Photon orbital angular momentum mode order multiple transformation device

Abstract

The application 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 filter module and a reflection module; the optical coordinate transformation module comprises a first phase part and a second phase part with an optical field phase modulation function; a vortex optical field carrying photon orbital angular momentum is emitted from the first phase part, the vortex optical field is transmitted to the reflection module after spiral decomposition and phase modulation of the first phase part, and then is transmitted to the second phase part; the second phase part changes the phase distribution from an angular spiral phase into an angular scaled spiral phase, and then outputs ideal vortex light through the optical 4f low-pass filter module; the photon orbital angular momentum mode order multiple transformation device realizes mode transformation of various multiples, greatly improves the efficiency of mode multiple transformation and the purity after change, and can be widely applied to the field of optical field regulation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication technology, in particular to a photon orbital angular momentum mode order multiple transformation device. BACKGROUND

[0002] Currently, there are two kinds of optical coordinate transformations proposed and used for OAM mode order multiple transformation operation.

[0003] The first kind of optical coordinate transformation is logarithmic polar coordinate transformation. The basic principle of realizing OAM mode order multiple transformation is as follows: first, the annular OAM mode exp(ilθ) is sheared and expanded into a long strip-shaped inclined plane wave mode by using logarithmic polar coordinate transformation; then, the long strip-shaped inclined plane wave mode is subjected to n times of optical field replication and splicing by using a fan-out grating element, so as to correspond to a phase shift of n×2π; finally, the long strip-shaped inclined plane wave mode is wrapped back into an annular OAM mode by using inverse logarithmic polar coordinate transformation, at this time, the OAM mode will become exp(inlθ), that is, the OAM mode order multiple transformation operation of n is realized. This scheme has a conversion efficiency of 100% in theory, and in principle, it can be used reversely to realize the OAM mode order multiple transformation operation of 1 / n, etc. However, its significant disadvantage is that it needs three steps of transformation, so the complexity is too high, and in practice, slight alignment deviation will cause the effect of OAM mode order multiple transformation operation to deteriorate significantly.

[0004] The second kind of optical coordinate transformation is fan-shaped transformation. The basic principle of realizing OAM mode order multiple transformation is as follows: the annular OAM mode is converted into a fan-shaped mode by using the feature of angular scaling (θ→θ / n) of fan-shaped transformation; n complementary fan-shaped transformation optical fields are generated by n parallel fan-shaped transformations to form a complete annular OAM mode exp(inlθ). Since the phase modulation required by the n parallel fan-shaped transformations is superimposed on the same diffraction screen, this scheme actually only needs 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, so it is more complex in wavefront control implementation, and because amplitude modulation will introduce loss. SUMMARY

[0005] To solve the above technical problems, the present application provides a photon orbital angular momentum mode order multiple transformation device and method.

[0006] To solve the above problems, the present application adopts the following technical scheme:

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

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

[0009] The optical coordinate transformation module comprises a first phase part and a second phase part with a light field phase modulation function.

[0010] The optical 4f low-pass filter module is parallel to the second phase part.

[0011] The vortex light field carrying the photon orbital angular momentum is emitted from the first phase part, and the vortex light field is transmitted to the reflection module after spiral decomposition and phase modulation of the first phase part, and then transmitted to the second phase part.

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

[0013] In the photon orbital angular momentum mode order multiple transformation device provided by at least one embodiment of the present disclosure, the center of the vortex light field is aligned with the center of the first phase part.

[0014] In the photon orbital angular momentum mode order multiple transformation device provided by at least one embodiment of the present disclosure, the reflection module reflects the vortex light field to the center of the second phase part.

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

[0016] In the photon orbital angular momentum mode order multiple transformation device provided by at least one embodiment of the present disclosure, the vortex light field is emitted from the center of the first phase part.

[0017] In the photon orbital angular momentum mode order multiple transformation device provided by at least one embodiment of the present disclosure, the optical 4f low-pass filter module comprises a first convex lens, an aperture, and a second convex lens.

