Three-port reflective optical circulator based on birefringent crystal

Abstract

The present invention discloses a three-port reflective optical circulator based on a birefringent crystal, belonging to the field of optical communications. The three-port reflective optical circulator comprises a first birefringent crystal, a half-wave plate assembly, a roof prism, a Faraday rotator crystal, a second birefringent crystal, a quarter-wave plate, and a reflector, which are arranged in sequence. The first port, the second port, and the third port are respectively located on a side of the first birefringent crystal away from the half-wave plate assembly. The birefringent crystal performs light splitting to split a light beam into two sub-beams, o-polarized light and e-polarized light, with mutually perpendicular polarization directions. The polarization directions of the sub-beams are controlled by the half-wave plate, the quarter-wave plate, and the Faraday rotator crystal. Finally, the birefringent crystal performs light combining, thus realizing the functions of the optical circulator with input at the first port and output at the second port, and with input at the second port and output at the third port. The three ports are located on the same side of the optical circulator, making it easier to arrange other components and miniaturizing the optical circulator.

Description

Technical Field

[0001] The present invention relates to the field of optical communications, in particular to a three-port reflective optical circulator based on a birefringent crystal. Background Art

[0002] An optical circulator is a very important multi-port input and output non-reciprocal optical passive device in fiber-optic communication systems. Its function is to transmit optical signals in a circular manner only along a specified port sequence. It has the characteristics of forward sequential transmission and reverse sequential isolation, which can complete the separation of forward and reverse transmitted light. Therefore, it has a wide range of applications in single-fiber bidirectional transmission systems, fiber Bragg grating-based dense wavelength division multiplexers, optical amplifiers, optical time-domain reflectometers, and traditional fields such as fiber sensing and fiber testing.

[0003] The three ports of a conventional three-port optical circulator based on a birefringent crystal are located on different sides of the circulator. This structure not only leads to structural redundancy, but also requires consideration of the placement of components in the module during optical path design, making it impossible to miniaturize the optical circulator. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, one of the objectives of the present invention is to provide a three-port reflective optical circulator based on a birefringent crystal, in which the three ports are located on the same side of the optical circulator.

[0005] One of the purposes of the present invention is achieved by the following technical solution:

[0006] A three-port reflective optical circulator based on a birefringent crystal is provided with a first port, a second port, a third port, a first birefringent crystal, a half-wave plate assembly, a roof prism, a Faraday rotator crystal, a second birefringent crystal, a quarter-wave plate and a reflector arranged in sequence, wherein the first port, the second port and the third port are respectively located on the side of the first birefringent crystal away from the half-wave plate assembly.

[0007] When the optical path from the first port to the second port is working, the angled light beam emitted from the first port is decomposed into o light and e light by the first birefringent crystal, the o light is deflected 45° clockwise by the half-wave plate component, and the e light is rotated 135° clockwise, and the roof prism collimates the angled o light and e light into parallel light beams; the Faraday rotator crystal rotates the o light and e light by 45° clockwise to form two beams of o light, and the two beams of o light pass through the second birefringent crystal and the 1 / After passing through the half-wave plate, the two reflected light beams are reflected by the reflector. The two reflected light beams are transformed into two e-beams by the quarter-wave plate. The two e-beams are deflected to the right in the second birefringent crystal and rotated 45° clockwise by the Faraday rotator crystal. After passing through the roof prism, the left sub-beam is rotated 45° counterclockwise by the half-wave plate assembly to become o-beam, and the right sub-beam is rotated 135° clockwise by the half-wave plate assembly to become e-beam. The o-beam and the e-beam are combined in the first birefringent crystal and emitted into the second port.

[0008] When the optical path from the second port to the third port is working, the parallel light beam emitted from the first port is decomposed into o-light and e-light by the first birefringent crystal. The o-light is deflected 45° clockwise by the half-wave plate assembly, and the e-light is rotated 135° clockwise. After passing through the roof prism, the Faraday rotator crystal rotates the o-light and the e-light by 45° clockwise to form two o-light beams. The two o-light beams pass through the second birefringent crystal and the 1 / 4 wave plate and are reflected by the reflector. The two reflected light beams pass through the 1 / 4 wave plate and become two e-light beams. The two e-light beams are deflected to the right in the second birefringent crystal and rotated 45° clockwise by the Faraday rotator crystal. They are deflected to the left when passing through the roof prism. Then, after passing through the half-wave plate assembly, the sub-beam on the left is rotated 45° counterclockwise to convert into o-light, and the sub-beam on the bottom is rotated 135° clockwise to remain e-light. The o-light and e-light are combined in the first birefringent crystal and emitted into the third port.

