An integrated free-space optical circulator

Abstract

The invention discloses an integrated free-space optical circulator, comprising a first polarization beam splitter component, a non-reciprocal polarization rotator, a half-wave plate and a second polarization beam splitter component which are sequentially arranged along an optical path; the first polarization beam splitter component, the non-reciprocal polarization rotator, the half-wave plate and the second polarization beam splitter component are integrated into one by gluing or deepening optical glue or optical glue process; the free-space optical circulator has three ports, namely a transmitting end, a receiving end and a common end, wherein the transmitting end and the receiving end are on the same side and the common end is on the other side; the invention has the advantages of small size, integrated structure, easy processing and mass production, low cost and high reliability.

Description

Technical Field

[0001] The invention relates to the field of optical communication devices, in particular to an integrated free-space optical circulator. Background Art

[0002] An optical circulator is a non-reciprocal optical passive device with multiple input and output ports. Its function is to make the optical signal only be transmitted along the specified port sequence. When the transmission sequence of the optical signal is changed, the loss is very large, so it can achieve signal isolation. The typical structure has N (N is greater than or equal to 3) ports, as shown in the attached manual. Figure 1 As shown, when light is input from port 1, light is output from port 2; when light is input from port 2, light is output from port 3, and so on.

[0003] The non-reciprocal characteristics of the optical circulator are realized by using the Faraday effect of magneto-optical materials. The Faraday effect refers to the phenomenon that the polarization plane of the electromagnetic wave (light wave) in the dielectric material rotates under the action of a magnetic field parallel to the propagation direction of light, and its rotation direction is independent of the propagation direction of light, that is, polarization is independent. After the light wave passes through the first polarizing element, it becomes polarized light. After passing through the Faraday rotator, the polarization direction of the polarized light rotates 45° and is parallel to the light transmission direction of the second polarizing element, allowing it to pass through; when the light is transmitted in the opposite direction, after passing through the Faraday rotator, the polarization direction of the light is perpendicular to the light transmission direction of the first polarizer and cannot pass through.

[0004] Due to the non-reciprocal and sequential transmission characteristics of the optical circulator, it can be used to separate the forward and reverse transmission optical signals in the same optical fiber, and is widely used in optical fiber communications, optical fiber sensing, and optical fiber testing systems to simplify the system structure and improve performance. The main related specific applications include: single-fiber bidirectional communication, fiber Bragg grating (FBG) combination application, erbium-doped fiber amplifier (EDFA), wavelength division multiplexing (WDM), dispersion compensation, optical signal upload / download, and can also be used as a coupler in optical time domain reflectometer (OTDR) and fiber gyroscope.

[0005] In the development of optical circulators, the pursuit of low-cost, small-scale integrated structures has been the main development trend in recent years. Summary of the invention

[0006] In view of the prior art, the object of the present invention is to provide a low-cost, small-sized integrated free-space optical circulator.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0008] An integrated free-space optical circulator comprises a first polarization beam splitter component, a non-reciprocal polarization rotator, a half-wave plate and a second polarization beam splitter component which are sequentially arranged along an optical path. The first polarization beam splitter component, the non-reciprocal polarization rotator, the half-wave plate and the second polarization beam splitter component are fixedly combined with each other into one body.

[0009] Furthermore, the first polarization beam splitter component, the non-reciprocal polarization rotator, the half-wave plate and the second polarization beam splitter component are integrated into one by gluing or deepening optical glue or fixing with optical glue.

[0010] Furthermore, the first polarization splitter component is two 45° right-angle prisms and a 45° rhombus prism glued or deepened with optical glue or optical glue into one, and the inclined surfaces of the two 45° right-angle prisms or the two inclined surfaces of the 45° rhombus prism are plated with PBS film.

[0011] Preferably, an anti-reflection film is coated on a side of the first polarization splitting component away from the non-reciprocal polarization rotator.

[0012] As a preferred embodiment, the first polarization beam splitter component can be a PBS (Polarization Beam Splitter) cuboid or parallelepiped assembly, which integrates two PBSs by gluing or deepening optical glue or optical glue, and can realize polarization beam splitting and light combining functions.

[0013] Furthermore, the second polarization splitter component is two 45° right-angle prisms and a 45° rhombus prism glued or deepened with optical glue or optical glue into one, and the inclined surfaces of the two 45° right-angle prisms or the two inclined surfaces of the 45° rhombus prism are plated with PBS film.