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

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

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

[0021] The photon orbital angular momentum mode order multiple transformation device provided by at least one embodiment of the present disclosure comprises a first phase part and a second phase part.

[0022] In a second aspect, the present disclosure provides a photon orbital angular momentum mode order multiple transformation method, comprising the following steps:

[0023] S1: inputting vortex light carrying orbital angular momentum to the first phase part.

[0024] S2: after passing through the first phase part, the light beam is emitted at a specific angle, expands along a spiral path and is phase-modulated to propagate to the reflection module, and then propagates to the second phase part through the reflection module, and the distortion phase introduced by the non-paraxial spiral transformation is eliminated through the second phase part.

[0025] S3: after the phase compensation of the second phase part, 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 a ring-shaped light intensity distribution is obtained through the optical 4f low-pass filtering system module.

[0026] S4: outputting the plane output ideal vortex light through the optical 4f low-pass filtering module, and completing the mode multiple transformation operation.

[0027] The present disclosure has the advantages of realizing mode transformation of various multiples, greatly improving the efficiency and purity of mode multiple transformation, and realizing simple and efficient vortex light mode order multiple transformation operation, and can be widely applied to the field of optical field regulation. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative labor.

[0029] Figure 1 It is a structural schematic diagram of the photon orbital angular momentum mode order multiple transformation device in the present disclosure.

[0030] Figure 2 It is a phase diagram distribution of the first phase part and the second phase part loaded by the spatial light modulator in the present disclosure.

[0031] Figure 3 It is a 2-order vortex light intensity distribution diagram generated in the embodiment.

[0032] Figure 4The intensity distribution of the first-order vortex light obtained after the second-order vortex light in the embodiment passes through the first and second phase plates and the 4f system.

[0033] In the figure:

[0034] 10, a reflection module;

[0035] 20, a first phase part;

[0036] 30, a second phase part;

[0037] 40, a substrate;

[0038] 50, a first convex lens;

[0039] 60, a diaphragm;

[0040] 70, a second convex lens. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments will be described clearly and completely below with reference to the accompanying drawings in the embodiments. Obviously, the described embodiments are only part of the embodiments, not all embodiments.

[0042] Embodiment 1

[0043] The embodiment provides a photon orbital angular momentum mode order multiple transformation method, including the following steps:

[0044] S1: inputting vortex light carrying orbital angular momentum to a first phase part, the first phase part being located at (x1, y1);

[0045] S2: after passing through the first phase part, the light beam is emitted at a specific angle, expands along a spiral path and propagates to a reflection module after phase modulation, and then propagates to a second phase part from the reflection module, and the distortion phase introduced by the non-axial spiral transformation is eliminated through the second phase part, the second phase part being located at (x2, y2);

[0046] S3: after phase compensation of the second phase part, 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 through an optical 4f low-pass filtering system module, ideal vortex light with annular intensity distribution is obtained. n is a scaling factor, that is, the multiple of mode multiple transformation.

[0047] S4: outputting ideal vortex light on a plane through the optical 4f low-pass filtering module, and completing the mode multiple transformation operation.

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

[0049] In the embodiment, the first phase part spiral decomposition is specifically the decomposition and mapping of the light field in the (r1, θ1) plane along the path of the logarithmic spiral line to the straight line in the (r2, θ2) plane, and the corresponding coordinate mapping relationship expression is as follows:

[0050]

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

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

[0053]

[0054] In the formula, a represents the change rate of the logarithmic spiral line; represents the integer part, and the value range of θ j is (-∞, +∞).

[0055] In the embodiment, the first phase modulation Q(x1, y1) can be expressed by the following partial differential equation group:

[0056]

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

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

[0059] The phase P(x2, y2) of the phase corrector is used to calculate the transformed light field E(x2, y2) by using the angular spectrum diffraction integral, 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), and finally the opposite value of the distortion phase is taken as 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] where F -1 {} is inverse Fourier transform, F{} is Fourier transform.