[0009] Furthermore, the first port, the second port and the third port are located in the same horizontal plane.

[0010] Furthermore, the second port is located between the first port and the third port.

[0011] Furthermore, the half-wave plate assembly includes two half-wave plates, which are arranged on the left and right.

[0012] Furthermore, the first birefringent crystal has a tilt angle.

[0013] Furthermore, the cross section of the first birefringent crystal along the optical path is a parallelogram.

[0014] Furthermore, the side surface of the first birefringent crystal facing the first port is tilted to the right.

[0015] Furthermore, the three-port reflective optical circulator based on the birefringent crystal further includes a three-fiber collimator, and the three-fiber collimator is located on a side of the first birefringent crystal away from the half-wave plate assembly.

[0016] Furthermore, the three-fiber collimator forms the first port, the second port and the third port.

[0017] Furthermore, the three-fiber collimator is located between the first port, the second port, the third port and the first birefringent crystal.

[0018] Furthermore, the three-port reflective optical circulator based on birefringent crystals further includes a filter, and the filter is located between the roof prism and the reflector.

[0019] Furthermore, the optical filter is located between the 1 / 4 wave plate and the reflecting mirror, or the optical filter is located between the second birefringent crystal and the 1 / 4 wave plate.

[0020] Compared to the prior art, the present invention provides a three-port reflective optical circulator based on a birefringent crystal, including a first birefringent crystal, a half-wave plate assembly, a roof prism, a Faraday rotator crystal, a second birefringent crystal, a quarter-wave plate, and a reflector, arranged in sequence. The first port, the second port, and the third port are respectively located on the side of the first birefringent crystal away from the half-wave plate assembly. The birefringent crystal performs light splitting to split the light beam into two sub-beams, o-polarized light and e-polarized light, with mutually perpendicular polarization directions. The polarization directions of the sub-beams are controlled by the half-wave plate, the quarter-wave plate, and the Faraday rotator crystal. Finally, the birefringent crystal is used to combine the light, thereby realizing the functions of the optical circulator with input at the first port and output at the second port, and input at the second port and output at the third port. The three ports are located on the same side of the optical circulator, making it easier to place other components and miniaturizing the optical circulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of a three-port reflective optical circulator based on a birefringent crystal according to the present invention;

[0022] Figure 2 for Figure 1 A side view of the optical path of a three-port reflective optical circulator based on a birefringent crystal, wherein light enters from a first port and exits from a second port;

[0023] Figure 3 for Figure 2A schematic diagram of the polarization direction of light entering from the first port and emitted from the second port observed from the perspective of the incident light;

[0024] Figure 4 A top view of the optical path of the incident light of the three-port reflective optical circulator based on birefringent crystals of the present invention;

[0025] Figure 5 A top view of the optical path of the outgoing light of the three-port reflective optical circulator based on the birefringent crystal of the present invention;

[0026] Figure 6 for Figure 1 A side view of the optical path of a three-port reflective optical circulator based on a birefringent crystal, wherein light enters from the second port and exits from the third port;

[0027] Figure 7 for Figure 6 Schematic diagram of the polarization direction of light entering from the second port and emitted from the third port observed from the perspective of incident light.

[0028] In the figure: 101, three-fiber collimator; 102, first birefringent crystal; 103, half-wave plate assembly; 104, roof prism; 105, Faraday rotator crystal; 106, second birefringent crystal; 107, 1 / 4 wave plate; 108, filter; 109, reflector. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may be another intermediate component through which it is fixed. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may be another intermediate component at the same time. When a component is considered to be "set on" another component, it may be directly set on the other component or there may be another intermediate component at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] See also Figure 1 A three-port reflective optical circulator based on a birefringent crystal includes a first port P1, a second port P2, and a third port P3. The first port P1, the second port P2, and the third port P3 are located on the same side of the optical circulator. Specifically, the first port P1, the second port P2, and the third port P3 are located at the same level, and the second port P2 is located between the first port P1 and the third port P3.

[0033] The three-port reflective optical circulator based on birefringent crystals includes a three-fiber collimator 101, a first birefringent crystal 102, a half-wave plate assembly 103, a roof prism 104, a Faraday rotator crystal 105, a second birefringent crystal 106, a quarter-wave plate 107, a filter 108 and a reflector 109, which are arranged in sequence.

