Optical device and optical communication device equipped with said optical device

Abstract

Suppresses crosstalk from the optical transmitter to the optical receiver. [Solution] The optical device comprises a first rotor that outputs a first Y-polarized light beam by rotating the polarization plane of a first X-polarized light beam, and a second rotor that outputs a second X-polarized light beam by rotating the polarization plane of a second Y-polarized light beam. The first rotor outputs a third Y-polarized light beam that passes in the opposite direction to the first X-polarized light beam without rotating its polarization plane, and the second rotor outputs a fourth X-polarized light beam that passes in the opposite direction to the second Y-polarized light beam without rotating its polarization plane. The optical device further comprises a third PBS that deflects the third Y-polarized light beam that has passed through the first rotor, a fourth PBS that deflects the fourth X-polarized light beam that has passed through the second rotor, a first converter that converts the third Y-polarized light beam to X-polarization, and a second converter that converts the fourth X-polarized light beam to Z-polarization.

Description

Technical Field

[0004] , ,

[0001] The present disclosure relates to an optical device that can be used, for example, in an optical communication device.

Background Art

[0002] Free space optical (FSO) communication is a communication method that transmits optical signals through free space instead of using a fixed medium such as an optical fiber. In the following description, the optical signal transmitted into free space for FSO communication is referred to as an "optical beam". An optical communication device for FSO communication (hereinafter simply referred to as an optical communication device) can be installed on the ground or mounted (installed) on a moving object such as a satellite, a ship, or an aircraft. An optical communication device installed on the ground can communicate with other optical communication devices installed on the ground or other optical communication devices mounted on moving objects. Also, an optical communication device mounted on a moving object can communicate with other optical communication devices installed on the ground or other optical communication devices mounted on other moving objects.

[0003] An optical communication device includes an optical transmitter (TX) that generates an optical beam (hereinafter referred to as a transmission beam) based on information to be transmitted to another optical communication device, an optical receiver (RX) that demodulates an optical beam (hereinafter referred to as a reception beam) received from the other optical communication device, and an optical antenna (ANT). The ANT can be commonly used for both transmission of the transmission beam and reception of the reception beam. When the same ANT is used for transmission of the transmission beam and reception of the reception beam, the optical communication device has an optical device that outputs the transmission beam from the TX to the ANT and outputs the reception beam from the ANT to the RX. In the following description, the optical device used to output the transmission beam from the TX to the ANT and output the reception beam from the ANT to the RX is referred to as a "transmit-receive separation device". Non-Patent Document 1 discloses the internal configuration of an optical circulator that can be used as a transmit-receive separation device.

Prior Art Documents

Non-Patent Documents

[0004] [Non-Patent Document 1] "Structure of a light circulator and how light travels (explained in video)," [online], Fiber Lab Co., Ltd., [Accessed August 28, 2024], Internet,<URL:https: / / www.fiberlabs.co.jp / tech-explan / about-circulator / > [Overview of the project] [Problems that the invention aims to solve]

[0005] Figure 1 shows the paths of the transmit and receive beams within a transmit / receive separation device based on the configuration described in Non-Patent Document 1. In the following, the three mutually orthogonal directions in three-dimensional space are referred to as the X, Y, and Z directions, and only two of these directions are shown in each figure. The remaining direction is the depth direction of each figure. Furthermore, optical beams whose electric field vibration directions are in the X, Y, and Z directions are referred to as "X-polarized," "Y-polarized," and "Z-polarized" optical beams, respectively. In Figure 1, the solid line represents the "X-polarized" optical beam, the dotted line represents the "Y-polarized" optical beam, and the dashed line represents the "Z-polarized" optical beam. Figure 1(A) shows the path of the transmit beam, and Figure 1(B) shows the path of the receive beam.

[0006] In the configuration shown in Figure 1, the polarization beam splitters (PBSs) 50 and 54 are positioned to deflect the X-polarized light beam by 90 degrees, while allowing the Y-polarized and Z-polarized light beams to travel in a straight line. Furthermore, the rotors 52 and 53 are configured to rotate the polarization plane of the light beam passing in the +Z direction by 90 degrees, but not the polarization plane of the light beam passing in the -Z direction. The rotors 52 and 53 are composed of, for example, a Faraday rotor that rotates the polarization plane by 45 degrees in the same direction regardless of the direction of the light beam's passage, and a half-wave plate that rotates the polarization plane of the passing light beam by 45 degrees, but the direction of rotation of the polarization plane differs depending on the direction of the light beam's passage.