[0063] In order to better understand the principle of the photon orbital angular momentum mode order multiple transformation method in the embodiment, the following will provide a transformation example:

[0064] As Figure 3 and 4 shown, specifically, the input photon orbital angular momentum mode, corresponding to the wavefront of the vortex light field has a specific angular spiral phase exp(il θ1), this example takes l = 2 as the input photon orbital angular momentum mode to realize the OAM mode multiple transformation operation of n = 1 / 2. The incident vortex light field sequentially passes through the first phase part and the spiral decomposition of the first phase part 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 ring 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 spiral phase exp(inl θ2). For the case of n = 1 / 2, it corresponds to the angular spiral phase exp(i2θ1) 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 to the optical 4f low-pass filtering module. After passing through the 4f low-pass filtering module, the ideal vortex light with ring intensity distribution can be obtained. The optical 4f low-pass filtering module outputs the above ideal vortex light with ring intensity distribution and angular spiral phase exp(inl θ2) on the output plane (x3, y3), that is, the output OAM order nl is n times of the input OAM order l, realizing the OAM mode multiple transformation operation. For the case of n = 1 / 2, it means that the input 2-order OAM beam will finally output a 1-order OAM beam.

[0065] Embodiment 2

[0066] As Figure 1 and 2 shown, the embodiment provides a photon orbital angular momentum mode order multiple transformation system, which includes 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 part 20 and a second phase part 30 with 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 incident from the first phase portion 20 . 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 back 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 each 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 portion, which is located at (x1, y1).

[0083] S2: After passing through the first phase part, the light beam is emitted at a specific angle, expands along a spiral path and is phase-modulated to propagate to the reflection module, and then propagates to the second phase part through the reflection module. The second phase part is located at (x2, y2).

[0084] S3: After passing through the second phase part, the phase distribution of the vortex light changes from the angular spiral phase exp(ilθ1) to the angular scaled spiral phase exp(inlθ2). Through the optical 4f low-pass filtering system module, the ideal vortex light with ring-shaped light intensity distribution is obtained. n is the scaling factor, i.e., the multiple of mode multiplication.

[0085] S4: The ideal vortex light is output on the output plane through the optical 4f low-pass filtering module, and the mode multiplication operation is completed.

[0086] In this embodiment, the first phase part 20 is specifically decomposed as the light field in the (r1, θ1) plane along the path of the logarithmic spiral line and mapped to a straight line in 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 spiral polar coordinate of the (x j , y j ) plane expressed in rectangular coordinates, n represents the scaling factor, and r0 represents the radial position of the mapping 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 change rate of the logarithmic spiral line; represents the integer part, and the value range of θ j is (-∞, +∞).

[0092] In this embodiment, the first phase modulation Q(x1, y1) can be expressed by the following partial differential equation group:

[0093]

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

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

[0096] The phase P(x2, y2) of the phase corrector is used to calculate the transformed light field E(x2, y2) by the angular spectrum diffraction integral, 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), and finally the opposite value of the distortion phase is taken as P(x2, y2). The above process can be represented as:

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

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

[0099] wherein, 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 application is not limited thereto, and any changes or substitutions not thought of through creative labor should be covered within the scope of protection of the present application; unless explicitly stated, any element, action or instruction used herein should not be interpreted as critical or essential.

Claims

1. A device for converting the order of photon orbital angular momentum mode into 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 incident 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 propagates 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 outputted 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 disposed 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.

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 back 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 filter module is located at the back 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 into 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, expanded along a spiral path, and phase modulated before propagating to the reflection module. From the reflection module, it propagates to the second phase section, where the distortion phase introduced by the non-paraxial spiral transformation is eliminated. 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 passes through the optical 4f low-pass filter system module to obtain the ideal vortex light with annular light intensity distribution; S4: The ideal vortex light is output through the output plane of the optical 4f low-pass filter module to complete the mode multiplication conversion operation.

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