Polarized light beam splitter and polarized light beam combiner with isolation function

Abstract

The embodiment of the invention relates to the technical field of optics, and discloses a polarized light beam splitter and a polarized light beam combiner with an isolation function, and the beam splitter comprises a single-core waveguide, a lens, a first birefringent crystal, a first Faraday rotator, a second birefringent crystal and a polarization-maintaining dual-core waveguide which are sequentially arranged in the forward direction of a light path, the first birefringent crystal, the first Faraday rotator and the second birefringent crystal are all of parallel plate structures. According to the embodiment of the invention, the device structure is simplified, and the device cost is reduced.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of optical technology, and specifically to a polarization beam splitter and a polarization beam combiner with isolation function. Background Art

[0002] In the design of optical products, it is often necessary to decompose a light beam into two linear polarized light outputs with polarization states perpendicular to each other, or to combine two linear polarized light beams into one optical waveguide. The product that realizes this function is a polarization beam splitter or a polarization beam combiner. In some scenarios, it is necessary to prevent the reverse light from returning to the incident light path while realizing beam splitting or beam combining, so as to avoid affecting the normal operation of the optical device at the incident end or even causing damage to the device. Therefore, it is necessary to add the function of reverse light isolation in the optical path.

[0003] In this regard, the early solution was to directly connect the polarization beam splitter / combiner and the isolator in series in the optical path to achieve beam splitting / combining while isolating the reverse light. Later, in order to achieve a more compact size and lower cost, the designers assembled the polarization beam splitter core / combiner core and the isolator core in series in the collimated optical path of a device to form a hybrid device with both polarization beam splitting / combining and optical isolation functions.

[0004] For the hybrid device that realizes the functions of polarized light splitting and optical isolation, the light beam is first converted into parallel light through a collimating lens, wherein the isolator core allows the o light and e light of the forward parallel light to be output in parallel with the input direction, and at the same time, the o light and e light in the reverse parallel light are both formed at an angle with the forward light to exit the isolator core, thereby realizing the effect of reverse light isolation. The polarized light beam splitter core decomposes the forward parallel light into o light and e light, and forms two beams of parallel light at a certain angle with the incident parallel light and in opposite deflection directions when exiting. The two beams of parallel light are then converged by a converging lens and respectively output from the two cores of the polarization-maintaining dual-core waveguide, thereby realizing the functions of polarized light splitting and optical isolation. When two linearly polarized lights are reversely introduced from the polarization-maintaining dual-core waveguide, they are merged into a beam of reverse parallel light after passing through the polarized light beam splitter core, and then enter the optical isolator core. The o light and e light in the reverse parallel light form a certain angle with the forward parallel light when exiting the isolator core, so that they cannot be coupled into the single-core waveguide after passing through the first collimating lens, thereby realizing the reverse light isolation function.

[0005] By setting the input end and the output end of the isolator core in the hybrid device that realizes the polarized light beam splitting and optical isolation functions inversely, a hybrid device with the polarized light beam combining and optical isolation functions can be formed.

[0006] The inventors of the present application have found in practice that the existing polarization light splitter / combiner with isolation function has a complex structure and high cost. Summary of the invention

[0007] In view of the above problems, the embodiments of the present application provide a polarization beam splitter and a polarization beam combiner with an isolation function in a non-parallel light solution to simplify the device structure and reduce the device cost.

[0008] According to one aspect of an embodiment of the present application, a polarization beam splitter with an isolation function is provided, comprising a single-core waveguide, a lens, a first birefringent crystal, a first Faraday rotator, a second birefringent crystal and a polarization-maintaining double-core waveguide arranged in sequence along the forward direction of an optical path, wherein the first birefringent crystal, the first Faraday rotator and the second birefringent crystal are all parallel plate structures; the single-core waveguide is used to introduce divergent light and output it to the lens; the lens is used to convert the divergent light into convergent light and output it to the first birefringent crystal; the first birefringent crystal is used to decompose the convergent light into a first crystal forward o light and a first crystal forward e light, whose polarization states are perpendicular to each other, and the first crystal forward o light and the first crystal forward e light are formed between them. After the first positive relative displacement is formed, the light is output to the first Faraday rotator; the first Faraday rotator is used to rotate the polarization states of the first crystal forward o light and the first crystal forward e light along the first rotation direction by an angle α and then output to the second birefringent crystal, wherein α=45°; the second birefringent crystal is used to make the first crystal forward o light and the first crystal forward e light form a second positive relative displacement, and then output to the two cores of the polarization-maintaining dual-core waveguide respectively; the distance between the two cores of the polarization-maintaining dual-core waveguide is equal to the sum of the first positive relative displacement and the second positive relative displacement between the first crystal forward o light and the first crystal forward e light, and the polarization states of the two cores of the polarization-maintaining dual-core waveguide are respectively aligned from the second birefringent crystal The polarization states of the first crystal forward o light and the first crystal forward e light output by the crystal, the polarization-maintaining double-core waveguide is used to output the first crystal forward o light and the first crystal forward e light; when two reverse linear polarized lights respectively aligned with the polarization states of the two cores of the polarization-maintaining double-core waveguide respectively enter the two cores of the polarization-maintaining double-core waveguide in the opposite direction along the optical path, the two cores of the polarization-maintaining double-core waveguide are used to output the two reverse linear polarized lights respectively to the second birefringent crystal, and the polarization states of the two reverse linear polarized lights are respectively aligned with the polarization states of the o light and the e light of the second birefringent crystal; the second birefringent crystal is used to form a second reverse relative displacement between the two reverse linear polarized lights, and then output them to the first Faraday rotator; the first Faraday The optical rotator is used to rotate the polarization states of two reverse linear polarized lights by an angle of α along a first rotation direction and then output them to a first birefringent crystal; the first birefringent crystal is used to form a first reverse relative displacement between the two reverse linear polarized lights. In the optical path between the forward input end of the first birefringent crystal and the forward output end of the second birefringent crystal, the polarization states of the two reverse linear polarized lights in the first birefringent crystal are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the optical path of the two reverse linear polarized lights in the first birefringent crystal deviates from the forward optical path in the first birefringent crystal. Finally, the two reverse linear polarized lights output by the first birefringent crystal cannot be coupled into the single-core waveguide after passing through the lens.

[0009] According to another aspect of an embodiment of the present application, a polarization light combiner with an isolation function is provided, comprising a polarization-maintaining dual-core waveguide, a first birefringent crystal, a first Faraday rotator, a second birefringent crystal, a lens, and a single-core waveguide, which are sequentially arranged along the forward direction of an optical path, wherein the first birefringent crystal, the first Faraday rotator, and the second birefringent crystal are all parallel plate structures; the two cores of the polarization-maintaining dual-core waveguide are used to introduce two linearly polarized lights that are respectively aligned with their polarization states and output them to the first birefringent crystal; the polarization states of the o light and the e light of the first birefringent crystal are respectively aligned with the polarization states of the two linearly polarized lights, and the first birefringent crystal is used to introduce two linearly polarized lights that are respectively aligned with their polarization states. The refracting crystal is used to form a first positive relative displacement between two linearly polarized lights, and then output the first crystal positive o light and the first crystal positive e light to the first Faraday rotator; the first Faraday rotator is used to rotate the polarization states of the first crystal positive o light and the first crystal positive e light by an angle α along a first rotation direction, and then output them to the second birefringent crystal, wherein α=45°; the second birefringent crystal is used to form a second positive relative displacement between the first crystal positive o light and the first crystal positive e light, and the sum of the first positive relative displacement and the second positive relative displacement makes the first crystal positive o light and the first crystal positive e light coincide with each other. The light is a beam of light, and is output to the lens in the form of divergent light; the lens is used to convert the divergent light into convergent light and output it to the single-core waveguide; when the reverse light enters the single-core waveguide in the reverse direction along the optical path, the single-core waveguide is used to output the reverse light to the lens in the form of divergent light; the lens is used to convert the reverse light into convergent light and output it to the second birefringent crystal; the second birefringent crystal is used to form a second reverse relative displacement between two reverse linear polarized lights whose polarization states are perpendicular to each other formed by the decomposition of the reverse light, and then output it to the first Faraday rotator; the first Faraday rotator is used to rotate the polarization states of the two reverse linear polarized lights by α along the first rotation direction The first birefringent crystal is used to form a first reverse relative displacement between the two reverse linear polarized lights. In the optical path between the forward input end of the first birefringent crystal and the forward output end of the second birefringent crystal, the polarization states of the two reverse linear polarized lights in the first birefringent crystal are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the optical path of the two reverse linear polarized lights in the first birefringent crystal deviates from the forward optical path in the first birefringent crystal. Finally, the two reverse linear polarized lights output by the first birefringent crystal cannot be coupled into any core of the polarization-maintaining dual-core waveguide.

[0010] The polarized light beam splitter / combiner with isolation function provided in the present application performs forward beam splitting and reverse isolation for non-parallel light, requires a small number of optical elements, and is conducive to reducing production costs. In addition, the first birefringent crystal, the first Faraday rotator, and the second birefringent crystal are all parallel plate structures, which are simple in structure and easy to process and manufacture.

[0011] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only used to illustrate the preferred embodiments and are not to be considered as limiting the present application. In the accompanying drawings:

[0013] Figure 1 A schematic diagram of the optical path of an existing polarization beam splitter provided in an embodiment of the present invention;

[0014] Figure 2a A schematic diagram of the birefringence phenomenon and light displacement of a positive birefringent crystal provided by an embodiment of the present invention;

[0015] Figure 2b A schematic diagram of the birefringence phenomenon and light displacement of a positive birefringent crystal provided by an embodiment of the present invention;

[0016] Figure 3a A schematic diagram of the birefringence phenomenon and light displacement of a negative birefringence crystal provided by an embodiment of the present invention;

[0017] Figure 3b A schematic diagram of the birefringence phenomenon and light displacement of a negative birefringence crystal provided by an embodiment of the present invention;

[0018] Figure 4 A schematic diagram of the forward light path of a single-stage isolated polarization beam splitter with isolation function provided in an embodiment of the present invention;

[0019] Figure 5 A schematic diagram of the reverse optical path of a single-stage isolated polarization beam splitter with isolation function provided in an embodiment of the present invention;

[0020] Figure 6a A schematic diagram of the structure and optical axis of a birefringent crystal A provided in an embodiment of the present invention;

[0021] Figure 6b A schematic diagram of the structure and optical axis of a birefringent crystal B provided in an embodiment of the present invention;

[0022] Figure 7a A schematic diagram of the displacement of forward light and reverse light in a birefringent crystal A provided in an embodiment of the present invention;

[0023] Figure 7b A schematic diagram of the displacement of forward light and reverse light in a birefringent crystal B provided in an embodiment of the present invention;

[0024] Figure 8a A schematic diagram of the optical paths of the forward o light from the first crystal and the corresponding reverse e light from the second crystal in the polarization beam splitter provided in Example 1 of the present invention;

[0025] Figure 8b A schematic diagram of the optical path of the forward e-light of the first crystal and the corresponding reverse o-light of the second crystal in the polarization beam splitter provided in Example 1 of the present invention;

[0026] Figure 9a A schematic diagram of the displacement of the forward light path in the polarization beam splitter provided in Example 1 of the present invention;

[0027] Figure 9b A schematic diagram of the displacement of the reverse o-light of the second crystal in the polarization beam splitter provided in Example 1 of the present invention;

[0028] Fig.9c A schematic diagram of the displacement of the reverse e-light of the second crystal in the polarization beam splitter provided in Example 1 of the present invention;

