A three-port reflective circulator and a method of manufacturing the same

Abstract

The application discloses a three-port reflective circulator and a preparation method thereof. The three-port reflective circulator comprises a three-fiber pigtail, a ring-shaped core and a plurality of glass tubes. The tail fiber end face of the three-fiber pigtail is subjected to a hot expansion core treatment. The ring-shaped core comprises a polarization beam splitting assembly, a rotary optical assembly and a refractive assembly. The polarization beam splitting assembly comprises a displacement crystal. The rotary optical assembly comprises a half-wave plate group, a rotary optical unit, a half-wave plate and a compensating plate. The refractive assembly comprises a collimating lens, a Wollaston prism and a mirror. The three-fiber pigtail and the ring-shaped core are sleeved by the plurality of glass tubes. In the application, the light emitted by the three-fiber pigtail passes through the polarization beam splitting assembly, the rotary optical assembly and the refractive assembly in sequence, is reflected by the mirror, and returns to the three-fiber pigtail by passing through the refractive assembly, the rotary optical assembly and the polarization beam splitting assembly in sequence. The three-port reflective circulator in the application has a more compact structure and a smaller size, and can be widely applied to the technical field of optical devices.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and in particular to a three-port reflective circulator and its fabrication method. Background Technology

[0002] A three-port fiber optic circulator is a non-reciprocal passive optical device that functions similarly to two independent optical isolators, enabling unidirectional conduction and reverse cutoff of optical signals. The difference lies in that the circulator integrates the output port of one isolator and the input port of the other into a common port, thus forming a reciprocating optical path "loop." 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 beams need to be collimated into a large spot (approximately 200 μm in size) with a small divergence before being separated into two polarized beams. This limits the length of the beam splitter, which cannot be made very small (the typical ratio of the beam splitter length to the spot separation distance is 10:1; considering the manufacturing error of the beam splitter and the effective aperture, the length of the beam splitter must be at least 3 mm). Otherwise, the two polarized beams cannot be completely separated. Therefore, the size bottleneck of the beam splitter in the three-port circulator restricts the overall size of the device. Summary of the Invention

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

[0005] On one hand, an embodiment of the present invention provides a three-port reflective circulator, including a three-fiber pigtail, a ring core, and several glass tubes. The pigtail end face of the three-fiber pigtail is thermally expanded. The ring core includes a polarization beam splitter assembly, an optical rotation assembly, and a refractive assembly. The polarization beam splitter assembly includes a displacement crystal. The optical rotation assembly includes a half-wave plate group, an optical rotation unit, a half-wave plate, and a compensation plate. The refractive assembly 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 from the three-fiber pigtail passes sequentially through the polarization beam splitter assembly, the optical rotation assembly, and the refractive assembly, and is reflected by the reflector, then sequentially passes through the refractive assembly, the optical rotation assembly, and the polarization beam splitter assembly back to the three-fiber pigtail.

[0006] Optionally, the half-wave plate group includes two half-wave plates with an optical axis 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 may include a spherical lens or a graduated refractive index lens.

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

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

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

[0012] On the other hand, embodiments of the present invention provide a method for fabricating a three-port reflective circulator, applied to the aforementioned three-port reflective circulator, comprising:

[0013] The optical rotation component is fixed on the polarization beam splitter to form a single crystal;

[0014] The single crystal is attached to one end of the collimating lens, and one end of the collimating lens is inserted into one end of the first glass tube and fixed.

[0015] The Wollaston prism and the reflector are attached and fixed to 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 tail into the other end of the first glass tube, adjust and fix it.

[0017] Optionally, fixing the optical rotation component on the polarization beam splitter to form a single crystal includes:

[0018] The displacement crystal is fixed, and the plane containing the 45° optical axis of the displacement crystal is used as the reference plane;

[0019] Two symmetrical 22.5° half-wave plates are attached side by side on the adjacent surfaces 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 rotator and the 22.5° half-wave plate are sequentially attached to the surface of the half-wave plate group to form the optical rotator unit; the length of the optical rotator 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 sheet is attached to the remaining surface of the half-wave plate group; the length of the compensation sheet 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 attached to 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 of the 45° half-wave plate in the first preset direction is equal to the length of the optical rotation unit.

