Polarization-maintaining circulator

Abstract

The invention relates to the technical field of optics, and discloses a polarization-maintaining circulator which comprises a dual-core waveguide, a first birefringent crystal, a first Faraday rotator, a second birefringent crystal, a lens and a second port which are sequentially arranged in the first direction and used for achieving a first port and a third port. The first birefringent crystal, the first Faraday rotator and the second birefringent crystal are all of a parallel plate structure, light input by the first port is transmitted to the second port in the first direction, light input by the second port is transmitted to the third port in the second direction, and the first direction is opposite to the second direction. By means of the mode, the device structure is simplified, and miniaturization of the circulator is achieved.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of optical technology, and in particular to a polarization-maintaining circulator. Background Art

[0002] An optical circulator is a multi-port non-reciprocal optical passive device that allows optical signals to be transmitted only along a specified port sequence and prevents optical signals from being transmitted in the reverse direction. Optical circulators are widely used in single-fiber bidirectional communication, optical signal add / drop, and dispersion compensation in optical communications and optical sensing.

[0003] At present, optical circulators are mainly divided into two categories of design. One is that port one, port two and port three face three different directions respectively, and the device appearance is rectangular. This structure occupies a large space and is extremely inconvenient to arrange; the other is that port one and port three face the same direction, and port two faces the opposite direction. The device appearance is cylindrical. Although this design solves the problem of large space occupation of the previous solution, the overall length is still long. In addition, both of the above solutions are parallel optical path designs, and both require the use of 2 or 3 collimators (such as waveguide + lens) and polarization beam splitters, at least one or more Faraday rotators, half-wave plates, Wollaston wedge angle pairs or polarization beam combiner components, resulting in many parts, complex processes and instability. Summary of the invention

[0004] In view of the above problems, an embodiment of the present application provides a polarization-maintaining circulator to simplify the device structure and achieve miniaturization of the device.

[0005] The embodiment of the present application provides a polarization-maintaining circulator, which is used to transmit light input from port one to port two in a first direction, and to transmit light input from port two to port three in a second direction, wherein the first direction is opposite to the second direction; the polarization-maintaining circulator comprises: a dual-core waveguide, a first birefringent crystal, a first Faraday rotator, a second birefringent crystal, a lens and the port two, which are sequentially arranged along the first direction, and the first birefringent crystal, the first Faraday rotator and the second birefringent crystal are all parallel plate structures; wherein the port one is a polarization-maintaining port, which is used to input divergent linearly polarized light. , the light input from the port one enters the first birefringent crystal as o light or e light; the first birefringent crystal is used to make the light input from the port one form a positive displacement toward the first birefringent crystal and then emit it to the first Faraday rotator; the first Faraday rotator is used to rotate the polarization state of the light input from the port one along a first rotation direction by an angle α and then emit it to the second birefringent crystal, wherein α=45°; the second birefringent crystal is used to make the light input from the port one form a positive displacement toward the second birefringent crystal and then emit it to the lens; the lens is used to perform optical shaping on the light input from the port one and then emit it to the port two; the port two is used to output the The light input from the port one is transmitted from the port one to the port two; the port two is also used to input light and direct the input light to the lens; the lens is also used to optically converge the light input from the port two and direct it to the second birefringent crystal; the second birefringent crystal is also used to make the light input from the port two form a reverse second birefringent crystal displacement and then direct it to the first Faraday rotator, the first Faraday rotator is also used to rotate the polarization state of the light input from the port two along the first rotation direction by the angle α and then direct it to the first birefringent crystal; the first birefringent crystal is also used to make the light input from the port two form a reverse second birefringent crystal displacement and then direct it to the first Faraday rotator The first birefringent crystal is displaced and directed toward the port three, wherein the polarization state of the light input from the port two in the first birefringent crystal is rotated 90° relative to the polarization state of the light input from the port one, and the o light and the e light are transformed, so that the light input from the port two deviates from the light input from the port one in the first birefringent crystal, and the lateral walk-off generated between the light input from the port one and the light input from the port two is equal to the dual-core spacing of the dual-core waveguide, so that the light input from the port two is coupled into the port three; the port three is used to output the light input from the port two, so as to realize the transmission of light from the port two to the port three.

[0006] The polarization-maintaining circulator provided in the present application is designed for non-parallel light paths to achieve transmission of optical signals along a specified port sequence and prevent optical signals from being transmitted in the reverse direction. No complicated optical elements are required, and a small number of optical elements are required, which is conducive to product miniaturization and reduction of 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.

[0007] The above description is only an overview of the technical solution of the embodiment of the present application. In order to more clearly understand the technical means of the embodiment 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 embodiment 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

[0008] The accompanying drawings are only used to illustrate the embodiments and are not to be considered as limiting the present application. In addition, the same reference symbols are used to represent the same components throughout the accompanying drawings. In the accompanying drawings:

[0009] Figure 1a A schematic diagram of the birefringence phenomenon and light displacement of a positive birefringent crystal provided in an embodiment of the present application;

[0010] Figure 1b A schematic diagram of the birefringence phenomenon and light displacement of a positive birefringent crystal provided in an embodiment of the present application;

[0011] Figure 2a A schematic diagram of the birefringence phenomenon and light displacement of a negative birefringence crystal provided in an embodiment of the present application;

[0012] Figure 2b A schematic diagram of the birefringence phenomenon and light displacement of a negative birefringence crystal provided in an embodiment of the present application;

[0013] Figure 3 A schematic diagram of the optical path of a three-port full polarization-maintaining waveguide polarization-maintaining circulator with all-optical waveguide input and output provided in Example 1 of the present application;

[0014] Figure 4 A schematic diagram of the structure and optical axis of the birefringent crystal A1 provided in an embodiment of the present application;

[0015] Figure 5 A schematic diagram of the structure and optical axis of the birefringent crystal B1 provided in an embodiment of the present application;

[0016] Figure 6a A schematic diagram of the displacement of forward light and reverse light in the birefringent crystal A1 provided in an embodiment of the present application;

[0017] Figure 6b A schematic diagram of the displacement of forward light and reverse light in the birefringent crystal B1 provided in an embodiment of the present application;

[0018] Figure 7 A schematic diagram of the optical paths of the o-light incident from port 1 and the e-light incident from port 2 in the polarization-maintaining circulator provided in Example 1 of the present application;

[0019] Figure 8 A schematic diagram of the displacement of linearly polarized light incident from port 1 to port 2 (first direction) and from port 2 to port 3 (second direction) in the crystal after the linearly polarized light incident from port 1 enters the birefringent crystal 22 as o-light in the polarization-maintaining circulator provided in Example 1 of the present application;

[0020] Fig. 9 A schematic diagram of the optical path of e-light incident from port three in the polarization-maintaining circulator provided in Example 1 of the present application;

[0021] Fig.10 A schematic diagram of the reverse isolation displacement of the linearly polarized light incident from port 3 to port 2 in the polarization-maintaining circulator provided in Example 1 of the present application after the linearly polarized light incident from port 3 enters the birefringent crystal 22 as e-light;

[0022] Fig.11 A schematic diagram of the optical path of a 4-port full polarization-maintaining waveguide polarization-maintaining circulator with all-optical waveguide input and output provided in Example 2 of the present application;

[0023] Fig.12 A schematic diagram of the optical paths of the e-light incident from the third port and the o-light incident from the fourth port in the polarization-maintaining circulator provided in Example 2 of the present application;

[0024] Fig.13 A schematic diagram of the displacement of linearly polarized light incident from port three to port four and from port four to port one in the polarization-maintaining circulator provided in Example 2 of the present application after the linearly polarized light incident from port three enters the birefringent crystal 22 as e-light;

[0025] Fig.14 A schematic diagram of the optical path of a single-stage isolated polarization-maintaining circulator with three ports and non-full polarization-maintaining waveguides with all-optical waveguide input and output provided in Example 3 of the present application;

[0026] Fig.15a A schematic diagram of the structure and optical axis of the birefringent crystal C1 provided in an embodiment of the present application;

[0027] Fig.15b A schematic diagram of the displacement of forward light and reverse light in the birefringent crystal C1 provided in an embodiment of the present application;

[0028] Fig.16a A schematic diagram of the displacement of linearly polarized light incident from port 1 to port 2 in the crystal after incident on the birefringent crystal 22 as o light in the polarization-maintaining circulator provided in Example 3 of the present application;

[0029] Fig.16b A schematic diagram of the displacement of light incident from port 2 to port 3 in the polarization-maintaining circulator provided in Example 3 of the present application after the light incident from port 2 enters the birefringent crystal 27 as o light and e light;

[0030] Fig.17a A schematic diagram of the optical path of o-light incident from port three in the polarization-maintaining circulator provided in Example 3 of the present application;

[0031] Fig.17b A schematic diagram of the optical path of e-light incident from port three in the polarization-maintaining circulator provided in Example 3 of the present application;

[0032] Fig.17c A schematic diagram of the reverse isolation displacement of the linearly polarized light incident from port 3 to port 2 in the polarization-maintaining circulator provided in Example 3 of the present application after the linearly polarized light incident from port 3 enters the birefringent crystal 22 as o light;

[0033] Fig.17d A schematic diagram of the reverse isolation displacement of the linearly polarized light incident from port 3 to port 2 in the polarization-maintaining circulator provided in Example 3 of the present application after the linearly polarized light incident from port 3 enters the birefringent crystal 22 as e-light;

[0034] Fig.18 A schematic diagram of the optical path of another 3-port non-full-polarization-maintaining waveguide single-stage isolated polarization-maintaining circulator with all-optical waveguide input and output provided in Example 4 of the present application;

[0035] Fig.19a A schematic diagram of the displacement of linearly polarized light incident from port 1 to port 2 in the crystal after incident on the birefringent crystal 27 as o light in the polarization-maintaining circulator provided in Example 4 of the present application;

[0036] Fig.19b A schematic diagram of the displacement of light incident from port 2 to port 3 in the polarization-maintaining circulator provided in Example 4 of the present application after the light incident from port 2 enters the birefringent crystal 24 as o light and e light;

[0037] Fig.20a A schematic diagram of the optical path of o-light incident from port three in the polarization-maintaining circulator provided in Example 4 of the present application;

[0038] Fig.20b A schematic diagram of the optical path of e-light incident from port three in the polarization-maintaining circulator provided in Example 4 of the present application;

[0039] Fig.20c A schematic diagram of the reverse isolation displacement of the linearly polarized light incident from port 3 to port 2 in the polarization-maintaining circulator provided in Example 4 of the present application after the linearly polarized light incident from port 3 enters the birefringent crystal 27 as o light;

[0040] Fig.20dA schematic diagram of the reverse isolation displacement of the linearly polarized light incident from port 3 to port 2 in the polarization-maintaining circulator provided in Example 4 of the present application after the linearly polarized light incident from port 3 enters the birefringent crystal 27 as e-light;