[0029] Fig.10 A schematic diagram of the forward light path of a polarization beam splitter with double-stage isolation and isolation function provided in an embodiment of the present invention;

[0030] Fig.11 A schematic diagram of the reverse optical path of a polarization beam splitter with double-stage isolation and isolation function provided in an embodiment of the present invention;

[0031] Fig.12a A schematic diagram of the structure and optical axis of a birefringent crystal C provided in an embodiment of the present invention;

[0032] Figure 12b A schematic diagram of the structure and optical axis of a birefringent crystal D provided in an embodiment of the present invention;

[0033] Fig.12c A schematic diagram of the structure and optical axis of a birefringent crystal E provided in an embodiment of the present invention;

[0034] Fig.13a A schematic diagram of the displacement of forward light and reverse light in a birefringent crystal C provided by an embodiment of the present invention;

[0035] Fig.13b A schematic diagram of the displacement of forward light and reverse light in a birefringent crystal D provided in an embodiment of the present invention;

[0036] Fig.13c A schematic diagram of the displacement of forward light and reverse light in a birefringent crystal E provided in an embodiment of the present invention;

[0037] Fig.14aA schematic diagram of the optical paths of the forward O light from the first crystal and the reverse O light from the third crystal in the polarization beam splitter provided in Example 2 of the present invention;

[0038] Fig.14b A schematic diagram of the optical paths of the forward e-light from the first crystal and the reverse e-light from the third crystal in the polarization beam splitter provided in Embodiment 2 of the present invention;

[0039] Fig.15a A schematic diagram of the displacement of the forward light path in the polarization beam splitter provided in Example 2 of the present invention;

[0040] Fig.15b A schematic diagram of the displacement of the reverse o-light of the third crystal in the polarization beam splitter provided in Example 2 of the present invention;

[0041] Fig.15c A schematic diagram of the displacement of the reverse e-light of the third crystal in the polarization beam splitter provided in Example 2 of the present invention;

[0042] Fig.16a The first birefringent crystal provided in the embodiment of the present invention is a schematic diagram of the structure and optical axis of a combined crystal;

[0043] Fig.16b A schematic diagram of the structure and optical axis of a first birefringent crystal as a combined crystal provided in another embodiment of the present invention;

[0044] Fig.17 A schematic diagram of the forward light path of a polarization beam combiner with a single-stage isolation function provided in an embodiment of the present invention;

[0045] Fig.18 A schematic diagram of the reverse optical path of a polarization beam combiner with isolation function and single-stage isolation provided in an embodiment of the present invention;

[0046] Fig.19a A schematic diagram of the optical path of the forward o light from the first crystal and the corresponding reverse e light from the second crystal in the polarized light combiner provided in Example 3 of the present invention;

[0047] Fig.19b A schematic diagram of the optical path of the forward e-light of the first crystal and the corresponding reverse o-light of the second crystal in the polarized light combiner provided in Example 3 of the present invention;

[0048] Fig.20a A schematic diagram of the displacement of the forward light path in the polarization beam combiner provided in Example 3 of the present invention;

[0049] Fig.20b A schematic diagram of the displacement of the reverse o-light of the second crystal in the polarization beam combiner provided in Example 3 of the present invention;

[0050] Fig.20cA schematic diagram of the displacement of the reverse e-light of the second crystal in the polarization beam combiner provided in Example 3 of the present invention;

[0051] Fig.21a A schematic diagram of the optical paths of the forward O light from the first crystal and the reverse O light from the third crystal in the polarized light beam combiner provided in Example 4 of the present invention;

[0052] Figure 21b The optical paths of the forward e-light of the first crystal and the reverse e-light of the third crystal in the polarization beam combiner provided in Embodiment 4 of the present invention;

[0053] Fig.22a A schematic diagram of the displacement of the forward light path in the polarization beam combiner provided in Example 4 of the present invention;

[0054] Figure 22b A schematic diagram of the displacement of the reverse o-light of the third crystal in the polarized light beam combiner provided in Example 4 of the present invention;

[0055] Fig.22c Schematic diagram of the displacement of the reverse e-light of the third crystal in the polarization beam combiner provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0056] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0058] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0059] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0060] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0061] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0062] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0063] The current polarization beam splitter 10 with isolation function is as follows Figure 1As shown, a light beam of any polarization state is introduced from the waveguide 1 and output to the first lens 2 as divergent light, and then enters the isolator core 3 after being collimated into parallel light by the first lens 2, wherein the isolator core 3 comprises a first wedge-shaped birefringent crystal 31, a Faraday rotator 32 and a second wedge-shaped birefringent crystal 33 arranged in sequence along the forward direction of the optical path, and the parallel light enters the first wedge-shaped birefringent crystal 31 and is decomposed into a first crystal forward o light and a first crystal forward e light, wherein the first crystal forward o light forms a deflection angle λ for output, and the first crystal forward e light forms a deflection angle γ for output, wherein the deflection angle refers to the angle between the incident light beam and the parallel light (i.e., the horizontal line), and the first crystal forward o light and the first crystal forward e light pass through the Faraday rotator 3 2, their respective polarization states rotate 45°, then the first crystal forward o light is input to the second wedge-shaped birefringent crystal 33, and the polarization state of the first crystal forward o light is aligned with the polarization state of the second wedge-shaped birefringent crystal 33, the first crystal forward e light is input to the second wedge-shaped birefringent crystal 33, and the polarization state of the first crystal forward e light is aligned with the polarization state of the second wedge-shaped birefringent crystal 33, after passing through the second wedge-shaped birefringent crystal 33, the first crystal forward o light forms a deflection angle of -λ, and the first crystal forward e light forms a deflection angle of -γ, and the final deflection angles of the first crystal forward o light and the first crystal forward e light after passing through the isolator core 3 are both 0°, and both are output in a direction parallel to the incident light. It should be noted that at the isolator core 3, since it is input as parallel light and output as parallel light, Figure 1 For the sake of simplicity, the specific deflection angles and specific optical paths of the first crystal forward o light and the first crystal forward e light are not shown, and the specific optical path principle is mainly based on the above text description.

[0064] Please continue reading Figure 1 The first crystal forward o light and the first crystal forward e light output from the isolator core 3 enter the third wedge-shaped birefringent crystal 41 in the beam splitter core 4 as parallel light. After passing through the third wedge-shaped birefringent crystal 41, the first crystal forward o light forms a deflection angle of -δ and is output to the fourth wedge-shaped birefringent crystal 42, and the first crystal forward e light forms a deflection angle of -ε and is output to the fourth wedge-shaped birefringent crystal 42. As shown in the figure, the optical axis of the third wedge-shaped birefringent crystal 41 is perpendicular to the optical axis of the fourth wedge-shaped birefringent crystal 42. Therefore, in the third wedge-shaped birefringent crystal 41 and the fourth wedge-shaped birefringent crystal 42, the polarization state of the forward o light of the first crystal is aligned with the polarization state of the o light of one of them, and is aligned with the polarization state of the e light of the other. Therefore, after passing through the fourth wedge-shaped birefringent crystal 42, the forward o light of the first crystal forms a deflection angle ε for output, and the forward e light of the first crystal forms a deflection angle δ for output. In the entire optical path of the beam splitter core 4, the total deflection angle of the forward o light of the first crystal is -δ+ε, and the total deflection angle of the forward e light of the first crystal is -ε+δ. Since the deflection angles of the o light and the e light in the wedge-shaped birefringent crystal are not equal, that is, δ≠ε, as shown in Figure 1As shown, the first crystal forward o light and the first crystal forward e light are finally emitted from the beam splitter core 4 in two opposite directions at a certain deflection angle. It should also be noted that the figure only schematically shows the two light beams separated at the fourth wedge-shaped birefringent crystal 42, and the specific o light and e light optical paths at the third wedge-shaped birefringent crystal 41 are not shown. The specific optical path principle is mainly based on the above text content.

[0065] Finally, the first crystal forward o light and the first crystal forward e light outputted by the beam splitter core 4 form converged light after passing through the second lens 5 and are respectively outputted to the two cores of the dual-core waveguide 6 to realize the beam splitting function.

[0066] For the reverse isolation function, the reverse optical path between the input end of the dual-core waveguide 6 and the output end of the Faraday rotator 32 in the isolator core 3 is exactly the same as the forward optical path. Since the Faraday rotator 32 rotates the forward light and the reverse light in the same direction, Figure 1 From the perspective from left to right in the figure, no matter it is forward light or reverse light, after passing through the Faraday rotator 32, the polarization state of the light beam is rotated 45° clockwise or 45° counterclockwise. Therefore, after the reverse light passes through the Faraday rotator 32, its polarization state is accumulated to form a 90° rotation relative to the forward light, and the o-light and the e-light are transformed in the first wedge-shaped birefringent crystal 31, and the deflection angles of the o-light and the e-light in the wedge-shaped birefringent crystal are different, that is, if the polarization state of the reverse o-light of the fourth crystal (the linear polarization light aligned with the polarization state of the o-light outputted in the reverse direction along the optical path by the fourth wedge-shaped birefringent crystal 42) is aligned with the o-light of the second wedge-shaped birefringent crystal 33, and forms a deflection angle of -λ after passing through the second wedge-shaped birefringent crystal 33, the polarization state of the reverse e-light of the fourth crystal (the linear polarization light aligned with the polarization state of the e-light outputted in the reverse direction along the optical path by the fourth wedge-shaped birefringent crystal 42) is aligned with the e-light of the second wedge-shaped birefringent crystal 33 , and after passing through the second wedge-shaped birefringent crystal 33, a deflection angle of -γ is formed. After passing through the Faraday rotator 32, due to the transformation of o-light and e-light, the polarization state of the reverse o-light of the fourth crystal is aligned with the polarization state of the e-light of the first wedge-shaped birefringent crystal 31, and the polarization state of the reverse e-light of the fourth crystal is aligned with the polarization state of the o-light of the first wedge-shaped birefringent crystal, that is, the reverse o-light of the fourth crystal forms a deflection angle γ, and the reverse e-light of the fourth crystal forms a deflection angle λ. In the reverse optical path of the isolator core 3, the reverse o-light of the fourth crystal accumulates to form a deflection angle of -λ+γ, and the reverse e-light of the fourth crystal accumulates to form a deflection angle of -γ+λ. Since the deflection angles of o-light and e-light in the wedge-shaped birefringent crystal are not equal, that is, γ≠β, the reverse o-light of the fourth crystal and the reverse e-light of the fourth crystal finally have a certain deflection angle and are respectively emitted from the isolator core 3 in two opposite directions. After passing through the first lens 2, they cannot enter the waveguide 1, thereby realizing the reverse light isolation function.

[0067] For the polarization beam combiner with isolation function, the isolator core in the above-mentioned polarization beam splitter with isolation function can be set in reverse, which will not be elaborated here.

[0068] Based on the above solution, it can be seen that the current polarization beam splitter / combiner with isolation function needs to be configured with an isolator core and a beam splitter core / combiner core at the same time, which has a complex structure and numerous optical components, resulting in high costs.

[0069] In this regard, the present application utilizes birefringent crystals and Faraday rotators to process the converged light, and through the reasonable combination and configuration of the birefringent crystals and Faraday rotators, forms a set of polarization beam splitter / combiner products with isolation function that has a simple structure and low cost.

