Three-port reflective circulator and preparation method thereof

Abstract

The invention discloses a three-port reflection-type circulator and a preparation method thereof, the three-port reflection-type circulator comprises a three-fiber tail fiber, an annular core and a plurality of glass tubes, the tail fiber end face of the three-fiber tail fiber is subjected to thermal core expansion treatment, the annular core comprises a polarization beam splitting assembly, an optical rotation assembly and a refraction assembly, the polarization beam splitting assembly comprises a displacement crystal, and the displacement crystal is connected with the optical rotation assembly. The optical rotation assembly comprises a half-wave plate group, an optical rotation unit, a half-wave plate and a compensation plate, the refraction assembly comprises a collimating lens, a Wollaston prism and a reflective mirror, and the three-fiber tail fiber and the annular core are sleeved through a plurality of glass tubes; wherein light emitted by the three-fiber tail fiber sequentially passes through the polarization beam splitting assembly, the optical rotation assembly and the refraction assembly, is reflected by the reflective mirror, sequentially passes through the refraction assembly, the optical rotation assembly and the polarization beam splitting assembly and returns to the three-fiber tail fiber. The three-port reflective circulator in the embodiment of the invention is more compact in structure and smaller in size, and can be widely applied to the technical field of optical devices.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and in particular to a three-port reflective circulator and a preparation method thereof. Background Art

[0002] The three-port fiber circulator is a non-reciprocal optical passive device, which is similar to two independent optical isolators in function, and can realize the one-way conduction and reverse cutoff of optical signals; the difference is that the circulator integrates the output port of one isolator and the input port of another isolator into a common port, thus forming a reciprocating "loop" of the optical path. Therefore, circulators are widely used in optical communication subsystems such as single-fiber bidirectional transmission systems, dispersion compensation units, wavelength blockers, channel equalizers, and wavelength selective switches.

[0003] In terms of optical path structure, since the polarization states of the two polarized beams need to be processed separately, the light beam needs to be collimated into a large spot with a small divergence (spot size is about 200um) before being separated into two polarized beams. This limits the length of the beam splitter and cannot be processed to a very small size (the typical value of the length of the beam splitter and the spot separation distance is 10:1. Considering the processing error of the beam splitter and the effective aperture, the length of the beam splitter must be at least 3mm). Otherwise, the two polarized beams cannot be completely separated. Therefore, the size bottleneck of the beam splitter in the three-port circulator limits the size of the overall device. Summary of the invention

[0004] In view of this, in order to solve one of the above problems, an object of an embodiment of the present invention is to provide a three-port reflective circulator and a preparation method thereof, which has a more compact structure and a smaller size.

[0005] On the one hand, an embodiment of the present invention provides a three-port reflective circulator, including a three-fiber pigtail, an annular core and several glass tubes, the pigtail end face of the three-fiber pigtail is subjected to thermal core expansion treatment, the annular core includes a polarization beam splitting component, an optical rotation component and a refractive component, the polarization beam splitting component includes a displacement crystal, the optical rotation component includes a half-wave plate group, an optical rotation unit, a half-wave plate and a compensation plate, the refractive component includes a collimating lens, a Wollaston prism and a reflector, the three-fiber pigtail and the annular core are sleeved by several of the glass tubes; wherein, the light emitted by the three-fiber pigtail passes through the polarization beam splitting component, the optical rotation component and the refractive component in turn, and is reflected by the reflector, and passes through the refractive component, the optical rotation component and the polarization beam splitting component in turn to return to the three-fiber pigtail.

[0006] Optionally, the half-wave plate group includes two half-wave plates with optical axes of 22.5°, and the 22.5° half-wave plates are symmetrically distributed.

[0007] Optionally, the optical rotation unit includes an optical rotation plate and a 22.5° half-wave plate.

[0008] Optionally, the collimating lens comprises a ball lens or a gradient index lens.

[0009] Optionally, the three-fiber pigtail is formed by three single-mode optical fibers inserted into a three-hole capillary, the three holes of the three-hole capillary are arranged in the same straight line, the first hole is spaced a preset distance from the second hole, and the second hole and the third hole are connected holes.

[0010] Optionally, the end face of the three-fiber pigtail is ground to a preset inclination angle.