[0041] Fig.21a A schematic diagram of the optical path of a three-port non-full-polarization-maintaining waveguide dual-stage isolation polarization-maintaining circulator with all-optical waveguide input and output provided in Example 5 of the present application;

[0042] Figure 21b A schematic diagram of the structure and optical axis of the birefringent crystal D1 provided in an embodiment of the present application;

[0043] Fig.21c A schematic diagram of the displacement of forward light and reverse light in the birefringent crystal D1 provided in an embodiment of the present application;

[0044] Fig.22a A schematic diagram of the displacement of linearly polarized light incident from port 1 to port 2 in the crystal after incident on the birefringent crystal 22 as o light in the polarization-maintaining circulator provided in Example 5 of the present application;

[0045] Figure 22b A schematic diagram of the displacement of light incident from port 2 to port 3 in the polarization-maintaining circulator provided in Example 5 of the present application after the light incident from port 2 enters the birefringent crystal 27 as o light and e light;

[0046] Fig.23a A schematic diagram of the optical path of o-light incident from port three in the polarization-maintaining circulator provided in Example 5 of the present application;

[0047] Figure 23b A schematic diagram of the optical path of e-light incident from port three in the polarization-maintaining circulator provided in Example 5 of the present application;

[0048] Fig.23c A schematic diagram of the reverse isolation displacement of the linearly polarized light incident from port 3 to port 2 in the polarization-maintaining circulator provided in Example 5 of the present application after the linearly polarized light incident from port 3 enters the birefringent crystal 22 as o light;

[0049] Fig.23d A schematic diagram of the reverse isolation displacement of the linearly polarized light incident from port 3 to port 2 in the polarization-maintaining circulator provided in Example 5 of the present application after the linearly polarized light incident from port 3 enters the birefringent crystal 22 as e-light;

[0050] Fig.24 A schematic diagram of the optical path of a three-port fully polarization-maintaining polarization-maintaining circulator with parallel light output from port two provided in Example 6 of the present application;

[0051] Fig.25aA schematic diagram of the optical path of a three-port non-full-polarization-maintaining single-stage isolated polarization-maintaining circulator with parallel light output from port two provided in Example 7 of the present application;

[0052] Fig.25b A schematic diagram of the optical path of another three-port non-full-polarization-maintaining single-stage isolated polarization-maintaining circulator with parallel light output from two ports provided in Example 8 of the present application;

[0053] Fig.26 A schematic diagram of the optical path of a three-port non-full-polarization-maintaining double-stage isolated polarization-maintaining circulator with parallel light output from port two provided in Example 9 of the present application;

[0054] Fig. 27 In the embodiment 10 of the present application provided Fig.24 A schematic diagram of the optical path of a polarization-maintaining circulator in which a filter is added to the polarization-maintaining circulator shown;

[0055] Fig.28a In the embodiment 11 of the present application provided Fig.25a A schematic diagram of the optical path of a polarization-maintaining circulator in which a filter is added to the polarization-maintaining circulator shown;

[0056] Fig.28b In the embodiment 12 of the present application provided Fig.25b A schematic diagram of the optical path of a polarization-maintaining circulator in which a filter is added to the polarization-maintaining circulator shown;

[0057] Fig.29 In the embodiment 13 of the present application provided Fig.26 A schematic diagram of the optical path of a polarization-maintaining circulator in which a filter is added to the polarization-maintaining circulator shown;

[0058] Fig.30a The first birefringent crystal provided in the embodiment of the present application is a schematic diagram of the structure and optical axis of a combined crystal;

[0059] Fig.30b A first birefringent crystal provided as another embodiment of the present application is a schematic diagram of the structure and optical axis of a combined crystal. DETAILED DESCRIPTION

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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).

[0066] 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.

[0067] In the process of implementing the embodiments of the present application, the inventors found that the existing circulators have complex structures, high costs, and poor process stability. In view of the above problems, the embodiments of the present application provide a converging light path circulator with a minimalist structure, which uses a birefringent crystal and a Faraday rotator to process the converging light. Ports 1 and 3 of the circulator face the same direction, have a simple structure, greatly reduce the space size, greatly simplify the manufacturing process, and greatly improve the manufacturability of the product.

[0068] For the phenomenon of double refraction and light displacement in crystals, see Figure 1a and Figure 1b Take the case of a light beam incident on positive birefringent crystal A. When the polarization state of the light beam incident on positive birefringent crystal A is not aligned with the o-light and e-light of positive birefringent crystal A, the light beam will be decomposed into o-light and e-light in positive birefringent crystal A. The o-light follows the law of refraction, and the angle of the light beam does not change. It enters and exits positive birefringent crystal A 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 positive birefringent crystal A, forming a certain displacement d before exiting positive birefringent crystal A. 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 negative birefringent crystal B is shown in the figure. Figure 2a and Figure 2b As shown, no further details are given here.

[0069] Since the e-ray deflection directions of positive birefringent crystals and negative birefringent crystals are opposite, for the sake of simplicity, the following is an example of a positive birefringent crystal. The angle θ between the optical axis of the positive birefringent crystal A 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-ray and the e-ray after the light passes through the positive birefringent crystal A. When 0°<θ<90°, such as Figure 1a As shown, the e-light is deflected upward to form a displacement d; when -90°<θ<0°, as shown Figure 1b As shown, 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.

[0070] According to one aspect of an embodiment of the present application, a polarization-maintaining circulator is provided, which is used to transmit light input from port one to port two in a first direction, and to transmit light input from port two to port three in a second direction, wherein the first direction and the second direction are opposite. Unless otherwise specified, in the drawings of the embodiments of the present application, ① represents port one, ② represents port two, ③ represents port three, and ④ represents port four. Unless otherwise specified, port 1 in all drawings is port one described in the text section of the present application, port 2 is port two described in the text section of the present application, and port 3 is port three described in the text section of the present application. For details, please refer to Figure 3, the figure shows the structure of a polarization-maintaining circulator provided by an embodiment of the present application. As shown in the figure, the polarization-maintaining circulator 100 includes a dual-core waveguide 21, a first birefringent crystal 22, a first Faraday rotator 23, a second birefringent crystal 24, a lens 25 and a port 2, which are sequentially arranged along a first direction to realize a port 1 and a port 3. The port 1 is a polarization-maintaining port, and the first birefringent crystal 22, the first Faraday rotator 23 and the second birefringent crystal 24 are all parallel plate structures.

[0071] The following describes the embodiments of the present application based on the transmission process of light between ports.

[0072] 1. Port 1 to Port 2:

[0073] Port 1 is used to input divergent linear polarized light with a fixed polarization direction. The light input from port 1 enters the first birefringent crystal 22 as o light or e light ( Figure 3 Take o light as an example for illustration). The first birefringent crystal 22 is used to make the light input from port one form a first crystal forward displacement and then emit it to the first Faraday rotator 23. The first Faraday rotator 23 is used to rotate the polarization state of the light input from port one by an angle of α (45°) along the first rotation direction and then emit it to the second birefringent crystal 24. The second birefringent crystal 24 is used to make the light input from port one form a second crystal forward displacement and then emit it to the lens 25. The lens 25 is used to perform optical shaping (which can be convergence or collimation) on the light input from port one and then emit it to port two. Port two is used to output the light input from port one, so as to realize the transmission of light from port one to port two.

[0074] In the first direction, the polarization state of the o-light of the first birefringent crystal 22 is aligned with the polarization state of the o-light or the e-light of the second birefringent crystal 24 after passing through the first Faraday rotator 23. Figure 3 In the specific embodiment shown, along the first direction of light, the polarization state of the o light of the first birefringent crystal 22 is aligned with the polarization state of the e light of the second birefringent crystal 24 after passing through the first Faraday rotator 23, that is, Figure 3 As shown in the figure, when the light input from port 1 enters the first birefringent crystal 22 as o light, it is emitted in the same direction as the incident light without optical path deviation. After passing through the first Faraday rotator 23, the polarization state is rotated by 45° (either clockwise or counterclockwise). After the rotation, the polarization state of the light is aligned with the polarization state of the e light of the second birefringent crystal 24, and optical path deviation occurs in the second birefringent crystal 24.

[0075] In some other embodiments, along the first direction, the polarization state of the o-light of the first birefringent crystal 22 can also be aligned with the polarization state of the o-light of the second birefringent crystal 24 after passing through the first Faraday rotator 23. The o-light of the first birefringent crystal 22 is also incident and emitted in the second birefringent crystal 24 in the same direction, and no optical path deviation occurs.

[0076] 2. Port 2 to Port 3:

[0077] Port 2 is used to input divergent linear polarized light with a fixed polarization direction and direct the input light toward lens 25. Lens 25 is used to optically converge the light input from port 2 and direct it toward second birefringent crystal 24. Second birefringent crystal 24 is used to make the light input from port 2 form a second crystal reverse displacement and direct it toward first Faraday rotator 23. In other embodiments, the light input from port 2 may also be randomly polarized light, which will be described in detail with specific embodiments below.

[0078] The first Faraday rotator 23 is used to rotate the polarization state of the light input from the second port by an angle of α (45°) along the first rotation direction and then emit it to the first birefringent crystal 22. As mentioned above, the rotation of the polarization state of the light beam by the Faraday rotator is Figure 3 In the figure, if viewed from left to right, the polarization states of the light from port 1 to port 2 and the light from port 2 to port 3 are both rotated in the clockwise direction or in the counterclockwise direction when passing through the first Faraday rotator 23. Therefore, after the light input from port 2 passes through the first Faraday rotator 23, its polarization state is rotated 90° in the first birefringent crystal 22 relative to the light input from port 1, and the o-light and the e-light are transformed.

[0079] Based on this, in the optical path, between port two and the output end of the first Faraday rotator 23 along the second direction, the optical paths of the light input from port one and the light input from port two are completely overlapped, except that the transformation and relative displacement of the o-light and the e-light occur in the first birefringent crystal 22.

[0080] The light continues to enter the first birefringent crystal 22. The first birefringent crystal 22 is used to make the light input from port 2 form the first crystal reverse displacement and then emit to port 3. As shown above, the polarization state of the light input from port 2 in the first birefringent crystal 22 is rotated 90° relative to the polarization state of the light input from port 1, and the o light and the e light are transformed, so that the light input from port 2 deviates from the light input from port 1 in the first birefringent crystal 22, and the lateral walk-off generated between the light input from port 1 and the light input from port 2 is equal to the dual-core spacing of the dual-core waveguide 21, so that the light input from port 2 is coupled into port 3. Port 3 is used to output the light input from port 2, so as to realize the transmission of light from port 2 to port 3. Among them, the lateral walk-off is equal to the relative displacement formed by the sum of the forward displacement of the first crystal, the forward displacement of the second crystal, the reverse displacement of the second crystal and the reverse displacement of the first crystal.

