the e-light. After entering the second birefringent crystal plate 14, the o-light is deflected upward at a certain angle, and the light is emitted straight. Therefore, the o-light continues to deviate by the same distance on the original upward deviation distance, and the distance between the o-light and the e-light is further increased.

[0051] After the o-light and the e-light are reflected to the second birefringent crystal plate 14, their transmission principle is the same as Figure 2 , so the o-light will be deflected downward and the e-light will be emitted in parallel, and the o-light will be emitted below the e-light. When the light passes through the Faraday rotator 13 and the first half-wave plate 122 in sequence, the polarization angle will not change. Specifically, after the light passes through the Faraday rotator 133, the polarization angle will rotate 45 degrees clockwise, and then reversely pass through the first half-wave plate 121 with an optical axis of -22.5°, the polarization angle will rotate -45 degrees clockwise, and the two will cancel each other out, so the polarization angles of the o-light and the e-light will not change.

[0052] The o-light and the e-light are respectively incident on the first birefringent crystal plate 11. Since the second birefringent crystal plate 14 has the same birefringent characteristics as the first birefringent crystal plate 11, the deflection angle and transmission path of the o-light and the e-light are the same as those in the second birefringent crystal plate 14. The o-light continues to be deflected downward, while the e-light is output in parallel. The two are transmitted separately and avoid the incident port 111. Therefore, no light will be emitted from the incident port 111, and reverse interception is successfully achieved.

[0053] In the above implementation scenario, the optical axis angle of the first half wave plate 121 is -22.5°, the optical axis angle of the second half wave plate 122 is 22.5°, and the Faraday rotator 13 is capable of changing the polarization angle of the light passing through in the forward or reverse direction by 45°. In other implementation scenarios, the optical axis angles of the first half wave plate 121 and the second half wave plate 122 can be other values. It is only necessary to realize that when the light passes through the first half wave plate 121 and the Faraday rotator 13 in sequence, the polarization angle will be deflected by 90°, and when the light passes through the Faraday rotator 13 and the second half wave plate 122 in sequence, the polarization angle will be deflected by 90°.

[0054] For example, if the optical axis angle of the first half wave plate 121 is -30°, and the optical axis angle of the second half wave plate 122 is +30°, then the Faraday rotator 13 can change the polarization angle of the light passing through the forward or reverse direction by 30°. Then when the light is transmitted in the forward direction, the circularly polarized light is divided into o light and e light after passing through the first birefringent crystal plate 11, and passes through the first half wave plate 121 and the Faraday rotator 13 in turn, and the polarization angle of the light is deflected by 90°, and the o light becomes e light, and the e light becomes o light. This part of the principle is basically the same as the above, and it will not be repeated here. The e light and the o light are combined into circularly polarized light in the second birefringent crystal plate 14 and then emitted, and the circularly polarized light is reflected by the reflector to the second birefringent crystal plate 14. The second birefringent crystal plate 14 divides the circularly polarized light into o light and e light. The o light and e light pass through the Faraday rotator 13 and the second half wave plate 122 in sequence. The polarization angle of the light is deflected by 90°. The o light becomes e light, and the e light becomes o light. The e light and the o light are combined into circularly polarized light in the first birefringent crystal plate 11 and then emitted, completing the forward transmission of the light.

[0055] When the light is transmitted in the reverse direction, the circularly polarized light is divided into o light and e light after passing through the first birefringent crystal plate 11, and passes through the second half wave plate 122 and the Faraday rotator 13 in sequence. The polarization direction of the light is deflected by -60°+30°=30°, so the o light and the e light cannot complete the conversion, and the light is not combined in the second birefringent crystal plate 14, and continues to be transmitted as light with polarization directions of 30° and 120°. When passing through the Faraday rotator 13 and the first half wave plate 121 in sequence, the polarization direction is deflected by 30°-60°=30°, and is transmitted as light with polarization directions of 60° and 150°. The light cannot be combined in the first birefringent crystal plate 11, and cannot be output through the output port.