[0014] Preferably, an anti-reflection film is coated on a side of the second polarization splitting component away from the non-reciprocal polarization rotator.

[0015] Among them, as a preferred embodiment, the second polarization splitting component can be a PBS rectangular or parallelepiped assembly, which integrates two PBSs by gluing or deepening optical glue or optical glue, and can realize polarization splitting and light combining functions.

[0016] Preferably, the refractive index of the glue used for bonding is adapted to the refractive index of the corresponding bonding surface, and the glue at least includes UV curing glue, heat curing glue or dual curing glue.

[0017] Furthermore, the non-reciprocal polarization rotator is a Faraday rotator, which includes a self-contained magnetic Faraday rotator or a non-self-contained magnetic Faraday rotator.

[0018] Furthermore, the half-wave plate is a single half-wave plate or a combination of multiple half-wave plates, and the optical axis of the half-wave plate forms an angle of 22.5° with the first polarization beam splitting component and / or the second polarization beam splitting component.

[0019] As a preferred embodiment, the design scheme of the present invention has three ports, namely, a transmitting end, a receiving end and a common end, wherein the transmitting end and the receiving end are on the same side, and the common end is on the other side; the three ports form two optical paths, namely, a first optical path and a second optical path; in the first optical path, the input optical signal is output from the transmitting end through the first polarization splitting component, the non-reciprocal polarization rotator, the half-wave plate, and the second polarization splitting component to the common end; in the second optical path, the input optical signal is output from the common end through the second polarization splitting component, the non-reciprocal polarization rotator, the half-wave plate, and the first polarization splitting component to the receiving end.

[0020] Furthermore, the end surface of the first polarization beam splitter component and / or the second polarization beam splitter component away from the non-reciprocal rotator is glued or deepened with optical glue, or the optical glue has a wedge-shaped piece.

[0021] As a further supplement to the design of the present invention, in order to improve the return loss (RL) performance of the circulator, the incident surface and the bottom surface of the overall structure may be processed into a non-90° relationship.

[0022] By adopting the above-mentioned technical scheme, compared with the prior art, the present invention uses fewer optical components, and the optical components are integrated together by gluing or deepening optical glue or optical glue technology. Therefore, it has the advantages of small size, structural integration, easy processing and mass production, low cost and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0024] Figure 1 It is the schematic diagram of the three-port optical circulator;

[0025] Figure 2 It is the schematic diagram of a four-port optical circulator;

[0026] Figure 3 It is a schematic diagram of the three-dimensional structure of Example 1 of the present invention;

[0027] Figure 4 for Figure 3 A schematic diagram of the optical path of the implementation structure shown;

[0028] Figure 5 for Figure 3 A schematic structural diagram of the embodiment structure from another side perspective;

[0029] Figure 6 It is a schematic diagram of the three-dimensional structure of Example 2 of the present invention;

[0030] Figure 7 for Figure 6 A schematic diagram of the optical path of the implementation structure shown;

[0031] Figure 8 for Figure 6 A schematic structural diagram of the embodiment structure from another side perspective;

[0032] Fig. 9 A schematic diagram of the optical path of the structure of the implementation of Example 3 of the present invention;

[0033] Fig.10 for Fig. 9 A schematic structural diagram of the implementation structure from another side perspective. DETAILED DESCRIPTION

[0034] Example 1

[0035] like Figures 3 to 5 As shown in one of the figures, it shows the implementation structure of Example 1 of the present invention, which includes a first polarization splitter component 103, a 45° Faraday rotator 104, a half-wave plate 105 and a second polarization splitter component 108 arranged in sequence along the optical path, and the first polarization splitter component 103, the 45° Faraday rotator 104, the half-wave plate 105 and the second polarization splitter component 108 are fixedly combined into one by gluing or deepening optical glue or optical glue. When gluing, the refractive index of the glue used for gluing is adapted to the refractive index of the corresponding bonding surface, and the glue at least includes UV curing glue or heat curing glue or dual curing glue.

[0036] Among them, the first polarization splitter component 103 is two 45° right-angle prisms and a 45° rhombus prism glued or deepened with optical glue or optical glue into one, and PBS films 101 and 102 are plated on the inclined surfaces of the two 45° right-angle prisms or the two inclined surfaces of a 45° rhombus prism. Preferably, the first polarization splitter component 103 is plated with an anti-reflection film on the side away from the 45° Faraday rotator 104.