[0081] In order to facilitate the understanding of the specific embodiment, the following description is made by taking the case where the light input from port 1 is incident normally on the first birefringent crystal 22 as an example. For the case where the light input from port 1 is incident obliquely, 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 description. 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 4 and Figure 5 , Figure 4 The structure and optical axis of the birefringent crystal A1 are schematically shown in FIG. Figure 5 Schematically shows the structure and optical axis of the birefringent crystal B1.

[0082] like Figure 4 As shown in , the birefringent crystal A1 is a parallel plate structure, with the light incident surface of port one as the plane where the x and y axes are located, and the first direction as the positive direction of the z axis, a three-dimensional rectangular coordinate system is established, wherein the normal line of the incident surface of the light input from port one at the birefringent crystal A1 is parallel to the z axis. The angle θ between the optical axis of the birefringent crystal A1 and the normal line of the light incident surface of port one (i.e., the z axis) is A1 The angle between the straight line where the e-light oscillation plane where the optical axis of the birefringent crystal A1 is located and the intersection of the xy plane and the y-axis is Figure 4 middle Figure 6a 6 and subsequent schematic diagrams of light displacement in the birefringent crystal A1 (the first direction is defined as the positive direction and the second direction is defined as the negative direction). The incident point of the light input from port 1 is used as the origin to form an x-axis and y-axis rectangular coordinate system on the incident surface of the birefringent crystal A1. Whether it is the relative displacement of the light input from port 1 or the relative displacement of the light input from port 2, the xyz coordinate system of the light input from port 1 is referred to. Figure 6aAs shown in , after the light input from port 1 is incident on the birefringent crystal A1, the forward o light component follows the law of refraction, does not shift in the xy plane, and exits the birefringent crystal A1 at the origin, that is, the displacement of the forward o light in the x-axis direction in the birefringent crystal A1 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=2a, and the displacement along the y-axis direction is set to DeyI=0. Correspondingly, the incident reverse o light also does not shift, and the displacement of the reverse e light along the x-axis direction in the birefringent crystal A1 is rDexI=-2a, rDeyI=0. Of course, other displacement values ​​can be used according to specific circumstances, and are not limited here.

[0083] like Figure 5 As shown in FIG, birefringent crystal B1 is also a parallel plate structure, and a three-dimensional rectangular coordinate system is established in birefringent crystal B1 in the same way as birefringent crystal A1. The angle θ between the optical axis of birefringent crystal B1 and the normal line of the light incident surface of port 1 (i.e., the z-axis) is B1 The angle between the straight line where the e-light oscillation plane where the optical axis of the birefringent crystal B1 is located and the intersection of the xy plane and the y-axis is Figure 5 middle Figure 6b FIG. 4 is a schematic diagram showing the displacement of light in the birefringent crystal B1. The coordinate system is established and referenced in the same manner as the birefringent crystal A1. Figure 6b As shown in , the displacement of the normal incident forward e-light in the birefringent crystal B1 is DexII=-a, DeyII=a, and correspondingly, the displacement of the normal incident reverse e-light in the birefringent crystal B1 is rDexII=a, rDeyII=-a. Of course, other displacement values ​​can be used according to specific circumstances, which are not limited here.

[0084] In the embodiment of the present application, the first birefringent crystal 22 adopts the above-mentioned birefringent crystal A1, and the second birefringent crystal 24 adopts the above-mentioned birefringent crystal B1. The angle θ1 between the normal line of the incident surface of the first birefringent crystal 22 and the optical axis of the first birefringent crystal 22 of the light input from port 1 is the first walk-off angle, -90°<θ1<0° or 0°<θ1<90°, and the first walk-off angle is used to control the forward displacement of the first crystal and the reverse displacement of the first crystal.

[0085] In the embodiment of the present application, the angle θ2 between the normal of the incident surface of the second birefringent crystal 24 and the optical axis of the second birefringent crystal 24 of the light input from port 1 is the second walk-off angle, -90°<θ2<0° or 0°<θ2<90°, and the second walk-off angle is used to control the forward displacement of the second crystal and the reverse displacement of the second crystal.

[0086] In the embodiment of the present application, an xyz coordinate system is established with the first direction as the positive direction of the z-axis; the e-light oscillation plane where the optical axis of the first birefringent crystal 22 is located intersects with the xy plane as a first straight line, and 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 24 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 in, or

[0087] for For details, please refer to Figure 4 About birefringent crystal A1 Description of For details, please refer to Figure 5 About birefringent crystal B1 By and The relationship is set to or It is ensured that the polarization state of the light emitted from the first birefringent crystal 22 can be aligned with the o-light or e-light of the second birefringent crystal 24 after passing through the first Faraday rotator 23. satisfy or

[0088] Regarding whether the port maintains polarization:

[0089] Figure 3 In the illustrated embodiment, all ports are polarization-maintaining ports, that is, a full polarization-maintaining solution is provided, wherein port 1, port 2, and port 3 are all polarization-maintaining ports, the polarization state of port 2 is aligned with the polarization state of light input from port 1 along the first direction and emitted through lens 25, and the polarization state of port 3 is aligned with the polarization state of light input from port 2 along the second direction and emitted through the first birefringent crystal 22. The following will be described by taking Embodiment 1, Embodiment 2, Embodiment 6, and Embodiment 10 as examples.

[0090] In some other embodiments, port 1 is a polarization-maintaining port, and whether port 2 and port 3 are polarization-maintaining is not limited. For example, port 2 can be a polarization-maintaining port or a non-polarization-maintaining port, and port 3 can be a polarization-maintaining port or a non-polarization-maintaining port. The circulator formed can be a full polarization-maintaining circulator or a non-full polarization-maintaining circulator. The following will be described by taking Embodiment 3, Embodiment 4, Embodiment 5, Embodiment 7, Embodiment 8, Embodiment 9, Embodiment 11, Embodiment 12 and Embodiment 13 as examples.

[0091] Characteristics of the input / output light of port 2:

[0092] Figure 3In the illustrated embodiment, port 2 is a single-core waveguide 26, which is used to output convergent light or input divergent light; lens 25 is used to converge light input from port 1 to form convergent light, and couple it into single-core waveguide 26, and single-core waveguide 26 is used to output convergent light; single-core waveguide 26 is used to input divergent linear polarized light and emit the divergent linear polarized light to lens 25, and lens 25 is used to converge light input from single-core waveguide 26 to form convergent light. The following will take embodiments 1 to 5 as examples for description.

[0093] In some embodiments, port 2 is used to output or input parallel light; lens 25 is used to collimate the light input from port 1 into parallel light and output it to port 2, and port 2 is used to output the parallel light; port 2 is used to input parallel light and direct the parallel light toward lens 25, and lens 25 is used to converge the light input from port 2 to form convergent light. The following will be described using embodiments 6 to 13 as examples.

[0094] The specific embodiments provided in this application are described in detail below.

[0095] Example 1

[0096] Please continue reading Figure 3 , which is a schematic diagram of the optical path of a polarization-maintaining circulator with three ports and all-polarization-maintaining waveguides with all-optical waveguide input and output provided in Example 1 of the present application.

[0097] In this embodiment, the first birefringent crystal 22 is the birefringent crystal A1, and the second birefringent crystal 24 is the birefringent crystal B1. Along the first direction, the polarization state of the light input from port 1 in the first birefringent crystal 22-second birefringent crystal 24 is oe.

[0098] See also Figure 7 , the figure shows the optical path of the o light input to port 1 and the optical path of the e light input to port 2 in the polarization-maintaining circulator provided in Example 1. With the first direction as the positive direction of the z-axis, an xyz coordinate system is established, such as Figure 7As shown in the figure, for the o light input to port 1, no optical path deviation occurs in the first birefringent crystal 22, and the light is emitted from the exit surface of the first birefringent crystal 22 along the same xy coordinate as its position on the incident surface; after passing through the first Faraday rotator 23, the polarization state of the light is rotated by 45° and aligned with the polarization state of the e light of the second birefringent crystal 24; after entering the second birefringent crystal 24, the optical path deviation occurs and the light is emitted from the second birefringent crystal 24. For the e-light input from port 2, between the input end of the second birefringent crystal 24 along the second direction and the output end of the first Faraday rotator 23 along the second direction, the optical paths of the o-light input from port 1 and the e-light input from port 2 overlap; however, after passing through the first Faraday rotator 23, the polarization state of the e-light input from port 2 rotates 45° along the same direction as the o-light input from port 1. Since the polarization state of the o-light input from port 1 rotates 45° along the direction when passing through the first Faraday rotator 23, the polarization state of the e-light input from port 2 rotates 90° cumulatively relative to the o-light input from port 1 in the first birefringent crystal 22. Specifically, Figure 7 The polarization directions of the o light input from the lower port one and the e light input from the lower port two change. In the first birefringent crystal 22, the polarization state of the e light input from the lower port two is perpendicular to the polarization state of the o light input from the upper port one, that is, the o light and the e light are transformed, so that the polarization state of the e light input from the upper port two is aligned with the polarization state of the e light of the upper port 22; then the e light input from the upper port two deviates from the optical path after entering the first birefringent crystal 22, so that it deviates from the o light input from the upper port one.

[0099] This embodiment also provides a schematic diagram of the projection positions of the incident point and the exit point of the light beam on each birefringent crystal in the xy plane. For details, please refer to Figure 8. After the o light input from port one enters the first birefringent crystal 22 at point A (i.e., the origin of the coordinate system), no displacement occurs in the first birefringent crystal 22, and it still exits at point A (0, 0). After passing through the first Faraday rotator 23, the o light input from port one enters the second birefringent crystal 24 and propagates in the polarization state of e light, and generates displacements DexII=-a and DeyII=a along the x-axis and y-axis directions, respectively, and exits at point B (-a, a). After the e light input from port two enters the second birefringent crystal 24 at point B, displacements DexII=a and DeyII=-a along the x-axis and y-axis directions, respectively, and exits at point A. After passing through the first Faraday rotator 23, the e light input from port two enters the first birefringent crystal 22 and continues to propagate in the polarization state of e light, and generates displacements DexII=-2a and DeyII=0 along the x-axis and y-axis directions, respectively, and exits at point C (-2a, 0) and couples into port three. Based on this, the incident point of the o light input from port one at the first birefringent crystal 22 is point A, the exit point of the e light input from port two at the first birefringent crystal 22 is point C, the two cores of the dual-core waveguide 21 are aligned with points A and C, and the polarization states of the two cores are aligned with the polarization states of the o light and the e light of the first birefringent crystal 22, respectively.

