A non-destructive vortex light field beam splitting device

Abstract

A non-destructive vortex light field beam splitting device comprises an annular cavity mode selection module, the annular cavity selection module comprises an input coupling mirror, a first dove prism, a second dove prism, a scanning lock cavity assembly, a concave mirror, and an output coupling mirror constituting an annular cavity; the input light beam is partially reflected and partially transmitted by the input coupling mirror, the LG light beam transmitted by the input coupling mirror sequentially passes through the first dove prism, the second dove prism, the scanning lock cavity assembly, the concave mirror, and the output coupling mirror, the output coupling mirror reflects and transmits part of the light, and the reflected LG light beam is also partially reflected and partially transmitted after entering the input coupling mirror, so that two OAM carrier light beams with opposite topological charges are changed from a degenerate state to a non-degenerate state.

Description

Technical Field

[0001] The invention relates to the fields of laser technology, nonlinear optical physics technology and atomic physics technology, and in particular to a non-destructive vortex light field beam splitting device. Background Art

[0002] The full degrees of freedom of light include frequency, intensity, polarization, and orbital angular momentum (OAM). The singularity of the intensity and phase distribution of OAM-carrying beams has inspired many exciting applications, such as optical manipulation and trapping, high-precision optical metrology, and quantum information processing. Mutually orthogonal OAM modes offer the possibility of spatial mode multiplexing for high-capacity classical optical communications. The infinite dimensionality of OAM modes makes dense encoding and coordinate-independent quantum key distribution more promising. For various applications based on multiple OAM modes, it is crucial to effectively identify and separate different OAM modes. In previous inventions, there are many ways to achieve this goal. For example, holographic gratings and single-mode fibers can be used as mode detectors for specific OAM modes. In this case, the mode detector is a projector, and we must use N projection measurements to measure N OAM modes. One disadvantage of this method is that the original state is completely destroyed after the measurement, and it is not very efficient. Therefore, effectively identifying beams of different orbital angular momentum (OAM) is of great significance for applications such as high-capacity optical communications and quantum information processing. Summary of the invention

[0003] In order to reduce the number of driving devices and improve the utilization of space, the present invention provides a non-destructive vortex light field beam splitting device. The present invention adopts the following technical solutions:

[0004] A non-destructive vortex light field beam splitting device comprises an annular cavity mode selection module, wherein the annular cavity selection module comprises an input coupling mirror, a first dove prism, a second dove prism, a scanning lock cavity assembly, a concave mirror, and an output coupling mirror constituting the annular cavity; an input light beam is partially reflected and partially transmitted by the input coupling mirror, an LG light beam transmitted by the input coupling mirror sequentially passes through the first dove prism, the second dove prism, the scanning lock cavity assembly, the concave mirror, and the output coupling mirror, the output coupling mirror reflects and transmits part of the light, and the reflected LG light beam is also partially reflected and partially transmitted after entering the input coupling mirror.

[0005] Specifically, the scanning lock cavity assembly includes a plane mirror and a piezoelectric sensor, and the piezoelectric sensor is mounted on the plane mirror.

[0006] Specifically, it also includes a beam generating module, which includes lasers arranged in sequence on the optical path, a phase modulation component that adds a relative phase to the Gaussian beam output by the laser, and a lens assembly that performs mode matching between the Laguerre-Gaussian beam carrying orbital angular momentum and the ring cavity.

[0007] Specifically, the phase modulation component is a spatial light modulator or a vortex phase plate.

[0008] Specifically, the beam generating module is further provided with a polarization conditioning component for controlling the polarization state of the Gaussian beam after the laser.

[0009] Specifically, a first reflector is arranged between the spatial light modulator and the polarization tempering component, and a second reflector is arranged between the spatial light modulator and the lens component.

[0010] Specifically, a third reflector is also arranged at the end of the lens assembly.

[0011] Specifically, the lens assembly includes a first lens and a second lens arranged in sequence on an optical path.

[0012] Specifically, the spatial light modulator includes an LCoS panel coated with an aluminum reflective film.

[0013] Specifically, it also includes an imaging module, which includes a charge coupled device and a fast photodiode. The charge coupled device is used to image the light beam of the output coupling mirror lens, and the fast photodiode is used to detect the light beam reflected and transmitted by the input coupling mirror and transmit it to the oscilloscope for imaging.

