Annular space optical orbital angular momentum mode converter

Abstract

The invention relates to the technical field of optical communication, and particularly discloses an annular space optical orbital angular momentum mode converter which comprises a rotating structure and a mode converter body composed of an optical modulation plane. The mode converter can convert coaxial OAM light beams into annularly distributed demodulation light, and can also convert the demodulation light at different positions into OAM light of different orders. Under the condition of a fixed optical path, an OAM light beam with a required order can be input at a demodulation side and can be output only by rotating a phase plane as a rotation axis, the output position of the output OAM light beam cannot be changed due to rotation of the phase plane, multiplexing and demultiplexing of an orbital angular momentum mode can be completed only through a rotation device, and the method is simple and convenient. And converting the size, the ring width ratio and the order. And convenience is provided for experiment operation. Meanwhile, when an optical path is fixed, multiplexing or mode conversion without changing the positions of optical fibers or devices at the input end and the output end can be achieved by rotating the devices, and convenience is provided for experimental optical path design.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to an annular space optical orbital angular momentum mode converter. Background Art

[0002] The current spatial orbital angular momentum mode converter is generally a vortex phase plate, a spatial light modulator, and a coordinate transformation (de)multiplexing element, etc. Among them, the l-order vortex phase plate is engraved with the phase of the l-order orbital angular momentum mode, which can modulate Gaussian light into l-order vortex light or modulate l-order vortex light into Gaussian light. Its disadvantages are:

[0003] (1) A vortex phase plate can only correspond to one vortex phase. If other orbital angular momentum modes need to be modulated or demodulated, a new vortex phase plate needs to be switched.

[0004] (2) The vortex phase plate generally corresponds to vortex light and Gaussian light, and the demodulation mode cannot be customized.

[0005] (3) In order to ensure that the vortex phase plate can cover the size of the light mode field, a vortex phase plate needs to have a certain application area, and a device composed of multiple vortex phase plates occupies a very large area.

[0006] Spatial light modulators can achieve optical conversion of orbital angular momentum modes by applying corresponding vortex phase plates or other phase structures on them. However, spatial light modulators are polarization-dependent devices and can only regulate one polarization at a time. Most optical communication systems require the use of two orthogonal polarization states. Therefore, the use of spatial light modulators will lose the number of polarization channels and part of the light energy. The coordinate transformation orbital angular momentum multiplexing or demultiplexing device is usually coaxial on one side of the orbital angular momentum mode. The orbital angular momentum mode is mapped into a strip light spot with an inclined phase, and then focused to different positions on the focal plane through a lens to achieve demodulation. However, the demodulation light spot array at the output end is usually arranged to correspond to the optical fiber array. However, if one optical fiber is required to achieve different orbital angular momentum modes, the optical axis position of the orbital angular momentum end will inevitably change.

[0007] Therefore, an annular space optical orbital angular momentum mode converter is proposed to solve the above problems. Summary of the invention

[0008] The object of the present invention is to provide a ring-shaped space optical orbital angular momentum mode converter.

[0009] To solve the above problems, the present invention adopts the following technical solutions:

[0010] A ring-shaped space optical orbital angular momentum mode converter comprises a rotating structure and a mode converter composed of an optical modulation plane.

[0011] The rotation axis of the rotating structure is the center of the optical modulation plane, and the rotating structure is configured to achieve rotation at any angle.

[0012] The center of the rotation axis of the rotating structure is the center of the orbital angular momentum mode (ie, the phase singularity).

[0013] The center of the rotation axis of the rotating structure is the center of the annular distribution area of ​​the demodulation light spot arrangement.

[0014] The optical modulation plane includes one or more optical modulation units.

[0015] The optical modulation plane is configured to follow the rotation axis of the mode converter to perform rotational motion at the same angle.

[0016] In the annular space optical orbital angular momentum mode converter provided by at least one embodiment of the present disclosure, the optical modulation unit is a phase modulation unit or a complex amplitude modulation unit.

[0017] In the annular space optical orbital angular momentum mode converter provided by at least one embodiment of the present disclosure, the plurality of optical modulation units are oriented in the same direction.

[0018] In the annular space optical orbital angular momentum mode converter provided by at least one embodiment of the present disclosure, the mode converter is a mode demultiplexer for the same coordinate transformation or a mode demultiplexer for multi-plane light field transformation.

[0019] In the annular space optical orbital angular momentum mode converter provided by at least one embodiment of the present disclosure, the rotating structure is arranged in a tubular shape.

[0020] In the annular space optical orbital angular momentum mode converter provided by at least one embodiment of the present disclosure, the mode converter is located inside the rotating structure.

[0021] In the annular space optical orbital angular momentum mode converter provided by at least one embodiment of the present disclosure, a plurality of the optical modulation units are arranged in an array.

[0022] In the annular space optical orbital angular momentum mode converter provided by at least one embodiment of the present disclosure, the mode demultiplexer of the same coordinate transformation adopts a logarithmic polar coordinate transformation method or a spiral transformation demultiplexing method.