[0070] For the phenomenon of double refraction and light displacement in crystals, see Figure 2a and Figure 2b Taking the case of a light beam incident on the positive birefringent crystal 21, when the polarization state of the light beam incident on the positive birefringent crystal 21 is not aligned with the o-light and e-light of the positive birefringent crystal 21, the light beam will be decomposed into o-light and e-light in the positive birefringent crystal 21, where the o-light follows the law of refraction, the light beam does not change its angle, and enters and exits the positive birefringent crystal 21 in the same direction as the incident light. However, the e-light does not follow the law of refraction, and will deviate from the optical path in the positive birefringent crystal 21, forming a certain displacement d before exiting the positive birefringent crystal 21. At this time, the relative displacement of the o-light and the e-light is d. The birefringence and light displacement phenomenon caused by the light beam incident on the negative birefringent crystal 22 is shown in the figure. Figure 3a and Figure 3b As shown, no further details are given here.

[0071] Since the e-light deflection directions of the positive birefringent crystal and the negative birefringent crystal are opposite, for the sake of simplicity, the following description is made by taking the positive birefringent crystal as an example. The angle θ between the optical axis of the birefringent crystal 21 and the normal of the incident surface can be called the walk-off angle, which is used to control the relative displacement of the o-light and the e-light after the light passes through the birefringent crystal 21. When 0°<θ<90°, Figure 2a As shown, the e-light is deflected upward to form a displacement d; when -90°<θ<0°, as shown Figure 2b As shown in the figure, the e-light is deflected downward to form a displacement of -d. Therefore, by changing the angle θ, the relative displacement of the o-light and the e-light at the output end can be changed.

[0072] According to one aspect of the embodiments of the present application, a polarization beam splitter with an isolation function is provided. Figure 4, the figure shows the structure of a polarization beam splitter with isolation function provided by an embodiment of the present application. As shown in the figure, the polarization beam splitter with isolation function 100 includes a single-core waveguide 110, a lens 120, a first birefringent crystal 130, a first Faraday rotator 140, a second birefringent crystal 150 and a polarization-maintaining double-core waveguide 160 arranged in sequence along the forward direction of the optical path, wherein the first birefringent crystal 130, the first Faraday rotator 140 and the second birefringent crystal 150 are all parallel plate structures.

[0073] For the forward beam splitting, Figure 4 As shown in FIG. 1 , the single-core waveguide 110 is used to introduce divergent light and output it to the lens 120 , wherein the divergent light can be in any polarization state. The lens 120 is used to convert the divergent light into convergent light and output it to the first birefringent crystal 130 .

[0074] The first birefringent crystal 130 is used to decompose the converged light into first crystal forward light ( Figure 4 The solid line in the first birefringent crystal 130) and the forward e-light of the first crystal ( Figure 4 After a first forward relative displacement is formed between the first crystal forward o light and the first crystal forward e light, the light beam is output to the first Faraday rotator 140.

[0075] The first Faraday rotator 140 is used to rotate the polarization states of the first crystal forward o light and the first crystal forward e light by an angle α (45°) along a first rotation direction and then output the polarization states to the second birefringent crystal 150 .

[0076] The second birefringent crystal 150 is used to form a second forward relative displacement between the forward o light of the first crystal and the forward e light of the first crystal, and then output them to the two cores of the polarization-maintaining dual-core waveguide 160 respectively.

[0077] exist Figure 4 In the specific embodiment shown, along the forward direction of the optical path, the polarization state of the forward o light of the first crystal is aligned with the polarization state of the e light of the second birefringent crystal 150 after passing through the first Faraday rotator 140, that is, Figure 4 As shown in FIG. 1 , when the convergent light output by the lens 120 enters the first birefringent crystal 130, the light that is emitted in the same direction as the incident light and does not deviate from the optical path is the first crystal forward light ( Figure 4The first birefringent crystal 130 has a first forward O light, and the first crystal has a forward O light. The forward O light of the first crystal passes through the first Faraday rotator 140 and the polarization state is rotated by 45° (it can be clockwise or counterclockwise). After the rotation, the polarization state of the forward O light of the first crystal is aligned with the polarization state of the e light of the second birefringent crystal 150, and the optical path deviates in the second birefringent crystal 150 (the optical path of the forward O light of the first crystal in the second birefringent crystal 150 is shown in FIG. Figure 4 The polarization state of the forward e-light of the first crystal is aligned with the polarization state of the o-light of the second birefringent crystal 150 after passing through the first Faraday rotator 140, and no optical path deviation occurs in the second birefringent crystal 150 (the optical path of the forward e-light of the first crystal in the second birefringent crystal 150 is as shown in FIG. Figure 4 The second birefringent crystal 150 is a light beam shown by a solid line in the second birefringent crystal 150, and finally the light-emitting surface of the second birefringent crystal 150 emits two light beams, namely, the first crystal forward o light and the first crystal forward e light, and the polarization states of the two light beams are perpendicular to each other and separated in position. For this embodiment, in order to realize the beam splitting function, it is necessary to ensure that the sum of the displacements of the first crystal forward o light and the first crystal forward e light in the two crystals are not equal.

[0078] In some other embodiments, along the forward direction of the optical path, the polarization state of the forward o light of the first crystal can also be aligned with the polarization state of the o light of the second birefringent crystal 150 after passing through the first Faraday rotator 140, and the forward o light of the first crystal is also incident and emitted in the same direction in the second birefringent crystal 150 without optical path deviation, while the forward e light of the first crystal deviates again in the second birefringent crystal 150. For this embodiment, in order to realize the beam splitting function, it is necessary to ensure that the sum of the displacements of the forward o light of the first crystal and the forward e light of the first crystal in the two crystals are not equal.

[0079] The distance between the two cores of the polarization-maintaining dual-core waveguide 160 is equal to the relative displacement between the first crystal forward o light and the first crystal forward e light formed by the sum of the first forward relative displacement and the second forward relative displacement, that is, the first crystal forward o light and the first crystal forward e light can enter the two cores of the polarization-maintaining dual-core waveguide 160 respectively after being emitted from the second birefringent crystal 150. The polarization states of the two cores of the polarization-maintaining dual-core waveguide 160 are respectively aligned with the polarization states of the first crystal forward o light and the first crystal forward e light output from the second birefringent crystal 150, and then the polarization-maintaining dual-core waveguide 160 is used to output the first crystal forward o light and the first crystal forward e light, so as to realize the beam splitting function along the forward direction of the optical path.

[0080] For isolation in the reverse direction along the optical path, such as Figure 5As shown in , when two reverse linear polarized lights respectively aligned with the polarization states of the two cores of the polarization-maintaining dual-core waveguide 160 respectively enter the two cores of the polarization-maintaining dual-core waveguide 160 in reverse directions along the optical path, the two cores of the polarization-maintaining dual-core waveguide 160 are used to output the two reverse linear polarized lights respectively to the second birefringent crystal 150, and the polarization states of the two reverse linear polarized lights are respectively aligned with the o-light polarization state and the e-light polarization state of the second birefringent crystal 150.

[0081] The second birefringent crystal 150 is used to form a second reverse relative displacement between the two reverse linear polarized lights and then output them to the first Faraday rotator 140. The first Faraday rotator 140 is used to rotate the polarization states of the two reverse linear polarized lights by an angle of α (45°) along the first rotation direction and then output them to the first birefringent crystal 130. As mentioned above, the rotation of the polarization state of the light beam by the Faraday rotator is Figure 5 In the figure, if viewed from left to right, the polarization states of the forward light and the reverse light are both rotated in the clockwise direction or in the counterclockwise direction when passing through the first Faraday rotator 140. Therefore, after the two reversely polarized lights pass through the first Faraday rotator 140, their polarization states are rotated by 90° in the first birefringent crystal 130 relative to the forward light, and the o-light and the e-light are transformed.

[0082] Based on this, in the optical path, from the reverse input end of the polarization-maintaining dual-core waveguide 160 to the reverse output end of the first Faraday rotator 140, the optical paths of the forward light and the reverse light completely overlap, except that the transformation of the o-light and the e-light occurs after the reverse output end of the first Faraday rotator 140.

[0083] Then, the two reverse linear polarized lights enter the first birefringent crystal 130. The first birefringent crystal 130 is used to form a first reverse relative displacement between the two reverse linear polarized lights. As shown above, in the optical path between the forward input end of the first birefringent crystal 130 and the forward output end of the second birefringent crystal 150, the polarization states of the two reverse linear polarized lights in the first birefringent crystal 130 are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the optical path of the two reverse linear polarized lights in the first birefringent crystal 130 deviates from the forward optical path in the first birefringent crystal 130. Finally, the two reverse linear polarized lights output by the first birefringent crystal 130 cannot be coupled into the single-core waveguide 110 after passing through the lens 120, thereby realizing the reverse isolation function.

[0084] In order to facilitate the understanding of the specific embodiment, the following is an example of a forward light incident on the first birefringent crystal 130. For the case of oblique incident forward light, the functions provided by the embodiment of the present invention are also applicable. To this end, two birefringent crystals are first provided as examples for explanation. In the specific embodiment, different solutions can be formed by using different alignment methods for the o-light and the e-light of the two birefringent crystals. For details, please refer to Figure 6a and Figure 6b , Figure 6a The structure and optical axis of the birefringent crystal A210 are schematically shown in FIG. Figure 6b Schematically shows the structure and optical axis of the birefringent crystal B220.

[0085] like Figure 6a As shown in , the birefringent crystal A210 is a parallel plate structure, with the positive light incident surface as the plane where the x and y axes are located, and the positive direction of the optical path as the positive direction of the z axis, a three-dimensional rectangular coordinate system is established, wherein the normal line of the positive light incident surface of the birefringent crystal A210 is parallel to the z axis. The angle θ between the optical axis of the birefringent crystal A210 and the normal line of the positive light incident surface (i.e., the z axis) is A The angle between the straight line where the e-light oscillation plane where the optical axis of the birefringent crystal A210 intersects with the xy plane and the y-axis is Figure 6a middle Figure 7a Schematic diagram of light displacement in the birefringent crystal A210 is shown in FIG. The x and y axes rectangular coordinate system is formed on the incident surface of the birefringent crystal A210 with the incident point of the forward light as the origin. Whether it is the relative displacement of the forward light or the relative displacement of the reverse light, it is all referenced to the xyz coordinate system of the forward light. Figure 7a As shown in , after the forward light is incident on the birefringent crystal A210, the forward o light component follows the law of refraction, does not shift in the xy plane, and exits the birefringent crystal A210 at the origin, that is, the displacement of the forward o light in the x-axis direction in the birefringent crystal A210 is DoxI=0, and the displacement in the y-axis direction is DoyI=0; the forward e light component does not follow the law of refraction, and the displacement along the x-axis direction is set to DexI=a, and the displacement along the y-axis direction is set to DeyI=a / tan(22.5°)=2.41a. Correspondingly, the incident reverse o light also does not shift, and the displacement of the reverse e light in the birefringent crystal A210 along the x-axis direction is rDexI=-a, rDeyI=-2.41a. Of course, other displacement values ​​can be used according to specific circumstances, and are not limited here.

[0086] like Figure 6bAs shown in FIG, the birefringent crystal B220 is also a parallel plate structure, and a three-dimensional rectangular coordinate system is established in the birefringent crystal B220 in the same manner as the birefringent crystal A210. The angle θ between the optical axis of the birefringent crystal B220 and the normal line of the positive light incident surface (i.e., the z-axis) is B The angle between the straight line where the e-light oscillation plane where the optical axis of the birefringent crystal B220 intersects with the xy plane and the y axis is Figure 6b middle Figure 7b FIG. 2 shows a schematic diagram of light displacement in the birefringent crystal B220. The coordinate system is established and referenced in the same manner as the birefringent crystal A210. Figure 7b As shown in , the displacement of the normal incident forward e-light in the birefringent crystal B220 is DexII=a, DeyII=a / tan(157.5°)=-2.41a, and correspondingly, the displacement of the normal incident reverse e-light in the birefringent crystal B220 is rDexII=-a, rDeyII=2.41a. Of course, other displacement values ​​can be used according to specific circumstances, which are not limited here.