[0011] Optionally, the distance between the end face of the three-fiber pigtail and the displacement crystal is less than 0.1 mm.

[0012] On the other hand, an embodiment of the present invention provides a method for preparing a three-port reflective circulator, which is applied to the above-mentioned three-port reflective circulator, comprising:

[0013] Fixing the optical rotation component on the polarization beam splitting component to form a single crystal;

[0014] Mounting the single crystal on one end of the collimating lens, inserting one end of the collimating lens into one end of the first glass tube and fixing it;

[0015] The Wollaston prism and the reflector are mounted and fixed on one end of the second glass tube, and the other end of the collimating lens is inserted into the other end of the second glass tube and fixed;

[0016] Insert the three-fiber pigtail into the other end of the first glass tube, debug and fix it.

[0017] Optionally, fixing an optical rotation component on the polarization beam splitting component to form a single crystal comprises:

[0018] Fix the displacement crystal, and use the plane where the 45° optical axis of the displacement crystal is located as a reference plane;

[0019] Two symmetrical 22.5° half-wave plates are attached side by side on the adjacent surface of the reference surface to form a half-wave plate group; the length of a single half-wave plate in the first preset direction is 1 / 2 of the length of the displacement crystal, and the length in the second preset direction is equal to the length of the crystal displacement;

[0020] The optical rotation plate and the 22.5° half-wave plate are sequentially mounted on the surface of the half-wave plate group to form the optical rotation unit; the length of the optical rotation unit in the second preset direction is 2 / 3 of the length of the displacement crystal, and the length in the first preset direction is equal to the length of the crystal displacement;

[0021] The compensation plate is mounted on the remaining surface of the half-wave plate group; the length of the compensation plate in the second preset direction is 1 / 3 of the length of the displacement crystal, and the length in the first preset direction is equal to the length of the crystal displacement;

[0022] A 45° half-wave plate is mounted on the surface of the optical rotation unit; the length of the 45° half-wave plate in the second preset direction is 1 / 3 of the length of the optical rotation unit, and the length in the first preset direction is equal to the length of the optical rotation unit.

[0023] Optionally, debug via:

[0024] Connecting the three fiber pigtails to the light source or the power meter respectively according to the preset channels to form a predetermined loop;

[0025] The position of the three-fiber pigtail is adjusted until the minimum parameter of the predetermined loop is found, and the debugging is completed.

[0026] The implementation of the embodiment of the present invention includes the following beneficial effects: In this embodiment, the three-port reflective circulator includes a three-fiber pigtail, a ring core and several glass tubes. The pigtail end face of the three-fiber pigtail is subjected to a thermal core expansion process to slow down the divergence of the light spot and shorten the length of the beam separation device (displacement crystal), thereby shortening the size of the entire device. The ring core includes a polarization beam splitting component, a rotation component and a refraction component. The polarization beam splitting component includes a displacement crystal. The rotation component includes a half-wave plate group, a rotation unit, a half-wave plate and a compensation plate. The refraction component includes a collimating lens, a Wollaston prism and a reflector. The three-fiber pigtail and the ring core are connected by several glass tubes. The light emitted by the three-fiber pigtail passes through the polarization beam splitting component, the rotation component and the refraction component in turn, and is reflected by the reflector. It passes through the refraction component, the rotation component and the polarization beam splitting component in turn and returns to the three-fiber pigtail. Through the reflective optical path design, the crystal material is reduced and the device structure is more compact. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a three-port reflective circulator provided by an embodiment of the present invention;

[0028] Figure 2 It is a structural schematic diagram of a single-mode optical fiber end face subjected to thermal core expansion treatment provided by an embodiment of the present invention;

[0029] Figure 3 is a schematic structural diagram of a three-hole capillary provided in an embodiment of the present invention;

[0030] Figure 4 is a schematic structural diagram of a displacement crystal provided by an embodiment of the present invention;

[0031] Figure 5 is a light path diagram of a half-wave plate provided by an embodiment of the present invention;

[0032] Figure 6 is a schematic structural diagram of a half-wave plate assembly provided by an embodiment of the present invention;

[0033] Figure 7 is a light path diagram of an optical rotator provided by an embodiment of the present invention;

[0034] Figure 8 is a light path diagram of an optical rotation unit provided by an embodiment of the present invention;