[0023] Alternatively, debugging can be performed using the following methods:

[0024] The three-fiber pigtails are connected to the light source or power meter respectively according to the preset channels to form a predetermined circuit;

[0025] Adjust the position of the three-fiber pigtail until the minimum parameter of the predetermined circuit is found, and the debugging is complete.

[0026] The implementation of this invention provides 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 end face of the three-fiber pigtail undergoes thermal expansion treatment to slow down the divergence of the light spot and shorten the length of the beam splitter (displacement crystal), thereby reducing the overall size of the device. The ring core includes a polarization beam splitter assembly, an optical rotation assembly, and a refractive assembly. The polarization beam splitter assembly includes a displacement crystal, the optical rotation assembly includes a half-wave plate group, an optical rotation unit, a half-wave plate, and a compensation plate, and the refractive assembly 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 from the three-fiber pigtail passes sequentially through the polarization beam splitter assembly, the optical rotation assembly, and the refractive assembly, and is reflected by the reflector. It then passes sequentially through the refractive assembly, the optical rotation assembly, and the polarization beam splitter assembly back to the three-fiber pigtail. Through the reflective optical path design, the amount of crystal material is reduced, and the device structure is more compact. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a three-port reflective circulator provided in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of a single-mode optical fiber whose end face has undergone thermal expansion treatment according to an embodiment of the present invention;

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

[0030] Figure 4 This is a schematic diagram of the structure of a displacement crystal provided in an embodiment of the present invention;

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

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

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

[0034] Figure 8 This is an optical path diagram of an optical rotation unit provided in an embodiment of the present invention;

[0035] Figure 9 This is an optical path diagram of a 45° half-wave plate provided in an embodiment of the present invention;

[0036] Figure 10 This is a schematic diagram of the structure of a single crystal provided in an embodiment of the present invention;

[0037] Figure 11 This is a schematic diagram of the structure of a Wollaston prism provided in an embodiment of the present invention;

[0038] Figure 12 This is an optical path diagram of a reflector provided in an embodiment of the present invention;

[0039] Figure 13 This is a schematic diagram of the structure of a pigtail end face provided in an embodiment of the present invention;

[0040] Figure 14 This is a schematic diagram showing the positions of a three-fiber tail and a displacement crystal provided in an embodiment of the present invention;

[0041] Figure 15 This is a polarization state change diagram of an optical path provided in an embodiment of the present invention;

[0042] Figure 16 This is a polarization state change diagram of another optical path provided in an embodiment of the present invention;

[0043] Figure 17 This is a flowchart of a method for preparing a three-port reflective circulator provided in an embodiment of the present invention;

[0044] Figure 18 This is a diagram illustrating the assembly process of a three-port reflective circulator provided in an embodiment of the present invention.

[0045] Figure 19 This is a diagram illustrating the assembly process of a single crystal according to an embodiment of the present invention;

[0046] Figure 20 This is a diagram illustrating the assembly process of another single crystal provided in an embodiment of the present invention;

[0047] Figure 21 This is a diagram illustrating the assembly process of another single crystal provided in an embodiment of the present invention;

[0048] Figure 22 This is a schematic diagram of another three-port reflective circulator provided in an embodiment of the present invention. Detailed Implementation

[0049] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.

[0050] See Figure 1 This invention provides a three-port reflective circulator, comprising a three-fiber pigtail, a ring core, and several glass tubes. The pigtail ends (P1, P2, P3) of the three-fiber pigtail undergo thermal expansion treatment. The ring core includes a polarization beam splitter assembly (M1), an optical rotation assembly (M2), and a refractive assembly. The polarization beam splitter assembly includes a displacement crystal, the optical rotation assembly includes a half-wave plate group, an optical rotation unit, a half-wave plate, and a compensating plate, and the refractive assembly includes a collimating lens (M3), a Wollaston prism (M4), and a reflector (M5). The three-fiber pigtail and the ring core are connected by several glass tubes. The light emitted from the three-fiber pigtail sequentially passes through the polarization beam splitter assembly (M1), the optical rotation assembly (M2), and the refractive assembly, and is reflected by the reflector (M5), then sequentially passes through the refractive assembly, the optical rotation assembly (M2), and the polarization beam splitter assembly (M1) before returning to the three-fiber pigtail.

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

[0052] Optionally, the three-fiber pigtail is formed by inserting three single-mode optical fibers into a three-hole capillary tube. The three holes of the three-hole capillary tube are all set on the same straight line. The first hole and the second hole are spaced apart by a preset distance, and the second hole and the third hole are connected.