[0087] Example 1

[0088] In this embodiment, the first birefringent crystal 130 uses the birefringent crystal A210, and the second birefringent crystal 150 uses the birefringent crystal B220. Along the forward direction of the optical path, the polarization state of the first crystal forward o light in the first birefringent crystal 130-second birefringent crystal 150 is oe.

[0089] See also Figure 8a, the figure shows the optical path of the first crystal forward o light in the polarization beam splitter with isolation function provided in Example 1 and the optical path of the reverse linear polarized light (named as the second crystal reverse e light in the figure and below for explanation) received by the polarization-maintaining dual-core waveguide 160 from the core of the first crystal forward o light. With the forward propagation direction of the optical path (from left to right) as the positive direction of the z-axis, an xyz coordinate system is established. As shown in the figure, for the first crystal forward o light propagating in the forward direction of the optical path, there is no optical path deviation in the first birefringent crystal 130, and it is emitted from the exit surface of the first birefringent crystal 130 along the same xy coordinate as its position on the incident surface; after passing through the first Faraday rotator 140, the polarization state of the first crystal forward o light rotates 45° and is aligned with the polarization state of the e light of the second birefringent crystal 150; after entering the second birefringent crystal 150, the first crystal forward o light deviates from the optical path, and after being emitted from the second birefringent crystal 150, it is coupled into one of the cores of the polarization-maintaining dual-core waveguide 160. For the reverse e-light of the second crystal propagating in the reverse direction along the optical path, the optical path of the reverse e-light of the second crystal coincides with the optical path of the forward o-light of the first crystal between the forward light output end of the second birefringent crystal 150 and the forward light input end of the first Faraday rotator 140; however, after passing through the first Faraday rotator 140, the polarization state of the reverse e-light of the second crystal rotates by 45° in the same direction. Since the polarization state of the forward o-light of the first crystal rotates by 45° in this direction when passing through the first Faraday rotator 140 in the forward optical path, the polarization state of the reverse e-light of the second crystal rotates by 90° cumulatively relative to the forward o-light of the first crystal, as shown in FIG. Figure 8a The polarization direction of the forward o light of the first crystal below changes and the polarization direction of the reverse e light of the second crystal changes. In the first birefringent crystal 130, the polarization state of the reverse e light of the second crystal is perpendicular to the polarization state of the forward o light of the first crystal, that is, the o light and the e light are transformed, so that the polarization state of the reverse e light of the second crystal is aligned with the polarization state of the e light of the first birefringent crystal 130; then the reverse e light of the second crystal deviates from the optical path after entering the first birefringent crystal 130, thereby deviating from the forward o light of the first crystal.

[0090] See also Figure 8b, the figure shows the optical path of the first crystal forward e-light in the polarization beam splitter with isolation function provided in Example 1 and the optical path of the reverse linear polarized light (named as the second crystal reverse o-light in the figure and below for explanation) inputted in the reverse direction by the core of the first crystal forward e-light received by the polarization-maintaining dual-core waveguide 160. As shown in the figure, for the first crystal forward e-light propagating in the forward direction along the optical path, the first crystal forward e-light deviates from the optical path in the first birefringent crystal 130 and then exits the first birefringent crystal 130; after passing through the first Faraday rotator 140, the polarization state of the first crystal forward e-light rotates 45° and is aligned with the polarization state of the o-light of the second birefringent crystal 150; after entering the second birefringent crystal 150, the first crystal forward e-light does not deviate from the optical path, and exits from the exit surface of the second birefringent crystal 150 along the same xy coordinate as its position at the incident surface, and then couples into the other core of the polarization-maintaining dual-core waveguide 160. For the reverse o light of the second crystal propagating in the reverse direction along the optical path, the optical path of the reverse o light of the second crystal coincides with the optical path of the forward e light of the first crystal between the forward light output end of the second birefringent crystal 150 and the forward light input end of the first Faraday rotator 140; after passing through the first Faraday rotator 140, the polarization state of the reverse o light of the second crystal rotates by 45°, and the polarization state rotates by 90° cumulatively relative to the forward e light of the first crystal, as shown in FIG. Figure 8b The polarization direction of the forward e-light of the first crystal below changes and the polarization direction of the reverse o-light of the second crystal changes in the opposite direction. In the first birefringent crystal 130, the polarization state of the reverse o-light of the second crystal is perpendicular to the polarization state of the forward e-light of the first crystal, and the o-light and e-light are transformed and propagated in the polarization state of o-light. Therefore, the reverse o-light of the second crystal is emitted from the exit surface of the first birefringent crystal 130 along the same xy coordinate as its position on the incident surface, and deviates from the forward e-light of the first crystal.

[0091] In summary, combined Figure 8a and Figure 8b It can be seen that the second crystal reverse e-light and the second crystal reverse o-light cannot enter the single-core waveguide 110 after passing through the first birefringent crystal 130, thus forming reverse isolation.

[0092] And in this embodiment, if Figure 8a and Figure 8bAs shown, the refractive indexes of the first crystal forward o light and the first crystal forward e light are different in the first birefringent crystal 130, so in the first birefringent crystal 130, the optical path of the first crystal forward o light is not equal to the optical path of the first crystal forward e light, and an optical path difference is generated between the two. The first crystal forward o light propagates as e light in the second birefringent crystal 150, and the first crystal forward e light propagates as o light in the second birefringent crystal 150, so the second birefringent crystal 150 can reduce the optical path difference generated by the first crystal forward o light and the first crystal forward e light at the first birefringent crystal 130. Further, by controlling the optical path difference between the first crystal forward o light and the first crystal forward e light in the first birefringent crystal 130, and the optical path difference between the first crystal forward o light and the first crystal forward e light in the second birefringent crystal 150, when the absolute values ​​of the two differences are equal, the optical path difference can be completely eliminated.

[0093] In order to more intuitively reflect the forward beam splitting and reverse isolation, this embodiment also provides a schematic diagram of the projection position of the incident point and the exit point of the light beam at each birefringent crystal in the xy plane. For details, please refer to Figures 9a to 9c , Figure 9a shows a schematic diagram of the displacement of the forward light, Figure 9b The schematic diagram of the displacement of the reverse e-light of the second crystal is shown in FIG. Fig.9c A schematic diagram of the displacement of the reverse o-light of the second crystal is shown in FIG.

[0094] like Figure 9aAs shown in , after the convergent light output by the lens 120 enters the first birefringent crystal 130 at point A (i.e., the origin of the coordinate system), it is decomposed into o-light and e-light, i.e., the first crystal forward o-light and the first crystal forward e-light. The first crystal forward o-light does not shift in the first birefringent crystal 130 and still emerges at point A (0, 0); the first crystal forward e-light is displaced DexI=a and DeyI=2.41a along the x-axis and y-axis directions respectively, and emerges at point C (a, 2.41a), and the first crystal forward o-light and the first crystal e-light undergo a first relative displacement. After passing through the first Faraday rotator, the forward o light from the first crystal enters the second birefringent crystal 150 and propagates in the polarization state of e light, and produces displacements DexII=a and DeyII=-2.41a along the x-axis and y-axis directions respectively, and emerges at point B (a, -2.41a); the forward e light from the first crystal enters the second birefringent crystal 150 and propagates in the polarization state of o light without displacement. Based on this, the coordinates of the first crystal's forward o-light incident point A are (0, 0), the x-axis coordinates of the exit point B are Dox=DoxI+DexII=0+a=a, the y-axis coordinates are Doy=DoyI+DeyII=0+(-2.41a)=-2.41a, and the coordinates of point B are (a, -2.41a); the coordinates of the first crystal's forward e-light incident point A are (0, 0), the x-axis coordinates of the exit point C are Dex=DexI+DoxII=a+0=a, the y-axis coordinates are Dey=DeyI+DoyII=2.41a+0=2.41a, and the coordinates of point C are (a, 2.41a). The two cores of the polarization-maintaining dual-core waveguide 160 are aligned with points B and C, and the polarization states of the two cores are aligned with the polarization states of the e-light and the o-light of the second birefringent crystal 150, respectively.

[0095] like Figure 9b and Fig.9cAs shown in the figure, the reverse o light of the second crystal enters the second birefringent crystal at point C, propagates in the second birefringent crystal 150 with the polarization state of o light, and after being rotated by the first Faraday rotator, propagates in the first birefringent crystal 130 with the polarization state of o light. The final emission coordinates are rDox=Dex+rDoxII+rDoxI=a+0+0=a, rDoy=Dey+rDoyII+rDoyI=2.41a+0+0=2.41a, and exits the first birefringent crystal at point C (a, 0). The reverse e-light of the second crystal enters the second birefringent crystal at point B, propagates in the second birefringent crystal 150 in the polarization state of e-light, and propagates in the first birefringent crystal 130 in the polarization state of e-light after being rotated by the first Faraday rotator. The final emission coordinates are rDex=Dox+rDexII+rDexI=a+(-a)+(-a)=-a, rDey=Doy+rDeyII+rDeyI=-2.41a+2.41a+(-2.41a)=-2.41a, and exits the first birefringent crystal 130 at point D (-a, -2.41a). Based on this, the emission point C (a, 2.41a) of the reverse o-light of the second crystal and the emission point D (-a, -2.41a) of the reverse e-light of the second crystal are both deviated from the incident point A (0, 0) of the convergent light, so that the reverse light cannot be coupled into the single-core waveguide 110 after passing through the lens, thereby realizing the reverse isolation function.

[0096] In another embodiment, the structure and optical path arrangement of the birefringent crystal are the same as those of the above-mentioned embodiment 1, with the difference that the Faraday rotation direction is changed so that the polarization state of the forward o light of the first crystal in the first birefringent crystal 130-the second birefringent crystal 150 is oo. By reasonably setting the dual-core spacing of the polarization-maintaining dual-core waveguide and the polarization state direction of the waveguide, the polarization splitting and reverse isolation functions can also be achieved. The specific polarization state changes and light displacements are similar and will not be elaborated here.

[0097] Finally, it should be noted that the above embodiments are only exemplary descriptions, and the deviation, direction and distance of the optical path do not constitute a limitation of the present application. Based on the structure proposed in the present application, on the basis of reasonable design of the structure and optical axis of the first birefringent crystal 130 and the second birefringent crystal 150, and the relationship between the polarization states of o-light and e-light, the solutions for forward optical path splitting and reverse optical path isolation should be included in the protection scope of the present application.

[0098] The polarization beam splitter 100 with isolation function provided in the present application performs forward beam splitting and reverse isolation on the converged light, and requires a small number of optical elements, which is conducive to reducing production costs. In addition, the first birefringent crystal 130, the first Faraday rotator 140 and the second birefringent crystal 150 are all parallel plate structures, which are simple in structure and easy to process and manufacture.

[0099] In an embodiment, an angle θ1 between a normal line of a forward light incident surface of the first birefringent crystal 130 and an optical axis of the first birefringent crystal 130 is a first walk-off angle, wherein -90°<θ1<0° or 0°<θ1<90°, and the first walk-off angle is used to control a first forward relative displacement between the first crystal forward o light and the first crystal forward e light and a first reverse relative displacement between the second crystal reverse o light and the second crystal reverse e light in the first birefringent crystal 130.