[0056] It can be known from the above description that in this embodiment, the optical axis angles of the first half wave plate and the second half wave plate are matched with the Faraday rotator so that when the light passes through the first half wave plate and the Faraday rotator in sequence, and passes through the Faraday rotator and the second half wave plate in sequence, the polarization angle will be deflected by 90°. Since the half wave plate has different deflection values ​​for the polarization angles of light incident from different directions, the polarization angle cannot be deflected by 90° when the light transmission direction is reverse. Therefore, the forward input light can be combined into circularly polarized light after being divided into e-light and o-light and then emitted from the output port, while the reverse input light cannot be combined into circularly polarized light and cannot be emitted from the incident port, thereby realizing the isolation function of unidirectional passage of light. By reasonably setting the optical elements, it does not rely on two single-stage isolators, the structure is stable, the isolation effect is stable, and no complex and precise adjustment is required, and the setting cost is low.

[0057] The utility model also provides an optical communication device, an incident optical fiber, an output optical fiber and Figure 1 The double-stage isolator shown in FIG. The input optical fiber and the output optical fiber are vertically arranged at the input port 111 and the output port 112 of the double-stage isolator 10, respectively.

[0058] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present utility model rather than to limit it. For those skilled in the art, the technical solutions described in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents; and all these modifications and replacements should fall within the scope of protection of the claims attached to the present utility model.

Claims

1. A double-stage isolator, characterized in that: include: A first birefringent crystal plate, one side of which is used as a light input / output side, and an incident port and an output port are respectively provided along two ends of the light input / output side perpendicular to the light transmission direction; A half wave plate assembly, located on a side of the first birefringent crystal plate away from the light input / light output side, comprising a first half wave plate and a second half wave plate which are arranged in series perpendicular to the light transmission direction; A Faraday rotator is located on a side of the half wave plate assembly away from the first birefringent crystal plate, and when light sequentially passes through the first half wave plate and the Faraday rotator, the polarization angle will be deflected by 90°; when light sequentially passes through the Faraday rotator and the second half wave plate, the polarization angle will be deflected by 90°; a second birefringent crystal plate, located at a side of the Faraday rotator away from the half wave plate group, and having the same birefringence characteristics as the first birefringent crystal plate; A reflecting mirror is located on a side of the second birefringent crystal plate away from the Faraday rotator.

2. The double-stage isolator according to claim 1, characterized in that: The polarization angle change value of the first half-wave plate for the light passing forward is the same as the polarization angle change value of the second half-wave plate for the light passing backward.

3. The double-stage isolator according to claim 2, characterized in that: The absolute values ​​of the optical axis angle of the first half-wave plate and the optical axis angle of the second half-wave plate are equal.

4. The double-stage isolator according to claim 3, characterized in that: The optical axis angle of the first half wave plate is -22.5°, and the optical axis angle of the second half wave plate is 22.5°.

5. The double-stage isolator according to claim 4, characterized in that: The Faraday rotator is capable of deflecting the polarization angle of light passing through in the forward or reverse direction by 45°.

6. The double-stage isolator according to claim 1, characterized in that: The widths of the first birefringent crystal plate and the second birefringent crystal plate along the light transmission direction are equal.

7. The double-stage isolator according to claim 1, characterized in that: The first half wave plate and the second half wave plate have equal widths along the light transmission direction and equal lengths perpendicular to the light transmission direction.

8. The double-stage isolator according to any one of claims 1 to 7, characterized in that: The light entering from the incident port and the light exiting from the exit port are both circularly polarized lights.

9. The double-stage isolator according to any one of claims 1 to 7, characterized in that: The first birefringent crystal plate and the second birefringent crystal plate are made of yttrium yttrium vanadate.

10. An optical communication device, characterized in that: comprising an incident optical fiber, an output optical fiber and a double-stage isolator as claimed in any one of claims 1 to 9; The incident optical fiber and the exit optical fiber are respectively vertically arranged at the incident port and the exit port of the double-stage isolator.

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