[0053] See Figure 3 In one specific embodiment, the three holes of the capillary are all located in the horizontal direction of the y-axis, and the hole diameter is the diameter of the optical fiber after the coating is stripped. Holes 1 and 2 are spaced apart by a certain distance, while holes 2 and 3 are connected. The distance between the first, second, and third holes is determined according to the actual application, and this embodiment does not impose specific limitations.

[0054] The polarization beam splitter consists of a shift crystal made of yttrium vanadate (YVO4), a material with a large difference in birefringence. When the optical axis is pointed at approximately 45°, the o / e beams have the maximum separation angle. At this angle, the ratio of the distance d from which the o / e beams are separated after the unpolarized light passes through the shift crystal to the length L of the shift crystal is approximately 1 / 10. In circulator applications, it is generally required in engineering that the beam 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. See also... Figure 4 The optical axis of the displacement crystal is located in the XZ plane, and the direction of the optical axis makes an angle of 45°±0.5° with the Z axis. Its function is to separate natural light in the X direction into two linearly polarized beams with mutually perpendicular polarization directions—o beam and e beam. The polarization direction of the o beam is perpendicular to the plane where the optical axis is located (i.e., parallel to the Y axis), and the polarization direction of the e beam is parallel to the plane where the optical axis is located.

[0055] Optionally, the half-wave plate group includes two half-wave plates with an optical axis of 22.5°, which are symmetrically distributed.

[0056] See Figure 5 A half-wave plate is a reciprocal crystal, and its function is to reciprocally rotate the polarization direction of linearly polarized light. When linearly polarized light is incident perpendicularly on a half-wave plate, 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 about the optical axis by an angle of 2A (when A = 22.5°, the polarization direction is rotated by 45°; when A = 45°, the polarization direction is rotated by 90°).

[0057] See 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 at 22.5° with the y-axis and are mirror images of each other. The function is to rotate the polarization direction of the incident light by 45°. When two beams of polarized light with perpendicular polarization states pass through the half-wave plate group (one beam passes through one wave plate while the other beam passes through the other half-wave plate), the polarization states of the two beams of polarized light can be transformed into parallel polarization states.

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

[0059] See Figure 7 An optical rotator is a non-reciprocal crystal whose function is to non-reciprocally rotate the polarization direction of linearly polarized light. That is, the rotation direction of the polarization state is independent of the propagation direction of the light and is only related to the direction of the applied magnetic field. When the magnetic ring (M21) applies a saturated magnetic field N→S along the positive Z-axis to the optical rotator (M22), the polarization direction of the linearly polarized light passing through this unit will rotate counterclockwise in the XY plane (generally satisfying the right-hand screw rule).

[0060] See Figure 8The optical rotation unit consists of a 45° optical rotation plate (M22) and a 22.5° half-wave plate (M23). When the magnetic ring (M21) applies a magnetic field from N to S along the positive 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 Z-axis and its polarization state rotates by 90°. When it passes through the optical rotation unit in the opposite direction, its polarization state rotates by 0°.

[0061] In one specific embodiment, the optical rotation component 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 Figure 9 The optical axis of the 45° half-wave plate is at 45° to the y-axis, and its function is to rotate the polarization direction of the incident polarized light by 90°. The compensator does not have optical rotation function; 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 Figure 10 , Figure 10 This diagram illustrates the structure of a single crystal composed of a displacement crystal and an optical rotation component from different sides. C1 represents the displacement crystal, C2 represents a 22.5° half-wave plate, C3 represents a 22.5° half-wave plate, and 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 containing the 45° optical axis of the displacement crystal is used as the reference plane (i.e., the X-Z plane). C2 and C3 are located on the upper surface of the reference plane C1 of the displacement crystal. C5 and C4 are located on part of the surface of the half-wave plate group and span across C2 and C3. C6 is located on the surface of C5, and C7 is located on part of the surface of C6.

[0064] Alternatively, the collimating lens may include a spherical lens or a graded-index lens.

[0065] Collimating lenses include, but are not limited to, spherical lenses or graded refractive index lenses. The function of a collimating lens is to collimate a Gaussian beam that diverges rapidly in free space (without fiber optic constraint) into a Gaussian beam that diverges more slowly.