[0037] Further, the second polarization splitter component 108 is two 45° right-angle prisms and a 45° rhombus prism glued or deepened with optical glue or optical glue into one, and PBS films 106 and 107 are plated on the inclined surfaces of the two 45° right-angle prisms or on the two inclined surfaces of a 45° rhombus prism. Preferably, the second polarization splitter component 108 is plated with an anti-reflection film on the side away from the 45° Faraday rotator 104.

[0038] Furthermore, the half-wave plate 105 is a single half-wave plate or a combination of multiple half-wave plates, and the optical axis of the half-wave plate 105 forms an angle of 22.5° with the first polarization beam splitter component 103 and / or the second polarization beam splitter component 108 .

[0039] See also Figure 4 , the working principle of the structure shown in this embodiment is:

[0040] The structure of this embodiment forms three ports and constitutes two optical paths, namely a first optical path and a second optical path.

[0041] In the first optical path, the input optical signal is separated from port 1 (transmitter, usually LD collimated light) through the upper PBS 101 of the first beam splitter component 103 into two beams of light with mutually perpendicular polarization states. Without loss of generality, the polarized light perpendicular to the paper surface is called S light and the polarized light parallel to the paper surface is called P light. Usually, the S light is weaker and is reflected. The P light continues to transmit forward and passes through the 45° Faraday rotator 104. Along the direction of light propagation, the polarization direction of the light is rotated 45° counterclockwise, and the angle with the optical axis of the half-wave plate 105 is 22.5°. After passing through the half-wave plate 105, along the direction of light propagation, the polarization direction of the light is rotated 45° clockwise and becomes P light again. After passing through the PBS 106 of the second polarization beam splitter component 108, it reaches the output of port 2 (the common end, usually a single-mode fiber collimator).

[0042] In the second optical path, the input optical signal is separated into S light and P light from port 2 through the upper PBS 106 of the second optical splitter component 108, wherein: for the S light, it passes through the upper PBS 106 of the second optical splitter component 108, the light is reflected and turned 90°, then incident on the PBS 107, then reflected and turned 90° again, and then incident on the half-wave plate 105, the optical axis of the half-wave plate forms an angle of 67.5° with the S polarized light, and after passing through the half-wave plate, along the propagation direction, the polarization direction of the light is rotated 135° counterclockwise compared with the original polarization direction, and then enters the 45° Faraday rotator 104, and after passing through 104, the polarization direction of the light is rotated 45° clockwise again, and finally the original incident polarization state is changed from S light to P light, and then enters the PBS 102 and is completely transmitted, and finally reaches the output of the third port (receiving end, usually a detector). For the P light, it passes through the upper PBS 106 of the second splitter component 108, the light is completely transmitted, and then enters the half-wave plate 105, the optical axis of the half-wave plate is 22.5° with the P polarized light, and after passing through the half-wave plate, along the propagation direction, the polarization direction of the light is rotated 45° clockwise compared with the original polarization direction, and then enters the 45° Faraday rotator 104, after passing through 104, the polarization direction of the light is rotated 45° clockwise again, and finally the polarization state of the original incident light changes from P light to S light, and then enters the PBS 101, is reflected by the PBS 101 and turned 90°, and then enters the PBS 102, is reflected by the PBS 102 again and turned 90°, and finally is combined with the P light of the second optical path, and arrives at the output of port 3 together.

[0043] Since the first polarization beam splitter component 103 and the second polarization beam splitter component 108 can be made into long and slender strips with very high angular accuracy in the same batch during processing, similarly, the 45° Faraday rotator 104 and the half-wave plate 105 can also be processed into strips with optimal length. The corresponding strips 103, 104, 105 and 108 are aligned without complicated debugging and alignment, and then assembled and integrated together by gluing or deepening optical glue or optical glue process, and finally the strips are cut into multiple finished products, which can greatly reduce the cost of processing and assembly.

[0044] In addition, since the size of the integrated free-space optical circulator can be made very small, this helps to significantly reduce the material cost of the circulator.

[0045] Finally, in terms of the performance of the optical circulator of the present invention, since the bonding or deepening of the optical glue or the assembly process of the optical glue used fully considers the refractive index matching between different interfaces, the assembly can be easily achieved with high precision, and the extinction ratio of the PBS film can also be very high. The device has very good performance and can achieve very small forward insertion loss and very high reverse isolation.