[0023] The beneficial effects of the present invention are as follows: through pure angle transformation, the conversion between orbital angular momentum modes and between orbital angular momentum and demodulation modes can be realized under the condition of fixed input and output ends or without changing the optical path and optical axis, so that the optical path is simpler and has higher stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 The figure is a schematic diagram of the overall structure of an annular space optical orbital angular momentum mode converter according to the present invention.

[0026] Figure 2 Schematic diagram of the array arrangement of optical modulation units.

[0027] Figure 3 This is the first phase plate for multi-plane light field control. The first pure phase modulation phase structure is shown.

[0028] Figure 4 The second phase plate for multi-plane light field control shows the second phase structure of pure phase modulation.

[0029] Figure 5 The third phase plate for multi-plane light field control shows the third phase structure of pure phase modulation.

[0030] Figure 6 The fourth phase plate for multi-plane light field control shows the fourth phase structure of pure phase modulation.

[0031] Figure 7 The fifth phase plate for multi-plane light field control, showing the fifth phase structure of pure phase modulation.

[0032] Figure 8 The sixth phase plate for multi-plane light field control shows the phase structure of the sixth pure phase modulation.

[0033] Fig. 9 is the input OAM beam, and the input end is a ring-shaped optical mode field.

[0034] Fig.10 After propagating through the first phase plate, the annular beam is unwound from the left and converges to the right.

[0035] Fig.11 After passing through the second phase plate, the light spot continues to converge to the right and gradually becomes a point-shaped light spot.

[0036] Fig.12 After passing through the third phase plate, the light spot continues to shape and converges toward the center.

[0037] Fig.13After passing through the fourth phase plate, the light spot finally converges to the designated position.

[0038] Fig.14 The mode field located on the sixth phase plane after propagating through the fifth phase plate will eventually converge into a point light spot of the corresponding designed mode field size, and the excess phase in the optical mode field will be smoothed out by the sixth phase plate to become the designed mode field, that is, the Gaussian mode.

[0039] Fig.15 for Figure 4 The rotated phase diagram of .

[0040] Fig.16 for Figure 5 The rotated phase diagram of .

[0041] Fig.17 for Figure 6 The rotated phase diagram of .

[0042] Fig.18 for Figure 7 The rotated phase diagram of .

[0043] Fig.19 for Figure 8 The rotated phase diagram.

[0044] Fig. 20 for Fig. 9 The rotated phase diagram has a rotation angle that makes the demodulated light spot modulation position correspond to each other, that is, before and after the rotation, two small circles presented by the phase in the diagram overlap.

[0045] In the figure:

[0046] 1. Rotating structure;

[0047] 2. Mode converter;

[0048] 3. Optical modulation unit. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments will be described clearly and completely below in conjunction with the drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments, rather than all the embodiments.

[0050] Example

[0051] Please refer to Figure 1 and 2 As shown, this embodiment provides a ring-shaped space optical orbital angular momentum mode converter, including: a rotating structure 1 and a mode converter 2 composed of an optical modulation plane.

[0052] The rotation axis of the rotating structure 1 is the center of the optical modulation plane, and the rotating structure 1 is configured to achieve rotation at any angle.

[0053] The center of the rotation axis of the rotating structure 1 is the center of the orbital angular momentum mode (ie, the phase singularity).

[0054] The center of the rotation axis of the rotating structure 1 is the center of the annular distribution area of ​​the demodulation light spot arrangement.

[0055] The optical modulation plane includes one or more optical modulation units 3 .

[0056] The optical modulation plane is configured to follow the rotation axis of the mode converter 2 and perform rotational motion at the same angle.

[0057] In this embodiment, the optical modulation unit 3 is a phase modulation unit or a complex amplitude modulation unit.

[0058] In this embodiment, the multiple optical modulation units 3 are oriented in the same direction.

[0059] In this embodiment, the mode converter 2 is a mode demultiplexer for the same coordinate transformation or a mode demultiplexer for multi-plane light field transformation.

[0060] In this embodiment, the rotating structure 1 is configured in a tubular shape.

[0061] In this embodiment, the mode converter 2 is located inside the rotating structure 1 .

[0062] In this embodiment, a plurality of optical modulation units 3 are arranged in an array.

[0063] In this embodiment, the mode demultiplexer of the same coordinate transformation adopts a logarithmic polar coordinate transformation mode or a spiral transformation demultiplexing mode.

[0064] The mode converter 2 can convert the coaxial OAM light beam into a demodulated light with an annular distribution, and can also convert the demodulated light at different positions into OAM light of different orders. In the case of a fixed optical path, at the input on the demodulation side, the OAM light beam of the required order can be output only by rotating the phase plane with the phase plane as the rotation axis, and the output OAM light beam will not change the output position due to the rotation of the phase plane. The multiplexing and demultiplexing of the orbital angular momentum mode, as well as the conversion of size, ring width ratio, and order can be completed only by rotating the device. It provides convenience for the operation of the experiment. At the same time, when the optical path is fixed, the multiplexing or mode conversion can be achieved without changing the position of the input and output optical fibers or devices by rotating the device, which provides convenience for the optical path design of the experiment.