[0035] Fig. 9 This is a light path diagram of a 45° half-wave plate provided by an embodiment of the present invention;

[0036] Fig.10 is a schematic diagram of the structure of a single crystal provided by an embodiment of the present invention;

[0037] Fig.11 is a schematic structural diagram of a Wollaston prism provided by an embodiment of the present invention;

[0038] Fig.12 is a light path diagram of a reflector provided by an embodiment of the present invention;

[0039] Fig.13 is a schematic structural diagram of a pigtail end face provided by an embodiment of the present invention;

[0040] Fig.14 It is a schematic diagram of the positions of a three-fiber pigtail and a displacement crystal provided by an embodiment of the present invention;

[0041] Fig.15 is a polarization state change diagram of an optical path provided by an embodiment of the present invention;

[0042] Fig.16 is a polarization state change diagram of another optical path provided by an embodiment of the present invention;

[0043] Fig.17 It is a flow chart of a method for preparing a three-port reflective circulator provided by an embodiment of the present invention;

[0044] Fig.18 is a diagram of the assembly process of a three-port reflective circulator provided by an embodiment of the present invention;

[0045] Fig.19 is a diagram of an assembly process of a single crystal provided by an embodiment of the present invention;

[0046] Fig. 20 is a diagram of an assembly process of another single crystal provided by an embodiment of the present invention;

[0047] Fig.21 is a diagram of an assembly process of another single crystal provided by an embodiment of the present invention;

[0048] Fig. 22 It is a schematic structural diagram of another three-port reflective circulator provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only provided for the convenience of explanation and description, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0050] See also Figure 1 The embodiment of the present invention provides a three-port reflective circulator, comprising a three-fiber pigtail, a ring core and a plurality of glass tubes, wherein the pigtail end faces (P1, P2, P3) of the three-fiber pigtail are subjected to a thermal core expansion process, the ring core comprises a polarization beam splitting component (M1), an optical rotation component (M2) and a refraction component, the polarization beam splitting component comprises a displacement crystal, the optical rotation component comprises a half-wave plate group, an optical rotation unit, a half-wave plate and a compensation plate, the refraction component comprises a collimating lens (M3), a Wollaston prism (M4) and a reflector (M5), and the three-fiber pigtail and the ring core are sleeved by a plurality of glass tubes; wherein the light emitted from the three-fiber pigtail passes through the polarization beam splitting component (M1), the optical rotation component (M2) and the refraction component in sequence, and is reflected by the reflector (M5), and passes through the refraction component, the optical rotation component (M2) and the polarization beam splitting component (M1) in sequence to return to the three-fiber pigtail.

[0051] See also Figure 2 The three-fiber pigtail can use single-mode optical fiber. The single-mode optical fiber includes a coating layer (M01), a cladding layer (M02) and a core (M03). The end faces of the three single-mode optical fibers need to be thermally expanded (TEC) to expand the mode field diameter (MFD) of the optical fiber to form an effective beam expansion area (M04).

[0052] Optionally, the three-fiber pigtail is formed by three single-mode optical fibers inserted into a three-hole capillary, the three holes of the three-hole capillary are arranged in the same straight line, the first hole is spaced a preset distance from the second hole, and the second hole and the third hole are connected holes.

[0053] See also Figure 3 In a specific embodiment, the three holes of the capillary are all in the horizontal direction of the y-axis, the hole size is the diameter of the optical fiber after the coating layer is stripped off, the hole positions 1 and 2 are separated by a certain distance, and the hole positions 2 and 3 are connected holes. The distances between the first hole position, the second hole position and the third hole position are determined according to actual applications, and this embodiment does not impose specific restrictions.

[0054] The polarization beam splitter consists of a displacement crystal. The displacement crystal uses yttrium vanadate (YVO4) material with a large difference in birefringence coefficient. When the optical axis points to about 45°, the o / e light has the largest separation angle. At this time, after the non-polarized light passes through the displacement crystal, the ratio of the distance d between the o / e light and the length L of the displacement crystal is about 1 / 10. In the application of circulators, engineering generally requires that the splitting distance d is greater than 1.5 times the spot size (let the spot size be wo, then d ≥ 1.5*wo) to completely separate the two beams. Figure 4 The optical axis of the displacement crystal is located in the XZ plane, and the direction of the optical axis forms an angle of 45°±0.5° with the Z axis. Its function is to separate the natural light in the X direction into two linear polarized lights, o light and e light, whose polarization directions are perpendicular to each other. Among them, the polarization direction of o light is perpendicular to the plane where the optical axis is located (that is, parallel to the Y axis), and the polarization direction of e light is parallel to the plane where the optical axis is located.

