Photon orbital angular momentum mode order multiple transformation device

Abstract

The invention relates to the technical field of optical communication, and particularly discloses a photon orbital angular momentum mode order multiple transformation device which comprises an optical coordinate transformation module, an optical 4f low-pass filtering module and a reflection module. The optical coordinate transformation module comprises a first phase part and a second phase part which have a light field phase modulation function; a vortex light field carrying photon orbital angular momentum enters from the first phase part, is subjected to spiral decomposition and phase modulation by the first phase part, then is propagated to the reflection module and then is propagated to the second phase part; the second phase part enables phase distribution to be converted from an angular spiral phase to an angular scaled spiral phase, and then ideal vortex light is output through the optical 4f low-pass filtering module; the photon orbital angular momentum mode order multiple conversion device realizes mode conversion of each multiple, greatly improves the efficiency of mode multiple conversion and the purity after change, and can be widely applied to the field of light field regulation and control.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a device for converting the order multiples of a photon orbital angular momentum mode. Background Art

[0002] Currently, two optical coordinate transformations have been proposed and used for the OAM mode order multiple conversion operation.

[0003] The first optical coordinate transformation is log-polar transformation, which realizes the basic principle of OAM mode order multiple transformation: first, the circular OAM mode exp(ilθ) is sheared and expanded into a long strip of inclined plane wave mode by log-polar transformation, and then the long strip of inclined plane wave mode is replicated and spliced ​​by fan-out grating elements to obtain a phase shift of n×2π. Finally, the long strip of inclined plane wave mode is wrapped back into the circular OAM mode by reverse log-polar transformation, and the OAM mode becomes exp(inlθ), that is, the OAM mode order n multiple transformation operation is realized. This scheme has the advantages of 100% conversion efficiency in theory, and in principle, it can be used in reverse to realize the OAM mode order 1 / n multiple transformation operation at the same time. However, its significant disadvantage is that it requires three-step transformation and is too complex. In practice, a slight alignment deviation will significantly deteriorate the effect of the OAM mode order multiple transformation operation.

[0004] The second type of optical coordinate transformation is the fan-shaped transformation. The basic principle of achieving the transformation of the OAM mode order multiple is: the fan-shaped transformation can realize the characteristic of angular scaling (θ→θ / n), and the annular OAM mode is converted into a fan-shaped mode; n complementary fan-shaped transformation light fields are generated through n parallel fan-shaped transformations to form a complete annular OAM mode exp(inlθ). Since the phase modulation required for n parallel fan-shaped transformations is superimposed on the same diffraction screen, this solution actually only requires one step of transformation, and the complexity is significantly reduced. However, the superposition of the above n phase modulations will correspond to the need for complex amplitude modulation, which is more complicated in wavefront control and will introduce losses due to amplitude modulation. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a device and method for converting the order multiples of the orbital angular momentum mode of photons.

[0006] To solve the above problems, the present invention adopts the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a device for converting the order of a photon orbital angular momentum mode, comprising: an optical coordinate transformation module, an optical 4f low-pass filtering module and a reflection module.

[0008] The reflection module is located between the optical coordinate transformation module and the optical 4f low-pass filtering module.

[0009] The optical coordinate transformation module includes a first phase unit and a second phase unit having a light field phase modulation function.

[0010] The optical 4f low-pass filter module and the second phase portion are parallel to each other.

[0011] A vortex light field carrying the orbital angular momentum of photons is injected from the first phase portion, and after being spirally decomposed and phase modulated by the first phase portion, the vortex light field propagates to the reflection module and then to the second phase portion.

[0012] The second phase section transforms the phase distribution from the angular spiral phase to the angularly scaled spiral phase and then outputs the ideal vortex light through the optical 4f low-pass filter module.

[0013] In the device for converting the order of a photon orbital angular momentum mode into multiples of a photon orbital angular momentum mode provided in at least one embodiment of the present disclosure, the center of the vortex light field is aligned with the center of the first phase portion.

[0014] In the device for converting the order of a photon orbital angular momentum mode into multiples according to at least one embodiment of the present disclosure, the reflection module reflects the vortex light field to the center of the second phase portion.