[0034] The first port P1, the second port P2, and the third port P3 are located on the side of the three-fiber collimator 101 away from the first birefringent crystal 102. The first port P1, the second port P2, and the third port P3 are optical fibers. The three-fiber collimator 101 collimates the light emitted from the first port P1 or the second port P2, or collimates the light emitted to the second port P2 or the third port P3.

[0035] In other embodiments, the first port P1 , the second port P2 , and the third port P3 may also be disposed inside the three-fiber collimator 101 .

[0036] The first birefringent crystal 102 has an inclination angle. Specifically, the cross section of the first birefringent crystal 102 along the optical path is a parallelogram. In this embodiment, the side surface of the first birefringent crystal 102 facing the first port is inclined downward.

[0037] The half-wave plate assembly 103 includes two half-wave plates, which are arranged on the left and right.

[0038] The filter 108 filters out light beams of unnecessary wavelengths, so that the incident light is transmitted as a light beam within a specified wavelength range.

[0039] Please continue reading Figures 2 to 5 When the optical circulator is in the first port P1-> second port P2 optical path, the propagation direction of the light beam is as follows: Figure 2 、 Figure 4 as well as Figure 5 As shown, Figure 2 The middle is a side view of the beam propagation, Figure 4 is the top view of the incident light, Figure 5 is the top view of the outgoing light, Figure 3 Schematic diagram of the polarization direction of light after passing through each optical element, observed from the perspective of incident light.

[0040] At this time, the divergent light beam emitted from the first port first passes through the three-fiber collimator 101 before being collimated into an angled beam. The angled beam then passes through the first birefringent crystal 102, where it is decomposed into two sub-beams with orthogonal polarization directions: ordinary light o and extraordinary light e. Because the first birefringent crystal 102 has a certain tilt angle, according to the law of refraction, the o-light is deflected to the left. According to the separation angle principle of the birefringent crystal, the extraordinary light e will produce a separation angle in the birefringent crystal, so the e-light is deflected to the right. After passing through the half-wave plate assembly 103, the o-light is transmitted along the left optical path. Therefore, after passing through the half-wave plate on the left side of the half-wave plate assembly 103, the polarization direction of the o-light is rotated 45° clockwise along the direction of the incident light. The e-light is transmitted along the optical path on the right side. Therefore, when it passes through the half-wave plate on the right side of the half-wave plate assembly 103, the polarization direction of the e-light is rotated 135° clockwise along the light transmission direction. When it passes through the roof prism 104, the angled o-light and e-light are collimated into parallel light beams after passing through the roof prism 104. After passing through the Faraday rotator crystal 105, the polarization directions of the two sub-beams are rotated 45° clockwise along the direction of the incident light. At this time, both sub-beams are o-light. After passing through the second birefringent crystal 106, since both sub-beams are o-light, neither of the two sub-beams will be deflected; after passing through the 1 / 4 wave plate 107, the filter 108 filters out the light beams of unnecessary wavelengths, so that the incident light is transmitted as a light beam in a specified wavelength range, and the light beam is transmitted to the reflector 109, and after reflection, it passes through the 1 / 4 wave plate 107 again. At this time, the two sub-beams are equivalent to passing through the 1 / 4 wave plate with the same optical axis direction twice, which is equivalent to passing through a half-wave plate. At this time, the polarization directions of the two sub-beams are rotated 90° clockwise along the light transmission direction, that is, the two sub-beams are changed from o-light to e-light; the two beams After reflection, the sub-beams pass through the second birefringent crystal 106. Both sub-beams are e-rays relative to the second birefringent crystal 106 and are therefore deflected downward. After reflection, they pass through the Faraday rotation crystal 105, rotating the polarization directions of the two sub-beams by 45° clockwise relative to the incident light direction. After reflection, they pass through the roof prism 104. Since the two sub-beams now enter the roof prism 104 perpendicularly, they are not deflected. They then pass through the half-wave plate assembly 103. The left sub-beam passes through the wave plate on the left side of the half-wave plate assembly 103, rotating its polarization direction by 45° counterclockwise relative to the direction of light propagation. This converts the left sub-beam from e-ray to o-ray. The right sub-beam passes through the wave plate on the right side of the half-wave plate assembly 103, rotating its polarization direction by 135° clockwise relative to the direction of light propagation. At this point, the right sub-beam retains its e-ray polarization state. Finally, they pass through the first birefringent crystal 102. Due to the tilt angle of the first birefringent crystal 102, according to the law of refraction, the o-ray is deflected to the right. According to the separation angle principle of the birefringent crystal, the extraordinary light e-light will produce a deviation angle in the birefringent crystal, so the e-light is deflected to the left. At this time, the o-light and the e-light are combined after passing through the first birefringent crystal 102 and finally transmitted to the second port P2.