[0055] Optionally, the half-wave plate set includes two half-wave plates with optical axes of 22.5°, and the 22.5° half-wave plates are symmetrically distributed.

[0056] See also Figure 5 The half-wave plate is a reciprocal crystal, which functions to reciprocally rotate the polarization direction of linearly polarized light. When linearly polarized light is incident on the half-wave plate vertically, if the angle between the polarization direction of the incident light and the optical axis of the half-wave plate is A, the transmitted light is still linearly polarized light, and its polarization direction is rotated by 2A from its original position about the optical axis (when A=22.5°, the polarization direction is rotated by 45°; when A=45°, the polarization direction is rotated by 90°).

[0057] See also Figure 6 Two 22.5° half-wave plates are placed side by side to form a half-wave plate group. The optical axes of the two wave plates are 22.5° to the y-axis and are mirror-symmetrical to each other. Their function is to rotate the polarization direction of the incident linear polarization light by 45°. When two beams of polarized light with perpendicular polarization states pass through the half-wave plate group (one beam of light passes through one wave plate, and the other beam of light passes through the other wave plate), the polarization states of the two beams of polarized light can be transformed into parallel to each other.

[0058] Optionally, the optical rotation unit includes an optical rotation plate and a 22.5° half-wave plate.

[0059] See also Figure 7 The optical rotator is a non-reciprocal crystal, and its function is to perform non-reciprocal rotation on the polarization direction of linearly polarized light, that is, the rotation direction of the polarization state has nothing to do with the propagation direction of the light, but is only related to the direction of the external magnetic field. When the magnetic ring (M21) applies a saturated magnetic field of N→S along the positive direction of the Z axis to the optical rotator (M22), the polarization direction of the linearly polarized light passing through the unit will rotate counterclockwise on the XY plane (generally satisfying the right-hand screw rule).

[0060] See also Figure 8The optical rotation unit is composed of a 45° optical rotation plate (M22) and a 22.5° half-wave plate (M23). When the magnetic ring (M21) applies a N→S magnetic field along the positive direction of the Z axis to the optical rotation plate (M22), and the half-wave plate is clamped at 22.5° to the Y axis, the linearly polarized light passes through the optical rotation unit along the positive direction of the Z axis, and the polarization state rotates 90°. When it passes through the optical rotation unit in the reverse direction, the polarization state rotates 0°.

[0061] In a specific embodiment, the optical rotation assembly is composed of a half-wave plate group consisting of two half-wave plates with an optical axis of 22.5°, an optical rotation unit consisting of an optical rotation plate and a 22.5° half-wave plate, a half-wave plate with an optical axis of 45°, and a compensation plate stacked and mounted.

[0062] See also Fig. 9 The optical axis of the 45° half-wave plate is 45° to the y-axis, and its function is to rotate the polarization direction of the incident linear polarization light by 90°. The compensation plate does not have an optical rotation function, and its main function is to compensate for the optical path difference generated by the optical rotation unit and the 45° half-wave plate.

[0063] See also Fig.10 , Fig.10 The schematic diagram of the structure of a single crystal composed of a displacement crystal and an optical rotation component on different sides shows that C1 represents a displacement crystal, C2 represents a 22.5° half-wave plate, C3 represents a 22.5° half-wave plate, C2 and C3 form a half-wave plate group, C4 represents a compensation plate, C5 represents an optical rotation plate, C6 represents a 22.5° half-wave plate, and C7 represents a 45° half-wave plate. The plane where the 45° optical axis of the displacement crystal is located is used as a reference plane (i.e., X-Z plane), C2 and C3 are set on the upper surface of the reference plane of the displacement crystal C1, C5 and C4 are set on a partial surface of the half-wave plate group and span C2 and C3, C6 is set on the surface of C5, and C7 is set on a partial surface of C6.