[0015] In the photon orbital angular momentum mode order multiple conversion device provided in at least one embodiment of the present disclosure, the first phase portion and the second phase portion are both arranged on a substrate, and the first phase portion and the second phase portion are respectively located on the front and back surfaces of the substrate.

[0016] In the device for converting the order of a photon orbital angular momentum mode into multiples of a photon orbital angular momentum mode according to at least one embodiment of the present disclosure, the vortex light field is injected from the center of the first phase portion.

[0017] In the device for converting the order of a photon orbital angular momentum mode into multiples of a photon orbital angular momentum mode provided in at least one embodiment of the present disclosure, the optical 4f low-pass filtering module includes a first convex lens, an aperture, and a second convex lens.

[0018] The aperture stop is located at a rear focal plane of the first convex lens, and the aperture stop is located at a front focal plane of the second convex lens.

[0019] The output light field plane of the optical 4f low-pass filtering module is located at the rear focal plane of the second convex lens, and the second phase portion is located at the front focal plane of the first convex lens.

[0020] The light fields at the front focal plane of the first convex lens and the back focal plane of the second convex lens satisfy a low-pass filtering relationship.

[0021] In the device for converting the order of a photon orbital angular momentum mode into multiples provided in at least one embodiment of the present disclosure, the first phase section and the second phase section are both one of a spatial light modulator, a diffractive optical element and a metasurface.

[0022] In a second aspect, an embodiment of the present invention provides a method for converting a photon orbital angular momentum mode order multiple, comprising the following steps:

[0023] S1: Input the vortex light carrying orbital angular momentum into the first phase section.

[0024] S2: After passing through the first phase section, the light beam is emitted at a specific angle, and at the same time, it is expanded along a spiral path and propagated to the reflection module after phase modulation, and then propagated from the reflection module to the second phase section, and the distortion phase introduced by the non-paraxial spiral transformation is eliminated after passing through the second phase section.

[0025] S3: After the phase compensation of the second phase section, the phase distribution of the vortex light is transformed from the angular spiral phase to the angular scaled spiral phase, and the ideal vortex light with annular light intensity distribution is obtained through the optical 4f low-pass filter system module.

[0026] S4: The ideal vortex light is output through the output plane of the optical 4f low-pass filter module to complete the mode multiple conversion operation.

[0027] The beneficial effects of the present invention are: achieving mode conversion of various multiples, greatly improving the efficiency of mode multiple conversion and the purity after the change, realizing simple and efficient vortex light mode order multiple conversion operation, and can be widely used in the field of light field control. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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.

[0029] Figure 1 It is a schematic diagram of the structure of the device for converting the order multiple of the photon orbital angular momentum mode in the present invention.

[0030] Figure 2 The phase diagram distribution of the first phase portion and the second phase portion loaded on the spatial light modulator of the present invention.

[0031] Figure 3 This is a light intensity distribution diagram of the second-order vortex light generated in the embodiment.

[0032] Figure 4This is the intensity distribution diagram of the 1st-order vortex light obtained after the 2nd-order vortex light passes through the first and second phase plates and the 4f system in the embodiment.

[0033] In the figure:

[0034] 10. Reflection module;

[0035] 20. first phase section;

[0036] 30. Second phase unit;

[0037] 40. substrate;

[0038] 50. The first convex lens;

[0039] 60. Aperture;

[0040] 70. Second convex lens. DETAILED DESCRIPTION

[0041] 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.

[0042] Example 1

[0043] This embodiment provides a method for converting the order of a photon orbital angular momentum mode into multiples, comprising the following steps:

[0044] S1: input the vortex light carrying orbital angular momentum into the first phase section, which is located at (x1, y1);

[0045] S2: After passing through the first phase section, the light beam is emitted at a specific angle, and at the same time, it is spread along the spiral path and phase modulated before propagating to the reflection module, and then propagated from the reflection module to the second phase section. After passing through the second phase section, the distortion phase introduced by the non-paraxial spiral transformation is eliminated. The second phase section is located at (x2, y2);

[0046] S3: After the phase compensation of the second phase unit, the phase distribution of the vortex light is transformed from the angular spiral phase exp(ilθ1) to the angular scaled spiral phase exp(inlθ2), and the ideal vortex light with annular light intensity distribution is obtained through the optical 4f low-pass filter system module. n is the scaling factor, that is, the multiple of the mode multiple conversion.