[0100] In an embodiment, an angle θ2 between a normal line of a forward light incident surface of the second birefringent crystal 150 and an optical axis of the second birefringent crystal 150 is a second walk-off angle, wherein -90°≤θ2<0° or 0°<θ2≤90°. The second walk-off angle is used to control a second forward relative displacement between the forward o light of the first crystal and the forward e light of the first crystal and a second reverse relative displacement between the reverse o light of the second crystal and the reverse e light of the second crystal in the second birefringent crystal 150, as well as an optical path difference between the accumulated o light and the e light of the first birefringent crystal 130 and the second birefringent crystal 150.

[0101] In the embodiment, the xyz coordinate system is established with the positive direction of the optical path (from left to right) as the positive direction of the z-axis. The intersection of the e-light oscillation plane where the optical axis of the first birefringent crystal 130 is located and the xy plane is the first straight line. The angle between the first straight line and the y-axis is The e-light oscillation plane where the optical axis of the second birefringent crystal 150 is located intersects with the xy plane to form a second straight line. The angle between the second straight line and the y axis is m=1 or 3.

[0102] for For details, please refer to Figure 6a About birefringent crystal A210 Description of For details, please refer to Figure 6b About birefringent crystal B220 By and The relationship is set to m=1 or 3, which ensures that the polarization state of the first crystal forward o light emitted from the first birefringent crystal 130 can be aligned with the o light or e light of the second birefringent crystal 150 after passing through the first Faraday rotator 140. satisfy m=1 or 3.

[0103] The reverse isolation function achieved by two birefringent crystals (the first birefringent crystal 130 and the second birefringent crystal 150) and one Faraday rotator (i.e., the first Faraday rotator 140) is called single-stage isolation. On this basis, if you want to achieve better isolation, you can also increase the number of Faraday rotators and birefringent crystals to form a double-stage isolation.

[0104] Specifically, see Fig.10 The polarization beam splitter 100 with isolation function that forms double-stage isolation also includes a second Faraday rotator 170 and a third birefringent crystal 180 that are sequentially arranged between the second birefringent crystal 150 and the polarization-maintaining dual-core waveguide 160 along the forward direction of the optical path. The second Faraday rotator 170 and the third birefringent crystal 180 are both parallel plate structures. An angle θ2 between the normal line of the forward light incident surface of the second birefringent crystal 150 and the optical axis of the second birefringent crystal 150 is a second walk-off angle, where -90°<θ1<0° or 0°<θ1<90°, and the second walk-off angle is used to control the second forward relative displacement and the second reverse relative displacement; an angle θ3 between the normal line of the forward light incident surface of the third birefringent crystal 180 and the optical axis of the third birefringent crystal 180 is a third walk-off angle, where -90°≤θ3<0° or 0°<θ3≤90°, and the third walk-off angle is used to control the third forward relative displacement and the third reverse relative displacement, as well as the accumulated optical path difference of the o-light and the e-light of the first birefringent crystal, the second birefringent crystal and the third birefringent crystal.

[0105] The xyz coordinate system is established with the reverse direction of the optical path as the positive direction of the z-axis. The intersection of the e-light oscillation plane where the optical axis of the second birefringent crystal 150 is located and the xy plane is the second straight line. The angle between the second straight line and the y-axis is The e-light oscillation plane where the optical axis of the third birefringent crystal 180 is located intersects with the xy plane to form a third straight line. The angle between the third straight line and the y axis is in, m=1 or 3, β=45°.

[0106] For the forward light path, Fig.10As shown in , the second birefringent crystal 150 is used to output the first crystal forward o light and the first crystal forward e light to the second Faraday rotator 170. The second Faraday rotator 170 is used to rotate the first crystal forward o light and the first crystal forward e light along the second rotation direction by an angle of β (45°) and then output them to the third birefringent crystal 180. The third birefringent crystal 180 is used to form a third forward relative displacement between the first crystal forward o light and the first crystal forward e light and then output them to the two cores of the polarization-maintaining dual-core waveguide 160 respectively. The polarization states of the two cores of the polarization-maintaining dual-core waveguide 160 are respectively aligned with the polarization states of the first crystal forward o light and the first crystal forward e light output from the third birefringent crystal 180, and the distance between the two cores of the polarization-maintaining dual-core waveguide 160 is equal to the sum of the first forward relative displacement, the second forward relative displacement and the third forward relative displacement between the first crystal forward o light and the first crystal forward e light.

[0107] For the reverse optical path, Fig.11As shown in , when two reverse linear polarized lights enter the two cores of the polarization-maintaining dual-core waveguide 160 in reverse directions along the optical path, the two cores of the polarization-maintaining dual-core waveguide 160 are used to output the two reverse linear polarized lights to the third birefringent crystal 180, respectively, and the polarization states of the two reverse linear polarized lights are aligned with the polarization states of the o-light and the e-light of the third birefringent crystal 180, respectively. The third birefringent crystal 180 is used to form a third reverse relative displacement between the two reverse linear polarized lights, and then output the third crystal reverse o-light and the third crystal reverse e-light to the second Faraday rotator 170. The second Faraday rotator 170 is used to rotate the polarization states of the third crystal reverse o-light and the third crystal reverse e-light along the second rotation direction by an angle of β (45°) and then output them to the second birefringent crystal 150. The second birefringent crystal 150 is used to form a second reverse relative displacement between the third crystal reverse o light and the third crystal reverse e light, and then output it to the first Faraday rotator 140. In the optical path between the forward input end of the second birefringent crystal 150 and the forward output end of the third birefringent crystal 180, the polarization states of the third crystal reverse o light and the third crystal reverse e light in the second birefringent crystal 150 are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the optical paths of the third crystal reverse o light and the third crystal reverse e light in the second birefringent crystal 150 deviate from the forward optical path in the second birefringent crystal 150. The first Faraday rotator 140 is used to rotate the polarization states of the third crystal reverse o light and the third crystal reverse e light along the first rotation direction by an angle of α (45°) and then output it to the first birefringent crystal 130. The first birefringent crystal 130 is used to form a first reverse relative displacement between the reverse o light of the third crystal and the reverse e light of the third crystal. In the optical path between the forward input end of the first birefringent crystal 130 and the forward output end of the second birefringent crystal 150, for the forward light and the reverse light (o light or e light) of the same polarization state in the second birefringent crystal 150, after the first Faraday rotator 140 rotates by an angle α (45°) along the first rotation direction, the polarization state of the reverse light is cumulatively rotated by 90° relative to the forward light, and the o light and the e light are transformed in the first birefringent crystal 130, so that the optical paths of the reverse o light of the third crystal and the reverse e light of the third crystal in the first birefringent crystal 130 deviate from the forward optical path in the first birefringent crystal 130 again, forming a second-level isolation effect. The sum of the third reverse relative displacement, the second reverse relative displacement and the first reverse relative displacement ultimately causes the third crystal reverse o light and the third crystal reverse e light output by the first birefringent crystal 130 to deviate from the forward optical path, and after passing through the lens 120, cannot be coupled into the single-core waveguide 110.

[0108] First see Figures 12a to 12c , the figure shows the structures and optical axes of several different birefringent crystals. Fig.12aAs shown in , the birefringent crystal C230 is a parallel plate structure, with the positive light incident surface as the plane where the x and y axes are located, and the positive direction of the optical path as the positive direction of the z axis, a three-dimensional rectangular coordinate system is established, wherein the normal line of the positive light incident surface of the birefringent crystal C230 is parallel to the z axis. The angle θ between the optical axis of the birefringent crystal C230 and the normal line of the positive light incident surface (i.e., the z axis) is C The straight line where the e-light oscillation plane where the optical axis of the birefringent crystal C230 is located intersects the xy plane, and the angle between this straight line and the y axis is Fig.12a middle Fig.13a FIG. 2 shows a schematic diagram of light displacement of the birefringent crystal C230. The rectangular coordinate system establishment method and reference method are the same as those for the birefringent crystal A210 and the birefringent crystal B220 described above. The same is true below and will not be described in detail here. Fig.13a As shown in the figure, the displacement of the forward o light along the x-axis direction is DoxIII=0, and the displacement along the y-axis direction is DoyIII=0; the displacement of the forward e light along the x-axis direction is DexIII=a, and the displacement along the y-axis direction is DeyI=a / tan(45°)=a; the displacement of the reverse o light along the x-axis direction is rDoxIII=0, and the displacement along the y-axis direction is rDoyIII=0; the displacement of the reverse e light along the x-axis direction is rDexIII=-a, and the displacement along the y-axis direction is rDeyIII=-a / tan(45°)=-a.

[0109] Similarly, if Figure 12b As shown in FIG. , the birefringent crystal D240 is a parallel plate structure, and its walk-off angle is θ D , the straight line where the e-light oscillation plane where the optical axis of the birefringent crystal D240 is located intersects the xy plane, and the angle between this straight line and the y axis is Figure 12b middle Fig.13b A schematic diagram of the light displacement of the birefringent crystal C230 is shown in the figure. As shown in the figure, the displacement of the forward o light along the x-axis direction is DoxIV=0, and the displacement along the y-axis direction is DoyIV=0; the displacement of the forward e light along the x-axis direction is DexIV=0, and the displacement along the y-axis direction is DexIV=-3a; the displacement of the reverse o light along the x-axis direction is rDoxIV=0, and the displacement along the y-axis direction is rDoyIV=0; the displacement of the reverse e light along the x-axis direction is rDexIV=0, and the displacement along the y-axis direction is rDeyIV=3a.

[0110] like Fig.12c As shown in FIG, the birefringent crystal E250 is a parallel plate structure, and its walk-off angle is θ E , the straight line where the e-light oscillation plane where the optical axis of the birefringent crystal E250 is located intersects the xy plane, and the angle between this straight line and the y axis is Fig.12c middle Fig.13c : A schematic diagram of the light displacement of the birefringent crystal E250 is shown in the figure. As shown in the figure, the displacement of the forward o light along the x-axis direction is DoxV=0, and the displacement along the y-axis direction is DoyV=0; the displacement of the forward e light along the x-axis direction is DexV=-a, and the displacement along the y-axis direction is DeyV=-a / tan(315°)=a; the displacement of the reverse o light along the x-axis direction is rDoxV=0, and the displacement along the y-axis direction is rDoyV=0; the displacement of the reverse e light along the x-axis direction is rDexV=a, and the displacement along the y-axis direction is rDeyV=-a.

[0111] For the double-stage isolated polarization beam splitter, the present application exemplarily provides the following embodiments for illustration:

[0112] Example 2

[0113] In this embodiment, the first birefringent crystal 130 adopts the birefringent crystal C230, the second birefringent crystal 150 adopts the birefringent crystal D240, and the third birefringent crystal 180 adopts the birefringent crystal E250. Along the forward direction of the optical path, the polarization state of the first crystal forward o light in the first birefringent crystal 130-second birefringent crystal 150-third birefringent crystal 180 is oeo.

[0114] In this embodiment, the optical path and polarization state of the forward O light of the first crystal and the corresponding reverse O light of the third crystal are as follows: Fig.14a As shown, the optical path and polarization state of the forward e-light of the first crystal and the corresponding reverse e-light of the third crystal change as shown in Fig.14b As shown, the displacement of forward light and reverse light is as follows Figures 15a to 15c As shown, the contents and related principles shown in the figure are consistent with the relevant description of the above-mentioned embodiment 1, and will not be repeated here. Finally, the first crystal forward o light exit point is point B (0, -3a), the first crystal forward e light exit point is point D (0, 2a), and the two cores of the polarization-maintaining dual-core waveguide 160 are aligned with point B and point D respectively. The exit point of the third crystal reverse o light is point B (0, -3a), and the exit point of the third crystal reverse e light is point F (0, 3a), and neither can return to the single-core waveguide 110, achieving reverse isolation.