[0100] See also Fig. 9 , the figure shows the optical path of the e-light incident from port three in the polarization-maintaining circulator provided in Example 1. The light input from port three enters the first birefringent crystal 22 as e-light. For the e-light input from port three, the optical path deviates in the first birefringent crystal 22 and is emitted from the first birefringent crystal 22; after passing through the first Faraday rotator 23, the polarization state of the light rotates 45° and is aligned with the polarization state of the o-light of the second birefringent crystal 24; after entering the second birefringent crystal 24, the optical path does not deviate, and it is emitted from the exit surface of the second birefringent crystal 24 along the same xy coordinate as its position on the incident surface. In the second birefringent crystal 24, the polarization state of the e-light input from port two differs by 90° from the polarization state of the e-light input from port three, that is, the o-light and the e-light are transformed, and the e-light input from port three deviates from the optical path of the e-light input from port two and cannot enter port two.

[0101] This embodiment also provides Fig. 9 Schematic diagram of the projection position of the incident and exit points of the light beams in the shown optical path in the xy plane at each birefringent crystal. For details, please refer to Fig.10. As mentioned above, the exit point of the e-light input to port three in the first birefringent crystal 22 is point C. It is emitted at point C and coupled into port three. Then the e-light input to port three is still incident on the first birefringent crystal 22 at point C in the polarization state of e-light, and produces displacements DexII=2a and DeyII=0 along the x-axis and y-axis directions in the first birefringent crystal 22, respectively, and is emitted at point A. After passing through the first Faraday rotator 23, the e-light input to port three enters the second birefringent crystal 24 and propagates in the polarization state of o-light without displacement, and is still emitted at point A. Based on this, the e-light input to port three deviates from the incident point B of the e-light input to port two in the second birefringent crystal 24 at the exit point A of the second birefringent crystal 24, so that it cannot be coupled into port two, realizing the reverse isolation function from port three to port two. According to the aforementioned coupling of the light input to port two into port three, it can be seen that this embodiment also realizes the reverse isolation from port two to port one.

[0102] In another embodiment, the optical path arrangement is the same as that of the above embodiment 1, except that the crystal The polarization state of the input o light from port 1 in the first birefringent crystal 22-second birefringent crystal 24 is oo, or the polarization state of the input e light from port 1 in the first birefringent crystal 22-second birefringent crystal 24 is eo, or the polarization state of the input e light from port 1 in the first birefringent crystal 22-second birefringent crystal 24 is ee, by reasonably setting the optical axes of the first birefringent crystal 22 and the second birefringent crystal 24 The circulator function of circular coupling and reverse isolation can also be achieved by matching the appropriate dual-core spacing of the dual-core waveguide and the polarization state direction of the waveguide. The specific polarization state changes and light displacements are the same and will not be elaborated here.

[0103] Example 2

[0104] Fig.11 This is a schematic diagram of the optical path of a 4-port fully polarization-maintaining waveguide polarization-maintaining circulator with all-optical waveguide input and output provided in Example 2 of the present application.

[0105] In this embodiment, the first birefringent crystal 22 is the birefringent crystal A1, and the second birefringent crystal 24 is the birefringent crystal B1. Along the first direction, the polarization state of the light input from port 1 in the first birefringent crystal 22-second birefringent crystal 24 is oe.

[0106] The polarization-maintaining circulator 100 of this embodiment is used to transmit light input from port one to port two in a first direction, transmit light input from port two to port three in a second direction, transmit light input from port three to port four in the first direction, and transmit light input from port four to port one in the second direction, wherein the first direction and the second direction are opposite.

[0107] The polarization-maintaining circulator includes: a first polarization-maintaining dual-core waveguide 21 for realizing port one and port three, a first birefringent crystal 22, a first Faraday rotator 23, a lens 25, a second birefringent crystal 24, and a second polarization-maintaining dual-core waveguide 26 for realizing port two and port four, which are arranged in sequence along a first direction. The first birefringent crystal 22, the first Faraday rotator 23, and the second birefringent crystal 24 are all parallel plate structures.

[0108] 1. Port 1 to Port 2:

[0109] Port one is used to input divergent linear polarized light with a fixed polarization direction. The light input to port one is o light (this embodiment uses o light as an example for explanation, and may also be e light) and enters the first birefringent crystal 22; the first birefringent crystal 22 is used to make the light input to port one form a first crystal forward displacement and then emit it to the first Faraday rotator 23; the first Faraday rotator 23 is used to rotate the polarization state of the light input to port one by an angle of α (45°) along a first rotation direction and then emit it to the lens 25; the lens 25 is used to converge the light input to port one to form converged light and then emit it to the second birefringent crystal 24; the second birefringent crystal 24 is used to make the light input to port one form a second crystal forward displacement and then emit it to port two; port two is used to output the light input to port one, so as to realize the transmission of light from port one to port two.

[0110] 2. Port 2 to Port 3:

[0111] Port 2 is used to input divergent linear polarized light with a fixed polarization direction. The light input from port 2 enters the second birefringent crystal 24 as o light or e light with the same polarization state as the light input from port 1; the second birefringent crystal 24 is used to make the light input from port 2 form a second crystal reverse displacement and then emit it to the lens 25; the lens 25 is used to converge the light input from port 2 to form converged light and then emit it to the first Faraday rotator 23; the first Faraday rotator 23 is used to rotate the polarization state of the light input from port 2 along the first rotation direction by an angle of α (45°) and then emit it to the first birefringent crystal 22; the first birefringent crystal 22 is used to make the light input from port 2 form a converged light and then emit it to the first birefringent crystal 22. The input light forms a reverse displacement of the first crystal and then emits to port three, wherein the polarization state of the light input from port two in the first birefringent crystal 22 is rotated 90° relative to the polarization state of the light input from port one, and the o light and the e light are transformed, so that the light input from port two deviates from the light input from port one in the first birefringent crystal 22, and the lateral walk-off generated between the light input from port one and the light input from port two is equal to the dual-core spacing of the first polarization-maintaining dual-core waveguide 21, so that the light input from port two is coupled into port three; port three is used to output the light input from port two, so as to realize the transmission of light from port two to port three.

[0112] 3. Port 3 to Port 4:

[0113] Port three is used to input divergent linear polarized light with a fixed polarization direction. The light input from port three enters the first birefringent crystal 22 as o light or e light with the same polarization state as the light input from port two; the first birefringent crystal 22 is used to make the light input from port three form a first crystal forward displacement and then emit it to the first Faraday rotator 23; the first Faraday rotator 23 is used to rotate the polarization state of the light input from port three by an angle of α (45°) along the first rotation direction and then emit it to the lens 25; the lens 25 is used to converge the light input from port three to form converged light and then emit it to the second birefringent crystal 24; the second birefringent crystal 24 is used to make the light input from port three form a converged light and then emit it to the second birefringent crystal 24 The input light forms a forward displacement of the second crystal and then is emitted to port four; wherein, the polarization state of the light input from port three in the second birefringent crystal 24 is rotated 90° relative to the polarization state of the light input from port two, and the o light and the e light are transformed, so that the light input from port three deviates from the light input from port two in the second birefringent crystal 24, and the lateral walk-off generated between the light input from port two and the light input from port three is equal to the dual-core spacing of the second polarization-maintaining dual-core waveguide 26, so that the light input from port three is coupled into port four; port four is used to output the light input from port three, so as to realize the transmission of light from port three to port four.

[0114] 4. Port 4 to Port 1:

[0115] Port four is used to input divergent linear polarized light with a fixed polarization direction. The light input from port four enters the second birefringent crystal 24 as o light or e light with the same polarization state as the light input from port three. The second birefringent crystal 24 is used to make the light input from port four form a second crystal reverse displacement and then emit it to the lens 25. The lens 25 is used to converge the light input from port four to form converged light and then emit it to the first Faraday rotator 23. The first Faraday rotator 23 is used to rotate the polarization state of the light input from port four by an angle of α (45°) along a first rotation direction and then emit it to the first birefringent crystal 22. The first birefringent crystal 22 is used to make the light input from port four form a first crystal reverse displacement and then emit it to port one, wherein the polarization state of the light input from port four in the first birefringent crystal 22 is rotated 90° relative to the polarization state of the light input from port three, and the o light and the e light are transformed, which are now the same as the polarization state of the light input from port one, and therefore enter port one in the reverse direction of the light input from port one, thereby realizing the transmission of light from port four to port one.

[0116] In this embodiment, the optical paths from port 1 to port 2 and from port 2 to port 3, the changes in the polarization state of light, and the changes in the displacement are similar to those in Embodiment 1. Figures 7 and 8 The following describes the optical transmission from port 3 to port 4 and from port 4 to port 1.

[0117] See also Fig.12 , the figure shows the optical paths of the e-light incident from the third port and the o-light incident from the fourth port in the polarization-maintaining circulator provided in Example 2. For the e-light input from the third port, the optical path deviates in the first birefringent crystal 22 and is emitted from the first birefringent crystal 22; after passing through the first Faraday rotator 23, the polarization state of the light rotates 45° and is aligned with the polarization state of the o-light of the second birefringent crystal 24; after entering the second birefringent crystal 24, the optical path does not deviate and is emitted from the exit surface of the second birefringent crystal 24 along the same xy coordinate as its position on the incident surface. For the o-light input from port four, the optical paths of the e-light input from port three and the o-light input from port four overlap between the input end of the second birefringent crystal 24 along the second direction and the output end of the first Faraday rotator 23 along the second direction; however, after passing through the first Faraday rotator 23, the polarization state of the o-light input from port four rotates 45° in the same direction as the e-light input from port three, and the polarization state of the o-light input from port four rotates 90° cumulatively relative to the e-light input from port three in the first birefringent crystal 22. In the first birefringent crystal 22, the polarization state of the o-light input from port four is perpendicular to the polarization state of the e-light input from port three, that is, the e-light and the o-light are transformed, so that the polarization state of the o-light input from port four is aligned with the polarization state of the o-light of the first birefringent crystal 22, and is now the same as the polarization state of the o-light input from port one, so it enters port one in the reverse direction of the o-light input from port one, realizing the transmission of light from port four to port one.

[0118] This embodiment also provides Fig.12 Schematic diagram of the projection position of the incident and exit points of the mid-light beam on each birefringent crystal in the xy plane. For details, please refer to Fig.13 . After the e-light input from port three enters the first birefringent crystal 22 at point C, it generates displacements DexII=2a and DeyII=0 along the x-axis and y-axis directions in the first birefringent crystal 22, respectively, and is emitted at point A. After passing through the first Faraday rotator 23, the e-light input from port three enters the second birefringent crystal 24 and propagates in the polarization state of o-light without displacement, still emits at point A and is coupled into port four. After the o-light input from port four enters the second birefringent crystal 24 at point A, it does not shift and still emits at point A. After passing through the first Faraday rotator 23, the o-light input from port four enters the first birefringent crystal 22 and continues to propagate in the polarization state of o-light without displacement, still emits at point A and is coupled into port one.