[0046] Wherein, further, the Faraday rotator includes a self-contained magnetic Faraday rotator or a non-self-contained magnetic Faraday rotator.

[0047] Example 2

[0048] like Figures 6 to 8 As shown in one, it shows the implementation structure of Example 2 of the present invention. The structure of this embodiment is roughly the same as that of Example 1 (corresponding numbers refer to the same components), and the difference is that the first polarization splitter component 103 and the second polarization splitter component 108 are glued or deepened with optical glue or the optical glue has a wedge-shaped piece 201, 202 on the end surface away from the 45° Faraday rotator 104, and the wedge-shaped surfaces between the two wedge-shaped pieces 201, 202 are parallel to each other.

[0049] By adding wedge-shaped pieces 201 and 202 and adjusting a suitable incident angle, the reflected light generated on the incident surface can be reflected away from the original incident light path without affecting other performances of the device, thereby increasing the echo reflection loss of the device, which is beneficial to improving the stability of the light source at the transmitting end.

[0050] The working principle of this embodiment is the same as that of embodiment 1. The optical path diagram is as follows: Figure 7 As shown, no further description is given here.

[0051] Example 3

[0052] like Fig. 9Or as shown in 10, it shows the implementation structure of Example 3 of the present invention. The structure of this embodiment is roughly the same as that of Example 1 (corresponding numbers refer to the same parts). This embodiment is based on Example 1, and the incident surface of the overall structure is processed into a non-90° surface with a small angle relative to the bottom surface or the side surface; at this time, by adjusting the appropriate incident angle, the reflected light generated on the incident surface can be reflected away from the original incident light path without affecting other performances of the device, thereby achieving the purpose of increasing the return loss.

[0053] Similarly, the working principle of this embodiment is the same as that of embodiment 1, and the optical path diagram is as follows: Fig.10 As shown, no further description is given here.

[0054] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes made to the present invention in form and details without departing from the spirit and scope of the present invention as defined in the appended claims are within the scope of protection of the present invention.

Claims

1. An integrated free-space optical circulator, characterized in that: It comprises a first polarization beam splitter component, a non-reciprocal polarization rotator, a half-wave plate, and a second polarization beam splitter component which are sequentially arranged along an optical path, wherein the first polarization beam splitter component, the non-reciprocal polarization rotator, the half-wave plate, and the second polarization beam splitter component are fixedly combined with each other as a whole; the first polarization beam splitter component, the non-reciprocal polarization rotator, the half-wave plate, and the second polarization beam splitter component are fixedly combined with each other as a whole by gluing or deepening optical glue or optical glue; the first polarization beam splitter component is two 45° right-angle prisms and a 45° rhombus prism which are glued or deepened with optical glue or optical glue as a whole, and a PBS film is plated on the inclined surfaces of the two 45° right-angle prisms or on the two inclined surfaces of a 45° rhombus prism; The second polarization beam splitter component is two 45° right-angle prisms and a 45° rhombus prism glued or deepened with optical glue or optical glue into one, and a PBS film is plated on the inclined surfaces of the two 45° right-angle prisms or the two inclined surfaces of a 45° rhombus prism; the half-wave plate is a single half-wave plate or a multi-piece combined half-wave plate, and the optical axis of the half-wave plate forms an angle of 22.5° with the first polarization beam splitter component and / or the second polarization beam splitter component.

2. The integrated free-space optical circulator according to claim 1, characterized in that: An anti-reflection film is coated on a side of the first polarization splitting component away from the non-reciprocal polarization rotator.

3. The integrated free-space optical circulator according to claim 1, characterized in that: An anti-reflection film is coated on a side of the second polarization beam splitting component away from the non-reciprocal polarization rotator.

4. The integrated free-space optical circulator according to claim 1, characterized in that: The refractive index of the glue used for bonding is adapted to the refractive index of the corresponding bonding surface, and the glue at least includes UV curing glue, heat curing glue or dual curing glue.

5. The integrated free-space optical circulator according to claim 1, characterized in that: The non-reciprocal polarization rotator is a Faraday rotator.

6. The integrated free-space optical circulator according to claim 1, characterized in that: The end surface of the first polarization beam splitter component and / or the second polarization beam splitter component away from the non-reciprocal rotator is glued or deepened with optical glue or the optical glue has a wedge-shaped piece.

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