[0014] The advantages of the present invention are:

[0015] (1) The present invention adopts a method of introducing a Dove prism into a ring cavity to effectively split different OAM carrier beams. Since the rotational symmetry of the two OAM carrier beams with opposite topological charges is destroyed, their transmission spectra will be split in the ring cavity. When the cavity matches the mode and impedance of one OAM carrier beam, the beam will be transmitted through the cavity, and the other OAM carrier beam will be reflected. Both beams will maintain their spatial shapes, that is, the two OAM carrier beams with opposite topological charges will change from a degenerate state to a non-degenerate state.

[0016] (2) The present invention can separate OAM carrier beams of different orders in the example device of the present invention, and the imaging effect is good, and the beam mode will not be destroyed. The mode detector in the prior art is a projector, which requires N projection measurements to measure N OAM modes. One disadvantage of this method is that the original state is completely destroyed after the measurement, and the efficiency is not high. The traditional ring cavity can select the light beam that resonates with the intracavity mode, but cannot distinguish the LG light with opposite topological charge, while the device of the present invention can do this.

[0017] (3) The dove prism is a right-angle prism with the top cut off, which reduces the weight of the prism and the internal reflection of stray light.

[0018] (4) The beam generating module causes two OAM carrier beams with opposite topological charges to change from a degenerate state to a non-degenerate state.

[0019] (5) The present application improves the purity of the input light beam by increasing the forward tilt phase of the spatial light modulator.

[0020] (6) The setting of polarization conditioning components can control the polarization state of Gaussian beam.

[0021] (7) The first reflector and the second reflector are used to adjust the angle of the light beam at the input and output ends of the phase modulation component.

[0022] (8) The third reflector adjusts the direction of the output light path of the light beam generating module.

[0023] (9) The first lens and the second lens form a 4-F system, thereby keeping the beam parameters unchanged.

[0024] (10) The imaging module images the output OAM carrier beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A module connection diagram of a non-destructive vortex light field beam splitting device provided by an embodiment of the present invention;

[0026] Figure 2 This is a diagram of the overall device after the modules are assembled in an embodiment of the present invention;

[0027] Figure 3 A light beam generating module device provided by an embodiment of the present invention;

[0028] Figure 4 The annular cavity mode selection module device provided in the embodiment of the present application;

[0029] Figure 5(a)-Figure 5(c) Numerical simulation and theoretical simulation results of cavity transmission and reflection coefficient under different cavity transmittance and impedance mismatch conditions provided by the embodiment of the present invention;

[0030] Figure 6(a)-Figure 6(d) Transmission spectra and experimental results of different input states provided by the embodiments of the present invention;

[0031] Figure 7(a) shows the reflection and transmission spatial shape diagrams obtained using a CCD camera;

[0032] Figure 7(b) shows the corresponding theoretical simulation results based on the experimental parameters.

[0033] The meanings of the symbols in the figure are as follows:

[0034] 1- Beam generation module 11- Laser

[0035] 12-polarization tempering component 121-first half-wave plate 122-first quarter-wave plate

[0036] 13- first reflecting mirror 14- spatial light modulator 15- second reflecting mirror

[0037] 16-first lens 17-second lens 18-third reflector

[0038] 21-Input coupling mirror 22-First prism 23-Second prism

[0039] 24- plane mirror 25- piezoelectric sensor 26- concave mirror 27- output coupling mirror

[0040] 31- Charge Coupled Device 32- Fast Photodiode DETAILED DESCRIPTION

[0041] like Figure 1-4 As shown, a non-destructive vortex light field beam splitting device comprises

[0042] A beam generating module 1 is used to generate LG beams carrying two different orbital angular momentum (OAM) on a target plane and output them in a superposition state;

[0043] The ring cavity mode selection module 2 splits the non-degenerate cavity modes of two OAM carrier beams with opposite topological charges, and transmits the OAM carrier beam resonating with the resonant cavity to output;

[0044] The imaging module 3 images the output OAM carrier beam.

[0045] The following is a detailed description of the above three modules:

[0046] 1. Beam generation module 1

[0047] The light beam generating module 1 comprises a laser 11 , a polarization tempering component 12 , a first reflector 13 , a phase modulation component, a second reflector 15 , a lens component, and a third reflector 17 which are sequentially arranged on the light path.