[0047] S4: The ideal vortex light is output through the output plane of the optical 4f low-pass filter module to complete the mode multiple conversion operation.

[0048] In this embodiment, the center of the vortex light field is aligned with the center of the first phase portion.

[0049] In this embodiment, the spiral decomposition of the first phase portion is specifically that the light field on the (r1, θ1) plane is decomposed along the path of the logarithmic spiral line and mapped to a straight line on the (r2, θ2) plane. The corresponding coordinate mapping relationship expression is as follows:

[0050]

[0051] In the formula, (r j ,θ j )(j=1,2,3) is the rectangular coordinate representation of (x j ,y j ) plane, n represents the scaling factor, and r0 represents the radial position mapped from (r0, 0) to the same point (r0, 0) in the above coordinate transformation.

[0052] In this embodiment, (r j ,θ j )(j=1,2,3) is expressed by the following formula:

[0053]

[0054] In the formula, a represents the speed of change of the logarithmic spiral; Indicates taking the integer part, θ j The value range of is (-∞, +∞).

[0055] In this embodiment, the first phase modulation Q(x1, y1) can be expressed by a set of partial differential equations as follows:

[0056]

[0057] k is the wave number of the incident vortex light field propagating between the first phase portion and the second phase portion, and d1+d2 is the distance between the first phase portion and the reflection module and between the reflection module and the second phase portion.

[0058] In this embodiment, the second phase modulation P(x2, y2) is expressed as follows:

[0059] The phase P(x2, y2) of the phase corrector is calculated by using the angular spectrum diffraction integral to transform the light field E(x2, y2), and then the distortion phase is obtained by calculating the phase difference between the transformed light field E(x2, y2) and the input light field E0(x1, y1). Finally, the opposite value of the distortion phase is taken to obtain P(x2, y2). The above process can be expressed as:

[0060] E(x2,y2)=F -1 {F{E0(x1,y1)exp [iQ(x1,y1)]}exp (ik z z)};

[0061] P(u, v)=arg[E0(x1, y1)]-arg[E(x2, y2)];

[0062] Among them, F -1 {} is the inverse Fourier transform, and F{} is the Fourier transform.

[0063] In order to better understand the principle of the method for converting the order of photon orbital angular momentum mode in the embodiment, a conversion example is provided below:

[0064] like Figure 3 and 4 As shown, specifically, the input photon orbital angular momentum mode, the corresponding vortex light field wavefront has a specific angular spiral phase exp(il θ1), and this example uses l=2 as the input photon orbital angular momentum mode to implement the OAM mode multiple conversion operation of n=1 / 2. The incident vortex light field is sequentially transformed through the first phase section and the spiral decomposition of the first phase section and the phase modulation Q(x1, y1) and P(x2, y2) to realize the spiral coordinate transformation. After the spiral transformation, the intensity distribution of the incident light field is transformed from the original annular distribution on the (x1, y1) plane to the spiral distribution on the (x2, y2) plane, and the phase distribution is transformed from the angular spiral phase exp(il θ1) to the angular scaled spiral phase exp(inl θ2). For the case of n=1 / 2, the corresponding angular spiral phase exp(i2θ1) is transformed into the angular spiral phase exp(i1θ2). After the transformation, the light field with spiral intensity distribution and angular spiral phase exp(inl θ2) distribution is incident on the optical 4f low-pass filter module. After passing through the 4f low-pass filter module, the ideal vortex light with annular intensity distribution can be obtained. The output plane (x3, y3) of the optical 4f low-pass filter module outputs the above-mentioned ideal vortex light with annular intensity distribution and angular spiral phase exp(inl θ2), that is, the output OAM order nl is n times the input OAM order l, realizing the OAM mode multiple conversion operation. For the case of n = 1 / 2, it means that the input 2nd order OAM beam will eventually output the 1st order OAM beam.