[0007] TX outputs a polarized multiplexed transmission beam, consisting of an X-polarized first transmission beam and a Y-polarized second transmission beam, to port #1 of the transmit / receive separation device 100. The transmission beam input to port #1 of the transmit / receive separation device 100 is input to PBS50 in a state where it is propagating in the +Z direction. PBS50 deflects the X-polarized first transmission beam in the +Y direction, and mirror 51 deflects the X-polarized first transmission beam from PBS50 in the +Z direction. Rotator 52 rotates the polarization plane of the X-polarized first transmission beam from mirror 51 by 90 degrees, thereby outputting the Y-polarized first transmission beam toward PBS54.

[0008] Furthermore, PBS50 allows the Y-polarized second transmission beam to propagate straight without deflection. Rotator 53 rotates the polarization plane of the Y-polarized second transmission beam from PBS50 by 90 degrees, thereby outputting the X-polarized second transmission beam. Mirror 55 deflects the X-polarized second transmission beam from Rotator 53 in the +Y direction, inputting the X-polarized second transmission beam to PBS54. PBS54 allows the Y-polarized first transmission beam, which propagates in the +Z direction, to propagate straight, and deflects the X-polarized second transmission beam, which propagates in the +Y direction, in the +Z direction. Therefore, PBS54 outputs a transmission beam propagating in the +Z direction, which is a polarization multiplexed combination of the Y-polarized first transmission beam and the X-polarized second transmission beam. This transmission beam is output to ANT via port #2 of the transmit / receive separation device 100.

[0009] The antenna outputs a polarized multiplexed received beam, consisting of a first Y-polarized received beam and a second X-polarized received beam, to port #2 of the transceiver / separator device 100. The received beam input to port #2 of the transceiver / separator device 100 is input to PBS54 in a state where it is propagating in the -Z direction. PBS54 directs the first Y-polarized received beam in a straight line. The rotator 52 outputs the first Y-polarized received beam from PBS54 towards the mirror 51 without rotating its polarization plane. The mirror 51 deflects the first Y-polarized received beam from the rotator 52 in the -Y direction. As the propagation direction is deflected in the -Y direction, the first received beam is converted from Y-polarized to Z-polarized. This Z-polarized first received beam is input to PBS50.

[0010] Furthermore, PBS54 deflects the second X-polarized received beam in the -Y direction. Mirror 55 deflects the second X-polarized received beam from PBS54 in the -Z direction. Rotator 53 outputs the second X-polarized received beam from mirror 55 towards PBS50 without rotating its polarization plane. PBS50 directs the first Z-polarized received beam, which propagates in the -Y direction, straight ahead, and deflects the second X-polarized received beam, which propagates in the -Z direction, in the -Y direction. Therefore, PBS50 outputs a received beam propagating in the -Y direction, which is a polarization multiplexed combination of the first Z-polarized received beam and the second X-polarized received beam. This received beam is output to RX via port #3 of the transmit / receive separation device 100.

[0011] In PBS50, ideally, the entire first transmit beam (X-polarization) from the TX should be deflected in the +Y direction. However, due to manufacturing imperfections, some of it is deflected in the -Y direction. In this case, the optical beam received by the RX contains components of the transmit beam. In other words, crosstalk occurs in the optical beam received by the RX. Since the power of the transmit beam is greater than the power of the received beam, the crosstalk affects the demodulation of the RX.

[0012] This disclosure provides a technology for suppressing crosstalk from an optical transmitter to an optical receiver. [Means for solving the problem]

[0013] According to one aspect of the present disclosure, the optical device includes: a first polarization beam splitter that separates an X-polarized first optical beam and a Y-polarized second optical beam orthogonal to the X-polarized first optical beam input from a first port; a first rotor that outputs the Y-polarized first optical beam by rotating the polarization plane of the X-polarized first optical beam; a second rotor that outputs the X-polarized second optical beam by rotating the polarization plane of the Y-polarized second optical beam; and a second polarization beam splitter that outputs the Y-polarized first optical beam and the X-polarized second optical beam from a second port, wherein the second polarization beam splitter separates the Y-polarized third optical beam and the X-polarized fourth optical beam input to the second port, and the first rotor separates the Y-polarized third optical beam passing in the opposite direction to the X-polarized first optical beam. The optical device further comprises: a third polarization beam splitter that deflects the Y-polarized third light beam that has passed through the first rotator; a fourth polarization beam splitter that deflects the X-polarized fourth light beam that has passed through the second rotator; a first converter that converts the Y-polarized third light beam to the X-polarized third light beam; a second converter that converts the X-polarized fourth light beam to the Z-polarized fourth light beam that is orthogonal to both the X-polarized and Y-polarized beams; and a fifth polarization beam splitter that outputs the X-polarized third light beam and the Z-polarized fourth light beam from a third port. [Effects of the Invention]