[0119] In summary, the incident point of the e-light input from port two on the second birefringent crystal 24 is point B (corresponding to the position of port two), the exit point of the e-light input from port three on the second birefringent crystal 24 is point A (corresponding to the position of port four), the two cores of the second dual-core waveguide 26 are aligned with points B and A, and the polarization states of the two cores are respectively aligned with the e-light polarization state and the o-light polarization state of the second birefringent crystal 24; the incident point of the e-light input from port three on the first birefringent crystal 22 is point C, the exit point of the o-light input from port four on the first birefringent crystal 22 is point A (corresponding to the position of port one), the two cores of the first dual-core waveguide 21 are aligned with points A and C, and the polarization states of the two cores are respectively aligned with the o-light polarization state and the e-light polarization state of the first birefringent crystal 22.

[0120] According to the aforementioned sequential coupling of input light from each port into the next port, it can be seen that input light from each port cannot be coupled into the previous port, thus achieving reverse isolation from each port to the previous port.

[0121] In another embodiment, the optical path arrangement is the same as that of the above embodiment 2, except that the crystal The polarization state of the input o light from port 1 in the first birefringent crystal 22-second birefringent crystal 24 is oo, or the polarization state of the input e light from port 1 in the first birefringent crystal 22-second birefringent crystal 24 is eo, or the polarization state of the input e light from port 1 in the first birefringent crystal 22-second birefringent crystal 24 is ee, by reasonably setting the optical axes of the first birefringent crystal 22 and the second birefringent crystal 24 The circulator function of circular coupling and reverse isolation can also be achieved by matching the appropriate dual-core spacing of the dual-core waveguide and the polarization state direction of the waveguide. The specific polarization state changes and light displacements are the same and will not be elaborated here.

[0122] Example 3

[0123] Fig.14 Schematic diagram of the optical path of a single-stage isolated polarization-maintaining circulator with three ports and non-full polarization-maintaining waveguides with all-optical waveguide input and output provided in Example 3 of the present application. In this embodiment, port one is a polarization-maintaining port, port two is a polarization-maintaining port or a non-polarization-maintaining port, and port three is a polarization-maintaining port or a non-polarization-maintaining port.

[0124] First, in the aforementioned Based on the birefringent crystal A1 and the birefringent crystal B1, another birefringent crystal C1 is described. Fig.15a and Fig.15b , schematically shows the structure and optical axis of the birefringent crystal C1. Fig.15a As shown in , the birefringent crystal C1 is a parallel plate structure, with the light incident surface of port one as the plane where the x and y axes are located, and the first direction as the positive direction of the z axis, a three-dimensional rectangular coordinate system is established, wherein the normal line of the light incident surface of port one at the birefringent crystal C1 is parallel to the z axis. The angle θ between the optical axis of the birefringent crystal C1 and the normal line of the light incident surface of port one (i.e., the z axis) is C1 The angle between the straight line where the e-light oscillation plane where the optical axis of the birefringent crystal C1 is located and the intersection of the xy plane and the y axis is Fig.15a middle Fig.15b FIG. 1 shows a schematic diagram of light displacement in the birefringent crystal C1. The rectangular coordinate system establishment and reference method are the same as those for the birefringent crystal A1 and the birefringent crystal B1 described above. The same applies to the following, and no further details are given here. Fig.15b As shown in , the displacement of the forward o light along the x-axis direction DoxIII=0, and the displacement along the y-axis direction DoyIII=0; the displacement of the forward e light along the x-axis direction DexIII=a, and the displacement along the y-axis direction DeyI=a / tan(45°)=a; the displacement of the reverse o light along the x-axis direction rDoxIII=0, and the displacement along the y-axis direction rDoyIII=0; the displacement of the reverse e light along the x-axis direction rDexIII=-a, and the displacement along the y-axis direction rDeyIII=-a / tan(45°)=-a. Of course, other displacement values ​​can be used according to specific circumstances, and are not limited here.

[0125] remove Figure 3In addition to the structure shown, the polarization-maintaining circulator of this embodiment also includes a third birefringent crystal 27 arranged between the second birefringent crystal 24 and the lens 25 along the first direction. The third birefringent crystal 27 is a parallel plate structure. The light input from port one forms a third crystal forward displacement in the third birefringent crystal 27, and the light input from port two forms a third crystal reverse displacement in the third birefringent crystal 27, thereby realizing a single-stage isolated polarization-maintaining circulator.

[0126] In the embodiment of the present application, the first birefringent crystal 22 adopts the above-mentioned birefringent crystal A1, the second birefringent crystal 24 adopts the above-mentioned birefringent crystal B1, and the third birefringent crystal 27 adopts the above-mentioned birefringent crystal C1. For details, please refer to the above description, which will not be repeated here. Along the first direction, the polarization state of the light input from port 1 in the first birefringent crystal 22-the second birefringent crystal 24-the third birefringent crystal 27 is oeo.

[0127] In the polarization-maintaining circulator provided in Example 3 of the present application, (the displacement of the linearly polarized light incident from port 1 to port 2 in the crystal after incident on the birefringent crystal 22 as o light is shown in FIG. Fig.16a The displacement of the light incident from port 2 into the birefringent crystal 27 as o light and e light from port 2 to port 3 in the crystal is shown in FIG. Fig.16b , align the port 1 and port 3 of the first dual-core waveguide 21 according to point A and point C in the displacement diagram, and align the polarization states of the two cores to the polarization states of the o light and the e light of the first birefringent crystal 22, respectively, so as to realize the sequential coupling from port 1 to port 2 and from port 2 to port 3. For the optical path of the o light incident from port 3 in the polarization-maintaining circulator, please refer to Fig.17a , the optical path of the incident light from port 3 is shown in Fig.17b , the linearly polarized light incident from port 3 enters the birefringent crystal 22 as o light, and then moves from port 3 to port 2 in the crystal in the reverse isolation displacement. Fig.17c , the linearly polarized light incident from port 3 enters the birefringent crystal 22 as e-light and then moves from port 3 to port 2 in the crystal in the reverse isolation displacement. Fig.17d The exit points D and E of the o-light and e-light incident from port three are both away from point B where port two is located, so reverse isolation from port three to port two can be achieved. 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.

[0128] The angle θ3 between the normal of the incident surface of the third birefringent crystal 27 and the optical axis of the third birefringent crystal 27 is the third walk-off angle, -90°<θ3<0° or 0°<θ3<90°, and the third walk-off angle is used to control the forward displacement of the third crystal and the reverse displacement of the third crystal. The xyz coordinate system is established with the first direction as the positive direction of the z-axis; the e-light oscillation plane where the optical axis of the second birefringent crystal 24 is located, and the intersection with the xy plane is the second straight line, and 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 27 is located intersects with the xy plane as the third straight line. The angle between the third straight line and the y axis is in, or 270°, used to couple light of any polarization state input from port two into port three.

[0129] for For details, please refer to Fig.15a About the birefringent crystal C By and The relationship is set to or and and The relationship is set to or 270°, ensuring that the polarization state of the light emitted from the first birefringent crystal 22 can be aligned with the o light or e light of the second birefringent crystal 24 after passing through the first Faraday rotator 23, and after entering the third birefringent crystal 27, the polarization state of the light in the second birefringent crystal 24 is compared to the oe conversion or eo conversion. satisfy or 270°.

[0130] In another embodiment, the optical path arrangement is the same as that of the above embodiment 3, except that the crystal The polarization state of the o light input from port 1 in the first birefringent crystal 22-the second birefringent crystal 24-the third birefringent crystal 27 is ooe, or the polarization state of the e light input from port 1 in the first birefringent crystal 22-the second birefringent crystal 24-the third birefringent crystal 27 is eoe, or the polarization state of the e light input from port 1 in the first birefringent crystal 22-the second birefringent crystal 24-the third birefringent crystal 27 is eeo, by reasonably setting the optical axes of the first birefringent crystal 22, the second birefringent crystal 24 and the third birefringent crystal 27 The circulator function of circular coupling and reverse single-stage isolation can also be achieved by matching the appropriate dual-core spacing of the dual-core waveguide and the polarization state direction of the waveguide. The specific polarization state changes and light displacements are the same and will not be elaborated here.

[0131] Example 4

[0132] Fig.18 Schematic diagram of the optical path of another 3-port non-full polarization-maintaining waveguide single-stage isolated polarization-maintaining circulator with all-optical waveguide input and output provided in Example 4 of the present application. In this embodiment, port 1 is a polarization-maintaining port, port 2 is a polarization-maintaining port or a non-polarization-maintaining port, and port 3 is a polarization-maintaining port or a non-polarization-maintaining port. The difference between this embodiment and Example 3 is that the insertion position of the third birefringent crystal 27 is different. The following is a detailed description:

[0133] remove Figure 3 In addition to the structure shown, the polarization-maintaining circulator of this embodiment also includes a third birefringent crystal 27 arranged between the dual-core waveguide 21 and the first birefringent crystal 22. The third birefringent crystal 27 is a parallel plate structure. The light input from port one forms a third crystal forward displacement in the third birefringent crystal 27, and the light input from port two forms a third crystal reverse displacement in the third birefringent crystal 27.

[0134] In the embodiment of the present application, the first birefringent crystal 22 adopts the above-mentioned birefringent crystal B1, and the second birefringent crystal 24 adopts the above-mentioned birefringent crystal A1. For details, please refer to the above description, which will not be repeated here. The third birefringent crystal 27 adopts the above-mentioned birefringent crystal C1. Along the first direction, the polarization state of the light input from the port 1 in - the third birefringent crystal 27 - the first birefringent crystal 22 - the second birefringent crystal 24 is oeo.

[0135] In the polarization-maintaining circulator provided in Example 4 of the present application, the displacement of the linearly polarized light incident from port 1 to port 2 in the crystal after incident on the birefringent crystal 27 as o light is shown in FIG. Fig.19a The displacement of the light incident from port 2 into the birefringent crystal 24 as o light and e light from port 2 to port 3 in the crystal is shown in FIG. Fig.19b , align the port 1 and port 3 of the first dual-core waveguide 21 according to point A and point D in the displacement diagram, and align the polarization states of the two cores to the polarization states of the o light and the e light of the third birefringent crystal 27, respectively, so as to realize the sequential coupling from port 1 to port 2 and from port 2 to port 3. For the optical path of the o light incident from port 3 in the polarization-maintaining circulator, please refer to Fig.20a , the optical path of the incident light from port 3 is shown in Fig.20b, the linearly polarized light incident from port 3 enters the birefringent crystal 27 as o light, and then moves from port 3 to port 2 in the crystal in the reverse isolation displacement. Fig.20c , the linearly polarized light incident from port 3 enters the birefringent crystal 27 as e-light and then moves from port 3 to port 2 in the crystal in the reverse isolation displacement. Fig.20d , the exit points C and E of the o light and e light incident from port three are both away from point B where port two is located, and reverse isolation from port three to port two can be achieved. 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.

[0136] The angle θ3 between the normal line of the incident surface of the third birefringent crystal 27 and the optical axis of the third birefringent crystal 27 of the light input from port 1 is the third walk-off angle, -90°<θ3<0° or 0°<θ3<90°, and the third walk-off angle is used to control the forward displacement and reverse displacement of the third crystal.