[0065] Specific example 1:

[0066] Please refer to Figures 3 to 14 As shown, Figures 3 to 8The six phase structures corresponding to the multi-plane light field conversion, the orbital angular momentum mode is modulated by these six phase structures, Figures 9 to 14 As shown in the figure, the intensity of the light field changes, thus changing the orbital angular momentum mode to a Gaussian mode. According to the principle of reversibility of the light path, when a point-shaped Gaussian light spot is input from the other side and passes through the reverse direction, Figures 3 to 8 The modulation of the 6-block phase structure shown in Figures 14 to 9 The reverse light field intensity changes will eventually be modulated into a ring-shaped orbital angular momentum mode. In this way, the orbital angular momentum mode and the Gaussian mode can be directly converted to each other. The orbital angular momentum mode corresponds to the Gaussian mode at different positions one by one.

[0067] The phase plate in this example can realize the direct conversion between orbital angular momentum mode and Gaussian mode at different positions. The orbital angular momentum mode corresponds directly one-to-one to the Gaussian mode at different positions. However, if the position of the phase plate is kept unchanged, different orbital angular momentum modes need to be received by optical fibers at different positions.

[0068] Specific example 2:

[0069] Please refer to Figures 15 to 20 As shown, Figure 5 A total of six phase plates are shown, and each phase plate is relative to Figure 3 After a certain angle of rotation. Assuming that the orbital angular momentum order corresponding to the output in Example 1 is m, and the output light spot with an orbital angular momentum order of n is on its lower side, it has undergone this angle of rotation. Figure 15-Figure 20 The output light spot of the n-order orbital angular momentum mode is the same as the output position of the m-order orbital angular momentum mode in specific example 1. By designing the light spot of the mode converter into a ring shape and rotating it, the conversion of orbital angular momentum modes of different orders can be completed without changing the input and output ends.

[0070] Specific example 3:

[0071] This example is based on Specific Example 1 and Specific Example 2. It can be seen from the above two specific examples that the input orbital angular momentum mode can output Gaussian light at a specific position, and the input Gaussian light at a characteristic position can output the corresponding orbital angular momentum mode, wherein the correspondence between Gaussian light and orbital angular momentum can be achieved by rotating the mode converter. Then, when we connect the two annular orbital angular momentum mode converters in reverse, by rotating the m-order output end of the previous mode converter to the same position as the n-order output end of the next mode converter, the transformation from the m-order orbital angular momentum mode to the n-order orbital angular momentum mode can be achieved. Due to the controllability of the multi-plane light field conversion design, the transformation of orbital angular momentum modes of different sizes and different ring width ratios can also be achieved. Therefore, the present invention can achieve the adjustable transformation of orbital angular momentum size, ring width ratio, and order only by rotation. At the same time, there is no need to change the position of the input and output ends.

[0072] Although the embodiments of the present application have been shown and described above, the scope of protection of the present invention is not limited thereto, and any changes or substitutions that are not conceivable through creative work should be included in the scope of protection of the present invention; unless explicitly stated, any elements, actions or instructions used in this document should not be interpreted as critical or necessary.

Claims

1. A toroidal space optical orbital angular momentum mode converter, characterized in that: include: Rotating structures and mode converters consisting of optical modulation planes; The rotation axis of the rotating structure is the center of the optical modulation plane, and the rotating structure is configured to achieve rotation at any angle; The center of the rotation axis of the rotating structure is the center of the orbital angular momentum mode; The center of the rotation axis of the rotating structure is the center of the annular distribution area of ​​the demodulation light spot arrangement; The optical modulation plane includes one or more optical modulation units; The optical modulation plane is configured to follow the rotation axis of the mode converter to perform rotational motion at the same angle.

2. The annular space optical orbital angular momentum mode converter according to claim 1, characterized in that: The optical modulation unit is a phase modulation unit or a complex amplitude modulation unit.

3. The annular space optical orbital angular momentum mode converter according to claim 2, characterized in that: The plurality of optical modulation units are oriented in the same direction.

4. The annular space optical orbital angular momentum mode converter according to claim 1, characterized in that: The mode converter is a mode demultiplexer for the same coordinate transformation or a mode demultiplexer for multi-plane light field transformation.

5. The annular space optical orbital angular momentum mode converter according to claim 1, characterized in that: The rotating structure is arranged in a tubular shape.

6. The annular space optical orbital angular momentum mode converter according to claim 5, characterized in that: The mode converter is located within the rotating structure.

7. The annular space optical orbital angular momentum mode converter according to claim 3, characterized in that: The plurality of optical modulation units are arranged in an array.

8. The annular space optical orbital angular momentum mode converter according to claim 4, characterized in that: The mode demultiplexer for the same coordinate transformation adopts a logarithmic polar coordinate transformation mode or a spiral transformation demultiplexing mode.

Images