[0014] According to this disclosure, crosstalk from the optical transmitter to the optical receiver can be suppressed. [Brief explanation of the drawing]

[0015] [Figure 1] A diagram illustrating the path of an optical beam within a transmit / receive separation device based on background technology. [Figure 2] Configuration diagram of an optical communication device according to an embodiment. [Figure 3]Diagram illustrating the placement and orientation of PBS. [Figure 4] A diagram illustrating the path of an optical beam within a transmit / receive separation device according to an embodiment. [Figure 5] A diagram illustrating the path of an optical beam within a transmit / receive separation device according to an embodiment. [Figure 6] A diagram illustrating the path of an optical beam within a transmit / receive separation device according to an embodiment. [Modes for carrying out the invention]

[0016] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined arbitrarily. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0017] <First Embodiment> Figure 2 is a configuration diagram of an optical communication device according to this embodiment. The transmit / receive decoupling device 100 has three ports #1, #2, and #3. Port #1 of the transmit / receive decoupling device 100 is connected to the optical transmitter (TX) 200, port #2 is connected to the optical antenna (ANT) 400, and port #3 is connected to the optical receiver (RX) 300. The transmit / receive decoupling device 100 outputs the optical beam input to port #1 from port #2. The transmit / receive decoupling device 100 outputs the optical beam input to port #2 from port #3. The transmit / receive decoupling device 100 in this embodiment suppresses the output of a component of the optical beam input to port #1 from port #3.

[0018] TX200 generates a transmission beam and outputs it to port #1 of the transmit-receive separation device 100. The transmission beam may be a polarization multiplexing of two transmission beams with orthogonal polarizations to each other. However, the transmission beam may be a single polarization. The transmission beam is output to ANT400 via the transmit-receive separation device 100. ANT400 transmits the transmission beam toward another optical communication device that is the communication partner. Further, ANT400 receives the transmission beam transmitted by the other optical communication device as a reception beam and outputs it to the transmit-receive separation device 100. The reception beam is output to RX300 via the transmit-receive separation device 100. RX300 demodulates the reception beam.

[0019] The transmit-receive separation device 100 has a plurality of PBSs. FIG. 3 is an explanatory diagram of the arrangement posture of PBSs in the present disclosure. Among the optical beams with three different polarizations, the optical beam deflected (reflected) by the PBS differs depending on the arrangement posture of the PBS. FIG. 3(A) is an arrangement posture that deflects the X-polarized optical beam and allows the Y- and Z-polarized optical beams to propagate straight, and will be referred to as the "X deflection posture" hereinafter. FIG. 3(B) is an arrangement posture that deflects the Y-polarized optical beam and allows the X- and Z-polarized optical beams to propagate straight, and will be referred to as the "Y deflection posture" hereinafter. FIG. 3(C) is an arrangement posture that deflects the Z-polarized optical beam and allows the X- and Y-polarized optical beams to propagate straight, and will be referred to as the "Z deflection posture" hereinafter. In FIG. 3(A), the X-polarized optical beam propagating in the +Z direction is deflected in the +Y direction, but there is also an arrangement posture in which the X-polarized optical beam propagating in the +Z direction is deflected in the -Y direction. However, since the positive or negative of the direction after deflection is not important, in the following description, the "X deflection posture" includes both the arrangement posture shown in FIG. 3(A) and the arrangement posture in which the X-polarized optical beam propagating in the +Z direction is deflected in the -Y direction. The same applies to the Y deflection posture and the Z deflection posture.

[0020] FIG. 4 is an explanatory diagram of the path of the transmission beam in the transmission / reception separation device 100 according to the present embodiment. Note that FIG. 4(A) is a plan view seen from the -X direction, and FIG. 4(B) is a cross-sectional view seen from the +Z direction at line 90 in FIG. 4(A). For the components that are the same as those described in FIG. 1, the same reference numerals are given, and the description thereof is basically omitted. The transmission / reception separation device 100 according to the present embodiment has, in addition to the configuration of FIG. 1, PBSs 10, 11, and 15, a half-wave plate (HWP) 12, and mirrors 13 and 14. Note that the mirror 14 in FIG. 4(B) is present on the other side of the PBS 10 in FIG. 4(A). Also, the PBS 15 in FIG. 4(B) is present on the other side of the mirror 13 in FIG. 4(A).