[0137] The xyz coordinate system is established with the first direction as the positive direction of the z-axis; the e-light oscillation plane where the optical axis of the first birefringent crystal 22 is located intersects with the xy plane as the first straight line, and the angle between the first straight line and the y-axis is The e-light oscillation plane where the optical axis of the third birefringent crystal 27 is located intersects with the xy plane as the third straight line. The angle between the third straight line and the y axis is in, or 270°, used to couple light of any polarization state input from port two into port three.

[0138] for For details, please refer to Fig.15a About the birefringent crystal C By and The relationship is set to or and and The relationship is set to or 270°, ensuring that the polarization state of the light emitted from the third birefringent crystal 27 is oe-converted or eo-converted after entering the first birefringent crystal 22 compared with the polarization state of the light in the third birefringent crystal 27, and the polarization state of the light emitted from the first birefringent crystal 22 can be aligned with the o-light or e-light of the second birefringent crystal 24 after passing through the first Faraday rotator 23. satisfy or 270°.

[0139] In another embodiment, the optical path arrangement is the same as that of the above-mentioned embodiment 4, except that the crystal The polarization state of the o light input from the first port in the third birefringent crystal 27-first birefringent crystal 22-second birefringent crystal 24 is oee, or the polarization state of the e light input from the first port in the third birefringent crystal 27-first birefringent crystal 22-second birefringent crystal 24 is eoe, or the polarization state of the e light input from the first port in the third birefringent crystal 27-first birefringent crystal 22-second birefringent crystal 24 is eoo, by reasonably setting the optical axes of the first birefringent crystal 22, the second birefringent crystal 24 and the third birefringent crystal 27. The circulator function of circular coupling and reverse single-stage isolation can also be achieved by matching the appropriate dual-core spacing of the dual-core waveguide and the polarization state direction of the waveguide. The specific polarization state changes and light displacements are the same and will not be elaborated here.

[0140] Example 5

[0141] The reverse isolation function achieved by three birefringent crystals (the first birefringent crystal 22, the second birefringent crystal 24 and the third birefringent crystal 27) and one Faraday rotator (i.e., the first Faraday rotator 23) is called single-stage isolation. On this basis, if you want to achieve better isolation, you can also increase the number of Faraday rotators to form double-stage isolation.

[0142] FIG. 21 is a schematic diagram of the optical path of a three-port non-full-polarization-maintaining waveguide double-stage isolation polarization-maintaining circulator with all-optical waveguide input and output provided in Example 5 of the present application.

[0143] In this embodiment, port one is a polarization-maintaining port, port two is a polarization-maintaining port or a non-polarization-maintaining port, and port three is a polarization-maintaining port or a non-polarization-maintaining port.

[0144] First, another birefringent crystal D1 used in this embodiment is described. Figure 21b and Fig.21c , schematically shows the structure and optical axis of the birefringent crystal D1. Figure 21b As shown in the figure, the birefringent crystal D1 is a parallel plate structure, with the light incident surface of port one as the plane where the x and y axes are located and the first direction as the positive direction of the z axis, a three-dimensional rectangular coordinate system is established, wherein the normal line of the light incident surface of port one at the birefringent crystal D1 is parallel to the z axis. The angle θ between the optical axis of the birefringent crystal D1 and the normal line of the light incident surface of port one (i.e., the z axis) is D1 The angle between the straight line where the e-light oscillation plane where the optical axis of the birefringent crystal D1 is located and the intersection of the xy plane and the y axis is Figure 21b middle Fig.21c FIG. 1 shows a schematic diagram of light displacement in the birefringent crystal D1. The rectangular coordinate system establishment and reference method are the same as those for the birefringent crystal A1 and the birefringent crystal B1 described above. The same applies to the following, and no further details are given here. Fig.21c As shown in , 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=0, and the displacement along the y-axis direction is DeyI=-2a; 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=0, and the displacement along the y-axis direction is rDeyIII=2a. Of course, other displacement values ​​can be used according to specific circumstances, and are not limited here.

[0145] remove Figure 3 In addition to the structure shown in the figure, the polarization-maintaining circulator of this embodiment further includes a second Faraday rotator 28 and a third birefringent crystal 27 (i.e., between the second birefringent crystal 24 and the lens 25) which are sequentially arranged along the first direction. Fig.14 On the basis of the embodiment 3 shown, a second Faraday rotator 28 is added between the second birefringent crystal 24 and the third birefringent crystal 27. The second Faraday rotator 28 and the third birefringent crystal 27 are both parallel plate structures. The second Faraday rotator 28 is used to rotate the polarization state of the light input from the first port by an angle α along the second rotation direction and then emit it to the third birefringent crystal 27, and is used to rotate the polarization state of the light input from the second port by an angle α along the second rotation direction and then emit it to the second birefringent crystal 24. The light input from the first port forms a third crystal forward displacement in the third birefringent crystal 27, and the light input from the second port forms a third crystal reverse displacement in the third birefringent crystal 27.

[0146] In the embodiment of the present application, the first birefringent crystal 22 adopts the above-mentioned birefringent crystal B1, the second birefringent crystal 24 adopts the above-mentioned birefringent crystal D1, and the third birefringent crystal 27 adopts the above-mentioned birefringent crystal C1. For details, please refer to the above description, which will not be repeated here. Along the first direction, the polarization state of the light input from port 1 in the first birefringent crystal 22-the second birefringent crystal 24-the third birefringent crystal 27 is oeo.

[0147] Fig.22a This is a schematic diagram of the displacement of the linearly polarized light incident from port 1 to port 2 in the crystal after it enters the birefringent crystal 22 as o light in the polarization-maintaining circulator provided in Example 5 of the present application. Figure 22bIn the polarization-maintaining circulator provided in Example 5 of the present application, a schematic diagram of the displacement of light incident from port 2 to port 3 in the crystal after entering the birefringent crystal 27 as o light and e light, aligning port 1 and port 3 of the first dual-core waveguide 21 according to point A and point B in the displacement diagram, and the polarization states of the two cores are respectively aligned with the polarization states of o light and e light of the first birefringent crystal 22, that is, sequential coupling from port 1 to port 2 and from port 2 to port 3 is achieved. For the optical path of o light incident from port 3 in the polarization-maintaining circulator, please refer to Fig.23a , the optical path of the incident light from port 3 is shown in Figure 23b , Fig.23c This is a schematic diagram of the reverse isolation displacement of the linearly polarized light incident from port 3 to port 2 in the polarization-maintaining circulator provided in Example 5 of the present application after the linearly polarized light incident from port 3 enters the birefringent crystal 22 as o light, Fig.23d In the polarization-maintaining circulator provided in Example 5 of the present application, a schematic diagram of the reverse isolation displacement from port three to port two in the crystal after the linearly polarized light incident from port three enters the birefringent crystal 22 as e-light is shown. The exit points E and A of the o-light and e-light incident from port three are both offset from point B where port two is located, so reverse isolation from port three to port two can be achieved. The contents and related principles shown in the figure are consistent with the relevant description of the above-mentioned Example 1 and will not be elaborated here.

[0148] The angle θ3 between the normal line of the incident surface of the third birefringent crystal 27 and the optical axis of the third birefringent crystal 27 for the light input from port 1 is the third walk-off angle, -90°<θ3<0° or 0°<θ3<90°, and the third walk-off angle is used to control the forward displacement and reverse displacement of the third crystal.

[0149] The xyz coordinate system is established with the first direction as the positive direction of the z-axis; the e-light oscillation plane where the optical axis of the second birefringent crystal 24 is located intersects with the xy plane as the second straight line, and 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 27 is located intersects with the xy plane as the third straight line. The angle between the third straight line and the y axis is in, 90°+α, 180°+α or 270°+α, in this embodiment Satisfy the above The third birefringent crystal 27 is used to couple the light of any polarization state input from the second port into the third port.

[0150] For the specific implementation of bipolar isolation, please refer to Fig.21a , Fig.23a and Figure 23b, the light of any polarization state incident from port three is incident on the first birefringent crystal 22, and the first birefringent crystal 22 is used to decompose the light of any polarization state incident from port three into port three incident o light and port three incident e light whose polarization states are perpendicular to each other, and respectively form the first crystal forward displacement of port three incident o light and port three incident e light, and then output them to the first Faraday rotator 23. The first Faraday rotator 23 is used to rotate the polarization states of port three input o light and port three incident e light along the first rotation direction by an angle α (45°) and then output them to the second birefringent crystal 24. The second birefringent crystal 24 is used to make port three input o light and port three input e light form the second crystal forward displacement and then output them to the second Faraday rotator 28. In the optical path between the first birefringent crystal 22-the first Faraday rotator 23-the second birefringent crystal 24, the polarization states of the port three input o light and the port three input e light in the second birefringent crystal 24 are rotated 90° relative to the port two input o light and the port two input e light, respectively, and the o light and the e light are transformed, so that the optical paths of the port three incident o light and the port three incident e light in the second birefringent crystal 24 deviate from the optical paths of the port two input o light and the port two input e light in the second birefringent crystal 24, thereby achieving the first-level isolation effect from port three to port two. The second Faraday rotator 28 is used to rotate the polarization states of the port three input o light and the port three input e light by an angle of α (45°) along the second rotation direction and then output them to the third birefringent crystal 27. The third birefringent crystal 27 is used to make the port three input o light and the port three input e light form a third crystal forward displacement. In the optical path between the second birefringent crystal 24-the second Faraday rotator 28-the third birefringent crystal 27, for the port three input light and the port two input light (o light polarization state or e light polarization state) of the same polarization state in the second birefringent crystal 24, after being rotated by the second Faraday rotator 28 along the second rotation direction by an angle α (45°), the port three input light transmitted along the first direction is cumulatively rotated by 90° relative to the port two input light transmitted along the second direction, and the o light and the e light are transformed in the third birefringent crystal 27, so that the port three input light and the port two input light of the same polarization state in the second birefringent crystal 24 have the port three input light deviate from the optical path of the port two input light in the third birefringent crystal 27 again, forming a second-level isolation effect from port three to port two. The sum of the forward displacement of the first crystal, the forward displacement of the second crystal and the forward displacement of the third crystal ultimately causes the port three input o light and the port three input e light output by the third birefringent crystal 27 to deviate from the optical path of the light incident on port two, and after being converged by the lens 25, they cannot be coupled into the single-core waveguide 26, thereby achieving a double-stage isolation effect from port three to port two.

[0151] According to the aforementioned sequential coupling of input light from each port into the next port, it can be seen that the input light from port two cannot be coupled into port one, thus achieving reverse isolation from port two to port one.