[0115] In some other embodiments, the structure and optical path arrangement of the birefringent crystal are the same as those of the above-mentioned embodiment 2, except that the polarization state of the forward o light of the first crystal in the first birefringent crystal 130-the second birefringent crystal 150-the third birefringent crystal 180 is any one of ooo, ooe or oee. The specific polarization state changes and light displacements are similar and will not be elaborated here.

[0116] It should also be noted that the above embodiments are only exemplary descriptions, and the deviation, direction and distance of the optical path do not constitute a limitation of the present application. Based on the structure proposed in the present application, on the basis of reasonable design of the structures and optical axes of the first birefringent crystal 130, the second birefringent crystal 150 and the third birefringent crystal 180, and the relationship between the polarization states of o-light and e-light, the solutions for realizing forward optical path splitting and reverse optical path isolation should be included in the protection scope of the present application.

[0117] In the polarization beam splitter 100 with isolation function provided in the embodiment of the present application, by adopting the first birefringent crystal 130, the first Faraday rotator 140, the second birefringent crystal 150, the second Faraday rotator 170 and the third birefringent crystal 180, which are all parallel plate structures and arranged in sequence, while ensuring that the component structure is simple and easy to process, a double-stage isolation of the reverse light beam is formed, thereby further improving the isolation effect.

[0118] Further, in some embodiments, the first birefringent crystal 130, and / or the second birefringent crystal 150, and / or the third birefringent crystal 180 are combined crystals, and the combined crystals are used to form the same relative displacement and compensate for the optical path difference.

[0119] Specifically, see Fig.16a and Fig.16b , the figure takes the first birefringent crystal 130 as a combined crystal as an example, and provides two exemplary explanations, such as Fig.16a As shown in FIG. 1 , the incident surface is also taken as the x-axis and y-axis planes, and the positive direction of the optical path is taken as the positive direction of the z-axis to establish a coordinate system. The first birefringent crystal 130 can be composed of a sub-birefringent crystal 131 and a sub-birefringent crystal 132. With the birefringent crystal 132 The same, and the sub-birefringent crystal 131 satisfies 0°<θ H-1 <90°, the sub-birefringent crystal 132 satisfies 0°<θ H-2 ≤90°, the positions of the sub-birefringent crystal 131 and the sub-birefringent crystal 132 can be interchanged to achieve the same function. Fig.16b As shown in FIG. 1 , the first birefringent crystal 130 may also be composed of a sub-birefringent crystal 133 and a sub-birefringent crystal 134. The angle difference is 90° or 270°, and the sub-birefringent crystal 133 satisfies 0°<θ H-3 ≤90°, the sub-birefringent crystal 134 satisfies 0°<θ H-4 <90°, the positions of the sub-birefringent crystal 133 and the sub-birefringent crystal 134 can be interchanged to achieve the same function. The second birefringent crystal 150 and the third birefringent crystal 180 are similar, and will not be described in detail here.

[0120] Taking the first birefringent crystal 130 as a combined crystal as an example, the sum of the relative displacements of the forward light in the two sub-birefringent crystals forms the same displacement as the first forward relative displacement in the first birefringent crystal 130. The combined crystal can be used to compensate for the optical path difference in a single birefringent crystal, and can also be used to compensate for the optical path difference of multiple birefringent crystals in the full optical path. When compensating a single crystal, the polarization states of the o-light and the e-light in the two sub-birefringent crystals that are both positive birefringent or both negative birefringent can be interchanged in a direction configuration to reduce the total optical path difference; or the two sub-birefringent crystals can be respectively positive birefringent crystals and negative birefringent crystals, and the same polarization state (both o-light or both e-light) is maintained in the positive birefringent crystal and the negative birefringent crystal, thereby reducing the optical path difference. By reasonably setting the angle θ and the thickness of the sub-birefringent crystals, the optical path difference of the o-light and the e-light in each sub-birefringent crystal can be changed. When compensating for the optical path difference of the entire optical path, the sub-birefringent crystal that compensates for the optical path difference in the combined crystal not only achieves the same displacement change as the other sub-birefringent crystal in the combined crystal, but also has its o-light and e-light optical path difference configuration opposite to the direction of the sum of the optical path differences of other birefringent crystals in the entire optical path, thereby reducing the total optical path difference or even making the optical path difference zero, thereby achieving the function of compensating for the optical path difference of the entire optical path.

[0121] According to another aspect of the embodiment of the present application, a polarization beam combiner with isolation function is also provided. Fig.17 and Fig.18 , the figure shows the forward optical path and the reverse optical path of the optical combiner respectively, and the polarization optical combiner 300 with isolation function comprises a polarization-maintaining dual-core waveguide 160, a first birefringent crystal 150, a first Faraday rotator 140, a second birefringent crystal 130, a lens 120 and a single-core waveguide 110 arranged in sequence along the forward direction of the optical path. The first birefringent crystal 150, the first Faraday rotator 140 and the second birefringent crystal 130 are all parallel plate structures.

[0122] like Fig.17As shown, the polarization-maintaining dual-core waveguide 160 is used to introduce two linearly polarized lights that are respectively aligned with their polarization states and output them to the first birefringent crystal 150. The polarization states of the o-light and the e-light of the first birefringent crystal 150 are respectively aligned with the polarization states of the two linearly polarized lights. The first birefringent crystal 150 is used to form a first positive relative displacement between the two linearly polarized lights, and then output them to the first Faraday rotator 140 as the first crystal positive o-light and the first crystal positive e-light. The first Faraday rotator 140 is used to rotate the polarization states of the first crystal positive o-light and the first crystal positive e-light along the first rotation direction by an angle α (45°) and then output them to the second birefringent crystal 130. The second birefringent crystal 130 is used to form a second positive relative displacement between the first crystal positive o-light and the first crystal positive e-light. The sum of the first positive relative displacement and the second positive relative displacement makes the first crystal positive o-light and the first crystal positive e-light overlap into one beam of light, and outputs them to the lens 120 as divergent light. The lens 120 is used to convert the divergent light into convergent light and output the convergent light to the single-core waveguide 110 .

[0123] like Fig.18 As shown in , when the reverse light enters the single-core waveguide 110 in the reverse direction along the optical path, the single-core waveguide 110 is used to output the reverse light in the form of divergent light to the lens 120, and the lens 120 is used to convert the reverse light into convergent light and output it to the second birefringent crystal 130. The second birefringent crystal 130 is used to form a second reverse relative displacement between two reverse linear polarized lights whose polarization states are perpendicular to each other formed by decomposing the reverse light, and then output it to the first Faraday rotator 140. The first Faraday rotator 140 is used to rotate the polarized light of the two reverse linear polarized lights along the first rotation direction by an angle α (45°) and then output it to the first birefringent crystal 150. The first birefringent crystal 150 is used to form a first reverse relative displacement between the two reverse linear polarized lights. In the optical path between the forward input end of the first birefringent crystal 150 and the forward output end of the second birefringent crystal 130, the polarization states of the two reverse linear polarized lights in the first birefringent crystal 150 are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the optical path of the two reverse linear polarized lights in the first birefringent crystal 150 deviates from the forward optical path in the first birefringent crystal 150. Finally, the two reverse linear polarized lights output by the first birefringent crystal 150 cannot be coupled into any core of the polarization-maintaining dual-core waveguide 160.

[0124] It is understandable that the structure of the optical elements and the optical principle used by the polarization light beam combiner 300 with isolation function can be the same as those of the polarization light beam splitter 100 with isolation function. The specific principle will not be described in detail here. The only difference is that the first rotation direction of the first Faraday rotator is rotated in the opposite direction relative to the polarization light beam splitter with isolation function, and the reverse light path of the beam splitter is used as the forward light path of the beam combiner, thus forming the polarization light beam combiner 300 with isolation function. For the polarization light beam combiner 300 with isolation function, please directly refer to the specific embodiments provided below:

[0125] Example 3

[0126] In this embodiment, the forward direction of the beam combiner optical path is from right to left, but for the convenience of analysis, the displacement analysis of the following embodiment still adopts the xyz coordinate system of the beam splitter (the positive direction of the z-axis is from left to right), and still adopts the same optical component configuration as the beam splitter embodiment 1, and the first birefringent crystal 150 still adopts the above Figure 6b The birefringent crystal B220 provided in the embodiment, the second birefringent crystal 130 still adopts the above Figure 6a The birefringent crystal A210 provided in the embodiment and the polarization-maintaining dual-core waveguide 160 still use the same dual-core spacing and polarization direction as in Example 1, and only the first rotation direction of the first Faraday rotator is reversely rotated, that is, the reverse isolation function of the beam splitter is changed to the forward beam combining function of the beam combiner. And along the forward direction of the optical path, the polarization state of the first crystal forward o light in the first birefringent crystal 150-second birefringent crystal 130 is oe.

[0127] The optical path of the polarization beam combiner with isolation function provided in this embodiment is as follows: Fig.19a and Fig.19b As shown, the specific principle is consistent with the above description of the embodiment of the beam splitter with isolation function. In this embodiment, the displacement of the forward light and the reverse light is as shown in Figures 20a to 20c The specific principle is consistent with the above description of Embodiment 1, and will not be described here. Finally, the first crystal forward o light and the first crystal forward e light both emerge from point A (0, 0), which can be coupled into the single-core waveguide; the second crystal reverse o light emerges from point A (0, 0), and the second crystal reverse e light emerges from point F (2a, 0), which cannot return to any core of the polarization-maintaining dual-core waveguide 160.

[0128] In another embodiment, the structure and optical path arrangement of the birefringent crystal are the same as those of the above-mentioned embodiment 3, with the difference that the Faraday rotation direction is changed so that the polarization state of the forward o light of the first crystal in the first birefringent crystal 150-the second birefringent crystal 130 is oo. By reasonably setting the dual-core spacing of the polarization-maintaining dual-core waveguide and the polarization state direction of the waveguide, the polarization beam combining and reverse isolation functions can also be achieved. The specific polarization state changes and light displacements are similar and will not be elaborated here.

[0129] Finally, it should be noted that the above embodiments are only exemplary descriptions, and the deviation, direction and distance of the optical path do not constitute a limitation of the present application. Based on the structure proposed in the present application, on the basis of a reasonable design of the structure and optical axis of the first birefringent crystal 150 and the second birefringent crystal 130, as well as the relationship between the polarization states of o-light and e-light, the solutions for realizing forward optical path combining and reverse optical path isolation should be included in the protection scope of the present application.

[0130] Furthermore, the coordinate system established by the polarization beam combiner with isolation function provided in the embodiment of the present application is the same coordinate system as the coordinate system established in the above description of the polarization beam splitter with isolation function 100, that is, in the beam combiner, the coordinate system is established with the reverse direction of the optical path as the positive direction of the z-axis, and the walk-off angles θ1 and θ2 of the first birefringent crystal 150 and the second birefringent crystal 130, as well as the angle between the straight line where the e-light oscillation plane where their optical axes are located intersects with the xy plane and the y-axis are and The requirements are the same as those for the beam splitter mentioned above and will not be elaborated here.