[0021] Note that for each PBS, its arrangement posture is shown by the polarization plane to be reflected. According to FIG. 4, PBSs 50, 54, and 11 are in the X deflection posture, PBS 10 is in the Y deflection posture, and PBS 15 is in the Z deflection posture.

[0022] The PBS 10 is provided between the mirror 51 and the rotator 52, and the PBS 11 is provided between the PBS 50 and the rotator 53. Since the PBS 10 is in the Y deflection posture, it allows the first transmission beam of the X polarization wave deflected by the mirror 51 to pass through. Also, since the PBS 11 is in the X deflection posture, it allows the second transmission beam of the Y polarization wave from the PBS 50 to pass through. Therefore, similar to FIG. 1, a transmission beam obtained by polarization multiplexing the first transmission beam of the Y polarization wave and the second transmission beam of the X polarization wave is output from port #2 of the transmission / reception separation device 100.

[0023] FIGS. 5 and 6 are explanatory diagrams of the path of the reception beam in the transmission / reception separation device 100 according to the present embodiment. FIG. 5(A) is a plan view seen from the -X direction, similar to FIG. 4(A), and FIG. 5(B) is a cross-sectional view seen from the +Z direction at line 90 in FIG. 5(A), similar to FIG. 4(B). FIG. 6 is a cross-sectional view seen from the +Y direction at line 91 in FIG. 5(A).

[0024] The first Y-polarized received beam from the rotor 52 is deflected in the -X direction at PBS 10. The mirror 14 deflects the Y-polarized first received beam deflected by PBS 10 in the -Y direction. In this process, the first received beam is converted to X polarization. The X-polarized first received beam is input to PBS 15. In this way, the mirror 14 functions as a converter that converts the Y-polarized first received beam to the X-polarized first received beam.

[0025] The X-polarized second received beam from the rotor 53 is deflected in the -Y direction at PBS 11. HWP 12 outputs a Z-polarized second received beam by rotating the polarization plane of the X-polarized second received beam by 90 degrees. Mirror 13 deflects the Z-polarized second received beam in the -X direction. The Z-polarized second received beam deflected by mirror 13 is input to PBS 15. In this way, HWP 12 functions as a converter that converts the X-polarized second received beam into a Z-polarized second received beam.

[0026] PBS15 outputs the first X-polarized received beam in the -Y direction without deflecting its propagation direction. PBS15 also deflects the second Z-polarized received beam in the -Y direction. Therefore, PBS15 outputs a polarized multiplexed received beam in the -Y direction, which is the result of combining the first X-polarized received beam and the second Z-polarized received beam. This received beam is output to RX via port #3 of the transmit / receive separation device 100.

[0027] As is clear from Figure 4(A), in PBS50, even if a portion of the X-polarized first transmit beam is deflected in the -Y direction, it is not output from port #3 of the transmit / receive separation device 100. Therefore, in the transmit / receive separation device 100 according to this embodiment, it is possible to suppress the output of a component of the optical beam input to port #1 from port #3.

[0028] In this embodiment, HWP12 was placed between PBS11 and mirror13, but it may also be placed between mirror13 and PBS15. In this case, mirror13 reflects the X-polarized second received beam from PBS11 in the -X direction. At that time, the second received beam is converted to Y polarization. HWP12 outputs a Z-polarized second received beam by rotating the polarization plane of the Y-polarized second received beam by 90 degrees. Therefore, in this configuration, HWP12 and mirror13 function as converters that convert the X-polarized second received beam to a Z-polarized second received beam.

[0029] Note that the configuration shown in Figure 4 is an example, and the propagation direction of each light beam can be changed according to the required shape and size of the transmitting / receiving separation device 100.

[0030] <Second Embodiment> In the configuration shown in Figure 4, a portion of the first Y-polarized transmit beam, which should be output from the rotor 52 toward PBS 54, may be reflected within the rotor 52 and output toward PBS 10. This first Y-polarized transmit beam reaches RX, similar to the first receive beam described in Figures 5 and 6. Also in the configuration shown in Figure 4, a portion of the second X-polarized transmit beam, which should be output from the rotor 53 toward the mirror 55, may be reflected within the rotor 53 and output toward PBS 11. This second X-polarized transmit beam is output from port #3 of the transmit / receive separation device 100, similar to the second receive beam described in Figures 5 and 6. Therefore, even in the configuration of the first embodiment, crosstalk may occur due to reflections within the rotor 52 and rotor 53.