[0152] In another embodiment, the optical path arrangement is the same as that of the above embodiment 5, except that the crystal The polarization state of the input o light from port 1 in the first birefringent crystal 22-second birefringent crystal 24-third birefringent crystal 27 is ooe, or the polarization state of the input o light from port 1 in the first birefringent crystal 22-second birefringent crystal 24-third birefringent crystal 27 is ooo, or the polarization state of the input o light from port 1 in the first birefringent crystal 22-second birefringent crystal 24-third birefringent crystal 27 is oee, or the polarization state of the input e light from port 1 in the first birefringent crystal 22-second birefringent crystal 24-third birefringent crystal 27 is oee, 7 is eoe, or the polarization state of the e-light input from port 1 in the first birefringent crystal 22-second birefringent crystal 24-third birefringent crystal 27 is eeo, or the polarization state of the e-light input from port 1 in the first birefringent crystal 22-second birefringent crystal 24-third birefringent crystal 27 is eee, or the polarization state of the e-light input from port 1 in the first birefringent crystal 22-second birefringent crystal 24-third birefringent crystal 27 is eoo, by reasonably setting the optical axes of the first birefringent crystal 22, the second birefringent crystal 24 and the third birefringent crystal 27 The circulator function of circular coupling and reverse double-stage isolation can also be realized by matching the appropriate dual-core spacing of the dual-core waveguide and the polarization state direction of the waveguide. The specific polarization state changes and light displacements are the same and will not be elaborated here.

[0153] Example 6

[0154] Fig.24 Schematic diagram of the optical path of a three-port fully polarization-maintaining polarization-maintaining circulator with parallel light output from port two provided in Example 6 of the present application. The difference between this embodiment and Example 1 is that port two of this embodiment does not use a single-core waveguide, and it outputs parallel light into free space. Lens 25 is used to collimate the light input from port one into parallel light, and output it to port two, and port two is used to output the parallel light; and port two is used to input parallel light and direct the parallel light to lens 25, and lens 25 is also used to converge the light input from port two to form converged light, and output it to port three. The optical path transmission and principles of the rest of this embodiment are similar to those of Example 1, and reference may be made to the description of Example 1.

[0155] Example 7

[0156] Fig.25aSchematic diagram of the optical path of a three-port non-full-polarization-maintaining single-stage isolated polarization-maintaining circulator with parallel light output from port two provided in Example 7 of the present application. The difference between this embodiment and Example 3 is that port two of this embodiment does not use a single-core waveguide, and it outputs parallel light to free space. Lens 25 is used to collimate the light input from port one into parallel light and output it to port two, and port two is used to output the parallel light; and port two is used to input parallel light and direct the parallel light to lens 25, and lens 25 is also used to converge the light input from port two to form converged light, and output it to port three. The optical path transmission and principles of the rest of this embodiment are similar to those of Example 3, and reference may be made to the description of Example 3.

[0157] Example 8

[0158] Fig.25b A schematic diagram of the optical path of another three-port non-full polarization-maintaining single-stage isolated polarization-maintaining circulator with parallel light output from port two provided in Example 8 of the present application. The difference between this embodiment and Example 4 is that port two of this embodiment does not use a single-core waveguide, and it outputs parallel light into free space. Lens 25 is used to collimate the light input from port one into parallel light and output it to port two, and port two is used to output the parallel light; and port two is used to input parallel light and direct the parallel light to lens 25, and lens 25 is also used to converge the light input from port two to form converged light, and output it to port three. The optical path transmission and principle of the rest of this embodiment are similar to those of Example 4, and reference may be made to the description of Example 4.

[0159] Example 9

[0160] Fig.26 Schematic diagram of the optical path of a three-port non-full-polarization-maintaining double-stage isolated polarization-maintaining circulator with parallel light output from port two provided in Example 9 of the present application. The difference between this embodiment and Example 5 is that port two of this embodiment does not use a single-core waveguide, and it outputs parallel light to free space. Lens 25 is used to collimate the light input from port one into parallel light and output it to port two, and port two is used to output the parallel light; and port two is used to input parallel light and direct the parallel light to lens 25, and lens 25 is also used to converge the light input from port two to form converged light, and output it to port three. The optical path transmission and principle of the rest of this embodiment are similar to those of Example 5, and reference may be made to the description of Example 5.

[0161] Examples 10-13

[0162] In some embodiments, a filter can be added between the lens and port 2 at the focal position of lens 25. Figure 27-29 ,in, Fig. 27 In the embodiment 10 of the present application provided Fig.24The optical path diagram of the polarization-maintaining circulator with a filter added to the polarization-maintaining circulator shown in the figure is as follows: Fig.28a In the embodiment 11 of the present application provided Fig.25a A schematic diagram of the optical path of a polarization-maintaining circulator in which a filter is added to the polarization-maintaining circulator shown; Fig.28b In the embodiment 12 of the present application provided Fig.25b The optical path diagram of the polarization-maintaining circulator is shown in FIG. 1 , which is a polarization-maintaining circulator with a filter added thereto. Fig.29 In the embodiment 13 of the present application provided Fig.26 Schematic diagram of the optical path of a polarization-maintaining circulator with a filter added to the polarization-maintaining circulator shown in the figure. In the embodiment shown in the figure, port 2 is used to output or input parallel light, and the polarization-maintaining circulator 100 also includes a filter arranged between the lens 25 and port 2 and located at the focal position of the lens 25, and the filter is used to reflect all or part of the parallel light output from port 1 to port 2.

[0163] Combined crystal:

[0164] Please continue reading Figure 3 The refractive index of the light o inputted from port 1 and the light e inputted from port 2 is different in the first birefringent crystal 22, so in the first birefringent crystal 22, the optical path length of the light o inputted from port 1 is not equal to the optical path length of the light e inputted from port 2, and an optical path length difference is generated between the two. Similar situations also exist in other embodiments.

[0165] Therefore, in some embodiments, the first birefringent crystal 22, and / or the second birefringent crystal 24, and / or the third birefringent crystal 27 are combined crystals, and the combined crystals can not only achieve the same displacement but also be used to compensate for the optical path difference.

[0166] Specifically, see 30a and Fig.30b , the figure takes the first birefringent crystal 22 as a combined crystal as an example, and provides two exemplary explanations, such as Fig.30a As shown in FIG. 1 , a coordinate system is established with the incident surface as the x-axis and y-axis planes and the first direction as the positive direction of the z-axis. The first birefringent crystal 22 can be composed of a sub-birefringent crystal 221 and a sub-birefringent crystal 222. With the birefringent crystal 222 The same, and the sub-birefringent crystal 221 satisfies 0°<θ H-1 <90°, the sub-birefringent crystal 222 satisfies 0°<θ H-2 ≤90°, the positions of the sub-birefringent crystal 221 and the sub-birefringent crystal 222 can be interchanged to achieve the same function. Fig.30b As shown in FIG. 1 , the first birefringent crystal 22 may also be composed of a sub-birefringent crystal 223 and a sub-birefringent crystal 224. The angle difference is 90° or 270°, and the sub-birefringent crystal 223 satisfies 0°<θ H-3 ≤90°, the sub-birefringent crystal 224 satisfies 0°<θ H-4 <90°, the positions of the sub-birefringent crystal 223 and the sub-birefringent crystal 224 can be interchanged to achieve the same function. The second birefringent crystal 24 and the third birefringent crystal 27 are the same, and will not be described in detail here.

[0167] Taking the first birefringent crystal 22 as a combined crystal as an example, the sum of the relative displacements of the light input from port 1 in the two sub-birefringent crystals forms a displacement equal to the relative walk-off amount of the o-light and the e-light in the first birefringent crystal 22. 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 configured in a direction that interchanges, thereby reducing 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.

[0168] Finally, it should be noted that the above embodiments are only exemplary descriptions, and the deviation of the optical path, the deviation direction and the deviation distance thereof 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 22, the second birefringent crystal 24 and the third birefringent crystal 27, the rotation direction of the Faraday rotator, and the relationship between the polarization states of the o-light and the e-light, the schemes for realizing the optical circulator should be included in the protection scope of the present application.

Claims

1. A polarization-maintaining circulator, characterized in that: Used to transmit light input from port 1 to port 2 in a first direction, and to transmit light input from port 2 to port 3 in a second direction, wherein the first direction is opposite to the second direction; The polarization-maintaining circulator comprises: a dual-core waveguide, a first birefringent crystal, a first Faraday rotator, a second birefringent crystal, a lens and the port 2, which are sequentially arranged along the first direction and are used to realize the port 1 and the port 3; the first birefringent crystal, the first Faraday rotator and the second birefringent crystal are all parallel plate structures; wherein, The port 1 is a polarization-maintaining port, used for inputting divergent linearly polarized light, and the light inputted from the port 1 enters the first birefringent crystal as o light or e light; The first birefringent crystal is used to make the light input from the first port shift forward toward the first birefringent crystal and then be emitted toward the first Faraday rotator; The first Faraday rotator is used to rotate the polarization state of the light input from the port 1 by an angle α along a first rotation direction and then emit it toward the second birefringent crystal, wherein α=45°; The second birefringent crystal is used to make the light input from the first port shift toward the second birefringent crystal and then be emitted toward the lens; The lens is used to optically shape the light input from the port 1 and then emit it to the port 2; The port 2 is used to output the light input by the port 1, so as to realize the transmission of the light from the port 1 to the port 2; The port 2 is also used to input light and direct the input light toward the lens; The lens is also used to optically converge the light input from the second port and then emit it to the second birefringent crystal; The second birefringent crystal is also used to make the light input from the second port to be emitted to the first Faraday rotator after being shifted by the second birefringent crystal in the reverse direction. The first Faraday rotator is further used to rotate the polarization state of the light input from the port 2 by the angle α along the first rotation direction and then emit it toward the first birefringent crystal; The first birefringent crystal is also used to make the light input from the port 2 form a reverse first birefringent crystal displacement and then be emitted to the port 3, wherein the polarization state of the light input from the port 2 in the first birefringent crystal is rotated by 90° relative to the polarization state of the light input from the port 1, and the o light and the e light are transformed, so that the light input from the port 2 deviates from the light input from the port 1 in the first birefringent crystal, and the lateral walk-off generated between the light input from the port 1 and the light input from the port 2 is equal to the dual-core spacing of the dual-core waveguide, so that the light input from the port 2 is coupled into the port 3; The port three is used to output the light input by the port two, so as to realize the transmission of the light from the port two to the port three.

2. The polarization-maintaining circulator according to claim 1, characterized in that: The angle θ1 between the normal of the incident surface of the first birefringent crystal and the optical axis of the first birefringent crystal at the first port input 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 forward displacement of the first birefringent crystal and the reverse displacement of the first birefringent crystal; and / or, The angle θ2 between the normal of the incident surface of the second birefringent crystal and the optical axis of the second birefringent crystal of the light input from the port 1 is the second walk-off angle, -90°<θ2<0° or 0°<θ2<90°, and the second walk-off angle is used to control the forward second birefringent crystal displacement and the reverse second birefringent crystal displacement.