[0041] Please continue reading Figures 4 to 7 When the optical circulator is in the first port P2-> second port P3 optical path, the top view of the light beam propagation direction is the same as that when the first port P1-> second port P2 optical path is in operation. Figure 4 as well as Figure 5 The side view of the beam propagation is shown in Figure 6 As shown, the polarization direction of light after passing through each optical element is as follows Figure 7 shown.

[0042] At this point, the divergent light beam output from the optical fiber at end P2 first passes through a three-fiber collimator 101 before being collimated into a parallel beam. The parallel beam then passes through a first birefringent crystal 102, where it is decomposed into two sub-beams with orthogonal polarization directions: ordinary light o and extraordinary light e. Because first birefringent crystal 102 has a certain tilt angle, according to the law of refraction, light o is deflected to the left. Based on the separation angle principle of a birefringent crystal, the extraordinary light e produces a separation angle within the birefringent crystal, causing light e to be deflected to the right. After passing through half-wave plate assembly 103, light o is transmitted along the left optical path. Therefore, after passing through the half-wave plate on the left side of half-wave plate assembly 103, the polarization direction of light o is rotated 45° clockwise relative to the direction of the incident light. The e-light beam propagates along the right optical path. Therefore, upon passing through the half-wave plate on the right side of half-wave plate assembly 103, its polarization direction rotates 135 degrees clockwise along the optical transmission direction. Upon passing through roof prism 104, both sub-beams are not deflected because they are incident perpendicularly on roof prism 104. Upon passing through Faraday rotator crystal 105, the polarization directions of both sub-beams rotate 45 degrees clockwise along the optical transmission direction. At this point, both sub-beams are o-light. After passing through the second birefringent crystal, since both sub-beams are o-light, neither of the two sub-beams will be deflected; after passing through the 1 / 4 wave plate 107, the light beam passes through the filter 108, and the filter 108 selectively passes the light signal of a specific wavelength. The light beam is transmitted to the reflector 109, and after reflection, it passes through the 1 / 4 wave plate 107 again. At this time, the two sub-beams are equivalent to passing through the 1 / 4 wave plate 107 with the same optical axis direction twice, which is equivalent to passing through a half-wave plate. At this time, the polarization directions of the two sub-beams are rotated 90° clockwise along the light transmission direction, that is, the two sub-beams are changed from o-light to e-light; the two sub-beams are reflected After passing through the second birefringent crystal 106, both sub-beams are deflected to the right, as they are both e-light. After reflection, they pass through the Faraday rotation crystal 105, rotating the polarization directions of the two sub-beams by 45° clockwise along the direction of light propagation. After reflection, they pass through the roof prism 104, where the two sub-beams form a certain angle with the roof prism 104. After refraction, the sub-beams are deflected toward the third port P3 (deflected to the left). After passing through the half-wave plate assembly 103, the left sub-beam passes through the wave plate on the left side of the half-wave plate assembly 103, and its polarization direction is rotated by 135° clockwise along the direction of light propagation. At this time, the right sub-beam is converted from e-light to o-light. The lower sub-beam passes through the wave plate on the bottom side of the half-wave plate assembly 103, and its polarization direction is rotated by 45° clockwise along the direction of light propagation. At this time, the right sub-beam still maintains the polarization state of e-light. Finally, it passes through the first birefringent crystal 102. Due to the certain tilt angle of the first birefringent crystal 102, according to the law of refraction, the o-light is deflected to the right. According to the separation angle principle of the birefringent crystal, the extraordinary light e-light will produce a deviation angle in the birefringent crystal, so the e-light is deflected to the left. At this time, the o-light and the e-light are combined after passing through the first birefringent crystal 102 and finally transmitted to the third port P3.

[0043] The present invention utilizes a birefringent crystal-based three-port reflective optical circulator to split a light beam into two mutually perpendicular sub-beams, o-polarized light and e-polarized light. The polarization directions of the sub-beams are controlled by a half-wave plate assembly 103, a quarter-wave plate 104, and a Faraday rotator crystal 105. Finally, the light is combined by a birefringent crystal, achieving the functions of an optical circulator with input at the first port and output at the second port, as well as input at the second port and output at the third port. The three ports are located on the same side of the optical circulator, making it easier to place other components and miniaturizing the optical circulator. This design not only significantly reduces the device's footprint and improves material utilization efficiency, but its compact structure also provides greater flexibility and adaptability in a variety of application scenarios, giving the optical circulator greater practical application potential and better adaptability to the stringent space utilization requirements of modern optical systems.