[0064] Optionally, the collimating lens comprises a ball lens or a gradient index lens.

[0065] The collimating lens includes but is not limited to a ball lens or a gradient refractive index lens. The function of the collimating lens is to collimate a Gaussian beam that diverges rapidly in free space (without optical fiber constraints) into a Gaussian beam that diverges more slowly.

[0066] See also Fig.11 Wollaston prism is composed of two wedges (M41 / M42) with mutually perpendicular optical axes. The wedge material is YVO4, the wedge angle is a predetermined design angle (N), the two crystal optical axes are on the XY plane, the crystal optical axis and the X axis form an angle of 45°±0.1°, and the overall shape is "cross". The function of Wollaston prism is to separate the incident natural light into two linear polarized light beams with mutually perpendicular polarization directions at a certain angle.

[0067] See also Fig.12The function of the reflector (M5) is to reflect the forward transmission light path.

[0068] Optionally, the fiber end faces of the three-fiber pigtail are ground to a preset inclination angle.

[0069] See also Fig.13 After the insertion is completed, the end face of the pigtail needs to be polished to a certain angle to reduce reflection and improve the product return loss parameters.

[0070] Optionally, the distance between the end face of the three-fiber pigtail and the displacement crystal is less than 0.1 mm.

[0071] In the optical path structure of the circulator, since the polarization states of the two polarized lights need to be processed separately, the O / E must be strictly separated, and the separation distance is at least 1.5 times the size of the light spot itself. Therefore, the displacement crystal is usually placed after the collimating lens to prevent the light beam from diverging too quickly. The embodiment of the present invention uses TEC technology to expand the core diameter, and at the same time controls the air gap between the pigtail and the displacement crystal within 0.1mm by controlling the length of the collimating lens, which can effectively suppress the rapid divergence of the light spot and the problem of a large light spot arriving at the front end of the displacement crystal. Fig.14 , P represents a three-fiber pigtail, M1 represents a displacement crystal, Q represents the observation position of the light spot, and D represents the spatial gap between the pigtail and the displacement crystal. In a specific embodiment, the mode field diameter of the optical fiber is expanded to 25um (MFD=25um), and the spot size obtained on the front end of the displacement crystal is examined when the displacement crystal is 1.5mm long. Under the simulation of zemax software, it can be obtained that when the air gap is 0.1mm, the spot size is only 0.07mm. Considering the tolerance of 1.5 times is 0.11mm size, it fully meets the engineering splitting requirements. The splitting distance of 0.15mm (1.5mm / 10) is greater than 0.11mm (1.5*spot size). In contrast, without thermal core expansion, the beam mode field diameter MFD=10.4um. Under the same condition of 1.5mm long displacement crystal, the distance between the light spot and the splitting on the end face is 0.15mm, which cannot be distinguished at all.

[0072] The working process of the three-port reflective circulator in this embodiment is as follows:

[0073] See also Fig.10 and Fig.15The optical path 1→2 (along the positive direction of the Z axis) starts from the pigtail aperture 1 and passes through the displacement crystal, 22.5° half-wave plate group, compensation plate, collimating lens, Wollaston prism, reflector, Wollaston prism, collimating lens, optical rotation unit, 22.5° half-wave plate group, displacement crystal and enters the pigtail aperture 2. The specific polarization state change process is as follows: natural light with a random polarization state (the polarization state is represented by a bidirectional cross arrow) is emitted from port 1, and after passing through the displacement crystal, it is separated into two beams of linear polarized light with polarization states perpendicular to each other in the X direction, which are represented by horizontal double arrows and vertical double arrows respectively; after the two beams of linear polarized light pass through the 22.5° half-wave plate group, the polarization directions of the two beams of light are the same and form a positive 45° angle with the XY plane; the two beams of polarized light with the same polarization direction are collimated by the lens and enter the Wollaston prism. At this time, the polarization directions of the two beams of polarized light are parallel to the optical axis direction of the first wedge angle in the Wollaston prism, and the light beams are deflected in the Y-axis direction, thereby the light beams are offset from position 1 to position 2 in the Y direction, and then return to the collimating lens through the reflection of the reflector and enter the optical rotation unit. The polarization states of the two beams of light do not deflect, and enter the 22.5° half-wave plate group again to undergo optical rotation and re-change back to two beams of polarized light with polarization states perpendicular to each other, and finally combine the light from the displacement crystal and output from port 2.