[0131] The polarization light beam combiner with isolation function provided in the present application is similar to the beam splitter, and has a simple structure, is easy to process and manufacture, and can reduce production costs.

[0132] The above provides a single-stage isolated polarization beam combiner, and the polarization beam combiner can also achieve double-stage isolation. The principle is the same as that of the double-stage isolated polarization beam splitter. The specific embodiments are as follows:

[0133] Example 4

[0134] In this embodiment, the forward direction of the beam combiner optical path is from right to left, but for the convenience of analysis, the displacement analysis of the following embodiment still uses the xyz coordinate system of the beam splitter (z axis is from left to right), and still uses the same optical component configuration as the beam splitter embodiment 1. The first birefringent crystal 180 uses the above-mentioned birefringent crystal E250, the second birefringent crystal 150 uses the above-mentioned birefringent crystal D240, and the third birefringent crystal 130 uses the above-mentioned birefringent crystal C230. The polarization-maintaining dual-core waveguide 160 still uses the same dual-core spacing and polarization direction as in embodiment 2, and only the first rotation direction and the second rotation direction of the first Faraday rotator and the second Faraday rotator are reversely rotated, that is, the reverse isolation function of the beam splitter is changed to the forward beam combining function of the beam combiner. Along the forward direction of the optical path, the polarization state of the first crystal forward o light in the first birefringent crystal 180-the second birefringent crystal 150-the third birefringent crystal 130 is oeo.

[0135] The optical path of the polarization beam combiner with isolation function provided in this embodiment is as follows: Fig.21a and Figure 21b As shown, the displacement of the forward light and the reverse light in this embodiment is as follows Figures 22a to 22c The specific principle is consistent with the relevant description of the above embodiment 2, and will not be repeated here. Finally, the first crystal forward o light and the first crystal forward e light exit points are both point A (0, 0), which can be coupled into the single-core waveguide. The third crystal reverse o light exit point is point A (0, 0), and the third crystal reverse e light exit point is point J (0, -a), and neither can return to any core of the polarization-maintaining dual-core waveguide 160.

[0136] In some other embodiments, the structure and optical path arrangement of the birefringent crystal are the same as those of the above-mentioned embodiment 2, except that the polarization state of the forward o light of the first crystal in the first birefringent crystal 180-the second birefringent crystal 150-the third birefringent crystal 130 is any one of ooo, ooe or oee, and the specific polarization state changes and light displacements are similar, which will not be elaborated here.

[0137] Finally, it should also be noted that the above embodiments are only exemplary descriptions, and the deviation, direction and distance of the optical path do not constitute a limitation of the present application. Based on the structure proposed in the present application, on the basis of reasonably designing the structures and optical axes of the first birefringent crystal 180, the second birefringent crystal 150 and the third birefringent crystal 130, and the relationship between the polarization states of the o-light and the e-light, the solutions for realizing forward optical path combining and reverse optical path isolation should be included in the protection scope of the present application.

[0138] In the polarization beam combiner 300 with isolation function provided in the embodiment of the present application, by adopting the first birefringent crystal 180, the first Faraday rotator 170, the second birefringent crystal 150, the second Faraday rotator 140 and the third birefringent crystal 130, which are all parallel plate structures and arranged in sequence, a double-stage isolation of the reverse light beam is formed while ensuring that the component structure is simple and easy to process, thereby further improving the isolation effect.

[0139] The first birefringent crystal 180, the second birefringent crystal 150 and the third birefringent crystal 130 in the polarization light beam combiner 300 with isolation function provided in the embodiment of the present application can also adopt combined crystals. For details, please refer to the description of the combined crystal in the above-mentioned beam combiner, which will not be repeated here.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application is described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way.

Claims

1. A polarization beam splitter with isolation function, characterized in that: It comprises a single-core waveguide, a lens, a first birefringent crystal, a first Faraday rotator, a second birefringent crystal and a polarization-maintaining double-core waveguide arranged in sequence along the forward direction of the optical path, wherein the first birefringent crystal, the first Faraday rotator and the second birefringent crystal are all parallel plate structures; The single-core waveguide is used to introduce divergent light and output it to the lens; The lens is used to convert the divergent light into convergent light and output it to the first birefringent crystal; The first birefringent crystal is used to decompose the converged light into a first crystal forward o light and a first crystal forward e light with polarization states perpendicular to each other, and after a first forward relative displacement is formed between the first crystal forward o light and the first crystal forward e light, the light is output to the first Faraday rotator; The first Faraday rotator is used to rotate the polarization states of the first crystal forward o light and the first crystal forward e light along the first rotation direction by an angle α and then output them to the second birefringent crystal, wherein α=45°; The second birefringent crystal is used to form a second forward relative displacement between the forward o light of the first crystal and the forward e light of the first crystal, and then output them to the two cores of the polarization-maintaining dual-core waveguide respectively; The distance between the two cores of the polarization-maintaining dual-core waveguide is equal to the sum of the first forward relative displacement and the second forward relative displacement between the first crystal forward o light and the first crystal forward e light, the polarization states of the two cores of the polarization-maintaining dual-core waveguide are respectively aligned with the polarization states of the first crystal forward o light and the first crystal forward e light output from the second birefringent crystal, and the polarization-maintaining dual-core waveguide is used to output the first crystal forward o light and the first crystal forward e light; When two reverse linear polarized lights respectively aligned with the polarization states of the two cores of the polarization-maintaining dual-core waveguide respectively enter the two cores of the polarization-maintaining dual-core waveguide in reverse directions along the optical path, the two cores of the polarization-maintaining dual-core waveguide are used to output the two reverse linear polarized lights respectively to the second birefringent crystal, and the polarization states of the two reverse linear polarized lights are respectively aligned with the polarization state of the o light and the polarization state of the e light of the second birefringent crystal; The second birefringent crystal is used to form a second reverse relative displacement between the two reverse linear polarized lights and then output the second reverse relative displacement to the first Faraday rotator; The first Faraday rotator is used for rotating the polarization states of the two reverse linearly polarized lights by the angle α along the first rotation direction and then outputting them to the first birefringent crystal; The first birefringent crystal is used to form a first reverse relative displacement between the two reverse linear polarized lights. In the optical path between the forward input end of the first birefringent crystal and the forward output end of the second birefringent crystal, the polarization states of the two reverse linear polarized lights in the first birefringent crystal are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the optical path of the two reverse linear polarized lights in the first birefringent crystal deviates from the forward optical path in the first birefringent crystal. Finally, the two reverse linear polarized lights output by the first birefringent crystal cannot be coupled into the single-core waveguide after passing through the lens.

2. The polarization beam splitter with isolation function according to claim 1, characterized in that: Along the forward direction of the optical path, the polarization state of the forward o-light of the first crystal is aligned with the polarization state of the o-light or the polarization state of the e-light of the second birefringent crystal after passing through the first Faraday rotator.

3. The polarization beam splitter with isolation function according to claim 1, characterized in that: An angle θ1 between the normal line of the forward light incident surface of the first birefringent crystal and the optical axis of the first birefringent crystal is a first walk-off angle, wherein -90°<θ1<0° or 0°<θ1<90°, and the first walk-off angle is used to control the first forward relative displacement and the first reverse relative displacement; and / or, The angle θ2 between the normal of the forward light incident surface of the second birefringent crystal and the optical axis of the second birefringent crystal is the second walk-off angle, -90°≤θ2<0° or 0°<θ2≤90°, and the second walk-off angle is used to control the second forward relative displacement and the second reverse relative displacement, as well as the accumulated optical path difference of the o-light and the e-light of the first birefringent crystal and the second birefringent crystal.

4. The polarization beam splitter with isolation function according to claim 1, characterized in that: Establishing an xyz coordinate system with the positive direction of the optical path as the positive direction of the z-axis; The intersection of the e-light oscillation plane where the optical axis of the first birefringent crystal is located and the xy plane is a first straight line, and the angle between the first straight line and the y axis is φ1; The intersection of the e-light oscillation plane where the optical axis of the second birefringent crystal is located and the xy plane is a second straight line, and the angle between the second straight line and the y axis is φ2; Among them, |φ2-φ1|=(m·90°±α), m=1 or 3.

5. The polarization beam splitter with isolation function according to claim 1, characterized in that: It also includes a second Faraday rotator and a third birefringent crystal which are sequentially arranged between the second birefringent crystal and the polarization-maintaining dual-core waveguide along the forward direction of the optical path, and the second Faraday rotator and the third birefringent crystal are both parallel plate structures; An angle θ2 between the normal line of the forward light incident surface of the second birefringent crystal and the optical axis of the second birefringent crystal is a second walk-off angle, where -90°<θ1<0° or 0°<θ1<90°, and the second walk-off angle is used to control the second forward relative displacement and the second reverse relative displacement; an angle θ3 between the normal line of the forward light incident surface of the third birefringent crystal and the optical axis of the third birefringent crystal is a third walk-off angle, where -90°≤θ3<0° or 0°<θ3≤90°, and the third walk-off angle is used to control the third forward relative displacement and the third reverse relative displacement, as well as the accumulated optical path difference of the o-light and the e-light of the first birefringent crystal, the second birefringent crystal and the third birefringent crystal; An xyz coordinate system is established with the positive direction of the optical path as the positive direction of the z-axis, the e-light oscillation plane where the optical axis of the second birefringent crystal is located, the intersection with the xy plane is a second straight line, and the angle between the second straight line and the y-axis is φ2; the e-light oscillation plane where the optical axis of the third birefringent crystal is located, the intersection with the xy plane is a third straight line, and the angle between the third straight line and the y-axis is φ3, wherein, |φ3-φ2|=(m·90°±β), m=1 or 3, β=45°; The second birefringent crystal is used to output the forward o light of the first crystal and the forward e light of the first crystal to the second Faraday rotator; the second Faraday rotator is used to rotate the forward o light of the first crystal and the forward e light of the first crystal along the second rotation direction by the angle β, and then output them to the third birefringent crystal; the third birefringent crystal is used to form a third forward relative displacement between the forward o light of the first crystal and the forward e light of the first crystal, and then output them to the two cores of the polarization-maintaining dual-core waveguide respectively; the polarization states of the two cores of the polarization-maintaining dual-core waveguide are respectively aligned with the polarization states of the forward o light of the first crystal and the forward e light of the first crystal output from the third birefringent crystal, and the distance between the two cores of the polarization-maintaining dual-core waveguide is equal to the sum of the first forward relative displacement, the second forward relative displacement and the third forward relative displacement between the forward o light of the first crystal and the forward e light of the first crystal; When two reverse linear polarized lights respectively enter the two cores of the polarization-maintaining dual-core waveguide in reverse directions along the optical path, the two cores of the polarization-maintaining dual-core waveguide are used to output the two reverse linear polarized lights to the third birefringent crystal respectively, and the polarization states of the two reverse linear polarized lights are respectively aligned with the o-light polarization state and the e-light polarization state of the third birefringent crystal; the third birefringent crystal is used to form the third reverse relative displacement between the two reverse linear polarized lights, and then output the third crystal reverse o-light and the third crystal reverse e-light to the second Faraday rotator; the second Faraday rotator is used to align the third crystal reverse o-light and the third crystal reverse e-light The polarization state is rotated by the angle β along the second rotation direction and then output to the second birefringent crystal; the second birefringent crystal is used to form the second reverse relative displacement between the reverse o light of the third crystal and the reverse e light of the third crystal, and then output to the first Faraday rotator, in the optical path between the forward input end of the second birefringent crystal and the forward output end of the third birefringent crystal, the polarization states of the reverse o light of the third crystal and the reverse e light of the third crystal in the second birefringent crystal are rotated by 90° relative to the forward light, and the o light and the e light are transformed, so that the reverse o light of the third crystal and the reverse e light of the third crystal in the second birefringent crystal are rotated by 90° relative to the forward light, and the o light and the e light are transformed, so that the reverse o light of the third crystal and the reverse e light of the third crystal in the second birefringent crystal are rotated by 90° relative to the forward light. The optical path of the reverse e-light of the third crystal deviates from the forward optical path in the second birefringent crystal; the first Faraday rotator is used to rotate the polarization states of the reverse o-light and the reverse e-light of the third crystal along the first rotation direction by the angle α and then output them to the first birefringent crystal; the first birefringent crystal is used to form the first reverse relative displacement between the reverse o-light of the third crystal and the reverse e-light of the third crystal, and in the optical path between the forward input end of the first birefringent crystal and the forward output end of the second birefringent crystal, for the forward light and the reverse light of the same polarization state in the second birefringent crystal, after passing through the first Faraday rotator, After the optical rotator rotates by an angle α along the first rotation direction, the polarization state of the reverse light is rotated by 90° relative to the forward light, and the o light and the e light are transformed in the first birefringent crystal, so that the optical paths of the third crystal reverse o light and the third crystal reverse e light in the first birefringent crystal deviate from the forward optical path in the first birefringent crystal again; the sum of the third reverse relative displacement, the second reverse relative displacement and the first reverse relative displacement ultimately causes the third crystal reverse o light and the third crystal reverse e light output by the first birefringent crystal to deviate from the forward optical path, and after passing through the lens, they cannot be coupled into the single-core waveguide.