[0031] Therefore, when the frequencies of the transmitting beam and receiving beam of an optical communication device are different, the transmit / receive separation device 100 can be configured to include a bandpass filter (BPF) that blocks the transmitting beam on the optical path through which only the receiving beam passes. For example, a first BPF can be provided on the optical path of the first receiving beam from PBS10 to PBS15, and a second BPF can be provided on the optical path of the second receiving beam from PBS11 to PBS15. The first BPF and the second BPF block the frequency band of the transmitting beam and allow the receiving beam to pass through.

[0032] As described above, the transmit / receive separation device 100 of this embodiment is applicable when the frequencies of the transmit beam and the receive beam are different, and can also suppress crosstalk caused by reflections in the rotor 52 and rotor 53.

[0033] Furthermore, the transmit / receive separation device 100 described in the first and second embodiments can be used not only in optical communication equipment for FSO communication, but also in optical communication equipment that transmits and receives optical signals using a single optical fiber core. In that case, ANT400 in Figure 2 becomes one of the optical fiber cores.

[0034] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention.

[0035] With the above configuration, crosstalk from the optical transmitter to the optical receiver can be suppressed. Therefore, it becomes possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote sustainable industrialization and foster innovation." [Explanation of Symbols]

[0036] 10, 11, 15, 50, 54: PBS, 52, 53: Rotator, 12: HWP, 13: Mirror

Claims

1. It is an optical device, A first polarization beam splitter separates a first optical beam with X polarization input from the first port and a second optical beam with Y polarization orthogonal to the X polarization, A first rotor that outputs the first light beam with Y polarization by rotating the polarization plane of the first light beam with X polarization, A second rotor that outputs the second light beam with X polarization by rotating the polarization plane of the second light beam with Y polarization, A second polarization beam splitter that outputs the first optical beam with Y polarization and the second optical beam with X polarization from a second port, Equipped with, The second polarization beam splitter separates the Y-polarized third light beam and the X-polarized fourth light beam that are input to the second port. The first rotator outputs the Y-polarized third light beam without rotating its polarization plane, which passes in the opposite direction to the X-polarized first light beam. The second rotator outputs the fourth light beam, which is X-polarized and passes in the opposite direction to the second light beam, which is Y-polarized, without rotating its polarization plane. The optical device further, A third polarization beam splitter that deflects the third optical beam with Y polarization that has passed through the first rotating device, A fourth polarization beam splitter that deflects the X-polarized fourth light beam that has passed through the second rotating device, A first converter that converts the Y-polarized third light beam into the X-polarized third light beam, A second converter that converts the X-polarized fourth light beam into a Z-polarized fourth light beam orthogonal to both the X-polarization and the Y-polarization, A fifth polarization beam splitter outputs the third optical beam with X polarization and the fourth optical beam with Z polarization from the third port, An optical device equipped with this feature.

2. The optical device according to claim 1, wherein the first optical beam with X polarization travels in a straight line through the third polarization beam splitter and is input to the first rotor.

3. The optical device according to claim 1, wherein the second optical beam with Y polarization travels in a straight line through the fourth polarization beam splitter and is input to the second rotor.

4. The optical device according to claim 1, wherein the first converter includes a mirror that deflects the Y-polarized third light beam and converts it into the X-polarized third light beam.

5. The optical device according to claim 1, wherein the second converter includes a half-wave plate that converts the X-polarized fourth optical beam, which has been deflected by the fourth polarization beam splitter, into the Z-polarized fourth optical beam.

6. The second converter includes a mirror that deflects the X-polarized fourth light beam, which has been deflected by the fourth polarization beam splitter, and converts it into the Y-polarized fourth light beam, A half-wave plate that converts the Y-polarized fourth light beam to the Z-polarized fourth light beam, The optical device according to claim 1, including the optical device described in claim 1.

7. The optical device according to claim 1, wherein the fifth polarization beam splitter causes the X-polarized third optical beam from the first converter to travel in a straight line and deflects the Z-polarized fourth optical beam from the second converter.

8. The first frequency band of the first and second light beams and the second frequency band of the third and fourth light beams are different. The optical device further, A first filter that blocks the light beam of the first frequency band in the optical path of the third light beam from the third polarization beam splitter to the fifth polarization beam splitter, A second filter that blocks the light beam of the first frequency band in the optical path of the fourth light beam from the fourth polarization beam splitter to the fifth polarization beam splitter, The optical device according to claim 1, comprising:

9. An optical device according to any one of claims 1 to 8, An optical transmitter connected to the first port of the optical device, An optical receiver connected to the third port of the optical device, An optical antenna connected to the second port of the optical device, An optical communication device equipped with the following features.

Images