[0048] The laser 11 is a continuous wave titanium sapphire laser. In this embodiment, the model is Coherent, MBR110, and is used to emit a Gaussian beam with a wavelength of 795 nm.

[0049] The polarization modulation component 12 includes a first half-wave plate 121 and a first quarter-wave plate 122. The wavelength of the first half-wave plate 121 is 795 nm, and the wavelength of the first quarter-wave plate 122 is 795 nm. By adjusting the fast axis directions of the first half-wave plate 121 and the first quarter-wave plate 122, the polarization state of the Gaussian beam can be controlled.

[0050] The surface of the first reflector 13 is coated with HR@795nm, and is used to reflect the Gaussian light beam with a wavelength of 795nm to the phase modulation component.

[0051] The phase modulation component in this embodiment is a spatial modulator 14. A vortex phase plate can also be used instead, which allows the Gaussian beam to add a relative phase and become a spiral light. The spatial light modulator 14 used in this embodiment can change the amplitude or intensity, phase, polarization state and wavelength of the spatial distribution of the light beam under the control of a time-varying electrical drive signal or other signal, or convert incoherent light into coherent light. The light beam emitted by the spatial light modulator 14 can be directly expressed as the incident light beam multiplied by the additional phase term, allowing the Gaussian beam to carry orbital angular momentum (OAM). The spatial light modulator 14 converts the Gaussian beam into a Laguerre Gaussian beam (LG beam) and outputs it. The spatial light modulator has a 1920*1080 (full HD) LCoS panel and an aluminum-plated reflective film for 400-850nm.

[0052] The surface of the second reflector 15 is coated with HR@795nm, and is used for reflecting the LG light beam with a wavelength of 795nm to the first lens 16 .

[0053] The lens assembly includes a first lens 16 and a second lens 17, which mode-match the LG beam carrying the OAM with the ring cavity.

[0054] The surface of the third reflector 18 is coated with HR@795nm, and is used to reflect the Gaussian beam with a wavelength of 795nm into the ring cavity mode selection module 2.

[0055] 2. Ring cavity mode selection module 2

[0056] The annular cavity mode selection module 2 includes an input coupling mirror 21, a first dove prism 22, a second dove prism 23, a plane mirror 24, a piezoelectric sensor 25, a concave mirror 26, and an output coupling mirror 27, which constitute the annular cavity. The piezoelectric sensor 25 is mounted on the plane mirror 24 and is used to scan and lock the cavity. The output beam of the beam generating module 1 is partially reflected and partially transmitted by the input coupling mirror 21. The LG beam transmitted by the input coupling mirror 21 passes through the first dove prism 22, the second dove prism 23, the plane mirror 24 and the piezoelectric sensor 25, the concave mirror 26, and the output coupling mirror 27 in sequence. The output coupling mirror 27 reflects and transmits part of the light, and the reflected LG beam is also partially reflected and partially transmitted after entering the input coupling mirror 21.

[0057] The input coupling mirror 21 has a reflectivity of 85% for the LG beam with a wavelength of 795 nm. The LG beam carrying OAM from the beam generating module 1 is incident on the input coupling mirror 21 .

[0058] There is a relative rotation angle α between the first dove prism 22 and the second dove prism 23 for inverting the image. After the LG beam enters from one of the inclined surfaces of the first dove prism 22 and the second dove prism 23, it will produce total reflection at the longest bottom surface, and then emit from the other opposite inclined surface. The LG beam is polarized after passing through the dove prism. When the LG beam passes through the first dove prism 22, a relative phase term is added, and the image is reversed at the same time, and then it is injected into the second dove prism 23. When the LG beam is emitted from the second dove prism 23, the image is reversed again, which is consistent with the direction of the image of the beam injected from the beam generating module 1, but a relative phase ΔΦ=2lα will be generated between the two OAM modes, where l is the topological charge of the beam carrying the orbital angular momentum. These two OAM modes will experience different phase changes during a round trip in the ring cavity, resulting in their spectrum splitting.

[0059] The surface of the plane mirror 24 is coated with HR@795nm, and is used to reflect the light beam emitted by the second prism 23 and reflect the light beam to the concave mirror 26, with a reflectivity greater than 99%.

[0060] The surface of the concave mirror 26 is coated with HR@795nm, and the reflectivity is greater than 99%.