[0065] Example 2

[0066] like Figure 1 and 2 As shown, this embodiment provides a photon orbital angular momentum mode order multiple conversion system, including an optical coordinate transformation module, an optical 4f low-pass filtering module and a reflection module 10.

[0067] The reflection module 10 is located between the optical coordinate transformation module and the optical 4f low-pass filtering module.

[0068] The optical coordinate transformation module includes a first phase unit 20 and a second phase unit 30 having a light field phase modulation function.

[0069] The optical 4f low pass filter module and the second phase unit 30 are parallel to each other.

[0070] The vortex light field carrying the orbital angular momentum of the photons is injected from the first phase portion 20 , and after being spirally decomposed and phase modulated by the first phase portion 20 , the vortex light field propagates to the reflection module 10 and then to the second phase portion 30 .

[0071] The second phase section 30 transforms the phase distribution from the angular spiral phase to the angularly scaled spiral phase and then outputs the ideal vortex light through the optical 4f low-pass filter module.

[0072] In this embodiment, the center of the vortex light field is aligned with the center of the first phase portion 20 .

[0073] In this embodiment, the reflection module 10 reflects the vortex light field to the center of the second phase portion 30 .

[0074] In this embodiment, the first phase portion 20 and the second phase portion 30 are both disposed on a substrate 40 , and the first phase portion 20 and the second phase portion 30 are located on the front and back surfaces of the substrate 40 .

[0075] In this embodiment, the vortex light field carrying the orbital angular momentum of photons is injected from the center of the first phase portion 20 .

[0076] In this embodiment, the optical 4f low-pass filtering module includes a first convex lens 50 , an aperture 60 and a second convex lens 70 .

[0077] The aperture 60 is located at the rear focal plane of the first convex lens 50 , and the aperture 60 is located at the front focal plane of the second convex lens 70 .

[0078] The output light field plane of the optical 4f low-pass filter module is located at the rear focal plane of the second convex lens 70 , and the second phase portion 30 is located at the front focal plane of the first convex lens 50 .

[0079] The light fields at the front focal plane of the first convex lens 50 and the back focal plane of the second convex lens 70 satisfy a low-pass filtering relationship.

[0080] In this embodiment, the first phase portion 20 and the second phase portion 30 are both one of a spatial light modulator, a diffractive optical element and a metasurface.

[0081] The working method of the photon orbital angular momentum mode order multiple conversion system comprises the following steps:

[0082] S1: Input the vortex light carrying orbital angular momentum into the first phase section, which is located at (x1, y1).

[0083] S2: After passing through the first phase section, the light beam is emitted at a specific angle, and at the same time, it is expanded along a spiral path and propagates to the reflection module after phase modulation, and then propagates from the reflection module to the second phase section. After passing through the second phase section, the distortion phase introduced by the non-paraxial spiral transformation is eliminated. The second phase section is located at (x2, y2).

[0084] S3: After the phase compensation of the second phase unit, the phase distribution of the vortex light is transformed from the angular spiral phase exp(ilθ1) to the angular scaled spiral phase exp(inl θ2), and the ideal vortex light with annular light intensity distribution is obtained through the optical 4f low-pass filter system module. n is the scaling factor, that is, the multiple of the mode multiple conversion.

[0085] S4: The ideal vortex light is output through the output plane of the optical 4f low-pass filter module to complete the mode multiple conversion operation.

[0086] In this embodiment, the spiral decomposition of the first phase unit 20 is specifically that the light field on the (r1, θ1) plane is decomposed along the path of the logarithmic spiral and mapped to a straight line on the (r2, θ2) plane. The corresponding coordinate mapping relationship expression is as follows:

[0087]

[0088] In the formula, (r j ,θ j )(j=1,2,3) is the rectangular coordinate representation of (x j ,y j ) plane, n represents the scaling factor, and r0 represents the radial position mapped from (r0, 0) to the same point (r0, 0) in the above coordinate transformation.

[0089] In this embodiment, (r j ,θ j )(j=1,2,3) is expressed by the following formula:

[0090]

[0091] In the formula, a represents the speed of change of the logarithmic spiral; Indicates taking the integer part, θ j The value range of is (-∞, +∞).