[0074] See also Fig.10 and Fig.16 , optical path 2→3 (along the positive direction of the Z axis) starts from the pigtail aperture 2 and passes through the displacement crystal, 22.5° half-wave plate group, optical rotation unit, collimating lens, Wollaston prism, reflector, Wollaston prism, collimating lens, 45° half-wave plate, optical rotation unit, 22.5° half-wave plate group, and displacement crystal to enter the pigtail aperture 3. The specific polarization state change process is as follows: natural light with random polarization state (polarization state is represented by a bidirectional cross arrow) is emitted from port 2, and after passing through the displacement crystal, it is separated into two beams of linear polarized light with polarization states perpendicular to each other in the X direction, represented by horizontal double arrows and vertical double arrows respectively; after the two beams of linear polarized light pass through the 22.5° half-wave plate group, the polarization directions of the two beams of light are the same and form a positive 45° angle with the XY plane, and then enter the optical rotation plate, and the polarization states of the two beams of light are simultaneously deflected by 90°, forming a negative 45° angle with the XY plane, and the two beams of polarized light with the same polarization direction are collimated by the lens and enter the Wollaston prism, and the light The situation of path 1→2 is different. At this time, the polarization directions of the two polarized light beams are vertically aligned with the optical axis direction of the first wedge angle in the Wollaston prism, and the light beam is deflected in another direction in the Y-axis direction, thereby the light beam is offset from position 2 to position 3 in the Y direction, and then returns to the collimating lens through the reflection of the mirror and enters the 45° half-wave plate. The polarization states of the two light beams are deflected 90° at the same time, and enter the optical rotation unit again. The polarization state is not polarized, and then enters the 22.5° half-wave plate group again for optical rotation, and two groups of mutually perpendicular linear polarized lights are obtained again. Finally, the light is combined from the displacement crystal and output from port 3.

[0075] Through simulation with ZEMAX software, the coupling efficiency of the two optical path simulation results was above 96%, reaching commercial standards.

[0076] See also Fig.17 The embodiment of the present invention provides a method for preparing a three-port reflective circulator, which is applied to the above-mentioned three-port reflective circulator, comprising:

[0077] S100, fixing an optical rotation component on a polarization beam splitting component to form a single crystal;

[0078] S200, mounting the single crystal on one end of the collimating lens, inserting one end of the collimating lens into one end of the first glass tube and fixing it;

[0079] S300, mounting and fixing a Wollaston prism and a reflector on one end of a second glass tube, and inserting the other end of a collimating lens into the other end of the second glass tube and fixing it;

[0080] S400, insert the three-fiber pigtail into the other end of the first glass tube, debug and fix it.

[0081] Specifically, first follow Fig.10 The polarization diversity unit and the optical rotation unit are stacked and fixed piece by piece by glue. Then, refer to Fig.18 , a fixed single crystal (N) is mounted on the end of the collimating lens (M3), the end of the collimating lens (M3) is inserted from one side of the first glass tube (S1), the front end of the collimating lens (M3) is exposed from the first glass tube (S1) for a certain length (for hanging the glass tube #2), and is fixed by glue. The first glass tube (S1) is covered with a magnetic ring (M21) to provide a saturated magnetic field for the optical rotator; then, the Wollaston prism (M4) and the reflector (M5) are glued and mounted and fixed on one side of the tube mouth of the second glass tube (S2), the other side of the second glass tube (S2) is covered with the exposed collimating lens (M3), the second glass tube (S2) is rotated to a suitable position, and is fixed by glue.