[0061] The surface of the lens of the output coupling mirror 27 is coated with HR@795nm, with a reflectivity of 95%, that is, the LG light beam resonating with the eigenmode of the ring resonator is transmitted and output, and 95% of the light beam in the cavity is reflected to the input coupling mirror 21, and then the light beam circulates in the ring cavity to form a stable resonant cavity.

[0062] For a ring cavity, the OAM mode is also the eigenmode of the ring cavity. The resonant frequency of the OAM mode and the ring cavity is ν pql for:

[0063]

[0064] Where c is the speed of light, L is the optical length of the cavity, q is an integer, l is the topological charge, p is the root index of the OAM beam, c / L is the minimum frequency difference of a specific mode, and the reflection coefficient C of the ring cavity of the present invention is R and the transmission coefficient C T It is expressed as:

[0065]

[0066]

[0067] Wherein R1, R4 are the reflectivities of the input coupling mirror 21 and the output coupling mirror 27 in the ring cavity, T1, T4 are the transmittances of the input coupling mirror 21 and the output coupling mirror 27 in the ring cavity, T1=1-R1, T4=1-R4 and T represents the transmittance of the ring cavity, including the sum of the transmittances of the two Dove prisms, the plane mirror 24 and the concave mirror 26, δ=δ1+ΔΦ is the phase change of the light beam in the ring cavity after one circle propagation, and δ1=2πc / L is the phase change of the light beam in the ring cavity without the Dove prism.

[0068] 3. Imaging module 3

[0069] The imaging module 3 includes a charge coupled device 31 and a fast photodiode 32. The charge coupled device 31 is used to image the light beam of the output coupling mirror 27 lens, and the fast photodiode 32 is used to detect the light beam reflected and transmitted by the input coupling mirror 21 and transmit it to the oscilloscope for imaging.

[0070] Based on this device, this scheme simulates the intracavity transmittance of different ring cavities and the transmission coefficient C of the ring cavity under impedance mismatch conditions. R and reflection coefficient C T .

[0071] The embodiment A is as follows: R4=0.95, T=0.98, the transmittance T of the ring cavity, the transmittance T4 of the output coupling mirror 27 and the phase δ of the light beam propagating in the ring cavity are fixed, and the reflection coefficient C of the ring cavity as shown in FIG5(a) is obtained by adjusting the reflectivity R1 of the input coupling mirror 21. R and the transmission coefficient C T Relationship curve with the reflectivity R1 of the input coupling mirror 21.

[0072] From Figure 5(a), the transmission coefficient C of the ring cavity R To reach the minimum value, the reflection coefficient C of the ring cavity T As R1 in Figure 5(a) increases, the impedance mismatch of the device increases, and the transmission coefficient C of the ring cavity T The value is decreasing, and the reflection coefficient C of the ring cavity R The value is increasing. The transmittance of the input coupling mirror 21 for the 795nm light beam is: 1-reflectivity of the output coupling mirror×transmittance of the Dove prism×transmittance of the Dove prism. The reflectivity of the output coupling mirror and the transmittance of the Dove prism are both 95%.

[0073] The specific embodiment b is as follows: R1 = R4 = 0.90, T = 1, as shown in FIG5(b), this embodiment simulates the resonance of the ring cavity with |1>, and the input mode is ), the reflection coefficient C of the ring cavity with different phase shifts ΔΦ R and the transmission coefficient CT In this example, we use quantum mechanical language to represent different OAM modes, defining When ΔΦ increases, the transmission spectra of modes |1> and |-1> split from the degenerate state to the non-degenerate state. When the transmission spectra of the two modes are completely separated, the transmitted mode only contains the mode that resonates with the ring cavity, and the other mode is completely reflected.

[0074] Embodiment c is as follows: For input mode ), when the mode matching coefficient M (the mode matching coefficient is the overlap ratio between the input mode and the cavity intrinsic mode) varies from 0 to 0.995, the spatial shapes of the transmitted and reflected beams are shown in Figure 5(c). When M = 0, the light of both modes is completely reflected and no mode of light is transmitted from the cavity; while for almost perfect mode matching M = 0.995, the light of one mode is completely reflected and the light of the other mode is completely transmitted.