[0044] The above embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patented invention. It should be noted that those skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention. These variations and improvements are equivalent modifications and improvements to the above embodiments based on the essential technology of the present invention and fall within the scope of protection of the present invention.

Claims

1. A three-port reflective optical circulator based on a birefringent crystal, comprising a first port, a second port, and a third port, characterized in that: The three-port reflective optical circulator based on the birefringent crystal further includes a first birefringent crystal, a half-wave plate assembly, a roof prism, a Faraday rotator crystal, a second birefringent crystal, a quarter-wave plate and a reflector arranged in sequence, the first port, the second port and the third port are respectively located on a side of the first birefringent crystal away from the half-wave plate assembly, the three-port reflective optical circulator based on the birefringent crystal further includes a three-fiber collimator, the three-fiber collimator is located on a side of the first birefringent crystal away from the half-wave plate assembly, and the three-fiber collimator is located between the first port, the second port and the third port and the first birefringent crystal, When the optical path from the first port to the second port is working, the divergent light beam emitted from the first port first passes through the three-fiber collimator and is collimated into an angled light beam; the angled light beam is decomposed into o light and e light by the first birefringent crystal, the o light is deflected 45° clockwise by the half-wave plate component, and the e light is rotated 135° clockwise, and the roof prism collimates the angled o light and e light into parallel light beams; the Faraday rotator crystal rotates the o light and e light by 45° clockwise to form two beams of o light, and the two beams of o light pass through the The second birefringent crystal and the quarter-wave plate are then reflected by the reflector. The two reflected light beams are converted into two e-beams by the quarter-wave plate. The two e-beams are deflected to the right in the second birefringent crystal and rotated 45° clockwise by the Faraday rotator crystal. After passing through the roof prism, the left sub-beam is rotated 45° counterclockwise by the half-wave plate assembly to become o-beam, and the right sub-beam is rotated 135° clockwise by the half-wave plate assembly to become e-beam. The o-beam and the e-beam are combined in the first birefringent crystal and incident on the second port. When the optical path from the second port to the third port is working, the divergent light beam emitted from the second port is collimated into a parallel light beam by the three-fiber collimator, and the parallel light beam is decomposed into o light and e light by the first birefringent crystal. The o light is deflected 45° clockwise by the half-wave plate component, and the e light is rotated 135° clockwise. After passing through the roof prism, the Faraday rotator crystal rotates the o light and the e light by 45° clockwise to form two beams of o light. The two beams of o light pass through the second birefringent crystal and the 1 After passing through the / 4 wave plate, the two beams of light are reflected by the reflector. The two beams of light after reflection pass through the 1 / 4 wave plate and become two beams of e light. The two beams of e light are deflected to the right in the second birefringent crystal, rotated 45° clockwise by the Faraday rotator crystal, deflected to the left when passing through the roof prism, and then pass through the half-wave plate assembly. The sub-beam on the left is rotated 45° counterclockwise and converted into o light, and the sub-beam on the bottom is rotated 135° clockwise and remains e light. The o light and the e light are combined in the first birefringent crystal and emitted into the third port.

2. The three-port reflective optical circulator based on a birefringent crystal according to claim 1, characterized in that: The first port, the second port, and the third port are located in the same horizontal plane.

3. The three-port reflective optical circulator based on a birefringent crystal according to claim 1, characterized in that: The second port is located between the first port and the third port.

4. The three-port reflective optical circulator based on a birefringent crystal according to claim 1, characterized in that: The half-wave plate assembly includes two half-wave plates, which are arranged on the left and right.

5. The three-port reflective optical circulator based on birefringent crystal according to claim 1, characterized in that: The first birefringent crystal has a tilt angle.

6. The three-port reflective optical circulator based on a birefringent crystal according to claim 5, characterized in that: The cross section of the first birefringent crystal along the optical path is a parallelogram.

7. The three-port reflective optical circulator based on a birefringent crystal according to claim 6, characterized in that: The side surface of the first birefringent crystal facing the first port is tilted rightward.

8. The three-port reflective optical circulator based on a birefringent crystal according to claim 1, characterized in that: The three-port reflective optical circulator based on birefringent crystal further includes a filter, which is located between the roof prism and the reflector.

9. The three-port reflective optical circulator based on a birefringent crystal according to claim 8, characterized in that: The optical filter is located between the 1 / 4 wave plate and the reflecting mirror, or the optical filter is located between the second birefringent crystal and the 1 / 4 wave plate.

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