[0066] See Figure 11 The Wollaston prism consists of two wedge-shaped plates (M41 / M42) with perpendicular optical axes. The wedge material is YVO4, and the wedge angle is a predetermined design angle (N). The optical axes of the two crystals lie in the XY plane, forming an angle of 45° ± 0.1° with the X-axis, and the overall shape is "crossed". The function of the Wollaston prism is to separate incident natural light into two linearly polarized beams with perpendicular polarization directions at a certain angle.

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

[0068] Optionally, the end face of the three-fiber pigtail is ground to a preset angle.

[0069] See Figure 13 After the fiber optic cable is inserted, the end face of the fiber needs to be ground to a certain angle. This is to reduce reflection and improve the product's 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 a circulator, since the polarization states of the two polarized beams need to be processed separately, the O / E polarization must be strictly separated, with a separation distance of at least 1.5 times the size of the beam spot itself. Therefore, the shifting crystal is usually placed after the collimating lens to prevent the beam from diverging too quickly. This embodiment of the invention uses TEC technology to increase the fiber core diameter, and simultaneously controls the length of the collimating lens to keep the air gap between the pigtail and the shifting crystal within 0.1 mm, effectively suppressing the problem of rapid beam divergence and resulting in a large beam spot reaching the front face of the shifting crystal. (See also...) Figure 14 P represents the three-fiber pigtail, M1 represents the shift crystal, Q represents the observation position of the beam spot, and D represents the spatial gap between the pigtail and the shift crystal. In a specific embodiment, the mode field diameter of the optical fiber is increased to 25 μm (MFD = 25 μm), and the beam spot size obtained from the front end face of the shift crystal is examined with a shift crystal length of 1.5 mm. Simulation using Zemax software shows that with an air gap of 0.1 mm, the beam spot size is only 0.07 mm, which, considering a tolerance of 1.5 times, is 0.11 mm, fully meeting the engineering requirements for beam splitting. The splitting distance of 0.15 mm (1.5 mm / 10) is greater than 0.11 mm (1.5 * beam spot size). In contrast, without thermal expansion, the beam mode field diameter MFD = 10.4 μm, and with the same 1.5 mm shift crystal length, the beam spot and splitting distance on the end face are both 0.15 mm, making them indistinguishable.

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

[0073] See Figure 10 and Figure 15The optical path 1→2 (along the positive Z-axis) starts from the pigtail aperture 1 and passes through the displacement crystal, 22.5° half-wave plate group, compensating plate, collimating lens, Wollaston prism, reflector, Wollaston prism, collimating lens, optical rotation unit, 22.5° half-wave plate group, and displacement crystal before entering the pigtail aperture 2. The specific polarization state change process is as follows: Randomly polarized natural light (polarization state is represented by a double-headed cross) is emitted from port 1. After passing through the displacement crystal, it is separated into two linearly polarized beams with mutually perpendicular polarization states in the X direction, represented by horizontal and vertical double-headed arrows, respectively. After passing through the 22.5° half-wave plate group, the polarization directions of the two beams are the same and form a positive 45° angle with the XY plane. The two beams 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 are parallel and aligned with the optical axis of the first wedge in the Wollaston prism. The beams are deflected in the Y-axis direction, resulting in a shift from position 1 to position 2 in the Y direction. Then, after being reflected by the mirror, they return to the collimating lens and enter the optical rotation unit. The polarization states of the two beams do not change. They re-enter the 22.5° half-wave plate group and undergo optical rotation, becoming two beams with mutually perpendicular polarization states again. Finally, they are combined by the displacement crystal and output from port 2.