3. The polarization-maintaining circulator according to claim 1, characterized in that: Establishing an xyz coordinate system with the first direction as the positive direction of the z-axis; The e-light oscillation plane where the optical axis of the first birefringent crystal is located intersects with the xy plane to form a first straight line, and 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 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 in, or 4. The polarization-maintaining circulator according to claim 1, characterized in that: Along the first direction, the polarization state of the o-light of the first birefringent crystal is aligned with the polarization state of the o-light or the e-light of the second birefringent crystal after passing through the first Faraday rotator.

5. The polarization-maintaining circulator according to claim 1, characterized in that: Both port 2 and port 3 are polarization-maintaining ports. The polarization state of port 2 is aligned with the polarization state of light input from port 1 along the first direction and emitted through the lens, and the polarization state of port 3 is aligned with the polarization state of light input from port 2 along the second direction and emitted through the first birefringent crystal.

6. The polarization-maintaining circulator according to claim 1, characterized in that: The port 2 is a polarization-maintaining port or a non-polarization-maintaining port, the port 3 is a polarization-maintaining port or a non-polarization-maintaining port, the polarization-maintaining circulator further comprises a third birefringent crystal disposed between the second birefringent crystal and the lens along the first direction, the third birefringent crystal is a parallel plate structure, the light input from the port 1 forms a positive third birefringent crystal displacement in the third birefringent crystal, and the light input from the port 2 forms a reverse third birefringent crystal displacement in the third birefringent crystal; The angle θ3 between the normal line of the incident surface of the third birefringent crystal and the optical axis of the third birefringent crystal of the light input from the port 1 is a third walk-off angle, -90°<θ3<0° or 0°<θ3<90°, and the third walk-off angle is used to control the forward displacement of the third birefringent crystal and the reverse displacement of the third birefringent crystal; The xyz coordinate system is established with the first direction as the positive direction of the z-axis; the e-light oscillation plane where the optical axis of the second birefringent crystal is located intersects with the xy plane as the second straight line, and 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 is located intersects with the xy plane to form a third straight line, and the angle between the third straight line and the y axis is in, Or 270°, for coupling light of any polarization state input from the port two into the port three.

7. The polarization-maintaining circulator according to claim 1, characterized in that: The port 2 is a polarization-maintaining port or a non-polarization-maintaining port, the port 3 is a polarization-maintaining port or a non-polarization-maintaining port, the polarization-maintaining circulator further comprises a third birefringent crystal disposed between the dual-core waveguide and the first birefringent crystal, the third birefringent crystal is a parallel plate structure, the light input from the port 1 forms a positive third birefringent crystal displacement in the third birefringent crystal, and the light input from the port 2 forms a reverse third birefringent crystal displacement in the third birefringent crystal; The angle θ3 between the normal line of the incident surface of the third birefringent crystal and the optical axis of the third birefringent crystal of the light input from the port 1 is a third walk-off angle, -90°<θ3<0° or 0°<θ3<90°, and the third walk-off angle is used to control the forward displacement of the third birefringent crystal and the reverse displacement of the third birefringent crystal; An xyz coordinate system is established with the first direction 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 The e-light oscillation plane where the optical axis of the third birefringent crystal is located intersects with the xy plane to form a third straight line, and the angle between the third straight line and the y axis is in, Or 270°, for coupling light of any polarization state input from the port two into the port three.

8. The polarization-maintaining circulator according to claim 1, characterized in that: The second port is a polarization-maintaining port or a non-polarization-maintaining port, the third port is a polarization-maintaining port or a non-polarization-maintaining port, the polarization-maintaining circulator further comprises a second Faraday rotator and a third birefringent crystal which are sequentially arranged between the second birefringent crystal and the lens along the first direction, the second Faraday rotator and the third birefringent crystal are both parallel plate structures, the second Faraday rotator is used to rotate the polarization state of the light input from the first port by the angle α along the second rotation direction and then emit it to the third birefringent crystal, and is used to rotate the polarization state of the light input from the second port by the angle α along the second rotation direction and then emit it to the second birefringent crystal, the light input from the first port forms a positive third birefringent crystal displacement in the third birefringent crystal, and the light input from the second port forms a reverse third birefringent crystal displacement in the third birefringent crystal; The angle θ3 between the normal line of the incident surface of the third birefringent crystal and the optical axis of the third birefringent crystal of the light input from the port 1 is a third walk-off angle, -90°<θ3<0° or 0°<θ3<90°, and the third walk-off angle is used to control the forward displacement of the third birefringent crystal and the reverse displacement of the third birefringent crystal; The xyz coordinate system is established with the first direction as the positive direction of the z-axis; the e-light oscillation plane where the optical axis of the second birefringent crystal is located intersects with the xy plane as the second straight line, and 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 is located intersects with the xy plane to form a third straight line, and the angle between the third straight line and the y axis is in, 90°+α, 180°+α or 270°+α, used to couple light of any polarization state input from the port two into the port three, and to achieve a double-stage isolation effect from the port two to the port one and from the port three to the port two.

9. The polarization-maintaining circulator according to any one of claims 1 to 8, 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 displacement, the combined crystals can also be used to compensate for optical path differences.

10. The polarization-maintaining circulator according to claim 1, characterized in that: The port 2 is a single-core waveguide, which is used to output convergent light or input divergent light; the lens is used to converge the light input from the port 1 to form convergent light, and couple it into the single-core waveguide, and the single-core waveguide is used to output the convergent light; the single-core waveguide is also used to input divergent linear polarized light and emit the divergent linear polarized light to the lens, and the lens is also used to converge the light input from the single-core waveguide to form convergent light; or, The port two is used to output or input parallel light; the lens is used to collimate the light input from the port one into parallel light and output it to the port two, and the port two is used to output the parallel light; the port two is also used to input parallel light and direct the parallel light toward the lens, and the lens is also used to converge the light input from the port two to form converged light.

11. The polarization-maintaining circulator according to claim 10, characterized in that: When the port two is used to output or input parallel light, the polarization-maintaining circulator also includes a filter arranged between the lens and the port two and located at the focal position of the lens, and the filter is used to reflect all or part of the parallel light output from the port one to the port two.

12. The polarization-maintaining circulator according to claim 1, characterized in that: Used to transmit light input from port one to port two in a first direction, transmit light input from port two to port three in a second direction, transmit light input from port three to port four in the first direction, and transmit light input from port four to port one in the second direction, wherein the first direction is opposite to the second direction; The polarization-maintaining circulator comprises: a first polarization-maintaining dual-core waveguide for realizing the port one and the port three, a first birefringent crystal, a first Faraday rotator, a lens, a second birefringent crystal, and a second polarization-maintaining dual-core waveguide for realizing the port two and the port four, which are arranged in sequence along the first direction, wherein the first birefringent crystal, the first Faraday rotator, and the second birefringent crystal are all parallel plate structures; wherein The port one is used to input divergent linear polarized light, and the light input from the port one enters the first birefringent crystal as o light or e light; the first birefringent crystal is used to make the light input from the port one shift positively toward the first birefringent crystal and then emit to the first Faraday rotator; the first Faraday rotator is used to rotate the polarization state of the light input from the port one by an angle α along a first rotation direction and then emit to the lens, wherein α=45°; the lens is used to converge the light input from the port one to form converged light and then emit to the second birefringent crystal; the second birefringent crystal is used to make the light input from the port one shift positively toward the second birefringent crystal and then emit to the port two; the port two is used to output the light input from the port one, so as to realize the transmission of light from the port one to the port two; The port 2 is also used to input divergent linear polarized light, and the light input from the port 2 enters the second birefringent crystal as o light or e light with the same polarization state as the light input from the port 1; the second birefringent crystal is also used to make the light input from the port 2 form a reverse second birefringent crystal displacement and then emit it to the lens; the lens is also used to converge the light input from the port 2 to form converged light and then emit it to the first Faraday rotator; the first Faraday rotator is also used to rotate the polarization state of the light input from the port 2 by the angle α along the first rotation direction and then emit it to the first birefringent crystal; the first birefringent crystal is also used to make the light input from the port 2 form a reverse second birefringent crystal displacement and then emit it to the lens; The first birefringent crystal is displaced and directed toward the port three, wherein the polarization state of the light input from the port two in the first birefringent crystal is rotated 90° relative to the polarization state of the light input from the port one, and the o light and the e light are transformed, so that the light input from the port two deviates from the light input from the port one in the first birefringent crystal, and the lateral walk-off generated between the light input from the port one and the light input from the port two is equal to the double-core spacing of the first polarization-maintaining double-core waveguide, so that the light input from the port two is coupled into the port three; the port three is used to output the light input from the port two, so as to realize the transmission of light from the port two to the port three; The port three is also used to input divergent linear polarized light, and the light input from the port three enters the first birefringent crystal as o light or e light with the same polarization state as the light input from the port two; the first birefringent crystal is used to make the light input from the port three form a positive first birefringent crystal displacement and then emit it to the first Faraday rotator; the first Faraday rotator is used to rotate the polarization state of the light input from the port three by the angle α along the first rotation direction and then emit it to the lens; the lens is used to converge the light input from the port three to form converged light and then emit it to the second birefringent crystal; the second birefringent crystal is used to make the light input from the port three form a positive second birefringent crystal displacement The refractive crystal is displaced and directed to the port four; wherein the polarization state of the light input from the port three in the second birefringent crystal is rotated 90° relative to the polarization state of the light input from the port two, and the o light and the e light are transformed, so that the light input from the port three deviates from the light input from the port two in the second birefringent crystal, and the lateral walk-off generated between the light input from the port two and the light input from the port three is equal to the double-core spacing of the second polarization-maintaining double-core waveguide, so that the light input from the port three is coupled into the port four; the port four is used to output the light input from the port three, so as to realize the transmission of light from the port three to the port four; The port four is also used to input divergent linear polarized light, and the light input from the port four enters the second birefringent crystal as o light or e light with the same polarization state as the light input from the port three; the second birefringent crystal is also used to make the light input from the port four form a reverse second birefringent crystal displacement and then emit it to the lens; the lens is also used to converge the light input from the port four to form converged light and then emit it to the first Faraday rotator; the first Faraday rotator is also used to rotate the polarization state of the light input from the port four by the angle α along the first rotation direction and then emit it to the first birefringent crystal; the first birefringent crystal is also used to make the light input from the port four form a reverse first birefringent crystal displacement and then emit it to the port one, wherein the polarization state of the light input from the port four in the first birefringent crystal forms a 90° rotation relative to the polarization state of the light input from the port three, the o light and the e light are transformed, and at this time they are the same as the polarization state of the light input from the port one, so they enter the port one in the reverse direction of the light input from the port one, thereby realizing the transmission of light from the port four to the port one.

13. The polarization-maintaining circulator according to claim 12, characterized in that: The first birefringent crystal and / or the second birefringent crystal are combined crystals. In addition to achieving the same displacement, the combined crystal can also be used to compensate for optical path difference.

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