[0075] The experimental and simulation results of the present invention for other different input modes are shown in FIG6. The input modes are respectively |0>+|1>, |1>+|2>, |-1>+|1> and |-2>+|2> transmission spectra. Figure 6(a)-6(d) As shown in . For high topological charge OAM modes, more irrelevant high cavity modes will appear in the transmission spectrum due to the impurities of the input mode and the resonance of other modes. Since the intracavity loss of higher OAM modes is also higher, larger diffraction and scattering losses occur, resulting in lower transmission efficiency. In the device of the present invention, the intracavity transmittance T = 0.90, the total mode and impedance matching coefficients are about 0.80-0.90, which means that the reflectance of the resonant mode is about 0.10-0.20. The present invention uses the Hasch-Coillaud (HC) method to lock the cavity to one of the input modes, and the reflection and transmission spatial shapes obtained using a CCD camera as a charge coupled device 31 and a fast photodiode 32 are shown in the image of Figure 7 (a). That is, it is obtained that: the emitted light beam has a clear ring shape and high mode purity, while the reflected light beam is distorted due to the partial reflection resonant mode generated by the mode mismatch. The image of Figure 7 (b) is the corresponding theoretical simulation result based on the experimental parameters.

[0076] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A non-destructive vortex light field beam splitting device, characterized in that: The invention comprises an annular cavity mode selection module, wherein the annular cavity mode selection module (2) comprises an input coupling mirror (21), a first dove prism (22), a second dove prism (23), a scanning lock cavity assembly, a concave mirror (26), and an output coupling mirror (27) constituting the annular cavity; the input light beam is partially reflected and partially transmitted by the input coupling mirror (21); the LG light beam transmitted by the input coupling mirror (21) sequentially passes through the first dove prism (22), the second dove prism (23), the scanning lock cavity assembly, the concave mirror (26), and the output coupling mirror (27); the output coupling mirror (27) reflects and transmits part of the light; and the reflected LG light beam is also partially reflected and partially transmitted after entering the input coupling mirror (21); The scanning lock cavity assembly comprises a plane mirror (24) and a piezoelectric sensor (25), wherein the piezoelectric sensor (25) is mounted on the plane mirror (24); There is a relative rotation angle between the first prism (22) and the second prism (23) α After the LG light beam enters one of the inclined surfaces of the first prism (22) and the second prism (23), it will be totally reflected at the longest bottom surface and then emitted from the other opposite inclined surface.

2. A non-destructive vortex light field beam splitting device according to claim 1, characterized in that: It also includes a beam generation module (1), which includes a laser (11) arranged in sequence on an optical path, a phase modulation component for adding a relative phase to a Gaussian beam output by the laser (11), and a lens assembly for performing mode matching between a Laguerre-Gaussian beam carrying orbital angular momentum and a ring cavity.

3. A non-destructive vortex light field beam splitting device according to claim 2, characterized in that: The phase modulation component is a spatial light modulator (14) or a vortex phase plate.

4. A non-destructive vortex light field beam splitting device according to claim 2, characterized in that: The beam generation module (1) is further provided with a polarization conditioning component (12) for controlling the polarization state of the Gaussian beam after the laser (11).

5. The non-destructive vortex light field beam splitting device according to claim 3, characterized in that: A first reflector (13) is arranged between the spatial light modulator (14) and the polarization tempering component (12), and a second reflector (15) is arranged between the spatial light modulator (14) and the lens component.

6. A non-destructive vortex light field beam splitting device according to claim 2, characterized in that: A third reflector (18) is also provided at the end of the lens assembly.

7. The non-destructive vortex light field beam splitting device according to claim 2, characterized in that: The lens assembly comprises a first lens (16) and a second lens (17) which are arranged in sequence on the optical path.

8. The non-destructive vortex light field beam splitting device according to claim 3, characterized in that: The spatial light modulator (14) comprises an LCoS panel and is coated with an aluminum reflective film.

9. The non-destructive vortex light field beam splitting device according to claim 2, characterized in that: It also includes an imaging module (3), the imaging module (3) including a charge coupled device (31) and a fast photodiode (32), the charge coupled device (31) is used to image the light beam of the output coupling mirror (27) lens, and the fast photodiode (32) is used to detect the light beam reflected and transmitted by the input coupling mirror (21) and transmit it to the oscilloscope for imaging.

Images