6. The polarization beam splitter with isolation function according to claim 5, characterized in that: Along the forward direction of the optical path, the polarization state of the forward o-light of the first crystal is aligned with the polarization state of the o-light or the polarization state of the e-light of the third birefringent crystal after passing through the second Faraday rotator.

7. The polarization beam splitter with isolation function according to claim 5, characterized in that: The first birefringent crystal, and / or the second birefringent crystal, and / or the third birefringent crystal are combined crystals. In addition to achieving the same relative displacement, the combined crystals can also be used to compensate for optical path differences.

8. A polarization beam combiner with isolation function, characterized in that: It comprises a polarization-maintaining double-core waveguide, a first birefringent crystal, a first Faraday rotator, a second birefringent crystal, a lens and a single-core waveguide which are sequentially arranged along the forward direction of the optical path, wherein the first birefringent crystal, the first Faraday rotator and the second birefringent crystal are all parallel plate structures; The two cores of the polarization-maintaining dual-core waveguide are used to introduce two linearly polarized lights that are respectively aligned with their polarization states and output them to the first birefringent crystal; The polarization states of the o-light and the e-light of the first birefringent crystal are respectively aligned with the polarization states of the two linearly polarized lights, and the first birefringent crystal is used to form a first positive relative displacement between the two linearly polarized lights, and then output the first crystal positive o-light and the first crystal positive e-light to the first Faraday rotator; The first Faraday rotator is used to rotate the polarization states of the first crystal forward o light and the first crystal forward e light along the first rotation direction by an angle α and then output them to the second birefringent crystal, wherein α=45°; The second birefringent crystal is used to form a second positive relative displacement between the positive o light of the first crystal and the positive e light of the first crystal, and the sum of the first positive relative displacement and the second positive relative displacement makes the positive o light of the first crystal and the positive e light of the first crystal overlap into one beam of light, and output it to the lens as divergent light; The lens is used to convert the divergent light into convergent light and output it to the single-core waveguide; When the reverse light enters the single-core waveguide in the reverse direction along the optical path, the single-core waveguide is used to output the reverse light to the lens in the form of divergent light; The lens is used to convert the reverse light into convergent light and output it to the second birefringent crystal; The second birefringent crystal is used to generate a second reverse relative displacement between two reverse linear polarized lights with polarization states perpendicular to each other formed by decomposing the reverse light, and then output the second reverse relative displacement to the first Faraday rotator; The first Faraday rotator is used for rotating the polarization states of the two reverse linearly polarized lights by the angle α along the first rotation direction and then outputting them to the first birefringent crystal; The first birefringent crystal is used to form a first reverse relative displacement between the two reverse linear polarized lights. In the optical path between the forward input end of the first birefringent crystal and the forward output end of the second birefringent crystal, the polarization states of the two reverse linear polarized lights in the first birefringent crystal are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the optical path of the two reverse linear polarized lights in the first birefringent crystal deviates from the forward optical path in the first birefringent crystal. Finally, the two reverse linear polarized lights output by the first birefringent crystal cannot be coupled into any core of the polarization-maintaining dual-core waveguide.

9. The polarization beam combiner with isolation function according to claim 8, characterized in that: Along the forward direction of the optical path, the polarization state of the forward o-light of the first crystal is aligned with the polarization state of the o-light or the polarization state of the e-light of the second birefringent crystal after passing through the first Faraday rotator.

10. The polarization beam combiner with isolation function according to claim 8, characterized in that: An angle θ1 between the normal line of the forward light incident surface of the first birefringent crystal and the optical axis of the first birefringent crystal is a first walk-off angle, wherein -90°<θ1<0° or 0°<θ1<90°, and the first walk-off angle is used to control the first forward relative displacement and the first reverse relative displacement; and / or, The angle θ2 between the normal of the forward light incident surface of the second birefringent crystal and the optical axis of the second birefringent crystal is the second walk-off angle, -90°≤θ2<0° or 0°<θ2≤90°, and the second walk-off angle is used to control the second forward relative displacement and the second reverse relative displacement, as well as the accumulated optical path difference of the o-light and the e-light of the first birefringent crystal and the second birefringent crystal.

11. The polarization beam combiner with isolation function according to claim 8, characterized in that: Establishing an xyz coordinate system with the reverse direction of the optical path as the positive direction of the z-axis; The intersection of the e-light oscillation plane where the optical axis of the first birefringent crystal is located and the xy plane is a first straight line, and the angle between the first straight line and the y axis is φ1; The e-light oscillation plane where the optical axis of the second birefringent crystal is located intersects with the xy plane to form a second straight line, and the angle between the second straight line and the y axis is φ2; Among them, |φ2-φ1|=(m·90°±α), m=1 or 3.

12. The polarization beam combiner with isolation function according to claim 8, characterized in that: It also includes a second Faraday rotator and a third birefringent crystal which are sequentially arranged between the second birefringent crystal and the lens along the forward direction of the optical path, and both the second Faraday rotator and the third birefringent crystal are parallel plate structures; An angle θ2 between the normal line of the forward light incident surface of the second birefringent crystal and the optical axis of the second birefringent crystal is a second walk-off angle, where -90°<θ1<0° or 0°<θ1<90°, and the second walk-off angle is used to control the second forward relative displacement and the second reverse relative displacement; an angle θ3 between the normal line of the forward light incident surface of the third birefringent crystal and the optical axis of the third birefringent crystal is a third walk-off angle, where -90°≤θ3<0° or 0°<θ3≤90°, and the third walk-off angle is used to control the third forward relative displacement and the third reverse relative displacement, as well as the accumulated optical path difference of the o-light and the e-light of the first birefringent crystal, the second birefringent crystal and the third birefringent crystal; An xyz coordinate system is established with the reverse direction of the optical path as the positive direction of the z-axis, the e-light oscillation plane where the optical axis of the second birefringent crystal is located, the intersection with the xy plane is a second straight line, and the angle between the second straight line and the y-axis is φ2; the e-light oscillation plane where the optical axis of the third birefringent crystal is located, the intersection with the xy plane is a third straight line, and the angle between the third straight line and the y-axis is φ3, wherein, |φ3-φ2|=(m·90°±β), m=1 or 3, β=45°; The second birefringent crystal is used to form a second forward relative displacement between the forward o light of the first crystal and the forward e light of the first crystal, and then output it to the second Faraday rotator; the second Faraday rotator is used to rotate the polarization states of the forward o light of the first crystal and the forward e light of the first crystal along the second rotation direction by the angle β, and then output it to the third birefringent crystal; the third birefringent crystal is used to form a third forward relative displacement between the forward o light of the first crystal and the forward e light of the first crystal, and the sum of the first forward relative displacement, the second forward relative displacement and the third forward relative displacement makes the forward o light of the first crystal and the forward e light of the first crystal overlap into a beam of light, and output it to the lens as divergent light; the lens is used to convert the divergent light into convergent light and output it to the single-core waveguide; When the reverse light enters the single-core waveguide in the reverse direction along the optical path, the single-core waveguide is used to output the reverse light in the form of divergent light to the lens; the lens is used to convert the reverse light into convergent light and output it to the third birefringent crystal; the third birefringent crystal is used to decompose the reverse light into a third crystal reverse o light and a third crystal reverse e light whose polarization states are perpendicular to each other, and then output them to the second Faraday rotator, so that the third crystal reverse o light and the third crystal reverse e light form the third reverse relative displacement; the second Faraday rotator is used to convert the polarization states of the third crystal reverse o light and the third crystal reverse e light along the The second rotation direction is rotated by the angle β and then output to the second birefringent crystal; the second birefringent crystal is used to make the reverse o light of the third crystal and the reverse e light of the third crystal form the second reverse relative displacement, and then output to the first Faraday rotator, in the optical path between the forward input end of the second birefringent crystal and the forward output end of the third birefringent crystal, the polarization states of the reverse o light of the third crystal and the reverse e light of the third crystal in the second birefringent crystal are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the reverse o light of the third crystal and the reverse e light of the third crystal in the second birefringent crystal are rotated 90° relative to the forward light, and the o light and the e light are transformed, so that the reverse o light of the third crystal and the reverse e light of the third crystal in the second birefringent crystal are rotated 90° relative to the forward light. The optical path of the reverse e light deviates from the forward optical path in the second birefringent crystal; the first Faraday rotator is used to rotate the polarization states of the reverse o light of the third crystal and the reverse e light of the third crystal along the first rotation direction by the angle α and then output them to the first birefringent crystal; the first birefringent crystal is used to form the first reverse relative displacement between the reverse o light of the third crystal and the reverse e light of the third crystal, and in the optical path between the forward input end of the first birefringent crystal and the forward output end of the second birefringent crystal, for the forward light and the reverse light of the same polarization state in the second birefringent crystal, after the first Faraday rotator After the device rotates by an angle α along the first rotation direction, the polarization state of the reverse light is rotated by 90° relative to the forward light, and the o light and the e light are transformed in the first birefringent crystal, so that the optical paths of the third crystal reverse o light and the third crystal reverse e light in the first birefringent crystal deviate from the forward optical path in the first birefringent crystal again; the sum of the third reverse relative displacement, the second reverse relative displacement and the first reverse relative displacement ultimately causes the third crystal reverse o light and the third crystal reverse e light output by the first birefringent crystal to deviate from the forward optical path, and cannot be coupled into any core of the polarization-maintaining dual-core waveguide.

13. The polarization beam combiner with isolation function according to claim 12, characterized in that: Along the forward direction of the optical path, the polarization state of the forward o-light of the first crystal is aligned with the polarization state of the o-light or the polarization state of the e-light of the third birefringent crystal after passing through the second Faraday rotator.

14. The polarization beam combiner with isolation function according to claim 12, characterized in that: The first birefringent crystal, and / or the second birefringent crystal, and / or the third birefringent crystal are combined crystals. In addition to achieving the same relative displacement, the combined crystals can also be used to compensate for optical path differences.

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