[0074] See Figure 10 and Figure 16 The optical path 2→3 (along the positive Z-axis) starts from the pigtail aperture 2 and passes sequentially through a shift crystal, a 22.5° half-wave plate group, a rotator unit, a collimating lens, a Wollaston prism, a reflecting mirror, a Wollaston prism, a collimating lens, a 45° half-wave plate, a rotator unit, a 22.5° half-wave plate group, and a shift crystal before entering the pigtail aperture 3. The specific polarization state change process is as follows: Randomly polarized natural light (polarization state represented by a double-headed cross) is emitted from port 2. After passing through the shift crystal, it is separated in the X direction into two linearly polarized beams with mutually perpendicular polarization states, represented by horizontal and vertical double-headed arrows, respectively. After passing through the 22.5° half-wave plate group, the two beams have the same polarization direction and form a positive 45° angle with the XY plane. Then, they enter the rotator unit, where the polarization states of both beams simultaneously undergo a 90° deflection, forming a negative 45° angle with the XY plane. The two beams with the same polarization direction are collimated by the lens and enter the Wollaston prism, where they interact with the optical... The situation is different for path 1→2. In this case, the polarization directions of the two polarized beams are both perpendicularly aligned with the optical axis of the first wedge in the Wollaston prism. The beams are deflected in another direction along the Y-axis, resulting in a shift from position 2 to position 3 in the Y-axis. After being reflected by the mirror, the beams return to the collimating lens and enter the 45° half-wave plate. The polarization states of the two beams are simultaneously deflected by 90°. They re-enter the optical rotation unit, where the polarization state is not polarized. Then, they re-enter the 22.5° half-wave plate group to rotate, obtaining two sets of mutually perpendicular linearly polarized beams again. Finally, the beams are combined by the shift crystal and output from port 3.

[0075] Simulation results using Zemax software showed that the coupling efficiency of both optical paths was above 96%, meeting commercial standards.

[0076] See Figure 17 This invention provides a method for fabricating a three-port reflective circulator, applied to the aforementioned three-port reflective circulator, comprising:

[0077] S100. Fix the optical rotation component on the polarization beam splitter to form a single crystal;

[0078] S200. Mount the single crystal onto one end of the collimating lens, insert one end of the collimating lens into one end of the first glass tube and fix it.

[0079] S300. Attach and fix the Wollaston prism and reflector to one end of the second glass tube, and insert the other end of the collimating lens into the other end of the second glass tube and fix it.

[0080] S400. Insert the three-fiber tail into the other end of the first glass tube, adjust and fix it.

[0081] Specifically, firstly according to Figure 10 The single crystal structure is arranged in a specific order, with polarization diversity units and optical rotation units stacked and fixed piece by piece using adhesive dispensing; then, refer to... Figure 18 A fixed single crystal (N) is attached to 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), and the front end of the collimating lens (M3) protrudes from the first glass tube (S1) for a certain length (for hanging glass tube #2). It is fixed with glue. A magnetic ring (M21) is wrapped around the first glass tube (S1) to provide a saturation magnetic field for the optical rotator. Then, the Wollaston prism (M4) and the reflector (M5) are glued and fixed to one side of the opening of the second glass tube (S2). The other side of the second glass tube (S2) is fitted onto the protruding collimating lens (M3). The second glass tube (S2) is rotated to a suitable position and fixed with glue.

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

[0083] S110, Fixed displacement crystal, with the plane containing the 45° optical axis of the displacement crystal as the reference plane;

[0084] S120. Two symmetrical 22.5° half-wave plates are attached side by side on the adjacent surfaces of the reference plane 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. Optical rotator and 22.5° half-wave plate are sequentially attached to the surface of the half-wave plate group to form an optical rotator unit; the length of the optical rotator 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. A compensation sheet is attached to the remaining surface of the half-wave plate group; the length of the compensation sheet 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.

[0087] S150. A 45° half-wave plate is attached to 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, the displacement crystal (polarization diversity component) is fixed with a clamp, and the plane containing the 45° optical axis of the displacement crystal is used as the reference plane (i.e., the X-Z plane); then, refer to... Figure 19 Two symmetrical half-wave plates are attached side-by-side to the upper surface of the displacement crystal (i.e., in the positive z-direction). The length of each half-wave plate in the x-direction is half the length of the displacement crystal, and its length in the y-direction is equal to the displacement of the crystal. Then, refer to... Figure 20 The clamp drives the displacement crystal to rotate 90° around the Z-axis to the YZ plane. An optical rotator (C8) is attached to the upper left side of the half-wave plate pair (left edge aligned). The optical rotator (C5) in the optical rotator (C8) faces downwards towards the half-wave plate pair, while the half-wave plate (C6) faces upwards away from the half-wave plate pair. The length of the optical rotator (C8) in the y-direction is 2 / 3 of the displacement crystal, and its length in the x-direction is equal to the crystal displacement. Then, refer to... Figure 21 Similarly, in the YZ plane, attach a compensating plate (C4) to the upper right side of the half-wave plate pair (aligned with the right edge). The length of the compensating plate (C4) in the y-direction is 1 / 3 of the displacement crystal, and its length in the x-direction is equal to the crystal displacement. Finally, refer to... Figure 10 On the YZ plane, a 45° half-wave plate (C7) is attached to the upper left side of the optical rotation unit (with the left edge aligned). 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] Alternatively, debugging can be performed using the following methods:

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

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

[0092] See Figure 22The three-fiber pigtails are connected to the light source and power meter according to the designed channel 1 / 2 / 3 fiber (1 connects to the light source → 2 connects to the power meter, 2 connects to the light source → 3 connects to the power meter) to form a predetermined circuit. The three-fiber pigtail (P) is pushed into the tube opening from the left side of the first glass tube (S1). The pigtail is finely adjusted up and down and back and forth until the minimum parameters of CH_1-2 and CH_2-3 are found. The pigtail is then fixed with glue.

[0093] The implementation of this invention provides 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 end face of the three-fiber pigtail undergoes thermal expansion treatment to slow down the divergence of the light spot and shorten the length of the beam splitter (displacement crystal), thereby reducing the overall size of the device. The ring core includes a polarization beam splitter assembly, an optical rotation assembly, and a refractive assembly. The polarization beam splitter assembly includes a displacement crystal, the optical rotation assembly includes a half-wave plate group, an optical rotation unit, a half-wave plate, and a compensation plate, and the refractive assembly 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 from the three-fiber pigtail passes sequentially through the polarization beam splitter assembly, the optical rotation assembly, and the refractive assembly, and is reflected by the reflector. It then passes sequentially through the refractive assembly, the optical rotation assembly, and the polarization beam splitter assembly back to the three-fiber pigtail. Through the reflective optical path design, the amount of crystal material is reduced, and the device structure is more compact.

[0094] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method for fabricating a three-port reflective circulator, characterized in that, A 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 undergoes thermal expansion treatment. The ring core includes a polarization beam splitter assembly, an optical rotation assembly, and a refractive assembly. The polarization beam splitter assembly includes a displacement crystal. The optical rotation assembly includes a half-wave plate group, an optical rotation unit, a half-wave plate, and a compensating plate. The refractive assembly includes a collimating lens, a Wollaston prism, and a reflector. The three-fiber pigtail and the ring core are connected by several glass tubes. Light emitted from the three-fiber pigtail sequentially passes through the polarization beam splitter assembly, the optical rotation assembly, and the refractive assembly, and is reflected by the reflector, then sequentially passes through the refractive assembly, the optical rotation assembly, and the polarization beam splitter assembly back to the three-fiber pigtail. The fabrication method includes: The optical rotation component is fixed on the polarization beam splitter to form a single crystal; The single crystal is attached to one end of the collimating lens, and one end of the collimating lens is inserted into one end of the first glass tube and fixed. The Wollaston prism and the reflector are attached and fixed to 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 tail into the other end of the first glass tube, adjust and fix it; The step of fixing the optical rotation component on the polarization beam splitter to form a single crystal includes: The displacement crystal is fixed, and the plane containing the 45° optical axis of the displacement crystal is used as the reference plane; Two symmetrical 22.5° half-wave plates are attached side by side on the adjacent surfaces of the reference plane 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; A rotator and a 22.5° half-wave plate are sequentially attached to the surface of the half-wave plate group to form the rotator unit; the length of the rotator 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 sheet is attached to the remaining surface of the half-wave plate group; the length of the compensation sheet 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 attached to 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 of the 45° half-wave plate in the first preset direction is equal to the length of the optical rotation unit.

2. The preparation method according to claim 1, characterized in that, Debug using the following methods: The three-fiber pigtails are connected to the light source or power meter respectively according to the preset channels to form a predetermined circuit; Adjust the position of the three-fiber pigtail until the minimum parameter of the predetermined circuit is found, and the debugging is complete.

3. The preparation method according to claim 1, characterized in that, The collimating lens includes a spherical lens or a graduated refractive index lens.

4. The preparation method according to claim 1, characterized in that, The three-fiber pigtail is formed by inserting three single-mode optical fibers into a three-hole capillary tube. The three holes of the three-hole capillary tube are all set on the same straight line. The first hole and the second hole are spaced apart by a preset distance, and the second hole and the third hole are connected.

5. The preparation method according to claim 1, characterized in that, The end face of the three-fiber tail is ground to a preset angle.

6. The preparation method according to any one of claims 1-5, characterized in that, The distance between the end face of the three-fiber tail and the displacement crystal is less than 0.1 mm.

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