[0092] In this embodiment, the first phase modulation Q(x1, y1) can be expressed by a set of partial differential equations as follows:

[0093]

[0094] k is the wave number of the incident vortex light field propagating between the first phase portion 20 and the second phase portion 30 , and d1+d2 is the distance between the first phase portion 20 and the reflection module 10 and between the reflection module 10 and the second phase portion 30 .

[0095] In this embodiment, the second phase modulation P(x2, y2) is expressed as follows:

[0096] The phase P(x2, y2) of the phase corrector is calculated by using the angular spectrum diffraction integral to transform the light field E(x2, y2), and then the distortion phase is obtained by calculating the phase difference between the transformed light field E(x2, y2) and the input light field E0(x1, y1). Finally, the opposite value of the distortion phase is taken to obtain P(x2, y2). The above process can be expressed as:

[0097] E(x2,y2)=F -1 {F{E0(x1,y1)exp[iQ(x1,y1)]}exp(ik z z)};

[0098] P(u, v)=arg[E0(x1, y1)]-arg[E(x2, y2)];

[0099] Among them, F -1 {} is the inverse Fourier transform, and F{} is the Fourier transform.

[0100] 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 device for converting the order of photon orbital angular momentum mode multiples, characterized in that: include: Optical coordinate transformation module, optical 4f low-pass filter module and reflection module; The reflection module is located between the optical coordinate transformation module and the optical 4f low-pass filtering module; The optical coordinate transformation module includes a first phase unit and a second phase unit having a light field phase modulation function; The optical 4f low-pass filter module and the second phase portion are parallel to each other; A vortex light field carrying the orbital angular momentum of photons is injected from the first phase portion, and the vortex light field is propagated to the reflection module after being spirally decomposed and phase modulated by the first phase portion, and then propagated to the second phase portion; After the second phase section transforms the phase distribution from the angular spiral phase to the angularly scaled spiral phase, the ideal vortex light is output through the optical 4f low-pass filter module.

2. The device for converting the order of photon orbital angular momentum mode according to claim 1, characterized in that: The center of the vortex light field is aligned with the center of the first phase portion.

3. The device for converting the order of photon orbital angular momentum mode according to claim 1, characterized in that: The reflection module reflects the vortex light field to the center of the second phase portion.

4. The device for converting the order of photon orbital angular momentum mode according to claim 1, characterized in that: The first phase portion and the second phase portion are both arranged on a substrate, and the first phase portion and the second phase portion are respectively located on the front and back sides of the substrate.

5. The device for converting the order of photon orbital angular momentum mode according to claim 3, characterized in that: The vortex light field is incident from the center of the first phase portion.

6. The device for converting the order of photon orbital angular momentum mode according to claim 5, characterized in that: The optical 4f low-pass filter module includes a first convex lens, an aperture and a second convex lens; The aperture is located at the rear focal plane of the first convex lens, and the aperture is located at the front focal plane of the second convex lens; The output light field plane of the optical 4f low-pass filtering module is located at the rear focal plane of the second convex lens, and the second phase portion is located at the front focal plane of the first convex lens. The light fields at the front focal plane of the first convex lens and the back focal plane of the second convex lens satisfy a low-pass filtering relationship.

7. The device for converting the order of photon orbital angular momentum mode according to claim 1, characterized in that: The first phase section and the second phase section are each one of a spatial light modulator, a diffractive optical element and a metasurface.

8. A method for converting the order of photon orbital angular momentum mode multiples, characterized in that: The following steps are involved: S1: inputting the vortex light carrying orbital angular momentum into the first phase section; S2: After passing through the first phase section, the light beam is emitted at a specific angle, and at the same time, it is spread along the spiral path and phase modulated, and then propagates to the reflection module, and then propagates from the reflection module to the second phase section, and the distortion phase introduced by the non-paraxial spiral transformation is eliminated by the second phase section; S3: After the phase compensation of the second phase section, the phase distribution of the vortex light is transformed from the angular spiral phase to the angular scaled spiral phase, and then the ideal vortex light with annular light intensity distribution is obtained through the optical 4f low-pass filter system module; S4: The ideal vortex light is output through the output plane of the optical 4f low-pass filter module to complete the mode multiple conversion operation.

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