[0082] Optionally, an optical rotation component is fixed on the polarization beam splitting component to form a single crystal, including:

[0083] S110, fix the displacement crystal, and use the plane where the 45° optical axis of the displacement crystal is located as the reference plane;

[0084] S120, attaching two symmetrical 22.5° half-wave plates side by side on the adjacent surface of the reference surface to form a half-wave plate group; the length of a single half-wave plate in the first preset direction is 1 / 2 of the length of the displacement crystal, and the length in the second preset direction is equal to the length of the crystal displacement;

[0085] S130, sequentially mounting an optical rotation plate and a 22.5° half-wave plate on the surface of the half-wave plate group to form an optical rotation unit; the length of the optical rotation unit in the second preset direction is 2 / 3 of the length of the displacement crystal, and the length in the first preset direction is equal to the length of the crystal displacement;

[0086] S140, mounting a compensation plate on the remaining surface of the half-wave plate group; the length of the compensation plate in the second preset direction is 1 / 3 of the length of the displacement crystal, and the length of the compensation plate in the first preset direction is equal to the length of the crystal displacement;

[0087] S150, mounting a 45° half-wave plate on the surface of the optical rotation unit; the length of the 45° half-wave plate in the second preset direction is 1 / 3 of the length of the optical rotation unit, and the length in the first preset direction is equal to the length of the optical rotation unit.

[0088] Specifically, first, a displacement crystal (polarization diversity component) is fixed with a fixture, and the plane where the 45° optical axis of the displacement crystal is located is used as a reference plane (ie, X-Z plane); then, refer to Fig.19 , two symmetrical half-wave plates are attached side by side on the upper surface of the displacement crystal (i.e. the positive z direction). The length of a single half-wave plate in the x direction is 1 / 2 of the displacement crystal, and the length in the y direction is equal to the crystal displacement; then, refer to Fig. 20 , the fixture drives the displacement crystal to rotate 90° around the Z axis to the YZ plane, and the optical rotation unit (C8) is attached to the upper left side of the half-wave plate pair (the left edges are aligned), wherein the optical rotation plate (C5) in the optical rotation unit (C8) is downward and close to the half-wave plate pair, and the half-wave plate (C6) in the optical rotation unit (C8) is upward and away from the half-wave plate pair. The length of the optical rotation unit (C8) in the y direction is 2 / 3 of the displacement crystal, and the length in the x direction is equal to the crystal displacement; then, refer to Fig.21 , also in the YZ plane, attach the compensation plate (C4) to the right above the half-wave plate pair (align the right edges). The length of the compensation plate (C4) in the y direction is 1 / 3 of the displacement crystal, and the length in the x direction is equal to the crystal displacement; finally, refer to Fig.10 In the YZ plane, a 45° half-wave plate (C7) is attached to the upper left side of the optical rotation unit (aligned with the left edge). The length of the 45° half-wave plate (C7) in the y direction is 1 / 3 of the optical rotation unit, and the length in the x direction is equal to that of the optical rotation unit.

[0089] Optionally, debug via:

[0090] Connect the three fiber pigtails to the light source or power meter according to the preset channels to form a predetermined loop;

[0091] Adjust the position of the three-fiber pigtail until the minimum parameters of the predetermined loop are found, and the debugging is completed.

[0092] See also Fig. 22, the three-fiber pigtail is connected to the light source and the power meter according to the designed channel 1 / 2 / 3 optical fiber (1 connected to the light source → 2 connected to the power meter, 2 connected to the light source → 3 connected to the power meter) to form a predetermined loop, and the three-fiber pigtail (P) is pushed into the tube mouth from the left side of the first glass tube (S1), and the pigtail is fine-tuned up and down and front and back until the minimum parameters of CH_1-2 and CH_2-3 are found, and the pigtail is fixed with glue.

[0093] The implementation of the embodiment of the present invention includes the following beneficial effects: In this embodiment, the three-port reflective circulator includes a three-fiber pigtail, a ring core and several glass tubes. The pigtail end face of the three-fiber pigtail is subjected to a thermal core expansion process to slow down the divergence of the light spot and shorten the length of the beam separation device (displacement crystal), thereby shortening the size of the entire device. The ring core includes a polarization beam splitting component, a rotation component and a refraction component. The polarization beam splitting component includes a displacement crystal. The rotation component includes a half-wave plate group, a rotation unit, a half-wave plate and a compensation plate. The refraction component includes a collimating lens, a Wollaston prism and a reflector. The three-fiber pigtail and the ring core are connected by several glass tubes. The light emitted by the three-fiber pigtail passes through the polarization beam splitting component, the rotation component and the refraction component in turn, and is reflected by the reflector. It passes through the refraction component, the rotation component and the polarization beam splitting component in turn and returns to the three-fiber pigtail. Through the reflective optical path design, the crystal material is reduced and the device structure is more compact.

[0094] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A three-port reflective circulator, characterized in that: The invention comprises a three-fiber pigtail, an annular core and a plurality of glass tubes, wherein the pigtail end face of the three-fiber pigtail is subjected to a thermal core expansion treatment, the annular core comprises a polarization beam splitting component, an optical rotation component and a refraction component, the polarization beam splitting component comprises a displacement crystal, the optical rotation component comprises a half-wave plate group, an optical rotation unit, a half-wave plate and a compensation plate, the refraction component comprises a collimating lens, a Wollaston prism and a reflector, and the three-fiber pigtail and the annular core are sleeved by a plurality of the glass tubes; wherein the light emitted by the three-fiber pigtail passes through the polarization beam splitting component, the optical rotation component and the refraction component in sequence, is reflected by the reflector, passes through the refraction component, the optical rotation component and the polarization beam splitting component in sequence, and returns to the three-fiber pigtail.

2. The three-port reflective circulator according to claim 1, characterized in that: The half-wave plate group includes two half-wave plates with optical axes of 22.5 degrees, and the 22.5 degree half-wave plates are symmetrically distributed.

3. The three-port reflective circulator according to claim 1, characterized in that: The optical rotation unit comprises an optical rotation plate and a 22.5° half-wave plate.

4. The three-port reflective circulator according to claim 1, wherein: The collimating lens includes a ball lens or a gradient refractive index lens.

5. The three-port reflective circulator according to claim 1, characterized in that: The three-fiber pigtail is formed by three single-mode optical fibers inserted into a three-hole capillary. The three holes of the three-hole capillary are arranged in the same straight line. The first hole is spaced a preset distance from the second hole, and the second hole and the third hole are connected holes.

6. The three-port reflective circulator according to claim 1, wherein: The end faces of the three-fiber pigtail are ground to a preset inclination angle.

7. The three-port reflective circulator according to any one of claims 1 to 6, characterized in that: The distance between the end face of the three-fiber pigtail and the displacement crystal is less than 0.1 mm.

8. A method for preparing a three-port reflective circulator, characterized in that: The three-port reflective circulator according to any one of claims 1 to 7, comprising: Fixing the optical rotation component on the polarization beam splitting component to form a single crystal; Mounting the single crystal on one end of the collimating lens, inserting one end of the collimating lens into one end of the first glass tube and fixing it; The Wollaston prism and the reflector are mounted and fixed on one end of the second glass tube, and the other end of the collimating lens is inserted into the other end of the second glass tube and fixed; Insert the three-fiber pigtail into the other end of the first glass tube, debug and fix it.

9. The preparation method according to claim 8, characterized in that: The optical rotation component is fixed on the polarization beam splitting component to form a single crystal, comprising: Fix the displacement crystal, and use the plane where the 45° optical axis of the displacement crystal is located as a reference plane; Two symmetrical 22.5° half-wave plates are attached side by side on the adjacent surface of the reference surface to form a half-wave plate group; the length of a single half-wave plate in the first preset direction is 1 / 2 of the length of the displacement crystal, and the length in the second preset direction is equal to the length of the crystal displacement; The optical rotation plate and the 22.5° half-wave plate are sequentially mounted on the surface of the half-wave plate group to form the optical rotation unit; the length of the optical rotation unit in the second preset direction is 2 / 3 of the length of the displacement crystal, and the length in the first preset direction is equal to the length of the crystal displacement; The compensation plate is mounted on the remaining surface of the half-wave plate group; the length of the compensation plate in the second preset direction is 1 / 3 of the length of the displacement crystal, and the length in the first preset direction is equal to the length of the crystal displacement; A 45° half-wave plate is mounted on the surface of the optical rotation unit; the length of the 45° half-wave plate in the second preset direction is 1 / 3 of the length of the optical rotation unit, and the length in the first preset direction is equal to the length of the optical rotation unit.

10. The preparation method according to claim 8, characterized in that: Debugging is done by: Connecting the three fiber pigtails to the light source or the power meter respectively according to the preset channels to form a predetermined loop; The position of the three-fiber pigtail is adjusted until the minimum parameter of the predetermined loop is found, and the debugging is completed.

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